Wireless Communication.docx - Air University

AIR UNIVERSITY(FINAL EXAMINATION: SUMMER 2007)Subject: TE432: Mobile Communications Total Marks: 100Class: BETE08(A/B) Time Allowed: 3 hr.Name: _______________________Roll No: _____________ Signature: _______________Attempt all problems. Provide your solution on the answer sheet provided with this exam. This is a closed bookclosed notes exam. Students are allowed to keep “Erlang table” with themselves and use of calculator is alsoallowed.QUESTION #1Short answer the flowing questionsa) Write the parameter of A-interface and Ater-interface.• A-interface (Speech/Data=1,TS=1 channel, SS7, X.25)• Ater-Inerface ((Speech/Data=300,1200,1200/75,2400,4800,9600,14400 bit/s), TS=4 channel, SS7,X.25, LAPD: O&M)b) Draw and define BTS architecture and its functionality of each components1

c) What are the permanent and temporary records of VLR and HLRo VLR• Permanent records (IMSI, Subscriber service provision)• Temporary records (Ciphering Items (Kc, Sres, Rand), LAI-TMSI)o HLR• Permanent records (MS-ISDN, IMSI, Subscriber service provision)• Temporary records (VLR address, Ciphering Items (Kc, Sres, Rand))d) Define the architectural type of handover topologies• Intra-Cell HO• Inter-Cell HO within the same BSC• Intra MSC HO• Inter MSC HOQUESTION #2Write the function of radio interface, A-bis and A interface of GSM interface architecture.A-biso Message exchanges between the BTS and the BSC:• Traffic exchanges.• Signaling exchanges for call set up and BTS operation and maintenance.o Physical access between BTS and BSC: PCM digital links at 2.048 Mbit/s (E1) or 1.544 Mbit/s (T1),carrying 32 or 24 timeslots at 64 kbit/s.o Speech:• Conveyed in timeslots at 4 x 16 kbit/s (remote transcoders).o Data:• Conveyed in timeslots at 4 x 16 kbit/s.• The initial user rate, which may be 300, 1200, 1200/75, 2400, 4800 9600 or 14400 bit/s isadjusted to 16 kbit/s.A-Interfaceo This Interface located between TRAU and MSC has these features:• Totally normalized to allow multivendor equipment.2

• Full interoperability in most cases and after testing.o Based on CCS7 protocol (either ETSI or ANSI).o The MTP layers (2 to 3) provide the basic transport system for all CCS7 signaling messages and areresponsible for signaling network management and signaling message handling:• Level 1: defines the physical characteristics for a 64 kbit/s signaling data link.• Level 2: ensures secure signaling link by providing error detection and correction,signaling link alignment and error monitoring.• Level 3: ensures that signaling messages are routed through the network in correctsequence and without loss or duplication even in case of link failure.QUESTION #3Draw and define the complete system architecture with its subsystems and components of GSM/DCS mobileradio network.o A GSM system is basically designed as a combination of three major sub-systems: the Network andSwitching Sub-system (NSS), the radio sub-system called the Base Station Sub-system (BSS), and theOperation Sub-System (OSS).o The Network and Switching Sub-system includes the equipment and functions related to end-to-end-calls,management of subscribers, mobility, and interfaces with the fixed network (PSTN). In particular, the NSSconsist of Mobile Switching Centers (MSC), Visitor Location Registers (VLR), Home Location Registers(HLR), Authentication Center (AUC), and Equipment Identity Register (EIR).o The Base Station Sub-system includes the equipment and functions related to the management of theconnection on the radio path. It mainly consists of one Base Station Controller (BSC), and several BaseTransceiver Stations (BTSs), linked by the Abis interface.3

o An optional equipment, the Transcoder / Rate Adapter Unit (TRAU) so called TransCoder Unit (TCU)within Nortel BSS products, is designed to reduce the amount of PCM links.o The Operation Sub-System is connected to all equipment in the switching system and to the BSC. OSSmainly contains Operation and Maintenance Center for NSS (OMC-S) and Operation and MaintenanceCenter devoted to the Radio subsystem (OMC-R). In order to ensure that network operators will haveseveral sources of cellular infrastructure equipment, GSM decided to specify:o The radio interface (or air interface or Um interface), between the BTS and the MS,o The A interface, between the NSS and the BSS.QUESTION #4Write the difference between following, draw diagram if necessary.A. CHANNEL MODES FOR TIME VARIANT MULTI-PATH AND TIME SPREADING OF THE SIGNALo The transmitted signal arrives at the receiver via multiple propagation paths, each of which has anassociated time delay, received signal is spread in time due to the multiple scatterers at different delays, It’stime dispersive.o Second characteristic is concerned with the time variations in the structure of the medium the response ofthe channel will change with time the received signal might appear at different times.B. LARGE SCALE AND SMALL SCALE PROPAGATION MODELSo It is due to path loss of signal as a function of distance and shadowing by large objects such as building andhills etc., this occurs as the mobile moves through a distance of the order of the cell size. Threephenomenon cause LSF (Refection, diffraction, scattering)o Small scale fading is used to describe the rapid fluctuations of the amplitudes, phases, or multipath delaysof a radio signals over a short period of time or travel distance.C. DOPPLER EFFECTS & IMPULSE RESPONSEo Doppler effect A shift in the frequency of an electromagnetic or sound wave due to the relative movementof the source or the observero The response of a system to an impulse which differs from zero for an infinitesimal time, but whoseQUESTION#5integral over time is unityDraw and define GSM Logical channels Architecture4

