Enhanced Spatial Modulation Research Articles

Joint Code Index Modulation Aided Enhanced Spatial Modulation for High-Rate MIMO Systems

In this paper, a novel scheme, which introduces the technology of the code index modulation (CIM) into the realm of enhanced spatial modulation (ESM), named CIM-ESM, is proposed to achieve high spectral efficiency and high energy efficiency in multiple-input multiple-output (MIMO) systems. In the CIM-ESM scheme, information bits are conveyed not only by modulated symbols and spreading code indices, but also by the indices of the active antenna and constellation combinations. Meanwhile, the mathematical expressions for the average bit error probability (ABEP) in the presence of channel estimation errors, data rate, energy efficiency, and complexity of the CIM-ESM scheme are deduced. To achieve a higher transmission rate and code utilization, we further propose an enhanced scheme, named joint CIM-ESM (JCIM-ESM) scheme. In the JCIM-ESM scheme, spreading codes are jointly selected to form spreading code pairs and the matching indices of the spreading code pairs are utilized to convey extra information bits. Finally, Monte Carlo simulation results corroborate the tightness of the derived ABEP expression in the high signal-to-noise ratio region and reveal that both the CIM-ESM and JCIM-ESM schemes can provide better performance than CIM spread spectrum (CIM-SS), generalized CIM-aided spatial modulation (GCIM-SM), generalized space CIM (GSCIM), and CIM-aided QSM (CIM-QSM) schemes.

Multi-Dimensional Polarized Modulation for Land Mobile Satellite Communications

In this article, a novel multiple-input multiple-out (MIMO) transmission scheme, called generalized polarized enhanced spatial modulation (GPESM), is proposed for dual-polarized land mobile satellite (LMS) communications. We first introduce the enhanced spatial modulation (ESM) technique for dual-polarized LMS communications, in which polarization dimension, spatial dimension and multiple signal constellations are used to transmit information and obtain substantial performance gain. Meanwhile, the theoretical upper bound for the average bit error probability (ABEP) of the proposed GPESM scheme is derived. In order to further improve the reliability of the system, we also propose two novel power allocation (PA) algorithms for GPESM system, which are the optimization-driven approximated max-min distance (AMMD)-based PA algorithm and the data-driven deep neural network (DNN)-based PA algorithm. To achieve an enhanced spatial diversity gain, we consider to apply a reconfigurable intelligent surface (RIS) to the GPESM system as a relay to assist in transmitting information. In this way, the user can receive the information transmitted by the satellite on one hand, and the information sent by the satellite via the RIS relay on the other hand. We also extend the above-mentioned two PA algorithms to the RIS-assisted GPESM systems. Our simulation results show that the RIS-assisted GPESM systems are capable of obtaining high bit error rate (BER) performance gain (up to 10 dB) compared to the standard GPESM system and two PA algorithms can further improve the performance to the systems.

An Experimental Investigation of Enhanced SM-OFDM Over Indoor Rician Multipath Channels

In this letter, we investigate enhanced spatial modulation (ESM) aided orthogonal frequency division multiplexing (OFDM) systems. ESM extends the conventional SM by introducing a series of signal constellations. Existing research shows that ESM displays performance superiority over SM in flat-fading channels. For frequency-selective fading channels, we design a practical implementation of an ESM&SM aided OFDM hybrid system to characterize the bit error rate (BER) performance of ESM and conventional SM with an experimental wireless testbed. Form the experimental results, it is found that ESM achieves better BER performance than SM on frequency-selective channels, which are consistent with the Monte Carlo simulation results.

Bridging Spatial Modulation With Spatial Multiplexing: Frequency-Domain ESM

Spatial modulation (SM) is a multi-input multi-output (MIMO) technique, which was originally introduced to reduce the number of radio frequency (RF) chains in a MIMO transmitter and thereby reduce cost and power consumption. Although it is very appealing in theory, this concept actually has two main problems: The first is that SM involves antenna switching, which degrades the spectral shaping and the Nyquist property of the transmitted signal. The second is the limited spectral efficiency due to the presence of silent antennas. In order to remedy the second problem, enhanced spatial modulation (ESM) was introduced in which multiple signal constellations are used, and information bits are conveyed not only by the transmitted symbols and the indices of the active antennas, but also by the constellation types activated. As for the problem of antenna switching, it actually disappears when SM is combined with OFDM, because the switching operation in frequency-domain SM (FD-SM) occurs at baseband. But the number of RF chains required becomes equal to the number of transmit antennas and the property of reduced number of RF chains, which was the original motivation for SM also disappears. FD-SM turns out to be a particular type of underloaded MIMO-OFDM system, which reduces the power requirements of the transmit power amplifiers rather than their number. In this paper, we introduce frequency-domain ESM (FD-ESM), which avoids both the spectral efficiency limitations and the antenna switching issues of the original SM. Exploiting the property that switching occurs at baseband and no savings in terms of the number of RF chains can be achieved in frequency-domain implementation, we design FD-ESM schemes in which the transmitted codewords do not include any zero-valued components. These designs bridge the concept of SM with spatial multiplexing, and they provide spectacular gains with respect to multi-stream SM (MSM) and also some significant gains compared to conventional spatial multiplexing.

