The present technical report documents the Phase I study outcome on the advanced receiver to cancel inter-user interference for MU-MIMO, with the detailed objectives as follows:

• Evaluate and specify advanced receiver to cancel inter-user interference for MU-MIMO
• Phase I: Study the performance gain, reference receiver assumption, interference modeling, testability, required signalling overhead, as well as impact on other WGs
  • Further discuss reference receiver assumption with below candidates
    • E-MMSE-IRC
    • R-ML
  • Target scenario: Focus on slot based transmission

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This technical report has documented the RAN4 evaluation on techniques to cancel downlink intra cell inter-user interference. The major work includes the determination of network scenario, interference modelling, interference suppressing receiver structure, required information analysis for each candidate receiver, link-level simulation parameters and performance evaluations. MU-MIMO scenario with gNB transmits PDSCH to the paired UEs through the same time-frequency resources is evaluated. gNBs equipped with 2Tx and 4Tx antennas are considered in the RAN4 performance evaluation. However, for the UEs capable of inter-user interference suppression ability discussed in this TR, they can also be used in the deployments with larger number of Tx ports configuration. For the interference suppressing receiver, both E-MMSE-IRC and R-ML are evaluated as candidate advanced receivers. RAN4 reaches consensus on the required information for both E-IRC and R-ML receiver. In addition, RAN4 has agreed the network default configuration assumptions. Therefore, the advanced receiving algorithm can be performed under these default assumptions. For some of the default assumptions, it is required for the network to indicate the UE whether the default assumption is valid or not by RRC signalling. For UE with R-ML receiver, DCI based network assistant signalling is required. PDSCH link-level simulations are performed to evaluate the performance gain of the candidate E-IRC and R-ML receiver over the baseline MMSE-IRC receiver under intra-cell inter-user interference scenario. 16 simulation cases that covers the advanced receiver with genie-aided required information, with co-scheduled UE DMRS port and FDRA information blind detection, and with co-scheduled UE modulation order blind detection (for R-ML receiver only), are selected for the evaluation. Different antenna and rank configurations for target and interference UEs, different propagation condition, and CBW configurations are included. Based on the simulation results, the performance gain of R-ML receiver over the baseline MMSE-IRC receiver is verified. Based on the above evaluations, it is recommended to select R-ML as the new advanced receiver for inter-user interference suppression receiver for MU-MIMO scenario in Rel-18, and to introduce necessary new UE capability and network assistant signalling for the selected receiver. It is also recommended to define NR PDSCH demodulation requirements for the selected inter-user interference suppression receiver for MU-MIMO scenario in Rel-18.