GSM Radio and Data Transmission Basics i:\hum_res\induction\mtel\opsind.ppt GSM Radio and Data Transmission Basics Praven Reddy Radio Network Planning and Optimisation MTN Western Cape Slide 1 Introduction You have already heard in the introduction that we are a cellular network operator. MTN and Vodacom are the only 2 GSM cellular operators in South Africa. Our task is to provide the network infrastructure and maintenance to ensure service requirements to the people of South Africa, based on mobile telephony. The operations department is responsible for the overall network project planning within MTN, from the radio equipment through to the fixed switching equipment. 1

TOPICS OF DISCUSSION The Principles of Cellular Communication GSM System Overview Radio Network Planning Evolution of GSM Data Services Slide 3 Topics of Discussion The purpose of my presentation today is to give you a basic understanding of cellular telephony, the systems we use at MTN, and our planning process. To this end we will cover the following topics: - The principles of cellular communication - GSM System Overview - Radio network planning and Optimisation - System planning and Value Added Services - Network Management centre 3

What is the Cellular Concept? Frequency Set 1 MTN MOBILE SWITCHING NETWORK TELKOM NETWORK RADIO BASE STATION CELL P S T N Frequency Set 2 MOBILE SWITCHING NETWORK RADIO BASE STATION CELL Frequency Set 1 Slide 4 Principles of Cellular Communication Radio Network Multiple radio base stations (RDSs) linked to the Mobile Switching equipment. Cell coverage provided in all major suburban areas and all main highways throughout RSA. Handover between cells allows call to continue non-stop until user decides to terminate call. Frequency allocated per cell allows for frequency re-use patterns to be created which provides high network capacity. The mobile switching network is coupled to the Telkom network therefore providing international access as well as national and local access to all telephone users in the RSA. RADIO BASE STATION CELL 4

Principles of Pre-Cellular Communication Slide5 5

Principles of GSM Cellular Communication Slide 6 6

7 Slide 7 GSM System Overview MS (Mobile Station) may be hand held, carphone, or vehicle mounted or payphone based. The SIM (Subscriber Identity module) carries user unique identity and services available to him/her. 7

GSM SYSTEM OVERVIEW HLR VLR AUC POI MS MSC BSC BTS IN EIR NMC + OMC TX RX HLR VLR AUC POI MS MSC BSC BTS Slide 9 The structure of the Network MSC - Mobile Switching Centre Switching traffic, call routing and logging Controlling operations of BSCs Control handover between different BSCs Carry traffic to Telkom network via POIs Switching mobile traffic via MSC and Telkom switches. POI - Point of Interconnect to Telkom Network HLR - Home Location Register contains subscriber information on the network & his current location. VLR - Visitor Location Register contains information on mobile subscribers currently visiting you local network. AUC - Authentication Centre contains information with regard to customer details regarding fraud and money availability. EIR - Equipment Identification Register lists approved mobile users. (MS handsets and MSISDNs). BSC - Base Station Controller controls numerous BTSs to MSCs. BTS - Base Transceiver Station allows MS onto the network via TRX/RSCs. NMC - Network Management Centre the control centre for all operations and engineering driven tasks. MS - Mobile Station Handset IN EIR NMC + OMC 9

GSM Radio Spectrum and Multiple Access Technique Multiple access scheme is FDMA/TDMA hybrid Modulation scheme used is Gaussian Minimum Shift Keying “Over the air” bit rate is 270 kbps ARFCN Channel separation is 200 kHz Duplex distance of 45 MHz in GSM 900, 95 MHz in DCS 1800 and 80 MHz in PCS 1900 Each ARFCN is broken up into 8 Time Slots 1st Time Slot per site is BCCH and 2nd Time Slot per site is SDCCH

FDMA vs. TDMA f3 a. FDMA b. TDMA 1 2 3 4 5 6 7 f2 f1

CALL TO MS 2 5 6 4 7 11 8 10 9 3 PSTN GSM PLMN BSC 10 HLR GMSC MSC / VLR HLR GMSC 10

Timing Advance Limitation Maximum Cell Radius 1 2 3 4 5 6 7 35km Timing Advance Limitation

RADIO NETWORK PLANNING The role of Network Planning plan growth ensure adequate coverage ensure adequate capacity cost effective design Slide 11 Radio Network Planning The role of network planning: To plan network growth Rollout of coverage to new areas To ensure adequate coverage Continuous coverage of the required areas without appreciable holes. Adequate depth of coverage to meet the company’s marketing plans. To ensure adequate network capacity Accommodating traffic in the busiest hour with only a small chance of blocking (congestion). To achieve cost effective design Lowest possible cost over the life of the network while meeting the quality targets. 11

