Establishing Radio Links forTruck Platooning at 60 GHz

Manigandan Sivasubramanian, No : 0925069Department of Electrical Engineering - Electro Magnetic Research Group

Eindhoven University of Technology, NetherlandsInternal Supervisor : Dr. Ir. Peter Smulders - Eindhoven University of Technology

External Supervisor : Ir. Jacco van de Sluis - TNO Automotive, Helmond.

Abstract—This thesis studies the channel propagation char-acteristics of 60 GHz communication band to use as secondaryredundant link for Truck Platooning. Truck Platooning uses ITS-G5 as the main communication link. Extensive measurements aretaken in indoor and ouoor environments to analyze the channelcharacteristics for various channel configurations. Channel pa-rameters retrieved from measurements are presented and theperformance of the communication channel is evaluated. Line-of-sight (LOS) and non-LOS (NLOS) scenarios on the lines ofvehicular communication are considered. It is observed that mul-tipath doesn’t affect the communication much in the environmentwhere there are metallic objects. In addition, asphalt road helpsin the propagation of signals thus better communication canbe expected. This allows for exploration on alternative antennaplacements.

I. INTRODUCTION

ITS (Intelligence Transport System) has been gaining sig-nificant attention in the recent days, combining state-of-the-art traffic system technology and wireless communication.There are various applications in ITS that require a reliablecommunication link such as collision avoidance, collisionnotification, many intelligent infrastructure applications etc.This thesis explores the usage of 60 GHz which falls under themillimeter wave frequency band for this purpose. Previouslythere have been many theoretical and practical researches [1-6]done to explore the possibility of using 60 GHz for vehicle-to-vehicle and vehicle-to-infrastructure applications.

There have been various experiments conducted to see theperformance of this communication channel. They have beenanalyzed with respect to path loss, small and large scale fadingcomponents and also there was research based on antennabeamforming as introduced in IEEE 802.11ad. There are veryfew experiments done in the outdoor environment to test theperformance of 60 GHz for vehicular applications. This thesisstudies the characteristics by performing various experimentswith the help of a 60 GHz development kit [7] and a 60GHz power measurement device [8]. They are analyzed intwo different outdoor environment with experiments focusingon scenarios related to vehicular communication. Fundamentalstudies of fading due to reflections of road and metallicsurface, which could cause degradation in radio wave prop-agation, are also studied.

II. ORGANIZATION OF THE PAPER

This paper is organized as follows. Section III starts withintroduction to IEEE 802.11ad and truck platooning. Sec-tion IV addresses the various radio propagation mechanismsfollowed by Section V which introduces and explains thedifferent outdoor scenarios considered and information aboutthe experimental setup. Section VI shows the results obtainedfrom experiments. Finally, the conclusions are given in SectionVII.

III. IEEE 802.11AD AND TRUCK PLATOONING

In the early days of the wireless networks, it was predictedthat wireless communication would be as pervasive as utilitylines and house wiring by 2020 [9]. Nowadays frequenciesbelow 6 GHz are too crowded to meet global traffic demands,the fifth generation (5G) of wireless standards are beingdeveloped for millimeter-wave (mmWave) frequency bands toprovide tens of gigabits per second data rates. This led TNO,a research based technology company from Netherlands,to focus on researching one of the frequency bands in themillimeter wave range for their truck platooning applications.The biggest feature of 60 GHz that has brought the attentionto use this band for vehicular communications is the largebandwidth availability when compared with the currentstandard used for this purpose. The standard which hasbeen followed and used presently, is the ITS-g5. This isan European standard and uses IEEE 802.11p amendment.Geo-networking is one of the main differentiating factorsbetween ITS-g5 and IEEE 802.11p which helps in identifyingvehicles with their geographic location. These standards bothoperate in the 5.9 GHz frequency band and are protocolsdeveloped for vehicular applications. One of the majordrawback of ITS-G5 is the limited available bandwidth whichisn’t enough to use for application like transmitting rawsensor data or transmitting live video for truck platooningor any other vehicular communication. As stated earlier, 60GHz has huge bandwidth availability and it is an unlicensedspectrum thus a potential band to explore.

