Daoxing Guo

A Robust Cooperative Spectrum Sensing-Assisted Multiuser Resource Allocation Scheme

Cognitive radio (CR), which is proposed as a solution for spectrum scarcity, imposes some threats to the network. One severe attack to cognitive radio network is the primary user emulation attack (PUEA), in which an attacker may transmit its signal with high power or mimic specific features of the primary user’s signal to prevent secondary users from accessing the licensed spectrum. In this paper, we study a subcarrier and power allocation problem for orthogonal frequency division multiple access-(OFDMA-) based CR systems in the presence of PUEA. To maximize the system throughput while keeping the interference introduced to the primary user (PU) below given thresholds with a certain probability, a joint design of a robust cooperative spectrum sensing and a resource allocation scheme is proposed. In the proposed scheme, the inaccurate classification of PU signals and PUEA signals provided by robust cooperative spectrum sensing is utilized by resource scheduling module. To further exploit the underutilized spectrum bands, we also evaluate the performance of the proposed scheme in the hybrid overlay/underlay spectrum access mechanism. Numerical results demonstrate the effectiveness of the proposed scheme compared to conventional scheme regardless of the number of SUs or the kind of spectrum access mechanism being used.

Blind recognition of BCH code based on Galois field fourier transform

Blind recognition of error correcting code over GF (2) have been studied intensively in past few years, however, few works have been involved the case of non-binary codes. In order to approach the problem, a novel method for blind recognition of Reed-Solomon (RS) codes is proposed in this paper, which is based on Galois Field Fourier Transform of code polynomial. Moreover, theoretical analysis of the proposed method is given, which allows us to obtain an optimum decision threshold (ODT) with the rule of minimum error probability. Simulation results show the efficiency of the proposed method.

The performance analysis of LDPC coded SFH/BPSK anti-jamming system

In order to improve the anti-jamming ability of frequency hopping (FH) system, a low-density parity-check (LDPC) coded SFH/BPSK anti-jamming communication system is established in this paper, and the simulations of the antijamming performance are carried out. Firstly, the system model which is used in simulations is established. Then, the antijamming ability against partial band jamming (PBJ) with different jamming factors is simulated and compared using different coding parameters. At the end, the superiority of the combination of LDPC codes and FH systems is proved, the effect of code rate and code length on the proposed system model is measured, and some numerical results of the anti-jamming performance are obtained, which can be used as guidance by determining applicable coding parameters for adaptive antijamming LDPC coded FH systems.

An accurate estimation algorithm of frequency and phase at low signal-noise ratio levels

A new accurate estimation algorithm of frequency and phase suited for low signal-noise ratio (SNR) environment is proposed here. Coarse estimation of frequency and phase is acquired from the peak frequency of the received signal. New interpolation technique and modified formula are made to get fine and unbiased estimation. Simulations indicate that, accurate results close to the Cramer-Rao bound (CRB) within a wide frequency offset range are achieved by using this algorithm.

A BICM-MD-ID scheme in FFH system for combatting partial-band interference

An iterative decoding scheme with diversity is proposed for LDPC coded FFH/MFSK system under partial-band interference. The performance gain is obtained by soft-information exchange between demodulator and decoder. Extrinsic information transfer (EXIT) chart is employed to study the iterative procedure, which indicates that the convergence speed of the system is fast. The simulation results show the presented scheme outperforms traditional FFH/BFSK system, and the gain increases as the jamming probability increases. In addition, a moderate modulation order should be chose carefully in practical system.

Joint Optimization of Repeater Gain Setting and Power Allocation in Satellite Communication Systems

The power allocation optimization algorithm can improve the efficiency of resource utilization, which is of great significance to the power restrained satellite communication systems. This paper taking both performance analysis of the end-to-end link and influence of repeater gain on power allocation into consideration, and a repeater gain settings based resource allocation model is built. On the basis of analyzing the above model, an algorithm of joint optimization of repeater gain setting and power allocation is proposed. After dual decomposition algorithm searching the optimal solution of power allocation with certain repeater gain, the proposed algorithm searches the optimal repeater gain by applying the steepest descent method. Simulation results show that global optimization solution of system capacity is obtained with detailed results of power allocation and repeater gain.

Design and Analysis of Efficient Algorithm for Counting and Enumerating Cycles in LDPC Codes

Since short cycles and trapping sets are culprits of performance and error floor of low-density parity-check (LDPC) codes, it is necessary to obtain information about the number and the distribution of all cycles in Tanner graphs. However, the established algorithms could not efficiently search all cycles on account of restrictions from both the structure and the girth of Tanner graphs. The proposed algorithm solve the above problems with message-passing schedule, counting and enumerating the cycles simultaneously. With information derived from the proposed algorithm, performance will be enhanced and error floor will be lower, which is meaningful for both adjustment and design of LDPC codes. Furthermore, the proposed algorithm can be applied on general bipartite graphs.

Increasing physical layer security through reliability-based HARQ

In this paper, we proposed a secure communication scheme based on Reliability-Based Hybrid Automatic Repeat reQuest (RB-HARQ) protocol over the additive white Gaussian noise (AWGN) wiretap channel. RB-HARQ protocol aims at retransmitting the unreliable bits required for the authorized users (Bob) successfully decoding and minimizing the information leakage that may benefit to eavesdropper (Eve). The secrecy level in this paper is assessed through the bit error rate (BER) at both the authorized user (Bob) and eavesdropper (Eve). Therefore, we analyze the BER of our proposed scheme through theoretical arguments and simulations. Numerical results suggest that RB-HARQ protocol can significantly enhance the security performance of our communication system.

Secure Communication Based on a Modified RB-HARQ Protocol

This paper presents a secure communication scheme based on a modified Reliability-Based Hybrid Automatic Repeat reQuest (RB-HARQ) protocol over the additive white Gaussian noise (AWGN) wiretap channel. RB-HARQ protocol is firstly implemented in the secure communication system and showed a significant enhancement of the physical layer security. The retransmission encoding scheme is the main difference between traditional RB-HARQ and modified RB-HARQ, which can encode the unreliable bits of the authorized user (Bob) and retransmit the encoded unreliable bits through the AWGN wiretap channel. With the retransmission encoding scheme, the maximum retransmission number of RB-HARQ protocol can be largely reduced and secure communication can still be ensured, which is much more practical in long distance communication system. Bit error rate (BER) at both the authorized user (Bob) and eavesdropper (Eve) is used to assess the secrecy performance in this paper. So we calculate the BER of our proposed scheme through theoretical analysis and simulations. The results suggest that the modified RB-HARQ protocol can strongly enhance the reliability and security of our system, with the maximum retransmission number at a low level.

A byzantine attack defender for censoring-enabled cognitive radio networks

This paper considers the problem of cooperative spectrum sensing (CSS) in the censoring-enabled Cognitive Radio Networks (CRNs) with a crowd of battery-powered Secondary Users (SUs), where only significant local observations are submitted to the Fusion Center (FC). However, in order to monopolize the spectrum usage or disrupt the networks operation, malicious SUs may try to send falsified sensing reports to the FC even they are uncertain about their observations, which make the existing robust CSS schemes ineffective. To tackle these challenges, we formulate an optimization problem to improve the performance of CSS in the censoring-enabled CRNs, and develop an expectation maximization based algorithm to solve it, where the presences of primary user and the reliabilities of each SU can be jointly estimated. Extensive simulation results show that the proposed robust CSS scheme outperforms the previous reputation-based approaches under various attack scenarios.