Contribution to Efficient Use of Narrowband Radio Channel

Předkládaná práce se soustředí na problematiku využívání úzkopásmového rádiového kanálu rádiovými modemy, které jsou určené pro průmyslové aplikace pozemní pohyblivé rádiové služby, specifikované v dominantní míře Evropským standardem ETSI EN 300 113. Tato rádiová zařízení se používají v kmitočtových pásmech od 30 MHz do 1 GHz s nejčastěji přidělovanou šířkou pásma 25 kHz a ve většině svých instalací jsou využívána ve fixních nebo mobilních bezdrátových sítích. Mezi typické oblasti použití patří zejména datová telemetrie, aplikace typu SCADA, nebo monitorování transportu strategických surovin. Za hlavní znaky popisovaného systému lze označit komunikační pokrytí značných vzdáleností, dané především vysokou výkonovou účinnosti datového přenosu a využívaní efektivních přístupových technik na rádiový kanál se semiduplexním komunikačním režimem. Striktní požadavky na elektromagnetickou kompatibilitu umožňují těmto zařízením využívat spektrum i v oblastech kmitočtově blízkým jiným komunikačním systémům bez nutnosti vkládání dodatečných ochranných frekvenčních pásem. Úzkopásmové rádiové komunikační systémy, v současnosti používají převážně exponenciální digitální modulace s konstantní modulační obálkou zejména z důvodů velice striktních omezení pro velikost výkonu vyzářeného do sousedního kanálu. Dosahují tak pouze kompromisních hodnot komunikační účinnosti. Úpravy limitů příslušných rádiových parametrů a rychlý rozvoj prostředků číslicového zpracování signálu v nedávné době, dnes umožňují ekonomicky přijatelné využití spektrálně efektivnějších modulačních technik i v těch oblastech, kde je prioritní využívání úzkých rádiových kanálů. Cílem předkládané disertační práce je proto výzkum postupů směřující ke sjednocení výhodných vlastností lineárních a nelineárních modulací v moderní konstrukci úzkopásmového rádiového modemu. Účelem tohoto výzkumu je efektivní a „ekologické“ využívání přidělené části frekvenčního spektra. Mezi hlavní dílčí problémy, jimiž se předkládaná práce zabývá, lze zařadit zejména tyto: Nyquistova modulační filtrace, navrhovaná s ohledem na minimalizaci nežádoucích elektromagnetických interferencí, efektivní číslicové algoritmy frekvenční demodulace a rychlé rámcové a symbolové synchronizace. Součástí práce je dále analýza navrhovaného řešení z pohledu celkové konstrukce programově definovaného rádiového modemu v rovině simulací při vyšetřování robustnosti datového přenosu rádiovým kanálem s bílým Gaussovským šumem nebo kanálem s únikem v důsledku mnohacestného šíření signálu. Závěr práce je pak zaměřen na prezentování výsledků praktické části projektu, v níž byly testovány, měřeny a analyzovány dvě prototypové konstrukce rádiového zařízení. Tato finální část práce obsahuje i praktická doporučení, vedoucí k vyššímu stupni využitelnosti spektrálně efektivnějších komunikačních režimů v oblasti budoucí generace úzkopásmových zařízení pozemní pohyblivé rádiové služby.he industrial narrowband land mobile radio (LMR) devices, as considered in this dissertation project, has been subject to European standard ETSI EN 300 113. The system operates on frequencies between 30 MHz and 1 GHz, with channel separations of up to 25 kHz, and is intended for private, fixed, or mobile, radio packet switching networks. Data telemetry, SCADA, maritime and police radio services; traffic monitoring; gas, water, and electricity producing factories are the typical system applications. Long distance coverage, high power efficiency, and efficient channel access techniques in half duplex operation are the primary advantages the system relays on. Very low level of adjacent channel power emissions and robust radio receiver architectures, with high dynamic range, enable for a system’s coexistence with various communication standards, without the additional guard band frequency intervals. On the other hand, the strict limitations of the referenced standard as well as the state of the technology, has hindered the increase in communication efficiency, with which the system has used its occupied bandwidth. New modifications and improvements are needed to the standard itself and to the up-to-date architectures of narrowband LMR devices, to make the utilization of more efficient modes of system operation practically realizable. The main objective of this dissertation thesis is therefore to find a practical way how to combine the favorable properties of the advanced nonlinear and linear digital modulation techniques in a single digital modem solution, in order to increase the efficiency of the narrowband radio channel usage allocated to the new generation of the industrial LMR devices. The main attention is given to the particular areas of digital modem design such as proposal of the new family of the Nyquist filters minimizing the adjacent channel interference, design and analysis of the efficient algorithms for frequency discrimination, fast frame and symbol

