-
Computer Networks. 01/2011; 55:1379-1393.
-
IEEE Journal on Selected Areas in Communications. 01/2011; 29:207-222.
-
Proceedings of the Global Communications Conference, GLOBECOM 2011, 5-9 December 2011, Houston, Texas, USA; 01/2011
-
[show abstract]
[hide abstract]
ABSTRACT: Unlike traditional unicast routing where a transmitting node needs to specify its single next-hop forwarder in a multi-hop wireless networks in an a priori manner, Opportunistic Routing allows multiple potential next-hop forwarders to be selected. Any selected node may forwards the packet towards the destination if it can decode the packet correctly. Existing opportunistic routing protocols tend to limit the size of the forwarding set for each transmitting node due to the communication overheads required to suppress unnecessary packet duplicates generated by multiple eligible next-hop forwarders. As such, they fail to capitalize on the key advantage of opportunistic routing, namely, the ability to utilize a large number of long but unreliable wireless links in progressing towards the destination. In this paper, we propose TORP, the Threshold-based Opportunistic Routing Protocol, which applies a novel threshold-based forwarding technique to reduce the coordination requirements between multiple potential next-hop nodes. This in turn, enables TORP to exploit the advantage of using numerous distant downstream nodes as next-hop forwarders. Simulation results show significant improvements in the end-to-end delay and total traffic load generated by TORP over unicast routing. Compared with the state-of-the-art ExOR protocol, TORP reduces the average end-to-end delays by 25-40% under typical network configurations and has the advantage of being more amenable to a fully-distributed implementation.
Wireless and Optical Communications Conference (WOCC), 2010 19th Annual; 06/2010
-
EURASIP J. Wireless Comm. and Networking. 01/2010; 2010.
-
Proceedings of IEEE International Conference on Communications, ICC 2010, Cape Town, South Africa, 23-27 May 2010; 01/2010
-
Proceedings of IEEE International Conference on Communications, ICC 2010, Cape Town, South Africa, 23-27 May 2010; 01/2010
-
Proceedings of the Sixth International Workshop on Vehicular Ad Hoc Networks, VANET 2009, Beijing, China, September 25, 2009; 01/2009
-
Proceedings of IEEE International Conference on Communications, ICC 2009, Dresden, Germany, 14-18 June 2009; 01/2009
-
INFOCOM 2009. 28th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 19-25 April 2009, Rio de Janeiro, Brazil; 01/2009
-
[show abstract]
[hide abstract]
ABSTRACT: A critical performance issue in providing VoIP service over wireless LANs is the voice packet delay due to handoffs as the user roams across different radio coverage regions. Most the recent research has focused on proactive approaches where control messages are transmitted from the mobile to prepare the access point and the other network nodes before the actual handoff occurs. Consequently, there is an increase in handoff control message traffic which will reduce the wireless LAN capacity to provide VoIP service. In this paper, we present a model for analyzing the effect of handoff control messages on the network capacity. To model the special "ON-OFF" characteristic of the voice sources in the real world, the Markov Modulated Poisson Process Model (MMPP) is used in the analysis. We assume that the control messages have higher priority than voice packets so that the service for voice packets also has an "ON-OFF" characteristic. The MMPP/MMPP/1 model was analyzed for different traffic characteristics (arrival rate and message lengths) depending on the handoff scheme used by the mobile stations in the network. For example, we show that the VoIP system capacity is reduced by 23% when the utilization of the control traffic is 4%. This analysis can provide a useful framework for the future development of different handoff schemes, trading off the higher success rate of handoff and decrease in network capacity.
Wireless Conference, 2008. EW 2008. 14th European; 07/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Recently, the idea of opportunistic routing has been widely explored to improve the performance of multi-hop wireless mesh networks. Most of the previous studies use simulations or empirical measurements to evaluate the performance gain of opportunistic routing and therefore are limited to relatively few types of scenarios. In this paper, we take an analytical approach to study the potential gain of opportunistic routing in multi- hop wireless networks. Unlike other analytical studies which use a deterministic channel model, our approach captures the key characteristics of opportunistic routing, i.e. its ability to take advantage of the numerous, yet unreliable wireless links in the network in a probabilistic manner and study the effectiveness of opportunistic routing under diverse radio propagation environment using lognormal shadowing and Rayleigh fading models. Our results show that, under typical network configurations and neglect overhead, the average progress per transmission of opportunistic routing in lognormal shadowing (Rayleigh fading) environment is about 3 (1.5) times higher than that of traditional unicast routing. Finally, we also demonstrate the potential benefits of using different forwarding regions and directional antennas in opportunistic routing.
