The demand for wireless mobile communications services is growing at an explosive rate, with the anticipation that communication to a mobile device anywhere on the globe at all times will be available in the near future. An array of antennas mounted on vehicles, ships, aircraft, satellites, and base stations is expected to play an important role in fulfilling the increased demand of channel requirement for these services, as well as for the realization of the dream that a portable communications device the size of a wristwatch be available at an affordable cost for such services. This paper is the first of a two-part study. It provides a comprehensive treatment, at a level appropriate to nonspecialists, of the use of an antenna array to enhance the efficiency of mobile communications systems. It presents an overview of mobile communications as well as details of how an array may be used in various mobile communications systems, including land-mobile, indoor-radio, and satellite-based systems. It discusses advantages of an array of antennas in a mobile communications system, highlights improvements that are possible by using multiple antennas compared to a single antenna in a system, and provides details on the feasibility of antenna arrays for mobile communications applications.

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Applications of antenna arrays to mobile communications. I. Performance improvement, feasibility, and system considerations

Channel holding time is of primary importance in teletraffic analysis of PCS networks. This quantity depends on user's mobility which can be characterized by the cell residence time. We show that when the cell residence time is not exponentially distributed, the channel holding time is not exponentially distributed either, a fact also confirmed by available field data. In order to capture the essence of PCS network behaviour, including the characterization of channel holding time, a correct mobility model is therefore necessary. The new model must be good enough to fit field data, while at the same time resulting in a tractable queueing system. We propose a new mobility model, called the hyper-Erlang distribution model, which is consistent with these requirements. Under the new realistic operational assumption of this model, in which the cell residence time is generally distributed, we derive analytical results for the channel holding time distribution, which are readily applicable to the hyper-Erlang distribution models. Using the derived analytical results we demonstrate how the distribution of the cell residence time affects the channel holding time distribution. The results presented in this paper can provide guidelines for field data processing in PCS network design and performance evaluation.

Teletraffic analysis and mobility modeling of PCS networks

This paper presents a study of channel occupancy times and handoff rate for mobile computing in MC (Mobile Computing) and PCS (Personal Communications Services) networks, using general operational assumptions. It is shown that, for exponentially distributed call holding times, a distribution more appropriate for conventional voice telephony, the channel occupancy times are exponentially distributed if and only if the cell residence times are exponentially distributed. It is further shown that the merged traffic from new calls and handoff calls is Poisson if and only if the cell residence times are exponentially distributed, too. When cell residence times follow a general distribution, a more appropriate way to model mobile computing sessions, new formulae for channel occupancy time distributions are obtained. Moreover, when the call holding times and the cell residence times have general (nonlattice) distributions, general formulae for computing the handoff rate during a call connection and handoff call arrival rate to a cell are given. Our analysis illustrates why the exponential assumption for call holding time results in the underestimation of handoff rate, which then leads to the actual blocking probabilities being higher than the blocking probabilities for MC/PCS networks designed using the exponential distribution approximation for call holding time. The analytical results presented in this paper can be expected to play a significant role in teletraffic analysis and system design for MC/PCS networks.

https://ir.nctu.edu.tw:443/bitstream/11536/32571/1/000074453400005.pdf

Channel occupancy times and handoff rate for mobile computing and PCS networks

In this paper, we propose a new model for the portable movement in personal communications services (PCSs) networks. Based on this model with general interservice time and registration area residence time distributions, an analytic expression for the probability that a portable moves across K registration areas (RAs) is obtained. The busy-line effect on this quantity is also studied and an analytic expression is presented. The result given in this paper is very useful for cost analysis for location updating and paging.

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Portable movement modeling for PCS networks

In a personal communication service (PCS) network, the call completion probability and the effective call holding times for both complete and incomplete calls are central parameters in the network cost/performance evaluation. These quantities will depend on the distributions of call holding times and cell residence times. The classical assumptions made in the past that call holding times and cell residence times are exponentially distributed are not appropriate for the emerging PCS networks. This paper presents some systematic results on the probability of call completion and the effective call holding time distributions for complete and incomplete calls with general cell residence times and call holding times distributed with various distributions such as gamma, erlang, hyperexponential, hyper-erlang, and other staged distributions. These results provide a set of alternatives for PCS network modeling, which can be chosen to accommodate the measured data from PCS field trials. The application of these results in billing rate planning is also discussed.

