AN IMPROVED METHOD OF MANAGING COLLISIONS IN A CONTACTLESS DATA INTERCHANGE SYSTEM

摘要

The method manages collisions in a system for interchanging data between portable objects and at least5 one data transceiver terminal suitable for co-operating with a plurality of said portable objects simultaneously present in communicating range of the terminal. The method comprises the following steps in successive: a) the terminal sends out call messages to the10 portable objects; b) a portable object conditionally sends a message to the terminal in response to the call with a probability that may be less than 100%, said response containing an identifier specific to the portable object;15 c) the receiver receives a response from an identified portable object, and in the absence of said response colliding with a response sent out by another portable object, a specific data communication link is established by the terminal and the identified portable20 object, and data is then interchanged, after which the method returns to step a) for a new iteration; and d) in the absence of collision-free reception, the method returns to step a) for a new iteration; According to the invention, the terminal sends out25 two types of call message: Query messages initializing the value of the probability of response by the portable objects; and Marker messages sent out in succession after Query messages, with Marker messages being suitable for causing the portable objects optionally to modulate said30 probability value on receiving a Marker message and in the absence of any prior response to a call message.