On the Achievable Diversity-Multiplexing Tradeoff in MIMO Fading Channels with Imperfect CSIT

TL;DR

This paper investigates the fundamental diversity-multiplexing tradeoff in MIMO fading channels with imperfect CSIT, showing that even imperfect channel knowledge can significantly enhance diversity gains and alter the tradeoff structure.

Contribution

It provides a detailed analysis of how imperfect CSIT affects the DMT in MIMO channels, deriving new formulas for diversity gain based on CSIT quality.

Findings

Imperfect CSIT can improve diversity gain at high multiplexing levels.

Derived explicit DMT expressions depending on CSIT quality lpha.

Different DMT regimes are identified based on lpha and antenna configurations.

Abstract

In this paper, we analyze the fundamental tradeoff of diversity and multiplexing in multi-input multi-output (MIMO) channels with imperfect channel state information at the transmitter (CSIT). We show that with imperfect CSIT, a higher diversity gain as well as a more efficient diversity-multiplexing tradeoff (DMT) can be achieved. In the case of multi-input single-output (MISO)/single-input multi-output (SIMO) channels with K transmit/receive antennas, one can achieve a diversity gain of d(r)=K(1-r+K\alpha) at spatial multiplexing gain r, where \alpha is the CSIT quality defined in this paper. For general MIMO channels with M (M>1) transmit and N (N>1) receive antennas, we show that depending on the value of \alpha, different DMT can be derived and the value of \alpha has a great impact on the achievable diversity, especially at high multiplexing gains. Specifically, when \alpha is above a certain threshold, one can achieve a diversity gain of d(r)=MN(1+MN\alpha)-(M+N-1)r; otherwise, the achievable DMT is much lower and can be described as a collection of discontinuous line segments depending on M, N, r and \alpha. Our analysis reveals that imperfect CSIT significantly improves the achievable diversity gain while enjoying high spatial multiplexing gains.