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Chengshan Xiao

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Shihezi Medical University ,China

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Papers by Chengshan Xiao

Further Results on Frequency-Domain Channel Equalization for Single Carrier Underwater Acoustic Communications

OCEANS 2008 - MTS/IEEE Kobe Techno-Ocean, 2008

A frequency-domain channel equalization and phase correction method was proposed in a previous wo... more A frequency-domain channel equalization and phase correction method was proposed in a previous work published in Oceans'07 conference, in which 10 −4 BER performance was presented for fixed-to-fixed source/receiver channels. The method is improved by using minimum mean square error (MMSE) estimation in channel updates rather than least squares estimation. It is applied to moving-to-fixed channels in the AUVFest'07 ocean experiment where single-carrier wideband transmission was employed with quadrature phase shift keying modulation. The moving source channels exhibit higher Doppler shift and larger Doppler drift than the fixed-to-fixed channels. Therefore, the number of symbols required for initial phase estimation is increased from 2 to 8 symbols when the groupwise phase correction algorithm is applied to the moving sources. Thirty-six packets with data block length of 512 symbols have been processed and 34 of them achieved an uncoded Bit Error Rate (BER) lower than 10 −2. The overall uncoded BER performance of all 36 packets is 1.81 × 10 −3 which is slightly higher than that of the fixed-to-fixed channels.

Statistical simulation models for Rayleigh and Rician fading

IEEE International Conference on Communications, 2003. ICC '03.

New simulation models are proposed for Rayleigh and Rician fading channels. First, the statistica... more New simulation models are proposed for Rayleigh and Rician fading channels. First, the statistical properties of Clarke's fading model with a finite number of sinusoids are analyzed. An improved Clarke's model is then proposed for the simulation of Rayleigh fading channels. Based on this improved Rayleigh fading model, a novel simulation model is proposed for Rician fading channels. The new Rician fading model employs a zero-mean stochastic sinusoid as the specular (line-of-sight) component, in contrast to all existing Rician fading simulators that utilize a non-zero mean deterministic specular component. The statistical properties of the proposed Rician fading model are analyzed in detail. It is shown that the probability density function of the Rician fading phase is not only independent of time but also uniformly distributed over [−π, π). This property is different from that of existing Rician fading models. The statistical properties of the new simulators are confirmed by extensive simulation results, finding good agreement with theoretical analysis in all cases. An explicit formula for the level crossing rate is derived for general Rician fading when the specular component has non-zero Doppler frequency.

$Based on Clarke’s model given by (1), Pop and Beaulieu [12], [13] recently developed a Rayleigh fading simulator by 2m setting a, = “\" in g(t). Thus, the lowpass fading process becomes$

Linear Precoding for Relay Networks with Finite-Alphabet Constraints

2011 IEEE International Conference on Communications (ICC), 2011

In this paper, we investigate the optimal precoding scheme for relay networks with finite-alphabe... more In this paper, we investigate the optimal precoding scheme for relay networks with finite-alphabet constraints. We show that the previous work utilizing various design criteria to maximize either the diversity order or the transmission rate with the Gaussian-input assumption may lead to significant loss for a practical system with finite constellation set constraint. A linear precoding scheme is proposed to maximize the mutual information for relay networks. We exploit the structure of the optimal precoding matrix and develop a unified two-step iterative algorithm utilizing the theory of convex optimization and optimization on the complex Stiefel manifold. Numerical examples show that this novel iterative algorithm achieves significant gains compared to its conventional counterpart.

Matched filter bound ofwireless systems over frequency selective channels with receiver timing phase offset

GLOBECOM '05. IEEE Global Telecommunications Conference, 2005., 2005

The sampler timing (phase) sensitivity of wireless communication systems is discussed in this pap... more The sampler timing (phase) sensitivity of wireless communication systems is discussed in this paper. Based on the matched filter bound technique, a tight error performance bound is derived for systems experiencing frequency selective Rayleigh fading, with the receiver timing offset being quantified in the error performance expressions. With the error performance bound, the timing phase sensitivity of systems with both symbol spaced receivers and fractionally spaced receivers is analyzed. Simulation results show that the new bound can accurately predict the performance of practical communication systems suffering both frequency selective fading and timing phase offset.

Low complexity soft-interference cancellation turbo equalization for MIMO systems with multilevel modulations

2013 IEEE Global Communications Conference (GLOBECOM), 2013

ABSTRACT This paper presents a low complexity soft-interference cancellation equalizer (SICE) for... more ABSTRACT This paper presents a low complexity soft-interference cancellation equalizer (SICE) for the turbo detection of multiple-input multiple-output (MIMO) systems operating in time dispersive channels. The SICE contains three time-invariant linear filters: a feedforward filter, a causal feedback filter and an anti-causal feedback filter. The feedforward filter is designed to suppress the intersymbol interference (ISI) due to time dispersive channels and the multiplexing interference from multiple transmit antennas. The causal (or anti-causal) feedback filter is developed to remove the residual interference caused by the symbols transmitted before (or after) the symbol under detection. The performance of the proposed SICE is verified through both extrinsic information transfer chart (EXIT) analysis and computer simulations. The analytical and simulation results demonstrated that the inclusion of the anti-causal soft decision during SICE is critical to the system performance. The EXIT chart analysis shows that the SICE performance approaches the ideal matched filter bound as the iteration progresses.

