Extension of ITU IMT-A Channel Models for Elevation Domains and Line-of-Sight Scenarios

0.5 MB·English

by  Zhimeng Zhong

Extension of ITU IMT-A Channel Models for
Elevation Domains and Line-of-Sight Scenarios
Zhimeng Zhong1 , Xuefeng Yin2 , Xin Li1 and Xue Li1
1Huawei Technology Company, Xi’an, China
2School of Electronics and Information Engineering, Tongji University, Shanghai, China
Email: [email protected] and [email protected]
Abstract—In this contribution, the 3-dimensional (3D) channel
characteristics, particularly in the elevation domains, are ex-
tractedthroughmeasurementsintypicalurbanmacroandmicro
3 environments in Xi’an China. Stochastic channel model param-
1 eters are obtained based on the high-resolution multi-path pa-
0 rameter estimates. Inaddition,amodifiedspatialchannelmodel
2 (SCM) for the line-of-sight (LoS) scenario is proposed where
the LoS polarization matrix is parameterized in accordance
n
with the reality. Measurement results justify the reasonability
a
of the proposed model. These works significantly improve the
J
applicability of the ITU SCM models in realistic 3D channel

8 simulations. Figure1. Thesystemdiagramofthemeasurement set-up
1

IndexTerms—3-dimensionalchannelmodels,elevationofarrival,
] elevation of departure, line-of-sight, and polarization matrix errors, such as that the cross-correlation matrix of large scale
n
parameters(LSPs)isnon-positivedefinite.Theelevationchar-
a
a- I. Introduction acteristics, such as mean elevation angular spread (MEAS),
extracted based on measurements have also been reported
t
a in literature [6], [7], [8]. However, these models focus on
d Multiple-inputMultiple-ouput(MIMO)enhancementsarepro-
the marginal elevation characteristics, rather than the joint
. posed in the 3rd Generation Partnership Project (3GPP) Re-
s characteristics in both azimuth and elevation, and thus, are
c leases 10 and 11 to support eNodeB (eNB) antenna configu-
i rations capable of adaptation in azimuth. Recently researches lack of applicability for 3D MIMO system-level evaluation.
s
y in enhancing system performance through the use of antenna Inthiscontribution,3D channelmeasurementcampaignscon-
h systems having a two-dimensional array structure has been ductedbyHuaweiPropagationResearchGrouparedescribed,
p
paidlotsofattentioninordertoprovidemorespatialdegreeof which have been performed in different urban scenarios with
[
freedominbothelevationandazimuthdomains[1].Additional the objective of extracting the full 3D channel characteristics

2 control in the elevation dimension enables new transmission particularly at the eNB. New measurement results for the
v techniques by using the 3-dimensional(3D)-beamforming or statistics of the LSPs, and the cross-correlationmatrix thereof
8
with the massive MIMO, such as the sector-specific elevation are elaborated. Furthermore, a questionable setting specified
1
5 beamforming (e.g., adaptive control over the vertical pattern in the WINNER+ SCM models for the polarization matrix
2 beamwidth and/or downtilt), advanced sectorization in the of the line-of-sight (LoS) path is corrected and verified with
1. verticaldomain,anduser-specificelevationbeamformingtech- measurement data.
0 niques. In order to evaluate the performance of the systems
The rest of the paper is organized as follows. Section II
3 utilizing these techniques, new channel models characterizing
1 channelsinbothverticalandhorizontaldimensionsin various introducesthemeasurementsetupandtheenvironmentswhere
: themeasurementswerecarriedout.InSectionIV,thechannel
v environments with different user locations are necessary.
characteristicsextractedfortheurbanmacro(UMA)andurban
i
X Existing directional channel models as proposed in 3GPP micro (UMI) scenarios are described and the updated values
r TR25.996 [2], the IMT-Advanced standards [3] and in the forthe ITU IMT-A modelparametersare reported.In Section
a
WINNER reports [4] have been widely adopted for devel- V,amistakeintheSCM,WINNER+,andITUIMT-Advanced
opment of wireless communication systems. However, with modelsfortheLoSscenarioisdiscussed,andthecorrection is
respect to the elevation characteristics of the radio channel, proposed. Finally conclusive remarks are provided in Section
these models are considered to be insufficient. For example, VI.
in the WIINNER+ project[5], 3D channelmodeling method-
ologyandparameterswereproposedbasedonliteraturesurvey
II. Measurementsetupandenvironments
ratherthan extensivemeasurements.Thus, the applicabilityof
the models suggested are questionable due to some obvious
A diagram for the measurement setup is illustrated in Figure
1, where the Agilent E4438C signal generator is applied
Thisworkissupported HuaweiResearch Project [Channel Characteristics
MapforOperational Wireless Communication Netowrks]. as an eNB, generating a pseudo-noise signal with 35MHz
1
(a) Measurement routes in Area A (Picture: (cid:13)c Baidu Maps)
Figure2. Antenna arraysateNB(left)andUE(right)sides
bandwidth and center frequencyof 2.6 GHz. Figure 2 depicts
the photographsof the antennasused in the eNB and the user
equipment(UE).TheeNBwasequippedwithaplanarantenna (b) A photograph taken in Area A
arraywith32antennaelementsconfiguredas16patches,each
consistingoftwoantennaswith±45◦ polarizations,7dBigain
and 90◦ beamwidth on both horizontal and vertical planes. A
crown-shaped antenna array is used in the UE, which has 50
antenna elements allocated on 25 patches with the structure
similar with those on the eNB antenna array. The horizontal
andverticalspacingsbetweenthenearestneighboringantennas
are0.5wavelength.Thedown-tiltingangleoftheeNBantenna
array is approximately 7◦.
The measurement was conducted emulating the downlink
scenarios, i.e. the eNB and the UE were considered as
the transmitter (Tx) and the receiver (Rx) respectively. The Figure3. Measurement routes andaphotograph taken inAreaA
high-resolutionchannelparameterestimationalgorithmSpace-
Alternating Generalized Expectation-maximization (SAGE) (a) Measurement routes in Area B (Picture: (cid:13)c Baidu Maps)
algorithm [9] was applied to estimation of 14 parameters for
individual paths, i.e. the delay, Doppler frequency, direction
(azimuth and elevation) of departure (DoD), direction of
arrival (DoA) and polarization matrix.
The measurementswere conductedin the “High-tech”district
of Xi’an, China. The UE was movingalong two routesin the
area A and area B as indicatedin Figure 3 and 4 respectively.
The photographs taken in the eNB side for the area A and
B are shown in Figure 3 and 4. It can be observed that the
area A and B are close to the definition of UMA and UMI
scenarios specified in the WINNER modeling [4] receptively.
The heights of the eNB antenna in area A and area B were
40 m and 14 m above the ground respectively. Notice that
consideringthelimitedeffectiveradiationoftheantennaarray
(b) A photograph taken in Area B
in the eNB, the estimation range of azimuth of departure
(AoD) and elevation of departure (EoD) are confined to be
[−180◦,0◦]and[0◦,180◦],respectively.Furthermore,theAoD
and EoD of the direction normal to the array plane are −90◦
and 90◦ respectively.
III. Verificationoftheparameterestimation
To ensure that the path parameters are correctly estimated,
the angular estimates obtained in the LoS scenario in the
case 4 in the area B are compared with their counterparts
calculated geometrically based on the map information and
Figure4. Measurement routes andaphotograph taken inAreaB
the antenna heights. It can be observed from Figure 4 that
2
(a) Estimated AoD of the LoS path
(a) Urban macroLoS scenario
−65 0.35
n
o Empiricaldata
−70 cti 0.3 Laplacianpdf
n
−75 fu0.25
] y
◦[ −80 sit 0.2
D n
Ao −85 de0.15
y
−90 bilit 0.1
a
−95 b
o0.05
r
P
−100
0 50 100 150 200 250 0
Snapshot index 60 70 80 EoD90[◦] 100 110 120
(b) Estimated EoD of the LoS path (b) Urbanmicro LoS scenario
0.25
96 n
o
94 ncti 0.2
u
92 f
y
◦[] 90 nsit0.15
D de
Eo 88 y 0.1
