Tanee Demeechai

Beat noise in a non-coherent optical CDMA system

In optical CDMA systems, many optical waves are simultaneously incident on each receiver photodiode. Since the photodiode also acts as a square-law detector to the optical fields, beat noise can occur in the passband of the receiver. We show that considerable amount of beat noise can occur in even a non-coherent system.

Pulse-shaping filters with ISI-free matched and unmatched filter properties

Pulse-shaping filters which have intersymbol-interference-free properties, with or without matched filtering at the receiver, may reduce the hardware cost of modem systems in some applications. A new class of such filters, with the one given by Xia (see ibid., vol.45, p.1157-58, 1997) as a special case, is proposed. This is done by showing that such a filter can be deduced from any one of a wide variety of ISI-free filters.

On noise-limited performance of noncomplementary spectral-amplitude coding optical CDMA systems

Bit-error rate performance of noncomplementary spectral-amplitude coding optical code-division multiple access in digital communication systems is analyzed, taking into account thermal, shot, source intensity, and beat noises. This analysis is, in principle, more accurate than a recent work that embodies a significant approximation.

IEEE 802.15.4 BPSK Receiver Architecture Based on a New Efficient Detection Scheme

This paper proposes a new differential-detection scheme for IEEE 802.15.4 BPSK receivers. The proposed detection scheme derives not only the decision variables for data detection but also a timing signal ready for synchronization by a simple technique. A receiver architecture based on the new detection scheme is then proposed. Based on simulation results on the receiver performance, it is shown that with a conventional radio-frequency front end the receiver could meet at a big margin the sensitivity requirement of the IEEE 802.15.4 standard.

New stimulation pattern design to improve P300-based matrix speller performance at high flash rate.

OBJECTIVE We propose a new stimulation pattern design for the P300-based matrix speller aimed at increasing the minimum target-to-target interval (TTI). APPROACH Inspired by the simplicity and strong performance of the conventional row-column (RC) stimulation, the proposed stimulation is obtained by modifying the RC stimulation through alternating row and column flashes which are selected based on the proposed design rules. The second flash of the double-flash components is then delayed for a number of flashing instants to increase the minimum TTI. The trade-off inherited in this approach is the reduced randomness within the stimulation pattern. MAIN RESULTS We test the proposed stimulation pattern and compare its performance in terms of selection accuracy, raw and practical bit rates with the conventional RC flashing paradigm over several flash rates. By increasing the minimum TTI within the stimulation sequence, the proposed stimulation has more event-related potentials that can be identified compared to that of the conventional RC stimulations, as the flash rate increases. This leads to significant performance improvement in terms of the letter selection accuracy, the raw and practical bit rates over the conventional RC stimulation. SIGNIFICANCE These studies demonstrate that significant performance improvement over the RC stimulation is obtained without additional testing or training samples to compensate for low P300 amplitude at high flash rate. We show that our proposed stimulation is more robust to reduced signal strength due to the increased flash rate than the RC stimulation.

Using CDMA to Enhance the MAC Performance of ISO/IEC 18000-6 Type C

This paper proposes an improved RFID anti-collision protocol that incorporates a CDMA technique without incurring bandwidth expansion in the framework of the ISO/IEC 18000-6 Type C standard.

An optimization study on multi-section dipole antenna designs for printed UHF RFID

In this paper, we present an optimization study on multi-section dipole antenna designs for printed UHF RFID, in which the antenna structure is divided into several unequal sections of radiating areas. The optimization work is extensively performed on the thickness, the length, as well as the width of each section in order to obtain optimal-performance multi-section printed dipole antennas at the lowest possible cost. The simulation results illustrate that a four-section dipole antenna structure with each succeeding section having the width approximately equal to half the width of its prior section achieves superior antenna efficiency performance. The conductive ink consumption of this antenna design is reduced around 51% when compared with the conventional flat layer design in order to achieve the same level of antenna efficiency performance as the ideal copper-trace dipole antenna.

Performance of a Frequency-Domain OFDM-Timing Estimator

A frequency-domain algorithm for OFDM-timing estimation is considered useful when the OFDM system is to operate in a known narrowband interference channel, e.g., in a cognitive radio OFDM-based overlay system. We generalize a recently proposed frequency-domain algorithm for OFDM-timing estimation and then analyze the performance of the algorithm. The algorithm is based on a complex timing metric that has the mean of which the angle depends in an affine manner on the time offset. By computing the mean of the metric and the mean square of the metric component orthogonal to the mean, from the power-delay profile and noise condition of the channel, the channel-induced bias of the estimator is quantified and the root-mean-square of the estimation error is estimated. The discrepancy between analysis and simulation results on the root-mean-square error is less than one nominal sampling interval for a useful range of operating conditions.

An efficient receiver scheme for IEEE 802.15.4 BPSK systems

This paper proposes an efficient receiver scheme for IEEE 802.15.4 BPSK systems. It is built upon a recent detection scheme by complementing the recent scheme with a simple synchronization scheme and some other necessary parameter estimation processes. The resulting scheme lends itself to low-powers, low-complexity, and effective fixed-point implementation.

Dependence of crosstalk-induced beat noise on signal synchronism

In optical on-off-keying networks, power of beat noise induced by crosstalks from different sources at the same nominal wavelength depends on state of synchronization between signal and crosstalks. In this paper, such a dependence is analytically quantified and its effect on the optical networks is studied.