# Mean excess delay ## Formula $\overline{\tau^2}=\frac{\sum_k p_k\tau_k^2}{\sum_k p_k}$ ## Root mean square delay spread $\sigma_\tau=\sqrt{\overline{\tau^2}-\left(\overline{\tau}\right)^2}$ Calculates the standard deviation of the channel. How it spreads the energy of the signal over time. ## Example Units are important! They y axis is in dB - convert to linear!!  This will affect the signal if it is in the realm of the signal width in time domain. ### Example If the transmitted signal duration is 1ms and the delay spread is $1.37\mu s$:  you don't really have multipath effects just some attenuation. ### Example: symbol width comparable to mean excess delay But what if the symbol width is $0.5\mu s$?  # References 1. [TELE4652-lecture-03](../03%20-%20University/TELE4652/Lectures/TELE4652-lecture-03.pdf) # Footnotes