Who can initiate an optional referendum at the national level?

Constitution 2004

http://www.wipo.int/wipolex/en/text.jsp?file_id=225262

Article 75 The Emir shall seek public opinion on important issues pertaining to the interests of the State in a referendum. The subject of such referendum shall be deemed acceptable if acknowledged by the majority of voters; and the results of the referendum shall be binding and effective from the date of its announcement. The results shall be published in the official Gazette.