![]() These delays are measured relative to the first detectable signal to at the receiver at t 0=0. The rms delay spread is the square root of the second central moment of the power delay profile and is defined to be ![]() Where P (τ) is the power measured at time τ. ![]() The mean excess delay is the first moment of the power delay profile and is defined to be The mean excess delay, rms delay spread and excess delay spread (X dB) are multipath channel parameters that can be determined from a power delay profile. In order to compare different multipath channels and to develop some general guidelines for wireless systems, parameters which grossly quantify the multipath channel are used. The delay profile determines to what extent the channel fading at two different frequencies f 1 and f 2 are correlated. This gives the "delay profile" of the channel. We can define the local-mean average received power with excess delay within the interval ( T, T + dt). ![]() Since the impulse response (IR) and the transfer function (TF) of a channel are related by the Fourier transform, it is intuitively understandable that the TFmagnitude shows more fades per bandwidth, the longer the IR.īecause of multipath reflections, the channel impulse response of a wireless channel looks likes a series of pulses.įigure is an example of impulse response and frequency transfer function of a multipath channel. The root-mean-square (RMS) delay spread is probably the most important single measure for the delay time extent of a multipath radio channel. ![]()
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