1.1 GSM Network Architecture………………………...03
1.2 Channel organization in GSM……………………...06
1.3 Different Interfaces in GSM………………………. 09
1.4 Different Subsystem of GSM……………………....10
Global System For Mobile Communication
Ø New rapidly expanding & successful technology.
Ø Fully Digitized technology for better speech quality.
Ø Available in almost every part of the world.
Ø Fully compatible with existing Fixed Line Network.
Ø Single number operation with World wide Roaming.
Ø Very well defined interfaces makes truly open system
Ø Encryption of user information
Ø Available versions, GSM 900, 1800 & 1900
Objectives of GSM:
Ø The system must be Pan European.
Ø The system must maintain a good speech quality.
Ø The system must use radio frequency as efficiently as possible.
Ø The system must have high/adequate capacity.
Ø The system must be compatible with ISDN and other data communication specifications.
Ø The system must maintain good security concerning both subscriber and transmitted information.
Advantages of GSM:
Ø GSM uses radio frequencies more effectively than the current systems.
Ø The data transmission services and the quality of the speech are better than in analog systems.
Ø There are two kinds of advanced security services available on the radio path: User Identity & Data Confidentiality.
Ø New services and ISDN compatibility are offered.
Ø It makes international roaming possible .The big uniform market hardens the competitions and lowers the prices. Later on it also leads to lower system costs.
Ø A big advantage is the experience of the analog systems and co-operation of the administrators, operators and the manufacturers.
GSM-900 System Specifications
Ø Frequency Range: 890 MHz to 915 MHz for Uplink
Ø 935 MHz to 960 MHz for Downlink.
Ø Uses TDMA technology for Downlink / Uplink.
Ø 124 Reusable Spot frequencies of 200 kHz bandwidth each by FDMA.
Ø Each Spot Frequency carries 8 Time slots for Traffic/Signaling.
Ø Separate Logical Signaling & Traffic channels.
Ø Compatible to ISDN & PSPDN.
1.1 GSM Network Architecture
MS: Mobile Station
BTS: Base Transceiver Station
BSC: Base Station Controller
MSC: Mobile Switching Center
VLR: Visitor Location Register
HLR: Home Location Register
AUC: Authentication Center
EIR: Equipment identity Register
SMSC: Short Message Service Center
VMSC: Voice Mail Service Center
PSTN: Public Switched Telephone Network
OMC: Operation and Maintenance Center
MS: Mobile Station
Mobile Station consist of two units
Mobile Hand set is one of the most complicated GSM device. It provides user the access to the Network. Each handset has unique identity no. called IMEI.
Subscriber Identity Module (SIM) is a removable module goes into the mobile handset. Each SIM has unique number called International Mobile Subscriber Identity (IMSI). It has built in Micro-computer & memory into it. It contains the ROM of 6 to 32KB, RAM of 128 to 256 bytes and EEPROM of 3 to 8KB
BTS: Base Transceiver Station
BTS has a set of transceivers to communicate with mobile in its area. One BTS covers one Cell. The capacity of the cell depends upon number of channels loaded on BTS. Each RF channel is shared by 8 users in TDMA mode. A BTS connects to BSC through Abis interface, which is 2.048Mbps. BTS commands the MS to set TX power, timing advancement and Handover.
BSC: Base Station Controller
BSC controls several BTSs. BSC manages channel allocation, & Handover of calls from one BTS to another BTS. BSC is connected to MSC via A interface. Transmission rate on A I/f is 2.048 Mbps (G.703). Interface between BSC & BTS is called A’bis I/f which uses any of the transmission media like fiber, micro link or coaxial line. Mostly Micro link is the best choice while connecting a series of BTS to BSC. BSC has database for all of its BTS’s parameters. BSC provides path from MS to MSC.
TCSM/TRAU: Transcoding & Sub-Multiplexer Unit or Transcoder Rate Adaptation Unit
The MSC is based on ISDN switching. The Fixed Network is also ISDN based. ISDN has speech rate of 64 kbps and Mobile communicates at 13 kbps. TCSM/TRAU converts the data rates between 13kbps GSM rate to 64kbps Standard ISDN rate. It can be collocated with the BTS, BSC or MSC or it can be a separate unit.
MSC: Mobile Switching Center
MSC is heart of the entire network connecting fixed line network and other operators to own Mobile network. MSC manages all call related functions and Billing information. MSC is connected to HLR & VLR for subscriber identification & routing incoming calls. MSC capacity is in terms of no of subscribers and E1 cards. MSC is connected to BSC at one end and Fixed Line network on other end. Charging Detail Record (CDR) is generated for each & every call in the MSC.
HLR: Home Location Register
All Subscribers data is stored in HLR. It has permanent data base of all the registered subscribers as well as the numbers which are not registered. It comprises of static information such as Mobile Subscriber ISDN (MSISDN), subscribed services and authentication key. All this information only exists once for each user in single HLR, which also supports charging and accounting. Most of the data available in the SIM is available in HLR.
VLR: Visitor Location Register
VLR is a secondary database which contains subscriber’s data. It stores all information needed for the MS user currently in the LA that is associated to the MSC. If a new MS comes into LA the VLR copies all relevant info for these users from HLR. This hierarchy of VLR & HLR avoid frequent HLR updates and long distance signaling of user interface.
AUC: Authentication Center
Authentication is a process to verify the subscriber SIM. Secret data & verification algorithm are stored in to the AUC. AUC & HLR combines to authenticate the subscribers. Subscriber authentication can be done on every call, if required.
EIR: Equipment identity Register
All subscriber's mobile handset data is stored in EIR. MSC asks mobile to send it IMEI & then checks it with data available in EIR. EIR has different classification for mobile handsets like, White list, Grey list & Black list. According to category the MS can make calls or can be stopped from making calls.
SMSC: Short Message Service Center
It provides text message service. It is used to send short messages from mobile to another mobile subscriber.
VMSC: Voice Mail Service Center
Voice Mail service is like an answering machine service offered to mobile subscriber. It contains the subscription data for all voice mail subscribers. It is connected to MSC.
OMC: Operation And Maintenance Center
All the network elements are connected to OMC. OMC monitors health of all network elements & carry out maintenance operation, if required. OMC link to BTSs are via parent BSC. OMC keeps records of all the faults occurred. OMC can also do Traffic analysis. OMC may prepares MIS Report for the network
1.2 Channel organization in GSM
In GSM 900, 25 MHz spectrum has been frequency divided into 124 bands, each having a bandwidth of 200 kHz. On each of the 200 kHz bands a carrier can be transmitted at the centre frequency of the band. The carriers are thus frequency division multiplexed.
FDD and FDMA organization in GSM
Each carrier is further time divided into timeslots (TSL) and each timeslot is referred to as a physical channel. It is possible to share a physical channel amongst many processes or users. This sharing is referred to as logical channels.
Physical channel and TDMA frame
TDMA frame and physical channel
Time Division Multiple Access (TDMA), is a method of sharing a resource (in this case a radio frequency) between multiple users, by allocating a specific time (known as the time slot) for each user.
This is in contrast to the analogue mobile systems where one radio frequency is used by a single user for the duration of the conversation. In Time Division Multiple Access (TDMA) systems each user either receives or transmits bursts of information only in the allocated time slot. These time slots are allocated for speech only when a user has set up the call. Some timeslots are, however, used to provide signalling and location updates etc. between calls. The main benefit of the time based system is higher capacity than in earlier systems.
In GSM, a TDMA frame is defined as a grouping of TSLs which are numbered 0 to 7 as shown above. It has duration of 4.615ms (8 x 577ms).
TDMA frames are transmitted one after another. Every TDMA frame is allocated a frame number.
Um is the acronym for the GSM radio interface. It is an open interface, i.e. it is very accurately specified and thus vendor independent. A subscriber can use mobile phones from any manufacturer without bothering about the operator’s GSM infrastructure and supplier, as long as the network elements are compliant with the GSM specifications.
Channels in GSM Air interface
In order to define how we organize the various channels we need to define what we mean by a channel. In GSM we have two type of channel, Physical and logical.
A physical channel is a single timeslot on a single frequency, thus there are eight physical channels per frequency, or per TDMA frame. The information contained within a physical channel is termed a burst.
A logical channel is contained within a burst, burst is information of a particular type. The way in which we organize these channels is partly dependent upon the application, but is dependent on whether the information is uplink (MS to BTS) or downlink (BTS to MS) or both.
There 11 logical channels to be mapped on to the physical channels, most of them signaling information. Obviously we cannot assign a logical channel to a single physical channel since this would require a lot of our available bandwidth.
So we require to map the logical channels in such a way that the signaling takes up the minimum space, while still maintaining the received service at the same time, allows maximum use of the remaining channels for the Traffic
Speech processing refers to all the functions the BTS performs in order to guarantee an error-free connection between the MS and the BTS. This includes tasks like speech coding (digital to analogue in the downlink direction and vice versa), channel coding (for error protection), interleaving (to enable a secure transmission), and burst formatting (adding information to the coded speech / data in order to achieve a well-organised and safe transmission).
1.3 Different Interfaces in GSM
Air dfinterface is located between Ms and BTS. The traffic channels in the Air Interface are allocated onto a TDMA frame. TDMA frame consist of eight time slots.
Abis interface is between BTS and BSC. It is a 2 Mbps interface which can carry up to 96 channels.
This interface is present between TRAU and BSC. Traffic channels and signaling channels coming from four different E1s from MSC are reallocated in the Transcoder.
It is present between TCSM and MSC. Traffic channel rate is 64kbps and they are located in time slot 1-15 and 17-31. TS 16 is used for CCS7 signaling.
1.7 Different Subsystem of GSM
Base Station Subsystem (BSS)
The Base Station Subsystem (BSS)
The Base Station Subsystem consists of the following elements:
1. BSC Base Station Controller
2. BTS Base Transceiver Station
3. TC Transcoder
The Base Station Controller (BSC) is the central network element of the BSS and it controls the radio network. This means that the main responsibilities of the BSC are: Connection establishment between MS and NSS, Mobility management, Statistical raw data collection, Air and A interface signalling support.
The Base Transceiver Station (BTS) is a network element maintaining the Air interface. It takes care of Air interface signalling, Air interface ciphering and speech processing. In this context, speech processing refers to all the functions the BTS performs in order to guarantee an error-free connection between the MS and the BTS.
The TransCoder (TC) is a BSS element taking care of speech transcoding, i.e. it is capable of converting speech from one digital coding format to another and vice versa. The BTS, BSC and TC together form the Base Station Subsystem
(BSS) which is a part of the GSM network taking care of the following major functions:
Radio Path Control
In the GSM network, the Base Station Subsystem (BSS) is the part of the network taking care of Radio Resources, i.e. radio channel allocation and quality of the radio connection. For this purpose, the GSM Technical Specifications define about 120 different parameters for each BTS. These parameters define exactly what kind of BTS is in question and how MSs may "see" the network when moving in this BTS area. The BTS parameters handle the following major items: what kind of handovers (when and why), paging organization, radio power
level control and BTS identification.
BTS and TC Control
Inside the BSS, all the BTSs and TCs are connected to the BSC(s). The BSC maintains the BTSs. In other words, the BSC is capable of separating (barring) a BTS from the network and collecting alarm information. Transcoders are also maintained by the BSC, i.e. the BSC collects alarms related to the Transcoders.
