Channel modeling and simulation of a Ka-band videoconferencing system

This project was funded by the EU 6th Framework Program (FP6) project TWISTER.The effect of propagation impairments phenomena is quite significant for systems operating in the Ka-band frequency range, resulting in a reduction in the end-to-end quality of a videoconferencing session. These systems generally utilize complex coding architectures, like the digital video broadcasting (DVB) standard, in order to maintain an acceptable quality of service (QoS) at low signal-to-noise ratios. Although these systems are finding more and more applications, the literature is still relatively poor in the description of models capable of representing such complex architectures. This paper proposes a videoconferencing channel model, developed in software, which can accurately model a complex videoconferencing system according to the DVB standard at the required quality and availability.peer-reviewe

A statistical bit error generator for emulation of complex forward error correction schemes

Forward error correction (FEC schemes are generally used in wireless communication systems to maintain an acceptable quality of service. Various models have been proposed in literature to predict the end-to-end quality of wireless video systems. However, most of these models utilize simplistic error generators which do not accurately represent any practical wireless channel. A more accurate way is to evaluate the quality of a video system using Monte Carlo techniques. However these necessitate huge computational times, making these methods unpractical. This paper proposes an alternative method that can be used in modeling of complex communications systems with minimal computational time. The proposed three random variable method was used to model two FEC schemes adopted by the digital video broadcasting (DVB) standard. Simulation results confirm that this method closely matches the performance of the considered communication systems in both bit error rate (BER) and peak signal-to-noise ratio (PSNR).peer-reviewe

Simulation of Error Control Schemes for Wireless and Satellite ATM

Abstract This paper summarizes the results of a set of simulations of error control schemes for transmission of ATM cells in Wireless and Satellite ATM networks. For Wireless ATM networks, we consider a scheme which incorporates separate FECs for ATM cell header and payload. This scheme is an effective scheme and achieves a trade-off between coding rate and bandwidth. A concatenated FEC scheme (RSCCC) is considered for Satellite ATM networks

Efficient iterative decoding algorithms for turbo and low-density parity-check (LDPC) codes

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Advanced transmitter and receivers in future wireless networks

O objectivo desta dissertação é aprofundar o estudo de tecnologias que permitam atingir comunicações mais eficientes e fiáveis nas futuras redes sem fios. Uma das tecnologias estudadas nesta dissertação e que ainda não existem muitos estudos é o Complex Rotation Matrix (CRM). Esta tecnologia é bastante útil em sistemas que usem multi-portadoras como o Orthogonal Frequency Division Multiplexing (OFDM) pois permite dividir a informação pelas várias sub-portadoras. Caso este sistema use também a tecnologia MIMO ainda permitirá a divisão da informação por várias antenas. As constelações hierárquicas são outro dos temas abordados nesta dissertação e são um método eficiente de entregar o mesmo conteúdo a diferentes utilizadores. Esta técnica poderá ser bastante útil tanto em sistemas de uma portadora como multi-portadoras. O Single Carrier (SC) é outra das tecnologias abordadas nesta dissertação. Um dos standards em que poderia ser utilizado tanto o OFDM com o SC é no Digital Video Broadcasting – Satellite services to Handhelds (DVB-SH). Este esquema de comunicação tem com propósito a entrega de conteúdos multimédia aos terminais móveis via comunicação com estações base ou por satélite. O uso de o OFDM no downlink (DL) e do SC no uplink (UL) no mesmo standard/protocolo teria repercussões também ao nível dos terminais móveis pois permitiria uma melhor eficiência na duração das baterias. Os resultados obtidos nesta tese visam sobretudo o estudo do CRM, estimação de canal e constelações hierárquicas. Para a obtenção de resultados foram efectuadas simulações com o método de Monte Carlo e Turbo Códigos. Os simuladores foram desenvolvidos em Matlab.The main purpose of this dissertation is the study of technologies that allow achieving more reliable and efficient communications in wireless systems. One of the technologies studied in this dissertation and practically new is the Complex Rotation Matrix (CRM). This technology is useful in systems that use multi-carrier as the Orthogonal Frequency Division Multiplexing (OFDM). The hierarchical constellations are other theme approached in this dissertation and it purpose efficiently is to deliver the same content to different users. Another technology studied in this dissertation was the Single Carrier (SC) with Frequency Division Equalization. The SC is a well-know technology and is used in several telecommunications systems. The goal is the future wireless communications adopt the two technologies in the same system and use one of them depending of the situation. The Digital Video Broadcasting – Satellite services to Handhelds (DVB-SH) is one standard that can take advantage of the using of the OFDM and SC in the same system. The main goal of the DVB-SH is deliver multimedia content via satellite communications or communications with base stations to mobile terminals. The mobile terminals can achieve a more efficiency in their batteries whether in a standard/protocol that uses OFDM in DL and SC in UL. The results obtained with this thesis have the purpose to study the CRM, channel estimation and hierarchical constellation. The simulators were developed in Matlab platform and Turbo Codes are the codification used, channel estimation is also used and all the simulations were made with the Monte Carlo method

Current optical technologies for wireless access

The objective of this paper is to describe recent activities and investigations on free-space optics (FSO) or optical wireless and the excellent results achieved within SatNEx an EU-framework 6th programme and IC 0802 a COST action. In a first part, the FSO technology is briefly discussed. In a second part, we mention some performance evaluation criterions for the FSO. In third part, we briefly discuss some optical signal propagation experiments through the atmosphere by mentioning network architectures for FSO and then discuss the recent investigations in airborne and satellite application experiments for FSO. In part four, we mention some recent investigation results on modelling the FSO channel under fog conditions and atmospheric turbulence. Additionally, some recent major performance improvement results obtained by employing hybrid systems and using some specific modulation and coding schemes are presented

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments