**5. Conclusion**

354 Wireless Communications and Networks – Recent Advances

RRutil maxUtil (no MG) maxUtil (MG)

> RRTd minTd (no MG) minTd (MG)

0 10000 20000 30000 40000 50000 60000 70000 80000 **time [sec]**

0 10000 20000 30000 40000 50000 60000 70000 80000 **time [sec]**

During the simulations we have used the following parameter values: *Nr* = 10, *Nall* = 150, *q* =

From the results we can conclude that the contention based bandwidth request procedure which uses multicast grouping almost always outperforms the case where no multicasting groups are used. This is the case if our comparison criterion is based on the transmission slots utilization. The same conclusion is not entirely valid if the criterion is based on the average bandwidth access delay. The round-robin mode of operation, as expected,

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0

Fig. 10. Measured delay.

1, *tfrm* = 10ms.

50

100

150

**Td [msec]**

200

250

300

Fig. 9. Measured utilization of the transmission slots.

**util**

The performance of a communication system (or protocol) is the major indicator for the successfulness of the standard that specifies that system. During the development process of new communication technologies, the aim is to increase the overall protocol performance, which automatically means to produce a better standard. The formal-based performance evaluation method described in this chapter, which uses SDL network prototyping, provides the most relevant results of the system performance without the need for its early and prematurely hardware implementation. This is crucial for the production of competitive communication products which will be free of hidden flows during the development process. The aim of this chapter was to emphasize the importance of conducting an early performance evaluation of the communication protocols and systems, and to suggest an appropriate solution for carrying out such an activity.

We have illustrated the proposed framework through an actual case study which targets the WiMAX bandwidth allocation methods. Three schemes were investigated: contention based bandwidth requesting without multicasting, contention based procedure with multicast grouping, and round-robin polling based bandwidth allocation scheme. With the help of the SDL performance model, we have found that the preferred scheme should be selected based on the network working conditions (i.e. number of active subscriber stations) and according to the performance criterion (transmission slots utilization or average bandwidth access delay).

The proposed new protocol etities which are product of the communication protocol engineering process are simple and accurate, and can be easily implemented at the BS side in order to optimize the performance of the WiMAX bandwidth request procedure.

The presented results are only a hint to the possible evaluation outcomes from the network emulations created using the proposed methodology.
