Graphical correspondence in electronic-mail networks using personalcomputers

A telegraphic technique for electronic-mail correspondence between industry-standard PC facilities equipped with a writing tablet is described. Algorithms for encoding graphical information into the fixed-word format used in the common message-handling architectures are discussed. It is proposed to adopt differential chain encoding which allows an efficient representation of graphics as strings of ASCII-compatible bytes. telematic service that is feasible with this PC networking approach is compared to standard facsimile transmission of compound documents with text and graphics     

Hardware fading simulator for a number of narrowband channels withcontrollable mutual correlation

A multipath fading simulator with a number of narrowband channels with controllable mutual correlation is described. With this simulator it is possible to test the influence of joint fading statistics of mutually correlated channels on a mobile data communication link with frequency diversity     

Skywave propagation over a multisection plane ground

The ground-loss profile along the path of a skywave for a sectionally homogeneous ground is investigated by means of the compensation theorem. A recurrence procedure, which is suitable for numerical work, has been satisfactorily tested against recent experimental results concerning m.f. skywave propagation over a path in South-East England, extending to 300 wavelengths from the shore.     

A method for intermodulation noise calculations in a cabletelevision network with HD-MAC, PAL and FM radio signals

A statistical method for calculating intermodulation noise in CATV systems whose traffic can be characterized as a sum of a large number of independent signals is presented. The method is demonstrated by calculating the signal-to-intermodulation-noise ratio in the various channels of a prototype cable network supporting HD-MAC, PAL, and FM radio signals. The spectra of these individual signals are simplified in order to perform part of the calculation analytically. It is shown that the signal-to-intermodulation-noise ratio decreases when the total signal power is increased. This method can be used to calculate the necessary back-off of a cable network for a given frequency plan and to determine suitable plans for loading and controlling CATV networks     

Enhanced throughput in packet radio channels with shadowing

The throughput of a slotted-ALOHA radio channel with log-normal shadowing has been derived. Uncorrelated packet shadowing is shown to assist receiver capture, so that the throughput always exceeds the throughput obtained in both `ideal' channels and channels with pure Rayleigh fading     

The European (r)evolution of wireless digital networks

Some of the European developments of two different personal communication services, digital cellular telephony and mobile data networks, are compared with each other and with developments in the United States. The related agendas for research and development of wireless technologies in the past decade are also reviewed and compared. The present status of European cellular telephony, the implementation of mobile data networks in Europe, cellular engineering issues, and economic and regulatory issues are discussed. GSM, the pan-European digital cellular telephony standard, and some essential technology differences between the circuit-switched and packet-switched radio systems and their relative merits in the increasingly competitive European environment are also reviewed     

Quasi-equispaced slot arrays with extremely low crosspolarisation

Crosspolarisation well below the prescribed side-lobe level of a travelling-wave array may be achieved, without using additional discriminating structures, by applying a circular, dielectric-filled waveguide with a sequence of circumferential gaps. Operated in the TM01 mode, a computer-designed X band prototype having a directivity of 27 dB was found to secure crosspolarisation of less than ?34 dB.     

Non-relativistic and relativistic scattering by short-range potentials

Relativistic and non-relativistic scattering by short-range potentials is investigated for selected problems. Scattering by the δ' potential in the Schr?dinger equation and δ potentials in the Dirac equation must be solved by regularization, efficiently carried out by a perturbation technique involving a stretched variable. Asymmetric regularizations yield non-unique scattering coefficients. Resonant penetration through the potentials is found. Approximative Schr?dinger equations in the non-relativistic limit are discussed in detail.     

Comments on `Analysis for spectrum efficiency in single celltrunked and cellular mobile radio'

Nagata and Akaiwa (see ibid., vol.VT-36, p.100-13, 1987) have committed a principal error in evaluating the area mean power of the local mean power sums with log-normal distribution. This results in overly optimistic estimates of spectrum efficiency for various mobile radio systems. The correct expression for the area mean power is given. An alternative technique for the determination of the area mean power and variance of the joint interference is also reviewed. This is more appropriate for the shadowing phenomena occurring in mobile communications than the (corrected) method proposed by Nagata and Akaiwa     

Packet radio in a Rayleigh channel

Statistical multiple access is analysed for a number of independent transmitter-receiver pairs exchanging data packets over a shared mobile-radio channel. Rayleigh fading `softens? the channel, resulting in less packet contentions and higher traffic capacity than for the standard Aloha channel.