DS-CDMA with power control error using weighted despreadingsequences over a multipath Rayleigh fading channel

摘要

Closed-form solutions for the average bit error rate (BER)nperformance of a direct-sequence code division multiple-access systemnwith imperfect power control are derived for both coherent andnnoncoherent reception operating over a multipath Rayleigh fadingnchannel. The RAKE structure receivers under consideration employndespreading sequences weighted by adjustable exponential chip waveformsnoptimized for multiple-access interference rejection. The chip-weightingnwaveforms employed are determined only by one parameter Γ whichnleads to easy tuning of the waveforms in practice to achieve the bestnperformance. The results indicate that the number of active usersnsupported at a given BER for the case of Γ tuned to maximize thenaverage signal to interference plus noise ratio Hˆ is much largernthan the case of Γ=0 (fixed or rectangular despreading sequence).nIt is shown that imperfect power control affects the irreducible BER fornthe case of Γ=0. On the other hand, the effect of imperfect powerncontrol on the BER performance for the case of Γ tuned to maximizenHˆ is equivalent to a reduction in the average signal-to-noisenratio, and, hence, system performance can be compensated by increasingnthe transmitter power. It is further shown that the effect due tonimperfect power control on BER performance is significant while that onnthe maximum value of Hˆ obtained by tuning Γ is ratherninsignificant