TELKOM
NIKA Indonesia
n
Journal of
Electrical En
gineering
Vol. 12, No. 10, Octobe
r 20
14, pp. 7299
~ 730
3
DOI: 10.115
9
1
/telkomni
ka.
v
12i8.532
3
7299
Re
cei
v
ed
De
cem
ber 9, 20
13; Re
vised
A
ugust 1, 20
14; Accepted
August 12, 2
014
2.4 GHz Radio Wave P
r
opagation Characteristics in
Coal Mine Workface Tunnels
Duan Zh
ao*
1
, Enjie Ding
2
,
Xin Wang
2
1
School of Infor
m
ation a
nd El
e
c
tronic Eng
i
ne
erin
g,
Chin
a U
n
iversit
y
of Min
i
ng a
nd T
e
chn
o
lo
g
y
,
Xuz
h
o
u
, 221
00
8, Jiang Su, C
h
in
a
2
Io
T
Perceptio
n Mine R
e
sear
ch Center, Ch
i
na Un
iversit
y
o
f
Mining a
nd T
e
chn
o
lo
g
y
,
Xuz
h
o
u
, 221
00
8, Jiang Su, C
h
in
a
*Corres
p
o
ndi
n
g
author, e-ma
i
l
: zhaod
ua
n10
27@
163.
com, enji
e
d
@
cumt.e
du.cn,
54
520
0
081
@qq.com
A
b
st
r
a
ct
W
e
propos
ed
a nove
l
ray-tr
acin
g bas
ed r
adi
o w
a
ves pr
opa
gati
on (RT
R
W
P
) Law
suitable for
und
er-tun
nel c
o
mpl
e
x coal
mine w
o
rkface. T
he ener
gy
co
nsu
m
pti
o
n
mo
del
eva
l
u
a
tion
in
c
o
mpl
e
x
c
o
al
mi
ne
w
o
rkface
is d
e
rive
d. T
h
e
o
retica
l a
n
a
l
ysi
s ab
out c
a
lcu
l
a
t
ing th
e
multip
l
e
refl
ectio
n
s of
the r
a
d
i
o w
a
v
e
s
in coa
l
min
e
w
o
rkface is a
l
so
provi
ded. C
o
mputer si
mu
lati
o
n
s an
d fiel
d tests in w
o
rkface tunn
els sh
ow
that
this prop
ose
d
RTRWP law can w
o
rk effectively to
d
e
scrib
e the a
c
tual rad
i
o w
a
ve pro
p
a
gati
on
envir
on
me
nts in compl
e
x coal
min
e
w
o
rkface
.
Ke
y
w
ords
:
coal
mi
ne w
o
r
k
face, Ray-tra
c
ing b
a
se
d ra
dio w
a
ves pr
o
pag
atio
n (RT
R
W
P
) law
,
multi
-
path
mo
de
l, ener
gy loss
Copy
right
©
2014 In
stitu
t
e o
f
Ad
van
ced
En
g
i
n
eerin
g and
Scien
ce. All
rig
h
t
s reser
ve
d
.
1
．
Introduc
tion
In rece
nt years, with the d
e
velopme
n
t of
wirele
ss
co
mmuni
cation
techn
o
logy, more an
d
more
wirel
e
ss devices a
r
e applied fo
r automat
i
c
monitori
ng in
coal mine.
However, the
prop
agatio
n cha
r
a
c
teri
stics of the radi
o wave
s in
coal mine tun
nels, e
s
pe
cia
lly in coal mine
workfa
ce tu
n
nels,
are
different f
r
om
th
em in f
r
ee
sp
ace. Be
ca
use the
co
al mi
ne
workfa
ce i
s
a
limited confin
ed sp
ace of heterog
eneity, whe
n
tran
smi
tting in such environ
ment, the radio
wav
e
s
have se
riou
s
attenuation a
nd com
p
lex p
r
opa
gation. T
herefo
r
e, re
searchin
g t
he cha
r
a
c
teri
stics of
radio
waves i
s
h
e
lpful t
o
p
r
ovide
a
better
use of
wi
reless
co
mmu
nicatio
n
s eq
u
i
pments in
co
al
mine work
face.
