Chih-Hsuan Chen CHTTL 2016/11/04

Transcription

1 Chih-Hsuan Chen CHTTL 2016/11/04 1/27

2 Background Rel-13 FD-MIMO Rel-14 efd-mimo NR MIMO 2/27

3 Spectrum extension Current Capacity Network Densification Spectrum efficiency 3/27

4 R8/R9 R10 R13 R14 2x2 MIMO 4x2/4x4 MIMO 8x8 MIMO CRS->DMRS/CSI-RS FD-MIMO up to 16 antenna port efd-mimo up to 32 antenna port Current status of most FDD operators Adopted by TDD operators (e.g. CMCC) RS becomes UE-specific Two Categories: nonprecoded and beamformed Overhead reduction, Hybrid CSI-RS, Advanced CSI, DMRSbased OL MIMO NR MIMO 4/27

5 Base station equipped with Active Antenna System (AAS) and able to exploit the full 3D channels Conventional BS can only do beamforming in one direction (horizontal) 3D beamforming Vertical sectorization Higher order MUMIMO Improve indoor coverage in urban scenario Increase cell-edge and average cell capacity Improve cell capacity 5/27

6 Rel-13 FD-MIMO specification primary includes the following parts: Non-precoded CSI-RS Increase CSI-RS port to 12 and 16 Beamformed CSI-RS CSI reporting enhancement To support non-precoded and beamformed CSI-RS DL DM-RS enhancement Additional DM-RS port to support higher order MU- MIMO SRS enhancement Increase SRS measurement resources 6/27

7 This category comprises schemes where different CSI-RS ports have the same wide beam width and direction and hence generally cell wide coverage. CSI-RS port number extends to 12- and 16-port Total number of antenna ports Number of antenna ports per CSI-RS configuration Number of CSI-RS configurations CSI-RS: 16 CSI-RS: Ref: TR , TS /27

8 Class A CSI reporting (non-precoded CSI-RS) PMI reporting is also two stage: W=W 1 W 2 12/16-port codebook: There are 5 parameters require RRC config. (N 1,N 2 ):dimension of two different directions (O 1,O 2 ):sampling factor for (N 1,N 2 ) Config={1,2,3,4}: codebook subset for beam selection and co-phasing (N1,N2) (O1,O2) combinations (8,1) (4,-), (8,-) (2,2) (4,4), (8,8) (2,3) {(8,4), (8,8)} (3,2) {(8,4), (4,4)} (2,4) {(8,4), (8,8)} (4,2) {(8,4), (4,4)} 8-port codebook Rank-1 codebook config. Ref: 3GPP R /27

9 This category comprises schemes where CSI-RS ports have narrow beam widths and hence not cell wide coverage, and at least some CSI-RS portresource combinations have different beam directions. CSI-RS port number per beam 8 CRI (CSI-RS Resource Indicator) + CSI feedback (PMI, RI, CQI) Ref: TR /27

10 Class B CSI reporting (beamformed CSI-RS) BS can configure K beams for UE K=1~8 CSI-RS port number for each beam=1,2,4,8 UE report CRI (CSI-RS Resource Indicator) to indicate the preferred beam CRI is wideband RI/CQI/PMI based on legacy codebook (i.e. Rel-12) CRI reporting period is integer multiple of RI Report CRI=2 RI/CQI/PMI is measured on CSI-RS 2 10/27

11 DL DM-RS enhancement Support additional DM-RS port for higher order MU-MIMO Support at most 8 layers MU-MIMO in Rel DM-RS REs with OCC = 4 for up to total 4 layers per scrambling sequence 1 bit is add to DCI format 2C and 2D SRS enhancement Improve SRS capacity Two mechanisms: Increasing the number of UpPTS SC-FDMA symbols utilized for SRS transmission Additional number of UpPTS symbol can be {2,4} Increase the number of SRS combs to 4 and increase cyclic shift from 8 to 12 Ref: TS /27

12 Timeline: ~ (RAN1#84b~#88) Aims to deal with the following aspects not addressed in Rel-13 FD-MIMO: At most 16 antenna ports CSI reports enhancements to enable efficient MU spatial multiplexing No support for higher robustness against CSI impairments (e.g. high mobility) and higher CSI accuracy Ref: RP /27

13 Reference signal related enhancements Support {20,24,28,32} CSI-RS ports Improve efficiency for UE-specific beamformed CSI-RS CSI-RS overhead reduction Increase the number of UL orthogonal DMRS ports CSI reporting enhancements Codebook for newly supported CSI-RS ports Hybrid CSI-RS and its CSI reporting Advanced CSI DM-RS based open-loop transmission 13/27

14 Support {20,24,28,32} CSI-RS ports Total number of antenna ports Illustration of CSI-RS ports: Number of antenna ports per CSI-RS configuration Number of CSI-RS configurations CSI-RS: 32 CSI-RS: Cause quite large overhead when CSI-RS is present (11.9% and 19%, respectively) 14/27

15 The CSI-RS overhead reduction is supported by comb-like transmission in frequency domain For CSI-RS ports > 16 Supported density: 1, ½, 1 3 RE/RB/port Each CSI-RS configuration can have different comb offset 32-port, Density=1 32-port, Density= port, Density=0.5, different comb offset 15/27

