Effect of pedestrian movement on MIMO-OFDM channel capacity in an indoor environment

Effects of pedestrian movement on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) channel capacity have been investigated using experiment and simulation. The experiment was conducted at 5.2 GHz by a MIMO-OFDM packet transmission demonstrator using four transmitters and four receivers built in-house. Geometric optics based ray tracing technique was used to simulate the experimental scenarios. Changes in the channel capacity dynamic range have been analysed for different number of pedestrian (0-3) and antennas (2-4). Measurement and simulation results show that the dynamic range increases with the number of pedestrian and the number of antennas on the transmitter and receiver array

Pedestrians effects on indoor MIMO-OFDM channel capacity

Temporal variations caused by pedestrian movement can significantly affect the channel capacity of indoor MIMOOFDM wireless systems. This paper compares systematic measurements of MIMO-OFDM channel capacity in presence of pedestrians with predicted MIMO-OFDM channel capacity values using geometric optics-based ray tracing techniques. Capacity results are presented for a single room environment using 5.2 GHz with 2x2, 3x3 and 4x4 arrays as well as a 2.45 GHz narrowband 8x8 MIMO array. The analysis shows an increase of up to 2 b/s/Hz on instant channel capacity with up to 3 pedestrians. There is an increase of up to 1 b/s/Hz in the average capacity of the 4x4 MIMO-OFDM channel when the number of pedestrians goes from 1 to 3. Additionally, an increment of up to 2.5 b/s/Hz in MIMO-OFDM channel capacity was measured for a 4x4 array compared to a 2x2 array in presence of pedestrians. Channel capacity values derived from this analysis are important in terms of understanding the limitations and possibilities for MIMO-OFDM systems in indoor populated environments

