# Low-Power, High Data-Rate Digital Capsule Endoscopy Using Human Body Communication
## 2 CEHBC System Architecture
### CEHBC Data Frame Structure  
Figure 3 presents the data frame structure of the CEHBC system. One frame signal requires the transmission time of at least 484 \(\times\) 660 \(\upmu\)s (= 319,440 \(\upmu\)s) to transmit the 480 \(\times\) 480 byte video graphics array (VGA) image signal. Before the transfer of the specific information data and the image data, the first two lines perform the functions of driving the receiver CDR, finding the best combination of reception electrodes, and acquiring the frame synchronization. The CEHBC Rx uses the CDR, so it needs a CDR lock time section of 100 \(\upmu\)s, which is configured with pattern data repeated with \"1\" and \"0\" bits for accurate operation of the CDR.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Description** \\ \hline application & Inbody-to-Onbody (capsule endoscopy) \\ main clock frequency & 32 MHz \\ modulation & direct digital frequency selective digital transmission (64 b Walsh code) \\ frequency band & 8–16 MHz \\ resolution & image data 480 \(\times\) 480 byte (3.13 f/s) \\ frame Length & 319,440 \(\upmu\)s \\ data rate & maximum 6 Mbps \\ preamble & combination of short preamble and long preamble \\ linesync & 5-bit pseudo-random noise (PN) code \\ cyclic redundancy check (CRC) & CRC-12 polynomial \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of capsule endoscopy with a human body communication (CEHBC) system.  
Figure 3: Data frame structure of the CEHBC system.  
The CEHBC data frame is different from that of a conventional communication system. The CEHBC uses preamble sections to generate a plurality of preamble signals. This method requires selection of the optimal combination of electrodes while varying the combination of receiving electrodes. At this time, the number of preamble transmissions is determined by the number of electrodes attached to the body, and it can be expressed in Equation (1). Here, CEnum is the number of electrode pair combinations, n is the total number of electrodes, and r is the number of electrodes selected:  
\[ECnum=\frac{n!}{r!(n-r)!} \tag{1}\]  
For example, if the number of the receiving electrode is eight, the CEHBC data frame uses 30 preamble sections that contain the 28 preamble sections (\(n=8\), \(r=2\)) to test the receiving environment, one preamble section for confirmation of the selected electrode pair, and one last preamble section to indicate the last preamble transmission. In addition, switch time (SWT) sections are the physical time needed to change the reception electrodes according to the chosen combination out of the 30 options. By comparing the preamble correlation values for 28 pieces of the received signal, the CEHBC system picks the electrode pair with the maximum correlation output and is able to select the electrode pair that has the most excellent reception accuracy and sensitivity.  
The LineSync section that generates the signal for synchronizing the line data is located in the first part of the line to prevent missing the synchronization during long frame intervals (3-484 lines). Then each line includes a LineNum section to indicate the line number of the transmission data, the data section, and the CRC section to determine whether an error occurred in the transmission data. The tail section indicates the last zone of the line. The data section in the third line is with the fixed pattern information to find the start of the image signal and exposure information of the camera. The data section in the fourth line is placed with the frame data information, indicating the number of the transfer frame. The data sections in the other lines are filled with 484 \(\times\) 480 byte image data.