Space-time Block Codes Research Articles

On SFBC Schemes for Enabling Virtual Array Concept in Monostatic ISAC Scenarios.

The integrated sensing and communication (ISAC) paradigm is being proposed for 6G as a new feature of the physical layer (PHY), for tackling dual-functional applications, i.e., demanding radio-sensing and communication functions, such as the Internet of Things (IoT) and autonomous driving systems. This work considers the integration of sensing and communications functionalities in a unique platform. To achieve this goal, the use of orthogonal space frequency block codes (SFBC) is proposed. SFBC code orthogonality enables both the separation of communications data streams at a user terminal and the estimation of target parameters. The SFBC enhances the communications link diversity without requiring channel state information knowledge at the transmitter and enable the virtual antenna array concept for enhancing the direction-finding resolution. The use of different SFBCs provides a tradeoff between achieved diversity and sensing resolution. For example, an Alamouti code, applicable for the case with two transmitting antennas, duplicates sensing resolution and achieves a diversity order of two while the use of a Tarokh code, applicable for a scenario with four transmitting antennas, provides a fourfold better resolution and diversity order of four. However, the code rate achieved with the Tarokh code is half of the one achieved with the Alamouti code. Furthermore, the unambiguous range is reduced since the bandwidth is divided to multiplex the different antenna signals. For its simplicity, good performance and reduced integration requirements, the method is promising for future ISAC systems.

Space-Time Block Coded Spatial Modulation for Indoor Visible Light Communications

Visible light communication (VLC) has been recognized as a promising technology for handling the continuously increasing quality of service and connectivity requirements in modern wireless communications, particularly in indoor scenarios. In this context, the present work considers the integration of two distinct modulation schemes, namely spatial modulation (SM) with space time block codes (STBCs), aiming at improving the overall VLC system reliability. Based on this and in order to further enhance the achievable transmission data rate, we integrate quasi-orthogonal STBC (QOSTBC) with SM, since relaxing the orthogonality condition of OSTBC ultimately provides a higher coding rate. Then, we generalize the developed results to any number of active light-emitting diodes (LEDs) and any <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> -ary pulse amplitude modulation size. Furthermore, we derive a tight and tractable upper bound for the corresponding bit error rate (BER) by considering a simple two-step decoding procedure to detect the indices of the transmitting LEDs and then decode the signal domain symbols. Notably, the obtained results demonstrate that QOSTBC with SM enhances the achievable BER compared to SM with repetition coding (RC-SM). Finally, we compare STBC-SM with both multiple active SM (MASM) and RC-SM in terms of the achievable BER and overall data rate, which further justifies the usefulness of the proposed scheme.

A Better Than Alamouti OSTBC for MIMO Backscatter Communications

Backscatter communications have received increasingly attention in Internet of Things (IoT) due to its advantages of requiring no internal battery and almost zero maintenance. However, the drawback of backscatter communications is that, its channel fades deeper than conventional channel. To improve the performance, multiple-input multiple-output (MIMO) techniques have been investigated for backscatter communications. By considering duty cycle, a particular behavior of backscatter communications, as a new performance criterion, we propose a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> orthogonal space-time block code for MIMO backscatter communications. The new code is a rotation of the classical Alamouti code, and in MIMO backscatter channels, this simple rotation will incur an improved duty cycle for both linear and nonlinear energy harvester models, as well as a same, or even better symbol error rate performance. We provide both rigorous mathematical proofs and numerical simulations to show the above results. An interesting thing is that, this new code does not outperform Alamouti code in conventional MIMO channels, which indicates that the space-time code design criteria for conventional channels is not the optimal one for backscatter channels, and existing space-time codes should be reconsidered and/or redesigned to achieve a higher performance in MIMO backscatter communications.

Low-Complexity and Robust Framework of Precoding for Multi-Panel Massive MIMO

Massive multiple-input multiple-output (m-MIMO) is used to improve the robustness of data transmission and high sum spectral efficiency in 5G systems. For 5G New Radio (NR) systems need to be designed to reduce cost and complexity, most notably hybrid analog-digital beamforming with large-scale antenna array which has become a major research target. In the downlink transmission, we propose a robust and low-complexity framework of precoding design to implement hybrid beamforming (BF) of large antenna arrays without limitation on the size of the antenna. Furthermore, a large number of antenna elements can be coupled into multiple panels m-MIMO for the purpose of reducing costs and saving power. This study proposes to use both azimuth and elevation angles parameters to provide low complexity adaptive beam control in panels m-MIMO system. In contrast to existing works, that aim to eliminate inter-user interference, this work is distinguished by adopting polarization function and space-time block code to the m-MIMO antenna arrays. We also propose a new multi-panel codebook design correspondingly with control parameters. The performance of the proposed framework is analysed with state-of-the-art research comparisons. To this end, the important factor of beamforming which is the Error Vector Magnitude (EVM) will be analyzed and simulated.

