Michael Tangemann

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.

Mean Waiting Time Approximations for Symmetric and Asymmetric Polling Systems with Time-Limited Service

Cyclic polling systems are frequently used as models for the performance evaluation of token passing Local Area Networks (LANs) such as Token Ring or Token Bus and High Speed Local Area Networks (HSLANs), e.g., FDDI (Fiber Distributed Data Interface). The model is characterized by Poisson arrival processes, general independent packet service and switchover times and infinite buffer lengths. Frequently, the service disciplines exhaustive service or limited service are considered, because many results for these disciplines are available in the literature [14, 15]. However, they are not always appropriate for modeling the time-limited service disciplines defined in the standards for Token Ring, Token Bus and FDDI.

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.

Introducing 3rd Generation Mobile Communication Services on Evolved GSM Platforms

Summary Today, with IMT 2000 and UMTS the global standards for 3rd generation mobile services have been created, field trials have been started, and network installations are currently being prepared. In parallel, nearly unnoticed by the public, the evolution of 2nd generation networks proceeds, enabling the support of 3rd generation services on the existing infrastructure. Therefore, we suggest to consider an evolved GSM platform to complement the transition to 3rd generation mobile systems. In this paper the development path of GSM from 2nd to 3rd generation will be sketched, and an extensive treatment of E-GPRS, the next GSM stage to be introduced, will be given. This includes a system overview and a simulation-based performance analysis showing the ability of GSM to provide 3rd generation services as well.