16 20/24/28/32-port codebook: There are 5 parameters require RRC config. (same as Rel-13) Number of CSI-RS ports (N 1,N 2 ):dimension of two different directions (O 1,O 2 ):sampling factor for (N 1,N 2 ) Config={1,2,3,4}: codebook subset for beam selection and cophasing The need to enhance Config. is to be discussed Rel-14 (N 1,N 2 ) (O 1,O 2 ) 20 (2,5) (8,4) (5,2) (4,4) (10,1) (4,-) 24 (2,6) (8,4) (3,4) (8,4) (4,3) (4,4) (6,2) (4,4) (12,1) (4,-) 28 (2,7) (8,4) (7,2) (4,4) (14,1) (4,-) 32 (2,8) (8,4) (4,4) (8,4) (8,2) (4,4) (16,1) (4,-) Number of CSI-RS ports Rel-13 (N 1,N 2 ) (O 1,O 2 ) 12 (2,3) (8,4), (8,8) (3,2) (8,4), (4,4) 16 (2,4) (8,4), (8,8) (4,2) (8,4), (4,4) (8,1) (4,-), (8,-) 16/27

17 To improve the efficiency of UE-specific BF CSI-RS Especially when the number of served UE is large Two schemes to reduce the BF CSI-RS overhead: Aperiodic CSI-RS: aperiodic NZP CSI-RS resource is supported (one-shot) Multi-shot CSI-RS: UE receives activation/release trigger containing a choice from multiple higher-layerconfigured NZP CSI-RS resources for a given CSI process 17/27

18 Multi-shot CSI-RS RRC configuration Activation/Release CSI request and reporting Configure a UE with K={1,2,,8} CSI-RS resource by RRC Activate N out of K CSI-RS resources per CSI process by MAC CE. Once activated, a CSI-RS resource remains active until released Aperiodic CSI-RS N=1, CQI/PMI/RI is reported N>1, CRI is reported along with CQI/PMI/RI One out of N CSI-RS resource is selected via UL-related DCI 18/27

19 Class B CSI-RS overhead reduction is similar to Class A Comb-like transmission in frequency domain For both periodic and aperiodic CSI-RS Supported density: 1, ½ RE/RB/port FFS: other density values 19/27

20 Main motivation: Reduce CSI-RS overhead and CSI feedback The need for enabling UE-specific BF CSI-RS when sufficiently accurate CSI is not available at the enb Currently only Mechanism 1 is supported: 1 st emimo-type: Class A, 2 nd emimo-type: Class B K=1 Realized by a single CSI process For 1 st emimo-type: Report i1 and 1-bit RI(if UE supports 8 layer, RI={1,3}) For 2 nd emimo-type: Report CQI, PMI,, RI No inter-dependence between CSI calculations across two emimo-types FFS: CSI reporting details 20/27

21 Motivation: Finer CSI feedback to better reach the full potential of larger antenna arrays. Current progress: For advanced CSI feedback, at least one of the following types of beam group is supported Type 1: Class A based W1 (non-orthogonal) Type 2: Unrestricted orthogonal W1 Type 3: Orthogonal beams with restricted beam pattern For advanced CSI feedback, RAN1 will specify only rank-1 and rank-2 codebooks FFS: rank /27

22 Motivation: Current DMRS-based MIMO only has CL-MIMO mode, which will suffer severe performance loss at high mobility Semi-open-loop MIMO RB-level precoding + RE-level PDSCH processing RE-level PDSCH processing is based on DMRS port 7/8 Rank-1: Tx diversity Rank-2: co-phasing cycling RB-level precoding Detailed scheme to be determined FFS: rank 3/4 Fixed beam selection/precoder cycling 22/27

23 Currently, NR MIMO is still in study item phase. Many aspects are be studied including the followings: Beamforming implementations Analog/Digital/Hybrid beamforming Single/multi-beam approach Initial access/rrm/control channel CSI reporting schemes Implicit/explicit/reciprocity-based CSI feedback CSI acquisition and RS design Non-UE-specific/UE-specific RS, periodic/aperiodic RS Multi-antenna transmission schemes CL/OL-MIMO, Single/Multi-point, SU/MU MIMO, Tx Diversity CSI timing relationship RS indication/rs Tx/CSI feedback trigger/csi reporting 23/27

24 Multi-beam based approaches Multiple beams are used for covering a DL coverage area and/or UL coverage distance of a TRP/a UE Example of multi-beam based approaches: beam sweeping Def: operation of covering a spatial area, with beams transmitted and/or received during a time interval in a predetermined way Single-beam based approaches Ref: R The single beam can be used for covering a DL coverage area and/or UL coverage distance of a TRP/a UE, similarly as for LTE cell-specific channels/rs Beam sweeping 24/27

25 Beam management has the following procedures P-1: is used to enable UE measurement on different TRP Tx beams to support selection of TRP Tx beams/ue Rx beam(s) P-2: is used to enable UE measurement on different TRP Tx beams to possibly change inter/intra-trp Tx beam(s) P-3: is used to enable UE measurement on the same TRP Tx beam to change UE Rx beam in the case UE uses beamforming 25/27

26 How to determine Tx/Rx beam Initial access/connected/mobility Joint/separate/Multi-stage Channel reciprocity assumptions Reduce overhead/latency UE movement/rotation/blockage Possible UE/TRP beam change Data/control channel beams Same or different beamwidth/direction Multi-beam multi-point operation Interference management 26/27

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