Peiliang Qiu

On cognitive radio networks with opportunistic power control strategies in fading channels

In this paper, we consider a cognitive radio system in fading wireless channels and propose an opportunistic power control strategy for the cognitive users, which serves as an alternative way to protect the primary users transmission and to realize spectrum sharing between the primary user and the cognitive users. The key feature of the proposed strategy is that, via opportunistically adapting its transmit power, the cognitive user can maximize its achievable transmission rate without degrading the outage probability of the primary user. If compared with the existing cognitive protocols, which usually try to keep the instantaneous rate of the primary user unchanged, our strategy relieves the cognitive users from the burden of detecting and relaying the message of the primary user and relaxes the system synchronization requirements. The achievable rate of a cognitive user under the proposed power control strategy is analyzed and simulated, taking into account the impact of imperfect channel estimation. A modified power control strategy is also proposed to reduce the sensitivity of our strategy to the estimation errors. Its effectiveness is verified by the simulations.

Cooperative ARQ in Wireless Networks: Protocols Description and Performance Analysis

Cooperative transmission is an efficient technique to realize diversity gain in wireless fading channels via a distributed way. In this paper, we consider a wireless network composed of a source, a relay and a destination terminal. We exploit the limited feedback from the destination and propose three different cooperative ARQ protocols, which combine the incremental relaying and selection relaying protocols. An analysis model to analyze and compare the data link layer packet error rate (PER) of different ARQ protocols in slow fading wireless channel is established. Furthermore, the spatial diversity performances of the various protocols are investigated and it is demonstrated that full spatial diversity (second-order in this case) can be achieved by the three proposed protocols. Simulation results are given, which verify the performance analysis. The tradeoff between performance and implementation complexity of the three protocols is also discussed.

Power-Aware Cooperative Relay Selection Strategies in Wireless Ad Hoc Networks

Cooperative diversity is an effective technique to combat multipath fading. When this technique is applied to ad hoc networks, it is a key issue to design distributed and power-efficient relay selection strategies. In this paper, we propose the power-aware relay selection (PARS) strategies to maximize the network lifetime. The PARS strategies are composed of the optimal power allocation(OPA) and three power-aware selection criteria. The OPA aims at minimizing the overall transmit power, while the three criteria select the relay that best help extend the network lifetime, based on both the OPA results and the residual power levels of the nodes. We combine our strategies with the opportunistic relay model, which is based on a 802.11b-like media access control (MRC) protocol, so the selection process can be done in a totally distributed way. Simulation results show that the proposed strategies have great improvement in both network lifetime and power efficiency

On the achievable rate region of gaussian cognitive multiple access channel

We consider the communication scenario where multiple cognitive users wish to communicate to the same receiver through AWGN channels, in the presence of primary transmission. The cognitive users are assumed to have the side information about the primary transmission. The achievable rate region of cognitive users is formulated under the constraint that the rate of primary transmission is not changed as if no cognitive users existed. Moreover, the maximum achievable sum-rate point of the rate region is characterized

Efficient ARQ protocols for exploiting cooperative relaying in wireless sensor networks

Cooperative relaying is an efficient technique to provide diversity in wireless sensor networks. In this paper, we exploit the limited feedback from the destination and propose a novel cooperative ARQ protocol, which combines the incremental relaying and selection relaying schemes. A relay node is requested to repeat the erroneously received packet, instead of the source node. Both simple and hybrid type I ARQ schemes are studied. An analysis model is established to analyze and compare the data link layer performances of different ARQ protocols in slow fading wireless channel. We prove two SNR thresholds of the relay-destination channel, above which the cooperative ARQ protocols have better performances than the traditional counterparts. In addition, the diversity performances of the various protocols are investigated and it is demonstrated that full order diversity (second-order in this case) can be exploited by the proposed cooperative ARQ protocol. Simulation results are given, which verify the theoretical analysis and comparison.

