Superposition of multiple signal at the receiver cause random amplitude variation which is known as Fading. A Diversity mechanism is used to decrease the effect of fading is called Diversity. In Diversity mechanism, multiple copies of the same data is transmitted to the receiver through multiple paths or channels and the decision is made by the receiver without knowing to the transmitter.
Types of Diversity:
- Space Diversity:
Replica of same signal is transmitted through different antenna. Space should be between adjacent antenna so that channel gain will be independent of signal path. Space diversity may give a path that avoid shadowing and also decrease the large scale fading. Space diversity offer different path without an increase in transmitter power or bandwidth.
- Time Diversity:
Time diversity is obtained by re-transmitting the same signal at separate interval of time. The re-transmission interval should be less than the coherence time. Time Diversity also does not require any increase in the transmission power.
- Frequency Diversity:
Frequency diversity is obtained by transmitting the same information on more than one carrier frequency or transmitting the same signal over different carrier frequency. In Frequency Diversity only one antenna is needed.
- Polarization Diversity:
Polarization Diversity require two transmitter and two receiving antennas with different polarization. The transmission wave with two different polarization constitute two different paths. This provide only two different diversity branches. Polarization Diversity uses half power by dividing the power between two different polarized antennas.
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