Can someone please explain in detail how to carry coherent source detection for DOA estimation? How to generate these source signals?

I can, but your questions are too general. The literature on this topic is vast, so you will need to narrow down what it is you are trying to understand.

Do you mean "source detection" as it is defined in the array processing literature (i.e. determining the number of signal sources)? Or are you interested more generally in DOA estimation?

Thanks for your reply. Actually to be more specific I want to ask, how the DOA estimation for coherent sources can be performed on sparse arrays i.e., Nested arrays, augmented nested arrays, improved nested arrays and so on. 

Also, I would like to add that I want to use spatial smoothing scheme as proposed by Piya Pal for sparse (nested arrays) exploiting the difference coarray. This scheme exploiting the difference coarray, in general is used for the DOA estimation of uncorrelated sources.

P. Pal and P.P. Vaidyanathan, Nested arrays: A novel approach to array processing with enhanced degrees of freedom, IEEE Transactions on Signal Processing, vol.58, no.8, pp.4167--4181, 2010.