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Throughput, stability and fairness of RFID anti-collision algorithms with Tag cooperation

Robles, R. ; Gameiro, A.

Intrnl. Journal on Advances in Telecommunications Vol. 5, Nº 3, pp. 229 - 238, March, 2012.

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Abstract
This paper addresses the design of a class of anti-
collision algorithms for passive RFID (radio frequency iden
tification) systems, where tags are allowed to cooperate by
relaying (if necessary) the signals of other tags towards the
destination. All the relayed signals are combined at the reader
side so as to improve tag detection probabilities. The work
is focused on asymmetrical scenarios where tags and readers
experience different channel statistics. The objective is to include
tag cooperation in RFID anti-collision algorithms. To achieve
this goal, a framework for medium-access-control and physical
(MAC/PHY) cross-layer design of cooperative RFID anti-collision
algorithms is here presented. A tag activity model is also proposed
where different tag states are initially selected according to the
tag activation SINR (signal-to-interference-plus-noise ratio). Tags
activated by high SINR values enter into states with relaying
capabilities, whereas those with low SINR values act as simple
sources of information (non-relaying state). Tags can change
state depending on the number of (re)transmissions performed.
A Markov model is used to calculate the system steady-state
probabilities. Instability is evaluated by the number of tags in
the backlog state, while fairness is evaluated by means of the Gini
index. Results show that tag cooperation is useful in networks
where tags with good channel states and low traffic requests
cooperate with tags with bad channel states and low traffic
requests.