10,667 research outputs found

    Dynamic Resource Allocation in Cognitive Radio Networks: A Convex Optimization Perspective

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    This article provides an overview of the state-of-art results on communication resource allocation over space, time, and frequency for emerging cognitive radio (CR) wireless networks. Focusing on the interference-power/interference-temperature (IT) constraint approach for CRs to protect primary radio transmissions, many new and challenging problems regarding the design of CR systems are formulated, and some of the corresponding solutions are shown to be obtainable by restructuring some classic results known for traditional (non-CR) wireless networks. It is demonstrated that convex optimization plays an essential role in solving these problems, in a both rigorous and efficient way. Promising research directions on interference management for CR and other related multiuser communication systems are discussed.Comment: to appear in IEEE Signal Processing Magazine, special issue on convex optimization for signal processin

    Opportunistic Interference Mitigation Achieves Optimal Degrees-of-Freedom in Wireless Multi-cell Uplink Networks

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    We introduce an opportunistic interference mitigation (OIM) protocol, where a user scheduling strategy is utilized in KK-cell uplink networks with time-invariant channel coefficients and base stations (BSs) having MM antennas. Each BS opportunistically selects a set of users who generate the minimum interference to the other BSs. Two OIM protocols are shown according to the number SS of simultaneously transmitting users per cell: opportunistic interference nulling (OIN) and opportunistic interference alignment (OIA). Then, their performance is analyzed in terms of degrees-of-freedom (DoFs). As our main result, it is shown that KMKM DoFs are achievable under the OIN protocol with MM selected users per cell, if the total number NN of users in a cell scales at least as SNR(Kβˆ’1)M\text{SNR}^{(K-1)M}. Similarly, it turns out that the OIA scheme with SS(<M<M) selected users achieves KSKS DoFs, if NN scales faster than SNR(Kβˆ’1)S\text{SNR}^{(K-1)S}. These results indicate that there exists a trade-off between the achievable DoFs and the minimum required NN. By deriving the corresponding upper bound on the DoFs, it is shown that the OIN scheme is DoF optimal. Finally, numerical evaluation, a two-step scheduling method, and the extension to multi-carrier scenarios are shown.Comment: 18 pages, 3 figures, Submitted to IEEE Transactions on Communication
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