Zenghua Zhao

Double-Blind Data Discovery Using Double Cross for Large-Scale Wireless Sensor Networks With Mobile Sinks

Large-scale wireless sensor networks (WSNs) with mobile sinks present new challenges on data discovery because the locations of the mobile sinks cannot be predetermined. In this paper, we study the double-blind data discovery problem in a WSN, where the mobile sink(s) and the sensed data do not know the locations of each other a priori. To address this problem, we first propose a Random Line Walk (RLW) mechanism for message forwarding, and based on this forwarding mechanism, we further propose an efficient data discovery mechanism called Double Cross. Double Cross exploits a simple geometric property of a planar, i.e., for a couple of pairs of orthogonal lines in a planar, the probability that they intersect within the planar is larger than 99%. However, it does not depend on the geographic location or directional information on a node, which is difficult to obtain in such networks. Instead, each sensor node only needs to know the distances between the neighbor nodes within its transmission range. Analytical and simulation results show that Double Cross can achieve a higher successful discovery rate with lower energy consumption, compared existing work.

Cross-Layer Adaptive Rate Control for Video Transport over Wireless Ad Hoc Networks

Video transport over wireless ad hoc networks poses a great challenge due to the high variability of the network bandwidth. In this paper, to improve the quality of receipt video, we proposed a cross-layer adaptive rate control mechanism, CLARC, which makes good use of both the routing information from the underlying network layer, and the frame loss feeding back from the application layer. The scheme tries to adapt the video encoder output bitrate as close as possible to the available network bandwidth. It is congestion-aware, robust to random error, and can co-exist with TCP friendly. We implemented an ad hoc video streaming testbed to validate the effectiveness of our scheme

Energy-efficient rate adaptation for outdoor long distance WiFi links

WiLD (WiFi-based Long Distance) mesh networks have been broadly deployed for bringing extremely low-cost IT revolution to developing regions. However, external WiFi/non-WiFi interferences severely aggravate network performance. Besides, over-provisioning transmission power without considering the channel dynamics and interferences can result in unnecessary energy consumption, which will eventually lead to the network outage. In this paper, an energy efficient rate adaptation algorithm is proposed for WiLD links. It adopts an online measurement of FDR (Frame Delivery Ratio)-RSSI mapping to choose bit rate based on the joint considerations of RSSI and transmission power. Moreover, a novel algorithm called CNP-CUSUM (Continuous Non-Parameter-Cumulative Sum) is presented to detect changes of external interference intensity at receivers by leveraging beacon loss ratio statistics. Our simulation results show that it significantly outperforms fixed bit-rate, fixed transmission power schemes by achieving higher energy efficiency and considerable link throughput gain.

Flow-Level Multipath Load Balancing in MPLS Network

Multi-Protocol Label Switching (MPLS) can efficiently support the explicit routes setup by the use of Label Switched Paths (LSPs) between an ingress Label Switched Router (LSR) and an egress LSR. Hence it is possible to distribute the network traffic among several paths to achieve load balancing, thus improving the network utilization, and minimizing the congestion. The packet-level traffic characteristics in the Internet is so complex that it is natural to do traffic engineering (TE) and control at the flow level. The emerging Multi-Protocol Label Switching (MPLS) has introduced an attractive solution to TE in IP networks. The main objective of this paper is to balance traffic at the flow level among the parallel Label Switched Paths (LSPs) in MPLS networks. We introduce a multipath load-balancing model at the flow level. In this model, each LSP is modeled as an M/G/1 processor-sharing queue. The load-balancing problem is then considered as an optimization problem. Based on the analysis of the model, we propose a heuristic but efficient mechanism that can make good use of the traffic characteristics at the flow level. Packet disorder is avoided effectively by dispatching packets belonging to one flow to the same path. This mechanism only need to be implemented in the ingress LSRs and the egress LSRs, while the intermediate LSRs only forward the packets. Apart from discussing the traffic allocation granularity, and the implementation issues in details, we have also performed extensive simulations using NS-2 with MPLS modules. The simulation results show that the load through the network is well balanced so that the network throughput is improved and the delay is decreased efficiently.

