Processing, transport, conversion and filtering of radio signals in fragmented frequency bands for different mobile standards

Report of the project CoMoRa (Cognitiv Mobile Radio) Last years research on efficient spectrum usage primarily focused on the increase of spectral efficiency. Whereas these project activities enabled a successful extension of the research area by solutions for an efficient, i.e. a complete and undisturbed usage of the available free spectrum. Within the Alcatel-Lucent project part, new approaches for processing and transport of digital radio signals of different radio standards have been evaluated. They allow a flexible and efficient usage of fragmented spectrum, especially in non-licensed bands. Furthermore, new base station solutions are proposed, allowing for a more efficient usage of network components and for a reduction of fabrication and operation costs. Solutions for distributed base station functions and their data interface allow simplifying the equipment at the antenna site. They include a fast control and a cooperation of antenna sites as basis for future solutions for improving the spectrum usage. Solutions for an efficient and simplified multi-antenna system for base stations are using the spatial degree of freedom for interference suppression in the receive chain of coexisting systems, and to avoid distortions on such systems in the transmit chain. Significant is a simplified feeding of a higher number of antennas, where the respective effort is not increasing proportional with the number of antenna elements. Key components of frequency agile and robust base stations assure a more efficient usage of non-licensed frequency bands. The fragmented operation of typical signal bands enables the usage of such bands by several mobile services. The increase of interference resistance in receivers by means of tunable bandstopp filters minimizes the probability of a radio link drop out, caused by external distortions. This allows increasing the operation time in non-licensed bands. Two different technical solutions for tunable filters have been verified by means of hardware prototypes. A low cost solution is based on printed circuit boards with the drawback of lower performance. With filters realized in a more complex technology, the targeted performance could be exceeded significantly, with sufficient margin for fabrication tolerances and for discrepancies due to application diversities. The key components of frequency agile and robust base stations, the tunable filters and the control and signal processing algorithms, are integrated into a lab set-up. The complete procedure to detect and remove the receiver overload is evaluated. Thereby the feasibility and performance of the analyzed solutions could be demonstrated successfully.