L.B. Lopes’s research while affiliated with University of Leeds and other places

We propose a new DCA algorithm to provide service to slow- and fast-moving users in an all-microcells network, that achieves lower average number of handovers (actual channel changes) than the average number of cell crossings per call. The algorithm selects a channel that is not currently in use within an area surrounding the initial cell, so the terminal does not need to change to a new communication channel when it reaches a new cell. The algorithm is presented in the context of a radio-fibre structure with centralised control in which a call handover becomes simply a radio port selection at the controller. The performance of the proposed algorithm is computed through network simulations in a Manhattan street environment under uniform traffic, and compared to FCA and DCA first available algorithms

Radio-fibre microcellular networks are composed by small-size cells that make use of a fibre optic network for the conveyance of RF signals from a central controller to remote antennae at cellsite. This structure is particularly suitable to accomplish receiver and transmitter macrodiversity since the same RF channel can be transmitted and received through multiple ports, thus providing a large coverage area in which mobiles do not have to switch channels when roaming. This paper investigates the performance of multitransmitter diversity in fading channels, in noise and interference limited conditions. The problem differs from diversity reception in that signal combining is now non-coherent. Results are presented in terms of radio coverage and cochannel reuse efficiency firstly under Rayleigh fading only and secondly in a city street microcell environment. Simulcasting is an effective shadowing counteraction in noise conditions and achieves similar performance to no diversity in interference conditions

Macroscopic diversity provides two or more independent copies of the transmitted signal which fade in an uncorrelated manner. The signals can be combined to fight against shadowing but also against fast fading avoiding the use of two antennas per site (microdiversity). It is suggested in this paper that macrodiversity can provide all the necessary fading protection (against fast as well as slow fading) in microcellular networks where the density of antennas is high. This paper investigates the performance of macrodiversity versus microdiversity from the radio coverage point of view. Two and four port combining are considered, firstly for a Rayleigh fading environment and later with a more elaborate microcellular channel model that includes Rician statistics for the received signal envelope, dual-slope path loss model and lognormal shadowing. The results show that macrodiversity is an effective fading countermeasure in microcellular environments. This work is motivated for the concept of a radio fibre microcellular network where optical fibre links are used for RF signal distribution from a central controller to remote antennae at cellsite. In these systems low-cost and compact radio access ports can be deployed anywhere. Therefore the question is how to obtain maximum radio coverage with minimum number of ports using diversity techniques

It is envisaged that over the next few years there will be a significant increase in the use of cellular based data services. However it is also envisaged that the majority of these cellular data users will be stationary or slow moving throughout the duration of their data connection. This lack of movement will cause very little variation within the radio channel and will therefore reduce the effect of any interleaving and FEC applied. Therefore to improve the situation some added form of diversity may be used. This paper investigates the benefit of slow frequency hopping (SFH) to the performance of two existing GSM (Global System for Mobile Communications) data channels and two previously proposed GSM data channels, in slow speed, noise limited conditions. The performance has been assessed using a comprehensive radio link simulator developed at Leeds

The demand for mobile communications has increased rapidly over the last decade. Due to limited spectrum availability, many service providers are looking for ways of improving the resource efficiency. A popular method of improving the capacity of a network is to use a dynamic channel allocation (DCA) strategy. The Digital Enhanced Cordless Telecommunications standard (DECT) uses a DCA strategy called least interfered channel (LIC). However the performance of the DCA algorithms can change considerably due to practical constraints such as number of transceivers at the base station. We compare the gains of two DCA algorithms, the second being autonomous reuse partitioning (ARP), for various environments in the form of grade of service and quality of service measures

An algorithm for the automatic placement of cellular base stations is presented. Initial observations show that the algorithm has the potential to place base sites in near optimum positions with respect to the offered traffic

A third generation TDMA based mobile radio system is considered in which all services are carried across the radio interface on ATM connections. Many future services will be variable rate and there is potential for exploiting this fact to improve the spectral efficiency of the mobile system. However, the gains which can be achieved in practice will be highly dependent on the connection admission control (CAC) procedures used. When an ATM terminal requests connection admission it supplies the CAC with only a limited amount of information concerning its bandwidth requirements. The lack of detailed information made available to the CAC can mean that calls which could be supported are instead refused admission. In this paper two different convolution-based CAC algorithms are considered. The first algorithm assumes the worst case cell arrival process which fits the source traffic descriptors declared by the terminal. It is shown that the statistical multiplexing gain achievable when this algorithm is used is very poor and sometimes nonexistent. A second algorithm is therefore considered which makes use of actual measurements of the cell arrival process of calls already admitted in order to provide an improved prediction of the performance which would be seen should the new call be admitted

Mobile communications has become extremely popular and the demand for higher cellular capacities has increased network congestion. Consequently many service providers are looking to improve efficiency within the cellular infrastructure. Adaptive antenna technology offers the possibility of increasing capacity by interference suppression. Implementation of adaptive antennas into current infrastructure cannot take place directly as the current channel allocation algorithms were not designed to consider the spatial properties of these antennas. The paper discusses how the protocol is dependent on two main criteria: are the arrays switched beam or adaptive antennas? Will the network use reduced reuse or channel multiplexing to capitalise on the interference suppression? It examines the protocol issues for Global System for Mobile (GSM) and Digital Enhanced Cordless Telecommunications (DECT), and provides simple channel allocation modifications to enable the use of adaptive arrays within mobile communication systems

A simple and effective metric for antenna diversity in DECT is introduced. Using a segment of only 2 to 4 bit periods, this metric provides a reliable estimation of the received signal quality. To emulate ideal selection diversity in a single receiver, this metric is calculated by performing two successive measurements on each antenna during the DECT preamble. When using a correlative clock timing, this diversity provides a performance improvement similar to an ideal CRC-driven selection diversity employing two parallel receivers. This offers a cheap and simple solution to DECT outdoor applications such as PCS

Dynamic channel allocation (DCA) is increasingly being proposed and employed in various forms within cellular and cordless environments. DCA is attractive as it removes the complex reuse planning required for fixed channel allocation (FCA) systems. The performance of two distributed DCA algorithms, first available (FA) and least interfered channel (LIC) are compared in the form of grade of service (GOS) and quality of service (QOS) measurements. A DECT (Digital European Cordless Telecommunications) environment is used to examine their performance