In this paper, a cognitive machine-to-machine(M2M) communication network is considered, in which a cellularnetwork shares the spectrum with the M2M communicationnetwork with M machine-type devices (MTDs), one half-duplexrelay, and one MTD gateway for data gathering. One keychallenge is that in the future 5G wireless networks, there willbe billions of those small MTDs, and therefore, a MTD selectionprotocol is required for managing data transmission betweenMTDs. A joint buffer-aided MTD selection and power allocationprotocol is proposed to maximize the MTDs’ sum-rate providedthat the induced interference to the cellular network is limited.In particular, in the proposed scheme, at each time slot andeach subcarrier, the cognitive M2M network optimally decideson whether to be silent or to select either the relay or one of theMTDs for data transmission. To this end, for each MTD, thereexists a buffer at the relay to avoid data loss. The closed-formexpressions for the power coefficients of MTDs are calculated.Simulation results show that the proposed policy improves thesum-rate of the CM2M network in comparison with the otherproposed schemes for M2M communication without buffer
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