Mitigation of am interference in digital transmission

The plain-old-telephone-system (POTS) is now increasingly used to carry high-speed data such as for Internet purpose. However, problem can occur if the telephone network is in close proximity to an AM radio transmitter, transmitting high power signal at a frequency which overlaps the bandwidth of the Internet transmission. The interfering electromagnetic field can induced enough current and voltage in the telephone network and causing significant data errors. This report presents a study on the effects of high-powered AM transmission at 576 kHz on a digital transmission system. A GTEM Cell was used to generate the 576kHz clectric field intensity varying from lV/m to 15 V/m with 80% amplitude modulation. The electric field is imposed on a section of the cable and the Bit Error Rate (BER) is noted using Data Tools 5000. Shielding technique was employed using four conducted materials (soft steel, hard steel, aluminum and copper) in order to test the attenuation of the electric field reaching the cable. Measured results showed that copper (a= 5.87 x 107 S/m, fr =1) can reduce up to 70% of the BER. The relationship between electric field E and BER for copper is expressed as BER = 2 x 10~5 e0-3"^' +2.48x10"^ indicating that the BER increases exponentially with the magnitude of the applied electric field. It is obvious from the work done in this project that any network situated near a high-powered electromagnetic field transmitter should employ a good shielded cabling system. It is recommended that further study need to be carried out to find ways of mitigating the effects of the interfering field such filtering and grounding

Cost effective DSL solutions for the developing countries.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Westville, 2004.Developing countries in Africa present a graphic picture of the digital divide. High costs associated with serving rural customers are the major cause of uneven distribution of services. Rural areas are characterised by a high rate of unemployment and a poor level of education. This results in a scenario where most of the residents are unable to utilize IT resources. Some people in these areas are not informed about the availability and importance of these technologies in the market. Those who are academically fit for accessing these technologies often cannot afford them. Some of the areas still have no existing telecommunications infrastructure. High deployment costs associated with broadband services makes it even more challenging to deploy such services in this environment. In Africa approximately 80% of the population is living in rural areas, which alone creates a demand for the coverage of rural regions. Leaving such a large number of residents not connected, means poor medical care, students cannot participate in distance learning programs which means poor quality of education, poor performance in businesses, poor farming and crippling delivery of government services. DSL technologies were originally designed to suit suburban to urban conditions. In this research it is shown that broadband services can be delivered to rural people by applying DSL technologies, using the existing telecommunications infrastructure. This will mean significant savings, as it does not need core network investments. DSL increases network capacity to a network, which is no longer limited to voice. With this technology a number different high bandwidth applications are delivered to the homes, schools, hospitals, telecentres and small businesses. The cost effectiveness of these technologies for several reach and rural traffic environment is investigated. This is done by investigating several promising DSL solutions in terms of diverse geography, demographics and other cost dictating parameters

Mitigation of impulsive noise for SISO and MIMO G.fast system

To address the demand for high bandwidth data transmission over telephone transmission lines, International Telecommunication Union (ITU) has recently completed the fourth generation broadband (4GBB) copper access network technology, known as G.fast. Throughout this thesis, extensively investigates the wired broadband G.fast coding system and the novel impulsive noise reduction technique has been proposed to improve the performance of wired communications network in three different scenarios: single-line Discrete Multiple Tone (DMT)- G.fast system; a multiple input multiple-output (MIMO) DMTG.fast system, and MIMO G.fast system with different crosstalk cancellation methods. For each of these scenarios, however, Impulsive Noise (IN) is considered as the main limiting factor of performance system. In order to improve the performance of such systems, which use higher order QAM constellation such as G.fast system, this thesis examines the performance of DMT G.fast system over copper channel for six different higher signal constellations of M = 32, 128, 512, 2048, 8192 and 32768 in presence of IN modelled as the Middleton Class A (MCA) noise source. In contrast to existing work, this thesis presents and derives a novel equation of Optimal Threshold (OT) to improve the IN frequency domain mitigation methods applied to the G.fast standard over copper channel with higher QAM signal constellations. The second scenario, Multi-Line Copper Wire (MLCW) G.fast is adopted utilizing the proposed MLCW Chen model and is compared to a single line G-fast system by a comparative analysis in terms of Bit-Error-Rate(BER) performance of implementation of MLCW-DMT G.fast system. The third scenario, linear and non-linear crosstalk crosstalk interference cancellation methods are applied to MLCW G.fas and compared by a comparative analysis in terms of BER performance and the complexity of implementation.University of Technology for choosing me for their PhD scholarship and The Higher Committee For Education Development in Iraq(HCED

Analysis of MIMO Communications Systems Based on Experimentally Observed Channels

