Method of identification of a tag on a moving item

A method of identification of an item in a system, the system comprising

• a conveyor belt,
• a reader comprising a first antenna, the first antenna being arranged at a read point along the conveyor belt and configured for receiving a signal transmitted from a tag, the reader being operable to receive at least one reading from the tag via the first antenna;
• wherein the reader is configured to extract from each reading retrieved by the first antenna a measurement of the phase of the signal transmitted by the tag;
• a conveyor belt controller configured to retrieve a first position of the item at a first time instant t1 before the first antenna and a second position of the item at a second time instant t2 after the first antenna, the first and second time instants t1, t2 defining a time window W,
• wherein the method comprises:
• placing an item on the conveyor belt;
• by the conveyor belt controller retrieving a first position of the item on the conveyor at the first time instant t1 before the read point of the first antenna and a second position of the item on the conveyor at the second time instant t2 after the read point of the first antenna, the first and second time instants t1, t2 defining a time window W;
• by the reader receiving readings from the tag via the first antenna;
• by the reader extracting, from each reading, a measurement of the phase of the signal transmitted by the tag;
• by the reader or by a local server performing a data processing of the phase measurements, which data processing comprises constructing a phase curve from the phase measurements, the phase curve expressing the signal phase in dependence of time, and determining a global maximum on the phase curve;
• by the reader associating the tag to the item if the global maximum lies within the time window W whereby the identification of the item is accomplished;
• wherein the reader further comprises at least one second antenna placed underneath an upper surface of the conveyor belt, the second antenna being displaced from the read point;
• wherein the method further includes:
• determining a time offset, the time offset corresponding to the time it takes for the conveyor belt to convey an item on the conveyor belt from the first antenna to the second antenna;
• determining a further time window that is offset by the time offset;
• and
• by the reader associating the tag to the item if at least one reading has been retrieved from the second antenna for the tag within the further time window.