Quasi-orthogonal Space-time Block Codes Research Articles

Coding techniques for diversity enhancement of dense wavelength division multiplexing MIMO‐FSO fault protection protocols systems over atmospheric turbulence channels

AbstractAn enhanced transmission is presented in a multiple‐input‐multiple‐output (MIMO) dense‐wavelength division multiplexed (DWDM) free‐space‐optical (FSO) communication link using diversity coding techniques under the effect of turbulent weather phenomenon. The findings show good performance with an (8 channels × 2.5 Gbps data rate/channel) 20 Gbps 1500 m transmission distance. The bit‐error‐rate (BER), outage probability (OP), and signal‐to‐noise ratio (SNR) of the diversity combining techniques using maximum‐ratio combining (MRC), selection combining (SC), and equal‐gain combining (EGC) technique are evaluated in this work. The obtained results illustrate that Alamouti, space‐time coding (STC), space‐time block coding (STBC), space‐time trellis code (STTC), orthogonal STBC (O‐STBC), and quasi‐orthogonal STBC (QO‐STBC) on the minimum mean‐square‐error, and MRC are worth implementing on the DWDM‐FSO wireless communication systems. The mitigation of atmospheric turbulence is achieved using MIMO diversity combining techniques coding. The simulation results for diversity coding techniques using QO‐STBC/STTC and SC/MRC in the MIMO‐DWDM FSO communication system can improve BER performance, OP, and SNR. The MRC exhibits the lowest OP and BER when compared with the SC and EGC. The numerical results demonstrate that the FSO communication link using DWDM QO‐STBC/STTC improves the power penalty at both BER values under varying atmospheric turbulence conditions for ST, MT, and WT, in comparison to FSO systems without DWDM QO‐STBC/STTC diversity coding techniques.

Application of maximum rank distance codes in designing of STBC-OFDM system for next-generation wireless communications

Space-Time Block Coded (STBC) Orthogonal Frequency Division Multiplexing (OFDM) satisfies higher data-rate requirements while maintaining signal quality in a multipath fading channel. However, conventional STBCs, including Orthogonal STBCs (OSTBCs), Non-Orthogonal (NOSTBCs), and Quasi-Orthogonal STBCs (QOSTBCs), do not provide both maximal diversity order and unity code rate simultaneously for more than two transmit antennas. This paper targets this problem and applies Maximum Rank Distance (MRD) codes in designing STBC-OFDM systems. By following the direct-matrix construction method, we can construct binary extended finite field MRD-STBCs for any number of transmitting antennas. Work uses MRD-STBCs built over Phase-Shift Keying (PSK) modulation to develop an MRD-based STBC-OFDM system. The MRD-based STBC-OFDM system sacrifices minor error performance compared to traditional OSTBC-OFDM but shows improved results against NOSTBC and QOSTBC-OFDM. It also provides 25% higher data-rates than OSTBC-OFDM in configurations that use more than two transmit antennas. The tradeoffs are minor increases in computational complexity and processing delays.

Performance Analysis of Multiple Input Multiple Output (MIMO) Multi-Carrier Code-Division Multiple Access (MC-CDMA) Combined with Quasi-Orthogonal Space Time Block Coding (QO-STBC) in Rayleigh Fading Channel

The need for a communication system with a higher data rate and mobility grows along with information and communication technology development. Combining MC-CDMA with the MIMO system and supporting the system with a good transmit diversity technique is a promising idea to provide the needed communication system, especially in high mobility conditions. MC-CDMA can support ubiquitous communications without affecting the achievable BER and is more capable of high-speed mobility. It integrates the benefit of both OFDM and CDMA. On the other hand, QO-STBC increases the bit rate without using additional bandwidth to transmit diversity in the MIMO system. So, this study proposed a system combining the MIMO MC-CDMA system with QO-STBC. The proposed system is investigated under high mobility conditions to see the system's performance. The simulation results show that our system performs better than the MC-CDMA STBC system and the QOSTBC system but not better than the MC-CDMA multilevel coding scheme. To reach the value of BER 10−3, MC-CDMA multilevel Coding requires less power, around 5 dB, than the proposed system.

