Ultra Wideband Radio Channel Modelling for Indoors

Most of the wideband radio channel models available today are not accurate enough for ultra wideband (UWB) applications occupying an extremely large bandwidth. In this paper, a procedure for indoor UWB radio channel measurements and modelling is presented. The example discussed here is based on the measurements carried out in the main building of the University of Oulu, Oulu, Finland. An average size lecture room was selected to represent typical university environment, and various radio links were measured for statistical variance. A radio frequency band from 2 to 8 GHz was covered by a vector network analyzer, and the measured S21 data were inverse Fourier transformed to achieve the corresponding impulse responses. Introduction In this paper, ultra wideband (UWB) radio channel measurements and procedures for channel modelling are presented. Statistical indoor UWB radio channel models are utilized in radio system simulators to enhance the accuracy of system performance evaluations. There is a rare supply of channel models covering several gigahertz frequency band, and the need of the UWB radio channel modelling is obvious. The example of the general radio channel modelling presented here is a case study based on the measurements that were carried out in the main building of the University of Oulu during summer 2001. Several sizes and different types of rooms, starting from the small meeting rooms to big auditoria, were then selected for the radio channel measurements. The areas of the rooms were between 30 m and 500 m, and the direct link separation varied between 1.5 m and 13 m. The frequency responses of the channel were recorded using a vector network analyser and the impulse responses were calculated via inverse discrete Fourier transform. The channel characterization and finally the channel models will be generated from the delay profiles (averaged impulse responses.) Methods for Radio Channel Measurements The key element of radio channel measurement is the coherence time of the channel, and the sounding has to be done within this limit. Otherwise the channel characteristics will change too much and the statistical presumptions do not hold. There are several techniques for wideband radio channel sounding. The ideal way for the UWB radio channel sounding is to use impulse transmission technique presented in Figure 1 [1]. This is a time domain sounding system, where the transmitted signal is a single impulse or a train of impulses and, for example, a digital sampling oscilloscope is used as a receiver to directly measure the channel impulse response. The advantage of this technique is that the probing bit sequence can be the same as the one used also in the final applications. The environment do not need to be static within the recordings but the coherence time assumptions still need to be valid. To be submitted to COST273 Workshop in Helsinki, May 29-30, 2002