Truck Platooning comprises a number of trucks equippedwith state-of-the-art driving support systems one closely fol-lowing the other. This forms a platoon with the trucks driven

by smart technology, and mutual communication. The im-portant motivation for introducing truck platooning is thereduction in fuel consumption and safety purposes. As trucksare equipped with safety related applications, the technologyemployed needs to be safe and reliable. Thus if there is asecond communication link that could provide support to theexisting link, connection between the trucks becomes morereliable. Hence the link performance of IEEE 802.11ad, whichis the current 60 GHz standard, is studied.

Fig. 1: Illustration of Truck Platooning with Communication

IV. RADIO WAVE PROPAGATION

There are two main type of interaction that happen betweenelectromagnetic waves and objects that constitute the environ-ment through which they propagate. The radio propagationis governed by mechanisms both for indoor and outdoorenvironment viz. free space propagation, reflection, diffraction,scattering etc.

A. Reflection, Diffraction and Scattering

Reflection occurs when an electromagnetic wave impingesupon an object that has very large dimensions compared towavelength of the propagating wave. Reflecting waves mayalso be partially refracted. The coefficient of reflection andrefraction are functions of material properties of the mediumand generally depend on the wave polarization, the angle ofincidence and the frequency of the propagating wave. Diffrac-tion becomes significant when the propagating path betweenthe transmitter and receiver is obstructed by a surface. Theobstructing surface cause waves to bend around the obstacle.

Scattering is a process where a wave is forced to deviatefrom a straight path by one or more localized non-uniformitiesin the medium through which it passes. At 60 GHz scatteringand transmission through most objects are reduced sincescattering occur when objects are similar in dimension to theoperating wavelength and transmission because of the limitedability to penetrate solid substances, but the reflection effectsare amplified. Reflection effects can be either constructive ordestructive depending on the objects as metallic objects helpsin signal propagation while non-metallic objects doesn’t help.

B. Multipath Channel Characteristics

The propagation channel is part of a communication linkbetween the transmitter and receiver antennas. A Millimeter-wave indoor channel as well as an outdoor radio channel,considered in this work, is essentially a multipath channel.If a single pulse is transmitted over a multipath channel thenthe received signal will appear as a pulse train, with eachpulse in the train corresponding to a line-of-sight component,

a distinct multipath component from a distinct scatterer or dif-fuse multipath from a group of scatterers. Channel parameterssuch as path loss and delay spread describe the properties ofthe channel.

It has been indicated in [10] that for a practical 100mstreet there is usually a direct line-of-sight on highways.However, this doesn’t hold for cities and suburbans roads dueto obstacles like buildings and trees. In addition to obstacleslike buildings and trees, the presence of humans also affectsthe radio propagation. The modeling as free space propagationis justified if the first fresnel zone is free of obstructions.

There is a maximum of absorption caused by the oxygenin the atmosphere which affects the propagation. Rain alsoreduces the received power depending on the rain rate. Rainis said to cause an attenuation of 17 dB/km [11], this meansthat a minimum fade margin of 8.5 dB must be added to thelink budget or a reduced transmission must be allowed.

C. Path Loss

Path loss is the average of the ratio of the transmitted powerto the received power between two antennas, usually expressedin decibels. It includes all kinds of losses associated with inter-actions between the propagating wave and any objects betweenthe transceivers. According to Friis transmission equation,operation at 60 GHz causes an additional propagation lossof around 22 dB when compared with the 5 GHz band uponconsidering the same gains of antennas, same transmitter (TX)receiver (RX) separation and equal transmit powers [12]. In-order to compensate for this loss and make better use ofthe frequency band there are some alterations that have beenmade to the new standard. This standard introduces antennabeamforming technique which helps in overcoming some ofthe losses which might incur at 60 GHz because of the highfrequency by effectively directing beams towards the receiver.The path loss exponent, n is a measure of decay in signalpower with distance, d , according to 1/dn. Path loss obeysthe distance power law, given in decibels as

PL(d) = PL(do) + 10nlog(d/do) (1)

where do is the reference distance which is determinedfrom measurements close to the transmitter. This value isusually chosen to be 1 meter. PL(d0) is the average measuredenergy at the reference distance and this value of power mainlydepends on the frequency.

At 60 GHz path loss is several orders larger than ITS-G5 ,as path loss and frequency are inversely proportional.

