Modified generalized quadrature spatial modulation performance over Nakagami‐m fading channel

In this paper, a new multiple‐input multiple‐output transmission technique calledquadrature spatial modulation (QSM)is proposed and analyzed in the presence of imperfect channel estimation at the receiver. In QSM, conventional spatial constellation diagram of spatial modulation (SM) system is expanded to include both in‐phase and quadrature components. As such, significant enhancement in the overall spectral efficiency is achieved while retaining all inherent advantages of SM technique, such as inter‐channel interference avoidance, single radio frequency chain transmitter and low receiver complexity. It is shown that significant performance enhancements can be achieved as compared with SM, Alamouti, and spatial multiplexing systems. Besides, the impact of Gaussian imperfect channel estimation on the performance of QSM system is studied. A closed‐form expression for the pairwise error probability of generic QSM system is derived and used to calculate a tight upper bound of the average bit error probability over Rayleigh fading channels with perfect and imperfect channel knowledge. Also, simple asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results highlight the accuracy of the conducted analysis. Copyright © 2014 John Wiley & Sons, Ltd.

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.

Motivated to enhance the error performance (EP) of generalised complex quadrature spatial modulation (GCQSM) systems, this study proposes a scheme that builds on GCQSM and uses hexagonal quadrature amplitude modulation (H-QAM) constellations which have the advantages of a maximised Euclidean distance with relatively low peak-to-average power ratio, compared to conventional QAM (C-QAM) systems. This in turn, leads to an enhancement of the EP of GCQSM schemes. The proposed scheme utilises a rotated hexagonal 8QAM (H-8QAM) set. Thus, the proposed scheme is herein named; Generalised QSM using H-8QAM (GQSM-H-8QAM). In this study, the EP of the proposed GQSM-H-8QAM scheme is investigated over Rayleigh frequency flat-fading channels with additive white Gaussian noise. Additionally, a theoretical average bit error probability (ABEP) expression of the GQSM-H-8QAM scheme is formulated and validated using Monte Carlo simulations. Compared to simulation results, the ABEP proves to be increasingly tight at high signal-to-noise ratio values. Obtained simulation results also show an improvement in the EP of the GQSM-H-8QAM scheme over various SM schemes like GCQSM, C-QSM and conventional-generalized spatial modulation (C-GSM), at the same spectral efficiency (SE). An improvement in the EP of 0.61 dB with SE of 8 bits/s/Hz is seen in 4times 4 GQSM-H-8QAM over 4times 4 GCQSM using C-8QAM, 2.58 dB over 4times 4 C-QSM-C-64QAM and a gain of 4.85 dB over 4times 4 C-GSM-C-64QAM.

The Spatial Modulation (SM) transmission scheme boosts the spectral efficiency and achieves the multiplexing gain by activating a single transmit antenna in each time slot. Radio wave propagation characteristics determined by the environment is a decisive factor for the SM system. In this paper, we investigate the performance of the SM scheme over real-world 4×4 Multi-Input Multi-Output (MIMO) channels measured in typical indoor scenarios. Firstly, a MIMO channel sounder is established. Based on the sounder, 15150 complex 4×4 MIMO channel matrices are measured inside a typical teaching building under both Line of Sight (LOS) and None Line of Sight (NLOS) scenarios. Secondly, by comparing the SM system over the measured channel and commonly-used channel models, we prove that both the Independently and Identically Distribute (i.i.d.) Rayleigh and the Spatial Correlation (SC) channel model are oversimplified, and that only practical experiences can yield definitive answers to the achievable real-world system performance. Thirdly, the Average Bit Error Probability (ABEP) performance of the SM system is studied based on the measured data under a variety of system configurations. The study of different receive antenna array settings (4×4, 4×2 and 4×1 MIMO setups) approves the significance of combining scheme at the receiver. SM systems employing different signal constellations (Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and 16 Quadrature Amplitude Modulation (16QAM)) are also investigated and some interesting results are revealed. Lastly, performance assessment of SM against State-Of-The-Art (SOTA) MIMO schemes (Space-Time Block Code (STBC) and Vertical Bell Labs Layered Space-Time (V-BLAST) code) is conducted. Results show that for a 4×4 MIMO, the low-complexity SM scheme outperforms both STBC and V-BLAST.

