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IEEE/ACM Trans. Netw. 01/2012; 20:271-284.
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IEEE Trans. Mob. Comput. 01/2012; 11:61-72.
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IEEE 8th International Conference on Mobile Adhoc and Sensor Systems, MASS 2011, Valencia, Spain, October 17-22, 2011; 01/2011
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Proceedings of the 8th Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks, SECON 2011, June 27-30, 2011, Salt Lake City, UT, USA; 01/2011
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IEEE/ACM Trans. Netw. 01/2010; 18:722-735.
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IEEE/ACM Trans. Netw. 01/2010; 18:243-256.
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IEEE Network. 01/2010; 24:4-5.
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Proceedings of the Seventh Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks, SECON 2010, June 21-25, 2010, Boston, Massachusetts, USA; 01/2010
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IEEE/ACM Trans. Netw. 01/2009; 17:391-404.
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03/2008: pages 251 - 275; , ISBN: 9780470396384
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INFOCOM 2008. 27th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 13-18 April 2008, Phoenix, AZ, USA; 01/2008
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INFOCOM 2008. 27th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 13-18 April 2008, Phoenix, AZ, USA; 01/2008
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Proceedings of the IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2008, 15-18 September 2008, Cannes, French Riviera, France; 01/2008
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ABSTRACT: Space-time communications can help combat fading and, hence, can significantly increase the capacity of ad hoc networks. Cooperative diversity or virtual antenna arrays facilitate spatio-temporal communications without actually requiring the deployment of physical antenna arrays. Virtual MISO entails the simultaneous transmission of appropriately encoded information by multiple nodes to effectively emulate a transmission on an antenna array. We present a novel multilayer approach for exploiting virtual MISO links in ad hoc networks. The approach spans the physical, medium access control and routing layers, and provides 1) a significant improvement in the end-to-end performance in terms of throughput and delay and 2) robustness to mobility and interference-induced link failures. The key physical layer property that we exploit is an increased transmission range due to achieved diversity gain. Except for space-time signal processing capabilities, our design does not require any additional hardware. We perform extensive simulations to quantify the benefits of our approach using virtual MISO links. As compared to using only SISO links, we achieve an increase of up to 150 percent in terms of the end-to-end throughput and a decrease of up to 75 percent in the incurred end-to-end delay. Our results also demonstrate a reduction in the route discovery attempts due to link failures by up to 60 percent, a direct consequence of the robustness that our approach provides to link failures
IEEE Transactions on Mobile Computing 07/2007; 6(6):579-594. · 2.28 Impact Factor
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ABSTRACT: The use of power control in wireless networks can lead to two conflicting effects. An increase in the transmission power on
a link may (i) improve the quality and thus the throughput on that link but, (ii) increase the levels of interference on other
links. A decrease in the transmission power can have the opposite effects. Our primary goal in this work is to understand
the implications of power control on interference and contention. We conduct experiments on an indoor mesh network. Based
on analysis of our experimental data, we identify three interference scenarios: a) the overlapping case, where the aggregate
throughput achievable with two overlapping links cannot be improved via power control; b) the hidden terminal case, where
proper power control can primarily improve fairness and, c) the potentially disjoint case, where proper power control can
enable simultaneous transmissions and thus improve throughput dramatically. We find that power control can significantly improve
overall throughput as well as fairness. However, to our surprise, we note that using virtual carrier sensing in conjunction
with power control generally degrades performance, often to a large degree.