Optimal diversity combining based on noisy channel estimation

2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577), 2004

The performances of coherent diversity receivers with noisy channel estimation are examined. Fadi... more The performances of coherent diversity receivers with noisy channel estimation are examined. Fading channel gain estimates are modeled as sums of the true fading channel gain values plus independent Gaussian distributed estimation errors. The optimal diversity receiver for coherent reception with noisy channel state information and independent and identically distributed fading channels is derived. Exact expressions for the average error probability of optimal diversity MPSK with noisy channel estimation are derived for Rayleigh and Ricean fading channels; closed-form expressions are obtained for some special cases. Some interesting observations regarding practical diversity receiver design for higher-order modulation formats are drawn.

Linear MIMO precoding in multi-antenna wiretap channels for finite-alphabet data

ABSTRACT In this paper, we investigate the secrecy rate of finite alphabet communications over mu... more ABSTRACT In this paper, we investigate the secrecy rate of finite alphabet communications over multiple-input, multiple-output, multiple-antenna eavesdropper (MIMOME) systems. Traditional precoder designs at the transmitter for achieving secrecy capacity (maximum secrecy rate) for MIMOME systems are developed according to the assumption of Gaussian input signals. Such designs may risk substantial secrecy rate loss when Gaussian inputs are replaced by practical finite alphabet inputs. To address this issue, we propose a linear precoding design to directly maximize the secrecy rate for MIMOME systems under the constraint of finite alphabet input. Exploiting convex optimization and matrix calculus, we present necessary conditions required of the optimal precoding design and develop an iterative algorithm for finding an efficient precoder. With finite alphabet input signals, maximum transmission power no longer corresponds to maximum secrecy rate as in the case of Gaussian input. We further derive closed-form results on the optimal transmission design for maximizing secrecy rate in low signal-to-noise ratio (SNR) region and near-optimal transmission power in a high SNR region.

Wireless communications

GLOBECOM '05. IEEE Global Telecommunications Conference, 2005., 2005

ABSTRACT Not Available

Adaptive Transmit Diversity with Quadrant Phase Constraining Feedback

Wireless Personal Communications, 2006

An adaptive transmit scheme with quadrant phase constraining feedback is proposed in this paper. ... more An adaptive transmit scheme with quadrant phase constraining feedback is proposed in this paper. With simple linear operations at both transmitter and receiver, the proposed algorithm can achieve better system performances with only 2M-2 bits of feedback information for systems with M transmit antennas. Theoretical performance bounds of the proposed transmit diversity scheme are derived. Simulation examples and theoretical analyses show that the proposed transmit diversity scheme outperforms not only the conventional open-loop transmit diversity techniques, but also some closed-loop transmit diversity techniques with more information transmitted in the feedback channel.

Time-Varying and Frequency-Selective Channel Estimation with Unequally Spaced Pilot Symbols

International Journal of Wireless Information Networks, 2004

In this paper, an accurate and computationally efficient algorithm is proposed for estimating tim... more In this paper, an accurate and computationally efficient algorithm is proposed for estimating time-varying and frequency-selective fading channel with unequally spaced pilot symbols. By employing the time-varying coefficient polynomial interpolation method, it is proved that the time-varying channel impulse response can be estimated by the product of a constant interpolation matrix and the fading information at pilot symbol positions. Furthermore. a least square off-line training algorithm is presented to optimally calculate the constant matrix, taking into consideration of the statistics of channel fading and noise. Simulation results indicate that the hit ermr rate performance of our new estimation algorithm is close to that of the perfect channel estimation.

Doppler Spread Estimation for Broadband Wireless OFDM Systems Over Rician Fading Channels

International Journal of Wireless Information Networks, 2009

In this paper, we present a new Doppler spread estimation algorithm for broadband wireless orthog... more In this paper, we present a new Doppler spread estimation algorithm for broadband wireless orthogonal frequency division multiplexing (OFDM) systems with fast time-varying and frequency-selective Rayleigh or Rician fading channels. The new algorithm is developed by analyzing the statistical properties of the power of the received OFDM signal in the time domain, thus it is not affected by the influence of frequency-domain inter-carrier interference (ICI) introduced by channel variation within one OFDM symbol. The operation of the algorithm doesn't require the knowledge of fading channel coefficients, transmitted data, or signal-to-noise ratio (SNR) at the receiver. It is robust against additive noise, and can provide accurate Doppler spread estimation with SNR as low as 0 dB. Moreover, unlike existing algorithms, the proposed algorithm takes into account the inter-tap correlation of the discrete-time channel representation, as is the case in practical systems. Simulation results demonstrate that this new algorithm can accurately estimate a wide range of Doppler spread with low estimation latency and high computational efficiency.

A modified sensitivity measure for linear digital systems

International Journal of Circuit Theory and Applications, 1995

In this paper a new sensitivity measure for state space systems is proposed. This new measure is ... more In this paper a new sensitivity measure for state space systems is proposed. This new measure is a modified form of Tavsanoglu and Thiele's measure but has three advantages: (1) it is more precise than Tavsanoglu and Thiele's measure when the parameters of the state space realizations contain 0 and *l; (2) it can be used to explain why the sparse Schur and Hessenberg realizations can give better actual sensitivity performance than the corresponding fully parametrized optimal realizations; (3) it is identical with the global round-off noise gain G = tr(QW) + y obtained by Hwang under a dynamic constraint.

