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Getting the most from OS X Wireless

Did you know that with OS X Snow Leopard or later, you can view more complete information about your wireless network simply by holding down your option key and clicking your wireless status?

What are all these additional numbers?

Good question. The answer is that those 'bar' status representations are just dumbed down numbers that don't mean a whole lot. Engineers and system designers use the term dBm as an actual measure of absolute power.

dBm (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. Compare dBW, which is referenced to one watt (1000 mW). In the more granular information about the signal strength. [wikipedia]

As of OS 10.6 Apple has made sure that you can obtain real information related to your signal strength. There is a whole lot of additional information that can be gleaned when you realize that your effective throughput is a measure of your signal strength in relation to noise in or adjacent to your channel.

OS X uses a BSD Unix like core operating system that has a wealth of information available for savvy users. But like many modern systems, it focuses on presenting as simple a display as possible.

Where is that information actually stored, the real answer lies in the Kernel / user space design model that exposes run time system information in text values. A sophisticated user can actually access more of this information through text, but there is more than enough data available for power users who know how to look.

One of the places you can go to find this information is in your system profiler. Note the example in my system profiler. There is more here than present even with the option click tip. This is really handy when you want to see if a neighbor's access point is causing you trouble, performing a site survey for a client that you want to provide meaningful data points with, or even if you are simply curious how things work.

The neighboring signal from MOTOROLA-0F2DC is in Channel 1. But just because MOTOROLA-0F2DC is operating in my channel does not necessarily mean that it will cause me grief.

Lets put this in some plain English terms so that the concept isn't so difficult too follow.

Imagine that you go to a working lunch in between some very important business meetings. During the course of the meal, your colleagues settle down into small groups of individuals politely talking amongst each other.  Everyone is 'broadcasting in your space" so to speak: Same language. Same locality. Same EM spectrum physics. But as long as most of them talk at a polite volume that does not make it difficult to maintain your own conversations, you are good to go.

Engineers call this ability to distinguish coherent information from noisy environments 'selectivity'.

Of course, we'll all experienced what happens when that 'noise floor' rises. One obvious example is the rude participant who always seems to need to over-talk everyone else.  You can solve the problems they create in a lot of ways. You can talk louder. You can also get closer to your peers.  Or you can consider more drastic solutions including either waiting for the disruption to pass or move to an entirely new venue.  Most of the time, you can find a solution through a little common sense.

But what about a nightclub-like environment where the noise floor is so extreme, that it has become saturated? In the worst cases, conversations cannot be effectively conducted by any means short of slobbering in your friends ear.

What is the end effect? No throughput.

Let me explain that concept in common sense terms as well. If you were to start reciting a really important list of things your friend needs to have organized for a trip the following day, you are likely facing some disappointment. They will not be able to make any sense of long, complex messages.

Conversely, if you shout "GUN" under the same conditions, that message will probably get through.

This is how it is with data communications.  Your system can almost always get small, urgent communications messages through. This confuses many novice users because that continued 'signal' makes it appear as though you are connected, you are wasting your time with larger attempts.

Back to MOTOROLA-0F2DC. It is indeed operating in my channel, but I saw that my signal strength is a very health -51 dBm, and substantially more than a full 20 dBm stronger than MOTOROLA-0F2DC's -79.

Truth told, it is some 28 dBm stronger. So why note 20? Because it is a reasonable target for signal separation that functions well with the selectivity built in to many commercial products.

ISP's often "double down" on their deliverable signal by operating their equipment in opposite signal polarities (horizontal vs vertical). These polarity changes also account for a 20 dBm or greater differential in received signal strength; allowing them to run two access points within the same channel, at the same strength, without causing self-inflicted interference.