Interleaver-Linked Receiver Beamforming with Transmitter Channel Equalization in TDD-IDMA-Based Random Access

Abstract

This paper proposes a novel interleaver-linked receiver beamforming method for time division duplex (TDD)-interleave division multiple access (IDMA)-based random access. When the number of receiver antennas at the base station is large in a massive multiple-input multiple-output (MIMO) scenario, the channel estimation accuracy per receiver antenna at the base station receiver is degraded due to the limited received signal power per antenna from the user terminal. This results in degradation in the receiver beamforming (BF) or antenna diversity combining and user detection. In the proposed method, a unique receiver BF vector applied at the base station is linked to each of the M interleavers prepared by the system. The user terminal selects an appropriate pair comprising a receiver BF vector and an interleaver in advance based on the channel estimation results in the downlink assuming channel reciprocity in a TDD system. Therefore, the per-receiver antenna channel estimation for receiver BF is not necessary in the proposed method. Furthermore, we also propose an application of a transmitter channel equalization to the proposed method for effective channel shortening in order to increase the orthogonal preambles for channel estimation prepared for each interleaver. Computer simulations results show that the proposed method greatly improves the accuracy of user detection and channel estimation which results in reducing the error rate compared to the conventional method that performs channel estimation at each antenna in a massive MIMO environment.