The space diversity method is also called the antenna diversity method. There was no guarantee of a direct path between the transmitter and receiver in the conventional method of wireless communications. Hence, the occurrence of Rayleigh fading signal was suspected.
Now let us talk about the different types of space diversity reception method given below :
- Selective diversity
- Feedback diversity
- Maximal ratio combining
- Equal gain diversity
1. Selective diversity :
Principle :
Selective diversity is one of the best signals among all the signals received from different branches at the receiving end.
In the selective diversity method, the branches that have the strongest received signal are combined and selected.
In this method suppose n number of the demodulator is used to provide n number of diversity branches. The gains of these n number of diversity branches can be adjusted to give the average signal to noise ratio for every diversity branch.
The antenna signal will be then sampled and the signal that possesses a good signal strength and the best signal is sent to the demodulator side.
2. Feedback diversity :
Principle :
The feedback diversity also referred to as the scanning type of diversity. In this method in a correct sequence n number of signals are scanned. The signals are continuously monitored so that they can pick up a signal in the sequence that is above some threshold value alpha.
For the signal received the process of scanning is initiated but the limitations of this method are that the decreases in the fading level were less than the diversity method.
The advantages of scanning diversity are easier implementation than other diversity techniques. It needs only one receiver.
3. Maximum ratio combining techniques :
Principle :
In this method is all the (N) branch signal are weighted with the necessary coefficients for each diversity branch signal and combined coherently in order that the decreases in fading will be more. This will improve the overall system of performance.
In this method, the signal is also combining all the signals in a weighted manner and co-phased manner, so as to have the highest achievable signal to noise ratio (SNR) at the receiver at all the times.
Advantages :
- The maximal ratio combiner produces as acceptable SNR value
- The accuracy of this method is high
- In this method also maximal ratio combiner results in best decreases in fading
4. Equal gain combiner :
In these techniques, all diversity branches are coherently added with the same weighting factor. These techniques also based on co-phases all the diversity branches and finally adds them up.
As the signal are co-phased from all branches they provide an equal number of gain factor. So in this method combining all the signal in a co-phased manner with the unity based weights for all signals levels, so as to have the highest achievable signal to noise ratio (SNR ratio) at the receiver at all the times.
Advantages :
- Several diversity branches are allowed
- Space diversity applicable to macroscopic diversity
- No extra bandwidth or power is needed