Statistical performance analysis of wireless communication in public transports

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-
6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 2, March – April (2013), © IAEME
290
STATISTICAL PERFORMANCE ANALYSIS OF WIRELESS
COMMUNICATION IN PUBLIC TRANSPORTS & IMPROVING
PERFORMANCE THROUGH
INTEGRATED HETEROGENEOUS NETWORK
Arindam Banerjee1
, Prof. Siladitya Sen2
1
(Electronics & Communication Engineering Department, Heritage Institute of Technology,
Kolkata, West Bengal, India)
2
(Electronics & Communication Engineering Department, Heritage Institute of Technology,
Kolkata, West Bengal, India)
ABSTRACT
There are many mobile subscribers in metropolition areas travelling in local trains.
Subscribers face lot of problems to make a call while in motion. In metro (underground)
railways, sometime there is no network coverage & inside local trains the voice quality is not
clear along with network problems. This paper focusses on causes behind these problems.
This also analyzes the performance after implementing heterogeneous network in high speed
public transports.Using heterogeneous network, the problems of network coverage, network
conjunctions etc will reduced enrormously. In this case there is intelligent integrator network
so call establishment time will reduced and the End to End delay will reduce. Cunulatively
the QoS of Wireless network is increased. Therefore a performance comparision is also
carried out in this paper. Such networks not only improve the performance of voice & data
communication but also improves network security.
Keywords : End to End Delay, high speed, Integrated Heterogeneous Network, Mobile
Users, Voice Quality.
1. INTRODUCTION
In past decade the telecom industry has been revolutionized by advancing
technologies. Advancing in technology simultaneously improve network capacity & network
performance. There are several wireless systems are in practice, like cellular [1], Wi-Fi [2],
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291
and WiMAX [3,4] etc. Each system uses its own spectrum as prescribed by law of
international body to avoid interference & other technical problems. Also, these wireless
communication systems operate independently, because the mechanisms of these systems are
fundamentally different. Therefore there is a manual switching systems among them. But in
manual shift may cause call drops & interruption in communication. To avoid this
inconvenience, an integrated network [5, 6], within which these systems can interwork, has
been designed for next generation wireless communication system. In such an integrated
network, mobile users can have seamless, continuous communication via the best available
service providing system with optimum uses of radio resources. Although the amount of
available radio spectrum for a particular form of wireless communication is decreasing
because of the increasing diversity of wireless networks, the traffic demand for wireless
networks is increasing with the increasing variety of broadband applications [7,8]. In this
scenario quality of service in high speed public transports like bus trains are still below
average for mobile voice & data communication network. Call drops, jitter, delay are high for
existing network.
An integrated network is designed to solve the problem for trains & statistical analysis of
the system also present in this paper.
2. NETWORK INTEGRATION
In this proposed network architecture two types of internetworking exists. Wi-
Fi/WiMAX internetworking & WiMAX/GSM inter networking. A call will route Wi-Fi to
GSM network via WiMAX network in case of trains or directly in case of buses. Two types
of interworking architecture approaches exist. They are tight couple loose couple and [9] and
[10] architecture.
2.1.Tight couple scheme
This scheme integrates two networks at the radio access network- core network level,
making the two different access technologies to work in unity with a single core network.
Considering the GSM and mobile WiMAX networks, in tight couple mode, the data streams
of WiMAX must traverse the in Network Coupler and the core network of GSM. This means
that each of these networks will have to modify their interfaces, protocols, and services in
order to meet the interworking requirements. This mode reduces latency in handover and
ensures seamless handover [11, 12].
2.2.Loose couple scheme
The loose couple interworking scheme offers a shared or joint interface for information
exchanges between the two networks. WiMAX uses the AAA (Authentication,
Authorization, Accounting) server of UMTS network, and unlike the tight couple, data
streams do not traverse the UMTS core network. This mode guarantees WiMAX network
independence but has high latency during handover [11, 13]. This makes it unsuitable for
real-time services following researches of handover between WLAN and UMTS [13].

