Performance improvements of virtual QOSTBC systems

In this paper we present a new simple cooperative relaying scheme. The proposed scheme is compared with simple cooperative schemes with virtual orthogonal space time block coding (OSTBC) and quasi orthogonal space time block coding (QOSTBC). Every of these three schemes includes one base station with two antennas, two relay stations each with a single antenna and one mobile station with a single antenna. The aim of the proposed scheme is to preserve, as much as it is possible bit error rate (BER) performance of the cooperative scheme with virtual OSTBC, but with increased code rate. It is shown that the presented scheme obviously outperforms simple cooperative scheme with virtual QOSTBC, while in comparison with simple cooperative scheme with virtual OSTBC has very similar BER performance and increased code rate.

In this paper, a simple decoded orthogonal frequency division multiplexing (OFDM) quasi orthogonal space time block coding (QOSTBC) wideband wireless system is proposed in the presence of Nakagami-m fading and imperfect channel state information (CSI). The proposed scheme preserves full diversity and full code rate with simple decoding complexity. The use of OFDM is to eliminate the problem of inter-symbol interference (ISI) caused by the frequency selectivity of the channel. Due to practical considerations, imperfect CSI is considered in this work to imitate real transmission scenarios. Simulation results show that in the case of Rayleigh fading and channel estimation error variance of 0, the proposed and the conventional schemes overlap. This shows the good capability of the OFDM technology on repealing the effect of ISI. In addition, it is noted that the performance improves as the Nakagami-m parameter increases. Moreover, it can be observed that as the imperfect estimation error variance increases the performance degrades.

Massive multiple-input multiple-output (MIMO) using a large number of antennas at both transmitter and receiver sides based on quasi-orthogonal space time block code (QOSTBC) is presented. Space-time block code (STBC) is a MIMO transmit strategy that applies transmit diversity and high reliability. QOSTBC is attractive because it achieves higher code rate than orthogonal STBC and lower decoding complexity than non-orthogonal STBC. We present the performance of massive MIMO systems using the QOSTBC with multiple antennas up to the 16 × 16 configuration. The performances of 2 × 2, 4 × 4, 8 × 8 and 16 × 16 massive MIMO systems have been presented. Simulation results show that the massive MIMO systems with QOSTBC give significant performance improvement with full rate and full diversity, compared with previously considered massive MIMO systems.

Orthogonal space-time block code (OSTBC) can achieve full diversity with a simple MLD, but OSTBC only achieves 3/4 of the maximum rate if more than two transmit antennas are used. To solve this problem, a quasi-orthogonal STBC (QOSTBC) scheme has been proposed. Even though a QOSTBC scheme can achieve the full rate, there are interference terms resulting from neighboring signals during detection. The existing QOSTBC using the pairs of transmitted symbols can be detected with two parallel MLD. Therefore, MLD based QOSTBC has higher complexity than OSTBC. To reduce the detection complexity, in this paper, we propose the heterogeneous constellation based QOSTBC for improving the detection property of QRD-MLD with maintaining a simple decoding structure.

A full-rate and full-diversity closed-loop quasi-orthogonal space time block coding scheme pioneered by Toker, Lambotharan and Chambers is proposed for application in virtual antenna arrays. The theoretical capacity and throughput gains are evaluated as a function of signal-to-noise ratio. It is shown that the scheme has particular benefits in both ergodic and non-ergodic channel environments, and outperforms virtual antenna arrays based solely upon conventional orthogonal space time block codes.

An 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.

In this paper, we propose a novel distributed space-time block coding (STBC) scheme for multi-relay system. We consider the full-duplex cooperation which is more spectrally efficient than the half-duplex cooperation. In full-duplex mode, the new scheme requires relay nodes to stack only every two successive symbols for swapping. Thus, the end-to-end delay may be lower than that induced by orthogonal STBC and conventional quasi-orthogonal STBC (QOSTBC) schemes. We show the new distributed STBC is capable of achieving cooperative diversity by using multi-dimensional rotated signal constellation. Besides, due to the simpler maximum-likelihood metric compared to that of conventional QOSTBC, the code achieves a lower decoding complexity without any performance degradation. To furthermore reduce complexity, the fast sphere decoder is adopted for the proposed code. The proposed transmission scheme is evaluated and compared in terms of performance by simulation.

This paper considers the problem of massive multiple-input-multiple-output (MIMO) wireless communication systems with quasi-orthogonal space-time block code (QOSTBC) transmission in the presence of spatial correlation effect (SCE) and mutual coupling effect (MCE). Conventional MIMO channels with QOSTBC transmission suffer from several drawbacks. The number of transmit antennas is restricted to a few in order to achieve full transmission rate. Therefore, it is difficult to make a quasi-orthogonal space time block coded massive MIMO system to achieve full transmission rate. Moreover, MIMO channel with QOSTBC transmission is usually considered for the case where the number of user equipments (UEs) is one. We present a joint beamforming and spatial precoding method to deal with the above drawbacks. The proposed method incorporates a beamforming scheme and spatial precoding to formulate an appropriate optimization process to effectively alleviate the considered problems. The resulting optimization problem will be solved by using a cooperative coevolutionary particle swarm optimization algorithm under two proposed fitness functions. During the optimization process, the proposed method finds the optimal beamforming coefficients of the precoding matrix, the optimal normalized positions of transmit and receive antenna elements for the case of using linear antenna arrays, and the optimal angle differences of transmit and receive antenna elements for the case of using circular arrays. Based on the proposed method, we are able to cure the performance degradation of a quasi-orthogonal space time block coded massive MIMO system due to the SCE and MCE. Moreover, the proposed method makes QOSTBC MIMO communications with full transmission rate for any number of transmit antennas achievable. Several simulation examples are presented to show the superior bit error rate (BER) performances of QOSTBC wireless MIMO scenarios with linear as well as circular antenna arrays by using the proposed method as compared to the existing methods.

Recently, a quasi-orthogonal space-time block code (QSTBC) capable of achieving a significant fraction of the outage mutual information of a multiple-input-multiple-output (MIMO) wireless communication system for the case of nT = 4 transmit and nR = 1 receive antennas was proposed. We generalize these results to nT = 2n transmit and an arbitrary number of receive antennas. Furthermore, we completely characterize the structure of the equivalent channel for the general case and show that for all nT = 2n and nR the eigenvectors of the equivalent channel are fixed and independent from the channel realization. Furthermore, the eigenvalues of the equivalent channel are independent identically distributed random variables each following a noncentral chi-square distribution with 4nR degrees of freedom. Based on these important insights into the structure of the QSTBC, we derive tight lower and upper bounds for the outage probability achieved with QSTBC. Finally, by utilizing the special structure of the QSTBC, we propose a new transmit strategy, which decouples the signals transmitted from different antennas in order to detect the symbols separately with a linear ML-detector rather than joint detection, an up to now only known advantage of orthogonal space-time block codes (OSTBC).

A novel QO-STBC scheme with linear decoding

The main aim of the physical layer is to boost the data rates over wireless channel with better quality of services (QOS), thereby, increasing the efficiency and reliability of new generation wireless communication systems especially 5G/6G system. Performance of various space time block codes like quasi orthogonal space time block codes and rotational quasi orthogonal space time block codes is investigated using various decoding algorithms like Sphere Decoder, K 1, K 2, K 3, K 4 Sphere decoders. The Sphere Decoder has been modified in terms of K detection algorithms based on spectral efficiency. Different modulations are used to validate the analytic analysis. Simulations are performed in MATLAB software and the results obtained shows the significant incremented spectral efficiency.

The link performance between base station (BS) and user equipment (UE) in long term evolution-advanced (LTE-A) system is already quite close to the Shannon limits and from a pure link-budget perspective, the highest data rates supported by LTE-A require a relatively high signal-to-noise ratio. In later releases of LTE-A, various tools such as relaying, enhancing the support for low-power BSs and improving the link budget are included. This paper studies the relay stations (RSs) for LTE-A downlink physical layer. Multi-input multi-output amplify-and-forward RS is used to enhance the received signal of UEs at cell edge. This paper proposes RSs with orthogonal space–time block codes (OSTBC) transmission for LTE-A system. The received signals for different UEs scenarios are mathematically derived and analyzed. The symbol error rate performance of proposed LTE-A system is illustrated for the scenarios of UEs. Results show that the proposed LTE-A system based RSs with OSTBC transmission improve link performance and achieve higher diversity gains.

We consider a multiple input and multiple output system with quasi-orthogonal space time block codes. Quasi-orthogonal space time block code (QOSTBC) is greatly used because it can achieve a good tradeoff between diversity and multiplexing. However, since the transmit code is not orthogonal, there exists interantenna interference at the receiver. By studying the post detection SNR of transmit symbols at each detection step of ordered interference cancellation (OSIC), we propose an ordered group interference cancellation (OGIC) at reduced complexity. Simulation results show that the proposed method can achieve near the performance of OSIC

In this paper, we present the bit-error rate (BER) performance of quasi-orthogonal space-time block code (QOSTBC) massive multiple-input multiple-output (MIMO) system employing up to 32 transmit and receive antennas. The QOSTBC, due to its advantages in transmission rate and decoding complexity, is an important transmit diversity scheme for more than 2 transmit antennas. As massive MIMO implies very large number of antennas, practically at least more than 15 antennas, a different number of transmit and receive antennas (i.e. 2×2, 4×4, 8×8, 16×16 and 32×32) using QOSTBC for the massive MIMO system are considered. The BER performance of the massive MIMO with antennas up to 32×32 using BPSK modulation scheme is analyzed. Simulation results show that the full-rate massive MIMO systems with QOSTBC give a significant performance improvement due to increasing diversity effect, compared with previously considered massive MIMO systems.

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.