An approach to achieve zero turnaround time in TDD operation on SDR front-end

Thanks to the digitization and softwarization of radio communication, the development cycle of new radio technologies can be significantly accelerated by prototyping on software-defined radio (SDR) platforms. However, a slow turnaround time (TT) of the front-end of an SDR for switching from receiving mode to transmitting mode or vice versa, are jeopardizing the prototyping of wireless protocols, standards, or systems with stringent latency requirements. In this paper, a novel solution called BaseBand processing unit operating in Half Duplex mode and analog Radio Frequency front-end operating in Full Duplex mode, BBHD-RFFD, is presented to reduce the TT on SDR. A prototype is realized on the widely adopted AD9361 radio frequency frontend to prove the validity of the proposed solution. Experiments unveil that for any type of application, the TT in time division duplex (TDD) operation mode can be reduced to zero by the BBHD-RFFD approach, with negligible impact on the communication system in terms of receiver sensitivity. The impact is measured for an in-house IEEE 802.15.4 compliant transceiver. When compared against the conventional TDD approach, only a 7.5-dB degradation is observed with the BBHD-RFFD approach. The measured sensitivity of -91 dBm is still well above the minimum level (i.e., -85 dBm at 2.4 GHz) defined by the IEEE 802.15.4 standard

CMCVT : a concurrent multi-channel virtual transceiver

State-of-the-art wireless Gateways (GW) used in Internet of Things (IoT) offer a single channel radio link, which limits the capabilities of the IoT network controlled by the GW, as the GW can only use a single channel at a time to communicate with the end-device(s). The quality of service (e.g., aggregate throughput, latency) offered by a single channel GW could be substantially improved by employing a multi-channel transceiver, which is capable of transmitting/receiving data on different radio channels simultaneously, particularly for larger wireless networks. However, current solutions available in both research and commercial communities only offer multi-channel receiver capabilities, and do not incorporate the multi-channel transmitter part. In addition, in terms of implementation, these multi-channel receivers duplicate single-channel hardware functionality. In this paper, for the first time, a novel concurrent multi-channel virtual transceiver is introduced. The virtual transceiver offers multi-channel capabilities and uses the same single-hardware hardware implementation for the Physical (PHY) layer by employing the virtualization technique. This new virtual transceiver concept is demonstrated for an IEEE 802.15.4 based 8 x 8 channel transceiver, implemented on an Field Programmable Gate Array (FPGA) of a modern Software Defined Radio and is compared with the existing duplication approach. The duplication approach consumes 9008 LUTs, and 12120 FFs, whereas the proposed approach occupies only 2959 LUTs and 2105 FFs, saving 67.15% LUTs and 82.63% FFs in comparison with the duplication approach. The experimental results reveal that the virtual transceiver provides the same performance (e.g., receiver sensitivity of -98.5dBm) as the transceiver achieved by duplicating the PHY layers but consumes much less hardware resources. (C) 2020 The Authors. Published by Elsevier GmbH

A Secure, Configurable, Wireless System for Transfer of Sensor Data from Aircraft to Ground

Modern aircraft are complex systems, equipped with hundreds of embedded sensors that record a wide repertoire of data during flight, such as crucial engine and airframe parameters, status of flight control system, air conditioning system, landing gear, life-saving and emergency systems. The data from the sensors is stored in the Flight Data Recorder. Maintenance personnel routinely transfer this sensor data to a ground terminal device to analyze it for aircraft health and performance monitoring purposes. Manual methods of extracting sensor data can be tedious and error-prone when large fleets of aircraft are involved. This paper presents a novel system to extract sensor data from aircraft to a ground terminal, wirelessly. The wireless system is implemented using unique, configurable wireless transmitter receivers (WTRs) designed for this purpose. The hardware for the wireless transfer of data was designed, interfaced with a modern aircraft’s system, and tested with the aircraft on the ground and another flying object. The data from the aircraft’s Flight Data Recorder was successfully transmitted and received wirelessly by the ground terminal, over a distance of 50 meters (with aircraft on ground) and 10 Kilometers (with a flying object), in a secure mode with zero packet loss. The WTRs have also qualified the requisite tests for airborne certification

Space-time-frequency methods for interference-limited communication systems

textTraditionally, noise in communication systems has been modeled as an additive, white Gaussian noise process with independent, identically distributed samples. Although this model accurately reflects thermal noise present in communication system electronics, it fails to capture the statistics of interference and other sources of noise, e.g. in unlicensed communication bands. Modern communication system designers must take into account interference and non-Gaussian noise to maximize efficiencies and capacities of current and future communication networks. In this work, I develop new multi-dimensional signal processing methods to improve performance of communication systems in three applications areas: (i) underwater acoustic, (ii) powerline, and (iii) multi-antenna cellular. In underwater acoustic communications, I address impairments caused by strong, time-varying and Doppler-spread reverberations (self-interference) using adaptive space-time signal processing methods. I apply these methods to array receivers with a large number of elements. In powerline communications, I address impairments caused by non-Gaussian noise arising from devices sharing the powerline. I develop and apply a cyclic adaptive modulation and coding scheme and a factor-graph-based impulsive noise mitigation method to improve signal quality and boost link throughput and robustness. In cellular communications, I develop a low-latency, high-throughput space-time-frequency processing framework used for large scale (up to 128 antenna) MIMO. This framework is used in the world's first 100-antenna MIMO system and processes up to 492 Gbps raw baseband samples in the uplink and downlink directions. My methods prove that multi-dimensional processing methods can be applied to increase communication system performance without sacrificing real-time requirements.Electrical and Computer Engineerin