Flow-level multipath load balancing in MPLS network

The packet-level traffic characteristics in the Internet are so complex that it is natural to do traffic engineering (TE) and control at the flow level. The emerging multi-protocol label switching (MPLS) has introduced an attractive solution to TE in IP networks. The main objective of this paper is to balance traffic at the flow level among the parallel label switched paths (LSPs) in MPLS networks. We first introduce a multipath load-balancing model at the flow level. In this model, each LSP is modeled as an M/G/1 processor-sharing queue. Based on the analysis of the model, we propose a heuristic but efficient mechanism that is implemented only at the ingress label switched routers (LSRs) and egress LSRs in the network. Extensive simulations using NS2 are performed with MPLS modules. The simulation results show that the load through the network is well balanced so that the network throughput is improved and the delay is decreased significantly.

Fast track article: A multi-layer experimental study of multimedia and QoS communication in wireless mesh networks

A significant issue in Mesh networks is to support multimedia transmissions while providing Quality of Service (QoS) guarantees to mobile users. For real-time multimedia streaming, unstable throughput or insufficient bandwidth will incur unexpected delay or jitter, and it remains difficult to provide comprehensive service guarantees for a wireless mesh environment. In this paper, we target the problem of providing multimedia QoS in wireless mesh networks. We design and implement a campus test-bed for supporting multimedia traffic in mobile wireless mesh networks, and investigate in detail some possible improvements on a number of layers to enable multimedia transmission over wireless networks with QoS support. We first study a number of improvements of some existing routing protocols to support multimedia transmissions. Some new admission control and rate control mechanisms are studied and their performance gains are verified in our experiments. In our new cross-layer adaptive rate control (CLARC) mechanism, we adaptively change the video encoders output bit rate based on the available network bandwidth to improve the quality of the received video. We also design a mobile gateway protocol to connect the MANET to Internet and a wireless LAN management protocol to automatically manage WLAN to provide some QoS.

Monitoring the high-voltage transmission lines based on two-tier wireless networks

Wireless networks have become an effective solution for remote surveillance and data gathering without an existing communication infrastructure. The poster presents a system for monitoring the high-voltage transmission lines. This system implemented a two-tier wireless network to gather the data for the high voltage transmission lines and transmit these data to the control center based on WiFi technology and Zigbee technology.

A Multi-layer Approach to Support Multimedia Communication in Mesh Networks with QoS

It is challenging to support multimedia transmissions over wireless networks, especially, wireless mesh networks, due to some natural resource constraints of wireless networks. In this paper, we investigate in detail some possible improvements on a number of layers to enable the multimedia transmission over wireless networks with QoS support. We implement all our protocols in some test-beds to study their real time performances. We first study a number of improvements of some existing routing protocols to support multimedia transmissions. Some new admission control and rate control mechanisms are studied and their performance gains are verified in our experiments. In our new cross-layer adaptive rate control (CLARC) mechanism, we adaptively change the video encoder’s output bit rate based on the available network bandwidth to improve the quality of the received video. We design and implement a campus test-bed for supporting multimedia traffics in mobile wireless mesh networks. We also design a mobile gateway protocol to connect the MANET to Internet and a wireless LAN management protocol to automatically manage WLAN to provide some QoS.

Double Cross: A Double-Blind Data Discovery Scheme for Large-Scale Wireless Sensor Networks

In this paper, we consider the double-blindness problem in large-scale wireless sensor networks (WSNs) with mobile sinks, where the mobile sink(s) and data do not know the locations of each other a priori. We first propose a random line walk mechanism for message forwarding and based on this forwarding mechanism we further propose an efficient data discovery scheme called Double Cross to address the double-blindness problem. Double Cross exploits a simple geometric property of a planar, i.e., for a couple of pairs of orthogonal lines in a planar, the probability that they intersect within the planar is larger than 99%. However, it does not depend on the geographic location or directional information of a node, which is difficult to obtain in such networks. Instead, each sensor only needs to know the distances between neighbor nodes within its transmission range. Analytical and simulation results show that Double Cross can achieve a high successful discovery rate with low energy consumption.

Node-Based Rate Constraints for QoS Flows in Wireless Ad-Hoc Networks

This paper proposes a set of node-based rate constraints called NABE (node-based available bandwidth estimation) to model the interference relationship among nodes in a wireless ad hoc network and to provide rate constraints for its QoS flows. We evaluate the performance of NABE from three different perspectives: its capacity, its complexity to implement the MAC layer protocol and its efficiency. Our simulation results demonstrate that, NABE can always admit the feasible flows as well as make full use of the bandwidth resource when serving as an admission control scheme in the presence of both intra-flow and inter-flow interference.