86 bilit
ba0.05
84 o
r
P
820 50 100 150 200 250 06 0 70 80 EoD90[◦] 100 110 120
Snapshot index
Figure5. EstimatedAoDandEoDforLOSpathincase4 Figure6. EoDdistribution inUMA&UMILOSscenarios
TableI
in the measurement case 4, the UE started from the location Channelmodelparametersextracted
A, moving to the location B, then back to A, and finally Scenarios UMI UMA
LoS NLoS LoS NLoS
arrivedatthelocationC.ThetheoreticalAoDandEoDforthe
Delayspread µ −7.08 −7.6 −6.66 -6.51
LoS path at the start and the end point of this measurement (DS)log ([s]) σ 0.34 0.8 0.56 0.2313
10
route are illustrated in Figure 4. Figure 5 (a) depicts the AoD ASDlog ([◦]) µ 0.84 1.1 0.61 1.05
10 σ 0.19 0.3 0.32 0.1
estimatesfortheLoSpath,whichisselectedtobethestrongest
path estimated by using the SAGE algorithm, versus the ASAlog10([◦]) µσ 10..6147 10..513 10..6188 10..8171
measurement snapshots. It can be seen that the AoD estimate ESDlog ([◦]) µ 0.27 0.6 0.11 0.8346
increasesgraduallyfrom −85◦ to−98◦,anddecreasesto −85◦ 10 σ 0.29 0.2 0.2 0.0452
when the UE arrived at the location A, and then increase ESAlog10([◦]) µσ 10..0168 00..8186 10..4493 10..2166
again up to −70◦ when the UE arrivedat the location C. This MeanEoD([◦]) -2 -2 2 -2
variation is consistent with the AoD’s trajectory calculated MeanEoA([◦]) 2 2 6 10
µ 9 N/A 9 N/A
theoretically based on the UE displacement. It can also be K-factor [dB]
σ 5 N/A 3.5 N/A
observed from Figure 5 (a) that there is a sudden change EoA,EoDdistribution Laplacian
of the AoD at the 180th measurement snapshot. This is due ClusterESD 1.45 3 1.16 2.332
ClusterESA 6.68 7 15.5 7
to the fact that the orientation of the Tx antenna array was
Perclustershadowingstd 3dB 3dB 3dB 3dB
adjusted manually at that moment in order to make sure that
ASD:AzimuthSpreadofDeparture
theUEcanbecoveredbythearray’smainlobe.Thearraywas ASA:AzimuthSpreadofArrival
tuned back to its originalposition finally. Figure 5 (b) depicts ESD:Elevation SpreadofDeparture
ESA:Elevation SpreadofArrival
the estimated EoDs of the LoS path versus the snapshots,
EoD:Elevation ofDeparture
which also fits well with the theoreticallycalculated EoDs. In EoA:Elevation ofArrival
addition, it is worth mentioningthat the estimated trajectories
of AoDsandEoDsare notsmoothdue to the limitedintrinsic
resolution of the measurement equipment in both delay and dimension in order to generate the 3D channel model for
angular domains. systemlevelsimulations.TableIreportsthestatisticalchannel
parameters extracted for both the elevation and azimuth do-
mainsattheeNB andUE sides,aswellasthedelaydomains.
IV. Measurementresults
Inthetable,DS,ASDandASArepresentthedelayspread,az-
A. Measurement-based 3D channel parameters imuth spread fordepartureand forarrival, respectively.These
parameterscanbe used to updatethe correspondingentriesof
The measurements were conducted with the objective of the table A1-7in [3] forITU channelmodelstandardsforthe
extending the ITU channel model [1] to include the elevation environments considered in the measurements.
3
TableII TableIII
Meanazimuthangularspread(MAAS)andmeanelevationangularspread Cross-correlationofLSPs(DS,ASD,ASA,ESDandESA,SF,K)
(MEAS)attheeNB
Scenarios UMI UMA
MAAS[◦] MEAS[◦] LoS NLoS LoS NLoS
UMALoS 4.6 1.77 ASDvsDS 0.42 0 0.21 0.4
UMANLoS 11.2 6.8 ASAvsDS 0.11 0.4 0.25 0.6
UMILoS 11.54 2.97 ASAvsSF −0.4 −0.4 −0.5 0
UMINLoS 13.3 6.28 ASDvsSF −0.5 0 −0.5 −0.6
DSvsSF −0.4 −0.7 −0.4 −0.4
ASDvsASA 0.11 0 0 0.4
The3DMIMOperformanceevaluationalsorequiresthepower ASDvsK −0.2 N/A 0 N/A
elevation spectrum and elevation spread at the eNB. Table II ASAvs K −0.3 N/A −0.2 N/A
DSvsK −0.7 N/A −0.4 N/A
