[Paper Review] Low Complexity Full Duplex MIMO: Novel Analog Cancellation Architectures and Transceiver Design

George C. Alexandropoulos, Melissa Duarte|arXiv (Cornell University)|Sep 22, 2018

Full-Duplex Wireless Communications24 references3 citations

TL;DR

This paper proposes two low-complexity analog self-interference cancellation architectures for full-duplex MIMO systems: one using a reduced number of analog taps and another using auxiliary (AUX) transmitters, both integrated with MUX/DEMUX for efficient signal routing. The key contribution is a joint optimization framework that designs analog cancellers and digital beamformers together, achieving up to 60 dB and 35 dB analog cancellation, respectively, with significantly reduced hardware complexity compared to conventional approaches.

ABSTRACT

Incorporating full duplex operation in Multiple Input Multiple Output (MIMO) systems provides the potential of boosting throughput performance. However, the hardware complexity of the analog self-interference canceller in emerging full duplex MIMO designs mostly scales with the number of transmit and receive antennas, thus exploiting the benefits of analog cancellation becomes impractical for full duplex MIMO transceivers, even for moderate number of antennas. In this paper, we present two novel architectures for the analog canceller comprising of reduced number of cancellation elements, compared to the state of the art, and simple multiplexers for efficient signal routing among the transmit and receive radio frequency chains. One architecture is based on analog taps (tap refers to a line of fixed delay, variable phase shifter, and attenuator) and the other on AUXiliary (AUX) Transmitters (TXs) that locally generate the cancellation signal. In contrast to the available analog cancellation architectures, the values for each tap or each AUX TX and the configuration of the multiplexers are jointly designed with the digital transmit and receive beamforming filters according to certain performance objectives. Focusing on a narrowband flat fading channel model as an example, we present a general optimization framework for the joint design of analog self-interference cancellation and digital beamforming. We also detail the sum rate optimization objective together with its derived solution for the latter architectural components. Representative computer simulation results demonstrate the superiority both in terms of hardware complexity and achievable performance of the proposed low complexity full duplex MIMO schemes over the lately available ones.

Motivation & Objective

• To address the high hardware complexity of analog self-interference (SI) cancellation in full-duplex MIMO systems, which scales with the number of transmit and receive antennas.
• To reduce the number of cancellation elements (taps or AUX TXs) required for effective SI mitigation in MIMO full-duplex transceivers.
• To develop a joint design framework that co-optimizes analog canceller parameters and digital beamforming filters for improved spectral efficiency.
• To enable practical deployment of full-duplex MIMO by minimizing hardware cost and complexity while maintaining high performance.

Proposed method

• Introduces a novel tap-based analog canceller architecture with a reduced number of taps, independent of the number of TX and RX antennas, using MUX/DEMUX for signal routing.
• Proposes an AUX TX-based canceller architecture where the number of auxiliary transmitters is minimized and not proportional to the number of antennas.
• Develops a general optimization framework that jointly designs analog canceller parameters (tap gains or AUX TX coefficients) and digital beamforming filters under a narrowband flat fading channel model.
• Uses a sum rate maximization objective function with derived closed-form solutions for beamforming and canceller parameters, enabling efficient computation.
• Models hardware impairments such as phase and amplitude errors in taps (±0.065° phase, ±0.01 dB amplitude) and phase noise in AUX TX chains (0.717° jitter) to reflect real-world limitations.
• Employs a noisy version of the ideal cancellation matrix, $\widehat{\mathbf{C}}_k$, incorporating random errors from taps or phase noise mismatches in AUX TXs.

Experimental results

Research questions

• RQ1 Can analog self-interference cancellation in full-duplex MIMO be achieved with significantly fewer hardware elements than the state-of-the-art, which scales with the number of antennas?
• RQ2 How can the joint design of analog cancellers and digital beamformers improve spectral efficiency while reducing hardware complexity?
• RQ3 What is the achievable analog cancellation performance (in dB) when using realistic hardware impairments such as phase and amplitude errors in taps or phase noise in AUX TXs?
• RQ4 How does the proposed architecture maintain high performance under non-ideal hardware conditions compared to conventional designs?

Key findings

• The proposed tap-based architecture achieves approximately 60 dB of analog self-interference cancellation per tap, even with hardware impairments of ±0.065° phase and ±0.01 dB amplitude error.
• The AUX TX-based architecture achieves approximately 35 dB of analog cancellation per auxiliary transmitter, under realistic phase noise conditions with 0.717° jitter.
• The number of required taps or AUX TXs can be chosen offline based on cost, size, or performance constraints, enabling flexible system design.
• Simulation results demonstrate superior performance in both spectral efficiency and hardware complexity compared to existing full-duplex MIMO schemes.
• The joint optimization framework successfully balances analog cancellation and digital beamforming, avoiding the need to sacrifice spatial degrees of freedom for SI mitigation.
• The use of MUX/DEMUX enables efficient signal routing in both architectures, reducing the need for complex interconnections and further lowering hardware cost.