User Association and Enabling Technologies in Next Generation 5G Ultra-Dense Networks – A Review

Embedding small cells and relay nodes in a macro-cellular network is a promising method for achieving substantial gains in coverage and capacity compared to traditional macro only networks. These new types of base-stations can operate on the same wireless channel as the macro-cellular network, providing higher spatial reuse via cell splitting. However, these base-stations are deployed in an unplanned manner, can have very different transmit powers, and may not have traffic aggregation among many users. This could potentially result in much higher interference magnitude and variability. Hence, such deployments require the use of innovative cell association and inter-cell interference coordination techniques in order to realize the promised capacity and coverage gains. In this paper, we review various techniques for user association and interference mitigation which are required to meet increased data demand in next generation 5G ultra-dense networ