MIMO Multichannel Beamforming in Rayleigh-Product Channels with Arbitrary-Power Co-Channel Interference and Noise

IEEE Transactions on Wireless Communications, 2012

ABSTRACT This paper investigates communication over multiple-input multiple-output Rayleigh-produ... more ABSTRACT This paper investigates communication over multiple-input multiple-output Rayleigh-product channels in the presence of both co-channel interference and thermal noise. We first present exact expressions for the marginal ordered eigenvalue distributions of the channel Gram matrix when multichannel beamforming is employed, from which we obtain exact results on the outage probability on each eigenmode. Our results are applicable to an extensive class of multichannel systems with generic system configurations. For particular scenarios of single-input multiple-output, keyhole, and multiple-input single-output channels, simplified closed-form expressions for the asymptotic distributions of the non-zero eigenvalue of the channel Gram matrix are derived. These results indicate that the diversity order is only determined by the second largest value among the number of transmit antennas, scatterers, and receive antennas. For these scenarios, we also derive concise closed-form expressions for the moments of the output signal-to-interference-plus-noise ratio, from which an explicit relationship to the moments in Rayleigh fading channels is revealed. These results are also used to investigate the impact of the number of channel scatterers on the bandwidth requirements for a given transmission rate and power, at low signal-to-noise ratios.

A Discrete-Time Model for Triply Selective MIMO Rayleigh Fading Channels

IEEE Transactions on Wireless Communications, 2004

A statistical discrete-time model is proposed for simulating wideband multiple-input multiple-out... more A statistical discrete-time model is proposed for simulating wideband multiple-input multiple-output (MIMO) fading channels which are triply selective due to angle spread, Doppler spread, and delay spread. The new discrete-time MIMO channel model includes the combined effects of the transmit filter, physical MIMO multipath channel fading, and receive filter, and it has the same sampling period as that of the MIMO receiver. This leads to very efficient simulation of physical continuous-time MIMO channels. A new method is also presented to efficiently generate the MIMO channel stochastic coefficients. The statistical accuracy of the discrete-time MIMO channel model is rigorously verified through theoretical analysis and extensive simulations in different conditions. The high computational efficiency of the discrete-time MIMO channel model is illustrated by comparing it to that of the continuous-time MIMO channel model. The new model is further employed to evaluate the channel capacity of MIMO systems in a triply selective Rayleigh fading environment. The simulation results reveal some interesting effects of spatial correlations, multipaths, and number of antennas on the MIMO channel capacity. Index Terms-Discrete-time channel model, multiple-input multiple-output (MIMO) channel, multiple-input multiple-output multipath channel capacity, Rayleigh fading, triply selective fading, wide-sense stationary uncorrelated scattering (WSSUS) multipath channel. I. INTRODUCTION T HE multiple-input multiple-output (MIMO) communication architecture has recently emerged as a new paradigm for high data rate wireless cellular communications in rich multipath environments. Using multiple-element antenna arrays at both the transmitter and receiver, which effectively exploits the spatial dimension in addition to time and frequency dimensions, this architecture shows channel capacity potential far beyond that of traditional techniques. In quasi-static, independent and identically distributed (i.i.d.) frequency flat Rayleigh fading channels, the MIMO capacity scales linearly with the number of antennas under some conditions [1], [2]. However, in practice,

Improved BDFE Using A Priori Information for Turbo Equalization

IEEE Transactions on Wireless Communications, 2008

Turbo equalization improves communication system performance by iteratively exchanging informatio... more Turbo equalization improves communication system performance by iteratively exchanging information between soft-input soft-output (SISO) equalizer and SISO channel decoder. The trellis-based maximum a posteriori probability (MAP) algorithm serves as the optimum SISO equalizer for turbo equalization. However, MAP algorithm is unsuitable for systems with large modulation constellation size and severe inter-symbol interference (ISI) due to its prohibitively high computational complexity. In this paper, an improved SISO block decision feedback equalizer (BDFE) is proposed for low complexity turbo equalization. Unlike other sub-optimum equalizers which perform symbol by symbol detection, the proposed equalizer generates the soft output for each data bit by collecting information from a sequence of samples as in MAP algorithm. The sequencebased equalization is enabled by using not only soft a priori input from channel decoder, but also hard a priori information obtained from BDFE in previous iteration. The combination of soft a priori information and hard a priori information renders better performance with less iterations compared to other suboptimum algorithms. In addition, the computational complexity of the proposed algorithm is on the same order as conventional SISO BDFE algorithm, and is much lower compared to the trellis-based MAP algorithm.

Linear Precoding for MIMO Multiple Access Channels with Finite Discrete Inputs

IEEE Transactions on Wireless Communications, 2011

In this paper, we study linear precoding for multiple-input multiple-output (MIMO) multiple acces... more In this paper, we study linear precoding for multiple-input multiple-output (MIMO) multiple access channels (MAC) with finite discrete inputs. We derive the constellationconstrained capacity region for the MIMO MAC with an arbitrary number of users and find that the boundary can be achieved by solving the problem of weighted sum rate maximization with constellation and individual power constraints. Due to the non-concavity of the objective function, we obtain a set of necessary conditions for the optimization problem through Karush-Kuhn-Tucker analysis. To find the optimal precoding matrices for all users, we propose an iterative algorithm utilizing alternating optimization strategy. In particular, each iteration of the algorithm involves the gradient descent update with backtracking line search. Numerical results show that when inputs are digital modulated signals and the signal-to-noise ratio is in the medium range, our proposed algorithm offers considerably higher sum rate than non-precoding and the traditional method which maximizes Gaussian-input sum capacity. Furthermore, a low-density parity-check coded system with iterative detection and decoding for MAC is presented to evaluate the bit error rate (BER) performance of precoders. BER results also indicate that the system with the proposed linear precoder achieves significant gains over the non-precoding system and the precoder designed for Gaussian inputs. Index Terms-Multiple-input multiple-output (MIMO), multiple access channels (MAC), linear precoding, finite discrete inputs.

