Nearest object priority based integrated rough surface ... - IEEE Xplore

STRATEGIES AND SCHEMES

Nearest Object Priority Based Integrated Rough Surface Scattering Algorithm for 3D Indoor Propagation Prediction ASMZ Kausar, AW Reza, KA Noordin, MJ Islam,

H

Ramiah

Department of Electrical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

Abstract:

Since rough surface scattering

and ray prediction accuracy are also presented.

has a great impact on the accuracy of

Keywords:

rough surface scattering; binary

the propagation prediction algorithm, an

space partitioning; ray tracing; nearest object

integrated algorithm for indoor propagation

priority; communications

prediction including rough surface scattering is proposed here. This algorithm is composed

I. INTRODUCTION

of a three dimensional (3�) ray tracing algorithm based on binary space partitioning

147

Proper modeling of indoor wireless commu­

(BSP) and a diffuse scattering algorithm based

nication system is necessary for achieving a

on Oren-Nayar's theory. Lack of accuracy and

higher degree of service quality. Rough sur­

prohibitive time consumption are the main

face scattering is one of the significant propa­

drawbacks of the existing ray tracing based

gation mechanisms,which has the capability

propagation prediction models. To defy these

to change the amount of the received signal by

shortcomings,the balanced BSP tree is used

changing the ray directions. For that reason,

in the proposed algorithm to accelerate the

rough surface scattering has a great impact on

ray tracing,while the nearest object priority

indoor propagation planning. Besides,proper

technique (NOP) and in contact surface

understanding about the scattering mechanism

(lCS) is used to eliminate the repeated ray­

has a great role in target identification,remote

object intersection tests. Therefore,the final

sensing, radio astronomy, and radar design.

criteria of this study are the time consumption

Consequently, accurate and efficient rough

as well as accuracy by predicting the field

surface scattering analysis is an important re­

strength and the number of received signals.

search area in electromagnetic.

Using the proposed approaches,our algorithm

Because of the multi-interaction between

becomes faster and more accurate than the

rays and object, scattering analysis is very

existing algorithms. A detailed comparative

complicated and difficult. A lot of research

study with existing algorithms shows that

work is progressing for the solution of rough

the proposed algorithm has at most 37.83%

surface scattering [1-14]. Among those,some

higher accuracy and 34.44% lower time

are experimental model [5,7],some are statis­

consumption. Moreover,effects of NOP and

tical model [4,9],and some are deterministic

ICS techniques and scattering factor on time

model [3,8] where deterministic models are China Communications· October 2014

popular for indoor propagation modeling.

is very time consuming because of the trun­

Therefore, less prediction time and higher

cated rough surface in KA-MoM. This surface

In this paper, an inte­

accuracy are prime concerns for determinis­

is usually very large in terms of wavelength,

grated technique is

tic model. However,the existing techniques,

particularly for low incident angles. In near

such as shooting and bouncing ray (SBR)

field technique,the edge diffraction is not con­

[15],bi-directional path tracing (BDPT) [16],

sidered. However,this causes lower accuracy.

brick tracing (BT) [17],radiosity [18],Kirch­

Hence, to improve the performance of the

hoff Approach-Method of Moments (KA­

ray tracing algorithm,researchers use some ac­

MoM) [19],and near field [14] require higher

celeration techniques. Most acceleration tech­

prediction time due to complex algorithms

niques have been used in two different ways

used. Moreover, the prediction accuracy is

[14]. To simplify the simulation environment

not so high. In SBR technique,the spherical

is one of the techniques to achieve accelera­

wavefront is covered by the ray cones. Two

tion,while intersection test calculation is the

successive cones overlap each other at the

other possible technique. For simplification of

edge. In that case,the receiver (Rx) located

the simulation environment,the edges,planes

in the overlapping area will then receive two

or whole objects are considered to reduce. For

rays and double ray counting error will be oc­

achieving acceleration,sometimes the feature

curred. The BDPT technique shows incorrect

of three-dimensionality is neglected or the

results for single floor multiple room environ­

number of objects involved is reduced. The

ments,where more than one transmitter ( Tx) is

intersection test calculation is needed to find

present. In that case,it also takes a lot of time

out the actual rays. For this,all possible paths

to create the ray paths. In BT technique,every

between Tx and Rx are tested to find the actual

wall of the building is discretized into its unit

path, and then ray tracing is conceded. This

cells,called bricks. Because of the truncation

path finding test is a matter of acceleration and

of the slab,the corner bricks show factual er­

a numerous researches have been conducted

ror,which results in erroneous analytic reflec­

for this purpose,such as the efficient visibili­

tion and transmission coefficient. Furthermore,

ty graphs both in 2D [20] and 3D cases [21],

BT technique only considers the walls of the

hybrid approaches with a 2D ray-path search

indoor environment. Without considering the

together with 3D ray tracing [22],etc.

objects,the accurate results cannot be found.

