Xiaorong Xu

An efficient anti-jamming piecewise coding in cognitive OFDM

An efficient anti-jamming piecewise coding based on cognitive OFDM modulation in cognitive radio network (CRN) is proposed in this paper. The optimal design methods of building piecewise code with low redundancy are presented. In cognitive OFDM, anti-jamming piecewise coding could recover the lost packets in parallel interference channels by implementing different number of parity check blocks, thus it could recover the lost packets and protect secondary users (SUs) from the interference by primary users (PUs). Frame error rate (FER) and throughput performance of SU employing anti-jamming piecewise coding are analyzed respectively. Performance comparison of piecewise coding and another anti-jamming rateless coding are presented simultaneously. Simulation results proved that, anti-jamming piecewise coding provides better FER performance by non-uniform sub-channel selection, and it could achieve better throughput performance with designed smaller overhead in low jamming rate situation.

Optimization of power allocation and outage probability of cooperative relay networks

In order to solve the extra power consumption caused by reducing complexity in cooperative relay networks, an optimized power allocation algorithm is proposed for the efficient incremental selection hybrid decode-amplify forward (ISHDAF) scheme. In the ISHDAF scheme, the transmission efficiency is improved by optimizing the power allocation, which is constrained by constant total power. And the outage probability is used as the objective function to optimize the whole power allocation. Then, rational allocation of the power of source and relay nodes can be obtained by the optimization of equal power allocation algorithm in the power limited wireless communication system. Simulation results show that the outage probability of a relay network is effectively reduced by the proposed scheme for the ISHDAF relay network. For an instance of a total power of 40W, there is a certain optimization of outage probability, when compared with that of the current HDAF scheme. Therefore, the proposed power allocation algorithm for the ISHDAF scheme can be effectively applied to optimize the power consumption in the relay network systems.

A sparse reconstruction algorithm with hierarchical Bayesian analysis for wideband spectrum detection

Bayesian Compressive Sensing (BCS) theory with hierarchical Bayesian analysis model is investigated in the process of wideband spectrum detection and data fusion for Cognitive Wireless Sensor Network (C-WSN). A sparse Bayesian reconstruction method is proposed, which is based on the spatial-temporal correlation structure of real non-stationary spectrum signals sensed by multiple cognitive sensor nodes. Novel wideband spectrum detection and data recovery algorithm are implemented by hierarchical Bayesian analysis model, with higher detection probability and lower reconstruction Mean-Square Errors (MSE). Numerical results confirm our theoretical derivations. It is indicated that, compared with Orthogonal Matched Pursuit (OMP) reconstruction algorithm which is based on greedy algorithm, the proposed Tree Structured Wavelet (TSW) BCS reconstruction scheme has advanced detection performance and lower MSE during data recovery process. Meanwhile, fast convergence could be realized in lower compression rate, which provides the effectiveness of our algorithm and proves that it is suitable for wideband spectrum sensing and data sparse reconstruction in large-scale Cognitive WSN.

A Primary User Emulation Attack Countermeasure Strategy and Energy-Efficiency Analysis in Cognitive Radio Networks

Due to the fact that security and energy efficiency are investigated separately in the conventional Primary User Emulation Attack (PUEA) countermeasure strategy in Cooperative Spectrum Sensing (CSS) process, the tradeoff between security and energy efficiency is discussed in this paper. CSS can improve detection performance whereas energy consumption will dramatically boost up with the increasing of cooperative users. To tackle this problem, we set CSS energy efficiency in the presence of PUEA as optimal objective, whereas secure detection performance and secure false alarm threshold as the constraint conditions. The optimal problem is resolved to achieve a trade-off between energy efficiency and security in the presence of PUEA attack. The optimal fusion threshold K and optimal cooperative user numbers can be obtained in secure CSS with energy efficiency maximization, which guarantees energy efficiency as well as secure CSS detection performance. The proposed PUEA countermeasure strategy detection performance is presented and compared with traditional Maximum Ratio Combining (MRC) fusion rule. Simulation results show that, the proposed strategy is immune to PUE interference power, and it provides high robustness to PUEA attack, which implements the trade-off between security and energy efficiency in Cognitive Radio Network (CRN) effectively.

A spectrum sensing data falsification countermeasure strategy in energy-efficient CRN

In cooperative detection, many secondary users (SUs) collaborate to sense spectrum holes, in order to enhance the reliability of spectrum sensing. However, some malicious SUs may interfere with cooperative spectrum sensing (CSS) performance by inducing false observation bits for fusion. An improved spectrum sensing data falsification (SSDF) countermeasure strategy is proposed. The strategy considers both energy-efficiency and security in cooperative detection phase. The optimal legitimate/malicious SU numbers can be determined with the objective of energy-efficiency maximization, under the constraints of message authentication code (MAC), CSS report distance and report error rate in the reporting sub-phase. In the proposed strategy, the tradeoff between security and energy-efficiency is investigated to guarantee secure CSS. Numerical results reveal that the proposed strategy outperforms a conventional SSDF defensive strategy with the same MAC security bits scenario. The improved SSDF countermeasure scheme provides significant enhancement of energy-efficiency and security performance in CRN secure CSS.

Joint iterative decoding and MMSE-SIC VBLAST detection of LDPC coded MIMO systems

A joint iterative low-density parity-check (LDPC) decoding and minimum mean square error with successive interference cancel (MMSE-SIC) vertical-Bell laboratories layered space-time (VBLAST) detection of LDPC coded multiple input multiple output (MIMO) system is proposed in an additive white Gaussian noise (AWGN) channel. It combines the LDPC decoding with VBLAST detection into a unified iterative framework by integrity and united method. It adopts the joint iterative message processing through the VBALST detector and the variable and check nodes of LDPC decoder. So it reduces the unnecessary information loss, which usually happens in separated coding and detection MIMO systems. Simulation results show that the proposed joint LDPC coded binary phase shift keying (BPSK) MIMO schemes outperforms the contrast scheme of simple concatenation about 0.3~0.5 dB at a bit-error-ratio (BER) of 10-5 in an AWGN channel. In addition, it only requires some rational coding and detection complexity, because it employs the sparse check matrices for encoding and applies joint processing for detection too. Therefore, the proposed joint LDPC decoding and MMSE-SIC VBLAST detection of an LDPC coded MIMO system can be efficiently applied in modern wireless digital communications for high performance.

Achievable bit rates of cognitive user with Vandermonde precoder in cognitive radio network

In cognitive radio network (CRN) where primary user (PU) and secondary user (SU) wish to communicate with their corresponding receivers simultaneously over frequency selective fading channels, the interference between PU and SU should be eliminated in order to realize spectrum sharing. Precoder division multiple access (PDMA) that implements Vandermonde precoder in cognitive orthogonal frequency division multiplexing (OFDM) is proposed, which benefits from the frequency selectivity of the cognitive channel to form a frequency beam-former. Vandermonde precoder enables SUs to achieve higher bit rate with optimal power allocation strategy under the condition of PU interference constraint. Numerical and simulation results are presented to prove theoretical derivations. It is shown that, achievable bit rates (ABR) of SU could be achieved with optimal power allocation scheme in CRN. Meanwhile, it is also verified that, with Vandermonde precoder to form PDMA, SU’s signal-to-noise ratio (SNR) and the target rate of PU could impact the ABR of SU significantly in CRN.