A Novel Resource Allocation Algorithm for Real-time Services in Multiuser OFDM Systems

The resource allocation algorithm to minimize the overall required transmit power while satisfying the QoS requirements of real-time services in OFDMA systems is discussed in this paper. We develop the concept of marginal utility for each subcarrier, which corresponds to the maximal power reduction when the very subcarrier is allocated to a user. We also propose a low computational complexity algorithm to calculate the marginal utility. Based on this, a novel subcarrier and bit allocation algorithm is presented. In order to achieve the minimization of overall required power, the subcarrier with the largest marginal utility is assigned to its corresponding user at each subcarrier allocation iteration. Part of the bits required by the user are then redistributed to the newly assigned subcarrier by the proposed marginal utility calculation algorithm. Simulation results show that the proposed algorithm can achieve a better performance than Zhangs algorithm at approximately the same computational complexity

Subcarrier and bit allocation for OFDMA systems with proportional fairness

A novel subcarrier and bit allocation algorithm for multiuser OFDM system is presented in this paper. The algorithm aims to achieve a maximum transmit rate subject to the overall transmit power constraint and user rate proportionality constraint. The algorithm consists of two steps. In the subcarrier allocation step, the power is assumed to be uniformly allocated on each subcarrier and the subcarriers are allocated to users under the proportional rate constraint. Then, at each bit assignment iteration of the bit allocation step, the algorithm assigns one bit to the user with the least normalized transmit rate and the user greedily allocates the bit and corresponding power to the subcarrier which requires the least additional power to carry one more bit. The computational complexity of the proposed algorithm is analyzed, as well as the fairness performance. Simulation results show that the algorithm can achieve a better performance than the existing algorithms

Optimal Partner Selection Strategies in Wireless Cooperative Networks with Fixed and Variable Transmit Power

Cooperative communication has emerged as a promising technique to enhance system reliability and performances in resource-limited wireless networks. Before any kind of cooperation ever starts, nodes in the network have to find someone to cooperate with and the helping node is so called partner. This paper concerns about the partner selection problem in centralized networks, where an AP assigns partner for each node and schedules all the transmission. Three optimal partner selection strategies with different aims are proposed and analyzed under fixed and variable transmit power respectively. They are the maximum total utility (MTU) strategy, the maximum minimum utility (MMU) strategy and the maximum product utility (MPU) strategy. Simulation results show that with variable transmit power, both system-level efficiency and node-level fairness can be greatly improved, and the three strategies successfully achieve their goals respectively.

A Cross-Layer Fair Resource Allocation Algorithm for OFDMA Systems

The rate adaptive resource optimization problem in OFDMA systems is addressed. A novel cross-layer subcarrier and bit allocation algorithm is proposed, which aims to maximize the system throughput with the overall transmit power constraint and user rate proportionality constraint. Different from existing non-cross-layer methods, the algorithm makes allocation policy based on not only channel condition but also queue status of each user. The algorithm consists of two steps. Firstly, subcarriers are assigned to users under the proportional rate constraint and queue length constraint, assuming that the power is uniformly allocated on each subcarrier. In the second step, the overall power is allocated via a proposed proportional greedy algorithm, with the consideration of buffer state information as well, which can increase the power usage efficiency in some cases. Simulation results show that the proposed cross-layer algorithm achieves a better performance than existing non-cross-layer algorithms

Resource Allocation in OFDM based Multihop Wireless Networks

OFDM modulation and multihop transmission are two important techniques for future wireless networks. This paper discusses the adaptive subcarrier and power allocation in OFDM based multihop networks. Both OFDM-TDMA and OFDM-FDMA access methods are considered. For OFDM-TDMA based multihop networks, a power allocation algorithm is proposed to maximize the end-to-end capacity for the constraint of the overall transmit power of all hops. For OFDM-FDMA based multihop networks, a joint subcarrier and power allocation algorithm is proposed. The performances of the proposed algorithms are evaluated, in both symmetric case (each hop has same average channel gain) and asymmetric case (the hops have different average channel gain). The results show that the OFDM-FDMA access method achieves a higher end-to-end capacity than the OFDM-TDMA access method, and the proposed adaptive resource allocation algorithms perform better than the fixed resource allocation strategy, in both cases