Repeat Accumulate code Division Multiple Access and its Hybrid Detection

TL;DR: It is shown that when a sufficiently high interleaver length is employed, the RA-CDMA system is capable of approaching the Gaussian channel's capacity.

Abstract: In this paper, we propose the novel concept of Repeat Accumulate Code Division Multiple Access (RA-CDMA), which employs unique, user-specific channel code generator matrices (interleavers) for differentiating the users. We also suggest a Multilevel Structured (MLS) interleaver generation technique for the sake of reducing the memory storage requirements of our system and compare its correlation properties to those of the conventional random interleaver. A novel hybrid detector is designed for our system with the aid of Extrinsic Information Transfer (EXIT) charts. Furthermore, we also design a low-complexity unequal power allocation scheme, assigning a different power to each user of this near-capacity transmission scheme. It is shown that when a sufficiently high interleaver length is employed, the RA-CDMA system is capable of approaching the Gaussian channel's capacity.