Guanding Yu

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.

Joint Mode Selection and Resource Allocation for Device-to-Device Communications

Device-to-device (D2D) communications have been recently proposed as an effective way to increase both spectrum and energy efficiency for future cellular systems. In this paper, joint mode selection, channel assignment, and power control in D2D communications are addressed. We aim at maximizing the overall system throughput while guaranteeing the signal-to-noise-and-interference ratio of both D2D and cellular links. Three communication modes are considered for D2D users: cellular mode, dedicated mode, and reuse mode. The optimization problem could be decomposed into two subproblems: power control and joint mode selection and channel assignment. The joint mode selection and channel assignment problem is NP-hard, whose optimal solution can be found by the branch-and-bound method, but is very complicated. Therefore, we develop low-complexity algorithms according to the network load. Through comparing different algorithms under different network loads, proximity gain, hop gain, and reuse gain could be demonstrated in D2D communications.

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

Cognitive radio enhanced interference coordination for femtocell networks

Adopting small cells, including femtocells, is a promising evolution of future wireless cellular systems to meet the explosive demand for high data rates. As the number of distributively deployed femtocell access points increases rapidly, interference coordination becomes the primary challenge in such heterogeneous networks. In this article, we apply several cognitive radio inspired approaches to enhance the interference coordination for femtocell networks. First, we apply spectrum sensing and statistical analysis to estimate the cross-tier interference between macrocells and femtocells. Based on this, interference coordination is investigated considering two kinds of spectrum sharing approaches. Finally, we introduce a cognitive relay scheme to improve interference coordination performance further.

On the Performance of IEEE 802.16 OFDMA System Under Different Frequency Reuse and Subcarrier Permutation Patterns

In interference-limited wireless cellular systems, interference avoidance and interference averaging are widely adopted to combat co-channel interference. In different types of wireless networks, these two basic frequency planning methods are implemented under variable system deployment strategies. With respect to the IEEE 802.16 OFDMA network, interference avoidance is usually carried out by carefully designing the frequency reuse patterns, while interference averaging is implemented by distributed subcarrier permutation, which can be further divided into multiple operation modes. In this paper, based on the system level simulation of the average signal to interference-plus-noise ratio (SINR) in the 802.16 system, the performance metrics of system throughput and outage probability are estimated. According to the predetermined evaluation criterions, the system performances under variable combination patterns of frequency reuse and subcarrier permutation are evaluated. Finally, the optimal frequency planning strategies, in terms of the frequency reuse pattern and the subcarrier permutation mode, is obtained, which can serve as a reference in practical network deployments.

Pricing-Based Interference Coordination for D2D Communications in Cellular Networks

A pricing-based joint spectrum and power allocation framework is proposed for decentralized interference coordination among device-to-device (D2D) communications and cellular users (CUs), with the quality-of-service guarantee. The interlayer interference from D2D pairs to CUs is controlled by the base station through setting a price for each D2D channel usage. The intralayer interference among D2D pairs is mitigated distributively using a game-theoretic approach, where the D2D pairs compete for the spectrum until a Nash equilibrium is achieved. The effectiveness of the proposed strategy, including a practical scheme with limited signaling overhead, is demonstrated through comparing with a centralized scheme.

Uplink channel reusing selection optimization for Device-to-Device communication underlaying cellular networks

Device-to-Device (D2D) communication as an underlaying cellular network empowers rich multimedia application, improves local communication, and enables local services, which would also bring out interference between cellular users and D2D terminals. In this paper, we study the challenges of the interference management in a hybrid network that D2D communication reuses uplink resource of cellular networks. We first introduce an interference coordination strategy for D2D communication. Then we design an optimal channel reusing selection algorithm for single cell scenario which is based on Hungarian algorithm. We also propose a heuristic algorithm to reduce the computational complexity. Our simulation results show that the heuristic algorithm has a close performance as the optimal algorithm with a significant decreasing of computational complexity, and both of the proposed algorithms could improve the system performance.

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

Joint Spectrum and Power Allocation for D2D Communications Underlaying Cellular Networks

This paper addresses the joint spectrum sharing and power allocation problem for device-to-device (D2D) communications underlaying a cellular network (CN). In the context of orthogonal frequency-division multiple-access systems, with the uplink resources shared with D2D links, both centralized and decentralized methods are proposed. Assuming global channel state information (CSI), the resource allocation problem is first formulated as a nonconvex optimization problem, which is solved using convex approximation techniques. We prove that the approximation method converges to a suboptimal solution and is often very close to the global optimal solution. On the other hand, by exploiting the decentralized network structure with only local CSI at each node, the Stackelberg game model is then adopted to devise a distributed resource allocation scheme. In this game-theoretic model, the base station (BS), which is modeled as the leader, coordinates the interference from the D2D transmission to the cellular users (CUs) by pricing the interference. Subsequently, the D2D pairs, as followers, compete for the spectrum in a noncooperative fashion. Sufficient conditions for the existence of the Nash equilibrium (NE) and the uniqueness of the solution are presented, and an iterative algorithm is proposed to solve the problem. In addition, the signaling overhead is compared between the centralized and decentralized schemes. Finally, numerical results are presented to verify the proposed schemes. It is shown that the distributed scheme is effective for the resource allocation and could protect the CUs with limited signaling overhead.