In this paper, a 3D ray tracing technique

Besides, in BT technique,after the first in­

integrated with a scattering technique is pro­

teraction between Tx and bricks,each related

posed,considering each interaction point of

bricks become new source of the ray. In that

a ray. The binary space partitioning (BSP)

case,all of those bricks have to consider as Tx

based technique is used for ray tracing,which

individually and test for the next interaction.

consumes less time than conventional ray

This process consumes a huge amount of time.

tracing technique. Oren-Nayar [23] scattering

The radiosity technique cannot be used for

technique is used to determine the reflected ra­

smooth surfaces. Hence,for the objects having

diance of the scattered rays and backward-for­

a smooth surface,this technique offers inaccu­

ward technique [24] is used for the simulation

rate results. Additionally, radiosity technique

purpose. These techniques are chosen for their

is mainly used for acoustic waves, not for

simplicity,accuracy,and ease of usability. The

electromagnetic waves. The propagation prop­

type of the ray-object contact point and dis­

erties of different media except air (e.g.,walls,

tinguished object will make a variation to the

woods, bricks, concretes) will be of course

scattering parameters. Therefore,we have also

different for either type of wave and cannot be

considered different types of objects. For min­

interchanged,which results in lack of accura­

imizing the intersection test time,a new tech­

cy. In KA-MoM technique, the coupled field

nique,namely,nearest object priority (NOP) is

calculation between object and rough surface

introduced here. In the existing algorithms,all

China Communications· October 2014

presented to develop a new indoor prop­ agation prediction algorithm including rough surface scatter­ ing.

148

of the objects should be tested for finding the

surfaces, which overcomes the limitation of

actual object. Therefore,the prediction time

radiosity technique. Diffraction from the edge

becomes extremely high. In our algorithm,we

of an object is also considered in the proposed

have a NOP technique for finding the nearest

technique which was not considered in KA­

object, which will minimize the intersection

MoM technique.

testing time. For reducing 3D computational

The mathematical approach of the proposed

complexity and saving the prediction time,we

hybrid technique along with the NOP and ICS

have introduced the novel concept of in con­

are presented in Section 2,while detailed re­

tact surface (lCS).

sults analysis are depicted in Section 3. Final­

As stated above,the major problems of ray

ly,a conclusion is made in Section 4.

tracing are ray-object intersection test time and accuracy. Therefore,the main contributions of

II. PROPOSED HVBRIDE TECHNIQUE

this paper are(i) The NOP and ICS for reducing the ray-object intersection test time. (ii) The enhancement of accuracy by intro­ ducing the ICS and rough surface scattering.

2.1 Scattering technique

The proposed hybrid technique is composed of scattering and ray tracing techniques. As we

(iii) The elimination of the limitations of

know that the scattering model cannot be used

the existing techniques (as described above).

directly with a ray tracing model [18],there­

The double ray counting problem of SBR tech­

fore,we have used the backward and forward

nique is overcome by using single ray instead

scattering function of objects and walls. On

of ray cone. The problem of incorrect results

the other hand,the Oren-Nayar [23] roughness

due to multiple rooms in BDPT technique is

technique is used to find out the reflected radi­

solved by using the proper use of NOP and

ance,which has a usage to find out the direc­

ICS and thus,the proposed technique shows

tion of the scattered rays.

decent results not only for single rooms but

First of all,the target is to find out the re­

also for multiple room environments. Unlike

flected radiance from the roughness technique,

BT technique,we have considered walls and

proposed by Oren-Nayar [23,25],which is the

objects of the environment for reducing the

modification of the Lambertian method [25,

chance of missing the rays due to the different

26]. Figure 1 shows different elements used to

ray-object interactions. Our proposed tech­

find out the reflected radiance. The reflected

nique can be used for both smooth and rough

radiance can be changed due to the presence of masking, shadowing,and inter-reflection effects. In case of shadowing,a facet is just partly illuminated due to the shadow of neigh­

z

boring facet. As the nearby facets create an

v

obstruction,the sensor can detect a facet partly 6r

because of masking. In inter-reflection,rays 6i

s

bounce between adjacent facets. In Figure 1, 8i represents the incidence =---��

r

angle and CPi represents an incident azimuth angle,while 8r denotes the reflected angle and CPr denotes the reflected azimuth angle. The

terminology of diffuse reflection is expressed in terms of reflected radiance Lr and incident radiance Li• Now,let us consider an isotropic surface of Fig.1 The geometry used to characterize the reflected radiance

