Space-time Coding Scheme Research Articles

Performance Enhancement for B5G/6G Networks Based on Space Time Coding Schemes Assisted by Intelligent Reflecting Surfaces with Higher Modulation Orders.

Intelligent Reflecting Surfaces (IRS) and Multiple-Input Single-Output (MISO) technologies are essential in the fifth generation (5G) networks and beyond. IRS optimizes the signal propagation and the coverage and is a viable approach to address the issues caused by fading channels that limits the spectral efficiency, while MIMO enhances data rates, reliability, and spectral efficiency by using multiple antennas at both transmitter and receiver ends. This paper proposes an IRS-assisted MISO system using the Orthogonal Space-Time Block Code (OSTBC) scheme to enhance the channel reliability and reduce the Bit Error Rate (BER) in wireless communication systems. The proposed system exploits the benefits from the transmit diversity gain of the OSTBC scheme as well as from the bit energy to noise power spectral density (Eb/No) improvement of the IRS technology. The presented work explores these combined technologies across different modulation schemes. The obtained results outperform the similar previously published works by considering higher-order modulation schemes as well as the deployment of rate ¾ OSTBC-assisted IRS. Moreover, the obtained results demonstrate that the integration of OSTBC with IRS can yield significant performance improvements in terms of Eb/No by 7 dB and 13 dB when using 16 reflecting elements and 64 reflecting elements, respectively.

Co‐Prime Modulation for Space‐Time‐Coding Digital Metasurfaces with Ultralow‐Scattering Characteristics

AbstractMulti‐dimensional modulation of electromagnetic (EM) waves is critical in various fields such as electronic and photonic systems. Space‐time‐coding (STC) digital metasurfaces, an innovative platform for programmable metasurfaces, offer a straightforward and robust solution for spatio‐temporal modulation, thereby enabling EM‐wave manipulations in both space and frequency. Conventional STC schemes rely on periodic temporal modulations that are uniform in space (i.e., with same modulation frequency in all metasurface elements), and therefore do not take advantage of spatio‐temporal coupling effects that can be induced by non‐uniform periodic modulations (i.e., with different modulation frequencies across the metasurface elements). Here, a novel approach involving non‐uniform spatio‐temporal modulation, alongside co‐prime modulation, is introduced. This approach enhances the fundamental principles of STC digital metasurfaces and facilitates the synthesis of angular scattering responses across different frequencies, guided by harmonic coupling conditions. The proposed strategy results in a more even distribution of the scattered intensity in both space and frequency. For validation, an experimental proof‐of‐principle for spatial‐spectral diffuse scattering is presented. The experimental outcomes align closely with theoretical predictions, underscoring the effectiveness of co‐prime modulation in achieving ultralow‐scattering characteristics in STC digital metasurfaces. Moreover, this technique holds promise for applications in secure wireless communications, radar jamming, and complex beamforming.

ALAMOUTI SPACE-TIME CODING FOR VEHICULAR COMMUNICATIONS IN THE PRESENCE OF CHANNEL ESTIMATION ERRORS

In this paper, the error performance of the Alamouti space-time coding (STC) scheme is investigated for vehicle-to-vehicle (V2V) communication systems over imperfect cascaded fading channels. In vehicular communication systems, perfect knowledge of the channel state information is not available to the users at all times due to the rapid movement of communicating vehicles and fast change of the rich scattering environment which makes the fading effects in wireless channels more severe. Therefore, in the analysis, we consider the erroneous estimation of the channel gain, which is more realistic for practical scenarios. For this purpose, we first derive the moment-generation function (MGF) of the channel fading coefficient with estimation error in the case of the cascaded Nakagami-m fading conditions. Then, using the MGF, we obtain the closed-form symbol-error-rate (SER) expressions of Alamouti STC with two transmitting and L receiving antennas for the M-PSK and M-QAM modulation schemes. Then, the exact ergodic capacity expression is derived for the proposed system. Furthermore, the analytical results are verified through Monte-Carlo simulations. Numerical results show that the SER performance of V2V communication systems can be improved significantly by using Alamouti STC even in case of harsh fading conditions and full channel-state information is not available due to estimation errors.

