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imulaio o igial Radio Modiale ael Model
Kui Li
GxSOC
Research Institute
Communication
University
of China Beijing, China
liki
_1497@yahoo.com.cn
Abstract-Th
paper analyzes the channel model of
igital
Radio Mondiale and discusses the parameters given by the specication. Watterson model is used to simulate the radio channel. We describe the implementation of Watterson channel model in details, including the channel multi-path and timing-variability. Multi-level interpolator is used in our realization scheme to improve calculation eciency. The simulation results are given and indicate that the timing and frequency selective fading effect of the DRM channel are well modeled.
Keywords D
WSSUS; Watterson
Model; Multi path;
Doppler Spread; Muliinterpolate
. INOON Digita Radio Mondiae (DRM)
is a
word-wide
specication for
Amplitde odlation
(AM) broadcasting.
It
is used to
repace te traditiona anaogue AM roadcasting
for its advantage such as robustness in fading channels, beter
adio qality, power
sings at the transmiting side. The
eqency
of DRM is below 30MHz.
t
this
roadcasting
equency band,
te
signals are transmited by sky-wave or ground-wave or both of them. The characteristics of DRM channel is
complex becase
of
te
instability of the
ionospere
and the
muti-hop
propagation beteen the
eart s
surface and
te ionospere.
It is a
typical multi-path
and time-varying channel that
presents
deep time and
eqency
selective fading. The channel
modeing
and simulation is signicant for the systems design,
impementation
and performance
evauation.
The DRM specication gives the channel model [1]. In this
paper,
we
discss
the model realization in detail based on the given
channe caracteristics
and parameters.
I. DRM
CHANNEL
M
OEL
DRM channel given by the
specication
is described as an
adaptable
parameters Wide Sense Stationary Uncorrelated Scatering
(WSSUS)
model.
is a
stocastic
time-varying
mode wit
a stationary statistics and several sets of
appropriate parameter vales.
The parameters include the
nmbers
of
multi-path, path
delay,
path
gain,
oppler
shi, and
Dopper
spread.
Tae-I
shows one of the six sets
parameters
given by the
specication.
The
nmber
of discrete multi-path, each
path
delay and gain describes the equency
seective
fading of the channel.
Te Doppler si
and spread presents
e channe s
time
seective
fading.
In
98--8-8-/$00 ©0 IEEE 35
Van Ming
GxSOC
Research Institute
Communication
University
of
Cina
Beijing, China yanming668@yahoo.com.cn the WSSUS model, each path of the channel is regarded as independent.
TABLE D
HANNL PAATS
Path
t
Path
Path
Path
4
el
0 2 ms 4 ms 6 ms
ath Gain,
nS
0.5
1
0.25 0.0625
Doppler Shi
0 1.2 Hz 2.4 Hz 3.6 Hz
Doppler Spread
0.1 Hz 2.4 Hz 4.8 Hz 7.2 Hz The WSSUS channel model is
expressed
as:
h T
L
T -Tn
(1)
P k
is the attenuation of the
k-t pat,
describing
te
relative
path
gain of each
path.
r
k
is the relative delay of the k-th
path.
{e k (t)}
are the time-variant
tap
weights, and they are zeros mean
complex-vaued
stationary Gaussian random
processes
with
nit
variance. The magnitudes
Ie k (t)1
are
Rayeig-distriuted
and
te
phases
(t)
are
uniformy distribted. Each
{e k (t)}
is
caracterized y
its
Power Density
Spectrum (PDS) that determines the average
speed
of variation in time. The
wi
of the
PDS
is quantied by
Dopper
spread
wich
is specied as 2-side
PDS
and contains 68% of the power. The PDS has a
Gassian
shape for the
ionosphere
path based on real observation. There might be a non-zeros center equency of
te PDS, wich
is an average equency
si
dened
y Doppler
shi. III.
MPLEMENTAION OF CHAEL ODEL
The WSSUS channel Model can be implemented by Watterson
mode
as
sown
in
Fig.
I.
Waterson
channe mode
is a
transversa
lter
were
taps
g k (t)
are complex and vary with time [2].
is an ideal discrete time delay model and the
vaues
of
deay
refer to
Tae-.
The taps of each path is independent [3][4][5].
{ g k(t)}
are
complex
valued stationary Gaussian random processes and
teir PDS
can be
descried y:
P f)=
P k
exp[_� f-fDSh k)2]
(2)
k _k 5
_k
P k
is
te
atenuation of
te k-t pat,
f DS P
_k
the
Dopper
spread and
h
k
is
te Doppler
shi.
se
l -
r t)
Figure 1. Watterson hannel Model.
The generation of time-varying taps can be divided into three independent
parts:
the
path
gain,
oppler
shi simulation and
oppler spread simlation,
as shown in Fig. 2.
r--------------
igure
2.
Three
Pars
of Taps in
Waterrson
Model
Te
g k (t)
can be expressed as:
g k(t)
=
P k . c k(t)·
}J _k
(3)
P k
and
Ck(t)
are
descried
in Section
I.
