Experimental Delay Tests in Causal THz Channel Model

In traditional radio propagation, the arrival time of the signal at the receiver from the transmitter is the propagation delay, which is given by the distance divided by the light speed, in the line of sight (LoS) scenario. However, in THz, the observable arrival time would be more than the propagation delay, and the extra delay is denoted as a molecular absorption (MA) delay. At first, this paper shows the presence of such MA delay based on the causal channel model that can provide an accurate impulse response for the target frequency band in THz. The comprehensive investigations of the impulse responses reveal that the MA delay is related to the frequency selectivity due to molecular absorption in THz. The causal channel model can also provide an appropriate phase response, and the MA delay can be approximated by the group delay. In addition, an estimated impulse response from the experimental tests also indicates the validity of the MA delay at the THz band.