Performance Of Spatial Modulation Research Articles

Spatial modulation based on reconfigurable antennas: performance evaluation by using the prototype of a reconfigurable antenna

In this paper, we study the performance of spatial modulation based on reconfigurable antennas. Two main contributions are provided. We introduce an analytical framework to compute the error probability, which is shown to be accurate and useful for system optimization. We design and implement the prototype of a reconfigurable antenna that is specifically designed for application to spatial modulation and that provides multiple radiation patterns that are used to encode the information bits. By using the measured antenna radiation patterns, we show that spatial modulation based on reconfigurable antennas works in practice and that its performance can be optimized by appropriately selecting the radiation patterns to use for a given data rate.

Effect of Synchronization Error on Optical Spatial Modulation

This paper examines the effect of synchronization error on the performance of spatial modulation (SM) technique in optical wireless communication (OWC) systems. SM exploits the deployment of multiple transmitters by encoding user information on their spatial domain. In most works related to SM, a perfect synchronization among these multiple transmitters is assumed. However, synchronization error can result from multipath propagation in OWC channel, and clock jitter and variation in propagation delay of each transmitter. Synchronization error degrades system performance and hence the need to investigate its effect. Using union bound technique, and defining synchronization errors as timing offsets in the received signals, we derive the symbol error rate for space shift keying (SSK), generalized SSK (GSSK), SM, and generalized SM (GSM) schemes, and we validate our analysis with tightly matched simulation results. Results show that degradation in performance increases with synchronization error. While SSK is tolerant for a small range of synchronization error, GSSK, SM, and GSM are significantly impaired. Our results also demonstrate the dependence of SM on channel gain values. We observe that the lower the channel gain of the transmitter in which synchronization error occurs, the lesser the impact of the synchronization error on the system performance.

Constellation Randomization Achieves Transmit Diversity for Single-RF Spatial Modulation

The performance of spatial modulation (SM) is known to be dominated by the minimum Euclidean distance (MED) in the received SM constellation. In this paper, a symbol-scaling technique is proposed for SM in the multiple-input–multiple-output (MIMO) channel that enhances the MED to improve the performance of SM. This is achieved by forming fixed sets of candidate prescaling factors for the transmit antennas (TAs), which are randomly generated and are known at both the transmitter and the receiver. For a given channel realization, the transmitter chooses the specific set of factors that maximizes the MED. Given the channel state information (CSI) readily available at the receiver for detection, the receiver independently chooses the same set of prescaling factors and uses them for the detection of both the antenna index (AI) and the symbol of interest. We analytically calculate the attainable gains of the proposed technique, in terms of its transmit diversity order, based on both the distribution of the MED and on the theory of classical order statistics. Furthermore, we show that the proposed scheme offers a scalable performance–complexity tradeoff for SM by varying the number of candidate sets of prescaling factors, with significant performance improvements, compared to conventional SM.

Cross-Entropy-Based Antenna Selection for Spatial Modulation

Euclidean distance optimized antenna selection (EDAS) can significantly improve the bit-error-rate (BER) performance of spatial modulation (SM) systems. However, the exhaustive search over all possible antenna subsets leads to inherently high-search complexity. In this letter, a cross-entropy-based antenna selection (CEAS) scheme is proposed, by formulating the antenna selection problem in SM as a combinatorial optimization one. Simulation results show that the proposed CEAS scheme achieves considerable reduction in search complexity, while approaching the optimal performance of exhaustive search.

Low-Complexity Transmit Antenna Selection in Large-Scale Spatial Modulation Systems

Transmit antenna selection (TAS) is an efficient way for improving the system performance of spatial modulation (SM) systems. However, in the case of large-scale multiple-input multiple-output (MIMO) configuration, the computational complexity of TAS in large-scale SM will be extremely high, which prohibits the application of TAS-SM in a real large-scale MIMO system for future 5G wireless communications. For solving this problem, in this paper, two novel low-complexity TAS schemes, named as norm-angle guided subset division (NAG-SD) and threshold-based NAG-SD ones, are proposed to offer a better tradeoff between computational complexity and system performance. Simulation results show that the proposed schemes can achieve better performance than traditional TAS schemes, while effectively reducing the computational complexity in large-scale spatial modulation systems.

