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Proceedings of the Global Communications Conference, GLOBECOM 2011, 5-9 December 2011, Houston, Texas, USA; 01/2011
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Wireless Networks. 01/2009; 15:1059-1073.
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ABSTRACT: Ultra-wideband (UWB) is a promising technology that can support high data rate communication for future Wireless Personal Area Networks (WPANs). To provide high throughput in UWB networks, we proposed a general framework for CSMA/CA based MAC protocol previously [17]. In this framework, multiple upper layer packets can be assembled into a single burst frame at the MAC layer, which can significantly improve the throughput performance by reducing overheads. Nevertheless, the burst assembly procedure may introduce extra packet delay, which is undesirable for some applications. In this paper, we address the performance issue in the burst-frame-based MAC protocol. In particular, we develop an analytical model to evaluate the delay performance of the burst-frame-based MAC protocol under unsaturated conditions. Our delay analysis is unique in that we consider the end-to-end packet delay, which is the duration from the epoch that a packet enters the queue at the MAC layer of the transmitter side to the epoch that the packet is successfully received at the receiver side. The analytical results give excellent agreement with the simulation results, which represents the accuracy of our analytical model. The results also provide important guideline on how to set the parameters of the burst assembly policy. Based on these results, we develop an efficient adaptive burst assembly policy so as to optimize the throughput and delay performance of the burst-frame-based CSMA/CA protocol.
Wireless Networks. 01/2009; 15:11.
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ABSTRACT: In this paper, we present a new decoding algorithm for the Wyner-Ziv (WZ) video coding scheme based on turbo codes. In this scheme, a video frame is encoded using a turbo code, and only a subset of the parity bits are sent to the decoder. At the decoder, the temporal correlation of the video sequence is exploited by using the previous frame as noisy side information (SI) for the current frame. However, there is a mismatch between the SI, which is available as pixel values, and the binary code bits. Previous implementations of the decoder use suboptimal approaches that convert pixel values to soft information for code bits. We present a new decoding algorithm for this application based on decoding on a hyper-trellis, in which multiple states of the original code trellis are combined. We show that this approach significantly improves performance without changing the complexity of the decoder. We also introduce a new technique for the WZ decoder to exploit the spatial correlation within a frame without requiring transform-domain encoding at the encoder, thereby reducing its complexity. Simulation results for fixed-rate transmission show a 9-10-dB improvement in the peak signal-to-noise ratio when compared to a WZ video codec that does bitwise decoding and utilizes only the temporal correlation.
IEEE Transactions on Circuits and Systems for Video Technology 06/2008; · 1.65 Impact Factor
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Security and Communication Networks. 01/2008; 1:107-124.
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ABSTRACT: Wireless LANs with multi-beam directional antennas have received intensive attention lately due to the potential gain in throughput performance. However, when the multi-beam directional antennas are introduced in this system, the ever popular contention-based medium access control protocol such as IEEE 802.11 MAC is no longer effective, and many challenging problems, such as beam-synchronization problem, beam-overlapping problem, mobility and receiver blocking problem (deafness problem), need to be resolved. In this paper, we propose a novel MAC protocol to carefully address these problems. In addition to improving communication efficiency, we also consider the backward compatibility in our design, whereby an IEEE 802.11 terminal can transparently access a multi-beam access point. Furthermore, we present an analytical model to evaluate the performance of multi-beam wireless LANs. Extensive simulation studies are used to validate the analytical model and show that our scheme can significantly improve the throughput performance
IEEE Transactions on Wireless Communications 03/2007; · 2.59 Impact Factor
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ABSTRACT: One of the most promising approaches to improving communication efficiency in wireless communication systems is the use of multiuser diversity. Although it has been widely investigated and shown feasible and efficient in cellular networks, there is little work for the ad hoc networks, especially in real protocol and algorithm design. In this paper, we propose a novel scheme, namely, the opportunistic medium access and auto rate (OMAR), to efficiently utilize the shared medium in IEEE 802.11-based ad hoc networks by taking advantage of diversity, distributed scheduling, and adaptivity. In an ad hoc network, especially in a heterogeneous ad hoc network or a mesh network, some nodes may need to communicate with multiple one-hop nodes. We allow such a node with a certain number of links to function as a clusterhead to locally coordinate multiuser communications. We introduce a CDF-based (cumulative distribution function) K-ary opportunistic splitting algorithm and a distributed stochastic scheduling algorithm to resolve intra and intercluster collisions, respectively. Fairness is formulated and solved in terms of social optimality within and across clusters. Analytical and simulation results show that our scheme can significantly improve communication efficiency while providing social fairness
IEEE Transactions on Mobile Computing 01/2007; 5(12):1764-1779. · 2.28 Impact Factor
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MONET. 01/2007; 12:57-68.