149

V

cavities with same facet slop 8a

and uniform distribution in orientation CPa. The China Communications· October 2014

isotropic surface of same facet slop is chosen

to determine the direction of the scattered

instead of different facet slop on behalf of

rays. Since the surface is considered as isotro­

reducing the computational complexities. Ac­

pic,the value of reflected radiance and other

cordingly,the radiance is determined as [23,

parameters except the incident and reflected

25]-

angle will be remain unchanged in all inci­

L: (B",Bj, cP, - CPj;tT)

dences if the object type is not changed. Now, the reflected angle is found by simply putting

K, (tT)+ cos (cp, - cP')· P

I

K2 (a;f3;cp, - cpj;tT)tanf3

--; Eo cos Bj +(1 - Icos (cp, - cP,) )· l

=

K3(a;f3;tT)tan

l,

(I)

(a+f3 ) -

Now,for prediction modeling,a scattering environment. This scattering cluster is used to find the backward and forward function

=

K,

=

K3

0.45

f 1

=

0.45

cT

(

"::� "::�

.09

(T'

.09

2

sin a if cos(rp, - rp,)

;;;. 0

(sin ( 2! n otherwise' ) ( 4af3 )2 9 ---;[2 ' a -

0.125 2 tT tT +0.0

Here,(J is the standard deviation as a mea­ sure of surface roughness, a

13

=

Min [Bj,B,], and

p

the scattered ray will be originated. cluster is used for the evaluation of the indoor

2

where the coefficients are tT2 KI 1 - 0.5 2 3 , tT +0. "

these values in Eq. (4). Thus,the direction of

=

Max [Bj,B,],

is the diffuse percentage

of walls and objects. The scattering cluster parameter varies according to the nature of interaction between the ray and the object,and the interface object type. During simulation, the simulated response is analyzed by impos­ ing the backward-forward function into the described ray tracing technique. The scattered direction is [24]-

for Lambert's Law. Eq. (1) is for masking and shadowing con­ ditions. For inter-reflection, the expression is

1

directive pattern for backward and forward

IE,12

=

[23]V, (B"B"cp, - CPj;tT) -

tT2

_

. -

2

=

p 0.17-Eo cos B, 1f

r I - cos (cp, - cP,) ( ----;213 )'1 . J I

where (2)

sulting from all effects is [23], =

•

"

EsoT'

IJfR

cos 1/1" 2 + cos I/Ir 2

+

and

IJfT

)

'"

)

"

' For backward direction

"'

; For forward direction '

(5) are the angle between the

scattering direction and the reflected or trans­

mitted ray direction,respectively,aR and aT are related to scattering lobe,and

Therefore,the total reflection radiance re­ L,(B"B"cp, - CPj;tT) L�(B"B"cp,CPj;tT)+L,2 (B"Bj,cp, - CPj;tT)

(1 2 (1

EsoR'

(3)

A modification has been done based on the

ESOR

and

ESOT

is

dependent on SR and S),respectively. The pre­ eminent values of SR and

aR

for building walls

are 0.4 and 3,respectively and the best values for S) and

a)

for a brick-wall sample are 0.5

and 3,respectively [24,27].

term K3 by assuming that there is no inter-re­

2.2 Ray tracing with proposed NOP

flection and the modified equation is as [23],

and ICS techniques

[A�,Max I+

L, (B"Bj, cP, - CPj;tT)

=

� Eo cos Bj

Al

where,

A2

=

=

1

[0, cos (B, - B,)]. '

smatanf3

In conjunction with the above backward and (4)

tT2

1 - 0.5� 33' . tT2 0.45 2 tT +0.09 .

The simplified Eq. (4) has the advantages

forward function, a ray tracing technique is used to predict the propagation path. For the proposed ray tracing algorithm,we have used the balanced BSP technique to minimize the simulation time and also to increase the ac­ curacy. In this technique, the objects of the indoor environment are arranged in a tree on the basis of partitioning until the smallest unit is found. Our partitioning algorithm splits the

China Communications· October 2014

150

subdivision by choosing the planes which are normal to any of the 3 axes in a round robin The BSP is a technique that recursively splits the target space using random plane. Mathematically [28][1,2],we can say that,if S be a group of n pair-wise separate objects in 3D space IR3, a binary space division parti­ tion for S is a recursively demarcated convex subdivision of space acquired by dividing the space into two uncluttered regions SI and S2 by a plane. Thus, it recursively constructs a

