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5G enablers for enhanced reliability and low latency in V2X communications

Dr. Malte SchellmannHuawei European Research Center (ERC)Munich, Germany

Acknowledgements to Dr. Zhao Zhao and Joseph Eichinger for their support in the preparation of slides.

contact: malte.schellmann@huawei.com

12th June 2018

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Outline

• 5G future radio• Features, targets and timeline

• 5G technologies• URLLC challenges• Enabling technologies for URLLC

• 5G proof of concept• V2X simulations and field tests

• Conclusions

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Post Smartphone Era

400MHz

100GHz

10GHz

D2D

VerticalsMBB

Open OTT

SDN-RAN

IoT

Capacity1000X

Speed100X

LatencyLess than

1ms

Links100x

Energy 1000X Reduce

Auto-drive

Medicare

Meters, Sensors

5G – From Mobile Internet to Connected World

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& SL

5G 20Gbps &1ms &106 Links/km2 & 99.999% &10 years

Key performance indicators (KPIs) of LTE and 5G

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Frequency bands for 5G

WRC15 WRC19

10 50403020 60 8070 901 542 63

Complementarybands for capacity

Primarybands for coverage & mobility

GHz

VisibleLight

Cellular Bands

Different Channel Characteristics with Sub 6GHz

Available in 2015 Available in 2019

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3GPP timeline:

• Phase 1 by Sep 2018/Rel-15

for more urgent commercial needs (to be agreed) Deployment 2H2020

• Phase 2 by Mar 2020/Rel-16

for all identified use cases/ requirements: Deployment 2H2021

NB: New Radio (NR) designforward compatible so that novel features can be added easily in later releases

5G Timeline LTE-V

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Outline

• 5G future radio• Features, targets and timeline

• 5G technologies• URLLC challenges• Enabling technologies for URLLC

• 5G proof of concept• V2X simulations and field tests

• Conclusions

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Fundamental trade-offs in the radio system design• Tradeoff between latency, reliability and

throughput (data volume)

-4 -3.5-1 -3 -2.5 -2 -1.5

Reliability (e in log scale)

-1

-1.5

Availability (a in log scale)

Ban

dwid

th u

nit r

equi

rem

ent

5.5

5

4.5

4

-2

3.5

3

2.5

2

1.5

1

LTE ( 90% availability, 90% reliability )

> 5x bandwidth for 5G V2X ( 99.99% reliability, 99% availability )

• Tradeoff between bandwidth, availability and reliability

Picture source (left): B. Soret et al., "Fundamental tradeoffs among reliability, latency and throughput in cellular networks," 2014 IEEE Globecom Workshops, 2014

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Deployment challenge for Ultra-Reliable CommunicationAvailability impact on uplink coverage

99.999%

99.99 %

90 % (LTE)

SNR level

The higher the availability requirement,the shorter the coverage for cellular and V2V

90%99.99%

Solutions: Retransmission (introduces delay)Antenna techniquesNetwork multi-connectivity

90%99.99% PC5

Uplink

ABC

Coverage Gap

Location

Availability: The probability that a desired quality-of-service level can bemet in the coverage area.

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time

Some basics from mobile radio system design• The waveform underlying LTE is orthogonal frequency

division multiple access (OFDM)• Multi-carrier transmission: The bandwidth is separated

into K sub-carriers, each one carrying a modulated data symbol of duration T

• Time for transmission is segregated into radio frames• One radio frame consists of N sub-frames,

which LTE calls „transmission time interval“ (TTI)• minimum duration of a frequency resource

being allocated to a user• constituted of M OFDM symbols

• A sub-frame can be assigned to either uplink (UL) or downlink (DL)

• Inside the OFDM symbols, fields are assigned for carrying control info or data

• Erroneously transmitted packets are repeated• Using „hybrid automatic repeat request“ (HARQ) protocol:

recipient sends „not acknowledged“ message, transmitter retransmits

frequency

1 N

Radio frame

sub-frame / TTI

1 M

cont

rol

control

data ......................

frequ

ency

Picture source (top): www.revolutionwifi.net

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OFDM numerology – Sizing the radio framesub-frame / TTI

1 M

frequ

ency

time

K subcarriers

M symbols

guard interval (GI)

