Guido Riva

A characterization of indoor space and frequency diversity by ray-tracing modeling

The performance of space and frequency diversity techniques at 1800 MHz in an indoor environment are investigated. Three linear signal combining techniques are considered: signal selection (SEL), maximal ratio combining (MRC), and equal gain combining (EGC). The computations of received fading envelopes are performed by means of an analytical model, based on a three-dimensional ray-tracing (RT)/uniform theory of diffraction (UTD) technique; the reliability of the adopted approach is confirmed by comparison with some test measurements. The electromagnetic field components are adequately processed to obtain the single branch and combined signal envelope. The results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage for both diversity techniques. Antenna spacings of about 0.75-1/spl lambda/ are nearly sufficient for achieving optimum performance, whereas frequency separation on the order of 10 MHz is needed for sufficiently decorrelated transmission on the two carriers.

On the performance of packet reservation multiple access with fixed and dynamic channel allocation

The evaluation of packet reservation multiple access (PRMA) is extended from a single cell case, investigated in several previous papers, to a cellular environment characterized by user mobility and by the interference from other cells. The analysis is based on a comparison of PRMA performances with those of classical circuit switching schemes. The comparison methodology is defined, and the comparison, performed by means of a simulation program based on a dynamic traffic model, is discussed. >

Investigation on a dynamic channel allocation for high capacity mobile radio systems

The potential of a dynamic channel-allocation scheme is described, in particular, to increase the system capacity and to counteract the traffic bursts typically experienced in cellular mobile radio systems as a consequence of traffic jam, accidents, traffic lights, etc. In order to accomplish these improvements, an effective procedure, monitoring the link quality of all the active calls, is required. Practical considerations necessitate implementation such a control just at the base station. The affordability of this approach is considered, assuming as input parameters the correlation among wanted and interfering signals in both mobile-to-base and base-to-mobile directions. A software simulation of cellular systems with a broad range of applications has been used to evaluate the feasibility of such a channel assignment method.<<ETX>>

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.

Comparisons of multiple access schemes for personal communication systems in a mixed cellular environment

The paper deals with the evaluation of performances of packet reservation multiple access (PRMA) and code division multiple access (CDMA) in a mixed cellular environment, composed by a regular grid of macrocells plus microcells deployed in the most congested areas. The investigation aims at evaluating the impact of the different interference mechanisms on traffic performance and bases on the comparison between two technical solutions proposed in literature. The approach is quite innovative since the analysis is carried out considering realistic spatial traffic statistics, which are characterized, even with a nominally uniform user distribution, by fluctuations resulting in uneven traffic loads on different cells. Different propagation models for macrocells and microcells have been adopted. >

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.

Performance analysis of an improved dynamic channel allocation scheme for cellular mobile radio systems

The introduction of dynamic channel allocation (DCA) schemes in future microcellular systems needs proper evaluation of their stability behavior. Some parameters are suggested for simplified analysis, and some comments, derived from software simulations in very simple situations, are made. A more realistic and general simulation showed the improvements, in terms of quality parameters and capacity, obtained with the proposed DCA algorithm. This should not be considered an optimal system, but just an indication of a good direction.<<ETX>>

Analysis of optimum resource management strategies in layered cellular structures

The paper deals with the identification of channel allotment criteria in a multilayered cellular environment composed by a regular grid of macrocells, plus a number of microcells deployed in the most congested areas. The optimum resource allotment between microcells and macrocells cannot be simply worked out by considering the expected traffic densities for each cell type, but it has to take into account their different functionalities, After a quick overview of the main working principles of such a multilayered architecture, the paper introduces some basic planning criteria. The analysis is carried out considering realistic traffic statistics and different propagation models for macrocells and microcells have been adopted.<<ETX>>

Investigation on dynamic channel allocation strategies suitable for PRMA schemes

Among the various packet multiple access schemes proposed for mobile radio operation, packet reservation multiple access (PRMA) method is discussed. The performance of a PRMA scheme in a cellular layout depends heavily on the adopted resource allocation scheme, which is required to keep the mutual interference below the desired limit. Due to its discontinuous transmission and to the high variability of the interference patterns, PRMA cannot control the interference level by simply monitoring the link quality. This evidence makes PRMA operations with dynamic channel allocation (DCA) really difficult to achieve. However, DCA seems to be necessary in microcellular environments, where traditional planning algorithms may fail due to the high complexity of propagation phenomena. The issue of compatibility between PRMA and DCA compatibility are proposed.<<ETX>>

Comparison of different hand-over strategies for high capacity cellular mobile radio systems

Preliminary results are presented for a computer program, which has already been used for spectrum efficiency evaluations, that starting from a dynamic traffic model gives interesting information on system performance when different hand-over criteria are used. The proposed simulation program is able to evaluate hand-over characteristics for strategies based on field strength, distance, and C/I (carrier/interference ratio). A detailed definition of the mobile ratio scenario in which the program will operate is presented.<<ETX>>