Content uploaded by Omar ALzoubi
Author content
All content in this area was uploaded by Omar ALzoubi on May 01, 2021
Content may be subject to copyright.
International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 5- April 2016
ISSN: 2231-5381 http://www.ijettjournal.org Page 224
Improve the Performance of Statistical
Properties for Deterministic Channel
Simulators
Omar Alzoubi #1, Mohieldin Wainakh *2
#,* Department of Communication Engineering & Higher Institute of Applied Sciences and Technology
Damascus, Syria
Abstract — This paper evaluates statistical properties
of Rice channel model, such as Autocorrelation
Function (ACF), Level Crossing Rate (LCR), Average
Duration of Fades (ADF), and Cumulative
Distribution Function (CDF). New computation
procedure of deterministic simulation model
parameters is presented. This procedure is a
combination of two methods, Method of Equal Areas
(MEA) and Method of Exact Doppler Spread (MEDS).
It is called a combination of MEA and MEDS.
Comparisons of statistical properties for both
reference and simulation models are introduced.
Finally, the results indicate a superiority of the new
method over the MEDS and MEA with respect to LCR
and ADF.
Keywords — Method of Equal Areas, Level Crossing
Rate, Average Duration of Fades, Method of Exact
Doppler Spread.
I. INTRODUCTION
The modeling of fading channels is of great
importance in the design, test and improve the
performance of cellular radio communication systems.
But the channel simulator must be efficient, flexible
and accurate. That depends on the design method of
simulator. The algorithm of channel simulator should
be simple to implement on the computer. Depending
upon the radio propagation environment various
multipath fading models are available in literature [1],
whereas [2] presents an explanation for many classical
fading channel models presented since 2005 until
present. Mobile fading channels are classified into two
categories, namely: frequency–nonselective and
frequency–selective fading channels. The first type is
modeled by using an appropriate stochastical models,
such as Rayleigh, Rice and Suzuki processes. These
processes play an important role in modelling mobile
fading channels with a different degree of complexity.
Frequency–selective channels can be modelled by
using (n-path) tap delay line model [3]. This model
requires 2n coloured Gaussian processes. Therefore,
computer simulation models can be implemented by
means of Rice method [4], which depend on
approximation of the coloured Gaussian processes by
finite sum of weighted sinusoids with phases
uniformly distributed. Finding proper design method
for computing parameters of simulation models,
provides deterministic processes at the output of
channel simulator with a statistical properties closed to
those of the corresponding stochastic processes.
Especially statistics of fading time intervals known as
level-crossing problem [5]. Level-crossing rate (LCR)
and average duration of fades (ADF) are a statistical
properties of second order. Analytical expressions for
these quantities have been derived for Rayleigh [6],
Rice [7]. The Statistics of deterministic processes are
similar (identical) to those for the reference model if
the number of sinusoids is sufficient (infinite). There
are many methods to calculate the parameters of
simulation model (doppler coefficients and discrete
doppler frequencies), for example, the Method of
Equal Areas (MEA) [8], which provides a satisfied
approximation of the desired statistics for Jakes
Doppler power spectral density even for a small
number of sinusoids, but it fails or requires large
number of sinusoids for other types of Doppler power
spectral densities such as those with Gaussian shapes
[9]. The MEA does not result in a periodic
autocorrelation function (ACF) due to unequal
distances between discrete Doppler frequencies [10].
Method of exact Doppler spread (MEDS) is another
method used to compute parameters in such way the
Doppler spread is the same for both reference and
simulation models [11]. A new design method for
calculating parameters of simulation model is
presented. This method is named a combination of
MEA and MEDS. The performance of the three
methods is evaluated by comparing ACF of reference
and simulation models because ACF is related to LCR
and ADF quantities. The statistics of reference and
simulation models are evaluated over Rice channel
model. It is noticed by simulation results that new
method improved statistical properties performance of
simulation model more than other methods.
