Multipacket Reception of Passive UHF RFID Tags: A Communication Theoretic Approach

Abstract

This work develops a communication theoretic model for the design and analysis at the physical layer of a reader receiver structure for passive UHF RFID. The objective is attaining multi-packet reception capabilities which in turn help the fast resolution of multiple tags through a more rapid and power efficient arbitration of the tags collisions. In particular, we derive a parametric continuous time model for the subspace of a tag signal at the noisy receiver/reader, which in addition to being affected by fading and receiver delay, exhibits wide variations in the symbol frequency and transmission delay, due to imperfections in the RFID hardware design. Our main contribution is in showing that channel fading, the difference in delay and the tags frequency dispersion can be transformed from foes to friends by exploiting them in a multipacket receiver. In fact, signals colliding from different tags are more easily separable by estimating the sensor specific variation in frequency and delay and using these estimates in a multiuser receiver. In our study, we specifically consider a successive interference cancellation algorithm followed by a maximum likelihood sequence decoder, that iteratively reconstructs one signal contribution at a time and then removes it from the received signal. Numerical simulations show that the estimates and proposed algorithm are effective in recovering collisions. The proposed algorithm is then incorporated into a numerical simulation of the Q-protocol for UHF RFID tags and is shown to be effective in providing fast and power efficient arbitration.

A smart collision recovery receiver for RFIDs

“…Moreover, in [12], we have identified a potential throughput increase of more than five times in the case of a reader that can recover from a collision of up to eight tags in one slot and acknowledge two of them. Fyhn et al showed that channel fading, the difference in delay and the tag frequency dispersion can be used for easier separation of colliding signals in a multipacket receiver in [13]. In [14], Ricciato et al achieved a 20% to 25% gain in throughput by applying inter-frame successive interference cancellation (ISIC) with respect to traditional intra-frame SIC.…”

Performance Enhancement of the Rfid Epc Gen2 Protocol by Exploiting Collision Recovery

“…Under the singlereceive-antenna detection scheme category, Zero Forcing (ZF) and Successive Interference Cancellation (SIC) are used in [6]. Maximum Likelihood (ML) sequence decoders are considered in [11][12][13].…”

“…Although a typical RFID Reader may only communicate with at most one Tag at a time based on current single-Tag detection techniques, it has been demonstrated that multi-packet reception is practically feasible with various novel ad-hoc algorithms, such as Zero Forcing (ZF) and Successive Interference Cancellation (SIC) [6], Zero Constant Modulus (ZCM) [7], Maximum Likelihood (ML) [11][12][13], etc.. Hence, it is realistic to assume that on the physical layer the Reader can separate and decode collided Tag signals.…”

“…We refer to the simple case where two Tags transmit during the same slot. Note that in such case the aforementioned techniques for collision recovery achieve excellent performance with, for instance, a probability of 85% to decode both Tag replies reported in [12]. A first possibility for the Reader is to acknowledge only one Tag and discard the other.…”

Multipacket reception MAC schemes for the RFID EPC Gen2 protocol

“…Multipacket reception, as a result of the implementation of collision recovery techniques, has been extensively investigated in the literature [6][7][8][9][10][11][12][13] yielding highly reliable results. The common aspect of these works is the exploitation of diversity-combining techniques for blind source separation, i.e.…”