BSP for {s n S lis E S} within SI and a BSP n

and let Pi be a random plane orthogonal to the

j-th coordinate path. Let Pi and Pi indicates

technique.

for {s

jects in a 3D space 1R3 shown in Figure 2(b),

S21s E S} within S2. This process

comes to an end when each cell of the BSP tree splits up at most single object of S. For constructing a balanced tree,we have used the window list concept. This window list concept

the set of objects lying in the part below the cut Pi and above the cut Pi' respectively. Next,

let Pi- indicates the set of objects,which are

intersected by the plane Pi' Let,the maximum

number of objects intersected by the plane Pi

kj . The profile k* of S is demarcated to be the minimum of all k/, i.e.,

is

'

k'

object-splitter intersection or not. An axis par­ [ 29 ]:

R

=

[a),b)]

X

[a2,bJ

X

[a3,b3].

(6)

Any plane P normal to any of the 3 axes

divides IR3 into two halves as shown in Fig­ ure 2(a). Any object R intersected by plane P

splits into two parts,which are non-overlap­ ping. More specifically,for any P E (ai' b), the plane xi=P splits the object R into two parts:

R"It

=

Right

=

[a),b)]

X

[a),b)]

x

[a2,bel [a2,bel

x

x

[a3,b3]

•••

[a3,b3]

•••

x

x

[ai,p], (7) [p,bJ(8)

Now,let S ={R],R2, ... ,Rn}={[a],b]],[a2,b2], ... , [a",bnD be a set of n feasibly overlapping ob-

min{k;, k;, k;}.

(9)

Let,l=mini at. r=maxi bi for 1:S i:S n , and x= be the set of objects in S close to x for each x E [1, r].x· is named the profile of S at x. Now, [I, r] will split into a non-overlapping set of T in parts of/],... ,m I and it is satisfied by the fol­

lowing [29 ]:

I Wi l � ok' (Wi),

will serve for all the cases whether there is an allel obstacle R in a 3D space 1R3 is defined as

=

(10)

w h e r e 62:2 i s a c o n s t a n t a n d k'(W) max(l,minl x· I) i s t he min im u m tE/i =

profile of the set Wi' Each set Wi' for 1:S j

:s

m, is termed as window and the systematic sequence W=( W ],W b "" Wn,) is called the win­

dow list W(IfI). Any inquiry series q=[q.Xl ,q.

x2]x[q.y],q'Y2] can be disintegrated into a max­ imum of three definite parts q" qm, and qn"The

final algorithm to create the balanced BSP tree is shown in Algorithm I . We can describe the proposed BSP algo­ rithm (Algorithm 1) in a simple and straight forward approach as below(i) First,select a partition plane, (ii) Partition all objects with the initial par­ tition plane,storing them in either the front list

s

or back list,and D

y

z

D

p

I�I�·I (a)

D x

(iii) Iterate through the front list and back

O

list,creating a new tree node,and attaching it to the left or the right leaf of the parent node.

�

There are four cases to deal with when an environment is partitioned by the plane:

o

(i) Object is in front of the plane, (ii) Object is behind the plane, (iii) Object is coincident with the plane,

F' j �

(iv) Object spans the plane. (b)

Fig. 2 Illustration of creation of window list (a) Single object (b) Multiple object

15 1

For the first two cases,the object is simply added to the appropriate node of the tree. For China Communications· October 2014

the last two cases,window list will be applied for adding the object in the back list or front list. The ICS (klmn),shown in Figure 3(a) is de­ fined as the effective surface within an object. The 3D objects we used in this study are made of cubes or cuboids as in Figure 3,which con­ sist of six faces and eight vertices,where each vertex has a unique coordinate point. Using these vertices of the object,we can calculate abscissa of Cl­ abscissa of C3 ,(\\) =

ordinate of k

----

=

=

ordinate of Cl ordinate of C3"

(12 )

I, m,and n coordinates can also be determined

in the same manner. Among all of the objects in an environ­ ment,only the closest object intersects with a specific ray. The NOP technique helps us to find out this closest object. To fonnulate NOP in Figure 3(b),we assume a vector q started from the ICS to the origin tween

0

0,

distance s be­

and plane P, vector I, which has a

unity length,and an angle Q between q and I.

