2007 Conference Record of the Forty-First Asilomar Conference on Signals, Systems and Computers, 2007
This paper focuses on noncoherent coding design for fast fading channels, where the receiver does... more This paper focuses on noncoherent coding design for fast fading channels, where the receiver does not have reliable channel state information. Unitary space-time codes and training based schemes have been proposed historically. We propose a data-dependent superimposed training scheme to improve the performance of training based codes. The transmitter is equipped with multiple training sequences and dynamically selects a training sequence for each data sequence to minimize channel estimation error. The set of training sequences are optimized to minimize pairwise error probability between codewords.
2002 IEEE International Conference on Communications. Conference Proceedings. ICC 2002 (Cat. No.02CH37333)
Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer... more Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer (DFE) for the downlink receiver of wideband code-division multiple-access (CDMA) systems using long scrambling code over frequency-selective channels. The DFE uses the tentative decision of the current symbol as feedback. The proposed DFE performs better than the chip-level linear equalizers (LE) and the DFE that feeds back only the symbols already decided. The performance gain increases with signal-to-noise ratio ( ...
This paper describes a feedback algorithm for tracking the dominant subspaces of continuously tim... more This paper describes a feedback algorithm for tracking the dominant subspaces of continuously time-varying channels in multiantenna communication systems. The nature of the problem is quantization of subspaces. It is well known that subspaces can be mathematically modeled as points in a Grassmann manifold. We model the variations between the dominant subspaces of channels at adjacent time instants to be along geodesics in the Grassmann manifold. Instead of quantizing the subspaces themselves, we propose to quantize the geodesic trajectory connecting two subspaces. More specifically, we quantize a key entity that characterizes a geodesic arc: the velocity matrix, which resembles angular speed in a one-dimensional complex space. Two techniques are proposed for quantizing the velocity matrix of the geodesic. In the first, a 1-bit feedback is utilized to indicate the preferred sign of a random velocity matrix of the geodesic. In the other, the velocity matrix is quantized using a Gaussian vector quantization codebook. Numerical results show that the performance of the proposed 1-bit feedback algorithm is better than a previously proposed Grassmannian subspace packing scheme at low-to-medium Doppler frequencies and better than a gradient sign feedback scheme at all Doppler frequencies. In our simulations, the Gaussian vector quantization algorithm is always better than the 1-bit feedback algorithm.
IEEE Transactions on Wireless Communications, 2005
Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer... more Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer (DFE) for the downlink receiver of multicode wideband code-division multiple-access systems over frequency-selective channels. First, the MMSE per symbol achievable by an optimal DFE is derived, assuming that all interchip interference (ICI) of the desired user can be eliminated. The MMSE of DFE is always less than or at most equal to that of linear equalizers (LE). When all the active codes belong to the desired user, the ...
Proceedings. (ICASSP '05). IEEE International Conference on Acoustics, Speech, and Signal Processing, 2005.
The paper describes a low rate feedback algorithm for conveying partial channel state information... more The paper describes a low rate feedback algorithm for conveying partial channel state information - specifically, the dominant row subspace of the channel matrix - from the receiver to the transmitter in a continuously time-varying multiple-antenna environment. Since subspaces are points on a complex Grassmann manifold, variations in subspaces are treated as a piecewise geodesic process on the manifold. The
GLOBECOM '03. IEEE Global Telecommunications Conference (IEEE Cat. No.03CH37489), 2003
Abstract Orthogonal frequency division multiplexing (OFDM) is known for its efficiency in combati... more Abstract Orthogonal frequency division multiplexing (OFDM) is known for its efficiency in combating frequency selectivity in wireless channels. Multiple transmit and/or multiple receive (MIMO) antennas can be employed with OFDM to achieve higher diversity or capacity. In traditional OFDM MIMO systems, transmitter beamforming and receiver combining are done in the frequency domain, which requires one discrete Fourier transform (DFT) per antenna. As recently proposed, transmitter beam-forming and receiver ...
This dissertation is dedicated to my wife Jijie for her patience, love, encouragement, and suppor... more This dissertation is dedicated to my wife Jijie for her patience, love, encouragement, and support. iii ACKNOWLEDGEMENTS I would like to thank my advisor, Prof. Douglas B. Williams for being a fantastic advisor. Prof. Williams always has great suggestions about research. I have always been greatly inspired by his research style, intellectual aspects, and insights. He has also been a good mentor concerning other aspects of life. I have really enjoyed discussing my future with him. I would like to thank my great group-mates, Soner¨Ozgür and Nicolas Gastaud. I wish to show my gratitude to Qing Zhao, who is one of my closest friends. I truly enjoyed every conversation I had with him about research and the future. In addition, inspiring talks with name a few, have always been rewarding. Finally, I would like to express my deepest gratitude to my family.
