Mac 101: Fix and extend your WiFi network

Mac 101 is an ongoing series aimed at bringing attention to important technical issues facing Mac owners.  A wide variety of topics will be explored  in an effort to inform as well as help make your day-to-day Mac computing experience a better one.
Our lives are filling up with more and more devices as the post-PC era takes a firm hold, as all of our devices are connected to each other and to the internet, wirelessly.  The problem is, we are not all professional radio engineers or even amateur radio operators.  Most of us are not familiar with how various radio frequencies penetrate. The following will help anyone with a WiFi network understand where and why their devices are not connecting to the network.
Luckily it doesn’t have to be that complicated. Sometimes by simply moving an existing wireless router base station, or adding a second base station to extend your network, you will rectify the most common of dead spots in most home networks. Here are some tips to walk you through the process.

Not Connected

Diagnose the problem

To start, there are a few basic things to look for: signal strength and noise.  Apple(s AAPL) has included several utilities for checking both the signal strength and the noise associated with the WiFi network your Mac is connected to.  Perhaps the quickest and easiest way to check the signal strength on a Mac is to hold down the Option key and click on the Airport Wi-Fi icon on the menu bar.  What you are looking for is the received signal strength indicator, or RSSI.  Basically, the stronger the signal, the closer the number is to zero.  Think of this measurement as the measured loss of signal strength from transmission to reception.  So an RSSI of -40 is much better then an RSSI of -70 since you are losing less of the original signal.
Check Wi-Fi Signal
Provided you are on an Airport network using one of Apple’s Airport WiFi networking products, you can use Apple’s Airport Utility for Mac to collect this information for all of your devices.  After entering the Airport router’s base station password (not the wireless network password), you should see a list of all of your wireless clients.  These are represented either by the device’s host name or by the device’s Media Access Control address (MAC address).  Mouse over any of the clients to review their individual signal strengths.  Knowing the location of each of your network devices, you can begin to get a picture of whether or not the location of your router is optimal for where your network resides.  The further away you get from the router, the weaker the signal strength will likely be.
Wi-Fi Diagnostics
But signal strength is not everything.  You should also figure out what noise is present in your network.  To start, either take a MacBook to an oft-used location furthest away from your router, or use the Mac on your network that has the weakest WiFi signal. The idea is to start on the outer edge of your network and work your way in.  Located in the /System/Library/CoreServices/ folder of Mac OS X Lion is the Wi-Fi Diagnostics utility.  This utility will help you determine both the signal strength as well as the noise in a given location for the Mac you’re testing.  Hopefully, you will find that you have a stronger Signal value than Noise value — the value you see in the utility for Signal is closer to zero than the value for Noise.
Next, subtract the Noise value from the Signal value to get your signal-to-noise ratio (S/N).  With a RSSI value of -67, and a Noise value of -87, you would have an S/N of 20, which is good.  The higher the S/N, the better network performance you will likely experience.

Some simple remedies

Once you have collected all of the data, it’s time to see if there is a quick and easy solution to your networking problems.

Sample Data

Degrading signal, low noise throughout: You may find that your environment has very little noise and that the signal is simply degrading by the time it reaches all of your devices.  This could be due to long distances or obstructions like walls and ceilings.  The first thing to try is to reposition your Airport base station to a more centrally located position. This will remedy situations where your network is clearly unbalanced, meaning all of your devices on one side of your house have a very high S/N value, and all of the devices on the other end of your house have a very low S/N value.

Sample Data

Strong noise throughout, many networks: If you find that both your Signal strength and Noise remain strong across all your devices regardless of location, you’ll want to check and see if there are a lot of other WiFi networks in your area.  To see if this is a problem, look again at the information provided by holding down the Option key when you click on the Airport Wi-Fi icon on the menu bar.  Only this time take notice of the RSSI values and assigned channel of all the other WiFi networks on the list.  You are looking for any networks with strong RSSI values on the same assigned channel as your network.
In extreme situations, changing the assigned channel of your WiFi network, repositioning your base station or even extending your network by adding an additional base station won’t help much at all. You will have to work things out with your neighbors and perhaps come up with a more communal solution for everyone.

Sample Data

Strong noise in pockets, no networks: This is a situation where something other than a WiFi network is causing interference.  The best thing to do is to start unplugging and powering off each of your electronic devices, one at a time, then check to see if your network has improved.  A good way to go about this is in reverse: unplug all of your electronic devices and home appliances to see if things improve.  If they don’t, then the interference is coming from something outside your environment.  Start plugging them in again one by one until you find the electronic device that is causing the problem. When you find the device or appliance that is causing the problem, consider replacing it.

Extending the range of your network

There are two main ways to extend the range of a wireless network.  The first is using a hard-wired ethernet connection to add an additional WiFi access point, also referred to as a roaming network.  The second is by extending the WiFi network by adding a second wireless base station. In this situation, the second base station is also a wireless client of the primary base station.

Primary and Secondary Base Stations

In both setups, the configuration of the wireless network on each base station is basically the same.  The difference is that one will be the primary and will “create a wireless network,” where the other will be secondary and will “extend a wireless network.”  Using the Airport Utility, edit the configuration of your primary base station and ensure that its Wireless setting for Network Mode is set to “Create a wireless network.”  Then use the Airport Utility to edit the secondary base station and ensure that its Wireless setting for Network Mode is set to “Extend a wireless network.”  On both, you will want to set the Wireless Network Name, Wireless Security and Wireless Password to the same settings.
Extend Airport Wi-Fi Network
Keep in mind that this is not a fix-all remedy and could actually make things worse by adding what is known as co-channel interference.  This is when the radio signal of each of your WiFi base stations are interfering with each other.  To help remedy this situation, you will want to place each base station as far apart from each other as possible.  Also with each deployed WiFi access point, you could degrade the throughput, or connection speed, of the network. This would not show up as a loss in signal, but a loss in network speed.  Since positioning each WiFi base station as close together as possible seems counterproductive, consider extending your network by adding the second WiFi access point via ethernet.
In the end, your best bet is always to try to position a single base station in an optimal location, and if necessary, establish a secondary WiFi access point over ethernet at a location far enough away from the primary base station to avoid each network from interfering with one another.  Though keep in mind, even in the most extreme of circumstances (such as the meltdown at Apple’s WWDC Keynote in 2010), not even Apple was able to remedy all WiFi network issues.