From the vector analysis [30],we know that, a dot product is equal to the product of the ab­ solute length of the two vectors,multiplied by the angle between them or sum of the product of the components. Mathematically,it can be

=

=

Iql cos Q

Input: a set of objects Output: a BSP tree of the objects 1. {plane partition;

2. list polygons; 3. BSP_tree

4.

q.x * l.x + q.y * l.y

+

. (\3) q.z * l.z

*front, *back;};

5. void Construct_BSP_Tree(BSP_tree *tree, list polygons)

6. { polygon *root=polygon.GetJrom_List 0;

8.

9.

I O.

tree->partition = root->Get]lane 0; tree->polygons.Add_To_List(root); list front_list, back_list;

11. polygon *poly;

12. while «poly=polygons.GetJrom_List()) !=O)

13. { int result=tree->partition.Classify_Polygon (poly); 14.

15. { 16.

switch(result) case IN_BACK_OF: backlist.Add_To_List(poly);

17.

break:

18.

case IN FRONT OF:

19.

-

-

frontlist.Add_To_List(poly);

W.

break:

21.

case SPANNING:

n.

polygon *front�iece, *back�iece;

�. �.

SplicPolygon(poly, tree->partition, front_piece, back_piece);

�.

�.

frontlist.Add_To_List(front_piece);

backlist.Add_To_List(back�iece); break})

n.

28. { �. 30.

if(! fronUist.Ts_EmptLList()) tree->front=new BSP tree: ConstrucCBSP_Tree(tree->front, fronUist);}

31. {

expressed as follows: dot (q, l)

Construct BSP Tree(Polygon Set) Assumption: a specified technique for building binary tree and a root plane

7.

the coordinate points of k as follows:

abscissa of k

Algorithm 1 The proposed balanced BSP algorithm

if(! backUist.ls_Empty_List()) tree->back=new BSP_tree; Construct_BSP_Tree(tree->back, back_list);})

However,one of the elements of vector q, IqlcosQ is in the direction of vector I. That

the object type can also be identified. Based on

means,if dot(q, l) is a less significant quan­

this identification, decision of the occurrence

tity than s,top of the plane is denoted and if

of reflection, refraction,and diffraction will

dot(q, l) is superior in respect to s,bottom of

be taken and the next ray will be generated ac­

the plane is denoted. Therefore,by subtracting

cordingly.

them,we found: Side

Side

=

=

sgn (s

Referring to Figure 3(b),suppose Ll is the - dot (q, I)),

(\4)

sgn(s-(q.x*l.x + q.y*l.y + q.z*l.z)). (\5)

source ray and L2 is the ICS (klmn) generated after the source ray incident to the 3D object. Here,(xj,Yj,Zj) with vector (aj,bj,cj) represents

of any object is facing the Tx by using Eq.

Ll, while (X2,Y2,Z2) with vector (a2,b2,c2) rep­ resents L2 or the [CS. Now,if these two lines

(15). If we can identity the nearest object then

intersect with each other,then the intersection

Now,we can quickly determine which side

China Communications· October 2014

152

to Rx. In this figure,only two rays Ll and L2 are shown as significant in the environment where multipath propagation takes place. III. RESULTS AND DISCUSSION

In the following,the simulation results of 3D (a)

indoor environments with rough surface scat­

Intersection point between Ll and ICS p Cl

tering are presented. The simulation results will be changed according to the scattering

__

factor [31],which varies for different objects. Therefore, during simulation, different types of objects have been used. The comparison is made between the proposed technique and the existing techniques, such as radiosity [18],near-field [14],KA-MoM [19],ST [17], BDPT [16], and SBR [15] techniques. For this comparison,we have used five different

(b)

indoor environments. The details of five dif­ Fig. 3 (a) Creation of lCS (b) Fundamentals of NOP

ferent realistic indoor environments are shown in Figure 4. The experimental settings of all algorithms are kept analogous to make a fair

point can be calculated. By using the cross

comparison. Some important parameters are

product [30] of these two vectors,we can find

given in Table I. The simulation is carried out for 10 different scenarios for each of the five

whether these lines are intersecting or not.