The BSS uses hierarchical synchronization which means that the MSC synchronizes the BSC and the BSC further synchronizes the BTSs associated with that particular BSC. Inside the BSS, synchronization is controlled by the BSC. Synchronization is a critical issue in the GSM
network due to the nature of the information transferred. If the synchronization chain is not working correctly, calls may be cut or the call quality may not be the best possible. Ultimately, it may even be impossible to establish a call.
Air & A Interface Signalling:
In order to establish a call, the MS must have a connection through the BSS. This connection requires several signalling protocols.
Connection Establishment between MS and NSS
The BSS is located between two interfaces, the Air and the A interface. From the call establishment point of view, the MS must have a connection through these two interfaces before a call can be established. Generally speaking, this connection may be either a signalling type of connection or a traffic (speech, data) type of connection.
Network Switching Subsystem (NSS)
The elements of Network Switching Subsystem that have been described so far are:
¨ MSC (Mobile Services Switching Centre)
¨ VLR (Visitor Location Register)
¨ HLR (Home Location Register)
The MSC is responsible for controlling calls in the mobile network. It identifies the origin and destination of a call (either a mobile station or a fixed telephone in both cases), as well as the type of a call. An MSC acting as a bridge between a mobile network and a fixed network is called a Gateway MSC. An MSC is normally integrated with a VLR, which maintains information related to the subscribers who are currently in the service area of the MSC. The VLR carries out location registrations and updates. The MSC associated with it initiates the
A VLR database is always temporary (in the sense that the data is held as long as the subscriber is within its service area), whereas the HLR maintains a permanent register of the subscribers. In addition to the fixed data, the HLR also maintains a temporary database
which contains the current location of its customers. This data is required for routing calls.
In addition, there are two more elements in the NSS: the Authentication Centre (AC) and the Equipment Identity Register (EIR). They are usually implemented as part of HLR and they deal with the security functions.
To sum up, the main functions of NSS are:
Ø Call Control This identifies the subscriber, establishes a call and clears the connection after the conversation is over.
Ø Charging: this collects the charging information about a call such as the numbers of the caller and the called subscriber, the time and type of the transaction, etc., and transfers it to the Billing Centre.
Ø Mobility management: This maintains information about the location of the subscriber.
Ø Signaling with other networks and the BSS This applies to interfaces with the BSS and PSTN.
Ø Subscriber data handling: This is the permanent data storage in the HLR and temporary storage of relevant data in the VLR.
Ø Locating the subscriber: This locates a subscriber before establishing a call.
Network Management Subsystem
The Network Management Subsystem (NMS) is the third subsystem of the GSM network in addition to the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS). The purpose of the NMS is to monitor various functions and elements of the network. These tasks are carried out by the NMS/2000 which consists of a number of Work Stations, Servers and a Router which connects to a Data Communications Network (DCN).
The NMS and the GSM Network
The operator workstations are connected to the database and communication servers via a Local Area Network (LAN). The database server stores the management information about the network. The communications server takes care of the data communications between
the NMS and the equipment in the GSM network known as “Network Elements”. These communications are carried over a Data Communications Network (DCN) which connects to the NMS via a router. The DCN is normally implemented using an X.25 Packet Switching Network.
The functions of the NMS can be divided into three categories:
These functions cover the whole of the GSM network elements from the level of individual BTSs, up to MSCs and HLRs.
The purpose of Fault Management is to ensure the smooth operation of the network and rapid correction of any kind of problems that are detected. Fault management provides the network operator with information about the current status of alarm events and maintains a history database of alarms. The alarms are stored in the NMS database and this database can be
Searched according to criteria specified by the network operator.
The purpose of Configuration Management is to maintain up to date information about the operation and configuration status of network elements. Specific configuration functions include the management of the radio network, software and hardware management of the network elements, time synchronization and security operations.
In performance management, the NMS collects measurement data from individual network elements and stores it in a database. On the basis of these data, the network operator is able to compare the actual performance of the network with the planned performance and detect both good and bad performance areas within the network.
2. BASE TRANSCEIVER STATION
2.1 BTS Overview…………………………………….17
2.2 Skeleton of BTS…………………………………...20
2.3 BTS Installation…………………………………...37
2.4 Commissioning of BTS…………………………...38
The BTS performs the radio functions of the Base Station Subsystem (BSS). The BTS receives and sends signals through:
• Air interface — frequencies that connect the BTS to the Mobile Station (MS)
• Abis interface — cable or radio link that connects the BTS to the Base Station Controller (BSC), which is the central element of the BSS
2.1 BTS Overview
Shown in figure is a BTS with 12 TRX and supporting equipments for its optimum performance.
Transceiver unit is the main part of BTS and the occupancy of a BTS is termed in number of TRX cards. Each card is responsible for transmitting and receiving the data and is solely responsible for anything related to radio. It receives the data to be transmitted from the baseband card, modulates it and forwards it to respective equipment. It receives the data caught by GSM antenna through respective equipments, demodulates it and sends it to baseband part for further processing.
Ideally each TRX card needs an antenna for its working. By various techniques like space diversity or cross polarization, either two or one antenna respectively is required for each TRX for optimum performance and coverage. A BTS can house maximum 12 TRX. So ideally we need total 12 or 24 antenna. This will increase the cost by 4 times plus the proximity of antennas will create tremendous interference.
This leads to employing equipments, which will combine the signals such that less number of antennas are used as far as possible. Such equipments are combiners, multicouplers and dual band variable gain duplex filter.
Combiners combines the transmit signal of number of TRX and forms one combine signal. There are two types of combiners: wideband and remote tune. Both differ in number of TRX it can combine. Wideband can combine 2 while remote tune can combine 6.
Multicoupler duplicates the received signal and facilitates to provide the received signal (main and diversity) to each TRX. Here also, it can handle 2 or 6 TRX signals.
Dual band variable gain duplex filter combines transmitted and received signals into one antenna and amplifies received signals with a variable-gain Low Noise Amplifier (LNA). Each unit has two identical parts. Each part has one Tx port and two Rx port, one each for main and diversity. The Tx port is fed by Tx out of the wide band combiner. As each unit has two identical parts, effectively Tx of 4 TRX are combined into one. Similarly in the receiving part, the Rx main and diversity ports are connected to the Multicoupler, which in turn duplicates the signal and gives to TRX. Thus even in the Rx part, four TRX can be handled. DVGA is connected to the antenna through feeders. Employing of the above equipments results into combining of Tx and Rx of four TRX into two feeders.
If remote tune combiner is used then DVGA is not used. Also multicoupler which can handle 6 TRX has to be used.
After the demodulation, the signal is sent to baseband card where the DSP occurs. Each card can handle two TRX. Similarly in the downlink path, the data received from BSC is digitally processed and sent to TRX for transmission.
Once the data is ready after digital processing, each card gives its data to transmission card for forwarding the data to BSC. The transmission card collects data and formats it into one E1 according to G.703 standards. It is sent to BSC via microwave link or fiber link whichever is feasible. Similarly in the downlink path, the transmission card reframes the E1 and distributes the data to appropriate baseband card.
Uplink and Downlink Path:
The uplink and downlink path is shown in the picture and is self explanatory
From the MS, the signal is received by the GSM Antenna. The signal is given to DVGA where it is bifurcated into two combined RXs. This combined Rxs are given to Multicouplers which further divides the signal into individual signal for Received main and diversity. This individual signals are fed to TRX which performs the demodulation of the signal and gives the information signal to Baseband card. It performs the DSP analysis and gives to the transmission unit. It constructs the E1 according to the format in BOI and gives it to BSC via transmission link.
Data from BSC is given to Baseband by transmission unit. DSP analysis is done and the information signal is given to TRX. The TRX modulates the signal and gives the modulated signal to wideband combiner. The combiner combines two TX signals into one and gives it to DVGA. DVGA gets one more combined TX signal from other wideband combiner. It combines both the signal and gives it to the antenna via the feeder to be transmitted to the MS.
2.2 Skeleton Of BTS:
The Base transceiver Station contains following Units:
1 Transceiver unit (TSxx)
2 2-way Receiver Multicoupler unit (M2xx)
3 Transceiver Baseband unit (BB2x)
4 BaseOperations and Interfaces unit (BOIx)
5 Transmission unit (VXxx)
6 Wideband Combiner unit (WCxx)
7 Dual Variable Gain Duplex Filter unit (DVxx)
8 DC/DC Power Supply unit (PWSB)
9 6-way Receiver Multicoupler unit (M6xx)
10 Remote Tune Combiner unit (RTxx)
11 AC/DC Power Supply unit (PWSA)
12 Bias Tee unit (BPxx)
13 Dual Band Diplex Filter unit (DU2A)
NOTE: Items 12 & 13 are not plug-in units
2.2.1 Power Supply Unit:
The PWSx unit consists of the following functional blocks:
• Power input
• Power switcher
Power input block
The power input block on the PWSA unit consists of the following components:
• input circuit (mains filter, inrush current limiter, and rectifier)
• Power Factor Correction (PFC) preregulator
The input voltage is applied to the input circuit. The PFC preregulator converts
the input voltage to a stabilized intermediate voltage for the power switcher block,
improving the power factor.
The power input block on the PWSB unit consists of the following components:
• Input circuit
• Step-up converter
The input circuit filters the input voltage and limits the inrush current. The step-up
Converter converts the filtered input voltage to a stabilized intermediate
voltage for the power switcher block.
The power input block includes a DC/DC converter that supplies operating
voltage for the control block.
Power switcher block
The power switcher block consists of switched-mode circuits that convert the
intermediate voltage into the output voltages.
The control block consists of the input and output control circuits that monitor
and control the PWSx unit operation. The control block handles the following
• overvoltage and undervoltage protection
• overcurrent protection
• temperature protection
• unit synchronization
• front-panel LED control
• processing of the I2C function received from the BOIx unit
The PWSB unit uses a floating input voltage of 48 VDC and produces the
following regulated output voltages for other BTS units:
• +3.4 VDC
• +5.1 VDC
• ±9.1 VDC
• +13.5 VDC
• +26.2 VDC
• +55 VDC
2.2.2 Dual Variable Gain Duplex Filter:
The DVxx performs the following primary functions:
• combines transmitted and received signals into one antenna
• amplifies received signals with a variable-gain Low Noise Amplifier (LNA)
The DVxx unit includes two identical duplex filter sections.
Each section comprises a duplexer, a variable-gain LNA, and an I2C-bus I/O buffer block. Each LNA defaults into the high-gain state at startup and can be switched to the low-gain state through the I2C-bus using the Site Manager.
The gain of the low gain path can also be adjusted. The DVxx unit includes an I2C EEPROM that stores the serial number, information about the insertion loss variation of TX filters, and other data.
This information is used to compensate the frequency-dependent power variation of the transmitter. The I2C-bus also carries alarm signals to indicate fault conditions for each LNA branch. The signals are relayed to the Base Operations and Interfaces (BOIx) unit, which generates the alarms and displays them to the user interface.
The M2xx and M6xx are passive units. The units divide Received (RX) and Diversity-Received (DRX) signals and distribute them to the Transceiver (TSxx) units.
