摘要:

In the near future, integrated voice/data services will be introduced and provided by the Integrated Services Digital Network [1]. To ease the transition to these new types of services, gateways may be provided which allow for existing high-speed data networks to support the integrated traffic types. In the paper, novel gateway designs are presented for integrating the flow of voice streams with existing broadband cable systems. The interface between the integrated voice subnetwork and the cable system is realised by a metropolitan area gateway (MAG) which is implemented at the broadband cable headend. Both fixed-frame (with realignment) and dynamic movable boundary designs are proposed. In both systems, an intelligent scheduling algorithm in the MAG dynamically allocates channel bandwidth using a variation of the data switch filtering (SWIFT) technique introduced in Reference 2. The MAG accomplishes this by coordinating the transmission of inbound and outbound voice packets in an upwardly compatible fashion with respect to the existing CSMA/CD data stations. This means that previously installed stations require no hardware or software modification. Also, the systems are suitable for use with standard ISDN voice streams. Results are presented which indicate that the new designs perform significantly better than previous compatible voice/data integration methods.

DOI:10.1049/ip-i-2.1990.0027

出版商:IEE    

年代:1990

数据来源: IET

摘要:

In some ARQ schemes, the combination of modulation and channel coding improves the performance of a communication system. The paper describes a new method for the integration of an error-detecting code withM-ary modulation. Euclidean distances are obtained among modulated signals using successive transmissions of the same codeword larger than those obtained by other similar schemes. The results of the theoretical analysis show that the described method allows improvement of both the error probability and the throughput of an ARQ protocol with respect to other schemes.

DOI:10.1049/ip-i-2.1990.0028

出版商:IEE    

年代:1990

数据来源: IET

摘要:

In block matching type motion compensation schemes, the image is divided into blocks of the same size. For each block a search is conducted in the previous frame to locate the best correspondence. For the scheme to succeed an implicit assumption has to be made that the motion within each block is uniform, an assumption which may not necessarily be correct, and as a result the quality of the prediction suffers. In the paper, a new motion compensation scheme based on block matching is presented, where the size for each block is variable. The proposed algorithm adaptively divides the image into blocks of variable size to meet the assumption on uniform motion for all blocks. The scheme has been successfully applied to simple interframe video coding. It is shown that the proposed algorithm can be extended to form the basis of a complete and efficient codec with low complexity. The possibility of the combination of the scheme with novel hybrid coding techniques to form sophisticated systems with low bit-rate performance, that compare favourably with other existing schemes, is also demonstrated.

DOI:10.1049/ip-i-2.1990.0029

出版商:IEE    

年代:1990

数据来源: IET

摘要:

M-QAM radio systems have been investigated in the last few years with the aim of implementing ever increasing values ofM. With a view to determining the actual spectral efficiency obtainable with an M-QAM system, adjacent and cochannel interference effects are investigated; consequently, degradations in signal-to-noise ratio required to guarantee a fixed error probability are evaluated. The algorithm proposed, which is also compared and checked with different, alternative methods already published, can achieve both accuracy of the results and efficiency in computing time. Thus it allows rapid system investigation whatever the value of spectrum efficiency, i.e. for any choice of radiofrequency channel spacing and any number of modulation states. The numerical results, obtained with different values of rolloff factor, emphasise the ever increasing sensitivity of system performance to adjacent and cochannel interference whenMincreases.

DOI:10.1049/ip-i-2.1990.0030

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper describes a new approach for a decision feedback equaliser using the multilayer perceptron structure for equalisation in digital communications systems. Results indicate that the perceptron based decision feedback equaliser provides better bit error rate performance relative to the least mean square decision feedback equaliser, especially in high noise conditions, also that bit error rate performance degrades less owing to decision errors and is also less sensitive to gain variation.

DOI:10.1049/ip-i-2.1990.0031

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Monomode optical fibres currently used in optical communication systems usually have bandwidths much greater than the information rate transmitted. This excess bandwidth can be used to improve receiver sensitivity. Pulse-position modulation (PPM) schemes are usually used in optical communication systems to improve receiver sensitivity. The paper analyses the sensitivity of the receiver of an optical PPM system, considering both wrong-slot error and false-alarm error. Coded optical PPM systems with direct and heterodyne detection are analysed. The performances of Reed-Solomon codes with different code rates are considered. Relations between bit-error probabilityPband the optimum efficiencypfor the uncoded and coded systems are obtained. It is found that system performance does not necessarily improve with coding. System performance improves only for codes that are capable of reducing the minimum required number of photons sufficiently to compensate for the decrease in system efficiency resulting from coding.

DOI:10.1049/ip-i-2.1990.0032

出版商:IEE    

年代:1990

数据来源: IET

摘要:

We examine the use of the 55–65 GHz band of the millimetre-wave radio spectrum for application in short range broadband radio networks for data and video systems. The physical properties of this absorption band, the safety considerations and the appropriate technology are assessed so as to be able to propose possible frequency plans and regulatory mechanisms. It is shown that a 100 fold increase in channel density can be achieved in this band, compared with non-absorption bands. We also show that practical systems can be implemented with the minimum of regulatory control, using state-of-the-art technology.

DOI:10.1049/ip-i-2.1990.0033

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The performance aspects of a set of error control line codes (ECLCs) are examined. These have been recently developed, and are derived from known linear error control codes (ECCs). As the error control characteristics are inherited directly from the parent ECC, special consideration is given to the linecoding characteristics, and in particular to spectral properties, disparity and runlength bounds, we also give consideration to a useful extension which controls more tightly the runlengths and disparity range. We obtain results for various different codes.

DOI:10.1049/ip-i-2.1990.0034

出版商:IEE    

年代:1990

数据来源: IET

摘要:

An optimal transmission-time burst assignment algorithm is described that is applicable to both satellite-switched and earth-station frequency-hopping TDMA networks. In contrast to previous work, the paper allows for multiple carriers (or transponders) per spot beam and multiple earth stations (in general, greater than the number of carriers) per spot beam. By dividing earth stations into groups, it efficiently addresses the burst-assignment problem for networks with a large number of earth stations relative to the number of TDMA carriers. Upper bounds are derived for the number of switching modes and traffic bursts to facilitate system planning. For earth stations of limited uplink and downlink agility, scenarios are described that are amenable to our burst-assignment algorithm. In another context, the burst-assignment algorithm can be used to solve a switching problem for a threetiered switching system for a terrestrial time-division digital network.

DOI:10.1049/ip-i-2.1990.0035

出版商:IEE    

年代:1990

数据来源: IET