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 :

• path loss depending on the distance
• variation of the number of active paths
• transitions where waves arise and vanish
• fluctuation of the propagation delays
• change of incidence directions due to MT movements

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

 

where 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 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.

  
Figure: Variation of the number of active paths

The number of active paths along the trajectory is then a Poisson process with the mean . 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.

  
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.

  
Figure: Path loss (shadowing)

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

 

 

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 as well as and are determined by the complexity of the furniture and equipment and their geometry, respectively.

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