Kaoru Gotoh

APD Measurement for Evaluating Disturbances Related to the Performance of Digital Communication Systems

The measured values of electromagnetic disturbances should strongly correlate with degradation in the communication quality of digital wireless communication systems. The Amplitude Probability Distribution (APD) of a disturbance represents statistical information as applicable measurement readings that meet the above requirement. In this paper, correlations between APD measurements of disturbances and the bit error rate (BER) as a quality degradation index for victim systems are quantitatively investigated. Disturbance regulation by APD measurements is discussed from the viewpoint of protecting systems from disturbances. This investigation specifically considers the situation in which a repetition pulse disturbance impacts PHS and W-CDMA systems assumed as victims. The results confirm high correlations between the APD and BER not only experimentally but also theoretically under some conditions. A disturbance regulation criterion based on APD measurements is thus proposed for compliance testing of electronic appliances with the potential to act as disturbance noise sources.

Characteristics of Radiation Noise from an LED Lamp and Its Effect on the BER Performance of an OFDM System for DTTB

The characteristics of radiation noise from an LED lamp and its effect on the bit error rate (BER) performance of an orthogonal frequency-division multiplexing (OFDM) system for digital terrestrial television broadcasting (DTTB) are investigated. The waveform and frequency spectrum of radiation noise from an LED lamp are measured. A sequence of noise pulses is observed, caused by the switching circuit of the LED, and spread over the broadcast band of Japan. The relationship between the radiation noise from the LED lamp and its effect on the BER performance of the OFDM system using 64-quadrature amplitude modulation (64QAM) is evaluated using amplitude probability distribution (APD) measured with various resolution bandwidths. The behavior of the APD of the noise is similar to Gaussian noise when the resolution bandwidth becomes narrow. The BER performance of the OFDM system subjected to the noise of the LED lamp is estimated from the APD results, which agree well with measured results subjected to the LED noise. The characteristics of sequential LED noise are similar to the effect of Gaussian noise on the BER performance of the OFDM system for DTTB. Therefore, the APD measurement is a useful method to estimate the characteristics and effect of noise from an LED lamp on the OFDM system.

Development and Evaluation of a Prototype Multichannel APD Measuring Receiver

Development of a multichannel APD measuring receiver is necessary to enable evaluation of the impact of wideband disturbance emissions on digital wireless communication services which use multicarrier transmission systems. We describe technical details of the worlds first multichannel APD measuring receiver which we have developed using a general-purpose ADC-FPGA board. Our measurements of the basic performance of this receiver show that the receiver is suitable for practical use. We also used the developed receiver to measure the APDs of disturbance emitted from a microwave oven at five frequency points (1 MHz apart). These results indicate the significance of the multichannel APD measuring receiver.

Band-limitation effect on statistical properties of class-A interference

The effect of band limitation on the statistical properties of Middletons class A noise model is investigated. It is found that a uniformly weighted sum of statistically independent and identically distributed class A random variables becomes a new class A random variable with reduced impulsiveness. It is also found that bandlimited noise becomes class A noise if the impulse response of the filter has a rectangular envelope waveform. Since matched filters employed by DS-SS (direct sequence spread spectrum) or OFDM (orthogonal frequency division multiplex) systems usually satisfy the above condition, the results can be widely applied to the evaluation of the error probability of signal detection in such communication systems subjected to class A interference.

An Expression for Maximum Bit Error Probability Using the Amplitude Probability Distribution of an Interfering Signal and Its Application to Emission Requirements

It has been demonstrated that the amplitude probability distribution (APD) of an interfering signal provides an approximation for the bit error probability (BEP) of a radio communication system subjected to interference. The expression for BEP can be applied to the definition of emission limits for protecting a radio system. For communication systems employing multilevel modulation, the expression in some cases underestimates the maximum BEP when the interference is impulsive. In this paper, an improved BEP expression that removes the underestimation risk is derived considering the probability of multiple bit errors caused by one symbol error. On the basis of the new expression, a method of defining emission requirements is proposed by introducing a limit line that restricts the slope of the APD curve.

