Xiao-Hong Peng

Radio range adjustment for energy efficient wireless sensor networks

In wireless ad hoc sensor networks, energy use is in many cases the most important constraint since it corresponds directly to operational lifetime. Topology management schemes such as GAF put the redundant nodes for routing to sleep in order to save the energy. The radio range will affect the number of neighbouring nodes, which collaborate to forward data to a base station or sink. In this paper we study a simple linear network and deduce the relationship between optimal radio range and traffic. We find that half of the power can be saved if the radio range is adjusted appropriately compared with the best case where equal radio ranges are used.

Improving Energy Efficiency in a Wireless Sensor Network by Combining Cooperative MIMO With Data Aggregation

In wireless sensor networks where nodes are powered by batteries, it is critical to prolong the network lifetime by minimizing the energy consumption of each node. In this paper, the cooperative multiple-input-multiple-output (MIMO) and data-aggregation techniques are jointly adopted to reduce the energy consumption per bit in wireless sensor networks by reducing the amount of data for transmission and better using network resources through cooperative communication. For this purpose, we derive a new energy model that considers the correlation between data generated by nodes and the distance between them for a cluster-based sensor network by employing the combined techniques. Using this model, the effect of the cluster size on the average energy consumption per node can be analyzed. It is shown that the energy efficiency of the network can significantly be enhanced in cooperative MIMO systems with data aggregation, compared with either cooperative MIMO systems without data aggregation or data-aggregation systems without cooperative MIMO, if sensor nodes are properly clusterized. Both centralized and distributed data-aggregation schemes for the cooperating nodes to exchange and compress their data are also proposed and appraised, which lead to diverse impacts of data correlation on the energy performance of the integrated cooperative MIMO and data-aggregation systems.

Energy-Efficient Multihop Cooperative MISO Transmission with Optimal Hop Distance in Wireless Ad Hoc Networks

In this paper, we investigate the hop distance optimization problem in ad hoc networks where cooperative multi-input-single-output (MISO) is adopted to improve the energy efficiency of the network. We first establish the energy model of multihop cooperative MISO transmission. Based on the model, the energy consumption per bit of the network with high node density is minimized numerically by finding an optimal hop distance, and, to get the global minimum energy consumption, both hop distance and the number of cooperating nodes around each relay node for multihop transmission are jointly optimized. We also compare the performance between multihop cooperative MISO transmission and single-input-single-output (SISO) transmission, under the same network condition (high node density). We show that cooperative MISO transmission could be energy-inefficient compared with SISO transmission when the path-loss exponent becomes high. We then extend our investigation to the networks with varied node densities and show the effectiveness of the joint optimization method in this scenario using simulation results. It is shown that the optimal results depend on network conditions such as node density and path-loss exponent, and the simulation results are closely matched to those obtained using the numerical models for high node density cases.

An Objective Approach to Measuring Video Playback Quality in Lossy Networks using TCP

In this work, we investigate a new objective measurement for assessing the video playback quality for services delivered in networks that use TCP as a transport layer protocol. We define the new metric as pause intensity to characterize the quality of playback in terms of its continuity since, in the case of TCP, data packets are protected from losses but not from delays. Using packet traces generated from real TCP connections in a lossy environment, we are able to simulate the playback of a video and monitor buffer behaviors in order to calculate pause intensity values. We also run subjective tests to verify the effectiveness of the metric introduced and show that the results of pause intensity and the subjective scores made over the same real video clips are closely correlated.

Robust H.264/AVC Video Transmission using Data Partitioning and Unequal Loss Protection

In this work, we present an adaptive unequal loss protection (ULP) scheme for H264/AVC video transmission over lossy networks. This scheme combines erasure coding, H.264/AVC error resilience techniques and importance measures in video coding. The unequal importance of the video packets is identified in the group of pictures (GOP) and the H.264/AVC data partitioning levels. The presented method can adaptively assign unequal amount of forward error correction (FEC) parity across the video packets according to the network conditions, such as the available network bandwidth, packet loss rate and average packet burst loss length. A near optimal algorithm is developed to deal with the FEC assignment for optimization. The simulation results show that our scheme can effectively utilize network resources such as bandwidth, while improving the quality of the video transmission. In addition, the proposed ULP strategy ensures graceful degradation of the received video quality as the packet loss rate increases.

