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3.9
Wireless Network Deployment and Troubleshooting
Ubee Interactive
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DDW3612 Subscriber User Guide
July, 2010
3.9
Wireless Network Deployment and Troubleshooting
This section provides the following information which may be useful in understanding,
deploying, and troubleshooting wireless environments:
“Wireless Speeds and Performance” on
page 52
“Received Signal Strength” on
page 52
“Estimating Wireless Cable Modem to Wireless Client Distances” on
page 53
“Wireless Channel Selection” on
page 55
3.9.1
Wireless Speeds and Performance
This section provides various topics on managing wireless speeds and performance:
“Received Signal Strength” on
page 52
“Estimating Wireless Cable Modem to Wireless Client Distances” on
page 53
“Wireless Channel Selection” on
page 55
3.9.1.1
Received Signal Strength
Received signal strength (RSSI) is measured from connected wireless client devices
to the wireless cable modem. This value can significantly impact wireless
speeds/performance. It is determined by:
materials (e.g. open air, concrete, trees, etc.)
distance between wireless clients and the wireless cable modem
wireless capabilities of the client devices
To determine the received signal strength, refer to “Wireless - Access Control” on
page 44
and review the
RSSI
value. A signal strength of -30dBm to -67dBm is
considered optimal. Levels of -67dBm and lower (e.g. -70, -80, etc.) will have a
downward impact on wireless data throughput. See the following sections for more
information:
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3.9
Wireless Network Deployment and Troubleshooting
DDW3612 Subscriber User Guide
July, 2010
53
3.9.1.2
Estimating Wireless Cable Modem to Wireless Client Distances
This section provides some guidelines on how far a wireless cable modem can be
placed in varying environments from wireless client devices. These variances include
the capabilities of wireless clients and the types of material through which the wireless
signal must pass. When the wireless cable modem and wireless clients reach the
distance threshold between each other, network performance degrades.
1.
Connect a wireless client to the wireless cable modem. Refer to “Connect/Validate
Wireless Clients” on
page 10
if needed.
2.
Place the wireless client at around one meter (three feet) away from the wireless
cable modem.
3.
Obtain the
RSSI
value for the connected client. Refer to “Wireless - Access
Control” on
page 44
. This value will be used in the formula further below.
4.
Use the table below to determine what materials the wireless signal must travel
through in order to reach the desired wireless coverage distance.
5.
Using the attenuation value from the materials table above, enter it in the following
formula. Additional explanation is provided further below.
Attenuation Considerations at 2.4GHz
Material
Attenuation
Connector/Cable
3.5dB
Free Space
.24dB / foot
Interior Drywall
3dB to 4dB
Cubicle Wall
2dB to 5dB
Wood Door (Hollow/Solid)
3dB to 4dB
Brick, Concrete Wall (Note 1)
6dB to 18db
Glass Window (not tinted)
2dB to 3dB
Double Pane Coated Glass
13dB
Bullet Proof Glass
10dB
Steel / Fire Exit Door
13dB to 19dB
Human Body
3dB
Trees (Note 2)
.15dB / foot
Note 1
: Different types of
concrete materials are used in
different parts of the world and
the thickness and coating differ
depending on whether it is used
in floors or interior or exterior
walls.
Note 2
: The attenuation caused
by trees varies significantly
depending upon the shape and
thickness of the foliage.
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3.9
Wireless Network Deployment and Troubleshooting
Ubee Interactive
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DDW3612 Subscriber User Guide
July, 2010
Formula
:
(Transmit Power,
use -30dBm
)
(Receiver Sensitivity,
use RSSI value
)
=
Allowable Free Space Loss
Allowable Free Space Loss
÷
Materials Attenuation Value
=
Optimal Distance
in Feet Between the Cable Modem and a Wireless Client
Example
:
(-30dBm)
-
(-67dBm)
=
37dBm (allowable free space loss for a 54Mbps
connection)
37dBm
÷
.24db/foot (for open space)
=
154.16 feet
6.
Once you know the optimal feet distance between individual wireless clients and
the wireless cable modem, you can resolve and prevent some performance issues.
7.
To check the wireless signal strength and speed, use the following steps for a
Windows computer connected wirelessly to the wireless cable modem. If the
wireless computer is not connected, refer to “Connect/Validate Wireless Clients”
on
page 10
.
Double-click the Wireless networking icon in the system tray.
Review the speed and signal strength in the Status window.
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3.9
Wireless Network Deployment and Troubleshooting
DDW3612 Subscriber User Guide
July, 2010
55
3.9.1.3
Wireless Channel Selection
In some environments, it may be necessary to change the wireless channel on which
the wireless cable modem operates. This may especially be the case in computing
environments, test environments, and other environments where they may be several
wireless access points operating in the 2.4Ghz range.
In some cases, you may want to segment your wireless traffic where a group of
devices operates on one channel and another group operates on another channel,
and so on. This is done by configuring the channel on each wireless access point
individually (if you have multiples). If you only have control over one wireless device in
an environment where they may be several, you can change the wireless channel on
your device to one that is not heavily used.
Note:
To change the wireless broadcast channel, refer to “Wireless - Radio” on
page 39
.
The diagram below show the channels available for selection in the Americas. Each
available channel is 22Mhz wide. Since channels overlap, it is always best to choose
channels that have the least overlap (typically 1, 6, and 11 in the Americas, and 1, 5,
9, and 13 in Europe). Overlapping channels are one possible source for wireless
network performance issues.
Source: Wikipedia.org, and IEEE article IEEE 802.11n-2009
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Wireless Network Deployment and Troubleshooting
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