A Unified Implementation Framework for Index Modulation Assisted MIMO Backscatter Communication

In this letter, a unified hardware implementation framework is designed for index modulation (IM) assisted multi-input multi-output (MIMO) backscatter communication, including space shift keying (SSK), spatial modulation (SM), SM assisted vertical bell labs space-time (SM-VBLAST), as well as SM assisted space-time block code (SM-STBC) schemes. Specifically, the concepts of SM-VBLAST and SM-STBC architectures are successfully applied into backscatter communication to balance an elegant tradeoff between spatial multiplexing and diversity gain. Then the coupled channel estimation and interference-cancellation-based signal detection algorithms are designed for hardware implementation. Furthermore, a unified IM-MIMO-based backscatter hardware prototype and experimental platform are designed. Experimental results verify that the proposed IM-MIMO implementation framework works efficiently and we can choose one proper IM-MIMO backscatter communication based on the required throughput, diversity gain as well as implementation complexity.

Utilization of harmonics in phaseless near-field microwave computational imaging based on space–time-coding transmissive metasurface

Based on a space–time-coding (STC) transmissive metasurface (TMS), we present the utilization of electromagnetic harmonic spectra in phaseless near-field microwave computational imaging (CI). Each element of the TMS integrates one PIN diode as a switch to independently regulate the transmission amplitude, giving rise to a 14-dB modulation depth at 21 GHz. Using the TMS and two standard horn antennas, a phaseless near-field microwave CI system is established in a single-pixel manner. A simple and effective space–time-coding scheme is detailed to covert a monochromatic signal into multiple harmonics that can be applied to sample the objects. To obtain the sensing matrix built by the harmonics, we propose a method that is developed from the Fresnel diffraction theory. Moreover, we experimentally validate our CI system by reconstructing two metallic objects. The reported STC scheme and the corresponding CI system using TMS could inspire future studies on low-cost imaging hardware development and harmonic wave utilization for high-resolution CI systems.

Low Complexity Deep Learning-Assisted Golden Code Sphere-Decoding with Sorted Detection Subsets

Golden code is a space-time block coding (STBC) scheme that has spatial multiplexing gain over the Alamouti STBC which is widely used in modern wireless communication standards. Golden code has not been widely adopted in modern wireless standards because of its inherent high detection complexity. However, detection algorithms like the sphere-decoding with sorted detection subsets (SD-SDS) have been developed to lower this detection complexity. Literature indicates that the SD-SDS algorithm has lower detection complexity relative to the traditional sphere-decoding (SD) algorithm, for all signal-to-noise ratio (SNR) values. The SD-SDS algorithm exhibits low detection complexity at high SNR; however, at low SNR the detection complexity is higher. We propose a deep neural network (DNN) aided SD-SDS algorithm (SD-SDS-DNN) that will lower the Golden code's SD-SDS low SNR detection complexity, whilst maintaining the bit-error-rate (BER) performance. The proposed SD-SDS-DNN is shown to achieve a 75% reduction in detection complexity relative to SD-SDS at low SNR values for 16-QAM, whilst maintaining the BER performance. For 64-QAM, the SD-SDS-DNN achieves 99% reduction in detection complexity relative to the SD-SDS at low SNR, whilst maintaining the BER performance. The SD-SDS-DNN has also shown to achieve low detection complexity comparable to that of the Alamouti linear maximum likelihood (ML) detector for a spectral efficiency of 8 bits/s/Hz. For a spectral efficiency of 12 bits/s/Hz, the SD-SDS-DNN achieves a detection complexity that is 90% lower than the Alamouti linear ML detector.

Inter-Multilevel Super-Orthogonal Space-Time Coding Scheme for Reliable ZigBee-Based IoMT Communications.

