Title :
Performance of adaptive iterative multiuser parallel decision feedback with different code rates
Author :
Woodward, Graeme ; Honig, Michael L.
Author_Institution :
Southern Poro Commun., Annandale, NSW, Australia
Abstract :
An adaptive receiver which combines multiuser parallel decision feedback with MAP decoding in an iterative manner is presented for synchronous coded DS-CDMA. Performance with various convolutional code rates is considered. optimal filters are derived using both minimum mean squared error (MMSE) and least squares (LS) criteria. When used with short (repeated) spreading codes, the adaptive LS receiver requires only a training sequence and timing for estimation of all filter coefficients. The adaptive receiver performs significantly better than the standard (soft) interference canceller, since the adaptive algorithm attempts to measure and exploit the joint statistics of the output of the MAP decoder with the input symbols. Numerical results are presented which illustrate how performance depends on the rate of the convolutional code, assuming similar decoding complexity. These results show that low code rates perform best at moderate loads and low received power. Higher code rates can achieve very low packet error rates for an overloaded system (number of users greater than the bandwidth expansion)
Keywords :
adaptive systems; cellular radio; code division multiple access; convolutional codes; decoding; feedback; filtering theory; least mean squares methods; least squares approximations; multiuser channels; packet radio networks; radio receivers; spread spectrum communication; MAP decoding; MMSE; adaptive LS receiver; adaptive algorithm; adaptive iterative multiuser parallel decision feedback; bandwidth expansion; cellular radio; code rates; convolutional code; decoding complexity; filter coefficients estimation; joint statistics; least squares; low packet error rates; low received power; minimum mean squared error; optimal filters; overloaded system; repeated spreading codes; short spreading codes; soft interference canceller; synchronous coded DS-CDMA; timing; training sequence; Adaptive filters; Convolutional codes; Feedback; Interference; Iterative decoding; Least squares methods; Measurement standards; Multiaccess communication; Performance evaluation; Timing;
Conference_Titel :
Communications, 2001. ICC 2001. IEEE International Conference on
Conference_Location :
Helsinki
Print_ISBN :
0-7803-7097-1
DOI :
10.1109/ICC.2001.937359