reports the mean azimuth angular spread (MAAS) and mean
SFvs K 0.5 N/A 0 N/A
elevationangularspread(MEAS)attheeNB.Figure6depicts Cross- ESDvsDS −0.07 −0.5 −0.3 −0.3
Correlations
theEoAdistributionsfortheUMAandUMILoSscenarios.It ESAvsDS 0.12 0 0.13 0
ESDvsASD 0 0.5 0 0.3
canbeobservedfromFigure6thattheLaplaciandistributions
ESAvsASD 0 0.5 0.44 −0.2
can be used to fit the empirical distribution derived from ESAvsASA 0.37 0 0.3 0
measurements. ESDvsASA −0.26 0 −0.2 0
ESDvsSF 0 0 0 0
Table III reports the cross-correlation coefficients between ESAvsSF 0 0 −0.8 −0.5
ESDvsK 0 N/A 0 N/A
differentlarge-scaleparameters(LSPs) based on the measure-
ESAvs K 0 N/A 0 N/A
ment results. Here, the cross-correlation coefficient of two ESDvsESA −0.2 0 −0.11 0
random variables, say a and b, are calculated as DS 7 10 30 40
ASD 8 10 18 50
N Correlation ASA 8 9 15 50
(ai−a¯)(bi−b¯)∗ distance ESD 8 9.5 16.5 50
C(a,b)= i=1 , [m] ESA 8 9.5 16.5 50
P SF 10 13 37 50
N N
|a −a¯|2 |b −b¯|2 K 15 N/A 12 N/A
i i
s i=1 i=1 SF:Shadow Fading
(cid:18) (cid:19)(cid:18) (cid:19) DS:DelaySpread
P P
where a¯ and b¯ denote the mean of a and b respectively. The
3Dchannelrealizationscanbegeneratedusingtheparameters
given in Tables I to III following the ITU channel generation
procedure. differenceto the verticaland horizontalpolarizedcomponents
being transmitted. The conventional setting of independent
Φvv and Φhh results in a consequence that the polarization
V. GeneratingchannelcoefficientforLOSpath staLtouSs of recLeoSived LoS component is different from that of
the transmittedsignal,which is inconsistentwith the common
In the case where the elevation domain is taken into account,
experience in reality.
the contribution of the nth cluster in the narrowband coeffi-
cients of the channel between the sth Tx antenna and the uth Tojustifytheamendmentsuggested,ameasurementcampaign
Rx antenna can be calculated as [4] was conducted to check the variability of polarization status
forthesignalsreceivedfromtheLoSpath.Figure7depictsthe
1
H (t)= H′ (t)+δ(n−1)HLoS(t), (1) premisesofthemeasurementintheopenrooftopenvironment
u,s,n K +1 u,s,n u,s,n
r R withclearLoSbetweentheTxandRxseparatedby40meters.
where H′ (t) represents the NLoS component and can be The Txwas equippedwith a patchconsistingof two antennas
u,s,n
written as(2), the same asin [4, EQ.(4.20)]in thecase where transmitting ±45◦ polarized waves respectively. By feeding
elevation domains are considered. Due to the limitation of differentphasesintotheinputsignalsatradiofrequencyofthe
space, the readers of interest are referred to [4] for detailed twoTxantennas,thetransmittedwavemayhavedesirablepo-
explanation of the notations arising in (2). larizations,suchasthelinear,ellipticalorcircularpolarizations
with either left-hand or right-hand circulations. For example,
In the case of clear LoS without obstructions, HLoS (t) is
u,s,n the vertical linearly-polarized waves and circularly-polarized
writtenas(3),wherethediagonalelementsofthepolarization
waves can be generated by tuning the phase difference to 0◦
matrix are co-phased, i.e.
and90◦,respectively.Furthermore,duringthemeasurements,a
φvv =φhh =φ , phasor-monitoringdevicewasappliedthatmakessurethecor-
LoS LoS LoS
rectphasedifferencebe maintainedbetweenthe two branches
which is different from the settings in the existing ITU and
of transmitted signals. The Rx was equipped with a dipole
3GPP geometry-based channel models that φvv and φhh are
LoS LoS antenna, which has tunable orientation that allows receiving
generated independently. This revision is important since in
EM waves with any desirable linear polarizations.
