Generalized Spatial Modulation Systems Research Articles

Low-Complexity GSM Detection Based on Maximum Ratio Combining

Generalized spatial modulation (GSM) technology is an extension of spatial modulation (SM) technology, and one of its main advantages is to further improve band efficiency. However, the multiple active antennas for transmission also brings the demodulation difficulties at the receiver. To solve the problem of high computational complexity of the optimal maximum likelihood (ML) detection, two sub-optimal detection algorithms are proposed through reducing the number of transmit antenna combinations (TACs) detected at the receiver. One is the maximum ratio combining detection algorithm based on repetitive sorting strategy, termed as (MRC-RS), which uses MRC repetitive sorting strategy to select the most likely TACs in detection. The other is the maximum ratio combining detection algorithm, which is based on the iterative idea of the orthogonal matching pursuit, termed the MRC-MP algorithm. The MRC-MP algorithm reduces the number of TACs through finite iterations to reduce the computational complexity. For M-QAM constellation, a hard-limited maximum likelihood (HLML) detection algorithm is introduced to calculate the modulation symbol. For the M-PSK constellation, a low-complexity maximum likelihood (LCML) algorithm is introduced to calculate the modulation symbol. The computational complexity of these two algorithms for calculating the modulation symbol are independent of modulation order. The simulation results show that for GSM systems with a large number of TACs, the proposed two algorithms not only achieve almost the same bit error rate (BER) performance as the ML algorithm, but also can greatly reduce the computational complexity.

Low Complexity Quasi-Optimal Detector for Generalized Spatial Modulation

Generalized Spatial Modulation (GSM) is a promising technique for high data-rates systems where the complexity of the optimal joint detector based on the Maximum Likelihood (ML) criterion increases dramatically in terms of the modulation order and the number of activated transmit antennas. In this letter, a novel detection scheme for GSM systems denoted by O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> SIC-ML is proposed to achieve the optimal performance with a controllable complexity-performance trade-off. The proposed detector is accompanied with ordering techniques for the transmit antenna combination and symbols to further reduce the complexity and improve the performance, respectively. The result reveals that O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> SIC-ML allows reaching the non-linear ML detector performance with a 99% complexity reduction.

Spatial Modulation for Joint Radar-Communications Systems: Design, Analysis, and Hardware Prototype

Dual-function radar-communications (DFRC) systems implement radar and communication functionalities on a single platform. Jointly designing these subsystems can lead to substantial gains in performance as well as size, cost, and power consumption. In this paper, we propose a DFRC system, which utilizes generalized spatial modulation (GSM) to realize coexisting radar and communications waveforms. Our proposed GSM-based scheme, referred to as spatial modulation based communication-radar (SpaCoR) system, allocates antenna elements among the subsystems based on the transmitted message, thus achieving increased communication rates by embedding additional data bits in the antenna selection. We formulate the resulting signal models, and present a dedicated radar processing scheme. To evaluate the radar performance, we characterize the statistical properties of the transmit beam pattern. Then, we present a hardware prototype of the proposed DFRC system, demonstrating the feasibility of the scheme. Our results show that the proposed GSM system achieves improved communication performance compared to techniques utilizing fixed allocations operating at the same data rate. For the radar subsystem, our experiments show that the spatial agility induced by the GSM transmission improves the angular resolution and reduces the sidelobe level in the transmit beam pattern compared to using fixed antenna allocations.

Hybrid Precoding Aided Secure Generalized Spatial Modulation in Millimeter Wave MIMO Systems

This letter studies the secrecy capacity of the millimeter Wave (mmWave) Generalized Spatial Modulation (GSM) system with hybrid precoding. First of all, the capacity of the mmWave GSM system with Gram-Schmidt precoding is analyzed. Secondly, the influence of the shared scatterers on the secrecy capacity is explored under the wire-tap channel. Finally, artificial noise, which has no influence on legitimate user but can interfere with the eavesdropping user, is adopted to prevent eavesdropping. Simulation results show that in the most SNR region, the secrecy capacity of the proposed scheme is higher than that of the system directly adopting orthogonal matching pursuit, phase extraction alternating minimization, and semidefinite relaxation alternating minimization precoding algorithms.

