Session 3: MAC Layer Issues |
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A Distributed CDMA Medium Access Control for Underwater Acoustic Sensor Networks |
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Abstract: In this paper, UW-MAC, a distributed Medium Access Control (MAC) protocol tailored for UnderWater Acoustic Sensor Networks (UW-ASNs), is proposed. It is a transmitter-based Code Division Multiple Access (CDMA) scheme that incorporates a novel closed-loop distributed algorithm to set the optimal transmit power and code length. UW-MAC aims at achieving three objectives, i.e., guarantee high network throughput, low channel access delay, and low energy consumption. Experiments show that UW-MAC outperforms existing MAC protocols tuned for the underwater environment under different architecture scenarios and simulation settings. Pages: 63-70 |
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Optimizing End-to-End TDMA Scheduling in Ad-hoc Networks on Random Topologies |
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Abstract: Despite its dominance as a MAC layer for adhoc communications, the CSMA/CA algorithm produces several deficiencies, like complex QoS capabilities, increased overhead, and the exposed terminal problem. The TDMA MAC layer, that mostly overcomes these issues, needs efficient scheduling in order to be employed in ad-hoc networks. At the same time, the current trend for QoS capable applications led to the development of numerous QoS routing schemes, that try to find paths within the network, that fulfill some QoS related limitations. TDMA scheduling schemes can be combined with QoS routing strategies for enhancing performance. However, the efficiency of the scheduling algorithms is closely related to the network topologies. In this paper, we study the problem of routing aware TDMA scheduling for ad-hoc networks, and the effect of the network topologies on it. Pages: 71-78 |
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Effective Bandwidth Control Policies for QoS-enabled Wireless Networks |
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Abstract: In this paper, an admission control policy is introduced, suitable for efficiently controlling traffic admissions under the Enhanced Distributed Channel Access (EDCA) method, which is employed as the basic access scheme in the latest IEEE802.11e draft specification. Moreover, based on a novel traffic renegotiation strategy, an adaptive bandwidth allocation scheme is presented, which monitors the admitted traffic bandwidth resources and provides constant QoS guarantees under unpredictable wireless environment conditions, such as channel degradation and data bursting. Pages: 79-84 |
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Abstract: A traffic estimator is developed and thereafter used to do the slot assignment in a traffic adaptive TDMA scheme. The traffic estimation is made packet-bypacket and locally in the nodes. The purpose of the work is to investigate the efficiency of such traffic estimation. To do that we compare traffic-adaptive TDMA, using our traffic estimator, to non traffic-adaptive TDMA and "optimal" TDMA, i.e., a centralized scheme having complete knowledge about the traffic situation. The introduced traffic estimator uses two steps in order to predict the traffic over the links in ad hoc networks. At first, an exponential filter is used to generate an estimate based on the size and the intensity of arrival of the transmissions. The estimation error of the exponential filter is further reduced by a multiplication of a function that considers queuing times in the links. The assessment of the traffic estimator and traffic adaptive TDMA is made for traffic sessions with delay constraints. Simulation results show that adding our traffic estimation to TDMA-based mobile ad hoc networks yields a significantly higher ratio of successfully transmitted sessions compared to the case without traffic estimation. Pages: 85-91 |