After receiving RX signals from the Dual Variable Gain Duplex Filter (DVxx) unit, the M2xx and M6xx distributes the RX signals to the TSxx units.
2.2.4 Wideband Combiner:
Front view of WCxx
The WCxx unit consists of the following components:
• one 2-way combiner
• two isolators
• one 50 Ù termination
• one heatsink for thermal dissipation
The WCxx unit combines transmit (TX) signals from two Transceiver (TSxx) units and feeds the combined signal to the TX port of the Dual Variable Gain Duplex Filter (DVxx) unit.
2.2.5 Transceiver Card:
Left isometric view
Block Diagram of Transceiver Card
Transceiver unit is the main part of BTS and the occupancy of a BTS is termed in number of TRX cards. Each card is responsible for transmitting and receiving the data and is solely responsible for anything related to radio. It receives the data to be transmitted from the baseband card, modulates it and forwards it to respective equipment. It receives the data caught by GSM antenna through respective equipments, demodulates it and sends it to baseband part for further processing.
The TSxx unit of the Nokia UltraSite EDGE BTS performs RF modulation/ demodulation and amplification for one RF carrier. The TSxx unit handles uplink signals from the Mobile Station (MS) to the BTS and downlink signals from the BTS to the MS.
The TSxx unit consists of the following modules:
• Transceiver (TRX)
• Frequency Hopping Synthesizer (FHS)
• Power Amplifier (PA)
• Power Supply (PSU)
The TRX module provides the main RF functions for the BTS. The TRX module has the following functional sections:
• Transmitter (TX)
• Receiver (RX)
• TRX loop
These functional sections communicate with the Transceiver Baseband (BB2x)
and Base Operations and Interfaces (BOIx) units through the backplane,
The functional sections process the following signals:
• data signals between the TSxx and BB2x units
• initialization and control signals from the BB2x unit to the TSxx unit
• status and alarm signals from the TSxx unit to the BB2x unit
The Interface converts the baseband (BB) data stream to GMSK modulation for the TX. It also converts the analogue RX frequency signal from the main and diversity branches to the data stream. It also handles clock distribution from the BB2x unit and alarm functions.
The intermediate frequency (IF) sections in the TX raise the signal to the carrier frequency. Thereafter, the RF section amplifies the signal to the desired output signal amplitude. The RF section also handles the signal power control. The TSxx unit supports 16 power levels with 2 dB steps, with a maximum range of 30 dB. Power levels from 0 to 6 are static; power levels from 7 to 15 are dynamic.
The RF section of the RX converts the carrier frequency signal to the IF frequency. The IF sections of the RX perform channel filtering and prevent interfering frequencies from distorting the signal. The IF sections also provide automatic gain control.
The TRX loop supports the self-testing of the TSxx unit. The tests are carried out by converting the frequency of the TX signal to the RX band. The signal is coupled from the TX output, and the resulting low-level signal is routed back through the RX path. The signal can be routed to the main branch or to the diversity branch.
Frequency Hopping Synthesizer (FHS)
The Frequency Hopping Synthesizer (FHS) module employs two FHSs — RX FHS and TX FHS—for RF frequency hopping. The RX FHS serves as the first local oscillator in the receiver. The TX FHS serves as the second local oscillator in the transmitter. Both the RX FHS and the TX FHS have two Phased Locked Loop (PLL) circuits. Each circuit contains a PLL, an amplification chain, and a switching network. The output buffer is common for both circuits. Each circuit has a voltage-supply regulator. Both FHSs work according to the Ping-Pong principle: The output frequency is taken alternately from the two PLLs.
The Power Amplifier (PA) module receives a GMSK-modulated signal from the TRX module and amplifies that signal to the appropriate level.
2.2.6 Baseband Card:
Block Diagram of Base Band Card
The BB2x unit of the Nokia UltraSite EDGE BTS has the following main
• performs digital signal processing for speech and data channels
• manages signaling for speech functions
The BB2x also:
• uses software downloaded from the Base Operations and Interfaces (BOIx) unit
• sets its timing according to references from the BOIx unit
• supports synthesized (RF) and Baseband (BB) frequency hopping
The BB2x unit has two independent BB sections. Each section communicates with the TRX module of one TSxx unit. Therefore, one BB2x unit can process two TSxx units, each with eight received and transmitted logical channels.
Each BB section consists of the following blocks:
• D-bus interface
• Control block
• Digital Signal Processor (DSP) block
• F-bus interface
The interface converts the BB data stream to TX. The interface also handles synthesizer control, clock distribution from the BB module, alarm functions, and TRX loop control.
In the downlink direction (BTS to MS), the BB2x unit sends transmission, initialisation, and synthesizer-control data to RF through a serial point-to-point line using HDLC protocol.
In the uplink direction (MS to BTS), the BB2x unit receives:
• I (In Phase) and Q (Quadrature) components of the normal and diversity branch data samples.
• RF alarms and status information through a serial point-to-point line
The D-bus interface synchronizes the signals transmitted and received through the D-bus. The D-bus interface also synchronizes data between the D-bus and Unit Controller (UC) processor and between the D-bus and Channel Digital Signal Processor (CHDSP).
The D-bus consists of the following buses:
• D1-bus, which transfers traffic and signaling data among the BB2x,VXxx, and BOIx units
• D2-bus, which transfers internal O&M communications (including software downloads) among the BOIx, BB2x, and Remote Tune Combiner (RTxx) units
The Control block handles the following functions:
• Clock generation and synchronization
• Alarm management
The Control block contains the UC processor, which runs the BTS software.
Digital Signal Processor
Each DSP block has an Equalizer DSP processor (EQDSP) and a Channel DSP processor (CHDSP).
Equalizer DSP processor
The EQDSP handles the following functions:
• Sample reception from RF
• Bit detection
• Channel equalization
Channel DSP processor
The CHDSP handles the following functions:
• sample transmission to RF
• channel decoding and encoding
• Ciphering and deciphering
The frequency-hopping bus (F-bus) between the BB2x units is used for BB hopping (moving TX and RX bursts between the BB2x units).
2.2.7 Transmission Card:
This card is the door to further hierarchy of GSM architecture. It deals with framing and deframing of E1 and cross connections.
In the block diagram FXC RRI is divided into the backplane and the application part. The backplane takes care of the cross-connections and interfaces to other transmission units within a node. The application part interfaces to either to radios or other RRI-units
Flex bus interfaces
The Flexbus interfaces handle the communication between the FXC RRI and the radio or another indoor unit.
• Cross-connection of data signals at 2 Mbit/s granularity
• Data rate adoption between 2M line interfaces and Flexbus interfaces
• Capacity bypassing from one Flexbus interface to another
• Alarm indication signal (AIS) detection
• Clock regeneration
E1 framer / deframer
• 16 x 2M framer/deframer
• 2M line termination
2.2.8 Base operations and Interface unit (BOIx)
The BOIx unit handles the control functions that are common to all other units in
Nokia UltraSite EDGE BTS.
These functions include:
Ø BTS initialisation and self-testing
Ø Operations and Maintenance (O&M) functions
Ø software downloads
Ø main clock functions
Ø timing functions
Ø collection and management of external and internal alarms
Ø delivery of messages to the Base Station Controller (BSC) through the
Ø Transmission (VXxx) unit
Ø cabinet control
The BSC or Nokia BTS Manager downloads software to the FLASH memory of the BOIx unit. (During download, an LED on the BOIx unit indicates the status of the board.) The BOIx unit downloads BTS software and configuration data to other BTS units.
The BOIx unit collects alarms from other active units and saves configuration information into non-volatile memory. The BOIx unit also controls the uplink and downlink cross-connection between the Transceiver Baseband unit (BB2x) and the Transceiver (TSxx) unit.
The BOIx unit detects unit alarms and performs recovery actions. In certain situations, the BOIx unit resets itself.
The BOIx unit generates an accurate reference clock signal for the TSxx unit, BB2x unit, and Remote Tune Combiner (RTxx) unit. The BTS can synchronize its frame clock and number with another Nokia Talk family BTS unit (with Talk as the clock master) or to another Nokia UltraSite EDGE BTS unit.
The mechanics of the BOIx unit provide EMI/EMC shielding for internal electrical components.
The following features are available with the BOIx unit:
Ø Self-testing to detect possible defects
Ø Local Management Port (LMP), an interface for the user to communicate with the main processor and control the BTS through the Nokia BTS Manager
Ø BTS software download, either from the BSC (through the Abis interface) or from Nokia BTS Manager
Ø One tri-colour LED that is controlled by the main processor and indicates the current status of the BOIx unit
Ø High-accuracy reference clock for timing generation; clock can be adjusted according to the Abis reference
The BOIx unit consists of the following functional blocks:
• Unit Controller (UC)
• Master Clock Generator (MCLG)
• Field Programmable Gate Array (FPGA)
The UC is the main BTS processor. It performs O&M communication through the
network and Nokia BTS Manager, and it controls the BTS units through the Dbus.
The BSC or Nokia BTSManager downloads software to the UC, which stores the
software in non-volatile memory. The UC downloads that software to the other
BTS units through the D2-bus. One tri-colour LED that is controlled by the main
processor indicates the current status of the BOIx unit.
Master Clock Generator
The MCLG generates the accurate clock for the BTS. Other common clock
signals (see Figure 3) are also derived from this clock reference and distributed to
The D-bus consists of two separate serial buses — D1-bus and D2-bus.
The BOIx unit, BB2x unit, and Transmission (VXxx) unit use the D1-bus to
transfer the following data over the Abis interface between the BTS and BSC:
• traffic and access channel data
• signalling data from the TRX module on the TSxx unit
• O&M signalling data
The BOIx, BB2x, and RTxx units use the D2-bus for internal O&M signaling and for internal communications, such as downloading software.
Field Programmable Gate Array
The FPGA handles the following functions:
• controls and monitors the status of the fans in the BTS
• checks the external frame clock
• allows flexible connections that are set by software between any TSxx unit and any BB2x unit
2.3 BTS Installation:
Commissioning of a BTS means setting up a new BTS or upgrading a BTS for working. The procedure is as follows:
After the BTS is constructed and the hardware is installed, various units inside the BTS are connected. Connections are on back panel through software settings as well as by wiring in front end.
After connections are over, hardware database is prepared on a laptop. Different units used in the database are added in the list. If the units need some configuration then they are done accordingly. Once all the units are included and configured, the software gives the wiring diagram. The wiring is checked with the wiring diagram.
Now the map of E1 is prepared. The traffic channels, TRX signaling, O&M signaling and EDGE signaling are mapped in the E1. TRX signaling is the telecom signaling of TRX with the BSC. O&M signaling transfer the detail and present configuration of BTS. EDGE signals are signals related to EDGE. This mapping depends on the level of signaling used like 16 kbps, 32 kbps or 64 kbps. If the site is in loop, then masking signals are also added. It has to be noted that this map has to be same as the map prepared by OMC. Then only the BTS will be able to communicate with the BSC.
Once the hardware database and E1 map are prepared, they are fed to the controller. Also the software needed for working of the BTS is installed in the controller.
The GSM antennas are mounted on the pole according to the sector directions provided by the planning. The feeders of the antenna are routed to the BTS shelter. Care is taken for minimum bending and avoiding losses. The cable loss and return loss of the antenna is measured by Site Master. Return loss and VSWR measurements should match the standards.
