MANETs is a type of Mobile Ad Hoc Networks and it contains a set of nodes that do not need central management to communicate with each other because each node can act as a sender, receiver and router at the same time. All these nodes can perform self-configuration. The ad hoc stationary or mobile networks face many challenges such as limited bandwidth, congestion and data transfer speed. Therefore, it is extremely important to develop an intelligent routing protocol to encounter these challenges. An evaluation study is also important to perform the backoff contention window effectively in order to know the obstacles and avoid them. This paper concentrates on the performance of backoff contention window using the main routing protocols such as DSR, DSDV and AODV for MANETs networks in crowded areas with random movement. The important parameters which include network throughput …

 Cognitive radio (CR) is a form of wireless communication in which a transceiver can intelligently detect which communication channels are in use. Upon the result of the detection, the system instantly moves into vacant channels while avoiding occupied ones. To improve the capacity of CR systems, the unused sub-channels by primary user (PU) could be aggregated. However, when secondary user (SU) system aggregates more channels, more collisions may occur. This collision occurs due to the PU backto reuse its channels during SU transmission on them. Moreover, there are other reasons for collisions as misdetection which happens when wrongly detected absence of PU may occur as well.

In this paper a Proposed Channel Aggregation Algorithm is introduced in which the CR data rate is maximized by aggregating multiple channels for the SU while satisfying the minimum collision requirements. Moreover, channel capacity is maximized under collision constraints. Matlab simulation is conducted to implement the proposed algorithm and the rustles showed that, very low collision probability was observed as compared to previous work. The capacity of CR was also improved as well.

Abstract:

The real-time service such as voice over internet protocol (VoIP) is considered the best type of conversational voice due to ability and the possibility of making a VoIP calls at any time and from anywhere with the lowest cost. In this paper, we explore the performance of UMTS and WiMAX networks for VoIP service. This work focuses on VoIP quality when sent under various network loads such as HTTP, Email, FTB and Video Conferencing. In UMTS network, the VoIP was congested with HTTP traffic, while in WiMAX network the VoIP was congested with many types of traffic such as HTTP, Email, FTP and Video Conferencing. These traffic flow effects on voice traffic are analyzed and evaluated in terms of end-to-end delay, jitter and packet loss with service quality (QoS). All simulation scenarios are performed with OPNET modeller 14.5.