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.

Kronecker Product-Based Space-Time Block Codes

This letter presents a new approach to construct space-time block codes (STBCs) based on the Kronecker product. The proposed Kronecker-structured STBCs (K-STBCs) are specially designed for constant modulus constellations and include the classical linear dispersion (LD) codes as a special case. Its inherent Kronecker structure offers additional coding gains due to the mutual spreading of multiple space-time codewords. At the receiver, an efficient algorithm is derived by recasting the decoding of the K-STBCs as a rank-one tensor approximation problem. The proposed decoding algorithm provides a good bit error ratio (BER) performance especially, in the low signal-to-noise ratio (SNR) regime. In particular, our numerical results show that K-STBCs outperform the existing quasi-orthogonal STBCs due to the denoising gain offered by the proposed rank-one approximation based detector.

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.

Millimeter Wave MISO-OFDM Transmissions in an Intra-Wagon Environment

In this paper, the maximum achievable throughput is analyzed in the intra-wagon channel when multiple-input single-output (MISO) and orthogonal frequency division multiplexing (OFDM), MISO-OFDM, techniques are used. This analysis is performed from real wideband propagation channel measurements at 28 and 37 GHz, two potential frequency bands to deploy the future fifth-generation (5G) wireless communications networks. Four different scenarios in terms of the access point (AP) and user equipment (UE) positions inside the wagon have been considered, using 4 and 8 antennas at the AP. The performance of both quasi-orthogonal space-time block code (QSTBC), combined with Hadamard matrices, and transmit beamforming techniques is studied and evaluated from simulation results. The simulation results take into account the signal-to-noise ratio (SNR) and the antenna correlation for each antenna array configuration at the AP. These results provide useful insight to better understand the intra-wagon channel properties and deploy the future 5G wireless networks in this particular scenario at mmWave frequencies, where high-data-rates are expected to support different types of digital applications.

Adaptive Switching Hybrid Blast-STBC MIMO System

Fading in a wireless channel has negative effects on the performance of communication systems. Bell Laboratories layered space-time (BLAST) has been used to get a high data rate while space-time block codes (STBC) have been used to get a low bit error rate (BER) performance. Under deep faded channels, hybrid BLAST-STBC systems are considered as a trade-off between BLAST and STBC systems. By exploiting the benefits of both systems, a new method to represent a 4 × 4 multiple-input and multiple-output (MIMO) system is proposed and studied, in which the transmission process is carried out adaptively between both 4 × 4 VBLAST, Quasi-Orthogonal STBC (QOSTBC) and Hybrid systems according to the transmit links state. The proposed adaptive switching hybrid system (ASHS) reduces the total transmitted power, achieves the maximum throughput by obtaining the best BER. An adaptive switching transmission scheme using the strategy of measuring the transmit links fading is investigated as well. The simulated results are obtained in an environment of a 4 × 4 MIMO system using MATLAB platform where the total transmitting power is normalized to unity. The detections are done using the maximum likelihood (ML) receiver. The proposed ASHS system shows a lot of advantages such as maximum throughput is obtained in bad channel states, no additional transmit power is needed and no additional bandwidth is needed. Finally, under deep fading condition, the proposed ASHS transmission scheme obtains the best BER, reduces wasting the total transmitted power, achieves the maximum throughput and obtains the best BER.

Data transmission scheme based on the DC-QOSTBC in indoor MIMO-VLC systems.

