With reference to telecommunications, what is meant by diversity? give the different types of diversity? which diversity is use in MW transmission? and why do we need diversity?
Diversity is a technique used in telecommunications to increase the message signal’s reliability by employing two or more independent communication channels with different properties. That is two channels used to transfer the same information. This improves the reliability of the received message because nothing can recover the data signal in a deep fade except getting more copies of the same message. This is based on the fact that the probability of at least one copy out of a fade increases with the number of diverse copies.
Therefore we need diversity in telecoms to overcome the problem of signal fading.
In Telecommunications, you will often hear of “Antenna diversity”
“Antenna diversity” is a method used to enhance radio communications and increase the likelihood of a packet passing between a receiver and a transmitter at a specific time and in a specific position in a dynamic environment.
There are various antenna diversity types such as; space diversity, frequency diversity, time diversity, polarization diversity, pattern diversity, directional diversity, transmit-receive diversity. The commonly used in telecom microwave communications are described below:
- Space Diversity: Replica of the same signal is transmitted through different antennas. This offers 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. It requires large bandwidth and more number of receivers hence high cost.
- 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.
- Pattern Diversity: It is also known as angular-diversity. This diversity allows the identical antennas to be located at same location but with a different pattern. These two co-located antennas with different patterns will provide a diverse path for multipath signal. It enhances the decorrelation of signal at closely spaced antennas.