Now the link with the BSC or next BTS is established. The configurations needed are already done in the transmission unit. Now the microwave radio is aligned with the opposite microwave. Until the required minimum received power level is not obtained, the alignment is carried out. Once obtained, the radio is locked. So now the link is ready.
The BTS is ready to work now. The BTS is unlocked from the OMC. Call testing is done to check whether each sector is working properly or not and whether handover is done perfectly or not.
2.4 Commissioning of BTS
Ø Related software
Ø Hardware configuration
Ø Traffic allocation
Ø Creating cross-connections
The BTS is commissioned with BTS HW Configurator, UltraSite BTS Hub Manager (if there are FXC units in the configuration), BTS Manager (includes FC E1/T1 transmission unit configuration).
The following Nokia software applications relate to the Nokia UltraSite EDGE BTS:
• NMS and BSC software
• Nokia SiteWizard
• BTS software
Nokia SiteWizard is a collection of software for managing the Nokia UltraSite EDGE BTS on site. The applications run under Windows NT 4.0, Windows 95, or Windows 98.
Nokia SiteWizard consists of the following applications:
• Nokia BTS Manager for managing Nokia UltraSite EDGE base stations
• Nokia E1/T1 Manager for FC E1/T1, FXC E1, and FXC E1/T1 transmission units
• Nokia RRI Manager for FXC RRI transmission units
• Nokia Hopper Manager for Nokia MetroHopper and FlexiHopper Radio
• Nokia UltraSite BTS Hub Manager for the hub part of the UltraSite EDGE BTS
• Nokia BTS HW Configurator for configuring the UltraSite EDGE BTS cabinet
The commissioning procedure in Nokia SiteWizard consists of the following tasks:
• starting Nokia BTS HW Configurator for defining the BTS cabinet configuration
• starting Nokia UltraSite BTS Hub Manager for commissioning the FXC transmission units in the hub part of the BTS
• starting Nokia BTS Manager for commissioning the BTS (and FC transmission unit)
Figure Commissioning Procedure
HW configuration definition
If there is no predefined HW configuration file available for the BTS, you can create the configuration with the Create New Configuration option in the Wizard. Creating a new configuration with the Wizard requires no BTS connection, so you can create the configuration in advance and save it as an .hwc file. A BTS HW configuration file (Basic Configs.hwc) with basic UltraSite BTS configurations is delivered with Nokia BTS HW Configurator.
Choose Nokia BTS HW Configurator from the Nokia Applications submenu in the Start à Programs menu in Windows.
Choose the Wizard command on the Configuration menu.
Select the Check BTS Configuration and Update BTS option and click Next.
Different Views of the Hardware Configurator:
BB2 – TSx Connection
Rx Main Cabling
RX Diversity Cabling
Manual FXC transmission unit configuration
The transmission of the BTS and its Hub node must be configured and tested during the commissioning with Nokia UltraSite BTS Hub Manager.
To access the Hub node:
1. Choose Nokia UltraSite BTS Hub Manager on the Nokia Applications submenu on the Start à Programs menu in Windows.
2. Choose the Connect Locally command on the Connection menu.
The equipment view opens automatically when the connection has been established.
If the connection fails, check the connection speed and LMP cable connection. Also, in the case of failure, make sure the manager SW installation is complete. You can also try the Connection à Connect... command and enter the connection parameters in the Connect to Node dialog box.
3. Right-click on a unit in the Equipment view and choose Install All from the pop-up menu.
Line interface settings
The line interface settings available for each transmission unit depend on the type of the unit: FXC E1(/T1) or FXC RRI.
Line interface settings for E1 120 ohm mode
TS0 fixed bits from 1 to 3 are reserved for CRC and frame locking. Bits from 4 to 8 are used for alarms and data transfer in national connections.
Line interface settings for T1 100 ohm interface mode
LIF settings with FXC RRI unit
If there are FXC RRI transmission units in the configuration, you also need to configure the outdoor units (Nokia FlexiHopper or Nokia MetroHopper microwave radios) connected to the RRI units.
1. Click a FXC RRI transmission unit in the Equipment view in UltraSite BTS Hub Manager.
2. Choose Radio Wizard on the FXC RRI menu to launch the Wizard. The Radio Wizard is launched from the Nokia RRI Manager application.
3. The Flexbus Settings page displays the type of the indoor unit and the outdoor units connected to each Flexbus
Select the capacity for each outdoor unit from the Capacity list and select the In Use option for each Flexbus you want to use.
Click Next to continue.
4. The Flexbus 1 settings page appears on the screen. The options on the page depend on the outdoor unit connected to the interface. The settings for the FlexiHopper outdoor unit are presented in Figure below.
Choose the Synchronization command on the Configure menu in Nokia UltraSite BTS Hub Manager. The Synchronization dialog box appears.
2. Select the Rx Clock timing option for Priority 1 and select the unit and interface that is used for synchronization (coming from uplink direction). You can define settings for other priorities in the same way
Click OK to accept the changes.
At this point of the commissioning procedure, you need to allocate BTS transmission capacity on the D-bus. The allocation is made with the Traffic Manager, which is a graphical tool that allows you to allocate BTS transmission capacity independent of which Nokia UltraSite transmission unit is used
Open Traffic Manager by choosing the Traffic Manager command on the Tools menu in Nokia UltraSite BTS Hub Manager.
Select the line interface used: Port 1 - Port 4 with FXC E1(/T1) and Port 1 - Port 16 with RRI transmission units. There is only Port 1 available for an FC E1/T1 unit, because it has only one line interface.
Click the TCHs button and then click in a cell in the Abis timeslot allocation table. Repeat this step to allocate transmission capacity to all TRXs in the BTS configuration.
From here onwards, you have two alternative ways to proceed.
Alternative 1. Click the TRXSIG button and then click the first bit in a timeslot in the Abis allocation table. Select the link speed from the pop-up menu. Repeat for all TRXs in the BTS configuration. Click the OMUSIG button and then click a cell in the Abis allocation table. Select the link speed from the pop-up menu.
Alternative 2. Click the TRXSIG on TCHs button and then click the first bit in a timeslot you reserved for TCHs in Step 3. Select the link speed from the pop-up menu. Repeat for all TRXs in the BTS configuration. Click the OMUSIG button and then click a cell in the Abis allocation table. Select the link speed from the pop-up menu.
Check that the signal timing (either 'Normal' or 'Satellite') is correctly set.
Click the OK button to send the information to the BTS.
The signal types are discussed
Signal Types :
OMUSIG: The BTS can have one OMUSIG which allocates 2, 4 or 8 bits in one time slot depending on the link speed used (16,32 or 64 kbit/s)
TCHs: The BTS must be allocated at least as many TCHs as there are TRXs installed in it (1 - 12). Each TCH allocates 2 contiguous time slots (16 bits) for a single TRX each of which is marked with the TRX number. The TCHs are numbered from 1 to 12 in order of which they are defined.
TRXSIG: The BTS must be allocated at least as many TRXSIGs as there are TRXs installed in it (1 - 12). Each TRXSIG can allocate 2, 4 or 8 bits in one time slot depending on the link speed used (16, 32 or 64 kbit/s). The TRXSIGs are numbered from 1 to 12 in order of which they are entered.
TRXSIG on TCHs: The TRXSIG can be reserved on a traffic channel (TCH) but then up to 4 radio time slots (8 bits) are lost. The signal type must always start from the first bit of the channel.
Cross-connections define how signals are routed from an FXC transmission unit to another transmission unit. Cross-connections are created into banks which are either active or inactive. The cross-connections in the active banks are in use, whereas those in the inactive banks can be used for creating or editing cross-connections.
Start creating cross-connections by choosing the View command on the Cross-connections menu in UltraSite BTS Hub Manager.
Open the inactive bank page.
Open the Add Cross-Connection dialog box.
4. Define the following settings according to the cross-connection plan:
· label, i.e. the name of the new cross-connection (max. 80 characters)
· cross-connection type;
· granularity (with nx64k set also its coefficient n)
5. For a FXC RRI Card, select a flexbus. Also select an interface and channel.
If the E1 is to be bypassed without being used at the site, then select another Flexbus. Also select interface and channel for second flexbus.
If the E1 is to be used at the site then select a channel and interface for the BOI port.
8. Activate the bank by selecting the Activate command from the Cross connections à Banks menu and click OK.
9. Close the views and the Cross-connection tool.
10. Exit UltraSite BTS Hub Manager.
Manual BTS commissioning
Manual commissioning can be done only with a non-commissioned BTS. If the BTS to be commissioned is already commissioned, you need to first run the Undo Commissioning procedure in BTS Commissioning Wizard. BTS SW is loaded to the BTS by the manufacturer. There is usually no need to locally load SW to the BTS during commissioning.
Start manual BTS commissioning as follows:
1. Choose Nokia BTS Manager from the Nokia Applications submenu on the Startà Programs menu in Windows.
2. Choose Wizard on the Commissioning menu.
3. Select the Manual Commissioning option and click Next.
4. Enter the following optional information on the Set Transmission Parameters page and click Next to continue.
·Site name ·Site ID ·BCF ID ·BSC ID ·IP Address ·Network ID
5. Click the Start Commissioning button to send the commissioning parameters to the BTS.
During the BTS/BSC start-up scenario the BSC checks the BTS SW and if it is not the correct one, the BSC loads SW to the BTS. This downloading will take from 5 to 20 minutes depending on the link speed, and the BCF is reset automatically, which means that the Supervision and Alarms windows disappear for a few seconds, but the commissioning procedure continues after the BTS has started normally. If no SW downloading takes place, the process will take about 10 seconds. After that the BSC sends the configuration data to the BTS.
When the BTS is ready for testing, the Wizard automatically proceeds to the next page and the BSC runs automatic tests on the Abis link and on each TRX installed in the BTS.
If there is no BSC connection (the BCF remains in the 'Waiting for LAPD') state and you click Next, the Wizard asks if you want to give the Use Current command. If you click Yes, the BTS starts to use the BTS SW in the BOI unit memory and the Wizard proceeds to the BTS Test Reporting page. If you click No, the BCF remains in the 'Waiting for LAPD' state, until the BSC connection (OMUSIG link) is established.
6. When the BCF is in the 'Supervisory' state and the TRXs are ready for testing, the BTS tests are run under the BSC's control. The BSC runs automatic tests on the Abis link and on each TRX installed in the BTS. The TRX test takes about 6 - 7 seconds for one TRX (one radio time slot per TRX is tested), while the Abis loop test takes about 30 seconds per TRX.
If the establishment of the BTS/BSC connection did not succeed and you gave the Use Current command in the previous step, you can click the Manual button to run local TRX tests.
7. Check EAC inputs 1- 12 if they will be used. Mark the required EACs as 'In Use'. After testing the EACs, mark them 'Checked'. When you have completed the testing (or checking), click Next.
8. Check EAC inputs 13 - 24 like inputs 1 - 12. When you have completed the testing (or checking) or if these EAC inputs will not be used, click Next.
9. Check the EAC outputs (if they will be used) by changing the EAC states. Mark the required EACs as 'In Use' . When you have finished the EAC output settings, click the Set Outputs button to send the information to the BTS. After you have completed checking, click Next.
