As this is intriguing part of standard draft from engineering point of view, I decided to include a short description what it really is.
Transmitter is shown on the image bellow:
The description included in the standard is quite brief in this topic, but it gives a basic idea of what is included in this solution:
“The EFC specification is designed to provide robust performance for HBC. EFC transmitter is implemented with only digital circuits and needs one electrode (instead of antenna), and EFC receiver can be implemented without any blocks related to RF carrier signals (mixer, VCO, ADC/DAC, etc.). These allows EFC device to have very low implementation complexity and low power consumption.
There are two bands of operation centered at 16MHz and 27MHz with the bandwidth of 4MHz. Both operating bands are for the United States, Japan, and Korea, and the operating band centered at 27MHz is for Europe.”
“The data to be transmitted is created by mapping 4 bits (a symbol) from FIFO to a 16-bit chip. […] The 16-bit chip is then spread by applying FSC. The spreading factor of FSC used determines the final data rate. “
Also what is interesting, with this kind of communication it’s hard to keep the spectrum in some normal shape, so a special care should be taken to limit interferences with a 400Mhz medical band:
“A transmit spectrum mask shall be used to remove harmonics and possible interference in other bands, especially with 400MHz medical band. The transmit power spectrum shall be less than 0 dBr (dB relative to the maximum spectral density of the signal) for , -3 dBr for , -0.5 dBr/MHz for as a function of the frequency, and -33 dBr for , where fc is channel center frequency and fBW is the channel bandwidth. The recommended transmit spectrum mask for fc=16MHz is shown in Figure [below]”