A smart collision recovery receiver for RFIDs

Abstract

In this work, we focus on framed slotted Aloha (FSA) and passive ultra high-frequency radio frequency identification multi-antenna systems with physical layer collision recovery. We modify the tags slightly by adding a so-called 'postpreamble' that facilitates channel estimation. Furthermore, we investigate the throughput performance of advanced receiver structures in collision scenarios. More specifically, we analyse the throughput of FSA systems with up to four receive antennas that can recover from a collision of up to eight tags on the physical layer and acknowledge all tags involved in that collision. Due to the higher collision recovery capabilities, the frame sizes can be significantly reduced, and thus, the throughput can be increased. We also derive analytically optimal frame sizes, given that a certain number of collisions can be resolved. We further study the constraints to the throughput due to the structure of our receiver and channel estimation for different collision scenarios. Furthermore, we propose a novel collision recovery method with two phases: first, a successive interference cancellation and, second, a projection of the constellation into the orthogonal subspace of the interference. Additionally, the inventory time, i.e. the number of slots necessary to successfully decode all tags in the reader range, is calculated and compared for different receiver types. A validation of our theoretical predictions is achieved by means of simulations. We show that by our proposed methods, we can realistically achieve more than ten times higher throughput or, equivalently, a reduction of the inventory time by more than 90%.

Exploiting joint sparsity in compressed sensing-based RFID

“…The light grey curves show the legacy approach used in [12][13][14] of T ps = e −1 ≈ 0.368 [33]. In [6][7][8], collision recovery schemes have been proposed that allow shortened frame sizes and, thus, increased throughput numbers. A reader with N R receive antennas can resolve up to 2N R collisions [8].…”

“…In [6][7][8], collision recovery schemes have been proposed that allow shortened frame sizes and, thus, increased throughput numbers. A reader with N R receive antennas can resolve up to 2N R collisions [8]. Assuming perfect channel knowledge and knowledge of the number of activated tags K, a reader with N R = 1 receive antenna can resolve one collision and features a maximal theoretical throughput of T ps = 0.841, while a reader with N R = 4 receive antennas achieves a maximal theoretical throughput of T ps = 4.479, for details, see [8].…”

“…where T ps is the throughput per slot [8], i.e., the number of tags acquired per slot, and the number 16 refers to the RN16 sequences utilized during acquisition. If the number of activated tags is known, the optimal choice of the frame size leads to a maximum average throughput For an increased number of jointly sparse vectors N B , fewer measurements are required to achieve the same number of CD.…”

“…1, we employ a widely used dyadic channel model (see, e.g., [6,8,25]) where the channel Algorithm 1 BASSAMP for jointly sparse signals [15] …”

“…These protocols separate the tag responses in the time domain. The authors in [6][7][8] improve FSA by performing collision recovery, which is accomplished by separating tag responses in the in-phase and quadraturephase plane and by employing multiple receive antennas at the reader to resolve multiple collisions.…”