Tag Archives: Wireless Networks

11/11/2015 – Talk by Moshin Jafri

Title:  Underwater Wireless Sensor Networks: Applications, Advances and Research challenges
Time: 13:00
Location: Meeting Room, building Zeta
Type: Survey
Speaker: Moshin Jafri
Abstract: Underwater Wireless Sensor Networks (UWSNs) have several applications such as sea mine detection and seismic monitoring. UWSNs consist of a large number of sensors and vehicles, deployed to transmit sensed data to the base station. They monitor swarms of underwater vehicles in environmental and military applications by exploiting their reconfigureability. In this talk, we discuss about the organizational architecture of UWSNs and the state of the art of various networking facets related to UWSNs. This talk serves as a summary of existing protocols, providing inspiration for the growth of underwater networks. We also outline the recent advancements in this area by focusing on the lower strata of the communication stack, and envision future trends. Current research ranges from low-power algorithms and modulations to energy-aware routing and MAC protocols. We highlight the key challenges such as high error rate, low network throughput and high energy consumption for data transmission. Furthermore, high propagation delay, Doppler shifts and time-varying multi-path effects constitute major research subjects, which require reliable communication systems in order to coordinate multiple devices, either mobile or stable.

11/03/2015 – Talk by Robbe Block

Title: Spatial Fairness in Multi-Channel CSMA Line Networks
Time: 14:00
Location: Meeting Room, building Zeta
Type: Research Result
Speaker: Robbe Block (University of Antwerp)
In this talk we will consider a line of wifi-hotspots placed in a single line. Starting from earlier results, we will show the steady state of this system has a product form solution and using this product form, a fast method to calculate the per-hotspot throughput will be given. Furthermore, for a single channel setting it was shown in previous work that a simple formula could be used to achieve fairness among the different nodes in the network. It will be shown that the same formula still achieves fairness in the multi-channel setting in either heavy or low traffic conditions, but no such simple formula exists in general. However, through numerical experiments, we see that the fairness index of the multi-channel system still remains very close to one, meaning the simple formula eliminates most of the unfairness in the network.

23/04/2014 – Talk by V-T. Hoang and M. Hussain

Title: Performance evaluation of TCP congestion control mechanisms ECN/RED and SAP-LAW in presence of UDP traffic
Time: 13:00
Location: Meeting room
Type: Research Result
Speaker: V-T. Hoang and M. Hussain

Internetworking often requires a large amount of users to share a common gateway to obtain the connectivity to the Internet. Congestion avoidance mechanisms are used to prevent the saturation of the gateway which represents a bottleneck of the system. The most popular congestion avoidance mechanisms are the Explicit Congestion Notification (ECN) and the Random Early Detection (ECN). Recently, a new method for the congestion avoidance has been proposed: the Smart Access Point with Limited Advertised Window (SAPLAW). The main idea is to hijack at the gateway the acknowledge packets in the TCP connections in order to artificially reduce the advertised destination window according to some bandwidth allocation policy. Therefore, the flux control mechanism is artificially exploited to control the congestion at the bottleneck. The advantage of this approach is that it does not drop any packet and does not require any modification in the TCP implementations at the clients. In this paper we propose stochastic models for the ECN/RED and SAP-LAW mechanisms in order to compare their performances under different scenarios. The models are studied in mean field regime, i.e., under a great number of TCP connections and UDP based transmissions while considering TCP greedy and temporary connection. in this paper we consider the presence of UDP traffic with bursts, and the case of not greedy TCP connections. The models for SAP-LAW are totally new. The comparison is performed in terms of different performance indices including average queue length, system throughput, expected waiting time.



28.02.2013 – Talk by Malik Mazhar Hussain

Title: An Introduction to Cognitive Networks
Time: 14:00
Location: Meeting room
Type: Introduction
Speaker: Malik Mazhar Hussain

A cognitive network is a network that has the capability of sensing the environment and adjusting the network parameters accordingly.  The purpose of this talk is to give an overview of the technology, and address some basic questions like why, when and where this technology can be used. The key challenges of cognitive networks with respect to routing, security, frequency management and implementation will be presented.