Wednesday, September 28, 2016

Using Unlicensed Spectrum for Air-to-Ground Networks

Gogo has announced an initiative to utilize unlicensed spectrum to power an new Air-to-Ground (ATG) network.  They profess a beam-forming network deployed to their 200 plus ground stations will deliver 100 Mbps.  I believe that it is possible both Gogo and SmartSky are pursuing a similar technology.  The following is my analysis on SmartSky, to which it may relate to Gogo ATG as well.

Smartsky have declined to reveal their fundamental radio technology in the past, rather stating:  
  • the technology is fundamentally 4G LTE 
  • they have 60 MHz 
  • they have successful flight test demonstrations 
  • they have survived diligence from investors and distribution partners 
  • Trust them, it works.
I have removed my outdated analysis from this blog, instead use the following links to learn about the grants issued to Harris, and how Smart Antenna Systems enable SmartSky Networks.  

There remains some uncertainty, but a few points are becoming clear:

The forward channel has about 28 MHz; the return channel a similar amount.  Together they don't quite add up to 60 MHz.  Furthermore, SmartSky compared their 60 MHz to Gogo 3 MHz (actually now 4 MHz) allocation.  I think the Gogo system can make full reuse of their spectrum forward and return.  In this case it should be 28 MHz compared to 4 MHz. 

Further consideration must be made to the value and utility of unlicensed Versus licensed spectrum.  Gogo ATG has struggled with too limited an allocation.  Inmarsat EAN and Verizon drone-net may have access to licensed spectrum comparable to SmartSky. 

Never-the-less, Gogo is also pursuing a similar unlicensed network.

With information available, assuming a spectral efficiency of 1.5, and taking into account the limitations expressed in 15.247 (c), an estimate can be made for the service capacity from one Remote Radio Head (RRH - the Harris access point) based on varying levels of demand:

case 1: 1 Mbps per airplane:    30 planes per beam,                 180 planes per RRH
case 2: 5 Mbps per airplane:      6 planes per beam,                   36 planes per RRH
case 3: 30 Mbps per airplane:    1 plane per beam,                       6 planes per RRH
case 4: 100 Mbps per airplane:  1 beam from 3 RRH per plane    2 planes per RRH

Stay tuned,

Peter Lemme
peter @

Follow me on twitter: @Satcom_Guru

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Peter Lemme has been a leader in avionics engineering for 35 years. He offers independent consulting services largely focused on avionics and L, Ku, and Ka band satellite communications to aircraft. Peter chairs the SAE-ITC AEEC Ku/Ka-band satcom subcommittee developing PP848, ARINC 791, and PP792 standards and characteristics. 

Peter was Boeing avionics supervisor for 767 and 747-400 data link recording, data link reporting, and satellite communications. He was an FAA designated engineering representative (DER) for ACARS, satellite communications, DFDAU, DFDR, ACMS and printers. Peter was lead engineer for Thrust Management System (757, 767, 747-400), also supervisor for satellite communications for 777, and was manager of terminal-area projects (GLS, MLS, enhanced vision).

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