Abstract
In this paper, we consider an underlay cognitive radio network where the spectrum is shared with the primary network. Due to the coexistence of primary and secondary networks, primary users (PUs) are interfered with by the inter-network interference, at the same time secondary users (SUs) counteract the intra-network (inter-user) interference. Based on the cooperative feedback between the primary network and the secondary network, the secondary transmitter (ST) applies the cognitive beamforming to suppress the interference to PUs while improving the sum rate of SUs. We herein propose an adaptive feedback bits allocation among multiple PUs and SUs where the quantized channel direction information (CDI) for the interference channel is forwarded to the ST in order to utilize the beamforming. Moreover, based on the cognitive beamforming, we adjust the transmit power of the ST under the constraint of the average interference at PUs. To jointly solve the feedback bits allocation and the transmit power control problems, we formulate an optimization problem which requires a little iterations compared with the separated feedback bits allocation and the transmit power control problems. Numerical results show that the proposed scheme significantly improves the sum rate of SUs while satisfying the average interference constraint at PUs.
Highlights
Cognitive radio (CR) has been extensively studied to overcome the spectrum scarcity problem by allowing the secondary users (SUs) to access the spectrum assigned for a primary network [1]
To jointly solve the feedback bits allocation and the transmit power control problems, we formulate an optimization problem which requires a little iterations compared with the separated feedback bits allocation and the transmit power control problems
We proposed a joint feedback bits allocation and transmit power control scheme when the total number of feedback bits is limited for CR networks
Summary
Cognitive radio (CR) has been extensively studied to overcome the spectrum scarcity problem by allowing the secondary users (SUs) to access the spectrum assigned for a primary network [1]. Considering that total feedback resource is limited in CR networks; it is desired to adaptively adjust the amount of the feedback bits for PUs and SUs. when the cognitive beamforming is adopted, the transmit power of the ST should be adjusted according to both the interference constraint and the allocated feedback bits for PUs. In previous studies of [7,12,15], the relationship between the transmit power and feedback bits has been investigated under the predetermined interference threshold, but a joint feedback bits allocation and transmit power control scheme has not been proposed. Based on the problem of allocating total feedback bits among PUs and SUs, we formulate an optimization problem to maximize the sum rate of SUs while satisfying the average inter-network interference constraint at PUs. We derive the upper bound of the transmit power of the ST when the amount of feedback bits for PUs is given.
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