Ll where e (0°

X

:s

L2 e

:s

=

1£111L21sin8.J],

(16)

changing the positions of Tx inside a particu­

180°) is the measure of the

lar environment. For every scenario,we have

smaller angle between Ll and L2, IL11 and IL21 are the magnitudes of vectors Ll and L2, and J] is a unit vector perpendicular to the plane

time and the number of predicted signals for

collected the necessary data for the execution all of the above mentioned techniques. The

containing L1 and L2. According to vector algebra,if Eq. (16) is

are represented graphically in Figures 5 and 6,

not zero then the two lines are considered as

respectively.

results obtained from 10 scenarios of Figure 4

intersecting and the intersecting point will be

Figure 5 represents the comparison between

determined. Hence,we can write the paramet­

the algorithms in terms of accuracy. The accu­

ric equations for Ll and L2 as below:

racy depends on the number of rays received

L1:

x=x,+a,*tby=y,+b,*t"z=z,+c,*tj, (17)

L2:

x=x2+a2*t],y=Y2+b2*t2,Z=Z2+C] *t], (18)

where tl and tz are two unknown parameters. Now,by solving Eqs. (17) and (18), we can determine the intersection point (x ,y,z ) of L1 and L2. Now,from this point,the next ray will

by the receiver. From this point of view,the proposed algorithm shows a better accuracy than other listed algorithms and this higher accuracy is due to implementation of ICS and NOP in the proposed algorithm. In case of execution time,the proposed al­ gorithm shows lower time consumption as in

be generated according to the object type. In

Figure 6. Here,SSP tree is used for ray trac­

an indoor environment,such as the one shown

ing,which decreases the time by arranging the

in Figure 4(a),the target here is to predict the path of the significant rays emanated from Tx 153

environments. These scenarios are created by

object details in an organized approach. The NOP technique also minimizes a huge amount China Communications· October 2014

of time for intersection test by choosing the exact object. Thus,the overall execution time becomes lower than the existing techniques. The results obtained for all five different environments are represented in Table [I. From the results, we can observe that,the proposed algorithm shows 37.83% better accuracy than SBR,20.54% better than radi­

(a)

osity method, 25.40% better than near field

(b)

technique, 35.13% better than KA-MoM technique, 13.51% better than BT method, and 11.35% better than BDPT technique. It also shows 12.89% lower time consumption than SBR algorithm, 24.32% lower than ra­ diosity algorithm, 34.44% lower than near field technique,26.86% lower than KA-MoM

o

technique,6.67% lower than BT method,and

(e)

27.94% lower than BDPT technique. 3.1 Effects of NOP and ICS

In our projected technique,rough surface scat­

rnJ ffil rID on

•

(d)

DO DD

an an

tering is included and its effects are described by using Scattering Factor (SF). SF is a sig­ nificant feature,which is affected by different wall materials and influences on the scattering angle. The scattering angle increases with the increase of SF. Consequently,the ray-object interaction probability increases, which raise the number of predicted signals and also the prediction time. Figure 7 shows

(e)

Fig. 4 Details a/five different indoor environments (a) Multipath propagation using

res and NOP onjirst environment (b)-(e) Remaining environments

the effect of SF on the number of predicted signals and time. The number of predicted

reducing time by managing the data efficiently

signals increases 39.94% for the increase of

than a single list. Again,NOP is reducing time

SF from 4 to 8 and 23.69% from SF 8 to 20.

by finding the nearest intersection point within

At the same time, 24.29% increased time

the shortest possible time. Thus,in two steps,

is needed for the increase of SF from 4 to 8

the time is reducing. On the other hand,for the

and 14.51% increased time from SF 8 to 20.

number of predicted signals,15.82% higher

Therefore,we can say that scattering has great

signal is predicted when NOP is included with

effect on the number of predicted signals and

scattering and 32.39% higher for inclusion of

prediction time of the ray tracing technique.

[CS. Here,NOP increases the signal predic­

From Figure 8,we can easily describe that

tion by detecting the nearest object accurately

the proposed technique performs better than

and thus,it does not give any ray to be unused.

the existing techniques. [n Figure 8,step-by­

Conversely, [CS increases the signal predic­

step improvement is described. As of Figure

tion by handling the surface rays accurately.

8,we found that the algorithm needs 18.33% less time when BSP is included with scattering and 34.29% less time when NOP is included with both BSP and scattering. Here, BSP is China Communications· October 2014

3.2 Performance with different types of antenna

Type of antenna is an important parame154

Table I Important parameters used in experiments

for data collection. In the figures,all of the

Factor

Value

4,8,20

Scattering Factor

10 cm

Wall Thiclmess

250 cm

Wall Height

2.4 GHz

Carrier Frequency

2.15 dBi

Antenna Gain for Dipole Antenna

18 dBi

Antenna Gain for Parabolic Antenna

5.2

Permittivity of Brick

ment achieved. However, a very negligible difference has been observed,which is occur­ ring due to multipath propagation phenomena. This identical result with the well-established existing techniques proves that,the proposed field strength. Hence,we can conclude that the

3

Permittivity of Wood

proposed technique can perform ray tracing

4

Permittivity of Plastic (PVC Board)

strength at the receiver end and good agree­

technique is accurately predicting the electric

3

Permittivity of Glass

techniques demonstrate almost similar field

accurately with lower time consumption than the existing techniques. IV. CONCLUSION

--Propsed --e-SBR

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'6

�

2C

0...

ct?i

I ---+--I � 3>-'1 -

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:--...

