Low-Cost Uplink Sparse Code Multiple Access for Spatial Modulation

Abstract

Spatial modulation (SM)-sparse code multiple access (SCMA) systems provide high spectral efficiency (SE) at the expense of using a high number of transmit antennas. To overcome this drawback, this letter proposes a novel SM-SCMA system operating in uplink transmission, referred to as rotational generalized SM-SCMA (RGSM-SCMA). For the proposed system, the following are introduced: a) transmitter design and its formulation, b) maximum likelihood and maximum a posteriori probability decoders, and c) practical low-complexity message passing algorithm and its complexity analysis.Simulation results and complexity analysis show that the proposed RGSM-SCMA system delivers the same SE with significant savings in the number of transmit antennas, at the expense of close bit error rate and a negligible increase in the decoding complexity, when compared with SM-SCMA. Index TermsSparse code multiple access (SCMA), spatial modulation (SM), message passing algorithm (MPA).

Improving Spectral Efficiency in the SCMA Uplink Channel

“…In the works described in [5][6][7][8][9][10][11], four codewords (M = 4), are encoded into two bits. The authors in [14][15][16] proposed to use SM-SCMA to increase SE. In SM-SCMA, the information of each user is divided in two parts; one part is used to select the active transmitting antenna and the other part is directly assigned to an SCMA codeword according to each user's codebook.…”

“…These systems can transmit three bits at a time: a 2-bit spatial symbol and 1-bit modulated symbol, using more than one antenna. In [16], the authors proposed Rotational Generalized Spatial Modulation (RGSM-SCMA), achieving an SE and BER similar to SM-SCMA using a lower number of antennas by activating more than one antenna at a time. In this work, we propose three-bit encoding using a combination of Singular Value Decomposition SCMA (SVD-SCMA) [11] with an 8-APSK constellation.…”

“…In this work, we propose three-bit encoding using a combination of Singular Value Decomposition SCMA (SVD-SCMA) [11] with an 8-APSK constellation. The SVD-SCMA performance is compared to the phase rotation method [5][6][7], SM-SCMA and RGSM-SCMA [16]. For the detection and decoding of SM-SCMA and RGSM-SCMA, MPA was used while for SVD-SCMA a receptor based on neural networks was implemented.…”

“…Once with SVD-SCMA the distances between the codewords are optimized, the next challenge is to increase the spectral efficiency by transmitting more bits simultaneously. Recently, spatial modulation [12,13] has been used to improve the SE in NOMA systems [14][15][16]. SM increases the SE by allocating part of the input data stream (spatial symbol), to activate an antenna to transmit the modulation symbol.…”

Coordinated Beamforming for Multi-Cell Non-Orthogonal Multiple Access-Based Spatial Modulation

“…Generalized SM (GSM) enhances SM capacity by utilizing MISO or MIMO antenna and activating more than one antennas [34]- [37]. Quadrature SM (QSM) extends capacity of GSM by using an extra modulation spatial dimension [38], [39] In addition, sparse code multiple access (SCMA) combined with SM (SM-SCMA) or QSM can also be utilized to handle the increasing number of users [40].…”