Iterative (turbo processing) receiver design of OFDM systems in the presence of carrier frequency offset.

In this paper, based on the principle of turbo processing, we propose two iterative receiver schemes for carrier fre- quency offset (CFO) compensation in orthogonal frequency division multiplexing (OFDM) systems. Our CFO compensation designs, one in time domain and the other in frequency domain, are based on joint estimation of time-varying channel and CFO. In our schemes, the random CFO problem, a challenge for conventional pilot-aid methods, can be effectively solved using iter- ative (turbo processing) schemes. Furthermore, our comparative study shows that time domain compensation (TDC) is simpler to implement but frequency domain cancellation consisting of an iterative equalizer (FDC-IE) has better bit error rate (BER) performance

Cooperative retransmission for wireless regenerative multirelay networks

This paper investigates retransmission (RT) mechanisms in wireless regenerative multirelay networks. Conventionally, the RT can be realized in a cooperative manner with the assistance of all available relays. However, this may result in high overall power consumption due to the RT of the same packets across the nodes, particularly when the number of relays is large. We propose a cooperative RT (CR) scheme based on relay cooperation (RC) and binary xor operations to significantly reduce the number of packets retransmitted to produce a more power-efficient system with nonoverlapped RTs. Significantly, we also derive the error probability of RT decisions at the source and relays and show that the proposed CR scheme improves the reliability of the RTs. Furthermore, by deriving the average number of packets to be retransmitted at the source and relays, we not only show that the proposed CR scheme reduces the number of RTs and removes overlapped retransmitted packets but determine the optimized number of relays used for the RT phase as well. Finally, simulation results are presented to demonstrate the validity of the analytical expressions

Efficient cooperative spectrum sensing for three-hop cognitive wireless relay networks

This paper is concerned with cooperative spectrum sensing (CSS) mechanisms in three-hop cognitive wireless relay networks (CWRNs). The data transmission from a source to a destination is realised with the aid of two layers of cognitive radio (CR) users which are in the transmission coverage of two primary users. In this paper, we first propose a new CSS scheme for a layer of CR users to improve the spectrum sensing performance by exploiting both local decisions at the CR users and global decisions at the fusion centre. Particularly, we derive the probabilities of missed detection and false alarm for a practical scenario where all sensing, reporting, and backward channels suffer from Rayleigh fading. The derived expressions not only show that our proposed CSS achieves a better sensing performance than the conventional scheme but also characterise the effects of the fading channels on the sensing reliability. Furthermore, we propose a CSS scheme for two CR layers in a three-hop CWRN using binary XOR operator to help reduce one phase of sensing for a higher system throughput

Network coding-based block acknowledgement scheme for wireless regenerative relay networks

This study is concerned with block acknowledgement (ACK) mechanisms in wireless regenerative relay networks. In an N-relay network, a total of (2N + 1) block ACK packets is required to acknowledge the data transmission between source and destination nodes via the N-relay nodes. In this study, the authors propose a block ACK scheme based on network coding (NC) to significantly reduce the ACK overheads by N block ACK packets. In addition, this achieves a reduction of N(N–1) computational operators. Particularly, we derive the error probability of the determination of the packets to be retransmitted at the source and relays, which shows that the NC-based scheme also improves the reliability of block ACK transmissions. Furthermore, asymptotic signal-to-noise (SNR) scenarios for forward links are considered and a general expression of error probability in multi-relay networks is derived for each SNR scenario. Finally, simulation results are presented to verify the analytical findings and demonstrate a lower number of data retransmissions for a higher system throughput

An efficient retransmission strategy for multi-source multi-destination relay networks over Rayleigh flat fading channels.