Borman Expressway Point-to-Point Wireless Modem

The Federal Highway Administration has a nationwide allocation of five frequency pairs in the 220-222 MHz Narrowband Radio Services band which are intended for application in Intelligent Transportation Systems. These frequencies are available for use by state DOTs (subject to FHWA approval) and provide an attractive solution for certain low to medium bit rate data communications applications. However, given the limited bandwidth available in these channels, very efficient modems will be required to make maximum beneficial use of this resource. The goal of this project was to design, field test, and deploy a digital radio which uses the 220-222 MHz spectral allocation and is suitable for stationary point-to-point data communications applications. The target application for this project was the control (pan, tilt, and zoom) of a video camera located at the interchange of I-65 and the Borman Expressway. The wireless link extends from the camera location to the traffic operations center (approximately 1.5 miles). There were three main tasks needed to produce a deployable modem: 1) interface circuitry was required between the 220 MHz modem and the camera control keypad and the camera pan/tilt/zoom receiver, 2) the fabrication of a compact and rugged transmitter was required, and 3) the fabrication of a compact and rugged receiver was required. The receiver size constraints were more exacting than those of the transmitter as the receiver is deployed in a roadside cabinet, while the transmitter is deployed in the traffic management center. The work plan was divided into a set of twelve tasks. The 220 MHz modem can serve INDOT as a general purpose link for low to medium rate data communications in a wide variety of applications. The most significant issue outstanding with regard to widespread implementation of the technology is the mass production cost and the availability of a reliable source of production versions of the device. Efforts are continuing at both Purdue and Ohio State toward further simplifications aimed at complexity reduction in the receiver. As topics for further study, the following should be considered: 1) a detailed cost/benefit analysis should be made comparing the 220 MHz technology to other alternative technologies, and 2) a preliminary design study of interoperability issues should be performed for the 220 MHz technology in transportation applications

Simplified Frame and Symbol Synchronization for 4–CPFSK with h=0.25

This paper examines the problem of rapid frame and symbol synchronization techniques intended particularly for constant envelope modulation formats M–CPFSK with modulation index h=1/M which are used in strictly bandwidth limited narrowband industrial applications. The data aided and non data aided versions of the algorithm based on digital frequency discrimination are discussed and compared against the synchronization techniques found in literature. Sample wise pattern correlation technique for joint frame and symbol synchronization is also studied. With the focus on a practical digital implementation the advantages and disadvantages of the described approaches are discussed

Robust Sampling Clock Recovery Algorithm for Wideband Networking Waveform of SDR

A novel technique for sampling clock recovery in a wideband networking waveform of a software defined radio is proposed. Sampling clock recovery is very important in wideband networking radio operation as it directly affects the Medium Access adaptive time slot switching rate. The proposed Sampling clock recovery algorithm consists of three stages. In the first stage, Sampling Clock Offset (SCO) is estimated at chip level. In the second stage, the SCO estimates are post-filtered to improve the tracking performance. We present a new post-filtering method namely Steady-State State-Space Recursive Least Squares with Adaptive Memory (S4RLSWAM). For the third stage of SCO compensation, a feedforward Lagrange interpolation based algorithm is proposed. Real-time hardware results have been presented to demonstrate the effectiveness of the proposed algorithms and architecture for systems requiring high data throughput. It is shown that both the proposed algorithms achieve better performance as compared to existing algorithms

Narrowband Interference Suppression in Wireless OFDM Systems

Signal distortions in communication systems occur between the transmitter and the receiver; these distortions normally cause bit errors at the receiver. In addition interference by other signals may add to the deterioration in performance of the communication link. In order to achieve reliable communication, the effects of the communication channel distortion and interfering signals must be reduced using different techniques. The aim of this paper is to introduce the fundamentals of Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA), to review and examine the effects of interference in a digital data communication link and to explore methods for mitigating or compensating for these effects

Robust synchronization for PSK (DVB-S2) and OFDM systems

The advent of high data rate (broadband) applications and user mobility into modern wireless communications presents new challenges for synchronization in digital receivers. These include low operating signal-to-noise ratios, wideband channel effects, Doppler effects and local oscillator instabilities. In this thesis, we investigate robust synchronization for DVB-S2 (Digital Video Broadcasting via Satellite) and OFDM (Orthogonal Frequency Division Multiplexing) systems, as these technologies are well-suited for the provision of broadband services in the satellite and terrestrial channels respectively.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An efficient receiver structure for sweep-spread-carrier underwater acoustic links

In this paper, we present an improved receiver architecture for sweep-spread-carrier modulation, a spread-spectrum technique proposed to effectively contrast the effects of time dispersion over multipath propagation channels in underwater acoustic wireless links. The proposed structure is capable of taking advantage of the energy received from all propagation paths rather than only from the strongest path, as envisaged in the pioneering paper introducing this modulation technique. A hardware version of the modem was implemented in the laboratory and its behavior was assessed and compared, using standard propagation models, to that exhibited by the traditional single-path-based scheme in terms of bit error rate. Results are presented showing that gains of a few decibels can be achieved in signal-to-noise-plus-interference ratio. Issues relevant to carrier/symbol synchronization, channel estimation, and sensitivity to Doppler distortion are also addressed

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