The Internet of Things (IoT) technology has revolutionized the healthcare industry by enabling a new paradigm for healthcare delivery. This paradigm is known as the Internet of Medical Things (IoMT). IoMT devices are typically connected via a wide range of wireless communication technologies, such as Bluetooth, radio-frequency identification (RFID), ZigBee, Wi-Fi, and cellular networks. The ZigBee protocol is considered to be an ideal protocol for IoMT communication due to its low cost, low power usage, easy implementation, and appropriate level of security. However, maintaining ZigBee’s high reliability is a major challenge due to multi-path fading and interference from coexisting wireless networks. This has increased the demand for more efficient channel coding schemes that can achieve a more reliable transmission of vital patient data for ZigBee-based IoMT communications. To meet this demand, a novel coding scheme called inter-multilevel super-orthogonal space–time coding (IM-SOSTC) can be implemented by combining the multilevel coding and set partitioning of super-orthogonal space–time block codes based on the coding gain distance (CGD) criterion. The proposed IM-SOSTC utilizes a technique that provides inter-level dependency between adjacent multilevel coded blocks to facilitate high spectral efficiency, which has been compromised previously by the high coding gain due to the multilevel outer code. In this paper, the performance of IM-SOSTC is compared to other related schemes via a computer simulation that utilizes the quasi-static Rayleigh fading channel. The simulation results show that IM-SOSTC outperforms other related coding schemes and is capable of providing the optimal trade-off between coding gain and spectral efficiency whilst guaranteeing full diversity and low complexity.

Design and Performance Analysis of a New STBC-MIMO LoRa System

LoRa is a modulation technology for low power wide area networks (LPWAN) with enormous potential in 5G era. However, the performance of LoRa system deteriorates seriously in fading-channel environments. To tackle this problem, in this paper we introduce multiple-input-multiple-output (MIMO) configuration employing space-time block coding (STBC) schemes into the LoRa system to formulate an STBC-MIMO LoRa system. Then, we investigate the theoretical performance of the proposed system over Rayleigh fading channels. To this end, we derive the distribution of the decision metric for the demodulator in the proposed system. Based on the above distribution, we propose a closed-form approximate BER expression of the proposed system when perfect and imperfect channel state information (CSI) are considered. Furthermore, we analyze the diversity order and the throughput of the proposed system. The results of the diversity analysis demonstrate that the diversity order of the system in the imperfect CSI scenario with fixed channel estimate error variance is zero. However, in the imperfect CSI scenario with a decreasing channel estimate error variance and the perfect CSI scenario, the system can achieve full diversity. In addition, the results of the throughput analysis show that the throughput of the proposed system is little affected by CSI conditions. Simulation results verify the accuracy of the theoretical analysis and the excellent performance of the proposed system. Due to such superiority, the proposed STBC-MIMO LoRa system can be considered as a good scheme for LPWAN.

Over-the-Air Computation Strategy Using Space–Time Line Code for Data Collection by Multiple Unmanned Aerial Vehicles

In this study, we investigated a data collection system for multiple unmanned aerial vehicles (UAVs) in the sky. To reduce the required data collection time for a time-division multiple access (TDMA)-based protocol, an over-the-air computation (OAC) strategy was employed, and the average values of data computed. In this method, multiple single-antenna sensing UAVs (sUAVs) report the sensing data to a two-antenna data-collection UAV (dUAV) through the OAC strategy. To this end, we propose an efficient OAC strategy using a space-time line code (STLC) scheme that can achieve a full spatial diversity gain. Using the efficient data collection protocol of the proposed STLC-OAC strategy, the overall operation time for data collection can be significantly reduced relative to s TDMA-based strategy. Furthermore, the proposed STLC-OAC strategy can reduce the normalized mean square error (NMSE) of the estimated average value of the data relative to that of the TDMA-based method. As the gap in the NMSEs between TDMA- and STLC-OAC-based strategies was observed to increase as the number of sUAVs increased, it can be concluded that the proposed STLC-OAC strategy is advantageous for UAV-based data collection systems, especially when a large number of sUAVs report the sensing data.

