Joint adaptive combining and multiuser downlink scheduling

In this paper, we propose two different types of downlink scheduling scheme based on assembling the schemes of 1) the switch-and-examine scheduling in the network layer and 2) the joint adaptive modulation and output-threshold maximum ratio combining (OT-MRC) in the physical layer and, thus, attempt to find an efficient cross-layer access scheme to exploit the user diversity as well as the high spectral efficiency and the antenna diversity gain. We consider a multiuser environment in which each base station (BS) equipped with a single antenna attempts to communicate with each user equipped with an L-finger RAKE receiver based on switch-and-examine transmission (SET) as a user selection-scheduling scheme. We propose two different SETs, i.e., spectrally efficient SET and feedback load-efficient SET. We analyze the performance of our proposed schemes and compare them with the optimal scheduling scheme in terms of average spectral efficiency and average number of estimated paths per user to quantify the complexity. Index Terms--Adaptive modulation, cross-layer optimization, diversity techniques, downlink scheduling scheme.