D. Fading

In a real propagating environment, path loss is not constantfor a given transmitter and receiver distance. Apart from free-space losses, there is also multipath and obstruction causingmultipath fading and shadowing, respectively. Fading is asignificant part of any wireless communication design andis important to predict. There are two different types offading: small scale fading and large scale shadowing. Smallscale fading is often handled in a wireless system with

diversity schemes, redundancy or even retransmit. Large scaleshadowing is fading that occurs on a large scale, changingwith environment. Large scale variation caused by shadowingof obstacles are shown to follow a log-normal distribution[13,14], which means that when measured in dB they followa Gaussian distribution. Path loss and large scale shadowingcomponent are found for various environment consideredin this research. As mentioned earlier reflection effects areamplified at 60 GHz and objects along a propagation pathat a given distance will be different for every path, causingvariation with respect to the value given by simple path lossmodels. Some environments and paths will suffer increasedloss, while others will be less obstructed and has increasedsignal strength. Thus it is highly recommended to know aboutthe environment and path’s fading component as the signalvary in all the environments. The effects of shadowing can beincluded in the path loss model in the above equation (1) byexpanding it to

PL(d) = PL(do) + 10nlog(d/do) +Xσ (2)

where Xσ is a zero mean Gaussian-distributed random vari-able in dB with standard deviation equal to σ (also expressedin dB).

In this research, the path loss exponent and shadowingcomponent has been found for three different environmentswhere the measurements were done. The values obtained inthese environments are listed in the following table.

Environment L(do)[dB] n σParking Lot - LOS 36.0 1.5 4.2

Storage Area - LOS 36.0 2.3 2.4Storage Area - NLOS 34.2 2.5 9.2

TABLE I: Measured path-loss parameter values

V. CHANNEL MEASUREMENTS AND ANALYSIS

In this section the obtained measured value of the signal atreceiver side under various scenarios are presented with de-tailed description of the environment in which measurementshave been conducted as the surrounding components play animportant role in the signal strength.

A. Description of Environment and measurements

A PEM-009 transceiver kit was employed to generate a sine-wave signal at 60 GHz. The Vubic PEM009-KIT developmentsystem is composed of a millimeter wave transmitter boardand receiver board that can be set up and operated using aPC via a simple USB interface on each board. The Rx andTx board assemblies have built-in reference crystal oscillatorwhich is capable of synthesizing frequencies in the 60 GHzband. During measurement, we made use of the 60.48 GHzchannel in the 60 GHz band which is the global channelmeant to be used for all research purposes. Two antennas withdifferent radiative patterns, that is, fan-beam and pencil-beamantennas were used in our measurements. Parameters of these

antennas, half power beam-width(HPBW), and antenna gainare listen in the table below.

Environment HPBW [degrees] L(do) [dB] nParking Lot E-plane:12.0 H-plane: 70.0 36.0 2.6

TABLE II: Measured path-loss parameters

In total four different types of measurements were taken intwo different locations on the campus of TNO in Helmond.Also measurements were taken in the laboratory condition atthe CWT/e laboratory at Eindhoven University of Technology.The two outdoor environments in which we conducted mea-surements are a storage area for vehicles and a parking lot inthe outdoor environment. Floor plan for the two environmentsare shown in Figure 2 and 3, respectively. The storage area hadmetal walls on three sides and an open area on the other side.Apart from the walls, there were occasionally parked trucksduring some measurements which will be discussed in furthersections. Furthermore, there were dust bins which were madeof plastic near the transceiver location. The transceiver waslocated almost in the middle of three wall as shown in Figure3. In contrast to the storage area, the parking lot had metalwalls on two sides and open area on the other two sides, asshown in Figure 4. The transceiver was kept 5 meters from oneside of the wall as shown and there were no cars parked duringour LOS measurements. Two cars were parked during NLOSmeasurement. Both of these locations had an asphalt floorwhich helped in signal propagation. During measurementsthere were no human activity in the area where the experimentswere conducted.