Block Deep Neural Network-Based Signal Detector for Generalized Spatial Modulation

Generalized Spatial Modulation (GSM) is being considered for high capacity and energy-efficient networks of the future. However, signal detection due to inter channel interference among the active antennas is a challenge in GSM systems and is the focus of this letter. Specifically, we explore the feasibility of using deep neural networks (DNN) for signal detection in GSM. In particular, we propose a block DNN (B-DNN) based architecture, where the active antennas and their transmitted constellation symbols are detected by smaller sub-DNNs. After N-ordinary DNN detection, the Euclidean distance-based soft constellation algorithm is implemented. The proposed B-DNN detector achieves a BER performance that is superior to traditional block zero-forcing (B-ZF) and block minimum mean-squared error (B-MMSE) detection schemes and similar to that of classical maximum likelihood (ML) detector. Further, the proposed method requires less computation time and is more accurate than alternative conventional numerical methods.

Frequency Domain Equalization for Single and Multiuser Generalized Spatial Modulation Systems in Time Dispersive Channels

In this letter, a low-complexity iterative detector with frequency domain equalization is proposed for generalized spatial modulation (GSM) aided single carrier (SC) transmissions operating in frequency selective channels. The detector comprises three main separate tasks namely, multiple-input multiple-output (MIMO) equalization, active antenna detection per user and symbol wise demodulation. This approach makes the detector suitable for a broad range of MIMO configurations, which includes single-user and multiuser scenarios, as well as arbitrary signal constellations. Simulation results show that the receiver can cope with the intersymbol interference induced by severe time dispersive channels and operate in difficult underdetermined scenarios.

Multi-User Linear Precoding for Downlink Generalized Spatial Modulation Systems

In this letter, a linear precoding scheme is proposed for downlink (DL) multi-user (MU) generalized spatial modulation (GSM) systems. The proposed precoding scheme achieves, not only inter-user interference (IUI) free, but also maximum signal-to-noise ratio (SNR). The former achievement leads to higher multiplexing gain, while the later results in higher diversity gain. By formulating the precoder design as a constrained optimization problem, the optimal precoding vectors are derived by using singular value decomposition (SVD). Outage and ergodic capacities of the proposed scheme are then analyzed, and compared to that of the conventional GSM scheme and the MU zero-forcing (ZF) transmit beamforming scheme by simulations. Simulation results indicate that the proposed scheme can effectively eliminate the IUI, and achieve significant diversity gain.

Codebook-based precoding for generalized spatial modulation with diversity

This paper investigates codebook-based precoding for spatial modulation (SM) and generalized spatial modulation (GSM) systems. Codebook-based precoding allows the system to dispense with full channel state information at the transmitter (CSIT). This considerably reduces the feedback overhead. Phase-only codebooks with systematic structure are investigated since they avoid increasing the peak to average power ratio of the transmitted signal. It is shown that the proposed phase-only codebooks yield equivalent performance to published codebooks that involve gain and phase. In addition, a gain-only codebook is designed to supplement the phase-only codebook and reduce the bit error rate (BER) further. We also compare the performance with the Grassmannian codebooks which are proposed for other multiple-in-multiple-out (MIMO) systems. In GSM systems, several antennas are simultaneously active as a transmit antenna combination (TAC). The BER performance of unprecoded GSM systems is typically inferior to SM systems due to correlation among TACs. However, with codebook precoding, this effect is mitigated, and the performance of the GSM system becomes superior to the SM system. We investigate codebook precoding for GSM systems where precoding is performed per-TAC or per-antenna. Moreover, we investigate the GSM system where the TACs are selected adaptively based on the achievable benefit from codebook precoding. Using computer simulation, it is shown that the performance of the proposed codebooks is very promising in both SM and GSM systems. Per-antenna precoding is superior to per-TAC precoding. Adaptive TACs selection further improves performance.

