Analysis of time variant reliability information used in a multilevel decoding scheme for RFID and sensor signals

In medicine and other high-tech sectors, mobile RFID or sensor transponder systems are designed with high-Q antenna coils to increase the energy efficiency. Hence, the range of inductively coupled systems is improved; however, the bandwidth is decreased by 1 over Q . As a result, the reading performance is not limited by the energy supply, but instead by a high bit error rate. In this paper, we describe how the data detection in such narrow-band systems can be improved by a multilevel decoding scheme composed of an advanced maximum-likelihood receiver in the first stage and a soft Viterbi decoding scheme utilizing time variant reliability information in the second stage. An analysis of potential time-variant reliability information is given. The analysis relies on an underlying Bayesian model, which provides an a-posteriori probability indicating the reliability of the received input. As the final building block, a last decoding stage is discussed, which can be composed of a forward error correction that further exploits the reliability information at the second decoder output. Overall, the suggested system architecture results in a notable improvement of both bit and packet error rate, thus allowing the use of high-quality-factor antennas for efficient and reliable mobile RFID systems.