Slow subcarrier-hopped Space Division Multiple Access OFDM systems

Recently Space Division Multiple Access (SDMA) assisted Multi-Input-Multi-Output (MIMO) OFDM systems invoking Multi-User Detection (MUD) techniques have attracted substantial research interests, which are capable of exploiting both transmitter multiplexing gain and receiver diversity gain. Furthermore, the classic Frequency-Hopping (FH) technique can be effectively amalgamated with SDMA-OFDM systems, resulting in Frequency-Hopped (FH) SDMA-OFDM. In this paper we devise a Turbo Trellis Coded Modulation (TTCM) assisted subcarrier-based FH/SDMA-OFDM scheme, which may be able to fully exploit the attainable frequency diversity, while exhibiting a high Multi-User-Interference (MUI) resistance. In the high-throughput scenario investigated, the proposed Uniform Slow-SubCarrier-Hopped (USSCH) SDMA-OFDM system was capable of achieving 6dB Eb=N0 gain at the BER of 10¡4 over the conventional SDMA-OFDM system, while maintaining a similar complexity

Multicarrier Rate-Splitting Multiple Access: Superiority of OFDM-RSMA over OFDMA and OFDM-NOMA

Rate-splitting multiple access (RSMA) is a multiple access technique generalizing conventional techniques, such as, space-division multiple access (SDMA), non-orthogonal multiple access (NOMA), and physical layer multi-casting, which aims to address multi-user interference (MUI) in multiple-input multiple-output (MIMO) systems. In this study, we leverage the interference management capabilities of RSMA to tackle the issue of inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) waveform. We formulate a problem to find the optimal subcarrier and power allocation for downlink transmission in a two-user system using RSMA and OFDM and propose a weighted minimum mean-square error (WMMSE)-based algorithm to obtain a solution. The sum-rate performance of the proposed OFDM-RSMA scheme is compared with that of conventional orthogonal frequency division multiple access (OFDMA) and OFDM-NOMA by numerical results. It is shown that the proposed OFDM-RSMA outperforms OFDM-NOMA and OFDMA under ICI in diverse propagation channel conditions owing to its flexible structure and robust interference management capabilities.Comment: Updated version of published paper in IEEE Communications Letters with correction in optimization problem (17b

A joint coded two-step multiuser detection scheme for MIMO OFDM system

Multiple-input, multiple-output (MIMO) communication is an effective scheme to improve wireless communication performance of multiuser applications. However, reliable communication in multiuser systems is affected by the presence of both multi-access interference (MAI) and inter-symbol interference (ISI) in multi-path channels. In this paper, we therefore investigate a transceiver design for a wideband multiuser-MiMO communication system, where the co-channel users are equipped with multiple transmit and multiple receive antennas. In particular, we propose a two-step interference cancellation scheme with an error correction coding technique for the receiver of a multiuser uplink system. The scheme employs orthogonal frequency division multiplexing (OFDM) modulation and space-time block codes (STBC). The receiver performs as a soft output multiuser detector based on minimum mean-squared error (MMSE) interference suppression at the first stage, and then, MAI cancellation is implemented with a bank of single-user channel decoders. The paper also includes computer simulations which help to improve the understanding of specific issues involved in the design of multiuser STBC-OFDM systems, and confirm the utility of the proposed approac

On Out-of-Band Emissions of Quantized Precoding in Massive MU-MIMO-OFDM

We analyze out-of-band (OOB) emissions in the massive multi-user (MU) multiple-input multiple-output (MIMO) downlink. We focus on systems in which the base station (BS) is equipped with low-resolution digital-to-analog converters (DACs) and orthogonal frequency-division multiplexing (OFDM) is used to communicate to the user equipments (UEs) over frequency-selective channels. We demonstrate that analog filtering in combination with simple frequency-domain digital predistortion (DPD) at the BS enables a significant reduction of OOB emissions, but degrades the signal-to-interference-noise-and-distortion ratio (SINDR) at the UEs and increases the peak-to-average power ratio (PAR) at the BS. We use Bussgang's theorem to characterize the tradeoffs between OOB emissions, SINDR, and PAR, and to study the impact of analog filters and DPD on the error-rate performance of the massive MU-MIMO-OFDM downlink. Our results show that by carefully tuning the parameters of the analog filters, one can achieve a significant reduction in OOB emissions with only a moderate degradation of error-rate performance and PAR.Comment: Presented at the 2017 Asilomar Conference on Signals, Systems, and Computers, 6 page

A First-Order Primal-Dual Method for Saddle Point Optimization of PAPR Problem in MU-MIMO-OFDM Systems

This paper investigates the use of a particular splitting-based optimization technique for constrained l∞-norm based peak-to-average power ratio (PAPR) reduction problem in multiuser orthogonal frequency-division multiplexing (OFDM) based multiple-input multi-output (MIMO) systems. PAPR reduction and multi-user interference (MUI) cancelation are considered in a saddle-point formulation on the downlink of a multi-user MIMO-OFDM system and an efficient primal-dual hybrid gradient (PDHG) inspired algorithm with easy-to-evaluate proximal operators is developed. The proposed algorithm converges significantly faster to satisfactory solutions with much improved asymptotical convergence rate than existing methods. Numerical results illustrate the superior performance of the proposed algorithm over existing methods in terms of PAPR reduction for different MIMO configurations

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft