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TR 36.863RAN4
Study on Cell-specific Reference Signals (CRS)
Interference Mitigation
for Homogenous Deployments of LTE

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V12.0.0 (Wzip)  2014/01  61 p.

Rapporteur:  Mr. Li, Shaohua

A study item for minimum performance requirements for interference Mitigation of Cell-specific Reference signals (CRS-IM) for LTE/LTE-Advanced (FDD/ TDD) homogeneous network was approved at the 3GPP RAN #59 meeting. This technical report summarizes the work that RAN4 has accomplished in this study item to assess the feasibility of CRS-IM UE receivers for Homogenous deployment. These receivers attempt to mitigate the CRS interference that arises from users operating outside the serving cell. CRS-IM has been studied in the Rel-11 Work Item on FeICIC. Due to its benefits under the condition where interference from CRS dominates but is negligible from data assuming data RE muting, the CRS-IM has been standardized under the above operation conditions for heterogeneous deployments and the corresponding requirements were specified in Release 11. At the same time, the enhanced performance requirements in homogeneous network deployment for MMSE interference rejection combining (MMSE-IRC) receiver were extensively studied and specified in Release 11.
The MMSE-IRC receiver can suppress both data and CRS interference without the need to differentiate them. However, the UE performance in homogenous deployment may be further improved by using the same CRS-IM capability as defined for FeICIC, especially when similar interference conditions arise under low traffic loading of neighbouring cells and under similar scope as in FeICIC i.e. synchronous network operation and UE reference receiver assuming single FFT processing. In past link level evaluations, this type of interference has been modelled as almost blank subframe, as defined in FeICIC WI, or full traffic, as defined in MMSEIRC receiver. The study item has developed models for this interference in terms of their powers relative to the total other cell interference power, and their resource allocation according to traffic loading levels. Some of these previously identified scenarios studied in Release 11 for specifying MMSE-IRC receiver performance requirements and the corresponding link/system parameters are reused.
The baseline detector structure is that of an MMSE-IRC detector as defined in combined with a CRS-IM receiver. The same CRS-IM receiver defined for FeICIC is reused here. LTE throughput estimates are developed using link level simulations. In addition, system level performance is assessed to determine the gains that interference mitigation receiver might provide in throughput and coverage. Complexity issues associated with implementing these types of receivers are also discussed.

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