Alexander Kuchar

Directional macro-cell channel characterization from urban measurements

We measured the angular power distribution at the mobile station in downtown Paris at 890 MHz. The transmit antenna was omnidirectional and placed high above rooftops. The receiver antenna, a 21/spl times/41 element rectangular synthetic array, was located on the roof of a van. The refined high-resolution evaluation method, particularly robust against nonstationary signal components, allows an angular resolution of better than 1/spl deg/ in both azimuth and elevation and a delay resolution of 33 ns. Combined angular/temporal domain measurements are crucial for the understanding of the propagation mechanisms. The evaluated sites showed strongly street-dominated propagation. We found a combined circular and rectangular distribution of scatterers around the mobile station in street-dominated environments. Propagation over the roofs was significant; typically 65% of energy was incident with elevation larger than 100. Our results corroborate the hypothesis on the importance of multiple reflections/diffractions in urban macro cells. We explain this behavior by two reasons: narrow streets favoring a canyon effect and strong scatterers without line-of-sight (LOS) to the mobile station.

Geometry-based directional model for mobile radio channels -principles and implementation

Adaptive antennas are used in mobile radio systems for improving coverage and increasing capacity. For realistic system design and simulation, channel models are required in order to assess the performance of such systems. We propose the so-called ‘geometry-based stochastic channel model’ (GSCM), which is easy to implement and has a low complexity even when the directional dimension of the channel is taken into account. In this model, we prescribe the probability density function (PDF) of the location of the scatterers. From this, the angularly resolved impulse response can be computed by a simple ray tracing. We then present various extensions of the model in urban environments, namely for diffraction losses and wave guiding by street canyons. We also discuss methods for efficiently implementing GSCM. Copyright

A real-time DOA-based smart antenna processor

We designed, built, and tested a real-time processor for a direction-of-arrival-based smart antenna GSM 1800 base station with eight half-wavelength spaced antenna elements. Its processing steps include direction-of-arrival (DOA) estimation, user identification, tracking, beamforming, and signal reconstruction. We demonstrate that the accuracy of DOA estimation is not of primary concern, but the robustness is. This can be assessed by a new parameter, the estimation range. Tracking of reliable user DOAs only, increases the robustness against interference. Our tracking concept is compatible with frequency hopping. We quantify the benefits of smart antennas by the statistics of the gain in carrier-to-interference ratio (C/I) and in signal-to-noise ratio (SNR), both measured at the 90 or 99% levels with actual transmitted data. In an urban environment with large angular spread and overlap of user and interferer signals, the C/I gain is as high as 18 dB. Interferer nulling increases the C/I gain only slightly, but enhances robustness against angular spread, particularly if broad nulls are applied. Separating SNR gain in its contributions due to beamforming and diversity gives valuable insight into the way of operation. In uplink, the processor can exploit angular diversity. The entire suite of processing steps is done within less than 1 ms, demonstrating that sophisticated DOA-based smart antenna processing is feasible in real time. Our solution does not require any change in the GSM standard.

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.

Capacity increase in cellular PCS by smart antennas

This paper considers the increase in spectral efficiency of a TDMA PCS system employing smart antennas at the base station. Two different strategies are analyzed: spatial filtering for interference reduction (SFIR) and space division multiple access (SDMA). Our results indicate that a cluster size of N/sub cl/=1 is possible by utilizing smart antennas. The use of SDMA increases the spectral efficiency over SFIR by 80%. Additionally, SDMA adds flexibility to the whole network.

Real-time smart antenna processing for GSM1800 base station

We successfully implemented a smart antenna array processor for a GSM1800 base station. The entire array processing run-time is only 1 ms, allowing real-time adaptation of the antenna pattern every GSM frame. The array processing is based on the estimation of the DOAs in the uplink. Separate DOA trackers for uplink and downlink, angular selection diversity, and beamforming with broad nulls guarantee robustness in mobile radio channels. Measurements in a LOS scenario show that the DOA estimation accuracy is on the order of 1/spl deg/ for 0 dB input SNR. BER measurements confirm the expected signal-to-noise gain of /spl ap/9 dB compared to the single antenna case. In case of one interferer a BER of 1% is reached for an input C/I of -6.5 dB.

Azimuth, elevation, and delay of signals at mobile station site

We analyzed channel sounder measurements at 890MHz in a dense urban environment where the receiver was located at the mobile station site. The joint information of delay, azimuth and elevation allows a thorough study of the main propagation mechanisms. There is a clear indication that street canyons dominate propagation in a dense urban environment, but scatterers all around the mobile station contribute to the power delay profile. For the macrocells investigated, there is a considerable over-the-roof propagation. Our results corroborate the hypothesis of multiple reflections/diffractions in urban macro cells.

Implementation Issues for Fully Adaptive DOA-Based Smart Antennas

Let us briefly review some principles of DOA estimation, uplink/downlink dif-ferences, related to FDD vs TDD; basic differences of smart antenna operation between TDMA and CDMA; and some GSM basics. These will help under-standing why we chose the particular solutions of the fully adaptive real-time smart antenna described in the section on the demonstrator A 3 P.