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Multicarrier Techniques for 4G Mobile Communications P

Examples of Multipath Fading Channels As discussed, when a signal is transmitted through a multipath fading channel, a channel model, which we assume, gives its received characteristics. For instance, the p.d.f. such as Rayleigh distribution and Ricean distribution describes the envelope fluctuation for an individual multipath component in the channel, the multipath intensity profile or spaced-frequency correlation function determines the frequency selectivity of the channel, and the Doppler power spectrum or spaced-time correlation function determines the time selectivity of the channel. Figure 2.5 shows examples of multipath delay profiles to describe frequency selectivity of a channel, which we often use in. | 22 Multicarrier Techniques for 4G Mobile Communications 2.7 Examples of Multipath Fading Channels As discussed when a signal is transmitted through a multipath fading channel a channel model which we assume gives its received characteristics. For instance the p.d.f. such as Rayleigh distribution and Ricean distribution describes the envelope fluctuation for an individual multipath component in the channel the multipath intensity profile or spaced-frequency correlation function determines the frequency selectivity of the channel and the Doppler power spectrum or spaced-time correlation function determines the time selectivity of the channel. Figure 2.5 shows examples of multipath delay profiles to describe frequency selectivity of a channel which we often use in this book for computer simulation. Here we can assume that the fading characteristic of each path is independent because ofWSSUS and we often assume a Rayleigh distribution for each envelope and a uniform distribution for each phase. In Figure 2.5 a there are a fixed number of paths with equidistant delays and the average received powers of multipaths are exponentially decaying. We often encounter this kind of profile in indoor environments 9 10 and we call it an exponentially decaying profile. On the other hand in Figure 2.5 b there are also a fixed number of paths with equidistant delays but the average received powers of multipaths are all the same. We often use this kind of profile to test a system performance 6 and we call it an independent and identically distributed i.i.d. profile. The time variation of a channel is determined by a lot of factors such as the height of transmitter receiver antenna the speed of transmitter receiver Figure 2.5 Examples of multipath delay profiles a an exponentially decaying multipath delay profile and b an i.i.d. multipath delay profile. Team-Fly Characteristics of Multipath Fading Channels 23 in motion the shape of the antenna the height of surrounding structures and so