Enhanced Spatial Modulation With Multiple Signal Constellations

Spatial modulation (SM) is a transmission scheme that uses multiple transmit antennas but only one transmit RF chain. At each time instant, only one among the transmit antennas will be active and the others remain silent. The index of the active transmit antenna will also convey information bits in addition to the information bits conveyed through modulation symbols. Pseudo-random phase precoding (PRPP) is a technique that can achieve high diversity orders even in single antenna systems without the need for channel state information at the transmitter and transmit power control. In this paper, we exploit the advantages of both SM and PRPP simultaneously. We propose a pseudo-random phase precoded SM (PRPP-SM) scheme, where both the modulation bits and the antenna index bits are precoded by pseudo-random phases. The proposed PRPP-SM system gives significant performance gains over SM system without PRPP and PRPP system without SM. Since maximum likelihood (ML) detection becomes exponentially complex in large dimensions, we propose a low complexity local search based detection (LSD) algorithm suited for PRPP-SM systems with large precoder sizes. Our simulation results show that with 4 transmit antennas, 1 receive antenna, 5 × 20 pseudo-random phase precoder matrix and BPSK modulation, the performance of PRPP-SM using ML detection is better than SM without PRPP with ML detection by about 9 dB at 102 BER. This performance advantage gets even better for large precoding sizes. We also propose a precoder index modulation (PIM) scheme, which conveys additional information bits through the choice of a precoding matrix among a set of pre-determined PRPP matrices. Finally, combining the PIM and PRPP-SM schemes, we propose a PIM-SM scheme which conveys bits through both antenna index as well as precoder index.

Quadrature spatial modulation (QSM) has been recently proposed for MIMO communication systems. It comes to enhance the overall throughput over conventional spatial modulation (SM) techniques. This article investigates the using of this new SM technique in Multi-user MIMO networks, denoted here as MU-QSM. Unlike existing SM techniques, the QSM creates additional spatial constellation dimension, and hence higher overall throughput can be obtained. The performance of the system mentioned is numerically analyzed for a number of users and compared to point-to-point networks. In addition, the experienced interference and receiver-complexity are analyzed too.

Permutation index-quadrature spatial modulation: A spectral efficient spatial modulation for next generation networks

This work presents an integrated framework that combines polar coding, spatial modulation, and symbol‐level guessing random additive noise decoding (symbol‐level GRAND) aided detection to enhance the reliability and latency performance of CRC‐aided polar codes in 6G ultrareliable low‐latency communication (URLLC) scenarios. The proposed polar‐coded spatial modulation (PCSM) scheme utilizes (CA‐polar) codes to encode information bits transmitted as antenna index and symbol bits over a MIMO Rayleigh fading channel. The receiver employs a two‐stage detection scheme comprising initial spatial signal processing for antenna and symbol detection, followed by symbol refinement through symbol‐level GRAND with final error correction achieved with CRC‐aided successive cancellation list (CA‐SCL) decoding. A sequential detection and decoding strategy is adopted, in which symbol‐level GRAND refines the detected bits before CA‐SCL polar decoding, reducing error propagation into the polar decoder and thereby lowering the overall decoding complexity. Performance of the scheme is evaluated for polar codeword length of 128 bits for modulation orders of 16‐QAM and 64‐QAM, highlighting the scheme's parametric flexibility under short codeword constraints. Simulations carried out in MATLAB demonstrate that error correction with symbol‐level GRAND‐aided detection achieves an improved bit error rate (BER) and a lower system complexity facilitating real‐time hardware realization.

In this paper, we study transmit codebook designs for spatial modulation with analog phase shifters. The proposed spatial modulation with analog phase shifters can send more spatial symbols than conventional spatial modulation, while reserving the low complexity of single RF-chain MIMO structure. The main idea is to transmit N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> different phase-shifted copies of a digitally modulated signal through N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> transmit antennas. In each time slot, the transmitted information bits are divided into two groups. The first group of the bits is mapped to the digitally modulated signal symbol. The second group of the bits is mapped to the spatial symbol, which determines the phase shift of each antenna. The transmit signal designs are carried out in open loop and closed loop scenarios, respectively. In open loop scenario, the transmit codebook is designed in two steps, i.e., generate the optimal spatial codebook according to Grassmannian line packing criterion, and find the optimal tradeoff between the cardinality of spatial codebook and the modulation order of signal symbol. In the closed loop scenario, the transmit codebook is designed according to the structure of Huffman tree. Extensive simulation results are given to validate the effectiveness of the proposed scheme in open loop scenario and close loop scenario, respectively.

In this paper, a new index modulation technique, referred to as the multi-mode generalized space-time index modulation (MM-GSTIM) is presented. MM-GSTIM is a high-rate index modulation scheme for multiantenna inter-symbol interference (MIMO-ISI) channels. The proposed MM-GSTIM is a single carrier scheme with zero padding (ZP). MM-GSTIM performs `mode-indexing' to efficiently increase the spectral efficiency. In a given MM-GSTIM frame, disjoint subsets of space-time slots are used to transmit modulation symbols from disjoint modulation alphabets (referred to as the modes). The choice of which space-time slots are used for transmission of a particular mode in an MM-GSTIM matrix conveys information bits. Thus, MM-GSTIM is a generalization of the well-known index modulation schemes such as spatial modulation (SM), generalized spatial modulation (GSM), and space-time index modulation. Here, an analytical characterization of the diversity order of the proposed MM-GSTIM scheme and the conditions required to maximize the transmission rate of multi-mode index modulation schemes are derived. Through simulations, it is shown that the proposed MM-GSTIM scheme can achieve better performance compared to other modulation schemes in MIMO-ISI channels.

