In this paper, the downlink nonorthogonal multiple access (NOMA) system is studied where purely discrete input distributions are found that achieve the capacity region to within a constant gap without successive interference cancellation (SIC). The approach is a two-step approach where the corresponding linear deterministic model is first studied and the results are then systematically translated into purely discrete input distributions for the original model. A simple yet powerful coding scheme, which adopts off-the-shelf turbo codes with pulse amplitude modulations (PAM) is then used to simulate the proposed input distributions. Simulation results show that the proposed simple scheme under turbo decoding, both with and without SIC, can operate close to information-theoretic bounds of the proposed input distributions, which lies outside the achievable rate region of any orthogonal multiple access (OMA)-type scheme.

In this paper, we propose a general phase rotated conjugate cancellation (PRCC) scheme for intercarrier interference (ICI) cancellation in orthogonal frequency division multiplexing (OFDM) systems. We also derive the optimal phase rotation for this general scheme such that the carrier-to-interference ratio would be maximized. It is shown that the previous conjugate cancellation (CC) scheme is equivalent to a special case of our proposed scheme. The general PRCC scheme not only inherits advantages of the conventional CC scheme, such as backward compatibility with the existing OFDM systems, low receiver complexity, and two-path diversity, but also provides better performance, especially at high frequency offset situations.

In this paper, we investigate the problem of downlink non-orthogonal multiple access (NOMA) over block fading channels. For the single antenna case, we propose a class of NOMA schemes where all the users’ signals are mapped into n-dimensional constellations corresponding to the same algebraic lattices from a number field, allowing every user attains full diversity gain with single-user decoding, i.e., no successive interference cancellation (SIC). The minimum product distances of the proposed scheme with arbitrary power allocation factor are analyzed and their upper bounds are derived. Within the proposed class of schemes, we also identify a special family of NOMA schemes based on lattice partitions of the underlying ideal lattices, whose minimum product distances can be easily controlled. Our analysis shows that among the proposed schemes, the lattice-partition-based schemes achieve the largest minimum product distances of the superimposed constellations, which are closely related to the symbol error rates for receivers with single-user decoding. Simulation results are presented to verify our analysis and to show the effectiveness of the proposed schemes as compared to benchmark NOMA schemes. Extensions of our design to the multi-antenna case are also considered where similar analysis and results are presented.

In this paper, we consider the use of lattice codes over Eisenstein integers for implementing a compute and-forward protocol in wireless networks when channel state information is not available at the transmitter. We extend the compute-and-forward paradigm of Nazer and Gastpar to decoding Eisenstein integer combinations of transmitted messages at relays by proving the existence of a sequence of pairs of nested lattices over Eisenstein integers in which the coarse lattice is good for covering and the fine lattice can achieve the Poltyrev limit. Using this result, we show that both the outage performance and error-correcting performance of the nested lattice codebooks over Eisenstein integers surpass those of lattice codebooks over integers considered by Nazer and Gastpar with no additional computational complexity.

In this paper, we propose a new downlink non-orthogonal multiuser superposition transmission scheme for future 5G cellular networks, which we refer to as the lattice partition multiple access (LPMA). In this proposed design, the base station transmits multilevel lattice codes for multiple users. Each user's code level corresponds to a distinct prime and is weighted by a product of all distinct primes of the other users excluding its own. Due to the structural property of lattice codes, each user can cancel out the interference from the other code levels by using the modulo lattice operation in a successive/parallel manner. LPMA can provide better user fairness in symmctrical broadcast channels, compared with non- orthogonal multiple access (NOMA). We demonstrate that the proposed LPMA shows a clear throughput enhancement over the current NOMA scheme.