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A Wireless Sensor Network (WSN) is composed of resource-constrained sensors with limited capabilities. Wireless Sensor Networks are subject to more packet loss and congestion. For efficient congestion control, an accurate and timely estimation of resource demands by measuring the network congestion level is necessary. To mitigate congestion, either the available resources have to be increased (resource...
Co-channel interference exists in IEEE 802.11 based wireless local area networks (WLANs) due to the limited number of non-overlapping channels in the current standards. In this paper, we investigate the impact of co-channel interference in carrier sense multiple access with collision avoidance (CSMA/CA) based WLANs via simulation. We find that the throughput unfairness among the users is severe in...
We investigate the network utility maximization (NUM) problem when layered modulation is used at the physical layer of a downlink wireless system. The key idea is to transmit to more than one users with favorable and unfavorable channel qualities at the same time by employing hierarchical constellations. We demonstrate that average throughput of users with unfavorable channel conditions are significantly...
A framework for the joint design of wireless network and controllers is proposed. Multiple control systems are considered where the sensor measurements are transmitted to the controller over the IEEE 802.15.4 protocol. The essential issues of wireless networked control systems (NCSs) are investigated to provide an abstraction of the wireless network for a co-design approach. We first present an analytical...
Low Extra Delay Background Transport (LEDBAT) congestion control algorithm is designed to address the unfairness problem of TCP aggravated by applications that use multiple TCP connections for data transfer. LEDBAT operates under the assumption that the queue delay at the access router of the bottleneck link will be the primary varying contributor to end-to-end one-way delay. However this assumption...
An accurate estimation of the available bandwidth of mesh nodes is the essential prerequisite of admission control mechanism, which provides QoS assurance in wireless mesh networks. Existing bandwidth estimation schemes do not accurately consider the influence of parallel transmission due to spatial reuse and act overly conservative. In this study, we proposed an accurate bandwidth estimation scheme,...
DCCP is proposed to replace UDP for its ability of congestion control while maintaining its promptness by ignoring lost packets as UDP does. The network would suffer less congestion. However, whether the applications that switch from UDP to DCCP can maintain their needed performance or not is a big question. This paper investigates this problem by evaluating DCCP based VoIP vs. a variety of TCPs using...
TCP does not perform well in networks with stochastic channels, with links that randomly drop packets or have long outages. Diversity routing has been proposed to improve TCP's performance in these networks. In diversity routing, a sublayer between TCP and the network replicates each transmitted packet and sends the multiple copies along parallel paths. As long as at least one of the copies reaches...
Maintaining the performance of reliable transport protocols, such as TCP, over wireless mesh networks is a challenging problem due to the unique characteristics of wireless mesh networks such as the lossy nature of the communication medium, absence of a base station, similarity in traffic pattern experienced by neighboring mesh nodes, etc. One of the reasons for the poor performance of conventional...
Mobile Ad Hoc Networks (MANETs) have been an important research topic for the last years, playing a crucial role within the fast growing sector of mobile communications. At the same time, video applications over mobile devices are becoming widely used by nowadays mobile clients, where the quality in the transmission of such contents will determine the success of these applications in the future. Therefore,...
The Application specific wireless sensor network differs basically from the general data network. It focuses on tight communication but restricted in storage, lifetime, power and energy. The WSNs consists of unbelievable network load and it leads to energy wastage and packet loss. Many of the existing concepts are developed for link level congestion control. The Rate optimization technique for node...
This paper presents S-SFQ which is a single queue design and implementation of the well-known Start-time Fair Queueing (SFQ). This aggregate queue orders packets based on their timestamps rather than order of arrivals. Through simulation, we show the performance gains of S-SFQ over other default single-queue schemes such as RED and FIFO in terms of link utilization and flow fairness. When sources...
The Randomly deployed wireless sensor nodes form an unpredictable structure. Normally wireless sensor networks are distinguished from conventional networks by their energy constraints and limited computational power. Huge volumes of data are sensed and generated by the sensor nodes when they are deployed in the dynamic environment. Mostly the source and sink nodes are not within each other's transmission...
In mobile ad hoc networks (MANETs) where there exist multiple Internet gateways, performing load balancing among available gateways is vital in order to take full advantage of the network capacity and improve the performance. However, performing load balancing in a wireless environment is very challenging due to the inherently interfering and unreliable nature that characterize wireless communication...
Many studies have shown that Vegas TCP has a better throughput and stability than Reno TCP in homogeneous networks with a single TCP flavor, but performs less well in heterogeneous networks in which two TCP flavors coexist. The progressive behavior of Reno TCP and the conservative behavior of Vegas TCP cause a bias when they are used simultaneously, and thus Vegas TCP fails to obtain a fair share...
An ad hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. A number of routing protocols such as Dynamic Source Routing (DSR), Ad Hoc on-Demand Distance Vector Routing (AODV) and Destination-Sequenced Distance-Vector (DSDV) have been implemented. In this paper, an attempt has...
We analyze TCP-controlled bulk file transfers in a single station WLAN with nonzero propagation delay between the file server and the WLAN. Our approach is to model the flow of packets as a closed queueing network (BCMP network) with 3 service centres, one each for the Access Point and the STA, and the third for the propagation delay. The service rates of the first two are obtained by analyzing the...
This paper addresses a H∞ TCP controller for end-to-end TCP congestion control. The proposed controller which is based on the algorithm of TCP Vegas is aimed to minimize error term in TCP Vegas and achieve one step optimal solution for TCP congestion control. A series of simulation experiments based on a single bottle-neck FIFO queue model are conducted to compare the new controller with TCP Vegas...
Distributed Coordination Function (DCF) of IEEE 802.11 WLANs prohibits concurrent transmissions to avoid packet collisions or interferences. This conservative transmission mechanism of DCF makes it hard to fully utilize the wireless capacity in terms of spatial reuse. Recent measurement studies demonstrate that a packet can survive the collision and can be decoded successfully by the receiver depending...
We present a lightweight algorithm for the estimation of the achievable throughput in IEEE 802.11 wireless networks. In particular, we consider a WLAN operating in infrastructure mode, where, through our algorithm, the access point (AP) can: (i) estimate the available bandwidth that a new station wishing to join the network can use, and (ii) evaluate the impact on the system performance of admitting...
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