Abstract
This paper investigates two resource allocation problems in cognitive relaying networks where both secondary network and primary network coexist in the same frequency band and adopt orthogonal frequency division multiplexing (OFDM) technology. The first one is the sum rate maximization problem of a secondary network under total power budget of a secondary network and tolerable interference constraint of a primary network. The second one is the sum rate maximization problem of a secondary network under separate power budgets of a secondary network and tolerable interference constraint of a primary network. These two optimization problems are completely different from those in traditional cooperative communication due to interference management constraint condition. A joint optimization algorithm is proposed, where power allocation and subcarrier pairing are decomposed into two subproblems with reasonable cost. The first one is a closed form solution of power allocation of the secondary network while managing the interference to a primary network under a constraint condition. The other is optimal subcarrier pairing at given power allocation. Simulation results reveal aspects of average signal to noise ratio (SNR), interference level, relay position, and power ratio on the sum rate of a secondary network.
Highlights
Cognitive radio technology can effectively alleviate the tension of spectrum resources and improve spectrum utilization because it allows secondary users to opportunistically access and simultaneously share spectrum resources by spectrum hole technology
A bit error rate constraint was incorporated in [12] in orthogonal frequency division multiplexing (OFDM) based cooperative cognitive radio networks, where the secondary user adapted its constellation size according to the distance to primary user
This paper considers cognitive amplify and forward (AF) relay networks operating in OFDM
Summary
Cognitive radio technology can effectively alleviate the tension of spectrum resources and improve spectrum utilization because it allows secondary users to opportunistically access and simultaneously share spectrum resources by spectrum hole technology. In [8], the optimal power allocation, subcarrier pairing, and relay selection matrix were found in OFDM cognitive two-way relay networks with imperfect spectrum sensing. A similar sum rate maximization problem of secondary users was considered in [9] in OFDM based two-way cognitive relaying networks, where a per subcarrier interference constraint was introduced to protect the primary users. A bit error rate constraint was incorporated in [12] in OFDM based cooperative cognitive radio networks, where the secondary user adapted its constellation size according to the distance to primary user. We design a joint optimization algorithm in the cognitive relaying networks, where the secondary user can switch between direct link and relaying link depending on the channel conditions while maintaining an acceptable interference size at the primary user. The subcarrier pairing is found when the power has been solved at the first step
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