Method for establishing a direct mode communication for terminals of a given direct mode communication group in at least one current cell (Cn) of a wideband radio communication system comprising a plurality of cellules, each cell of the system comprising a base station, the method comprising the following steps: - a transmission of a request (RQ-DMO) to set up a direct mode communication channel to the current base station (BSn) of the current cell by a terminal (Tm) of the group registered with said base station, the request comprising an identity (ID-DMO) of the group and quality of service parameters (P-QoS) specific to the requested direct mode communication, - after the request is received by the current base station, a setting up of a direct mode communication channel (C-DMO) by allocating blocks of free resources selected from among a set of blocks of resources allocated to the current cell, according to the quality of service parameters, - a determining of a timing advance value (TAn) by the current base station (BSn) according to at least one piece of temporal data, - a transmitting of a message of the setting up (MA-DMO) of the channel, transmitted by the current base station to the terminals registered with said current base station, the message comprising the identity (ID-DMO) of the group, parameters for setting up (P-DMO) the established channel and the determined timing advance value (TAn), and - after reception of the message of the setting up by the terminals of the group registered with the current base station, an access of each of said terminals to the direct mode communication channel (C-DMO) using the parameters for setting up (P-DMO) transmitted to communicate directly with said other terminals of the group and a synchronisation of the terminals with each other according to the timing advance value (TAn). - a transmission of a request (RQ-DMO) to set up a direct mode communication channel to the current base station (BSn) of the current cell by a terminal (Tm) of the group registered with said base station, the request comprising an identity (ID-DMO) of the group and quality of service parameters (P-QoS) specific to the requested direct mode communication, - after the request is received by the current base station, a setting up of a direct mode communication channel (C-DMO) by allocating blocks of free resources selected from among a set of blocks of resources allocated to the current cell, according to the quality of service parameters, - a determining of a timing advance value (TAn) by the current base station (BSn) according to at least one piece of temporal data, - a transmitting of a message of the setting up (MA-DMO) of the channel, transmitted by the current base station to the terminals registered with said current base station, the message comprising the identity (ID-DMO) of the group, parameters for setting up (P-DMO) the established channel and the determined timing advance value (TAn), and - after reception of the message of the setting up by the terminals of the group registered with the current base station, an access of each of said terminals to the direct mode communication channel (C-DMO) using the parameters for setting up (P-DMO) transmitted to communicate directly with said other terminals of the group and a synchronisation of the terminals with each other according to the timing advance value (TAn).