Project to study the benefits of channel bonding in 802.11n.Examined the effect of distance, RSSI, channel used and interference on both 20MHz and 40MHz channels.

1. 1
Evaluating the Effect of Channel Bonding on
Throughput in 802.11n
Prabhat Kuchibhotla
School of Information Sciences
University of Pittsburgh
PRK44@pitt.edu
Vaideesh Ravi Shankar
School of Information Sciences
University of Pittsburgh
VAR29@pitt.edu
Abstract—The IEEE 802.11 is a set of Media Access Control
(MAC) and Physical Layer specifications for the Wireless Local
Area Network (WLAN) communication at various frequency
bands. The 802.11 a/b/g standards used channels of 20MHz
spacing. These operated with the Single Input Single Output
(SISO) antenna technology. The next IEEE standard 802.11n
operated with a Multiple Input Multiple Output (MIMO) smart
antenna technology and introduced a new channel bonding
scheme where it bonds or combines two adjacent 20MHz-width
channels into a single 40MHz-width channel. The idea behind
doing this is to double the bandwidth available to the clients.
iPerf3 throughput measurement tool was used to measure the
maximum throughput that could be achieved in the WLAN. An
improvement in the throughput was observed when channel
bonding was enabled in the WLAN. The plots for the Distance vs
Bandwidth were plotted and shown in the results section. The
experiment was conducted with two different access points for a
broader observation scope.
Keywords—Throughput, Channel Bonding, Interference,
WLAN
I. INTRODUCTION
The IEEE 802.11 is a set of MAC and Physical Layer
specifications for the WLAN communication at various
frequency bands. The 802.11a uses the Orthogonal Frequency
Division Multiplexing (OFDM) based air interface at the
physical layer and operates at the 5GHz band which is a
relatively unused frequency band when compared to the
2.4GHz band. But in 802.11a, the signals had much smaller
wavelengths and thus had a tendency to get absorbed by the
solid objects which resulted in reduced throughput. The next
standards that came in, 802.11b/g, operated at the 2.4GHz
band. This frequency band is open for the public to use in their
Personal Area Networks (PAN). Even though there was some
interference due to the traffic from other devices operating at
the 2.4GHz band, the signals here had much greater
wavelengths which increased the overall throughput.
The IEEE 802.11n standard provided the opportunity for
achieving higher bandwidths by incorporating channel
bonding. 802.11n uses MIMO smart antenna technology
instead of SISO which was used in the earlier 802.11 standards
[1]. In channel bonding, two adjacent 20MHz-wide channels
could be combined into a single 40MHz-wide channel. It is
pretty obvious that the usage of a single 40MHz channel should
be more advantageous than usage of a 20MHz channel.
However, channel bonding by itself doesn’t provide all
advantages but the antenna technology that is used plays a
major role. Since 802.11n uses MIMO smart antenna
technology, all problems faced in using SISO are now
mitigated [2].
Channel bonding comes with a few drawbacks as well. In
channel bonding, the bandwidth used is doubled from the
normal case, resulting in wider bandwidths. When the channel
width is increased, the SNR is reduced by almost 3dB which
increases the effective Bit Error Rate (BER) [3]. When a
40MHz channel is used, to achieve the same SNR, the
transmission power needs to be increased and in turn, to
maintain the same BER, a higher SNR needs to be achieved.
But since the 802.11n devices have fixed maximum
transmission power, it cannot be increased further and thus the
SNR decreases which increases the BER. To improve the
performance, a tradeoff has to be made between higher
transmission rates and susceptibility to interference.
When channel bonding is enabled, the performance also
depends on the environment of the WLAN. That is, the
performance of using 40MHz channels depends on the number
of wireless networks in the same range. If there are other
WLANs using 20MHz channels in the same range, the
interference faced by one 40MHz channel (channel bonding) is
more than that faced by one 20MHz channel (without channel
bonding). Thus, channel bonding gives best performance when
used in the environment where there are zero or few interfering
WLANs. Also, channel bonding shows negative effects on
throughput when the signal strength is low. When the received
signal strength at the 802.11n enabled device is low, the
throughput attained without channel bonding is actually better
than that attained with channel bonding [4].