VI. RECEIVED POWER

The received power at a separation distance d from thetransmitter is related to the path loss and can be representedby

Pr(d) = Pt +Gt +Gr − PL(d) (3)

in decibels, where Pr(d) is the received power, Pt is thetransmitted power, Gt and Gr are the antenna gain of thetransmitted and receiver antenna, respectively. PL(d) is thepath loss at a reference distance d. The value of n and σ areempirically derived by linearly fitting the measured path lossin dB over log-distance. This method of estimation of log-distance path loss model values (n and σ) is used accordingto [15]. The procedure starts with estimating received powerusing (1). Once the value is estimated, the sum of squarederrors between the measured and estimated values is given by

J(n) =

k∑i=1

(Original(i)− Pi(i))2. (4)

The value of n which minimizes the mean square error canbe obtained by equating the derivative of J(n) to zero and

Tx Rx

30 m

15 m

12 m

Metal Wall

Metal Wall

Me

tal W

all

O

pe

n A

rea

Bin

s

Parked Truck

Asphalt Road Surface

Warehouse

Doors

Fig. 2: Floor Plan of Storage Area

Tx Rx

5 m

Metal Walls

Me

tal W

all

s O

pe

n A

rea

Asphalt Road Surface

Warehouse

Doors

Open Area

12

m

Fig. 3: Floor Plan of Parking Lot

then solving for n. The values of n and σ obtained using thismethod are given in Table 1 in the previous section.

The received power measured under LOS conditions in both

indoor and the two outdoor environment are shown in Figure 4.The values of received power taken in the indoor environmentsagainst varying distances upto 15 meters are shown in Figure

0 5 10 15

Distance between Transmitter and Receiver (m)

-60

-55

-50

-45

-40

-35

-30

-25

-20R

ece

ive

d P

ow

er

(dB

m)

LOS Measurements - Indoor Environment

LOS - Faraday Cage

LOS with Shadowing

LOS - Corridor

0 2 4 6 8 10 12 14 16

Distance between Transmitter and Receiver (m)

-60

-55

-50

-45

-40

-35

-30

-25

-20

Re

ceiv

ed

Po

we

r (d

Bm

)

LOS Measurements - Parking Lot

Measured Value

Free-space Value

0 2 4 6 8 10 12

Distance between Transmitter and Receiver (m)

-55

-50

-45

-40

-35

-30

-25

-20

Re

ceiv

ed

Po

we

r (d

Bm

)

LOS Measurements - Same Antenna Heights

Measured Value

Free-space Value

a) LOS Measurements - Indoor Environment b) LOS Measurements - Parking Lot

c) LOS Measurements -

Storage Area

Fig. 4: Received Power - LOS Measurements in Outdoor and Indoor Environment

5a. The red curve represents the measurements taken insidea faraday cage (CWT/e propagation lab) and the blue curvewith an increase of about +20 dBm represents the signalpropagation in the presence of a human body/obstruction in theline-of-sight which has been marked as LOS with Shadowing.It is known that human body can cause significant attenuationin the signal propagation at 60 GHz as been reported earlier[16]. The Blue curve in the figure shows how much effectpresence of human body can cause. The black curve representsa proper indoor scenario, and these measurements were takenin a corridor with less human interaction and obstructions.

The other two sub-figures (b and c) of figure 4, show themeasurements taken in a parking lot and storage area. The bluecurve in both these figures represents the calculated value ofreceived power using free space propagation equation. In themodels used at UHF for the decay of power with separationdistance, the slope usually depends on the environment and onbreak-point distances which is why before going for testing the

applications, propagation characteristics needs to be analyzed.There are break-point in both these outdoor environmentsbeyond a certain point where the received power values ofmeasured and free-space value do not agree upon and thepath loss exponent increases beyond 2. The received signalat a reference distance (do = 1m) of 25 dBm is close to thetheoretical free-space value of 23.5 dBm at the storage areathan at the parking lot, also in the far end of the curve i.e atabout 15 meters distance between the transceivers differencein power level between measured and free-space value at thestorage area is better than parking lot due to the presenceof metal walls which acts as a good reflectors, helping inmaintaining a good signal level. Thus an environment withgood metal structures helps in better propagation of signals at60 GHz.