Evaluation of interference between MB-OFDM UWB and wireless LAN systems using a GTEM cell

In this study, the electromagnetic interference of an MB-OFDM UWB system with an IEEE802.11a wireless LAN was evaluated using a GTEM cell. Band #3 (out-of-band radiation for 11a) in the band plan of the MB-OFDM UWB system and Band #4 (in-band radiation for 11a) were assumed to be two different types of interference. As a result, when the frequencies of the MB-OFDM UWB corresponded to Band #3, the MB-OFDM UWB system may not interfere with the wireless LAN. In the other band, although the interference power of the MB-OFDM UWB was less than the receiver noise of the wireless LAN, the MB-OFDM UWB system interfered with the wireless LAN. In addition, the separation distance was evaluated from the power inputted to the GTEM cell. As a result, for the vicinity of the minimum receiver sensitivity of the wireless LAN, the separation distance was about 3 m. Finally, the amplitude probability distribution (APD) of the MB-OFDM UWB system that was the interference source was evaluated. As a result, the APD characteristics of MB-OFDM UWB were slightly different from those of additive white Gaussian noise (AWGN).

Relation between electromagnetic noise from LED light bulb and its impact on bit error rate performance of DTTB

A relation between electromagnetic noise from an LED light bulb and its impact on BER performance of the DTTB is estimated from the APD measurement. First, the APD of the noise is measured with various resolution bandwidths. The characteristic of the APD of the noise is similar to the Gaussian noise when the resolution bandwidth becomes narrow. Then, the BER performance of the DTTB subjected to the noise of the LED light bulb is estimated from the APD result with the resolution bandwidth that is nearly equal to the subcarrier band range of the DTTB. As a result, the BER of the estimated result agrees well with measured results which are subjected to the LED light bulb and the Gaussian noise. Therefore, the effect of the noise from the LED light bulb on the DTTB is similar to the effect of the Gaussian noise.

Probe calibration by using a different type of probe as a reference in GTEM cell above 1GHz

Calibration of an electric field probe using a different type and size of probe as a reference is carried out in a GTEM cell from 1 to 6GHz. We compared our results with those of calibration in an anechoic chamber to determine the effectiveness of the calibration. The difference between the calibration factors of the GTEM cell and the anechoic chamber increases when the probe is calibrated in an area in which the electric field distribution is nonuniform. Therefore, it is important to place the probe in an area with good uniformity or maintain the uniformity of the electric field in the GTEM cell when calibrating electric field probes with different dimensions.

Evaluation of Electromagnetic Interference Between UWB System and Wireless LAN Using a GTEM Cell

We propose the method of the interference evaluation between the UWB and the wireless LAN by using the GTEM cell that can test the receiver with the antenna built-in type in the paper. We show that the GTEM cell can be used in the frequency band of DS-UWB by the evaluation of the frequency response. The interference evaluation was conducted between wireless LAN IEEE 802.11 a and DS-UWB. As a result, even when the UWB signal is smaller than the receiver noise of wireless LAN, the throughput characteristics deteriorate than those in a case of the noninterference. Moreover, the signal of the DS -UWB was nearly equivalent to the AWGN in a case of the throughput variation of 64QAM Finally, we evaluated the separation distances in regulation limits of FCC and Japan.

Effect on electric field of foam block in GTEM cell

The effect on the electric field of a foam block in a GTEM cell was numerically investigated using the finite integration (FI) method. In particular, we focused on the frequency range of 1–16 GHz, for which the effect has not yet been sufficiently analyzed. We only modeled the tip of the GTEM cell, to focus on the change in the electric field strength from the foam block and also to reduce the computational resources required. We showed that the foam block increases the electric field strength when it is placed at the tip of the GTEM cell. Even though the change in the electric permittivity was small, the effect on the electric field strength was great. We then compared the analysis results with measurement results and found that good agreement was obtained between the two. We also investigated the effect that the size of the foam block has on the electric field. The electric field strength was found to increase when the block size increased. We concluded that the foam block may affect the electric field and increases the electric field strength in a GTEM cell.