Title :
A near ideal noise whitening filter for an asynchronous time-varying CDMA system
Author :
Wei, Lei ; Rasmussen, Lars K.
Author_Institution :
Dept. of Eng., Australian Nat. Univ., Canberra, ACT, Australia
fDate :
10/1/1996 12:00:00 AM
Abstract :
A near ideal noise whitening filter for a time-varying code-division multiple-access (CDMA) system is examined. First, the structure of the ideal noise whitening filter is determined. The ideal noise whitening filter for a time-varying CDMA system is dependent on unknown future system parameters and is, therefore, impractical. A near ideal, realizable whitening filter is introduced as a solution. The convergence of the factorization method for a time-varying CDMA system is considered. The truncation of the number of taps of the ideal noise whitening filter is studied and a metric function based on the near ideal noise whitening filter for a tree search detection algorithm is formulated. Simulation results are obtained for five and ten-user time-varying CDMA systems with binary random signature sequences of length 10 and a rectangular chip waveform. The results show that the near ideal noise whitening filter can accurately approximate the ideal noise whitening filter at a low complexity level. The performance degradation of a suboptimal tree search detector for a time-varying, asynchronous CDMA system using a typical near ideal noise whitening filter is minimal compared to an identical system using the ideal noise whitening filter
Keywords :
binary sequences; code division multiple access; convergence of numerical methods; filtering theory; noise; signal detection; time-varying systems; tree searching; asynchronous time-varying CDMA system; binary random signature sequences; code division multiple access; factorization method convergence; filter taps truncation; metric function; near ideal noise whitening filter; rectangular chip waveform; sequence length; simulation results; suboptimal tree search detector; system parameters; tree search detection algorithm; Australia; Degradation; Detection algorithms; Detectors; Matched filters; Maximum likelihood detection; Multiaccess communication; Noise level; Spread spectrum communication; Time varying systems;
Journal_Title :
Communications, IEEE Transactions on
