# Low-Power, High Data-Rate Digital Capsule Endoscopy Using Human Body Communication
## 2 CEHBC System Architecture
### CEHBC Physical Structure  
Figure 2 shows a block-diagram of the proposed system consisting of a CEHBC transmitter (Tx), electrocardiogram (ECG) electrodes, and the CEHBC receiver (Rx). Figure 2a is the CEHBC Tx including the lens, an image sensor, light emitting diodes (LEDs), CEHBC Tx interface (CEHBC-TXIF), the CEHBC Tx digital block (CEHBC-TXD), a signal electrode, a ground (GND) electrode, and batteries. Figure 2b is the CEHBC Rx comprising a CEHBC analog front end (CEHBC-AFE), a CEHBC Rx digital block (CEHBC-RXD), a CEHBC Rx interface (CEHBC-RXIF), and a micro controller unit (MCU). Figure 1: Example of the use of the wireless capsule endoscopy (WCE) system to explore the state of the small intestine. Figure 2: Block-diagram of the proposed capsule endoscopy with a human body communication (CEHBC) system: **(a)** CEHBC transmitter; **(b)** CEHBC receiver. The CEHBC Tx is inside the capsule that is inserted into the human body. The CEHBC Rx and the receiving ECG electrodes are placed on the exterior of the human body. The CEHBC Tx is capsule -shaped, and it is swallowed. On one end, the CEHBC Tx is a transparent dome-shaped lens that is able to observe the appearance of internal organs. A sensor captures the image showing the internal condition while LEDs illuminate the space near the sensor. The CEHBC-TXIF stores the image data from the image sensor in the memory and converts the raw data to the input data formats that are available in the CEHBC-TXD. The CEHBC-TXD transmits the signal that is modulated by the FSDT technique using HBC. The signal electrode radiates the Tx signal. The GND electrode serves as the reference ground for the system. Batteries supply the voltage that is needed to operate the entire endoscope. The CEHBC-TXD transmits the image data, configuring a one-frame signal. The CEHBC-TXD is composed of a preamble generator, a LineSync generator, a cyclic redundancy check (CRC) encoder, a serial-to-parallel (S2P), a frequency selective (FS) spreader, and a multiplexor (MUX) block. The preamble generator creates the signals that are needed to acquire synchronization of the frame signal, and it selects the optimal electrode pair. The LineSync generator makes the signals that are needed to acquire synchronization, and it compensates for the polarity of each line-by-line signal that carry the image data. The CRC encoder generates parity bits to determine whether errors have occurred during the transfer of the image data. The S2P block changes the data rate to apply the FSDT techniques. The FS spreader enables the spread of data and movement of the frequency band. The multiplexer (MUX) block routes the generated data values into a specified transmission frame period. The receiver of the capsule endoscope receives signals from a plurality of ECG electrodes attached to the exterior of the human body. The signal received from an electrode is a low-amplitude signal and it should be converted into a digital signal via the CEHBC-AFE block. The converted digital signal is input into the CEHBC-RXD block, which performs reverse digital signal processing (such as the de-spreading and demodulation) of the CEHBC-TXD block. The CEHBC-RXIF transmits the demodulated image signal to the MCU or to the PC software. It is possible to observe the image of the organ interior via the image viewer. The CEHBC-AFE consists of a switch block, a differential amplifier, a filter block, a clock, and data recovery (CDR). The switch block changes the channel of the electrode combination to select the optimal combination of receiving electrodes. The differential amplifier amplifies the low amplitude signal. The filter block removes the noise, and the CDR processes the asynchronous data. The CEHBC-RXD is made up of a preamble processing unit, LineSync block, FS de-spreader, parallel-to-serial (P2S) convertor block, and a CRC decoder. The preamble processing unit finds the start of the frame data received and selects the best electrode pair.