Approximate Message Passing Detector Based Upon Probability Sorting for Large-Scale GSM Systems

Large-scale generalized spatial modulation (GSM) technology has great potential in constructing low-complexity massive multiple-input multiple-output wireless systems, with a simplified structure which employs only a few radio frequency (RF) chains. However, detection is a very complex problem for large-scale GSM systems. In this correspondence paper, we have proposed an innovative probability sorting based approximate message passing (PS-AMP) detector. Specifically, in the proposed scheme, an approximate message passing method is used to obtain the probability for activation of each transmit antenna, and a method based upon probability sorting is developed to ascertain the signal search space. Simulation results demonstrate that the proposed PS-AMP detector exhibits a better bit error rate performance with a reduced complexity compared to its conventional counterparts.

LR-aided sphere decoding of generalized spatial modulation signals

This paper presents a new low complexity sphere decoding (SD) for the generalized spatial modulation (GSM). We introduce a pre-processing stage using the lattice reduction (LR) aided minimum mean squared error (MMSE) equalization in the GSM systems. This stage speeds up the search in the decoding tree and provides a lattice dependent (LD) initial choice of the radius. Moreover, we derive a lattice independent (LI) initial radius that guarantees the optimal performance at a high signal-to-noise ratio (SNR). We also propose an iterative method to increase the radius in order to achieve the maximum likelihood (ML) performance at all SNRs. We show that the proposed algorithm achieves the ML performance while requiring prominently less computational complexity (CC) than an exhaustive search. In addition, we analyze the CC of the resulting algorithm at high SNRs and we derive an analytical expression for the complexity. The simulation results demonstrate a noticeable decrease in the CC of the proposed sphere decoding algorithm in comparison with its counterparts, particularly at low SNRs.

Media‐based single‐symbol generalized spatial modulation

SummarySingle‐symbol generalized spatial modulation (GSM) improves upon the limitation of spatial modulation (SM) by reducing the number of required transmit antennas to achieve high data rates. In this paper, we investigate the application of media‐based modulation (MBM) based on radio frequency mirrors to single‐symbol GSM, with the aim of improving error performance. The theoretical average bit error probability of the proposed scheme is derived, employing a lower bound approach and used to validate the Monte Carlo simulation results. Finally, the effect of optimal and suboptimal mirror activation pattern selection employing Euclidean distance and channel amplitude coupled with antenna correlation is investigated for the proposed media‐based single‐symbol GSM system. The Monte Carlo simulation results obtained demonstrate a significant improvement over the conventional SM, GSM, and media‐based SM (MB‐SM) schemes in terms of error performance and spectral efficiency.

Transmit Antenna Subset Selection in Generalized Spatial Modulation Systems

The existing literature on transmit antenna selection (TAS) aided spatial modulation (SM) systems extensively deals with the Euclidean distance (ED) based TAS owing to its high transmit diversity gain. In this paper, we consider the ED-TAS aided generalized spatial modulation (GSM) system that transmits multiple symbols in each channel use and characterize its attainable diversity gain. Second, we show that the minimum ED of the received constellation does not grow beyond a certain point when the size of the signal set is sufficiently large, which facilitates low-complexity implementations of the ED-TAS aided SM system. Our numerical studies revealed that a signal-to-noise gain of about 8 dB is achievable by employing ED-TAS in the GSM system compared to its counterpart dispensing with ED-TAS.

Fully generalised spatial modulation technique for underwater communication

A novel transmission scheme called fully generalised spatial modulation (FGSM) is proposed for underwater communication, where any subset of available transmitting antennas ( N t ) is activated at a time instant to transmit the data constellation symbol and the index of the active antenna is also harnessed to carry information. The FGSM offers better energy efficiency (EE) than previous spatial modulation (SM) and generalised SM systems. The proposed FGSM system is tested in an acoustic underwater multipath channel. Simulation results show that it can significantly improve the average bit error rate (ABER) as well as EE.

