PRMA performance in cellular environments with self-adaptivechannel 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     

A measurement-based methodology for the determination of validitydomains of prediction models in urban environment

The choice of a given propagation model has a major impact on the accuracy and effectiveness of cellular planning, especially in an urban environment, where a higher degree of detail is required. Rigorous models, such as those based on ray optics, are generally heavily time-consuming; furthermore, they are accurate only if high-resolution databases (of buildings, land usage, etc.) are available, and the cost of these databases is increasingly affecting the operators' budget. Therefore, one should use them only in their “validity domain,” i.e., the area where they are both reliable and necessary: using complex tools where it's not needed implies an overhead in terms of computation time and, above all, database cost. For this reason, increasing interest and effort are being devoted by operators, manufacturers, and system planners in general to determine the validity domains of propagation models in an urban environment. We introduce a new methodology, based on objective indicators related to field strength statistics, to determine these domains     

A characterization of indoor space and frequency diversity byray-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 0.75-1λ 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     

Narrowband characterization of 60 GHz radio propagation in indoor environment

The increasing demand for high speed data and multimedia services forces indoor radio communications to exploit new, almost fully available bands. Among the possible radio spectrum parts, the 60 GHz band seems to provide a good solution to move on. Thus, the paper deals with mobile radio channel characterization in indoor environment at 60 GHz; this is accomplished by means of an electromagnetic computer model, based on a fully 3D ray tracing approach. The channel has been characterized both in terms of radio coverage and of radio signal statistics, evaluating the best fitting cumulative distributions, the relationship between their parameters and the corresponding environment characteristics and addressing the improvements achievable by means of space diversity techniques.     

Comparisons of multiple access schemes for personal communicationsystems 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     

Adaptive antenna arrays for reducing the delay spread in indoorradio channels

The performance in terms of channel delay-spread reduction resulting from the use of adaptive antenna arrays are evaluated in a typical indoor environment. The propagation channel is simulated by means of a 3-D ray-tracing program. The impact of the geometric structure of the arrays as well as of the system bit-rate is discussed     

On the performance of packet reservation multiple access with fixedand 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