AG Kommunikationstheorie


Resource Allocation in OFDM-based Cognitive Radio Systems


This thesis is concerned with the development and assessment of margin adaptive resource allocation algorithms for OFDM-based transmission systems. Besides the rate constraint, an additional interference constraint is introduced ensuring the undisturbed operation of legacy transmission systems within the OFDM spectrum. Thus a model for the interference within the OFDM spectrum based on the superposition of normalized sinc2-functions is created and applied to conventional resource allocation algorithms. For the single user case, an adapted version of the waterfilling algorithm is derived using convex optimization techniques. The discrete case is covered by introducing an additional step to the Levin- Campello algorithm to reduce power on subcarriers causing excess interference. For the multiuser case, the Lagrangian Dual is examined to derive a method to assign subcarriers and allocate power based on the dual method framework by Wong. Especially, as the determination of optimal parameters for the multiuser scenarios cannot be guaranteed by the adapted algorithms, additional metrics to measure the degree of the rate and interference constraint violation are introduced.

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