Linear MMSE Receivers for Random CDMA in Wireless Networks With Equal Transmit Powers

The performance of single-hop links in ad-hoc wireless systems using direct-sequence (DS) code-division-multiple-access (CDMA) with random signature sequences and linear minimum-mean-square-error (MMSE) receivers is investigated. Expressions for the average signal-to-interference-plus-noise-ratio (SINR) and spectral efficiency (b s^-1 Hz^-1 link^-1) were derived for a representative link in the presence of interferers distributed randomly on a plane with uniform area density p interferers m^-2. Nodes transmit with equal power P, which decays with distance r as r^-alpha. An expression for the optimum spreading factor given system parameters is also provided. It is found that for a given link length r, the average spectral efficiency when operating with the optimum spreading factor is approximately inversely proportional to pipr². The corresponding spectral efficiency is proportional to pipr². The parameter pipr² can be interpreted as approximately the average number of interferers closer to the receiver than the desired transmitting node