Zhi Yan

Exact Outage Performance of Cognitive Relay Networks with Maximum Transmit Power Limits

In this letter, considering a cognitive relay network with the maximum transmit power limit in a spectrum sharing scenario, the exact outage probability of secondary system is derived over Rayleigh fading channels, and the theoretical analysis is validated by simulations. The results show that both the maximum transmit power limit and the interference power constraint cause the outage saturation phenomenon, and more relays for secondary system can provide better outage performance.

Outage Performance Study of Cognitive Relay Networks with Imperfect Channel Knowledge

This letter presents the outage performance analysis for a cognitive relay network (CRN) with imperfect channel knowledge estimations. Under the condition of imperfect channel state information (CSI) estimations of interference links between primary and secondary systems, especially the links from both secondary transmitter and secondary relays to primary users, the exact outage probability is derived over Rayleigh fading channels and is verified through simulations. The simulation results show that: 1) increasing the number of relays is an effective approach to mitigate the outage performance degradation caused by the imperfect CSI; 2) the imperfect CSI of the secondary transmitter-primary user (PU) link has a greater impact on the outage performance than that of the secondary relay-PU link.

On the Study of Outage Performance for Cognitive Relay Networks (CRN) with the Nth Best-Relay Selection in Rayleigh-fading Channels

Relay selection is an effective way to achieve considerable performance gains in cognitive relay networks (CRN). In practice, the best relay may not always be selected, thus the study of the small Nth best relay selection will be very beneficial for CRN design. In this paper, performance analysis for underlay cognitive decode-and-forward relay networks with the small Nth best-relay selection scheme is studied over independent and identically distributed (i.i.d.) Rayleigh fading channels. Closed-form expression for the exact outage probability is derived, which can be used to evaluate the impact of the relay selection scheme, the number of relays, the interference power constraint and the transmit power limit on the outage performance. The theoretical analysis is validated by Monte-Carlo simulations. The results show that both the relay selection scheme and the number of relays have great impact on the outage performance of cognitive relay networks.

Performance Analysis of Cognitive Relay Networks Over Nakagami-

In this paper, we present performance analysis for underlay cognitive decode-and-forward relay networks with the Nth best relay selection scheme over Nakagami-m fading channels. Both the maximum tolerated interference power constraint and the maximum transmit power limit are considered. Specifically, exact and asymptotic closed-form expressions are derived for the outage probability of the secondary system with the Nth best relay selection scheme. The selection probability of the Nth best relay under limited feedback is discussed. In addition, we also obtain the closed-form expression for the ergodic capacity of the secondary system with a single relay. These expressions facilitate in effectively evaluating the network performance in key operation parameters and in optimizing system parameters. The theoretical derivations are extensively validated through Monte Carlo simulations. Both theoretical and simulation results show that the fading severity of the secondary transmission links has more impact on the outage performance and the capacity than that of the interference links does. Through asymptotic analysis, we show that the diversity order for the Nth best relay selection scheme is min(m1, m3) × (M - N) + m3, where M denotes the number of cognitive relays, and m1 and m3 represent the fading severity parameters of the first-hop transmission link and the second-hop transmission link, respectively.

m

Recently, heterogeneous networks (HetNet) have been widely studied as an effective approach to provide high network capacity and coverage, which jointly utilizes the technologies of cognitive radio and cooperative communications. However, the dense and random deployment of small-cells (e.g., micro, pico and femtocells) raises important questions about the energy consumption for HetNets. In this paper, we study the optimal energy efficiency of a two-tier heterogeneous network consists of a macro-cell and many small-cells under coverage performance constraints for different spectrum deployments (including orthogonal and co-channel spectrum deployments). Firstly, we derive the closed-form expressions of coverage performance for each tier based on stochastic geometry. Then the relationship between energy efficiency and the density of small-cells for the two-tier network is evaluated, the optimal density of small-cells that maximize energy efficiency under coverage performance constraints for the two-tier network is obtained. The theoretical analysis is validated by simulations.The results show that the energy efficiency of the two-tier networks with orthogonal spectrum deployment is better than that with co-channel spectrum deployment. The results also show that the optimal density of small-cells for maximal energy efficiency is only dependent on the coverage performance of small-cells in orthogonal spectrum deployment scenario. However, in co-channel spectrum deployment scenario, the optimal density of small-cells for maximal energy efficiency is jointly decided by the coverage performance of both macro-cell and small-cell. This work provides an essential understanding for successful deployment of green heterogeneous networks.

