Wireless Transmission Explained in Simple Terms

Wireless Transmission Explained

This article is an attempt to explain in simple terms the issues involved in understanding and applying a wireless solution for your application.

Speed: This really is a deceptive concept.  Everyone wants a faster network, but the speed of the transmission will always be the same.  Since the data travels on radio waves, the "speed" will always be the speed of light.  Let's use a road traveling metaphor to explain.  Imagine that any road you travel on will always have a 65 mph speed limit.  In our analogy, 65 mph would equal the speed of light.  In fact, it would be both the maximum and minimum you could travel on any road whether it were an eight lane superhighway or a two lane dirt road.

 

Bandwidth:  While bandwidth is usually equated with the "speed" of a connection (10mbs), this is not really an accurate term.  As explained above, the "speed" is not accurate in the first place; secondly, the amount of data transferred per second is related to the bandwidth but not the same thing.  Bandwidth is really a measure of the width of the band in your frequency.  The wider the band, the more room you have on your path to your destination.  Let's use the road analogy again:  A wide band could be imagined as an eight lane superhighway, and a narrow band could be visualized as two lane dirt road.  
Examples: 
C band has a downlink 3.7-4.2 GHz Generally used for satellite communications voice and data transmission, this provides 500MHz of Bandwidth
The unlicensed ISM band at 900MHz 902-928 has only  26MHz of bandwidth

Frequency: This is another important and often misunderstood term.  The tendency is to think that the higher the frequency means higher bandwidth and more "speed".  The frequency only measures the cycles per second, but we won't get into the science of it.  For our purposes, let's imagine that frequency represents the surface of a road.  The higher the frequency, the more slippery the road gets.  Higher frequencies are more likely to dissipate over longer distances than lower frequencies, they bounce rather than penetrate.  Hence, the higher the frequency, the wider the road (more bandwidth) needs to be to get to your destination.  Most frequencies are already taken or are very crowded.  While there may be many roads available to your destination, you are only allowed to travel on a few of them.  http://en.wikipedia.org/wiki/Frequency_range

 

Channel Width:  This is another factor that confounds many novices in wireless transmission.  Unfortunately, our road analogy won't be very helpful for this one.  Let's use the analogy of water flowing uphill through a pipe.  You'll need a certain amount of force/water pressure (signal strength) to get the water uphill.  The smaller the pipe (channel width), the further you will be able to send the water up the hill.  Of course, you won't be able to send as much water (data) at one time as you could with a bigger pipe (wider channel), but it will travel further.
 
Signal Strength:  This is defined as transmission (tx) power measured in decibels (db).  Let's consider the signal strength to be analogous to the amount of fuel and reliability of the vehicle on the road.  You'll need enough fuel to get where you're going, and your car better be in good condition to get to your destination.  You might encounter a lot of traffic (noise) and bad weather (interference) along the way.
 
Noise:  Certain unlicensed frequency bands such as the 2.4Ghz band provide ample bandwidth at a relatively low frequency, but they are in such heavy use that traveling a long distance on such a highway is problematic.  Think of it as a highly congested super highway.  The road is excellent, free, and wide.  Unfortunately, everyone wants to use it to get where they are going, so the traffic (noise) can be difficult. You'll need to judge whether that road will get you to your destination. 
 
Interference:  Microwave ovens, certain appliances, walls, buildings, and rain can contribute to interference.  The higher frequencies are more susceptible to physical interference such as weather, walls, and buildings.  Pretend that data can be represented by vehicles traveling on a road.   The speed limit on any possible road (wireless network) is the same  whether it is a cross country eight lane superhighway (high bandwidth) or a two lane dirt road (low bandwidth), the speed limit will always be 65 miles per hour (speed of light).   It seems that you will get there quicker on the eight lane superhighway, but if there is too much traffic, you might get there at all.
 
Throughput:  This can be measured in the amount of data that your system can successfully transmit.  The higher the available throughput, the better the system.  It is measured in bits per second such as 3Mbs on a DSL connection or 100Mbs for an Ethernet LAN.  It is up to the installer/designer of the wireless connection to evaluate all the variables listed above to achieve the highest possible throughput.

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