A multi‐user CDMA receiver utilizing decorrelating detector with additional dummy pilot response

Abstract

SUMMARYA pilot assisted CDMA system which uses extended spreading sequences with guard sequences under a quasi-synchronous condition is capable of separating the interference components included in the input of a de-correlating receiver by solving a system of linear equations. The performance of such a system, however, depends on the property of the de-correlating matrix consisting of the received pilots, which correspond to the respective user spreading sequences and the multi-path channel conditions. That is, the regularity of the matrix often tends to degrade, and the rank reduces occasionally primarily due to the multi-paths, resulting in solutions that are vulnerable to AWGN. The present paper proposes an effective technique to solve this problem by introducing a virtual user into a group of real users that are to be served. The simulation results indicate a remarkable improvement in the bit-error-rate (BER) performance. In addition, based on the BER performance, the system has a RAKE-like function that has power-sum characteristics.

Sequential detection CDMA multi-user receiver

“…This important factor is examined in conjunction with noise amplification of DD by the preceding works of this paper [17][18][19].…”

“…In these previous works, the relation between process gain L (spreading sequence length) and the number of active users K has been treated very little. This important factor is examined in conjunction with noise amplification of DD by the preceding works of this paper [17][18][19].…”

“…This paper intends to improve the performance of multi-user receivers using LT techniques, without using coding methods such as the Turbo code. Assumed are in addition such factors that accurate pilot responses (signatures made of spreading sequences and channel gains) for all the users are given, a quasi-synchronization is maintained by controlling the transmit timing of each user, with a closed-loop control [20] and an enveloped spreading sequence which is made by surrounding the core sequence by guard sequences to avoid ISI [17][18][19] is used at the transmitter. In the operation of DD or MMSE, the performance degrades with the AWGN noise amplification (including interference noise for MMSE).…”

“…feature in both delay and attenuation. For a large number of paths, p k can be modelled as a complex-valued gaussian random process because the central limit theorem is applicable [17,23].…”

Sequential detection CDMA multiuser receiver

“…Therefore, the available user population K is resultantly forced to limit, and the frequency utilization efficiency degrades. [2]- [4] This paper intends to increase bandwidth efficiency by detecting from the best user to worst user sequentially in solving a DD (or MMSE) system of linear equations.…”