II. DESCRIPTION OF RICE REFERENCE MODEL
Rayleigh and Rice channels are the most important
channel models in mobile communications. They are
comparatively easy to describe, and they can be
implemented in software and hardware very
efficiently and with a high degree of precision [12].
Usually, Rayleigh and Rice processes are preferred for
modelling fast-term fading, whereas slow-term fading
is modelled by a lognormal process [12,13]. The Rice
International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 5- April 2016
ISSN: 2231-5381 http://www.ijettjournal.org Page 225
model is often applicable in an indoor environment,
whereas the Rayleigh model characterizes outdoor
settings. The Rice model also becomes more
applicable in smaller cells or in more open outdoor
environments [14]. A Rice process
()t
is obtained
by taking the absolute value of the nonzero-mean
complex Gaussian process
12
( ) ( ) ( ) ( )
pt t j t m t
, i.e. [12,13]:
( ) ( )tt
(1)
The zero-mean complex Gaussian random process
12
( ) ( ) ( )t t j t
represents scattered component
in the received signal with uncorrelated real and
imaginary parts, and variances
2
0
( ) 2 ( ) 2 , 1,2
i
Var t Var t i
.
In the following, the line-of-sight (LOS) component of
the received signal will be described by a complex
sinusoid of the form [12,13]:
(2 )
12
( ) ( ) ( ) j f t
m t m t jm t e
(2)
where
,
f
, and
denote the amplitude, the
Doppler frequency, and the phase of LOS component,
respectively. A typical shape for the Doppler power
spectral density (PSD) of the complex Gaussian
processes is given by the Jakes PSD [5,12,13]:
2
0max
2
max max
max
2,
1 ( )
()
0
ff
f
f
Sf f
ff
(3)
where
max
f
denotes the maximum Doppler frequency.
Taking the inverse Fourier transform of the Jakes PSD
results in the following ACF [12,13]:
2
0 0 max
( ) 2 2r J f
(4)
where
0.J
is the zeroth-order Bessel function of the
first kind. The probability density function (PDF) of
Rice process
()t
is given by [12,13]:
22
2
0
20
22
00
( ) ( ), 0
x
xx
P x e I x
(5)
where
0()I
designates the zeroth-order modified
Bessel function of the first kind. If the LOS
component does not exist, the Rice process
()t
results in the Rayleigh process
)(t
, whose statistical
signal variations are described by the Rayleigh
distribution [12,13]:
2
2
0
2
2
0
,0
()
0, 0
x
xex
Px
x
(6)
The cumulative distribution function (CDF) of
()t
defined by
( ) [ ( ) ]
r
F r p t r
can be
expressed by [15]:
00
( ) 1 ( , )
r
F r Q
(7)
where
(.,.)Q
is the Marcum function.
The LCR and ADF of Rice Processes
()t
belong to
the statistical properties of the second degree, are very
important in assessing the performance of channel
simulators, They will be denoted here by
()Nr
and
()Tr
, respectively. LCR is defined as the rate (in
crossings per second) at which the envelope
()t
crosses the pre-given level
r
in the positive (or
negative) going direction. LCR of Rice process can be
represented by [12,13]:
( ) ( )
2
N r p r
(8)
It is obvious from (8) that LCR of Rice process is
proportional to its PDF
()pr
by the constant
which is the reverse curve of ACF
(0), 1,2
ii
ri
. For the case of isotropic
scattering, where the ACF
()
ii
r
is given by (4),
the quantity
may be written as [12,13]:
2
0 max
2( )f
(9)
The ADF
()Tr
is the mean value for the length of all
time intervals over which the envelope
()t
remains
below a given level
r
. In general, the ADF is defined
by [12,13]:
()
() ()
Fr
Tr Nr
(10)
III. DETERMINISTIC RICE SIMULATION MODEL
An efficient simulator for the Rice fading channels
is obtained by using the concept of Rice’s sum of
sinusoids [4]. According to this principle, we replace
the zero-mean Gaussian processes
1()t
and
2()t
of
reference model by [12,13]:
, , ,
1
( ) cos(2 ) 1,2
i
N
i i n i n i n
n
t c f t i
(11)
where
i
N
denotes the number of sinusoids. Thus our
task is to simulate the above two processes in such a
way that the first and second order statistics of both
models (reference and simulation models) are as close
as possible (ideally identical). The parameters
,in
c
,
,in
f
, and
,in
are called Doppler coefficients,
Doppler frequencies and Doppler phases of simulation
model, respectively. By analogy with (1), the received
International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 5- April 2016
ISSN: 2231-5381 http://www.ijettjournal.org Page 226
envelope of Rice fading channel can be modeled
according to:
( ) ( )tt
(12)
In general, the ACF of
1()t
and
2()t
are given by
[12,13]:
2,,
1
( ) cos(2 ), 1,2
2
i
ii
Nin in
n
c
r t f t i
(13)
In the next section, we present a new computation
method for simulation model parameters. For reasons
of comparison, we also investigate the statistical
properties of simulation model for two other
parameter computation methods.
