A transmitter module for unidirectional communication with a receiver module, the transmitter module comprising: a carrier detection portion for making an identification in a manner such that one of presence and absence of communication of at least one communication signal, within a communication medium, having a frequency component corresponding to one of at least one predetermined frequency component is identifiable, at least one preliminary identified signal being produced based on the identification, and detection signals being communicable from the carrier detection portion based on the at least one preliminary identified signal; the transmitter module being characterised by further comprising: a source processing portion coupled to the carrier detection portion, the source processing portion for receiving and processing an information signal to produce a processed information signal, the source processing portion processing the information signal in a manner such that an appropriate carrier signal is modulated with the information signal, the appropriate carrier signal being based on the detection signals communicated from the carrier detection portion, the source processing portion further processing the information signal so that the further processed information signal includes an indication signal, the indication signal being associable with absence of communication of the at least one communication signal in the communication medium; and/or the further processed information signal is produced by encoding the modulated appropriate carrier signal with a unique code, the transmitter module further comprising: a source transmission portion coupled to the source processing portion, the source transmission portion for receiving and processing the processed information signal to produce a source signal, wherein the source signal is communicable from the source transmission portion to the receiver module via the communication medium. a carrier detection portion for making an identification in a manner such that one of presence and absence of communication of at least one communication signal, within a communication medium, having a frequency component corresponding to one of at least one predetermined frequency component is identifiable, at least one preliminary identified signal being produced based on the identification, and detection signals being communicable from the carrier detection portion based on the at least one preliminary identified signal; the transmitter module being characterised by further comprising: a source processing portion coupled to the carrier detection portion, the source processing portion for receiving and processing an information signal to produce a processed information signal, the source processing portion processing the information signal in a manner such that an appropriate carrier signal is modulated with the information signal, the appropriate carrier signal being based on the detection signals communicated from the carrier detection portion, the source processing portion further processing the information signal so that the further processed information signal includes an indication signal, the indication signal being associable with absence of communication of the at least one communication signal in the communication medium; and/or the further processed information signal is produced by encoding the modulated appropriate carrier signal with a unique code, the transmitter module further comprising: a source transmission portion coupled to the source processing portion, the source transmission portion for receiving and processing the processed information signal to produce a source signal, wherein the source signal is communicable from the source transmission portion to the receiver module via the communication medium. a source processing portion coupled to the carrier detection portion, the source processing portion for receiving and processing an information signal to produce a processed information signal, the source processing portion processing the information signal in a manner such that an appropriate carrier signal is modulated with the information signal, the appropriate carrier signal being based on the detection signals communicated from the carrier detection portion, the source processing portion further processing the information signal so that the further processed information signal includes an indication signal, the indication signal being associable with absence of communication of the at least one communication signal in the communication medium; and/or the further processed information signal is produced by encoding the modulated appropriate carrier signal with a unique code, the transmitter module further comprising: a source transmission portion coupled to the source processing portion, the source transmission portion for receiving and processing the processed information signal to produce a source signal, wherein the source signal is communicable from the source transmission portion to the receiver module via the communication medium. a source transmission portion coupled to the source processing portion, the source transmission portion for receiving and processing the processed information signal to produce a source signal, wherein the source signal is communicable from the source transmission portion to the receiver module via the communication medium.