비면허대역 셀룰라 통신을 위한 성능 향상 기법

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2021.8. 박세웅.The 3rd generation partnership project (3GPP) has standardized long-term evolution (LTE) licensed-assisted access (LTE-LAA) that uses a wide unlicensed band as an alternative solution to the insufficient bandwidth problem of the existing LTE. 3GPP cellular communications in unlicensed spectrum allow transmission only after completing listen-before-talk (LBT) operation. For downlink, the LBT operation helps cellular traffic to coexist well with Wi-Fi traffic. However, cellular uplink transmission is attempted only at the time specifically determined by the base station after having a successful LBT and the user equipment (UE) may suffer transmission failure and delayed transmission due to Wi-Fi interference. As a result, cellular uplink traffic does not coexist well with Wi-Fi traffic. NR-U suffers from the collision issue because its channel access mechanism is similar to that of Wi-Fi. Wi-Fi solves the collision problem through the request-to-send/clear-to-send (RTS/CTS) mechanism. However, NR-U has no way of solving the collision problem. As a result, NR-U suffers severe performance degradation due to collisions as the number of contending nodes increases. In this dissertation, we consider the following two enhancements to cellular communication in the unlicensed spectrum: (i) Uplink channel access enhancement for solving poor uplink performance and (ii) collision minimization for efficient channel utilization. First, we mathematically analyze the problem of unfairness between cellular and Wi-Fi for uplink channel access. To address the coexistence problem in unlicensed spectrum, we propose a standard-compliant approach, termed UpChance, which allows the UE to use a minimum length of uplink reservation signal (RS) and the base station to determine the optimal timing for the UE's uplink transmission. Through ns-3 simulation, we verify that UpChance improves the performance of fairness and random access completion time by up to 88% and 99%, respectively. Second, we propose to extend an RS duration and use a split RS for reservation in NR-U that consists of front RS and rear RS and design a new collision minimization scheme, termed R-SplitC, that contains two components: new split RS operation and contention window size (CWS) control. New split RS operation helps to minimize collisions in NR-U transmissions, and CWS control works to protect the performance of other communication technologies such as Wi-Fi. We mathematically analyze and evaluate the performance of our scheme and confirm that R-SplitC improves network throughput by up to 100.6% compared to the baseline RS scheme without degrading Wi-Fi performance. In summary, we propose standard-compliant uplink channel access enhancement scheme and collision minimization scheme for cellular communication in unlicensed spectrum. Through this research, we achieve enhancements of network performance such as throughput and fairness.3세대 파트너십 프로젝트는 기존 LTE의 부족한 대역폭 문제에 대한 대안으로 넓은 비면허 대역을 사용하는 라이선스 지원 접속을 표준화하고 있다. 비면허 대역에서 3GPP 셀룰러 통신은 LBT 동작을 완료한 후에만 전송을 허용한다. 다운링크의 경우 LBT 작업을 통해 셀룰러 트래픽이 와이파이 트래픽과 잘 공존할 수 있습니다. 그러나, 셀룰러 업링크 전송은 LBT 성공 후 기지국에 의해 특별히 결정된 시간에만 시도되며, 사용자 장비는 와이파이의 간섭으로 인해 전송 실패와 전송 지연을 겪을 확률이 높다. 따라서 셀룰러 업링크 트래픽이 와이파이 트래픽과 잘 공존하지 못한다. 라이선스 지원 접속 기술은 또한 채널 액세스 메커니즘이 와이파이의 채널 액세스 메커니즘과 유사하기 때문에 동시 전송으로 충돌 문제를 겪고 있다. 와이파이는 RTS/CTS 메커니즘을 통해 충돌 문제를 해결한다. 그러나 현재 라이선스 지원 접속 기술은 충돌 문제를 해결할 방법이 존재하지 않는다. 따라서 라이선스 지원 접속 기술은 경합 노드 수가 증가함에 따라 충돌로 인해 심각한 성능 저하를 겪는다. 본 논문에서는 비면허 대역에서 셀룰러 통신에 대한 다음과 같은 두 가지 개선을 고려한다. (i) 업링크 성능 저하를 해결하기 위한 업링크 채널 액세스 향상 및 (ii) 효율적인 채널 활용을 위한 충돌 최소화. 