06/2007: pages 83-93;
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ABSTRACT: We propose a MAC protocol for use in multihop wireless networks that deploy an underlying UWB (ultra wide band)-based physical layer. We consider a multiband approach to better utilize the available spectrum, where each transmitter sends longer pulses in one of many narrower frequency bands. The motivation comes from the observation that, in the absence of a sophisticated equalizer, the size of a slot for transmitting a UWB pulse is typically dictated by the delay spread of the channel. Therefore, using a wider frequency band to shorten the transmission time for each pulse does not increase the data rate in proportion to the available bandwidth. Our approach allows data transmissions to be contiguous and practically interference free, and, thus, highly efficient. For practicality, we ensure the conformance of our approach to FCC-imposed emission limits. We evaluate our approach via extensive simulations, and our results demonstrate the significant advantages of our approach over single-band solutions: the throughput increases significantly and the number of collisions decreases considerably. Finally, we analyze the behavior of our MAC protocol in a single-hop setting in terms of its efficiency in utilizing the multiple bands
IEEE Transactions on Mobile Computing 05/2007; 6(4):351-366. · 2.28 Impact Factor
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ABSTRACT: We find that current group communications protocols are far from "one size fits all", they are typically geared toward and optimized for particular scenarios. Multicasting, in general, works well if the density of group members is sparse and in low mobility; broadcasting, in contrast, works well with a high density of group members and in high mobility. Due to the dynamics of the network, one strategy may be preferable to the other at different times and in different localized regions. In this paper, we first quantify the trade-offs between broadcasting and multicasting and evaluate the suitability of a strategy in various scenarios of deployment. Based on the lessons learned, we design a protocol that adapts in response to the dynamics of the network. We named our protocol Fireworks. Fireworks is a hybrid two-tier multicast/broadcast protocol that provides efficient and lightweight multicast dissemination and self-adapts in response to variations in the density and distribution of group members to provide efficient performance. Fireworks creates pockets of broadcast distribution in areas with many members, while it creates and maintains a multicast backbone to interconnect these dense pockets. Fireworks offers packet delivery statistics comparable to that of a pure multicast scheme but with significantly lower overheads. We also show that Fireworks has a lower level of degrading influence on the performance of coexisting unicast sessions than either traditional multicast or broadcast methods
IEEE Transactions on Mobile Computing 04/2007; 6(3):264-279. · 2.28 Impact Factor
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ABSTRACT: Cooperative diversity facilitates spatio-temporal communications without requiring the deployment of physical antenna arrays. While physical layer studies on cooperative diversity have been extensive, higher layer protocols which translate the achievable reduction in the SNR per bit for a given target BER, into system wide performance enhancements are yet to mature. The challenge is that appropriate higher layer functions are needed in order to enable cooperative diversity at the physical layer. We focus on network-wide broadcasting with the use of cooperative diversity in ad hoc networks. We design a novel distributed network-wide broadcasting protocol that takes into account the physical layer dependencies that arise with cooperative diversity. We perform extensive simulations that show that our protocol can outperform the best of the noncooperative broadcasting protocols by: (a) achieving up to a threefold increase in network coverage and, (b) by decreasing the latency incurred during the broadcast by about 50%. We also construct an analytical model that captures the behavior of our protocol. Furthermore, we show that computing the optimal solution to the cooperative broadcast problem is NP-complete and construct centralized approximation algorithms. Specifically, we construct an O(N <sup>epsi</sup>)-approximation algorithm with a computational complexity of O(N4/epsi); we also construct a simpler greedy algorithm.. The costs incurred with these algorithms serve as benchmarks with which one can compare that achieved by any distributed protocol
IEEE Journal on Selected Areas in Communications 03/2007; · 3.41 Impact Factor
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ABSTRACT: It is well known that the current ad hoc protocol suites do not scale to work efficiently in networks of more than a few hundred nodes. Most current ad hoc routing architectures use flat static addressing and thus, need to keep track of each node individually, creating a massive overhead problem as the network grows. Could dynamic addressing alleviate this problem? In this paper, we argue that the use of dynamic addressing can enable scalable routing in ad hoc networks. We provide an initial design of a routing layer based on dynamic addressing, and evaluate its performance. Each node has a unique permanent identifier and a transient routing address, which indicates its location in the network at any given time. The main challenge is dynamic address allocation in the face of node mobility. We propose mechanisms to implement dynamic addressing efficiently. Our initial evaluation suggests that dynamic addressing is a promising approach for achieving scalable routing in large ad hoc and mesh networks
IEEE/ACM Transactions on Networking 03/2007; 15(1):119-132. · 2.03 Impact Factor
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IEEE Trans. Mob. Comput. 01/2007; 6:579-594.