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ABSTRACT: IEEE 802.11 is the most important standard for wireless local area networks (WLANs). In IEEE 802.11, the fundamental medium access control (MAC) scheme is the distributed coordination function (DCF). To understand the performance of WLANs, it is important to analyze IEEE 802.11 DCF. Recently, several analytical models have been proposed to evaluate the performance of DCF under different incoming traffic conditions. However, to the best of the authors' knowledge, there is no accurate model that takes into account both the incoming traffic loads and the effect of imperfect wireless channels, in which unsuccessful packet delivery may occur due to bit transmission errors. In this paper, the authors address this issue and provide an analytical model to evaluate the performance of DCF in imperfect wireless channels. The authors consider the impact of different factors together, including the binary exponential backoff mechanism in DCF, various incoming traffic loads, distribution of incoming packet size, queueing system at the MAC layer, and the imperfect wireless channels, which has never been done before. Extensive simulation and analysis results show that the proposed analytical model can accurately predict the delay and throughput performance of IEEE 802.11 DCF under different channel and traffic conditions
IEEE Transactions on Vehicular Technology 10/2006; · 1.92 Impact Factor
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ABSTRACT: The recent Federal Communications Commission regulations for ultra-wideband (UWB) transmission systems have sparked a surge of research interests in the UWB technology. One of the important application areas of UWB is wireless sensor networks. The proper operations of many UWB sensor networks rely on the knowledge of physical sensor locations. However, most existing localization algorithms developed for sensor networks are vulnerable to attacks in hostile environments. As a result, attackers can easily subvert the normal functionalities of location-dependent sensor networks by exploiting the weakness of localization algorithms. In this paper, we first analyze the security of existing localization techniques. We then develop a mobility-assisted secure localization scheme for UWB sensor networks. In addition, we propose a location-based scheme to enable secure authentication in UWB sensor networks.
IEEE Journal on Selected Areas in Communications 05/2006; · 3.41 Impact Factor
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ABSTRACT: Most existing routing protocols for mobile ad hoc networks (MANETs) use a single routing strategy for different types of networks. Routing protocols suitable for small networks may not scale well in large networks. Routing protocols that perform well in sparse networks may not be suitable for dense networks. To achieve good performance, different routing strategies should be used for different types of networks. This philosophy motivates our design of a new routing protocol called the adaptive cell relay (ACR) routing protocol. Our ACR protocol can adapt the routing strategy for networks with different node density so high efficiency, low delay, and scalability can be achieved. Extensive simulation results demonstrate that the ACR has much better performance and scalability than a popular routing protocol-location-aid routing (LAR). In addition, both the analysis and the simulations show that the ACR routing protocol incurs only about 25% of the routing overhead of the LAR routing protocol.
IEEE Transactions on Vehicular Technology 02/2006; · 1.92 Impact Factor
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ABSTRACT: Efficient routing is very important for mobile ad hoc networks (MANETs). Most existing routing protocols consider homogeneous ad hoc networks, in which all nodes are identical, i.e., they have the same communication capabilities and characteristics. Although a homogeneous network model is simple and easy to analyze, it misses important characteristics of many realistic MANETs such as military battlefield networks. In addition, a homogeneous ad hoc network suffers from poor performance limits and scalability. In many ad hoc networks, multiple types of nodes do coexist; and some nodes have larger transmission power, higher transmission data rate, better processing capability, and are more robust against bit errors and congestion than other nodes. Hence, a heterogeneous network model is more realistic and provides many advantages (e.g., leading to more efficient routing protocol design). In this paper, we present a new routing protocol called multiclass (MC) routing, which is specifically designed for heterogeneous MANETs. Moreover, we also design a new medium access control (MAC) protocol for heterogeneous MANETs, which is more efficient than IEEE 802.11b. Extensive simulation results demonstrate that the MC routing has very good performance, and outperforms a popular routing protocol-zone routing protocol, in terms of reliability, scalability, route discovery latency, overhead, as well as packet delay and throughput.
