Digital techniques for mobile radio chirp sounders

The theory of chirp sounding is reviewed. This is followed by a description of a digital mobile radio chirp sounder which is implemented using direct digital frequency synthesisers (DDFS), field programmable gate arrays and microcontrollers. The gate arrays and the microcontroller provide the user interface via either a keypad or a PC, generate the programming words for the DDFS and two phase-locked-loop (PLL) synthesisers, synchronise the transmitter´s sweep to the receiver´s sweep and implement a beat-frequency-oscillator DDFS. The results demonstrate that the digital chirp sounder provides full programmability of the various chirp waveform parameters, bandwidths of up to 90 MHz which are suitable for both indoor and outdoor environments, offline processing to obtain different channel characteristics, and moderate averaging to obtain a dynamic range better than 35 dB