the case where the LoS path is of free-space propagation,the
polarization status of the transmitted EM wave shall be unaf- Figure 8 reports the received power at the output of the
fected, which occurs if and only if the diagonal elements of Rx with linear polarizations from 0◦ to 360◦. Notice that
the LoS path polarizationmatrix do not introduceextra phase the polarization slant angle of 0◦ is referred to the vertical
4
H′ (t)= P M Frx,u,V(Ψ¯n,m) T exp(jφvnv,m) κn−,1mexp(jφvnh,m) Ftx,u,V(Φ¯n,m) exp j2π r¯s·Φ¯n,m+r¯u·Ψ¯n,m+v¯Ψ¯n,mt (2)
HuL,osS,n(t)=p KnRXm=1"FFrrxx,,uu,,HV((ΨΨ¯¯nL,omS))#Tqeκxn−p,1m(jeφxLpo(Sj)φhnv,m)q0exp(jφhnh,Fm)tx,u,V("Φ¯FLtxo,Su),H(eΦx¯pn,mj)2#π ¯rs(cid:18)·Φ¯L(cid:0)oS +λ0¯ru·Ψ¯LoSλ+0v¯Ψ¯LoStλ0 (cid:1)(cid:19) (3)
u,s,n KR+1"Frx,u,H(Ψ¯LoS)# " 0 exp(jφLoS)#"Ftx,u,H(Φ¯LoS)# (cid:18) λ0 λ0 λ0 (cid:19)
(cid:0) (cid:1)
−70
Circularly-polarizedwave beingtransmitted
B] Linearly-polarizedwave beingtransmitted
d
[−75
al
n
g
si
d−80
e
v
ei
c
e
r
e−85
h
t
f
o
r
e−90
w
o
P
−95
0 50 100 150 200 250 300 350
PolarizationSlant Angle at Rx [◦]
Figure8. PowerofthereceivedsignalwhentheRxpolarizationvariesfrom
Figure7. MeasurementinaLoSenvironment.Theantennas markedbythe 0◦ to360◦ polarizations
redandblueellipses arefortheTxandRxrespectively.
spatial channel models. Measurement results justified the
polarization direction in the measurement. It can be observed
reasonability of the changes for real LoS cases.
from Figure 8 that when the circularly-polarized wave was
transmitted, the received power remained stable regardless of
the polarizations of Rx antenna. When the vertical linearly- References
polarizedwavewastransmitted,i.e.thepolarizationwasalong
0◦, the received power achieved the maxima when the Rx [1] Study on 3D-channel model for Elevation Beamforming and Massive
polarization matched the Tx polarization, i.e. being 90◦ or MIMOstudies forLTE,3GPPRP-121412Std.
270◦ polarized, and reduced to the minima when the Rx [2] Spatial channel model for Multiple Input Multiple Output (MIMO)
simulations,, 3GPPTR25.996Std.
and Tx polarizations were orthogonal. It is evident that the
polarization of the transmitted waves does not change in the [3] Guidelines for evaluation of radio interface technologies for IMT-
Advanced(12/2009),ITU-RM.2135-1Std.
LoSscenarioconsideredinthemeasurement,implyingthatthe
diagonalelementsoftheLoSpolarizationmatrixdointroduce [4] WINNERIIinterimchannelmodels,IST-4-027756WINNERD1.1.1Std.
the same phase variation to both the vertical and horizontal [5] D5.3:WINNER+FinalChannel Models,P.Heino, ed.Std.
polarized waves.
[6] K. Kalliola, H. Laitinen, P. Vainikainen, M. Toeltsch, J. Laurila, and
E.Bonek,“3-ddouble-directionalradiochannelcharacterizationforurban
macrocellularapplications,”IEEETrans.OnAntennasandPropagations,
VI. Conclusions vol.51,no.11,nov.2003.
[7] K. Kalliola, K. Sulonen, H. Laitinen, O. Kivekas, J. Krogerus, and
In this contribution, the stochastic channel characteristics P. Vainikainen, “Angular power distribution and mean effective gain of
mobile antenna in different propagation environments,” IEEETrans. On
extracted based on measurements for urban macro and micro
Vehicular Technology, vol.51,no.5,sep2002.
scenariosinXi’an,Chinahavebeenreportedwithemphasisin
[8] J. Medbo, H. Asplund, J.-E. Berg, and N. Jalden, “Directional channel
theelevationofarrivalandofdeparturedomains.Theelevation
characteristics in elevation and azimuth at an urban macrocell base
angular spreads and the cross-correlation coefficients thereof station,” in Antennas and Propagation (EUCAP), 2012 6th European
with otherlarge-scalechannelparameterswere calculated and Conference on,march2012,pp.428–432.
compared with the existing 3-dimensional (3D) ITU IMT- [9] X. Yin, B. H. Fleury, P. Jourdan, and A. Stucki, “Polarization esti-
Advanced channel models for urban scenarios. The channels mation of individual propagation paths using the SAGE algorithm,” in
Proceedings of the IEEE International Symposium on Personal, Indoor
generated by using the updated model parameters yield non-
andMobileRadioCommunications(PIMRC),Beijing,China,Sep.2003.
negative definite correlation matrices which is difficult to
obtain by using the existing models. In addition, modification
were proposed for the conventional settings of the LoS-
path polarization matrix defined in the WINNER+/ITU/3GPP
5