The Ad-Hoc mode for wireless communication is not used frequently. But the demand for Wi-Fi communication is continuously increasing as use of Smart-phones and Laptops has enormously popular recent years. Through Ad-Hoc mode users can communicate point to point with mobility feature without using any central BSS. Wireless Ad-Hoc mode uses electromagnetic wave and so this technology has losses and limitations caused by free space propagation media as well as attenuation for interferences.

1. Experimental simulation and Real world Study on Wi-Fi Ad-
Hoc Mode for different radio propagation effects and standards
Mohammad Nazmul Hossain
Department of Computer Science, Bonn-Rhein-Sieg
University of Applied Sciences, Sankt Augustin, Germany
Email: nazmul@engineer.com
Towfique Imam Chowdhury
Department of Computer Science, Bonn-Rhein-Sieg
University of Applied Sciences, Sankt Augustin, Germany
Email: towfique.pbl@gamil.com
Abstract—The Ad-Hoc mode for wireless communication is not
used frequently. But the demand for Wi-Fi communication is
continuously increasing as use of Smart-phones and Laptops has
enormously popular recent years. Through Ad-Hoc mode users
can communicate point to point with mobility feature without
using any central BSS. Wireless Ad-Hoc mode uses
electromagnetic wave and so this technology has losses and
limitations caused by free space propagation media as well as
attenuation for interferences. We have performed the Ad-Hoc
communication study between two nodes, who have mobility, by
simulating on NS-3 platform and also in real world using two
laptops with Wi-Fi Ad-Hoc antenna installed. We have studied for
different 802.11 standards as well as in propagation models. We
have tried to find out the best propagation model and 802.11
standard for different situations according to the availability of
resources and evaluating their performance. The results and
findings are discussed and reported bellow. Off course we have
found considerable results for various situations.
Keywords—802.11, propagation, scattering, Wi-Fi channel
I. INTRODUCTION
Wi-Fi 802.11 has two modes of operation: infrastructure mode
and Ad-Hoc mode. Infrastructure network has an access point
(AP) including a service set identifier (SSID) through which all
the devices connect to the network and communicate with each
other. On the other hand Ad-Hoc devices connect with each
other directly by making an Independent Basic Service Set
(IBBS) also identified by a SSID and communicate each other
with point-to-point connection. The connection is called Ad-Hoc
because each node is willing to forward data to other node. This
technology helps to transfer data immediately one to one without
any need of 3rd party control.
The main advantages of a Wi-Fi Ad-Hoc communication are it
is self-configuring, self-healing connection, nodes are free to
move and ready to connect with devices “on the fly” - anywhere,
anytime [1]. The word Ad-Hoc is actually a Latin word means
'for this purpose'. Basically Ad-Hoc network is a temporary
network made for a purpose such as: transferring data between
two laptops, smart-phones or make a temporary mobile network
[2].
1) Hochschule Bonn-Rhein-Sieg
2) Technische Hochschule Köln
Ad-Hoc mode is very useful emergency services such as:
military network, communication during earthquake, weather
data collection from sensors as well as vehicle collision
avoidance, Internet sharing etc.
For an Ad-Hoc communication the license free frequencies and
channels are used defined by 802.11 protocols. These
frequencies are free to use by anyone which are 2.4GHz and
5GHz. The transmission power is limited and the modulations
are based on DSSS, FHSS, OFDM, MIMO-OFDM and OFDM
single carrier. The data speed and loss is depends on
transmission power, reflection, refraction, diffraction and
absorption by the surroundings, polarization of the antenna and
interference. As these frequencies are free to use so it is obvious
that a lot of others could use the same frequency and same
channel at the same time. So channel selection could be a factor
to avoid transmission losses.
Hence, in this paper we have studied data transfer between two
nodes varying the 802.11 protocols as well as for different
propagation loss models at different distances using NS-3
platform and also in real world.
To research and establish any technology in the real world pre-
implementation experiment and simulation is a good practice.
