www.huawei.com 5G enablers for enhanced reliability and low latency in V2X communications Dr. Malte Schellmann Huawei European Research Center (ERC) Munich, Germany Acknowledgements to Dr. Zhao Zhao and Joseph Eichinger for their support in the preparation of slides. contact: [email protected]12 th June 2018
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www.huawei.com
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.
• 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
Page 10
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
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
Page 13
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
Page 14
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% :
Page 15
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%
Page 16
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
Page 17
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.
Page 19
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
Page 20
5G-V2N prototype gNB Radio configurationLTE R12 URLLC Prototype
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
Page 21
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
Page 22
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?
Page 23
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
Page 24
• 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.