Utilization and fairness in spectrum assignment for opportunistic spectrum access

The Open Spectrum approach to spectrum access can achieve near-optimal utilization by allowing devices to sense and utilize available spectrum opportunistically. However, a naive distributed spectrum assignment can lead to significant interference between devices. In this paper, we define a general framework that defines the spectrum access problem for several definitions of overall system utility. By reducing the allocation problem to a variant of the graph coloring problem, we show that the global optimization problem is NP-hard, and provide a general approximation methodology through vertex labeling. We examine both a centralized strategy, where a central server calculates an allocation assignment based on global knowledge, and a distributed approach, where devices collaborate to negotiate local channel assignments towards global optimization. Our experimental results show that our allocation algorithms can dramatically reduce interference and improve throughput (as much as 12-fold). Further simulations show that our distributed algorithms generate allocation assignments similar in quality to our centralized algorithms using global knowledge, while ∗ A part of this work has been presented at IEEE International conference on communications (ICC), May, 2005. C. Peng Department of Automation, Tsinghua University, Beijing, China e-mail: [email protected] H. Zheng ( ) · B. Y. Zhao Department of Computer Science, University of California, Santa Barbara, CA, USA e-mail: [email protected] B. Y. Zhao e-mail: [email protected] incurring substantially less computational complexity in the process.