In　this　paper,　we　propose　a　joint　differential　pulse　position　modulation　and　differential　chaos　shift　key　modulation　(DPPM-DCSK),　where　one　bit　modulates　the　reference　PPM　signal　by　chaotic　signal,　and　the　other　$m_{c}$　bits　are　mapped　by　the　position　index　of　this　chaotic　pulse　in　the　information　signal.　In　particular,　in　the　DPPM-DCSK,　the　information-carrying　PPM　signal　for　the　current　symbol　also　serves　as　the　reference　for　the　next　symbol.　It　can　avoid　the　energy　and　rate　wastes　in　the　conventional　PPM-DCSK.　Moreover,　we　redesign　the　differential　Walsh　codes　(WC)　for　DPPM-DCSK　to　enable　multi-user　communications.　The　numerical　bit-error-rate　(BER)　performance　of　the　proposed　DPPM-DCSK-WC　over　multipath　Rayleigh　fading　channels　are　derived　and　then　verified　by　simulations.　The　results　demonstrate　that　the　DPPM-DCSK-WC　can　achieve　performance　gains　of　more　than　2 dB　over　the　conventional　PPM-DCSK　and　DDCSK-WC　for　multi-user　scenarios,　and　this　gain　can　be　up　to　5 dB　in　the　high-delay　channels　at　a　BER　of　${{10}^{-4}}$.　In　addition,　the　superior　performance　of　the　proposed　scheme　is　proved　over　ultra-wideband　(UWB)　wireless　channels,　which　indicates　its　great　potential　for　chaotic-based　wireless　applications.　IEEE