Guoan Bi

A Hierarchical Game Theoretic Framework for Cognitive Radio Networks

We consider OFDMA-based cognitive radio (CR) networks where multiple secondary users (SUs) compete for the available sub-bands in the spectrum of multiple primary users (PUs). We focus on maximizing the payoff of both SUs and PUs by jointly optimizing transmit powers of SUs, sub-band allocations of SUs, and the prices charged by PUs. To further improve the performance of SUs, we allow SUs who share the same sub-band to cooperate with each other to send and receive signals. To help us understand the interaction among SUs and PUs, we study the proposed network model from a game theoretic perspective. More specifically, we first formulate a coalition formation game to study the sub-band allocation problem of SUs and then integrate the coalition formation game into a Stackelberg game-based hierarchical framework. We propose a simple distributed algorithm for SUs to search for the optimal sub-bands. We prove that the transmit power and sub-band allocation of SUs and the price charged by PUs are interrelated by the pricing function of PUs. This makes the joint optimization possible. More importantly, we prove that if the pricing coefficients of PUs have a fixed linear relationship, the sub-band allocation of SUs will be stable and the Stackelberg equilibrium of the hierarchical game framework will be unique and optimal. We propose a simple distributed algorithm to achieve the Stackelberg equilibrium of the hierarchical game. Our proposed algorithm does not require SUs to know the interference temperature limit of each PU, and has low communication overheads between SUs and PUs.

Game Theoretic Analysis for Spectrum Sharing with Multi-Hop Relaying

This paper studies spatial spectrum sharing (SSS) based multi-user cognitive radio (CR) networks that allow secondary users (SU) to access the licensed spectrum as long as the interference powers of primary users (PU) to be lower than a certain threshold. Although recent results have shown that multi-hop relaying has a great potential on improving the performance of CR networks, finding effective methods to control and manage SUs to achieve the optimal performance is still a challenging problem. In this paper, we model CR networks as a non-cooperative game in which each SU obtains benefits through both spectrum sharing by paying prices to PUs and multi-hop relaying by paying price to nearby SUs. Optimal power allocation methods for SUs are investigated under different assumptions and pricing functions. The conditions under which the optimal Nash Equilibrium (NE) is obtained when all SUs use multi-hop relaying are discussed. Our results are extended into large multi-user CR networks with K source-to-destination pairs. Two distributed algorithms are proposed. The first one is a sub-gradient based power allocation algorithm in which SUs can iteratively adjust their transmit powers to approach the payoff of a NE. The other one is a Q-learning based relay selection algorithm which enables each SU to iteratively search for a NE-achieving relaying scheme.

A Simple Distributed Power Control Algorithm for Cognitive Radio Networks

This paper studies the power control problem for spectrum sharing based cognitive radio (CR) networks with multiple secondary source-to-destination (SD) pairs. A simple distributed algorithm is proposed for the secondary users (SUs) to iteratively adjust their transmit powers to improve the performance of the network. The proposed algorithm does not require each SU (or PU) to negotiate with other SUs (or PUs) during the communication. It is proved that the proposed algorithm can obtain a time average performance as good as that achieved when the Nash equilibrium (NE) is chosen in hindsight. More specifically, the average performance of CR networks will converge to an ε-Nash equilibrium at a rate of Tε = O (exp (1/ε)). A sub-optimal algorithm is also introduced to further improve the convergence rate to Tε/log Tε = O (1/ε). Numerical results are presented to show the performance of the proposed algorithms under different settings.

Distributed optimization for cognitive radio networks using Stackelberg game

This paper considers frequency-division spatial spectrum sharing (FD-SSS) based cognitive radio (CR) networks. In this network, the spectrum of primary users (PU) can be divided into a number of sub-bands each of which can only be accessed by one secondary user (SU). This setting combines both advantages of spatial spectrum sharing and temporal spectrum sharing methods. However, there are three major problems for this system: 1) how to optimally allocate the available subbands to all SUs, 2) how to distributively optimize the transmit powers for SUs to maintain the received interference power of PUs, 3) how to control the accessibility of SUs in the licensed spectrum. In this paper, we introduce a Stackelberg game based hierarchical framework to optimize the performance of FD-SSS based CR networks. More importantly, we show that, by using a simple pricing function for PUs, the above three problems can be solved simultaneously. We prove that the proposed game has a unique Stackelberg equilibrium (SE) and then introduce a simple distributed algorithm to let SUs and PUs converge to the SE. Comparing to the existing results, our setting does not require SUs to communicate with each other or to know the interference temperature of PUs.

A Survey on Protograph LDPC Codes and Their Applications

Low-density parity-check (LDPC) codes have attracted much attention over the past two decades since they can asymptotically approach the Shannon capacity in a variety of data transmission and storage scenarios. As a type of promising structured LDPC codes, the protograph LDPC codes not only inherit the advantage of conventional LDPC codes, i.e., excellent error performance, but also possess simple representations to realize fast encoding and efficient decoding. This paper provides a comprehensive survey on the state-of-the-art in protograph LDPC code design and analysis for different channel conditions, including the additive white Gaussian noise (AWGN) channels, fading channels, partial response (PR) channels, and Poisson pulse-position modulation (PPM) channels. Moreover, the applications of protograph LDPC codes to joint source-and-channel coding (JSCC) and joint channel-and-physical-layer-network coding (JCPNC) are reviewed and studied. In particular, we focus our attention on the encoding design and assume the decoder is implemented by the belief propagation (BP) algorithm. Hopefully, this survey may facilitate research in this area.

