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Simulation and Results

The mobile communications system modelgif is shown in figure 6. It is an open system; mobile hosts are generated at rate with inter-arrival time specified by Exp Pulse Mean, initiate a call for an average exponential duration specified by Mean Session Length, and exit the system when either the call is complete or the mobile moves out of all cell areas.

 

  figure522


Figure 6: Top Level Mobile System.

The first step is to create the base stations and their cell areas. The total number of base stations is:

equation527

and they are located in a square array. They all have the same number of channels, Total Channels for Base Station. Each cell area can be approximated as a circle with radius:

equation531

Mobile hosts are created in Create Mobile Users. All the mobile parameters are uniformly distributed, except the session duration which is exponential and agrees with equation 1 of our analysis. New mobiles enter the system with an interarrival time of Exp Pulse Mean. The mobile host will arrive at a location uniformly distributed anywhere in the area covered by all cells. Since a mobile makes one call in its lifetime, a mobile host represents a single connection. Thus,

equation538

where B is the number of base stations.

The following modules act upon the mobile hosts throughout their lifetime. The mobile hosts are assigned the nearest base station Assign Base Station to Mobiles Users, and an available channel from that base station Assign Channel to Mobile Users. Then all mobile hosts dwell in their cell areas for time Delta Time Delay Mobile Users. The mobile host then moves to its next location which may be uniformly chosen from Direction of Motion Options and may lead to a new cell or completely outside the cellular system Move Mobile Users.

After moving, the quality of signal is checked and if below a given criteriagif the channel is released (Release Channel) and the mobile host is reassigned to a new base station (Assign Base Station to Mobile Users).

Note that the direction of travel by a mobile user is uniformly chosen from North, South, East, or West. A more sophisticated analysis of speed and direction is contained in [6].

The simulation results are shown in Figures 7 and 8. These results agree with the results of the analysis shown in Figures 4 and 5.

   figure559
Figure 7: Channel Usage Probability for 0.6 Call/Sec.

   figure564
Figure 8: Channel Usage Probability for 0.01 Call/Sec.


next up previous
Next: Summary Up: Mobile Systems Analysis Previous: Example

Steve Bush
Sun Aug 25 17:38:45 CDT 1996