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Opnet University Program



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University: University of Rennes 1, France.
Bernard Cousin.  
Department: Networks, Telecommunications and Services.




Ph.D. students and teaching assistants of our research group will use OPNET in order to evaluate the performance of their propositions. They believe the richness of the environment provided in OPNET and the availability of existing model sets, such as the Wireless Module, will provide an efficient support for their research. These research activities focus on two main axes: routing protocols and medium access protocols, both in the wireless context.


Research works on routing protocol specification apply to wireless self-organized networks. The proposed protocol is an indirect routing strategy that completely distributes the routing information throughout the network, using the peer-to-peer concepts. The need for efficient location mechanisms is an important issue in self-organizing networks where topologies become larger and more complex in their addressing structures. An easy-managed location service for self-organizing networks has been designed in this context. The proposal defines a logical multidimensional space that is a strict mathematical representation of the network geographic space. This logical space is used for addressing and routing, while location is performed in an easy-managed one-dimensional structure obtained by the use of Hilbert space-filling curves. The proposed location service follows a rendez-vous-based communication abstraction, where node location information is distributed throughout the topology. Routing is performed in a hop-by-hop basis with greedy next-hop choice, which requires only a limited amount of signalling information. Their first experiments focus on fairness evaluation of various spaces management operations. Their results show that the proposal assures a fair distribution of control overhead among nodes. The effects of various system parameters have been examined, such as degree of nodes' occupation, network density, and network variability. Their future work using OPNET will include (a) a more detailed comparison to other approaches, (b) a more detailed evaluation of control overhead (e.g. size of routing tables, number of control messages exchanged), (c) an evaluation of the data path performance (e.g. average data delay achieved under geographic routing), and, (d) an evaluation of the location path performance (e.g. average management-related packet delay achieved under the Twins architecture). Their work also concerns routing in self-organizing networks. They study the geographic routing without GPS, by assigning virtual positions and using a location algorithm that does not incurs traffic overhead. They need an efficient simulator that can generate large topologies, where the algorithms can be evaluated and compared with other existing works.


                                  Fig. 1: OFDM wireless Network

Research activities are also focused on developing new access protocols designed for Orthogonal Frequency Division Multiplexing (OFDM) based wireless networks. OFDM is a promising modulation technique for supporting high-speed transmission of broadband traffic in the frequency selective fading environment encountered in wireless networks. Research activities aim at developing new multiple access schemes best adapted to OFDM based physical layers. The research efforts consist in designing an access protocol that maximizes the system throughput while providing more fairness in resource allocation than other existing multiple access schemes such as OFDM-TDMA or OFDM-FDMA. The protocol shall support the traffic heterogeneity of multimedia applications and Quality of Service differentiation (cf Fig. 1). The OPNET simulation platform will be used in order to design and evaluate the performances of our proposal. Our first experiments will focus on rather restrictive and simple hypotheses: fixed terminals with only one type of traffic. More complex situations will then be tested: mobile terminals moving in accordance with a mobility pattern such as the "Random Weighted Waypoint" and concurrently transmitting several types of traffic with different QoS constraints.


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