Cao Zhigang

TP-Satellite: A New Transport Protocol for Satellite IP Networks

As a result of the exponential growth of the worldwide Internet, satellite systems are used to support broadband Internet access. Existing TCP protocols perform very well for Internet access on wired networks. However, in the case of satellite channels, due to the effects of high bandwidth asymmetry, long propagation delay, high sporadic bit error rate (BER) and burst errors, TCP performance degrades significantly. In this paper, a new end-to-end transport protocol, TP-Satellite, is proposed for satellite IP networks. TP-Satellite replaces the traditional slow start algorithm with a novel super start algorithm. In order to distinguish congestion events from link errors, a new scheme is introduced, which is based on alternate transmission of different class priority packets. Bandwidth asymmetry problems are addressed by the adoption of a modified negative acknowledgement (M-NACK) strategy, which periodically sends M-NACK packets. Simulation results show that TP-Satellite enhances the throughput performance on the forward path, reduces the bandwidth used in the reverse path, and offers a fair share of network resources.

Carrier Frequency Offset estimation for interleaved OFDMA uplink based on subspace processing

This paper investigates Carrier Frequency Offset (CFO) estimation in the uplink of the Orthogonal Frequency-Division Multiple Access (OFDMA) systems with the interleaved subcarrier assignment. CFOs between the transmitters and the uplink receiver will destroy orthogonality among different subcarriers, hence resulting in inter-carrier interference and multiuser interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. Compared with the previously known methods, it not only has a relatively low implementation complexity but is also suitable for random subchannel assignment.

Robust recognition of noisy speech using speech enhancement

In this paper, a robust speech recognition system in the presence of additive background noise is studied. We adopt speech enhancement as the front-end processing module to improve the signal-to-noise ratio (SNR) of the input noisy speech for recognition in the latter stage. Three different speech enhancement algorithms were tested on six types of additive noises. Experimental results show that the cascading of the speech enhancer and a hidden Markov model (HMM) based speech recognizer can significantly improve recognition accuracy in noisy environments.

A Convergence Scheme for Digital Video/Audio Broadcasting Network and Broadband Wireless Access Network

This paper introduces a convergence scheme for digital video/audio broadcasting (BCT) network and broadband wireless access (BWA) network. This convergence scheme supports the architecture based on both PMP topology and mesh topology. It works in the mode of time division with full spectrum multiplexing. Its frame length, BCT time-slot length and BWA time-slot length are adaptive to the arrival traffic and the whole network performance. Then the transmission and the process delay of the token and the performance of the network were analyzed. The main method used is based on M/G/l queue with vacation and time-limited service. The generating function and the mean values for the traffic load distribution in BCT BS and BWA BSs were given. Then it was simulated on the self-similar traffic background and compare with the fixed time-slot allocation scheme. This scheme can reduce the Hurst parameter in some extent.

A wavelet filter optimization algorithm for speech recognition

A wavelet filter optimization algorithm is proposed. The proposed algorithm is based on wavelet matrix parameterization, through which wavelet filters can be factorized to a smaller set of parameters. Based on the cross validation cost function defined in this paper, Monte Carlo simulation is used to search the optimal wavelet filters for speech recognition. Using this wavelet filter optimization algorithm, we can obtain optimal wavelet filters for an isolated word recognition system. Also in this paper, mel wavelet cepstral coefficients, the speech feature generated by the optimized symmetrical shift-invariant wavelet, is described. Simulation results show that the continuous density HMM based isolated word recognition system can be optimized to achieve a recognition rate of 100% for 10 digits.

Dynamic Source Routing algorithm in low-earth orbit Satellite Constellation

In recent years, several IP-based algorithms have been developed for low-earth orbit (LEO) satellite networks. In this work, a new dynamic source routing algorithm in satellite constellation based on flood routing is developed. This source routing algorithm consists of such main mechanisms as route discovery, route maintenance, route cache and earth station agency, capable of processing routing tasks on-board and reducing the size of on-board memory by the cooperation of satellite nodes and earth station agencies. The performance of the DSRSC routing algorithm is evaluated through a simple Globalstar-like LEO satellite constellation network model. With the analysis and evaluation of performance, our new routing algorithm is suitable to be used in LEO satellite constellation network.

Fast identification of digital amplitude modulation level at low signal-to-noise ratio

In order to rapidly and automatically identify the modulation level of digital amplitude modulated signals at low signal-to-noise ratio (SNR), a method of identifying the modulation levels of M-ary quadrature amplitude modulation (M-QAM) and M-ary amplitude shift keying (M-ASK) is proposed. In this method, wavelet transform with the optimal scale is used to identify the modulation levels of M-QAM and M-ASK signals. The performance of this method was investigated through simulations. Simulation results show that when the SNR is not lower than −4 dB, the percentage of correct identification of M-QAM is higher than 93 %, and when the SNR is not lower than −10 dB, the percentage of correct identification of M-ASK is higher than 90 %, using only 100 observed symbols. It shows that this method can rapidly acquire good performance at a low SNR.

Compensation of nonlinear distortion using a new method combining predistortion with reconstruction in OFDM systems

This paper presents a new method of nonlinear distortion compensation for OFDM systems. The proposed scheme compensates for the performance degradation due to the nonlinear distortion by using the combination of predistortion and reconstruction. The computer simulation results show that the proposed scheme can compensate for degradation due to the nonlinear distortion significantly. Furthermore, since the proposed scheme utilizes the iterative method, its implementation is relatively simple.

A novel carrier recovery method for CPFSK demodulation

Continuous phase frequency shift keying (CPFSK) is a power and bandwidth efficient modulation. This paper proposes a novel method for carrier recovery in CPFSK demodulation. Its complexity is very low, and it is also easy to implement, especially for software implementation. The proposed method has an excellent bit error rate performance.

Cross-layer designed effective bandwidth estimation for broadband multimedia satellite networks with adaptive forward error control

Two effective bandwidth estimation methods for broadband multimedia satellite networks with adaptive forward error control (AFEC) were proposed in the paper. Effects of the dynamic code rate of AFEC would be taken into account in estimating the effective bandwidth. First, a fluid approximation method is applied to estimate the effective bandwidth values for general time-varying satellite channels and satellite communication network with multiple-code-rate AFEC. But the requirements of the method are strict and its computing complexity is high for practical purposes. Based on this method, the authors propose a second estimation method by using a modification factor. The numerical results show the second method is simple, effective and widely applicable.