Two-Layer LDPC Codes for Low Complexity ML Detection in GSM Systems

Although maximum-likelihood (ML) detection is able to achieve optimal performance in generalized spatial modulation (GSM) systems, its exhaustive search leads to an intractable computational complexity. In this letter, two-layer low-density parity-check (TL-LDPC) codes are proposed to reduce the combinations of transmission vectors in LDPC coded GSM systems. Simulation results show that the complexity of the ML detection in the TL-LDPC-coded GSM systems is much lower than that of the ML detection in conventional LDPC-coded GSM systems with a negligible performance loss.

A Unified Precoding Scheme for Generalized Spatial Modulation

Generalized spatial modulation (GSM) activates $n_{t}$ out of $N_{t}~(1 \leq n_{t} available transmit antennas, and information is conveyed through $n_{t}$ modulated symbols as well as the index of the $n_{t}$ activated antennas. GSM strikes an attractive tradeoff between spectrum efficiency and energy efficiency. Linear precoding that exploits channel state information at the transmitter enhances the system error performance. For GSM with $n_{t}=1$ (the traditional SM), the existing precoding methods suffer from high computational complexity. On the other hand, GSM precoding for $n_{t} \geq 2$ is not thoroughly investigated in the open literature. In this paper, we develop a unified precoding design for GSM systems, which universally works for all $n_{t}$ values. Based on the maximum minimum Euclidean distance criterion, we find that the precoding design can be formulated as a large-scale nonconvex quadratically constrained quadratic program problem. Then, we transform this challenging problem into a sequence of unconstrained subproblems by leveraging augmented Lagrangian and dual ascent techniques. These subproblems can be solved in an iterative manner efficiently. Numerical results show that the proposed method can substantially improve the system error performance relative to the GSM without precoding and features extremely fast convergence rate with a very low computational complexity.

Improved Layered Message Passing Algorithms for Large-Scale Generalized Spatial Modulation Systems

Generalized spatial modulation (GSM) is a novel multiple-input multiple-output technique, which relies on a sparse use of radio-frequency front-ends at the transmitter. In this letter, a pair of detectors based on the layered message passing (LaMP) detector are proposed for large-scale GSM. Specifically, a threshold-aided LaMP detector (T-LaMP) is proposed with the purpose of reducing the computational complexity of LaMP detector. In addition, for the sake of achieving further GSM system performance improvements, a probability-ranking-aided LaMP detector (PR-LaMP) is also proposed. Simulation results show that T-LaMP detector is able to achieve similar performance as LaMP with lower complexity, while PR-LaMP detector is able to achieve considerable performance gain.

Optimization of the Cut-Off Rate of Generalized Spatial Modulation with Transmit Precoding

Spatial modulation (SM) and generalized spatial modulation (GSM) are emerging multiple input multiple output (MIMO) schemes that use transmitter (TX) antenna switching for data transmission. Their operating principle makes optimization of channel capacity and mutual information usually more difficult than for conventional MIMO schemes which are not based on antenna switching. We propose to use channel cut-off rate as a relevant and more tractable metric for performance optimization of spatial modulation (SM)/GSM systems, as it constitutes a practical lower-bound of channel capacity. In particular, we propose four TX precoding schemes for increasing the cut-off rate of SM/GSM systems. We show that those TX precoding schemes which are designed for increasing array gain provide the largest improvement of cut-off rate for low signal-to-noise ratio (SNR). On the other hand, the TX precoding schemes that are designed for increasing the minimum Euclidean distance of GSM symbols are more suitable for application to medium to high SNR setups and correlated channels. The proposed precoding schemes are shown to be able to enhance mutual information, and the gain is shown to be of the same order of magnitude as the gain of the corresponding channel cut-off rate.

