Finding spectrum for mobile
Larry Downes has a good piece on the hunt for 300-500 MHz of mobile Internet spectrum and how the FCC is working to complete an inventory check on spectrum allocation. When it comes to mobile Internet, physics and practical engineering and usability requirements limits us to frequencies between 300 MHz and 3700 MHz. Less than 300 MHz and the antennas needed are too big to carry, and even 300 MHz might be too big for a mobile phone and might only work in a tablet device or notebook computer. Higher than 2.5 GHz and it gets more difficult to get the signal to propagate and work its way around terrain and other obstacles, but it might be possible to get near line of sight applications to work at up to 3.7 GHz.
Realistically speaking, truly mobile applications need to be between 500 MHz and 2500 MHz which is a 2000 MHz patch of spectrum with a practical total carrying capacity of 2 Gbps to 10 Gbps per cell if all 2000 MHz are converted to mobile Internet services. That sounds like a lot of capacity until we consider the fact that each cell is potentially needed by thousands of users, and the fact that most of that mobile spectrum is allocated to something other than mobile Internet. Within that 2000 MHz, it will be challenging to get 300 to 500 MHz freed up for mobile Internet services. The picture below can be clicked and expanded to show what resides in this spectrum space. The FCC also has a more detailed document on the 300 to 3000 MHz spectrum.
It is unclear who or what is going to get squeezed or bumped off of this spectrum map. Some of the analog data and voice applications can certainly be compressed and shrunken (digital technology is effectively a system that shares spectrum far more efficiently than analog radio communications), but that would require changes in hardware which is expensive. Spectrum is like land and once it’s occupied, it becomes very hard to evict the tenants.