Abstract
We propose a new Non-Orthogonal Multiple Access (NOMA) coding scheme based on the use of a Rate Compatible Modulation (RCM) encoder for each user. By properly designing the encoders and taking advantage of the additive nature of the Multiple Access Channel (MAC), the joint decoder from the inputs of all the users can be represented by a bipartite graph corresponding to a standard point-to-point RCM structure with certain constraints. Decoding is performed over this bipartite graph utilizing the sum-product algorithm. The proposed scheme allows the simultaneous transmission of a large number of uncorrelated users at high rates, while the decoding complexity is the same as that of standard point-to-point RCM schemes. When Rayleigh fast fading channels are considered, the BER vs SNR performance improves as the number of simultaneous users increases, as a result of the averaging effect.
Highlights
O RTHOGONAL Multiple Access (OMA) has been used in past generations of mobile communication systems due to processing limitations or low traffic demands
Considered as a point-to-point Rate Compatible Modulation (RCM) code, an RCMMAC structure satisfies the three properties of good RCM codes, as mentioned in Section II.C: i) it is regular in rows, with a "total" design weight set W by construction; ii) its weight set creates diverse symbol values which can carry the information of all users; and iii) the constructed encoding matrix is regular in columns
We have considered the case where the λ users transmit in an asymmetric way, while maintaining a total sum-rate R equal to 6, 7.4 and 9 bits per complex channel symbol
Summary
O RTHOGONAL Multiple Access (OMA) has been used in past generations of mobile communication systems due to processing limitations or low traffic demands. Authors in [16] accommodate up to 100 users using IDMA They are able to achieve high power efficiency, with a BER performance 1.4 dB away from the theoretical limit for a 16-user case and a total throughput of 2 bits per channel use. To the best of our knowledge, there are no examples in the literature of coding schemes for non-SIC power-balanced NOMA suitable for operating at high spectral efficiency and large number of MAC users. The research of such coding schemes is pivotal to satisfy the ever increasing connectivity and throughput demands of modern wireless networks.
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