Norman C. Beaulieu

Energy-Efficient Optimal Power Allocation for Fading Cognitive Radio Channels: Ergodic Capacity, Outage Capacity, and Minimum-Rate Capacity

Green communications is an inevitable trend for future communication network design, especially for a cognitive radio network. Power allocation strategies are of crucial importance for green cognitive radio networks. However, energy-efficient power allocation strategies in green cognitive radio networks have not been fully studied. Energy efficiency maximization problems are analyzed in delay-insensitive cognitive radio, delay-sensitive cognitive radio, and simultaneously delay-insensitive and delay-sensitive cognitive radio, where a secondary user coexists with a primary user and the channels are fading. Using fractional programming and convex optimization techniques, energy-efficient optimal power allocation strategies are proposed subject to constraints on the average interference power, along with the peak/average transmit power. It is shown that the secondary user can achieve energy efficiency gains under the average transmit power constraint, in contrast to the peak transmit power constraint. Simulation results show that the fading of the channel between the primary user transmitter and the secondary user receiver and the fading of the channel between the secondary user transmitter and the primary user receiver are favorable to the secondary user with respect to the energy efficiency maximization of the secondary user, whereas the fading of the channel between the secondary user transmitter and the secondary user receiver is unfavorable to the secondary user.

On the Performance of Three Suboptimum Detection Schemes for Binary Signaling

The penalties incurred in using the sample-and-sum, weighted partial decision, and binary Partial decision detectors are analyzed. Even though these schemes are inferior to the digital matched filter detector, they could be used in systems with more modest computational capabilities. Analytic expressions are obtained for the losses when the number of samples M is large. Examples are also given which indicate how these losses vary with M .

Optimal Detection of Hard-Limited Data Signals in Different Noise Environments

A number of digital techniques for detecting binary antipodal signals are based on examining the polarities of the received signal samples and ignoring their amplitudes. The structure of the optimum detector for the hard-limited samples is derived, and its performance is compared to those of some commonly used schemes in impulsive as well as Gaussian noise environments. The optimum receiver for M -ary signaling based on received signal samples quantized to an arbitrary number of levels is obtained and compared to other detectors.

Joint Source and Relay Beamforming Design for Full-Duplex MIMO AF Relay SWIPT Systems

A full-duplex MIMO amplify-and-forward relay network with simultaneous wireless information and power transfer is considered. Based on the minimum mean-square-error criterion, this letter formulates a joint optimization problem of source and relay beamformers under their transmit powers constraints and the users energy-harvesting constraint. Through alternating optimization, a joint beamforming design with successive convex approximation is derived, which is proved to converge. To reduce the complexity, a low-complexity channel parallelization-based design is also proposed. Numerical results for the MSE and BER show that the proposed schemes perform well for this system.

Cognitive radio networks with asynchronous spectrum sensing and access

Cognitive radio technology can significantly improve spectrum utilization efficiency by enabling SUs to access the licensed spectrum dynamically without causing excessive interference to PUs. Currently, most of the existing research on cognitive radio networks has been conducted based on an assumption that SUs can perfectly synchronize with PUs. However, when SUs are working with unknown behaviors of PUs, the synchronous assumption becomes invalid. To tackle this issue, we introduce several approaches for asynchronous spectrum sensing and asynchronous spectrum access, respectively, with which SUs can access the primary channels dynamically even without achieving synchronization with the PUs. In this article, we discuss the key techniques, corresponding solutions, and potential application scenarios of the asynchronous spectrum sensing and access schemes. Specifically, we present two asynchronous spectrum sensing schemes under non-cooperative and cooperative scenarios, respectively. Meanwhile, a distributed asynchronous spectrum access algorithm is also illustrated. Moreover, the proposed schemes are compared with existing works under the same framework, which enables readers to understand the motivation, problem formulation, methodology, and results of the asynchronous spectrum sensing and spectrum access schemes.

User Association for Energy-Load Tradeoffs in HetNets With Renewable Energy Supply

A user association algorithm is proposed for energy consumption and traffic load balancing tradeoffs among heterogeneous base stations in heterogeneous networks with renewable energy supply. The concept of topology potential is introduced to represent the attraction between base stations and users, which takes the traffic load of users and the available renewable energy of base stations into consideration for energy-load tradeoffs. Then the user association optimization problem is formulated for base station utility proportional fairness. The proposed algorithm is proved to converge to the global optimum of the formulated optimization problem. Simulation results demonstrate the effectiveness of the proposed algorithm in achieving load balancing as well as in making the best use of renewable energy harvested by base stations.

Accurate Statistical Analysis of a Single Interference in Random Networks with Uniformly Distributed Nodes

Wireless networks with a finite number of nodes uniformly distributed in a finite region are considered. A closed-form expression for the distribution of the power of a single interferer incident on a receiving node in the network is derived. The node is assumed to be placed at an arbitrary location in the network in contrast to most of the existing literature in which this node is located at the center of the region. The analysis is conducted for two packet traffic patterns, namely, slotted-synchronous and slotted-asynchronous patterns. It is observed that the distribution is independent of the location of the receiving node. Tight upper and lower bounds for the distribution of the interference power are derived.

Shared Relay Networks with Linear Receivers at the Relay: Two-Cell Case

The downlink performance of a two-cell relay enhanced wireless network is investigated. A single relay is shared by the two base stations in the system. The relay is assumed to be placed in a geographic region covered by both base stations. The relay station is operating in the decode-and-forward mode. Closed-form approximations which estimate the exact results extremely closely are derived for the outage probability and the ergodic rate of the system. The impact of finite rate channel state information feedback on the user ergodic rate is examined.

Optimum Combining for Cooperative Relaying in a Poisson Field of Interferers

Spatial point processes are commonly used to model the placement and the number of interferers in modern wireless networks, where the ad hoc deployment of transmitters is common. The homogeneous Poisson point process (PPP) is the most popular spatial point process used to model co-channel interference. Optimum combining (OC) is the diversity combining technique that maximizes the signal-to-interference-plus-noise ratio at the receiver. The performance of OC in cooperative relaying in an interferer field modeled by a homogeneous PPP is analyzed. Both decode-and-forward (DF) and amplify-and-forward (AF) relay protocols are studied. Multirelay transmission and relay selection techniques are considered. Accurate approximations for the outage probability are derived for DF and AF relaying when the destination is able to estimate the noise-plus-interference correlation matrix (NICM) perfectly. An approximation for the outage probability of DF relaying is obtained when the destination only estimates the channel state information of the closest interferer. Relay selection outperforms multirelay transmission in both DF and AF relaying protocols. The interference correlation at the relays significantly degrades the outage performance. Limited estimation of the NICM results in better performance than conventional maximal-ratio combining, although it fails to achieve diversity gains.

Optimum Combining in Dual-Hop AF Relaying for Maximum Spectral Efficiency in the Presence of Co-Channel Interference

The performance of optimum combining (OC) in amplify-and-forward (AF) relaying systems in the presence of co-channel interference (CCI) is analyzed using a tight approximation for the signal-to-interference-plus-noise ratio (SINR) at the destination. Two types of relaying protocols are studied, all-relay transmission with OC and best-relay transmission with OC. When CCI is present only at the destination, both relaying protocols achieve diversity gains up to M when interferer powers are scaled with the source and the relay powers, where M is the number of relays. Best-relay transmission with OC maximizes the spectral efficiency as each communication consumes only two time slots.