A. NLOS Condition

The NLOS measurements were also taken in the outdoorenvironment. These were taken in both the storage area as

well as in the parking lot. At the time of measurement therewas a truck parked in the storage area which also lead usin determining the performance of communication in thepresence of a vehicle in the propagating part. The NLOScondition curve represents the measurement taken when thetransmitter and receiver antenna were facing 90 degrees toeach other, thus there was no clear line of sight, but we couldstill receive signals due to the presence of metallic objects inthe environment though there is a difference of almost 12 dBmwith the LOS conditions. The results are shown in Figure 5.

1 2 3 4 5 6 7 8 9 10

Distance between Transmitter and Receiver (m)

-60

-55

-50

-45

-40

-35

-30

-25

Rec

eive

d P

ower

(dB

m)

Outdoor Measurements - NLOS Condition

NLOS ConditionLOS ConditionLOS with Obstruction Vehicle

Fig. 5: NLOS Measurements - Outdoor Environment

LOS with obstruction vehicle was taken as a special casewhere a truck is introduced at a certain point in the trans-mission path. This scenario is shown in figure 6. One mayexpect a loss of signal or more attenuation in the signal asit is obstructed by a truck, but interestingly there was only aslight deviation in the value of signal power from the LOScondition probably because of the ground reflection as thevehicle ground clearance was 0.90 meters and the heightof both transmitter and receiver was 1.10 meters. The roadsurface made of asphalt acting as a reflector, helped in signalpropagation. This results shows that if the antennas are keptclose to the ground, then signal propagation can take placebecause of the reflection from the road surface.

Fig. 6: Obstruction by a truck scenario

B. LOS with difference in antenna heights

This experiment was done with difference in antenna heightsin the vehicle storage area with less interference for thepurpose of using two ray model. In order to put things in

perspective, YesFigure 7 shows the two-ray model. Therehas been previous reports on experiments with 60 GHz thatdifferent antenna heights causes difference in the receivedpower because of reflection properties [17]. This situation wastested in this experiment with the transmitter at 1.10 metersand receiver at 0.90 meters. The difference in height betweentransmitter and receiver antenna was 0.20 meters.

Fig. 7: Illustration of Two ray Model

Figure 8 shows the results obtained. The large variationin the received power is mainly because of the differencein antenna height which causes the signal to get reflected,resulting in the signal reaching receiver in more than fewpaths. The change in received power is due to multipathpropagation. The environment also plays a big role in thisexperiment and since we had metallic walls surrounding theexperiment, there will be good reflections in the signals.

0 2 4 6 8 10 12 14 16

Distance between Transmitter and Receiver (m)

-55

-50

-45

-40

-35

-30

-25

-20

Re

ceiv

ed

Po

we

r (d

Bm

)

LOS Measurements - Di�erent Antenna Heights

Measured Value

Free-space Value

Fig. 8: Results of the LOS Communication - Different AntennaHeights

C. Received Power Measured at a fixed distance in varyingAntenna Angle

This is a special case in which the transmitter and receiverwere kept at a fixed distance of 2 meters and then thereceiver antenna which is a directional horn antenna wasrotated mechanically at different angles to find out how thepower of the transmitter signal varies at different angles. Theenvironmental description is important as there is a goodvariation in the signal power at different angles. This technique

Signal Generator

60 GHz

Transmitter

RF Power

Sensor

Open

Area

5m2m

Tx

Rx

Metal

Wall

Metal Wall

Fig. 9: Environment and block diagram of the rotating antennatechnique experiment

is called the rotating antenna technique usually employed forfinding the antenna characteristics as well as direction in whichthe signal power is better.

Figure 9 show the environment and the block diagram ofthe experiment. It was conducted in an environment wherethere was wall on one side of the transceiver and the otherside was an open area. The distance between the wall and theunits was 5 meters. The antenna that we used was the same asused before, a fan-beam antenna with a half-power beam-width(HPBW) of 70 degrees in the H-plane which is considerablybroad. A continuous wave was generated and transmitted at60.48 GHz frequency whose power was measured at variousantenna angle by a RF power sensor capable of workingbetween 56 - 70 GHz directly. The results of measurementstaken are shown in fig 10 in the form of a polar plot.

