 system, however, suffers from strong self-loop interference (SLI) due to its own transmission. The self-interference cancellation techniques, such as time-domain cancellation, passive isolation, and spatial suppression, help in suppressing the self-interference to a level that FD system results in higher SE than half-duplex system. 4.5 Single-Pair/Multi-Pair One-Way/Two-Way Relay Models 4.5.1 Single User Pair Relay Model The relay transmission can happen either in one-way or two-way. With one-way, four resources are required for exchanging information between two users. On the contrary, with two-way, we only require two resources, thereby resulting in higher SE [13]. Figure 4.4a and b shows the half-duplex one-way and half-duplex two-way relay transmission, respectively. A full-duplex relay, as mentioned earlier, simultaneously transmits and receives on the same time/frequency resource. The full-duplex one-way relay, therefore, can double the SE as compared to half-duplex one-way relay, as with full-duplex relay we can transmit using one resource [15]. Two-way full-duplex relaying, on the other hand, allows a user pair to exchange their information with one another via a relay using only one resource [22], resulting in further increase in the system SE. Figure 4.5a and b depicts the full-duplex one-way and full-duplex two-way transmission, respectively. E. Sharma and P. Singh Slot-1 Slot-2 Slot-3 Slot-4 Slot-I Slot-II MAC Phase BC Phase Fig. 4.4 Half-duplex relay. (a) One-way relay. (b) Two-way relay 4.5.2 Multi-Pair Two-Way Relay Model The authors in [23-25] extended the single-pair relay model to multi-pair relay model, where multiple user pairs exchange information via relay. Consider a two-way multi-pair relay model as shown in Fig. 4.6, with full-duplex relay and full-duplex users. This architecture will be discussed in more detail in Sect. 4.8. Due to the full-duplex relay and user, the system will have following interfer- ences: (1) self-interference at the users and at the relay and (2) users on the same