Power allocation, bit loading and sub-carrier bandwidth sizing for OFDM-based cognitive radio
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RESEARCH
Open Access
Power allocation, bit loading and sub-carrier bandwidth sizing for OFDM-based cognitive radio Vinay Thumar1*, Taskeen Nadkar1, Tej Gopavajhula1, Uday B Desai2 and Shabbir N Merchant1
Abstract The function of the Radio Resource Management module of a Cognitive Radio (CR) system is to evaluate the available resources and assign them to meet the Quality of Service (QoS) objectives of the Secondary User (SU), within some constraints on factors which limit the performance of the Primary User (PU). While interference mitigation to the PU spectral band from the SU’s transmission has received a lot of attention in recent literature; the novelty of our work is in considering a more realistic and effective approach of dividing the PU into sub-bands, and ensuring that the interference to each of them is below a specified threshold. With this objective, and within a power budget, we execute the tasks of power allocation, bit loading and sizing the sub-carrier bandwidth for an orthogonal frequency division multiplexing (OFDM)-based SU. After extensively analyzing the solution form of the optimization problems posed for the resource allocation, we suggest iterative algorithms to meet the aforementioned objectives. The algorithm for sub-carrier bandwidth sizing is novel, and not previously presented in literature. A multiple SU scenario is also considered, which entails assigning sub-carriers to the users, besides the resource allocation. Simulation results are provided, for both single and multi-user cases, which indicate the effectiveness of the proposed algorithms in a CR environment. Keywords: cognitive radio, OFDM, interference mitigation, power allocation, bit loading, sub-carrier bandwidth sizing
I. Introduction A new paradigm, called Cognitive Radio (CR), has emerged in the field of wireless communication, to alleviate the imbalance between spectrum allocation and its use [1,2]. CR entails the temporary usage of unused portions of the spectrum (spectrum holes or white spaces), owned by the licensed users (Primary Users–PUs), to be accessed by unlicensed users (Secondary Users–SUs). Built on the platform of software-defined radio (SDR), a CR node is rendered reconfigurable: the SDR allows the operating parameters such as frequency range, modulation type or output power to be reconfigured in software, without making any alteration in the hardware [2]. It is anticipated that the Next-Generation (xG) communication networks will be based on CR [2]. These networks will provide high bandwidth to mobile users via heterogenous wireless architectures and dynamic spectrum access techniques. Besides the tasks of spectrum * Correspondence: [email protected] 1 Indian Institute of Technology, Bombay, 400076, India Full list of author information is available at the end of the article
sensing, spectrum allocation, spectrum sharing and spectrum mobility, one of the key functions of CR nodes in spectrum-aware xG networks is spectrum utilization. The spectrum utilization function entails efficient Radio Re
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