However simulations only shows the predictions and probable
results, but in testbed we will find the real results which have big
difference with simulations. Keeping in mind these issues we
have performed our experiments in the NS-3 platform and
conducted the same experiments in testbeds.
In section II we have described the software and hardware
part for the experiments. Section III describes some propagation
models we have used to simulate, followed by the information
of 802.11 protocols in section IV. Then we have shown our
experiment results and observations on section V.
II. METHODOLOGY
Following is described our working methodology. Part A
describes Simulation procedure. Part B describes practical
experiment procedure.
A. Simulation
For simulation we have used NS3 open source software which
is run inside a Linux based operating system named Ubuntu14.4.

2. This free software is licensed under Gnu GPLv2 license and is
publicly available for research and educational use [3]
This simulator has built in models of different kinds of models
for most of the real world network perspectives. So network and
communication engineers can develop their designs, test and
modify them by analyzing their designs in simulated
environment. It is true that this simulations do not presents the
actual scenarios but it will give the researchers a basic idea about
their implementations before execute them in the real world.
We have used four (4) different 802.11 standards (a, b, g, and n)
for our experimental simulation and tried some propagation loss
models. We have tried to change the transmission power and
observed the differences of throughput, packet loss, and jitter by
changing the distances between two (2) nodes. Not surprisingly,
we have found the variations which represents nearly to our
theoretical knowledge.
Off course this free software is still under development process
and has a lot of limitations. For example we are using NS3
version 3.25 and for 802.11n implementations it has some bugs
and developers are working on this. As it is an open source
software, anyone can join developer team and contribute to
improve this software.
The models and libraries are written based on C++ and Python
language and users can choose this two or any of this language.
We have choose C++ and wrote our own script using the built in
network models and libraries for our experiment.
1. We have setup 2-nodes and set the network as adhoc mode
using class ‘WifiMacHelper’ and placed the nodes at a
fixed distance in a 3d scenario using 'MobilityHelper'
class.
2. Then we have installed the network stacks using
'InternetStackHelper' class and set up the UDP
protocol by defining port no. as '9'.
3. Unidirectional (Constant Bit Rate) transmission between the
server and client in a saturated medium is maintained using
'OnOffHelper' class.
4. Transmitted and received packets as well as throughput is
calculated using 'FlowMonitorHelper' class.
5. Simulation has run for 15 seconds to get statistically relevant
results.
6. Simulation has done for different distances from minimum
to maximum according to the throughput received.
7. Parameters like channel models, transmission power, system
loss, propagation loss models are varied and observed.
B. Real world experiment
For real world experiment we have used two TP-Link
WR841ND wireless routers. These routers run the OpenWRT
operating system. We have configured these for adhoc mode
with 802.11n standard and 2.4GHz frequency band. There two
routers are connected to individual Laptops by Ethernet cables.
These two laptops runs on Ubuntu operating system. For data
stream we have used 'iperf' to generate udp data and send it to
the other laptop using the wireless router through the air
medium. Here one laptop was set as client and other was server
by iperf software.
Figure 1: Ad-Hoc node configuration for testbed
We have conducted our experiment at the 8th floor of the TH
Köln University of Deutz Campus in a 30 meters long corridor.
We have tried the data transmission within distance 5 meters up
to 30 meters between those two routers. Off course there was
clear line of sight and the firewalls of two laptops were turned
off. But we could not avoid the inferences created by other Wi-
Fi transmitters at the same frequency around us.
III. FACTORS CONSIDERED
As we are using here Wi-Fi media there are different effects
during propagation the carrier will encounter. Though there are
different types of propagation losses described by different
scientists, in real world every loss theory have effect on the data
transmission. For NS3 simulation each propagation loss theory
is classified so that one can understand and acquire knowledge
for each effects individually.
A. Propagation loss models
There are a different types of propagation loss models in NS3.
We have used these two types of models for our simulation.
