Resource Management in Cognitive/Cooperative Radio Networks: Power Control, Admission Control, and Scheduling

Abstract

Efficient resource utilization is the foremost problem in wireless networks. Resource management issues include allocating transmit power to obtain an acceptable signal quality, minimizing overall energy consumption, limiting interference due to the broadcast nature of wireless communications, and managing connections. To address these issues in cognitive/cooperative radio networks, this dissertation focuses on several techniques to minimize total power and maximize system throughput in various environments such as wireless cellular systems, cooperative relaying systems, and cognitive radio (CR) networks.

First, we provide a method for adjusting pilot power to reduce the total power consumption in DS-CDMA systems. Pilot signals need additional transmit power, while at the same time the amount of power used for each traffic channel should be decreased through the use of channel estimation. This interdependency between pilot and traffic channel powers is considered in the proposed method. The convergence and monotonicity property of the proposed method are also proved. Numerical results show convergence in the transmit power and that the proposed method achieves significant power-saving.

Second, we investigate the application of distributed power control (DPC) and opportunistic power control (OPC), respectively, in cooperative relaying systems. We begin by re-defining and extending the existing power control algorithms for a relaying environment. We then show the convergence using standard techniques and simulation. Numerical results show that DPC with relays achieves a significant improvement in both outage performance and power consumption. On the other hand, in OPC, certain negative effects in terms of capacity arise when using relays, since their use increases the amount of interference that severely affects the opportunistic capacity.

Third, we present a distributed and interactive admission and power control protocol for spectrum underlay environments in CR networks. The proposed protocol guides distributed secondary users (SUs) to achieve their own targets while restricting their power in order to avoid interrupting primary users (PUs). Each PU will finally achieve its target if the PU system is originally feasible and the transmit powers of non-removed SUs converge to a fixed point. The proposed scheme protects PUs perfectly in the sense that all of the PUs obtain their targets after power control. Numerical investigation shows how safely the PUs are protected, and how well the SUs are admitted as a function of the protocol parameters.

Finally, we present an active cooperative sensing scheme and test three scheduling algorithms in a power-controlled primary cellular uplink. For active cooperative sensing, an SU sends a probing signal to interfere with the PUs. It then estimates the amount of interference at each PU and controls the transmit power to avoid impairing the communication of the PUs through cooperation with other SUs. We then investigate a round-robin scheduling, maxmal system throughput scheduling, and a multiple SU scheduling algorithm that are suitable for use with the active cooperative sensing scheme. Numerical results are provided to evaluate the system throughput and transmission block fairness for SUs under different scheduling algorithms.