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The WiMAX channel access is controlled by one of the several available Medium Access Control (MAC) procedures. This paper studies the contention-based bandwidth request procedure based on our original analytical model, facilitated by numerical analysis and simulation. We optimize the key parameters of the contention procedure in order to minimize the average bandwidth access delay, thus ensuring the highest possible quality of service to the WiMAX users. We also propose procedures for efficient and accurate estimation of all input parameters to carry out the procedure for bandwidth request optimization. We show that the analytical model and the estimation methods are highly accurate. The practical implementation of the proposed optimization is simple and results in gains of the delay and bandwidth utilization compared to the non-optimized case.

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Wireless networks are built upon a shared medium which makes it easy for an adversary to launch a Denial of Service (DoS) attack. Jamming, as a part of DoS attacks at physical layer, is one of the main security considerations within the wireless networks. It holds the potential to totally cripple the network and cause a loss of service and revenue. Jamming attacks can severely interfere with the normal operation of wireless networks and, consequently, mechanisms are needed that can cope with jamming attacks. Jamming techniques vary from simple ones based on the continual transmission of interference signals, to more sophisticated attacks that aim at exploiting vulnerabilities of the particular used protocol. Considering the fact that the jamming is one of most common attacks against military communications, this paper is examining the wireless military network behavior in the presence of such attacks. For this purpose we simulate the effects of the various jamming attacks using OPNET Modeler. Several effective counter-measures against low power jamming are proposed. These measures are based on both transmit power and packet reception power threshold optimization, supported by spread spectrum techniques. The results are considerably improved when all of these mechanisms are combined