A telecommunication system comprising at least a control center and at least one mobile unit moving along a track comprising a plurality of stations, said at least one mobile unit and said at least one control center handling a broad band bi-directional communication of data/signal with roaming between said mobile unit and a plurality of wireless access points integrated in a network with said at least one control center and distributed along said track, each of said at least one mobile unit comprising onboard receiving-transmitting means for connection with said wireless access points, characterized in that it further comprises a control application continuously controlling the communication between the mobile unit and a present access point, wherein: - a received signal decision threshold is set under which a level of the received signal triggers a roaming; - a transmission rate decision threshold is set under which a detected transmission rate triggers a roaming, the transmission rate decision threshold being a transmission rate under which a prefixed required bandwidth performance cannot be obtained; - a time is set between two subsequent comparisons of the level of the received signal and the detected transmission rate, with said respective decision thresholds; a time is set during which the access point presently detected is deemed valid; - a time is set lapsing between the scan of a channel and the scan of a subsequent channel; - a roaming event is triggered when either said level of the received signal or said detected transmission rate are under said respective decision thresholds, or when said set time for deeming valid the access point is lapsed; - a predetermined and programmable list of channels are scanned, said channels including only frequencies provided along the path of the mobile unit preliminarily detected and selected in order to attain the maximum bandwidth available, the selected channels being stored for speeding up a successive scan; - a list of the valid access points is updated; - the communication is reassociated from said present access point to a new access point in said list, in case the received signal level of the new access point exceeds the signal level of the present access point by a value corresponding to an established hysteresis threshold. - a received signal decision threshold is set under which a level of the received signal triggers a roaming; - a transmission rate decision threshold is set under which a detected transmission rate triggers a roaming, the transmission rate decision threshold being a transmission rate under which a prefixed required bandwidth performance cannot be obtained; - a time is set between two subsequent comparisons of the level of the received signal and the detected transmission rate, with said respective decision thresholds; a time is set during which the access point presently detected is deemed valid; - a time is set lapsing between the scan of a channel and the scan of a subsequent channel; - a roaming event is triggered when either said level of the received signal or said detected transmission rate are under said respective decision thresholds, or when said set time for deeming valid the access point is lapsed; - a predetermined and programmable list of channels are scanned, said channels including only frequencies provided along the path of the mobile unit preliminarily detected and selected in order to attain the maximum bandwidth available, the selected channels being stored for speeding up a successive scan; - a list of the valid access points is updated; - the communication is reassociated from said present access point to a new access point in said list, in case the received signal level of the new access point exceeds the signal level of the present access point by a value corresponding to an established hysteresis threshold.