Contention-based Wireless Networks Research Articles

Bandwidth-Satisfied and Coding-Aware Multicast Protocol in MANETs

Network coding is a promising technology proven to improve the performance of wireless networks. To successfully design a quality-of-service (QoS)-satisfied routing protocol with network coding, the bandwidth consumption of a coding host should be determined. Furthermore, coding opportunities should be increased to improve network capacity. Nevertheless, it is challenging to determine whether a host can be a coding host and to determine the bandwidth consumption of a coding host in a mobile ad hoc network (MANET). In this paper, we first present and define the coding conditions to identify a coding host. The bandwidth consumption of a coding host is then estimated under the contention-based wireless networks with a random access mechanism. Finally, we propose a bandwidth-satisfied and coding-aware multicast routing protocol (BCMRP). By taking into account the residual bandwidth of the carrier-sense neighbors of the forwarders, the proposed protocol can satisfy the bandwidth requirements of the requested flow and other ongoing flows. As a consequence of considering coding opportunities in multicast tree construction, the proposed multicast protocol can reduce the total bandwidth consumption. The simulation results show that BCMRP outperforms the prior multicast routing protocols in receiving ratio, admission ratio, and total bandwidth consumption.

Improving Performance of Ieee 802.11 by a Dynamic Control Backoff Algorithm Under Unsaturated Traffic Loads

The IEEE 802.11 backoff algorithm is very important for controlling system throughput over contentionbased wireless networks. For this reason, there are many studies on wireless network performance focus on developing backoff algorithms. However, most existing models are based on saturated traffic loads, which are not a real representation of actual network conditions. In this paper, a dynamic control backoff time algorithm is proposed to enhance both delay and throughput performance of the IEEE 802.11 distributed coordination function. This algorithm considers the distinction between high and low traffic loads in order to deal with unsaturated traffic load conditions. In particular, the equilibrium point analysis model is used to represent the algorithm under various traffic load conditions. Results of extensive simulation experiments illustrate that the proposed algorithm yields better performance throughput and a better average transmission packet delay than related algorithms.

Dynamic Pricing and Queue Stability in Wireless Random Access Games

We study the interaction among users of contention-based wireless networks, where the performance of the network is highly correlated with user transmission probabilities. Considering the underlying user incentives, we make use of the conceptual framework of noncooperative game theory to obtain a distributed control mechanism to limit the contention among wireless nodes by taking into account queue stability and injecting linear pricing to punish greedy behavior. We present a comprehensive analysis of the game including existence and uniqueness of Nash equilibrium point, convergence dynamics, and robustness properties. Utilizing linear pricing enables us to move the equilibrium point of the game to a desirable region. We obtain conditions on linear prices necessary to achieve stability of user queues in the asymmetric and symmetric cases. In addition, we propose dynamic pricing algorithms, in which wireless users play the game without cooperation while the base station adjusts the linear price of each user. Under limited knowledge of game parameters, we present a dynamic equal pricing algorithm that moves the Nash equilibrium to the aggregate throughput maximizing solution. The theoretical results are verified, and the convergence and efficiency of the proposed game are illustrated via simulations.

Channel Access Allocation for Scalable Video Transmission Over Contention-Based Wireless Networks

Contention-based wireless networks make use of random access delay in the medium access control (MAC) layer to share the channel efficiently among users. This channel access scheme poses challenges to video traffic which is delay-sensitive. When channel access is limited, how to optimally allocate channel access and judiciously drop video packets remains an open issue. In this paper, we investigate the optimal channel access allocation and preemptive packet drop strategy for scalable video packets using contention-based MAC. We first establish a relationship to associate the characteristics of video packets, the cumulative distribution function of channel access delays and the expected video quality at the receiver. Based on the relationship, we define a video utility function that explicitly takes into account cumulative distribution of channel access delay over contention-based wireless links, video packet length and truncation, packet loss rate and quality impacts of SVC layers. As the analytical model of the video utility function is rather complex for optimization, we further propose an approximation model for the video utility function to transform the optimization problem into a convex problem which is a solvable by using the dual decomposition method. Simulation results confirm that our proposed method achieves better PSNR performance over the existing approach, especially when the total channel access for the video traffic is limited.

Voice capacity analysis of WLANS with channel access prioritizing mechanisms

Voice over IP applications in wireless networks have gained increasing popularity in recent years. As a delay-sensitive real-time application, a VoIP flow is usually given higher priority in accessing the shared wireless channel than delay-insensitive non-real-time flows. In contention-based wireless networks two widely used prioritizing MAC mechanisms are class-dependent arbitration interframe space and class-dependent contention window. In this article we propose an analytical model to evaluate the effect of the two mechanisms on voice capacity (the maximum number of two-way voice flow pairs supportable) of ad hoc mode and infrastructure mode wireless LANs. We show that the AIFS mechanism has a relatively strong effect on WLAN voice capacity in the ad hoc mode, but not in the infrastructure mode; and the CW mechanism, when properly configured, has a mild effect on voice capacity in both modes.