A WiFi communication system for the exchange of data between a railway vehicle, travelling over a railway network, and a terminal, on the ground, a frequency band allocated to the system being subdivided into a plurality of channels (Fi), said system comprising - a mobile unit, on board the railway vehicle, designed for transmitting and receiving radio signals in a current operating channel; and, - a cellular infrastructure, on the ground, comprising, connected to each other by means of a communication network: - a plurality of access points (20 - 43), each access point being capable of transmitting and receiving radio signals and, in particular, transmitting beacons for establishing or maintaining a communication link, on a current operating channel, between said access point and a mobile unit,,said current operating channel being adjustable; - at least one interference detection device (28, 38, 48) for detecting interferences, which is capable of identifying the channels of the frequency band that are unusable; and, - at least one frequency management device (29, 39, 49) for managing frequencies which is capable of assigning, based on the unusable channels, a current operating channel to each access point, characterised in that for each access point, the said frequency management device (29, 39, 49) is capable of generating an association table, specific to the access point considered, which associates with each virtual channel (CVi) of a plurality of virtual channels, a current operating channel of an access point situated in the neighbourhood of the access point considered and of transmitting the association table to the access point considered; and in that each access point includes a beacon generation means for generating beacons comprising pieces of information of the association table transmitted by the frequency management device; and in that the mobile unit is capable of extracting, from a beacon received, the said pieces of information for updating an onboard association table, stored by the mobile unit, and of using the said onboard association table for searching a channel on which to establish a new communication link. - a mobile unit, on board the railway vehicle, designed for transmitting and receiving radio signals in a current operating channel; and, - a cellular infrastructure, on the ground, comprising, connected to each other by means of a communication network: - a plurality of access points (20 - 43), each access point being capable of transmitting and receiving radio signals and, in particular, transmitting beacons for establishing or maintaining a communication link, on a current operating channel, between said access point and a mobile unit,,said current operating channel being adjustable; - at least one interference detection device (28, 38, 48) for detecting interferences, which is capable of identifying the channels of the frequency band that are unusable; and, - at least one frequency management device (29, 39, 49) for managing frequencies which is capable of assigning, based on the unusable channels, a current operating channel to each access point, - a plurality of access points (20 - 43), each access point being capable of transmitting and receiving radio signals and, in particular, transmitting beacons for establishing or maintaining a communication link, on a current operating channel, between said access point and a mobile unit,,said current operating channel being adjustable; - at least one interference detection device (28, 38, 48) for detecting interferences, which is capable of identifying the channels of the frequency band that are unusable; and, - at least one frequency management device (29, 39, 49) for managing frequencies which is capable of assigning, based on the unusable channels, a current operating channel to each access point,