10-5m-2, 10-4m and 10-4m-2 Density of users X 10-4m-2 Bias of macroBS tier and femtoBS tier 1, and 1 Power allocation factor from User 1 and User 2 0.1, and 0.9 Coverage range of macroBS, femtoBS, and D2D 1000 m, 5 m, and 2 m Channel exponent coefficients from macroBS tier, 3, 4, and 3 femtoBS tier, and D2D tier providing coverage to a larger area as compared to the femtoBS tier and D2D tier, the coverage range of the macroBS tier is largest followed by the coverage range of the femtoBS tier and then the D2D tier. The D2D tier has the smallest coverage range as compared to the macroBS tier and the femtoBS tier. The exact values of the considered coverage range of the macroBS tier, femtoBS tier, and the D2D tier can be found in Table 5.1. It is further assumed that at the D2D tier, the D2D transmitter (DTx) has a fixed D2D receiver (DRx), thereby forming a D2D pair. However, in situations when the D2D tier is involved in cooperation, the D2D pair is converted to a D2D group [60] wherein the DTx serves its DRx and the offloaded macroU using NOMA rule. Otherwise the D2D tier does not employ NOMA. However, the femtoBS tier always operates using NOMA. Furthermore, it is important to note that since this chapter deals with D2D-Coop, it becomes necessary to assume a sufficiently high D2D density such that a DTx is always available whenever cooperation is required. Therefore, this work considers a high D2D tier density, as given in Table 5.1, to rule the case when DTx is unavailable for cooperation. The connection policy used at the macroBS tier is the commonly used nearest neighbor (NN) connection policy. Furthermore, bounded path loss model is con- sidered. The bounded path loss model ensures the path loss to be smaller than 1 under circumstances where the distance of the connecting link is very small [61]. A system bandwidth of 1Hz is considered for simplicity. Offloading is performed from the macroBS tier to the femtoBS tier for congestion relief at the macroBS tier. This offloading can be biased in favor of either m