IV. COMPUTATION METHODS FOR SIMULATION
MODEL PARAMETERS
We present three different methods for the
determination of the Doppler coefficients
,in
c
and the
corresponding discrete Doppler frequencies
,in
f
. The
Doppler phases
,, (1,2,3)
in i
, are realizations of a
random variable uniformly distributed within the
interval
(0,2 ]
[12,13]. The procedures are MEA,
MEDS, and the new one is named by Combination of
MEDS and MEA. Here we will not present in detail
the simulation modeling employing sum of sinusoids.
But for the interested reader we refer to [12,13] for
detailed and well-presented analysis of the main
methods used in the sum of sinusoids simulation
scheme.
A. Method of Equal Areas (MEA)
The gains
,in
c
have been designed in terms of
fulfilling the power constraint
22
00
.The
frequencies
,in
f
can be found by partitioning the
Doppler power spectral density of
()
it
into
i
N
sections of equal power and using the upper frequency
limits, related to these areas. The gains
,in
c
and
frequencies
,in
f
are computed by [10,12,13]:
,0
2
in i
cN
(14a)
, max sin( )
2
in i
n
ff N
(14b)
respectively for
1,2,..., , 1,2
i
n N i
.
B. Method of Exact Doppler Spread (MEDS)
The MEDS is documented in [12,13]. For the
computation of the gains
,in
c
, the same is valid as it
was described for the previous method. The
frequencies
,in
f
are determined in such a way that the
Doppler spread of the simulation model is exactly
equal to the Doppler spread of the reference model for
any number of sinusoids
i
N
. The formulas for
,in
c
and
,in
f
by applying the MEDS are given by [12,13]:
,0
2
in i
cN
(15a)
, max 1
sin[ ( )]
22
in i
f f n
N
(15b)
respectively, for
1,2,..., , 1,2
i
n N i
.
C. Combination of MEDS and MEA
The new method relies on the application of both
methods MEDS, MEA, but we must apply the method
MEDS on the first half number of sinusoids
2
i
N
.
Therefore
,in
c
and
,in
f
are given as follows:
, 1 0 2
in i
cN
(16a)
, 1 max 1
sin[ ( )]
22
in i
f f n
N
(16b)
where
1,2,...., 2, 1,2
i
n N i
, then MEA method
is applied on the second half of sinusoids number:
, 2 0 2
in i
cN
(17a)
, 2 max 1
sin[ ( )]
22
in i
f f n
N
(17b)
where
( 2) 1,( 2) 2,..., , 1,2
i i i
n N N N i
.
Finally we get the formulas for
,in
c
and
,in
f
according to combination of MEDS and MEA by
, , 1 , 2
[ ; ]
i n i n i n
c c c
and
, , 1 , 2
[ ; ]
i n i n i n
f f f
respectively.
