4-G Cellular Systems

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4-G Cellular Systems
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What is 4-G?

• No formal definition
• High data speed 100 Mbps to 1Gbps anywhere,
  anytime
• Enable voice, data and streamed multimedia
  (enough speed for streaming HDTV, digital video
  broadcasting, video chat, ) with low latency
• Based on TCP/IP (Internet protocol) only (3-G
  systems use both circuit switched and packet
  switched networks)

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Technologies used in 4-G

• It uses OFDMA and other new technologies (Single
  Carrier FDMA, Interleaved FDMA, Multi-carrier
  CDMA, ) instead of CDMA, which is used by all
  3-G systems. The problem with CDMA is it cannot
  adjust spectrum allocated to users (all users get
  the same amount of spectrum). Also, the highest
  data rate is limited.
• MIMO (Multiple-Input Multiple-Output) antennas
• New modulation techniques (64QAM Quadrature
  amplitude modulation)

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MIMO

• Multiple antennas used by the transmitter and the
  receiver
• Parallel streams are transmitted simultaneously
  by those antennas
• Data rate is increased (if 4 pairs of antennas
  are used, the data rate can be increased by 4
  times)
• Can also increase reliability

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64QAM

• The amplitude of two waves, 90 degrees
  out-of-phase (in quadrature) are changed
  (modulated) to represent the data signal.
• Phase modulation is a special case of QAM.

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4-G Systems

• WiMax
• UMB (Ultra Mobile Broadband)
• LTE (Long Term Evolution)

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UMB

• To bring CDMA2000 (US standard) to 4-G
• Based on Internet (TCP/IP) networking
• Peak rates of up to 280 Mbps
• Support handoffs with CDMA2000 and 1xEV-DO
• Use OFDMA
• In Novemver 2008, Qualcomm, UMBs lead sponsor,
  announced it was ending development of the
  technolgy, favoring LTE instead.

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LTE (Long Term Evolution)

• To bring UMTS (Europe 3G) to 4-G
• Uses OFDMA for downlink with a maximum of 2048
  subchannels
• Download rate 326 Mbps for 4x4 antennas for
  every 20 MHz of bandwidth
• Uses Single Carrier Frequency Division Multiple
  Access (SC-FDMA) for uplink. A problem with
  OFDMA is the high peak-to-average power ratio.
  SC-FDMA can provide higher power efficiency which
  is crucial for mobile stations.
• Uses 64QAM modulation
• Uses MIMO and beam forming with up to 4 antennas
• All IP Network

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LTE (cont.)

• Downlink peak data rates 300Mbps per 20MHz of
  spectrum and uplink data rates, 75 Mbps per 20
  MHz
• Supports at least 200 active users per cell in
  5MHz

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Comparison of LTE and WiMax

• Similar technologies
• WiMax is already in the market in Pakistan and
  Sprint Nextel and Clearwire has deployed it in
  the US (first in Baltimore this year). LTE is
  still under standardization.
• LTE is the upgrade for GSM network that accounts
  for over 85 of all mobile subscribers in the
  world. The existing GSM/GPRS/EDGE operators can
  use their current infrastructure (base station
  towers) with new equipment to upgrade to LTE. A
  WiMax operator has to start from scratch.
• ATT and Verizon will roll out LTE in 2011/2012.
  Qualcomm supports LTE.