대용량 IoT 네트워크를 위한 희소 확산 다중접속기법 연구

학위논문 (석사)-- 서울대학교 대학원 : 전기·정보공학부, 2017. 2. 심병효.This paper addresses a problem of massive connectivity with millions of Internet of Things (IoT) devices. Massive connectivity is one of the most important requirements for the next generation of networks. In this paper, we propose sparse spreading multiple access which overloads a large number of users on limited sizes of resources as a solution for massive connectivity. o do this, first, a single low density signature (LDS) codebook is used for accessing the medium to transmit data and a pilot signal. The number and length of the signature is designed to maximize the access rate. Second, a compressed sensing method is utilized for estimating user activity and channel impulse response vector from overloaded pilot signals. To maximize successive detection rates, we organize a particular spreading signature by concatenating multiple codewords from the LDS codebook and utilize the active user information and estimated channel information jointly. Third, an adaptive message passing algorithm (MPA) is applied to minimize inter-code interference between users who use the same sparse code casually.1 Introduction 1 2 Sparse Spreading Multiple Access 5 2.1 Uplink Multiple Access System 5 2.2 Sparse Spreading Multiple Access 6 2.3 Pilot and Data Transmission Process 6 3 Detecting Active users, Channel and Data 12 3.1 Overall Structure of active user detection and channel estimation 12 3.2 Joint Active User Detection and Frequency Response Estimation 14 3.3 Channel Impulse Response Estimation 18 3.4 Data Detection with MPA 22 4 Simulation Results and Discussion 26 4.1 Simulation Setup 26 4.2 Simulation Results 29 5 Summary and Conclusions 38 Abstract (In Korean) 42Maste