Blind multiuser detection for asynchronous MC-CDMA systems without channel estimation

This paper presents a blind adaptive decorrelating detector for asynchronous multicarrier code-division multiple-access (MC-CDMA) systems with Rayleigh-fading channels. This detector is derived by making use of the cross-correlation matrix between the consecutively received signals. The main attraction of the detection algorithm is its simplicity, since the detector can be implemented blindly without channel estimation, except for the synchronization of the desired user. To implement the proposed detector, a new adaptive subspace-tracking algorithm for any Hamiltonian matrices is developed, while the previously reported subspace-tracking methods can only estimate the subspace of a positive Hamiltonian matrix. Since a common drawback of the multiuser detector based on the subspace method is the existence of a phase factor that usually deteriorates the performance of the detector, a new method is developed to compensate for the phase of the proposed detector, based on the property of the complex white Gaussian noise. Results of extensive computer simulations show the performance improvement of the proposed detector.

Sequence Design for Cognitive CDMA Communications under Arbitrary Spectrum Hole Constraint

To support interference-free quasi-synchronous code-division multiple-access (QS-CDMA) communication with low spectral density profile in a cognitive radio (CR) network, it is desirable to design a set of CDMA spreading sequences with zero-correlation zone (ZCZ) property. However, traditional ZCZ sequences (which assume the availability of the entire spectral band) cannot be used because their orthogonality will be destroyed by the spectrum hole constraint in a CR channel. To date, analytical construction of ZCZ CR sequences remains open. Taking advantage of the Kronecker sequence property, a novel family of sequences (called quasi-ZCZ CR sequences) which displays zero cross-correlation and near-zero auto-correlation zone property under arbitrary spectrum hole constraint is presented in this paper. Furthermore, a novel algorithm is proposed to jointly optimize the peak-to-average power ratio (PAPR) and the periodic auto-correlations of the proposed quasi-ZCZ CR sequences. Simulations show that they give rise to single-user bit-error-rate performance in CR-CDMA systems which outperform traditional non-contiguous multicarrier CDMA and transform domain communication systems; they also lead to CR-CDMA systems which are more resilient than non-contiguous OFDM systems to spectrum sensing mismatch, due to the wideband spreading.

Design and Analysis of Root-Protograph LDPC Codes for Non-Ergodic Block-Fading Channels

We investigate the performance of the protograph low-density parity-check (LDPC) codes over Nakagami block-fading (BF) channels with multiple receive antennas. Using the modified protograph extrinsic information transfer (PEXIT) algorithm, we observe that the existing protograph LDPC codes, which have been shown to possess excellent error performance over additive white Gaussian noise channels, cannot perform well over non-ergodic BF channels. To address this problem, a simple design scheme is proposed to construct three new root-protograph (RP) LDPC codes, i.e., the regular RP code, the improved RP1 (IRP1) code, and the IRP2 code. The convergence analysis, error-performance analysis, and simulated results show that the three proposed RP codes outperform the existing protograph LDPC codes and regular quasi-cyclic LDPC code. Furthermore, the IRP1 code and the IRP2 code are superior to the regular RP code and the regular root-LDPC code and exhibit outage-limit-approaching error performance. Consequently, these two proposed IRP codes appear to be better alternatives as compared to other error-correction codes for slowly-varying wireless communication systems.

Performance of antenna diversity reception with correlated Rayleigh fading signals

This paper studies the performance of antenna diversity reception with selection combining (SC) and maximal ratio combining (MRC) in a correlated Rayleigh fading environment. Simple PDF expressions are derived for the output SNR of the SC and MRC diversity receivers. Based on the PDF, the average BERs for DPSK and NCFSK modulation are calculated to show the effects of the correlation. Moreover, the relationship between the average BER and the diversity antennas separation is given. The presented numerical results show that SC and MRC diversity reception can achieve a good performance only if the distance between two diversity antennas is larger than 0.3/spl lambda/.

Rate-Compatible Root-Protograph LDPC Codes for Quasi-Static Fading Relay Channels

We investigate the protograph low-density parity-check (LDPC) codes over quasi-static fading (QSF) relay channels with coded cooperation (CC) in this paper. A new construction method is proposed for designing the full-diversity rate-compatible root-protograph (RCRP) codes for such a relaying protocol. The asymptotic word error rate (WER) and bit error rate (BER) of the RCRP codes are analyzed by exploiting a new protograph extrinsic information transfer (PEXIT) algorithm. Furthermore, the expression of outage probability is also developed to characterize the error performance of RCRP codes. Both theoretical and simulated results suggest that the RCRP codes not only outperform the conventional regular rate-compatible protograph (RCP) codes in terms of error performance with code rates ranging from 0 to 1/2 but approach the outage limit as well.