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4-G Cellular Systems

4-G Cellular Systems. What is 4-G?. 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

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4-G Cellular Systems

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  1. 4-G Cellular Systems

  2. What is 4-G? • 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)

  3. 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)

  4. 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

  5. 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.

  6. 4-G Systems • WiMax • UMB (Ultra Mobile Broadband) • LTE (Long Term Evolution)

  7. 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, UMB’s lead sponsor, announced it was ending development of the technolgy, favoring LTE instead.

  8. 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

  9. 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

  10. 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. • AT&T and Verizon will roll out LTE in 2011/2012. Qualcomm supports LTE.

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