V. COMPARISON OF STATISTICAL PROPERTIES FOR
BOTH REFERENCE AND SIMULATION MODELS
This The statistical properties of reference model for
Rice fading channel are compared with the
corresponding simulation results by using equations
(7, 8,10). Assuming that simulation model parameters
have been found in one of the previously described
methods, In this case, the parameters are known
quantities and the ACF
()
ii
r
of simulation model
can be calculated for
1,2i
by means of (13),
whereas ACF
()
ii
r
of reference model is obtained
from (4). Both ACFs
()
ii
r
,
()
ii
r
are compared
with
12, 1,2
i
Ni
through Fig. 1, Fig. 2, and Fig.
3, where the computation of simulation model
parameters was based on MEDS, MEA, and
combination of MEDS and MEA, respectively.
International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 5- April 2016
ISSN: 2231-5381 http://www.ijettjournal.org Page 227
Fig. 4, Fig. 5, and Fig. 6 show comparisons of ACFs
with
25, 1,2
i
Ni
, we observe that
( ) ( )
i i i i
rr
if
[0,0,15]
[sec] for all
methods, but Fig. 3 and Fig. 6 show that the error has
become less between the reference and simulation
models, especially in the last three sinusoidal
harmonics of ACF in comparison with MEA and
MEDS. This means that ACFs of both reference and
simulation models are more closer according to the
new method than MEA and MEDS, and of course this
result will affects the statistical properties later when
LCR and ADF are evaluated. Throughout the
following section the number of sinusoids was
assumed
18N
and
29N
for the deterministic
Gaussian processes of the Rice (Rayleigh) fading
channel. The CDF of deterministic Rice (Rayleigh)
processes is shown in Fig. 7. It is noticed that the
simulation results in Fig. 4 are very close to the CDF
of reference model for all used methods over Rice
fading channel model. This is not surprising, because
the MEA and MEDS use the same procedure
concerning the gains
,in
c
, which is, as mentioned
above, i.e.,
22
00
. Another observation from Fig. 7
, it has been shown that the performance of a
combination of MEDS and MEA according to the
CDF for both reference and simulation models, is
better than MEDS, MEA. In Fig. 8, the normalized
LCR of deterministic Rice (Rayleigh) processes for all
introduced methods is shown, it can be observed that
the LCR of simulation model is very close to that of
reference model according to the combination of
MEDS and MEA. Finally, we present the
corresponding graphs for the ADF in Fig. 9. The
results documented in the figures (7-9) indicate a
superiority of the combination of MEDS and MEA
over the MEDS and MEA with respect to LCR and
ADF.
VI. CONCLUSION
The concept of Rice’s sum of sinusoids enables an
efficient design for Rice (Rayleigh) simulation
models. A study of statistical properties of such types
of simulation models was the topic of the present
paper. Especially for the CDF, LCR, and ADF. New
computation method of deterministic simulation
model parameters is presented, this method is a
combination of MEA and MEDS. We discussed and
evaluated the performance of different parameter
computation methods by comparing ACFs of both
reference and simulation models. It is observed that
ACFs of reference and simulation models are more
closer according to the new method than MEA and
MEDS. In addition, the new method gave us an
excellent results corresponding with CDF,LCR, and
ADF of deterministic simulation model, therefore, we
can say that the deterministic simulation model, based
on the combination of MEDS and MEA, will be very
close in its statistical properties to the reference
model. Finally, the improved performance of
statistical properties of deterministic simulation fading
channel models lead to get a high accuracy and
efficiency fading channel simulator.
