A network element for a cellular communication system comprises a signal processing logic module arranged to: generate a single system information message; generate a variable si-Windowlength parameter for transmission to the at least one wireless communication unit; and determine availability for downlink transmissions to the at least one wireless communication unit. The modulator is configured to modulate a receiver detect signal at a frequency that is higher than a noise frequency, below which high amplitude noise can develop. The distances and direction from the electromagnetic radiation emitting and receiving device to the fixed and temporary marks is determined during an initial measurement by the electromagnetic radiation emitting and receiving device from a first scanning position.