Comparative Study of Radio Channel Propagation ......4G systems, and considering backward compatibility with 3G systems, it would be desirable for the former to also have cellular

Comparative Study of Radio Channel PropagationCharacteristics for 3G/4G Communication Systems

Chan-Byoung Chae, Changho Suh, Marcos Katz, DS Park, and Frank H.P. Fitzek†Samsung Electronics Co., Ltd, P.O.BOX 105, Suwon, Korea.

E-mail: [email protected], Tel: +82-31-279-4828, Fax: +82-31-279-5130†Department of Communications Technology, Aalborg University

Neils Jernes Vej 12, 9220 Aalborg łst, Denmark

Abstract— A propagation model for 3G/4G communicationsystems is considered in this paper. The analysis method isbased on high frequency ray-tracing and the uniform theoryof diffraction. The ray contributions includes diffraction frombuilding edges, reflection from the ground and building and thedirect wave. According to the elevation angle of the impingingsignal, different propagation components will be presented in thecomposite received signal. We compared propagation character-istics in 3G/4G communication systems using the above analysismethod. The dependency of radio wave propagation with thegeometry of the scenario and the frequency band is investigatedin detail. The numerical results can be applied in cell planningof new cellular systems.

I. I NTRODUCTION

In this paper, we compare the radio propagation characteris-tics for 3G and 4G radio environments, for the particular andimportant case where a dominant obstacle is in the path ofthe signal transmitted from the base station (BS). In a typicalcellular system such as 3G, the signal level at a given positioncan be predicted by analyzing the propagation characteristicsof the channel. Results are very much dependant upon locationand height of the BS. Thus, the information of the propagationcharacteristics of the radio channel is useful in cell planningof a cellular system. From the standpoint of services for future4G systems, and considering backward compatibility with 3Gsystems, it would be desirable for the former to also havecellular network characteristics.

In this paper the Uniform Theory of Diffraction (UTD) [1]will be used to characterize a typical cellular channel. Moreprecisely, the two-dimensional propagation model for buildingblockage, developed in [2] for satellite communications, willbe employed here for characterizing a cellular environment.The rational for using the same model is the fact that thesame propagation phenomena takes place in both scenarios,e.g., direct incident wave as well as diffraction and reflectioncomponents. The main difference between both cases is theactual dimensions of the problem setting.

The radio propagation channel for a Broadband WirelessLocal Loop (B-WLL) system operating at 28GHz has beencharacterized in [3] by using the UTD through according tothe model of [1] and [2]. By applying the UTD, the raycontributions are formulated as the sum of direct, reflectedand diffracted waves. In this paper, we assume that carrier

frequency is 2GHz for 3G systems and 5 and 60GHz for 4Gsystems. It is widely accepted and demonstrated that cellularnetwork operation can be achieved in the 2 and 5GHz band butnot necessary in the 60 GHz band due to the high attenuationimposed by the channel. Results for the 60GHz band, includedhere as a reference, will show us this limitation. The propa-gation characteristics of 2 GHz and 5/60 GHz are analyzedusing the computationally efficient UTD method developed in[3]. Two basic scenarios are considered in this paper, buildingblockage and tree blockage, the difference being that in theformer the first- and second-order diffractions are modeledwhereas in the latter only the first-order diffraction compo-nent is taken into account. The incident Shadow Boundary(ISB) defines the limit angleφISB below which the directwave will be obstructed by the building while the ReflectionShadow Boundary (RSB) defines the equivalent angleφRSB

for reflected wave contributions. The computed results showthat in the incident shadow region(0 ≤ θ ≤ φISB), the signalattenuation is larger for the 5 GHz case and in the reflectionshadow region(φRSB ≤ θ ≤ 90o), the signal level at 5 GHzis more fluctuant than that at 2 GHz according to the incidentangle.

II. PROBLEM FORMULATION

The geometry of the propagation model for a cellular-basedpropagation scenario is illustrated in Figs. 1 and 2 for cases ofbuilding and tree blockage, respectively. In the model, a BSis located at the top of a high-rise building. The main purposeof this paper is to provide accurate results for cell planningbased on the actual propagation phenomena. This would helpto find appropriate coordinates(xBS , yBS , zBS) for placingthe BS when the surrounding environment is known. For thisanalysis, the received signal strength is independent of themobile station’s (MS) speed, since the building/tree is assumedof infinite extent in the direction of movement of the MS.Depending on the incident or elevation angleθ, different raycomponents can reach the MS. The different regions are alsoillustrated in Figs.1 and 2. This section follows the model andnotation of [1] and [2]. Three main contributing componentswill be present at the receiving end, namely a) incident ordirect, b) reflected and c) diffracted waves. In what followseach contributing component will be analyzed in detail.