Multiuser channel estimation for CDMA systems over frequency-selective fading channels

IEEE Transactions on Wireless Communications, 2005

In this paper, a pilot-assisted minimum mean square error (MMSE) multiuser channel estimation alg... more In this paper, a pilot-assisted minimum mean square error (MMSE) multiuser channel estimation algorithm is proposed for quasi-synchronous code-division multiple-access (CDMA) systems that undergo frequency-selective channel fading. The frequency-selective multiuser fading channel is represented as a symbol-wise time-varying chip-spaced tapped delay line filter with correlated filter taps. The multiuser channel tap coefficients at pilot symbol positions are estimated under the MMSE criterion with the help of the channel intertap correlation matrix, which is determined by the combined effects of the physical fading channel, transmit filter, and receive filter. In the development of the estimation algorithm, the channel intertap correlation matrix is deemed as an essential factor, and a novel iterative method is proposed for the joint estimation of the channel intertap correlation and filter tap timing based on the received pilot samples. Simulations show that the information of the channel intertap correlation is critical to the performance of the channel estimation, and the channel taps at different delays cannot be assumed uncorrelated for CDMA systems experiencing frequency-selective fading.

Fast Time-Varying Dispersive Channel Estimation and Equalization for an 8-PSK Cellular System

IEEE Transactions on Vehicular Technology, 2006

In this paper, a novel channel-estimation scheme for an 8-PSK enhanced data rates for GSM evoluti... more In this paper, a novel channel-estimation scheme for an 8-PSK enhanced data rates for GSM evolution (EDGE) system with fast time-varying and frequency-selective fading channels is presented. Via a mathematical derivation and simulation results, the channel impulse response (CIR) of the fast fading channel is modeled as a linear function of time during a radio burst in the EDGE system. Therefore, a least-squares-based method is proposed along with the modified burst structure for time-varying channel estimation. Given that the pilot-symbol blocks are located at the front and the end of the data block, the LS-based method is able to estimate the parameters of the time-varying CIR accurately using a linear interpolation. The proposed time-varying estimation algorithm does not cause an error floor that existed in the adaptive algorithms due to a nonideal channel tracking. Besides, the time-varying CIR in the EDGE system is not in its minimum-phase form, as is required for low-complexity reducedstate equalization methods. In order to maintain a good system performance, a Cholesky-decomposition method is introduced in front of the reduced-state equalizer to transform the time-varying CIR into its minimum-phase equivalent form. Via simulation results, it is shown that the proposed algorithm is very well suited for the time-varying channel estimation and equalization, and a good bit-error-rate performance is achieved even at high Doppler frequencies up to 300 Hz with a low complexity.

$where U € C\Nat+4-))x(Nat+"-1) is a lower triangular matrix from the Cholesky decomposition. The expression (33) is based on the assumption that the input data symbols x; are indepen- dent, i.e., Roz = EsIn,+1-1 with EL, being the symbol energy, and o2 is the variance of the AWGN nx, while the signal-to- noise ratio SNR = E,/o?. where trace(-) will return the sum of the diagonal elements of a matrix. According to the orthogonality principle [19, pp.256-258], the matrix B minimizing o? must satisfy B - Rzy = W-Ry,y, where Rag = E(A- B®). Therefore, the minimum value of a? can be obtained as$

Mobile speed estimation for TDMA-based hierarchical cellular systems

IEEE Transactions on Vehicular Technology, 2001

In this paper, a new algorithm is presented for estimating mobile speed for handoff in hierarchic... more In this paper, a new algorithm is presented for estimating mobile speed for handoff in hierarchical cellular systems. The proposed algorithm is based on normalized autocorrelation values of received signals to estimate mobile speed; it contains six steps. First, the instantaneous power of the received baseband signal is calculated to remove the frequency offset and data/speech information-bearing signals, while keeping the Doppler frequency information. Second, the calculated power signal is filtered using a low-pass linear phase finite impulse response filter to suppress interference and noise. Third, the filtered power signal is decimated to ease the computational burden, while the decimation factor is properly chosen to avoid frequency aliasing. Fourth, autocorrelation values of the decimated filtered power signals are calculated on shifting slot by slot to suppress the "slot burst frequency" interference. Fifth, the calculated autocorrelation values are normalized to suppress the power fluctuation of the received signals. Finally, the normalized autocorrelation values are compared with thresholds to estimate mobile speed. The simulation results indicate that the new algorithm works very well for both nondispersive channels and dispersive channels to distinguish fast and slow moving mobiles. The method has very low latency, with results being available typically within 1 s after communication is established, and it can report estimation result every second or less. The algorithm has been implemented by software code into Nortel's base-station radios and tested in Nortel's wireless communications labs. The lab test results are very close to the computer simulation results, which have very good estimation accuracy.

Efficient equalization and symbol detection for 8-PSK EDGE cellular system

IEEE Transactions on Vehicular Technology, 2003

In this paper, a new method is presented for channel equalization and symbol detection of an enha... more In this paper, a new method is presented for channel equalization and symbol detection of an enhanced data rate for global system for mobile (GSM) communication and IS-136 evolution (EDGE) cellular system in which eight phase-shift keying (8-PSK) modulation is employed. The new method iteratively minimizes the Euclidean distance between the detected and received signal sequences, with neighbor symbol perturbation to reduce the computational complexity. The new algorithm is computationally efficient and can also be easily implemented into commercial signal processors. Simulation results comparing our method with the reduced-state sequence-estimation (RSSE) method, both with and without set partitioning, are presented. Index Terms-Channel equalization, coherent symbol detection, enhanced data rate for global system for mobile (GSM) communication and IS-136 evolution (EDGE) cellular system.

