Mutual proximity and exposure time can provide critical information to assess the risk of propagation of highly contagious viruses such as SARS- CoV2. To this extent, Bluetooth Low Energy (BLE) represents the best candidate in the low range communication technologies to estimate the proximity distance between smartphones by means of ranging algorithm based on Received Signal Strength Indicator (RSSI) measurements. Although promising, the high variability of the radio propagation channel for ISM-band technologies suggests that a deep analysis of BLE is needed in order to isolate the different propagation factors. In this paper we show, through extensive measurements, the fluctuation of BLE channel in various environments and provide a ray tracing model to fully capture the BLE channel behavior. Results show how unpredictable BLE measurements become at increasing distances and under different positioning configurations, leading to misleading detections for contact tracing apps. A possible solution could be to introduce the use of mathematical models to capture core aspects of population mobility in order to estimate realistic exposure information.

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.

Future wireless personal communications will find important applications in indoor environments; hence, an accurate analysis of the propagation characteristics within buildings and their impact on system design parameters is highly desirable. The performance of space diversity techniques in an indoor environment is investigated. Three linear signal combining techniques are considered: signal selection, maximal ratio combining and equal gain combining. The calculation of received fading envelope in the environment has been performed by using a 3D ray-tracing/UTD technique. The obtained results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage, as well as the good agreement with the general achievements of previous experimental works.

The paper deals with the evaluation of the impact of non-uniform user distribution on cellular CDMA performance. A peak-shaped traffic model, typical of urban environments, is included in a simulation program which computes the carrier to interference ratio for the up-link of CDMA system. First, considering the usual hexagonal lay-out, the reduction of the traffic volume with respect to the uniform traffic distribution case is evaluated; then, some possible countermeasures are presented, basing on the optimization of the received power levels required by each base station.

The personal communication systems envisaged for the future will have to accommodate a wide range of services with different quality requirements (on delays, retransmission rates, etc.), and often characterized by relatively short traffic burst interleaved by 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 are currently studied. In this paper a self-adaptive assignment method (channel segregation), originally developed for TDMA/FDMA systems, is conveniently adapted for PRMA operations. Simulations show good performance, provided that values of some system variables are correctly chosen. These results encourage further studies in order to refine adaptive methods suitable for cellular, packet switched personal communications systems.>