Contribution aux études en communications numériques pour les réseaux optiques sans fil

As portable computers and communication terminals become more powerful and are more widely deployed, the demand for very high data rate wireless networks has exploded. An optical wireless (OW) transmission represents an attractive solution for many indoor and home applications. Because of the difficulties and the cost of the phase control and detection in wireless optics, current systems use intensity modulation techniques and direct detection (IM/DD). OW systems offer several advantages including the potential to achieve very high data rates and the immunity to radio frequency (RF) interferences. OW techniques benefit from a wide unregulated bandwidth that can be reused in a dense fashion. However, this bandwidth will be limited by the characteristics of the optical components, the product's availability and the propagation properties. Taking the demand for very high data rates and good link budgets into consideration requires scientific advances in different fields, such as the following : The optical receiver components and their key characteristics The bandwidth efficient modulation schemes allowing high data rates transmissions with limited bandwidth. This dissertation is a contribution to the second field. Particularly, we investigate the adaptation of coded orthogonal frequency division multiplexing (COFDM) and COFDM/OQAM (also referred as COFDM/Offset quadrature amplitude modulation) to OW constraints. The modified COFDM and the modified COFDM/OQAM increase the data rate and mitigate the inter symbol interference (ISI). We also propose spatial division multiplexing techniques combined to these multi-carrier modulations for OW networks. Both, non-iterative and iterative receivers are studied.RENNES1-BU Sciences Philo (352382102) / SudocCESSON SEVIGNE-Télécom Breta (350512301) / SudocBREST-Télécom Bretagne (290192306) / SudocSudocFranceF

On free-space optic communication with alamouti-type coding and direct detection

International audienceBy transmitting unipolar positive signals, a novel association of Alamouti space-time coding to free-space optic(FSO) communication is presented. We examine intensity modulation (IM) based on electrical fast Fourier transform (FFT)design with Hermitian symmetry. The proposed technique aims at limiting signal fading due to scintillation. It maximizes the spatial diversity, increases the reliability, and makes it possible to use digital complex QAM modulations while preserving direct detection (DD)

Diffuse infrared personal optical wireless based and modified OFDM/OQAM

International audienceInfrared personal optical wireless (POW) refers to use of free-space propagation of infrared for short range communications in an indoor context. POW offers several advantages over radio technologies, making it an attractive solution for home networks. Orthogonal modulations such as OFDM are currently used in many radio transmission standards. Among these modulations, OFDM/OQAM is an interesting alternative to classical OFDM, as it does not require the use of guard interval and it has an optimal spectral efficiency. In this paper, over a diffuse infrared channel based on experimental measurements, and with a modified scheme adaptable to optical system constraints, we investigate the combination of OFDM/OQAM and POW technology. Using intensity modulation and direct detection, we show that our modified OFDM/OQAM system increases the bit rate of POW communications, mitigates the effects of inter symbol interference (ISI), and could outperform conventional OFDM schemes with cyclic-prefix

Coded OFDM and OFDM/OQAM for intensity modulated optical wireless systems

International audienceInfrared optical wireless (OW) is a promising technology associating free-space propagation and infrared radiation for home networks. OW offers several advantages over radio technologies, making it an attractive solution for short range communications. However, OW technology is not as mature as for radio; further advanced studies regarding optical components and physical layer issues are still open. Coded orthogonal modulations such as Coded OFDM (COFDM) are currently used in many radio and fixed transmission systems. Among these modulations, COFDM/OQAM is an interesting alternative to classical COFDM modulation, as it does not require the use of a guard interval and it has an optimal spectral efficiency. In this paper, we present a comparative study of modified COFDM and modified COFDM/OQAM schemes adapted to intensity modulation and direct detection over a diffuse channel based on experimental measurements. If M-ary QAM modulation is used, the two schemes offer the possibility to increase the bit rate of OW communications. They also mitigate the effects of inter symbol interference (ISI). On the other hand, modified COFDM/OQAM could outperform modified COFDM schemes with a cyclic-prefix

Hybrid wireless optics (HWO): Building the next-generation home network

Gigabit home access networks (HANs) are a pivotal technology to be developed if the European Union (EU) Vision of the Future Internet is to be realised. Consumers will require such HANs to be simple to install, without any new wires, and easy enough to use so that information services running on the HAN will be “just another utility,” as, for instance, electricity, water and gas are today. The hOME Gigabit Access (OMEGA) HAN project [1] aims at bridging the gap between home and access network, providing Gbit/s connectivity to users. The project considers a combination of various technologies such as radio frequency (RF) and free-space or wireless optical links (FSO-operating at infrared and visible wavelengths) in order to meet user demands and provide wireless connectivity within and the home and its surroundings. When combined with power-line communications this enables a home backbone that meets the “without new wires” vision. A technology-independent MAC layer will control this network and provide services as well as connectivity to any number of devices the user wishes to connect to it in any room in a house/apartment, and further, this MAC layer will allow the service to follow the user from device to device. In order to make this vision come true, substantial progress is required in the fields of optical-wireless physical layers, in protocol design, and in system architecture

On free-space optic communication with alamouti-type coding and direct detection

International audienceBy transmitting unipolar positive signals, a novel association of Alamouti space-time coding to free-space optic(FSO) communication is presented. We examine intensity modulation (IM) based on electrical fast Fourier transform (FFT)design with Hermitian symmetry. The proposed technique aims at limiting signal fading due to scintillation. It maximizes the spatial diversity, increases the reliability, and makes it possible to use digital complex QAM modulations while preserving direct detection (DD)

Modified OFDM/OQAM for personal optical wireless with direct detection

International audiencePersonal optical wireless (POW) refers to use of free- space propagation of light for short range communications in an indoor context. POW offers several advantages over radio technologies, making it an attractive solution for home networks. Orthogonal modulations such as OFDM are currently used in many radio transmission standards. Among these modulations, OFDM/OQAM is an interesting alternative to classical OFDM modulation, as it does not require the use of guard interval and it has an optimal spectral efficiency. In this paper, with a modified scheme adaptable to optical system constraints, we investigate the combination of OFDM/OQAM and POW technology over multipath optical wireless channels. Using intensity modulation and direct detection, we show that our modified OFDM/OQAM system increases the bit rate of POW communications and mitigates the effects of inter symbol interference (ISI) due to optical light reflections

Coded OFDM and OFDM/OQAM for Intensity Modulated Optical Wireless Systems

Abstract — Infrared optical wireless (OW) is a promising technology associating free-space propagation and infrared radiation for home networks. OW offers several advantages over radio technologies, making it an attractive solution for short range communications. However, OW technology is not as mature as for radio; further advanced studies regarding optical components and physical layer issues are still open. Coded orthogonal modulations such as Coded OFDM (COFDM) are currently used in many radio and fixed transmission systems. Among these modulations, COFDM/OQAM is an interesting alternative to classical COFDM modulation, as it does not require the use of a guard interval and it has an optimal spectral efficiency. In this paper, we present a comparative study of modified COFDM and modified COFDM/OQAM schemes adapted to intensity modulation and direct detection over a diffuse channel based on experimental measurements. If M-ary QAM modulation is used, the two schemes offer the possibility to increase the bit rate of OW communications. They also mitigate the effects of inter symbol interference (ISI). On the other hand, modified COFDM/OQAM could outperform modified COFDM schemes with a cyclic-prefix. Index Terms — OW, optical wireless, infrared, FSO, intensity modulation, IM/DD, COFDM, OQA

Improved bit error rate estimation over experimental optical wireless channels

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