• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.7
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• pp.1777-1791
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• 2012

This paper considers a downlink cognitive radio (CR) network where one secondary user (SU) and one primary user (PU) share the same base station (BS). The spectrum of interest is divided into a set of independent, orthogonal subchannels. The communication of the PU is of high priority and the quality of service (QoS) is guaranteed by the minimum rate constraint. On the other hand, the communication of the SU is of low priority and the SU opportunistically accesses the subchannels that were previously discarded by the PU during power allocation. The BS assigns fractions ?? and 1 ?? of the total available transmit power to the PU and the SU respectively. Two power allocation schemes with opportunistic subchannel access are proposed, in which the optimal values of ??'s are also obtained. The objective of one scheme is to maximize the rate of the SU, and the objective of the other scheme is to maximize the sum rate of the SU and the PU, both under the PU minimum rate constraint and the total transmit power constraint. Extensive simulation results are obtained to verify the effectiveness of the proposed schemes.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.4 no.2
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• pp.37-43
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• 2005

A simple scheduler satisfying the proportional fairness (PF) was introduced in wireless access networks and revealed that it can achieve a good compromise between total throughput and user fairness. Though it has received much attention for some time, its application was mainly restricted to the single channel systems. In this paper, we study how to implement the PF scheduler in the multi-channel environments such as OFDMA/TDMA. Besides the traditional PF-SC scheme, we propose a new PF-OPT scheme that is the genuine PF scheduler in a sense of maximizing the total log-utility of users. The simulation results show that PF-OPT gives large throughput under the heterogeneous subchannel statistics.