Wimax standards and Security The Wimax

FIGURE 4.7
Blocking probability versus number of subscriber stations.

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Requested bandwidth (n × 64 Kbps), where h = 2 and SS = 50


FIGURE 4.8
Sensitivity analysis on requested bandwidth.

These simulation results provide a guideline for engineering the QoS services for the WiMAX subscribers. For example, a network engineer may allocate only 50% of the bandwidth for MSTR of UGS and MRTR of rtPS/nrtPS, so that the network can have sufficient capacity to serve BE sub- scribers. If the arrival rate for UGS and rtPS/nrtPS is one request per minute

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Time series (20 min)

FIGURE 4.9
Channel utilization of UGS-only traffic.



=
(λ 1) with average data size of 2 MB, the engineer guideline is to support up to 50 subscribers. If the engineering rule changes to 70% for UGS and rtPS/nrtPS subscribers, the network could support up to 75 subscribers.

2. 
   Simulation of IEEE 802.16 QoS Scheduling
   

The UL and DL bandwidths are controlled by the BS. In the case of DL data transmission, the frames are combined into burst and broadcasted to all SSs. In the case of UL data transmission, an SS waits for its polling interval and transmits the data only when it is polled. In the simulation runs, we exclude the manual provision of UGS as it is similar to a circuit-switched service. The simulation is based on the dynamic bandwidth requests as illustrated in Figure 4.5. After the request/grant process for admission, a user request is entered into the scheduling queues of UGS, rtPS, nrtPS, and BE. The scheduler uses the poll/grant mechanism to determine how to serve the jobs in the queues. In the simulation, we use two sampling intervals—10 ms (for UGS and rtPS) and 50 ms (for nrtPS and BE). The configuration of simulation profile is given as follows:

• 
  DL/UL bandwidth = 14 Mbps.
  
• 
  Basic channel = 64 Kbps (DS0).
  
• 
  Number of DL/UL channels: 14 M ÷ 64 K = 218 channels.
  
• 
  Number of SSs = 100.
  
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  Request arrival rates per station (λ): 2/min (light traffic) and 5/min (heavy load).