Best Paper Award 2015

Best Paper Award

Weighted-Combining Calibration on Multiuser MIMO Systems with Implicit Feedback

Hayato FUKUZONO，Tomoki MURAKAMI，Riichi KUDO，Yasushi TAKATORI，
Masato MIZOGUCHI

[Trans. Commun., Apr. 2015]

Hayato FUKUZONO

Tomoki MURAKAMI

Riichi KUDO

Yasushi TAKATORI

Masato MIZOGUCHI

  Multiuser multiple-input multiple-output (MIMO) systems in wireless communications improve throughput, on which a base station with multiple antennas performs downlink transmission to multiple users with a shared time and frequency resource. While multiuser MIMO systems need to acquire channel state information (CSI), explicit feedback, that feeds downlink CSI estimated at users back to the base station, degrades transmission efficiency. Implicit feedback reduces the overhead remarkably by exploiting uplink CSI for downlink transmit beamforming, relying on channel reciprocity on time division duplexing. For implicit feedback, it is necessary to employ schemes that calibrate uplink CSI for transmission and to receive highly accurate circuitry responses.
  This paper proposes weighted-combining calibration (WCC), a highly accurate calibration scheme for uplink CSI. In WCC, the base station calculates multiple calibration coefficients, and then combines the coefficients with minimum mean square error (MMSE) weights. This paper shows that the mean square error (MSE) of calibration coefficients is analytically derived, and that WCC offers a diversity effect that improves calibration accuracy. Indoor experiments are performed on a multiuser-orthogonal frequency division multiplexing (OFDM) system, built using measurement hardware. Experimental results verify that the channel reciprocity can be exploited on the developed multiuser MIMO-OFDM system and that WCC is effective in indoor environments.
  Because this paper reveals the superiority of the proposed scheme, WCC, from theoretical analyses and radio experiments, it has received high acclaim and richly deserves this award. In massive MIMO systems in which base stations are equipped with a large number of antennas, implicit feedback becomes more advantageous. because the higher number of antennas makes the overhead associated with CSI acquisition larger.This paper is expected to pave the way for future MIMO systems.