Chungui Liu

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.

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.

Research of Asynchronous Leader Election Algorithm on Hierarchy Ad Hoc Network

Leader election is a very important problem, not only in wired networks, but in mobile ad hoc networks as well. However, due to the node mobility and network performance, cluster leader node may be lost which will affect the communication severely. According to the features of poor mobility of low-level node, in this paper, we present a low-level asynchronous algorithm with the collision avoidance mechanism, and solved the problem above. And we designed experiments in application layer. The leader-elected time was got from those experiments and the result was compared with synchronous algorithm. This algorithm can be used in fire fighting, construction supervision and rescue work in which a hierarchy ad hoc network is required to dynamically established. By electing a new leader in case of previous leader loss, the algorithm can enhance the robustness of whole network.

Capacity Analysis and Experimental Study with Multiple Interfaces and Multiple Channels in 802.11 Mesh Networks

A key challenge in multihop wireless network is to provision for sufficient network capacity to meet user requirements. The contributions of this paper are two-fold: (a) we analyses wireless bandwidth, the ratio between the number of channels and the number of interfaces, the ratio between the number of gateways and the number of mesh routers, and the impact on the capacity of mesh backbone, and present the asymptotic upper bound of the average throughput of mesh routers (b) based on insights from capacity analysis, we built TJU MeshNet testbed and develop a multi-interface routing protocol (MIRP). We implement the proposed protocol in our testbed to demonstrate the feasibility in practice.

Design and Implementation of Web Course Evaluation Based on Cloud Model

The evaluation model of online course should be dynamic, layered, multi-attribute, which can provide the comprehensive and timely feedback for the online course developers and teachers and better promote the construction and development of online courses. Based on the original model, this paper further improves the model algorithm and evaluates an online courses, and compare with the evaluation results of the traditional probabilistic model and fuzzy model. The results show that the cloud model can provide more comprehensive evaluation results.

Research for Supporting Emotional Education of Network Based on Moodle

The emotional education is a significant goal of education. Only pay more attention to the emotional factors in network teaching, we can cultivate the healthy human nature learners. This paper will introduce the Moodle platform and have a thorough discuss on how to use Moodle to realize network emotional education from the teaching function Moodle included.

Challenges and Experiences of Building Multimedia Transmission Testbeds in Wireless Mesh Network

Wireless mesh networks (WMN), with static wireless back-bone and multi-hop communication, as protocols typically employed in WMN are, for the most part, not designed for real-time communications. WMNs experimentation is subjected to stochastic factors such as channel contention, interference, node mobility and access latency add delay and degrade the quality of the stream, pose new design challenges. In this paper, we report on our effort and experience to design our WMN testbed. As a case study, second, we introduce the TJU MeshNet architecture. We share our lessons learned from this effort and believe that they will be valuable to other researchers who develop experimental wireless mesh networks and business applications.

Load-Balancing Algorithm to Improve Throughput Capacity in Wireless Mesh Backbone Networks

Wireless Mesh Networks are an emerging architecture based on multi-hop transmission. It is also the ideal solution of wireless broadband Internet access. In this paper, we design the load balancing and route algorithm of the interfaces and routers in wireless mesh backbone network. We have done the extensive experiments and made the performance evaluations for the proposed algorithms on TJU MeshNet testbed. The experimental results show that our approaches improve the network capacity greatly. Meanwhile, our evaluation demonstrates that our load balancing algorithm with multi-interface routing protocol (MIRP) can effectively utilize the channel resources, optimize resource allocation and improve the overall WMNs performance.

Improved Frequency Domain Differential Demodulation for Fast Fading HF Channels

The bit error rate (BER) of MDPSK-OFDM in frequency domain over fading HF channels is evaluated, and the optimum value of subcarrier number is given and the upper and lower bound of BER is obtained. The convention differential demodulation scheme is sensitive to the value of subcarrier number in time-variant multipath channel. Improved frequency domain differential demodulation (FDDD) scheme for fast fading HF channel is proposed. In addition, the simulation results show that our proposed scheme is superior to the conventional differential demodulation technique at fast fading HF channel.