K-user spread-accumulate code for multiple-access channel

A K-user spreading accumulate (SA) code for the synchronous MAC is proposed, where both channel noise and mutual interference between users are mitigated jointly. In the system with K-user SA code, for each user, each bit in the information bit vector is first spread into chips. While some of chips are interleaved as that in the conventional IDMA scheme, the remaining chips are interleaved and accumulated. The K-user SA code not only preserves the capability of mitigating mutual interference, but also introduces a capability of error correction without any increase of the total code rate, compared with the conventional IDMA scheme. Moreover, since the spreading length can be flexibly split into two parts, one for conventional spread and other for repeat in the equivalent RA code, the K-user SA code is suitable to an application to an adaptive transmission system. In the system, for a given total code rate, the split rate within the spreading length is adaptively adjusted depending on the channel state information, and thus give a lower bit-error-rate (BER), compared with the conventional RA-IDMA code.