Shengli Fu

Closed-form designs of complex orthogonal space-time block codes of rates (k+1)/(2k) for 2k-1 or 2k transmit antennas

This paper presents a closed form designs of complex orthogonal space-time block codes of rates (k + I)/(2k) for 2k-1 or 2k transmit antennas

On capacity of random wireless networks with physical-layer network coding

Throughput capacity of a random wireless network has been studied extensively in the literature. Most existing studies were based on the assumption that each transmission involves only one transmitter in order to avoid interference. However, recent studies on physical-layer network coding (PLNC) have shown that such an assumption can be relaxed to improve throughput performance of a wireless network. In PLNC, signals from different senders can be transmitted to the same receiver in the same channel simultaneously. In this paper, we investigate the impact of PLNC on throughput capacity of a random wireless network. Our study reveals that, although PLNC scheme does not change the scaling law, it can improve throughput capacity by a fixed factor. Specifically, for a one-dimensional network, we observe that PLNC can eliminate the effect of interference in some scenarios. A tighter capacity bound is derived for a two-dimensional network. In addition, we also show achievable lower bounds for random wireless networks with network coding and PLNC.

WiMAX networks: from access to service platform

Recently, WiMAX has been proposed as an attractive wireless communication technology for providing broadband access for metropolitan areas. Despite its salient features from the technical perspective, the success of the WiMAX network depends on its capability of providing cost-effective solutions for a variety of existing and potential services. To address this issue, we advocate the design of a new network layer that can support multihop communications efficiently in WiMAX networks and that can fully exploit the features of the WiMAX standards. In particular, we first identify services that are important for broadband wireless network providers and investigate the requirements for different services. We then discuss now to design WiMAX networks by considering issues of efficiency, security, and reliability. The key observation is that WiMAX can be properly complemented by advanced connection management and network coding techniques.

Cooperative Network Coding for Wireless Ad-Hoc Networks

In wireless ad-hoc networks, a major challenge is how to provide robust and efficient communication. To achieve this goal, cooperative communication and network coding have been proven to be effective. In the literature, most existing studies focus on the performance of the two schemes separately. In our study, we will investigate the performance of system that combines them tightly together. In particular, we will propose a unified two-way traffic model that can characterize the features of both of them. Based on this model, we develop a new cooperative network coding scheme to further improve the system throughput. Both decode-and-forward and amplify-and-forward techniques are discussed for the two-way traffic model. Numerical results show that the new scheme can significantly improve the performance over traditional schemes.

Audio/visual mapping with cross-modal hidden Markov models

The audio/visual mapping problem of speech-driven facial animation has intrigued researchers for years. Recent research efforts have demonstrated that hidden Markov model (HMM) techniques, which have been applied successfully to the problem of speech recognition, could achieve a similar level of success in audio/visual mapping problems. A number of HMM-based methods have been proposed and shown to be effective by the respective designers, but it is yet unclear how these techniques compare to each other on a common test bed. In this paper, we quantitatively compare three recently proposed cross-modal HMM methods, namely the remapping HMM (R-HMM), the least-mean-squared HMM (LMS-HMM), and HMM inversion (HMMI). The objective of our comparison is not only to highlight the merits and demerits of different mapping designs, but also to study the optimality of the acoustic representation and HMM structure for the purpose of speech-driven facial animation. This paper presents a brief overview of these models, followed by an analysis of their mapping capabilities on a synthetic dataset. An empirical comparison on an experimental audio-visual dataset consisting of 75 TIMIT sentences is finally presented. Our results show that HMMI provides the best performance, both on synthetic and experimental audio-visual data.

Integration of wireless sensor networks in environmental monitoring cyber infrastructure

Wireless sensor networks (WSNs) have great potential to revolutionize many science and engineering domains. We present a novel environmental monitoring system with a focus on overall system architecture for seamless integration of wired and wireless sensors for long-term, remote, and near-real-time monitoring. We also present a unified framework for sensor data collection, management, visualization, dissemination, and exchange, conforming to the new Sensor Web Enablement standard. Some initial field testing results are also presented. The monitoring system is being integrated into the Texas Environmental Observatory infrastructure for long-term operation. As part of the integrated system, a new WSN-based soil moisture monitoring system is developed and deployed to support hydrologic monitoring and modeling research. This work represents a significant contribution to the empirical study of the emerging WSN technology. We address many practical issues in real-world application scenarios that are often neglected in the existing WSN research.

SER Performance Analysis for Physical Layer Network Coding over AWGN Channels

While original network coding is proposed over the data link layer, recent work suggests that it can also be implemented on the physical layer. In fact it is more natural for wireless networks because of its omnidirectional transmission. In this paper, we investigate the symbol-error-rate (SER) for binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK), but the approaches can be generalized to other constellation schemes. The closed-form SER results are derived for physical layer network coding over AWGN channels. The theoretical analysis is also validated by numerical simulation.

Channel Coding Design to Support Asynchronous Physical Layer Network Coding

In this paper, we discuss the channel coding design to support the two-phase Physical-Layer Network Coding (PLNC) under a typical three-node network coding scenario. We prove, even two source nodes could use different channel codes, the error correction capability at the relay node is bounded by that of the weaker one, i.e. the code with a smaller minimum distance. Therefore, we propose to use the same channel code at two source nodes, which can also provide potential to simplify the joint PLNC-channel decoding procedure (PLNC-DEC) at the relay node. Moreover, we propose a channel coding scheme based on linear convolutional codes to relax the strict synchronization requirement, which is difficult to achieve in some real applications. The proposed coding scheme is robust to the synchronization error between two source nodes and enables the relay node to perform the PLNC-DEC with only one Viterbi decoding procedure. Compared to the three-phase network coding scheme, the proposed scheme reduces the decoding/demodulation complexity of the relay node almost by half and achieves significant throughput gain.

Cooperative wireless networks based on physical layer network coding

Designing a wireless network is always challenging because of the harsh environment of wireless channels. While significant progress has been made over the last decade, most of the techniques were developed and optimized based on the point-to-point communication model. Recently, the cooperative communication model has attracted a lot of attention due to the fact that it may achieve significantly better performance than the traditional wireless network models. In this article we develop a generic wireless network design framework based on physical layer network coding as a novel cooperation technique. In this framework several transmitters in a cooperative network may transmit signals simultaneously to the same receiver to improve overall performance. The topics addressed in this article include network capacity, modulation, channel coding, and security issues from a viewpoint fundamentally different from the traditional communication models.

On the performance of two-way relay channels using space–time codes

In this paper, we explore the advantages of network coding and space–time coding in improving the performance of two-way-relayed communications where two terminals absent of direct links exchange information through a single relay in between. Network coding allows embracing the interference from other terminals thereby turning it into a capacity boost. The application of space–time codes yields higher capacity by exploiting the spatial diversity. The joint performance of both techniques is studied in this paper. Specifically, we consider the class of decode-and-forward (DF) relaying strategy, evaluated in terms of symbol error rate using BPSK and QPSK modulations by both theoretical analysis and simulation. Based on our results, DF outperforms the amplify-and-decode and partial-decode-and-forward protocols. Copyright