Channel Allocation Methods Research Articles

PRMA performance in cellular environments with self-adaptive channel allocation strategies

The personal communication systems envisaged for next years will have to accommodate a wide range of services with different quality requirements (on delays, bit error rates, etc.), and will often be characterized by a high burstiness (i.e., with relatively short traffic bursts, alternating with comparatively long silence periods). Therefore, an extension of packet communications to the cellular scenario is appealing for its inherent flexibility. The packet reservation multiple access (PRMA) protocol is considered. On the other hand, the current trend in reducing cell sizes poses major planning problems, which cannot be properly coped with by the usual fixed channel allocation methods; therefore, adaptive allocation schemes, which are able to avoid any frequency planning, are currently studied. A review of adaptive channel allocation strategies in view of application to packet switching is carried out. Then, a self-adaptive assignment method (channel segregation) originally developed for circuit switched systems is selected and conveniently adapted for PRMA operations. Simulations show good performance, provided that values of some system variables are correctly chosen.

Advanced planning criteria for cellular systems

This article provides a review of the most up-to-date frequency planning techniques suitable for current digital cellular systems. Frequency planning is becoming a key issue in the current scenario, with exceedingly high growth rates in many countries which compel operators to re-configure networks virtually on a monthly basis. Therefore, the search for smart techniques, which may considerably alleviate planning efforts (and associated costs) becomes extremely important for operators in a competitive market. Although reference is made particularly to a market leader (GSM and its offspring), the considerations reported are quite general, and can be applied to any TDMA/FDMA system. The article examines such well-known concepts as fractional loading, frequency hopping, and intelligent antennas in order to elaborate on them and show how they may impact conventional planning methodology and deprive complex dynamic channel allocation methods of any practical interest. The evaluation of this impact is extended to mixed cellular architectures, starting from a real case for the city of Munich and finally identifying some basic guidelines for cell planning.

Capacity of digital cellular TDMA systems

The capacity of digital TDMA (time-division multiple-access) systems is addressed. It is projected that capacity improvement will be of the order of 5-10 times that of analog FM without adding any cell sites. For example, the North American TIA (Telecommunication Industry Association) standard offers around 50 Erlang/km/sup 2/ with a 3-km site-to-site distance. In addition, the TDMA principle allows a faster handoff mechanism (mobile assisted handoff), which makes it easier to introduce microcells with a cell radius of about 200 m. This gives substantial additional capacity gain beyond the 5-10 factor given above. TDMA makes it possible to introduce adaptive channel allocation (ACA) methods. ACA is a mechanism that provides efficient microcellular capacity. ACA also eliminates the need to plan frequencies for cells. It is concluded that the air-interface of digital TDMA cellular may be used to build personal communication networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multitransmitter digital signal transmission by using offset frequency strategy in a land-mobile telephone system

In a high-capacity land-mobile telephone system which employs a small zone technique, it is advantageous to provide control channels separate from voice channels. We first review two control channel allocation methods: the individual control zone system and the multiple control zone system. From the viewpoints of efficient frequency utilization and reliable call processing, the multiple control zone system is shown to be preferable. It is experimently verified that an offset carrier frequency strategy is well suited to the realization of this system. Simulation test results are presented which determine the design parameters. Offset carrier frequency allocation methods concerning three types of fundamental zone configuration are derived. The carrier frequency synchronization and the phase adjustment of the modulation signals are investigated for the actual system construction.