Channel State Feedback Schemes for Multiuser MIMO-OFDM Downlink

TL;DR

This paper compares different channel state feedback schemes for MIMO-OFDM downlink, introducing a novel time-domain quantization method that leverages frequency correlation and outperforms existing schemes.

Contribution

The paper proposes a new time-domain channel quantization scheme based on rate-distortion theory, exploiting frequency correlation in MIMO-OFDM systems, and demonstrates its superior performance and simplicity.

Findings

Time-domain quantization outperforms other feedback schemes.

No complex codebook design needed for efficient feedback.

The new scheme achieves full multiplexing gain under certain conditions.

Abstract

Channel state feedback schemes for the MIMO broadcast downlink have been widely studied in the frequency-flat case. This work focuses on the more relevant frequency selective case, where some important new aspects emerge. We consider a MIMO-OFDM broadcast channel and compare achievable ergodic rates under three channel state feedback schemes: analog feedback, direction quantized feedback and "time-domain" channel quantized feedback. The first two schemes are direct extensions of previously proposed schemes. The third scheme is novel, and it is directly inspired by rate-distortion theory of Gaussian correlated sources. For each scheme we derive the conditions under which the system achieves full multiplexing gain. The key difference with respect to the widely treated frequency-flat case is that in MIMO-OFDM the frequency-domain channel transfer function is a Gaussian correlated source. The new time-domain quantization scheme takes advantage of the channel frequency correlation structure and outperforms the other schemes. Furthermore, it is by far simpler to implement than complicated spherical vector quantization. In particular, we observe that no structured codebook design and vector quantization is actually needed for efficient channel state information feedback.