Abdulghani M. Elazreg

Distributed quasi-orthogonal space-time coding for two-way wireless relay networks

The contribution in this paper is to consider distributed quasi orthogonal space-time block coding (D-QO-STBC) for two-way (TW) wireless relay networks. In particular we exploit a two time slot protocol and both open-loop and closed-loop D-QO-STBC with full cooperative diversity. In the open-loop approach constellation rotation is exploited to improve performance, whereas two feedback terms are used in the closed-loop schemes. Our end-to-end bit error rate simulations show that TW closed-loop D-QO-STBC and rotated open-loop D-QO-STBC are approximately 8 dB and 7.5 dB better than the distributed Alamouti TW approach at 10−4 bit error rate (BER), which confirms the advantage of four relay schemes in relay networks.

Orthogonal space time block coding for two-way wireless relay networks under imperfect synchronization

In this paper distributed space time block codes (D-STBCs) are applied within an asynchronous two-way cooperative wireless relay network using two relay nodes. A parallel interference cancelation (PIC) detection scheme with low structural and computational complexity is applied at the terminal nodes in order to overcome the effect of imperfect synchronization among the cooperative relay nodes. Simulation results based on end-to-end bit error rate (BER) illustrate that the PIC detection algorithm can mitigate the inter symbol interference (ISI) introduced by the asynchronism, and that only a small number of iterations is necessary within the PIC detection to improve the system performance.

Closed-loop extended orthogonal space time block coding for four relay nodes under imperfect synchronization

In future collaborative wireless communication systems with high data rate, interference cancellation is likely to be required in cooperative networks at the symbol level to mitigate synchronization errors. In this paper, we therefore examine closed-loop extended orthogonal space time block coding (CL EO-STBC) for four relay nodes and apply parallel interference cancellation (PIC) detection scheme to mitigate the impact of imperfect synchronization. Simulation results illustrate that the closed-loop EO-STBC scheme under imperfect synchronization can achieve good performance with simple linear processing and outperform previous methods. Moreover, a PIC scheme is shown to be very effective in mitigating impact of imperfect synchronization with low structural and computational complexity.

Distributed one bit feedback extended orthogonal space time coding based on selection of cyclic rotation for cooperative relay networks

In this paper, a novel closed-loop distributed extended orthogonal space time block code (D-EO-STBC) with one-bit feedback based on selection of phase rotation is proposed for two relay nodes each relay equipped with two antennas. In this scheme, only one-bit of feedback is used to determine the transmission phase terms applied to the symbols from the antennas of each relay nodes. This is considerably lower feedback overhead than previous feedback schemes. This feedback information is based upon channel state information (CSI) available at the destination node. In addition, the transmission rate over each hop in the network is unity and full cooperative diversity is obtained by the approach. Furthermore, this proposed scheme is applied to asynchronous relay networks using orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) at the source node to combat the timing error at relay nodes, which operate in a simple distributed STBC mode. End-to-end bit error rate (BER) simulation results show that the proposed scheme can enhance the performance of the system with feedback limited to only one-bit and outperform previous feedback methods.

Sub-optimum detection scheme for asynchronous cooperative relay networks

In this study, a new sub-optimum detection scheme is proposed which employs closed-loop extended orthogonal space–time block coding and outer convolutive coding within an asynchronous cooperative wireless relay network to achieve full data rate and full diversity gain between the relays and destination node together with coding gain. Simulation results confirm that the proposed scheme can effectively suppress intersymbol interference induced by asynchronism between the relay nodes at the destination node.

Distributed Closed-Loop Quasi-Orthogonal Space Time Block Coding with four relay Nodes: overcoming Imperfect Synchronization

In this paper, closed-loop quasi-orthogonal space time block coding(QO-STBC) is exploited within a four relay node transmission scheme to achieve full-rate and increase the available diversity gain provided by earlier two relay approaches. The problem of imperfect synchronization between relay nodes is overcome by applying a parallel interference cancellation (PIC) detection scheme at thedestination node. Bit error rate simulations confirm the advantages of the proposed methodology for a range of levels of imperfect synchronization and that only a small number of iterations is necessary within the PIC detection.

Near-optimum detection scheme with relay selection technique for asynchronous cooperative relay networks

A new near-optimum detection scheme for asynchronous wireless relay networks is proposed to cancel the interference component at the destination node caused by timing misalignment from the relay nodes. The detection complexity at the destination node as compared with a previous sub-optimum detection scheme is reduced. Closed-loop extended orthogonal space time block coding and outer convolutive coding are utilised to maximise end-to-end performance. A relay selection technique is also proposed in this study for two dual-antenna relay nodes to enhance the system performance by selecting the best links and the smallest time delay error among the relay nodes. Simulation results confirm that the proposed near-optimum detection scheme with relay selection is very effective at removing intersymbol interference at the destination node and achieving full cooperative diversity with unity data transmission rate between the relay nodes and the destination node.

Distributed Space Time Transmission with Two Relay Selection and Parallel Interference Cancellation Detection to Mitigate Asynchronism

In this paper, we select the best two relays from a set of available relays, each of which is equipped with two antennas, based on the instantaneous path gains. Closed-loop quasi orthogonal space time block coding is then applied over the selected two relays to maximize cooperative diversity. parallel interference cancellation detection is also applied at the destination node to mitigate the problem of imperfect synchronization between the relay nodes. End-to-end bit error rate simulations confirm that the selection scheme yields a significant improvement in performance over the conventional scheme without using relay selection. Furthermore, the bit error rate simulations confirm the advantages of the detection scheme for a range of levels of asynchronism, and that only a small number of iterations is required in the parallel interference cancellation technique.

Cooperative multi-hop wireless network with robustness to asynchronism

We investigate the use of a timing synchronization technique within cooperative multi-hop networks with and without direct transmission between the source and destination nodes. In particular, we employ a parallel interference cancellation (PIC) technique to combat the effect of timing misalignment of the received signal at both the relay and the destination nodes. We compare the advantage in using direct transmission (DT) to assist in reducing the end-to-end bit-error-rate (BER) at the receiver with using multiple level cooperation among all nodes of each hop without direct transmission. Using 8-PSK constellation signals, our simulation results show that increased cooperation among neighboring nodes delivers improved end-to-end BER as compared to direct transmission assisted cooperation.