Generalized designs for precoded receive spatial modulation derived from non-orthogonal space time block codes

Generalized designs for precoded receive spatial modulation derived from non-orthogonal space time block codes

STBC Identification for Multi-User Uplink SC-FDMA Asynchronous Transmissions Exploiting Iterative Soft Information Feedback of Error Correcting Codes

With the advancement and widespread implementation of multiple-input multiple-output (MIMO) wireless communication systems over the last decade, space-time block coding (STBC) identification has become a critical task for intelligent radios. Previous examinations of STBC identification were focused on single-user transmissions over single-carrier and multi-carrier systems in combination with uncoded broadcasts. Practical systems, on the other hand, contain many users and employ error-correcting codes. For the first time in literature, this work explores the problem of STBC identification for multi-user uplink transmissions in single-carrier frequency division multiple access (SC-FDMA) systems. We take another step closer to real systems by addressing asynchronous transmissions and by conducting multi-user channel estimation. We also exploit the outputs of the channel decoder, which is usually used in many practical systems, to improve the identification and estimation processes. The mathematical analysis demonstrates that the maximum-likelihood (ML) solution of STBC identification, channel estimation, and synchronization can be executed by an iterative approach. The space-alternating generalized expectation-maximization (SAGE) algorithm is used to separate the overlaid signals arriving at the base-station (BS). The parameters under consideration for each user are then updated using an expectation-maximization (EM) processor. Simulation results show that the proposed architecture outperforms other identification methods published in the literature while maintaining a reasonable level of processing time.

The Research of STBC in MIMO System

MIMO technology refers to the use of multiple transmitting antennas and multiple receiving antennas to improve the quality of information transmission. MIMO technology includes space-time coding, channel modeling, channel estimation, and other technologies. This paper mainly studies the space-time coding technology and precoding technology in the MIMO system through Matlab. First, the Alamouti coding is extended to the MIMO system with more transmitting and receiving antennas. This way can get a space-time block code. Finally, this paper will introduce the precoding technology and compare it with simulation analysis by simulating and analyzing its bit error performance.

An Alternative Encoding of the Golden Code and its Low Complexity Detection

The Golden code is a full-rate full-diversity (FRFD) space-time block code. The encoder of the Golden code takes four complex symbols and generates two pairs of Golden codewords. The encoding of each Golden codeword can be regarded as superposition coding with “complex” power allocation. In this paper, we propose an alternative encoding of the Golden code which can be regarded as superposition coding with “real” power allocation. The Golden code with “complex” power allocation or “real” power allocation is hereinafter referred to as the C-Golden code or R-Golden code, respectively. The R-Golden code also preserves the FRFD property. The R-Golden code can be easily implemented in passband modulation using in-phase and quadrature components compared to the C-Golden code. An equivalent received signal model of the R-Golden code system is constructed, then used to derive a closed-form on the lower bound of the average bit error probability. We further propose a low complexity detection scheme, the fast essentially maximum-likelihood detection with adaptive signal detection subset (FE-ML-ASDS) for the R-Golden code. Both simulation and theoretical results show that both the C-Golden code and the R-Golden code achieve the same error performance. Compared to the fast essentially ML detection with signal detection subset (FE-ML-SDS), at high signal-to-noise ratios, the proposed FE-ML-ASDS further reduces detection complexity by at least 68% for the 16QAM or 64QAM R-Golden code with three receive antennas.

ASM-ROBOT: A Cyber-Physical Home Automation Controller with Memristive Reconfigurable State Machine

In the next 5 to 10 years, digital Artificial Intelligence with Machine Circuit Learning Algorithms (MCLA) will become the mainstream in complex automated robots. Its power concerns, ethical perspectives, including the issues of digital sensing, actuation, mobility, efficient process-computation, and wireless communication will require advanced neuromorphic process variable controls. Existing home automated robots lack memristic associative memory. This work presents Cyber-Physical Home Automation System (CPHAS) using Memristive Reconfigurable Algorithmic State Machine (MRASM) chart. A process control architecture that supports Concurrent Wireless Data Streams and Power-Transfer (CWDSPT) is developed. Unlike legacy systems with power-splitting (PS) and time-switching (TS) controls, the MRASM-ROBOT explores granular wireless signal controls through unmodulated high-power continuous wave (CW). This transmits infinite process variables using Orthogonal Space-Time Block Code (OSTBC) for interference reduction. The CWDSPT transmitter and receiver circuit design for signal processing are implemented with complexity noise-error reduction during telemetry data decoding. Received signals are error-buffered while gathering control variables' status. Transceiver Memristive neuromorphic circuits are introduced for computational acceleration in the design. Hardware circuit design is tested for system reliability considering the derived schematic models for all process variables. Under small range space diversity, the system demonstrated significant memory stabilization at the synchronous iteration of the synaptic circuitry.

