Estimation and Mitigation of Channel Non-Reciprocity in Massive MIMO

Abstract

Time-division duplex (TDD) based massive MIMO systems rely on the reciprocity of the wireless propagation channels when calculating the downlink precoders based on uplink pilots. However, the effective uplink and downlink channels incorporating the analog radio front-ends of the base station (BS) and user equipments (UEs) exhibit non-reciprocity due to non-identical behavior of the individual transmit and receive chains. When downlink precoder is not aware of such channel non-reciprocity (NRC), system performance can be significantly degraded due to NRC induced interference terms. In this work, we consider a general TDD-based massive MIMO system where frequency-response mismatches at both the BS and UEs, as well as the mutual coupling mismatch at the BS large-array system all coexist and induce channel NRC. Based on the NRC-impaired signal models, we first propose a novel iterative estimation method for acquiring both the BS and UE side NRC matrices and then also propose a novel NRC-aware downlink precoder design which utilizes the obtained estimates. Furthermore, an efficient pilot signaling scheme between the BS and UEs is introduced in order to facilitate executing the proposed estimation method and the NRC-aware precoding technique in practical systems. Comprehensive numerical results indicate substantially improved spectral efficiency performance when the proposed NRC estimation and NRC-aware precoding methods are adopted, compared to the existing state-of-the-art methods.

Modeling and estimation of massive MIMO channel non-reciprocity: Sparsity-aided approach

“…In this approach, as described in [12] in more details, the BS first transmits an N × N orthonormal pilot matrix called P which yields…”

“…In this respect, we present a novel method to estimate the BS transceiver non-reciprocity matrix building on simple pilot-signaling from [12] and the resulting sparsity of the corresponding signal model.…”

Mean‐based reciprocity calibration in TDD massive MIMO system

“…Proof: See Appendix 2. □ The observed PDF from (17) shows the infinite variance and its mean is not directly tractable. If we confine the range of mismatch coefficients then the finite mean can be easily calculated using the numerical technique.…”

“…Let Z 1 and Z 2 are two statistically independent RVs having PDFs f Z 1 (z 1 ) and f Z 2 (z 2 ), where f Z 1 (z 1 ) = 2z 1 b 0 2 /(z 1 2 + b 0 2 ) 2 and Putting u = z 2 2 and solving through integration by parts, we calculate this definite integral and obtain (17).…”

Relaying Systems With Reciprocity Mismatch: Impact Analysis and Calibration

“…To further relieve the impact of the reciprocity mismatch at the UE side, O. Raeesi et al proposed an calibration approach incorporating a dedicated round-trip pilot signaling with feasible pilot overhead for the acquisition of calibration coefficients at the BS [26].…”