Wireless Communication

Chapter: Wireless Propagation Channels
Section: Channel Models, Indoor Propagation

Long-term Fluctuations

Different important effects giving rise to long-term fluctuations have been implemented in the SRCM :

The simulation of path loss is based on the extended linear model as proposed in [5]:

  equation268

where tex2html_wrap_inline1015 means the free-space loss at 1 m distance and d denotes the distance between the transmitter station and the MT. A power decay exponent of n=2 and a path attenuation of tex2html_wrap_inline1021 reveal to be in good agreement with experimental results.

Following [6] the locations along the trajectory where paths become active form a Poisson process with a certain occurrence rate. The length of the active segments is exponentially distributed.

   figure359
Figure: Variation of the number of active paths

The number of active paths tex2html_wrap_inline1023 along the trajectory is then a Poisson process with the mean tex2html_wrap_inline1025 . Figure 4 illustrates the variation of the number of dominant impinging waves.

The power variation of the multipath components in transition situations is simulated by means of smooth monotone functions as suggested similarly in [7] .

MT movement will also cause fluctuations of the delay and the incidence direction of the wave components. The location dependency is described in [2]. No model has been developed yet to characterize the spatial dependency of the varying incidence directions due to a lack of experimental data.

   figure368
Figure: Long-term fluctuations of the power and delay of the waves

Figure 5 shows the influence of a dynamic incidence constellation resulting in fluctuations of the power and delay of the waves.

For sake of completeness it should be mentioned that because of the simulation of the changing number of active paths as previously described the so-called shadowing usually represented by a lognormal process in classic channel models is inherently embodied in the SRCM.

   figure377
Figure: Path loss (shadowing)

Figure 6 presents this fact in form of a successive approximation of the target function (9).

 

  table289


Table: Parameter set for the WAND-SRCM at 5.2 GHz [2]

As an example, Table 3 shows the parameter set of the SRCM developed for the European ACTS project AC085 WAND (Wireless ATM Network Demonstrator) [2]. Obviously, the delay spread is related to the room size while tex2html_wrap_inline1025 as well as tex2html_wrap_inline1001 and tex2html_wrap_inline1003 are determined by the complexity of the furniture and equipment and their geometry, respectively.

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Wireless Communication © Peter E. Leuthold and Pascal Truffer, 1999