시공간 블록 코드의 난수 코드를 활용한 데이터 보호 기법

This paper proposes a random coded data protection technique in space-time block code. The traditional space-time block coding technique could be faced with open radio environments, so it has to overcome severe radio hijacking problems. In case of trying to avoid open radio issue, usually source data blocks are encrypted but it occurs heavy burden to the transmitter and receiver. This paper proposes a simple random coded timing sequence of data blocks, its effect results in received signals

Demonstration of a 2 × 2 MIMO-UWOC system with large spot against air bubbles

In order to reduce turbulence-induced scintillation and deal with alignment problems, a 2×2 multiple-input multiple-output (MIMO) underwater wireless optical communication (UWOC) system is proposed and experimentally demonstrated. With help of the large divergence angle of light beams and large field of view (FOV) of the detectors, the effect of high-density air bubbles is greatly eliminated. Simulation and experimental results confirm that, in most intensity-modulation/direct-detection (IM/DD) MIMO-UWOC systems, the repetition coding (RC) scheme performs better than the space-time block coding (STBC) scheme. In a 50 m swimming pool, the maximum horizontal offset can reach 97.9 cm, which is 421% and 192% higher than that of STBC multiple-input single-output (MISO) and RC-MISO/STBC-MIMO schemes, respectively. With a data rate of 233 Mbps and a transmission distance of 50 m, the large detection range can meet a variety of underwater wireless communication requirements. The experiment indicates that, when the difference in the transmission distance between the two optical signals is higher than 1 m, the bit error rate (BER) of the RC scheme increases sharply, while the BER of the STBC scheme is stable. The MIMO coding scheme needs to be selected according to the actual application environment.

SCMA-MIMO system with adaptation to the channel state

Sparse code multiple access (SCMA) is one of the promising implementations of non-orthogonal multiple access (NOMA) methods. SCMA provides high spectral efficiency and a large number of network resources. We describe a communication system with SCMA, space-time block coding (STBC), multiple input multiple output (MIMO) technology, and orthogonal frequency division multiplexing (OFDM). The architecture of such systems, including algorithms of formation and processing of signals is considered. A method for adapting signals to the state of the spatial channel transmission based on information about the matrix of channel coefficients is proposed. The application of such adaptation allows to compensate the influence of the channel and to reduce the probability of bit errors. We consider the bit error rate (BER) performance of the communication system in different channel models and show the effectiveness of the proposed methods.

Study of the STBC based MIMO System Modeling and Evaluation

There are many applications using the small MIMO antenna structure for performance improvement. The Long Term Evolution (LTE) and Wi-Fi wireless modems are good example of the MIMO based modeling. Many coding techniques have been designed for enhancing the performance of the MIMO channels. This paper has presented the comprehensive study of the Coding techniques used for MIMO system specially using the Space Time Block Codes (STBC). Basically the coding techniques are used for improving the estimation of the MIMO Channel states information (CSI). Various design challenges of the channel estimation for wireless communication are addressed and problems are identified. The comparison of various SCBC based MIMO channel estimation methods have been tabulated based on the BER and MSE performances.

Blockwise Phase Rotation-Aided Analog Transmit Beamforming for 5G mmWave Systems

In this letter, we propose a blockwise phase rotation-aided analog transmit beamforming (BPR-ATB) scheme to improve the spectral efficiency and the bit-error-rate (BER) performance in millimeter wave (mmWave) communication systems. Due to the phase angle optimization issues of the conventional analog beamforming, we design the BPR-ATB for reducing the rotated beamspace of the equivalent channel and improving the minimum Euclidean distance. To verify the effectiveness of the proposed BPR-ATB scheme, we employ an Alamouti coding technique at the transmitter and evaluate the bit-error-rate performance for mmWave multiple-input and single-output systems. The simulation results show that the proposed BPR-ATB scheme outperforms the conventional discrete Fourier transform-based ATB scheme.

Outage probability analysis in multi-user FSO/RF and UAV-enabled MIMO communication networks

This paper considers a mixed free-space optical/radio frequency (FSO/RF) system, which facilitates the communication between a ground central unit (CU) and multiple ground users (GUs) via a hovering unmanned aerial vehicle (UAV) acting as a decode-and-forward (DF) aerial relay. It is considered that the CU employs multiple transmit apertures and is interconnected with the aerial relay via an FSO link with transmit aperture selection (TAS), whereas the relay communicates with the GUs over multiple-input multiple-output (MIMO) RF links with orthogonal space–time block coding (OSTBC) transmission. It is assumed that the optical channels are mainly affected by atmospheric attenuation as well as geometric and misalignment loss (GML). Besides, the atmospheric turbulence is assumed weak for short-range links. Also, fully correlated shadowed conditions are considered in the RF links and the MIMO channels are modeled using the Nakagami/Inverse Gamma (IG) composite fading distribution. Opportunistic GU scheduling is applied in the downlink and novel closed-form mathematical formulas for the outage probability (OP) are derived. The results demonstrate the theoretical derivations and the performance benefits of the proposed approach.

