Channel sounder for 5.5 GHz wireless channels

A channel sounder based on correlation of a maximum-length sequence is described. The sounder is designed for the evaluation of the absolute path loss and multipath delay spread of a fixed wireless local loop channel at 5.5 GHz. The sounder achieves good performance with relatively simple hardware. There are two key issues which must be addressed: compensation for drift and offset between the local oscillators and compensation for the distortion caused by the non-ideal nature of the measurement chain. Two-stage down-conversion is used with the second stage and subsequent processing being performed in software. A novel method of allowing for local oscillator drift without the use of a hardware carrier tracking mechanism is presented. The intermediate frequency is estimated by software before second-stage demodulation. Distortion due to the measurement chain is compensated by means of a matched filter. Measurement of absolute path loss and time variance of the channel are also considered. Example results are presented.