David J. Skellern

A realistic large-signal MESFET model for SPICE

A comprehensive large-signal MESFET model that provides a realistic description of measured characteristics over all operating regions is presented, It describes subthreshold conduction and breakdown. It has frequency dispersion of both transconductance and drain conductance, and derates with power dissipation. All derivatives are continuous for a realistic description of circuit distortion and intermodulation. The model has improved descriptions of capacitance and bias dependence. It has small-signal S-parameter accuracy extended to a wide range of operating conditions. The model is implemented with new techniques for continuity and dispersion. These provide accurate prediction of circuit performance and also improve simulation speed.

Comparing four IP based mobile host protocols

Abstract Host mobility is becoming an increasingly important issue because of the recent arrival of notebook and palm top computers, the development of wireless network interfaces and the implementation of global networks. This paper compares four recent proposals for mobile host protocols (MHPs) that are compatible with the TCP/IP protocol suite. A set of requirements for an MHP is proposed and it is observed that while all proposals perform the basic task none of the proposals entirely satisfy the requirements.

Determination of device structure from GaAs/AlGaAs HEMT DC I-V characteristic curves

A procedure for the inverse modeling of GaAs/AlGaAs HEMT structures from the DC I-V characteristic is described. The procedure allows important structural parameters, including the aluminum fraction, dopant density, doped layer thickness, spacer layer thickness, physical gate length, source resistance, drain resistance, and the saturated electron velocity, in the 2DEG and in the doped AlGaAs to be obtained. The accuracy of the inverse modeling procedure is established by comparison of the derived HEMT structure with experimental results. >

An architectural framework for the support of integrated services by broadband customer premises equipment

The ATM customer premises equipment (CPE) architecture proposed in this paper supports a broad range of user applications with varying service requirements. A backplane bus was chosen as a cost effective, reliable means of providing the necessary internal interconnection bandwidth. Incorporating a novel access mechanism and graceful performance degradation under fault conditions, this bus provides a foundation for Quality of Service provision. Essential functions including traffic management, connection admission control and signalling are then built on top of this. A prototype system which uses a semi-custom ASIC to implement the backplane access mechanism is briefly described. The architecture provides a flexible basis for service provision, allowing a single CPE device to meet a variety of end user requirements. Results of simulations showing the effectiveness of internal bandwidth access mechanisms are presented.

Outage contours and cell size distributions in cellular and microcellular networks

The paper describes an interference model that provides a simplified description of cellular and microcellular outage contours. The model and computer simulations indicate that cell size variation increases as microcellular systems become more interference limited. Some cellular and microcellular systems are modelled.

An improved FET model for computer simulators

Described is an alternative simple description of FET drain current that provides the flexibility of an extra parameter which can be chosen to approximate the Shockley expression or general power law. An empirical polynomial expression which uses only integer powers is used to provide computational efficiency. The expression gives the designer a more accurate FET model which is consistent for both large- and small-signal simulations. >

An Integrated Propagation-Mobility Interference Model for Microcell Network Coverage Prediction

This paper presents a new interference model for microcellular networks which integrates radio propagation parameters and user terminal mobility. This model uses a parameter denoted the “interference to noise ratio” (INR) to obtain a simplified description of mobile link outage contours as a function of the location of the fixed and mobile radio ports. The INR is used to demonstrate that microcell networks are more interference limited than macrocell networks, and thus are more affected by user terminal mobility. Expressions are derived for the INR and user terminal cell radius distributions. It is shown that in microcell systems a significant proportion of terminals may not be able to meet a contiguous coverage criterion, and that closer microcell spacing can reduce rather than improve the coverage quality. Examination of cochannel and adjacent channel reuse ratios in DCA microcell systems suggest that the closer frequency reuse is primarily responsible for these coverage effects. Monte Carlo simulations are used to test the analytical theory. These results may form the basis of a design methodology for microcell systems.

Interference distributions in microcell ensembles

An interference model developed for arbitrary microcellular networks, based upon a parameter called the ‘Interference to Noise Ratio’ or INR, is used to derive interference and cell radius statistics for mobile stations in a microcellular network. The theoretical INR and cell radius statistics for simple interference environments show good agreement with numerical Monte Carlo simulations. For more complex environments, it is hypothesised that the Central Limit Theorem could be applied to approximate the behaviour of an interferer ensemble, enabling the cell radius statistics for a network to be expressed in terms of the system design parameters. Simulations of microcell ensembles that support this hypothesis are presented.

PIAF: A Knowledge-based/Algorithmic Top-down Floorplanning System

Over the last few years, techniques have been developed to automate the process of placing predefined circuit blocks and the routing of their interconnections. Few efforts have been directed at the more complex problem of floorplanning which involves not only placement but also specification of undefined cells to allow chip assembly in a way that minim&es area and satisfies performance constraints. Top-down floorplanning considers that block details may not be known and predictions or estimations have to be carried out. The infinite solution space of this design problem makes the es.timation process tricky, in that certain design attributes mu.st be instantiated without committing other important attributes. The classification of the attributes and the priority scheme used in their instantiation determine the floorplanning strat-

System design for contiguous cell coverage in high density microcellular networks

This paper examines whether microcellular networks can be designed to provide contiguous cell coverage for a given proportion of mobile terminals. Simulation results using a general microcellular interference model show that contiguous cell coverage may not be possible for an acceptable proportion of mobile terminals even if the call loss rate is low.