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| Apr 05, 2007 3:05 pm |
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re: re: How much can you put in a 5 pound bag? |
Ken Hilving
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The RF equivalent of WDM is FDM, and it has a long history.
A key difference between wireless and wired (copper or fiber) is that the signals are not constrained in wireless.
If we run out of capacity over a wired network, we can add or activate additional paths fairly easily. The new paths can use the same frequencies (waves) and modulation techniques, allowing us to double our capacity. This can be done time and again along a given physical path until we run out of physical room for new wires. We can then expand that room (new conduit) and press onward. This is a huge potential growth ceiling, especially when using fiber.
In wireless, we have to worry about interference. For a given frequency we can only use it once within a geographical footprint. That footprint is based on signal strength, and we have to be far enough beyond its range before using it again or we have interference.
Operating in free space, we also have to consider environmental factors. Certain frequencies are effectively blocked by certain materials such as plants and buildings. Just as you block visible light but x-rays pass through you, various materials block different frequencies of RF.
We also have a greater concern for interference from other RF noise. For example, solar flares can disrupt certain frequencies. http://news.yahoo.com/s/nm/20070404/sc_nm/space_gps_dc_1
In addition to these issues, we have the other uses in the radio spectrum. We have traditional radio and broadcast TV, GPS, satellite radio and TV, HDTV which demands more spectrum, two way radio communications, radar, RFID, and more.
While we have made significant improvements in our ability to transmit and receive within a narrow band, and this has increased the number of discrete signals available, we still face a ceiling within any given geographical area. That ceiling is based on signal strengths, footprint, and blockage.
So what's it all mean? There is a limit to how much can be transmitted using wireless within a given area. As we increase the amount of data per user, we decrease the number of possible users at a given time.
My first question is where is that limit and how close are we to reaching it as we move to 3G and a more balanced traffic flow from user generated content?
My next question is what solutions to expanding that limit are on the horizon?
For those of us who remember the early days of computers, watching Moore's Law approach its limit in silicone technology is incredible. Given the rate of innovation and commercialization of wireless, I wonder if I will see that maxed out as well. Private Reply to Ken Hilving (new win) |
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