Chapter 8 Cellular Network Outline The Development of Cellular Networks Cellular technologies and terminologies Second generation digital networks Third generation packet networks Other services 1 2 Conventional Radio First used in 1921 in stand-alone mode Police could only talk to another police officer Connected to PSTN (mobile telephony) in 1946 $2,000 - $3,000 per phone One transmitter and receiver cover entire city All users share the same frequency spectrum Range limited Limited capacity and low quality 500 KHz of bandwidth can accommodate 20 conversations/ Spotty quality, a lot of static and dropped call Now: aviation, trucking, taxis, marine 3 Figure 8.1 Precellular mobile service. 4
Cellular 1983: first cells in Chicago and Baltimore Use frequency spectrum much more efficiently Cellular adds capacity due to its ability to reuse frequency spectrum Channels are reused by use of low-power radio transmitters, each serving a geographic area called a cell Conventional 20 1 MHz Bandwidth, 50 KHz bandwidth is used per call, 1000/50 = 20 5 6 Conventional 20 Cellular 90 1 MHz Bandwidth, 50 KHz bandwidth is used per call, 1000/50 = 20 7 Frequency reuse pattern of 3 8
Cellular 90 Basic Principles Cellular (1) Frequency reuse pattern of 3 9 Cells are depicted as hexagons 3 cells form a cluster, pattern of clusters repeated over and over In reality shape varies by geography/terrain served Cell configuration minimizes interference caused by reuse of a channel Cells serving dense areas are assigned more channels 10 Basic Principles Cellular (2) If congested, cells are further subdivided or split into smaller cells using lower powered transmitters System can grow gradually User s mobility tracked from cell to cell in order to change radio channels appropriately Handoff: tracking of user along with changes in channel usage Paging: shared radio channel used to broadcast the numbers of mobile units being called Cellular Telephony 11 12
Figure 6-15: Cellular Telephony Figure 6-15: Cellular Telephony, Continued PSTN Mobile Telephone Switching Office PSTN Mobile Telephone Switching Office Cellsite Cellsite G G Channel 47 B D H K N Service area is divided into Bcells. D H K N A C E F I J L M O Handoff P Cellsite in each cell communicates A E with cellphones. C MTSO controls all cellsites, links cellular system to PSTN. F I J L M O P 13 14 PSTN Channel 47 Figure 6-15: Cellular Telephony, Continued Mobile Telephone Switching Office B D G H K Cellsite N Cellular Technology Handoff Moving between cells in a system (city) Roaming Moving between systems (cities, countries) Often restricted to avoid cellular fraud A E L P C I O Why cells? F M So channels can be reused in different cells. Channel reuse allows more customers J to be supported. 16 15
Channel Reuse Traditional cellular technologies Used FDMA, sometimes with TDMA within channels Could not reuse channels in adjacent cells Typically, a channel is reused roughly every seven cells (frequency reuse pattern of 7) So if there are 25 cells, each channel will be reused about three times A Ch 47 B C E Ch 47 H D 17 Example of capacity calculation If You have 1200 khz of bandwidth Each cellular call uses 50 khz of bandwidth You want to use channel reuse pattern of 3 You want your network to have 36 cells How many can your network handle with a cellular network? 1200 khz / 3 sets of frequency = 400 khz per cell 400 khz per cell / 50 khz per call = 8 per cells 8 per cells * 36 cells = 288 How many can your network handle with a conventional network? 1200 khz/ 50 khz per call = 24 18 Channel Reuse, Continued Newer cellular systems use CDMA Code division multiple access Type of spread spectrum transmission that allows multiple subscribers to transmit simultaneously in a single channel Allows channel reuse in adjacent cells If there are 25 cells, each channel can be reused 25 times CDMA supports many more customers because of greater channel reuse Cellular Market Slow to become popular in US, too expensive 1990 finally showed large increase Due to decreases in charges 1988-1990 1990: 5 million users -vs- 1996 44 million 88% increase Europe higher penetration, higher use 19 20
First Generation All analog Incompatible standard AMPS (Advanced mobile phone service) in US NMT470 Seven different standards in Europe Analog Cellular As this service became more affordable Used in business Used as personal tool Became extremely popular Now capacity constraints in metro area s Digital cellular developed to add more capacity 21 22 Limitations of Analog Cellular Change in signals and errors introduced during hand offs between base stations and wireless network High error rate and static at cell boundary slow speed CDPD Cellular Digital Packet Data or IP wireless Developed by IBM to transmit data over spare capacity in analog networks Good for transmitting short, bursty messages: email, credit card information, alarm monitoring Speeds slow, about 4800 bps Not widely used 23 24
Outline The Development of Cellular Networks Cellular technologies and terminologies Second generation digital networks Third generation packet networks Other services 25 Spectrum Review: Frequency, Hertz, and Bandwidth Frequency: Number of times in each second that each radio wave completes a cycle Hertz: Cycles per second Spectrum: Available bandwidth Available frequency resource Airwaves, which are composed of ranges of frequencies Come from light spectrum Have more specific meaning than bandwidth 26 Spectrum is used in pair 897.5 905. 942.5 950 AIS GSM900 Higher frequency band for downlink (DL) Base station to handset More loss at high frequency, but also more transmission power at base station Lower frequency band for uplink (UL) Use Frequency Division Duplexing (FDD) 27 28
FDMA/TDMA/FDD/TDD (1) FDMA/TDMA/FDD/TDD (2) Frequency Division Multiple Access FM and AM radio station A mean for multiple people to access network resource by using different frequency Frequency Time Division Multiple Access T1 and E1 line A mean for multiple people to access network resource by using different time A mean for multiple people to talk at a dinner table by talking at different time Frequency Frequency Division Duplexing (FDD) Frequency Base station transmits on Frequency 2 Handset transmits on Frequency 1 Time Division Duplexing (TDD) Frequency Handset transmits on Timeslot 1 Base station transmits on Timeslot 2 Station 3 on Frequency 3 Station 2 on Frequency 2 Station 1 on Frequency 1 Time User 1 on Timeslot 1 User 2 on Timeslot 2 User 3 on Timeslot 3 Time 29 Time Time Duplexing is another form of multiplexing Multiplex transmissions between handset and base station on a single medium (airspace) 30 Spectrum Limitations Spectrum is a limited resource Goal of new wireless technologies is to do more with less and to be able to share the spectrum with increasing number of users Spectrum first stretched by setting up hexagonal shaped cells Digital adds capacity through multiplexing: CDMA or TDMA Spectrum Allocation Different portions of the spectrum assigned to: Public agencies, aviation, marine Satellite or mobile services Spectrum is allocated in chunk of frequency bands Residential cordless: 46-49 MHz 3 MHz chunk FM radio: 88-107 MHz 31 32
Thailand Frequency chart Thailand Frequency chart Land mobile MARITIME MOBILE 505 KHz 526.5 MOBILE Mobile-satellite MOBILE (Earth-to-space) MOBILE RADIO ASTRONOMY MOBILE AERONAUTICAL RADIONAVIGATION FIXED FIXED FIXED FIXED MHz 312 315 322 328.6 335.4 AM BROADCASTING 1606.5 KHz MOBILE FIXED MOBILE Mobile Fixed AERONAUTICAL RADIONAVIGATION AERONAUTICAL MOBILE (R) FIXED FM BROADCASTING 75.4 MHz 87 108 117.975 137 33 MOBILE FIXED FIXED RADIONAVIGATION-SATELLITE MOBILE-SAT. (Earth-to-space) STANDARD FREQUENCY AND TIME SIGNAL-SATELLITE (400.1 MHz) Space operation (s-e) Mobile expt.aero. mobile Mobile expt. aero. mobile SPACE RES. (s-e) Fixed Fixed EARTH EXPLO.- SAT.(E-s) MET.- SAT.(E-s) Mobile-satellite (spaceto-earth) MOBILE MOBILE- SAT. (s-e) MET.-SAT. (E-s) MET.-SAT. (s-e) SPACE OPER. (s-e) EARTH EXPLO.-SAT. (E-s) MET. AIDS MET. AIDS MET. AIDS 387 390 399.9 400.05 400.15 401 402 403 34 Spectrum Characteristics TV channels and mobile radio services are allocated very high frequency bands (VHF) in the 30- MHz range 30 MHz means that each wave has 30 million cycles or hertz per second Low frequency (LF): Long distance, More immune to obstacles Less capacity and large antenna High frequency (HF) More susceptible to rain and weather conditions Spectrum Allocation Administered on both international and national level International level by ITU International Telecommunication union Particularly for Satellite and broadcast TV National level by PTD (Post Telegraph Department) Soon to be transferred to NTC and NBC Auction vs Beauty contest Japan: Award spectrum based on capability 35 36
Interference When transmissions use the same airspace (frequency) in the same area, they may interfere with each other Particularly troublesome with unlicensed spectrum like WiFi (802.11) and Bluetooth Unlicensed spectrum refers to a piece of spectrum that is available free to companies who do not wish to apply for a license Significantly lowers the cost of deploying service, but also susceptible to uncontrolled interference Still regulated, but does not require license Outline The Development of Cellular Networks Cellular technologies and terminologies Second generation digital networks Third generation packet networks Other services 37 38 Second Generation Digital voice and packet data Capacity driven With 25 khz bandwidth, AMPS can support 1 call, but GSM can support 4-6 Enable features like caller ID, call forwarding, 3-way, SMS, and message notification USA: TDMA and CDMA Others: GSM Benefits More difficult to tap than first generation analog service Longer handset battery life (5 days vs 8 hours) Digital Cellular Offered over same frequencies as their analog cellular service 3 to 10 more capacity than analog service Overall capacity increased by sharing a radio channel among a number of voice channels Made possible by digital multiplexing Softer handoff, are rarely dropped 39 40
GSM Global System for Mobile Telephone 1987: European Union choose GSM as standard for delivery of wireless channel US started with two other standards Most widely used worldwide Subscriber Identification Module (SIM) card simplifies customer management Based on Time Division Multiplexing (TDM) Divide 200 khz channel into eight timeslots 7 for traffic, and 1 for control signaling and SMS USA Market Have two competing standards TDMA(Time Division Multiple Access) Based on TDM Time Division Multiplexing Use TDM as a way to enable multiple subscribers to share a single channel Quite similar to GSM in Europe, but not identical Also known as D-AMPS (Digital-advanced mobile phone service) CDMA(Code Division Multiple Access) 41 42 TDMA Same band of frequencies is shared by all the Short bursts of digital data from each conversation are sent In a form of timeslot Packets are reassembled at destination Originated in satellite communication CDMA Also called spread spectrum Each phone call combined with a code which only one phone plucks from the air Dispersed signals are pulled out of the background noise by a receiver which knows the code Developed by Qualcomm Inc. More flexible and has higher data transmission rate Will evolve into CDMA2000-1X that Hutch uses 43 44
FDMA/TDMA/CDMA (1) FDMA/TDMA/CDMA (2) Frequency Division Multiple Access Time Division Multiple Access Code Division Multiple Access Frequency Code Frequency Code Frequency Code Station 2 on Code 2 Station 1 on Code 1 Station 3 on Frequency 3 Station 2 on Frequency 2 Station 1 on Frequency 1 User 1 on Timeslot 1 User 2 on Timeslot 2 User 3 on Timeslot 3 Station 3 on Frequency 3 Station 2 on Frequency 2 Station 1 on Frequency 1 Time Time Time 45 46 TDMA and CDMA TDMA is based on time Multiple people take turn to speak in a classroom CDMA is based on code Multiple people speak simultaneously but with a difference language Both use a single frequency pair One for uplink and another one for downlink Market Condition Hugh investment CAT CDMA project cost 7,000 million bahts for about 50 provinces Telenor bought 40% of DTAC for THB9,200M That makes DTAC worth about THB 23,000M At about 5 million customers, that s 4600 bahts per customer Singapore Telecom bought 50% of AIS for THB75,000M That makes AIS worth about THB 150,000M At about 13 million customers, that s 11600 bahts per customer 47 48
Mobile Network Structure Cell site or base station Consists of antenna and Base Transceiver Station (BTS) Transceiver = Transmitter + Receiver Convert wireless traffic from customer to appropriate landline protocol BTS Controller: Assign call to frequency Switching equipment Route traffic within mobile networks Connections to other networks and PSTN 49 Figure 8.3 The mobile telephone switching office (MTSO) connects the cellular network to the public switched telephone network. The backhaul network connects cells to the mobile switch. 50 Base Station (1) Base Station (2) Most expensive part of the networks Also called Cell, which is the physical area in which a set of frequencies is used Connected to antenna by coaxial cabling Convert signal between GSM/CDMA to those compatible with landline networks Base Station Controller (BSC) is used to setup a call, assigning radio channels and page the handset One BSC manages multiple BTS 51 52
