Radio-over-fiber systems employing remote antenna units (RAUs based on coherent optical heterodyne detection of two phase uncorrelated lasers and envelope detection have been recently demonstrated. By using two uncorrelated lasers, this system concept allows simple implementation that can additionally be improved, if thermally uncooled lasers are used. Although such asynchronous receiver design is mildly affected by the laser phase noise it suffers from the wavelength drift that occurs between the uncooled laser sources. Also, there are performance penalties due to high laser line-width when complex modulation formats are used for transmission. In this work, we analyze the performance of heterodyne based optical receivers, using OOK and vector modulation formats.