Optimization of Grant-Free NOMA With Multiple Configured-Grants for mURLLC

15 pages, 15 figures, submitted to IEEE JSAC SI on Next Generation Multiple Access. arXiv admin note: text overlap with arXiv:2101.0051515 pages, 15 figures, submitted to IEEE JSAC SI on Next Generation Multiple Access. arXiv admin note: text overlap with arXiv:2101.0051

A Framework of Non-Orthogonal Slotted Aloha (NOSA) Protocol for TDMA-Based Random Multiple Access in IoT-Oriented Satellite Networks

There is an urgent demand for massive machine-type terminals to have access into time-division multiple access (TDMA)-based satellite networks by means of random multiple access (RMA). Several RMA protocols have been proposed by exploiting packet repetitions and interference cancellation to achieve high throughput. In this paper, a framework of non-orthogonal slotted aloha (NOSA) protocol is reported to achieve even higher throughput. With a specifically designed tile-based frame structure, it introduces the intra-tile sparse mapping as a special kind of pre-coded packet repetitions and exploits the joint multi-packet detection to blindly detect superimposed packets. By further employing inter-tile packet repetitions and interference cancellation, the NOSA protocol is able to achieve high throughput with affordable complexity while keeping the same transmission efficiency as and comparable power consumptions to available protocols. Simulation results show that the NOSA prototype has the potential in providing RMA for massive machine-type terminals in practical TDMA-based satellite networks