Y.P.Zhang [1
] and
Guo
r
ui
Han
[2]
provi
ded th
eoretical mo
del
and
expe
riment
result
s of
radio
wave p
r
opa
gation in
coal min
e
tu
nnel
s re
sp
ect
i
vely. Kermani, M.H. also
gives the UHF
sign
als’ p
r
op
agation cha
r
a
c
teri
stics in coal mine tun
nels
[3]. However, these studies a
r
e ba
sed
on 90
0MHz freque
ncy b
a
n
d
and th
e co
nclu
sio
n
s
do
n’t become a
unified the
o
ry, there is
stil
l no
resea
r
ch on
highe
r fre
que
ncy radio
wa
ves (fo
r
exa
m
ple, commo
n u
s
ed
2.4G
Hz ra
dio
wav
e
s)
prop
agatio
n in coal mine
workface tunnel
s. So, we prop
osed RTRWP (Ra
y
-Tra
cing b
a
s
ed
Radi
o Waves Propa
gation
)
Law
ba
sed
o
n
ray tra
c
in
g
method to
give a theo
retica
l explanatio
n
o
f
the wirele
ss
cha
nnel
s in
coal mi
ne workfa
ce tu
nn
els. In additi
on, this pa
pe
r gives th
e d
e
tail
comp
uting m
e
thod of energy loss a
c
cording to
RTRWP Law. Simulation re
su
lts sho
w
that the
energy loss calcul
ated by this metho
d
is sim
ilar to the experime
n
t result
s and
RTRWP La
w is
well ap
plied for re
se
archin
g the radio
wave prop
agati
on ch
ara
c
te
ri
stics in co
al mine wo
rkface.
2
．
Ra
y
-tracing
Bas
e
d Ra
dio
Wav
es Propagation
(RT
R
WP
) La
w
There are lot
s
of hydrauli
c
s
upp
orts i
n
the co
al min
e
wo
rkfa
ce,
whi
c
h
con
s
i
s
t of four
wall
s, thre
es
are m
e
tal b
a
ffle plates an
d the re
si
dua
l one i
s
the
coal wall. The
pro
pag
ation
of
wirel
e
ss radi
o wave
s in such
spe
c
ial
ci
rcu
m
sta
n
ces
is different from the gene
ral free sp
ace. As
is sho
w
n in F
i
gure
1, the l
e
ft side i
s
co
al wall, the to
p and
bottom
side
s a
r
e
st
eel baffle pl
ates
and i
n
the
mi
ddle i
s
hydra
u
lic
su
ppo
rts.
As th
e
exi
s
tence of
the
hydrauli
c
su
p
ports,
the
ra
dio
rays h
a
ve en
ergy which h
a
ve ene
rgy lo
ss i
n
the
scattering p
r
o
c
e
s
s could
not transmit fo
r a l
ong
distan
ce.
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 10, Octobe
r 2014: 729
9
– 7303
7300
(,
)
nn
x
y
11
(,
)
nn
x
y
n
d
1
n
d
00
(,
)
x
y
00
(,
)
x
y
00
(2
,
)
ax
y
Figure 1. Sch
e
matic Di
ag
ram of the Co
al Mine
Wo
rkfa
ce
Figure 2. Vertical Inci
dent
Plane Prop
ag
ating
in Coal Mine Work
fac
e
CFRWP L
a
w reveal
s the
radio
wave
s
prop
agatio
n i
n
co
al mine
workfa
ce, an
d also
gives the jud
g
ment metho
d
that whethe
r the radi
o ra
y can tran
smi
t
cro
ss all hy
drauli
c
supp
o
r
ts
to the destina
tion point.