Investigation of H.264 Video Streaming over an IEEE 802.11e EDCA Wireless Testbed

Although a number of investigations have been conducted using IEEE 802.11e enabled networks to stream class differentiated video, very few reports are available based on a real testbed. In our work, we set up a wireless testbed for H.264 video streaming through assigning the partitioned video packets onto the DCF MAC layer and different access classes of the EDCA MAC layer. We investigate three assignment schemes: 1) DCF is used and all the traffic is treated equally; 2) video traffic is assigned to each of the access classes in turn; and 3) the packets are assigned according to their importance and the class priority. In addition to the video stream we introduce TCP traffic from three clients in the best effort class. We show that video quality can be improved through properly assigning packets to wireless access classes compared to the standard best effort scheme. Importantly, we show, based on our testbed results, that the single class assignment can achieve better performance than the multi-class assignment suggested by other researchers. Finally we show that virtual contention between traffic classes at the access point is an important issue to address.

A Hierarchical Unequal Packet Loss Protection Scheme for Robust H.264/AVC Transmission

In this paper, we are concerned with robust H.264/AVC video transmission over lossy packet networks and present a hierarchical unequal packet loss protection (HULP) scheme in a transmission system that efficiently combines erasure coding, H.264/AVC error resilience techniques and importance measures in video coding schemes. The importance of the video stream packets is distinguished by three criteria: the frame sequence number in a group of pictures (GOP), the per-frame bitrate and the H.264/AVC data partition type. Using a fixed amount of redundancy, more important packets of a video stream are protected with a more powerful erasure code than the less important packets. We demonstrate the effectiveness of this approach by system implementation and performance evaluation. In the presence of packet loss, we show that the received video quality, as measured by PSNR, is significantly improved when the HULP scheme is used. More importantly, in our experiments, HULP can achieve higher PSNR values and better user perceived quality, but requiring less redundancy, than equal loss protection (ELP) schemes.

On Construction of the

Two product array codes are used to construct the (24,12,8) binary Golay code through the direct sum operation. This construction provides a systematic way to find proper (8,4,4) linear block component codes for generating the Golay code, and it generates and extends previously existing methods that use a similar construction framework. The code constructed is simple to decode

(24, 12, 8)

There has been considerable research into the performance of the enhanced IEEE 802.11e standard in recent years. Majority of the performance analysis has been based on simulations and analytical models, with little testing done in a real-world environment. We investigate the behaviors of the Enhanced Distributed Channel Access (EDCA) and legacy Distributed Coordination Function (DCF) based on a testbed operating in a realistic working environment. Both TCP/UDP streams representing traffic types such as FTP and VoIP are tested. Quality of Service (QoS) metrics such as Throughput and Delay are calculated directly from a passive capture of the channel. These metrics can also be converted into physical layer requirements such as Signal to Noise ratio. EDCA and DCF are shown to have similar performances with single streams of traffic, which are contributed directly by the loss effect at the MAC layer.

Golay Codes

In this paper, a robust H.264/AVC video transmission system over lossy packet network is investigated and implemented. The H.264/AVC standard has defined a new data partition scheme which can be used to perform unequal loss protection (ULP) in video transmission systems. However, few actual implementation and experiments which integrate data partition and loss protection algorithms have been reported. Based on the H.264/AVC data partitioning mechanism, we implement three loss protection schemes using Reed-Solomon and XOR parity codes, namely equal loss protection (ELP), ULP and partition A protection only (PAP). The performance of each scheme is evaluated under different network environments. Experimental results and performance analysis show that ELP has higher peak signal-to-noise ratio (PSNR) values than ULP and PAP, but PAP requires the least redundancy and offers the best tradeoffs between PSNR values and redundancy among all the three schemes.