Google caa srg1813 and 1815. 1815 will be more applicable, rnp 4 is more readily associated with airspace rather than approaches. There are a couple of faa docs out there too.
Google Icao gold and the ICAO pbn ops manual (ICAO 9613) for the in depth communications and procedures stuff.
Edit:this will help lots too.
http://www.icao.int/APAC/Documents/e...sion%202_4.pdf
Hope this helps.