1. FriisPropagationLossModel: Friis transmission equation is
used to determine the power received by antenna with G1, while
transmitted from another antenna with gain G2 at a distance with
certain frequency [4]. The equation is as follows:
𝑃𝑟 = (𝑃𝐿𝐹).
𝑃 𝑡 𝐺 𝑡 𝐺 𝑟 𝑐2
(4𝜋𝐷𝑓)2 (1)
Where, PLF = polarization loss factor
Pt = transmitted power
Pr = received power
Gt = transmitter gain
Gr = receiver gain
D = distance between two antenna
c = speed of light (299 792 458 m/s)

3. The polarization loss factor (PLF) implies that if the polarization
between two antennas are not matched, the loss will be
multiplied [4]
However the Friis propagation loss model in NS3 is suitable for
small range of distance.
2. TwoRayGroundPropagationLossModel
While FriisPropagationLossModel is used for small distance,
TwoRayGroundPropagationLossModel is used for long
distance calculations. Due to the oscillation caused by
constructive and destructive combination of the two rays this
model do not give good result for short distances [5]
The equation is as follows:
𝑃𝑟 = (𝑃𝐿𝐹).
𝑃 𝑡 𝐺 𝑡 𝐺 𝑟 𝐻 𝑡 𝐻 𝑟
𝐷4 𝐿
(2)
Here, Ht = height of the transmitter antenna
Hr = height of the receiver antenna.
3. JakesPropagationLossModel
This model is modeled based on multipath scattering effects. It
considers one transmitter and a receiver and calculated Doppler
Effect for scattering waves and their different oscillations. It is
mostly used for densely build Manhattan areas where scattering
reflection and refraction is a great factor.
B. Wi-Fi operating channels
The specifications for Media Access Control (MAC) and
physical layer (PHY) for wireless local area network (WLAN)
are defined by the Institute of Electrical and Electronics
Engineers (IEEE) LAN/LAN committee (IEE 802).
802.11
protocol
Frequen
cy GHz
Bandwidth
MHz
Data rate Mbps Modulation
a 5 20 6, 9, 12, 18, 24,
36, 48, 54
OFDM
b 2.4 22 1, 2, 5.5, 11 DSSS
g 2,4 20 6, 9, 12, 18, 24,
36, 48, 54
OFDM
n 2.4/5 20 400 ns GI : 7.2,
14.4, 21.7, 28.9,
43.3, 57.8, 65, 72.2
800 ns GI : 6.5, 13,
19.5, 26, 39, 52,
58.5, 65
MIMO-
OFDM
n 2.4/5 40 400 ns GI : 15, 30,
45, 60, 90, 120,
135, 150
800 ns GI : 13.5,
27, 40.5, 54, 81,
108, 121.5, 135
MIMO-
OFDM
a.
Collected from Wikipedia
Table 1: 802.11 Wi-Fi channel standards [6]
The first wireless network standard was 802.11 (in 1997) which
is followed by 802.11 a, b, g, n, ac, ad and more is coming in
future.
We have used 802.11 a, b, g and n for our NS3 simulation. The
standards shown in the table 1.
C. Traffic Load
Since the bandwidth of 802.11 is limited in theory and in
practice it is less. If two nodes communicate each other with full
load, then the channel will be fully utilized and network will be
busy. As a result congestion occurs which leads to packet loss,
jitter and can cause performance degradation of network. To
avoid this we have tried to keep the traffic to a tolerable value.
D. INTERFERENCES
Interference is the main factor of Throughput for wireless
communication. As the Wi-Fi channels we are using here are
free of license, it is obvious that there lot of other users will use
the same channel. As a result interference will occur. We have
tried the android software 'Wi-Fi Analyzer' to observe the
channel graph to find out the less used channel at the moment.
Remind that, we have configured our router to channel 5, but it
is changeable by logging in to the router.