The radius value of each circle represents the receivedpower in dBm and each vertical line represents the angle indegrees. The points from A to I are the measured value ofreceived power in various angle. The point on zeroth angle (A)represents the direct angle of transmitter and receiver, points tothe left of it are values taken on the metal walls side and pointsto the right of it are values taken on the open area side. PointsB and I are almost the same angle variation of the receiver butbecause of the metal wall presence, point B has better signalstrength close to point A than I. This is probably becauseof the metal walls which act as a good reflector, also thetransmitter antenna beamwidth is 70 degrees which must coverboth these points comfortably and thus we should be seeing

Fig. 10: Polar plot of received power at a fixed distance fromtransmitter in various antenna angles

signal strength almost equally, but the open area environmentfor point I doesn’t help in good signal reflections. At point Ewhere the receiver antenna is facing the opposite direction tothat of the transmitter where the signal strength is expectedto be low, seems to have better signal because of the metalwalls which acts as a good reflection. The point next to it,i.e, point F suffers significant loss of signal power. This isprobably because of the open area environment which doesn’tact as a good reflector. Thus we can conclude that even ata fixed point, the signal strength is strongly governed by thepresence of good reflectors.

VII. APPLICATION: DATA TRANSMISSION AT 60 GHZ

Transmission of a modulated data signal was chosen as theapplication to demonstrate at 60 GHz. In-order to performthis experiment we made use of Rohde and Schwarz AMIQ ,SMIQ and FSIQ. AMIQ is the unit which generates I and Qsignals based on the input it receives from a software calledWINIQSIM.

The software is capable of generating random data signalwhich are then QPSK modulated and sent to the AMIQ withthe help of RS-232 serial cable. Upon generation of I and Qsignal, it is transmitted with the help of a 60 GHz transmitterand received. The received signal is then sent to SMIQ, whichis a carrier signal generator generating 500 MHz signal. Thisgenerator is capable of receiving the transmitted I and Q signaland finally the transmitted signal is analyzed with the help ofFSIQ which is a signal analyzer. The block diagram of theexperiment is shown in figure 11.

The experiment was conducted in laboratory conditions andto verify the signal transmitted we verified the constellationdiagram of the QPSK signal we used and result of theexperiment is shown in Figure 12. The transmitted QPSKsignal was received, successfully.

RS

-23

2R

S-2

32

AMIQ SMIQ

FSIQWinIQSim

Serial

Cable

I/Q Modulation

Generator

i(t) q(t)

60 GHz Transceivers

i(t) q(t)

Signal Generator

Signal Analyzer

Transmitter Side Receiver Side

BNC Cable

60 GHzTransmitter

60 GHz

Receiver

Rx

Fig. 11: Block diagram of message transmission at 60 GHz

Fig. 12: Measured output of the constellation diagram fromWINIQSIM

VIII. CONCLUSION

In this graduation work, a secondary redundant commu-nication link at 60 GHz for truck platooning, which hasITS-G5 as the primary link, is explored. ITS-G5 has limitedbandwidth availability for development of new applicationsand an additional communication link will make the systemmore reliable. Therefore, IEEE 802.11ad which is a 60 GHzcommunication protocol, has been introduced, studied andtested as additional communication channel for truck pla-tooning. Various experiments have been executed to studythe signal strength of a 60 GHz communication link in theoutdoor environment in various scenarios. Though we haven’tconducted experiments with trucks directly, we still were ableto draw some interesting conclusions.

In most of the experiments we conducted, the presence ofmetallic objects like walls acted as a good reflector and helpedin signal propagation. The signal strength in NLOS conditionsdiffered only by 13 dB even in the worst case because ofthe presence of metallic reflectors. In the tests we conducted,we were also able to find that the asphalt road surface helpsin signal propagation by reflecting the signal even in casean obstructing vehicle completely blocks the transmitter andreceiver units. If these units are placed in the bottom of trucks,then with roads acting as a good reflector, signal propagation

between trucks is possible at 60 GHz. Also in the environmentswhere we conducted the experiment, path loss exponent valuewas fairly between 2-3, which implies that the performance of60 GHz communication is not so much affected by multipathin areas with good metal reflectors.

We have studied the propagation characteristics, large scaleshadowing effects and shown data transmission as applicationat 60 GHz. The future works should include the slow andfast fading effects in these environments and demonstrationof various applications at 60 GHz. Another important futureactivity should be to test and validate how asphalt road surfacecan be used for signal propagation in areas where there are lessmetallic objects, as this allow for exploration on alternativeantenna placements.

