Jinglong Zhou

Improving Packet Delivery Ratio Estimation for Indoor Ad Hoc and Wireless Sensor Networks

Many protocols in wireless sensor networks use Packet Delivery Ratio (PDR) as a metric to select the best route, transmission rate or power. PDR is normally estimated either by counting the number of received hello/data messages in a small period of time, i.e., less than 1 second, or by taking the history of PDR into account. The first method is accurate but requires many packets to be sent, which costs too much energy. The second one is energy efficient, but fails to achieve good accuracy. Therefore in this paper we propose a novel estimation method which takes advantage of receiving signal strength. We show with extensive experimental results that the proposed method is 25% more accurate than the second estimation method, while being simple and energy efficient at the same time.

A Novel Link Quality Assessment Method for Mobile Multi-Rate Multi-Hop Wireless Networks

Accurate and fast wireless link quality assessment (LQA) for wireless channels would bring huge benefits for mobile multi-hop and multi-rate wireless ad hoc and sensor networks in the form of improved end-to-end performance. In this paper, we propose a novel LQA method based on cross-layer information. The method is implemented in a real test-bed, which is based on IEEE 802.11b/g, and achieved a significant LQA improvement up to 50% in mobile scenarios without introducing overhead. The effectiveness of accurate and fast LQA is demonstrated by feeding it into the routing layer to enable the route decisions to adapt faster during changing situations, especially in mobile scenarios. The experiment results show that the proposed LQA method can lead to faster and smarter routing decisions and higher end-to-end throughput compared to traditional methods, which only use hello packets to determine the link quality in mobile scenario.

Simulation-Based Analysis of TCP Over Beyond 3G Cellular Multi-Hop Networks

Next-generation communications networks will comprise third-generation (3G) cellular and multi-hop ad hoc networks, in particular, the Universal Mobile Telecommunications System (UMTS) and the IEEE 802.11 ad hoc networks. The paper has evaluated the performance of transmission control protocol (TCP) over an integrated UMTS and IEEE 802.11 multi-hop ad hoc network for bulk data transfers. The IEEE 802.11b was used. The TCP performance was evaluated for four dedicated UMTS radio channels with bit rates ranging from 64 kb/s to 2 Mb/s with varying block error rates. The throughput simulation results show that the UMTS radio channel is the performance bottleneck for bit rates up to 128 kb/s. However, for a 2 Mb/s channel, the performance is solely constrained by the IEEE 802.11b multi-hop ad hoc network. We have showed that the performance can be improved by using a larger TCP packet size

An Investigation of Link Quality Assessment for Mobile Multi-hop and Multi-rate Wireless Networks

Wireless ad hoc networks will be an important component in future communication systems. The performance of wireless ad hoc networks can be improved by link quality-aware applications. Wireless link quality is dynamic in nature, especially in mobile scenarios. Therefore, accurate and fast packet delivery ratio estimation is a prerequisite to good performance in mobile, multi-hop and multi-rate wireless ad hoc networks. In this paper, we propose a novel packet delivery ratio estimation method that improves the accuracy and responsiveness of the packet delivery ratio estimation. The proposed link quality estimation components are implemented in a IEEE 802.11b/g test-bed. The experiment results show that the accuracy of the packet delivery ratio estimation can improve up to 50% in mobile scenarios without introducing overhead. We also show the end-to-end performance impact of this improved estimation on route selection using different routing metrics and configurations. The measurement results show that our packet delivery ratio method leads to better route selection in the form of increased end-to-end throughput compared to traditional methods, which respond slowly to the link dynamics.

ns-2 models for simulating a novel beyond 3G cellular multi-hop network

Universal Mobile Telecommunications System (UMTS) is a third-generation cellular network that enables high-speed wireless Internet connectivity. On the other hand, the IEEE 802.11 ad hoc mode enables peer-to-peer short-range communications without infrastructure support. In this paper, we describe the design and implementation of a novel integrated UMTS and IEEE 802.11 ad hoc network modules in the Network Simulator (ns-2). The implementation is described from an overall design architecture to the realization of different architectural parts. A new mobile gateway is specially designed for the integrated network. With the hierarchical addressing mechanism, routing for the integrated network from wired network via UMTS network to the ad hoc network is realized. Simulations were carried out to validate the design and implementation in ns-2. Using our ns-2 modules, protocol designers can design and evaluate new protocols that run on such an integrated network.