10. Check the BTS Commissioning Report.
11. Click Finish to save the report.
12. Choose the Exit command on the File menu to quit BTS Manager.
13. Disconnect your laptop PC from the BTS's LMP port.
3. RADIO UNITS
3.2 Indoor Units………………………………………... .71
3.3 Outdoor Unit………………………………………....73
3.4 Commissioning FlexiHopper………………………...77
In the early 1970s, digital transmission systems began to appear, utilizing a method known as Pulse Code Modulation (PCM), first proposed by STC in 1937. PCM allowed analog waveforms, such as the human voice, to be represented in binary form, and using this method it was possible to represent a standard 4 kHz analog telephone signal as a 64 kbps digital bit stream. Engineers saw the potential to produce more cost effective transmission systems by combining several PCM channels and transmitting them down the same copper twisted pair as had previously been occupied by a single analog signal.
In Europe, and subsequently in many other parts of the world, a standard TDM scheme was adopted whereby thirty 64 kbps channels were combined, together with two additional channels carrying control information, to produce a channel with a bit rate of 2.048 Mbps.
As demand for voice telephony increased, and levels of traffic in the network grew ever higher, it became clear that the standard 2 Mbps signal was not sufficient to cope with the traffic loads occurring in the trunk network. In order to avoid having to use excessively large numbers of 2 Mbps links, it was decided to create a further level of multiplexing. The standard adopted in Europe involved the combination of four 2 Mbps channels to produce a single 8 Mbps channel. This level of multiplexing differed slightly from the previous in that the incoming signals were combined one bit at a time instead of one byte at a time i.e. bit interleaving was used as opposed to byte interleaving. As the need arose, further levels of multiplexing were added to the standard at 34 Mbit/s, 140 Mbps, and 565 Mbps to produce a full hierarchy of bit rates.
Plesiochronous Digital Hierarchy:
The multiplexing hierarchy described appears simple enough in principle but there are complications. When multiplexing a number of 2 Mbit/s channels they are likely to have been created by different pieces of equipment, each generating a slightly different bit rate. Thus, before these 2 Mbit/s channels can be bit interleaved they must all be brought up to the same bit rate adding 'dummy' information bits, or 'justification bits'. The justification bits are recognizing as such when demultiplexing occurs, and discarded, leaving the original signal. This process is known as plesiochronous operation, from Greek, meaning "almost synchronous".
The same problems with synchronization, as described above, occur at every level of the multiplexing hierarchy, so justification bits are added at each stage. The use of plesiochronous operation throughout the hierarchy has led to adoption of the term "plesiochronous digital hierarchy", or PDH
Limitations of PDH:
The problem of flexibility in a plesiochronous network is illustrated by considering what a network operator may need to do in order to be able to provide a business customer with a 2 Mbit\s leased line. If a high-speed channel passes near the customer, the operation of providing him with a single 2 Mbit\s line from within that channel would seem straightforward enough. In practice, however, it is not so simple.
The use of justification bits at each level in the PDH means that identifying the exact location of the frames in a single 2 Mbit\s line within say a 140 Mbit\s channel is impossible. In order to access a single 2 Mbit\s line the 140 Mbit\s channel must be completely demultiplexed to its 64 constituent 2 Mbit\s lines via 34 and 8 Mbit\s. Once the required 2 Mbit\s line has been identified and extracted, the channels must then be multiplexed back up to 140 Mbit\s.
Obviously this problem with the "drop and insert" of channels does not make for very flexible connection patterns or rapid provisioning of services, while the "multiplexer mountains" required are extremely expensive.
Another problem associated with the huge amount of multiplexing equipment in the network is one of control, maintenance and thereby reliability. On its way through the network, a 2 Mbit\s leased line may have traveled via a number of possible routes. The only way to ensure it follows the correct path is to keep careful records of the interconnection of the equipment.
However, as the amount of reconnection activity in the network increases it becomes more difficult to keep records current and the possibility of mistakes increases. Such mistakes are likely to affect not only the connection being established but also to disrupt existing connections carrying live traffic.
Another limitation of the PDH is its lack of performance monitoring capability. Operators are coming under increasing pressure to provide business customers with improved availability and error performance, and there is insufficient provision for network management within the PDH frame format for them to be able to do this.
Synchronous Digital Hierarchy:
PDH has reached a point where it is no longer sufficiently flexible or efficient to meet the demands being placed on it. As a result, a synchronous transmission has been developed to overcome the problems associated with plesiochronous transmission, in particular the inability of PDH to extract individual circuits from high capacity systems without having to demultiplex the whole system.
Synchronous transmission can be seen as the next stage in the evolution of the transmission hierarchy. A concerted standards effort has been involved in its development. The opportunity of defining this new standard has been used to address a number of other problems. Among these have been network management capabilities within the hierarchy, the need to define standard interfaces between equipment, and European transmission hierarchies.
This standards work culminated in CCTTT Recommendations G.707,G.708, and G.709 covering the Synchronous Digital Hierarchy (SDH). These were published in the CCTTT Blue Book in 1989. In North America ANSI published its SONET standards, which can now be thought of as a subset of the worldwide SDH standards.
In addition to the three main CCTTT recommendations, a number of working groups were set up to draft further recommendations covering other aspects of the SDH, such as the requirements for standard optical interfaces and standard O&M functions.
The CCTTT recommendations define a number of basic transmission rates within the SDH. The first of these is 155 Mbit\s, normally referred to as STM - 1 (where STM stands for 'synchronous Transport Module'). Higher transmission rates of STM - 4 and STM - 16 (622 Mbit\s and 2.4 Gbit\s respectively) are also defined, with further levels proposed for study.
The recommendations also define a multiplexing structure whereby an STM - 1 signal can carry a number of lower rate signals as payload, thus allowing existing PDH signals to be carried over a synchronous network. This process will be explained in more detail below.
Principles of SDH:
Despite its obvious advantages over PDH, SDH would have been unlikely to gain acceptance if its adoption had immediately made all existing PDH equipment obsolete. This is why the CCTTT Recommendations made provisions from the outset for any currently used transmission rate to be packaged into an STM - 1 frame. All plesiochronous signals between 1.5 Mbit\s and 140Mbit\s can be accommodated, with the ways in which they can be combined to form an STM - 1 signal defined in Recommendation G.709. The SDH multiplexing hierarchy is shown in figure 1 below. A brief explanation of how the hierarchy works follows.
Figure plesiochronous digital hierarchy
SDH defines a number of "Containers", each corresponding to an existing plesiochronous rate. Information from a plesiochronous signal is mapped into the relevant container. The way in which this is done is similar to the bit stuffing procedure carried out in a conventional PDH multiplexer. Each container then has some control information known as the "path overhead" added to it . The path overhead bytes allow the network operator to achieve end-path monitoring of things such as error rates. Together the container and the path overhead form a "Virtual Container".
In a synchronous network, all equipment is synchronized to an overall network clock. It is important to note, however, that the delay associated with a transmission link may vary slightly with time. As a result, the location of virtual containers within an STM - 1 frame may not be fixed. Associating a pointer with each VC accommodates these variations. The pointer indicates the position of the beginning of the VC in relation to the STM - 1 frame. It can be incremented or decremented as necessary to accommodate of the position of the VC.
G.709 defines different combinations of virtual containers, which can be used to fill up the payload area of an STM - 1 frame. The process of loading containers and attaching overhead is repeated at several levels in the SDH, resulting in the "nesting" of smaller VCs within larger ones. This process is repeated until the largest size of VC (a VC - 4 in Europe) is filled, and this is then loaded into the payload of the STM - 1 frame. When the payload area of the STM - 1 frame is full, some more control information bytes are added to the frame to form the "Section Overhead". The section overhead bytes are so-called because they remain with the payload for the fiber section between two synchronous multiplexers. Their purpose is to provide communication channels for functions such as O&M facilities, alignment and a number of other functions.
When a higher transmission rate than 155 Mbit\s of STM - 1 is required in synchronous network, it is achieved by using a relatively straightforward byte - interleaved multiplexing scheme. In this way, rates of 622 Mbit\s (STM - 4) and 2.4 Gbit\s (STM - 16) can be achieved.
Benefits of SDH
Synchronous transmission overcomes the limitations experienced in a plesiochronous network. It allows the network to evolve to meet the new demands being placed upon it. Synchronous offers a number of benefits, both to telecom, network operators, and to end users.
One of the main benefits seen by a network operator is the network simplification brought about through the use of synchronous equipment. A single synchronous Multiplexer can perform the function of an entire plesiochronous "Multiplexer mountain", leading to significant reductions in the amount of equipment used. Lower operation costs will also result due to the reduction in required spare inventory, simplified maintenance, the reduction in floor space required by equipment and lower power consumptions. The more efficient "drop and insert" of channels offered by an SDH network, together with its powerful network management capabilities, will lead to greater ease in provisioning of high bandwidth lines for new multimedia services, as well as ubiquitous access to those services. Thus, the simplification of the network, and the new flexibility this brings, opens up the potential for the network operator to generate new revenues.
The deployment of optical fiber throughout the network and adoption of the SDH network elements makes end-to-end monitoring and maintenance of network integrity a possibility. The network management capability of the synchronous network will enable immediate identification of link and node failure. Using self-healing ring architectures, the network will be automatically reconfigured with traffic instantly rerouted until the faulty equipment has been repaired.
Thus, failures in the network transport mechanism will be invisible on an end-to-end basis. Such failures will not disrupt services, allowing network operators to commit to extremely high availability of service figures, and guarantee high levels of network performance.
Provision of network management channels within the SDH frame structure means that the synchronous network will be fully software controllable. Network management systems will not only perform traditional event management functions such as dealing with alarms in the network, but will also provide a host of other functions, like performance monitoring, configuration management, resource management, network security, inventory management, and network planning and design.
The possibility of remote provisioning and centralized maintenance will result in a great savings in time spent by maintenance personnel in traveling to remote sites, and this of course corresponds to a reduction of expenses.
BANDWIDTH ON DEMAND
In a synchronous network it will be possible to dynamically allocate network capacity, or bandwidth, on demand. Users anywhere within the network will be able to subscribe at very short notice to any service offered over the network, some of which may require large amounts of bandwidth. An example of this is dial-up video-conferencing. Users will be able to obtain the required bandwidth for a video-conferencing link just by dialing the appropriate number, as opposed to the current situation where video-conferencing links must reserved days in advance.
Many other new services become possible in a synchronous network. These will represent new sources of revenue for network operators, and provide increased conveniences for users. Some examples of such services are high-speed packet switched services, LAN interconnection and High Definition TV (HDTV).
The synchronous digital hierarchy offers network operators a future-proof network solution, plus the ability to upgrade software and extensions to existing equipment. They can be confident their investment in equipment is money well spent because synchronous has been selected as the bearer network for the next generation of telecommunication networks, the Broadband ISDN (B-ISDN). B-ISDN will enable all users to have access to the network at rates in the order of Mega bits per second.
The Transmission Units connects more than one Base Transceiver Station (BTS) to the rest of the network.
Transmission units are available for the following mediums:
2) Fiber optic
q Radio Link Transmission:
The BSS network of Vodafone in Navsari is under MSC of Surat. It has 2 BSC and approximately 105 BTSs.
