摘要:

With spectral congestion increasing, and plans announced to dramatically increase the number of mobile telephone users over the coming decade, many approaches are being considered to reduce the bandwidth requirements of each user. One approach is the use of quadrature amplitude modulation (QAM), a particular form of multilevel modulation where each symbol contains several bits of information. The use of QAM for mobile radio applications is considered and it is shown that this form of multilevel modulation can offer an attractive solution to current bandwidth restrictions in microcellular networks. An advanced variable-rate system is also considered and hardware development of a QAM modem discussed.

DOI:10.1049/ecej:19920032

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The European Telecommunications Standards Institute was founded in 1988 as a private non-profit-making organisation to serve Europe's needs for telecommunications standardisation. It now has a membership of over 300 PTTsorganisations. Its emphasis on a managed process and ability to accelerate its activities through project teams has led ETSI to have one of the best standards production machines in the world. The paper reviews the role and working of ETSI.

DOI:10.1049/ecej:19920033

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The oscillator is arguably the most essential part of any communication system: it defines a channel frequency, or timing and synchronisation in a digital system. The phase noise of any oscillator has a fundamental lower limit. It limits the achievable efficiency of spectrum use and degrades the error rate in practical applications. Any low-noise oscillator can be described as a positive-feedbackQmultiplier circuit. Such a model shows that phase noise is minimised if the square of the effective circuitQand the signal-to-noise ratio in the oscillator are maximised. This simple fact is true for all oscillators and it provides the basis for more efficient and lower noise designs.

DOI:10.1049/ecej:19920037

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Work towards defining standards for digital television transmission codecs has been proceeding for many years. A draft specification for 140 Mbit/s coding using blanking removal and differential pulse code modulation is given in CCIR Recommendation 721. A draft specification for a codec operating at 30–45 Mbit/s and using the discrete cosine transform has been defined by the European Telecommunications Standards Institute. The paper briefly reviews bit-rate-reduction techniques and describes the 140 and 34 Mbit/s codecs.

DOI:10.1049/ecej:19920038

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Optical fibre offers a virtually limitless communications bandwidth when used as the physical medium for a local-area network (LAN). However, conventional multiple-access schemes are limited in their ability to exploit this potential. Direct-sequence spread-spectrum systems are a class of code division multiple-access (CDMA) systems that encode data using high-rate sequences to spread data over a much wider bandwidth than normally required for transmission. The paper first considers the problems to be overcome in the design of future high-speed optical networks and then suggests the application of CDMA techniques as a possible solution. There follows an introduction to basic CDMA principles which is then extended to cover the particular coding, modulation and processing considerations to be taken into account when applying CDMA to an optical medium. These considerations are then used to develop a classification scheme which forms the basis for a review of current approaches in the application of CDMA techniques to optical-fibre local-area networks.

DOI:10.1049/ecej:19920039

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The results of the activity on the feasibility model of a broadband customer premises network developed in the RACE 1011 Project ‘Business customer premises network’ (BCPN) are presented. The model represents a selected subset of the system architecture building blocks specified by the project. It has been physically implemented, with the aim of verifying the preferred topology (developed with attention to evolution aspects) and validating the key features of the system concept. In particular, the transmission and interface functions, the ATM test terminal built by the project and the router for interconnecting a standard Ethernet are described.

DOI:10.1049/ecej:19920041

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The ATM Technology Testbed being built by the partners of the RACE Project R1022 and due to be operational in Basel by mid 1993 is described. The result of five-years work by the project team, this testbed will provide a vehicle for advanced experiments that will lead to a greater understanding of the properties of large asynchronous transfer mode (ATM) systems. Included in the paper is an overall description of the system and its constituent building blocks, as well as an outline of the experiments that will be performed on it.

DOI:10.1049/ecej:19920042

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper describes an advanced coherent multichannel (CMC) communications demonstrator that has been designed by the RACE 1010 consortium. This fully engineered demonstrator examines the application of CMC techniques to broadband signal distribution (e.g. television and high-definition television) in the local loop. Ten 140 Mbit/s digitised video signals are transmitted on ten optical carriers 10 GHz apart. Up to 1000 receiver terminals can be served from a single central transmitter assembly. The paper explores the system operation, system specifications, and subsystem results that have been achieved.

DOI:10.1049/ecej:19920043

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper presents ongoing work in the RACE R1056 project which is related to the integration and verification part of the RACE programme. The project goal is to establish a basic business integrated broadband communications (IBC) demonstrator in an evolutionary hybrid network environment. The demonstrator configuration consists of a switching node, a customer access and a customer premises network; its physical implementation is described. Some key business services which are to be demonstrated together with the supporting user terminals are presented.Test objectives cover verification of the hardware performance, interface compatibility and verification of a new transfer mode technique: ATM (asynchronous transfer mode). Verification activity covers the network performance (verification of end-to-end connections and measurements of key parameters). Evaluation activities cover network performance and its relationship to the quality of service perceived by a user.

DOI:10.1049/ecej:19920044

出版商:IEE    

年代:1992

数据来源: IET

摘要:

RACE Project 1036 is developing the technology for a broadband customer premises network (CPN) using wavelength and time division multiplexing (WTDM). Features include close wavelength spacing (4 nm in the 1500 nm band), high-speed time multiplexing (2.5 Gbit/s, STM-16), and a layered control protocol. An initial demonstrator with two wavelengths carrying TV signals at 155 Mbit/s was exhibited in the autumn of 1990 and is now evolving into the final demonstrator due at the end of 1992 which will show 16 wavelengths and a 2.5 Gbit/s multiplex of HDTV, TV, and sound. The paper describes the devices made in the Project, the demonstrators, and the performance results achieved so far.

DOI:10.1049/ecej:19920045

出版商:IEE    

年代:1992

数据来源: IET