In this chapter, the fundamental concepts of spatial modulation are introduced. We start in Chapter 2.1 with the channel models, i.e. the AWGN channel and the MIMO Rayleigh fading channel. The AWGN channel is employed in Chapter 3 to compare different signal constellations, whereas the Rayleigh fading channel is used for all MIMO transmission schemes. In Section 2.2, we discuss various spatial modulation transmission schemes from the literature, including spatial modulation, generalized spatial modulation, generalized multistream spatial modulation and the most recently-introduced spatial permutation modulation.

On channel estimation for spatial modulated systems over time-varying channels

As a promising technique in multi-antenna systems, spatial modulation (SM) introduces the spatial domain into its constellation by mapping more information with antenna selection, in addition to the signal domain. To further improve the capacity performance of SM, an iterative algorithm for the spatial-domain design is proposed in this letter, where the optimal probability of activating each transmit antenna is obtained to maximize the instantaneous capacity of SM. By comparing the metrics of outage and ergodic capacity with the conventional SM, illustrative numerical results not only demonstrate the throughput achieved in the proposed scheme, but also substantiate the domination of the proposed scheme over the conventional SM.

Cooperative communications with spatial modulation (SM) scheme have been studied for high speed and reliable wireless transmission systems. For common SM technique, the transmit antenna is selected by the input information bits randomly. However, the real channel condition corresponding to the active antenna determines the performance of SM system directly. SM-index modulation (SM-IM) scheme can modulate the index of the active transmit antenna and the modulated SM symbol into a new transmit symbol, which can be employed to get rid of the poor channel conditions' impact on the performance of SM systems. To further improve the system performance, we propose a cooperative communication system based on SM-IM scheme in this paper, which can avoid the disadvantages of the poor channel allocation of the cooperative SM system. Closed-form expression of the average bit error rate (BER) of the proposed SM-IM cooperative system is derived. Simulation results and analysis show that the proposed scheme outperforms the typical dual-hop SM cooperative system significantly.

A novel multiple-input and multiple-output (MIMO) transmission scheme termed as generalized quadrature spatial modulation (G-QSM) is proposed. It amalgamates the concept of quadrature spatial modulation (QSM) and spatial multiplexing for the sake of achieving a high throughput, despite relying on a low number of radio frequency (RF) chains. In the proposed G-QSM scheme, the conventional constellation points of the spatial multiplexing structure are replaced by the QSM symbols, hence the information bits are conveyed both by the antenna indices as well as by the classic amplitude/phase modulated (APM) constellation points. The upper bounds of the average bit error probability (ABEP) of the proposed G-QSM system in high throughput massive MIMO configurations are derived. Furthermore, an efficient multipath orthogonal matching pursuit (EM-OMP)-based compressive sensing (CS) detector is developed for our proposed G-QSM system. Both our analytical and simulation results demonstrated that the proposed scheme is capable of providing considerable performance gains over the existing schemes in massive MIMO configurations.

The prospect of ultra-massive multiple-input multiple-output (UM-MIMO) technology to combat the distance problem at the Terahertz (THz)-band is considered. It is well-known that the very large available bandwidths at THz frequencies come at the cost of severe propagation losses and power limitations, which result in very short communication distances. Recently, graphene-based plasmonic nano-antenna arrays that can accommodate hundreds of antenna elements in a few millimeters have been proposed. While such arrays enable efficient beamforming that can increase the communication range, they fail to provide sufficient spatial degrees of freedom for spatial multiplexing. In this paper, we examine spatial modulation (SM) techniques that can leverage the properties of densely packed configurable arrays of subarrays of nano-antennas, to increase capacity and spectral efficiency, while maintaining acceptable beamforming performance. Depending on the communication distance and the frequency of operation, a specific SM configuration that ensures good channel conditions is recommended. We analyze the performance of the proposed schemes theoretically and numerically in terms of symbol and bit error rates, where significant gains are observed compared to conventional SM. We demonstrate that SM at very high frequencies is a feasible paradigm, and we motivate several extensions that can make THz-band SM a future research trend.

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.

In this paper, a new multiple-input multiple-output (MIMO) transmission technique, which is called double spatial modulation (DSM), is proposed as a new high-rate generalized spatial modulation (SM) scheme. DSM scheme aims to improve the spectral efficiency of classical SM by increasing the number of active transmit antennas. In the DSM scheme, incoming data bits determine two modulated symbols as well as their corresponding activated transmit antenna indices. One of the modulated symbols is directly transmitted over its corresponding activated transmit antenna, while the other one is transmitted with a rotation angle, which is optimized for M-ary quadrature amplitude modulation (M-QAM) signal constellation, over the second activated transmit antenna. The error performance of the proposed DSM scheme is compared with the recently proposed emerging SM schemes such as quadrature SM (QSM) and enhanced SM (ESM). Our computer simulations show that the DSM scheme provides considerably better error performance than QSM and ESM schemes for different spectral efficiency values. In addition, the pairwise error probability (PEP) of DSM is derived and the average bit error probability (ABEP) over uncorrelated Rayleigh fading channels is obtained for different M-QAM constellations.

This paper proposes a scheme to recover signals transmitted with Spatial Modulation (SM) and Spatial Multiplexing (SMux) techniques in MIMO channels. In order to recover the transmitted signals, combined algorithms have been used. Two algorithms which uses Successive Interference Cancellation (SIC) and Maximum Likelihood (ML) are proposed. Monte Carlo simulations show that the proposed SIC-ML algorithm outperforms previous schemes by 4dB approximately. Overall the new algorithm performs very close the optimal ML algorithm but with a reduced implementation complexity. The proposed segmented ML-ML algorithm performs very close to the ML join-detection algorithm but with reduced complexity.