Chaos-Based Space-Time Trellis Codes With Deep Learning Decoding

In this brief we propose a space-time trellis code scheme based on three-dimensional chaotic attractors. The chaotic trajectories are represented by the symbolic dynamics generated by a labeled Poincaré section and are transmitted by multiple antennas, defining a chaos-based space-time trellis code (CB-STTC). This code is defined by a finite state encoder that maps information sequences to restricted sequences satisfying the dynamics of the attactor. We also propose a neural network architecture capable of learning how to decode the CB-STTC. Finally, the frame error rate of the proposed CB-STTC is analyzed with maximum likelihood and neural network decoding.

Performance analysis of mixed MISO RF/SIMO FSO relaying systems

This paper investigates the end-to-end performance of a dual-hop mixed multiple-input single-output (MISO) radio-frequency (RF)/ single-input multiple-output (SIMO) free-space optical (FSO) relaying system. The Rayleigh distribution and the Gamma-Gamma (ΓΓ) distribution are adopted to describe the RF link and the turbulence effects of the FSO link, respectively. We consider Alamouti-type space-time block coding (A-STBC) and transmitter antenna selection (TAS) schemes from the source to the relay. There are amplify-and-forward (AF) with fixed gain and variable gain protocols for the relay. The closed-form expressions of the outage probability, outage capacity, average symbol error rate (SER) and channel capacity are derived in this paper. We discuss the end-to-end performance of different coding and relay schemes under different turbulence conditions.

Frame Structure Design for Vehicular-to-Roadside Unit Communications Using Space–Time Line Code Under Time-Varying Channels

This paper proposes the application of a space-time line code (STLC) scheme to vehicular-to-roadside unit communication systems. For the STLC encoding, channel state information is estimated before the data transmission. Thus, owing to the channel variation, the discrepancy between the estimated and actual channels degrades the communication performance, particularly at the end of the data frame. Considering the time-varying channels, a frame length is designed to maximize the worst-case throughput of the frame end and numerically validated.

Performance analysis of bi-directional relay selection strategy for wireless cooperative communications

This paper proposes a new two-way double-relay selection strategy for wireless cooperative communication systems with its bit error rate (BER) performance analysis. In this work, two relays are first chosen to maximize the overall system performance in terms of BER. Then, either the two-phase or three-phase protocol is performed to achieve two-directional communications between the communicating terminals through the selected relay nodes that apply orthogonal space-time coding (STC) scheme in a distributed fashion to improve the overall system performance with linear decoding complexity. In other words, the proposed strategy offers an improvement in the reliability of the system and enjoys very low decoding complexity by enabling a symbol-wise decoder. On the other hand, another improvement in the performance at the communication terminals is achieved by performing a network coding method at the selected relay nodes. Furthermore, we offer also analytical approximation of the BER performance for the proposed strategy where the simulation results match perfectly the analytical ones. From the simulation results section, the proposed strategy shows a substantially improved BER performance as compared to the current ones.

Space-time coding waveform design for MIMO radar transmit beamforming with minimum MFL

In this paper, we utilize a space-time coding (STC) scheme to synthesize the multiple-input multiple-output (MIMO) radar transmit beampattern and meanwhile consider the matched filtering loss (MFL) of equivalent signal in waveform design. To solve the MFL optimization problem, we propose a simulated annealing based (SA-based) algorithm to effectively find the optimal solution of STC waveform matrix. Our STC method for waveform design has suppressed the fluctuation of equivalent signal so that has the advantage of achieving the minimum MFL nearly, compared to the conventional methods for constant-envelope constraint waveform design (e.g. cyclic algorithm (CA) method). Simulation results demonstrate the effectiveness of the proposed algorithm.