2

6

4

8

No. of Scenario s

---.A.-

Radiosity

sented to develop a new indoor propagation

Near field

prediction algorithm including rough surface

KA-MoM

--e-- BT

--*-

In this paper,an integrated technique is pre­

BDPT

10

scattering. The BSP is used in combination with the ray tracing for the acceleration pur­ pose. This decreases the prediction time and also increases the accuracy. For better accu­ racy,rough surface scattering is introduced, which is analyzed by Oren-Nayar theory and

Fig.S Comparison in terms o/number o/predicted rays

forward-backward function of objects and walls. A concept of ICS is introduced for

450"--

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.-

--------

-.

------

-.,,-------� -- Proposed

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400

3

-.

------

I

I

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II--e-SBR

1',

50

3

00

25

2

6 No. of Scenarios

4

increasing the accuracy of the proposed algo­

8

rithm, while NOP technique is presented to reduce the intersection test time. The obtained

---+---

Radiosily

results from this study show that the proposed

�N,a'fi'"

algorithm achieves as a maximum 37.83%

---.A.-

KA-MoM

--e--

---*-

BT BOPT

10

Fig.6 Comparison in terms 0/computation time

higher accuracy and 34.44% lower time con­ sumption than that of the existing algorithms. The proposed hybrid technique can not only be used in radio signal prediction but also it can be used for target identification,remote sensing,or in particular areas in electromag­ netic research where rough surface scattering is crucial. Although scattering is included in the pro­

ter, which has influence on the electric field strength. For different types of antenna, the results will be different. Figure 9 shows the electric field strength in the receiver side for half wave dipole antenna with 2.15 dBi gain and parabolic antenna with 18 dBi gain. In all cases, 2.4 GHz operating frequency is used

155

posed algorithm for propagation prediction, this can be also used in inverse scattering for determining object characteristics,such as its shape,internal construction,etc. based on data of how it scatters the incoming radiation or particles. In this paper,we have proposed ray tracing technique for indoor environments. We China Communications· October 2014

cannot directly use this technique for outdoor

Table II Results for all five environments

environments or corridors. Hence, there is a great chance of improvement of this algorithm in the future. Our next target is to gear up the

SBR

existing algorithm for inverse scattering and

Radiosity

then,we will make this algorithm a universal

Near field

ray tracing tool for using in any kind of envi­

KA-MoM

ronments. ACKNOWLEDGEMENT

BT BDPT Proposed

2

Time (ms) 3

295

231

258

3 91

283

371

248

328

345

250

329

243

260 236

Our sincere thanks go to the University of

291

225

312

221

201

224

203

218

301

References

E i=

HG, Siwiak K, Win Ml. A Comprehensive Stan­

80

60

dardized Model for Ultrawideband Propagation Channels. IEEE Transactions on Antennas and

2

v

Propagation 2006; 54(11):3151-3166. Pan XM, Cai L, Sheng XQ. An efficient high (/)

ro

order multilevel fast multipole algorithm for

213

172

233

139

106

154

146

131

147 117

94

152

158

168

156

181

194

[3 .0

_._

._. .

--

--'

4 6 No. of Scenarios

3

93

4

113

142

136

178

114

146

79

167

102

138

139

165

5

179 143

165

187

182

203

161

199

SF=8 SF=4

_._

._..

--

--'

t5 '6 !!!

ray tracing techniques using ray frustums for wireless propagation models. Progress In Elec­

[3 .0

--

.Ql 350

Kim H, Lee HS. Accelerated three dimensional

8

10

(a)

400

(/) '0 Q)

Electromagnetics Research 2012; 126:85-100.

SF=20 SF=8 SF=4

a..

'0 250

tromagnetics Research 2009; 96:21-36.

0

Poli L, Rocca P. Exploitation of T E-TM scatter­

z

ing data for microwave imaging through the multi-scaling reconstruction strategy. Progress

200

2

In Electromagnetics Research 2009; 99:245-260. [5]

254

184

215

122

c

electromagnetic scattering analysis. Progress In

[4]

193

204

2

Q)

Molisch AF, Cassioli D, Chia-Chin C, Emami S, Fort A, Kannan B, Karedal J, Kunisch J, Schantz

[3]

236

146

No. ofP"edicted Rays

t-..,

Grant (UMRG) scheme (RG098/12ICT).

