Differential Transmission Schemes for Generalized Spatial Modulation

Massive multiple‐input multiple‐output (MIMO) systems with hundreds of correlated antennas at base station are capable of offering abundant spatial resources. When spatial‐domain modulation is applied to these systems, the spatial modulation (SM) using only one radiofrequency chain benefits practical implementation, but suffers from significantly reduced multiplexing gain offered by the massive number of antennas. By contrast, the generalised SM (GSM) allows to simultaneously activate multiple transmit antennas, which improves spatial multiplexing gain, but degrades the achievable error performance, as its design pays no attention to the antenna correlation. The authors propose an antenna grouped SM (GrSM) scheme, which is capable of circumventing the shortcomings of both the SM and GSM schemes suffered in massive MIMO scenarios. In the proposed GrSM scheme, transmit antennas are partitioned into multiple groups, where the relatively strongly correlated antennas within individual groups are used to implement component SM schemes, while the relatively weakly correlated antennas in different groups are beneficial to obtain multiplexing gain. In order to further improve the spectral efficiency, adaptive modulation is integrated with GrSM to form the adaptive GrSM (AGrSM). The achievable error and spectral efficiency performance of GrSM and AGrSM systems are investigated based on both mathematical analysis and Monte‐Carlo simulations, which are also compared with that of the conventional SM and GSM schemes, when massive MIMO communication scenarios are considered. Their studies and performance results show that GrSM is a promising transmit scheme for massive MIMO, which can outperform both the SM and GSM schemes.

This paper proposes a differential modulation scheme based on quasi-orthogonal space-time block codes (STBCs) when neither the transmitter nor the receiver has knowledge of the channel. A system with four transmit antennas is considered and divided into two subsystems. Each subsystem is equivalent to a system with two transmit antennas and uses differential STBC modulation. Based on the encoding and decoding for the two subsystems, the overall encoding and decoding algorithm for the original system is derived. We also compare the performance of our differential detection with that of the corresponding coherent detection in terms of achieved signal-to-noise ratio (SNR) for a given transmission power and propose a quantitative measure to estimate the performance difference between the coherent quasi-orthogonal code and our differential detection. Furthermore, we show that our differential modulation scheme can be extended to a system with more than four transmit antennas. Compared with the existing differential modulation schemes for four and eight transmit antennas, the proposed scheme has a lower bit-error rate (BER) and provides full diversity and pair-wise decoding complexity.

In multi-user multiple input multiple output (MIMO) systems, the non-orthogonal multiple access (NOMA) method based spatial modulation (SM) and generalized spatial modulation (GSM) can mitigate inter-user interference. However, the spectral efficiency of these methods is restricted because of antenna configuration. In this paper, a combination of the variable active antenna spatial modulation (VASM) scheme with the downlink power domain NOMA system, so-called NOMA-VASM, is proposed to improve spectral efficiency while main-taining mitigation of inter-user interference. In the novel NOMA-VASM, the antenna configuration is arbitrary and the number of enabled transmitting antennas (TAs) can be altered, so it is easier to increase spectral efficiency compared to NOMA-SM and NOMA-GSM. Monte Carlo simulations were performed under various scenarios, and the results showed that NOMA-VASM outperformed conventional NOMA-SM and NOMA-GSM in terms of spectral efficiency, average bit-error-rate (ABER) performance, and required number of TAs.

We show that certain signal constellations invoked for classic differential encoding result in a phenomenon we term as the {\\em unbounded differential constellation size} (UDCS). Various existing differential transmission schemes that suffer from this issue are identified. Then, we propose an enhanced algebraic field extension based differential spatial modulation scheme (AFE-DSM) and its enhanced counterpart that strikes a diversity-rate trade-off (AFE-DSM-DR), both of which overcome the UDCS issue without compromising its full transmit diversity advantage. Furthermore, the proposed schemes are extended to incorporate amplitude and phase shift keying (APSK) in order to exploit all the available degrees of freedom. Additionally, we propose a pair of detection schemes specially designed for APSK aided differential transmission schemes. Explicitly, we conceive the buffered minimum mean squared error (B-MMSE) detector and buffered maximum likelihood (B-ML) detector, which exploit the knowledge of previously detected symbols in order to further improve the detection performance. Our simulation results have shown that the proposed detectors are capable of bridging the performance gap between the conventional differential detector (CDD) and the coherent detector that has full channel state information. Specifically, when employing the proposed APSK aided AFE-DSM scheme operating at a rate of 2 bits per channel use (bpcu), the B-MMSE and B-ML detectors are observed to give about 3 dB and 3.5 dB signal-to-noise ratio gain with respect to their CDD counterpart at a bit error ratio of $10^{-5}$.

Reconfigurable intelligent surface (RIS) has been recently put forward as a promising technique for 6G and beyond 5G. In this paper, two differential schemes are proposed for reflecting modulation (RM) aided spatial modulation (SM) system: differential RM aided SM (DRM-SM) and differential SM aided RM (DSM-RM). Compared with the existing differential modulation scheme for RIS based systems, our proposed schemes not only dispense with channel state information (CSI) at the transceiver and RIS, but also improve the transmission rate. Finally, through the Monte Carlo simulations, it is shown that DRM-SM and DSM-RM schemes can achieve independent error performance advantages under different hardware facilities.

In this paper, we propose a layered spatial modulation (L-SM) scheme that combines a multi-layered coding scheme with the spatial modulation. At each antenna selection, the number of active transmit antennas equals the number of layers. The proposed L-SM scheme maximizes the diversity order and coding gain at each antenna selection. The exact pairwise and upper bound bit error probabilities are derived. Several examples of different spatial modulation schemes and the proposed L-SM scheme are simulated with the same number of transmit antennas and same spectral efficiency. As expected, the proposed L-SM scheme satisfies significant increase in the performance compared to all existing spatial modulation schemes.

