Kui Xu

Outage performance of AF-based time division broadcasting protocol in the presence of co-channel interference

In this paper, we investigate the outage performance of time division broadcasting (TDBC) protocol in independent but non-identical Rayleigh flat-fading channels, where all nodes are interfered by a finite number of co-channel interferers. We assume that the relay operates in the amplified-and-forward mode. A tight lower bound as well as the asymptotic expression of the outage probability is obtained in closed-form. Through both theoretic analyses and simulation results, we show that the achievable diversity of TDBC protocol is zero in the interference-limited scenario. Moreover, we study the impacts of interference power, number of interferers and relay placement on the outage probability. Finally, the correctness of our analytic results is validated via computer simulations.

On the design of relay selection strategy for two-way amplify-and-forward mobile relaying

Opportunistic relay selection (RS) is an efficient method to obtain diversity gain in analogue network coding (ANC) protocol with multiple relays. However, in networks with mobile relays, the channel state information (CSI) used in the RS procedure becomes outdated because of the time-varying nature of fading channels, which severely deteriorates the system performance. In this study, the authors study the RS strategy which aims to optimise the outage performance of the ANC protocol with multiple mobile relays. RS schemes for two different cases are designed, that is, (i) the scheme with only the outdated CSI during the RS procedure, and (ii) the scheme with both the outdated CSI and the statistical knowledge of channels during the RS procedure. The closed-form expressions of the outage probabilities as well as the asymptotic expressions are analytically derived for the proposed schemes, and moreover, the achievable diversities are analysed based on the asymptotic expressions. Simulation results are presented to evaluate the performances while validate the theoretical analyses for the proposed schemes.

On Max-SINR receiver for Hexagonal Multicarrier Transmission over doubly dispersive channel

In this paper, a novel receiver for Hexagonal Multicarrier Transmission (HMT) system based on the maximizing Signal-to-Interference-plus-Noise Ratio (Max-SINR) criterion is proposed. Theoretical analysis shows that the prototype pulse of the proposed Max-SINR receiver should adapt to the root mean square (RMS) delay spread of the doubly dispersive (DD) channel with exponential power delay profile and U-shape Doppler spectrum. Simulation results show that the proposed Max-SINR receiver outperforms traditional projection scheme and obtains an approximation to the theoretical upper bound SINR performance within the full range of channel spread factor. Meanwhile, the SINR performance of the proposed prototype pulse is robust to the estimation error between the estimated value and the real value of time delay spread.

A practical HARQ scheme with network coding for LTE-A broadcasting system

In order to improve broadcasting efficiency in LTE-A system, a novel HARQ scheme with network coding (NC) technology is presented in this paper. The implementation level of XORing NC is selected based on LTE system, and an XORing NC Combined (XNCC) strategy is developed to perform combined retransmission. The main idea of proposed scheme is to retransmit lost packets for multiple receivers simultaneously utilizing NC technology. Moreover, we extend the proposed scheme to relay broadcasting system. The simulation results illustrate that compared with traditional retransmission scheme, the average number of transmissions of the proposed NC-HARQ scheme can be sharply decreased, and the coding gains can be attributed to the potential advantage of NC technology.

Joint design of LDPC and Physical-layer Network Coding for bi-directional relay system in the presence of insufficient timing synchronization

Physical-layer Network Coding (PNC) has shown its power for improving the throughput effectively of the bi-directional relay system. Most of the existing PNC schemes are carried out under the assumption of perfect synchronization. In this paper, we provide some new insights into the joint design of Low-Density Parity-Check (LDPC)-coded and PNC for asynchronous bi-directional relay system with BPSK signaling. In particular, a novel LDPC and PNC joint design method is proposed for mitigating the performance degradation caused by the different timing offsets between relay and two source nodes. Simulation results show that the proposed joint design of LDPC and PNC scheme outperforms traditional method for bi-directional relay system in the presence of insufficient timing synchronization.

Broadcasting efficient opportunistic network coding for multisource-multidestination scenarios

Network coding across multicast transmission can significantly reduce the number of retransmissions for wireless broadcasting. However, most of the existing network coding schemes for these scenarios base on the assumption that each source has priori knowledge of the others, which restricts the application of network coding seriously. In this paper, we propose a multi-relay opportunistic network coding (MR-OPP-NC) scheme for multisource-multidestination (MSMD) broadcasting scenarios without the above mentioned assumption. In specific, a joint network coding and opportunistic selected scheme is designed in decode-and-forward strategy. Simulation results show that the MR-OPP-NC scheme proposed outperforms the pure opportunistic relaying scheme in delay performance.

Asymmetric network coding for two-way OFDM relay system with power allocation

Asymmetric data transmission commonly exists in two-way orthogonal frequency division multiplexing (OFDM) relay system. In this paper, we propose a novel asymmetric network coding scheme for two-way OFDM relay system with power allocation to improve the throughput and bit error rate (BER) performance. In the multiple access channel (MAC) phase, the relay receives asymmetric data from two terminals, respectively. The Max-Min power allocation is used to improve the system BER performance during the MAC phase. In the broadcast (BC) phase, a novel asymmetric network coding scheme based on the thought of adaptive modulation (AM) is proposed. The stronger link can reliably transmit more data by using higher-order modulation. The weaker link can adaptively reduce the modulation order with the help of bit-inserting zero approach and well-designed signal constellation and bit labeling, hence, improve the transmission reliability. Simulation results validate that the proposed scheme outperforms the symbol-inserting zeros scheme in BER and throughput.

Distribution of PAPR in LOFDM systems based on extreme value theory

The extreme value theory and the assumption that lattice orthogonal frequency division multiplexing (LOFDM) signal converges weakly to a Gaussian random process are employed to derive peak-to-average-power ratio (PAPR) in LOFDM systems. Two complementary cumulative distribution functions (CCDF) of LOFDM system with equal and unequal subcarrier power allocation are given, respectively. Computer simulations have been conducted, to validate the analytical results, showing a very good match between the identified PAPR distribution and that of real LOFDM signals. Our theoretical analysis is confirmed by numerical simulations that the PAPR problem of LOFDM systems is more deteriorative than that of standard OFDM systems.

Outage probability analysis of asymmetrical bi-directional multi-relay system based on network coding

In this paper, we construct a practical asymmetrical bi-directional multi-relay system model with considering the effect of distance between source nodes and destination nodes. Then two outage probability expressions of the system based on network coding and physical-layer network coding with decode-and-forward are given. Theory analysis is proved correct by Monte Carlo simulations. Also we analyze the system average outage probability with different situations of power allocation coefficient, locations of the relay nodes, SNR and the number of relay nodes, indicating the inherent relationship between power allocation coefficient and total system power as well as the number of relay nodes. Simulation results indicate that the optimal power allocation coefficient of the system based on network coding and physical-layer network coding varies with respect to the distance between source nodes and destination nodes, and the outage probability of physical-layer network coding outperforms network coding scheme. Meanwhile, simulation results show that the system outage probability performance improves with the number of relay nodes increasing.