GNU radio

Electric Field Measurement for Biomedical Application Using GNU Radio... 

This paper reports preliminary experiment where the human body was measured by a new experimental system. The previous experimental system consisted of a general-purpose spectrum analyzer that only measured amplitude of input signal in a certain frequency range. The new measurement system, introduced in this paper, consisted of a GNU Radio compliant peripheral and GNU Radio software. GNU Radio is an open source project where user can build special purpose receiver and transmitter in conjunction with a simplified peripheral. The measurement results indicated advantages of the new experimental system with GNU Radio. 

Keywords— electric field intensity, biomedical measurement, permittivity, GNU Radio, SDR. 

Fig. 2 Measurement system built with GNU Radio Companion (GUI of GNU Radio upper) and FFT plot of the received signal (lower)...

Advantages of the GNU Radio measurement system were discussed in comparison with the former system that consisted of generic spectrum analyzer. 

GNU Radio is an open source project of Software Defined Radio (SDR). It includes software drivers, library for C++ and Python [8], and graphic user interface (GUI) to build user-specified SDR. The project targeted peripherals whose specifications are open to the public. 

For the comparison, the same subject was measured 10 times by the spectrum analyzer with sweep generator built in the analyzer that was used in the previous studies. The other conditions were the same as the measurement by GNU Radio system. 

Figure 3 shows the relation between amplitude of the received signal and distance of the subject from home position. Ten measured data under each measurement condition were averaged and standardized (or divided) by the amplitude at home position of the moving table. Because the signal changes of the GNU Radio was remarkably greater than that of the spectrum analyzer, Y scales of the two measurements differed each other. 

Fig. 4 Relation between amplitude of the signal and subject location for each measurement where (a) GNU Radio and (b) spectrum analyzer were used respectively...

The peak heights of the GNU Radio and the spectrum analyzer from the respective minimum signal strength were 0.08 and 0.017, respectively. This difference was thought to be caused by unwanted signal leakage, too. 

The other difference was fiucmations along the signal curves. The signal of the GNU Radio was smoother than that of the spectrum analyzer. Figure 4 shows all 10 measured signal intensities under each condition. Obviously, the signal strengths of spectrum analyzer were more turbulent than those of the GNU Radio. 

Table 2 shows variances where the signal strength was standardized by signal changes, or respective maximum value subtracted by respective minimum value. All GNU Radio variances were significantly smaller than those of the spectrum analyzer at the significance level of 1%. 

Results of the experiment suggest GNU Radio contributed more precise measurement than generic measurement device. The authors plan to build prototype of the measurement system utilizing the GNU Radio and scan the human body two-dimensionally. Proper application of the method would be surveyed according to progress of the study. 

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