Signal Space Diversity Technique Research Articles

Construction and implementation of teacher support services model under “5G+Smart Education”

Abstract With the development of network technology, the convenience and flexibility of smart education have made it right to meet the needs of teachers’ professional development, which has led to its rapid development. As traditional smart campus data networks suffer from long construction periods, high costs, and poor flexibility of wired networks, existing wireless networks may suffer from audio delays, lagging, and other problems. Now with the addition of 5G networks, it is not only able to provide a new design concept and teaching method for modern teaching, but it is also of great significance to improve the comprehensive strength of schools and accelerate the construction and implementation of teacher support service models. In this paper, we investigate URLLC and eMBB multiplexing mechanisms in 5G, introduce the signal space diversity technique based on rotational modulation, and propose SSD-based URLLC and eMBB multiplexing mechanisms. The SSD-based URLLC and eMBB multiplexing mechanisms are validated through downlink-level simulations. The results show that the BER is improved by about 1.0dB at 10-6 orders of magnitude, and the BER is improved by about 1.0dB at 10-3 orders of magnitude under the simulation verification of the Rayleigh channel compared to the case without spatial diversity. In the simulation of the spatial diversity multiplexing mechanism of the TDL-A-1000 channel, the BER is improved by about 1.5dB at 10-6 orders of magnitude, and the BER is also improved by about 1.5dB at 10-3 orders of magnitude compared with the case without spatial diversity. In summary, the SSD-based multiplexing mechanism proposed in this paper can reduce data BER, improve data transmission reliability, and make the construction and implementation of the teacher support services model in smart education faster and more convenient.

Demonstration of Spatial Modulation Using a Novel Active Transmitter Detection Scheme with Signal Space Diversity in Optical Wireless Communications.

Line-of-sight (LOS) indoor optical wireless communications (OWC) enable a high data rate transmission while potentially suffering from optical channel obstructions. Additional LOS links using diversity techniques can tackle the received signal performance degradation, where channel gains often differ in multiple LOS channels. In this paper, a novel active transmitter detection scheme in spatial modulation (SM) is proposed to be incorporated with signal space diversity (SSD) technique to enable an increased OWC system throughput with an improved bit-error-rate (BER). This transmitter detection scheme is composed of a signal pre-distortion technique at the transmitter and a power-based statistical detection method at the receiver, which can address the problem of power-based transmitter detection in SM using carrierless amplitude and phase modulation waveforms with numerous signal levels. Experimental results show that, with the proposed transmitter detection scheme, SSD can be effectively provided with ~0.61 dB signal-to-noise-ratio (SNR) improvement. Additionally, an improved data rate ~7.5 Gbit/s is expected due to effective transmitter detection in SM. The SSD performances at different constellation rotation angles and under different channel gain distributions are also investigated, respectively. The proposed scheme provides a practical solution to implement power-based SM and thus aids the SSD realization for improving system performance.

Signal Space Diversity-Based Distributed RIS-Aided Dual-Hop Mixed RF-FSO Systems

Reconfigurable intelligent surface (RIS) is a recently emerged promising technology for beyond-5G (B5G)/6G wireless networks. In this letter, we propose to employ a signal space diversity (SSD) technique to improve the performance of distributed RIS-aided dual-hop mixed radio frequency (RF)-free-space optical (FSO) communication systems. The source-relay, source-RIS, and RIS-relay links are assumed to undergo independent but not identically distributed (i.n.i.d.) Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> fading. The destination node is equipped with multiple FSO apertures and the relay-destination links follow Gamma-Gamma (GG) distributed atmospheric turbulence (AT) model with pointing errors (PEs). Novel approximate closed-form expressions for the system’s symbol error rate (SER) are derived for both the exhaustive RIS-aided (ERA) and opportunistic RIS-aided (ORA) configurations. The numerical results show that using the SSD technique at both the RF and FSO links significantly improves the spectral efficiency and the diversity order of the system considered.

Coordinated and Non-Coordinated Direct-and-Relay Transmission: A Signal Space Diversity Approach

In this work, two signal-space diversity (SSD) based schemes are proposed for a system where one user is directly in contact with both the base station and the relay, while the other user is only in contact with the relay. The first scheme combines the coordinated direct and relay transmission (CDRT) technique with SSD to improve the achievable sum-rate of the system and is called the SSD-based CDRT (SSD-CDRT) scheme. On the other hand, the second scheme exploits only the SSD technique to improve the diversity order of one of the users and is termed SSD based non-CDRT (SSD-nCDRT). Various performance metrics such as outage probability, system outage throughput, diversity order, and achievable sum-rate are evaluated in closed-form for both schemes to compared them with their counterparts non-orthogonal multiple access (NOMA) based schemes, i.e., NOMA-CDRT and NOMA-nCDRT schemes. The comparative study confirms that the proposed SSD-CDRT and SSD-nCDRT are superior to NOMA-CDRT and NOMA-nCDRT, respectively, in terms of all the considered performance metrics.