Automatic Wi-Fi Fingerprint System based on Unsupervised Learning

Recently, smartphones and Wi-Fi appliances have been generalized in daily life, and location-based service(LBS) has gradually been extended to indoor environments. Unlike outdoor positioning, which is typically handled by the global positioning system(GPS), indoor positioning technologies for providing LBSs have been studied with algorithms using various short-range wireless communications such as Wi-Fi, Ultra-wideband, Bluetooth, etc. Fingerprint-based positioning technology, a representative indoor LBS, estimates user locations using the received signal strength indicator(RSSI), indicating the relative transmission power of the access point(AP). Therefore, a fingerprint-based algorithm has the advantage of being robust to distorted wireless environments, such as radio wave reflections and refractions, compared to the time-of-arrival(TOA) method for non-line-of-sight(NLOS), where many obstacles exist. Fingerprint is divided into a training phase in which a radio map is generated by measuring the RSSIs of all indoor APs and positioning phase in which the positions of users are estimated by comparing the RSSIs of the generated radio map in real-time. In the training phase, the user collects the RSSIs of all APs measured at reference points set at regular intervals of 2 to 3m, creating a radio map. In the positioning phase, the reference point, which is most similar to the RSSI, compares the generated radio map from the training phase to the RSSI measured from user movements. This estimates the real-time indoor position. Fingerprint algorithms based on supervised and semi-supervised learning such as support vector machines and principal component analysis are essential for measuring the RSSIs in all indoor areas to produce a radio map. As the building size and the complexity of structures increases, the amount of work and time required also increase. The radio map generation algorithm that uses channel modeling does not require direct measurement, but it requires considerable effort because of building material, three-dimensional reflection coefficient, and numerical modeling of all obstacles. To overcome these problems, this thesis proposes an automatic Wi-Fi fingerprint system that combines an unsupervised dual radio mapping(UDRM) algorithm that reduces the time taken to acquire Wi-Fi signals and leverages an indoor environment with a minimum description length principle(MDLP)-based radio map feedback(RMF) algorithm to simultaneously optimize and update the radio map. The proposed UDRM algorithm in the training phase generates a radio map of the entire building based on the measured radio map of one reference floor by selectively applying the autoencoder and the generative adversarial network(GAN) according to the spatial structures. The proposed learning-based UDRM algorithm does not require labeled data, which is essential for supervised and semi-supervised learning algorithms. It has a relatively low dependency on RSSI datasets. Additionally, it has a high accuracy of radio map prediction than existing models because it learns the indoor environment simultaneously via a indoor two-dimensional map(2-D map). The produced radio map is used to estimate the real-time positioning of users in the positioning phase. Simultaneously, the proposed MDLP-based RMF algorithm analyzes the distribution characteristics of the RSSIs of newly measured APs and feeds the analyzed results back to the radio map. The MDLP, which is applied to the proposed algorithm, improves the performance of the positioning and optimizes the size of the radio map by preventing the indefinite update of the RSSI and by updating the newly added APs to the radio map. The proposed algorithm is compared with a real measurement-based radio map, confirming the high stability and accuracy of the proposed fingerprint system. Additionally, by generating a radio map of indoor areas with different structures, the proposed system is shown to be robust against the change in indoor environment, thus reducing the time cost. Finally, via a euclidean distance-based experiment, it is confirmed that the accuracy of the proposed fingerprint system is almost the same as that of the RSSI-based fingerprint system.