Analysis of DVB-H network coverage with the application of transmit diversity

This paper investigates the effects of the Cyclic Delay Diversity (CDD) transmit diversity scheme on DVB-H networks. Transmit diversity improves reception and Quality of Service (QoS) in areas of poor coverage such as sparsely populated or obscured locations. The technique not only povides robust reception in mobile environments thus improving QoS, but it also reduces network costs in terms of the transmit power, number of infrastructure elements, antenna height and the frequency reuse factor over indoor and outdoor environments. In this paper, the benefit and effectiveness of CDD transmit diversity is tackled through simulation results for comparison in several scenarios of coverage in DVB-H networks. The channel model used in the simulations is based on COST207 and a basic radio planning technique is used to illustrate the main principles developed in this paper. The work reported in this paper was supported by the European Commission IST project—PLUTO (Physical Layer DVB Transmission Optimization)

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

The next-generation wireless technologies, commonly referred to as the sixth generation (6G), are envisioned to support extreme communications capacity and in particular disruption in the network sensing capabilities. The terahertz (THz) band is one potential enabler for those due to the enormous unused frequency bands and the high spatial resolution enabled by both short wavelengths and bandwidths. Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds. Starting from the motivation and use cases, we survey the development and historical perspective of THz communications and sensing with the anticipated 6G requirements. We explore the radio propagation, channel modeling, and measurements for THz band. The transceiver requirements, architectures, technological challenges, and approaches together with means to compensate for the high propagation losses by appropriate antenna and beamforming solutions. We survey also several system technologies required by or beneficial for THz systems. The synergistic design of sensing and communications is explored with depth. Practical trials, demonstrations, and experiments are also summarized. The paper gives a holistic view of the current state of the art and highlights the issues and challenges that are open for further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications Surveys & Tutorial

THz ISAC: A Physical-Layer Perspective of Terahertz Integrated Sensing and Communication

The Terahertz (0.1-10 THz) band holds enormous potential for supporting unprecedented data rates and millimeter-level accurate sensing thanks to its ultra-broad bandwidth. Terahertz integrated sensing and communication (ISAC) is viewed as a game-changing technology to realize connected intelligence in 6G and beyond systems. In this article, challenges from THz channel and transceiver perspectives, as well as difficulties of ISAC are elaborated. Motivated by these challenges, THz ISAC channels are studied in terms of channel types, measurement and models. Moreover, four key signal processing techniques to unleash the full potential of THz ISAC are investigated, namely, waveform design, receiver processing, narrowbeam management, and localization. Quantitative studies demonstrate the benefits and performance of the state-of-the-art signal processing methods. Finally, open problems and potential solutions are discussed

Design and implementation of low complexity wake-up receiver for underwater acoustic sensor networks

This thesis designs a low-complexity dual Pseudorandom Noise (PN) scheme for identity (ID) detection and coarse frame synchronization. The two PN sequences for a node are identical and are separated by a specified length of gap which serves as the ID of different sensor nodes. The dual PN sequences are short in length but are capable of combating severe underwater acoustic (UWA) multipath fading channels that exhibit time varying impulse responses up to 100 taps. The receiver ID detection is implemented on a microcontroller MSP430F5529 by calculating the correlation between the two segments of the PN sequence with the specified separation gap. When the gap length is matched, the correlator outputs a peak which triggers the wake-up enable. The time index of the correlator peak is used as the coarse synchronization of the data frame. The correlator is implemented by an iterative algorithm that uses only one multiplication and two additions for each sample input regardless of the length of the PN sequence, thus achieving low computational complexity. The real-time processing requirement is also met via direct memory access (DMA) and two circular buffers to accelerate data transfer between the peripherals and the memory. The proposed dual PN detection scheme has been successfully tested by simulated fading channels and real-world measured channels. The results show that, in long multipath channels with more than 60 taps, the proposed scheme achieves high detection rate and low false alarm rate using maximal-length sequences as short as 31 bits to 127 bits, therefore it is suitable as a low-power wake-up receiver. The future research will integrate the wake-up receiver with Digital Signal Processors (DSP) for payload detection. --Abstract, page iv

Location-aware and Cooperative Communication in an OFDM based Ultra-wideband Radio System

