This　letter　proposes　a　differential　permutation　index　differential　chaos　shift　keying　(DPI-DCSK)　modulation　for　wireless　communications.　The　conventional　PI-DCSK　has　the　disadvantage　of　wasting　transmission　energy　and　the　loss　of　system　performance.　In　M　-ary　DPI-DCSK,　one　chaotic　sequence　to　be　sent　represents　current　modulated　{M}　-ary　symbol　as　well　as　the　reference　of　next　modulation　symbol　in　a　data　frame,　which　can　fully　utilize　the　transmission　energy　with　the　same　hardware　implementation　as　PI-DCSK.　The　bit　error　performance　of　the　proposed　DPI-DCSK　over　the　multipath　Rayleigh　fading　channel　is　theoretically　analyzed.　The　simulation　results　show　that　the　proposed　DPI-DCSK　achieves　a　performance　gain　of　more　than　3　dB　over　PI-DCSK,　especially　in　high-delay　multipath　fading　channels.　The　performance　advantage　of　the　proposed　scheme　is　also　illustrated　in　practical　ultra-wideband　(UWB)　channels.　Thus,　DPI-DCSK　is　an　efficient　alternative　transmission　scheme　for　chaos-based　wireless　communication,　such　as　indoor　applications　of　transmitted-reference　UWB　communications.　©　1997-2012　IEEE.