• Traffic Channels (TCH)ooTCH transport user information (speech/data)TCH are bidirectional dedicated channels between the network and the MH• Broadcast Channels (BCH)oTo help the MH (Mobile Handset) measures• to turn to a BTS• to listen for the cell information• to start roaming, waiting for calls to arrive, making calls• Because BTSs are not synchronized with each other, every time a MH decides to camp to anothercell, its FCCH, SCH, and BCCH must be read.• Common Control Channels (CCCH)oCCCH support the establishment of a dedicated communication path (dedicated channel) between the MH andthe BTSoThree types of CCCH• Paging Channel (PCH)• Random Access Channel (RACH)• Access Grant Channel (AGCH)• Dedicated Control Channels (DCCH)oDCCH are used for transferring nonuser information between the network and the MH• Messages on DCCH Including• channel maintenance• mobility management• radio resource management5

oFour kinds of DCCH• Stand alone Dedicated Control Channel (SDCCH)• Cell Broadcast Channel (CBCH)• Slow Associated Control Channel (SACCH)• Fast Associated Control Channel (FACCH)• Frequency Correction Channel (FCCH)oProvide MH with the frequency reference of the system• To enable the Mobile Handset (MH) to synchronize with the frequencyoTransmission properties• Transmit on the down-link• Point to multi-point• Synchronization Channel (SCH)oMH synchronize with the structure within the locative cell• MH can receive information from the proper time slots on the TDMA structureoTo ensure a GSM BTS is chose• The Base Station Identity Code (BSIC) can only be decoded by a GSM BTSoTransmission properties• Transmit on down-link• Point to multi-point• Broadcast Control Channel (BCCH)oBTS broadcast cell information to MH• LAI ( Location Area Identity), to start roaming, waiting for calls to arrive, making calls• maximum output power allowed in the cell• information about BCCH carriers for the neighboring cells• MH will perform measurement to BTSoTransmission properties• Transmit on down-link• Paging Channel (PCH)6

oUsed by BTS to page particular MH in the cell• MH actively listen to PCH to check contact info within certain time• Contact could be incoming call or short messageoContact info on PCH include• IMSI (MH’s identity number), or• TMSI (temporary number)oTransmission properties• Transmit on down-link• point to point• Access Grant Channel (AGCH)oThe network assigns a signaling channel via AGCH• A Stand alone Dedicated Control Channel (SDCCH) is assignedoTransmission properties• Transmit on down-link• Point to point• Random Access Channel (RACH)oUsed by MH to request a dedicated channel for call setup• Shared by any MH attempts to access the network• Channel request message contains the reason for the access attemptoTransmission properties• Transmit on up-link• Point to point• Stand alone Dedicated Control Channel (SDCCH)oooTransfer signaling information between the BTS and the MHTypically used for location updating prior to use of a traffic channelTransmission properties• Bidirectional channel, transmit on both up and down-link• Point to point7

• Cell Broadcast Channel (CBCH)oooTo carry Short Message Service Cell Broadcast (SMSCB)Use the same physical channel as SDCCHTransmission properties• Transmit on down-link• Point to multi-point• Slow Associated Control Channel (SACCH)oCarries control and measurement parameters along with routine data necessary to maintain a radio linkbetween the MH and the BTS• On the uplink, MS sends averaged measurements (signal strength and quality) of current andneighboring BCCH• On downlink, MS receives information about transmitting power to use and an instruction withtime advance/retardoTransmission properties• Bi-direction channel, transmit on both up and down link• Point to point• Fast Associated Control Channel (FACCH)oAn FACCH is used over a TCH where it steals time slots from a TCH• a 20 ms segment of speech is stolen to carry handover signaling informationoAppears on demandQUESTION#6Write the type of GSM Bursts, draw its frame structure and explain each fields of its frame burstA timeslot is a 576 ms time interval, i.e. 156.25 bits duration, and its physical contents are known as a burst. Fivedifferent types of bursts exist in the system. Different TDMA frame divisions distinguish them8

.The normal burst (NB)Used to carry information on traffic and control channels, except for RACH. It contains 116 encrypted bits.The frequency correction burst (FB)Used for frequency synchronization of the mobile. The contents of this burst are used to calculate an unmodulated,sinusoidal oscillation, onto which the synthesizer of the mobiles is clocked.The synchronization burst (SB)Used for time synchronization of the mobile. It contains a long training sequence and carries the information of aTDMA frame number.The access burst (AB)Used for random access and characterized by a longer guard period (256 ms) to allow for burst transmission from amobile that does not know the correct timing advance at the first access to a network (or after handover).The dummy burst (DB)Transmitted as filler in unused timeslots of the carrier; does not carry any information but has the same format as anormal burst (NB).9

QUESTION#7a. Draw and define complete uplink channel to normal burst and their fields in the GSM900, Where thecarrier frequency of each FDM is 200khz for full rate traffic channelooFreq. Carrier: 200 kHzTDMA: 8 time slots per freq carriero No. of carriers = 25 MHz / 200 kHz = 125o Max no. of user channels = 125 * 8 = 1000oConsidering guard bands = 124 * 8 = 992 channelsQUESTION #810