Tung Kim - Academia.edu (original) (raw)

Papers by Tung Kim

2009 Conference Record of the Forty-Third Asilomar Conference on Signals, Systems and Computers, 2009

A multiple-antenna Gaussian wiretap channel in which the number of antennas at the source is not ... more A multiple-antenna Gaussian wiretap channel in which the number of antennas at the source is not larger than that at the eavesdropper is considered. Without feedback, the secrecy capacity over such a channel generally converges to a constant at high signal-to-noise ratio (SNR). A half-duplex secure protocol allowing the destination to actively broadcast random keys over insecure channels is proposed. It is shown that using multiple antennas at the destination is instrumental in achieving a secrecy rate that grows linearly with log SNR. The pre-log factor of the secrecy rate, i.e. the secure degree of freedom, is characterized, revealing an interesting interplay between the numbers of antennas at the three communication nodes.

Reliable communication over delay-constrained block-fading channels with discrete inputs and mism... more Reliable communication over delay-constrained block-fading channels with discrete inputs and mismatched (imperfect) channel state information at the transmitter (CSIT) is studied. The CSIT mismatch is modeled as Gaussian random variables, whose variances decay as a power of the signal-to-noise ratio (SNR). A special focus is placed on the large-SNR decay of the outage probability when power control with long-term power constraints is used. Without explicitly characterizing the corresponding power allocation algorithms, we derive the outage exponent as a function of the system parameters, including the CSIT noise variance exponent and the exponent of the peak power constraint. It is shown that CSIT, even if noisy, is always beneficial and leads to important gains in terms of exponents. It is also shown that when multidimensional rotations or precoders are used at the transmitter, further exponent gains can be attained, but at the expense of larger decoding complexity.

2007 IEEE Information Theory Workshop, 2007

The problem of optimal dimension and power allocation to maximize the asymptotic outage exponent ... more The problem of optimal dimension and power allocation to maximize the asymptotic outage exponent over a decodeand-forward fading relay channel with quantized channel state feedback (CSF) is studied. Three different scenarios are considered: relay-source, destination-relay, and destination-source feedback. It is found that even with just one bit of CSF from the relay to control the source power is sufficient to achieve the multiantenna upperbound in a range of multiplexing gain, with fixed-length codes, i.e., with coding schemes significantly simpler than "dynamic decode-and-forward." CSF from destination to control the relay power slightly outperforms dynamic decodeand-forward at high multiplexing gains. CSF from destination when the source-relay channel gain is unknown to the destination, achieves a diversity exponent equal to K times the diversity exponent of dynamic decode and forward, for any multiplexing gain. This linear growth of diversity with the number of feedback levels stands in sharp contrast to the exponential growth for multiantenna channels (fully cooperative transmitters).

2007 IEEE International Symposium on Information Theory, 2007

Abstract The problem of source-channel coding over a multiple-antenna channel with quantized chan... more Abstract The problem of source-channel coding over a multiple-antenna channel with quantized channel state information at the transmitter (CSIT) is considered. Upperbounds on the distortion exponents achieved with partial CSIT are developed. The achievable distortion exponent of some hybrid schemes with heavily quantized feedback under both short-and long-term power constraints is also derived. The results demonstrate that excellent performance can be achieved by combining simple schemes with a very coarse feedback ...

2009 43rd Annual Conference on Information Sciences and Systems, 2009

Resource allocation for half-duplex bidirectional relaying networks using partial channel state i... more Resource allocation for half-duplex bidirectional relaying networks using partial channel state information (CSI) at the transmitters is considered, with an emphasis on the diversity-multiplexing tradeoff (DMT). It is assumed that there is a direct link between the sources. It is shown that decode-and-forward (DF) two-way relaying does not suffer from a diversity loss when the multiplexing gain is high, a

2011 IEEE International Symposium on Information Theory Proceedings, 2011

The original compress-and-forward relaying scheme uses the technique of random binning at the rel... more The original compress-and-forward relaying scheme uses the technique of random binning at the relay node and successive decoding at the destination node. Recently, a scheme (termed the quantize-and-forward scheme in this paper) without binning and using joint decoding at the destination node has been proposed, which has been shown to achieve the same rate as the original compress-and-forward scheme. Since

2009 47th Annual Allerton Conference on Communication, Control, and Computing (Allerton), 2009

