# Low-Power, High Data-Rate Digital Capsule Endoscopy Using Human Body Communication
## 4 CEHBC System Measurement and Performance
### Performance of the CEHBC System  
Figure 10 displays the operation results transferred by utilizing the CEHBC system presented in this paper. Figure 10a is the output of the AFE amplifier. This result shows a process of testing 28 pairs of electrodes according to the selection algorithm, and displays a signal selected to transmit an image. The last preamble was selected with the electrode pair of preamble 27. The signal received from the selected electrode pair was a signal of a particular range level that was neither too large nor too small. Thus, the selected signal did not saturate, even after passing through the amplifier, and it had a state in which the signal judgment could be accurately performed. Therefore, it was confirmed that the electrode selection algorithm maintains the optimum received signal quality state. Figure 10b is an output image that arose from the transmission of the image data. Both images in Figure 10b have a common hardware structure that supports the same f/s and power consumption, with the only difference being the TX input type. Figure 10b (left) is the known pattern used for the functional verification of the implemented CEHBC system. Figure 10b (right) is the output image utilizing the CEHBC system, for which the source data is the image taken from the complementary metal-oxide-semiconductor (CMOS) image sensor. Table 3 exhibits the synthesized results of the CEHBC Tx digital block and CEHBC Rx digital blocks. The CEHBC Tx digital block was implemented using an Actel IGLOO AGLN125V5 FPGA (IGLOO nano version, Microsemi, San Jose CA, United States). It used about 52.25% (CEHBC-TXIF: 35.28%, CEHBC-TXD: 16.96%) of the total chip logic and consumed 6.34 mW of the power (CEHBC-TXIF: 2.63 mW, CEHBC-TXD: 3.71 mW). The power consumption value was predicted using calculating tools (Libero v11.8, Vivado March 2015). The CEHBC Rx was implemented using a Xilinx Artix7 XC7A50T FPGA (ARTIX version, XILINX, San Jose, CA, United States); it used about 16% of the total chip logic and consumed 114 mW of power. Figure 10: Operation results of the proposed system: (**a**) Output of the analog front end (AFE) amplifier; (**b**) Image results received by the CEHBC system: (left) Image data using a known pattern, (right) Image data using the CMOS image sensor. The BER results obtained from the saline tank experiment are as follows. The diameter size of the water tank is 22 cm and height is 30 cm. The signal used in the test was the known-pattern image signal of Figure 10b (right). The variables that could control the noise were set to a direction and a distance between the electrode and the capsule endoscope. The directions of the capsule varied for each electrode (E1-E8), and the BER performance was measured according to the distance between the electrode and the capsule. Each BER performance showed the error result from receiving 100 images with 480 \(\times\) 480 pixels. Table 4 represents the results of BER performance of CEHBC system. When the interval was 6 cm/11 cm, the image data was received without error. We confirmed that it was possible to receive images in all directions. When the gap was less than 1 cm, the distance between the electrode and the capsule was too close and led to the saturation condition of the signal, and made BER performance poor (>0.5). In actual clinical trials, such a condition may occur when the gap between the organs and the skin is small, such as for a child, and therefore algorithms developed in the future for processing a large received signal should be considered. Table 5 displays a comparison of the performance of the proposed CEHBC-TXD and the existing WCE transmitters. The CEHBC-TXD presented in this paper utilizes the HBC communication scheme, while the other WCE transmitters employ a RF communication scheme using another frequency band. Because it uses HBC communication implemented mostly by digital logic, the CEHBC system has low power consumption (3.71 mW).