Low-Complexity MIMO MMSE Receiver with Performance Enhancement via Coordinate Interleaving

Multiple-input multiple-output (MIMO) Minimum mean-square error (MMSE) receivers are widely adopted in the latest communication standards and reducing the complexity of these receivers while preserving the error performance is highly desirable. In this work, we study the error performance and implementation complexity of MIMO MMSE receivers when combined with a coordinate interleaved signal space diversity (SSD) technique. Contrary to the well-known trade-off between the error performance and implementation complexity, the proposed system leads to a considerably simplified MIMO MMSE receiver with significant performance gains when compared to the original MIMO MMSE receiver. Unlike the standard MIMO MMSE receiver, the proposed coordinate interleaved technique induces a block diagonal transmit correlation matrix providing both performance enhancement and complexity reduction. The results show that the error performance can be improved more than 10[Formula: see text]dB with up to 71% computational complexity reduction. The complexity comparison between the original and proposed approaches is also verified by means of field-programmable gate array (FPGA) implementation.

Performance analysis of cooperative power‐line communication system with signal space diversity

AbstractPower‐line communication (PLC) is a cost‐effective and promising communication technology for many smart grid applications. However, the presence of additive and multiplicative power line noises deteriorate the performance of a PLC system. In this paper, we propose signal space diversity (SSD) technique for a cooperative PLC system. The additive PLC channel noise is assumed to be Bernoulli‐Gaussian–distributed. The multiplicative PLC channel noise gain is characterized by log‐normal distribution. The closed‐form expressions of the average symbol error rate (SER) and outage probability of cooperative PLC system with SSD have been derived in this paper. It has been shown that the proposed cooperative PLC system results in achieving better spectral efficiency, as well as the reliability of the received signal.

Multipoint-to-Multipoint Cooperative Multiuser SIM Free-Space Optical Communication: A Signal-Space Diversity Approach

In this paper, a novel signal-space diversity (SSD) technique based multipoint-to-multipoint cooperative scheme for a multiuser free-space optical communication system is proposed. In SSD technique, constellation points of the transmitted signal are rotated by a certain angle and in-phase and quadrature components of two different symbols are interleaved to obtain diversity from the signal space. In the proposed scheme, the diversity of each cooperative user gets improved through joint encoding/decoding of the rotated symbols using subcarrier intensity modulation (SIM). The joint encoding/decoding can be done by connecting all the users' transceivers by wires that ensure the availability of the information of a user to all other users. The average symbol error rate for the proposed scheme under log-normal and gamma-gamma channel models is evaluated analytically and corroborated through Monte Carlo simulations. It is reported through intensive analyses and comparisons that the proposed cooperative scheme not only achieves full diversity order but also outperforms non-cooperative and repetition coding schemes.

Enhancing Spatial Modulation System Performance Through Signal Space Diversity

Signal space diversity (SSD) is considered in this letter to enhance the performance of spatial modulation (SM) multiple-input multiple-output systems. SSD implies that the phase of the modulated quadrature amplitude modulation/phase shift keying symbol is rotated such that each incoming bit is represented by both the in-phase (I) and the quadrature (Q) components of the complex symbol. The resultant I and Q components are then interleaved over time to achieve a diversity gain and enhance the system performance. In this letter, SSD technique is applied to SM to achieve a transmit diversity and enhance the error performance without sacrificing spectral efficiency. The novel scheme is called diversity-enhanced SM (DE-SM) . An analytical framework for evaluating the proposed DE-SM scheme is conducted, where the average bit error rate is formulated in an upper bound expression. Obtained results reveal the significant enhancement of DE-SM especially in single-receive antenna systems. The impact of the involved different parameters including optimum phase rotation are also investigated and studied.

Reed Muller coded-cooperative diversity for multiple relays with signal space diversity and MRC reception at the destination

Recently, Reed---Muller (RM) codes have been investigated for half-duplex coded-cooperative relay communication systems. RM coded-cooperative (RMCC) diversity promised considerably low encoding and decoding complexity as compared to its predecessor channel codes. In this paper, we investigate the bit error rate (BER) performance of RMCC diversity for multiple relays operating in half-duplex mode with binary phase shift keying (BPSK) and quadrature amplitude modulation such as 4-QAM. In order to improve the BER performance of 4-QAM modulation, we use well known signal space diversity (SSD) technique in the proposed system. At the destination, maximal ratio combining is used for signal detection and joint majority logic decoding is used to recover information transmitted at the destination. Monte Carlo simulations show that the RMCC diversity gains increase manifolds with inclusion of multiple relays and for higher modulation i.e., 4-QAM, SSD provides additional diversity gains over the conventional 4-QAM system. Theoretical expressions for average BER are also derived and are validated with the help of Monte Carlo simulations.