II. PROJECT OBJECTIVES
1. Setup a WLAN with an 802.11n access point and two
802.11n enabled clients.
2. Configure the channel bandwidth used by the AP and
client to 20MHz initially.
3. Measure the throughput obtained in the first case with
20MHz channel spacing using iPerf3 throughput
measurement tool.

2. 2
4. Configure the channel bandwidth used by the AP and the
client to 40MHz.
5. Measure the throughput obtained in this case with
40MHz channel spacing using the iPerf3 throughput
measurement tool.
6. Analyze the throughput change in both cases and the
effect of channel bonding and the received signal strength
on the throughput.
III. TEST ENVIRONMENT
The testbed consists of an ASUS RT-N12 and TP-LINK
Wireless-N router which are 802.11b/g/n certified and act as
Access Points (AP) and Dell Inspiron 15 3537 and Lenovo
Yoga 3 laptops act as clients. The router initially is connected
to the internet via a modem and the clients are connected to the
router in the 2.4GHz band. Initially, the default channel
spacing for the router operating in the 2.4GHz band is set to
20MHz in the router configuration page. Once this is done, the
wireless properties of the clients (laptops) must be changed
accordingly. By default, these clients operate on 20MHz
channels. To enable channel bonding, the channel spacing used
in by the AP must be changed to 40MHz and on the clients’
side, the 20MHz/40MHz channel spacing co-existence must be
enabled to allow the client to accept the 40MHz channel. If this
is not done, the client will not be able to receive data from the
AP at the same rate at which they are being sent.
To understand the characteristics of channel bonding, we
take measurements over varying parameters (distance, channel
number and channel bandwidth). The change in Received
signal strength indicator (RSSI) and the throughput are
measured for varying distance, channel used and channel
bandwidth. The distance is varied from the distance where the
client receives maximum RSSI to the distance where the client
receives minimum RSSI. Using the 20 MHz channel on the
2.4GHz band provides the user with 11 channels of which only
channels 1, 6 and 11 are non-overlapping. Using any other
channel reduces the throughput due to interference of the
overlapping channels. The 40 MHz channel provides the user
with 1 non overlapping channel in the 2.4GHz band. The
channel bandwidth is varied between a 20MHz channel and a
40MHz channel.
Node Configuration
The testbed consists of a router (ASUS RT-N12 and TP-
LINK), two clients and a server. All the laptops are equipped
with 802.11n wireless adapters which are Broadcom 802.11ac
BCM4352 and Dell Wireless 1705 802.11b/g/n respectively.
The testbed is setup in a home environment with multiple
rooms. Closed doors and other wireless systems in the 2.4GHz
range are used to take measurements with effect of
interference. iPerf3 is a throughput measurement tool and
WirelessMon (version 4.0) software is used to take RSSI
measurements. WirelessMon is a software tool that allows
users to monitor the status of wireless WiFi adapter(s) and
gather information about nearby wireless access points and hot
spots in real time.
The distance of the server and client pair from the router
are varied to plot the effect of distance and RSSI on throughput
with and without channel bonding.
Measurement Environment
Once the testbed is setup, for measuring the throughput in
the WLAN in the first case where 20MHz channels are used,
the iPerf3 tool is used. The iPerf3 tool is used to send data
packets from one device to another when both devices are
connected to the same Access Point (AP). iPerf3 is used
through the Command Prompt on Windows Operating System
(OS) and the Terminal on Linux OS. This needs one device to
act as the server and the other as a client. Therefore, from the
server device’s command prompt, ‘iperf3 –s’ command is
given which enables this device’s port to listen. The default
port used is 5201 at the server’s side. Once this is done, the
client device can now request data from the server by ‘iperf3 –c
*IP address of server device*’ command. The iPerf3 sends data
packets in intervals of 1 second and returns the throughput
attained for each interval and also the average overall
throughput attained in the WLAN. Once all measurements are
taken for the first case, the channel bandwidth used in changed
from 20MHz to 40MHz at the router configuration page to
enable channel bonding and the iPerf3 throughput
measurement process is repeated for this case.
Parameters affecting the Throughput
Throughput can be defined as the rate at which the
destination host receives the data sent from the source
measured in bits/time unit (usually bits/sec). Instantaneous
throughput is the rate at a given point in time and average
throughput is rate averaged over a larger time period. In this
experiment we take measurements to study changes in
throughput for varying parameters.
