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Hi All,
On the upcoming BBCR group meeting on Thursday (Oct. 29) at 3:00 pm, Essam Saleh Altubaishi will give a talk on
“Adaptive Relaying Schemes in Cooperative Wireless Networks”
The abstract is as follows:
In wireless communication networks, characteristics of the channel are usually under continuous change due to multipath fading. Also, a user receives interference from other transmission, which is time varying, and the background noise is also constantly varying. As a result, the capacity of wireless link experiences high variability. Furthermore, the spectrum over wireless channel is limited, and the required radio spectrum is increased as a consequence of increasing demand of multimedia services. Based on these facts, the future wireless networks should be characterized by quick and effective “adaptation” at every stage and for every available resource. One of the promising techniques for compacting the multipath fading is the Cooperative Diversity (CD). It basically enables an intermediate node or multiple nodes between a transmitter and a receiver to cooperate together to achieve spatial diversity. However, this diversity comes with the expense of a reduction in the spectral efficiency. Therefore, it is important to design cooperative systems that have the capability to identify when the direct or cooperative transmission is more beneficial.
In this research, we would like to investigate the performance of adaptive relaying schemes that can improve the spectral efficiency by efficient utilization of the resources. In these schemes, we assume that the transmission rate is not fixed by employing adaptive modulation. We have started with a single relay amplify and forward incremental relaying with adaptive modulation. A simple but an efficient Generalized Switching Policy (GSP) is introduced to maximize the average spectral efficiency while maintaining the target Bit Error Rate (BER). The performance of this GSP over independent non-identical Rayleigh fading channels is derived in terms of average spectral efficiency, average BER, and outage probability, then verified by using Monte Carlo simulation. Results show that the GSP not only outperforms both the conventional direct transmission and the AF fixed relaying but also the Outage Switching Policy (OSP) of AF incremental relaying proposed recently. This work will be extended to consider multiple-relay but with relay selection since in multiple-relay environment, the spectral efficiency is decreased linearly by the number of relays used. Similarly, in the decode and forward scheme, performance analysis of adaptive relaying scheme with adaptive modulation will be investigated.
Regards,
Albert
Hi All,
This Thursday (Oct. 15) at 3:00 pm, Mohammed Towhidul Islam will give a talk on
“Collaborative Data Access for Mobile Distributed Networks”
The abstract is as follows:
The tremendous growth in usages of mobile computing devices, including smart phones, personal digital assistants and sensors with increasing functionality and the advances in wireless technologies have fueled the utilization of mobile collaborative computing known as mobile P2P (MP2P) in our daily life (exchanging traffic condition in busy high way, sharing price-sensitive financial information, getting the most recent news), in national security (exchanging information and collaborating to uproot a terror network, communicating in a hostile battle field) and in natural catastrophe (seamless rescue operation in a collapsed and disaster torn area). Nevertheless, MP2P faces technical challenges including resource constraints such as processing power, storage and energy on mobile devices, security and privacy threat,disrupted and disconnected network topology and heterogeneity of devices.
The specific objective of our research is to develop a data dissemination system for mobile distributed networks using a MP2P technique that maximizes the amount of required objects distributed among the interested users and at the same time minimizes the object acquisition time. Our proposed system will provide specific methodologies to address important factors such as low bandwidth, high latency, limited device availability and mobility to ensure quality of service. To utilize system bandwidth from every aspect, our system will present an optimum packet size for distribution based on the available bandwidth (in communication layers). To utilize the small storage efficiently, we will apply cooperative caching among the mobile devices and tune-up the storage management policy to gain the maximum performance out of the system. In addition, we will devise a method of multicast for efficient data dissemination among the users which are connected through multihop network. We will also cogitate about the relative size and urgency of objects in a network and will define a method that achieves the optimum query-response performance of our system.
Regards,
Albert
This Thursday, Oct. 8, at 3:00 pm, Ibrahim Alsolami will give a talk on
"Modulation Level Coding for Wireless Network Coding"
The abstract is as follows:
When intermediate nodes encode messages in wireless network coding, a
question arises: at what modulation level should the encoded message be
broadcasted? Should it be limited to a receiver with a low modulation level
requirement to maintain an acceptable BER or should it be broadcasted at
the desired modulation level of a receiver with a higher rate requirement?
Such conflicting requirements typically arise when one receiver has a low
channel capacity while the other has a higher one. In this presentation, we
will introduce a new coding scheme to satisfy users with diverse modulation
requirements, simultaneously.
