chih-hsuan chen chttl 2016/11/04 - 工研院資通所參與4g,...

1/27 中華電信研究院版權所有

Chih-Hsuan Chen

CHTTL

2016/11/04

2/27

中華電信研究院版權所有

Background

Rel-13 FD-MIMO

Rel-14 eFD-MIMO

NR MIMO

3/27


Current

Capacity

Spectrum

extension

Network

Densification

Spectrum

efficiency

4/27


R8/R9

• 2x2 MIMO

• 4x2/4x4 MIMO

R10

• 8x8 MIMO

• CRS->DMRS/CSI-RS

R13

• FD-MIMO

• up to 16 antenna port

R14

• 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: non-

precoded and beamformed

Overhead reduction,

Hybrid CSI-RS,

Advanced CSI, DMRS-

based OL MIMO

NR MIMO

5/27


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)

Improve indoor coverage in urban scenario

Increase cell-edge and average cell capacity

Improve cell capacity

3D beamforming Vertical sectorization

Higher order MUMIMO

6/27


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

7/27


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

Ref: TR 36.897, TS 36.211

Total number of

antenna ports

Number of antenna ports

per CSI-RS configuration

Number of CSI-RS

configurations

12 4 3

16 8 2

12 CSI-RS: 16 CSI-RS:

8/27


Class A CSI reporting (non-precoded CSI-RS)

PMI reporting is also two stage: W=W1W2

12/16-port codebook:

There are 5 parameters require RRC config.

• (N1,N2)：dimension of two different directions

• (O1,O2)：sampling factor for (N1,N2)

• 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 R1-156217

9/27


This category comprises schemes where CSI-RS ports have narrow beam widths and hence not cell wide coverage, and at least some CSI-RS port-resource combinations have different beam directions.

CSI-RS port number per beam ≦ 8

Ref: TR 36.897

CRI (CSI-RS Resource Indicator) + CSI feedback (PMI, RI, CQI)

10/27


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

11/27


DL DM-RS enhancement Support additional DM-RS port for higher order MU-MIMO

Support at most 8 layers MU-MIMO in Rel-13

• 12 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 36.212

12/27


Timeline: 2016-04~2017-02(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-160623

13/27


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

14/27


Support {20,24,28,32} CSI-RS ports

Illustration of CSI-RS ports:

Total number of

antenna ports

Number of antenna ports

per CSI-RS configuration

Number of CSI-RS

configurations

20 4 5

24 8 3

28 4 7

32 8 4

20 CSI-RS: 32 CSI-RS:

Cause quite large overhead when CSI-RS is present (11.9% and 19%, respectively)

15/27


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=0.5 32-port, Density=0.5,

different comb offset

16/27


20/24/28/32-port codebook:

There are 5 parameters require RRC config. (same as Rel-13)

• (N1,N2)：dimension of two different directions

• (O1,O2)：sampling factor for (N1,N2)

• Config={1,2,3,4}: codebook subset for beam selection and co-phasing

– The need to enhance Config. is to be discussed

Number of CSI-RS ports

(N1,N2) (O1,O2)

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

(N1,N2) (O1,O2)

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,-)

Rel-13 Rel-14

17/27


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-layer-configured NZP CSI-RS resources for a given CSI process

18/27


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

Activation/Release:

Note 1: If K<=2, N=K, else N={1,2,…,min(4,K)}

Note 2: N should not exceed Nmax (UE capability, can be

different for aperiodic and multi-shot CSI-RS)

Note 3: Activation/release mechanism is skipped for aperiodic

CSI-RS when K=1 or N (not for multi-shot since it needs to

exist for a certain period)

One out of N CSI-RS resource is

selected via UL-related DCI

Aperiodic CSI-RS:

Note 1: only PUSCH based A-CSI reporting is supported

Note 2: Aperiodic CSI-RS transmission is in the same DL

subframe as the associated UL-related DCI

N=1, CQI/PMI/RI is reported

N>1, CRI is reported along with CQI/PMI/RI

RRC configuration

Activation/Release

CSI request and reporting

Aperiodic CSI-RS Multi-shot

CSI-RS

19/27


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

20/27


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:

1st eMIMO-Type: Class A, 2nd eMIMO-Type: Class B K=1

Realized by a single CSI process

For 1st eMIMO-Type:

• Report i1 and 1-bit RI(if UE supports 8 layer, RI={1,3})

For 2nd eMIMO-Type:

• Report CQI, PMI,, RI

No inter-dependence between CSI calculations across two eMIMO-Types

FFS: CSI reporting details

21/27


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 3-4

22/27


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 – Fixed beam selection/precoder cycling

FFS: rank 3/4

23/27


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

…

24/27


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

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

Ref: R1-168468

25/27


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

26/27


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

…

chih-hsuan chen chttl 2016/11/04 - 工研院資通所參與4g,...

Documents