[2]

193

5

160 rl--,-----r---�--r====, --SF=20

Malaya for offering extensive financial sup­ port under the University of Malaya Research

[1]

4

Hasar Uc. A new microwave method based on

4 6 No. of Scenarios

8

10

(b)

transmission scattering parameter measure­ ments for simultaneous broadband and stable permittivity and permeability determination.

Fig. 7 Effects of scattering factor

Progress In Electromagnetics Research 2009; 93:161-176. [6]

Pinel N, Johnson JT, Bourlier C. A Geometrical From a Rough Layer With Two Rough Surfaces.

Dielectric Rough Surfaces. IEEE Transactions on

2010; 58(3):809-816.

Antennas and Propagation 2011; 59(1):180-188. [10] Hongzhen C, Yueting l, Hongqi W, Chibiao D.

Tarng J H, Liu WS, Huang Y F, Huang JM. A

SAR Imaging Simulation for Urban Structures

novel and efficient hybrid model of radio mul­

Based on Analytical Models. IEEE Geoscience

tipath-fading channels in indoor environments.

and Remote Sensing Letters 2012; 9(6): 1127-

IEEE Transactions on Antennas and Propagation

1131.

2003; 51(3):585-594. [8]

Bin L, lengyuan L, Yang D. A Fast Numerical Method for Electromagnetic Scattering From

IEEE Transactions on Antennas and Propagation [7]

[9]

Optics Model of Three Dimensional Scattering

[11] Mani F, Oestges C. A Ray Based Method to

Li lX. Numerical simulation bistatic scattering

Evaluate Scattering by Vegetation Elements.

from three-dimensional conducting rough sur­

face with forward & backward method-based

IEEE Transactions on Antennas and Propagation

vector basic functions. lET Microwaves, Anten­

[12] De Rousiers C, Bousseau A, Subr K, Holzschuch

nas & Propagation 2010; 4(1):54-61.

China Communications· October 2014

2012; 60(8): 4006-4009. N, Ramamoorthi R. Real-T ime Rendering of

156

250..-,

Rough Refraction. IEEE Transactions on Visual­

---r---'---�- I-I

ization and Computer Graphics 2012; 18(10): 1591-1602. [13] Junwen D, Va-Qiu J. Scattering Simulation and

Vi'

Reconstruction of a 3-D Complex Target Using

E

'Q;' 1501 � E

i=

� �

r

,I

Downward-Looking Step-Frequency Radar. IEEE

" x/ I ,p...,"1,1

Transactions on Geoscience and Remote Sens­ ing 2011; 49(10): 4035-4047.

-- Scattering Only

100 50 I'

[14] Ouattara V B, Mostarshedi S, Richalot E, Wiart J,

-e- Scattering+BSP

Picon O. Near- and Far-Field Models for Scat­

--e- Scattering+BSP +NOP , 4

2

6

tering Analysis of Buildings in Wireless Commu­

8

No. of Scenarios

10

nications. IEEE Transactions on Antennas and Propagation 2011; 59(11): 4229-4238. [15] Tao V B, Lee H, Bao HJ. KD-tree based fast ray

(a)

tracing for RCS prediction. Progress In Electro­

en

magnetics Research 2008; 81:329-34l.

ro

c OJ

[16] Cocheril V, Vauzelle R. A new ray-tracing based wave propagation model including rough sur­

US

"0

faces scattering. Progress In Electromagnetics

2

Research 2007; 75:357-381.

()

'5

[17] T hiel M, Sarabandi K. A Hybrid Method for

0..

�

Indoor Wave Propagation Modeling. IEEE Trans­

-- Scattering Only

'0 ci z

actions on Antennas and Propagation 2008;

-e- Scattering+NOP

56(8):2703-2709.

[18] Franek 0, Andersen JB, Pedersen GF. Diffuse

II ==e=,,;;; Sc;;;a,;;tte ;; r;;;ing,g+�N ;; O � P=+�1 C�S=' L...----'-_____J

100 II�

4

2

6

8

No. of Scenarios

10

Scattering Model of Indoor Wideband Propaga­ tion. IEEE Transactions on Antennas and Propa­ gation 2011; 59(8):3006-3012.

(b)

[19] Zhang XV, Sheng XQ. Highly efficient hybrid method for monostatic scattering by objects on

a rough surface. lET Microwaves, Antennas &

Fig.8 Effects of scattering, NOp, and ICS on (a) Time and (b) No. of received valid

signals

Propagation 2010; 4(10):1597-1604.

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