Novel detection schemes for generalized quadrature spatial modulation

SummarySpatial Modulation (SM) is a technology that incorporates digital modulation and coding with multiple antennas to achieve high data rates along with improved energy efficiency. Quadrature spatial modulation (QSM), which extends the transmitted signals to in‐phase and quadrature domains, has recently been proposed to improve spectral efficiency (SE) for SM. In this paper, we have considered a combination of Generalized QSM (GQSM) and Quasi Orthogonal Space Time Block Codes (QOSTBC). We propose a new detection scheme for the GQSM and use three different prevailing detection schemes for QOSTBC. We present Bit Error Rate (BER) versus average SNR performance for the combined system using M‐QAM constellations with quasi‐static spatially uncorrelated Rayleigh fading channels and computational complexity in terms of numbers of addition/multiplication and search time. We have compared the considered system with prevailing GQSM system and shown that the prevailing system, as per active antenna permutation (AAP) in GQSM, offers number of transmitted bits ranging from 2 to 9 whereas the proposed system offers number of transmitted bits ranging from 6 to 16 in the same bandwidth. Thus, there is a visible gain in SE. Furthermore, we have compared the BER performance of the considered system with the performance of maximum likelihood detector (MLD) and spatial modulation (SM). In the considered system, the QOSTBC improves the diversity gain. Hence, we have shown that the considered Scheme 3 substantially outperforms the SM. Further, the considered system with Scheme 3 has nearly similar BER performance with the maximum likelihood detector (MLD), which has higher computational complexity.

Enhancing Ambient Backscatter Communication Utilizing Coherent and Non-Coherent Space-Time Codes

Ambient backscatter communication (AmBC) leverages the existing ambient radio frequency (RF) environment to implement communication with battery-free devices. The key challenge in the development of AmBC is the very weak RF signals backscattered by the AmBC Tag. To overcome this challenge, we propose the use of orthogonal space-time block codes (OSTBC) by incorporating multiple antennas at the Tag as well as at the Reader. Our approach considers both coherent and non-coherent OSTBC so that systems with and without channel state information can be considered. To allow the application of OSTBC, we develop an approximate linearized and normalized multiple-input multiple-output (MIMO) channel model for the AmBC system. This MIMO channel model is shown to be accurate for a wide range of useful operating conditions. Two coherent detectors and a non-coherent detector are also provided based on the proposed AmBC channel model. Simulation results show that enhanced bit error rate performance can be achieved, demonstrating the benefit of using multiple antennas at the Tag as well as the Reader.

Examination of the multiple-input multiple-output space-time block-code selective decode and forward relaying protocol over non-homogeneous fading channel conditions

With the tremendous increase in wireless user traffic, investigation on the end-to-end reliability of wireless networks in practical conditions such as non-homogeneous fading channel conditions is becoming increasingly widespread. Because they fit well to the experimental data, generalized channel fading distributions like κ–μ are well suited for modeling diverse fading channels. This paper analyzes the symbol error rate (SER) and outage probability (OP) performance of multiple-input multiple-output (MIMO) space-time block-code (STBC) selective decode and forward (S-DF) network over κ–μ fading channel conditions considering the additive white Gaussian noise (AWGN). First, the closed-form (CF) analytical expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the received signal-to-noise ratio (SNR) as well as its moment generating function (MGF) are derived. Second, the OP performance is then investigated for various values of the channel fading parameter and SNR regimes. The simulation findings show an increase in SER performance with an improved line-of-sight (LOS) component. Furthermore, the results show that the S-DF relaying systems can function properly even when there is no fading or LOS component. The OP has been increasing with the increase in the value of μ and κ. In medium and high SNR regimes, simulation results exactly match with analytical results.

A New Transmit Diversity Technique for FSK Exploiting its Orthogonality

We propose a new transmit diversity technique for frequency shift keying (FSK). The main idea behind our proposed scheme is to exploit the orthogonality between FSK carriers in order to render signals transmitted from different antennas orthogonal at the receiver, which results in full diversity. Since the proposed scheme achieves antenna orthogonality within one time unit while the well-known Alamouti space-time block code (STBC) needs two time units, it succeeds to be more robust against time-selectivity of the channels than the STBC without deteriorating peak-to-average power ratio (PAPR) of the signal. Simulation demonstrates that the proposed scheme has an error floor that is ten times lower than the STBC over time-selective channels.

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.