This thesis presents an analysis of multiple-input/multiple-output (MIMO) communications systems where the objective is to provide a unified solution to the problems of (i) crosstalk coupling in transmission line channels (ii) multi-path fading in the time variant high frequency wireless channel. In the case of transmission line channels, a comparative analysis is presented of the performance of MIMO communications systems based on balanced CAT 5 twisted-pair transmission lines, balanced twisted-pair telephone transmission lines scheme as well as unbalanced flat-pair transmission lines. The unbalanced flat-pair transmission lines are viewed as a model for digital subscriber lines (DSLs) which may be deemed out-of-range for high speed internet connections because of the circumstances of poor balance, high insertion losses and high degrees of crosstalk. This comparative analysis is then extended to examine effect of imperfect knowledge of the transmission line channels on MIMO communications system performance. In the case of wireless channels, an analysis is presented which investigates the effect of both the Rayleigh and Ricean channels on MIMO communications system performance. Again the analysis of the wireless channels is extended to examine the effect of imperfect knowledge of the channel on MIMO communications systems performance. All of the analyses in this work are based on experimentally observed channels. In the case of the transmission line channels, it is concluded that MIMO communications systems do offer the possibility of high speed internet connectivity on transmission lines that, hereto, would have been considered out-of-range for such services. Considering the CAT 5 transmission line channels, it is concluded that the MIMO communications system provide enhancement at frequencies above 50 MHz and therefore the possibly of extending length and coverage above the standard 100 metres is proposed. On the other hand, the improved performance of the twisted-pair telephone transmission lines is consistent over the range from 300 kHz to 100 MHz when the MIMO system is applied. For all the transmission line channels that are examined, the extent of imperfect knowledge of the channel that can be allowed while maintaining a reasonable MIMO communications system performance is indicated. In the case of the wireless channels, it is concluded that MIMO communications system performance is better in the case of Rayleigh channel than in the case of Ricean channel provided that the degree of correlation of the multi-path channel impulse response components is equivalent. Also, as the number of transmitters and receivers, N T, increases the effect of a given degree of imperfect knowledge of the wireless channel becomes more detrimental on MIMO communication system performance. This work thus indicates the extent of imperfect knowledge of the wireless channel that can be allowed while maintaining a reasonable MIMO communications system performance. The trade-off between increased capacity gain and decreased accuracy of knowledge of the channel as the dimension, N T, was increased is highlighted

Interference mitigation techniques for wireless OFDM

Orthogonal Frequency Division Multiplexing (OFDM) is a promising multicarrier wireless system for transmission of high-rate data stream with spectral efficiency and fading immunity. Conventional OFDM system use efficient IFFT and FFT to multiplex the signals in parallel at the transmitter and receiver respectively. On the other hand, wavelet based OFDM system uses orthonormal wavelets which are derived from a multistage tree-structured wavelet family. The Fourier based and wavelet based OFDM systems are studied in this dissertation. Two types of QAM schemes, circular and square modulations are used to compare the performance in both OFDM systems. A new approach of determining exact BER for optimal circular QAM is proposed. In addition, the presence of narrowband interference (NBI) degrades the performance of OFDM systems. Thus, a mitigation technique is necessary to suppress NBI in an OFDM system. Recent mitigation techniques can be broadly categorized into frequency domain cancellation, receiver windowing and excision filtering. However, none of the techniques considers wavelet based OFDM. Therefore, an interference cancelation algorithm has been proposed to work for both OFDM platforms. The performance results of two OFDM schemes applicable to digital video broadcasting (DVB)-terrestrial system and under the effect of impulsive noise interference are also studied. BER performances are obtained in all results. It has been shown that wavelet based OFDM system has outperformed Fourier based OFDM system in many cases