첫째, 업링크 채널 액세스를 위한 셀룰러와 와이파이 사이의 불공정성 문제를 수학적으로 분석한다. 비면허 대역에서의 공존 문제를 해결하기 위해, 우리는 단말이 최소 길이의 업링크 예약 신호를 사용하고 기지국이 단말의 업링크 전송에 대한 최적의 타이밍을 결정할 수 있는 UpChance라는 표준을 만족하는 상향 링크 채널 접근 방식을 제안한다. ns-3 시뮬레이션을 통해 UpChance가 공정성과 랜덤 액세스 완료 시간을 각각 최대 88%, 99% 향상시키는 것을 검증한다. 둘째, 우리는 전방 예약신호와 후방 예약신호로 구성된 분할 예약 신호를 사용하고 경합 창 크기를 추가적으로 제어하는 R-SplitC라는 새로운 충돌 최소화 체계를 제안한다. 새로운 분할 예약 신호는 라이선스 지원 접속 기술의 전송간의 충돌을 최소화하는 데 도움을 주며, 경합 창 크기 제어는 와이파이와 같은 다른 통신 기술의 성능을 보호한다. 우리는 우리 체계의 성능을 수학적으로 분석하고 평가하여 R-SplitC가 와이파이 성능을 저하시키지 않고 기존의 예약 신호 체계에 비해 네트워크 처리량을 최대 100.6% 향상시키는 것을 확인한다. 요약하면, 우리는 비면허 대역에서 셀룰러 통신을 위한 업링크 채널 액세스 향상 기법 및 충돌 최소화 기법을 제안한다. 본 연구를 통해, 우리는 최첨단 기술에 비해 처리량 및 공정성과 같은 네트워크 성능의 향상을 달성한다.1 Introduction 1 1.1 Motivation 1 1.2 Main Contributions 2 1.2.1 Uplink Channel Access Enhancement for Cellular Communication in Unlicensed Spectrum 2 1.2.2 R-SplitC: Collision Minimization for Cellular Communication in Unlicensed Spectrum 3 1.3 Organization of the Dissertation 4 2 Uplink Channel Access Enhancement for Cellular Communication in Unlicensed Spectrum 5 2.1 Introduction 5 2.2 Related Work and Preliminaries 7 2.2.1 Related Work 7 2.2.2 Preliminaries 8 2.3 Mathematical Analysis for Unfairness between Uplink Cellular and Wi-Fi 10 2.3.1 PRACH scenario 10 2.3.2 UL data scenario 13 2.4 Proposed Scheme 17 2.4.1 UE Operation 18 2.4.2 eNB Operation 19 2.5 Performance Evaluation 24 2.5.1 Simulation Environments 24 2.5.2 UL data transmission 25 2.5.3 Random access 27 2.6 Summary 29 3 R-SplitC: Collision Minimization for Cellular Communication in Unlicensed Spectrum 37 3.1 Introduction 37 3.2 Related Work and Preliminaries 39 3.2.1 Related Work 39 3.2.2 NR-U 40 3.2.3 listen-before-talk (LBT) 41 3.2.4 reservation signal and mini-slot 41 3.2.5 Wi-Fi 42 3.3 Proposed Scheme 44 3.3.1 New RS structure 46 3.3.2 CWS control 48 3.4 Performance Analysis 49 3.4.1 Throughput Analysis for R-Split 49 3.4.2 Throughput Analysis for R-SplitC 55 3.5 Performance Evaluation 57 3.5.1 Performance Evaluation for an NR-U only Network 58 3.5.2 Performance Evaluation for an NR-U/Wi-Fi Network 61 3.6 Summary 65 4 Concluding Remarks 67 4.1 Research Contributions 67 4.2Future Work 68 Abstract (In Korean) 75 감사의글 78박

Glossary, Acronyms, Abbreviations: Space transportation system and associated payloads

A glossary of terms (and definitions) in current usage for the space transportation system and associated payloads, as well as acronyms and abbreviations, are presented

STS and Cargo Glossary, acronyms, and abbreviations

Definitions are provided, and acronyms and abbreviations are explained

Space Transportation System and associated payloads: Glossary, acronyms, and abbreviations

A collection of acronyms now in everyday use in the Shuttle world are listed. It is a combination of lists that were prepared at the Kennedy and Johnson Space Centers and by the Air Force

Space transportation system and associated payloads: Glossary, acronyms, and abbreviations

A collection of some of the acronyms and abbreviations now in everyday use in the shuttle world is presented. It is a combination of lists that were prepared at Marshall Space Flight Center and Kennedy and Johnson Space Centers, places where intensive shuttle activities are being carried out. This list is intended as a guide or reference and should not be considered to have the status and sanction of a dictionary

Space Transportation System and associated payloads: Glossary, acronyms, and abbreviations

A collection of acronyms in everyday use concerning shuttle activities is presented. A glossary of terms pertaining to the Space Transportation System is included