This BTSs and BSCs are inter connected through various mediums and various topologies.
The sites are connected to the nodes in different topologies like Star, loop or chain.
Loop star chain
Each topology has its pros and cons. The decision of topology to be implemented depends on factors like geographical location, nearby sites and protection issues. For e.g. If the sites are on highway or in remote area, then we prefer chain. In cities, we go for loops. Loops require additional resources but it provides the protection which is necessary.
Mediums are Microwave and Fiber optics. At present the main nodes are connected through Fiber while communication between main nodes and rest of sites is through microwave link.
Figure microwave medium
As stated before, microwave medium or links is usually used for providing transmission medium to the locations where still fiber network has not reached.
A microwave link is a point to point link between two locations. The origination is the node providing transmission and the destination is location where the transmission will be used. The E1s will be transmitted in bundles. The E1s to be used at a particular site will be dropped and rest will be by passed. The capacity of link is not fixed. A backbone link is of maximum STM1 while the links between sites can be of 2,4,8 or16 E1s.
Hops of NERA and NEC are capable of STM1 while Nokia is capable of maximum 16 E1s capacity.
For microwave link, we require following equipments:
· Microwave antenna
· Indoor unit
· Outdoor unit
3.2 Indoor Units:
There are a number of Radio Link Transmission Units. Each indoor unit can support two outdoor units (excluding FC RRI).
FIU 19 unit
The interface capacity of FIU 19 unit can be from 4 x 2 up to 16 x 2 Mbit/s. It can be expanded easily with plug-in units in 4 x 2 Mbit/s increments. The 16 x 2 Mbit/s interface capacity requires the expansion unit, which is the same size as the main unit.
The 2 Mbit/s cross connection function is integrated into FIU 19.
Up to four outdoor units can be connected to one FIU 19 unit. When four Outdoor units are connected, an additional plug-in unit is required and one of the transmission directions must be protected.
Note: The power consumption of an average IU + OU combination is 35 W.
Functions of IDU
IDU convert RF signal to IF signal in Uplink and also convert IF signal to RF signal in downlink
· IDU operate on negative voltage (-48v) .
· FIU 19 have three plug in unit. Each have 4 x 2Mbit/s capacity.
· Q1 bus used for remotely logine through TNMS. Which is connected on top of BTS (Q!ss)
· Q2 is used if second IDU is used. It is connected with Q1 of second IDU.
· One Flexbus is used for droping 2 Mbits / s and other flex bus used for bypass 2 Mbits / s.
· If FXC RRI used as transmission unit, then Indoor unit is not used.
· a signal connected to the Q1-1 port is routed to the Flexbus interfaces (radio path), to FIU 19 processor, and out from the Q1-2 port. The same applies vice versa to a signal connected to the Q1-2 port.
· Multiplexing and Demultiplexing also done in IDU
Q1 Management helps in managing the transmission equipment remotely. Q1 bus is the management connection to the Nokia Management System (NMS).
Each network element is given a Q1 port network element address and an LMP network element address. Network element addresses run from 0 to 3999. Each network element is also given a Q1 port group address and an LMP group address. Group addresses run from 4050 to 4059.
The Q1 port address is used when managing the network element (NE) remotely. NEs within the same Q1 bus must have unique network element addresses. The Q1 group address is common to a group of network elements. With it, operations can be done to the whole group simultaneously.
The LMP address is used when managing the network element locally and it can be the same from site to site.
3.3 Outdoor Unit
· All frequency bands use the same technical concept and a similar mechanical construction. The only mechanical difference between outdoor unit is the length of the collar which houses the antenna filter; the lower the frequency the longer the filter and the collar.
· Typical Maximum output power is 16 – 20 dBm.
Function of ODU(out door unit)
· ODU convert IF signal to RF signal in uplink direction and also convert RF signal to IF signal in downlink direction.
· ODU also done modulation ( /4 QPSK) and demodulation, amplification.
Two types of Outdoor Unit
· HIGH ODU (27 dbm)
· LOW ODU (23 dbm)
Flexi Hopper :
25dbm -6 dbm
Nokia FlexiHopper Microwave Radio
A Nokia FlexiHopper network element consists of an indoor unit (IU) and an outdoor unit (OU). The units are connected together with a single coaxial cable, Flexbus. The Flexbus cable can be up to 300 m long.
The Nokia FlexiHopper Microwave Radio family includes models for the 13, 15, 18, 23, 26, and 38 GHz frequency bands. The radio transmission capacity of all Nokia FlexiHopper models is 2 x 2, 4 x 2, 8 x 2, or 16 x 2 Mbit/s. This can be selected using the node manager or the network management system (NMS) without any hardware changes.
One indoor unit supports two outdoor units
Nokia supplies four different indoor units for Nokia FlexiHopper to provide optimal features for different environments. All frequency bands use the same indoor units. One indoor unit (excluding FC RRI) can support two outdoor units. Up to four outdoor units can be connected to one FIU 19 indoor unit. When four outdoor units are used, one of the transmission directions must be protected. The full radio capacity from 2 x 2 Mbit/s up to 16 x 2 Mbit/s is available with all indoor unit models. The add/drop capacity varies according to the indoor unit model. The same indoor units can also be used with Nokia MetroHopper at 4 x 2 Mbit/s radio capacity.
Easy to use management system
Nokia FlexiHopper can be fully controlled and managed locally by
• Nokia Hopper Manager (with FIU 19 and RRIC)
• Nokia SiteWizard (with FC RRI and FXC RRI)
or remotely with the Nokia NMS.
Flexbus: single cable interconnections
The bidirectional Flexbus cable connects all system elements together. Flexbus carries 1 - 16 x 2Mbit/s signals and control data between the elements of the node, from the indoor unit to the outdoor unit, as well as from one indoor unit to another indoor unit. Flexbus also feeds power to the outdoor unit.
Figure The basic Nokia FlexiHopper node configuration, one indoor unit and one outdoor unit and Flexbus
Forward error correction and interleaving:
Nokia FlexiHopper radios use forward error correction (FEC) and interleaving to improve signal quality. The FEC is continuously on and the interleaving is selectable between off, 2-depth, and 4-depth modes. The forward error correction uses Reed-Solomon coding (RS (63,59)). The code uses 4 redundancy symbols for every 59 data symbols, so the redundancy of the coding is 6.4%. Together with interleaving also errors of burst type can be corrected. Maximum error correction effectiveness is achieved with 4-depth interleaving.
When the interleaving is in use, transmission delay increases slightly. This is normally not a problem, but in long chains of radio-links the delay accumulates, and it might be necessary to turn the interleaving off. Acceptable delay for a chain of links should be determined in transmission planning stage and the interleaving status set accordingly.
ALCQ (Adaptive Level Control with Quality measure)
ALCQ is a method for automatic transmit power control. This feature enables the radio transmitter to increase or decrease the transmit power automatically, according to the response received from the other end of the hop. This approach achieves more efficient utilization of radio frequencies than the constant level approach. The controlled use of transmit power reduces interference between systems, which in turn allows tighter packing of radio links within the same geographical area or at network star points.
The maximum transmit power is set with Nokia Hopper Manager. When ALCQ is in use, the radio always tries to transmit at minimum power. The minimum power is calculated from the fading margin value which is also set with Nokia Hopper Manager. This value can be obtained by doing a fading margin measurement test or the value calculated by the transmission planning can be used.
If the fading increases rapidly (multipath fading), the radio reacts immediately by increasing the power, but not higher than the set maximum value. After the fading conditions resume to normal, the power is gradually decreased. ALCQ also reacts to slow changes in fading conditions by gradually increasing the transmit power.
Automatic fading margin measurement
During the commissioning of a microwave radio, the operator may wish to measure the fading margin of the radio hop. Traditionally this has required much work and additional hardware, such as RF (radio frequency) attenuators. In Nokia FlexiHopper, the fading margin measurement is automatic and can be started simply by using software.
3.4 Commissioning Nokia FlexiHopper
Connecting the communication cable
If Nokia Hopper Manager is used for local management, the computer must be connected to the indoor unit using the communication cable. The cable has a D9 (female) serial connector at one end and a BQ connector at the other.
Connect the BQ connector to the local management port (LMP) of the indoor unit (FIU 19 or RRIC). Connect the other end to COM1 or COM2 port of the PC.
Figure Connecting the communication cable
The Equipment View window is opened whenever you are managing a network element or virtual node file. This window is also the connection to the network element. If this window is closed, the connection is closed.
The window displays the configuration of the managed network element. This window can also be used to access the settings and identifications of each unit. Pressing the right mouse button while the mouse pointer is over a unit will display a menu.
The status information for the radio hop and the LED status of the functional entities of the node can also be shown in this window. This information is updated periodically. The settings for this automatic refresh can be changed from the View Settings controls in the window.
Figure Nokia Hopper Manager window with FIU 19 Equipment View windo
1. Switch the power on.
2. Connect the LMP cable between the PC and the indoor unit and start Nokia Hopper Manager.
3. Set up the connection to the network element and run commissioning wizard.
To commission a network element, click Manage → Commission.... This will start the commissioning wizard.
4. Click Next to continue with the commissioning wizard.
5. Enter the site information (optional).
• Equipment name
• Group name
• Site name
• Site location.
6. Check for any connected outdoor units by selecting the appropriate Flexbus interfaces from the list and clicking Start. This will turn on the Flexbus power. Nokia Hopper Manager will notify you when any connected outdoor units are found. If you know that the Flexbus power is already on (for example, if it can be seen on the Equipment View window), you can bypass the scanning process and move to the next page.
7. Select the station type and protection mode.
8. Select if the Flexbus interfaces are in use and set their capacities.
9. Select the settings for the Q1 port and the local management port.
• Baud rate • Q1 group address • Q1 address.
10. Select the Q1 bus routing, which defines the way Q1 commands are routed through the network element.
11. Select the settings for the outdoor units connected to each Flexbus interface:
• Tx frequency • Maximum Tx power • Tx power on/off.
12. When you have entered all the required settings a summary of commissioning settings is displayed. It contains all the settings you have defined for the radio(s). Check that the settings are correct and click
Next to send the settings to the node. You can also go back in case you want to adjust the
settings on previous pages.
13. After sending the commissioning settings, you can check the hop status of all the connected outdoor units. For each Flexbus interface the connected outdoor unit is shown along with its current state and received input level.
14. On the last page you can set the node clock and installation information for the units. After you have done this, click Finish to complete the wizard.
Note: The status of the hop will not be ready before also the other end of the hop is commissioned successfully.
15. Fine-align the antenna.
16. Make the cross-connections with the manager.
• FIU 19: using Nokia Hopper Manager.
• RRIC: using TruMan.
17. Make any additional settings with the manager. These settings can include:
• Interleaving depth
• Identification data.