Simulation-based analysis of a multi-hop integrated UMTS and WLAN network

The next generation communication networks will comprise of third-generation (3G) and fourth-generation (4G) cellular and multi-hop ad hoc networks. In particular, the Universal Mobile Telecommunications System (UMTS) and the IEEE 802.11 ad hoc networks will play a significant role. The UMTS can provide Internet service in wide areas with excellent mobility support while IEEE 802.11 can provide high speed last hop connectivity in indoor environment. The performance of the offered end-to-end TCP connection when these two different technologies come together to serve the users is an important aspect to be studied. In this paper, we build an analytical model to model the complete process of TCP packet transfer over this integrated network. The delay and end-to-end throughput are modeled. We also verify the simulation results considering the usual error rate in UMTS channels. Our analytical results match well with the simulation models that are widely used. Apart from modeling the Internet connectivity, our model can be used for multitude of tasks, such as gateway selection, resource reservation, etc., in the next generation cellular multi-hop networks.

Adaptable Link Quality Estimation for Multi Data Rate Communication Networks

QoS-sensitive applications transmitted over wireless links require precise knowledge of the wireless environment. However, the dynamic nature of wireless channel, together with its different configurations and types, makes so called link quality estimation (LQE) a difficult task. This paper looks into the design of an accurate and fast LQE method for a multi data rate environment. We investigate the impact of various conditions on the LQE accuracy. In result, two different link quality estimation sources, i.e., based on hello packet delivery ratio and signal strength, are measured and their performances are compared. We find that these two methods are not always accurate. As an improvement we propose an adaptive LQE method that chooses different LQE indicators depending on the wireless environment. The performance of the proposed method is verified via an extensive measurement campaign.

Cross Layer Design for Enhanced Quality Routing in Personal Wireless Networking

With more and more consumer devices becoming capable of wireless communication, the need for good quality ad hoc networking becomes more imminent. Self-configuring and self-adapting multi-hop networking will provide an excellent solution for wireless personal area networks (WPAN) as well as wireless home networks. In such networks, scalability is rarely believed to be a real issue. Instead, the issues are related to the end-to-end quality due to wireless links with constantly and rapidly changing quality. Hence, the network layer not only needs to adapt accurately but also in time. This paper looks into the design of accurate and fast wireless link quality assessment (LQA) options. We investigate the possibility to use cross layer information to improve this process which can be used by the routing layer to adapt faster and more accurately to changing situations. Experiments are done and the result shows the importance of adapting the new LQA options.

Link quality-based transmission power adaptation for reduction of energy consumption and interference

Today, many wireless devices are mobile and battery powered. Based on the fact that battery capacity is still limited, energy saving is an important issue in wireless communication. Meanwhile, the number of wireless devices continues to increase and this creates interference problems between wireless devices. In this paper, we look at transmission power control and propose a mechanism that tries to achieve minimum energy consumption or emission under any circumstance. Lower transmission power levels may result in more retransmissions, but in total, energy consumption or emission still can be reduced in many scenarios. To evaluate the performance of our mechanism, we used real wireless channels in an indoor environment to carry out measurements. The measurement results indicate that a significant amount of energy consumption or emission reduction can be achieved for the transmitter in most scenarios compared to using a fixed transmission power level for all packets.

Link quality-based transmission power adaptation for energy saving in IEEE 802.11

Today, many wireless devices are mobile and battery powered, which means that the service duration is highly dependent on energy consumptions and battery capacities. Based on the fact that battery capacity is still limited, energy saving is an important issue in wireless communication. Many methods have been proposed to save energy in wireless communication, such as power-aware routing and sleep mode. However, another important approach, transmission power adaptation, is not yet well discussed. In this paper, we propose a mechanism that selects the appropriate transmission power level to transmit packets instead of using a fixed default power level for all packets, which is common in IEEE 802.11. Lower transmission power levels may result in more retransmissions, but still consumes less energy. In total, energy can be saved and interference can be reduced by selecting a good transmission power level. We propose a two phase power saving mechanism and implemented it in a real test-bed. To evaluate the performance of our mechanism, we used an indoor environment to carry out measurements. The measurement results indicate that a significant amount of energy can be saved for the transmitter in most scenarios compared to using a fixed transmission power level for all packets.