Diversity means variety. Inradio technology, there are various diversity methods that make diverse use of the available radio transmission path. Diversity can refer to the transmission frequencies, to multi- antenna systems or to the information content, and is then also referred to as frequency diversity, timediversity, antennadiversity, receiverdiversity and spatial diversity.
In radio transmission, it is possible to transmit the same information simultaneously from several antennas. This antenna diversity is implemented with multiple input multiple output( MIMO). Similarly, common wave networks work by broadcasting the same information over multiple transmitters. With frequency diversity, the same signal is broadcast on different frequencies, or, as with spatial multiplexing, the spatial dimension is included. The received signals are combined in a combiner to form an overall signal. Another technique is that of polarization diversity. Here, different signals with the same carrier frequency can be polarizedorthogonally or circularly using polarization.
Furthermore, there are diversity techniques that combine several techniques. Space Time Block Coding( STBC), for example, exploits the temporal and spatial components in addition to the spectral dimension by transmitting the signals from multiple antennas with a time offset. This technique is called STBC coding; if the temporal component is replaced by the frequency component, it is called Space Frequency Block Coding (SFBC). Furthermore, there is True Diversity, which is used in wireless microphone technology. It is a redundancy method to improve reception and minimize signal dropouts. True Diversity transmits on two frequencies, it works with two separate True Diversity receivers and two antennas. Depending on reception conditions, the system switches to the stronger received signal.
Diversity techniques improve transmission quality and make more efficient use of the available radio link. They are ideal for mobile receiving equipment located in moving trains and motor vehicles. For example, two receive antennas improve reception by 5 dB to 9 dB with a 50% reduction in the error rate.