Boon Poh Ng

A flexible array synthesis method using quadratic programming

A highly flexible synthesis method for an arbitrary array is proposed to best approximate a desired array pattern in a minimum-mean-square-error sense. The basic idea of the technique is to form a quadratic program with its cost function given by the mean-square error between the array response and a properly selected pattern described by a known mathematical function. This quadratic program can be a constrained or unconstrained optimization problem depending on the requirements of the desired array pattern. In formulating the quadratic program, no assumption has been made on the gain/phase response or characteristics of the individual array elements. Therefore, one can synthesize an array of arbitrary shape to any appropriate pattern with the characteristic of the array elements taken into consideration as long as one is able to model the array accurately. The proposed method is used to synthesize arrays of different shapes, linear as well as planar arrays (including rectangular and circular planar arrays), using a Chebyshev polynomial or zero function as a design template, to illustrate the feasibility of the proposed method. >

A Real-Time Indoor WiFi Localization System Utilizing Smart Antennas

In this paper, we study issues associated with the implementation of a real-time WiFi localization system for an indoor environment. This system utilizes smart antennas to receive signal strength from a mobile target (access point) and send the signal strength information to a data processing station. This information is combined to find the direction of arrival of the signal and triangulate the mobile target position. No prior radio-frequency finger-printing is required, thus reducing the computational complexity. We present experimental results to illustrate the performance and accuracy of the localization system for an indoor environment set-up1.

MUSIC-Like DOA Estimation Without Estimating the Number of Sources

This paper presents a new direction-of-arrival (DOA) estimation algorithm, where DOA estimation is realized in the framework of beamforming by introducing a new optimization problem. The new optimization problem aims to minimize the variance of the array output subject to retaining the output power at the look direction and precluding a trivial solution. The proposed algorithm is equivalent to the multiple signal classification (MUSIC) algorithm in some special cases, it is therefore named as the MUSIC-like method. However, different from the classical MUSIC algorithm, the new method is not based on subspace decomposition and the number of sources is hence not required for direction finding. This enables us to avoid performance deterioration caused by incorrect source number estimation. The effectiveness and advantage of the proposed algorithm is theoretically investigated, and computational complexity is also addressed. To verify the theoretical analysis, computer simulations are implemented and comparisons with other algorithms are made.

Applications of the SRV constraint in broadband pattern synthesis

In this paper, the spatial response variation (SRV) is defined to measure the fluctuation of the array spatial response within the desired frequency band. Applying the SRV constraint in the optimization formulations to produce the frequency invariant beampattern (FIBP) is investigated. An efficient way to formulate the FIBP synthesis problems is proposed. Examples are demonstrated to show the effect of applying the SRV constraint in broadband pattern synthesis.

Sequency-Ordered Complex Hadamard Transform: Properties, Computational Complexity and Applications

In this paper, the generation of sequency-ordered complex Hadamard transform (SCHT) based on the complex Rademacher matrices is presented. The exponential form of SCHT is also derived, and the proof for the unitary property of SCHT is given. Using the sparse matrix factorization, the fast and efficient algorithm to compute the SCHT transform is developed, and its computation load is described. Certain properties of the SCHT matrices are derived and analyzed with the discussion of SCHT applications in spectrum analysis and image watermarking. Relations of SCHT with fast Fourier transform (FFT) and unified complex Hadamard transform (UCHT) are discussed.

A Practical Simple Geometry and Gain/Phase Calibration Technique for Antenna Array Processing

A calibration technique is proposed in this paper for an arbitrary array. This technique estimates the array sensor gain/phase and geometry with a set of simultaneous equations formed by using the MUSIC null spectrum property. Note that the technique does not use iterative calculation in estimating the array parameters and hence it has no convergent problem; however, it requires that n directions of arrival (DOAs) of signal sources to be known to calibrate the array which is perturbed n-dimensionally. The efficacy of the method is demonstrated by means of simulations and on experimental data collected with an antenna array operating in high-frequency radio band.

Ultra wideband direction finding using digital channelization receiver architecture

In this paper, UWB direction finding technique using digital channelization receiver architecture Is proposed. The basic idea of this technique is to split the UWB array output into multiple frequency channels and then down-convert each channel into much lower frequency, hence allowing the low sampling rate ADC to be used. Estimation of the DoA of UWB source is achieved by forming a direction finding function using the spectral information from channelizers output. A thorough performance analysis from simulation results is presented to verify the proposed technique and to investigate the effect of the systems parameters on the performance

Multiple UWB Emitters DOA Estimation Employing Time Hopping Spread Spectrum

In this paper, UWB Direction of Arrival (DoA) estimation using channelization receiver architecture proposed in [1] is extended to cover the case of multiple UWB emitters employing Time Hopping Spread Spectrum (TH-SS) multiple access technique. The DoA estimation is based on the spectral lines extracted from the channelizer. When considering the multiple-emitter case, these spectral lines are dependent on the hopping sequences assigned to the emitters (as derived in [2]). The principle behind the proposed method is to set the channelizer’s frequencies at which only the spectral lines from the desired UWB emitter are present while those from the other emitters are absent. This requires a proper design of the hopping sequences that govern the transmission of all emitters. First, an additive white Gaussian noise channel is considered to demonstrate the fundamental principle. Then, the estimation in a realistic multipath channel is addressed. Simulation results show that the direction finding function successfully indicates the DoA of the desired signal when the channelizer’s frequencies are set for the detection of that signal.

Conjugate Symmetric Sequency-Ordered Complex Hadamard Transform

A new transform known as conjugate symmetric sequency-ordered complex Hadamard transform (CS-SCHT) is presented in this paper. The transform matrix of this transform possesses sequency ordering and the spectrum obtained by the CS-SCHT is conjugate symmetric. Some of its important properties are discussed and analyzed. Sequency defined in the CS-SCHT is interpreted as compared to frequency in the discrete Fourier transform. The exponential form of the CS-SCHT is derived, and the proof of the dyadic shift invariant property of the CS-SCHT is also given. The fast and efficient algorithm to compute the CS-SCHT is developed using the sparse matrix factorization method and its computational load is examined as compared to that of the SCHT. The applications of the CS-SCHT in spectrum estimation and image compression are discussed. The simulation results reveal that the CS-SCHT is promising to be employed in such applications.

Performance of SCHT Sequences in Asynchronous CDMA System

In this letter, the performance of a new set of spreading sequences for a direct sequence (DS) code division multiple access (CDMA) system is examined. These new sequences are derived from sequency-ordered complex Hadamard transform (SCHT). Various correlation properties are presented and the performance of the new sequence is analyzed by comparing it with the other well-known existing spreading sequences, such as UCHT, WHT, Gold, small set of Kasami and m-sequences. According to the simulation results, it is shown that the SCHT sequences provide smaller mean square cross correlation values and offer better average bit error rate for an asynchronous CDMA system over the multipath fading channel.