292
3. NETWORK MANAGEMENT
There are many steps involved in network management. Spectrum assignment is the
first step of it. As in public transport like train or bus numbers of passengers are variable then
requirement of radio resources is a time varying function. While we incorporate many
networks so maintaining proper throughput for overall network is one of the major criteria.
At a particular time system calculate instantaneous load i(t) or i in a sub-network(a network
dominate by a Wi-Fi access point). Let there are n number of sub-network (s) then total
instantaneous load of the system:
I(t)= ( )
1
n
s
i ts
=
∑ … (1).
Network conjunction occurred after a threshold value l for sub network & L for total
network. so after l’ (l’<l) & L’ (L’<L) system ask for extra channel so that network can work
properly when threshold value become la (la<l’) & La (La<L’) extra assigned channels will
return.
THROUGHPUTWi-Fi= ……….. (2)
n is number of Wi-Fi stations, Us is the used capacity of Wi-Fi system & Cs is the total
capacity of the Wi-Fi system. Combine throughput for WiFi & WiMAX system will be
THROUGHPUT WiFi/WiMAX= 1
1
( )
'
1'
( )
n
s
s
n
s
ss
s
I t u
C
U
I t u
c
u
=
=
 
 
 
 
 
× 
 
 
∑
∑
….. (3)
C’ & U’ are ideally total capacity & used capacity of a WiMAX system. But this through put
will degraded due to different kind of losses like velocity, different geographical scenario etc
& which will be denoted by DL. Therefore available throughput will be,
THROUGHPUT WiFi/WiMAX= 1
1
( )
'
1'
( )
n
s
s
n L
s
ss
s
I t u
C
D
U
I t u
c
u
=
=
 
 
 
  −
 
× 
 
 
∑
∑
……. (4)
( ) ( )L L L LD P V t E t= + + ….. (5)
1
1
( )
1
( )
n
s
s
n
s
ss
s
I t u
I t u
c
u
=
=
×
∑
∑

293
PL stands for propagation loss which is a constant & unavoidable factor which includes losses
due to Transmitters & Receivers designing. VL is velocity losses. EL is extra environmental
losses depends on different kind of fading, obstacles, propagation model. Both VL & EL are
time varying so DL can also represented as a time varying factor DL(t). In wireless
communication channels there are two types of fading effects those are
I. Large Scale Fading
II. Small Scale Fading
Large-scale fading which depends on distance, is the slow variation of the mean
signal power over time. Also this depends on the presence of obstacles in the signal path and
on the position of the mobile unit. The large-scale fading is assumed to be a slow process and
is commonly modeled as having lognormal statistics [14, 15].
Small-scale fading is also called Rayleigh or Rician fading because if a large number
of reflective paths is encountered the received signal envelope is described by a Rayleigh or a
Rician probability density function (PDF) [16]. The small-scale fading under consideration is
assumed to be a flat fading where there is no inter-symbol interference. It is also assumed that
the fading level remains approximately constant for (at least) one signaling interval. With this
model of fading channel the main difference with respect to an AWGN channel resides in the
fact that fading amplitudes are now Rayleigh or Rician distributed random variables, whose
values affect the signal amplitude (and, hence, the power) of the received signal. The fading
amplitudes can be modeled by a Rician or a Rayleigh distribution, depending on the presence
or absence of specular signal component. Fading is Rayleigh if the multiple reflective paths
are large in number and there is no dominant line-of-sight (LOS) propagation path. If there is
also a dominant LOS path, then the fading is Rician distributed The fading amplitude ri at the
ith
time instant can be represented as
( )2 2
r x yii i
β= + + ………… (6)
where β is the amplitude of the specular component and xi, yi are samples of zero-mean
stationary Gaussian random processes each with variance σ0
2
. The ratio of specular to defuse
energy defines the so-called Rician K-factor, which is given by
2
2
0
2
K
β
σ
= …………. (7)
The best- and worst-case Rician fading channels associated with K-factors of K = ∞ and K =
0 are the Gaussian and Rayleigh channels with strong LOS and no LOS path, respectively.
So, the Rayleigh fading channel can be considered as a special case of a Rician fading
channel with K = 0. The Rician PDF is given by [16]
( ) ( )
22 2
0 02 2
00
exp / 2Rice
r r
f r r I
β
β σ
σ σ
 
