A graph-coloring secondary resource allocation for D2D communications in LTE networks

The Long Term Evolution (LTE) system, and especially its current release, LTE-Advanced, is considered as the next step in mobile broadband networks. Two of the main challenges faced by the LTE system are: i) to offer ubiquitous and highly reliable wireless services, and ii) to efficiently utilize the assigned spectrum portion. A promising approach towards this direction is to allow the establishment of direct device-to-device (D2D) communications in the assigned spectrum. In this paper, we study how the traffic load between users located in the same cell (intra-cell communications) can be served by D2D transmissions utilizing uplink spatial spectrum opportunities. Aiming at decongesting the base station (or eNB) and letting more resources for the inter-cell traffic (e.g., web services) extra functionality is added to system users (or UEs) for providing interference information to eNB. The collected information is represented by an enriched node contention graph (eNCG) utilized by graph-coloring algorithms to provide an interference-free secondary allocation. Results show that spatial spectrum opportunities can sufficiently serve the intra-cell traffic, while increased data rates can be offered to the inter-cell traffic.