Secure communication over a half-duplex relay system in the presence of an external wiretapper is... more Secure communication over a half-duplex relay system in the presence of an external wiretapper is investigated. In such a scenario, conventional relaying protocols generally provide secrecy rates that converge to a finite constant in the high signal-to-noise ratio (SNR) regime. It is shown in this work that strictly superior performance can be achieved by allowing the destination to transfer random keys in the form of known interference to the relay insecurely over the wireless medium. When there is no direct link between the source and the destination, an amplify-and-forward (AF) protocol is shown to achieve a secrecy rate that scales as 1/2 log SNR, if each of the legitimate nodes has a single antenna only. However, in the presence of a direct link between source and destination, this scaling rule no longer applies. The bottleneck of the AF scheme in the presence of a direct source-destination link is identified, motivating the use of multiple antennas at the destination to almost surely guarantee a secure degree of freedom of one half over the channel. The results hold even if the eavesdropper has more antennas than the source and the relay combined.

GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009

The problem of bidirectionally transmitting two analog sources over a fading channel with the hel... more The problem of bidirectionally transmitting two analog sources over a fading channel with the help of a relay is studied. In the regime of high signal-to-noise ratios, upper and lower bounds on the exponent of the end-to-end expected distortion are derived. It is shown that simple two-way relaying protocols based on the separation of source and channel coding can provide

ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 2007

ABSTRACT

2009 IEEE International Symposium on Information Theory, 2009

Communication over delay-constrained block-fading channels with discrete inputs and imperfect cha... more Communication over delay-constrained block-fading channels with discrete inputs and imperfect channel state information at the transmitter (CSIT) is studied. The CSIT mismatch is modeled as a Gaussian random variable, whose variance decays as a power of the signal-to-noise ratio (SNR). We focus on the large-SNR behavior of the outage probability when transmit power control is used. We derive the outage exponent as a function of the system parameters, including the CSIT noise variance exponent and the exponent of the peak power constraint. It is shown that CSIT, even if noisy, is always beneficial and leads to significant gains in terms of exponents. It is also shown that when precoders are used at the transmitter, further exponent gains can be attained at the expense of higher decoding complexity.

2006 International Zurich Seminar on Communications

IEEE Signal Processing Magazine, 2012

ABSTRACT A smart grid improves the efficiency of power grids via the aid of modern communication,... more ABSTRACT A smart grid improves the efficiency of power grids via the aid of modern communication, signal processing, and control technologies. While smart grid integration enables power grid networks to be smarter, it also increases the risk of cyberattacks due to the strong dependence on the cyberinfrastructure in the overall system. In this article, the coordinated datainjection attack detection problem in the smart grid is considered. Specifically, the data-injection attack model is first introduced and a thorough survey of existing detection methods is then given. Afterward, three important efforts to enrich the detection solution are presented in detail: 1) attacker versus defender dynamics, where possible interactive attack and defense strategies are discussed in the context of secure phasor measurement unit (PMU) placement 2) distributed attack detection and state recovery, where the focus is how to achieve the optimal centralized performance with a distributed approach 3) quickest detection (QD), where the trade off between the detection speed and detection performance is studied. A list of associated key open problems in this area is then presented to conclude this article.

IEEE Transactions on Wireless Communications, 2008

A simple structure to exploit both long-term and partial short-term channel state information at ... more A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is combined with a unitary transformation based on the long-term channel statistics. The heavily quantized feedback link is directly optimized to maximize the expected achievable rate under different power constraints, using vector quantization and convex optimization techniques on a sample channel distribution. Robustness against errors in the feedback link is also pursued with tools in channel optimized vector quantization. Simulations indicate the benefits of the proposed scheme.

IEEE Transactions on Smart Grid, 2011

IEEE Transactions on Smart Grid, 2011

IEEE Transactions on Signal Processing, 2009

The problem of source-channel coding over a multiple-antenna (MIMO) channel with quantized channe... more The problem of source-channel coding over a multiple-antenna (MIMO) channel with quantized channel state information at the transmitter (CSIT) is considered. Upper bounds on the distortion exponents achieved with partial CSIT under a long-term power constraint are developed. It is shown that the distortion exponent with perfect CSIT grows unbounded as the ratio between the channel and source bandwidth increases, while the exponent achieved with any feedback link of fixed, finite resolution is bounded above by a polynomial of the product between the number of transmit and number of receive antennas. The resolution of the feedback link should grow with the bandwidth ratio to make the distortion exponent scale as fast as that in the perfect-CSIT case. We show that in order to achieve the optimal scaling the CSIT feedback resolution must grow logarithmically with the bandwidth ratio for MIMO channels, and faster than linear for the single-input single-output channel. The achievable distortion exponent of some hybrid schemes with heavily quantized feedback is also derived. The results demonstrate that dramatic performance improvement over the case of no CSIT can be achieved by combining simple schemes with a very coarse CSIT feedback.