Further Results on Frequency-Domain Channel Equalization for Single Carrier Underwater Acoustic Communications

OCEANS 2008 - MTS/IEEE Kobe Techno-Ocean, 2008

A frequency-domain channel equalization and phase correction method was proposed in a previous wo... more A frequency-domain channel equalization and phase correction method was proposed in a previous work published in Oceans'07 conference, in which 10 −4 BER performance was presented for fixed-to-fixed source/receiver channels. The method is improved by using minimum mean square error (MMSE) estimation in channel updates rather than least squares estimation. It is applied to moving-to-fixed channels in the AUVFest'07 ocean experiment where single-carrier wideband transmission was employed with quadrature phase shift keying modulation. The moving source channels exhibit higher Doppler shift and larger Doppler drift than the fixed-to-fixed channels. Therefore, the number of symbols required for initial phase estimation is increased from 2 to 8 symbols when the groupwise phase correction algorithm is applied to the moving sources. Thirty-six packets with data block length of 512 symbols have been processed and 34 of them achieved an uncoded Bit Error Rate (BER) lower than 10 −2. The overall uncoded BER performance of all 36 packets is 1.81 × 10 −3 which is slightly higher than that of the fixed-to-fixed channels.

Statistical simulation models for Rayleigh and Rician fading

IEEE International Conference on Communications, 2003. ICC '03.

New simulation models are proposed for Rayleigh and Rician fading channels. First, the statistica... more New simulation models are proposed for Rayleigh and Rician fading channels. First, the statistical properties of Clarke's fading model with a finite number of sinusoids are analyzed. An improved Clarke's model is then proposed for the simulation of Rayleigh fading channels. Based on this improved Rayleigh fading model, a novel simulation model is proposed for Rician fading channels. The new Rician fading model employs a zero-mean stochastic sinusoid as the specular (line-of-sight) component, in contrast to all existing Rician fading simulators that utilize a non-zero mean deterministic specular component. The statistical properties of the proposed Rician fading model are analyzed in detail. It is shown that the probability density function of the Rician fading phase is not only independent of time but also uniformly distributed over [−π, π). This property is different from that of existing Rician fading models. The statistical properties of the new simulators are confirmed by extensive simulation results, finding good agreement with theoretical analysis in all cases. An explicit formula for the level crossing rate is derived for general Rician fading when the specular component has non-zero Doppler frequency.

$Based on Clarke’s model given by (1), Pop and Beaulieu [12], [13] recently developed a Rayleigh fading simulator by 2m setting a, = “\" in g(t). Thus, the lowpass fading process becomes$

Linear Precoding for Relay Networks with Finite-Alphabet Constraints

2011 IEEE International Conference on Communications (ICC), 2011

In this paper, we investigate the optimal precoding scheme for relay networks with finite-alphabe... more In this paper, we investigate the optimal precoding scheme for relay networks with finite-alphabet constraints. We show that the previous work utilizing various design criteria to maximize either the diversity order or the transmission rate with the Gaussian-input assumption may lead to significant loss for a practical system with finite constellation set constraint. A linear precoding scheme is proposed to maximize the mutual information for relay networks. We exploit the structure of the optimal precoding matrix and develop a unified two-step iterative algorithm utilizing the theory of convex optimization and optimization on the complex Stiefel manifold. Numerical examples show that this novel iterative algorithm achieves significant gains compared to its conventional counterpart.

Matched filter bound ofwireless systems over frequency selective channels with receiver timing phase offset

GLOBECOM '05. IEEE Global Telecommunications Conference, 2005., 2005

The sampler timing (phase) sensitivity of wireless communication systems is discussed in this pap... more The sampler timing (phase) sensitivity of wireless communication systems is discussed in this paper. Based on the matched filter bound technique, a tight error performance bound is derived for systems experiencing frequency selective Rayleigh fading, with the receiver timing offset being quantified in the error performance expressions. With the error performance bound, the timing phase sensitivity of systems with both symbol spaced receivers and fractionally spaced receivers is analyzed. Simulation results show that the new bound can accurately predict the performance of practical communication systems suffering both frequency selective fading and timing phase offset.

Low complexity soft-interference cancellation turbo equalization for MIMO systems with multilevel modulations

2013 IEEE Global Communications Conference (GLOBECOM), 2013

ABSTRACT This paper presents a low complexity soft-interference cancellation equalizer (SICE) for... more ABSTRACT This paper presents a low complexity soft-interference cancellation equalizer (SICE) for the turbo detection of multiple-input multiple-output (MIMO) systems operating in time dispersive channels. The SICE contains three time-invariant linear filters: a feedforward filter, a causal feedback filter and an anti-causal feedback filter. The feedforward filter is designed to suppress the intersymbol interference (ISI) due to time dispersive channels and the multiplexing interference from multiple transmit antennas. The causal (or anti-causal) feedback filter is developed to remove the residual interference caused by the symbols transmitted before (or after) the symbol under detection. The performance of the proposed SICE is verified through both extrinsic information transfer chart (EXIT) analysis and computer simulations. The analytical and simulation results demonstrated that the inclusion of the anti-causal soft decision during SICE is critical to the system performance. The EXIT chart analysis shows that the SICE performance approaches the ideal matched filter bound as the iteration progresses.

