4. Communication and information coding

Once the RFID tag circuits have been powered (by remote interrogator supply or battery-assisted technology), the next step is to adapt the information to the transmission channel, so that it can be transmitted from the interrogator to the tag(s) (uplink), or from a tag to the interrogator (downlink).

It's useful to distinguish between modulation and coding of information. Coding refers to the way in which the information to be transmitted is represented. This information is a sequence of logical "0s" and "1s". Due to the limited processing resources in RFID tag chips, the codes used remain simple and do not, until now, employ complex mappings. The codes used must therefore represent each logical bit in isolation. Groupings in the form of symbols of 2 or even 3 bits (as in complex I/Q modulations) are not current practice. Modulation is the way in which the information...