Tower and Backhaul In the USA, tower is owned by a real estate company Cellular operator leases space on the tower and leases link from tower to their switching center Save on operating cost In Thailand, each operator own their own tower Backhaul is the high speed link between (1) BTS and BSC, and (2) BSC to MSC Also represent a major cost factor 53 Mobile Switching Center MSC or Mobile Telephone Switching Office (MTSO) Switch between cellular networks and PSTN Also support roaming Capability to use voice or mobile data devices in other carriers networks Home Location Register (HLR) keep billing and calling plan for subscriber Visitor Location Register (VLR) handle roaming (visiting) user Tied together with Signaling System 7 (SS7) 54 Roaming Figure 8.4 Mobile switching center, Signaling System 7 (SS7), and registers containing subscriber databases. 55 Primarily to accommodate international user SS7 gateway is needed to translate between incompatible SS7 type Enhanced roaming: Enable non-voice services like Accessing a voicemail Directory assistance: 411, 1113 Emergency : 911, 191 56
Number Portability Enhanced 911: E911 Enable subscribers to keep their mobile telephone number when they change wireless providers within a local area USA, Australia, UK, and Hong Kong Possible because each user has both Mobile telephone number or directory number Mobile identification number (MIN) Wireless carrier looks up national database with directory number to find MIN And use MIN information to route a call Also made possible by SS7 57 Locating the caller Connecting caller to the appropriate local emergency response center Provide information like: caller number, BTS location, and GPS location GPS: Global Positioning Satellite Also available in network-based triangulation Longitude/Latitude information also needs to be translated to street address Also available from Hutch 58 Outline The Development of Cellular Networks Cellular technologies and terminologies Second generation digital networks Third generation packet networks Mobile commerce Slow-speed packet data and push-to-talk Satellite and paging Third Generation (3G) Digital packet data capable of carrying voice, video, and data Driven by capacity expansion and advanced services ITU started an IMT-2000 effort which consists of two sets of standards: CDMA2000 and WCDMA ITU: International Telecommunications Union IMT: International Mobile Telephone 59 60
Two Transitioning Paths GSM GPRS EDGE WCDMA GSM: Slow speed circuit-switched data GPRS: Packet-switched data at 30 Kbps EDGE: Higher speed packet-switched data Faster download speed when subscriber is closer to the base station CDMA CDMA2000 CDMA2000 DO CDMA2000-1X: Packet-switched data CDMA2000-1X EV DO: Dedicated data carrier GPRS General Packet Radio Services Average transmission speed of 30 Kbps Peak transmission speed of 64 Kbps Data overlay network on top of GSM Use a dedicated voice channel for shared data transmission Permanent partitioning cause inefficient use of spectrum Connection is always on Nature of packet-switched network 61 62 EDGE Enhanced Data Rates for Global Evolution Average transmission speed of 100 Kbps Peak transmission speed of 384 Kbps Considered to be a 2.5G technology Available in countries like Italy, US, and Cambodia Dynamically shared capacity with GSM More efficient assignment of voice and data to channels as they become available Also offer higher data speed if subscriber is closer to the base station or not moving WCDMA Wideband CDMA Also called UMTS Universal Mobile Telecommunications System Average transmission speed of 384 Kbps Peak transmission speed of 2 Mbps Natural evolution path for GSM operator Available in countries like Japan, Italy, and UK 13.3 Millions subscribers as of December 2004 Completely new air interface Reuse many core network components from GSM 63 64
WCDMA Upgrading Path Cellular Cell size GSM GPRS EDGE WCDMA Large spectrum cost From GSM s 200 khz to WCDMA s 5 MHz Large upfront payment in US and Europe Small upfront payment and revenue sharing in Asia Large equipment cost Higher bandwidth and higher frequency shorten the coverage area of each base station Need much more base stations than GSM GSM GSM GSM GSM WCDMA WCDMA GSM WCDMA WCDMA GSM GSM GSM 65 66 WCDMA flavors WCDMA is available in multiple versions WCDMA Release 99 (1999) Peak/Average download speed of 2000/220 Kbps WCDMA Release 4 Peak/Average download speed of 2000/384 Kbps WCDMA Release 5 Peak/Average download speed of 14/2 Mbps WCDMA Release 6 Same download speed, double upload speed to 5/1.4 Mbps CDMA2000 1x 1x = Use the same amount of spectrum as earlier CDMA network (1.25 MHz) But voice capacity is doubled over CDMA Also reuse many switching components from CDMA Average transmission speed of 64 Kbps Peak transmission speed of 153.6 Kbps Faster speed if you are closer to the base station Natural evolution path for CDMA operator Available in countries like USA, Thailand (Hutch), China, Brazil, Australia, India, and South Korea 145 Millions subscribers as of December 2004 67 68
