3.9

Wireless Network Deployment and Troubleshooting

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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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3.9.1.2

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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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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3.9.1.3

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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