ABSTRACT
Contents 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3.2 Model and Problem Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.2.1 Case Study: CR Users Employing OFDMA . . . . . . . . . . . . . . . . . . 63 3.3 Power Control for a Single Secondary Transmitter-Receiver Pair . . . 65 3.4 Power Control for Multiple Secondary Users . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.4.1 Centralized Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.4.1.1 Joint Power Control and Admission Control . . . . . . . . 70
3.4.2 Distributed Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 3.4.3 Case Study: Power Control with Best Subband Selection
for CR Users Employing OFDMA. . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.4.3.1 Best Subcarrier Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.4.3.2 Nonoverlapping Subcarrier Selection . . . . . . . . . . . . . . . . 74 3.4.3.3 Overlapping Subcarrier Selection . . . . . . . . . . . . . . . . . . . . 75
3.5 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.5.1 Baseline Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.5.2 CR Network with OFDMA Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.6 Discussions and Open Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Several recentmeasurement reports show that the assigned spectrum from0 to 3GHz are highly underutilized. To achieve much better spectrum utilization and viable frequency planning, cognitive radios (CRs) are under development to dynamically capture the unoccupied spectrum. Although Federal Communication Commission (FCC) proposes spectrum sharing between a legacy TV system and a CR network to increase spectrum utilization, one of the major concerns is that the interference from the CR network should not violate the quality-of-service (QoS) requirements of the primary users. Specifically, can secondary users (CR network) even operate without causing excessive interference to primary users (TV users)? Furthermore, can certain QoS for secondary users be provided under such constraints? So far, most of the previous works address these two issues by time sharing the spectrum between the TV system and the CR network.
