  A constant need to increase the network capacity for meeting the growing
demands of the subscribers has led to the evolution of cellular communication
networks from the first generation (1G) to the fifth generation (5G). There
will be billions of connected devices in the near future. Such a large number
of connections are expected to be heterogeneous in nature, demanding higher
data rates, lesser delays, enhanced system capacity and superior throughput.
The available spectrum resources are limited and need to be flexibly used by
the mobile network operators (MNOs) to cope with the rising demands. An
emerging facilitator of the upcoming high data rate demanding next generation
networks (NGNs) is device-to-device (D2D) communication. An extensive survey on
device-to-device (D2D) communication has been presented in this paper,
including the plus points it offers, the key open issues associated with it
like peer discovery, resource allocation etc, demanding special attention of
the research community, some of its integrant technologies like millimeter wave
D2D (mmWave), ultra dense networks (UDNs), cognitive D2D, handover procedure in
D2D and its numerous use cases. Architecture is suggested aiming to fulfill all
the subscriber demands in an optimal manner. The Appendix mentions some ongoing
standardization activities and research projects of D2D communication.
