The potential approaches to achieve channel reciprocity in FDD system with frequency correction algorithms

Abstract

Channel reciprocity is an inherit feature of time division duplex (TDD) system, which is widely used to get uplink (UL)/downlink (DL) channel knowledge from DLIUL channel measurements without additional feedback. While in frequency division duplex (FDD) system, the transmitter usually obtains the DL channel state information (CSI) through a variety of feedback strategies in order to enhance the system performance. However, the impacts of feedback overhead and delay on Multiple-Input-Multiple-Output (MIMO) performance can't be ignored. The paper focuses on the potential approaches to realize FDD channel reciprocity so as to reduce the feedback channel overhead. Compared with TDD system, UL and DL are allocated by different frequencies in FDD system thus the frequency correction is needed to achieve channel reciprocity. The paper presents the performance analysis and comparison of typical frequency correction algorithms, especially the algorithms based on the long-term statistical channel characteristics, which mainly include the channel covariance matrix, the channel space-time correlation, and the direction of arrival (DoA). The potential application scenario for each approach is presented as conclusion.

Uplink-Downlink Channel Covariance Transformations and Precoding Design for FDD Massive MIMO

“…We use the reciprocity of the ASF in UL and DL to estimate the DL covariance matrix from the observation of noisy channel vectors freely available through the UL pilots. The ASF reciprocity was also assumed implicitly in several past works [9][10][11] by considering only ASFs with spike discrete components. Recent works [12][13][14] generalize these results to arbitrary ASFs consisting of both discrete spike and also continuous components, and show that such Uplink-Downlink covariance transformation (UDCT) is still feasible for sufficiently large number of BS antennas M although establishing the stability of UDCT is quite challenging when only a noisy estimate of the UL covariance matrix is available.…”

Design, Simulation & Concept Verification of 4 × 4, 8 × 8 MIMO With ZF, MMSE and BF Detection Schemes

“…To observe the anticipated signal from the objective transmit aerial at the reception end, all the interference signals are nullified or minimized by inverting the effect of the channel by multiplying a suitable weight matrix , such that [17]:…”

Adaptive SU/MU-MIMO Scheduling for LTE-A Downlink Cellular Networks

“…A closed-form relationship is further derived in [7], where the estimation accuracy of MU-MIMO CQI is determined by the selection of an IUI factor. In [10] and the references therein, the frequency correction algorithms have been used to achieve channel reciprocity in FDD systems. In this paper, we will use the statistics CSI to estimate the MU-SINR, and further evaluate the performance of our proposed scheduling methods.…”