Cellular Internet of Things (IoT) and machine-to-machine (M2M) communications have recently received considerable attention as major candidate technologies to develop a hyper-connected society. Among various research issues in cellular IoT/M2M communications, cellular random access (RA) is one of active research areas since the RA is a starting mechanism to communicate between each node and eNodeB. However, the conventional RA mechanism may reveal critical limitations for supporting a significantly large number of nodes, low-latency services, and ultra reliability in the fifth generation (5G) cellular networks. Therefore, in this dissertation, we first propose a novel concept of tagged preambles, which can deliver additional information with its own preamble index at the first step of the RA procedure. We address various features of the proposed tagged preambles and their detection method. Moreover, we propose a tagged preambles based random access mechanism in order to innovate the current cellular RA system. Then, the proposed tagged preambles based RA mechanism plays important roles in the following novel cellular RA schemes.
In the first technical issue, we propose an `early preamble collision detection (e-PACD) scheme' for reliable and low-latency random access. The proposed e-PACD scheme enables faster preamble collision detection based on tagged preambles at the first step of the RA procedure and faster collision notification at the second step of the RA procedure, compared to the conventional preamble collision detection, which is done at the third step of the RA procedure and the conventional collision notification, which is done at the fourth step of the RA procedure. As a result, the proposed e-PACD scheme effectively enables us to avoid resource wastes on physical uplink shared channel (PUSCH) since the proposed e-PACD scheme disables nodes with collided preambles to proceed the remaining third and fourth steps of the RA procedure.
In the second technical issue, we propose a `preamble collision resolution (PACR) scheme' based on captured multiple timing advance (TA) values for a massive number of TA-aware machine nodes. In the proposed PACR scheme, each of TA-aware nodes can obtain its exclusive PUSCH resources for the third step of the RA procedure by comparing both of its transmitted PA index and its own TA value with those in RA response (RAR) messages. As a result, the proposed PACR scheme can significantly improve the RA success probability and reduce the RA delay.
In the third technical issue, we propose a `message-embedded random access (MERA) scheme' for small-sized data transmissions. The proposed MERA scheme can deliver short message bits based on message-embedded preambles at the first step of the RA procedure. Since the proposed MERA scheme does not require any resource scheduling mechanisms and extra resources on PUSCHs but only utilizes physical random access channel (PRACH), it is significantly effective to reduce control and signalling overheads and to save radio resources on PUSCH. As a result, the proposed MERA scheme can be utilized for connection-less small-sized data transmission for various IoT/M2M applications.
When eNodeB needs to collect a set of data from a significantly large number of machine nodes belonging to a specific group, it may encounter an RA overload or a congestion problem due to a limited number of preamble resources and PUSCH resources in the RA procedure. Thus, in the last technical issue, we propose an `efficient group data collection mechanism (e-GDCM)'. The proposed e-GDCM effectively adjusts an access class barring (ACB) factor by considering both of the number of available preambles and the number of available PUSCH resources, and manage the RAs from a group of machine nodes by using a distinct group root number for their exclusive preamble transmissions. As a result, the comprehensive result of the proposed e-GDCM can give network operators an insight into effectively collecting a set of group data for various cellular IoT/M2M communication applications.
본 학위논문에서는 5세대 셀룰러 IoT/M2M 통신에서의 극다수 노드 수용과 짧은 전송 지연시간의 요구조건을 만족시키기 위해 태그가 달린 프리앰블을 새롭게 제안하고 이에 기반한 임의접속 메커니즘을 통해 기존 임의접속 시스템의 문제점들을 해결함과 동시에 다양한 기능을 갖는 새로운 임의접속 기술들을 제안한다. 새롭게 제안한 태그가 달린 프리앰블에 기반한 셀룰러 임의접속 기술들은 아래와 같다. (1) Early Preamble Collision Detection Scheme (e-PACD): 임의접속 첫 번째 단계에서 신속하게 프리앰블의 충돌 여부를 검출하고 이를 임의접속 두 번째 단계에 알리는 기술이다. 이를 통해 상향공유채널(PUSCH)을 낭비 없이 완전히 이용하고 짧아진 프리앰블 충돌 응답시간으로 인해 임의접속 지연시간 측면에서도 이점을 보였다. (2) Preamble Collision Resolution Scheme (PACR): 태그가 달린 프리앰블로부터 다수의 timing advance (시간정렬) 값을 검출하고 임의접속응답 메시지 안의 프리앰블 인덱스 정보와 시간정렬정보를 동시에 비교하는 방식으로 프리앰블 충돌 문제를 해결한다. 이를 통해 임의접속 성공률을 매우 향상 시킬 수 있다. (3) Message-Embedded Random Access Scheme (MERA): 태그가 달린 프리앰블을 이용하여 짧은 메시지 정보를 전달하는 새로운 임의접속 방식이다. 보내고자하는 짧은 메시지 비트 값을 프리앰블 인덱스와 태그 인덱스에 담고 이를 임의접속 첫 번째 과정에서 보낸다. 이를 통해 기존의 제어목적으로 사용하던 임의접속채널(PRACH)을 통해 각 노드들이 짧은 메시지 정보를 보낼 수 있게 되어 부가적인 data throughput을 얻게 된다. (4) Efficient Group Data Collection Mechanism (e-GDCM): 그룹 데이터 전송으로 인한 극심한 동시 임의접속 수를 제어하기 위해 효율적인 그룹 데이터 수집 메커니즘을 제안하였다. 본 메커니즘은 이용 가능한 프리앰블 수뿐만 아니라 상향공유채널(PUSCH) 자원 양을 동시에 고려하여 총 그룹 데이터 수집시간, 상향공유채널(PUSCH) 이용률, 전송 성공률 측면에서의 이득을 보인다. 이를 통해 네트워크 사업자는 요구조건에 따라 다양한 그룹 데이터 수집 운영계획을 세울 수 있다.
