Tazuko Tomioka

High-Sensitivity Carrier Sensing Using Overlapped FFT for Cognitive Radio Transceivers

A noise suppression technique using overlapped FFT for carrier sensing of cognitive radio is proposed. The energy detection method is modified. A broadband signal is FFTed and the averaged power of each bin throughout the carrier-sensing period is calculated and judged against a threshold. At the process, adjacent FFT frames are overlapped greatly but with sufficiently large interval compared to the sample-by-sample sliding window. As a result, the averaging effect of noise increases and false alarm (FA) and misdetection (MD) probabilities are improved with much smaller computation amount than the sample-by-sample sliding window case. Simulations on FA and MD probabilities are performed and the effectiveness is confirmed. A model to explain the phenomenon using oversampling was introduced.

A/D Converter Clipping Noise Suppression for High-Sensitivity Carrier-Sensing of Cognitive Radio Transceiver

A technique for suppressing the clipping noise of an analogue to digital converter (ADC) is proposed to achieve the high-sensitivity carrier-sensing of a cognitive radio transceiver. When a large bandwidth cognitive radio transceiver performs carrier-sensing, it must receive a radio wave that includes many primary user transmissions. The radio wave may have high peak to average power ratio and clipping noise may be generated. Clipping noise becomes an obstacle to the achievement of high- sensitivity carrier-sensing In the proposed technique, the original values of the samples clipped by an ADC are estimated by interpolation. Polynomial spline interpolation to the clipped signal is performed in the first step, and then SINC function interpolation is applied to the spline interpolated signal. The performance was evaluated and about 20 dB suppression of clipping noise was achieved with the medium degree of clipping.

Frequency control techniques in coherent multichannel LAN's

This paper describes frequency control techniques for cold start and channel recognition functions in coherent multichannel local area networks. A Z-cut quartz etalon can be used to stabilize the optical transmitter frequencies. The capture range and the influence of humidity on a Fabry-Perot etalon are discussed. The frequency deviation of the optical transmitter was estimated to be less than /spl plusmn/1 GHz in the long term. A double AFC loop has been proposed for local LD frequency control. It showed a wide capture range of /spl plusmn/100 GHz. Coherent FDM receiver switching to the desired channel was demonstrated over a range from 0 to 40/spl deg/C in an experiment. >

A Proposal of High-Flexibility Short-Range Cognitive Radio System

A new cognitive radio (CR) system for short-range high-capacity wireless communication is proposed. A transceiver selects 1 GHz-bandwidth main bands from the frequency range of 3-12 GHz, and places single-carrier modulated sub-bands at unused frequencies. The frequencies of main bands and sub-bands are flexibly changed according to the occupancy condition. A transceiver performs two kinds of carrier sensing. Longer duration carrier sensing is performed to recognize frequency occupancy conditions and determine the frequencies of main bands and sub-bands. Shorter duration carrier sensing is performed, which checks the sub-band frequencies just before transmitting to detect whether any primary system signal is included or not. The transceiver estimates the type of detected interference and transmission will be stopped if it is from a primary user. This system realizes the reduction of interference to other systems, and improves the throughput of the CR system itself. Furthermore, some of the key technologies to realize the proposed system are introduced.

Comparison of Techniques to Mitigate Wavelength Contention in a Photonic Network with Frequent Optical Path Setups

The characteristics of various techniques, including some new techniques, in mitigating wavelength contention in optical path setups were compared by simulations. The assumed network here is a WDM photonic network in which each node is equipped with a limited number of wavelength-tunable optical transceivers. In the photonic network, the frequency of optical path setups and releases is very high, because optical path lifetime is short and optical transceivers are time-shared, and therefore, the wavelength contention becomes a serious problem. In this paper, we propose four new techniques to mitigate the phenomenon. In those techniques, a new small-sized parameter, the history numbers, was introduced based on the conceptual requirements of the assumed network, namely, low-cost and low additional control load. The four proposed techniques are history recording (HR), history notifying (HN), conditional random selection (CRS), and HN with dithering target (HNDT). We have evaluated the characteristics of those techniques along with those of two conventional techniques: no mitigation and random selection (RS). The simulations were carried out while varying four parameters: the maximum generation number, the optical path lifetime, the number of wavelengths, and the number of optical transceivers per node. Consequently, it is clarified that for a sufficient number of wavelengths, namely, almost no limitation on number of wavelengths, the CRS technique is advantageous, and for a small number of wavelengths the HNDT technique is advantageous.

Proposal of an A/D Converter Clipping Noise Suppression Technique for High-Sensitivity Carrier-Sensing of Cognitive Radio Transceiver

A technique for suppressing the clipping noise of an analogue-to-digital converter (ADC) is proposed to realize a cognitive radio transceiver that offers high sensitivity carrier-sensing. When a large bandwidth cognitive radio transceiver performs carrier-sensing, it must receive a radio wave that includes many primary user transmissions. The radio wave may have high peak-to-average power ratio (PAPR) and clipping noise may be generated. Clipping noise becomes an obstacle to the achievement of high-sensitivity carrier-sensing. In the proposed technique, the original values of the samples clipped by an ADC are estimated by interpolation. Polynomial spline interpolation to the clipped signal is performed in the first step, and then SINC function interpolation is applied to the spline interpolated signal. The performance was evaluated using the signals with various PAPR. It has been found that suppression performance has a dependency on the number of samples clipped at once rather than on PAPR. Although there is an upper limit for the number of samples clipped at once that can be compensated with high accuracy, about 20dB suppression of clipping noise was achieved with the medium degree of clipping.