Multi-user detector for direct sequence-code division multiple access (DS/CDMA) channels

Abstract

The present invention combines multi-user detection with packet combining. In multi-user detection, the receiver jointly demodulates user's data by exploiting the structure of multi-user interference, the packet combining is an enhancement of standard automatic repeat request protocol, in which the erroneous packet are not discarded but preserved and combined with retransmitted ones to improve subsequent decisions. One embodiment of the two-stage detector uses a first stage in which the packets are combined and then decoded, in order to improve tentative decisions for interference cancellation. The decoder output is then used in the second stage to cancel the interference, and then the combining is performed once again, before the final decoding. For the two-stage detection we consider two decoding schemes in the first stage. One is the soft input / soft output maximum a posteriori probability decoding of the combined packets, then a soft interference cancellation is performed in the second stage. In the second embodiment, we use the hard decision Viterbi / Turbo decoding, and a hard interference cancellation in the second stage. In the simulation we include power control, quantization, and timing, phase and amplitude estimation. The results indicate that the proposed scheme with packet combining and multi-user detection employed jointly significantly improve performance in the high channel load, increasing the robustness of the system.

Description

technical field [0001] The present invention relates to a multi-user detector for Direct Sequence-Code Division Multiple Access (DS / CDMA) channels, in particular to a detector for packet retransmission. Background technique [0002] The Automatic Repeat Request (ARQ) protocol is a well-known technique used for handling transmission errors caused by noisy channels. In most implementations of the ARQ protocol, its sole purpose is error detection. When one or more errors are detected in the received data block, a retransmission request is sent back to the originating transmitter and the erroneous data block is discarded. The main disadvantage of ARQ schemes is that, especially at low signal-to-noise ratios (SNR), the number of retransmissions required before correct reception can be high, resulting in unacceptably low traffic. The bottom line is that various improvements to the ARQ protocol have been proposed in the literature [1], [2], [3] with the aim of enhancing performan...

AI Technical Summary

Problems solved by technology

Although they have polynomial complexity in terms of the number of users and provide significant performance gains over traditional detectors, they still only provide suboptimal performance

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