Design of a TAS-STBC-ESM(F) Transceiver and Performance Analysis for 20 bpcu

This paper proposes an index modulation-based transceiver design termed transmit antenna selected space-time block coded enhanced spatial modulation with flexible coefficients (TAS-STBC-ESM(F)). A new 1024-QAM signal design based on multiple constellations and a codebook design that uses flexible coefficients and rotation angles are proposed. A new detection scheme, namely, Iter-BLAST, for generalized detection is introduced, and its complexity is analyzed. For 20 bpcu, the TAS-STBC-ESM(F) transmitter with Iter-BLAST, ML, Iter-LC-LORD, and compressed sensing-based detection schemes is studied over the $\alpha -\mu $ fading channel. Closed-form expressions for the ABEP, outage probability, and capacity of the proposed system are derived. The introduction of flexible coefficients, antenna selection methods, and multiple constellations in the transmitter design shows a 5.5-dB improvement over an enhanced spatial modulation (ESM) system and a 3-dB improvement over the STBC-ESM system. For a 20 bpcu, $64\times 64$ MIMO system, the floating point operations of the CS-based ESM detection algorithm are 13.9 times those of Iter-BLAST, and the error performance improvement is 10.8%. The proposed transceiver design will be a promising solution for 5G and massive MIMO that addresses the tradeoff between spectral and energy efficiencies.

Signal constellations employing multiplicative groups of Gaussian and Eisenstein integers for Enhanced Spatial Modulation

In this paper, we propose two new signal constellation designs employing Gaussian and Eisenstein Integers for Enhanced Spatial Modulation (ESM). ESM is a novel technique which was propounded by Cheng et al. The advantage of ESM over other Spatial Modulation (SM) schemes lies in its ability to enhance spectral efficiency while keeping the energy efficiency intact. This is done by activating either one or two antennas judiciously depending upon the required trade-off. In ESM, information radiated from the antennas depends upon index of the active transmit antenna combination(s) and also on the set of constellation points chosen, which may include points from multiple constellations. In this paper, we propose signal constellations based on multiplicative groups of Gaussian and Eisenstein integers. The set comprising of Gaussian and Eisenstein integers serves as primary and secondary constellation points for Gaussian Enhanced Spatial Modulation (GESM) scheme. The secondary constellation points are deduced from a single geometric interpolation from the primary constellation points. The Monte Carlo simulation results indicate that the proposed nonuniform constellations achieve impressive SNR gains compared to conventional constellation points used in the design of ESM. This new design has been described for MIMO employing 4 × 4 and 8 × 8 antenna configurations with only two active antennas. Furthermore, a closed form expression for the pairwise error probability (PEP) for the GESM scheme has been deduced. The PEP is utilized to determine the upper bound on the average bit error probability (ABEP). Our simulations indicate that the proposed GESM from Gaussian and Eisenstein integers scheme outperforms all the other variants of SM including conventional ESM by at least 2.5 dB at an average bit error ratio (ABER) of 10−5. Close correspondence between the theoretical analysis and the Monte Carlo simulation results are observed.

New Signal Designs for Enhanced Spatial Modulation

In this paper, we present three new signal designs for enhanced spatial modulation (ESM), which was recently introduced by the present authors. The basic idea of ESM is to convey information bits not only by the index(es) of the active transmit antenna(s) as in conventional SM, but also by the types of the signal constellations used. The original ESM schemes were designed with reference to single-stream SM and involved one or more secondary modulations in addition to the primary modulation. Compared with single-stream SM, they provided either higher throughput or improved signal-to-noise ratio (SNR). In this paper, we focus on multi-stream SM (MSM) and present three new ESM designs leading to increasing SNR gains when they are operated at the same spectral efficiency. The secondary signal constellations used in the first two designs are derived through a single geometric interpolation step in the signal constellation plane, while the third design also makes use of additional constellations derived through a second interpolation step. The new ESM signal designs are described for MIMO systems with four transmit antennas out of which two are active, but we also briefly present extensions to higher numbers of antennas. Theoretical analysis and simulation results indicate that the proposed designs provide a significant SNR gain over MSM.