Optimal diversity combining based on noisy channel estimation

2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577), 2004

The performances of coherent diversity receivers with noisy channel estimation are examined. Fadi... more The performances of coherent diversity receivers with noisy channel estimation are examined. Fading channel gain estimates are modeled as sums of the true fading channel gain values plus independent Gaussian distributed estimation errors. The optimal diversity receiver for coherent reception with noisy channel state information and independent and identically distributed fading channels is derived. Exact expressions for the average error probability of optimal diversity MPSK with noisy channel estimation are derived for Rayleigh and Ricean fading channels; closed-form expressions are obtained for some special cases. Some interesting observations regarding practical diversity receiver design for higher-order modulation formats are drawn.

Linear MIMO precoding in multi-antenna wiretap channels for finite-alphabet data

ABSTRACT In this paper, we investigate the secrecy rate of finite alphabet communications over mu... more ABSTRACT In this paper, we investigate the secrecy rate of finite alphabet communications over multiple-input, multiple-output, multiple-antenna eavesdropper (MIMOME) systems. Traditional precoder designs at the transmitter for achieving secrecy capacity (maximum secrecy rate) for MIMOME systems are developed according to the assumption of Gaussian input signals. Such designs may risk substantial secrecy rate loss when Gaussian inputs are replaced by practical finite alphabet inputs. To address this issue, we propose a linear precoding design to directly maximize the secrecy rate for MIMOME systems under the constraint of finite alphabet input. Exploiting convex optimization and matrix calculus, we present necessary conditions required of the optimal precoding design and develop an iterative algorithm for finding an efficient precoder. With finite alphabet input signals, maximum transmission power no longer corresponds to maximum secrecy rate as in the case of Gaussian input. We further derive closed-form results on the optimal transmission design for maximizing secrecy rate in low signal-to-noise ratio (SNR) region and near-optimal transmission power in a high SNR region.

Wireless communications

GLOBECOM '05. IEEE Global Telecommunications Conference, 2005., 2005

ABSTRACT Not Available

Adaptive Transmit Diversity with Quadrant Phase Constraining Feedback

Wireless Personal Communications, 2006

An adaptive transmit scheme with quadrant phase constraining feedback is proposed in this paper. ... more An adaptive transmit scheme with quadrant phase constraining feedback is proposed in this paper. With simple linear operations at both transmitter and receiver, the proposed algorithm can achieve better system performances with only 2M-2 bits of feedback information for systems with M transmit antennas. Theoretical performance bounds of the proposed transmit diversity scheme are derived. Simulation examples and theoretical analyses show that the proposed transmit diversity scheme outperforms not only the conventional open-loop transmit diversity techniques, but also some closed-loop transmit diversity techniques with more information transmitted in the feedback channel.

Time-Varying and Frequency-Selective Channel Estimation with Unequally Spaced Pilot Symbols

International Journal of Wireless Information Networks, 2004

In this paper, an accurate and computationally efficient algorithm is proposed for estimating tim... more In this paper, an accurate and computationally efficient algorithm is proposed for estimating time-varying and frequency-selective fading channel with unequally spaced pilot symbols. By employing the time-varying coefficient polynomial interpolation method, it is proved that the time-varying channel impulse response can be estimated by the product of a constant interpolation matrix and the fading information at pilot symbol positions. Furthermore. a least square off-line training algorithm is presented to optimally calculate the constant matrix, taking into consideration of the statistics of channel fading and noise. Simulation results indicate that the hit ermr rate performance of our new estimation algorithm is close to that of the perfect channel estimation.

Doppler Spread Estimation for Broadband Wireless OFDM Systems Over Rician Fading Channels

International Journal of Wireless Information Networks, 2009

In this paper, we present a new Doppler spread estimation algorithm for broadband wireless orthog... more In this paper, we present a new Doppler spread estimation algorithm for broadband wireless orthogonal frequency division multiplexing (OFDM) systems with fast time-varying and frequency-selective Rayleigh or Rician fading channels. The new algorithm is developed by analyzing the statistical properties of the power of the received OFDM signal in the time domain, thus it is not affected by the influence of frequency-domain inter-carrier interference (ICI) introduced by channel variation within one OFDM symbol. The operation of the algorithm doesn't require the knowledge of fading channel coefficients, transmitted data, or signal-to-noise ratio (SNR) at the receiver. It is robust against additive noise, and can provide accurate Doppler spread estimation with SNR as low as 0 dB. Moreover, unlike existing algorithms, the proposed algorithm takes into account the inter-tap correlation of the discrete-time channel representation, as is the case in practical systems. Simulation results demonstrate that this new algorithm can accurately estimate a wide range of Doppler spread with low estimation latency and high computational efficiency.

A modified sensitivity measure for linear digital systems

International Journal of Circuit Theory and Applications, 1995

In this paper a new sensitivity measure for state space systems is proposed. This new measure is ... more In this paper a new sensitivity measure for state space systems is proposed. This new measure is a modified form of Tavsanoglu and Thiele's measure but has three advantages: (1) it is more precise than Tavsanoglu and Thiele's measure when the parameters of the state space realizations contain 0 and *l; (2) it can be used to explain why the sparse Schur and Hessenberg realizations can give better actual sensitivity performance than the corresponding fully parametrized optimal realizations; (3) it is identical with the global round-off noise gain G = tr(QW) + y obtained by Hwang under a dynamic constraint.

