Partial Access for LDPC-Coded-IDMA Systems
Akira Osamura, Guanghui Song, Tomotaka Kimura, Jun Cheng · 2019
A partial-access scheme is proposed for coded-IDMA (interleave-division multiple-access) systems. Similar to conventional IDMA systems, the transmitter of each user consists of a concatenation of channel encode, spreading, and user-specific interleaving. The only difference is that after spreading, some 0s are inserted into the chip sequence. Among the transmitted symbols of -1, 0, 1, symbol 0, however, implies a non-energy transmission or non-access to the channel. In the IDMA receiver, we use a customary joint iterative decoding based on a single factor graph. In our proposed IDMA systems, partial access not only greatly decreases the complexity of the joint decoding; it also decreases the number of short loops in the factor graph. Our extrinsic information transfer (EXIT) analysis and bit-error-rate (BER) simulations show that the proposed partial-access scheme outperforms conventional full-access-IDMA systems in a low SNR range.