We propose a data transmission scheme based on the dimming coding and quasi-orthogonal space-time block coding (QOSTBC) to improve the performance of indoor multiple-input multiple-output visible-light communication (MIMO-VLC) systems. After channel coding, the dimming coding was first applied to encode the input information bits into dimming bits. Then these encoded dimming bits were mapped to different symbols by head pulse position modulation. Finally, the symbol matrix was constructed on the basis of QOSTBC; then the light-emitting diodes would be activated to transmit the optical signals carrying the information according to the symbol matrix. The Monte Carlo simulations demonstrated the superiority of the proposed scheme in channel capacity and bit error ratio (BER). The channel capacity was a good approximation to the actual one, even though the full diversity gain could not be completely achieved. The BER could achieve 0.4×10-6 when the number of photodetectors was two.

Performance and evaluation of Volterra Nonlinear Equalizer for coherent RoF mobile front-haul network: a case study of QOSTBC-OFDM and QOSTBC-GFDM waveforms

In this paper, we propose and investigate a multi-Gigabits-per-second baseband signal over Standard Single-Mode Fiber (SSMF) link using a 16-Quadrature Amplitude Modulation (16-QAM). This architecture can be deployed within the context of fifth-generation (5G) Cloud Radio Access Network (C-RAN). It consists of 4 × 4 Quasi-Orthogonal Space–Time Block Code Generalized Frequency Division Multiplexing (QOSTBC-GFDM) and Orthogonal Frequency Division Multiplexing (QOSTBC-OFDM) waveforms. It is based on the implementation of a third order Volterra Nonlinear Equalizer (VNLE) in the Remote Radio Unit (RRU). The VNLE has been efficiently employed to reduce the impact of the harmful effect of the photonic devices. A Zero Forcing (ZF) equalizer has been used at the User Equipment (UE) to overcome the wireless channel impairments. Our research shows that VNLE can be a promised solution to compensate signal distortions and non-linearity effects. Furthermore, this study shows that QOSTBC-GFDM is more efficient than QOSTBC-OFDM in terms of Out-Of-Band (OOB) emission and Spectral Efficiency (SE). Moreover, a comparable performance between the two waveforms in terms of Bit Error Rate (BER) and Error Vector Magnitude (EVM) is attained.

Waveform Design for Space–Time Coded MIMO Systems with High Secrecy Protection

In this paper, we present a new secrecy-enhancing scheme for multi-input-multi-output (MIMO) systems using a space–time coding scheme. We adopt a quasi-orthogonal space–time block coding (QO-STBC) scheme that was originally designed to improve the performance of the MIMO system, and propose an efficient waveform design that can enhance the secrecy, as well as improve the error rate performance. Channel- and signal-dependent artificial interference (AI) is added to the proposed waveform, so that only a legitimate receiver can successfully retrieve information. We investigate the secrecy capacity of the proposed scheme, and demonstrate that the proposed scheme provides highly enhanced secrecy performance, compared to the conventional schemes. The performance simulation results reveal that the transmitted information can be properly extracted only at the legitimate receiver.

Generalized Space Time Block Coded Spatial Modulation for Open-Loop Massive MIMO Downlink Communication Systems

In this paper, we propose a generalized space-time block coded spatial modulation (GSTBC-SM) scheme for open-loop massive multiple-input and multiple-output (MIMO) downlink communication systems. Specifically, we firstly partition the information bits into multiple groups with each group modulated by the spatial modulation (SM), where the SM symbols are invoked for orthogonal STBC (OSTBC) and quasi-orthogonal STBC (Q-OSTBC) structures. Then, message passing (MP) and block minimum mean square equalization (B-MMSE) detectors are designed for our GSTBC-SM systems, to achieve near-optimal performance with significantly reduced complexity in massive MIMO configurations. Finally, we derive the theoretical average bit error probability (ABEP) of the proposed scheme. The main contribution is that the propose scheme achieves high transmission rate and diversity gain even with small number of radio frequency (RF) chains at the transmitter. Simulation results verify the theoretical derivations and show that the proposed GSTBC-SM scheme provides near 20 dB gain over the conventional GSTBC scheme under massive MIMO configurations.

