Kelvin Ki-Yui Ho

Analysis and design of a highly reliable transport architecture for ISDN frame-relay networks

The authors explore control strategies in the design of a high-performance transport architecture for integrated services digital network (ISDN) frame-relay networks. For real-time congestion control, buffer management, priority queueing, adaptive windowing, and selective frame, discard policies are described that can effectively maximize network efficiency while preventing unfair usage of shared network resources. Virtual-circuit routing strategies are proposed that ensure an efficient distribution of traffic loads across the network despite variations in traffic patterns and topology changes. It is shown that source routing provides significant performance benefits over link-by-link routing, particularly in large networks that are not so densely connected. Routing table update and call acceptance mechanisms are described that provide for efficient bandwidth management in the network. Fault-tolerant strategies are described that include fast failure detection and local reroute. These strategies are capable of restoring affected virtual circuits in less than 10 s, which is adequate for session maintenance under most application scenarios. >

Architectural design of a code division multiple access cellular system

A design of the code-division multiple access (CDMA) cellular system architecture is presented. The base station architecture is based on a universal platform that can support CDMA and other cellular standards such as AMPS and TDMA in the same base station. The mobile switching center (MSC) architecture is enhanced to support the various CDMA system features such as soft handoff and variable bit rate vocoding. In particular, the digital cellular switch (DCS) at the MSC provides a frame relay packet switching interface to the base station. It is shown that such a packet switching interface can support more voice channels that the conventional DS0/DS1 circuit switching interface and is an essential element in achieving the soft handoff capability.<<ETX>>

Random-access systems with a time varying channel

A random multiple-access system which employs a collision resolution algorithm for accessing a common time-varying channel is considered. The channel is assumed to be in one of two states. In each state, the channel is characterized by a general discrete memoryless channel and the transitions between the two states are assumed to be Markovian. A set of sufficient conditions for the ergodicity (stability) of the system is established. As an example, the case when the Capetanakis tree algorithm operates with a time-varying noisy channel is examined. The stability of this system is analyzed, and the throughput is evaluated. >

Performance analysis of some channel access schemes in cellular communication systems

The quasi-optimal maximum packing policy which gives the lowest blocking rates for dynamic channel assignment is considered. The authors formulate the stochastic model and apply an efficient approximation to compute the performance measures. The authors have previously shown that the analysis of a stochastic model of a maximum packing policy is equivalent to that of a fixed-route circuit-switched network. Thus, some of the performance measures in cellular communication systems can be obtained by using the well-developed exact simulation and approximation methods used in analyzing circuit-switched networks. Formal costs associated with each connection are used to show how dynamic channel assignment with maximum packing can improve the service and increase the total revenue. The results support an argument for the realization of the dynamic channel assignment and rearrangement in cellular communication systems.<<ETX>>

The design of a third generation personal communications system

The author discusses the design of a spectrum efficient system for the third-generation wireless personal communications system. The focus is on the radio interface of the system. The author analyzes and compares the various alternatives and recommends a radio interface which is based on the direct-sequence code-division-multiple-access technique. The system supports up to forty voice channels in a 1.25 MHz bandwidth. With microcell technology, the recommended system achieves a system capacity of 13000 users per square kilometer per MHz.<<ETX>>

Random access systems with a time varying channel

A random multiple-access system which uses a collision resolution algorithm for accessing a common time-varying channel is considered. The channel is assumed to be in one of two states. In each state the channel is characterized by a general discrete memoryless channel, and the transitions between the two states are assumed to be Markovian. A set of sufficient conditions for the ergodicity (stability) of the system is established. As an example, the case when the Capetanakis tree algorithm operates with a time-varying noisy channel is examined. The stability of this system is analyzed and the throughput is evaluated.<<ETX>>