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Fig. 2. Tree blockage propagation model and different regions based on the BS elevation angle

The ray contributions to the received signal as a functionof the elevation angle can be formulated as follows

• 0 ≤ θ ≤ φISB (within the incident shadow region)

1) ground reflections and then second-order diffrac-tions;

2) first and second-order diffractions;3) first and second-order diffractions followed by re-

flections from the ground.

• φISB ≤ θ ≤ φRSB ; 1), 2), and 3) as above: 4) directwave.

• φRSB ≤ θ ≤ 90o; 1), 2), 3), and 4) as above: 5) groundreflections.

A. The Incident Waves

The diffracted fields toward the MS can be computed bydetermining the incident field at the blocking building edges.For the soft (i.e., horizontal) polarization, the incident electricfield is in the z direction. The incident plane wave for softpolarization is given by

Eiz(reference) = E0e

−jk0ρ′ = E0e−j 2π

λ0ρ′

Eiz(mobile) = Ei

z(reference)·ej 2π

λ0[(wb+xm) cos φ+hm sin φ)].

(1)

For hard (vertical) polarization, the magnetic field is in thez direction. The evaluation of the incident plane wave forhard polarization is carried out in the same fashion as forsoft polarization.

Hiz(reference) = H0e

−jk0ρ′ = H0e−j 2π

λ0ρ′

Hiz(mobile) = Hi

z(reference)·ej 2π

λ0[(wb+xm) cos φ+hm sin φ)].

(2)

B. The Reflected Waves

In situations when the BS elevation angles exceed the RSB(θ > φRSB), a wave reflected from the ground will also reachthe MS antenna. At the MS, the reflected waves with respectto the field at the reference point are expressed as [2]

Erz (mobile) =Ei

z(reference) · Γs(ψ)·ej 2π

λ0[(wb+xm) cos φ−hm sin φ)]

Hrz (mobile) =Hi

z(reference) · Γh(ψ)·ej 2π

λ0[(wb+xm) cos φ−hm sin φ)]

Γs,h(ψ) is the reflection coefficient and given by

Γs,h(ψ) =cosψ − 1

a

√εr − sin2 ψ

cosψ + 1a

√εr − sin2 ψ

(3)

Base Station Elevation Angle (θ)

0 20 40 60 80

Nor

mal

ized

Sig

nal L

evel

(dB

)

-40

-30

-20

-10

0

10

fc=2GHzfc=5GHzfc=60GHz

θISB=34.99o θRSB=52.43o

Fig. 3. Normalized signal level versus BS elevation angle for hardpolarization in case of building blockage

Base Station Elevation Angle(θ)

0 20 40 60 80

Nor

mal

ized

Sig

nal L

evel

(dB

)

-80

-60

-40

-20

0



Fig. 4. Normalized signal level versus BS elevation angle for soft polarizationin case of building blockage

whereψ is the incidence angle at the ground, measured withrespect to the normal at the reflection point, i.e.,

ψ =π

2− θ = φ− π

2. (4)

For typical mobile communications environments, the follow-ing expression for ground relative permittivity was used:

εr = 15− j90

f(MHz). (5)

where a = 1 for soft polarization anda = εr for hardpolarization.

C. The Diffracted Waves

In a building blockage scenario the diffracted wave contri-butions to the received signal at the MS are represented by thefirst and second-order diffractions from the two edgesw1 andw2, respectively (see Fig. 1). The first-order diffraction termfrom edgew1 is [2]

Edz (ρ1) = Ei

z(w1)·Ds(L, φ1, φ′1, n1) · e−jk0ρ1

√ρ1

(6)

0 5 10 15 20

Nor

mal

ized

Sig

nal L

evel

(dB

)

-50

-40

-30

-20

-10

0

10

Distance between Buliding and Receiver(m)

hard polarization


Fig. 5. Normalized signal level versus distance between building and receiverfor hard polarization

Distance between Buliding and Receiver(m)

0 5 10 15 20

Nor

mal

ized

Sig

nal L

evel

(dB

)

-100

-80

-60

-40

-20

0


soft polarization

Fig. 6. Normalized signal level versus distance between building and receiversoft polarization

The UTD diffraction coefficients are given by

Ds(L, φ1, φ′1, n1)

=− e−jπ/4

2n2π·√

λ0·({

cot[π + (φ− φ′)

2n

]F

[2π

L

λ0g+(φ− φ′)

]

+ cot[π − (φ− φ′)

2n

]F

[2π

L

λ0g−(φ− φ′)

]}

∓ cot[π + (φ + φ′)

2n

]F

[2π

L

λ0g+(φ + φ′)

]

+ cot[π − (φ + φ′)

2n

]F

[2π

L

λ0g−(φ + φ′)

])}

(7)

The minus sign between the curly bracket is used for softpolarization and the plus sign for hard polarization. AlsoL isthe distance parameter,n is the wedge index(n1 = n2 = 1.5),andF is the Fresnel transition integral.

The present model includes multiple reflection and diffrac-tion terms in different regions. The first-order diffraction term

0 20 40 60 80-40

-30

-20

-10

0

10


Nor

mal

ized

Sig

nal L

evel

(dB

)


hard polarization


Fig. 7. Normalized signal level versus BS elevation angle for hardpolarization in case of tree blockage


0 20 40 60 80

Nor

mal

ized

Sig

nal L

evel

(dB

)

-50

-40

-30

-20

-10

0

10


soft polarization


Fig. 8. Normalized signal level versus BS elevation angle for soft polarizationin case of tree blockage

from edgew1 is given by

Edz (ρ1)|w1 =Ei

z(reference) · ej2π(wbλ0

cosφ+hbλ0

sinφ)

Ds(L1, φ1, φ′1, n1) · e−j2π

ρ1λ0√

ρ1

(8)

The distance parameterL is given by

L =ρρ′

ρ + ρ′(9)

where ρ is the distance from the diffraction point to theobservation point, andρ′ is the distance from the source pointto the diffraction point. Since the source distance is muchgreater than the observation distance(ρ′ >> ρ thenL1 ' ρ1.Note that the

√λ0 term in the diffraction coefficient of eq.

8 can be incorporated into the amplitude spreading factor.This way all physical dimensions are converted into electricalquantities. The second-order diffraction from edgew2 to edge

0 2 4 6 8 10 12-50

-40

-30

-20

-10

0

10


Nor

mal

ized

Sig

nal L

evel

(dB

)

Distance between Tree and Receiver(m)

hard polarization

Fig. 9. Normalized signal level versus distance between tree and receiverfor hard polarization

Distance between Tree and Receiver(m)

0 2 4 6 8 10 12

Nor

mal

ized

Sig

nal L

evel

(dB

)

-80

-60

-40

-20

0


soft polarization

Fig. 10. Normalized signal level versus distance between tree and receiversoft polarization

w1 for soft polarization are equal to zero, becauseDs = 0 atgrazing incidence.

Similarly, for hard polarization the first-order diffractionterm from edgew1 is

Hdz (ρ1)|w1 =Hi

z(reference) · ej2π(wbλ0

cosφ+hbλ0

sinφ)

Dh(L1, φ1, φ′1, n1) · e−j2π

ρ1λ0√

ρ1

(10)

For the second-order diffraction term from edgew2 to w1,this term can be expressed as

Hdz (ρ1)|w2w1 = Hi

z(reference) · ej2π(hbλ0

sinφ)

·Dh(L2, φ2, φ′2, n2)|φ2=0 · e−j2π

ρ2λ0√

ρ2|ρ2=wb

·Dh(L21, φ1, φ′1, n1)|φ′1=0 ·

e−j2πρ1λ0√

ρ1

(11)

TABLE I

MEAN PARAMETERS FORSUBURBAN ENVIRONMENT IN CASE OF BUILDING AND TREE BLOCKAGE

System φISB φRSB θ0dB,soft θ0dB,hard θ−20dB,soft θ−20dB,hard

2GHz/Building 34.99o 52.43o 38.40o 38.67o 27.12o 3.98o



2GHz/Tree 21.80o 57.99o 26.94o 27.00o 9.45o 28.11o

5GHz/Tree 21.80o 57.99o 25.12o 25.19o 12.25o 28.14o

60GHz/Tree 21.80o 57.99o 22.76o 22.77o 19.76o 19.88o

where

L2 ' ρ2 = wb

L21 =wbρ1

wb + ρ1

(12)

Terms higher than third-order are usually not necessary foraccurate computations [4]. Note that in tree blockage, we onlyconsider the first-order diffractions from the top of the tree.

III. A NALYTICAL RESULTS

We derive the normalized signal level according to theelevation angleθ between BS and blocking building. Thenormalized signal level is defined as

Ss =∣∣∣∣Etotal

z (mobile)Ei

z(reference)

∣∣∣∣. (13)

Sh =∣∣∣∣Htotal

z (mobile)Hi

z(reference)

∣∣∣∣. (14)

In typical moderate suburban environment, one to five-storybuildings are commonly found. In this study a four-storybuilding was assumed. In addition, the following parameters,defined in Figs.1 and 2., were used: building heighthb = 10m, building width wb = 10 m, MS receiver antenna heighthm = 3 m, MS locationxm = 10 m from the blockingbuilding, tree heightht = 5 m and tree locationxm = 5 mfrom the MS. A knife-edge approximation was used for thetree, as showed in Fig. 2. For the above defined parametersand according to the geometry of the system we have that(φISB = 34.99o), (φRSB = 52.43o) for the building blockagesetting and(φISB = 21.80o), (φRSB = 57.99o) for thetree blockage setting. The normalized signal level versus BSelevation angleθ is illustrated in Figs. 3, 4, 7 and 8. Figs. 3and 7 correspond to hard polarization cases while Figs. 4 and8 correspond to the soft polarization cases. The contributionsof different wave components as identified in Section II canbe clearly observed in the three well defined regions in thefigures. Indeed, in the incident shadow region the diffractedwaves are the principal contributing components, in the regionlimited by φISB andφRSB the direct wave component is alsoadded, and in the reflection shadow region the ground reflectedcomponents are further added to the composite received signal.Note that in the incident shadow region the attenuation dueto building blockage is more severe than that caused by treeblockage. As can be appreciated, for a building blockagescenario the difference of the signal strength at20o wasapproximately 15 dB when low and high frequency bands

are considered, as it could be expected. Figs. 5, 6, 9 and 10show the results of normalized signal level as a function ofthe distance between the building or tree and the MS receiver.The shadowing effect of the building or tree is evident whenthe MS approaches such an obstacle. Note also that as thefrequency increases, the signal attenuation becomes larger inthe incident shadow region. In other words, line of sight (LOS)becomes the dominant mechanism for propagation. Finally,as it can appreciated from Figs. 3-10, in the 60 GHz bandattenuation is severe, rendering such a high frequency bandnot suitable for cellular operation.

In Table 1, the values ofφISB , φRSB , θ−20dB,soft/hard,θ0dB,soft/hard are the mean values for 2 GHz, 5GHz, and 60GHz, respectively. We could get an insight on the differenceof propagation characteristics between 3G/4G communicationsystems through the above Table 1.

IV. CONCLUSION

A propagation model for building and tree blockage ap-plicable to 3G/4G cellular communication systems has beenconsidered in this paper. High frequency ray-tracing methodsand UTD were used to analyze typical propagation scenar-ios. The ray contributions includes diffraction from buildingedges, reflection from the ground and building, as well as thedirect wave. According to the angle of the impinging wavedifferent components will be present in the composite receivedsignal. We compared the propagation characteristics for 3G/4Gcommunication systems using the above mentioned analysismethod. Results strongly depend on the geometry of the con-sidered propagation scenario as well as on the frequency. Wecan observe that channel attenuation increase with frequency,thus, high frequency bands will impose significant limitationsto the link budget. This may justify the use of multihoppingapproached in some scenarios of future 4G systems

REFERENCES

[1] P.A. Tirkas, C.M.Wangsvick, and C.A.Balanis, “Propagation Model forBlockage in Satellite Mobile Communications System,”IEEE Trans.MTT, Vol.46, No.7 pp. July 1998

[2] C.A.Balanis, “Antenna Theory Analysis and Design,” 2nd ed., New York:Wiely, 1996

[3] Chan-Byoung Chaeet al, “’Radio Propagation for Building and TreeBlockage at B-WLL,” Telecommunications Review,Vol.9, No.5 pp.727-740, Korea, 1999

[4] L.A.Polka, C.A. Balanis, and A.C. Polycarpou, “High-frequency methodsfor multiple diffraction modeling: Application and comparison,”J.Electromagnetic Waves and Applications, Vol.8, No. 9/10, pp.1223-1246,1994

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Comparative Study of Radio Channel Propagation ......4G systems, and considering backward compatibility with 3G systems, it would be desirable for the former to also have cellular