Vehicular Millimeter Wave Communications: Opportunities and Challenges Professor Robert W. Heath Jr. Wireless Networking and Communications Group Department of Electrical and Computer Engineering The University of Texas at Austin

www.profheath.org

Introduction u 

Dedicated Short Range Communication is a mature technology ª Based on 15 year old WiFi technology ª Products already available on market •  Arada LocoMate, Redpine Signals, etc.

ª Supports very low data rates (27 Mbps max) u 

Connected vehicles will need gigabit per second (Gbps) data rates ª Expanding number of sensors: radar, LIDAR, camera, etc. ª Can not achieve Gpbs in the small 10 MHz channels in 5.9GHz band

u 

How can higher data rates be achieved? Using the millimeter wave (mmWave) band!!

* http://www.aradasystems.com/

Arada LocoMate Mini*

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Why millimeter wave?

DSRC (75 MHz)

3 GHz

u  u 

28 GHz

30 GHz Note: log scale

30 GHz

Automotive Radar 22-29 GHz

38-49 GHz

Automotive Radar (76-81 GHz) 7 GHz @ 60 GHz

70-90 GHz

300 GHz

Huge amount of spectrum (possibly repurposed) at mmWave bands Technology advances make mmWave possible in low cost consumer devices

* United States radio spectrum frequency allocation chart as of 2011

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MmWave for WLAN/WPAN Standard

Bandwidth

Rates

Approval Date

WirelessHD

2.16 GHz

3.807 Gbps

Jan. 2008

IEEE 802.11ad

2.16 GHz

6.76 Gbps

Dec. 2012

u 

Standards developed @ unlicensed 60 GHz band

Dell Laptop**

Epson projector**

ª WirelessHD: Targeting HD video streaming ª IEEE 802.11ad: Targeting Gbps WLAN u 

Compliant products already available ª Dell Alienware laptops, Epson projectors, etc. ª 11ad Chipset available from Wilocity, Tensorcom, Nitero

u 

Wilocity’s chipset***

Extension of 802.11ad is underway (>20 Gbps)*

* http://www.ieee802.org/11/Reports/ng60_update.htm ** http://www.wirelesshd.org/consumers/product-listing/ *** http://www.dailytech.com/

Tensorcom’s chipset*** 4

MmWave is coming for 5G cellular mmWave BS Wireless backhaul

Conventional BS Indoor user

Control signals

Femtocell

Buildings LOS links

Data center

u  u 

Multiple-BS access for fewer handovers and high rate

mmWave D2D Non-line-of-sight (NLOS) link

Repurpose existing mmWave spectrum for mobile cellular applications ª MmWave used to provide high throughput in small geographic areas MmWave cellular networks differ from < 3GHz networks ª Directional beamforming for signal power and reduced interference ª Sensitivity to blockages, indoor coverage more challenging

*T. S. Rappaport, R.W. Heath, Jr. , J. N. Murdock, R. C. Daniels, Millimeter Wave Wireless Communications, Pearson, 2014 **T. Bai, A. Alkhateeb, and R. W. Heath Jr, “Coverage and Capacity of Millimeter-Wave Cellular Networks,” IEEE Coomm. Mag, vol.52, no.9, Sept. 2014 ***T. Bai and R.W. Heath Jr, “Coverage and Rate Analysis for Millimeter-Wave Cellular Networks,” IEEE Trans. Wireless Comm., vol.14, no.2, Feb. 2015

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MmWave for automotive radar 79 GHz! MRR!

Stop&Go!

79 GHz! SRR! Precrash!

77 GHz LRR! ACC!

u  u  u 

Cross Traffic Alert! (CTA)!

Precrash!

Blind Spot ! Detection! (BSD)! Lane Change Assistance! (LCA)!

Type

LRR

MRR

SRR

Frequency band (GHz)

76-77

77-81

77-81

Bandwidth (GHz)

0.6

0.6

4

Range (m)

10-25 0

1-100

0.15-3 0

Distance accuracy

0.1

0.1

0.02

Long range radar (LRR) is used for automatic cruise control (ACC) Medium range radar (MRR) supports CTA, LCA, stop&go and BSD Short range radar (SRR) is used for parking aid and precrash applications

*J. Hasch, E. Topak, R. Schnabel, T. Zwick, R. Weigel, and C. Waldschmidt,“Millimeter-wave technology for automotive radar sensors in the 77 GHz frequency band,” IEEE Transactions on Microwave Theory and Techniques, vol. 60, no. 3, pp. 845–860, 2012. **R. Mende and H. Rohling, “New automotive applications for smart radar systems,” in Proc. German Radar Symp., Bonn, Germany, Sep. 3–5, 2002, pp. 35–40. ***R. Lachner, “Development Status of Next generation Automotive Radar in EU”, ITS Forum 2009, Tokyo, 2009, [Online]. Available. http://www.itsforum.gr.jp/Public/ J3Schedule/ P22/ lachner090226.pdf

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Potential of mmWave V2V Sharing GPS observation improves accuracy

Example of data fusion (Measurement)* u 

Enhanced local sensing capability in connected cars ª  Share high rate sensor data: radar, LIDAR, video, IR video, other sensors ª  Data fusion from other cars can enlarge the sensing range

u 

Enable the transition from driver assisted to autonomous vehicles ª  Develop a better understanding of the local environment ª  Seamlessly scales with more vehicles

* NHTSA, “Vehicle safety communications applications (VSC-A) final report,” Sep. 2011

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Potential of mmWave V2I

u 

Cloud processing of sensor data from vehicles ª Centralized driver assistance and traffic management ª Precise traffic monitoring and congestion control ª Improved safety through more accurate window into the roadway

u 

Infotainment services ª Video, multimedia, and data for passengers 8

Vehicular mmWave challenges: Channel modeling u 

V2V channels ª Low antenna height ª Both TX and RX are moving

u 

MmWave channel characteristics*

Typical antenna height: 1.5 m

ª High path loss ª High penetration loss and poor diffraction capability u 

Channel classifications considered at 5.9GHz is unlikely to scale ª More sensitive to antenna orientation ª More sensitive to traffic density (higher blockage probability) ª Effect of directive transmission is unknown

u 

Few measurements available

* T. S. Rappapport, R. W. Heath Jr., R. C. Daniels, and J. N. Murdock, “Millimeter Wave Wireless Communications,” Pearson Prentice-Hall, 2014 ** S. Takahashi, et al., “Distance dependence of path loss for millimeter wave inter-vehicle communications,” in VTC 2003-Fall, Oct. 2003, ** W. Schafer, “Channel modelling of short-range radio links at 60 GHz for mobile intervehicle communication,” in IEEE 41st VTC, May 1991.

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Vehicular mmWave challenges: Antenna placement

u 

A classic problem even at low frequencies* ª Shadowing becomes blockage for mmWave ª Directional transmission adds another challenge

u 

V2V require 360 degree coverage but antennas can not penetrate car ª Front bumper location causes blockage at the back side ª Rooftop location causes blockage at the front side due to roof curvature ª Sensitive to antenna orientation

* C. Mecklenbrauker, et al., “Vehicular channel characterization and its implications for wireless system design and performance,” Proceedings of the IEEE, vol. 99, no. 7, pp. 1189-1212, July 2011.

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Vehicular mmWave challenges: Beam alignment

Sector level training

Hierarchical Beam Codebook

u 

Beam level training

Beam Sweeping Example

Beamforming with narrow beams required to compensate high path loss ª  Narrow beam needed for reasonable coverage range ª  Narrow beam needed to suppress Doppler spread

u 

Existing methods are designed for low mobility environment ª  Beam sweeping based on hierarchical beam codebook

u 

Alignment overhead within coherence time: gain vs. overhead tradeoff

* J. Wang, et al., “Beam codebook based beamforming protocol for multi-Gbps millimeter-wave WPAN systems,” JSAC, vol. 27, no. 8, pp. 1390-1399, Oct. 2009. * K. Hosoya, et al., “Multiple sector id capture (MIDC): A novel beamforming technique for 60-GHz band multi-Gbps WLAN/PAN systems,” IEEE Trans. On Antennas and Propagation, vol. 63, no. 1, pp. 81-96, Jan. 2015.

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Preliminary result: Coherence time and beamwidth

u 

Mathematical expression relating coherence time and beamwidth ª  Accounts for beam pointing angular difference as oppose to classical models ª  Dependent on angle between beam direction and direction of travel ª  There exists optimal beamwidth maximizing the coherence time

*Vutha Va, and Robert W. Heath, Jr, "Basic Relationship between Channel Coherence Time and Beamwidth in Vehicular Channels,'' Submitted to IEEE Vehicular Technology Conference (VTC 2015-Fall), 2015.

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Combining communication and radar at mmWave

Communication Signal

Car-1 Data Matrix state_car1(t) radar_car2(t- Δ12) comm_car2(t- Δ1c) comm_EmergencyVan(t- Δ1e) radar_Pedestrian(t- Δ1p)

Direction of Cruise state_car0(t) comm_Emergency(t- Δ2e) radar_car1(t- Δ01 ) state_Car2(t) comm_car1(t- Δ0c ) Car-2 Data Matrix comm_car2(t- Δ02) Emergency Event comm_Emergency(t- Δ0e) comm_Pedestrian(t- Δ0p)

Emergency Van

Radar Multi-beam

Car-0 Data Matrix

u 

MmWave is already used for radar, why not share with communication? ª  Combines the objectives of radar and communication ª  Shared hardware reduces cost, size, and spectrum usage 13

A communication-radar framework Radar Pulse STF

Data Communication CEF

Header

BLK

BLK

…

BLK

Optional Subfields

Channel Estimation for Communication Common Waveform: SCPHY Frame Structure of IEEE 802.11ad Steerable, Multi-level Scanning

Signal Energy Source

MmWave USRP (TX)

TX Antenna

SRR MRR

LRR

RX Antenna

MmWave (RX)

Recording System

Laptop

MIMO cable Ethernet MmWave Prototype Testbed

u  u 

Common optimized waveform for radar and communication Develop software-defined radio prototype w/ National Instruments

*Preeti Kumari, Nuria González Prelcic and Robert W. Heath, Jr, ``Investigating the IEEE 802.11ad Standard for Millimeter Wave Automotive Radar,'' Submitted to IEEE 14 Vehicular Technology Conference (VTC 2015-Fall), 2015.

MmWave communication-radar challenges u 

u 

Optimization of sensing and data communication ª LFM # waveform provides low data rate ª DSSS# exhibits poor radar performance ª No single waveform yet available ª Interference issue Assumption of full-duplex ª Separate transmit and receive antenna ª Use of directional antennas Communication-radar (RadCom) Application Scenario

LFM# : Linear frequency modulated waveform, which is a radar waveform DSSS# : Direct spread spectrum, which is a communication waveform *L. Han and K.Wu,``Joint wireless communication and radar sensing systems-state of the art and future aspects,'' IET Microwaves, Antennas & Propagation, vol. 7, no. 11, 15 pp. 876-885, 2013.

TX Antenna Array wt Mt s

Transmit Beamforming Point Target

wr Mr

Amplitude

Preliminary result: Range and velocity estimation

Delay Index Composite Ambiguity Function

Receive Combining

a256

RX Antenna Array

-Gb128 -Ga128 Gb128 -Ga128 -Gb128 Ga128 -Gb128 -Ga128 -Gb128 Car-B

Gu512

Gv512 Ga128 Ga128

Car-A Direction of Cruise

Combining Long Range Radar and V2V MmWave Communication

u 

b256

Gv128

-Ga128

16 X Ga128 + -Ga128 Preamble Sequences

IEEE 802.11ad waveform works well for radar ª  Leverages existing WLAN receiver algorithms for parameter estimation ª  Special structure of preamble enables improved radar performance

*Preeti Kumari, Nuria González Prelcic and Robert W. Heath, Jr, ``Investigating the IEEE 802.11ad Standard for Millimeter Wave Automotive Radar,'' Submitted to IEEE 16 Vehicular Technology Conference (VTC 2015-Fall), 2015.

Conclusions u 

MmWave brings new benefits to V2V and V2I ª Higher data rates using existing mmWave radar waveforms ª Exchange of sensor/camera/radar data among connected vehicles ª Sensor fusion between communication and radar for collision avoidance

u 

Many challenges remain to make mmWave a reality

D-STOP at UT is making fundamental progress in mmWave for V2X 17