Abstract
This paper considers an uplink cell-free massive multi-input multi-output (mMIMO) system with multi-antenna access points (APs) and users, assuming low-resolution analog-to-digital converter (ADC) architecture is employed at the APs. Leveraging on the additive quantization noise model (AQNM), we derive a tight approximate expression for uplink spectral efficiency (SE). This trackable finding provides us with a tool for easily quantifying the impacts of the number of antenna arrays and the number of quantization bit of low-resolution ADCs. We find 5-bit is required in a cell-free mMIMO with low-resolution ADCs to achieve the same SE as a cell-free mMIMO with full-precision ADCs. Besides, when the number of antennas of the user is small, deploying more antennas at the users can boost the sum SE. Then, to further highlight the potential of low-resolution ADCs architecture, we also investigate the tradeoff between the SE and energy efficiency (EE) with design issues surrounding the quantization bit of low-resolution ADCs and the number of antenna arrays. The resulting observations reveal that by choosing a proper quantization bit, the cell-free mMIMO with low-resolution ADCs has the capability to enjoy a better SE-EE tradeoff compared to the perfect ADCs counterpart.
Highlights
Cell-free massive multi-input multi-output antenna system has gained tremendous recent research interest for its enormous potential to significantly enhance the spectral efficiency (SE) and energy efficiency (EE) [1]
As is known to all, using low-resolution analog-to-digital converter (ADC) architecture in cell-free massive multi-input multi-output (mMIMO) can reduce the hardware cost and power consumption, but it inevitably leads to performance degradation
Motivated by the above cited observations, we consider an uplink cell-free mMIMO system with multi-antenna access points (APs) and users, assuming low-resolution ADCs architecture is employed at the APs
Summary
Cell-free massive multi-input multi-output (mMIMO) antenna system has gained tremendous recent research interest for its enormous potential to significantly enhance the spectral efficiency (SE) and energy efficiency (EE) [1]. Under the same quantization model, the authors in [12] investigated the uplink and downlink rate performance of cell-free mMIMO with low-resolution ADCs at the APs over Rician fading channels. Its unique insights suggested the channel estimation overhead may be dominated when the number of antennas of the user is large Both [15], [16] neglected the implementation of the low-resolution ADCs at the APs. As is known to all, using low-resolution ADCs architecture in cell-free mMIMO can reduce the hardware cost and power consumption, but it inevitably leads to performance degradation. Motivated by the above cited observations, we consider an uplink cell-free mMIMO system with multi-antenna APs and users, assuming low-resolution ADCs architecture is employed at the APs. In particular, the specific contributions of this paper are summarized as follows: 1) Leveraging on the AQNM, we derive a tight approximate SE expression for uplink cell-free mMIMO with matched filtering receiver.
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