5G 이후 무선 네트워크를 위한 무선 접속 기술 향상 연구

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 박세웅.Recently, operators are creating services using 5G systems in various fields, e.g., manufacturing, automotive, health care, etc. 5G use cases include transmission of small packets using IoT devices to high data rate transmission such as high-definition video streaming. When a large-scale IoT device transmits a small packet, power saving is important, so it is necessary to disconnect from the base station and then establish a connection through random access to transmit data. However, existing random access procedures are difficult to satisfy various latency requirements. It is attractive to use a wide bandwidth of the millimeter wave spectrum for high data rate transmission. In order to overcome the channel characteristics, beamforming technology is applied. However, when determining a beam pair between a transmitter and a receiver, interference is not considered. In this dissertation, we consider the following three enhancements to enable 5G and beyond use cases: (i) Two-step random access procedure for delay-sensitive devices, (ii) self-uplink synchronization framework for solving preamble collision problem, and (iii) interference-aware beam adjustment for interference coordination. First, RAPID, two-step random access for delay-sensitive devices, is proposed to reduce latency requirement value for satisfying specific reliability. When devices, performing RAPID and contention-based random access, coexist, it is important to determine a value that is the number of preambles for RAPID to reduce random access load. Simulation results show that RAPID achieves 99.999% reliability with 80.8% shorter uplink latency, and also decreases random access load by 30.5% compared with state-of-the-art techniques. Second, in order to solve preamble collision problem, we develop self-uplink synchronization framework called EsTA. Preamble collision occurs when multiple devices transmit the same preamble. Specifically, we propose a framework that helps the UE to estimate the timing advance command using a deep neural network model and to determine the TA value. Estimation accuracy can achieve 98–99% when subcarrier spacing is 30 and 60 kHz. Finally, we propose IBA, which is interference-aware beam adjustment method to reduce interference in millimeter wave networks. Unlike existing methods of reducing interference by scheduling time and frequency resources differently, interference is controlled through beam adjustment. In IBA, it is important to reduce search space of finding new beam pair to reduce interference. In practical, it is impossible to search beam pair of all combinations. Therefore, through Monte Carlo method, we can reduce search space to achieve local optimum. IBA achieve enhancement of lower 50%throughput up to 50% compared with only applying beam adjustment. In summary, we propose a two-step random access, a self-uplink synchronization framework, and interference-aware beam adjustment for 5G and beyond use cases. Through these researches, we achieve enhancements of network performance such as latency and throughput compared with state-of-the-art techniques.최근 사업자는 제조, 자동차, 헬스 케어 등 다양한 분야에서 5G 시스템을 사용하여 서비스를 만들고 있다. 5G 사용 사례에는 IoT 장치를 이용한 작은 패킷 전송에서고화질 비디오 스트리밍과 같은 고속 데이터 전송까지 포함된다. 대규모 IoT 장치가작은 패킷을 전송하는 경우 전력 소모 절약이 중요하므로 기지국과의 연결을 끊은다음 랜덤 액세스를 통해 다시 기지국과 연결하여 데이터를 전송해야한다. 그러나기존의 랜덤 액세스 절차는 다양한 지연시간 요건을 만족시키기 어렵다. 한편, 높은데이터 전송 속도를 위해 넓은 대역폭의 밀리미터파 대역을 사용한다. 이때, 밀리미터파 대역 채널 특성을 극복하기 위해 빔포밍 기술이 적용된다. 그러나 현재 5G표준에서 송신기와 수신기 사이의 빔 쌍을 결정할 때, 간섭은 고려되지 않는다. 이논문에서는 5G 및 그 이후의 네트워크에서 다양한 사용 사례를 지원하기 위해 다음세 가지 개선 사항을 고려한다. (i) 지연에 민감한 장치를 위한 2 단계 랜덤 액세스절차, (ii) 프리앰블 충돌 문제를 해결하기 위한 자체 상향링크 동기화 프레임 워크,그리고 (iii) 간섭을 줄이기 위한 간섭 인식 빔 조정이다. 첫째, 지연에 민감한 장치를 위한 2 단계 랜덤 액세스인 RAPID는 특정 신뢰도를 만족시키기 위한 지연시간을 줄이기 위해 제안되었다. RAPID와 경합 기반 랜덤 액세스를 수행하는 장치가 공존할 경우 RAPID가 랜덤 액세스 부하를 줄이기 위해 RAPID를 위해 할당되는 프리앰블 수를 결정하는 것이 중요하다. 시뮬레이션 결과에 따르면 RAPID는 99.999%의신뢰도를 만족시키는 지연시간을 최신 기술에 비해 80.8% 줄이면서, 랜덤 액세스부하를 30.5% 줄인다. 둘째, 프리앰블 충돌 문제를 해결하기 위해 자체 상향링크 동기화 프레임워크인 EsTA를 개발한다. 프리앰블 충돌은 여러 장치가 동일한 프리앰블을 전송할 때 발생한다. 구체적으로, 단말이 심층 신경망 모델을 사용하여 timing advance(TA) command를 추정하고 TA값을 결정하는 프레임 워크를 제안한다. 네트워크 시스템의 부반송파 간격이 30 및 60 kHz 일 때, TA command 추정 정확도는98–99%를 달성 할 수 있다. 마지막으로, 밀리미터파 네트워크에서 간섭을 줄이기 위한 간섭 인식 빔 조정 방법인 IBA를 제안한다. 시간과 주파수 자원을 다르게 예약하여 간섭을 줄이는 기존의 방법과 달리 IBA는 빔 조정을 통해 간섭을 제어한다.이 때, 간섭을 줄이기 위해 새로운 빔 쌍을 찾는 검색 공간을 줄이는 것이 중요하다.현실적으로 모든 빔 쌍의 조합을 검색하는 것은 불가능하다. 따라서 IBA는 Monte Carlo 방법을 통해 검색 공간을 축소하여 local optimum을 달성하도록 설계되어야한다. IBA는 5G 표준의 빔 조정 방법과 비교했을 때, 하위 50% throughput의 중간값이최대 50%까지 향상된다. 요약하면, 우리는 5G 및 그 이후의 다양한 사용 사례를 위해서 2 단계 랜덤 액세스, 자체 상향링크 동기화 프레임 워크, 그리고 간섭 인식 빔조정 방법을 제안한다. 이 연구를 통해 최신 기술에 비해 지연시간 및 처리량과 같은네트워크 성능이 향상된다.1 Introduction 1 1.1 5G Vision, Applications, and Keywords 1 1.2 Overview of Existing Approach 3 1.3 Main Contributions 4 1.3.1 RAPID: Two-Step Random Access 4 1.3.2 EsTA: Self-Uplink Synchronization 5 1.3.3 IBA: Interference-Aware Beam Adjustment 5 1.4 Organization of the Dissertation 6 2 RAPID: Contention Resolution-based Random Access Procedure using Context ID for IoT 7 2.1 Introduction 7 2.2 Background 10 2.2.1 RRC State 10 2.2.2 Random Access Procedure 11 2.2.3 Uplink Latency in RRC INACTIVE State 13 2.2.4 Related Work 14 2.3 RAPID: Proposed Random Access Procedure 15 2.3.1 Overview 15 2.3.2 Criterion of Applying RAPID 16 2.3.3 Preamble Set and RACH Period Allocation 17 2.3.4 Preamble Transmission 18 2.3.5 RAR Transmission 19 2.3.6 AS Context ID Allocation 21 2.3.7 Number of Preambles for RAPID 22 2.4 Access Pattern Analyzer 22 2.4.1 Overview 22 2.4.2 APA Operation 23 2.4.3 Margin Value 26 2.4.4 Offset Index Decision 26 2.5 Random Access Load Analysis 27 2.5.1 System Model 28 2.5.2 Markov Chain Model for 4-Step RA 29 2.5.3 Average Random Access Load for 4-Step RA 34 2.5.4 Markov Chain Model for RAPID 34 2.5.5 Average Random Access Load for RAPID 37 2.5.6 Validation of Analysis 38 2.5.7 Optimization Problem 41 2.6 Performance Evaluation 42 2.6.1 Simulation Setup 42 2.6.2 Number of Preambles for RAPID 43 2.6.3 Performance of RAPID 43 2.6.4 Performance of APA 48 2.7 Summary 48 3 EsTA: Self-Uplink Synchronization in 2-Step Random Access 49 3.1 Introduction 49 3.2 Background 51 3.2.1 Overview of 2-Step CBRA 51 3.2.2 Channel Structure for msgA 52 3.2.3 TA Handling for the Payload 54 3.2.4 2-Step Random Access in Recent Literature 56 3.3 Challenges of 2-Step Random Access 57 3.3.1 Preamble Allocation 57 3.3.2 Resource Mapping for msgA 58 3.3.3 DFT Operation in gNB 58 3.3.4 Detected Collision Problem 58 3.4 EsTA: Proposed Self-UL Synchronization Procedure 59 3.4.1 Overview 60 3.4.2 Overall Procedures 60 3.4.3 Performance Evaluation 61 3.4.4 Future Research Perspectives 65 3.5 Summary 65 4 IBA: Interference-Aware Beam Adjustment for 5G mmWave Networks 67 4.1 Introduction 67 4.2 Background 68 4.2.1 Beam Management in 5G NR 68 4.2.2 System-Level Simulation and 3D Beamforming for 5G NR 70 4.3 Motivation 70 4.3.1 Throughput Degradation by Interference 70 4.4 IBA: Proposed Interference Management Scheme 72 4.4.1 Overall Procedure 72 4.4.2 Reduction of Search Space 72 4.4.3 Algorithm for IBA 75 4.5 Performance Evaluation 76 4.6 Summary 78 5 Concluding Remarks 79 5.1 Research Contributions 79 5.2 Future Work 80 Abstract (In Korean) 89 감사의 글 92Docto

