A　recently　proposed　network-coded　multiple　access　(NCMA),　consisting　of　XOR　-based　channel　decoding　and　multi-user　complete　decoding　(MUD-CD),　can　significantly　improve　throughput　over　conventional　successive　interference　cancellation　(SIC)　decoding　under　near　power-balanced　channels.　In　this　paper,　we　propose　an　improved　NCMA　(I-NCMA)　for　non-orthogonal　multiple　access　(NOMA)　in　the　5G　wireless　communications,　consisting　of　multiple　users　and　a　single　base　station　(BS).　At　the　transmitter　side,　the　proposed　scheme　enables　all　users　to　simultaneously　transmit　messages　to　the　BS　in　the　same　time　and　frequency.　At　the　receiver　side,　we　propose　a　joint-user　channel　decoding　(JU-CD)　to　jointly　decode　all　user　messages　by　a　single　decoder.　Then,　the　extrinsic　messages　from　JU-CD　can　be　jointly　utilized　by　MUD-CD　for　decoding　all　user　messages.　Also,　other　than　conventional　NCMA　that　mainly　deals　with　two　users,　I-NCMA　adapts　to　the　NOMA　networks　with　an　arbitrary　number　of　users.　Simulation　results　indicate　that　the　proposed　I-NCMA　achieves　a　better　decoding　performance　than　both　SIC　and　conventional　NCMA　over　near　power-balanced　channels　in　the　low-to-medium　SNR　regime,　while　retaining　a　performance　close　to　conventional　NCMA　in　the　high　SNR　regime.