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

Joint work with Preeti Kumari and Vutha Va

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?

2 Arada LocoMate Mini* * http://www.aradasystems.com/

Using the millimeter wave (mmWave) band!!

Why millimeter wave?

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3 GHz 30 GHz

30 GHz 300 GHz

DSRC (75 MHz) 28 GHz

7 GHz @ 60 GHz

38-49 GHz 70-90 GHz

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

Note: log scale

* United States radio spectrum frequency allocation chart as of 2011

Automotive Radar (76-81 GHz)

Automotive Radar 22-29 GHz

MmWave for WLAN/WPAN

u  Standards developed @ unlicensed 60 GHz band 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  Extension of 802.11ad is underway (>20 Gbps)*

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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

Wilocity’s chipset***

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

Epson projector**

Dell Laptop**

MmWave is coming for 5G cellular

u  Repurpose existing mmWave spectrum for mobile cellular applications ª MmWave used to provide high throughput in small geographic areas

u  MmWave cellular networks differ from < 3GHz networks ª Directional beamforming for signal power and reduced interference ª Sensitivity to blockages, indoor coverage more challenging

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Buildings Femtocell

Conventional BS

mmWave D2D

Indoor user

mmWave BS

Control signals

Multiple-BS access for fewer handovers and high rate

Wireless backhaul

Data center

LOS links

Non-line-of-sight (NLOS) link

*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

MmWave for automotive radar

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

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*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

ACC !

Stop&Go!

Cross Traffic Alert !(CTA)!

Pre-crash!

Pre-crash !

Lane Change Assistance !

(LCA) !

Blind Spot !Detection !

(BSD) !

79 GHz!MRR !

77 GHz LRR !

79 GHz!SRR !

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

0.15-30

Distance accuracy 0.1 0.1 0.02

Potential of mmWave V2V

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

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

Example of data fusion (Measurement)*

Sharing GPS observation improves accuracy

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

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Vehicular mmWave challenges: Channel modeling u  V2V channels

ª Low antenna height ª Both TX and RX are moving

u  MmWave channel characteristics* 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

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Typical antenna height: 1.5 m

* 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.

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

11 * 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.

Vehicular mmWave challenges: Beam alignment

u  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

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Hierarchical Beam Codebook Beam Sweeping Example Sector level training Beam level training

* 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.

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

13 *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.

Combining communication and radar at mmWave

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

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state_car0(t) radar_car1(t- Δ01 ) comm_car1(t- Δ0c ) comm_car2(t- Δ02)

comm_Emergency(t- Δ0e) comm_Pedestrian(t- Δ0p)

state_car1(t) radar_car2(t- Δ12) comm_car2(t- Δ1c)

comm_EmergencyVan(t- Δ1e) radar_Pedestrian(t- Δ1p)

comm_Emergency(t- Δ2e) state_Car2(t)

Car-0 Data Matrix

Car-1 Data Matrix

Car-2 Data Matrix

Direction of Cruise

Communication Signal

Emergency Van

Radar Multi-beam

Emergency Event

A communication-radar framework

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

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

MmWave USRP (TX)

Steerable, Multi-level Scanning

LRR SRR MRR

MIMO cable

Ethernet

Signal Energy Source TX Antenna RX Antenna MmWave

(RX) Recording

System Laptop

STF CEF BLK … BLK Header BLK Optional Subfields

Radar Pulse Data Communication

Channel Estimation for Communication

MmWave Prototype Testbed

Common Waveform: SCPHY Frame Structure of IEEE 802.11ad

MmWave communication-radar challenges

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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, pp. 876-885, 2013.

Communication-radar (RadCom) Application Scenario

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

u  Assumption of full-duplex ª Separate transmit and receive antenna ª Use of directional antennas

Preliminary result: Range and velocity estimation

u  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

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Delay Index

Am

plitu

de

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

Composite Ambiguity Function

Car-A

wt

wr s

Mt

Mr

TX Antenna Array

RX Antenna Array

Direction of Cruise

Point Target

Transmit Beamforming

Receive Combining

Car-B

Combining Long Range Radar and V2V MmWave Communication

-Ga128 -Gb128 Gb128 -Ga128 -Gb128 Ga128 -Ga128 -Gb128 -Gb128

Gu512 Gv512 Gv128

a256 b256

Ga128 Ga128 -Ga128

16 X Ga128 + -Ga128

Preamble Sequences

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

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