PLANNING THE NETWORK Maximum achievable cell size limited by maximum radio communication range ranges are greatest in rural areas (few obstructions) ranges least in high density urban conditions Maximum traffic capacity per cell depends on the number of channels per cell determined by frequency re - use achieved (limited by interference) Thus, both traffic and coverage considerations result in: smaller cells in towns larger cells in rural areas. Slide 12 12

Principles of Omni-directional Radio Cellular Coverage Omni Directional Sites omni - directional sites are typical in small towns or where geography limits coverage Omni - directional coverage pattern Slide 13 13

Principles of Sectored Radio Cellular Coverage Sectorised Sites three cells fed from one site is generally more cost - effective for providing wide - area coverage and high capacity Omni - directional coverage pattern Slide 14 14

Co-Channel Interference Adjacent Channel Interference 87 Co-Channel Interference 87 86 90 90

Network Rollout Before After D3 C3 D4 D2 C2 D1 C4 C1 D5 D7 C7 D6 C5 C6 Slide 15 Radio Network Planning Network growth. 15

SYSTEM PLANNING MSC Voice Mail Platform Short Message Service IN Platform Slide 21 System Network Planning Voice Mail System Voice answering unit that stores all messages if the user is not available. SMS Short message service which allows text data to be transmitted. Basically on a similar platform as paging unit. 21

Evolution of GSM Data Services GSM Phase 1 – dealt only with voice GSM Phase 2 – “data and fax over cellular” 9.6 kbps Allowed due to SS 7 or C 7 Signaling over GSM Network. SS 7 is a set of techniques or protocols designed to provide transfer and delivery of Signaling information. GSM Phase 2+ HSCSD, GPRS, EDGE Phase 3 – 3G (3rd Generation) UMTS

Why Analog Modems won’t work over GSM ? Analog modems use high frequency tones to communicate In GSM, Human speech is sampled (20ms) and non voice tones are discarded. GSM Speech Coder is based on a Residually Excited Linear Predictive Coder. [260 bits for each 20 ms sample – 13 kbps] Coder therefore cannot process analog audio tones GSM Data Call – digital air interface Data over the air at 9.6 kbps IWU or DTI at the MSC converts digital data to analog for PSTN transmission

Transparent vs Non-transparent Data Communication Transparent data transmission means that there is no GSM error correction supplied over the air interface. Non Transparent communication utilises "Radio Link Protocol" (RLP) that ensures more robust transmission. RLP is a GSM network based error correction utility. Here the GSM network's IWU adds error correction codes to control the flow of data. Transmitted data first obtains an acknowledgement from the receiver that the data was correctly received. If no acknowledgement is received from the receiver, the network will buffer data and utilise forward error correction to help emulate uninterrupted data transmission throughout.

GSM Data Evolution UMTS EDGE GPRS HSCSD GSM Circuit Switched Speed i:\hum_res\induction\mtel\opsind.ppt GSM Data Evolution Speed 2 Mbps UMTS 384 kbps EDGE 170 kbps GPRS 38.4 kbps HSCSD 9.6 kbps Slide 1 Introduction You have already heard in the introduction that we are a cellular network operator. MTN and Vodacom are the only 2 GSM cellular operators in South Africa. Our task is to provide the network infrastructure and maintenance to ensure service requirements to the people of South Africa, based on mobile telephony. The operations department is responsible for the overall network project planning within MTN, from the radio equipment through to the fixed switching equipment. GSM Circuit Switched Time 1999 2000 2001 2002 1

High Speed Circuit Switched Data HSCSD is connection orientated Maximum data rate - 38.4 kbps on Downlink Multiple Time Slots in TDMA frame are used -typically 4 TS on Downlink and 2 Uplink (currently limited by handset equipment e.g. Nokia Cardphone v.2.) Suited to time sensitive, real time services where a Grade/Quality of Service has been specified.

General Packet Radio Service GPRS is packet based radio data transmission technology – data rates up to 170 kbps Optimised for “bursty transmission” sources like wireless Internet and multimedia applications Main Benefits - users are always connected, always online. - users only charged for amount of data transferred - users can also simultaneously have a voice call and a data call (Equipment dependent - Class B)

Enhanced Data Rate for GSM Evolution Advantage – EDGE can offer data rates of 384 kbps for wireless multimedia IP based services. 48 kbps/TS up to 69.2 kbps/TS in good radio conditions. Disadvantage – need a new phone as modulation scheme is changing. Was GMSK, now QPSK. But why bother with EDGE when 3G UMTS is around the corner ? Help Networks that could not afford 3G Licenses cope with radio spectrum that already exists. Also Ease of Implementation – same TDMA Frame, Logical Channel structure and 200 kHz channels … just different modulation scheme.

Universal Mobile Telephony Service 3G UMTS Standard – data speeds up to 2 Mbps ? Cellular Band 1885-2025 MHz and 2110-2200 MHz Satellite Band 1980-2010 MHz and 2170-2200 MHz Modulation scheme WCDMA Videophones a reality ?