erform D2D-Coop for the given Case-1. In Fig. 5.4, we show graphically why D2D-Coop is not used. In Fig. 5.4, P-1 denotes the direct path from femtoBS to the offloaded user (CU 1), and P-2 P-3 denotes the path using D2D-Coop. As can be seen from Fig. 5.4a, P-2 is a forward path; however, P-3 is the backward path which is unnecessary when the communication can occur directly using path P-1. Hence, we do not perform D2D-Coop for this case. To make the visualization simpler, Fig. 5.4b shows an enlarged view of only the paths followed while serving the offloaded user using D2D-Coop for Case-1. Case-2 (as shown in Fig. 5.5) holds the following conditions: 1. Offloaded user is a cell edge user (far user), denoted by "EU 1." 2. Available pairing user should be a cell center user (near user). 5 NOMA for 5G and Beyond Wireless Networks (OmacroU) (OmacroU) femtoBS femtoBS (Available pairing user) P-1: Direct path from femtoBS to OmacroU P-3: Path using D2D-Coop Fig. 5.5 Justification for using D2D-Coop when offloaded user is cell edge user 3. However, available pairing user is another cell edge user (and not a cell center user), denoted by "EU 2." Thus, EU 2 cannot be used for pairing. 4. Hence, D2D-Coop is used. 5. D2D transmitter required for performing D2D-Coop needs to be a cell center user (near user), denoted by "Cooperating DTx." In Fig. 5.5, P-1 denotes the direct path from femtoBS to the offloaded user (EU 1) and P-2 P-3 denotes the path using D2D-Coop. It is true that retransmission will take place when the D2D transmitter is cell center user and offloaded user is a cell edge user. However, a forward path will be used, i.e., using P-3 from Fig. 5.5a, unlike a backward path as in Case-1. To make the visualization simpler, Fig. 5.5b shows an enlarged view for only the path followed while serving the offloaded user using D2D-Coop for Case-2. Authors would also like to add that when the offloaded user is a cell edge user, it can also be served using direct path P-1 (as the authors claim for Case-1), since the path us