Chi Xuefen

Adaptive FEC Algorithm Based on Prediction of Video Quality and Bandwidth Utilization Ratio

This paper proposes a channel error adaptive FEC algorithm to balance the conflict between the QoS of video transmission and the bandwidth utilization ratio in wireless IP networks. Two analytic models are derived, one is playable frame rate in MPEG video stream, another is effective utilization ratio of FEC. Based on these analytic models, quality of video stream and effective utilization ratio of FEC under different network conditions (presented by packet loss probability in this paper) are predicted. Then optimal amount of redundant packets is calculated and decided, which makes both the quality of video stream and the effective utilization ratio of FEC approximate their maximum. The simulation results show that the proposed algorithm improves system performance in both the QoS of wireless video transmission and the utilization of bandwidth.

Fabrication, Characterization and Properties of Superparamagnetic Reduced Graphene Oxide/Fe3O4 Hollow Sphere Nanocomposites

Abstract The reduced graphene oxide wrapped Fe3O4 hollow nanospheres have been synthesized by a simple self-assembly process driven by electrostatic interaction. The structure, the chemical component and the morphology were characterized by XRD, SEM, TEM, FTIR, and Raman spectroscopy. Result show that the fabricated nanocomposites exhibit superparamagnetic property with the saturation magnetization of 70.2 A·2·kg−1 at room temperature and allow rapid separation in water solution under an external magnetic field. The high magnetism and excellent water dispersibility make the nanocomposites ideal candidates for various important applications such as magnetic resonance imaging, biosensors, communication, and microwave absorption.

Adaptive FEC algorithm based on prediction of video quality and bandwidth utilization ratio

In this paper, a channel adaptive FEC algorithm is proposed which balances the trade-off between the QoS of video transmission and the bandwidth utilization ratio in wireless IP networks. Our algorithm can dynamically adjust to a suboptimal number of FEC redundant packets to cater to the time-varying wireless channel. For the sake of obtaining the suboptimal amount of FEC redundant packets, we derive two analytical models, one is the playable frame rate in MPEG video stream, another is the effective utilization ratio of FEC. Based on these analytical models, a suboptimal value of redundant packets, which makes both the quality of video stream and the effective utilization ratio of FEC approximate their maximum, is calculated by predicting the quality of video stream and effective utilization ratio of FEC under different network conditions (characterized by packet loss probability in this paper). The simulation results indicate that the QoS of wireless video transmission and the bandwidth utilization ratio are improved by employing the proposed algorithm.

Investigation of Relaying Node Placement in Wireless Mesh Networks

The aim of this paper is to use analytical means to discover the effective functional range of a node in Wireless Mesh Networks (WMNs) and to determine the optimized position of the relaying node when placed between two mesh routers in WMNs. A simple source to destination model with two transmission distance schemes and simple relaying node model with three relaying node position schemes were designed for analyzing the network capacity. The main results are achieved by analyzing the capacity of network model and simulation programs are also developed in OPNET Modeler. The main contribution of the paper is analytically to show the relaying node can operate to forward packets to receiver when the relaying node is deployed within the range of both transmitter and receiver when the receiver is deployed out of the range of the transmitter. It also shows that in the relaying node functional area, the maximum capacity could be achieved when the relaying node is deployed in the middle between the transmitter and the receiver.

Jitter analysis of real-time services in IEEE 802.15.4 WSNs and wired IP concatenated networks

Abstract It is challenging and significant to explore the impacts of non-real-time services on real-time services from the perspective of jitter. Most of current researches on jitter made too many mathematical hypotheses on networks and traffic. This paper puts forward a tandem queuing model to characterize the real communication scenario where heterogeneous services are served by IEEE 802.15.4 wireless sensor networks (WSNs), and then the packets served successfully are fed to Internet protocol (IP) networks. By analyzing the contention access processes in IEEE 802.15.4 WSNs, the authors derive the departure processes of the two types of services, i.e., the arrival processes of IP networks. The IP network is modeled as a queuing system, in which the real-time service is forwarded accompanied by the non-real-time service. Investigating the jitter of real-time services is intractable. Therefore, this paper abstracts this problem as a dynamic queuing system evolving on a dynamic time interval. Referring the transient analysis method (TAM), this paper obtains the queue length in a random time interval which is scaled by the arrival of real-time services. Queue length evolution is closely connected with the jitter. Benefiting from the derivation in probability generation domain, the jitter of real-time services is obtained.

A Novel Adaptive FEC Scheme Integrating Multi-Layer Functions

A novel packet-level adaptive FEC scheme of the hierarchical video stream in wireless communications is proposed, in which cross layer design is deployed. We formulate the Euclidean Distance of receiving sequence, which is used to estimate packet error rate of wireless channel by receiving side. We extend the analytical model of playable frame rate of video and connect it to the effective utilization rate of FEC. In our scheme, sending end derives real time packet error rate based on the Euclidean Distance metric, which is acknowledged by receiving end, and then computes the number of FEC redundant packets. This number of FEC redundant packets is second-best solution because it makes both playable frame rate of video and FEC effective utilization near to their maximums. The simulation results show that the proposed scheme is able to promote the quality of video services.

Evaluation of Error Control Mechanisms Based on System Throughput and Video Playable Frame Rate on Wireless Channel

Error control mechanisms are widely used in video communications over wireless channels. However for improving end-to-end video quality; they consume extra bandwidth and reduce effective system throughput. In this paper, considering the parameters of system throughput and playable frame rate as evaluating metrics, we investigate the efficiency of different error control mechanisms. We develop a throughput analytical model to present system effective throughput for different error control mechanisms under different conditions. For a given packet loss probability, both optimal retransmission times in adaptive ARQ and optimal number of redundant packets in adaptive FEC for each type of frames are derived by keeping the system throughput as a constant value. Also, end to end playable frame rates for the two schemes are computed. Then which error control scheme is the most suitable for which application condition is concluded. Finally empirical simulation experimental results with various data analysis are demonstrated.