Signal processing techniques for mobile multimedia systems

Recent trends in wireless communication systems show a significant demand for the delivery of multimedia services and applications over mobile networks - mobile multimedia - like video telephony, multimedia messaging, mobile gaming, interactive and streaming video, etc. However, despite the ongoing development of key communication technologies that support these applications, the communication resources and bandwidth available to wireless/mobile radio systems are often severely limited. It is well known, that these bottlenecks are inherently due to the processing capabilities of mobile transmission systems, and the time-varying nature of wireless channel conditions and propagation environments. Therefore, new ways of processing and transmitting multimedia data over mobile radio channels have become essential which is the principal focus of this thesis. In this work, the performance and suitability of various signal processing techniques and transmission strategies in the application of multimedia data over wireless/mobile radio links are investigated. The proposed transmission systems for multimedia communication employ different data encoding schemes which include source coding in the wavelet domain, transmit diversity coding (space-time coding), and adaptive antenna beamforming (eigenbeamforming). By integrating these techniques into a robust communication system, the quality (SNR, etc) of multimedia signals received on mobile devices is maximised while mitigating the fast fading and multi-path effects of mobile channels. To support the transmission of high data-rate multimedia applications, a well known multi-carrier transmission technology known as Orthogonal Frequency Division Multiplexing (OFDM) has been implemented. As shown in this study, this results in significant performance gains when combined with other signal-processing techniques such as spa ce-time block coding (STBC). To optimise signal transmission, a novel unequal adaptive modulation scheme for the communication of multimedia data over MIMO-OFDM systems has been proposed. In this system, discrete wavelet transform/subband coding is used to compress data into their respective low-frequency and high-frequency components. Unlike traditional methods, however, data representing the low-frequency data are processed and modulated separately as they are more sensitive to the distortion effects of mobile radio channels. To make use of a desirable subchannel state, such that the quality (SNR) of the multimedia data recovered at the receiver is optimized, we employ a lookup matrix-adaptive bit and power allocation (LM-ABPA) algorithm. Apart from improving the spectral efficiency of OFDM, the modified LM-ABPA scheme, sorts and allocates subcarriers with the highest SNR to low-frequency data and the remaining to the least important data. To maintain a target system SNR, the LM-ABPA loading scheme assigns appropriate signal constella tion sizes and transmit power levels (modulation type) across all subcarriers and is adapted to the varying channel conditions such that the average system error-rate (SER/BER) is minimised. When configured for a constant data-rate load, simulation results show significant performance gains over non-adaptive systems. In addition to the above studies, the simulation framework developed in this work is applied to investigate the performance of other signal processing techniques for multimedia communication such as blind channel equalization, and to examine the effectiveness of a secure communication system based on a logistic chaotic generator (LCG) for chaos shift-keying (CSK)

Sistema de comunicaciones tierra-tierra mediante anillo de fibra óptica entre emplazamientos de navegación aérea

El proyecto que se expondrá a continuación trata de dar solución a los requisitos especificados por el cliente principal, basados en el diseño e instalación de un sistema de comunicaciones mediante fibra óptica entre los distintos emplazamientos de navegación aérea existentes dentro de un aeropuerto. Dentro de un complejo aeroportuario existen distintos emplazamientos que albergan ayudas para navegación aérea, y es imprescindible la comunicación entre todos. Dentro de ellos se encuentra la Torre de Control desde donde se controlan y gestionan todas las operaciones de las aeronaves. También forman parte los diferentes emplazamientos que dan soporte al aterrizaje, despegue y navegación. Se realizará una revisión de todas las tecnologías de comunicaciones existentes, como son las basadas en multiplexación de la frecuencia, tiempo y longitud de onda. También los protocolos de comunicaciones como pueden ser SNMP (Protocolo Simple de Gestión de Red), TCP (Protocolo de Control de Transporte), IP (Protocolo de Internet) y Ethernet. Para dar solución al presente proyecto, se utilizará SDH (Jerarquía Digital Síncrona) como principal tecnología. Sobre SDH se pueden destacar mejoras en la velocidad de transmisión, mayor fiabilidad con mecánicos automáticos de protección ante fallos y gran capacidad de ampliación en el futuro. El diseño y ejecución del proyecto se llevará a cabo cumpliendo unas directrices comunes, que responden a unos estándares de gestión de proyectos, mediante herramientas como el diagrama de tiempos de ejecución del proyecto, normativas de seguridad, informes de seguimiento, etc. Por último, se obtendrán las conclusiones finales técnicas de cara a la mejora en futuros proyectos que se realicen en similares condiciones.This project is a solution to the specified requirements by the primary client, based on the design and installation of a fiber optic communication between different air navigation sites in an airport. Inside an airport there are many sites that have air navigation aids and the communication is essential between them. The Control Tower is the principal site where you can control and manage all aircraft operations. Also includes various sites that support the landing, takeoff and navigation. A revision of the existing communication technologies will be provided, such as those based on frequency, time and wavelength division multiplexing. Also the communications protocols such as SNMP (Simple Network Management Protocol), TCP (Transport Control Protocol), IP (Internet Protocol) and Ethernet. To solve this project, SDH (Synchronous Digital Hierarchy) has been used as the main technology in this project. Regarding SDH, it can be highlighted improvements in transmission speed, higher reliability with automatic mechanical failure protection and highly scalable in the future. Design and implementation will be carried out in compliance with standard guidelines, which meet standards of project management, using tools such as the timing diagram, safety regulations, monitoring reports, etc. Finally, technical conclusions for the enhancement in future project carried out in similar conditions, will be obtained.Ingeniería Técnica en Sistemas de Telecomunicació