This paper considers the reliable transmission for wireless multisource multidestination relay networks where multiple sources want to distribute information to a set of destinations with the assistance of a relay. Simply, applying automatic repeat request (ARQ) protocols for retransmission of lost or erroneous packets may cause a considerable delay with a significantly increased number of retransmissions when multiple sources and multiple destinations are taken into consideration. To solve this problem, we propose a new ARQ protocol based on network coding (NC) to significantly reduce the number of retransmissions of the lost packets. In our proposed NC-based ARQ protocol, the relay detects packets from different sources, then combines and forwards the packets which are lost at the destinations using NC. In order to guarantee that all lost packets are retransmitted in an efficient way, we propose two packet-combination algorithms for the retransmissions at the relay and sources. Furthermore, we analyze the transmission bandwidth of different ARQ protocols over Rayleigh flat fading channels and provide the numerical results to demonstrate the superior performance of the proposed NC-based ARQ protocol over some existing schemes

An efficient network coded ARQ for multisource multidestination relay networks over mixed flat fading channels

This paper proposes a new reliable automatic repeat request (ARQ) transmission protocol for wireless multisource multidestination relay networks over mixed fading channels. Conventional application of ARQ protocols to retransmit lost or erroneous packets in relay networks can cause considerable delay latency with a significant increase in the number of retransmissions when networks consist of multiple sources and multiple destinations. To address this issue, a new ARQ protocol based on network coding (NC) is proposed where the relay detects packets from different transmission sources, then uses NC to combine and forward lost packets to their destinations. An efficient means for the retransmission of all lost packets is proposed through two packet-combination algorithms for retransmissions at the relay and sources. The paper derives mathematical formulation of transmission bandwidth for this new NCbased ARQ protocol and compares analytical and simulation results with some other ARQ protocols over both mixed Rayleigh and Rician flat fading channel. The mixed fading model permits investigation of two typical fading scenarios where the relay is located in the neighbourhood of either the sources or the destinations. The transmission bandwidth results show that the proposed NC-based ARQ protocol demonstrates superior performance over other existing ARQ schemes

Efficient cooperative spectrum sensing for cognitive wireless relay networks over Rayleigh flat fading channels

This paper is concerned with cooperative spectrum sensing (CSS) mechanisms in cognitive wireless relay networks (CWRNs). Conventionally, the decision of available spectrum for cognitive radio (CR) users is carried out based on the global decision at a fusion center (FC). In this paper, we propose a new CSS scheme to improve the spectrum sensing performance by exploiting both local decisions at the CR users and global decisions at the FC. Particularly, by deriving the probabilities of missed detection and false alarm for a practical scenario where all sensing, reporting, and backward channels suffer from Rayleigh fading, we show that our proposed CSS scheme achieves an improved sensing performance over the conventional scheme. Furthermore, we propose a CSS scheme based on network coding (NC) for a specific CWRN where the transmission from a source node to a destination node is realized with the aid of two groups of CR users located in the transmission coverage of two primary users (PUs). The proposed NC-based CSS scheme helps reduce one phase of sensing for a higher system throughput compared to the conventional scheme which requires eight phases in total to monitor all available spectrums of both PUs

An efficient cooperative retransmission for wireless regenerative relay networks

This paper considers retransmission mechanisms in wireless regenerative relay networks. The retransmission can be realized in a cooperative manner with the assistance of all available relays. This may result in a high overall power consumption due to a considerable number of overlapped packets in the retransmission, especially when the number of relays is large. In this paper, we propose a cooperative retransmission (CR) scheme based on relay cooperation and binary XOR operation to significantly reduce the number of packets to be retransmitted for a more power efficient system with non-overlapped retransmission. Particularly, we derive the error probability of the retransmission decision at the source and relays, which shows that the proposed CR scheme also improves the reliability of the retransmission. Finally, simulation results are presented to verify the analytical findings and show that the proposed CR scheme reduces the number of retransmissions and removes overlapped retransmitted packets

Network coding-based block ACK for wireless relay networks.

This paper considers block acknowledgement (BACK) mechanisms in wireless regenerative relay networks. Conventionally, a total of (2N + 1) BACK packets are required in wireless regenerative N-relay networks to acknowledge the data transmission between the source and destination via the relays. In this paper, based on network coding (NC) we propose an efficient BACK scheme to significantly reduce the required acknowledgment load by N BACK packets. Importantly, by deriving the error probability of the determination of the packets to be retransmitted at the source or relays, it is found that the utilised NC helps improve the reliability of BACK transmissions. Furthermore, some asymptotic scenarios of the forward links are considered and a general expression of error probability in multi-relay networks is derived for each scenario. Finally, simulation results are shown to verify the analytical finding