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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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)
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.
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.