A study item for further improved minimum performance requirements for LTE/LTE-Advanced UE (FDD/ TDD) was approved at the 3GPP RAN #53 meeting . This technical report summarizes the work that RAN4 has accomplished in this study item to assess the feasibility of interference mitigation UE receivers. These receivers attempt to cancel the interference that arises from users operating outside the serving cell. This type of interference is also referred to as 'inter-cell' interference. In past link level evaluations, this type of interference has been modelled as AWGN, and as such can not be cancelled. The study item has developed models for this interference in terms of the number of interfering eNode Bs to consider, and their powers relative to the total other cell interference power, the latter ratios referred to as Dominant Interferer Proportion (DIP) ratios. DIP ratios have been defined based on three criteria; median values of the corresponding cumulative density functions, weighted average throughput gain, and field data.
The LTE basic receiver structure is that of an LMMSE receiver which takes into account not only the channel response matrix of the serving cell, but also the channel response matrices of the most significant interfering cells. LTE throughput estimates are developed using link level simulations, which include the other-cell interference. 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. The content of each specific clause of the report is briefly described as follows.
of this document defines the scope and objectives of this feasibility study.
describes the receiver methods that can be applied to Interference Cancellation/ Mitigation (IC) receivers.
describes the network scenarios that were defined and used to generate the interference statistics, which were then used to develop the interference models described in clause 6
defines the interference models/profiles that were developed in order to assess the link level performance of enhanced receivers. The DIP ratio is defined as a key statistical measure, which forms the basis of the three types of interference profiles considered.
The objective of this study is to evaluate the feasibility and potential performance improvements of interference cancellation/mitigation techniques for LTE/ LTE-Advanced FDD and TDD UE receivers, based on realistic network scenarios. Scope of the work includes:
Identify realistic deployment scenarios, traffic models, interference models, and performance metrics to evaluate the performance of advanced receiver to mitigate inter-cell interference.
Evaluation should be based on realistic modelling of inter-cell interference, including both synchronous and asynchronous operations among macro eNBs, different precoders, ranks and powers applied over consecutive subframes, and effect of CRS and control channels to which different precoder is applied compared with data channels.
Study and evaluate feasibility and potential gain by advanced receiver at link and system levels:
Identify the scenarios and conditions where inter-cell interference mitigation is effective
Identify the receiver structures that could be a baseline to specify performance requirement.
Receiver structures targeting spatial domain interference mitigation such as IRC are to be considered as a starting point.
Receiver structures targeted to TDM-eICIC are only to be studied under the eICIC enhancements WI.
Details of interference modelling for performance requirements and conformance testing shall be specified in the WI phase. Some complexity considerations should be taken into account during the SI phase to avoid over simplified model later on that doesn't reflect the performance benefits found.