Pulse Position-Based Spatial Modulation for Molecular Communications

Multiple-input-multiple-output (MIMO) approaches have been recently introduced to molecular communications (MC) in order to increase the communication throughput. For MIMO systems, index modulation (IM) suggests encoding information bits using the indices of the available antennas, rather than employing spatial multiplexing or performing other space-time coding schemes. Recent works have shown that utilizing the available MIMO antennas with the IM-based approaches improve the error performance of a molecular MIMO system, courtesy of molecular-IM’s robustness against inter-symbol interference and inter-link interference (ILI). Inspired by IM’s prospects on the MC, this letter proposes a novel family of the IM-based schemes to the MC realm. The proposed schemes combine position-based constellations with antenna indices to encode bits in and yield reliable error performances due to their robustness against the ILI.

BER Assessment of FBMC Systems Augmented with Different Space-Time Coding Schemes Over Diverse Channels

Diverse methodologies of encoding schemes like space-time block codes (STBC), orthogonal space-time block codes (OSTBC) &quasi-orthogonal space-time block codes (QOSTBC) are being proposed as alternatives of basic Alamouti space-time encoding scheme for multiple input multiple output (MIMO) scheme for existing wireless communication systems. Since filter bank multi-carrier (FBMC) scheme is an integral part of the 5th generation (5G) cellular systems, the performance of these schemes needs to be investigated for FBMC methodology also. Alamouti and Space-time block codes are widely used in MIMO system because of their ability to achieve full diversity and the different channels are used at the receiver. In this work, we proposed different approaches for the bit error rate (BER) of Alamouti, STBC3, and STBC4 in FBMC. These approaches are based on the type of space-time encoding and number of receiving antennas being used for each space time encoding scheme for analyzing the MIMO-FBMC. Moreover, we also investigation the performance of these proposed MIMO schemes over Rayleigh and additive white Gaussian noise (AWGN) channel and compared it with the performance of BER or signal to noise ratio (SNR) of different channels.

Delay-tolerant distributed space-time coding with feedback for cooperative MIMO relaying systems

An adaptive delay-tolerant distributed space-time coding (DSTC) scheme equipped with a feedback channel is proposed for two-hop cooperative multiple-input multiple-output (MIMO) networks. A maximum likelihood receiver and adjustable code matrices subject to a power constraint with a decode-and-forward cooperation strategy are considered with different DSTC antenna configurations. In the proposed delay-tolerant DSTC schemes, an adjustable code matrix is employed to transform the space-time coded matrices at the relay nodes. Stochastic gradient and least squares algorithms are also developed with reduced computational complexity. The proposed algorithms are then extended to a cooperative MIMO system using amplify-and-forward strategy and opportunistic relaying algorithms in order to develop a delay-tolerant coding scheme combined with optimal relay selection strategies. An upper bound on the pairwise error probability and a rank criterion analysis are derived which indicate the advantage of the proposed algorithms. Simulation results show that the proposed algorithms obtain significant performance gains and address the delay issue in cooperative MIMO systems as compared to existing DSTC schemes.

Atmospheric channel model of maritime visible light communication based on repeated coding