IV. EXPERIMENT RESULTS AND OBSERVATIONS
In this section we are showing our experiment results and
describing our observations. In part A and B we are going to
discuss our result and observations we have found from the
simulation done on NS3. In part C and D we are going to discuss
our real world experiment findings.
A. Simulation results
a. Using FriisPropagationLoss model
Selecting the 'FriisPropagationLoss' model with CBR (constant
bit rate) data rate 53Mbps we have simulated for five different
802.11 standards (a, b, g, n_2.4Ghz, n_5GHz). The result we
have found is shown in the fig: 2. As we can see from the figure
the maximum throughput we have found 21 Mbps at distance 0
meter when the standard is 802.11n 5 GHz (5 GHz frequency).
But it started falling after 600 meters and after 2500 meters is
goes to 0 Mbps.
On the other hand for 2.4 GHz frequency (802.11n 2.4 GHz) we
can see (fig 2) at minimum distance it has throughput nearly 19
Mbps. But it does not falls as quick as we decrease distance
rather that it covers more distance up to 4000 meters. 802.11a
standard also operates on 5 GHz frequency but throughput
performance is lower than 802.11n 5 GHz. For 802.11g and
802.11b we have got 9.5 Mbps and 4.5 Mbps but the distance
they cover is same and also like 802.11n 2.4 GHz (4000 meters).

4. b. Using Jakes propagation Loss model
Selecting the 'FriisPropagationLoss' model with CBR (constant
bit rate) data rate 53Mbps we have simulated for five different
802.11 standards (a, b, g, n_2.4Ghz, n_5GHz). The result we
have found is shown in the fig: 3. we can see from the figure the
maximum throughput we have found is 43 Mbps for 802.11n at
5 GHz frequency. The throughput goes down to 5 Mbps at
distance 2500 meters. And after 5000 meters it goes to zero (0).
802.11a starts from 20 Mbps and goes to zero after 2500 meters.
802.11n at 2.4 GHz and 802.11g goes together from 9 Mbps and
goes to zero after 4000 meters. And 802.1b starts at 4.5 Mbps
and at 4000 meters it goes to zero throughput.
Figure 3: Throughput vs Distance for Jakes propagation loss
model
We have found Throughput for using TwoRayGround and Friis
propagation model nearly the same. That’s why we have not
discussed the result of TwoRayGroundPropagationLossModel.
B. Simulation observations
According to the Friis propagation model of equation (1) we
know that the effect of this model is depends on the transmitter
gain, receiver gain and distance between them. And the best
overall network performance we have found for 802.11n at 2.4
GHz frequency. Because using this propagation loss effect the
throughput of 802.11n_2.4 GHz is comparatively good and it
can also serve comparatively good range of distance see fig 2.
Friis propagation model gives good result for short distance
range [7]. So our observation is for short distance and for free
line of sight 802.11n at 2.4 GHz is better to use. If we want to
utilize the standard to get maximum throughput, then we can use
802.11n at 5GHz frequency. But then, the range will be a factor
because this standard goes noticeably down after 1500 meter (fig
2).
On the other, hand Jakes model is based on scattering
characteristics. Hence reflected, diffracted waves summons
additional throughput sometimes. As we can see from figure 3
the throughput for 802.11n at 5 GHz frequency is now
noticeably higher.
As Jakes propagation model is modeled based on densely built
Manhattan areas [8] , so we can say 802.11n at 5GHz frequency
is better for outdoor areas where scattering, reflection are the
main loss factors.
If we look at the jitter comparison graph fig 4 we can see using
802.11n at 5 MHz band for outdoor (Jakes model) causes very
low jitter. 802.11a standard is also good but 802.11n at 2.4 GHz
band has higher jitter. This jitter is calculated at 1000m node
distance.
