Separation of multiple passive RFID signals using Software Defined Radio

We present a practical design of an RFID reader that is capable of reading multiple passive tags through joint decoding. The reader is implemented and analyzed using the GNU Software Defined Radio system. We use low frequency (LF) 125kHz commodity MIT ID cards in the experiment, and discuss extensions to decoding high frequency (HF) tags. This design reconsiders opportunities available in the lower layers of RFID design. Physical layer communication is analyzed rigorously and a complete system design is introduced as a result. We demonstrate this by exploring the differences in amplitudes and phase offsets among signal components, multiple tags can be separated and efficiently decoded using joint decoding. System performance is analyzed with both implementation and simulation. Based on these results, we summarize opportunities for improving industrial auto-collision algorithms with multiple-tag decoding capability.