Overview of Mobile Communication Systems

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Overview of Mobile Communication Systems

• Transferring knowledge to future leaders

Presented by Professor Johnson I Agbinya
jagbinya_at_uwc.ac.za
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History of Cellular Networks

• First Ever Mobile Network
• Deployed by Bell Mobile System
• In New York (1970)
• Used one High Powered Transmitter (limited in
  range, power and scope)
• Good coverage
• Limited capacity
• Limited mobility
• Inefficient use of bandwidth

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Single Cell Network
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First (Generation) Cellular Network

• By Nippon Telephone Telegraph (NTT)
• In Japan (NTT System)
• In 1979 (Analog system)
• Operated in the 800 MHz range
• Used 25 kHz channel spacing
• Used 5 kHz guard band

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First Generation Cellular Networks (1)

• Operate Mostly in the 800 MHz range
• First 1G cellular networks Early 1980s
• Analog systems
• Nordic Mobile Telephone (NMT)
• Advanced Mobile Phone System (AMPS)
• Total Access Communication System (TACS)

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First Generation Cellular Networks (2)Nordic
Mobile Telephone (NMT)

• Operated in the 450 MHz range
• In the Scandinavia (1981)
• Analog system
• Architecture
• Duplex system (10 MHz separation in links)
• 180 channels (1.2 kbps, very low rate)
• Frequency modulation ( 5 kHz deviation )
• Digital control signal (FSK)

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First Generation Cellular Networks (3)Advanced
Mobile Phone System (AMPS)

• Operated in the 800 to 900 MHz band
• USA (1983) - after NMT introduction
• Analog system
• 40 MHz spectrum allocation (10 MHz link
  separation)
• 666 channels (10 kbps rate)
• 20 MHz per operator (333 channels)
• Latter increased to 416 channels (25 MHz /
  operator)
• 30 kHz per channel
• 21 control channels (FSK, 8 kHz deviation)

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First Generation Cellular Networks
(3a)Limitations of AMPS

• Low calling capacity
• Limited Spectrum
• No room for spectrum growth
• Poor data communication
• Minimal privacy (low security of user
  information)
• Inadequate fraud protection (subject to cloning)

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First Generation Cellular Networks (4)Total
Access Communication System (TACS)

• Operated in the 900 MHz band
• UK (1985) - after introduction of AMPS
• Analog system
• 45 MHz (duplex) uplink and downlink separation
• 1000 channels (8 kbps rate)
• 25 kHz per channel
• Frequency modulation ( 9.5 kHz deviation )
• digital control channels (FSK, 6.4 kHz deviation)

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Second Generation Cellular Networks

• Pushed by demand for
• more subscribers
• limited frequency resource
• saturated networks
• need for better system security
• Digital Systems

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2G Cellular Networks (1)

• 2G Access technologies
• GSM (Global System for Mobile communication)
• Combination of FDMA and TDMA
• Europe, Africa, Asia/Pacific regions
• CDMA (Code Division Multiple Access)
• North America, parts of Asia/Pacific
• TDMA (Time Division Multiple Access)
• South America (mostly)

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2G Cellular Networks (1)

• CDMA (orthogonal codes given to users)
• FDMA (Spectrum divided as f W / N)
• TDMA (Time duration T1 Tf / N)
• Channels are non-overlapping

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2G Cellular Networks (2)

• CDMA (IS-95 series networks)
• Users are identified by orthogonal codes
• Uses spread spectrum digital modulation
  techniques (1.25 MHz bandwidth, 1.2288 Mchip)
• Rake receivers popular
• Rejection of Interference high
• Suffers from cell breathing (contraction and
  expansion of cell range as a function of the
  number of users on network)

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2G Cellular Networks (3)

• TDMA (GSM and TDMA networks)
• Users share frequencies but transmit at different
  time slots
• Most popular air interface
• Used mostly in Europe and Africa
• Limited in data rates
• cell range dependent on transmitted power and
  environmental effects

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2G Cellular Networks (4)

• Examples of TDMA networks
• IS-54 (dual mode TDMA/AMPS)
• IS-54B
• electronic serial number
• better authentication
• better caller ID
• IS-54C
• Evolution path is through EDGE to 3G

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2G Cellular Networks (5)

• Characteristics of IS-54 and EIA-553

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2G Cellular Networks (6)

• TDMA Characteristics
• IS54 standard specifies traffic on digital voice
  channels
• initial implementation triples the calling
  capacity of AMPS systems
• capacity improvements of 6 to 15 times that of
  AMPS are possible
• many blocks of spectrum in 800 MHz and 1900 MHz
  are used
• all transmissions are digital
• TDMA/FDMA supported 7. 3 callers per channel (6
  callers on half rate later), providing 3 times
  the AMPS capacity

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2G Cellular Networks (7)

• Characteristics of IS-54 networks
• 30 kHz channel spacing
• DQPSK encoding at 24.3 kbaud rate
• 6 time slots
• 48.6 kbps channel capacity (48.6/6 kbps per TS)
• vector sum excited linear prediction (VSELP)
  vocoder at 7.95 kbps
• dual mode handsets to accommodate AMPS
• 3 times capacity of AMPS

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2G Cellular Networks (8)

• Characteristics of PDC networks
• Operated in Japan (1991)
• 25 kHz channel spacing
• 80 MHz link spacing (810-826, 956-980 MHz
  1429-1453, 1477-1501 MHz)
• Used space diversity to reduce carrier
  interference
• Reuse factor of 4
• DQPSK modulation at 42 kbps signaling rate
• mobile assisted handoff and VSELP at 6.7 kbps

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2G Cellular Networks (9)

• Characteristics of PCS 1900 networks
• North American implementation of DCS 1800 (GSM)
• 80 MHz link separation
• Uplink and downlink are paired mirror images of
  each other

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Evolution of 2G Networks to 3G

• Politics of GSM and CDMA competition means
  different designation of cdma2000 1x EV (is it a
  2.5G or 3G network?)

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Evolution of CDMA Networks to 3G

• IS-95 to cdma2000 1xRTT (144 kbps)
• cdma2000 1x EV-DO (DO for data only)
• Voice carried on IS-95 network
• 1.25 MHz channels
• Reuses IS-95 channels (saves costs)
• Peak rate to be 2.4 Mbps in future

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Evolution of GSM Networks to 3G

• GSM to GPRS (171.2 kbps)
• Voice on GSM and data on GPRS (2.5G)
• GPRS uses packet switching
• GPRS to EDGE
• EDGE is considered a 3G network
• packet switching capacity of 384 kbps
• will support both voice and data
• uses more time slots to increase capacity

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3G Networks

• All employ wideband CDMA (W-CDMA)
• UMTS (European ETSI/3GPP standard)
• CDMA2000 (American standard)
• Uses packet switching (UTRA FDD and TDD)
• Peak rate to be 2.4 Mbps
• First networks deployed in 2001
• BT (UMTS in Isles of Man)
• NTT DoCoMo (Japan) - FOMA

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3G Networks - UTRA FDD and TDD

• Frequency Division Duplex
• distinct frequency bands for each user
• forward band - traffic from base station to
  mobile
• reverse band - traffic from mobile to base
  station
• Time Division Duplex
• communication on a single frequency
• distinct time slots for forward and reverse links
• small time differences between the slots for one
  person to make transmission look simultaneous

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