Enabling Technologies for Ultra-Reliable and Low Latency Communications: From PHY and MAC Layer Perspectives

© 1998-2012 IEEE. Future 5th generation networks are expected to enable three key services-enhanced mobile broadband, massive machine type communications and ultra-reliable and low latency communications (URLLC). As per the 3rd generation partnership project URLLC requirements, it is expected that the reliability of one transmission of a 32 byte packet will be at least 99.999% and the latency will be at most 1 ms. This unprecedented level of reliability and latency will yield various new applications, such as smart grids, industrial automation and intelligent transport systems. In this survey we present potential future URLLC applications, and summarize the corresponding reliability and latency requirements. We provide a comprehensive discussion on physical (PHY) and medium access control (MAC) layer techniques that enable URLLC, addressing both licensed and unlicensed bands. This paper evaluates the relevant PHY and MAC techniques for their ability to improve the reliability and reduce the latency. We identify that enabling long-term evolution to coexist in the unlicensed spectrum is also a potential enabler of URLLC in the unlicensed band, and provide numerical evaluations. Lastly, this paper discusses the potential future research directions and challenges in achieving the URLLC requirements

Compressive Sensing Based Grant-Free Communication

Grant-free communication, where each user can transmit data without following the strict access grant process, is a promising technique to reduce latency and support massive users. In this thesis, compressive sensing (CS), which exploits signal sparsity to recover data from a small sample, is investigated for user activity detection (UAD), channel estimation, and signal detection in grant-free communication, in order to extract information from the signals received by base station (BS). First, CS aided UAD is investigated by utilizing the property of quasi-time-invariant channel tap delays as the prior information for the burst users in internet of things (IoT). Two UAD algorithms are proposed, which are referred to as gradient based and time-invariant channel tap delays assisted CS (g-TIDCS) and mean value based and TIDCS (m-TIDCS), respectively. In particular, g-TIDCS and m-TIDCS do not require any prior knowledge of the number of active users like the existing approaches and therefore are more practical. Second, periodic communication as one of the salient features of IoT is considered. Two schemes, namely periodic block orthogonal matching pursuit (PBOMP) and periodic block sparse Bayesian learning (PBSBL), are proposed to exploit the non-continuous temporal correlation of the received signal for joint UAD, channel estimation, and signal detection. The theoretical analysis and simulation results show that the PBOMP and PBSBL outperform the existing schemes in terms of the success rate of UAD, bit error rate (BER), and accuracy in period estimation and channel estimation. Third, UAD and channel estimation for grant-free communication in the presence of massive users that are actively connected to the BS is studied. An iteratively UAD and signal detection approach for the burst users is proposed, where the interference of the connected users on the burst users is reduced by applying a preconditioning matrix to the received signals at the BS. The proposed approach is capable of providing significant performance gains over the existing algorithms in terms of the success of UAD and BER. Last but not least, since the physical layer security becomes a critical issue for grant-free communication, the channel reciprocity in time-division duplex systems is utilized to design environment-aware (EA) pilots derived from transmission channels to prevent eavesdroppers from acquiring users’ channel information. The proposed EA-pilots based approach possesses a high level of security by scrambling the eavesdropper’s normalized mean square error performance of channel estimation