This paper explores the optimal number of antennas within generalized spatial modulation (GSM) scheme with single and multiple radio frequency (RF) chains. The main focus of our work is on the number of total transmit antennas and active transmit antennas as per the GSM transmission, that optimizes the system's power efficiency. Accordingly, the bandwidth efficiency of the transmission and receiver complexity are analytically calculated. The performance of the multiple-RF-chain GSM scheme is compared with SM and GSM. Moreover, Monte Carlo simulations are carried out to analyze and verify the analysis of power efficiency as a function of the number of transmit antennas.

In this paper, for the sake of enhancing the security of wireless transmission, we proposed a novel system based on spatial and direction modulation (SDM) combined with generalized spatial modulation (GSM) which is aided by covert information mapping (CIM), termed as the CIM-GSDM system. In such a system, the legitimated user is equipped with distributed receivers so as to demodulate the conveyed signal by exploiting its indices while disturbing eavesdroppers for information security. More specifically, part of the information is modulated into the indices of the legitimated distributed receiver subsets with the aid of the mapped covert information and the interference matrix, while another part of the message is arranged by conventional amplitude-phase modulation. The proposed system can reap the benefits from both GSM and CIM to make eavesdropper suffer great mixture. Furthermore, the detection scheme and theoretical analysis of error performance are discussed as well. The simulation results exhibit that the bit error rate (BER) performance of legitimate user is much better than that of the eavesdropper while the proposed scheme improves the security compared to the original CIM-SDM system at the same spectral efficiency.

This paper considers the optimal constellation design for the generalized spatial modulation (GSM). The signal and spatial parts of the constellation are jointly designed where the signal part is not restricted to the conventional amplitude/phase modulation constellation points. The design problem is formulated as an optimization problem where a set of multi-dimensional constellation points that minimizes the average symbol error rate (SER) is selected. A gradient search algorithm is proposed to solve the optimization problem. Numerical results demonstrate the improved SER performance and increased energy efficiency of the proposed generalized signal- spatial constellation (GSSC) scheme as compared to previous spatial modulation (SM), GSM, and conventional MIMO schemes.

Spatial modulation (SM) uses a single antenna for transmission each time to avoid synchronization and interferences among transmitter antennas, and differential SM (DSM) is a kind of SM technique that does not need pilot symbols and channel estimation. The original noncoherent detection for DSM is very complicated, so various low-complexity detectors have been proposed. However, they are still too complicated to be applied to DSM with many transmitter antennas. In this paper, low-complexity DSM schemes for dozens or hundreds of transmitter antennas are designed. Two bit-mapping schemes are proposed: one is group arrangement for maximizing data rates, and the other is full mapping so that DSM can be easily detected at the receiver. A low-complexity detection algorithm that is less complicated than all existing fixed-complexity detectors is proposed as well. In addition, two detection strategies for the proposed bit mapping methods are proposed. Simulation results show that the proposed low-complexity DSM schemes have satisfactory error performance.

In this work an Artificial Neural Network with Radial Basis Function (RBF) is employed to model a predictor, utilized in Differential Pulse Code Modulation (DPCM) scheme. The RBF predictor estimates the magnitude of signal incoming to DPCM, the error between incoming signal and estimated one is applied to quantiser unit. The resultant error contains a few bit word length and is transmitted in data format towards a receiver unit. The output of the RBF predictor is added to error at the receiver part of DPCM to produce actual output. In this study application of RBF predictor in DPCM is explained. The potential offered by DPCM scheme using RBF predictor leads to a considerable amount of reduction in word length of filter coefficients.

Performance Analysis of Different Phase Shift Keying Modulation Schemes in Aeronautical Channels

In order to improve the efficiency of the normal pulse position modulation, differential multi-pulse position modulation (DMPPM) scheme is proposed. It has made full use of the advantages of multi-pulse position modulation (MPPM) and differential pulse position modulation (DPPM), and has become one of the most efficient modulation schemes in wireless laser communication. Based on the atmospheric channel affected only by transmission path attenuation and additive Gauss white noise, by analyzing the symbol length, the bandwidth requirement and the peak power of L-level pulse position modulation, MPPM, DPPM and DMPPM, the calculation formula of error rate for various modulation schemes is derived under the optimal demodulation conditions. The simulation results show that DMPPM has advantages on symbol length, bandwidth requirement and peak power. Under the condition of the same signal-to-noise ratio, the error rate of DMPPM is larger. Nevertheless, the error rate performance can be effectively improved by increasing the modulation order or reducing the pulse number.

Differential modulation has recently been proposed for wireless relay networks. However, it suffers from a 3-dB performance loss as in point-to-point communication systems. In this paper, we propose a new differential modulation scheme, which is referred as generalized differential modulation (GDM) for wireless networks with amplify-and-forward relaying. In the proposed scheme, each frame transmitted by the source is divided into several blocks, and each block consists of one reference symbol and several normal symbols. The reference symbol in each block is differentially encoded based on the previous reference symbol, whereas the normal symbols are differentially encoded based on the reference symbol in the same block. At the destination, the signals from the source and the relays are combined to improve communication reliability. The proposed scheme has the advantage of allowing power allocation among the reference symbol and the normal symbols to improve the system performance. Numerical results show that the proposed GDM scheme can perform very close to the coherent receiver with perfect channel state information (CSI) in slow-fading channels.

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.