Fig. 1 ACFs of reference and simulation models using
MEA
(Ni=12, fmax = 91 Hz,
2
01
)
Fig. 2 ACFs of reference and simulation models using
MEA
(Ni=25, fmax = 91 Hz,
2
01
)
Fig. 3 ACFs of reference and simulation models using
MEDS
(Ni=12, fmax = 91 Hz,
2
01
)
International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 5- April 2016
ISSN: 2231-5381 http://www.ijettjournal.org Page 228
Fig. 4 ACFs of reference and simulation models using
MEDS
(Ni=25, fmax = 91 Hz,
2
01
)
Fig. 5 ACFs of reference and simulation models using
MEDS+MEA
(Ni=12, fmax = 91 Hz,
2
01
)
Fig. 6 ACFs of reference and simulation models using
MEDS+MEA
(Ni=25, fmax = 91 Hz,
2
01
)
Fig. 7 Comparison of CDF for deterministic Rayleigh
(
0
) and
Rice (
3
) processes with (
2
1 2 0
8, 9, 1NN
)
Fig. 8 Comparison of LCR for deterministic Rayleigh
(
0
) and
Rice (
3
) processes with (
2
1 2 0
8, 9, 1NN
)
Fig. 9 Comparison of ADF for deterministic Rayleigh
(
0
) and
Rice (
3
) processes with (
2
1 2 0
8, 9, 1NN
)
ACKNOWLEDGMENT
I would like to express my sincere gratitude to my
Prof. Mohieldin Wainakh, who accepted graciously
supervision of this research.
International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 5- April 2016
ISSN: 2231-5381 http://www.ijettjournal.org Page 229
REFERENCES
[1] P.M. Shankar, Fading and Shadowing in Wireless Systems,
Springer, New York, Dordrecht Heidelberg London, 2012.
[2] J. F. Paris, ―Advances in the Statistical Characterization of
Fading: From 2005 to Present‖, International Journal of
Antennas and Propagation, 2014.
[3] J. D. Parsons, The Mobile Radio Propagation Channel.
Chichester, England: John Wiley & Sons, 2nd ed, 2001.
[4] S.O. Rice : ―Mathematical Analysis of Random Noise‖, Bell
Syd. Tech. J., vol. 23, pp. 282-332, July 1944 and vol. 24, pp.
46-156, Jan. 1945.
[5] A. Papoulis, Probabilities, Random Variables, and Stochastic
Processes, 3rd ed. New York: McGraw-Hill, 1991.
[6] W. C. Jakes (Ed.), Microwave Mobile Communications. New
York: IEEE Press, 1993.
[7] S. O. Rice, ―Distribution of the duration of fades in radio
transmission: Gaussian noise model‖, Bell Syst. Tech. J., vol.
37, pp. 581–635, May 1958.
[8] M. Pätzold, U. Killat, and F. Laue, ―A deterministic model
for a shadowed Rayleigh land mobile radio channel‖, in Proc.
5th IEEE Int. Symp. Personal, Indoor, and Mobile Radio
Communications (PIMRC’94), Hague, The Netherlands, Sept.
1994, pp. 1202–1210.
[9] M. Pätzold, U. Killat, F. Laue, and Y. Li, ―On the statistical
properties of deterministic simulation models for mobile
fading channels‖, IEEE Trans. Veh. Technol., vol. 47, no. 1,
pp. 254–269, Feb. 1998.
[10] M. Pätzold, U. Killat, and F. Laue, ―A deterministic digital
simulation model for Suzuki processes with application to a
shadowed Rayleigh land mobile radio channel‖, IEEE Trans.
Veh. Technol., vol. 45, no. 2, pp. 318–331, May 1996.
[11] M. Pätzold and F. Laue, ―Level-crossing rate and average
duration of fades of deterministic simulation models for Rice
fading channels‖, IEEE Trans. Veh. Technol., vol. 48, no. 4,
pp. 1121–1129, July 1999.
[12] M. Pätzold, MOBILE RADIO CHANNELS , John Wiley &
Sons, 2012.
[13] M. Pätzold, Mobile Fading Channels. Chichester: John
Wiley & Sons, 2002.
[14] S. Venkateswarlu, Sastry JKR, ―Justification of Rayleigh
Faded Channel for Data Transmission in Wireless
Environment‖, International Journal of Engineering Trends
and Technology (IJETT), vol.4, no. 4, pp. 166-168, Aug
2014.
[15] J. Proakis, Digital Communications, 2nd ed. New York:
McGraw-Hill, 1989.
