I heard that one application of Khintchine's inequality is the proof of Littlewood-Paley theorem. I only know a proof of Littlewood-Paley theorem using vector version of Calderon-Zygmund theorem. Can anyone provide me a reference (e.g. a textbook) containing a proof of Littlewood-Paley theorem by using Khintchine's inequality?
Remark: I don't write down the statements of the theorems mentioned above since only experts know the reference. I don't need a proof written here since it can be very lengthy. I just need a reference book.