A Tapped-Delay Line Channel Model

In addition to providing channel information such as the rms delay spread, the power-delay profile фе(т), also provides a means for modeling the channel using a tapped-delay line (FIR) model. From Eq. (5), an(t) is the amplitude/gain coeffi­cient for a path arriving with delay Tn(t). A typical power-de — lay profile is shown in Fig. 14, which in the second figure, is uniformly sampled into equal delay bins. In general, the dif­ferent bins contain a number of received signals (correspond­ing to different paths) whose times of arrival lie within the particular delay bin. These signals are represented by an im­pulse at the center of each delay bin that has an amplitude with the appropriate statistical distribution (Rayleigh, Ri — cean, etc.). In deriving this model, two assumptions are made:

Time flat Frequency selective

Time selective Frequency selective

Frequency flat

Time selective

Time flat

Frequency flat

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Symbol duration (Ts)

Figure 13. A typical power delay profile and the method of sampling the power delay profile to generate a tapped-delay line model.

• there are sufficient number of rays clustered together in each delay bin;

• the statistical distribution of the envelope is known.

The rate of sampling the power-delay profile is affected by the time resolution desired and also the bandwidth of the trans­mitted signal. The next step after sampling the power-delay profile is to use a threshold (say X dB below the peak of the power-delay profile), and using the threshold to truncate

A Tapped-Delay Line Channel Model

those samples below the threshold. This model can be imple­mented by using a tapped-delay line or FIK model, thereby allowing us to model any arbitrary channel.

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