IEEE Transactions on Information Theory, 2009

The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel... more The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel state information at the source transmitter (CSIT) is studied, with a focus on the asymptotically high signal-to-noise ratio (SNR) regime. A novel upper bound on the diversity-multiplexing tradeoff (DMT) is derived, taking into account the quality of the CSIT. It is shown that from a DMT perspective, the decode-and-forward (DF) protocol is strictly optimal over a certain range of the multiplexing gains. When the quality of the CSIT is sufficiently high, the DMT performance of the DF protocol with noisy CSIT equals that of the dynamic DF protocol shifted above by a constant diversity gain, which depends only on the quality of the CSIT about the source-destination link. When the quality of the CSIT reduces, DF relaying is still DMT-optimal, but only over a smaller range of the multiplexing gains. In an intermediate range of the multiplexing gains, nonorthogonal schemes provide some additional gains when the CSIT quality is sufficiently low. It is also shown that the DMT of the amplify-andforward (AF) protocol is offset by a constant term depending on the quality of the CSIT of the source-destination link only.

IEEE Transactions on Information Theory, 2009

The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel... more The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel state information at the source transmitter (CSIT) is studied, with a focus on the asymptotically high signal-to-noise ratio (SNR) regime. A novel upper bound on the diversity-multiplexing tradeoff (DMT) is derived, taking into account the quality of the CSIT. It is shown that from a DMT perspective, the decode-and-forward (DF) protocol is strictly optimal over a certain range of the multiplexing gains. When the quality of the CSIT is sufficiently high, the DMT performance of the DF protocol with noisy CSIT equals that of the dynamic DF protocol shifted above by a constant diversity gain, which depends only on the quality of the CSIT about the source-destination link. When the quality of the CSIT reduces, DF relaying is still DMT-optimal, but only over a smaller range of the multiplexing gains. In an intermediate range of the multiplexing gains, nonorthogonal schemes provide some additional gains when the CSIT quality is sufficiently low. It is also shown that the DMT of the amplify-andforward (AF) protocol is offset by a constant term depending on the quality of the CSIT of the source-destination link only.

IEEE Transactions on Information Theory, 2008

2009 Conference Record of the Forty-Third Asilomar Conference on Signals, Systems and Computers, 2009

A multiple-antenna Gaussian wiretap channel in which the number of antennas at the source is not ... more A multiple-antenna Gaussian wiretap channel in which the number of antennas at the source is not larger than that at the eavesdropper is considered. Without feedback, the secrecy capacity over such a channel generally converges to a constant at high signal-to-noise ratio (SNR). A half-duplex secure protocol allowing the destination to actively broadcast random keys over insecure channels is proposed. It is shown that using multiple antennas at the destination is instrumental in achieving a secrecy rate that grows linearly with log SNR. The pre-log factor of the secrecy rate, i.e. the secure degree of freedom, is characterized, revealing an interesting interplay between the numbers of antennas at the three communication nodes.

Reliable communication over delay-constrained block-fading channels with discrete inputs and mism... more Reliable communication over delay-constrained block-fading channels with discrete inputs and mismatched (imperfect) channel state information at the transmitter (CSIT) is studied. The CSIT mismatch is modeled as Gaussian random variables, whose variances decay as a power of the signal-to-noise ratio (SNR). A special focus is placed on the large-SNR decay of the outage probability when power control with long-term power constraints is used. Without explicitly characterizing the corresponding power allocation algorithms, we derive the outage exponent as a function of the system parameters, including the CSIT noise variance exponent and the exponent of the peak power constraint. It is shown that CSIT, even if noisy, is always beneficial and leads to important gains in terms of exponents. It is also shown that when multidimensional rotations or precoders are used at the transmitter, further exponent gains can be attained, but at the expense of larger decoding complexity.

2007 IEEE Information Theory Workshop, 2007

The problem of optimal dimension and power allocation to maximize the asymptotic outage exponent ... more The problem of optimal dimension and power allocation to maximize the asymptotic outage exponent over a decodeand-forward fading relay channel with quantized channel state feedback (CSF) is studied. Three different scenarios are considered: relay-source, destination-relay, and destination-source feedback. It is found that even with just one bit of CSF from the relay to control the source power is sufficient to achieve the multiantenna upperbound in a range of multiplexing gain, with fixed-length codes, i.e., with coding schemes significantly simpler than "dynamic decode-and-forward." CSF from destination to control the relay power slightly outperforms dynamic decodeand-forward at high multiplexing gains. CSF from destination when the source-relay channel gain is unknown to the destination, achieves a diversity exponent equal to K times the diversity exponent of dynamic decode and forward, for any multiplexing gain. This linear growth of diversity with the number of feedback levels stands in sharp contrast to the exponential growth for multiantenna channels (fully cooperative transmitters).

2007 IEEE International Symposium on Information Theory, 2007

Abstract The problem of source-channel coding over a multiple-antenna channel with quantized chan... more Abstract The problem of source-channel coding over a multiple-antenna channel with quantized channel state information at the transmitter (CSIT) is considered. Upperbounds on the distortion exponents achieved with partial CSIT are developed. The achievable distortion exponent of some hybrid schemes with heavily quantized feedback under both short-and long-term power constraints is also derived. The results demonstrate that excellent performance can be achieved by combining simple schemes with a very coarse feedback ...

2009 43rd Annual Conference on Information Sciences and Systems, 2009

Resource allocation for half-duplex bidirectional relaying networks using partial channel state i... more Resource allocation for half-duplex bidirectional relaying networks using partial channel state information (CSI) at the transmitters is considered, with an emphasis on the diversity-multiplexing tradeoff (DMT). It is assumed that there is a direct link between the sources. It is shown that decode-and-forward (DF) two-way relaying does not suffer from a diversity loss when the multiplexing gain is high, a

2011 IEEE International Symposium on Information Theory Proceedings, 2011

The original compress-and-forward relaying scheme uses the technique of random binning at the rel... more The original compress-and-forward relaying scheme uses the technique of random binning at the relay node and successive decoding at the destination node. Recently, a scheme (termed the quantize-and-forward scheme in this paper) without binning and using joint decoding at the destination node has been proposed, which has been shown to achieve the same rate as the original compress-and-forward scheme. Since

2009 47th Annual Allerton Conference on Communication, Control, and Computing (Allerton), 2009

Secure communication over a half-duplex relay system in the presence of an external wiretapper is... more Secure communication over a half-duplex relay system in the presence of an external wiretapper is investigated. In such a scenario, conventional relaying protocols generally provide secrecy rates that converge to a finite constant in the high signal-to-noise ratio (SNR) regime. It is shown in this work that strictly superior performance can be achieved by allowing the destination to transfer random keys in the form of known interference to the relay insecurely over the wireless medium. When there is no direct link between the source and the destination, an amplify-and-forward (AF) protocol is shown to achieve a secrecy rate that scales as 1/2 log SNR, if each of the legitimate nodes has a single antenna only. However, in the presence of a direct link between source and destination, this scaling rule no longer applies. The bottleneck of the AF scheme in the presence of a direct source-destination link is identified, motivating the use of multiple antennas at the destination to almost surely guarantee a secure degree of freedom of one half over the channel. The results hold even if the eavesdropper has more antennas than the source and the relay combined.

GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009

The problem of bidirectionally transmitting two analog sources over a fading channel with the hel... more The problem of bidirectionally transmitting two analog sources over a fading channel with the help of a relay is studied. In the regime of high signal-to-noise ratios, upper and lower bounds on the exponent of the end-to-end expected distortion are derived. It is shown that simple two-way relaying protocols based on the separation of source and channel coding can provide

ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 2007

ABSTRACT

2009 IEEE International Symposium on Information Theory, 2009

Communication over delay-constrained block-fading channels with discrete inputs and imperfect cha... more Communication over delay-constrained block-fading channels with discrete inputs and imperfect channel state information at the transmitter (CSIT) is studied. The CSIT mismatch is modeled as a Gaussian random variable, whose variance decays as a power of the signal-to-noise ratio (SNR). We focus on the large-SNR behavior of the outage probability when transmit power control is used. We derive the outage exponent as a function of the system parameters, including the CSIT noise variance exponent and the exponent of the peak power constraint. It is shown that CSIT, even if noisy, is always beneficial and leads to significant gains in terms of exponents. It is also shown that when precoders are used at the transmitter, further exponent gains can be attained at the expense of higher decoding complexity.

