Showing papers by "Wai-Choong Wong published in 2009"
01 Sep 2009
TL;DR: A MAC protocol using a two-level opportunistic spectrum access strategy, called CR-CSMA, is proposed to efficiently schedule secondary users' packets, and yet to protect primary users' operations.
Abstract: In this paper, we consider the medium access control (MAC) protocol design problem for random access cognitive radio networks. A MAC protocol using a two-level opportunistic spectrum access strategy, called CR-CSMA, is proposed to efficiently schedule secondary users' packets, and yet to protect primary users' operations. We employ normalized throughput and average packet delay as network metrics, and derive closed-form expressions to evaluate our protocol. For various offered traffic rates of secondary users and frame lengths, the optimal performances of secondary users can be achieved at the same spectrum sensing time, and also there exists a tradeoff between performance and agility.
20 citations
07 Sep 2009
TL;DR: A dynamic association mechanism that takes load balancing, link quality and association oscillation avoidance into consideration and measures the real-time traffic load through channel based load detection and suits both coordinated and uncoordinated wireless mesh networks is proposed.
Abstract: In this paper, we propose a dynamic association mechanism that takes load balancing, link quality and association oscillation avoidance into consideration. The metric introduced in this association mechanism measures the real-time traffic load through channel based load detection and suits both coordinated and uncoordinated wireless mesh networks. Because of the random characteristics of wireless links and the variability of network conditions, dynamic re-association should be involved. To avoid association oscillation during re-associations, we introduce oscillation avoidance schemes, which consist of periodic client station (STA) scan and re-association threshold. We further evaluate our dynamic association mechanism through simulations in the context of IEEE 802.11 based wireless mesh networks.
13 citations
TL;DR: This work proposes sensor node wakeup schemes based on combinatorics block design to address energy-related issues when common assumptions fail, and proposes a dual wakeup design for sensing and communications as these are two very different tasks.
4 citations
08 Dec 2009
TL;DR: A link quality estimator which use the packet loss rate, round trip time, available bandwidth and feedback information from receiver to continuously tracks the channel error probability and the collision probability of the receiver by using an Unscented Kalman Filter (UKF).
Abstract: Due to the complexity and time-variation of wireless channel, it is a great challenge to measure and estimate the channel quality accurately in wireless ad hoc network. To address this problem, we propose a link quality estimator which use the packet loss rate (PLR), round trip time (RTT), available bandwidth (ABW) at the sender and the feedback information from receiver to continuously tracks the channel error probability and the collision probability of the receiver by using an Unscented Kalman Filter (UKF). Through experiments we demonstrate that our link estimator can quickly adapt to the temporal dynamics of the links and accurately predict the link quality, which is more accurate than the traditional broadcasting-based method.
3 citations
08 Dec 2009
TL;DR: A firmware platform for communication between the CAN bus in vehicle and a host PC for car control is built to make use of the availability of Controller Area Network messages for the various new applications of car control.
Abstract: To make use of the availability of Controller Area Network (CAN) messages for the various new applications of car control, such as active safety, traffic efficiency and driver assistance, the objective of this paper is to build a firmware platform for communication between the CAN bus in vehicle and a host PC for car control. The firmware has two ports which are connected to the CAN bus so as to monitor the signal transferring in the CAN bus and send out the command CAN signal into the CAN bus. It also has a Universal Serial Bus (USB) interface which exchanges data between the firmware (hereafter called main board) and a host PC. The main board is designed to be capable of supporting high speed CAN communication that the bit rate can be up to 1Mbps.
3 citations
TL;DR: The generalized butterfly graph (GBG) is presented and its application to video stream authentication and two variants of the GBG authentication, packet sorting and unequal authentication protection, which apply unequal treatment to different packets based on their importance are explored.
Abstract: This paper presents the generalized butterfly graph (GBG) and its application to video stream authentication. Compared with the original butterfly graph, the proposed GBG provides significantly increased flexibility, which is necessary for streaming applications, including supporting arbitrary bit-rate budget for authentication and arbitrary number of video packets. Within the GBG design, the problem of constructing an authentication graph is defined as follows: given the total number of packets to protect, the expected packet loss rate for the network, and the available overhead budget, how should one design the authentication graph to maximize the probability that the received packets are verifiable? Furthermore, given the fact that media packets are typically of unequal importance, we explore two variants of the GBG authentication, packet sorting and unequal authentication protection, which apply unequal treatment to different packets based on their importance. Lastly, we examine how the proposed GBG authentication can be applied within the context of rate-distortion-authentication (R-D-A) optimized streaming: given a media stream protected by GBG authentication, the R-D-A optimized streaming technique computes an optimized transmission schedule by recognizing and accounting for the authentication dependencies in the GBG authentication graph.
3 citations
14 Jun 2009
TL;DR: The problem of jointly optimizing the transmitter and receiver beamforming weights in the downlink of a cyclic prefix-free MC-CDMA system over multipath fading channels is addressed and the performance of the optimization process is supported by simulation results.
Abstract: The problem of jointly optimizing the transmitter and receiver beamforming weights in the downlink of a cyclic prefix-free MC-CDMA system over multipath fading channels is addressed in this paper. Both the base station and user terminals are equipped with antenna arrays to leverage on the spatial information provided by the antenna arrays. The precoding and equalization matrices are designed with the aim of minimizing the overall mean-squared-error (MSE) of the system subject to a power constraint for each transmitter antenna, which has the additional benefit of reducing the probability of clipping of the transmitted signals from the transmitter. This is highly favorable for a MC-CDMA system due to the multi-carrier modulation involved. The performance of the optimization process is supported by simulation results.
1 citations
26 May 2009
TL;DR: This paper proposes DINCast to optimize application-level shared-tree multicast to form a special logical data loop and use this loop instead of the RP as multicast sources, and demonstrates its effectiveness in optimizing multicast delay.
Abstract: Application-level multicast suffers some disadvantages in terms of high multicast delay, overloading at Rendezvous Point (RP) and single-point of failure. In this paper, we propose DINCast to optimize application-level shared-tree multicast. The general idea of DINCast is to form a special logical data loop and use this loop instead of the RP as multicast sources. To demonstrate its effectiveness, we first analyze multicast delay with the inclusion of transmission delay, queuing delay and propagation delay of a typical symmetrical shared-tree multicast. We evaluate three placement schemes of DINCast. Our simulation results show that DINCast is effective in optimizing the multicast delay over the shared-tree multicast and the reduced rate of multicast delay may be up to 50%. Next, for any multicast tree, we carry out further simulations to optimize multicast delay. The experimental results show that DINCast can achieve better performance than original shared-tree Multicast.
1 citations
01 Dec 2009
TL;DR: A novel cross layer design which employs an adaptive link estimator to ensure reliable transmissions and can quickly adapt to the temporal dynamics of the links, accurately predict the link characteristics and improve the robustness of video transmission over mobile ad hoc networks is proposed.
Abstract: Video transmission over wireless ad hoc networks is very sensitive to temporal dynamics of the wireless channel. In order to achieve good end to end performance, it is necessary for upper layers to quickly adapt to the variations of the wireless links. Based on this motivation, we propose a novel cross layer design (CLD) which employs an adaptive link estimator to ensure reliable transmissions. The link-quality estimation scheme can provide accurate link quality information for routing decisions and predicts the link characteristics for the next time interval by using a Kalman filter. Through simulations and experiments we demonstrate that the proposed cross layer approach can quickly adapt to the temporal dynamics of the links, accurately predict the link characteristics and improve the robustness of video transmission over mobile ad hoc networks.