2007 Conference Record of the Forty-First Asilomar Conference on Signals, Systems and Computers, 2007
This paper focuses on noncoherent coding design for fast fading channels, where the receiver does... more This paper focuses on noncoherent coding design for fast fading channels, where the receiver does not have reliable channel state information. Unitary space-time codes and training based schemes have been proposed historically. We propose a data-dependent superimposed training scheme to improve the performance of training based codes. The transmitter is equipped with multiple training sequences and dynamically selects a training sequence for each data sequence to minimize channel estimation error. The set of training sequences are optimized to minimize pairwise error probability between codewords.
2002 IEEE International Conference on Communications. Conference Proceedings. ICC 2002 (Cat. No.02CH37333)
Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer... more Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer (DFE) for the downlink receiver of wideband code-division multiple-access (CDMA) systems using long scrambling code over frequency-selective channels. The DFE uses the tentative decision of the current symbol as feedback. The proposed DFE performs better than the chip-level linear equalizers (LE) and the DFE that feeds back only the symbols already decided. The performance gain increases with signal-to-noise ratio ( ...
This paper describes a feedback algorithm for tracking the dominant subspaces of continuously tim... more This paper describes a feedback algorithm for tracking the dominant subspaces of continuously time-varying channels in multiantenna communication systems. The nature of the problem is quantization of subspaces. It is well known that subspaces can be mathematically modeled as points in a Grassmann manifold. We model the variations between the dominant subspaces of channels at adjacent time instants to be along geodesics in the Grassmann manifold. Instead of quantizing the subspaces themselves, we propose to quantize the geodesic trajectory connecting two subspaces. More specifically, we quantize a key entity that characterizes a geodesic arc: the velocity matrix, which resembles angular speed in a one-dimensional complex space. Two techniques are proposed for quantizing the velocity matrix of the geodesic. In the first, a 1-bit feedback is utilized to indicate the preferred sign of a random velocity matrix of the geodesic. In the other, the velocity matrix is quantized using a Gaussian vector quantization codebook. Numerical results show that the performance of the proposed 1-bit feedback algorithm is better than a previously proposed Grassmannian subspace packing scheme at low-to-medium Doppler frequencies and better than a gradient sign feedback scheme at all Doppler frequencies. In our simulations, the Gaussian vector quantization algorithm is always better than the 1-bit feedback algorithm.
IEEE Transactions on Wireless Communications, 2005
Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer... more Abstract We investigate a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer (DFE) for the downlink receiver of multicode wideband code-division multiple-access systems over frequency-selective channels. First, the MMSE per symbol achievable by an optimal DFE is derived, assuming that all interchip interference (ICI) of the desired user can be eliminated. The MMSE of DFE is always less than or at most equal to that of linear equalizers (LE). When all the active codes belong to the desired user, the ...
Proceedings. (ICASSP '05). IEEE International Conference on Acoustics, Speech, and Signal Processing, 2005.
The paper describes a low rate feedback algorithm for conveying partial channel state information... more The paper describes a low rate feedback algorithm for conveying partial channel state information - specifically, the dominant row subspace of the channel matrix - from the receiver to the transmitter in a continuously time-varying multiple-antenna environment. Since subspaces are points on a complex Grassmann manifold, variations in subspaces are treated as a piecewise geodesic process on the manifold. The
GLOBECOM '03. IEEE Global Telecommunications Conference (IEEE Cat. No.03CH37489), 2003
Abstract Orthogonal frequency division multiplexing (OFDM) is known for its efficiency in combati... more Abstract Orthogonal frequency division multiplexing (OFDM) is known for its efficiency in combating frequency selectivity in wireless channels. Multiple transmit and/or multiple receive (MIMO) antennas can be employed with OFDM to achieve higher diversity or capacity. In traditional OFDM MIMO systems, transmitter beamforming and receiver combining are done in the frequency domain, which requires one discrete Fourier transform (DFT) per antenna. As recently proposed, transmitter beam-forming and receiver ...
This dissertation is dedicated to my wife Jijie for her patience, love, encouragement, and suppor... more This dissertation is dedicated to my wife Jijie for her patience, love, encouragement, and support. iii ACKNOWLEDGEMENTS I would like to thank my advisor, Prof. Douglas B. Williams for being a fantastic advisor. Prof. Williams always has great suggestions about research. I have always been greatly inspired by his research style, intellectual aspects, and insights. He has also been a good mentor concerning other aspects of life. I have really enjoyed discussing my future with him. I would like to thank my great group-mates, Soner¨Ozgür and Nicolas Gastaud. I wish to show my gratitude to Qing Zhao, who is one of my closest friends. I truly enjoyed every conversation I had with him about research and the future. In addition, inspiring talks with name a few, have always been rewarding. Finally, I would like to express my deepest gratitude to my family.
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Papers by Jingnong Yang