The aim of this paper is to get an insight of the interference estimation for multi-layer multi-user multiple-input and multiple-output (ML-MU-MIMO) transmission for LTE-Advanced (long term evolution) systems. Different interference-aware receivers have been investigated in ML-MU-MIMO with the presence of co-layer, intra-cell and inter-cell interferences. User-specific reference signal (UE-RS) based channel estimation and various interference covariance estimation schemes in LTE-Advanced systems are investigated together analytically and numerically. Our investigation has shown the significant influence of the interference estimation schemes on the system performance at the link level. Furthermore, the simulation results have shown the advanced MMSE receiver together with UE-RS based interference estimation as the most robust receiver structure for the signal detection in ML-MU-MIMO transmission.
The concept of heterogeneous networks (HetNets) has been introduced in LTE-Advanced systems in order to improve overall capacity and cell-edge user performance. However, such uncoordinated deployments sharing the same spectrum present new interference issues that are difficult to combat with conventional interference management schemes. In this paper interference issues in a macro-femto scenario in LTEAdvanced downlink, where all eNodeBs allocate the same resources, have been investigated. The interference-unaware Maximum Ratio Combining (MRC) receiver, the MRC receiver with prewhitening and an interference-aware receiver with switching principle are applied at the user equipment (UE) and their performance investigated for different interference levels using Monte-Carlo simulations. The results have shown that the interference-unaware MRC receiver is not suitable in HetNet deployments, as it saturates in error-floor at an intolerable bit error ratio. The MRC receiver with prewhitening mitigates the impact of interference and delivers acceptable performance. However, further improvements can be achieved by applying the interference-aware receiver with switching principle. To combat interference in interference rich scenarios, a switching principle between the MRC receiver with prewhitening and non-linear interference cancellation with prewhitening has been introduced and its performance investigated. The results have shown that by cancelling the interference only when necessary, the interferenceaware receiver with switching principle can guarantee robust and reliable performance in interference rich scenarios. When the amount of interference decreases, the MRC receiver with prewhitening is sufficient for data reception.
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