Application Of Spread Spectrum Techniques Research Articles

Systematic Reduction of Peak and Average Emissions of Power Electronic Converters by the Application of Spread Spectrum

This paper deals with the application of spread spectrum techniques on power electronic converters to reduce electromagnetic disturbances. These techniques aim for a spreading of the harmonics in a frequency domain in order to distribute the power over a wider frequency range. By doing so, the levels of the harmonics drop. In this paper, both peak and average detector measurements are considered. It is shown that different parameters are required to minimize either peak or average emissions. The reduction of peak and/or average emissions is mathematically described for a sine wave as a harmonic of pulse width modulation signals. These spread harmonics overlap for high orders and/or high-frequency variations. It is shown that this effect is a limiting factor for spread spectrum in practical applications. The resulting maximum achievable reduction is analyzed. From these results, parametrization strategies are derived to fulfill specific requirements. In test setups, the precision of the proposed parametrization strategies is demonstrated. Additionally, it is shown that the results for peak measurements can also be applied to quasi-peak measurements.

Jammer Sensing and Performance Analysis of MC-CDMA Ultrawideband Systems in the Presence of a Wideband Jammer

Jamming, either intentional or unintentional, is a big, and increasingly prevalent, problem for many wireless communications systems. A well-known countermeasure is the application of spread spectrum techniques that spread the information over a bandwidth possibly larger than that of the jammer thereby exploiting processing gain for jammer suppression; an especially attractive spreading technique is multi-carrier code division multiple access (MC-CDMA), due to its flexibility to shape transmit spectra, resilience to inter-symbol interference, and ease of implementation. Such spreading needs to be combined with spectral notching at the receiver RF frontend, to avoid saturation of the low-noise amplifiers. Such notching, in turn, requires the receiver to sense the band over which the jammer is operating. In this paper, we consider an MC-CDMA transceiver that is being jammed by a wideband non-stationary jammer. For a Rayleigh fading channel, we derive the symbol error rate for the case that the jammer parameters are available at the receiver. We derive the Maximum-Likelihood-based and Log-Likelihood Ratio-based jammer parameter estimators for both the case where channel state information is available during jammer sensing and when it is not. The performance of various jammer parameter estimation schemes is studied using Monte Carlo simulations and with the channel impulse responses collected from the wireless propagation measurements conducted in the 10–12 GHz band.

Analytic Performance of Monopulse Spread Spectrum Tracking System in Multiple-target Scenario

With the application of spread spectrum technique in satellite tracking, the accuracy of CDMA-based multiple-target tracking needs to be analyzed. In this paper,we present the analytic form of the multiple-target tracking performance through mathematical deduction, together with simulation results.

Spread Spectrum OFDM Modem for HF Voice-Band Link over Fading Channels

This paper deals with the application of spread spectrum techniques to MultiCarrier HF modems. OFDM modems are a special option for the transmission over the high dispersive HF medium in front of single carrier modems. Our present contribution is now focused on the application of Spread Spectrum techniques to improve its fading robustness. The transmission bandwidth is the standard voice band channel in the HF band where the spread spectrum characteristic means that one symbol is transmitted over N times the spectrum in the classical N-OFDM scheme. The motivation of this idea is the observation of the OFDM modems behaviour over fading channels with deep nulls showing a quite different performance between carriers: those in the vicinity of deep nulls provide a much higher Bit Error Rate (BER) than others far away of the nulls. Our proposal intends to spread different symbols over all the subcarriers simultaneously in order to homogenize performances. This approach, performed by orthogonal codes, shows an evident link with MC-CDMA techniques. In addition, Multi User Detection (MUD) strategies as Interference Cancellation (IC) with coherent detection are also applied in order to improve its performance.

Infrared wireless communication using spread spectrum techniques

The performance of nondirected line-of-sight indoor wireless infrared communication systems is mainly affected by ambient light-induced shot noise, multipath dispersion and interference produced by artificial light sources. Application of spread spectrum techniques to combat multipath dispersion and artificial light interference is presented, with bit error rate analysis considering these two effects. Experiments were carried out to verify the bit error rate analysis and to demonstrate the practical performance of a spread spectrum system. For the line-of-sight link investigated, both experimental and analytical results show that a spread spectrum system operating at 2 Mbit/s and with spreading factor 31 suffers a power penalty of less than 0.5 optical dB due to multipath dispersion, and less than one optical dB penalty is incurred under the influence of 10 dB artificial light interference.