18. Monitor the hop for at least half an hour.
19. Save a copy of the node to a file.
20. Back up the IU and OU configurations (recommended in 2IU+2OU protected mode).
21. Export the alarm log and the measurements and statistics recorded for the network element to a file.
22. Close the connection to the node.
4. BASE STATION CONTROLLER
4.1 General design of the BSC………………………….. 88
4.2 Functionality of BSC……………………………….. 88
4.3 overview Of Block Diagram……………………….. . 93
4.4 Cabling……………………………………………... 96
4.5 Establishment of Link for new site with BSC……… 99
4.1General design of the BSC
BSC is the main module of Base Station Subsystem. The main features of the BSC platform are:
· BSC2E/A and BSCE expandability in 16 TRX steps from 16 TRXs to up to 128 TRXs and above that to 256 TRXs in the Large Capacity BSC configuration. With the High Capacity BSC option the expandability reaches up to 512 TRXs.
· the modular architecture allows you to build economically dimensioned switching systems according to your needs, and it also reduces the cost of surplus capacity and enables new facilities to be readily added.
General design of the BSC
· The GSM/EDGE BSC is based on a modular software (SW) and hardware (HW) structure. Because there are exact specifications for the interfaces between different modules, new functions can easily be added without changing the architecture of the system. Thus, the GSM/EDGE BSC can have a long operational lifespan and still always have up-to-date features.
The distributed architecture of the GSM/EDGE BSC is implemented by a multiprocessor system. In a multiprocessor system the data processing capacity is divided among several computer units, each of which has a microcomputer of its own. Call handling capacity depends on the number of Call Control Computer Units. The capacity of the BSC can easily be increased by adding more Call Control Computer Units to the BSC.
4.2 Functionality of BSC
The BSC can be located flexibly in the GSM network. It can be installed as stand-alone, on the same site as the Base Transceiver Station (BTS) it controls, or at a remote location, which can be either co-located or non-co-located with the MSC. The most common solution is to locate the BSC remotely from the MSC near the BTSs it controls and install the Transcoder Submultiplexer (TCSM) at the MSC site. Submultiplexing can then be used between the BSC and TCSM to reduce transmission costs. The BSC manages a variety of tasks ranging from channel administration to short message service. The main functionalities of BSC are explained in brief below.
Management of terrestrial channels
• Indication of blocking on the A interface channels between the BSC and the MSC
• Allocation of traffic channels between the BSC and the BTSs
• Concept support for flexible channel assignments, for example, half rate and high speed circuit switched data
Management of radio channels
• Management of channel configurations, that is, how many traffic channels and signaling channels can be used in the BSS. This is done in connection with radio network configuration.
• Management of traffic channels (TCH) and stand-alone dedicated control channels (SDCCH).
This function can be subdivided into the following tasks:
- Resource management
- channel allocation
- Link supervision
- channel release
- Power control
• Management of broadcast control channels (BCCH) and common control channels (CCCH).
This function can be subdivided into the following tasks:
- channel management
- random access
- access grant
• Management of frequency hopping:
The BSC is in charge of frequency hopping management which enables effective use of radio resources and enhanced voice quality for a GSM subscriber.
The frequency of the mobile is changed in connection with handovers which are executed and controlled by the BSC. Such a handover can be one of the following three types:
- intra-BSC, intra-cell (both intra-TRX and inter-TRX), which means that the handover takes place within the area controlled by the BSC and the mobile stays in the same cell
- intra-BSC, inter-cell, which means that the mobile stays in the area of the BSC but moves from one cell to another
- inter-BSC, both outgoing and incoming, which means that the
mobile moves into the area of another BSC
Management of signaling channels between the BSC and the BTSs
The BSC supervises all 16, 32 or 64 kbit/s permanent point-to-point LAPD Signaling connections, consisting of one connection per Transceiver Unit (TRX) and BTS Operation and Maintenance Unit (OMU).
The BSC offers the possibility for the following maintenance procedures:
• Fault localization for the BSC
• Reconfiguration of the BSC
• Reconfiguration support to the BTS
• Updating of the software in the BSC, TCSM2 and BTS
During normal operation, the BSC offers various possibilities for the operator:
• Modification of the parameters of the BSC and the BTS
• Modification of the radio network parameters
• Configuration of the BSC hardware
• Administration of the BSC equipment
The BSC has a user-friendly interface with plain-text messages and commands, which are easy to learn and use. This user interface complies with the recommendations of the International Telecommunication Union (ITU-T).
Short Message Service (SMS)
The BSC forwards mobile originating and mobile terminating short messages transparently.
Cell Broadcast Messages (CB)
Cell Broadcast provides the BSC with the short message service cell broadcast (SMSCB) capabilities defined by GSM recommendations. The SMSCB is a basic teleservice that is used for broadcasting short messages to mobile stations in a specified area within the PLMN.
Full Rate/Half Rate/EFR
The BSC supports Full Rate traffic channels, Half Rate traffic channels, and Enhanced Full Rate traffic channels.
Adaptive Multi Rate Codec
Adaptive Multi Rate Codec (AMR) introduces a new set of codecs and adaptive algorithm for codec changes and thus can provide significantly better speech quality and more capacity on the air interface. With AMR we can achieve very good speech quality in full rate (FR) mode even in low C/I conditions or increase the speech capacity by using the half rate (HR) mode and still maintain the quality level of current FR calls. Optimal interworking with power control and handover algorithms together with enhanced quality measurements (FER Measurement feature) will provide full benefits and interworking with prior Nokia top-of-the world capacity features including Intelligent Frequency Hopping (IFH). The Adaptive Multi Rate (AMR) codec consists of a family of codecs (source and channel codes with different trade-off bit-rates) operating in the GSM FR and HR channels. The idea behind the AMR codec concept is that it is capable of adapting its operation optimally according to the prevailing channel conditions.
General Packet Radio Service (GPRS)
Data and internet services will be the areas of future growth in mobile communications. Mobile data is the key to open the door to the high revenue corporate sector and to value-added services for consumers. GPRS is a major step forward in mobile data. It gives customers the benefits of instant IP connectivity on-the-move and of being continuously connected. GPRS provides the possibility of being charged only for transferred data in addition to more efficient use of limited air interface resources. GPRS provides packet radio access for a GSM/GPRS mobile. The benefit of GPRS is that it can use the same resources that circuit-switched connections do by sharing the overhead capacity. This means that one mobile uses the resources only for a short period of time, that is, when there is data to be sent or received. The sharing of resources together with a very fast method of reserving radio channels makes the air interface usage even more efficient.
Enhanced Data Rates for Global Evolution (EDGE) provides services such as Enhanced GPRS (EGPRS) allowing much higher data rates than current GPRS configurations. In EGPRS, the maximum standardized data rate per time slot will triple and the peak throughput, with all eight time slots in the air interface, will be up to 473 kbit/s. The basic concept, therefore, is to provide a higher data rate on the 200kHz carrier. EDGE, using 8-PSK modulation, enables gross data rate of 69.2 kbit/s per radio time slot by transmitting 3-bits/symbol with the existing symbol rate. With multi-slot reservation, EDGE offers an evolution path for GSM to support medium rate multimedia applications. The user can send more data per radio time slot with the same amount of air time used and operators do not need to invest in another frequency band and license to offer higher data rate services like mobile multimedia.
Figure shows the block structure of the GSM/EDGE BSC.
2.3 Overview of Block Diagram
Figure: Block diagram of the GSM/EDGE BSC with Bit Group Switch
The most important functional units of the BSC are:
Group Switch (GSWB), which is used for switching speech and data, and connecting signalling circuits.
The GSWB is composed of 1...4 SW64B plug-in units. The capacity of each SW64B plug-in unit is 32 incoming and outgoing 4.096 Mbit/s serial buses (64 2.048 Mbit/s PCM circuits). A maximum-size GSWB can handle 128 4.096 Mbit/s serial buses (i.e. 256 2.048 Mbit/s PCM circuits).
The GSWB switches the 8 kbit/s channels of its incoming 4.096 Mbit/s serial buses to the 8 kbit/s channels of the outgoing 4.096 Mbit/s serial buses specified by the control computer of the switch (the MCMU). The GSWB can also switch faster channels, in which case the switching is performed for one 8 kbit/s partial channel at a time.The capacity of the GSWB is 128 or 192 PCMs
Base Station Controller Signalling Unit (BCSU):
The BSC Signalling Unit (BCSU) performs those BSC functions that are highly dependent on the volume of traffic. The BCSU is housed in a cartridge of its own. It consists of two parts, which correspond to the A and Abis interfaces. The second optional Packet Control Unit (PCU) is included in each BCSU.
The A interface part of the BCSU is responsible for the following tasks:
performing the distributed functions of the Message Transfer Part (MTP) and the Signalling Connection Control Part (SCCP) of SS7
controlling the mobile and base station signalling (Base Station Subsystem Application Part, BSSAP)
performing all message handling and processing functions of the signalling channels connected to it.
The Abis interface part of the BCSU controls the Radio interface channels associated with transceivers (TRXs) and Abis signalling channels. Every speech circuit on the Abis interface is mapped one-to-one to a GSM-specific speech/data channel on the Radio interface. The handover and power control algorithms reside in this functional unit.
Marker and Cellular Management Unit (MCMU),
The Marker and Cellular Management Unit (MCMU) controls and supervises the Bit Group Switch and performs the hunting, connecting and releasing of the switching network circuits. The range of the tasks it handles makes up a combination of general marker functions and radio resource management functions.
The MCMU is connected to the other computer units of the exchange, OMU and BCSU, through the message bus.
The MCMU performs the control functions of a switching matrix and the BSC-specific management functions of the radio resources.
Operation and Maintenance Unit (OMU)
The Operation and Maintenance Unit (OMU) is an interface between the BSC3i and a higher-level network management system and/or the user. The OMU can also be used for local operations and maintenance. The OMU receives fault indications from the BSC3i. It can produce local alarm printouts to the user or send the fault indications to Nokia NetAct. In the event of a fault, the OMU automatically activates appropriate recovery and diagnostics procedures within the BSC3i. Recovery can also be activated by the MCMU if the OMU is lost.
The OMU consists of microcomputers and contains I/O interfaces for local operation.
The tasks of the OMU can be divided into four groups:
Ø traffic control functions
Ø maintenance functions
Ø system configuration administration functions
Ø system management functions
Exchange Terminals (ET)
The ET performs the electrical synchronization and adaptation of external PCM lines. It performs the AMI or B8ZS (ET2A), or HDB3 (other ET2 plug-in units) coding and decoding, inserts the alarm bits in the outgoing direction and produces PCM frame structure. All ET2 plug-in units contain two separate ETs but the ET1E plug-in units of the first generation BSC contain only one ET.
Clock and Synchronisation Unit (CLS) :
The CLS generates the clock signals necessary for the BSC. The oscillator of the CLS is normally synchronized to an external source, usually an MSC, through a PCM line. Up to two additional PCM inputs are provided for redundancy.
The high-speed Message Bus (MB)
which interconnects the call control computers and the OMU.
Information contained by the cabling lists (PCI cartridge)
Information contained by the cabling lists (non-PCIcartridge)
Cable Identification Label
At both ends, each intracabinet cable has a sticker which indicates one of the
cabinets where the cable connects to and its sequential number. Each cable is also
provided with a marking slip which indicates the type and function of the cable.
For details, see Figure Information contained by the labels attached to the cables,
Information contained by the labels attached to the cables
4.5 Establishment of Link for new site with BSC
The establishment of link of BTS with BSC we need to follow the following steps at BSC.
