B.T. Tan

Adaptive error coding using channel prediction

In this paper, we construct a finite-state Markov chain model for a Rayleigh fading channel by partitioning the range of the received signal envelope into K intervals. Using a simulation of the classic two-ray Rayleigh fading model, a Markov transition probability matrix is obtained. Using this matrix to predict the channel state, we introduce an adaptive forward error correction (FEC) coding scheme. Simulation results are presented to show that the adaptive FEC coding scheme significantly improves the performance of a wireless communication system.

Overmodulation in subcarrier multiplexed video FM broad-band optical networks

The probability of an SCM (subcarrier multiplexed) signal falling outside the linear region of a laser diode is calculated in order to determine the overmodulation that may be practically employed for multichannel video distribution in single-octave SCM networks. The overmodulation is predicted as a function of the number of subcarriers in single-octave SCM systems supporting up to about 70 FM video channels, for SNRs (signal-to-noise ratios) of 47 dB (I/PAL), and 56 dB (M/NTSC). The RMS optical modulation index (OMI) is demonstrated to be a more useful performance parameter than the linear OMI in SCM systems carrying a large number of channels. A 47 dB weighted SNR (with 4 dB margin) is deemed sufficient for acceptable picture quality in cable distribution systems, whereas a 56 dB value would be required for long-distance point-to-point optical links. RMS OMI values of around 70 and 50, respectively, can be employed. >

On Binary DPSK Error Rates Due to Noise and Intersymbol Interference

This paper presents a new series for evaluating the conditional bit error rate (BER) of a given transmitted data sequence in a band-limited binary differential-phase-shift-keyed system. This series involves modified Struve functions and it was found to have converged quickly. The conditional BER can then be averaged over all possible bit sequences to yield the system BER. The results obtained are close to those reported by G. J. Marshall. In our analysis the noise samples a bit period apart were assumed to be uncorrelated.

Series Representations for Rice's Ie Function

Two new series representations for the Rice function Ie (k, x) are presented. One of the series involves the modified Struve functions and the other involves the modified Bessel functions. These two series complement each other in their convergence speeds as functions of the values of k and x . The truncation error bounds are derived for both series. Therefore, they can be used alternatively with high efficiency and known precision.

Effects of the ground on power-line communications

In this paper, a radiated-emission model of broad-band power-line communications (PLCs) in the frequency range from 1 to 30 MHz is presented. The model is based on the full-wave approach with the formulations of the extracted Maxwell equations. The transmission characteristic of the power line is obtained with the boundary conditions. The effects of the ground on the transmission characteristic and radiation are emphasized. Experiments were made to check the validity and accuracy of our model. It shows that the model is useful in predicting the effect of the ground on the radiation of straight PLCs.

Improved design for symmetrical six-port microstrip coupler (based on double-ring-with-star topology)

Other researchers have designed a symmetrical six-port microstrip coupler that yields a bandwidth of 7%. It has been found in this paper that a change of the design topology allows the couplers bandwidth to be increased. A simple-to use computer model of the double-ring-with-star prototype has also been developed and tests have confirmed that good agreement can be expected between the predicted and measured results.

Design and analysis of discrete Fourier transform coding techniques in the presence of AWGN

The discrete Fourier transform (DFT) has been proposed as a suitable technique for data transmission over channels that introduce impulse noise. However, in the presence of band-limited additive white Gaussian noise (AWGN), the performance of DFT coding is degraded. This paper deals with techniques for single impulse correction and combating the detrimental effect of band-limited AWGN.

Double-through equalization technique an efficient strategy for processing of teletext signals

In urban areas teletext signals are easily corrupted by multipath propagation which is produced as a result of reflection of the signal on the surrounding buildings. An efficient strategy for processing of teletext signals under multipath propagation is presented. A distinct feature of the teletext transmission which makes it different from the conventional data transmission systems is that the data is transmitted in the form of packet during each vertical blanking interval (VBI) of the TV signal. This means that there is an ample time during each TV frame for processing the teletext signal that has been received in the last VBI. Noting this, we propose a semi-off-line processing scheme, called double-through equalization, as an efficient mean of processing the teletext signals. Practical results are presented which shows that using the double-through equalization scheme the bit error rate can be reduced by 20-30 dB compared to the case where no equalizer is used.

Public CT2 system with two-way calling

In the current implementation of most CT2 systems, only handset initiated calls are allowed. The paper describes a design to allow two-way calling for the CT2 system with minimal modification to the current CT2 infrastructure as well as the public switched telephone network (PSTN). The design makes use of centralized databases in home location register (HLR) and visitor location register (VLR) to track the location of the handsets. A diagram of the CT2 two-way calling system is depicted. The authors also did a computer simulation of the proposed system to determine the potential area of congestion in the system.

Overmodulated single-octave subcarrier multiplexed optical networks for multichannel FM video distribution

In subcarrier multiplexed (SCM) multichannel FM video systems, the carrier-to-noise ratio per channel may be increased by overmodulating the laser diode source. The authors predict the overmodulation that may be employed in practice for single-octave SCM transmission in passive optical networks. It is shown that optical modulation indices (OMI) exceeding 500% may be used if the number of subcarriers is large. A 47 dB signal-to-noise ratio (with 4 dB margin) is deemed sufficient for acceptable picture quality in cable distribution systems, while a 56 dB value would be required for long-distance point-to-point optical links.<<ETX>>