method for switching a transmission signal to a different transmission signal in a receiver of digital broadcasting system and receiver for a digital broadcasting system

摘要

The invention relates to changing the signal source in a digital broadcasting system receiver which receives the digital broadcasting system's OFDM signal having for synchronization purposes a frame containing in a predetermined position a period without any signal, a so called zero symbol. The receiver has a first receiving chain (31, 32, 33, 34) for the signal from a first source, and a second receiving chain (35, 36, 37, 38; 31, 32, 37, 38) for the signal from a second source. From either receiving chain a signal (S1, S2) to be detected can be swithced (21) to an A/D converter (23) and an OFDM detector (24). In each chain a gating signal (GATE1, GATE2) obtained from the detection of a corresponding zero symbol switches on a corresponding noise detector (18c, 18ab) to detect noise during the zero symbol, and correspondingly a level detector (17c, 17ab) to interrupt the level detection during said period. The signal to noise ratio compared to corresponding limits is determined with the aid of corresponding comparators (19c, 19ab) and reference signals (REF1, REF2). If the signal to noise ratio of the first receiving chain is lower than the corresponding limit, and if the signal to noise ratio of the second receiving chain is higher than the corresponding limit, then the signal (S2) of the second receiving chain is switched (21) to be detected instead of the signal (S1) of the first receiving chain. IMAGE