On the performance of code word diversity based quasi orthogonal space time block codes in multiple-input-multiple-output systems

In the recent past, a lot of researches have been put into designing a Multiple-Input-Multiple-Output (MIMO) system to provide multimedia services with higher quality and at higher data rate. On par with these requirements, a novel Quasi Orthogonal Space Time Block Code (QOSTBC) scheme based on code word diversity is proposed, which is a multi-dimensional approach, in this paper. The term code word diversity is coined, since the information symbols were spread across many code words in addition to traditional time and spatial spreading, without increasing transmission power and bandwidth. The receiver with perfect channel state information estimates the transmitted symbols with less probability of error, as more number of samples is available to estimate given number of symbols due to the extra diversity due to code words. The simulation results show a significant improvement in the Bit Error Rate (BER) performance of the proposed scheme when compared with the conventional schemes.

Improved Signal Detection Techniques for QOSTBC System in Fast Fading Channel

Most existing quasi-orthogonal space time Block coding (QO-STBC) schemes have been developed relying on the assumption that the channel is at or remains static during the length of the code word symbol periods to achieve an optimal antenna diversity gain. However, in time-selective fading channels, this assumption does not hold and causes intertransmit-antenna-interferences (ITAI). Therefore, the simple pairwise maximum likelihood decoding scheme is not sufficient to recover original transmitted signals at the receiver side. To avoid the interferences, we have analyzed several signal detection schemes, namely zero forcing (ZF), two-step zero forcing (TS-ZF), minimum mean square error (MMSE), zero forcing - interference cancelation - decision feedback equalizer (ZF-IC-DFE) and minimum mean square error - interference cancelation { decision feedback equalizer (MMSE-IC-DFE). We have proposed two efficient iterative signal detection schemes, namely zero forcing - iterative interference cancelation - zero forcing { decision feedback equalization (ZF-IIC-ZF-DFE) and minimum mean square error - parallel interference cancelation - zero forcing – decision feedback equalization (MMSE-IIC-ZF-DFE). The simulation results show that these two proposed detection schemes significantly outperform all conventional methods for QOSTBC system over time selective channel.

QOSTBC coded MIMO system with reduced complexity and optimised decoding for rank deficient channels

In multiple-input multiple-output (MIMO) systems, rank deficient channels are the most common and key areas of research. In these channels, the number of transmit antennas (M Tx) is higher than receive antennas (M Rx) and subsequently the unknown variables are more than the number of equations. In such situations, the conventional sphere decoder (SD) fails due to the presence of zero diagonal elements in Cholesky decomposition. This study analyses the quasi-orthogonal space-time block code (QOSTBC) of symbol rate-2 for M Tx = 4 with modified double-layer SD detection to overcome rank deficiency problem. The first half of transmitted symbols is detected using two partially dependent SDs with optimised search radii. The remaining half is detected by employing single symbol maximum likelihood detection. Simulation and analytical results indicate that the proposed detection scheme reduces bit error rate and complexity compared to existing techniques.

Joint Space-time Coding and Power Domain Non-orthogonal Multiple Access for Future Wireless System

According to information theory, non-orthogonal transmission can achieve the multiple-user channel capacity with an onion-peeling like successive interference cancellation (SIC) based detection followed by a capacity approaching channel code. However, in multiple antenna system, due to the unideal characteristic of the SIC detector, the residual interference propagated to the next detection stage will significantly degrade the detection performance of spatial data layers. To overcome this problem, we proposed a modified power-domain non-orthogonal multiple access (P-NOMA) scheme joint designed with space-time coding for multiple input multiple output (MIMO) NOMA system. First, with proper power allocation for each user, inter-user signals can be separated from each other for NOMA detection. Second, a well-designed quasi-orthogonal space-time block code (QO-STBC) was employed to facilitate the SIC-based MIMO detection of spatial data layers within each user. Last, we proposed an optimization algorithm to assign channel coding rates to balance the bit error rate (BER) performance of those spatial data layers for each user. Link-level performance simulation results demonstrate that the proposed time-space-power domain joint transmission scheme performs better than the traditional P-NOMA scheme. Furthermore, the proposed algorithm is of low complexity and easy to implement.

