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.

Radio Frequency Identification (RFID) systems are gaining momentum in various applications of logistics, inventory, etc. A generic problem in such systems is to ensure that the RFID readers can reliably read a set of RFID tags, such that the probability of missing tags stays below an acceptable value. A tag may be missing (left unread) due to errors in the communication link towards the reader e.g. due to obstacles in the radio path. The present paper proposes techniques that use multiple reader sessions, during which the system of readers obtains a running estimate of the probability to have at least one tag missing. Based on such an estimate, it is decided whether an additional reader session is required. Two methods are proposed, they rely on the statistical independence of the tag reading errors across different reader sessions, which is a plausible assumption when e.g. each reader session is executed on different readers. The first method uses statistical relationships that are valid when the reader sessions are independent. The second method is obtained by modifying an existing capture-recapture estimator. The results show that, when the reader sessions are independent, the proposed mechanisms provide a good approximation to the probability of missing tags, such that the number of reader sessions made, meets the target specification. If the assumption of independence is violated, the estimators are still useful, but they should be corrected by a margin of additional reader sessions to ensure that the target probability of missing tags is met.Index Terms-Missing tag problem, set cardinality estimation, error probability estimation, RFID networks

The technology of Radio Frequency IDentification (RFID) is being deployed in many applications, such as logistics and inventorying. However, a generic problem in all RFID systems is to ensure that the RFID readers can reliably read a set of RFID tags, such that the probability of missing tags stays below some acceptable value. This paper introduces statistical methods to deal with the problem of missing RFID tags. These methods are applied at the reliability layer, which initiates multiple reader sessions by invoking certain MAC-layer arbitration (anti-collision) protocols to collect tag responses. The reliability layer obtains a running estimate of the probability of having at least one tag missing. This estimate is used to detect if an additional reader session is required. We present several estimators, which can be used at the reliability layer to obtain an estimate of the probability of missed tags after R reader sessions have been carried out. These estimators are derived under idealized assumptions. However, when tested under more realistic conditions, which violate these ideal assumptions, the estimators exhibit high robustness and provide a very close approximation of the true probability of missing tags.

The technology of Radio Frequency IDentification (RFID) enables many applications that rely on passive, battery-less wireless devices. If a RFID reader needs to gather the ID from multiple tags in its range, then it needs to run an anti-collision protocol. Due to errors on the wireless link, a single reader session, which contains one full execution of the anti-collision protocol, may not be sufficient to retrieve the ID of all tags. This problem can be mitigated by running multiple, redundant reader sessions and use the statistical relationship between these sessions. On the other hand, each session is time-consuming and therefore the number of sessions should be kept minimal. We optimize the process of running multiple reader sessions, by allowing only some of the tags already discovered to reply in subsequent reader sessions. The estimation procedure is integrated with an actual tree-based anticollision protocol, and numerical results show that the reliable tag resolution algorithm attain high speed of protocol execution, while not sacrificing the reliability of the estimators used to assess the probability of missing tags.

Greenlandic governance institutions have been criticised for their colonial heritage of centralisation and lack of democratic participation. In the same manner, Greenlandic fisheries management is notorious in the academic literature for its centralised and locally illegitimate character. While recognising the lack of localised co-management fisheries governance institutions in Greenland, we argue that something has yet to be said about power and user participation in the centralised institutions that have developed. From a symbolic interactionist perspective we dissect the centralised institutions in terms of a differentiated cast of actors and their interaction and argue that participation and power come in many institutional guises as the complex cast of actors within the centralised system represent themselves and others. If we are to understand power and participation in Greenlandic fisheries governance, we need to understand the creation of alliances of the subject-positions that seek control of the self-rule fisheries governance decision-making.