MIMO Multichannel Beamforming in Rayleigh-Product Channels with Arbitrary-Power Co-Channel Interference and Noise

IEEE Transactions on Wireless Communications, 2012

ABSTRACT This paper investigates communication over multiple-input multiple-output Rayleigh-produ... more ABSTRACT This paper investigates communication over multiple-input multiple-output Rayleigh-product channels in the presence of both co-channel interference and thermal noise. We first present exact expressions for the marginal ordered eigenvalue distributions of the channel Gram matrix when multichannel beamforming is employed, from which we obtain exact results on the outage probability on each eigenmode. Our results are applicable to an extensive class of multichannel systems with generic system configurations. For particular scenarios of single-input multiple-output, keyhole, and multiple-input single-output channels, simplified closed-form expressions for the asymptotic distributions of the non-zero eigenvalue of the channel Gram matrix are derived. These results indicate that the diversity order is only determined by the second largest value among the number of transmit antennas, scatterers, and receive antennas. For these scenarios, we also derive concise closed-form expressions for the moments of the output signal-to-interference-plus-noise ratio, from which an explicit relationship to the moments in Rayleigh fading channels is revealed. These results are also used to investigate the impact of the number of channel scatterers on the bandwidth requirements for a given transmission rate and power, at low signal-to-noise ratios.

A Discrete-Time Model for Triply Selective MIMO Rayleigh Fading Channels

IEEE Transactions on Wireless Communications, 2004

A statistical discrete-time model is proposed for simulating wideband multiple-input multiple-out... more A statistical discrete-time model is proposed for simulating wideband multiple-input multiple-output (MIMO) fading channels which are triply selective due to angle spread, Doppler spread, and delay spread. The new discrete-time MIMO channel model includes the combined effects of the transmit filter, physical MIMO multipath channel fading, and receive filter, and it has the same sampling period as that of the MIMO receiver. This leads to very efficient simulation of physical continuous-time MIMO channels. A new method is also presented to efficiently generate the MIMO channel stochastic coefficients. The statistical accuracy of the discrete-time MIMO channel model is rigorously verified through theoretical analysis and extensive simulations in different conditions. The high computational efficiency of the discrete-time MIMO channel model is illustrated by comparing it to that of the continuous-time MIMO channel model. The new model is further employed to evaluate the channel capacity of MIMO systems in a triply selective Rayleigh fading environment. The simulation results reveal some interesting effects of spatial correlations, multipaths, and number of antennas on the MIMO channel capacity. Index Terms-Discrete-time channel model, multiple-input multiple-output (MIMO) channel, multiple-input multiple-output multipath channel capacity, Rayleigh fading, triply selective fading, wide-sense stationary uncorrelated scattering (WSSUS) multipath channel. I. INTRODUCTION T HE multiple-input multiple-output (MIMO) communication architecture has recently emerged as a new paradigm for high data rate wireless cellular communications in rich multipath environments. Using multiple-element antenna arrays at both the transmitter and receiver, which effectively exploits the spatial dimension in addition to time and frequency dimensions, this architecture shows channel capacity potential far beyond that of traditional techniques. In quasi-static, independent and identically distributed (i.i.d.) frequency flat Rayleigh fading channels, the MIMO capacity scales linearly with the number of antennas under some conditions [1], [2]. However, in practice,

Improved BDFE Using A Priori Information for Turbo Equalization

IEEE Transactions on Wireless Communications, 2008

Turbo equalization improves communication system performance by iteratively exchanging informatio... more Turbo equalization improves communication system performance by iteratively exchanging information between soft-input soft-output (SISO) equalizer and SISO channel decoder. The trellis-based maximum a posteriori probability (MAP) algorithm serves as the optimum SISO equalizer for turbo equalization. However, MAP algorithm is unsuitable for systems with large modulation constellation size and severe inter-symbol interference (ISI) due to its prohibitively high computational complexity. In this paper, an improved SISO block decision feedback equalizer (BDFE) is proposed for low complexity turbo equalization. Unlike other sub-optimum equalizers which perform symbol by symbol detection, the proposed equalizer generates the soft output for each data bit by collecting information from a sequence of samples as in MAP algorithm. The sequencebased equalization is enabled by using not only soft a priori input from channel decoder, but also hard a priori information obtained from BDFE in previous iteration. The combination of soft a priori information and hard a priori information renders better performance with less iterations compared to other suboptimum algorithms. In addition, the computational complexity of the proposed algorithm is on the same order as conventional SISO BDFE algorithm, and is much lower compared to the trellis-based MAP algorithm.

Linear Precoding for MIMO Multiple Access Channels with Finite Discrete Inputs

IEEE Transactions on Wireless Communications, 2011

In this paper, we study linear precoding for multiple-input multiple-output (MIMO) multiple acces... more In this paper, we study linear precoding for multiple-input multiple-output (MIMO) multiple access channels (MAC) with finite discrete inputs. We derive the constellationconstrained capacity region for the MIMO MAC with an arbitrary number of users and find that the boundary can be achieved by solving the problem of weighted sum rate maximization with constellation and individual power constraints. Due to the non-concavity of the objective function, we obtain a set of necessary conditions for the optimization problem through Karush-Kuhn-Tucker analysis. To find the optimal precoding matrices for all users, we propose an iterative algorithm utilizing alternating optimization strategy. In particular, each iteration of the algorithm involves the gradient descent update with backtracking line search. Numerical results show that when inputs are digital modulated signals and the signal-to-noise ratio is in the medium range, our proposed algorithm offers considerably higher sum rate than non-precoding and the traditional method which maximizes Gaussian-input sum capacity. Furthermore, a low-density parity-check coded system with iterative detection and decoding for MAC is presented to evaluate the bit error rate (BER) performance of precoders. BER results also indicate that the system with the proposed linear precoder achieves significant gains over the non-precoding system and the precoder designed for Gaussian inputs. Index Terms-Multiple-input multiple-output (MIMO), multiple access channels (MAC), linear precoding, finite discrete inputs.