 = − +   
 
…. (8) 0r ≥

294
Where I0 is the zero-order modified Bessel function of the first kind. Now, if there is no
dominant propagation path, K = 0 and I0 = 1 yielding the worst-case Rayleigh PDF
( )
2
2 2
0 0
exp
2
Rayleigh
r r
f r
σ σ
− 
=   
……. ..(9) 0r ≥
The Rician Cumulative Distribution Function (CDF) takes the shape of [16]
( ) ( ) 2
0 0
1 exp I
m
Rice
m
m
r
C r
r
β β
γ
σ
∞
=
   
= − −       
∑ …… (10)
Where γ = (K + r2
/ 2σ0
2
). Clearly, this formula is more difficult to evaluate than the PDF of
(8) due to the summation of an infinite number of terms. However, in practical terms it is
sufficient to increase m to the value, where the last terms contribution becomes less than 0.1
percent. Having described the main fading statistics let us consider the effects of the Doppler
frequency shift. Doppler shift from the carrier frequency fc occurs when the distance between
the mobile receiver and the transmitter is changing. The magnitude of the Doppler frequency
shift fm is determined by
cvf
f
m C
= …… (11)
where ν is the mobile station velocity and c = 3⋅108 m/s is the speed of light. The Doppler
frequency fm is often called fading bandwidth or fading fate of the channel. The relationship
between Fm and the coherence time Tm of the channel (i.e., the time over which the
channel’s response to a sinusoid is essentially invariant) is given by [17]
0.5
Tm
f
m
≈ ……… (12)
The Doppler power spectral density S(f) of the mobile channel is often expressed as
( )
( )2
1
1 /
S f
f f fmmπ
=
−
……. (13)
The above equality holds for frequency shifts of f in the range ±fm about the carrier
frequency fc. Some important notes are in order here. First, the primary factor, which affects
the performance of digital communication systems in a mobile environment, is the small-
scale fading. So, we will consider Rayleigh and Rician fading channels from now on[18, 19].
There is also scattering effects but which can be neglected if the scattered wave power is
known.
There is also scattering effects which can be neglected if the scattered wave power is known.
Standered deviation of fading is given by

295
[ ]
2
1
1
( ) ( )
n
e i d i
i
M d M d
n
σ
=
= −∑
…….(14)
( )e iM d is the path loss value at a distance id & Md(di) is a veriable which is given by
0
10
( ) log
d
dd iM d k
 
 
 = − ……… (15)
3.1. Hand off Management
In this network both horizontal & vertical hand offs are to be managed. When the
mobile terminal switching between the networks with the same technology (WiMAX to
WiMax) this process called horizontal hand-off (HHO). When the mobile users switching in
different networks which have different technology (GSM to WiFi) the vertical hand-off
(VHO) occur. As the there is fixed path in railway so horizontal hand offs can be managed
pre calculated manner. But then also unpredictability of microwave radiation may create
problem in network coverage as shown in fig 1. Where pre-calculation predict a normal hand
off between A to C. But due to the radiation pattern, at hand-off point there is no network
coverage by C. Therefore mobile system itself find available network and register in it.
Figure 1: Schamatic Diagram of Radiation Pattern
So there must be an inbuilt network scanning algorithm in mobile system employing through
WiMAX.