Fading Channels

Mobile big data contains vast statistical features in various dimensions, including spatial, temporal, and the underlying social domain. Understanding and exploiting the features of mobile data from a social network perspective will be extremely beneficial to wireless networks, from planning, operation, and maintenance to optimization and marketing.

Energy-Efficiency Study for Two-tier Heterogeneous Networks (HetNet) Under Coverage Performance Constraints

In this paper, considering a relay assisted hybrid overlay/underlay cognitive radio system with peak interference power constraints for protecting the primary system, the upper bound of outage probability of secondary system with power limit is derived. The results show that the outage performance of secondary system improves with the increase of maximum tolerated interference power before a specific threshold, but it keeps unchanged after the threshold. The results also show that more relays can provide higher diversity gain to get better outage performance in this kind of cognitive radio system. It is also indicated that the outage performance of secondary system is affected by the activity behavior of primary network, and relay cooperation can decrease this kind of affection.

Social Computing for Mobile Big Data

Considering the effect of imperfect channel state information (CSI), we study the performance of a cluster-based cognitive multihop wireless sensor network with decode-and-forward (DF) partial relay selection over Nakagami-m fading channels. The closed-form expressions for the exact outage probability and bit error rate (BER) of the secondary system are derived and validated by simulations. Asymptotic outage analysis in high SNR regime reveals that the diversity order is determined by the minimum fading severity parameter of all the secondary transmission links, irrespective of the CSI imperfection. It is shown that the fading severity of the secondary transmission links has more influence on the outage performance than that of the interference links. We also conclude that, for secondary nodes whose transmit power is restricted by the interference constraint of the primary user, increasing the number of relaying hops is an effective way to improve their transmission performance. Besides, increasing the number of available relays in each relay cluster can mitigate the performance degradation caused by CSI imperfection.

Outage performance of relay assisted hybrid overlay/underlay cognitive radio systems

In order to fully utilize the scarce spectrum resources and improve the efficiency of wireless spectrum resource utilization, dynamic spectrum access is proposed as a solution. There are two kinds of dynamic spectrum access system, one is overlay dynamic spectrum, and the other is dynamic spectrum access under interference temperature constraints. In this paper, we use a three-dimensional Markov chain to model the dynamic spectrum access under interference temperature constraints, and analyze the performance of secondary users in the system. Two important parameters, i.e., secondary user interrupting probability and blocking probability are derived using the proposed model. The performance of secondary users in different dynamic spectrum access systems are analyzed and compared. The numerical results show that the performance of secondary users can be improved significantly in dynamic spectrum access under interference temperature constraints comparing to overlay dynamic spectrum access. Specially, the advantage of interference temperature constraints based dynamic spectrum access is more notable on the condition that there are not enough resources to provide to secondary users for access.

Cognitive Multihop Wireless Sensor Networks over Nakagami-m Fading Channels

Cognitive network and cooperative communications are two promising techniques for efficient utilization of scarce radio resources and guaranteeing quality of services (QoS) in wireless heterogeneous networks (HetNet). This paper presents an architecture for the integration of cognitive networks and cooperative communications in wireless HetNet. Based on the proposed architecture several techniques related to the integration of cognition and cooperation are evaluated in typical cases and scenarios, for example, cognitive relay network, cognition in two-tier HetNet, geolocation-based cognition, cognitive and cooperative gateway, etc. Simulations and analysis are performed which has shown that the combination of cognition and cooperation can significantly improve the system performance.