Multiuser channel estimation for CDMA systems over frequency-selective fading channels

IEEE Transactions on Wireless Communications, 2005

In this paper, a pilot-assisted minimum mean square error (MMSE) multiuser channel estimation alg... more In this paper, a pilot-assisted minimum mean square error (MMSE) multiuser channel estimation algorithm is proposed for quasi-synchronous code-division multiple-access (CDMA) systems that undergo frequency-selective channel fading. The frequency-selective multiuser fading channel is represented as a symbol-wise time-varying chip-spaced tapped delay line filter with correlated filter taps. The multiuser channel tap coefficients at pilot symbol positions are estimated under the MMSE criterion with the help of the channel intertap correlation matrix, which is determined by the combined effects of the physical fading channel, transmit filter, and receive filter. In the development of the estimation algorithm, the channel intertap correlation matrix is deemed as an essential factor, and a novel iterative method is proposed for the joint estimation of the channel intertap correlation and filter tap timing based on the received pilot samples. Simulations show that the information of the channel intertap correlation is critical to the performance of the channel estimation, and the channel taps at different delays cannot be assumed uncorrelated for CDMA systems experiencing frequency-selective fading.

Fast Time-Varying Dispersive Channel Estimation and Equalization for an 8-PSK Cellular System

IEEE Transactions on Vehicular Technology, 2006

In this paper, a novel channel-estimation scheme for an 8-PSK enhanced data rates for GSM evoluti... more In this paper, a novel channel-estimation scheme for an 8-PSK enhanced data rates for GSM evolution (EDGE) system with fast time-varying and frequency-selective fading channels is presented. Via a mathematical derivation and simulation results, the channel impulse response (CIR) of the fast fading channel is modeled as a linear function of time during a radio burst in the EDGE system. Therefore, a least-squares-based method is proposed along with the modified burst structure for time-varying channel estimation. Given that the pilot-symbol blocks are located at the front and the end of the data block, the LS-based method is able to estimate the parameters of the time-varying CIR accurately using a linear interpolation. The proposed time-varying estimation algorithm does not cause an error floor that existed in the adaptive algorithms due to a nonideal channel tracking. Besides, the time-varying CIR in the EDGE system is not in its minimum-phase form, as is required for low-complexity reducedstate equalization methods. In order to maintain a good system performance, a Cholesky-decomposition method is introduced in front of the reduced-state equalizer to transform the time-varying CIR into its minimum-phase equivalent form. Via simulation results, it is shown that the proposed algorithm is very well suited for the time-varying channel estimation and equalization, and a good bit-error-rate performance is achieved even at high Doppler frequencies up to 300 Hz with a low complexity.

$where U € C\Nat+4-))x(Nat+"-1) is a lower triangular matrix from the Cholesky decomposition. The expression (33) is based on the assumption that the input data symbols x; are indepen- dent, i.e., Roz = EsIn,+1-1 with EL, being the symbol energy, and o2 is the variance of the AWGN nx, while the signal-to- noise ratio SNR = E,/o?. where trace(-) will return the sum of the diagonal elements of a matrix. According to the orthogonality principle [19, pp.256-258], the matrix B minimizing o? must satisfy B - Rzy = W-Ry,y, where Rag = E(A- B®). Therefore, the minimum value of a? can be obtained as$

Mobile speed estimation for TDMA-based hierarchical cellular systems

IEEE Transactions on Vehicular Technology, 2001

In this paper, a new algorithm is presented for estimating mobile speed for handoff in hierarchic... more In this paper, a new algorithm is presented for estimating mobile speed for handoff in hierarchical cellular systems. The proposed algorithm is based on normalized autocorrelation values of received signals to estimate mobile speed; it contains six steps. First, the instantaneous power of the received baseband signal is calculated to remove the frequency offset and data/speech information-bearing signals, while keeping the Doppler frequency information. Second, the calculated power signal is filtered using a low-pass linear phase finite impulse response filter to suppress interference and noise. Third, the filtered power signal is decimated to ease the computational burden, while the decimation factor is properly chosen to avoid frequency aliasing. Fourth, autocorrelation values of the decimated filtered power signals are calculated on shifting slot by slot to suppress the "slot burst frequency" interference. Fifth, the calculated autocorrelation values are normalized to suppress the power fluctuation of the received signals. Finally, the normalized autocorrelation values are compared with thresholds to estimate mobile speed. The simulation results indicate that the new algorithm works very well for both nondispersive channels and dispersive channels to distinguish fast and slow moving mobiles. The method has very low latency, with results being available typically within 1 s after communication is established, and it can report estimation result every second or less. The algorithm has been implemented by software code into Nortel's base-station radios and tested in Nortel's wireless communications labs. The lab test results are very close to the computer simulation results, which have very good estimation accuracy.

Efficient equalization and symbol detection for 8-PSK EDGE cellular system

IEEE Transactions on Vehicular Technology, 2003

In this paper, a new method is presented for channel equalization and symbol detection of an enha... more In this paper, a new method is presented for channel equalization and symbol detection of an enhanced data rate for global system for mobile (GSM) communication and IS-136 evolution (EDGE) cellular system in which eight phase-shift keying (8-PSK) modulation is employed. The new method iteratively minimizes the Euclidean distance between the detected and received signal sequences, with neighbor symbol perturbation to reduce the computational complexity. The new algorithm is computationally efficient and can also be easily implemented into commercial signal processors. Simulation results comparing our method with the reduced-state sequence-estimation (RSSE) method, both with and without set partitioning, are presented. Index Terms-Channel equalization, coherent symbol detection, enhanced data rate for global system for mobile (GSM) communication and IS-136 evolution (EDGE) cellular system.