Figure 2 i
s
th
e platform
of the ro
of in coa
l
mine workfa
ce
，
a
is th
e width of the co
al mine
work
fac
e
,
k
i
s
the di
stan
ce between th
e two
sup
port
s
,
S
is
the se
nding point,
D
is the recei
v
ing
point,
S
1
is the mirror poi
nt in the first reflection a
nd
S
2
is the mirror p
o
int
in the seco
nd
reflectio
n
. Th
e judgme
n
t method is
sho
w
n as follo
w:
a)
Acco
rdi
ng to the cha
r
a
c
teristic of ar
ith
m
etic pro
g
re
ssi
on (the di
stan
ce betwe
en of
hydrauli
c
su
p
ports is eq
ua
l), get the
a
b
scissa
of th
e
n
hydra
u
lic
su
ppo
rt’s ci
rcle
cente
r
:
1
0
2
0
()
(
1
)
n
n
x
nd
n
k
yy
(1)
b)
Gives the eq
uation of
S
1
D
is
y-K
(
x+
x
s
)
+y
s
=0,
K
is the
slope of
S
1
D
(|
K
| is relevant to
the numbe
r o
f
times of reflection
).
c)
Find out th
e
cro
s
s-point of
S
1
D
and li
ne
y=
y
0
, whose
coo
r
din
a
te is
''
(,
)
nn
x
y
located
betwe
en
n
a
nd
n+1
hydraulic
sup
port
;
'
(/
(
)
)
n
n
ceil
x
d
k
,
ceil
is a function
mean
s to take the smalle
st integer whi
c
h is not less than the ind
e
p
ende
nt variab
le.
d)
Cal
c
ulate th
e
distan
ce
d
n
and
d
n+1
which
are
the
distan
ce
be
tween
n
a
nd
n+1
hydrauli
c
sup
ports’
circle
center an
d ray
S
1
D
.
00
2
|(
)
|
1
nn
n
yK
x
x
y
d
K
(2)
If
d
n
>d
0
a
nd
d
n+1
>d
0
, ray
S
1
D
can
g
o
thro
ugh
h
y
drauli
c
sup
port
n
bet
ween
n+
1
,
otherwise, the vertical inci
dence plane
will be hindered by
the hydrauli
c
support
s.
3. Multi-path Loss Mode
l Based on
CFRWP La
w
i
n
Coal Mine
Work
-face
The CF
RWP Law i
s
helpfu
l
to find all the pat
hs th
at the ra
dio ray
s
prop
agate
cross all
hydrauli
c
sup
ports from th
e tran
smitter
to the re
ceiv
er. That m
e
a
n
s
CF
RWP
L
a
w i
s
u
s
eful
to
resea
r
ch the
multi-path lo
ss of the ra
dio
waves i
n
co
al mine workf
a
ce. So, we prop
ose deta
i
l
comp
uting m
e
thod of multi-path en
er
gy loss acco
rdin
g to RTRWP Law.
Since, we
kn
ow that the p
o
we
r of re
cei
v
i
ng point in the dire
ct line
of sight is:
2
22
(4
)
tt
r
r
PG
G
P
dL
(
3
)
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
2.4 GHz Ra
di
o Wa
ve Pro
p
agation
Cha
r
acteri
stics
in
Coal Min
e
Workfa
ce T
unn
els (Dua
n Zh
ao)
7301
P
t
,
G
t
,
G
r
,
are
the tra
n
smit
power, tran
smit
gain, re
ce
ive
gain and
wavele
ngth;
d
an
d
L
are the
path l
ength a
nd
system lo
sses
(usu
ally
the value i
s
1). If the ra
dio
wav
e
s reflect
k
times
in the transmi
ssi
on path, th
e receive po
wer
can b
e
calcul
ated by the Equation
(4).
2
2
22
(4
)
tt
r
rk
k
PG
G
P
dL
(
4
)
k
is
decay fac
t
or
after
reflec
ted
k
time
s which i
s
related
with reflectivity and the
numbe
r of ref
l
ection
s.
In coal mi
ne
workfa
ce, the
roof an
d the
bottom is m
e
tal, while
one
side i
s
coal
wall and
the othe
r thre
e sid
e
s
are m
e
tal baffles
a
nd they of
diff
erent
refle
c
tivity. So, how can we calcula
t
e
the po
we
r o
f
receiving p
o
int after th
e ra
dio
wav
e
refle
c
ted
k
times in t
h
is
com
p
licated
transmissio
n environ
ment?
