Flexible RF systems and antennas for future vehicular communications

Abstract

Up to now vehicular communication systems used dedicated components for each of the communications standards. Future global fragmentation of standards, services and frequencies and the ongoing increase of communication standard plurality will render this approach impossible or at least uneconomical.<br />This thesis describes the outcomes of my research effort to make those systems more flexible, more efficient and also simply cheaper.<br />Furthermore some completely new architectures have been introduced.<br />Starting with the first element in the receive system chain a novel concept of a vehicular communication antenna is presented. To the authors best knowledge it is the first published antenna that combines the following features. Capability of performing well in MIMO scenarios over a frequency range of at least 4.2 GHz (1.8 ... 6.0 GHz - from UMTS to 802.11p in the ITS band and beyond), while additionally being capable of receiving the lower GSM bands (0.85 ...1.0 GHz) with one antenna.<br />Featuring a GPS (1.575 GHz) antiresonance for reduced coupling at this broadband pole with supplemental GSM resonance. A second achievement in antenna design was an antenna array that leveraged advantages by bespoke (tailor-made) antenna elements for this application to reduce the overall element count to a fraction of prior developments. By concentrating even the elements gain towards the possible directions of the GEO from a moving car, the array gain factor needed is lower. Furthermore the elements are vertically polarized and thus do not need any polarization tracking. Another phased array system was realized by my diploma student Maxim Zaretskiy. Its purpose is the detection of RFID tags carried by children to enable collision warnings and autonomous deceleration in case of anticipated collisions.<br />Moving further down the receiver's chain, a new transmitter architecture was proposed and implemented. It features transmit capabilities for four individual modulation signals for digital beam forming, MIMO or combined architectures and operates from 0.6 to 5.0 GHz as standalone device or up to 6.0 GHz with an external LO gererator. A similar system with a single channel was realized by my diploma student Irene Herranz for the receive case.<br />To abstract the communication standards from the services from the users an abstraction layer was defined to ease vehicular integration of new communication technology and reduce the quality assurance costs for control unit testing.<br />For the demonstration of the power of MIMO services and the capability of multi-antenna systems a mobile WiMAX vehicular prototype has been implemented. The WiMAX prototype showed exceptional performance even at high moving speeds and demonstrated enjoyable applications which could be embedded with a high-speed data connection.<br />During the research work 7 patent applications have been filed and 6 IEEE papers have been published.<br />Future research is planned in even higher integration of the electronics. Moreover a tighter connection to an SDR system shall be established to make the overall system as flexible as the analog electronics researched in this work. In near future the broadband MIMO antennas could be advanced to camouflaged appearance as the safety system antennas in the radiator grid were. Last but not least the GEO antenna array should be tested in action and developed further towards true series producibility.<br />