Asymptotic analysis of the conventional decision feedback receiver in flat fading channels

The spectral efficiency presents the ultimate limit on the data rate per unit bandwidth of a certain communication system. For the DS-CDMA systems spectral efficiency has been derived for optimal and linear multiuser receivers in the case of synchronous reception, fading and non-fading environment as well as single and multi-cell cellular networks. The most pervasive model employed in all these analyses is the large system random signature model. For the decision feedback receivers the previous research handled only the non-fading case while the case of fading channels remained unknown. This paper analyses the spectral efficiency of the decision feedback receiver in a fading channel with and without power ordering. The results show that in the case of power ordering before cancellation the multiuser diversity effect previously encountered by S. Shamai (Shitz) and Verdu (see IEEE Trans. on Inform. Theory, vol.47, p.1302-27, May 2001) occurs. Multiuser diversity is the effect where the spectral efficiency of a certain multiple-access system improves in fading channels due to the multiplicity of users that share the system and provide the necessary power diversity. Also, analyzed in this paper is the case of imperfectly estimated channel gains in fading environments or the case of imperfect power control. The spectral efficiency loss incurred by this estimation error is analyzed in the case of the conventional decision feedback receiver.