Factors that affect the throughput are
1. Distance of the client and server from the router. Increase
in distance decreases RSSI. However, the decrease in
RSSI with distance varies for both 20 MHz and 40 MHz
channels.
2. Channel number used by the client and server affects the
throughput. Non-overlapping channels provide a better
throughput for both 20 MHz and 40 MHz channels. Non-
overlapping channels are different for both 20 MHz and
40 MHz channels.
3. High RSSI provides better throughput. RSSI decreases
with increase in distance. However, there are cases where
a lesser distance from the router exhibits an inferior RSSI
than a comparatively larger distance. This happens
because of obstructions and their properties such as
reflection, refraction and diffraction.
4. Throughput measured at the server and the clients also
changes because of the channel bandwidth used by the
server and clients. 20 MHz and 40MHz channels provide
different throughputs. Distance of the server and client
pair from the router effect the throughput of the channels
to a great extent.

3. 3
IV. RESULTS
Effect of distance and RSSI on Throughput
First, the client and server pair are connected the ASUS
RT-N12 router and is kept at a distance from the AP where the
RSSI is maximum. The channel bandwidth of the router is set
at 20MHz channel bandwidth. The settings of the wireless
network adapter of the client and server systems are set to work
on the 20GHz channel. Throughput and RSSI measurements
are taken for varying distance of the client and server from the
router. With increase in distance the throughput decreases. The
measurements are shown as follows. In this experiment
distances are varied from 1 meter to 8 meters from the router.
The readings and graph below are measured using an ASUS
RT-N12 router.
Fig. 1: Throughput Measurement – 20MHz (distance 1m)
Figure 1 shows the screenshot of the command prompt
window on the client’s side. Here, iPerf3 sends 10 data packets
of an average packet size of 2.5 Mbytes over 10 time intervals
of 1 second each. iPerf3 measures and returns the throughput
attained in each time interval and the average throughput
attained in Mbits/sec. It can be seen that the throughput
attained at this distance is 22Mbits/sec.
Fig. 2: Throughput Measurement – 20MHz (distance 8m)
Figure 2 shows the screenshot of the command prompt
window on the server’s side. In this case, measurements are
taken when the client-server pair is kept at a distance of almost
8m from the AP. It can be seen that the throughput attained at
this distance is 11.6Mbits/sec.
RSSI and throughput measurements are taken for varying
distance of the client-server pair from the AP. The plots and
values are shown in figure 3.
Fig. 3: Effect of distance and RSSI on Throughput (20MHz)
From figure 3, it can be seen that the throughput and RSSI
decrease with increase in distance between the router and
client-server pair. However, there are cases where a client-
server pair at a lesser distance from the router as compared to a
greater distance, has a low RSSI. The throughput measured at a
distance of 3m from the AP has a greater throughput than that
measured at a distance of 2m from the same as can be seen in
the figure 3. The throughput attained at distance of 2m and 3m
from the AP are 20.1Mbits/sec and 21Mbits/sec respectively.
This occurs due to obstructions and their properties such as
reflection, refraction and diffraction.
Once all measurements are taken for the case of 20MHz
channel bandwidth, the channel bandwidth is changed to
40MHz in the router configuration page and the same process
is repeated. Figure 4 shows the plot for effect of distance and
RSSI on throughput for 40MHz channel bandwidth case.
Fig. 4: Effect of distance and RSSI on Throughput (40MHz)
From figure 4, it can be seen that the throughput attained
when channel bonding is enabled is much higher than in the
normal case when a 20MHz channel is used. Slight deviations
in RSSI and Throughput attained are seen at a distance of 4m
which can be accounted for reflection, refraction and
diffraction properties.
The entire process is now repeated with the TP-LINK
router. The channel bandwidth used is first kept at 20MHz for

4. 4
the first case to take measurements for RSSI and throughput
attained with varying distance. The plots and corresponding
values are shown in figure 5.
Fig. 5: Effect of distance and RSSI on Throughput (20MHz)
Figure 5 shows the effect of distance and RSSI on the
throughput without channel bonding using the TP-LINK router.