Low complexity and high diversity gain non-linear constellation precoded MIMO-OFDM system with subcarrier grouping

The maximum distance separable codes based non-linear signal space diversity technique provides flexibility in the design of diversity channels and diversity orders. Still, in actual practice, these diversity orders can only be truly augmented by increasing the constellation size. In this paper, we enhance the diversity order/gain by introducing multiple-input multiple-output (MIMO) to the existing non-linear constellation precoded orthogonal frequency division multiplexing (NCP-OFDM) system with subcarrier grouping. Though, it still suffers from the complexity of maximum likelihood (ML) decoding, which exponentially increases with the number of antennas. Assuming the channel is quasi-static in nature, we exploit it to reduce the complexity by introducing space-time block-codes (STBC). The ML decoding complexity of a 2×2 system is of O(224) whereas, by using STBC it reduces to O(213). In addition, we propose an algorithm for decoding, called the maximum scaling coefficient selection (MSCS) to further reduce the complexity to O(28). Simulation results show that there was only a marginal performance loss when using the MSCS algorithm based on ML decoding. Furthermore, the simulation results demonstrate how the diversity gain is maximized by adding additional antennas and by introducing STBC.

Enhanced quadrature signaling-based cooperative transmission with full rate and full diversity

Quadrature signaling-based cooperative transmission is an efficient and simple scheme to obtain spatial diversity. However, this scheme causes date rate loss compared with direct transmission. In this work, our focus is on recovering from the data rate loss while simultaneously achieving spatial diversity. Particularly, an enhanced quadrature signaling-based cooperative scheme was designed, which can realize full-rate transmission by using the signal space diversity (SSD) technique. Then, accurate bit error rate (BER) expression for the full-rate scheme was derived over independent and non-identically distributed (INID) Rayleigh fading channels. Specifically, a closed-form BER expression is obtained, which is quite tight over the whole SNR range, and thus allows for rapid and efficient evaluation of system performance under various channel conditions. Moreover, an asymptotic approximation of the BER was derived to show that the full-rate scheme can achieve full diversity. Simulation results verify the tightness of the analysis and show that the full-rate scheme significantly outperforms the traditional quadrature signaling-based scheme by about 2 dB with the same complexity order.

A Novel Nonlinear Constellation Precoding for OFDM Systems with Subcarrier Grouping

This paper proposed a novel nonlinear constellation precoding (NCP) technique based on maximum distance separable (MDS) codes in orthogonal frequency-division multiplexing (OFDM) systems. The proposed method envisage to maximize both the diversity and coding gains for any number of diversity channels and desired diversity orders. The novel NCP technique combined with subcarrier groping in OFDM systems to replace the most existing linear constellation precoding (LCP) scheme. In this scheme, the full set of subcarriers are splitted into smaller groups and the codewords are constructed from $$q$$ q point constellation mapper with MDS encoder. The maximum-likelihood (ML) decoder is used in the most existing signal space diversity technique which is replaced by diversity channel selection (DCS) to reduce the decoding complexity with the cost of marginal performance loss. The effect of the Inter-carrier interference (ICI) introduced by the carrier frequency offsets (CFO) also analyzed in the proposed OFDM system. The superiority of the proposed novel NCP technique over the previously proposed designs is verified by simulation results.

On Bit Error Performance of Full-Rate Signal Space Cooperative Communication over Nakagami-m Fading Channels

Signal space cooperative (SSC) system can realize full-rate transmission while achieving maximum cooperative diversity gain at the same time by using the signal space diversity technique. In this letter, we investigate the bit error rate (BER) performance of the SSC system over independent and non-identically distributed (i.ni.d.) Nakagami-m fading channels. Particularly, an accurate analytical expression for the overall BER is derived. Moreover, a tight approximation for the BER is obtained to reveal that the achievable diversity order of the SSC system is {{m}_{SD}}+\min { {{m}_{SR}},{{m}_{RD}} }, where m_SD, m_SR, and m_RD are the Nakagami fading parameters for the source-destination, source-relay, and relay-destination channels, respectively. Simulation results are presented to verify our theoretical analysis.

Space–Frequency Convolutional Coding for Frequency-Asynchronous AF Relay Networks

In this paper, we design a space-frequency (SF) convolutional coding scheme for amplify-and-forward (AF) relay networks that contain multiple distributed relay nodes. The frequency-asynchronous nature of the distributed system is considered in our design. Orthogonal frequency-division multiplexing (OFDM) modulation is adopted, which is robust to certain timing errors. We exploit the signal space diversity technique and employ an extended cyclic prefix (CP) at the source node. The relay nodes need to perform only simple operations, e.g., convolution and amplification, and they need no information about the channels and the frequency offsets. Attributed to the extended CP, the multiple frequency offsets can directly be compensated at the destination. We further prove that both spatial and multipath diversity can be achieved by the proposed scheme. Numerical results are provided to corroborate the proposed studies.

