Wideband channel characterisation with a chirp sounder

Frequency modulated continuous wave (FMCW) or chirp sounders have become more widely used for the characterisation of the mobile radio channel. In comparison with PRBS sounders, chirp sounders have a bandwidth which is limited to the swept bandwidth of the signal. In contrast, PRBS sounders require shaping of the spectrum to reduce the sidelobes level. In addition, chirp sounders that employ a heterodyne detector result in bandwidth compression which permits the use of low speed analogue to digital converters. They also offer the advantage of obtaining the channel characteristics either over the entire transmitted bandwidth or subsections. This advantage enables the simultaneous measurement of the channel characteristics over a wide bandwidth without having to repeat them as in PRBS sounders. To enable the measurement of both the indoor and outdoor environments, the bandwidth of the sounder should vary between 10-100 MHz to obtain a spatial resolution of 3-30 m. The measurement of the Doppler frequency requires the waveform repetition rate of 90 Hz for a 5m/s speed and 500 Hz for a 100 km/h vehicle speed at 1.8 GHz for indoor and outdoor measurements, respectively. A wideband channel sounder using a flexible design to obtain chirp waveforms with variable bandwidths and variable repetition rates is described. Outdoor measurements, with a 5 MHz bandwidth, in Dublin are presented