IEEE Transactions on Vehicular Technology 02/2006; · 1.92 Impact Factor
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IEEE Trans. Mob. Comput. 01/2006; 5:1764-1779.
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Proceedings of the Global Telecommunications Conference, 2006. GLOBECOM '06, San Francisco, CA, USA, 27 November - 1 December 2006; 01/2006
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Proceedings of the Global Telecommunications Conference, 2006. GLOBECOM '06, San Francisco, CA, USA, 27 November - 1 December 2006; 01/2006
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Wireless Communications and Mobile Computing. 01/2006; 6:333-346.
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ABSTRACT: To efficiently support quality of service (QoS) in future wireless networks, it is important to model a wireless channel in terms of connection-level QoS metrics such as data rate, delay and delay-violation probability. To achieve this, in D. Wu and R. Negi (2003), we proposed and developed a link-layer channel model termed effective capacity (EC) for flat fading channels. In this paper, we apply the effective capacity technique to modeling frequency selective fading channels. Specifically, we utilize the duality between the distribution of a queue with superposition of N i.i.d. sources, and the distribution of a queue with a frequency-selective fading channel that consists of N i.i.d. sub-channels, to model a frequency selective fading channel. In the proposed model, a frequency selective fading channel is modeled by three EC functions; we also propose a simple and efficient algorithm to estimate these EC functions. Simulation results show that the actual QoS metric is closely approximated by the QoS metric predicted by the proposed EC channel model. The accuracy of the prediction using our model can translate into efficiency in admission control and resource reservation.
Quality of Service in Heterogeneous Wired/Wireless Networks, 2005. Second International Conference on; 09/2005
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ABSTRACT: Ultra-wideband (UWB) communication is becoming an important technology for future wireless personal area networks (WPANs). A critical challenge in high data rate UWB system design is that a receiver usually needs tens of micro-seconds or even tens of milliseconds to synchronize with the transmitted signals, known as the timing acquisition problem. Such a long synchronization time will cause significant overhead, since the data rate of UWB systems is expected to be very high. To address the overhead problem, we previously proposed a general framework for MAC protocols in high data rate UWB networks. In this framework, a node can aggregate multiple upper-layer packets into a larger burst frame at the MAC layer. In this paper, we analyze the unsaturated throughput performance of a burst-frame-based MAC protocol within the framework. Numerical results from the analytical method give excellent agreement with the simulation results, indicating the accuracy of our analytical method.
Communications, 2005. ICC 2005. 2005 IEEE International Conference on; 06/2005
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ABSTRACT: We consider the problem of quality of service (QoS) provisioning for K users sharing a downlink time-slotted fading channel. We develop simple and efficient schemes for admission control, resource allocation, and scheduling, which can yield substantial capacity gain. The efficiency is achieved by virtue of recently identified multiuser diversity. A unique feature of our work is explicit provisioning of statistical QoS, which is characterized by a data rate, delay bound, and delay-bound violation probability triplet. The results show that compared with a fixed-slot assignment scheme, our approach can substantially increase the statistical delay-constrained capacity of a fading channel (i.e., the maximum data rate achievable with the delay-bound violation probability satisfied), when delay requirements are not very tight, while yet guaranteeing QoS at any delay requirement.
IEEE Transactions on Vehicular Technology 06/2005; · 1.92 Impact Factor
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ABSTRACT: A critical challenge in ultra-wideband (UWB) system design is that a receiver usually needs tens of microseconds or even tens of milliseconds to synchronize with transmitted signals; this is known as the timing acquisition problem. Such a long synchronization time causes significant overhead, since the data rate of UWB systems is expected to be very high. We address the timing acquisition problem at the medium access control (MAC) layer, and propose a general framework for medium access control in UWB systems; in this framework, a transmitting node can aggregate multiple upper-layer packets into a larger burst frame at the MAC layer. Furthermore, we design a MAC protocol based on the framework, and analyze its saturation throughput performance. Compared to sending each upper-layer packet individually, which is a typical situation in exiting MAC protocols, the proposed MAC can drastically reduce the synchronization overhead. Numerical and simulation results show that the proposed MAC can significantly improve the performance of UWB networks, in terms of both throughput and end-to-end delay.
Wireless Communications and Networking Conference, 2005 IEEE; 04/2005
