Asymptotic analysis of the conventional decision feedback receiver in fading channels

Spectral efficiency presents the ultimate limit on data rate per unit bandwidth of a certain communication system. For direct sequence code division multiple access (DS-CDMA) systems the spectral efficiency has been derived in case of synchronous reception for optimal and linear multiuser receivers, flat fading and non-fading environments as well as single and multi-cell cellular networks. The most pervasive model employed in all these analyzes is the large system random signature model. For the decision feedback receivers, previous research handled only the non-fading case while the case of fading channels remained unknown. This paper analyzes the spectral efficiency of the popular conventional decision feedback receiver in flat and frequency selective fading channels with and without power ordering. Results show that, in the case of power ordering before cancellation and very large system loads, the spectral efficiency of this receiver in fading channels can be even larger than in the case of channels with no fading. We also discuss and identify optimal power control laws for the conventional decision feedback receiver with and without power ordering. The power control law which equalizes single user capacities in the case of power ordering is also discussed.