Wireless Network Design: Optimization Models and Solution ...

318 Hang Jin and Li Guo
1. Guarantee the packet delay for users with real-time service: VoIP and gaming
2. Guarantee the throughput of FTP and Web users to be within the max. service
rate and sustain rate defined by the service level of each individual user.
So the basic procedure of the radio resource allocation is:
1. First allocate radio resource to Gaming and VoIP users to ensure the packet delay
requirement;
2. Allocated radio resource to FTP and Web users, whose user throughput is less
than the sustain rate defined in his service level;
3. Finally, allocate the remaining resource to those users whose throughput is lesser
than the max. service rate but larger than the sustain rate.
In this experiment, 200 active users are simulated. The fairness metric defined in
IEEE 802.16j [10] is employed in the experiment. In IEEE 802.16j, the fairness is
defined as the reciprocal of the standard deviation of the normalized throughput
with the mean throughput ¯x = 1
K
F =
K
∑
k=1
� K
K
∑ (
k=1
xk
− 1)2
¯x
xk . This metric grows with larger fairness, and
is not bounded. The output of the experiment shows that the fairness of 200 users is
1.53, which is slightly better than Fair-Time scheduler.
From the above experiments, we can see that through proper design of radio resource
allocation scheme in WiMax system, we can satisfy the various performance
requirements.
13.6 Conclusion
In this chapter, we have discussed the optimization problem for radio resource management
in OFDMA-based WiMax systems. Radio resource allocation in WiMax is
a classic optimization problem with multiple factors. Various optimization solutions
exist with different metrics and tradeoff between complexity and performance exist
among those solutions. The dynamic features in most of the aspects of OFDMAbased
WiMax systems impose difficulty on the optimization solution of a radio resource
allocation problem. A Particular performance metric and requirement needs
to be considered in the design of each radio resource allocation algorithm.