|최근 스마트폰과 Wi-Fi가 실생활에 보편화되면서 위치기반 서비스에 대한 개발 분야가 실내 환경으로 점차 확대되고 있다. GPS로 대표되는 실외 위치 인식과 달리 위치기반 서비스를 제공하기 위한 실내 위치 인식 기술은 Wi-Fi, UWB, 블루투스 등과 같은 다양한 근거리 무선 통신 기반의 알고리즘들이 연구되고 있다. 대표적인 실내 위치인식 알고리즘 중 하나인 Fingerprint는 사용자가 수신한 AP 신호의 상대적인 크기를 나타내는 RSSI를 사용하여 위치를 추정한다. 따라서 Fingerprint기반의 알고리즘은 장애물이 많이 존재하는 비가시 거리에서 TOA 방식에 비해 전파의 반사 및 굴절과 같이 왜곡된 무선 환경에 강인하다는 장점이 있다. Fingerprint는 실내의 모든 AP의 RSSI들을 측정하여 Radio map을 제작하는 과정인 학습 단계와 생성된 Radio map의 RSSI들을 실시간으로 측정된 RSSI와 비교하여 사용자의 위치를 추정하는 위치인식 단계로 나누어진다. 학습 단계에서는 위치를 구분하기 위하여 사용자가 2~3m의 일정한 간격으로 설정된 참조 위치들마다 측정되는 모든 AP들의 RSSI를 수집하고 Radio map으로 제작한다. 위치인식 단계에서는 학습 단계에서 제작된 Radio map과 사용자의 이동에 의해 측정되는 RSSI의 비교를 통해 가장 유사한 RSSI 패턴을 가지는 참조 위치가 실시간 실내 위치로 추정된다. 서포트 벡터 머신(SVM), 주성분 분석(PCA) 등과 같이 지도 및 준지도 학습기반의 Fingerprint 알고리즘은 Radio map을 제작하기 위해 모든 실내 공간에서 RSSI의 측정이 필수적이다. 이러한 알고리즘들은 건물이 대형화되고 구조가 복잡해질수록 측정 공간이 늘어나면서 작업과 시간 소모가 또한 급격히 증가한다. 채널모델링을 통한 Radio map 생성 알고리즘은 직접적인 측정 과정이 불필요한 반면에 건물의 재질, 3차원적인 구조에 따른 반사 계수 및 모든 장애물에 대한 수치적인 모델링이 필수적이기 때문에 상당히 많은 작업량이 요구된다. 따라서 본 논문에서는 이러한 문제점들을 해결하고자 학습 단계에서 Wi-Fi 신호의 수집시간을 최소화하면서 실내 환경이 고려된 Unsupervised Dual Radio Mapping(UDRM) 알고리즘과 위치인식 단계에서 Radio map의 최적화가 동시에 가능한 Minimum description length principle(MDLP)기반의 Radio map Feedback(RMF) 알고리즘이 결합된 비지도학습기반의 자동 Wi-Fi Fingerprint를 제안한다. 학습 단계에서 제안하는 UDRM 알고리즘은 뉴럴 네트워크 기반의 비지도 학습 알고리즘인 Autoencoder와 Generative Adversarial Network (GAN)를 공간구조에 따라 선택적으로 적용하여 하나의 참조 층에서 측정된 Radio map을 기반으로 건물전체의 Radio map을 생성한다. 제안하는 비지도 학습 기반 UDRM 알고리즘은 지도 및 준지도 학습에서 필수적인 Labeled data가 필요하지 않으며 RSSI 데이터 세트의 의존성이 상대적으로 낮다. 또한 2차원 실내 지도를 통해 실내 환경을 동시에 학습하기 때문에 기존의 예측 모델에 비해 Radio map의 예측 정확도가 높다. 제안한 알고리즘에 의해 제작된 Radio map은 위치인식 단계에서 사용자의 실시간 위치인식에 적용된다. 동시에 제안하는 MDLP 기반의 자동 Wi-Fi 업데이트 알고리즘은 새롭게 측정되는 AP들의 RSSI의 분포특성을 분석하고 그 결과를 Radio map에 피드백한다. 제안한 알고리즘에 적용된 MDLP는 무분별한 RSSI의 업데이팅을 방지하고 추가되는 AP를 Radio map에 업데이트함으로서 위치인식의 성능을 향상시키고 Radio map의 크기의 최적화가 가능하다. 제안한 알고리즘은 실제 측정기반의 Radio map과 서로 비교를 통해 제안한 Fingerprint 시스템의 높은 안정성과 정확도를 확인하였다. 또한 구조가 다른 실내공간의 Radio map 생성 결과를 통해 실내 환경 변화에 강인함과 학습 시간 측정을 통한 시간 비용이 감소함을 확인하였다. 마지막으로 Euclidean distance 기반 실험을 통하여 실제 측정한 RSSI기반의 Fingerprint 시스템과 제안한 시스템의 위치인식 정확도가 거의 일치함을 확인하였다.Contents Contents ⅰ Lists of Figures and Tables ⅲ Abstract ⅵ Chapter 1 Introduction 01 1.1 Background and Necessity for Research 01 1.2 Objectives and Contents for Research 04 Chapter 2 Wi-Fi Positioning and Unsupervised Learning 07 2.1 Wi-Fi Positioning 07 2.1.1 Wi-Fi Signal and Fingerprint 07 2.1.2 Fingerprint Techniques 15 2.2 Unsupervised Learning 23 2.2.1 Neural Network 23 2.2.2 Autoencoder 28 2.2.3 Generative Adversarial Network 31 Chapter 3 Proposed Fingerprint System 36 3.1 Unsupervised Dual Radio Mapping Algorithm 36 3.2 MDLP-based Radio Map Feedback Algorithm 47 Chapter 4 Experiment and Result 51 4.1 Experimental Environment and Configuration 51 4.2 Results of Unsupervised Dual Radio Mapping Algorithm 56 4.2 Results of MDLP-based Radio Map Feedback Algorithm 69 Chapter 5 Conclusion 79 Reference 81Docto

Terahertz Wireless Channels: A Holistic Survey on Measurement, Modeling, and Analysis

Terahertz (0.1-10 THz) communications are envisioned as a key technology for sixth generation (6G) wireless systems. The study of underlying THz wireless propagation channels provides the foundations for the development of reliable THz communication systems and their applications. This article provides a comprehensive overview of the study of THz wireless channels. First, the three most popular THz channel measurement methodologies, namely, frequency-domain channel measurement based on a vector network analyzer (VNA), time-domain channel measurement based on sliding correlation, and time-domain channel measurement based on THz pulses from time-domain spectroscopy (THz-TDS), are introduced and compared. Current channel measurement systems and measurement campaigns are reviewed. Then, existing channel modeling methodologies are categorized into deterministic, stochastic, and hybrid approaches. State-of-the-art THz channel models are analyzed, and the channel simulators that are based on them are introduced. Next, an in-depth review of channel characteristics in the THz band is presented. Finally, open problems and future research directions for research studies on THz wireless channels for 6G are elaborated.Comment: to appear in IEEE Communications Surveys and Tutorial

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin