Jörgen Nordberg

Face Detection using Local SMQT Features and Split up Snow Classifier

The purpose of this paper is threefold: firstly, the local successive mean quantization transform features are proposed for illumination and sensor insensitive operation in object recognition. Secondly, a split up sparse network of winnows is presented to speed up the original classifier. Finally, the features and classifier are combined for the task of frontal face detection. Detection results are presented for the MIT+CMU and the BioID databases. With regard to this face detector, the receiver operation characteristics curve for the BioID database yields the best published result. The result for the CMU+MIT database is comparable to state-of-the-art face detectors. A Matlab version of the face detection algorithm can be downloaded from http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=13701& objectType=FILE.

Adaptive Fingerprint Binarization by Frequency Domain Analysis

This paper presents a new approach for fingerprint enhancement by using directional filters and binarization. A straightforward method for automatically tuning the size of local area is obtained by analyzing entire fingerprint image in the frequency domain. Hence, the algorithm will adjust adaptively to the local area of the fingerprint image, independent on the characteristics of the fingerprint sensor or the physical appearance of the fingerprints. Frequency analysis is carried out in the local areas to design directional filters. Experimental results are presented.

Non-coherent detection of impulse radio UWB signals based on fourth order statistics

Non-coherent receivers are an attractive solution for impulse radio (IR) ultra wideband (UWB) systems due to their low-complexity implementation and low power consumption. However, low-complexity detection is achieved at the expense of some loss in performance. In this paper, a non-coherent detection scheme based on fourth order statistics, i.e., kurtosis, is proposed for low data rate IR-UWB systems. The performance of a conventional energy detector (ED) and the proposed kurtosis detector (KD) is compared in terms of bit-error-rate (BER). The simulation results validate that the KD receiver outperforms a conventional ED receiver on both additive white Gaussian noise (AWGN) and IEEE 802.15.4a multipath channels.

Robust Weighted Non-Coherent Receiver for Impulse Radio UWB PPM Signals

This letter proposes an energy detection based robust weight estimation scheme for pulse-position modulated (PPM) impulse radio ultra-wideband (IR-UWB) signals using weighted non-coherent receiver (WNCR). Conventional data-aided WNCR (DA-WNCR) scheme estimates the weighting coefficients, or channel state information (CSI), using a large number of training symbols over time-varying channels. In contrast, the proposed Robust WNCR (R-WNCR) scheme is non-data-aided (NDA), adaptive and robust to channel variations. The proposed R-WNCR estimates the weighting coefficients adaptively based on the received stochastic data, and the weight estimation process is refined using a decision directed approach.

On histograms and spatiograms - introduction of the mapogram

This paper introduces the concept of a mapogram. A ma- pogram may be viewed as a special form of spatiogram, which is a histogram containing additional spatial information. Additionally, this paper presents theory relevant to the creation of a proposed mapogram. A similarity measure derived from the Bhattacharyya coefficient is obtained in order to make comparisons between mapograms. Examples using a mapogram are given.

Improved Adaptive Fingerprint Binarization

In this paper improvements to a previous work are presented. Removing the redundant artifacts in the fingerprint mask is introduced enhancing the final result. The proposed method is entirely adaptive process adjusting to each fingerprint without any further supervision of the user. Hence, the algorithm is insensitive to the characteristics of the fingerprint sensor and the various physical appearances of the fingerprints. Further, a detailed description of fingerprint mask generation not fully described in the previous work is presented. The improved experimental results are presented.

Detection of Impulse Radio Ultra-Wideband Signals using Recursive Transmitted Reference Receivers

For the detection of impulse radio (IR) UWB signals, complex RAKE receiver or low-complexity transmitted reference (TR) autocorrelation receivers can be used. However, there is a performance loss associated with the low-complexity TR scheme. This paper proposes recursive structures of the conventional TR and averaged TR schemes to improve the detection performance of IR-UWB signals. The performance of proposed schemes is evaluated over the standard IEEE 802.15.4a multipath channels. The performance is compared with conventional TR receivers in terms of uncoded bit-error-rate (BER), assuming that the channel is quasi-static. For averaged and recursive averaged TR schemes, the TR sequence is also slightly modified. The simulation results validate that the proposed schemes has better performance by about 2 dB than the conventional TR and averaged TR receivers.

An Energy-efficient Signaling and Detection Scheme for Transmitted Reference UWB Systems

The transmitted reference (TR) schemes do not require the complex task of channel estimation and provide a simple receiver structure. However, the low-complexity detection in conventional TR scheme is achieved at the expense of 50% energy/rate loss. In this paper, an energy-efficient TR signaling and detection scheme is presented with the aim to improve the performance of conventional TR impulse radio UWB system. The proposed scheme is a combination of the conventional TR scheme and the differential TR scheme. The simulation results validate that the proposed TR scheme utilizes 1.76 dB less energy per bit and recovers 25% rate loss of conventional TR scheme, while maintaining the same BER performance. Further, the proposed ATR scheme improves the BER performance by about 2 dB using simple averaging of the reference pulses.

Design of spreading sequences using a modified bridging method

The performance of a code division multiple access system depends on the correlation properties of the employed spreading code. An auto-correlation function with a distinct peak enables proper synchronization and suppresses intersymbol interference. Low cross-correlation values between spreading sequences are desired to suppress multiple access interference. However, these requirements contradict each other and a trade-off needs to be established. In this paper, a modified bridging method is proposed to minimize cross-correlation with auto-correlation being allowed to lie within a fixed region. This approach is applied to the design of complex spreading sequences.

Non-Coherent Fourth-Order Detector for Impulse Radio Ultra Wideband Systems: Empirical Evaluation Using Channel Measurements

Low-complex and low-power non-coherent energy detectors (EDs) are interesting for low data rate impulse radio (IR) ultra wideband (UWB) systems, but suffer from a loss in performance compared to coherent receivers. The performance of an ED also strongly depends on the integration interval (window size) of the integrator and the window position. This paper presents a non-coherent fourth-order detector (FD) which can discriminate between Gaussian noise signals and non-Gaussian IR-UWB signals by directly estimating the fourth-order moment of the received signal. The performance of the detectors is evaluated using realistic channels measured in a corridor, an office and a laboratory environment. The results show that bit-error-rate (BER) performance of the proposed FD receiver is slightly better than the ED in low signal-to-noise ratio (SNR) region and its performance improves as the SNR increases. In addition, BER of the FD receiver is less sensitive to overestimation of the integration interval making it relatively robust to variations of the channel delay spread. Finally, a criteria for the selection of integration time of the proposed detector is suggested.