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-   -   Spectrum Crunch (http://www.risingsun4x4club.org/forum2/showthread.php?t=17356)

subzali 02-21-2012 11:03 AM

Spectrum Crunch
 
Just saw this today:

http://money.cnn.com/2012/02/21/tech...ectrum_crunch/

http://money.cnn.com/2010/03/16/tech...dex.htm?iid=EL

DaveInDenver 02-21-2012 12:03 PM

These types of articles are misleading since they interchange spectrum for capacity, which is not correct. I think the carriers allow this intentionally because of the way our FCC allocates spectrum and gives exclusive use to favored bidders. They all jockey to get 'ownership', which gives them control of who uses it and ultimately leads to non-uniform utilization. This phenomenon is called spectrum warehousing, where some companies 'buy' spectrum just to sit on it as its value increases. The reality is that we are nowhere near capacity for the spectrum we have, although we are subject to some unbreakable physical laws (e.g. Shannon-Harley et. al.). This is one shift in perspective that will happen, that EM spectrum is treated like property instead of a fungible good like air or light.

Mendocino 02-21-2012 12:23 PM

There is a lot of spectrum available, its just not in "popular" places. Check out "TV Whites Spaces" (TVWS) and dynamic spectrum access.

DaveInDenver 02-21-2012 01:28 PM

Quote:

Originally Posted by Mendocino (Post 204792)
There is a lot of spectrum available, its just not in "popular" places. Check out "TV Whites Spaces" (TVWS) and dynamic spectrum access.

Not to mention that spectral efficiency will increase, just like it has for roughly the past century of RF communications. You've heard of Moore's Law on the doubling of computing power, there is an analog called Cooper's Law. He ran Motorola's mobile phone division for years. Anyway, he observed that spectral efficiency doubled every 30 months, IOW a given spectrum's capacity to carry information concurrently. This has held true since 1895 until today. So in Marconi's day it took MHz of spectrum to carry a single conversation where now billions of simultaneous conversations can occur in the same spectrum.

http://www.arraycomm.com/wp-content/...CoopersLaw.png

So when a cell phone carrier declares that they'll need 10 times the 'spectrum' in 15 years, they mean they'll need 10 times the capacity in 15 years. Then figure that in 15 years technology will allow existing spectrum to carry around 50 times (6 periods of doubling is 64 times the capacity) the information it does now. In Cooper's day they could never have imagined 64QAM and OFDMA that allows ~108Mbps in 1.4MHz of spectrum. Back when AMPS and PCS phones were leading edge 1.4MHz of spectrum might have carried a hundred phone calls and now it can handle a few thousand. This is without much change in total quality, both being approximately 15Kbps (or equivalent) sub-channels.

Mendocino 02-21-2012 03:02 PM

Nicely done Dave, maybe you should work with me.:)

Quote:

Originally Posted by DaveInDenver (Post 204801)
Not to mention that spectral efficiency will increase, just like it has for roughly the past century of RF communications. You've heard of Moore's Law on the doubling of computing power, there is an analog called Cooper's Law. He ran Motorola's mobile phone division for years. Anyway, he observed that spectral efficiency doubled every 30 months, IOW a given spectrum's capacity to carry information concurrently. This has held true since 1895 until today. So in Marconi's day it took MHz of spectrum to carry a single conversation where now billions of simultaneous conversations can occur in the same spectrum.

http://www.arraycomm.com/wp-content/...CoopersLaw.png

So when a cell phone carrier declares that they'll need 10 times the 'spectrum' in 15 years, they mean they'll need 10 times the capacity in 15 years. Then figure that in 15 years technology will allow existing spectrum to carry around 50 times (6 periods of doubling is 64 times the capacity) the information it does now. In Cooper's day they could never have imagined 64QAM and OFDMA that allows ~108Mbps in 1.4MHz of spectrum. Back when AMPS and PCS phones were leading edge 1.4MHz of spectrum might have carried a hundred phone calls and now it can handle a few thousand. This is without much change in total quality, both being approximately 15Kbps (or equivalent) sub-channels.



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