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【期刊论文】Integrated MMSE-FW-LA scheme for robust ASR at low SNRs
曹志刚, Tao Xu and Zhigang Cao
ELECTRONICS LETTERS 24th October 2002 Vol. 38 No.22,-0001,():
-1年11月30日
A novcl feature weight (FW) algorithm and an intcgratcd schemc cdled MMSE-FW-LA are proposed. The schcmc combines the minimum mean square error (MMSE)-based enhancemcnt, the FW algorithm and the log-add (LA) modcl compensation. Expcrimcntal cvaluations show that this schcmc can improve thc recognition performance significantly, cspecially at low SNRs.
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【期刊论文】Flexible Construction of Irregular Partitioned Permutation LDPC Codes With Low Error Floors
曹志刚, Jingyu Kang, Pingyi Fan, Member, IEEE, and Zhigang Cao, Senior Member
IEEE COMMUNICATIONS LETTERS, VOL. 9, NO.6, JUNE 2005,-0001,():
-1年11月30日
Irregular partitioned permutation (IPP) low-density parity-check (LDPC) codes have been recently introduced to facilitate hardware implementation of belief propagation (BP) decoders. In this letter, we present a new method to construct IPP LDPC codes with great flexibility in the selection of code parameters. Meanwhile, small stopping sets are avoided in the code construction, thus good error floor performance can be achieved.
Error floor,, low-density parity-check codes,, permutation matrix,, stopping set.,
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【期刊论文】Dynamic Spatial Subchannel Allocation With Adaptive Beamforming for MIMO/OFDM Systems
曹志刚, Ya-Han Pan, Khaled Ben Letaief, Fellow, IEEE, and Zhigang Cao, Senior Member
IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 3, NO.6, NOVEMBER 2004,-0001,():
-1年11月30日
Orthogonal frequency division multiplexing (OFDM) has been widely regarded as an effective modulation technique for mitigating the effects of intersymbol interference in a frequency selective fading channel and for providing reliable high-data-rate transmission over wireless links. Adaptive antenna arrays at the base and mobile stations can achieve further increases in system's capacity and bandwidth efficiency, as well as in quality-of-service improvement in conventional OFDM systems. The conventional adaptive antenna-arrays-based OFDM systems always use the subcarriers characterized by the largest eigenvalues to transmit the OFDM block symbols. In this paper and in contrast to previous work, we propose dynamic spatial subchannel allocation with adaptive beamforming for broadband OFDM wireless transmission systems. The proposed system adaptively selects the eigenvectors associated with the relatively large spatial subchannel eigenvalues to generate the beamforming weights at the mobile and base stations and then dynamically assigns the corresponding best spatial subchannels to transmit the OFDM block symbols. It is shown that the proposed system can achieve better performance than an adaptive antenna-arrays-based OFDM system without dynamic spatial subchannel allocation over multipath fading channels. Simulation results also reveal that the proposed system is far less susceptible to feedback delay in rapid time-varying channels and a little more sensitive to channel estimation errors than conventional adaptive antenna-arrays-based OFDM systems. The performance of the proposed system combined with adaptive modulation is also considered.
Adaptive antenna arrays,, adaptive modulation,, dynamic spatial subchannel allocation,, joint transmit and receive beamforming,, multiple-input multiple-output (, MIMO), ,, orthogonal frequency-division multiplexing (, OFDM), .,
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【期刊论文】Combining MMSE enhancement with LA model adaptation for robust automatic speech recognition
曹志刚, Pei Ding and Zhigang Cao
ELECTRONICS LETTERS 12th April 2001 Vol. 37 NO.8,-0001,():
-1年11月30日
A new scheme for robust automatic speech recognition is presented. The scheme combines minimum mean square error (MMSE)-based enhancement with Log-Add (LA) model adaptation. Experimental evaluations show that the proposed MMSE-LA scheme can achieve significant improvement in recognition across a wide range of signal-to-noise ratios, especially in very noisy environments.
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【期刊论文】Co-Channel Interference Cancellation for Space-Time Coded OFDM Systems
曹志刚, Junqiang Li, Khaled Ben Letaief, Fellow, IEEE, and Zhigang Cao, Senior Member
IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 2, NO.1, JANUARY,-0001,():
-1年11月30日
Space-time coded orthogonal frequency division multiplexing (OFDM) is a promising scheme for future wideband multimedia wireless communication systems. The combination of space-time coding (STC) and OFDM modulation promises an enhanced performance in terms of power and spectral efficiency. Such combination benefits from the diversity gain within the multiple-input-multiple-output ST coded system and the matured OFDM modulation for wideband wireless transmission. However, STC transmit diversity impairs the system's interference suppression ability due to the use of multiple transmitters at each mobile. In this paper, we propose an effective co-channel interference (CCI) cancellation method that employs angle diversity based on null-steering beamforming or minimum variance distortion response beamforming. It is shown that the proposed method can effectively mitigate CCI while preserving the space-time structure, thereby, significantly improving the system's interference suppression ability without significant bit-error rate performance degradation. Furthermore, it is demonstrated that the proposed method can significantly combat the delay spread detrimental effects over multipath fading channels without the use of interleaving.
Adaptive antenna arrays,, beamforming,, interference cancellation,, orthogonal frequency division multiplexing (, OFDM), ,, transmit diversity,, wireless data communications.,
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