Broadband multibeam satellite radio communication system, configured for fractional reuse of frequencies of a total band BT allocated to a forward channel, comprising - a satellite having a multibeam transmission antenna system, configured to cover a geographical service area which is broken down into a plurality of transmission spots (26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50), having a first grid G1 of transmission spots (26, 28, 30, 36, 38, 40, 46, 48, 50) and a second grid G2 of transmission spots (32, 34, 42, 44), the transmission spots (26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50) of the first grid G1 and the transmission spots (32, 34, 42, 44) of the second grid G2 being positioned and their radiation patterns being configured so that there are points of intersection (62, 64, 66, 68) between the roll-off isocontours of a whole number m, greater than or equal to three, of partially overlapping adjacent spots, the number m denoting the order of multiplicity of the points of intersection; and - a set of receiving terminals (14, 16) which are distributed over all of the transmission spots, each receiving terminal (14, 16) comprising a geographical positioning means and a receiving means according to an allocated transmission resource; - a forward channel transmission resource planner and allocator, which is implemented in the form of one or more electronic processors and which is configured to assign to a receiving terminal (14, 16), when it makes a request, a forward channel transmission resource in terms of a frequency sub-band of the total band BT and a polarization state taken from among a first polarization state P1 and a second polarization state P2 in accordance with the geographical position of the receiving terminal (14, 16) and a forward channel transmission resource allocation plan (102, 302) according to which each transmission spot (26, 28, 30, 32, 34, 36, 38) is constituted by a central internal zone (106, 108, 110, 112, 114, 116, 118) and a peripheral zone (126, 128, 130, 132, 134, 136, 138) surrounding the central internal zone; and the first polarization state and the second polarization state are respectively allocated to the spots of the first grid G1 and the spots of the second grid G2, and the same main band BP of frequencies in one piece or in multiple pieces, forming a dominant part of the total band BT in terms of occupied band, is allocated wholly to each central internal zone (106, 108, 110, 112, 114, 116, 118) of the spots of the first and second grids; and the frequencies of the total band BT which are not part of the main band BP form a secondary band BS in one piece or in multiple pieces which is broken down into a whole number n, greater than or equal to 2, of secondary sub-bands each in one piece which are, separately or adjacently, distributed over all of the peripheral zones (126, 128, 130, 132, 134, 136, 138) of the transmission spots according to a multicoloured diagram with n colours of secondary sub-bands; and the points of intersection between the spots of the first and second grids are quadruple points of intersection, that is to say, having an order of multiplicity equal to 4. - a satellite having a multibeam transmission antenna system, configured to cover a geographical service area which is broken down into a plurality of transmission spots (26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50), having a first grid G1 of transmission spots (26, 28, 30, 36, 38, 40, 46, 48, 50) and a second grid G2 of transmission spots (32, 34, 42, 44), the transmission spots (26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50) of the first grid G1 and the transmission spots (32, 34, 42, 44) of the second grid G2 being positioned and their radiation patterns being configured so that there are points of intersection (62, 64, 66, 68) between the roll-off isocontours of a whole number m, greater than or equal to three, of partially overlapping adjacent spots, the number m denoting the order of multiplicity of the points of intersection; and - a set of receiving terminals (14, 16) which are distributed over all of the transmission spots, each receiving terminal (14, 16) comprising a geographical positioning means and a receiving means according to an allocated transmission resource; - a forward channel transmission resource planner and allocator, which is implemented in the form of one or more electronic processors and which is configured to assign to a receiving terminal (14, 16), when it makes a request, a forward channel transmission resource in terms of a frequency sub-band of the total band BT and a polarization state taken from among a first polarization state P1 and a second polarization state P2 in accordance with the geographical position of the receiving terminal (14, 16) and a forward channel transmission resource allocation plan (102, 302) according to which