Terry, it's hard to believe that imperfections sufficient to prevent tiling wouldn't have telegraphed badly through a carpet. Irregularities of 1/8" or so won't hurt anything. However, if it's worse than that, significantly out of level, or not flat, then a self-leveling compound is the way to go. Get one designed for concrete and ceramic. Laticrete (www.laticrete.com) makes an execellent one, but there are other good ones. Cement bd. would not be appropriate.