A Cyclotomic Lattice Based Closed Loop QOSTBC for Four Transmit Antennas

Drawback of the Space Time Block Code (STBC) is, for complex constellations, full rate and full diversity design exist only for two transmit antennas. In this paper, we propose a novel closed loop Quasi Orthogonal Space Time Block Code (QOSTBC) system based on cyclotomic lattices for four transmit antennas. It is a full rate and full diversity design where the information bits are mapped into four dimensional (4-D) lattice points. The bit error and symbol error performance of the system are evaluated by simulation.

Omnidirectional Quasi-Orthogonal Space–Time Block Coded Massive MIMO Systems

Common signals in public channels of cellular systems are usually transmitted omnidirectionally from the base station (BS). In recent years, both discrete and consecutive omnidirectional space–time block codings (STBC) have been proposed for massive multiple-input multiple-output (MIMO) systems with a uniform linear array (ULA) configuration to ensure cell-wide coverage. In these systems, constant received signal power at discrete angles, or constant received signal sum power in a few consecutive time slots at any angle is achieved. In addition, an equal-power transmission per antenna and a full spatial diversity can be achieved as well. In this letter, by utilizing the property of orthogonal complementary codes (OCCs), a new consecutive omnidirectional quasi-orthogonal STBC (QOSTBC) design is proposed, in which constant received sum power at any angle can be realized with the equal-power transmission per antenna through one STBC transmission, and a higher diversity order of four can be achieved. Moreover, the proposed design can be further extended to the uniform planar array (UPA) configuration with the two-dimensional OCCs.

Multi-Dimensional Space-Time Block Coding Aided Downlink MIMO-SCMA

Multiple-input multiple-output (MIMO) and sparse code multiple access (SCMA) are two key techniques supporting high spectral efficiency and massive connectivity. In this paper, we consider the downlink MIMO communication scenario where SCMA is used for multiuser access. We aim to improve the performance of the traditional single-input single-output SCMA (SISO-SCMA) by exploiting the transmit diversity of multiple antennas at the transmitter. Specifically, we propose a multi-dimensional space-time block code (MSTBC) aided downlink MIMO-SCMA and derive the design criteria of MSTBC that can achieve full diversity while keep the symbol rate same as the traditional SISO-SCMA system. In particular, the MSTBC-2 for two transmit antennas and the MSTBC-4 for four transmit antennas are designed by extending the Alamouti code and quasi-orthogonal STBC into multi-dimension. Due to the orthogonality/quasi-orthogonality of the two MSTBCs, a linear decoder is available at the receiver, which keeps the complexity of the proposed MSTBC aided MIMO-SCMA almost the same as the conventional SISO-SCMA. Furthermore, the performance of the proposed schemes is evaluated based on both Monte Carlo simulations and analytical results. Simulation results show that the proposed MSTBC aided MIMO-SCMA can significantly outperform the conventional SISO-SCMA, STBC-MIMO-OFDM, and multiplexing MIMO-SCMA schemes.

A Minimum Mean-Square-Error (MMSE) Decoder for Quasi-Orthogonal Space–Time Block Code

The quasi-orthogonal space–time block code (QO-STBC) was introduced to achieve a full transmission rate for the four antennas system. In this paper, a decoding method for the QO-STBC is proposed to improve the bit-error-rate (BER) and to solve a rank-deficient problem. The proposed algorithm is based on the minimum mean-square-error (MMSE) technique. To overcome the implementation problem from the MMSE, an estimation method of the noise variance is developed in this paper. The proposed algorithm is implemented without matrix inversion, therefore, the proposed algorithm achieves a better BER than the conventional algorithms, as it has a low computational complexity. The simulation results show the low BER of the proposed algorithm in a Rayleigh fading channel.