| The rapid growth of wireless communication technology and various wireless communication applications result in the huge demand on wireless spectrum resource. Cognitive radio (CR) as an intelligent wireless communication technology can improve spectrum efficiency via using the sensing mechanism to detect the idle spectrum and making the unauthorized users access the idle spectrum.Orthogonal frequency division multiplexing (OFDM) technologies with real-time channel status information can dynamic allocate resource and adjust subcarrier. The advantages of OFDM technology include high spectrum efficiency, high anti-interference ability and high transmission rate. The combination of cognitive radio technology and OFDM technology can give play to the advantages of them. Therefore, it has received more and more extensive attentions and researches.Recently, traditional schemes on CR have already achieved great research results, and reached high transmission rate with perfect channel state information. However, in practical CR systems, imperfect channel state information, time-delay and other interference uncertainties can lower the performance of cognitive users. Thus, the effect of these uncertainties should be considered.Besides, due to serious environmental problem and the slow development of battery technology, green communication has received more and more extensive attentions. Instead of considering on transmission rate in traditional schemes, green communication focus on how to prolong usage cycle of communication spots and enhance awareness of energy conservation. It can not only guarantee the basic requirement on communication quality but also improve performance on energy efficiency.In this paper, the robust energy efficiency maximization in OFDM-based CR networks with multiuser scenario is proposed. Considering bounded uncertainties, interference temperature constraint is transferred into equivalent convex set. Convex optimization method is used to obtain quasi-concave mathematic property and realize energy efficiency maximization viafractional programming technique and convex optimization. Simulation results show that the proposed worst-case robust scheme can strictly guarantee quality of service requirement of PUs with bigger uncertain parameter. And due to lower allocated transmit power and resulted noise plus interference to PUs, energy efficiency performance of the worst-case robust scheme is better than that of the non-robust scheme with increasing uncertain parameter, the sum number of SUs and interference. |
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