We give the method a
s
follow.
First, cal
c
ul
ate decay facto
r
k
.
The follo
win
g
analy
s
is is a
bout the
con
d
ition that th
ere i
s
m
+0 reflec
tive rays or
m+n
reflective heli
c
al curve
s
in the tran
smi
ssi
on acco
rdin
g to the RTRWP Law.
If the firs
t reflec
tion
on the
metal baffle, the
number of
reflec
tions
on metal baffle is
m
/2
(
m
is even n
u
mbe
r)
or
(
m
+1)/
2
(
m
is o
dd num
be
r),
while th
e nu
mber
of refle
c
tion
s on
co
a
l
wall
is
m
/2 (
m
is e
v
en numbe
r)
or (
m
-1)/
2 (
m
is odd n
u
mbe
r). The
n
cal
c
u
l
ation method
of
k
is
:
22
12
11
22
12
mm
n
k
mm
n
RR
RR
(
5
)
is the refle
c
ti
vity of coal mine wo
rkface
，
R
1
is the
ref
l
ectivity of the metal baffle on the
side wall
，
R
2
is the reflecti
vity of the metal baffle on
the roof a
n
d
bottom,
m
is the numb
e
r
of
ref
l
ect
i
o
n
s
in side wall
s,
n
is the numb
e
r
of reflection
s
betwe
en ro
of and bottom.
If the first refl
ection
on
coa
l
wall, the n
u
m
ber
of refle
c
tions o
n
coal
wall i
s
m
/2 (
m
is even
numbe
r) or (
m
+1)/
2 (
m
is
odd n
u
mb
er), while
the
nu
mber of refle
c
tion
s on
coa
l
wall i
s
m
/2 (
m
is
even numb
e
r) or (
m
-1
)/2 (
m
is odd num
ber). Then
ca
lculatio
n method of
k
is
:
22
12
11
22
12
mm
n
k
mm
n
RR
RR
(
6
)
is the refle
c
ti
vity of coal mine wo
rkface
，
R
1
is the
ref
l
ectivity of the metal baffle on the
side wall,
R
2
is the reflecti
vity of the metal baffle on
the roof a
n
d
bottom,
m
is the numb
e
r
of
ref
l
ect
i
o
n
s
in side wall
s,
n
is the numb
e
r
of reflection
s
betwe
en ro
of and bottom.
If the elec
tric field
E
i
in
the in
cid
ent
plane,
we
ca
ll it hori
z
o
n
ta
l inci
dent
or
vertical
polari
z
atio
n; i
f
the ele
c
tri
c
field
E
i
pe
rpe
ndicular to th
e in
cide
nce
plane,
we
cal
l
it the verti
c
al
incid
ent or ho
rizo
ntal pola
r
i
z
ation. So, we can g
e
t
the reflectio
n
co
e
fficient of the vertical in
cide
nt
wave (3
) an
d hori
z
ontal in
ci
dent wave (4) from the air to the medium
[1, 2].
2
2
co
s
s
i
n
co
s
s
i
n
ri
r
i
r
i
ri
r
i
E
E
(
3
)
2
2
cos
s
i
n
cos
s
i
n
ir
i
r
p
i
ir
i
E
E
(
4
)
r
is
the relative dielec
tric
cons
tant,
i
is i
n
cide
nce a
ngl
e. For the
ro
ugh
refle
c
tor,
the
reflectio
n
co
e
fficient need t
o
be co
rrecte
d
by multiplying the scattering co
efficient
s
[9]
：
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 10, Octobe
r 2014: 729
9
– 7303
7302
22
0
cos
c
os
[8
(
)
]
[
8
(
)
]
hi
h
i
s
exp
I
(
5
)
Secon
d
, cal
c
ulate the tran
smissio
n
dist
ance
L
.
Acco
rdi
ng to Fermat'
s
pri
n
ciple, the 3-di
m
ensi
onal tra
n
smi
ssi
on pat
h of the radio
waves
can
be map
ped
in
two
2-dim
e
n
s
ion plane (verti
ca
lly incid
ent
plane
and
h
o
rizontal i
n
ci
dent
p
l
a
n
e
)
,
as
is
s
h
ow
n in
F
i
gu
r
e
3
.
