Local PAPR-Aware Precoding for Energy-Efficient Cell-Free Massive MIMO-OFDM Systems

Abstract

Orthogonal frequency division multiplexing (OFDM) based Cell-free massive multiple-input multiple-output (CF-mMIMO) is the most promising combination that can provide uniformly better quality of service for users than cellular technology in sub-6GHz bands. To make OFDM based CF-mMIMO more cost-effective and more powerefficient, the access points (APs) should be implemented by using low-cost and low-quality transceiver hardware.However, transmitting OFDM signals with high peak-to-average power ratio (PAPR) via such hardware causes severe hardware impairments (HWI), damaging the system performance. Moreover, the PAPR reduction in CF-mMIMO-OFDM has never been studied in the open literature. In this paper, we present a smart and original PAPR reduction technique, referred to as localPAPRfree adequate for cell-free architecture. Interestingly, the proposed technique can be implemented in a distributed and scalable fashion, achieving benefits of CF-mMIMO-OFDM. Specifically, the PAPR reduction scheme is formulated as a simple convex optimization problem solved via an efficient and steepest iterative method. In addition, we present a theoretical study to analyze the downlink (DL) spectral-efficiency (SE) and energy-efficiency (EE) performance of CF-mMIMO-OFDM under power amplifier (PA) non-linearity. In an original way, we derive closed-form expressions for the DL SE and EE for the local full-pilot zero-forcing (FZF) precoding scheme with large-scale fading over independent Rayleigh block fading channels while taking into account channel estimation errors and pilot contamination. This analysis can provide important insights into the practical impact of power-efficient PA. Numerical results show that the proposed localPAPRfree algorithm offers excellent PAPR reduction performance while guaranteeing high transmission quality.

Deep learning‐assisted reconfigurable intelligent surface for enhancing 6G mobile networks

“…For example, to efficiently use the MIMO antenna arrays in communication, one exclusive radio frequency band is needed with multiple active components such as the Analog to Digital Converter (ADC), frequency up‐converter, low‐noise amplifier, and per active antenna element, which consumes immense power and cost, specifically at mmWave spectrum. To tackle these problems in future mobile networks, a lot of researchers have discussed energy efficient and low complexity and cost techniques to sustain the high performance of the system, by utilizing simple hardware components with techniques that are better energy efficient in addition to the allocation of the green resource and design of transceiver signal processing methods 2–4 . In addition, using the massive MIMO architecture is a potential Fifth Generation (5G) mobile network technology by exploiting the extensive spatial multiplexing to provide the system with high spectral efficiency 5–9 …”