| Wireless CommunicationChapter: Wireless Propagation Channels |
A stochastic radio channel model (SRCM) has been developed in order to simulate realistic channel impulse responses (CIR) according to a wide range of possible physical situations within a given category of environments.
The transceiver characteristics as well as nearly all dispersion effects, that means the different phenomena of multipath propagation, short- and long-term fluctuation, are implemented in the SRCM. Under certain conditions, some effects that are expected to have only little impact to the system performance can be neglected. This may result in a considerable reduction of the model complexity. Further improvements of the SRCM, especially with regard to the consideration of terminal movements along arbitrary trajectories with varying velocity, are envisaged.
The novel channel sounder concept ECHO 24 operating in the 24 GHz range exhibits some attractive features. The coherent test signal demodulation achieved by a fiber-optical connection between the transmitter and the receiver yields the complex time variant CIR which allows the extraction of the necessary SRCM parameters. Moreover, the transmitter of the sounder system can easily be moved through the rooms, corridors and staircases of a building even over long distances due to the thin and flexible fiber cable with a very low attenuation. In order to measure also the incidence directions of the impinging wave an appropriate antenna array is under development. Because of the modular structure of the channel sounder a shift of the operation range to 60 GHz or even higher frequencies is possible without major change.
Among the different algorithms for the calculation of the SRCM parameters from the measured data the SAGE (Space-Altering Generalized Expectation-Maximization) algorithm reveals to be a powerful tool. Thanks to the advanced semiconductor signal processing devices, even an on-line multiple parameter extraction, i.e. complex amplitude, delay, incidence direction and Doppler shift of the impinging wave components, seems to be possible in the near future. Thus, the SAGE algorithm will also be a promising signal processing scheme for the next generation of wireless communication systems using smart antennas.