CDMA2000 1xEV-DO Evolution Data Only Also called HDR or High Data Rate Dedicated spectrum only for packetswitched data i.e., require another 1.25 MHz of spectrum Higher efficiency for data transmission Average transmission speed of 1 Mbps Peak transmission speed of 2.4 Mbps CDMA2000 Upgrading Path Less costly and less complex than GSM WCDMA Sameamount of spectrum is needed Samenumber of base station is needed 69 70 3G Network Terminology Core network: Radio network controller, signaling gateways, home location registers, visitor location registers, and mobile switches Radio access network (RAN): Radio network controller, base transceiver station and base station controller Transport network: Links between equipments and to other networks 71 Figure 8.7 Third generation network architecture as defined by the 3GPP. 72
Evolution to IP Like SS7 in landline network, cellular network is also evolving to separate switching and call processing to a separate device Enable higher capacity by allowing all data traffic to be carried by IP packets Lower equipment cost by using softswitch Switching equipment based on general purpose computer The air interface for voice traffic will still be circuit-switching for some time More suitable for voice communication More efficient use of expensive spectrum Wireless Video Cellular telephone infrastructure is inappropriate for large scale video broadcast DMB: Digital Multimedia Broadcasting Video and Audio streams are transmitted from a satellite and landline networks Commercially available in South Korea and Japan MediaFLO: Forward link only Reuse a single TV spectrum for digital streams Being deployed in the USA DVB-H: Digital Video Broadcast Handheld Trail in the UK, Singapore, USA 73 74 1 st gen Analog FDMA Low capacity Static and drop call The differences between 2 nd gen Digital TDMA & CDMA 4 6 times capacity of analog Soft handoff 3 rd gen Digital CDMA 4 6 times capacity of analog Soft handoff Outline The Development of Cellular Networks Cellular technologies and terminologies Second generation digital networks Third generation packet networks Other services 4.8 Kbps 30 Kbps 384 Kbps No enhanced service Caller ID & SMS IP-Based services Short battery life Long battery life Long battery life 75 76
Mobile Commerce Operators do not typically create any mobile application Instead, they provide billing and delivering services to third party content developer Operator share revenue with content developer e.g., half of the 5 Bahts SMS fee goes to operator Electronic Payments E-wallet chip: Store credit card data or electronic money within the phone Used by NTT DoCoMo in Japan Wirelessly pay for vending machine and concert tickets E-wallet site: Store credit card data and handle payment from cellular users to Internet-based retailer 77 78 Operating System As mobile device grows in complexity, so do its operating systems Major players are Symbian, Microsoft, Palm, Linux, Research in motion, and Sun Make enormous attempt to attract application developer to their platform IMS - IP Multimedia System Equipment and software that make it possible to store, transmit, administer, transform, and bill for multimedia services Common infrastructure to enable application and content developer to develop an IP-based application that will run over multiple platforms GSM, CDMA2000, WCDMA, WiFi, etc. Video phone, games, shopping 79 80
Geo-synchronous Satellite Orbit 22, miles above the earth surface Rotate with the earth, making them look stationary from the ground Transmitter converts electrical signal to RF (radio frequency) signal Satellite is a bent-pipe, reflecting the signal back to earth Receiver converts RF signal back to electrical signal Some satellite architecture also use a hub, which is a routing device with large dish 81 82 Satellite Equipment Satellite phone 0.25 second delay in conversation LEO: Low Earth Orbit Closer to the Earth Enable higher data speed and lower delay VSAT: Very Small Aperture Terminal 18 to 36 diameter Popular for deployment with a lot of terminals 83 84
Microwave Other Antennae Point-to-point communication 85 86