Grant-Free Random Access in Pilot-Reused Multicell Massive MIMO Systems with Backoff Mechanisms  

作　　者：Qi Zhang Jun Zhang Shi Jin 

机构地区：[1]Jiangsu Key Laboratory of Wireless Communications,Nanjing University of Posts and Telecommunications,Nanjing 210003,China [2]National Mobile Communications Research Laboratory,Southeast University,Nanjing 210096,China

出　　处：《China Communications》2023年第9期185-195,共11页中国通信（英文版）

基　　金：supported in part by the National Natural Science Foundation of China under Grant 62171231 and 62071247;in part by the National Key Research & Development Program of China under Grant No. 2020YFB1807202 and 2020YFB1804900

摘　　要：Grant-free random access(RA)is attractive for future network due to the minimized access delay.In this paper,we investigate the grantfree RA in multicell massive multiple-input multipleoutput(MIMO)systems with pilot reuse.With backoff mechanism,user equipments(UEs)in each cell are randomly activated,and active UEs randomly select orthogonal pilots from a predefined pilot pool,which results in a random pilot contamination among cells.With the help of indicators that capture the uncertainties of UE activation and pilot selection,we derive a closed-form approximation of the spectral efficiency per cell after averaging over the channel fading as well as UEs’random behaviors.Based on the analysis,the optimal backoff parameter and pilot length that maximize the spectral efficiency can be obtained.We find that the backoff mechanism is necessary for the system with large number of UEs,as it can bring significant gains on the spectral efficiency.Moreover,as UE number grows,more backoff time is needed.

关 键 词：backoff mechanism grant-free RA multicell massive MIMO 

分 类 号：TN929.5[电子电信—通信与信息系统]