Numerology: Number set (M, K, GI) constituting a sub-frame• For fixed bandwidth: More subcarriers smaller subcarrier

spacing (SCS) longer symbol duration• Guard interval (GI) for protection against multi-path creates overhead:

longer symbol duration smaller overhead

LTE: A „one-fits-all“ solution with constant numerology:• M = 14, SCS = 15 KHz, GI = 7% yields TTI length = 1 ms• shorter TTI possible only by using „mini-slots“ covering less symbols M

boundary boundary

Sub-frame #1 Sub-frame #2

Default GI & 15 KHz SCS

Long GI & 15 KHz SCS

Default GI & 30 KHz SCS 5G: Support for multiple numerologies:

• SCS of 15 kHz * 2n (up to 480 KHz, depending on carrier frequency)• GI of different length, e.g. 7% (default) and 25 % (long)• Alignment with frame structure to allow switching between

numerologies on integer TTI basis without gaps

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Limitation of Reliability and Latency of LTE

• Limitation of current LTE› Frame structure with 1ms TTI length › HARQ process with fixed timing› Processing latency due to control info and

Turbo channel coding (earliest repetition after 2 TTIs N+2)

• Possible further enhancement› Mini-slots (minimum 3 OFDM symbols)› N+2 instead of N+4 (compatibility is an issue)

Current LTE LTE in future releases

LTE in future II

HARQ Latency N+4 N+4 N+2

TTI length 1ms 200 us 200 us

Limitation Only for small packet (<1 kbit)

Only for small packet,backward compatibility

# of (Re)-Tran. Reliability Worst Case Latency

1 Tran. 90% 6.5 ms 1.3 ms 0.9 ms

2 Tran. 99% 11.5 ms 2.3 ms 1.5 ms

3 Tran. 99.9% 16.5 ms 3.3 ms 2.1 ms

4 Tran. 99.99% 21.5 ms 4.3 ms 2.7 ms

PHY point-to-point latency

LTE is not capable of fulfilling URLLC requirement, not even with aggressive enhancements

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New design of N+1 HARQ for URLLC

# Transmission Latency Reliability

1 312 us (2.5 TTI) 95%

2 688 us (5.5 TTI) 99.9%

3 1.0 ms (8.5 TTI) 99.99%

4 1.3 ms (10.5 TTI) 99.999%

Subframe Setting HARQ

D U D U D U D U N+1

D D U U D D U U N+2

D D U D D U D U N+2

D D D U D D D U N+3

Achieving 1ms with 99.99%

New assignments for UL and DL frames allow for acknowledgement of data in succeeding frame:

DL UL DL ULtime

frequ

ency

New numerology: M = 7, SCS = 60 KHz

Increase reliability per transmission to 95% :

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N+0 HARQ setting

Latency = N+ 0 HARQ

# Transmission Latency Reliability

1 187 us (1.5 TTI) 95%

2 440 us (3.5 TTI) 99.9%

3 688 us (5.5 TTI) 99.99%

4 940 us (7.5 TTI) 99.999%

Self-Contained TTI to achieve N+0 HARQ latency: A single TTI contains DL data and UL slot (= OFDM

symbol) for data acknowledgement (ACK / NACK)

Suitable for small cell/ hotspots

Not suitable for macro-cell coverage

New design of N+0 HARQ for URLLC

Achieving 1ms with 99.999%

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Path for High Reliable Re-Transmission

1ms HARQ

1. Tran 2. Tran 3. Tran 4. Tran

Frequency/time hopping

Multi-antenna beam-forming

Multi-link/cooperative diversity

1. Tran

2. Tran

3-order higher diversity is achievable only by spatial and multi-link design

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Multi-Antenna for Reliable Communication• Use of multiple antennas at transmitter side enables to

direct the radio wave by spatial beam-forming› By concentrating transmit power into one direction,

reception SNR can be increased› Using multiple beams allows to serve different users on the

same frequency at the same time› Using multiple beams for one user opens up independent

propagation paths offering diversity gains

• Use of multiple antennas at receiver side enables to suppress interference from other beams

› Maximize Signal-to-Interence-and-Noise Ratio (SINR) › Increase link robustness

• Mobile channel requires beam tracking and prediction› Beam has to follow the car to avoid signal loss. › As the trajectory of the car is known in advance, beam prediction

becomes feasible.

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Outline

• 5G future radio• Features, targets and timeline

• 5G technologies• URLLC challenges• Enabling technologies for URLLC

• 5G proof of concept• V2X simulations and field tests

• Conclusions

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5G-V2N prototype gNB Radio configurationLTE R12 URLLC Prototype

Latency improvement

SCS [KHz] / symbol length [us] 15 / 66.67 60 / 16.67

Shorter slot length 1ms (14 OFDM symbols)

0.25ms (14 OFDM symbols)

HARQ RTT [ms] 8 ms (FDD) 0.75 msGP length[us] At least 66.67 (1

symbol)31.25

UL grant free transmission N/A Yes

Reliabilityimprovement

Retransmission A/N based HARQ A/N-less and A/N based HARQ combine

MIMO mode configurable BS: 8T8RUE: 2T2R

MIMO mode: SFBC

FEC Turbo Polar (CRC-aided SC List = 8)

Waveform OFDM Filtered-OFDM

Polar code is preferred because it exhibits no error floor important for URLLC. 0 0.5 1 1.5 2 2.5 3 3.5 4

Es/No (dB)

10 -3

10 -2

10 -1

10 0

BLE

R

AWGN, 1T1R, 4RB, MCS=9, code rate = 616/1104

Turbo

Polar

• Simulation for LTE data channel: Outstanding BLER performance

• Simulation verification: No error floor @ 99.999% reliability

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5G V2x Proof of Concept: Cooperative emergency braking

Radio delayms

Packet deliveryrate %

Error rate %

Distance in m

result

100 90 10 -0.4 crash

100 100 0 +0.45 Small margin

20 90 10 1,14 ok

20 100 0 1,18 ok

0.75 90 10 1.36 ok

0.75 99 1 1,36 ok

0.75 100 0 1,38 ok

100ms / 100

Distance between cars

No safety distance

Good safety distance

Very stable safety distance

0.75 ms / 90

100ms / 90

Distance between cars

Very stable distance even during brake

Distance between cars

Test Case:• Different parameter for delay and reliability• Cars with 50 km/h driving speed• Starting distance between cars: 1.60m

• Stable distance between cars even after emergency brake• Low latency enables tight coupling of automatic functions of both cars

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1 ms latency enables scheduling gain: Support of larger number of cars with latency guarantee

LTE1 message per TTI of length 1 mslatency guarantee of 17 ms (after 2 retransm.) 3 ms margin (= 3 TTIs)

Support for (1+3) = 4safety messages with latency guarantee of 20 ms

5G1 messages per TTI of length 250 µslatency guarantee of 1.5 ms 18.5 ms margin (= 74 TTIs)

Support for (1+74) = 75safety messages with latency guarantee of 20 ms

5G can support 19x more cars with guaranteed latency within the same bandwidth.

Illustrative example: Assume V2X control message with 1500 bits payload fits into a single TTI Maximum 2 retransmissions to achieve a reliability of 99.9% New frame structure for 5G with 250 µs TTI length (M=14) and 60 kHz subcarrier spacing Question:

How many transmissions of safety messages can be supported with a latency guarantee of 20 ms?

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5G V2X Proof of Concept: Cooperative Platooning (done 06/2017)

5G

Additional reliability offered by 5G system enables 20 % gain in longitudinal distance and 50% gain in lateral deviation compared to 802.11p

Scheduling gain of 5G based networks is not tested (no guaranteed quality of service)

50% less distance

20% gainCones

802.11p

Testing high-density platooning: Lateral and longitudinal deviation of the vehicle following the trajectory of the platoon leader

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• Besides eMBB, 5G offers the two novel services URLLC and mMTC.• Supporting high reliability, low latency and massive access. • Laying the foundation for the automated control & Internet of Things.

• 5G provides new technologies to enable short latency and high reliability.• Flexible numerology and new frame structure• enhanced HARQ relying on spatial and multi-link diversity

• Field tests with a 5G prototype have been carried out, which have proven superior performance compared to existing systems.

Conclusions

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