Low Complexity Demapping of Rotated and Cyclic Q Delayed Constellations for DVB-T2

The new digital video broadcasting standard DVB-T2 includes the mandatory use of constellation rotation and cyclic Q delay (CRCQD) as a signal-space diversity technique. After transmission on the channel by orthogonal frequency division multiplexing (OFDM), at the receiver the constellation does not exhibit the regular shape of QAM and in particular optimum demapping must be jointly performed on the real-imaginary axis for both hard and soft decoding. We propose a low complexity demapping strategy for the CRCQD modulation. In the proposed approach, only a subset of the constellation points close to the received samples is considered for demapping. The proposed method is compared with existing techniques both in terms of complexity and performance over reference DVB-T2 channels.

Inter-Relay Interference in Two-Path Digital Relaying Systems: Detrimental or Beneficial?

This Letter studies the two-path digital relaying systems, where two relay nodes alternately forward messages from the source to the destination. By applying the signal space diversity (SSD) technique, a novel adaptive scheme is proposed to deal with the inter-relay interference (IRI). Our work reveals that, with careful protocol design, the IRI becomes a beneficial resource that can be utilized rather than a detrimental factor that has to be suppressed. Simulation results demonstrate that, in high average SNR regions, the proposed method outperforms the existing alternatives in terms of symbol error probability.

Signal Space Diversity Techniques with Fast Decoding Based on MDS Codes

In wireless communication systems, signal space diversity techniques are usually adopted to combat channel fading by exploiting time diversity, frequency diversity, spatial diversity or a combination of them. Most existing schemes to achieve signal space diversity are based on linear constellation spreading. In this paper, we propose a novel nonlinear signal space diversity technique based on maximum distance separable (MDS) codes. The new technique provides a design flexibility for almost any number of diversity channels and desired diversity orders. We also propose a simple and suboptimal diversity channel selection (DCS) decoding for our new scheme. DCS decoding can greatly reduce the decoding complexity at a cost of marginal performance loss relative to the optimal detection while keeping the diversity order. Simulation results show that with the same throughput but a lower decoding and implementation complexity, our scheme can have superior performance than the optimal linear spreading schemes over either independent fading or additive white Gaussian noise (AWGN) channels.

Channel estimation in bit-interleaved coded modulation with iterative decoding

This study improves the fading channel estimation in bit-interleaved coded modulation systems with iterative decoding (BICM-ID) and signal space diversity (SSD) by embedding a training sequence. Existing training schemes work well at high signal-to-noise ratio (SNR) or slowly time-varying channels whereas the applications of BICM-ID are beneficial at low SNR and fast time-varying fading channels. Motivated by the power/bandwidth efficiency of the SSD technique and the fact that superimposed training outperforms pilot symbol-assisted modulation (PSAM) training over relatively fast time-varying channels, a new superimposed training sequence is explored. The proposed training sequence inserts pilot bits into the coded bits prior constellation mapping and signal rotation. This becomes a superimposed training sequence in the rotated symbols and helps the estimator to track fast variation of the channel gains. A soft iterative channel estimator is developed to work with the superimposed training sequence. The performance of the proposed scheme, namely SSD-pilot, is shown to be superior to PSAM scheme. To gauge the performance improvement achieved with the proposed channel estimation, an analytical bound on the asymptotic bit error probability for BICM-ID using SSD over correlated fading channels is provided. The Cramer-Rao bound on the mean-square error of the channel estimator is also derived to evaluate the performance of the iterative channel estimator.

Full-rate distributed space-time codes for cooperative communications

A full-rate distributed space-time (ST) code design is proposed for amplify-and-forward cooperative wireless channels. By employing a signal space diversity technique at the source node and a unique signature vector at each relay node, the proposed distributed ST codes can achieve full cooperative diversity and full rate. The achievable diversity gain is shown to be M + 1, where M is the number of relay nodes. Optimal power allocation is also proposed to maximize the coding gain under a total power constraint.

Bit-interleaved coded modulation with iterative decoding using constellation shaping over Rayleigh fading channels

We propose to investigate the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) over Rayleigh fading channel by using constellation shaping (CS). The (CS) is implemented by inserting shaping block codes between mapping and channel coding functions, in order to generate non-equiprobable distribution of a 16-ary QAM signal constellation. Simulation results carried out on 2-bit/s/Hz 16-QAM BICM-ID indicate that is possible to obtain a gain of 1.2 dB at a BER of 10 - 3 compared to the equiprobable 16-QAM BICM-ID schemes. It is also shown that, the error floor level can reduced by applying the signal space diversity technique.