D2D
In voice-centric systems it was implicitly accepted that two parties willing to establish a call
would not be in close proximity. In the age of data, this premise might no longer hold, and it
could be common to have situations where several co-located devices would like to wirelessly
share content (e.g., digital pictures) or interact (e.g., video gaming or social networking). Handling these communication scenarios via simply connecting through the network involves gross
inefficiencies at various levels:
• Multiple wireless hops are utilized to achieve what requires, fundamentally, a single hop.
This entails a multifold waste of signaling resources as well as higher latency.
• Transmit powers of a fraction of a Watt (in the uplink) and several Watts (in the downlink)
are consumed to achieve what requires, fundamentally, a few milliWatts. This, in turn, entails unnecessary levels of battery drain and interference to all other devices occupying the same signaling resources elsewhere.
• Given that the path losses to possibly distant base stations are much stronger than direct link ones, the corresponding spectral efficiencies are also lower. While it is clear that D2D has the potential to handle local communication more efficiently, local high-data-rate exchanges could also be handled by other radio access technologies such as Bluetooth or WiFi direct. Use cases requiring a mixture of local and nonlocal content or a mixture of low-latency and high-data-rate con