The path gain
directy multipies
on each path.
Multipy
}_k
to
eac pat
to
reaize
the
Dopper
shi effect. The
key
of
oppler spread
eect
simlation
is the taps
C k (t)
generation.
Te
zero-means, unit varance stochastic processes
{Ck (t)}
ave
Gaussian
Probaiity Density
Function (PDF) and Gaussian
shapes
PDS which are
controled y
the
Doppler
spread, as described in Section
I.
We generate
C k (t)
trogh
the following three
steps:
1
Generate a zero mean and unit variance
compexvaued
Gaussian
wite
noise. 2. Filter the
Gassian
white noise to forming a color noise with the required PDS. 3.
Ierpoate te tered sampes
for
matc
the
samping
rate. This
process
illustrates in Fig. 3.
36
Figure
3.
Generation of Time-varing Taps
Te compex-vaued
Gaussian white noise is produced by
Box-Muler algoritm. In
step-2, because ltering is a linear
operation,
the color noise has the same PDF with the srcinal
wite
noise.
Te
lter is designed based on the
PDS
requirements and its coefcients are dened
y:
r;
22
h(t)
=
e
J
{
(4)
f DS P
is the Doppler
spread.
The pass band width of the Gaussian lter is controlled by
oppler spread
We can
calclate
the
taps
by a lower speed for efciency
ecause te channe
timing
seective
fading is far lower than the system
sampling eqency, bt
it
mst
be at least 32 times than the Doppler
spread
values for accuracy [6]. At the same time, an
ierpoator
is used for match
te
sampling equency of taps and
signa sampes.
F or different values of
oppler
spread, the taps updating rate maybe different to dozens of times. At this condition, use the same sets of lter coefcients and through adjustable
mlti-level
interpolator control the lter pass band can
simpi
the
simuation
design.
IV.
IULATION RESULTS
The simulation of multi-path and Doppler shi of the channel is straightforward. The key
point
of the model
simuation
is
te
time-varying taps generation. The magnitude and phase of the
compex-valued
stationary Gaussian random
processes
sample nction
C k (t)
is shown in
Fig
and
Fig.
5.
Te
magnitude is
Rayeigdistribted
and the
phase
is uniformly
distribted
as
expected.
igure
4.
The
magnitudes distribution
of
C k
Figure
5.
The angles distribution of
C k
The power density spectrum of
ck
(t)
is shown in Fig. 6 and
Fig.
7. The magnitude in time-domain is
sown
in
Fig.
8 and Fig. 9. The
vale
of the Doppler
spread
decides the timeselective fading degree.
Te
simulation results show
tey matc
well.
Figure
6.
The PDS of
Ck
,
Doppler spread
=
7
2
H
z
Figure
7.
The
S
of
Ck
(t),
oppler
sp rea d
=
AHz
V.
CONLUSION
In is
paper, we discuss the
DM channe
model in detail.
Te aterson
model is used to
simuation
the channel. The tapped delay line with time-varying taps
simuates te
equency and time
seective
fading.
37
Figure
8.
Magnitude of
C k
in time domain, Doppler spread
=
7
2
H
z
Figure
9.
Magnitude of
C k
in time domain, Doppler spread
=
2AHz
e generate the taps
y
ltering Gaussian
wite
noise to form color noise with required PDS which derives om the channel Doppler spread. In our simulation scheme,
mltievel
interpolate is used to adapt wide dynamic range of
Doppler
spread.
Te
simulation
resuts
show
tat te
scheme can
simlate
the DRM channel accurately and efciently.
REFEENES
[I]
ETSI ES
201980 V2.1.1 (2004-06),
igital adio
Mondiale
(M)
System Specification.
[ 2]
C C
Watterson, J.
R
Juroshek, W. D. Bensema, Experimental onrmation of an
H
hannel
odel , IEEE
Trans. On omm. Tech, Vol. OM-18,No. 6,Dec.
1970. [ 3]
Yip,
K.
W, Ng, T.S., An analytic discrete-time model for a fading dispersive
WSSUS
channel,
IEEE Vehicular
Technology onference,
1994
I EEE
44th, 8-10
June
1994
age(s):
180-184
vo!.
1. [ 4]
Angling,
M l,
Davies, N.
C
An assessment of a new ionospheric channel model driven by measurements of multi-path and Doppler spread,
IEEE Frequency
Selecltion and Management
Techniques
for HF ommunications (Re No.
1999/017),
EE olloquium on,
29-30
March
1999
Page(s):
41 4/6. [ 5]
Behm,
C 1
A narrowband high equency channel simulator with delay spread, IEEE HF Radio Systems and Techniques, Seventh
Inteational
onference on (on
Pub . No.
441),7-10
July
1997
Page(s)
388-391. [ 6]
W Furman,
1
Nieto, Harris orporation, Understanding HF channel simulator requirements in order to reduce
H
moderm performance measurement variabilit, Proceedings of HF
I,
the Nordic HF onference, August
2001.

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