1. First go to the BSC and connect the LMP with the laptop.
There are three types of ET (Exchange Terminal) in BSC
1. CCS7 for TCSM
2. A-bis for BTS
3. GB for OMC
2. connection of particular BTS to BSC is done with the A-bis ET (exchange Terminal) of
3. Check the ET availability.
ZUSI : ET ;
This command will show all ET which are available for use.
4. Chose ET number of type SENH (this ET is connected with BCSU).
5. Check the Type
This command shows several information check the PROC parameter it should be ABIPRB (i.e. it is of A-bis type ET).
6. Now check Creation
ZDSB : : : PCM=
This checking is required in case of BSC 3i type of BSC because unlike other lower version BSC this will not show the LED indication for the freely available ET of particular number.
7. Finally to activate that ET following Three commands have to be executed.
1. ZUSC : ET,
2. ZUSC : ET,
3. ZUSC : ET,
8. After activation of ET connect the wire of that ET with the wire of SDM in the Rack of
that ET using Crimping Tool.
9. Now Check the Alarm on that ET number using following Command:
This command will show the following Alarms:
1. Fault Rate Monitoring
Here notice that if we get the Alarm like “Incoming Signal Missing” then swap the wires.
This Two Alarm will be removed when we give loop.
5. METRO HUB
5.1 Requirement of Metrohub………………………….101
5.2 Metrohub Structure………………………………...102
5.3 Protection Method………………………………….103
5.4 Transmission Network Protection Using Loop……105
Nokia Metro Hub
Nokia Metro Hub Transmission Node which is offer flexible network configuration capabilities
5.1 Requirement of Metrohub
protection are required against failures, such as cable-cut, equipment failure, heavy Media rain and multi path fading, and against obstacles in the line-of-sight, such as cranes and growing trees.
Nokia Metro Hub provides the network with fast and automatic traffic protection. It offers cost-effective protection for radio and wire line connections.
Nokia Metro Hub is designed for Abis applications, and traffic protection switching takes place within a fraction of a second, which allows phone conversations to stay alive during switching.
Loop topology allows you to maximize transmission network availability and also to secure the transmission capability. This can, for instance, be helpful when using radios in rainy weather. Nokia Metro Hub also provides power section redundancy and battery back-up functionality as options for added security.
The growing amount of traffic in the network requires flexible transmission capacity expansion. This is accomplished by adding transmission units into the Nokia Metro Hub cabinet when needed. With these units, Nokia Metro Hub can be connected, for example, to ten Nokia Flexi Hopper radio outdoor units, with up to 16 x 2 Mbit/s capacity each, or to ten Nokia Metro Hopper radio outdoor units, with 4 x 2 Mbit/s capacity, via a single cable. The maximum interface capacity is 160 x 2 Mbit/s.
But logical capacity of metrohub is 54 x 2Mbit/s.
5.2 Metrohub Structure
Different unit in Metrohub
Transmission unit ( FXC RRI, FXC E1, FXC E1/T1)
Power supply card
The interface unit (DIUx) includes the digital interfaces needed for local super- vision, maintenance and operation: Q1 and LMP. The unit also contains an interface for connecting up to ten external alarms and four controls (EAC). There is also switch sensor inside the unit and a LED on the unit.
The interface unit provides the following interfaces:
Local management ports (LMP)
Q1 external ports
EAC (10 external alarm inputs, and 4 external control outputs)
Extension interface (for future use).
Power supply card
The power system comprises the power interface panel (DIPx) and one power supply unit (DSUx). As an option, it is possible to use an additional DSUx as a redundant power supply. To gain maximum reliability for the power system, use a redundant power supply unit with an optional internal battery unit (DBBx).
The Power interface panel contains the following interfaces:
AC supply input
DC supply input
Battery back-up connection
DC supply outputs
5. 3 Protection methods
In single use, the signal is not protected against equipment or propagation faults. In the event of a fault, the connection remains broken until the equipment fault has been repaired or the cause for the propagation fault goes away.
Note: ALCQ can provide some protection against propagation faults.
Three types of transmission protection are available with Nokia FlexiHopper:
1. Equipment protection,
2. Propagation protection, and
3. Loop protection.
1. Equipment protection
Equipment protection protects a single transmission link against faults in the equipment. In equipment protection a pair of Nokia FlexiHopper outdoor units (and possibly also a pair of indoor units) are protecting each other.
Equipment protection can be implemented by any of the following methods (currently available with the FIU 19 and RRIC indoor units):
• hot standby (HSB)
• hot standby + space diversity (HSB+SD)
• Frequency diversity (FD): In frequency diversity, two transmitters are transmitting the same signal simultaneously on different frequencies.
• Polarization diversity (PD): Polarization diversity is otherwise identical to frequency diversity, but instead of two frequencies, the signal is transmitted on two polarizations simultaneously.
2. Propagation protection
Propagation protection is used to minimize the number of traffic interruptions due to interference in the transmission path. In propagation protection, a pair of Nokia FlexiHopper outdoor units (and possibly also a pair of indoor units) are protecting each other.
The changeover caused by propagation interference is error-free (hitless).
Propagation protection can be implemented by any of the following methods (currently available with the FIU 19 and RRIC indoor units):
• hot standby + space diversity (HSB+SD)
• frequency diversity (FD)
• polarisation diversity (PD).
5. 4 Transmission network protection using loop topology
Nokia Loop Protection is considered the most efficient way to protect traffic in a transmission network such as a GSM base station subsystem.
Nokia Loop Protection protects
Network management connections.
A transmission loop formed with Nokia elements consists of one loop master and several loop slaves.
The loop principle is that the transmitted signal is always sent in both directions but the received signal must be chosen from only one direction. The loop master sends pilot bits on the basis of which the switching decision is made. Each individually protected slave station needs one pilot bit.
Network synchronization must also be ensured in a loop network and it follows the loop principle in a similar way. The synchronization switching takes place independently from the pilot bits by having a master clock bit (MCB) and a loop control bit (LCB).
Each network element decides individually from which direction the signal and the synchronization will be received, and so it does not require any external or additional supervision for its decision.
Protecting payload traffic
A pilot bit is a special bit with a preset value (zero), sent among the protected traffic in a known position.
For example, protecting a 2 Mbit/s link requires one bit out of the 2 Mbit/s stream to be reserved for this purpose. Similarly, if the traffic is protected at a partial 2 Mbit/s level, for example, because two different base transceiver stations share one 2 Mbit/s line, one pilot bit is required for each slave station.
The location of the pilot bit is defined in the network plan, and it is often within one of the last time slots of the 2 Mbit/s frame. In principle, the location can be selected freely, but a harmonized practice in the network may be advisable for easy site commissioning and network documentation.
The state of a pilot bit is set to 0 (zero) at the sending station, which sends identical digital streams (payload and the pilot bit protecting it) in directions 1 and 2 in the loop.
Any failure in the connection between the sending station and the intended destination causes the pilot bit to change from zero to one (based on AIS). The target station, receiving a "one" instead of a "zero" then knows that the connection is faulty.
The following figure shows the loop principle between the loop master and one slave. The traffic in the other slave stations is bypassed.
Masking pilot bits
The principle of masking in the loop network is to use the logical "AND" operation with "0", when the result is always "0", and masking with "1" when the output is the same as the input signal (either unchanged "0" or "1").
In loop slave sites, each node must forward the pilot bits from other slave stations unchanged and send its own pilot bit as zero in both loop directions. This is done with "Bi-directional Masked" type of cross-connection.
The following figure presents the pilot bit masking of the second slave node (bit 2) and other pilot bits forwarding in the loop. The view is from a cross-connection termination point setting.
Pilot bit sent from a loop master Pilot bit masking in the second loop slave
Two types of Switching
Nokia Loop Protection can be configured either as equal switching or priority switching.
The difference between these is that in the priority switching the connection returns to the initial route as soon as the problem on that link is solved, whereas with the equal switching the system stays on the chosen link until it gets faulty. The equal switching provides better stability for the connection, and it is therefore the recommended choice for a BSS network.
Protecting network synchronization
The implementation mechanism for an automatic detection and recovery of missing or looped network synchronization is based on loop network clock control bits carried within the protected 2 Mbit/s stream:
one bit for detecting if the incoming signal is synchronized by the original network synchronization master or not (master clock bit, MCB),
one bit for detecting any breaks or loop backs in the synchronization chain Loop Control Bit, LCB).
The loop master sets the MCB and LCB to "0" (zero) state in both directions.
Any station using a certain received signal for synchronization sends the LCB back as 1”,
Then counterpart knows that the synchronization of the incoming stream is inherited in such a way that it must not be used for synchronization to avoid a loop back or otherwise faulty synchronization. The same applies to all slaves to make sure the synchronization remains intact.
During the period of training we came to know about the practical aspects of implementation and maintenance of GSM network that sound our knowledge in telecom. TELECOM is one of the disciplines field with challenges and prospect. Indeed, having entered this splendid world, we are greedier for the new.
In my training period I have done practical work like maintenance of the BTS(Base transceiver station) in BSS department. In maintenance of BTS, I have done various function like patching, cross connection, commissioning of BTS etc.
Access Grant Channel
Alarm Indication Signal
Broadcast Control Channel
Base Control Function
BSC Signaling Unit
Bit Error Rate
Base Station Controller
Base Station System
Base Station System Network Doctor
Base Transceiver Station
Common control channels
Dedicated GPRS capacity
Dynamic Abis pool
Data Communication Network
echo canceling unit
Equipment Identity Register
European Telecommunications Standardization Institute
Fast associated control channel
Frequency Control Channel
Fault Rate Monitoring
The Gateway GPRS support node
Gaussian Minimum Shift Keying
General Packet Radio Service
Global System for Mobile Communication
Home Location Register
Hopping Sequence Number
International Mobile Equipment Identity
International Mobile Subscriber Identity
Integrated Services Digital Network
key performance index
Location Area Code
Local Area Network
The ISDN Link Access Protocol on the D channel
Mobile Allocation Input-Output offset
Mobile Allocation Input-Output step
Mobile Allocation Frequency List
Mobile Country Code (of the visited country)
Man to Machine Language
Mobile Network Code (of the serving PLMN)
Mobile switching center
Network health report
Network Management Subsystem
Network Service Entity Identifier
Network and Switching Subsystem
Operation and Maintenance
Operation and Maintenance Centre
Operation and Maintenance Unit
Pulse Code Modulation
Packet Control Unit
Personal Identification Number
Public Land Mobile Network
Packet Switched Public Data Network
Public Switched Telephone Network
Radio Access Configuration
Random access channel
Radio Network Manager
Slow associated control channel
Stand-alone dedicated control channel
The Serving GPRS Support Node
Subscriber Identity Module
Short Message Service
Traffic control channels
Transcoder and Sub-multiplexer
Time Division Multiple Access
Terminal Equipment Identity
Top Level User Interface
TRX priority in channel allocation
Visitor Location Register
Wideband Code Division Multiple Access
Ø Systra manual
Ø Nokia metro site GSM user base station user manual
Ø Nokia ultrasite EDGE based station user manual
Ø Nokia Talk-family Documentation GSM 900/1800/1900 BTS
Ø Digital cellular telecommunications system
Ø http://www.nokiasiemensnetworks.com/global/Innovation Technology/Industryforums.htm