Adaptive Joint Detection of Cochannel Signals for TDMA Handsets

Adaptive Joint Detection of Cochannel Signals for TDMA Handsets In mobile communication systems, downlink (forward-link) system capacity is limited by the ability of mobile receivers to recover the desired signal in the presence of cochannel interference. Joint detection of the desired and cochannel signals is a useful approach to improving receiver performance, thus increasing system capacity. We show that a practical single-antenna joint detection receiver can provide significant gains in system capacity for the time-division multiple-access standard Telecommunications Industry Association/Electronic Industry Association/Interim Standard -136 (TIA/EIA/IS-136 or IS-136). For a sectorized system, joint detection provides a capacity gain of 47% in a typical urban environment. When used in conjunction with transmit beamforming, the synergy between the two approaches leads to a capacity gain of over 200%. In determining these gains, practical aspects of the IS-136 system are considered, namely unsynchronized networks, limited receiver complexity, and adaptability. A semiblind acquisition process, that uses the training sequence of the desired user only, is employed because the desired and interfering base stations are not synchronized. The receiver complexity is controlled by processing only one sample per symbol period, even though it is shown that multiple samples per symbol period should ideally be used. Finally, because receiver performance may be limited by its own intersymbol interference instead of cochannel interference, an adaptive joint detection process is used, which selects between joint demodulation and single-user equalization for each slot.