It can be seen that the performance is very similar to that as
seen in ASUS RT-N12 router but not as good as the latter.
The channel bandwidth is changed to 40MHz in the router
configuration page to take measurements of throughput and
RSSI with varying distance and to analyze the effect of channel
bonding on the throughput. The plots and corresponding values
are shown in figure 6.
Fig. 6: Effect of distance and RSSI on Throughput (40MHz)
Figure 6 shows the effect of distance and RSSI on the
throughput attained with channel bonding. It can be seen that
higher throughput is attained with channel bonding. Next, the
effect of channel used on the throughput is looked at.
Effect of Channel used on the Throughput
In the 802.11 a/b/g/n standards, the 2.4GHz band provides
the user with 11 channels of 20MHz bandwidth each where 3
non-overlapping channels exist as shown in figure 7. These are
channels 1, 6 and 11. As can be seen in figure 7, the channels
other than 1, 6 and 11 overlap with the adjacent channels and
thus experience interference. Interference from adjacent
channels reduces the throughput in the rest of the channels.
Fig. 7: Representation of non-overlapping Channels [9]
The throughput measurements were taken for different 20
MHz channels operating in the 2.4GHz band and are shown in
figure 8.
Fig. 8: Effect of Channel used on Throughput (20MHz)
When channel bonding is enabled, since two adjacent
20MHz channels are combined into a single 40MHz channel,
there exists two overlapping channels with least interference as
in shown in figure 9. Either channel 4 or channel 9 is used by
default.
Fig. 9: Representation of 40MHz channels [10]
Fig. 10: Effect of Channel used on Throughput (40MHz)

5. 5
The throughput measurement were taken for different 40
MHz channels operating in the 2.4GHz band and are shown in
figure 10. Maximum throughput is observed when channel 9 is
used which combines channels 6 and 11. Next, the effect of
interference on the throughput with and without channel
bonding.
Effect of interference on Throughput in 20MHz and 40 MHz
channel bandwidth cases
Signals having a high frequency have small wavelength and
thus have a tendency to get absorbed by the solid objects which
results in reduced throughput. 40 MHz channels have a lower
transmission range due to this reason. 40 MHz channels
provide higher throughputs than the 20 MHz channels when
the distance between the server-client pair from the router is
less. As the distance increases, the rate at which the throughput
degrades for the 40 MHz channel is greater than that at which it
degrades for the 20 MHz channel. The throughput measured at
the farthest distance between client-server pair and the AP in
both cases of 20MHz and 40MHz channel bandwidth is
compared and plotted as shown in figure 11.
Fig. 11: Throughput at farthest Distance for 20MHz & 40MHz
From figure 11, it can be seen that the when the distance
between the client-server pair and the AP is large, the RSSI
drops and thus the throughput reduces. The rate at which it
reduces when 40MHz channels are used is much greater than
that at which it reduces when 20MHz channels are used. Thus,
at the same very low RSSI, the throughput attained when
20MHz channel is used is much better than that when a 40MHz
channel is used.
V. CONCLUSION
From this project, it was seen that there was a significant
improvement in the throughput performance when channel
bonding was enabled but this was limited to certain conditions.
Channel bonding improved the throughput performance only
when there are zero or very few interfering WLANs and other
devices operating in the same frequency band in the same
environment. Also at larger distances from the AP, throughput
attained with channel bonding was observed to be lower than
that obtained without channel bonding. Therefore, maximum
throughput can be attained with intelligent channel bonding
where the router switches from using 40MHz to 20MHz if
there is large interference.
VI. REFERENCES
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doi:10.1109/TMC.2013.73
[2] R. Chandra, R. Mahajan, T. Moscibroda, R. Raghavendra
and P. Bahl, “A case for adapting channel width in
wireless networks,” in Proc. ACM SigComm, Seattle,
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[3] M. Y. Arslan et al., “Auto-configuration of 802.11n
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[4] K. Pelechrinis, T. Salonidis, H. Lundgren, and N. Vaidya
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[5] “IEEE 802.11n-2009 Amendment 5: Enhancements for
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[9] https://programmingsoul.wordpress.com/tag/technology/
[10]http://www.computerforum.com/threads/wireless-mode-
broadcasting-error.234009