Impact of Channel Sounder Frequency Offsets on the Estimation of Channel Parameters

We investigate the design of a multiple input multiple output (MIMO) channel sounder appropriate for the broadband fixed wireless access (FWA) scenario. To this end a 4 transmit 4 receive antenna system was simulated in order to investigate the effect of equipment imperfections on the estimation of channel parameters, for example, K-factor, power delay profile (PDP), antenna correlation coefficients (ACC) and signal angle of arrival (AOA). The channel employed in the simulation is based on the SUI-3 model [8]. The accuracy of the channel estimation results is dependent upon the frequency offset between the phase lock loop (PLL) reference oscillators used at the transmitter and receiver. Consequently, high cost rubidium reference sources are usually used since they can reduce the frequency offset to almost zero owing to their frequency stability (aging) of about 5times10^-10 per year [13], equivalently, 5times10^-4 ppm per year. We wish to determine how much frequency offset can be tolerated before the estimation results become unacceptable. To this end we have conducted extensive system simulations that have revealed that acceptable accuracy can be achieved using relatively low performance and therefore inexpensive reference sources.