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?

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

7 * 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

10 * 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

12 *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

14 *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