On the other hand for indoor (Friis) 802.11b and 802.11n_5
looking better but 802.11n at 2.4 has comparatively medium
jitter. For both environment (indoor or outdoor) using 802.11n
at 5 GHz band cause relatively low jitter
Figure 4: Jitter comparison between Friis and Jakes
propagation loss model at 100m range
C. Real world results
For the real world experiment we have meausred data
throughput for 15 seconds. What we have found is really
impressive. In figure 5 we can see the throughput is decreasing
as the distance between the two nodes is increasing. It is clearly
shows the signal atenuation due to decrease of signal power
over time as it propagates through the medium. The mediam is
here free line of sight and with no obstacles. Rather that we have
faced with some other inferences because of other wireless
connections using 802.11n at 2.4GHz band. Fig 8 shows the
interferences in 2.4 GHz band at different channels.
Figure 2: Throughput vs Distance for Friis Propagation loss model

5. Figure 5: Throughput vs distance in different times
Figure 6 shows the throughputs for different distances between
the nodes in bar graph. We have taken 4 iterations for each
distance. We can see from here that we have got maximum of
around 5 Mbps throughput at 5 meters distance. At 30 meters of
distance we have found very low throughput. In figure 7 the pie
graph shows nothing at 30 meters distance. But in figure 6 we
can see very small amount of throughput for 30 meters of
distance.
At 20 meter distance throughput is slightly better than 15 m
distance which we do not expected. The possible cause for this
kind of situation can be interferences. We have already said that,
as we can see in figure 8, there are an amount of interferences
due to other wireless connections using the same 2.4 GHz band
we have used. So the effect of interferences at 15 meters is
greater than at 20 meters distance.
Figure 6: Throughput observations at different distances
Figure 7: Throughputs for different distances
We have also tried other channels within this 2.4 MHz band but
this channels 5 gave us the best result of throughput. We have
used an android software named ‘wifi analyzer’ to find out the
best channel in the 802.11n at 2.4 band. We have observed that
the best channel at that moment to get better network
performance was channel 5 (fig 8).
In figure 9 and figure 10 we have shown the throughput
comparison between channel 5 and channel 13. Figure 9 shows
throughput for 15 meters of node distance. Figure 10 shows
throughput at 30 meters of distance. The green bars are the
throughputs fin channel 5 and the red bars are the throughputs in
channel 13. The result is channel 5 is better than channel 13. This
is because the number of interference in channel 13 is more than
channel 5.
Figure 8: Channel users using ‘wifi analyzer’ android software
Figure 9: Throughput comparison between channel 5 and
channel 13 at 15 meters of distance
Figure 10: Throughput comparison between channel 5 and
channel 13 at 30 meters of distance

6. V. CONCLUDING REMARKS
In this paper we have presented our experimental findings and
observations for wireless communication between two Ad-Hoc
nodes. We have used simulations in NS3 and also testbed
experiment. We have considered two model effects (Friis and
Jakes) for simulation in NS3 using 802.11 a, b, g, n_2.4 and n_5
standards. We have tried for maximum data transmission with
maximum transmission power to observe the results at
maximum capacity. Our experiments shows that for free line of
sight and at indoor transmission 802.11n at 2.4 GHz band is
better. For outdoor transmission 802.11n at 5 GHz is better. In
real world experiment using 802.11n at 2.4 GHz band we could
not transmit more than 9 Mbps data. This should have been
more. The factor behind this is interference. Because of this
interference we have got even worse results at further distances.
We have discussed it at previous section using figure 8.
VI. REFERENCES
[1] Chai Keong Toh. Ad Hoc Mobile Wireless Networks. United States:
Prentice Hall Publishers, 2002.
[2] http://techterms.com/definition/adhocnetwork
[3] https://www.nsnam.org/overview/what-is-ns-3/
[4] http://www.antenna-theory.com/basics/friis.php
[5] https://www.nsnam.org/docs/models/html/propagation.html
[6] https://en.wikipedia.org/wiki/IEEE_802.11
[7]https://www.nsnam.org/doxygen/classns3_1_1_two_ray_ground_propagati
on_loss_model.html#details
[8] https://en.wikipedia.org/wiki/Rayleigh_fading