Star-QAM Signaling Constellations for Spatial Modulation

The performance of spatial modulation (SM)-assisted multiple-input-multiple-output (MIMO) communication systems is highly dependent on the specific amplitude/phase modulation (APM) signal constellation adopted. In this paper, we conceive new star-quadrature amplitude modulation (star-QAM)-aided SM schemes. Our goal is to minimize the system's average bit error probability (ABEP). More specifically, a new class of star-QAM constellations is introduced for SM, which is capable of flexibly adapting ring ratios of the amplitude levels. Then, under a specific MIMO configuration and a predetermined transmission rate, a simple and efficient ring-ratio optimization algorithm is proposed to minimize the ABEP. Moreover, to improve further the performance of our star-QAM-aided SM scheme, a diagonal precoding technique is proposed, and a low-complexity minimum-distance-based approach is conceived for extracting the precoding parameters. Our numerical results show that the proposed star-QAM-aided SM arrangement provides beneficial system performance improvements compared with the identical-throughput maximum-minimum distance (MMD) QAM and phase-shift keying (PSK) benchmarkers. Moreover, our precoding scheme is capable of further improving the attainable system performance at a modest feedback requirement.

Improving the Diversity of Spatial Modulation in MISO Channels by Phase Alignment

The performance of spatial modulation (SM) is known to depend on the minimum Euclidean distance in the received SM constellation. In this letter, a symbol scaling technique is proposed for spatial modulation in the multiple-input-single-output (MISO) channel that enhances this minimum distance. It achieves this by aligning the phase of the relevant channels so that the received symbol phases are distributed in uniformly spaced angles in the received SM constellation. In contrast to existing amplitude-phase scaling schemes that are data-dependent and involve an increase in the transmitted signal power for ill conditioned channels, here a phase-only shift is applied. This allows for data-independent, fixed per-antenna scaling and leaves the symbol power unchanged. The results show an improved SM performance and diversity for the proposed scheme compared to existing amplitude-phase scaling techniques.

On the Performance of Spatial Modulation: Optimal Constellation Breakdown

Spatial modulation (SM) is a new transmission technique for multi-antenna systems in which the transmit antennas are used to modulate the signal. In this paper, the symbol error rate (SER) performance of SM is investigated. In SM, a signal domain modulation (i.e. amplitude-phase modulation) and an antenna domain modulation (i.e. space shift keying) are combined together to achieve a certain transmission rate while exploiting the properties of two independent modulation domains. A key question is the fine balance between the constellation sizes in the two domains when a constant rate is targeted. For a fixed rate, there are many ways to assign constellation vectors to the spatial and signal domains. In this paper, we investigate optimal constellation breakdown between space and signal domains. The analysis is based on the union bound of the error probability of SM with two typical APM schemes, i.e. phase-shift keying (PSK) and square quadrature amplitude modulation (S-QAM). It is shown that, at any transmission rate, there exists an optimal APM dimension in which the SER is minimized. Furthermore, a trade-off between the number of transmit antennas and the transmit power is introduced.

On the Mutual Information and Precoding for Spatial Modulation with Finite Alphabet

In this letter, we investigate the effect of finite alphabet inputs on the performance of spatial modulation (SM) for multiple-input-single-output (MISO) channels. The closed-form expression of the mutual information is first derived in an information-theoretic framework. With careful analysis of the expression, we develop a precoding scheme to improve the performance of SM. Utilizing the theory of traditional constellation design, the precoding coefficient is obtained by maximizing the minimum Euclidean distance. Numerical results demonstrate substantial difference in the mutual information between SM with finite alphabet inputs and SM with Gaussian inputs, and show that our precoding scheme achieves significant gains.

Performance of Spatial Modulation in the Presence of Channel Estimation Errors

This work investigates the negative effects of channel estimation errors on the performance of spatial modulation (SM) when operating over flat Rayleigh fading channels. The pairwise error probability of the SM scheme is derived in the presence of channel estimation errors and an upper bound on the average bit error probability is evaluated for M-PSK and M-QAM signalling. It is shown via computer simulations that the derived upper bound becomes very tight with increasing signal-to-noise ratio (SNR) and the SM scheme is quite robust to channel estimation errors.

Performance of Spatial Modulation in Correlated and Uncorrelated Nakagami Fading Channel

Spatial Modulation (SM) has been proposed to avoid interchannel interference and the need of exact time synchronization amongst antennas of the Multiple Input Multiple Output (MIMO) transmission system. In this paper, we study the performance of SM in a Nakagami fading environment. Exact integral expressions for calculating the symbol error rate of multilevel Quadrature Amplitude Modulation (M-QAM) of SM in correlated and uncorrelated Nakagami fading channels are derived. The analytical and simulation results match closely over a wide range of SNR values.