Beyond Equal-Power Sparse NOMA: Two User Classes and Closed-Form Bounds on the Achievable Region.

Non-orthogonal multiple access (NOMA) is a promising technology for future beyond-5G wireless networks, whose fundamental information-theoretic limits are yet to be fully explored. Considering regular sparse code-domain NOMA (with a fixed and finite number of orthogonal resources allocated to any designated user and vice versa), this paper extends previous results by the authors to a setting comprising two classes of users with different power constraints. Explicit rigorous closed-form analytical inner and outer bounds on the achievable rate (total class throughput) region in the large-system limit are derived and comparatively investigated in extreme-SNR regimes. The inner bound is based on the conditional vector entropy power inequality (EPI), while the outer bound relies on a recent strengthened version of the EPI. Valuable insights are provided into the potential performance gains of regular sparse NOMA in practically oriented settings, comprising, e.g., a combination of low-complexity devices and broadband users with higher transmit power capabilities, or combinations of cell-edge and cell-center users. The conditions for superior performance over dense code-domain NOMA (taking the form of randomly spread code-division multiple access), as well as a relatively small gap to the ultimate performance limits, are identified. The proposed bounds are also applicable for the analysis of interference networks, e.g., Wyner-type cellular models.

Statistical-mechanics approach to wide-band digital communication.

The emerging popular scheme of fourth generation wireless communication, orthogonal frequency-division multiplexing, is mapped onto a variant of a random field Ising Hamiltonian and results in an efficient physical intercarrier interference (ICI) cancellation decoding scheme. This scheme is based on Monte Carlo (MC) dynamics at zero temperature as well as at the Nishimori temperature and demonstrates improved bit error rate (BER) and robust convergence time compared to the state of the art ICI cancellation decoding scheme. An optimal BER performance is achieved with MC dynamics at the Nishimori temperature but with a substantial computational cost overhead. The suggested ICI cancellation scheme also supports the transmission of biased signals.