Joint estimation of time delays and DOAs for DS-CDMA system over multipath Rayleigh fading channels
An approximate maximum likelihood (ML) method for joint estimation of time delays and directions-... more An approximate maximum likelihood (ML) method for joint estimation of time delays and directions-of-arrivals (DOAs) for the direct-sequence code-division multiple-access (DS-CDMA) systems over the multipath Rayleigh fading channels is developed. The proposed estimation scheme is developed by modeling the known training sequence of the desired user as the desired signal and the multiple access interference (MAI)-plus-AWGN as unknown colored Gaussian noise uncorrelated with the desired signal. An efficient iterative algorithm for estimating channel parameters (the time delays and DOAs of multipath signals) is proposed to reduce the computational complexity. The algorithm transforms the multi-dimensional maximization problem into two simple one-dimensional (1-D) maximization problems based on an iterative scheme. Analytical and simulation results are presented to illustrate the performance in comparison with the Cramer-Rao bounds (CRBs). It is shown that the proposed algorithm is near-far resistant for both time delay and DOA estimation and little performance loss is observed in comparison with the CRBs at reasonable SNRs.
On estimating temporal and spatial channel parameters for DS-CDMA system over multipath Rayleigh fading channels
We develop an approximate maximum likelihood (ML) method for joint estimation of time delays and ... more We develop an approximate maximum likelihood (ML) method for joint estimation of time delays and directions-of-arrivals (DOA) for direct-sequence code-division multiple-access (DS-CDMA) systems over multipath Rayleigh fading channels. In developing the proposed estimation scheme, we model the known training sequence of the desired user as the desired signal and the multiple access interferences (MAI)-plus-AWGN as unknown colored Gaussian noise uncorrelated with the desired signal. To reduce computational complexity, a fast algorithm realization is proposed taking advantage of the ridge structure of the objection function. Analytical and simulation results are presented to illustrate the performance in comparison with the Cramer-Rao bounds (CRB). It is shown that the proposed algorithm is near-far resistant for both time delay and DOA estimations, with almost no performance loss compared with CRB.
IEEE Transactions on Signal Processing, May 1, 1993
We present a computationally simple scheme, which uses only the phase angles of the complex-value... more We present a computationally simple scheme, which uses only the phase angles of the complex-valued data, to estimate frequencies of two sinusoids in white Gaussian noise. The envelope data is used to resolve the inherent ambiguity. At high SNR, satisfactory results are obtained from simulations and comparison with Cramer-Rao bounds.
Multiuser detection for integrated multi-rate CDMA
We extend the LMMSE multiuser detector to multi-rate CDMA systems, where different users have dif... more We extend the LMMSE multiuser detector to multi-rate CDMA systems, where different users have different quality-of-service (QoS) requirements. The proposed LMMSE detectors can work on dual-rate mode according to different computational constraints. Only the signature of the desired user is needed in using the proposed multi-rate LMMSE detectors. The proposed detectors have better detection performance and less computational requirement than the dual-rate decorrelating detectors. Computer simulations verified analytical results and conjecture.
Reduced-rank multiuser detectors based on vector and matrix conjugate gradient wiener filters
Using the notion of expanding subspace and the framework of reduced-rank signal processing, we pr... more Using the notion of expanding subspace and the framework of reduced-rank signal processing, we present our latest discovery on applying the vector and matrix conjugate gradient (CG) methods to design reduced-rank linear MMSE multiuser detectors (MUD) for code division multiple access (CDMA) systems. We show that for a synchronous CDMA system with K users, each using a distinct length N
Differential transceiver design for DS-CDMA systems with transmit diversity
The performance of new differential detection schemes with transmit diversity (TD) for direct-seq... more The performance of new differential detection schemes with transmit diversity (TD) for direct-sequence code division multiple access (DS-CDMA) systems is evaluated. Two TD schemes are considered. One is the orthogonal transmit diversity (OTD) and the other is the space-time transmit diversity (STTD). To enable blind detection, the two schemes of differential encoding/decoding in combination with the minimum variance distortionless response (MVDR) receiver are proposed. Both schemes provide full spatial diversity and require no channel state information at the transmitter as well as the receiver. The performance of the proposed OTD+MV and STTD+MV transceivers are much better than that of the conventionally used OTD+MF (matched filter) and STTD+MF receivers. The STTD+MV outperforms the OTD+MV at the price of a higher receiver complexity.
Lucky ranging in underwater environments subject to spatial coherence loss
For passive ranging in environments subject to unknown fluctuating spatial coherence losses, we d... more For passive ranging in environments subject to unknown fluctuating spatial coherence losses, we derive a new lucky maximum likelihood estimator based on the probabilistic assumption that each collected data snapshot is either coherent or purely incoherent with some probability. Our lucky range estimator can be interpreted as first ranking the coherence quality of each data snapshot according to an array gain-like quantity during the parameter search, followed by accumulation of likelihood surfaces out of data snapshots of high spatial-coherence. This effectively avoids the wash-out or the smearing results encountered in the traditional procedures of utilizing a long integration time without a prior screening for the data spatial-coherence. A connection to the adaptive coherence estimator (ACE) is revealed. Also established is an equivalence between the lucky MLE and the Kullback-Leibler (KL) divergence based spatial coherence test.
Joint Detection and Direction-of-Arrival Estimation using Bayesian method
Maximum a posterior (MAP) estimator has been shown to perform perfectly for direction-of-arrival ... more Maximum a posterior (MAP) estimator has been shown to perform perfectly for direction-of-arrival (DOA) under the assumption that the number of sources is known. Specifically, in this work we proposed a MAP estimator for DOA, and extend it to a new approach called DDBM for joint detection and DOA estimation simultaneously. Results of both simulation and experiment demonstrate that the proposed method outperforms the AIC and MDL for detection, and also is better than MUSIC and MiniNorm for estimation simultaneously, whereas the computational burden would not aggravate.
Rank reduction for rapid timing acquisition in multiple access communications
... Under the condition of the near-Gaussian interference-plus-noise, the maximum likelihood esti... more ... Under the condition of the near-Gaussian interference-plus-noise, the maximum likelihood estimate of τ1 simply corresponds to the maximum of an objective function J(τ1) in (5) or its scaled version JACE(τ1). ... 2004. [7] H. Ge, K. Wang, and KC Hong, Fast Delay Estima-tion for ...
The probability density function of SINR loss of the dominant mode rejection beamformer
The dominant mode rejection (DMR) adaptive beamformer (ABF) is a reduced rank subspace algorithm,... more The dominant mode rejection (DMR) adaptive beamformer (ABF) is a reduced rank subspace algorithm, which replaces the covariance matrix in the Minimum Variance Distortionless Response (MVDR) beamformer with an eigenvalue reshaped covariance estimate out of the sample covariance matrix (SCM). Signal-to-interference-plus-noise ratio (SINR) loss quantifies the performance of an ABF designed with SCM with respect to its nominal version designed with the true ensemble covariance matrix (ECM). This paper conjectures that the SINR loss of the DMR beamformer is beta-distributed, derives and provides an approximated expression for the beta probability density function. For the simple case of single interferer present in white noise, the performance of the DMR beamformer only depends on the number of snapshots. Monte-Carlo simulations are carried out to verify our derived results.
Bayesian approach of multiuser separation and interference suppression in CDMA communication systems
Based on Bayesian philosophy, we propose a simplified detection scheme for multiuser separation i... more Based on Bayesian philosophy, we propose a simplified detection scheme for multiuser separation in CDMA communication systems. The proposed detector uses a multi-stage approach to achieve improved detection performance. In the first stage, we use a marginal Bayesian estimate to get a tentative estimate of the random signal vector. In the second stage, a refined estimate of the multiuser information bit is obtained by incorporating the correlation structure of the noise. This detector avoids the multidimensional integration associated with the general multi-dimensional Bayesian estimate. Simulation results show improved performance over existing detectors of comparable simplicity.
On the structure of the multi-mode filters for passive wavefront curvature ranging in a distributed array system
This work presents some new results on the structures of, and our interpretation on, the multi-ra... more This work presents some new results on the structures of, and our interpretation on, the multi-rank filters used for passive wavefront curvature (WFC) ranging. Such a WFC ranging systems uses a large-scale distributed arrays with many spatially separated modular arrays, operating under environments subject to a spatial coherence loss. Working on the modular array level beamformed data, the multi-rank filters along with the weighting coefficients provide further spatial filtering capability to rake in spatial coherence existing in the distorted wavefronts impinging on different modular arrays. Such multi-rank filters can improve ranging performance through different combining schemes, beyond what achieved by the bearing-only based triangulation. For a real-valued inter-module spatial coherence matrix, the derived multi-rank filters follow a nicely balanced structure comprised of in-phase and quadrature (I/Q) modes with varying spatial directions. The results provide a simple solution for us to discovering levels of coherence existing in different modes for multi-mode combining.
Reduced complexity maximum likelihood detection for v-blast systems
Proposed and studied in this work is a reduced complexity maximum likelihood (ML) detection schem... more Proposed and studied in this work is a reduced complexity maximum likelihood (ML) detection scheme, which uses a predecoder guided local exhaustive search, for V-BLAST systems. A polygon searching algorithm and an ordered successive interference cancellation (O-SIC) sphere searching algorithm are major components of the proposed multistep ML detectors. The effects of predecoder's performance on the total decoding complexity was studied by simulation. The complexity of the proposed algorithm depends on the operating signal to noise ratio (SNR) of the system. At reasonable high SNRs, its complexity is comparable to that of O-SIC algorithm, a commonly used decoding algorithm for V-BLAST. For V-BLAST systems using a large number of transmit antennas, we also propose a new detection algorithm termed ordered group-wise interference cancellation (O-GIC) to further reduce decoding complexity. The O-GIC based detection scheme is not a ML detection scheme, however, its performance is shown to outperform that of the O-SIC.
