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It is challenging for the base station (BS) to serve multiple cell-edge users concurrently with data rate guarantee due to limited power and spectrum resource. Using the relay enhances cell-edge user received signal strength by short-distance communication in low transmit power. Non-orthogonal multiple access (NOMA), a promising spectral efficient technology for the 5-th generation network (5G), enables the relay to transmit multiple messages to cell-edge users concurrently. In this paper, a Collaborative NOMA Assisted Relaying (CNAR) system for 5G is proposed with the collaboration of the source-relay (S-R) and relay-destination (R-D) NOMA link. The relay decodes its own message from the S-R NOMA signal and transmits the remaining part with adjusted power to cell-edge users in the R-D link. Then the exact expression of system outage probability is derived by analyzing the outage behavior in S-R and R …