Communications, 2008. ICC '08. IEEE International Conference on; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: The delay performance of delay tolerant networks (DTN) can be improved by adding or replacing mobile nodes with higher mobility or transmit power. In this paper, we examine the design trade-offs in heterogeneous DTNs with two types of mobile relay nodes: normal and super. First we present the range of parameters in the Random Direction (RD) mobility model in which we have validated the Markovian assumption on the node inter-encounter intervals. Next, we describe the two-dimensional continuous time Markov chain (CTMC) model with absorption state, used for evaluating the performance of the heterogeneous DTNs. We demonstrate that the performance improvement of adding super nodes is not linear. For example, replacing 10% of the normal nodes with super nodes ones can achieve 40% of the delay reduction versus replacing all of them. Finally, Fluid Flow Approximation (FFA) and Moment Closure Methods for solving the CTMC with various error rates (about 10%) were developed to allow faster analysis of networks with large number of nodes.
Communications, 2008. ICC '08. IEEE International Conference on; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Cognitive radio (CR) technology can achieve higher spectrum efficiency by exploring the unused spectrum in licensed band. Most of the existing work focuses on maximizing the spectrum utilization but ignores the immediate influence from primary users to network throughput. In this paper, we investigate the importance of planned link restoration in cognitive radio networks. We formulate the link restoration problem as an integer programming problem. By considering both channel assignment and interference between links, the link through-put can be guaranteed even when primary users appear, and therefore can provide the needed reliability for real-time wireless applications. We consider a link failure model which captures the induced link failures from multiple primary users operating on one frequency channel. Under this failure model, our algorithm explores the sharing of backup capacity. We compare our algorithm to two baseline restoration schemes. Our algorithm performs very well in terms of capacity usage and throughput reliability. By reserving 24.8% of network capacity, our algorithm meets the guarantee requirement in all simulation cases, while "no restoration" just meets the guarantee requirement in 50.8% of all simulation cases.
Communications, 2008. ICC '08. IEEE International Conference on; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: We propose FRASA, Feedback Retransmission Approximation for Slotted ALOHA, to study the stability region of finite-user slotted ALOHA under collision channel. With FRASA, we derive in closed form the boundary of the stability region for any number of users in the system, which is shown to be accurate via simulations. We use convex hulls and supporting hyperplanes to construct convex and piece-wise linear outer and inner bounds on the stability region of FRASA respectively to facilitate network optimization. We hope the analytical findings with FRASA can provide more insights on the characterization of the capacity region of other types of wireless random access networks, and enable traffic engineering with linear constraints in the design of wireless mesh networks.
Network Protocols, 2007. ICNP 2007. IEEE International Conference on; 11/2007
-
[show abstract]
[hide abstract]
ABSTRACT: We study the stability of finite-user infinite-buffer slotted ALOHA with partial interference. For the case of two users, there is a gradual, transition from the collision channel to the orthogonal channel when the link separation increases. The stability region can be either convex or nonconvex, depending on the link separation and the transmission probability vector. A partial characterization on the boundary of the stability region in closed form for the case of general number of users is also given. We hope this work can provide insight in designing traffic engineering algorithms in wireless mesh networks with practical random access protocols like 802.11.
Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
-
[show abstract]
[hide abstract]
ABSTRACT: In evaluating the performance of a wireless network, the interference between wireless links plays a key role. In previous works, interference was assumed to be a binary phenomenon, i.e., either the links mutually interfere with each other, or they do not interfere. However, there were experimental results contradicting this binary assumption. We term this as partial interference . In this paper, we present an analytical framework to characterize partial interference in a single-channel wireless network under unsaturated traffic conditions, and use 802.11b with basic access scheme and differential binary phase shift keying as an illustration. An analogy is drawn between partial interference and code division multiple access to demonstrate their similarities. The gain in capacity across unit cut by exploiting partial interference can be as high as 67% under scheduling in a modified Manhattan network.
Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: Real-time traffic has stringent delay requirement. However, bandwidth limited and error-prone wireless networks often show significant delay jitter. Traditional packet discarding schemes designed for high speed wired networks, such as random early detection (RED), are inadequate for wireless networks with high latency and delay variability. This paper describes an analytical framework for designing lifetime packet discard policies and proposes the channel state aware packet discard on expiration likelihood (CAPEL) algorithm, which only admits packets with expiration likelihood below a predefined requirement. Its effectiveness for improving goodput is quantified under a time varying channel modeled by the Markov-modulated Poisson process (MMPP). In addition, we use Gamma distribution to approximate the conditional system time distribution under the MMPP channel. It is verified to be accurate by simulation.
Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
-
Proceedings of the 66th IEEE Vehicular Technology Conference, VTC Fall 2007, 30 September - 3 October 2007, Baltimore, MD, USA; 01/2007
-
Proceedings of the 65th IEEE Vehicular Technology Conference, VTC Spring 2007, 22-25 April 2007, Dublin, Ireland; 01/2007
