Cyril J. Burkley

Low complexity GMSK modulator and demodulator for integrated circuit implementation

The design of a reduced-complexity modulator and demodulator using Gaussian minimum shift keying (GMSK) is presented. Both modulator and demodulator follow the European Conference of Postal and Telecommunications Administrations (CEPT), Group Special Mobile (GSM) recommendations. A single ROM modulator circuit and a coherent demodulator using De Buda (1972) clock and carrier techniques are used to give reduced complexity designs. The demodulator is a coherent receiver that uses phase-locked loops in the clock and carrier recovery circuits. Both the modulator and demodulator designs give satisfactory performance at reduced complexity, and are suitable for implementation on silicon.<<ETX>>

Catastrophicity Test for Time-Varying Convolutional Encoders

A new catastrophicity test for convolutional encoders whose rate and generator polynomials vary with time is presented. Based on this test computationally efficient algorithm to determine whether or not a time-varying convolutional encoder is catastrophic is derived. This algorithm is shown to be simpler than the catastrophicity test proposed by Balakirsky [1]. Furthermore, the algorithm can easily be generalised to rate k/n time-varying convolutional encoders.

Enumeration of Convolutional Codes and Minimal Encoders

A full analysis of equivalent encoders is presented which is subsequently used to enumerate the minimal encoders generating a convolutional code. We extend the known results on rate 1/n minimal encoders to the rate k/n case and derive enumerators for minimal encoders, canonical systematic encoders and Convolutional codes. Numerical results show that the majority of codes have minimal encoders whose overall constraint length is more of less evenly distributed among the k rows and these codes are more likely to have good distance properties.

The pan-European GSM signalling requirements for the Abis interface

The introduced global system for mobile communications (GSM) is implemented from design principles based on time division multiple access and frequency division multiple access with signalling control achieved by a combination of the integrated services digital network (ISDN) and common channel signalling CCITT No.7 (SS7) standards. This paper examines and presents measurements of the signalling attributes at the air and Abis interfaces within the GSM network. The transfer of information over the interfaces is controlled by the use of the GSM implementation of the ISDN and SS7 standards. A network model, consisting of a base station, a mobile unit and appropriate measuring instrumentation, is used representing the activity of both the air and Abis interfaces. A call is made and the performance of the associated signalling is analysed. The results show the different measurements of signalling in the GSM system for various conditions. The modifications to the Abis interface for GSM signalling in order to conform to ISDN and CCITT No.7 standards are also presented.<<ETX>>

Fading rate and multipath delay effects on signal acquisition using sliding correlation in a multi-user environment

The ability of spread spectrum systems to combat interference can only be realised if the receiver is precisely synchronised with the incoming signal. The use of the sliding correlator for the acquisition of direct sequence spread spectrum signals is a popular method. Previous work considered either the single user in the fading and delay mobile environment or multi-users in the additive white Gaussian noise environment. In this paper the acquisition performance of the sliding correlator for direct sequence spread spectrum signals is investigated for the uplink case and in an environment where interference is caused both by multiple users and by multipath delays with different fading rates. The results show that a longer correlator length is required for optimum mean acquisition time in a slow fading environment. However in the multi-user, multipath environment when larger delays are present, the use of a longer correlation length is necessary in order to optimise the mean acquisition time.

The generation of bandwidth efficient modulation schemes using direct digital synthesis

This paper describes the generation of bandwidth efficient modulation techniques for indoor wireless communication and other applications using direct digital synthesis. Direct digital synthesis is an attractive alternative to traditional implementation methods. It allows the generation of efficient and easily modifiable modulation schemes. The Hewlett Packard Frequency Agile Signal Simulator (HPFASS) is one system which uses direct digital synthesis. It allows the introduction of various channel distortions: fading, co-channel and adjacent channel interference and quantifiable noise.<<ETX>>

The performance of GTFM in a frequency-selective Rayleigh fading channel

Generalized tamed frequency modulation (GTFM) is a bandwidth-efficient digital modulation technique suitable for use in land mobile radio systems. The authors examine the influence of both frequency-flat and frequency-selective Rayleigh fading on GTFM with discriminator detection. In addition, the effects of cochannel and adjacent channel interference are considered in the frequency-flat fading channel. Results are presented in the form of bit-error-rate (BER) curves at several vehicle speeds and multipath delay spreads. For frequency-flat fading channels it is shown that the irreducible error rate is proportional to the square of the maximum Doppler frequency normalized to the bit rate. In slow frequency-selective channels the irreducible error rate is found to be proportional to the square of the normalized delay spread. Finally, the relative insensitivity of the error rate to the shape of the power delay profile is verified for small delay spreads. Simulations also indicated that for small delay spreads (d<or=0.2) the BER is not affected by the speed of the clock recovery circuit.<<ETX>>

Improving the performance of CDMA systems in a multipath delay and fading environment

In this paper, a new channel filter is proposed for a CDMA direct-sequence spread-spectrum system in a multi-user and multipath delay and fading environment. In the proposed system, the channel filter is placed before the acquisition system to overcome the multipath delay and co-channel interference effects. Monte Carlo simulation is used to evaluate and compare the performance of the system in terms of multi-user interference and multipath delay both with and without the proposed channel filter. Results show that the proposed technique can significantly improve the overall system performance. Details of the system configuration, the design concept of the channel filter and the simulation techniques used are discussed.

Clustering analysis on questionnaire data for program accreditation

The aim of the SOCRATES EIE-Surveyor project is to be a reference point for electrical and information engineering in Europe, bringing together representatives from 27 out of 31 eligible countries. One of the tasks of the project is the evaluation of the accreditation processes in the participating countries. A questionnaire about the accreditation process was developed and sent to project partners in each participating country. The main areas investigated the nature of the accreditation body, the criteria, which are evaluated, the structure of the visit and the decision formulation. The results of the questionnaire, was analyzed using clustering analysis and more precisely hierarchical, in order to compare the answers in 17 European countries and to find similarities among them. As distance measures the Euclidian metric and the city block distance was used. Average linkage, and Ward clustering algorithms was utilized.

Comparison of the Acquisition Performance of the Matched Filter and Integrate-and-Dump Receivers in a Multipath Delay and Fading Environment

The Matched Filter and the Integrate-and-Dump circuit techniques are both attractive acquisition methods for CDMA systems. Acquisition using the matched filter technique has attracted considerable interest in recent years since it shows a better performance in the presence of Gaussian noise. On the other hand acquisition using an integrate-and-dump circuit is attractive because it is less complex to implement. However, the acquisition performance can be affected significantly by the channel characteristics. In this paper, a numerical method and a computer simulation have been developed in order to compare the two acquisition systems in different propagation environments. Results show that the acquisition using a matched filter is much faster than that using the integrate-and-dump circuit for the reception of spread-spectrum signals in the presence of Gaussian noise. However, in a multipath delay and fading environment, the results show that the mean acquisition time using the matched filter is not always faster than that using the integrate-and-dump circuit. The results show that it depends on the fading, the delay, the number of users and the signal-to-noise ratio.