T
hen
the tran
smissi
on di
stan
ce
L
ca
n b
e
cal
c
ul
ated
re
spe
c
ti
vely
by the classi
cal image met
hod in the two incid
ent pla
nes.
Figure 3. Pro
pagatio
n Paths in Inci
dent
Plane
Fi
gure 4. Cal
c
ulatio
n of Propag
ation Di
stance
Third, we the received po
wer ca
n be cal
c
ulate
d
by formula (4
) wh
e
n
get
L
and
k
.
4. Simulations and Expe
riment
In orde
r to simulate the multi-path lo
ss of 2.4G
Hz ra
dio wave
s, we me
asu
r
ed the
corre
s
p
ondin
g
pa
ram
e
ters in
coal
mine
wo
rkfa
ce
(Ji
ahe
Coal
Min
e
, Xuzh
ou,
China),
whi
c
h
are
s
h
ow
n
as
fo
llo
w
:
01
5.13
,
0
.5
,
1
,
3
.2
r
am
d
m
u
v
2
2.4
,
2.4
,
0.15
r
fG
H
z
e
26
12
1.62578
*10
,
7
.7
*10
In ord
e
r to
confirm the
th
eoreti
c
al m
o
del, we
also
have carried
on the
scene
test in
Jiah
e coal mi
ne wo
rkfa
ce,
usin
g 2.4G
Hz WIFI A
cce
ss Point whose emissive po
wer is 0d
bm an
d
receive thre
shold is -90d
b
m
.
Figure 5. Experime
n
t Re
su
lts and Simul
a
tion Re
sult
s
0
5
10
15
20
25
30
35
40
45
-
100
-9
5
-9
0
-8
5
-8
0
-7
5
-7
0
-6
5
-6
0
D
i
r
e
c
t
i
o
n of
P
r
opagat
i
o
n z
RS
S
I
/
dbm
db
m
Si
m
u
l
a
ti
o
n
R
e
s
u
l
t
E
x
per
i
m
ent
D
a
t
a
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
2.4 GHz Ra
di
o Wa
ve Pro
p
agation
Cha
r
acteri
stics
in
Coal Min
e
Workfa
ce T
unn
els (Dua
n Zh
ao)
7303
Table 1. Re
ceived Powe
r
and Received
Packet
s
Rate in Coal Min
e
Wo
rkfa
ce
Distance/m
1
2 3
5
9 15
20
25
30
35
45
RSSI
/dbm
-64
-75
-83
-75
-83
-82
-90
-91
-92
-93
-94
Packets received
rates %
100
100
99.4
99.8
97.2
95.4
79
16.8
45.2
44.8
10.8
Acco
rdi
ng to
experim
ent result, the effe
ctive
tran
smit
ting ran
ge in
coal fa
ce i
s
a
bout 20
meters; Re
ce
ived sig
nal in
tensity and
p
a
ckets
re
ceiv
ed rates
are
sho
w
n i
n
Ta
ble 1. Fig
u
re
5
sho
w
s the rel
a
tionship bet
wee
n
the the
o
retical cal
c
ul
ation re
sult a
nd the actu
al survey result.
5. Conclusio
n
Based
on
th
e an
alysis of
pro
p
o
s
ed
CFRWP La
w,
2.4GHz
radi
o
wave
s tran
smissi
on
multi-path
attenuatio
n
cha
r
acteri
stic in
coal min
e
wo
rkface i
s
studi
ed. By the
co
mpari
s
o
n
of t
he
simulatio
n
re
sult a
nd th
e a
c
tual
experi
m
ent data,
it
ca
n be
con
c
lud
ed that th
e th
eoreti
c
al
mod
e
l
is ba
sically consi
s
tent wit
h
the
actual
measurement
results. So, this the
s
is off
e
rs
a method
for
wirel
e
ss tra
n
smi
ssi
on
rese
arch in
workfa
ce, a
nd the resu
lts are
help
f
ul for wi
rel
e
ss
comm
uni
cati
on in
work
face.
Referen
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