Uplink Spectral and Energy Efficiency of Cell-Free Massive MIMO with Optimal Uniform Quantization

Manijeh Bashar*, Hien Quoc Ngo, Kanapathippillai Cumanan, Alister G. Burr, Pei Xiao, Emil Bjornson, Erik G. Larsson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


This paper investigates the performance of limited-fronthaul cell-free massive multiple-input multiple-output (MIMO) taking account the fronthaul quantization and imperfect channel acquisition. Three cases are studied, which we refer to as EstimateQuantize, QuantizeEstimate, and Decentralized, according to where channel estimation is performed and exploited. Maximum-ratio combining (MRC), zero-forcing (ZF), and minimum mean-square error (MMSE) receivers are considered. The Max algorithm and the Bussgang decomposition are exploited to model optimum uniform quantization. Exploiting the optimal step size of the quantizer, analytical expressions for spectral and energy efficiencies are presented. Finally, an access point (AP) assignment algorithm is proposed to improve the performance of the decentralized scheme. Numerical results investigate the performance gap between limited fronthaul and perfect fronthaul cases, and demonstrate that exploiting relatively few quantization bits, the performance of limited-fronthaul cell-free massive MIMO closely approaches the perfect-fronthaul performance.

Original languageEnglish
Article number9212395
Pages (from-to)223-245
Number of pages23
JournalIEEE Transactions on Communications
Issue number1
Early online date5 Oct 2020
Publication statusPublished - 1 Jan 2021

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  • Bussgang decomposition
  • C-RAN
  • cell-free massive MIMO
  • energy efficiency
  • optimal uniform quantization
  • quantization

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