Visible light communication (VLC) is a new type of wireless communication technology, and its applications in offshore ships and ship-shore lamp signal systems are drawing increasing attention as a supplement of communication net. In maritime environment, VLC system is affected by many factors, of which the wave fluctuation and atmospheric turbulence are the most noticeable. The turbulence will make signal intensity fluctuate randomly, and thus reducing the performance of VLC system operating in the atmosphere. To establish an effective VLC network in the actual marine environment, an effective channel transmission model needs to be established and used to study the performance of the maritime VLC link. Considering large aperture diameter receiver with the aperture averaging effect, log-normal distribution model is employed to deduce the mathematical expression of average bit error rate of maritime VLC system in atmospheric turbulence. By using time-diversity to transmit interleaved symbols with repeated coding in a maritime VLC system, it is possible to ensure that the code-word passes through multiple channels to resist the deep fade performance, and to reduce the bit error rate due to the occurrence of deep fading in a single channel. In the actual application process, in order to improve the system performance, the average signal-to-noise ratio usually increases with the transmission power increasing, but for a VLC system, there are some difficulties in making the high-power high-rate visible light transmitters. And the power will produce light pollution and even damage the naked eye. The implementation of the repetitive coding principle is simple, and in some special cases it is even better than the complex orthogonal space-time coding and other schemes, so studying the system performance of the repetitive coding scheme is of considerable value for practical application. Based on the modified Pierson-Moskowitz spectrum, the effect of wave height, transmission distance, atmospheric turbulence intensity, receiver aperture size and visibility on the average bit error rate of VLC system are analyzed. The performance of the VLC system between lighthouse and ship is affected by the fluctuations of the sea waves, and the average bit error rate changes with randomness and complexity like the sea waves in a short distance. As the wind speed increases, the marine environment becomes worse and the average bit error rate is undulate. The average bit error rate of maritime VLC increases with the increasing of transmission distance and atmospheric turbulence intensity, and with the decreasing of receiver aperture size, wavelength and average signal-to-noise ratio. Atmospheric turbulence intensity and visibility have a significant effect on the system performance, and it should be emphatically considered to take measures to reduce the influence. Increasing receiver aperture and repetitive coding are effective to a certain extent. In the present work a new model is proposed for evaluating the performance of a maritime VLC system and providing reference for practical application.

Space–Time Line Code

This paper characterizes rate-one (i.e., full rate) full-spatial-diversity-achieving communication schemes based on the channel state information (CSI) availability and antenna configurations, i.e., CSI at a transmitter (CSIT) or CSI at a receiver (CSIR) and the numbers of transmit and receive antennas M and N (denoted by M × N), respectively. The maximum ratio combining (MRC), maximum ratio transmission (MRT), and space-time block code (STBC) schemes are rate-one full-spatial-diversity-achieving method facilitated for communication systems with: 1) 1 × N and CSIR; 2) M × 1 and CSIT; and 3) M × 1 and CSIR, respectively. A novel space-time line code (STLC) is then introduced for a 1 × 2 system with CSIT, and it is extended to an M × 2 STLC. The proposed STLC uses CSI for encoding at the transmitter and enables the receiver to decode the STLC symbols without CSI. Also, the STLC encoding matrices with various code rates and decoding (combining) schemes are designed for the M × 3 and M × 4 STLC systems: A code rate of 3/4, 1/2, and 3/7 for the M × 3 systems and a code rate of 3/4, 4/7, and 1/2 for the M × 4 systems. For each STLC scheme, a full-diversity achieving STLC decoding method is designed. Based on analyses and numerical results, we verify that the proposed STLC scheme achieves a full diversity order, i.e., MN, and is robust against CSI uncertainty. It is also shown that the array processing gain is inversely proportional to the code rate. To verify the merit of STLC, we introduce a joint operation with STBC and STLC schemes, called an STBLC system. The STBLC system achieves full-spatial-diversity gain in both uplink and downlink communications. The new STLC achieving full-spatial diversity is scalable for various code rates and expected to be applied to various wireless communication systems along with MRC, MRT, and STBC.

Distributed Space-Time Coding Based on the Self-Coding of RLI for Full-Duplex Two-Way Relay Cooperative Networks

In this paper, we consider full-duplex two-way relay cooperative networks, which allow the relaying of communications in both directions simultaneously and over the same frequency band. We propose a self-coded distributed space-time coding (SC-DSTC) scheme, in which the relay node performs a self-convolutional encoding and forms a distributed linear convolutional space-time code together with the direct link. The self-convolutional code at the relay is realized by using the stronger part of residual loop interference. The encoding process is implemented for both directions simultaneously through the local loop channel by a single amplifying factor, which is optimized when the loop channel information is imperfect. The simulation results show that the proposed SC-DSTC scheme can achieve asynchronous full cooperative diversity and is robust to the loop channel state information error at the relay when it is dominant among the interference and noise.