Spread spectrum techniques for indoor wireless IR communications

Multipath dispersion and fluorescent light interference are two major problems in indoor wireless infrared communications systems. Multipath dispersion introduces intersymhol interference at data rates above 10 Mb/s, while fluorescent light induces severe narrowband interference to baseband modulation schemes commonly used such as OOK and PPM. This article reviews the research into the application of direct sequence spread spectrum techniques to ameliorate these key channel impairments without having to resort to complex signal processing techniques. The inherent properties of a spreading sequence are exploited in order to combat the ISI and narrowband interference. In addition, to reduce the impact of these impairments, the DSSS modulation schemes have strived to be bandwidth-efficient and simple to implement. Three main DSSS waveform techniques have been developed and investigated. These are sequence inverse keying, complementary sequence inverse keying, and M-ary biorthogonal keying (MBOK). The operations of the three systems are explained; their performances were evaluated through simulations and experiments for a number of system parameters, including spreading sequence type and length. By comparison with OOK, our results show that SIK, CSIK, and MBOK are effective against multipath dispersion and fluorescent light interference becausc the penalties incurred on the DSSS schemes are between 0-7 dB, while the penalty on OOK in the same environment is more than 17 dB. The DSSS solution for IR wireless transmission demonstrates that a transmission waveform can he designed to remove the key channel impairments in a wireless IR system

A New Scheme for Spreading & De-spreading in the Direct Sequence Spread Spectrum Mechanism

Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) techniques are widely used to implement code-division multiple access (CDMA) in wireless communication systems.  Both DSSS and FHSS systems help reducing the effects of interference on the transmitted information making it robust against channel impairments.  DSSS uses a signal bandwidth that is much broader than the information signal bandwidth.  Traditionally, the wide band signal is generated by multiplying the narrowband information signal with a binary code, often designated as a spreading code, to generate the wideband signal that is transmitted. The original information signal can be recreated at the receiver by multiplying the received wideband signal by the same binary code (now designated as a de-spreading code) used to generate the wideband transmitted signal.  To extract the original information signal, the spreading and de-spreading codes must be in synchronism at the receiver and amplitude match with each other.  A new modification for the direct sequence spread spectrum is proposed in this paper. The mechanism introduced in this approach implicates generating the wideband signal by circularly shifting the spreading code (PN) by n places, where n represents the value of the current byte of information signal. The yielded signal is modulated using BPSK modulator before transmitting it.  The original information signal is extracted at the receiver by correlating the received signal (which is actually the original spread sequence circularly shifted by n places) with a locally generated replica of the spreading code.  The position of the maximum value of the cross-correlation vector represents the value of the information signal byte.  The proposed configuration has been implemented using Simulink simulator and the obtained results show that its performance is identical with the conventional DSSS

Downlink space-frequency preequalization techniques for TDD MC-CDMA mobile radio systems

The paper considers downlink space-frequency preequalizations techniques for time division duplex (TDD) MC-CDMA. We consider the use of antenna arrays at the base station (BS) and analytically derive different preequalization schemes for two different receiver configurations at the mobile terminal: a simple despread receiver without channel equalization and an equal-gain combiner (EGC) conventional receiver. We show that the space-frequency preequalization approach proposed allows to format the transmitted signals so that the multiple access interference at mobile terminals is reduced allowing to transfer the most computational complexity from mobile terminal to the BS. Simulation results are carried out to demonstrate the effectiveness of the proposed preequalization schemes.European project IST-2001-32620 - MATRICEFCT - POSI/CPS/46701/200

Nearly orthogonal, doppler tolerant waveforms and signal processing for multi-mode radar applications

In this research, we investigate the design and analysis of nearly orthogonal, Doppler tolerant waveforms for diversity waveform radar applications. We then present a signal processing framework for joint synthetic aperture radar (SAR) and ground moving target indication (GMTI) processing that is built upon our proposed waveforms. ^ To design nearly orthogonal and Doppler tolerant waveforms, we applied direct sequence spread spectrum (DSSS) coding techniques to linear frequency modulated (LFM) signals. The resulting transmitted waveforms are rendered orthogonal using a unique spread spectrum code. At the receiver, the echo signal can be decoded using its spreading code. In this manner, transmit orthogonal waveforms can be matched filtered only with the intended receive signals. ^ Our proposed waveforms enable efficient SAR and GMTI processing concurrently without reconfiguring a radar system. Usually, SAR processing requires transmit waveforms with a low pulse repetition frequency (PRF) rate to reduce range ambigu- ity; on the other hand, GMTI processing requires a high PRF rate to avoid Doppler aliasing and ambiguity. These competing requirements can be tackled by employing some waveforms (with low PRF) for the SAR mission and other waveforms (with high PRF) for the GMTI mission. Since the proposed waveforms allow separation of individual waveforms at the receiver, we can accomplish both SAR and GMTI processing jointl

IQ imbalance reduction in a SMI multi-antenna receiver by using a code multiplexing front-end

International audienceIn this paper, we address the IQ imbalance sensibility of the code multiplexing front-end architecture. This innovative architecture has been recently proposed in order to reduce the analog complexity of an antenna diversity receiver front-end. An interesting characteristic of this structure is that the resulting IQ imbalance is equal for each received baseband signal. Associated with Single Matrix Inversion algorithm, this property ensures a high IQ imbalance robustness. A global antenna diversity system including analog front-end and digital processing has been implemented in order to perform simulation validation. Results show that the bit error rate does not increase significantly with the multiplexing and this increase is compensated for a high IQ imbalance

Infrared ranging in multipath environments for indoor localization of mobile targets

