Ingo Gaspard

On the systematic measurement errors of correlative mobile radio channel sounders

We show that measurements of time-varying mobile radio channels obtained with uncalibrated correlative channel sounders are affected by four different types of systematic errors (commutation, pulse-compression, aliasing, and misinterpretation error). We analyze these errors and provide upper error bounds that are formulated in terms of channel and sounder parameters. Based on these error bounds, we provide guidelines for a judicious choice of important sounder parameters. Computer simulations using a simple two-path channel illustrate our theoretical results. Finally, we show how our results can be used to assess the accuracy of measured channel data.

Model Scenarios for Direction-Selective Adaptive Antennas in Cellular Mobile Communication Systems – Scanning the Literature

Intelligent antennas offer the possibility of greatly increasing the capacity of cellular mobile radio systems. We give a comprehensive overview of the literature concerning model scenarios for applications of direction-selective intelligent antennas. Measurement campaigns and simplified models are described that have been derived from these measurements or from physical considerations. Furthermore, directional fading simulators are reviewed which are essential for testing of smart antenna systems.

Position assignment in digital cellular mobile radio networks (e.g. GSM) derived from measurements at the protocol interface

Measurements are carried out at the protocol interface between base transceiver station and base station controller unit for optimization of the base station subsystem in an existing digital mobile network. At this interface it is possible-in contrast to measurements at the air interface-to gain mass data (e.g. received power, BER, signaling information) with low expenditure. The collected data allow however, only for a very rough estimation of the terminal positions. In this paper a method is presented to assign measurement data from the protocol interface to the related location of the mobile with the aid of field strength prediction. The application of the position assignment method is demonstrated within the GSM network. To validate this approach measurements were taken from the German GSM D1 net and were compared with exact position assignments by means of GPS. On the base of location assignment methods there are new experimental possibilities available, e.g. identification of traffic hot spots or areas of bad interference conditions.

WSSUS - channel models for broadband mobile communication systems

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.

Channel modeling based on comprehensive measurements for DVB-T mobile applications

Due to the increasing interest on mobile multimedia applications with high data rate, new channel models (WSSUS-models) have to be derived, which are adapted for broadband mobile radio channels. Previously defined models (e.g. for GSM by COST 207) are not valid for systems having greater bandwidth. The presented procedure is based on measurements taken by a channel sounder applied in a regular DVB-T network in Berlin.

Bounds on the systematic measurement errors of channel sounders for time-varying mobile radio channels

We show that correlative sounders for time-varying mobile radio channels are affected by various systematic measurement errors. We identify and analyze these errors and provide quantitative error bounds in terms of channel and sounder parameters. Furthermore, we propose a novel calibration method yielding substantially improved accuracy. Experiments using measured data and computer simulations illustrate the theoretical results. The findings allow to assess the accuracy of existing measurements as well as to devise improved measurement techniques.

Dynamic Resource Assignment (DRA) with Minimum Outage in Cellular Mobile Radio Networks

The assignment of resources to cells of a cellular mobile radio network is an important task in design and operation of a network. In practice, the number of resource units that are available for assignment to the cells is limited. As a consequence, not all cells can generally receive as many resource units as demanded and outage, defined as the number of resource units requested but not assigned, occurs. In this paper, the dynamic assignment of resources to the cells of a cellular network is discussed under the assumption that the number of resource units available for the assignment is not in all cases sufficient to fulfil the resource demand of every cell and that the occurring outage has to be minimised. An efficient method of determining the number of resource units required for outage-free resource assignment is presented. This method is used to determine outage probability and a lower bound for the amount of outage. Finally, a policy based algorithm for the assignment of resources with very low complexity is presented and its performance in terms of amount of outage compared to the lower bound evaluated.

Impact of the channel estimation onto the BER-performance of PSAM-OFDM systems in mobile radio channels

Pilot symbol assisted modulation (PSAM) of the subcarriers of an OFDM system seems to be very attractive for high data rate radio systems. It is used, or will be in the near future, in broadcast systems like DVB-T and DRM. Nevertheless, for highly time- and frequency-dispersive radio channels, the channel estimation based on the interpolation between the pilot symbols in time and frequency is very critical. We derive expressions for the gross BER as a function of channel correlation and interpolation filter in time and frequency. Also adjacent channel interference due to Doppler effects is taken into account. Example results are given for the European DVB-T system, which is also a system candidate for the broadband downlink of a new platform concept to enable asymmetric IP-based mobile multimedia services. This concept is under investigation within the German research project UMT-Splus/COMCAR.

Mobile reception of the terrestrial DVB-system

The European standard for the terrestrial digital video broadcasting, DVB-T, is primarily designated to the stationary and portable reception of video services. In most European countries this standard is already introduced or will be introduced very soon. Because of the increasing demand for mobile reception and the migration of communication and broadcasting, e.g. in the area of multimedia communications, it is of importance for the network operator to analyze the capabilities, but also the limitations of the available DVB-T-system operated in a mobile environment. In this paper we will show by means of measurements and hardware simulations that mobile reception of the DVB-T-system is possible for certain sets of parameters. It turns out that mobile reception in single frequency networks is possible for moderate vehicle speeds if robust modulation schemes like QPSK and 16-QAM together with high FEC protection ratios, e.g. code rate 1/2 and 2/3 are chosen. We found out that in general the maximum speed in single frequency networks (SFN) is lower than in multi-frequency networks (MFN) for the same set of parameters.

Capacity enhancement of narrowband CDMA by intelligent antennas

A standard-compatible upgrade of IS95-CDMA base station (BS) transceivers by smart antennas can at least double the cellular radio capacity at the cost of a moderately increased transceiver complexity. This is demonstrated for the adoption of a beam diversity concept. At the sectorized BS, uniform linear antenna arrays are employed. An intelligent adaptive receiver antenna is implemented based on the DFT beamspace transform and angular-temporal RAKE combining. Downlink transmission utilizes beam selection. In Monte-Carlo-based performance assessments a special point of emphasis is put on the real-world-like modeling of the directional radio propagation phenomena. Small and large area channel models for densely built-up urban macro-cells are used which were determined from the results of a spatio-temporally sensitive sounding campaign at 1.9 GHz. Thus, the analysis results are valid for the important application case of larger urban cells operated in the PCS and IMT-2000 bands.