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Modeling PCS networks under general call holding time and cell residence time distributions

A new analytical model for finding the call blocking probability of a cellular mobile system with directed retry is developed. It can give very accurate results for systems with both uniform and nonuniform traffic distributions. With that, we are able to formulate a second analytical model for obtaining the probability of additional handoffs due to directed retry. Numerical results show that the probability of additional handoff due to directed retry is more sensitive to the percentage of cell overlap than to the mean path length travelled by a mobile unit. In our example of a cellular system with a typical 30% cell overlap the probability of additional handoff is about 0.02. The use of directed retry, therefore, is expected to cause only a minimum amount of additional load in handoff processing and has only a minimal effect on the probability of handoff failure. >

Blocking and handoff performance analysis of directed retry in cellular mobile systems

A new compact pattern based dynamic channel assignment strategy called CP-based DCA is proposed. The strategy aims at dynamically keeping the cochannel cells of any channel to a compact pattern. A compact pattern of a channel is defined as the pattern with minimum average distance between cochannel cells. CP-based DCA consists of two phases: channel allocation and channel packing. Channel allocation is used to assign an optimal idle channel to a new call. Channel packing is responsible for the restoration of the compact patterns and is performed only when a compact channel is released. Simulation results indicate that the CP-based DCA always performs better than the borrowing with directional channel locking (BDCL) strategy. The latter being the strategy that gives the lowest blocking probability among the class of known strategies that do not require system-wide information. In the designed example, CP-based DCA is shown to have 5% more traffic-carrying capacity than that of the BDCL in case of uniform traffic and 9% more traffic-carrying capacity in case of non-uniform traffic, both at a blocking rate of 0.02. Besides, the number of channels reassigned per released call in CP-based DCA is at most one and is therefore another advantage over BDCL. >

Compact pattern based dynamic channel assignment for cellular mobile systems

Develops a simple but very accurate analytical model for a channel borrowing based dynamic channel assignment strategy in both one-dimensional (linear) and two-dimensional (planar) microcellular systems. The approach is to decouple a particular cell together with its neighbors, i.e., those cells under its interference range, from the rest of the system for finding the blocking probability of that cell. The authors call this the cell group decoupling analysis. This analysis is applicable to both homogeneous and heterogeneous traffic distributions. In linear microcellular systems, they show that the effect of this decoupling causes the blocking probability so obtained to be an upper bound. The bound is found to be very tight when compared with simulation results. In planar microcellular systems, the analytical model can no longer guarantee an upper bound on the blocking probabilities. But very close agreement with the simulation results is observed. Also, the analysis gives accurate results to boundary cells as well as inner cells, and is therefore quite different from the other approaches which neglect boundary effects. >

Cell group decoupling analysis of a channel borrowing based dynamic channel assignment strategy in microcellular radio systems

A wavelength concentrator which functions as an optical PABX is proposed. The concentrator consists of an optical coupler and a controller for assigning wavelengths to nodes. Nodes connected to the wavelength concentrator are assumed to have limited channel access capabilities in the sense that only a small number of fixed laser transmitters are available for each. A simplified Hungarian algorithm which can give a maximal matching of the active nodes' transmitter wavelengths to the available wavelength channels is proposed. Simulation results indicate that with only a very small number of fixed laser transmitters at each node, the wavelength blocking performance can approach that of a non-blocking concentrator, or a system where the nodes have no restriction on the use of wavelengths. >

K.L. Yeung

Papers

Blocking and handoff performance analysis of directed retry in cellular mobile systems

Compact pattern based dynamic channel assignment for cellular mobile systems

Cell group decoupling analysis of a channel borrowing based dynamic channel assignment strategy in microcellular radio systems

A wavelength concentrator for WDMA networks