A method of assigning radio frequencies to base stations of a first radio telecommunications network operating in a first radio frequency band and co-existing with at least a second radio telecommunications network ( 110,110-1;115,115-1) operating in a second radio frequency band at least partially overlapping the first radio frequency band, the method comprising: 1 - providing: a) a description of the mutual interference of the base stations of the first radio telecommunications network; b) a description of the interference caused by the second radio telecommunications network to the base stations of the first radio telecommunications network; c) a description of the interference caused by the base stations of the first radio telecommunications network to the second radio telecommunications network; d) a description of the mutual interference of base stations of the second radio telecommunications network, wherein said providing a), b), c) and d) is based on simulations of electromagnetic field propagation; 2 - defining a cost function for quantitatively evaluating a radio frequency assignment plan for the base stations of the first radio telecommunications network; 3 - based on the provided descriptions a), b), c) and d), calculating an initial radio frequencies assignment plan for the base stations of the first radio telecommunications network; 4 - calculating at least one alternative radio frequency assignment plan starting from the initial radio frequency assignment plan; 5 - calculating a value of the cost function for the alternative radio frequency assignment plan, wherein said steps 4 and 5 comprises calculating a plurality of alternative radio frequencies assignment plans and calculating a value of the cost function for each alternative radio frequency assignment plan of said plurality, said plurality of alternative radio frequencies assignment plans being a number of alternative radio frequencies assignment plans which, in a space of solutions having a given metric defined by the cost function, are in the neighbourhood of the initial radio frequency assignment plan; 6 - selecting as a candidate radio frequency assignment plan for the base stations of the first radio telecommunications network one of the alternative radio frequency assignment plans based on the respective values of the cost function, and 7 - assigning to the base stations of the first radio telecommunications network frequencies in accordance with the radio frequency assignment plan selected in step 6. 1 - providing: a) a description of the mutual interference of the base stations of the first radio telecommunications network; b) a description of the interference caused by the second radio telecommunications network to the base stations of the first radio telecommunications network; c) a description of the interference caused by the base stations of the first radio telecommunications network to the second radio telecommunications network; d) a description of the mutual interference of base stations of the second radio telecommunications network, wherein said providing a), b), c) and d) is based on simulations of electromagnetic field propagation; a) a description of the mutual interference of the base stations of the first radio telecommunications network; b) a description of the interference caused by the second radio telecommunications network to the base stations of the first radio telecommunications network; c) a description of the interference caused by the base stations of the first radio telecommunications network to the second radio telecommunications network; d) a description of the mutual interference of base stations of the second radio telecommunications network, 2 - defining a cost function for quantitatively evaluating a radio frequency assignment plan for the base stations of the first radio telecommunications network; 3 - based on the provided descriptions a), b), c) and d), calculating an initial radio frequencies assignment plan for the base stations of the first radio telecommunications network; 4 - calculating at least one alternative radio frequency assignment plan starting from the initial radio frequency assignment plan; 5 - calculating a value of the cost function for the alternative radio frequency assignment plan, wherein said steps 4 and 5 comprises calculating a plurality of alternative radio frequencies assignment plans and calculating a value of the cost function for each alternative radio frequency assignment plan of said plurality, said plurality of alternative radio frequencies assignment plans being a number of alternative radio frequencies assignment plans which, in a space of solutions having a given metric defined by the cost function, are in the neighbourhood of the initial radio frequency assignment plan; 6 - selecting as a candidate radio frequency assignment plan for the base stations of the first radio telecommunications network one of the alternative radio frequency assignment plans based on the respective values of the cost function, and 7 - assigning to the base stations of the first radio telecommunications network frequencies in accordance with the radio frequency assignment plan selected in step 6.