RFID Tag Counting Over Lossy Wireless Channels

A low-latency, accurate RFID counting scheme can be used as a fundamental building block to support more elaborated RFID query operations. RFID counting algorithms of such nature have been proposed recently by Kodialam et. al. [2], [3]. One distinct feature of these schemes is that they do not require the reader to explicitly identify individual tags and thus can help to preserve privacy of the RFID users. However, these schemes all assume a perfect communication channel between the reader and the tags which is not achievable in practice. Recent empirical measurement studies have found that the radio communication between an RFID reader and a set of seemingly "in-range" tags are still unreliable and non-deterministic due to ever-changing channel conditions. Worse still, given the stringent cost constraint, it is unlikely that standard channel estimation procedures can be applied for individual tags. In this paper, we propose a new algorithm, PELOC (Probabilistic Estimator for Lossy Channels), which can estimate the size of an RFID tag-set over unreliable, lossy wireless channels. In particular, PELOC can provide a good estimate while assuming no prior knowledge of channel parameters. It is scalable over a wide range of tagset size using a small, fixed protocol frame-size, which is critical for low-cost RFID tags with typically sub-par synchronization or timing control. PELOC is also adaptive in the sense that, it self-tunes the algorithm parameters according to the tag-set size and channel characteristics which are both unknown a priori.