This chapter discusses the average bit error ratio (ABER) performance analysis for the different space modulation techniques (SMTs). The ABER is computed for space shift keying (SSK), spatial modulation (SM), quadrature space shift keying (QSSK), and quadrature spatial modulation (QSM) over Rayleigh flat fading channels. The chapter proposes a general framework for the performance analysis of the different SMTs over arbitrary fading channels, in the presence of spatial correlation and imperfect channel estimation. The derivation of the average error probability for SMTs can be computed by deriving the pairwise error probability (PEP). The chapter presents Monte Carlo simulation results to study the ABER performance of SMTs, generalized space modulation techniques (GSMTs), quadrature space modulation techniques (QSMTs), and differential space modulation techniques (DSMTs) system with different configurations. The derivation of the instantaneous PEP in the presence of imperfect channel knowledge at the receiver is similar to the derivation of perfect channel knowledge.

In spatial modulation (SM) systems, when channel state information is available at the transmitter, adaptive power allocation can be exploited to enhance the SM performance. In this paper, optimal power allocation in SM systems is considered from an information-theoretical view. First, as there is no closed-form expression of the SM capacity, the instantaneous mutual information is formulated in an analytic form for SM systems with two transmit antennas. Then, two power-allocation algorithms are proposed to maximize the SM mutual information. One is a sub-optimal power-allocation algorithm that is established in closed form to maximize the upper bound of SM mutual information. The other is an iterative algorithm for optimal power allocation that is proposed to achieve the maximum mutual information of SM systems while dramatically reducing the operational complexity compared with global computer searching. To evaluate the performance of the proposed power-allocation algorithms, numerical and simulation results are reported in terms of outage capacity and ergodic capacity, which demonstrates that the proposed power-allocation algorithms significantly improve the SM performance, compared with conventional equal-power allocation.

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.

Spatial modulation (SM) presents a pragmatic approach for transmitting information, where the modulator uses well known amplitude/phase modulation (APM) techniques such as phase shift keying (PSK) and quadrature amplitude modulation (QAM), but also employs the antenna index to convey additional information. Nevertheless, the spectral efficiency of SM can be further improved. On this note, to further enhance the spectral efficiency of SM, quadrature SM (QSM) modulation was proposed. In coded channels, therefore, typically soft-output detection coupled with soft-input channel decoding yields significant signal-to-noise ratio (SNR) gain. Hence, in this paper, soft-output maximum-likelihood detector (SOMLD) for QSM modulated system is proposed. Monte Carlo simulation results demonstrate that there is a close agreement between the error performances of the proposed SOMLD scheme and those of its hard-decision maximum-likelihood detector counterpart in uncoded channels, while significant signal-to-noise ratio (SNR) gains are yielded in coded channels. Keywords: Multiple-input multiple-output, quadrature spatial modulation, soft-output detection, space shift keying, spatial modulation

In this paper, we propose a new multiple-input multiple-output (MIMO) transmission scheme, called parallel complex quadrature spatial modulation (PCQSM). The proposed technique is based on the complex quadrature spatial modulation (CQSM) to further increase the spectral efficiency of the communication system. CQSM transmits two different complex symbols at each channel use. In contrast with CQSM, the new transmission scheme splits the transmit antennas into groups, and modulates the two signal symbols using the conventional CQSM before transmission. Based on the selected modulation order and the number of possible groups that can be realized, the incoming bits modulate the two signal symbols and the indices of the transmit antennas in each group. We demonstrated that while the complexity and performance of the proposed scheme is the same as that of CQSM, the number of required transmit antennas is significantly reduced. The proposed PCQSM achieves such a benefit without requiring any additional radio frequency (RF) chains. The results obtained from Monte Carlo simulation showed that at a Bit Error Rate (BER) of 10−4, the performance of the PCQSM with two antenna groups closely matches that of CQSM, and outperformed quadrature spatial modulation (QSM) and parallel quadrature spatial modulation (PQSM) by over 0.7 dB. As the number of antenna groups increased to 4, the BER performance of PCQSM with reduced number of transmit antenna and modulation order matches that of QSM. The BER of the proposed scheme using maximum likelihood (ML) receiver is also analyzed theoretically and compared with the BER obtained via simulations.

SummaryGeneralised spatial modulation (GSM) is a recently developed multiple‐input multiple‐output (MIMO) technique aimed at improving data rates over conventional spatial modulation (SM) systems. However, for identical antenna array size and configurations (AASC), the bit error rate (BER) of GSM systems in comparison with SM systems is degraded. Recently, a GSM system with constellation reassignment (GSM‐CR) was proposed in order to improve the BER of traditional GSM systems. However, this study focused on M‐ary quadrature amplitude modulation (M‐QAM) schemes. The focus of this paper is the application of a circular constellations scheme, in particular, amplitude phase shift keying (APSK) modulation, to GSM and GSM‐CR systems. An analytical bound for the average BER of the proposed M‐APSK GSM and M‐APSK GSM‐CR systems over fading channels is derived. The accuracy of this bound is verified using Monte Carlo simulation results. A 4 × 4 16‐APSK GSM‐CR system achieves a gain of 2.5 dB at BER of 10−5 over the traditional 16‐APSK GSM system with similar AASC. Similarly, a 6 × 4 32‐APSK GSM‐CR system achieves a gain of 2 dB at BER of 10−5 over equivalent 32‐APSK GSM system.

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.

In spatial modulation (SM) system, the information bits can be transmitted through two ways, the selection of both the transmit antenna and the constellation symbol. However, conventional bit-to-symbol mapping scheme in SM system only selects the transmit antenna or the constellation symbol independently. With the consideration of the similarity among the transmit antennas and the joint selection of the transmit antenna and the constellation symbol, cosine similarity based bit to symbol-and-antenna mapping scheme is proposed in this paper to reduce the hamming distance between adjacent symbols and achieve better system performance. Simulation results and performance analysis show that the proposed scheme can improve the system average bit error rate (BER) effectively compared with the conventional bit-to-symbol mapping scheme.

One of the main limitations in Spatial Modulation (SM) systems is the lack of transmit diversity, which directly impacts its error rate performance. The lack of the transmit diversity refers to activating only a single transmit antenna in SM systems. In this paper, we propose a novel scheme that aims at improving the performance of SM systems by achieving half-full transmit diversity. The proposed scheme, called Half-Full Transmit-Diversity SM (HFTD-SM), divides the transmit antennas into two-antenna groups. From each group, only a single antenna is activated, and all active transmit antennas emits one modulated symbol. The proposed HFTD-SM scheme is shown to outperform the conventional SM performance in terms of spectral efficiency, error rate, and design flexibility, while maintaining the main property of SM representing by the need of only a single RF chain. Simulation results corroborate the superior performance of the proposed scheme as compared to other SM variants in the literature.

Recently, asynchronous non-orthogonal multiple access (ANOMA), that can further enhance the performance of NOMA, has gained much attention. Considering the demands of resource-constrained wireless communications and green communications, power-efficient minimum shift keying-type (MSK-type) signals have also been introduced into uplink ANOMA, but they are only for a basic flat fading channel and perfect conditions. In this paper, an uplink ANOMA based on MSK-type signals with imperfect channel state information and successive interference cancellation over generalized fading channels is proposed, and its ergodic capacity is investigated. Specifically, the system model is first established. Then, a moment generating function (MGF)-based ergodic capacity expression applicable to general fading channels with known MGF is derived. Based on the expression, the integral expressions for the ergodic capacity over Rayleigh and Rician fading channels are exactly derived, respectively, and their closed-form expressions are also provided by exploiting the Gauss-Laguerre method. Further, their expressions with perfect conditions, asymptotic expressions at high signal-to-noise ratio (SNR), and high SNR slopes are also derived. The accuracy of the expression is verified by numerical and simulation results. It also shows the superiority of the proposed scheme over conventional OMA and ANOMA with linear modulation, and the relationship between system performance and time offsets, imperfect conditions, channel differences, and modulation formats.

In this paper, the average bit error rate performance of quadrature spatial modulation (QSM) transmission technique over double complex Nakagami-m fading channels is investigated. In the proposed scheme, in which all terminals are in motion as mobiles or vehicles. The average bit error rate is derived by using pairwise error probability and upper bound union expressions, which are defined for the QSM transmission technique. In this context, the mean vector and variance matrix of double complex Nakagami-m fading channels has been presented using of properties of its statistics. Furthermore, at the receiver side, the impact of Gaussian imperfect channel state information on the performance is considered, and analytical expression is presented. Finally, it has been demonstrated that Monte Carlo simulation results prove the exactness of analytical results under different system settings and the severity of fading parameters.