A High Capacity Preamble Sequence for Random Access in 5G IoT Networks: Design and Analysis

摘要

Abstract 5G NR aims to enable the high density of Internet of Things (IoT), around one million (106)documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}$$(10^{6})$$end{document} connections per square kilometer, through the Massive Machine Type Communication (mMTC). 5G NR employs a Random Access (RA) Procedure for uplink synchronization between User Equipment (UE) and Base Station (gNB). The Zadoff-Chu (ZC) preamble sequence is widely used as the preamble sequence for RA procedure. These ZC sequences have limitations in terms of the total number of unique preambles generated, forcing the reuse of preambles. An increase in the reuse of preambles increases the probability of collision of the preamble of a UE, resulting in the failure of uplink synchronization. This necessitates the study of alternate preamble sequences with higher preamble capacity. In this paper, we propose a preamble sequence called the mALL sequence using the concept of cover sequences to generate a large number of unique unambiguous preambles. We compare the performance of mALL sequence with the ZC sequence and other combination sequences proposed in the literature using the metrics namely, periodic correlation, detection probability, effects of diversity combining, Peak to Average Power Ratio (PAPR), Cubic Metric(CM), and the effects of Carrier Frequency Offset (CFO) on preamble detection. We show that the newly proposed mALL sequence achieves a much higher preamble capacity (104documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}$$10^4$$end{document} times) compared to the legacy ZC sequence, without any deterioration in the correlation properties, detection performance. Further, mALL sequence exhibits a better performance in terms of Cubic Metric. Results also show that the detection of mALL sequence is unambiguous in presence of CFO implying a better detection performance in presence of non-idealities. Thus mALL sequence is a potential candidate to cater to the mMTC use case of 5G. This paper also presents the comparison between Zadoff-Chu, m-sequence and Alltop sequence and their detection performance in RA procedure for different number of receive antennas.