This paper deals with an efficient dynamic channel allocation (DCA) technique applicable to terrestrial mobile cellular networks. A channel (or resource) is a fixed frequency bandwidth (FDMA), a specific time-slot within a frame (TDMA), or a particular code (CDMA), depending on the multiple access technique used. A cost function has been defined by which the optimum channel to be assigned on demand can be selected. In addition, a suitable mobility model has been derived to determine the effects of handovers on network performance. The performance of the proposed DCA technique has been derived by computer simulations in terms of call blocking and handover failure probabilities. Comparisons with the classical fixed channel allocation (FCA) technique and other dynamic allocation algorithms recently proposed in the literature have been carried out to validate the proposed technique. >

Handover and dynamic channel allocation techniques in mobile cellular networks

In a wireless communications network served by a high altitude platform (HAP) the cochannel interference is a function of the antenna beamwidth, angular separation and sidelobe level. At the millimeter wave frequencies proposed for HAPs, an array of aperture type antennas on the platform is a practicable solution for serving the cells. We present a method for predicting cochannel interference based on curve-fit approximations for radiation patterns of elliptic beams which illuminate cell edges with optimum power, and a means of estimating optimum beamwidths for each cell of a regular hexagonal layout. The method is then applied to a 121 cell architecture. Where sidelobes are modeled as a flat floor at 40-dB below peak directivity, a cell cluster size of four yields carrier-to-interference ratios (CIRs), which vary from 15 dB at cell edges to 27 dB at cell centers. On adopting a cluster size of seven, these figures increase, respectively, to 19 and 30 dB. On reducing the sidelobe level, the improvement in CIR can be quantified. The method also readily allows for regions of overlapping channel coverage to be shown.

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Optimizing an array of antennas for cellular coverage from a high altitude platform

Self RF engineering is made possible for a wireless communication system by adding to the self-configuration capability the ability to set autonomously the power levels of the system base stations. The same data is employed as in self configuration. A further improvement for systems using the IS 136 Air Interface Standard consists of the capability to collect the required data through the functionalities of the MAHO/MACA (Mobile Assisted Hand Off/Mobile Assisted Channel Assignment). Improved system-initialization procedures are presented.

Method for self-calibration of a wireless communication system

In a cellular system, if there are too many data users in a cell, which we refer to as a hot cell, data may suffer large delay, and system's quality of service (QoS) may degrade. A dynamic channel-allocation scheme assigns more channels to those hot cells under centralized control (CC). In mobile-assisted data forwarding (MADF), we add an ad-hoc overlay to the fixed cellular infrastructure and special channels-called forwarding channels-are used to connect users in a hot and its surrounding cold cells without going through the hot cell's base station. The forwarding-channel management in MADF is done by the mobile units themselves to relieve the load on the CC. We find that, using MADF, under a certain delay requirement, the system performance can be greatly improved.

MADF: a novel approach to add an ad-hoc overlay on a fixed cellular infrastructure

This paper deals with the performance evaluation of various resource management strategies that are suitable for low Earth orbit mobile satellite systems (LEO-MSSs). A user mobility model has been proposed and its statistical parameters have been derived. Both fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques have been considered. Moreover, in order to reduce the handover failure probability, we have assumed that interbeam handover requests which do not immediately obtain service can be queued. In particular, two different queuing disciplines have been compared: (a) the first input first output (FIFO) scheme and (b) a new technique called last useful instant (LUI) which is based on the knowledge of the maximum time within which the handover procedure must be accomplished. Implementation aspects for the LUI technique in a LEO-MSS have been discussed also in comparison with the measurement-based priority scheme (MBPS), previously proposed in the literature on this subject. The efficiency of the LUI queuing scheme as regards the FIFO technique has been investigated by simulations for both DCA and FCA techniques. An analytical approach has been also presented in order to allow the performance evaluation of the FCA scheme with different handover queuing disciplines.

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Handover queuing strategies with dynamic and fixed channel allocation techniques in low Earth orbit mobile satellite systems

We determine the call blocking performance of channel-allocation algorithms where every channel is available for use in every cell and where decisions are made by mobiles/portables based only on local observations. Using a novel Erlang-B approximation method, together with simulation, we demonstrate that even the simplest algorithm, the timid, compares favorably with impractical, centrally administered fixed channel allocation. Our results suggest that an aggressive algorithm, that is, one requiring call reconfigurations, could provide a substantially reduced blocking probability. We also present some algorithms which take major steps toward achieving the excellent blocking performance of the hypothetical aggressive algorithm but having the stability of the timid algorithm. >

Z. Miljanic

Papers

Call blocking performance of distributed algorithms for dynamic channel allocation in microcells