Die auf dem orthogonalen Frequenzmultiplex (OFDM, Orthogonal Frequency Division Multiplexing) basierende Ultra-Breitband-(UWB, Ultra-wideband) Technologie stellt eine verheißungsvolle Technologie dar, um hohe Datenübertragungsraten und Lokalisierungs- und deren Tracking-Anwendungen zu realisieren. Im Gegensatz zu anderen Systemen ist die Reichweite von OFDM UWB Systemen durch eine strenge Regulierung sehr stark begrenzt. Darüber hinaus ist die Lokalisierung nicht zufriedenstellend. Damit sind bereits die beiden größten Nachteile im Bezug auf bestehende OFDM UWB System benannt. Die Motivation und Hauptaufgabe dieser Arbeit ist damit die Lösung der eben genannten Nachteile. Es wird ein OFDM UWB System vorgestellt, das Space Frequency Block Coding (SFBC) und FFH OFDM miteinander verbindet. Dieses vereinte System wertet die räumliche und frequentielle Diversität eines OFDM-Symbols aus und zeigt dabei eine hohe Güte in der Punkt-zu-Punkt Kommunikation. Beim Design von kooperativen UWB-Systemen wird ein AF-(Amplify-and-Forward) basiertes echtzeitfähriges SFBC-TFC (Time Frequency Code) Protokoll vorgestellt. In Kombination mit den oben genannten Strategien, kann eine Erhöhung in den Reichweite von OFDM UWB Systemen erreicht werden. In den Ausführungen zur Ortung anhand von OFDM UWB Signalen wird ein Algorithmus entwickelt, der aufgrund einer Kanalschätzung eine Minimierung des Phasenversatzes zwischen geschätztem und realem Kanal im Frequenzbereich durchführt. Diese Minimierung erwirkt eine Unterdrückung der Energie am Ende der Kanalimpulsantwort (CIR, Channel Impulse Response) im Zeitbereich. Zum Zweck der einfachen Implementierbarkeit wird das RTT (Round-Trip-Time) Messprotokoll in WiMedia UWB Systemen dahingehend verändert, dass das mobile Gerät keine Minimierung vornimmt. Es leitet seine Informationen an das mit ihm Kommunizierende, stationäre Gerät weiter, das direkt den gesamten Zeitversatz innerhalb des RTT berechnet. Der vorgeschlagene Algorithmus und das vorgeschlagene Protokoll haben ein besseres Ortungsvermögen als bekannte UWB Lokalisierungsprozeduren und bedürfen nur etwas zusätzlicher Berechnungsleistung. Diese Arbeit zeigt, dass Systeme mit hohen Datenraten wie OFDM UWB auch eine gute Lokalisierungsgenauigkeit erreichen können. Zusätzlich ist die Schwachstelle einer limitierten Reichweite ebenso kompensiert worden. Diese Erweiterungen dienen der Entwicklung von nützlichen UWB-Applikationen und sichern den Anteil der OFDM UWB Technik im Markt der drahtlosen Kommunikationssysteme der Zukunft.The Orthogonal Frequency Division Multiplexing (OFDM) based Ultra-wideband (UWB) is one of the most promising technologies for high data rate transmission and localization and tracking applications. However, the restricted transmit power causes a shorter communication range compared to other indoor radio systems. In addition, the ranging functionality is still not well supported by the current OFDM based UWB technology. These two drawbacks are the main disadvantages existing in the current OFDM UWB systems. To get rid of the two drawbacks, is the motivation and main task of this thesis. Within the scope of this thesis, a joint design of Space Frequency Block Coding (SFBC) with Fast Frequency Hopping (FFH) OFDM scheme is investigated in a multiple antenna OFDM UWB system. The joint scheme is able to exploit spatial and frequency domain diversity within one OFDM symbol, and can improve the data transmission quality in point-to-point communication. To the cooperative communication in UWB systems, an Amplify-and-Forward (AF) based distributed SFBC-TFC (Time Frequency Code) protocol is designed. In combination with the aforementioned strategies an increase in the communication range is achieved. Within the scope of this thesis, accurate ranging schemes for the OFDM UWB systems are designed. Fine ToA detection method based on the estimated channel is developed. The fine ToA is estimated by minimizing the accumulated energy of the tail taps of the estimated Channel Impulse Response (CIR). For the purpose of a feasible implementation, the Round-Trip-Time (RTT) measurement protocol in [WiM09] is modified in a way that the complicated computational tasks are burden onto the powerful device. The proposed fine ToA detection method and modified RTT protocol provides an accurate ranging capability and ensures feasible implementation to the MB-OFDM UWB systems. In carrying out this scheme, only some computational tasks are needed, no extra hardware support is required. It is shown in this thesis, OFDM UWB systems with very high data rate transmission and good ranging capability could be achieved, and the weakness of limited communication range is also compensated. These improvements will cause the rise of more valuable UWB applications for customers and ensures a bright future for the OFDM UWB technique

Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years

Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions

COMPRESSIVE QUANTIZATION FOR SCALABLE CLOUD RADIO ACCESS NETWORKS

With the proliferation of new mobile devices and applications, the demand for ubiquitous wireless services has increased dramatically in recent years. The explosive growth in the wireless traffic requires the wireless networks to be scalable so that they can be efficiently extended to meet the wireless communication demands. In a wireless network, the interference power typically grows with the number of devices without necessary coordination among them. On the other hand, large scale coordination is always difficult due to the low-bandwidth and high-latency interfaces between access points (APs) in traditional wireless networks. To address this challenge, cloud radio access network (C-RAN) has been proposed, where a pool of base band units (BBUs) are connected to the distributed remote radio heads (RRHs) via high bandwidth and low latency links (i.e., the front-haul) and are responsible for all the baseband processing. But the insufficient front-haul link capacity may limit the scale of C-RAN and prevent it from fully utilizing the benefits made possible by the centralized baseband processing. As a result, the front-haul link capacity becomes a bottleneck in the scalability of C-RAN. In this dissertation, we explore the scalable C-RAN in the effort of tackling this challenge. In the first aspect of this dissertation, we investigate the scalability issues in the existing wireless networks and propose a novel time-reversal (TR) based scalable wireless network in which the interference power is naturally mitigated by the focusing effects of TR communications without coordination among APs or terminal devices (TDs). Due to this nice feature, it is shown that the system can be easily extended to serve more TDs. Motivated by the nice properties of TR communications in providing scalable wireless networking solutions, in the second aspect of this dissertation, we apply the TR based communications to the C-RAN and discover the TR tunneling effects which alleviate the traffic load in the front-haul links caused by the increment of TDs. We further design waveforming schemes to optimize the downlink and uplink transmissions in the TR based C-RAN, which are shown to improve the downlink and uplink transmission accuracies. Consequently, the traffic load in the front-haul links is further alleviated by the reducing re-transmissions caused by transmission errors. Moreover, inspired by the TR-based C-RAN, we propose the compressive quantization scheme which applies to the uplink of multi-antenna C-RAN so that more antennas can be utilized with the limited front-haul capacity, which provide rich spatial diversity such that the massive TDs can be served more efficiently