On the Diversity-Multiplexing Tradeoff of Unconstrained Multiple-Access Channels
Yair Yona, Meir Feder · IEEE Transactions on Information Theory · 2015
In this paper, the optimal diversity-multiplexing tradeoff (DMT) is investigated for the multiple-input multiple-output fading multiple-access channel with no power constraints (infinite constellations). For K users (K > 1), M transmit antennas for each user, and N receive antennas, infinite constellations in general and lattices in particular are shown to attain the optimal DMT of finite constellations for N ≥ (K + 1)M - 1, i.e., user limited regime. On the other hand, for Nmax [1, (N - M + 1)/M], considering the shaping region in the decoding process plays a crucial role in pursuing the optimal DMT. By investigating the cases in which the infinite constellations are optimal and suboptimal, this paper also gives a geometrical interpretation to the DMT of infinite constellations in multiple-access channels.