[Paper Review] LuMaMi28: Real-Time Millimeter-Wave Massive MIMO Systems with Antenna Selection

MinKeun Chung, Liang Liu+12 more|arXiv (Cornell University)|Sep 7, 2021

Millimeter-Wave Propagation and Modeling4 citations

TL;DR

This paper presents LuMaMi28, a real-time 28 GHz massive MIMO testbed with a 16-chain fully-digital base station and user equipment (UE) equipped with beam-switchable antennas for real-time antenna selection. The system demonstrates that UE-side antenna selection yields up to 3.32× median throughput gain with MRC processing, particularly benefiting high-gain patch antennas in mobile scenarios.

ABSTRACT

This paper presents LuMaMi28, a real-time 28 GHz massive multiple-input multiple-output (MIMO) testbed. In this testbed, the base station has 16 transceiver chains with a fully-digital beamforming architecture (with different pre-coding algorithms) and simultaneously supports multiple user equipments (UEs) with spatial multiplexing. The UEs are equipped with a beam-switchable antenna array for real-time antenna selection where the one with the highest channel magnitude, out of four pre-defined beams, is selected. For the beam-switchable antenna array, we consider two kinds of UE antennas, with different beam-width and different peak-gain. Based on this testbed, we provide measurement results for millimeter-wave (mmWave) massive MIMO performance in different real-life scenarios with static and mobile UEs. We explore the potential benefit of the mmWave massive MIMO systems with antenna selection based on measured channel data, and discuss the performance results through real-time measurements.

Motivation & Objective

• To develop a flexible, real-time mmWave massive MIMO testbed for evaluating practical system performance under real-life propagation conditions.
• To investigate the impact of user equipment (UE) beam-steering and antenna selection on mmWave system performance in static and mobile environments.
• To compare the performance gains of different UE antenna types—yagi (wide beamwidth, lower gain) and patch (narrow beamwidth, higher gain)—under varying beamforming and precoding schemes.
• To evaluate the effectiveness of antenna selection in reducing path loss and improving throughput in mobility scenarios with realistic hardware impairments.

Proposed method

• The base station employs a fully-digital beamforming architecture with 16 transceiver chains and supports spatial multiplexing for multiple UEs.
• User equipment (UE) units are equipped with beam-switchable antenna arrays that select the beam with the highest channel magnitude from four predefined beams in real time.
• Two types of UE antennas are evaluated: a yagi array with wider beamwidth and lower peak gain, and a patch array with narrower beamwidth and higher gain.
• Real-time measurements are conducted in three scenarios: static (rotation), horizontal mobility, vertical mobility, and circular mobility, using both MRC and ZF precoding at the base station.
• Channel state information is collected in real time, and throughput performance is evaluated via cumulative distribution functions (CDFs) of uplink data rates.
• Hardware impairments such as phase noise and power amplifier nonlinearities are considered in the testbed design, reflecting real-world mmWave system constraints.

Experimental results

Research questions

• RQ1 How does real-time UE antenna selection impact uplink throughput in mmWave massive MIMO systems under static and mobile conditions?
• RQ2 What is the performance difference between yagi and patch array antennas in terms of beam selection gain and throughput improvement?
• RQ3 How do MRC and ZF precoding schemes affect the effectiveness of antenna selection in mmWave systems?
• RQ4 To what extent does mobility degrade system performance, and can antenna selection mitigate this degradation?
• RQ5 What is the achievable throughput gain from antenna selection in noise-limited versus interference-limited scenarios?

Key findings

• The achievable beam selection gain is 10.0 dB for the yagi array and 12.8 dB for the patch array antenna in the 3–11 m distance range between base station and UE.
• In mobility environments, antenna selection increases median uplink throughput by 3.32× for the yagi-equipped UE and 1.97× for the patch-equipped UE when using MRC precoding.
• With ZF precoding, both UEs achieve similar throughput gains from antenna selection (1.13× and 1.15× for yagi and patch, respectively), indicating minimal benefit from selection in interference-limited scenarios.
• The patch antenna UE achieves 4× higher median throughput than the yagi UE when no antenna selection is used, highlighting the advantage of high-gain, narrow-beam antennas.
• In the vertical mobility route, antenna selection improves the lowest throughput by 1.63× (yagi) and 1.83× (patch) under ZF, indicating benefit in noise-limited conditions.
• Peak throughput differences between antenna selection and no selection are most pronounced for the patch antenna (6.4 vs. 4.43 Mbit/s), suggesting beamwidth and gain trade-offs matter in close-range, line-of-sight scenarios.