2006 International Zurich Seminar on Communications

IEEE Signal Processing Magazine, 2012

ABSTRACT A smart grid improves the efficiency of power grids via the aid of modern communication,... more ABSTRACT A smart grid improves the efficiency of power grids via the aid of modern communication, signal processing, and control technologies. While smart grid integration enables power grid networks to be smarter, it also increases the risk of cyberattacks due to the strong dependence on the cyberinfrastructure in the overall system. In this article, the coordinated datainjection attack detection problem in the smart grid is considered. Specifically, the data-injection attack model is first introduced and a thorough survey of existing detection methods is then given. Afterward, three important efforts to enrich the detection solution are presented in detail: 1) attacker versus defender dynamics, where possible interactive attack and defense strategies are discussed in the context of secure phasor measurement unit (PMU) placement 2) distributed attack detection and state recovery, where the focus is how to achieve the optimal centralized performance with a distributed approach 3) quickest detection (QD), where the trade off between the detection speed and detection performance is studied. A list of associated key open problems in this area is then presented to conclude this article.

IEEE Transactions on Wireless Communications, 2008

A simple structure to exploit both long-term and partial short-term channel state information at ... more A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is combined with a unitary transformation based on the long-term channel statistics. The heavily quantized feedback link is directly optimized to maximize the expected achievable rate under different power constraints, using vector quantization and convex optimization techniques on a sample channel distribution. Robustness against errors in the feedback link is also pursued with tools in channel optimized vector quantization. Simulations indicate the benefits of the proposed scheme.

IEEE Transactions on Smart Grid, 2011

IEEE Transactions on Smart Grid, 2011

IEEE Transactions on Signal Processing, 2009

The problem of source-channel coding over a multiple-antenna (MIMO) channel with quantized channe... more The problem of source-channel coding over a multiple-antenna (MIMO) channel with quantized channel state information at the transmitter (CSIT) is considered. Upper bounds on the distortion exponents achieved with partial CSIT under a long-term power constraint are developed. It is shown that the distortion exponent with perfect CSIT grows unbounded as the ratio between the channel and source bandwidth increases, while the exponent achieved with any feedback link of fixed, finite resolution is bounded above by a polynomial of the product between the number of transmit and number of receive antennas. The resolution of the feedback link should grow with the bandwidth ratio to make the distortion exponent scale as fast as that in the perfect-CSIT case. We show that in order to achieve the optimal scaling the CSIT feedback resolution must grow logarithmically with the bandwidth ratio for MIMO channels, and faster than linear for the single-input single-output channel. The achievable distortion exponent of some hybrid schemes with heavily quantized feedback is also derived. The results demonstrate that dramatic performance improvement over the case of no CSIT can be achieved by combining simple schemes with a very coarse CSIT feedback.

IEEE Transactions on Information Theory, 2009

The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel... more The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel state information at the source transmitter (CSIT) is studied, with a focus on the asymptotically high signal-to-noise ratio (SNR) regime. A novel upper bound on the diversity-multiplexing tradeoff (DMT) is derived, taking into account the quality of the CSIT. It is shown that from a DMT perspective, the decode-and-forward (DF) protocol is strictly optimal over a certain range of the multiplexing gains. When the quality of the CSIT is sufficiently high, the DMT performance of the DF protocol with noisy CSIT equals that of the dynamic DF protocol shifted above by a constant diversity gain, which depends only on the quality of the CSIT about the source-destination link. When the quality of the CSIT reduces, DF relaying is still DMT-optimal, but only over a smaller range of the multiplexing gains. In an intermediate range of the multiplexing gains, nonorthogonal schemes provide some additional gains when the CSIT quality is sufficiently low. It is also shown that the DMT of the amplify-andforward (AF) protocol is offset by a constant term depending on the quality of the CSIT of the source-destination link only.

IEEE Transactions on Information Theory, 2009

The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel... more The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel state information at the source transmitter (CSIT) is studied, with a focus on the asymptotically high signal-to-noise ratio (SNR) regime. A novel upper bound on the diversity-multiplexing tradeoff (DMT) is derived, taking into account the quality of the CSIT. It is shown that from a DMT perspective, the decode-and-forward (DF) protocol is strictly optimal over a certain range of the multiplexing gains. When the quality of the CSIT is sufficiently high, the DMT performance of the DF protocol with noisy CSIT equals that of the dynamic DF protocol shifted above by a constant diversity gain, which depends only on the quality of the CSIT about the source-destination link. When the quality of the CSIT reduces, DF relaying is still DMT-optimal, but only over a smaller range of the multiplexing gains. In an intermediate range of the multiplexing gains, nonorthogonal schemes provide some additional gains when the CSIT quality is sufficiently low. It is also shown that the DMT of the amplify-andforward (AF) protocol is offset by a constant term depending on the quality of the CSIT of the source-destination link only.

IEEE Transactions on Information Theory, 2008