Esta tesis aborda el problema de la medida de diferencias de distancia mediante señales ópticas afectadas por multicamino, aplicada a la localización de agentes móviles en espacios interiores. Los avances en robótica, entornos inteligentes y vehículos autónomos han creado un campo de aplicación específico para la localización en interiores, cuyos requerimientos de precisión (en el rango de los cm) son muy superiores a los demandados por las aplicaciones de localización orientadas a personas, en cuyo contexto se han desarrollado la mayor parte de las alternativas tecnológicas. La investigación con métodos de geometría proyectiva basados en cámaras y de multilateración basados en medida de distancia con señales de radiofrecuencia de banda ancha, de ultrasonido y ópticas han demostrado un rendimiento potencial adecuado para cubrir estos requerimientos. Sin embargo, todas estas alternativas, aún en fase de investigación, presentan dificultades que limitan su aplicación práctica. En el caso de los sistemas ópticos, escasamente estudiados en este contexto, los trabajos previos se han basado en medidas de diferencia de fase de llegada de señales infrarrojas moduladas sinusoidalmente en intensidad. Una infraestructura centralizada computa medidas diferenciales, entre receptores fijos, de la señal emitida desde el móvil a posicionar, y calcula la posición del móvil mediante trilateración hiperbólica a partir de éstas. Estas investigaciones demostraron que se pueden alcanzar precisiones de pocos centímetros; sin embargo, las interferencias por multicamino debidas a la reflexión de la señal óptica en superficies del entorno pueden degradar esta precisión hasta las decenas de centímetros dependiendo de las características del espacio. Así pues, el efecto del multicamino es actualmente la principal fuente de error en esta tecnología, y por tanto, la principal barrera a superar para su implementación en situaciones reales. En esta tesis se propone y analiza un sistema de medida con señales ópticas que permite obtener estimaciones de diferencias de distancia precisas reduciendo el efecto crítico del multicamino. El sistema propuesto introduce una modulación con secuencias de ruido pseudoaleatorio sobre la modulación sinusoidal típicamente usada para medida de fase por onda continua, y aprovecha las propiedades de ensanchamiento en frecuencia de estas secuencias para reducir el efecto del multicamino. El sistema, que realiza una doble estimación de tiempo y fase de llegada, está compuesto por una etapa de sincronización que posibilita la demodulación parcialmente coherente de la señal recibida, seguida de un medidor diferencial de fase sobre las componentes desensanchadas tras la demodulación. Las condiciones de multicamino óptico típicas en espacios interiores, con una componente de camino directo claramente dominante, permiten que el proceso de demodulación recupere más potencia del camino directo que del resto de contribuciones, reduciendo el efecto del multicamino en la estimación final. Los resultados obtenidos demuestran que la aplicación del método propuesto permitiría realizar posicionamiento a partir de señales ópticas con el rendimiento adecuando para aplicaciones de robótica y guiado de vehículos en espacios interiores; además, el progresivo aumento de la potencia y el ancho de banda de los dispositivos optoelectrónicos disponibles permite esperar un incremento considerable de las prestaciones de la propuesta en los próximos años

Sistema de comunicação por luz visível baseado em FPGA

Mestrado em Engenharia Electrónica e TelecomunicaçõesO crescente desenvolvimento da indústria electrónica veio acelerar as potencialidades de variadíssimos dispositivos de comunicação. A comunicação hoje em dia é de fácil acesso para qualquer pessoa, onde quer que esteja. Em situações desfavoráveis exige-se que o sistema de comunicação tenha a capacidade de atenuar as interferências que corrompem o sinal de informação desejado. Vários sistemas de comunicação e dispositivos sofisticados têm sido desenvolvidos com intuito de salvaguardar as pretensões e os anseios à medida que os nossos hábitos e necessidades se tornam mais exigentes alterando. Apesar de ter surgido no auge da segunda guerra mundial o sucesso de técnica por espalhamento de espectro (Spread Spectrum) só ficou comprovado há cerca de duas décadas por falta de tecnologias avançadas. O espalhamento de espectro é uma das técnicas de modulação de sinal de transmissão com propriedades que não se encontram em nenhuma outra técnica de modulação. Um dos objectivos desta dissertação é desenvolver um sistema de comunicação spread spectrum por meio de luz visível. A disseminação dos bits de dados foi feita recorrendo uma das duas principais técnicas de espalhamento de espectro: o espalhamento por sequência directa (Direct Sequence Spread Spectrum, DSSS), usando a sequência de Barker modificada de comprimento 10. Todo o sistema de comunicação foi desenvolvido em software MATLAB utilizando a ferramenta de suporte System Generator da Xilinx para posterior lançamento numa plataforma FPGA. Arquitectura do receptor usa um conversor analógico digital de 14 bits de resolução e um Matched Filter para uma rápida sincronização e aquisição de dados.The increasing development, of the electronics industry the potential for a variety of different communication devices has accelerated. Communications today are easily accessible to anyone, wherever one is. Under unfavorable situations the communication system must have the ability to mitigate interference that corrupts the desired information in the signal. Several communication systems and sophisticated devices, have been developed with a view to safeguard the aspirations and desires as our habits and needs are changing. Although originated at the height of the second world war the success of spread spectrum technology has only been demonstrated about two decades ago due to the lack of advanced technologies. Spread spectrum is a modulation technique for signal transmission with unique properties not found in any other modulation technique. One of the objectives of this dissertation is the development and implementation of a spread spectrum communication system using visible light. The spread of the data bits was done using one of two main spread spectrum techniques - Direct Sequence Spread Spectrum (DSSS) - using a modified Barker sequence of length 10. The entire communication system was developed using the MATLAB software tool to support the Xilinx System Generator for later release on a platform FPGA. The receiver architecture uses 14-bit analog to digital converter resolution and a Matched Filter for a quick data synchronization and acquisition