Adaptive Parametric Schemes for Analysis and Synthesis of Musical Signals
Journal of The Audio Engineering Society, 2001
An adaptive approach to the analysis and synthesis of musical signals is presented. These musical... more An adaptive approach to the analysis and synthesis of musical signals is presented. These musical signals are modeled as nonstationary time-varying signals with mixed spectra. A frame-by-frame-based analysis and synthesis approach is adopted to capture the important time-varying nature of the musical signals. Through data analysis the relationship between a number of factors is discussed, such as modeling accuracy and efficiency, frame length, model order, and accuracy of parameter estimation. Once the signal parameters have been extracted from data analysis, the sounds are synthesized using these parameters. Analysis and synthesis results using variable model orders and variable frame lengths in combination with high-resolution parameter estimation and residual modeling are presented. The results show that the proposed algorithms are computationally efficient and effective when synthesizing piano and trumpet tones.
Low Complexity Channel Estimation and Equalization for Block Transmission Systems
MILCOM 2005 - 2005 IEEE Military Communications Conference
In this work, a channel estimation scheme is introduced to single carrier block transmission syst... more In this work, a channel estimation scheme is introduced to single carrier block transmission systems. Compared to the conventional method, the proposed scheme has similar estimation accuracy but with higher transmission efficiency and lower complexity. Under the anti-polar constellation constraint, the optimal training sequence design is studied. Furthermore, a simplified minimum mean square error (MMSE) block equalizer is derived. Numerical results show that the proposed equalizer outperforms the conventional method
Low-rank MMSE detector for synchronous DS-CDMA
Conference Record of the Thirty-Third Asilomar Conference on Signals, Systems, and Computers (Cat. No.CH37020)
ABSTRACT
Maximum likelihood parameters estimation in non-uniform noise fields using moving array
This work develops an iterative solution to maximum likelihood estimation of source parameters in... more This work develops an iterative solution to maximum likelihood estimation of source parameters in unknown but partially correlated non-uniform noise field when a moving array is used for data collection. With the proposed solution, the temporal frequencies and the direction of arrivals (DoAs) of source signals can be obtained effectively. Computer simulated experiments are carried out to demonstrate the feasibility of the developed method under different array motions.
A multichannel cross-spectrum density estimator based on canonical correlation analysis
2012 IEEE 7th Sensor Array and Multichannel Signal Processing Workshop (SAM), 2012
In this work, the problem of multichannel cross-spectrum density (MCSD) estimation is studied. Ba... more In this work, the problem of multichannel cross-spectrum density (MCSD) estimation is studied. Based on a multichannel data model, the classic periodogram based MCSD estimator and the minimum variance (MV) based MCSD estimator are tested for cross-spectrum density estimation. Our major contribution in this work is a canonical correlation analysis (CCA) based MCSD estimator, relying on the inherent maximization arguments of CCA. It is demonstrated through a model based multichannel simulation example that the newly proposed CCA-MCSD estimator is of high frequency resolution as well as good sidelobe suppression properties, and can serve as an excellent candidate for MCSD estimation.
Proceedings. (ICASSP '05). IEEE International Conference on Acoustics, Speech, and Signal Processing, 2005.
Realizing the large user capacity planned for ultrawideband (UWB) systems motivates multiuser det... more Realizing the large user capacity planned for ultrawideband (UWB) systems motivates multiuser detection (MUD). However, it is impractical to implement conventional chip-rate MUD methods, because UWB signaling gives rise to high detection complexity and difficulty in capturing energy scattered by dense multipath. In this paper, we develop a reception model for UWB multiple access based on frame-rate sampled signals in lieu of chip-rate samples. This model enables low-complexity MUD, of which we examine a reduced-rank Wiener filter for blind symbol detection. We show that frame-rate UWB samples have a small number of distinct eigenvalues in the data covariance matrix, resulting in warp convergence of reduced-rank filtering. The proposed MUD method exhibits good performance at low complexity, even in the presence of strong frequencyselective multipath fading.
In this Letter, the authors present a closed-form derivation of the probability density function ... more In this Letter, the authors present a closed-form derivation of the probability density function (PDF) for the notch depth (ND) of the dominant mode rejection adaptive beamformer (ABF). Their PDF expression closely approximates the true PDF for the case of single interferer at reasonable levels of interference-to-noise ratio. Their simulation results illustrate the close approximation between proposed distribution function and the ND histogram over a wide range of snapshots for fixed number of sensors.
Uploads
Papers by Hongya Ge