Abstract: A method of modelling a system which includes the transmission and reception of a signal, said method comprising the steps of:(i) creating a number of blocks, each block comprising a piece of program code and each block being a representation of an aspect of the system, wherein each block has a pre-defined output; and (ii) forming connections between the blocks, each connection comprising a bus for transferring data between blocks, wherein each bus has the same pre-defined format such that in use blocks can be connected in different configurations without redefining the block outputs.