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 for detecting interferences, which is capable of identifying the channels of the frequency band that are unusable; and, - at least one frequency management device 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 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 for detecting interferences, which is capable of identifying the channels of the frequency band that are unusable; and, - at least one frequency management device 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 for detecting interferences, which is capable of identifying the channels of the frequency band that are unusable; and, - at least one frequency management device for managing frequencies which is capable of assigning, based on the unusable channels, a current operating channel to each access point, <EOS>