Line of sight (LOS) or near line of sight often plays an important role in radio coverage for example for broadband fixed wireless access systems (BFWA) operating at high frequencies in urban areas. For coverage prediction and cell planning, complex ray tracing calculations based on detailed 3-D building information are usually necessary. In this article, a simple model is presented that directly predicts the average LOS coverage ratio for a given scenario defined by the cell size and base station height. The advantage of this model is the use of only four statistical parameters describing the area characteristics. These parameters can be easily estimated from only a small part of the database. The prediction model presented has been verified using 2.5-D building databases from typical urban areas. Despite the simplicity of the model, the results show a good agreement with ray tracing calculations.

Traditionally mobile radio channels are modeled as linear stochastic systems. It can be shown that stochastic modeling approaches have some physical limits, in particular if the bandwidth is very high. With this paper we want to introduce a new and alternative understanding of the physical effects the mobile radio channel is based on. Instead of analyzing time- and frequency domain by conventional methods from the field of stochastic signal processing we use algorithms which are focused on the signal's phase space. We learned that a colored Poincare-plot is a very powerful tool to characterize the mobile radio channel in that phase space. The results of characterizing the channel as a conservative dynamical system show that there are interesting mechanisms, which have not been considered in mobile radio channel modeling until now. Because this paper is too short to give a satisfactory introduction to the nonlinear dynamics of conservative systems, we focused on examples and the most important terms

In this paper we identify several shortcomings in GSM-R use for high-speed trains. Especially cell reselection and handover last too long. If they are combined with Group Receive Mode this causes additional problems. One single solution can help to cope with them. If handover and cell reselection are aided by location information they can be accelerated. Three strategies how to derive location information in railway environment are briefly explained. The location information is taken to determine the next serving cell. This shortens preparation time for cell reselection significantly. Railway environment makes it easy to estimate the location. In the outlook we show how to transform the results given here to new applications for area-wide mobile communication systems

We analyze how to speed-up handover in and between GSM (global system for communications) and UMTS (universal mobile telecommunications system). On one hand these systems face problems with high-speed users, e.g. those moving in a high-speed train. On the other hand it is known that there are security problems in GSM authentication, which also weaken UMTS when having handovers between both systems. Therefore additional authentication is integrated into the handover process. We show how and how much time can be saved in the handover process to allow additional authentication. Several approaches are compared and one implementation that can be done without changes of the hardware components or specifications in UMTS and GSM is shown.

We analyze how to speed-up handover in GSM and UMTS. There are several reasons to speed up handovers. On one hand these systems face problems with high-speed users, e.g. those moving in a high-speed train. This is important because the European railway organization decided to use GSM as their communication system for signaling and train control. As GSM was designed for speed up to 250 km/h there are problems with handovers and cell camping for higher speed. As the passengers in the train are going to communicate via UMTS the handovers of UMTS have also to be speed up. On the other hand it is known that there are security problems in GSM authentication that also weaken UMTS when having handovers between both systems. Therefore it is proposed to have an additional authentication just before the handover from UMTS to GSM. We analyzed how and how much time can be saved and show that we can also make use of the network topology to integrate additional authentication to secure the communication for example between the dispatcher and the train

Due to the increasing interest in mobile multimedia applications requiring high bandwidths, channel models need to be derived which represent properly broadband mobile radio channels. Previously defined models, e.g. for GSM by COST 207, are not verified for systems having such large bandwidths. In contrast, the presented new propagation models have been derived based on broadband measurements, taken by a channel sounder applied to a DVB-T network, and on the WSSUS theory, which is well known and adaptable to existing narrowband simulation systems.

By use of array antennas in mobile radio communications, a gain for the desired signal and more efficient rejection of interference can be achieved, either through diversity or beamforming techniques. Their use depends, basically, on the correlation coefficient between signals on the different array elements, that is influenced by the existence of direct line of sight (LOS). As yet, arrays are located only at the base station, but their use at the mobile station is also possible. In. this work, advanced direction of arrival (DOA) and delay estimation algorithms with a uniform circular array (UCA) located at the mobile station are analysed. These techniques demand a highly accurate calibration of the array to reduce the effects of both inter-element coupling and non-omni directional antenna pattern. On the basis of measurements in an anechoic room calibration is performed, and a unitary delay-DOA algorithm is adapted and implemented for circular arrays. The results obtained from a measurement campaign show that at a high percentage of locations the DOA of the first multipath component coincides with the direction towards the transmitter in azimuth. This result implies the use of array antennas also in mobile stations where enough space is available, e.g. on the roof of cars and trains.

The rationale for Ka-band propagation studies is discussed, and the relevant measurement program carried out in Germany by the Research Centre of the Deutsche Bundespost Telekom is reviewed. Current problems are briefly presented. Radiometer measurements from a 30 GHz site diversity experiment are discussed. The results indicate that availabilities of 99.9% can be achieved with diversity spacings of about 15 km. If, however, much lower values of around 97-99% are acceptable, margins of 3 dB are sufficient in single-site operation with gaseous and cloud absorption being of similar statistical importance as rain. Measurements carried out with the OLYMPUS satellite at 12.5, 20, and 30 GHz are also discussed. A comparison with the predictions based on the current CCIR procedures shows that rain attenuation is overestimated for time percentages above 0.01%, whereas depolarization is underestimated significantly. Instantaneous frequency scaling of attenuation and scintillations is discussed, and an improved scaling procedure for the latter is presented.>