Timing of energy and data transmission
The reading and writing of the memory chip of the RFID tag as well as the simultaneous supply of energy (with passive transponders) must be coordinated in time. There are basically three different methods:
The data access to the memory chip of the transponder can be distinguished:
- Writing data access: Uplink to the transponder
- Reading data access: Downlink to the reader
Half duplex (HDX)
In half-duplex mode, the RFID read/write device and transponder transmit alternately, while the operating frequency is constantly pending.
Full duplex (FDX)
With the full duplex method, RFID read/write device and transponder can send and receive simultaneously. For this to work, the transmission paths (uplink and downlink) must be separated. In most cases, two sidebands are used for the operating frequency. The operating frequency itself is used for energy transmission and is continuously available.
In sequential systems, the data exchange between RFID read/write device and transponder runs alternately, as in half-duplex. However, the carrier frequency is only available during an uplink, i.e. data access writing to the transponder.
Sequential systems use active and semi-active tags, which have their own energy source, i.e. battery, and only need to be "activated" by this carrier frequency.
Here is an overview of the different data and energy transmissions: