A Quick Fix of My Wi-Fi Connection Issue – Bad Wireless Channel Condition

No comments    yoichi

December 25th, 2011 

I was in a hotel where there was no wired internet access, I had Emobile Internet access which was only internet access at that time but I wanted more than one devices to be connected at the same time. I setup Internet Connection Sharing with my MacBook Pro in order to share emobile connection to the other devices via Wi-Fi. The setup procedure was perfect however it didn’t work somehow – my Wi-Fi connection dropped out repeatedly. After my more-than-an-hour investigation, I finally found the root cause of the issue. It was wireless signal interference – Wi-Fi channel number overlap between me and my neighbors in the hotel.

This below is how I setup Internet connection sharing with my MacBook and How I resolved the issue.

Sharing Emobile Connection to Computers Using Wi-Fi

Assuming that your Macbook is connected to the Internet using a Emobile modem.

1. Open System Preferences > Click Sharing

2. Select Internet Sharing (However don’t turn on Internet Sharing Yet, otherwise you won’t be able to edit Wi-Fi Option)

3. Choose “Share your connection from” and “To computers using” like this:

• Share your connection from: Emobile Modem (ex. HUAWEIMobile-Modem)
• To computers using: Wi-Fi

4. Click Wi-Fi Options and configure an internet-sharing network. Here is my configurations:

• Network Name: mbp-shared-wifi
• Channel: 11 (default)
• Security: 128-bit WEP

5. Turn on Internet Sharing

That is all need to be done for internet sharing. You should be able to join the shared network “mbp-shared-wifi” if the channel( more specifically one of 11 802.11 channels) that you chose is not interfered by any sources of signals near the network.

Finding Out The Right Wi-Fi Channel

The purpose here is to find out the right channel for the internet sharing, the one which is least occupied.

Airport Command included in Mac OS X

airport is a built-in command line tool that enables you to manage 802.11 interfaces and to get all sort of information for 802.11 interface.

First, the tool is not located at one of paths which are included in $PATH, so let’s create a symlink to the tool like this:

A command line “airport -s” performs a wireless broadcast scan and gives you a list of Wi-Fi networks nearby. It reports information about SSID, BSSID, RSSI, channel, authentication, and so on.

Now you want to know which channel is used least from the output of “airport -s”. This command line below gives you numbers of how many of access points(SSIDS) use each channel.

From the result above, it would be good to choose channel 8, 3, or 10. I chose channel 3 this case. I setup the internet sharing again with the channel 3, and confirmed that I was able to to join the shared network “mbp-shared-wifi”.

Also pay attention to RSSI

You may want to pay attention to RSSI. According to wikipedia, RSSI is the relative received signal strength in a wireless environment, in arbitrary units. RSSI is an indication of the power level being received by the antenna. Therefore, the higher the RSSI number (or less negative in some devices), the stronger the signal.

Simply, the channel with lower value of RSSI is less likely to cause interference than the one with higher value of RSSI. It would be good to choose the channel with least value of RSSI for the internet sharing.

Web Based Tool – Wifi Stumbler

There is a local wifi scanning web service, called “Wifi Stumbler“. This service provides you the information to choose the best wireless channel to choose. A good thing about this is that this is free web serivce, you don’t need airport command or any kind of wifi scanning software to install on your computer. See the site for more detail. Here is the scanned output of my wifi environment by Wifi Stumbler.

http://tools.meraki.com/stumbler

REFERENCES

• http://en.wikipedia.org/wiki/IEEE_802.11
• http://www.microsoft.com/athome/setup/wirelesstips.aspx
• http://wlanbook.com/mac-os-x-wifi-wireless-scanner/
• http://en.wikipedia.org/wiki/Received_signal_strength_indication
• http://tools.meraki.com/stumbler
• http://lifehacker.com/5538927/wifi-stumbler-scans-local-wi+fi-to-find-an-interference+free-channel

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Posted in: Environment Setup, Random Topics

Tags: airport, mac, RSSI, wifi

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