Coordinated Interference Mitigation Precoding in Unsynchronized Small Cell LTE Networks

Next generation long term evolution (LTE) systems evolve towards small cell networks (SCNs) to enable the tremendous data growth through extreme frequency reuse. However, shrinking the cell size to boost the spectral efficiency comes at the expense of increased co-channel interference (CCI) and is the dominant limiting factor from achieving higher network capacities. Consequently, downlink (DL) scenarios in the cell edge become particularly crucial, as the user equipment (UE) is typically surrounded with multiple interfering small cells. To overcome this limitation, in this paper we focus on cooperative interference mitigation schemes where UEs in good channel condition empower the cell edge UE to mitigate the CCI through linear precoding schemes. We provide a practical realization of the cooperative interference mitigation precoding scheme and determine the set of reference signal configuration to enable the promised performance in unsynchronized SCNs with varying timing offsets (TOs) among the receive signals. With simulation results at the link level, we show that estimating and compensating the TO reliable channel state information (CSI) can be achieved for the non- colliding CSI mapping scheme and as a result near optimum DL transmission can be achieved at the cell edge UE in practical SCNs.