Chapter 13Multiuser CDMA Fi-Wi Systems

Fourth-generation (4G) wireless systems promise data rates up to 1 Gb/s over the air interface for truly interactive wireless multimedia experience [2008]. However, many technical issues need to be resolved before providing these high data rates. One fundamental, but important, concern is the RF power required for transmitting these extremely high bit rates–as we have indicated in Chapter 1. A simple investigation shows that since the energy per bit is inversely proportional to the bit rate, the received SNR will decrease proportionally with bit rate even with the same transmitted power and path loss. The increment of free-space path loss with carrier frequency makes the situation worse at high carrier frequencies, which some 4G operators may want to use. Furthermore, the number of symbols that will experience ISI under the same multipath conditions will also increase significantly at these high bit rates. The power consumption of hand-held devices will be much higher in this scenario due to the increased transmit power and additional signal processing requirements. All these issues suggest that the cell size should be significantly small in 4G networks. Therefore, the Fi-Wi approach will be an ideal solution.

Direct sequence code division multiple access (DS-CDMA) has been investigated for 4G wireless networks for a number of good reasons [2002, 2006]. DS-CDMA does not require synchronization among users and enables low-power transmission. ...

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