Precoding Aided Generalized Spatial Modulation With an Iterative Greedy Algorithm

This paper divides antennas at the transmitter into several transmit antenna groups (TAGs) and extends the generalized spatial modulation (GSM) idea to a new precoding-aided multiple-input multiple-output system, which is referred to as precoding-aided GSM (PGSM) system. To mitigate the influence caused by correlated channels, we consider the interleaved grouping scheme which leads to a minimum antenna correlation within the same TAG. To select the receive antenna subset with low complexity, we propose an iterative greedy (IG) algorithm that contributes to a maximum equivalent channel gain with low-computational complexity. To reduce the complexity of maximum likelihood (ML) detector, a low complexity IG algorithm-based ML (IG-ML) detector is also derived. Simulation results show that the bit error rate (BER) performance gain up to 3.5 dB is obtained by the proposed PGSM with IG-ML detector over the PGSM with an ordered block minimum mean-squared error detector at a given BER of 10−4. It is also shown that the proposed PGSM with the IG-ML detector achieves a similar BER performance in a high signal-to-noise power ratio region compared with that of an ideal precoding for the GSM with an optimal ML detector.

Transmit Antenna Combination Optimization for Generalized Spatial Modulation Systems

Generalized spatial modulation (GSM), where both the transmit antenna combination (TAC) index and the amplitude phase modulation (APM) symbols convey information, is a novel low-complexity and high efficiency multiple-input multiple-output (MIMO) technique. In conventional GSM (C-GSM), the legitimate TACs are selected randomly to transmit the APM symbols. However, the number of the TACs must be a power of two, hence the excess TACs are discarded, resulting in wasting some resource. To address these issues, in this paper, an optimal TAC set-aided enhanced GSM (E-GSM) scheme is proposed, where the optimal TAC set is selected with the aid of the channel state information (CSI) by maximizing the minimum Euclidean distance. Furthermore, a hybrid mapping GSM (HM-GSM) scheme operating without CSI knowledge is investigated, where the TAC selection and bit-to-TAC mapping are both taken into consideration for optimizing the average Hamming distance. Finally, an enhanced high throughput GSM (E-HT-GSM) scheme is developed, which makes full use of all the TACs. This scheme is capable of achieving an extra one bit transmission rate per time slot. Moreover, the rotated phase is employed and optimized for the reused TACs. Our simulation results show that the proposed E-GSM system and HM-GSM system are capable of outperforming the C-GSM system. Furthermore, the E-HT-GSM system is capable of obtaining one extra bit transmission rate per time slot compared with the C-GSM system.

Performance of Generalized Spatial Modulation MIMO Over Measured 60GHz Indoor Channels

In this paper, we study the capacity and symbol error probability (SEP) of generalized spatial modulation (GSM) multiple-input multiple-output (MIMO) using measured channels that are obtained by channel sounding in an indoor office environment at 60GHz. Spatial modulation (SM) and GSM are emerging low-complexity MIMO schemes that have been extensively researched for low-GHz (below 6GHz) communications. Recently, they have been considered and shown to be promising also for (mmWave) communications. In the simplest possible case, they require only one RF chain both at the transmitter (TX) and receiver (RX), and thus, are especially attractive for mmWave communications, in which the number of RF chains needs to be as low as possible. Despite of some early works on the theoretical analysis of SM/GSM for mmWave communications, there have been no investigations using real-world channel data. We focus on the office line-of-sight (LOS) scenario and investigate three problems: 1) the performance of GSM using the extracted LOS component of measured channels; 2) the impact of non-LOS NLOS components on the performance of GSM; and 3) possible simple modulation and reception algorithms for GSM that rely only on the LOS component of the channel. The results being reported in this paper not only validate the main claims of previous studies based on ideal pure LOS channels, but also lead to novel findings. One major conclusion is that NLOS components are harmful to the SEP of GSM and should be avoided. As another important outcome, our results strongly motivate the use of precoding in GSM systems to simultaneously improve the channel capacity and reduce the physical size of MIMO arrays (thus eliminating one major issue of LOS GSM).