Best Regards,
Albert
This Thursday (Oct. 1) at 3:00 pm, Mahdi Asefi will give a talk on
“Classification-Based Path Selection Scheme for Video Streaming over Multi-Hop Networks”
The abstract is as follows:
A classification-based approach is proposed to select optimal path for video streaming over multi-hop mesh networks. Our main contribution is to translate the path selection over multi-hop networks as a standard classification problem. Classification distance measure to be minimized is based on average PSNR values of received video packet at the destination node. We also consider long range dependence (LRD) characteristics of variable bit rate (VBR) video encoders by modeling the link as a fractional Brownian motion queue. In our method, a support vector machine is applied at each hop to assign optimal next hop (partial path) for each video packet received at that hop. Wireless channel conditions (WCC) including packet loss probability of the channel and maximum achievable rate are used as class prototypes. Sample feature vectors include video content features (VCF) and video encoding parameters (VEP) extracted from video sequences. Classifiers are trained offline using vast collection of video sequences and wireless channel conditions in order to result in optimal performance during real time path selection. Our method substantially reduces the complexity of conventional exhaustive optimization methods while results in high quality (low distortion). Simulations are conducted over an elementary multi-hop structure and cascades of such structure which not only proves the superiority of our method in terms of low complexity and high PSNR performance, but also provides important insights that can guide the design of network infrastructures and streaming protocols for video streaming.
Regards,
Albert
The slides includes: DTN Research Groups, Mobility models in DTN, Simulation Tools for DTN, Analytical Papers in DTN.
I would recommend you to subscribe to the “dtn interest mailing list” for news on the latest DTN developments.
http://bbcrlab-pc9.bbcrlabpcnet.uwaterloo.ca/blog/wp-content/uploads/2009/08/bjc-Useful-Resources-for-DTN-20090804.pdf
A Good Overview on DTN:
[1] Zhensheng Zhang, “Routing in intermittently connected mobile ad hoc networks and delay tolerant networks: overview and challenges,” Communications Surveys & Tutorials, IEEE , vol.8, no.1, pp.24-37, First Quarter 2006
Recent Developments in DTN Research:
[2] Special Issue on Delay and Disruption Tolerant Wireless Communication, IEEE Journal on Selected Areas in Communications, vol. 26 no. 5, May 2008.
[3] Delay Tolerant Research Group (http://www.dtnrg.org)
Delay Tolerant Network: A Tutorial
http://bbcrlab-pc9.bbcrlabpcnet.uwaterloo.ca/blog/wp-content/uploads/2009/07/bjc-DTN-A-Tutorial-200907232.pdf
You can also get tons of recent research activities by visiting websites of other research groups referenced on the footnote of slides!
In today’s group meeting, David will give a talk on
Delay Tolerant Networks (DTNs): A Tutorial
“Challenges and Applications of Delay Tolerant Networks”
The abstract is as follows:
In this presentation, I will present a tutorial on delay tolerant networks. It will be a general overview of the network architecture covering following topics:
What is Delay Tolerant Network?
What is Different from Traditional Networks?
What are Some Examples/Applications?
What are the Challenges?
What new Ideas and Protocols have been Proposed?
What are the Open Research Issues?
Click here for the presentation file.
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This Thursday, Mohamed Elsalih Mahmoud will give a talk on “A New Research Direction for Stimulating Cooperation in Multi-hops Wireless Networks”. The abstract is as follows:
In recent years the interest in multi-hop wireless networks has been growing significantly. In these networks, the mobile nodes work as routers to relay packets generated from other nodes. The nodes’ cooperation is essential for proper network operation. Selfish nodes do not cooperate to save their resources and thus to improve the efficiency of their devices. However, they use the other devices to relay their packets. This selfish behavior causes fairness, performance and security problems in the network. In the literature, reputation and credit based mechanisms have been proposed to enforce and stimulate the nodes? cooperation respectively. In reputation based mechanisms, the network nodes monitor each other to identify and punish selfish nodes. A reputation system is used to differentiate between a node?s unwillingness and inability (due to mobility or full buffer) to cooperate and also to suppress the impact of false accusations. These mechanisms do not achieve fairness because they do not differentiate among nodes with different contributions to the network. In addition, they are not efficient because the nodes work in promiscuous modes which are provably inefficient. In credit based mechanisms, credits are used to stimulate the nodes? cooperation and to achieve fairness by rewarding cooperative nodes. These mechanisms impose huge overhead due to extensively using cryptographic mechanisms to secure the payment process. Although, lots of papers have been published to alleviate the aforementioned problems, we believe that they are essential. Therefore, this paper proposes a novel direction which combines the features of the two existing solutions. Fairness is achieved by using credits to reward cooperative nodes. The overhead is much reduced with using a cheating detection system (CDS) to secure the payment system instead of using cryptographic primitives. Our simulations show that the overhead of implementing the proposed solution is incomparable with the existing mechanisms, and the cheating detection system can detect the cheaters efficiently at different attacking strategies and under high ratio of attackers.
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