On the Optimal Energy Efficiency and Spectral Efficiency Trade-Off of CF Massive MIMO SWIPT System

Abstract

This paper studies a cell-free (CF) massive multi-input multi-output (MIMO) simultaneous wireless information and power transmission (SWIPT) system and proposes a user-centric (UC) access point (AP) selection method and a trade-off performance optimization scheme for spectral efficiency and energy efficiency. In this system, users have both energy harvesting and information transmission functions, and according to the difference between energy harvesting and information transmission, a flexible AP selection scheme is designed. This paper analyses the trade-off between energy efficiency and spectral efficiency, proposes an evaluation index that takes into account both energy efficiency and spectral efficiency, and jointly optimizes the AP selection scheme and the uplink (UL) and downlink (DL) time switching ratio to maximize the trade-off performance. Then, the non-convex problem is converted to a geometric planning (GP) problem to solve. The simulation results show that by implementing a suitable AP selection scheme and UL and DL time allocation, the information processing scheme on the AP side has a slight loss in spectral efficiency, but the energy efficiency is close to the performance of global processing on the central processing unit (CPU).

Energy Efficiency Trade-off with Spectral Efficiency in MIMO Systems

“…Fourth step computes the SE-EE relation for the selection of multiple UEs as formulated in Eqs. ( 22)- (24) where MP CC , CP l , and K time UEs are considered. The change of EE concerning change in SE computes tradeoff scenario and the derivate of EE concerning SE is taken by logarithm function-based approximation.…”

“…The second algorithm is the improved Lion algorithm, which is formed to increase the convergence speed and help make a better trade-off between SE and EE. In [24], a user-centric (UC) access point selection method has been proposed to improve the performance of the MIMO system. In [25], the effect of antenna channel on MIMO throughput calculated that the spatial multiplexing efficiency would be reduced due to power imbalance.…”

“…Therein, we also consider signal-to-noise-ratio (SNR) as weight parameter. The notations β l l , β l l , β j l , β j j , and β l j and each UE in cell l preserves the same average channel gain β l l from BS to be served [24]. The average channel gain β j l is also similar for that of BS of the cell j when each UE in cell j has same average gain as β l j and β j j .…”

“…( 17)- (19) Step 4: Compute SE-EE relation for the selection of multiple UEs as Eqs. ( 22)- (24) Step 5: Compute receive combining vectors for UL as in Tab. 2.…”