  We consider the resource allocation problem in cellular networks which
support Device-to-Device Communications (D2D). For systems that enable D2D via
only orthogonal resource sharing, we propose and analyze two resource
allocation policies that guarantee access fairness among all users, while
taking advantage of multi-user diversity and local D2D communications, to
provide marked improvements over existing cellular-only policies. The first
policy, the Cellular Fairness Scheduling (CFS) Policy, provides the simplest
D2D extension to existing cellular systems, while the second policy, the D2D
Fairness Scheduling (DFS) Policy, harnesses maximal performance from
D2D-enabled systems under the orthogonal sharing setting. For even higher
spectral efficiency, cellular systems with D2D can schedule the same frequency
resource for more than one D2D pairs. Under this non-orthogonal sharing
environment, we propose a novel group scheduling policy, the Group Fairness
Scheduling (GFS) Policy, that exploits both spatial frequency reuse and
multiuser diversity in order to deliver dramatic improvements to system
performance with perfect fairness among the users, regardless of whether they
are cellular or D2D users.
