Abstract
We study the scenario in which a large number of machine-type communication devices (MTCDs) communicate with each other by utilizing the help of the base station (BS) through some MTCD gateways. We consider an overlay mode of an orthogonal frequency division multiple access (OFDMA) based cellular system using orthogonal beamforming to provide broadband wireless access for the MTCD gateways. In order to avoid the interference with mobile users, the beamforming vectors to the MTCD gateways have to be orthogonal to the channel vectors of mobile users, which become a beamforming constraint for the MTCD gateways. However, with limited feedback of channel state information (CSI) at a BS, the orthogonal beamforming constraints may not be achieved. In such a practical case, conventional feedback schemes are feasible but not efficient due to the orthogonality constraints. In this paper, we propose a novel multiple beam selection (MBS) approach with limited feedback for MTCD gateways by taking into account the previous orthogonality constraints. Simulation results show that the performance improvement of the proposed approach over the conventional ones is generally about 10% when a BS is equipped with an array of 6 elements.
Highlights
Machine-to-machine (M2M) communication networks have been proposed to connect machines without the intervention from human beings
In an M2M network, there are lots of machine-type communication devices (MTCDs). These MTCDs access a cellular network by some MTCD gateways [3], which are assumed as secondary users in the cellular network
In the last subsection, the effect of limited feedback of signal-tointerference-plus-noise ratio (SINR) is shown with different number of users in Group II
Summary
Machine-to-machine (M2M) communication networks have been proposed to connect machines without the intervention from human beings. As for the overlay mode based on the orthogonal beamforming that we consider in this paper, the conventional feedback strategies are no longer suitable; using conventional feedback schemes, the BS acquires an approximation of each users’ channel directions the resulting beamforming vectors designed according to this approximation will not be best aligned with the MTCD gateways’ channel direction. We propose a new multiple beam selection (MBS) strategy with limited feedback of CSI. This paper addresses joint beamforming, scheduling, and feedback for broadband wireless access to provide high throughput for MTCD gateways. The design of beamforming vectors and limited feedback from each user are closely connected due to the orthogonal constraint for MTCD gateways. We denote the probability of an event X by Pr(X). log and log represent the natural logarithm and binary logarithm, respectively
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