296
3.1.1. Proposed Mixed Algorithm for Horizontal Hand offs
If T Ts≥ // actual time is greater than or equal to the schedule time for hand off
If RC< Rmin // Radiation coverage provided by C is less than min requirement
If N S
S S∈ // services required for mobile network is belongs to the service set
MS send the request to hand off
(CHECK THE BANDWIDTH AVAILABILITY/ NETWORK CAPACITY)
CASE 1:
11
' '
N n
n n b nn
mn
m b B A m b AvailableBandwidth+
==
+ + ≤∑∑
Accept in Network
CASE 2:
1
N
n n b
n
m b B A AvailableBandwidth
=
+ + ≤∑
Accept in Network
Else Reject the request
Else Continue Scanning
Else Hand off in C
Else Wait for time
3.1.2. Proposed Algorithm for Virtical Hand off
This network will follow a location and power based hand off algorithm between GSM & WiFi
network
CHECK THE LOCATION
IF PL =DLN // Subscriber location is near to Wi-Fi zone or max power form other WiFi
If Active Call=0!
Hand off: Start Hand Off sequencing
Else wait (either PL=DL or Active Call=0)
Goto Hand off;
End
3.2. Intelligent Searching of Receiver Number
Fig 2: Schematic Diagram of Network

297
In every compartment of a train there will be two three access points which will be
connected with a Wi-Fi service providing network. There will be one such network in each coach
those are connected with WiFi/WiMAX integrator or the main service provider in train. This
integrator also maintain connection with WiMAX Base Stations. In this scenario a MS wants to
make a call. There are three probabilities-
I. Both the user are in same compartment
II. Both the users are in same train
III. Both the users are in different locations
Traditional systems use same mechanism to find called party it may consume unnecessary
few seconds for first two cases. For a compartment there maximum capacity of passengers will be
100~120 or 150. Let assume there are 12 coaches. Maximum number of load will be 1200~1440
or 1500 users. Therefore in network there will be two extra VLR. One with WiFi network
provider in compartment other with the network integrator. This are special type VLR where the
other information like call rate, plans, other call management issues etc can be stored. In
compartment the memory stack is divided with respect to the number of access points. The
memory of VLR with integrator is divided with respect to the number of coaches. Therefore in
intelligent searching mechanism while a call request is forwarding then the call request before
proceeding to regular MSC it activated two pointers for two VLR simultaniously. A parallel
searching mechanism is carried out in memories. But in integrator VLR searching will be omitted
for the memory from which the call is forwarded. If any one among two pointer is successful to
trace the user the call will established. As there is processors in GHz frequency so searching 150
or (150x11) stack take much less time than traditional system. Which will decreases end to end
delay & increase throughput.
4. PERFORMANCE ANALYSIS
In traditional wireless network the jitter will vary due to surrounding cercumstances,
velocity of train, wind, number of subscribers, geographical conditions etc. So the Jitter is quite
high for traditional network in fig 3 represented in red line. Same thing occur in the case of
throughput. Throughput is fluctuating for traditional network. For the integrated network
approximation of 0.12% is taken and the throughput remain constant. In integrated network the
throughput is constantly high because it use Wi-Fi throughput which is high. Flat & low jitter,
with low end to end delay helps to achieve this performance.
Figure 3: Jitter Comparision Figure 4: Average Throughput Comparision

298
Figure 5: Reduction Of Average End To End Delay
In case of end to end delay 100 calls taking randomly in same train for 1500 users it shows
better reduced performance. This reduction directly impact on throughput.
5. CONCLUSION
Using heterogeneous network is the best solution for handling the increasing load of
subscribers. This proposed network shows better performance in terms of low & flat jitter,
high & constant throughput, low end to end delay. Therefore the quality of service is also
increased. Such network can be applied for security like explosive detection, & other security
measure by just adding distributed sensor array with this network. This is conclude that this
heterogeneous network can able to solve the voice clearity problem for the subscribers
travelling in train. For Indian scenario this is very important as many people travelling trains
in Mumbai, Kolkata, etc metropolition cities.
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