This paper proposes a new multiple-input–multiple-output (MIMO) technique called quadrature spatial modulation (QSM). QSM enhances the overall throughput of conventional SM systems by using an extra modulation spatial dimension. The current SM technique uses only the real part of the SM constellation, and the proposed method in this paper extends this to in-phase and quadrature dimensions. It is shown that significant performance enhancements can be achieved at the expense of synchronizing the transmit antennas. Additionally, a closed-form expression for the pairwise error probability (PEP) of generic QSM system is derived and used to calculate a tight upper bound of the average bit error probability (ABEP) over Rayleigh fading channels. Moreover, a simple and general asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results corroborate the accuracy of the conducted analysis and show the significant enhancements of the proposed QSM scheme.

Quadrature Spatial Modulation

A novel multiple-input multiple-output (MIMO) transmission scheme, called space-time block coded spatial modulation (STBC-SM), is proposed. It combines spatial modulation (SM) and space-time block coding (STBC) to take advantage of the benefits of both while avoiding their drawbacks. In the STBCSM scheme, the transmitted information symbols are expanded not only to the space and time domains but also to the spatial (antenna) domain which corresponds to the on/off status of the transmit antennas available at the space domain, and therefore both core STBC and antenna indices carry information. A general technique is presented for the design of the STBC-SM scheme for any number of transmits antennas. Besides the high spectral efficiency advantage provided by the antenna domain, the proposed scheme is also optimized by deriving its diversity and coding gains to exploit the diversity advantage of STBC. A low-complexity maximum likelihood (ML) decoder is given for the new scheme which profits from the orthogonality of the core STBC. The performance advantages of the STBC-SM over simple SM and over V-BLAST are shown by simulation results for various spectral efficiencies and are supported by the derivation of a closed form expression for the union bound on the bit error probability.

Space-Time Block Coded Spatial Modulation

Generalized spatial modulation (GSM) uses N antenna elements but fewer radio frequency (RF) chains (R) at the transmitter. In GSM, apart from conveying information bits through R modulation symbols, information bits are also conveyed through the indices of the R active transmit antennas. In this letter, we derive lower and upper bounds on the the capacity of a (N, M, R)-GSM MIMO system, where M is the number of receive antennas. Further, we propose a computationally efficient GSM encoding method and a message passing-based low-complexity detection algorithm suited for large-scale GSM-MIMO systems.

On the Capacity and Performance of Generalized Spatial Modulation

Capacity analysis for millimeter–wave (mmWave) quadrature spatial modulation (QSM) multiple-input multiple-output (MIMO) system is presented in this paper. QSM is a new MIMO technique proposed to enhance the performance of conventional spatial modulation (SM) while retaining almost all its inherent advantages. Furthermore, mmWave utilizes a wide-bandwidth spectrum and is a very promising candidate for future wireless systems. Detailed and novel analysis of the mutual information and the achievable capacity for mmWave–QSM system using a 3-D statistical channel model for outdoor mmWave communications are presented in this paper. Monte Carlo simulation results are provided to corroborate derived formulas. Obtained results reveal that the 3-D mmWave channel model can be closely approximated by a log–normal fading channel. The conditions under which capacity can be achieved are derived and discussed. It is shown that the capacity of QSM system can be achieved, by carefully designing the constellation symbols for each specific channel model.

Quadrature Spatial Modulation for 5G Outdoor Millimeter–Wave Communications: Capacity Analysis

Spatial modulation (SM) is a new modulation technique where the information to be sent is encoded using one or more symbols and the subspace over which the symbols are transmitted. Unfortunately, a general capacity analysis that encompasses different forms of SM systems has not been developed. In this paper, we consider a general form of SM, where the number of transmitted data streams is allowed to vary. We refer to this form of SM as generalized spatial modulation with multiplexing (GSMM). A Gaussian mixture model (GMM) is shown to accurately model the transmitted spatially modulated signal using a precoding framework. Using this transmit model, a closed-form expression for the achievable rate when operating over Rayleigh fading channels is evaluated, and tight upper and lower bounds for the achievable rate are proposed. The expressions of the achievable rate obtained are flexible enough to accommodate any form of SM—where any subspace can be used for the transmission—by adjusting the precoding set. Simulations are presented to show the tightness of the proposed bounds. The effect of the system dimensions and a comparison with other prominent capacity results are also demonstrated in simulations.

On the Achievable Rate of Generalized Spatial Modulation Using Multiplexing Under a Gaussian Mixture Model

Spatial Modulation (SM) is a newly introduced wireless transmission scheme, and Space Shift Keying (SSK) is its simplified version. Their capacity performance has not been well examined to date. Starting from basic definitions of information theory, through theoretical analyses and numerical calculations, this paper evaluates the capacity of SM systems in various channels. Our conclusion is that under Rayleigh fading channels, the capacity of the SSK system is limited by the Signal-to-Noise Ratio (SNR) or the number of transmit antennas, whichever one is smaller. From the capacity point of view, the SM system is better than the Single-Input and Single-Output (SISO) system, but worse than the Multiple-Input and Single-Output (MISO) system. The correlation between transmit antennas will degrade the performance of the SSK system. Line-of-Sight (LOS) may cause performance degradation for SSK, but capacity increases for SM.

Wang Pichao

Papers

Ergodic capacity analysis of spatially modulated systems