ACKNOWLEDGMENT

The author would like to thank Dr. Peter Smulders fromEindhoven University of Technology and Ir. Jacco van de Sluisfrom TNO for their valuable guidance and inputs throughoutthe project.

REFERENCES

[1] Eshar Ben-Dor, Theodore S. Rappaport, Yijun Qiao, Samuel J. Lauffen-burger, ”Millimeter-wave 60 GHz Outdoor and Vehicle AOA PropagationMeasurements using a Broadband Channel Sounder” , Global Telecom-munications Conference (GLOBECOM 2011), 2011 IEEE.

[2] A. Kato, et.al., ”Research Activity on 60 GHz Band Inter-VehicleCommunication at Yokosuka Research Park,” Technical Report of IEICEITS2001-6, 2001.

[3] Atsushi Yamamoto et.al. , ”Effect of road undulation on the propagationcharacteristics of inter-vehicle communications in the 60 GHz band”,Wireless Communications and Applied Computational Electromagnetics,2005. IEEE.

[4] T. Wada, et.al., ”Theoretical Analysis of Propagation Characteriosticsin Millimeter Waves Inter-Vehicle Communication System,” Trans. onIEICE J81-B-II, No.12, pp.1116-1125, 1998.

[5] S. Noda, et. al., ”Propagation characteristics of 60 GHz millimeterwave for ITS inter-vehicle communications (4) -shadowing effect byinterrupting vehicle-,” ITST2000, pp.263-266, 2000.

[6] Suiyan Geng, Jarmo Kivinen, Xiongwen Zhao, and PerttiVainikainen,”Millimeter-Wave Propagation Channel Characterization forShort-Range Wireless Communications”, IEEE TRANSACTIONS ONVEHICULAR TECHNOLOGY, VOL. 58, NO. 1, JANUARY 2009.

[7] 60 GHz Transmit/Receive (Tx/Rx) Development Sys-tem User Guide, Pasternack [Online]. Available FTP:https://www.pasternack.com/images/ProductPDF/PEM009-KIT.pdf

[8] Keysight E8486A Power Sensor User Guide, Keysight Technologies [On-line]. Available FTP: http://literature.cdn.keysight.com/litweb/pdf/E8486-90001.pdf?id=1918720

[9] T. S. Rappaport,”The wireless revolution”, IEEE Communications Mag-azine, 29(11):5271, Nov. 1991.

[10] N.D.Hawkins, R.Steel, D.C.Richard,”Path Loss Characteristics of 60GHz Transmissions”, Electronics Letters 24th October 1985 Vol 21 No22.

[11] L.J.Ippolito, R.D.Kaul, R.G.Wallace, ”Propagation Effects Handbook forSatellite Systems Design”, Nasa Reference Publication 1082(03) ThirdEdition.

[12] A Maltsev et al., ”Characteristics of indoor millimeter-wave channel at60 GHz in application to perspective WLAN system”, inProc. EuCAP10,2010, pp 1-5.

[13] C. Chrysanthou, H.L. Bertoni, Variability of sector averaged signals forUHF propagation in cities, in IEEE Transactions on Vehicular Technol-ogy, Volume 39, Issue 4, pp. 352358, November 1990.

[14] L.J. Greenstein, V. Erceg, Y.S. Yeh, M.V. Clark, A new path-gain/delay-spread propagation model for digital cellular channels, in IEEE Transac-tions on Vehicular Technology, Volume 46, Issue 2, pp. 477485, May1997

[15] Theodore S.Rappaport, ”Wireless Communications - Principle and Prac-tice”, Second Edition, Prentice Hall Communications Engineering andEmerging Technology Series.

[16] T. Wu, T. S. Rappaport, C. M. Collins, The Human Body and Millimeter-Wave Wireless Communication Systems: Interactions and Implications,accepted in 2015 IEEE International Conference on Communications(ICC), Jun. 2015.

[17] A.Kato, K.Sato, M.Fujise,”ITS Wireless Transmission Technology.Technologies of Millimeter-Wave Inter-Vehicle Communications: Prop-agation Characteristics”, Journal of the Communications Research Labo-ratory, vol. 48, iss. No. 4, p. 99-110, December-2001.