Non-orthogonal　multiple　access　(NOMA)　is　becoming　important　in　5G,　therefore,　it　is　widely　researched.　Note　that　the　users　served　in　NOMA　are　often　paired　to　prevent　excessive　interference.　However,　if　the　channel　condition　of　direct　downlink　from　the　service　node　to　one　user　is　serious,　the　node　may　require　the　other　user　with　better　channel　condition　to　relay　this　user＇s　signals,　especially　when　the　pure　relay　is　difficult　to　deploy.　This　relay　transmission　is　helpful　for　NOMA　communication,　but　two　problems　should　be　considered:　(i)　how　to　persuade　the　relay　user　(i.e.,　the　user　with　better　channel　condition)　to　expend　extra　resources　for　relay;　(ii)　how　to　suppress　eavesdropping　in　the　relay　transmission,　especially　for　the　signals　of　indirect　communication　user　(i.e.,　the　user　with　worse　channel　condition).　To　solve　these　problems,　we　propose　a　novel　signal-level　scheme.　In　this　scheme,　on　one　hand,　the　node　increases　the　spectral　efficiency　of　relay　user,　and　does　the　wireless　power　transfer　to　make　the　relay　user　supplement　his/her　energy　by　energy　harvesting.　On　the　other　hand,　a　signal　transformation　method　is　designed　to　deal　with　each　signal　of　indirect　communication　user.　This　transformation　hides　privacy　information　of　indirect　communication　user,　but　does　not　disrupt　the　relay　transmission.　Utilizing　the　proposed　scheme,　the　above　problems　are　effectively　solved　by　the　compensation　for　the　relay　user　and　the　signal　protection　for　the　indirect　communication　user.