Research On Pilot And Power Allocation For Cell-free Massive MIMO

With the rapid development of the 5th generation mobile communication system,a large number of intelligent products,interactive services and intelligent applications emerge rapidly,which brings huge challenges to mobile communication.Therefore,there is an urgent need to carry out research on the 6th generation(6G)mobile communication system.Cell-free massive multiple-input multiple-output(MIMO),as one of the key enabling technologies of 6G network,has attracted many scholars at home and abroad to conduct research.This thesis studies the pilot and power allocation for cell-free massive MIMO.The details are as follows:1.Aiming at the problem that the location distribution of access points(AP)in the cell-free massive MIMO system is too ideal,this thesis simulates the location distribution of AP based on the Poisson point process,and proposes a pilot allocation scheme based on the tabu search algorithm.In the existing literature,most of the cell-free massive MIMO systems consider the assumption that AP locations follow random or uniform distribution.This idealized assumption should be considered in the simulation stage,rather than relying on this rather idealized assumption in theoretical analysis.To this end,this thesis firstly derives the expression of downlink signal to interference-plus-noise ratio(SINR)under the condition that the AP locations are simulated by the Poisson point process.Then,the closed-form expression of SINR is derived by using deterministic equivalent analysis tools.Finally,the expression of downlink achievable rate is derived,and an optimization problem aiming at maximizing downlink sum-rate is established,and a pilot allocation scheme based on tabu search algorithm is proposed.The simulation results show that compared with the pilot random allocation scheme,the pilot allocation scheme proposed in this thesis can improve the downlink sum-rate by 15.1%.2.Aiming at the problem of channel capacity degradation caused by the finite length of the coding block,this thesis proposes a power allocation scheme that maximizes the minimum achievable downlink rate for a cell-free massive MIMO system enabled by simultaneous wireless information and power transfer(SWIPT)technology under the finite block length information theory.First,this thesis derives the expressions of the instantaneous energy and average energy collected by the user equipment.Then,under the finite block length information theory,the downlink SINR is derived,and the expression of the downlink achievable rate is further derived.Finally,an optimization problem aiming at maximizing the minimum achievable downlink rate is established,and a power allocation scheme based on dichotomy is proposed.The simulation results show that,compared with the average power allocation,the power allocation scheme proposed in this thesis can provide a gain of 6.3%,while also ensuring the fairness among users to a certain extent.