Sunday 15 March 2015

Air-Ground-Air communications in Mission Critical scenarios

In-flight communications have always fascinated me. While earlier the only possibility was to use Satellites, a hot topic for in the last few years has been Air-Ground-Air communications.

Some of you may remember that couple of years back Ericsson showed an example of using LTE in extreme conditions. The video below shows that LTE can work in these scenarios.

Now there are various acronyms being used for these type of communications but the one most commonly used is Direct-Air-to-Ground Communications (DA2GC), Air-to-Ground (A2G) and Ground-to-Air (G2A).

While for short distance communications, LTE or any cellular technology (see my post on Flying Small Cells) may be a good option, a complete solution including communication over sea would require satellite connectivity as well. As I have mentioned in a blog post before, 75Mbps connectivity would soon be possible with satellites.

For those interested in working of the Air-Ground-Air communications, would find the presentation below useful. A much detailed ECC CEPT report from last year is available here.

The next challenge is to explore whether LTE can be used for Mission Critical Air Ground Air communications. 3GPP TSG RAN recently conducted study on the feasibility and the conclusions are as follows:

There is a common understanding from companies interested in the topic that:

  1. Air-to-Ground communications can be provided using the LTE standards (rel-8 and beyond depending on the targeted scenarios).
  2. 3GPP UE RF requirements might need to be adapted
  3. It may be possible to enhance the performance of the communications with some standards changes, but these are in most cases expected to be non-fundamental optimizations
  4. Engineering and implementation adaptations are required depending on the deployment scenario. In particular, the ECC report [1] comments that from implementation point of view synchronization algorithms are to be modified compared to terrestrial mobile radio usage in order to cope with high Doppler frequency shift of the targeted scenario. In addition, some network management adaptations might be needed. From engineering perspective the Ground base station antenna adjustment has to be matched to cover indicated aircraft heights above ground up to 12 km by antenna up-tilt. It is also expected that the inter-site distances would be dominated by the altitudes to be supported [5].
  5. A2G technology using legacy LTE has been studied and successfully trialed covering different kinds of services: Surfing, downloading, e-mail transmission, use of Skype video, audio applications and Video conferencing. Related results can be found in several documents from ECC and from companies [1], [2], [3]. The trials in [1] and [2] assumed in general a dedicated spectrum, and the fact that the communications in the aircraft cabin are using WIFI or GSMOBA standards, while LTE is used for the Broadband Direct-Air-to-Ground connection between the Aircraft station and the Ground base station.
  6. It is understood that it is possible to operate A2G communications over spectrum that is shared with ground communications. However, due to interference it is expected that the ground communications would suffer from capacity losses depending on the deployment scenario. Therefore, it is recommended to operate A2G communication over a dedicated spectrum.
  7. It can be noted that ETSI studies concluded that Spectrum above 6 GHz is not appropriate for such applications [4].
  8. LTE already provides solutions to allow seamless mobility in between cells. Cells can be intended for terrestrial UEs and cells intended for A2G UEs which might operate in different frequencies.
  9. Cell range in LTE is limited by the maximum timing advance (around 100km). Larger ranges could be made possible by means of implementation adaptations. 


Oliver Thomas (via 3GPP LTE/LTE-A Standards Linkedin group) said...

"Except of cell size [sic], and parameter adaptation for synchronization/handover processes in eNBs no difference of DA2GC ground network to usual terrestrial LTE networks"
"Altitude of about 10 km (first flight phase)."

Very interesting! I guess at that altitude, the relative speeds of the communicating entities is not actually that high, so might actually be a less extreme use case to that of a high speed train.

Louis GIBAULT (via 3GPP LTE/LTE-A Standards Linkedin group) said...

At the altitude where planes fly the main problem will be interferences since at 10km hight you are in line of sight with every LTE relay landing 300km around (unless specific spectrum bands are allocated to this application).

On your drawing if you replace the plane by something flying lower, like an helicopter, this will be will be more realistic, and this may be a particularly useful case for example to do the coverage of a disaster place during a civil security mission.

Unknown said...

In US, DA2G commercial service is already available. Only one company provides it. New company is planning same service with LTE. The aim of CEPT study is to provide same service in Europe.
The objective of 3GPP study is just answer for French administration.
NGMN 5G white paper proposes to include DA2G service into the 5G vision. I think it is more interesting topic for DA2G.

Anonymous said...

LTEA can support Doppler shift up to 600Hz (PRACH) ref 3GPP.

If an aircraft is flying towards a cell, level flight, 1000kph, at a height of 10,000m and is at a ground distance of say 10km from the cell, what is the closing speed to the cell?

it is 1000*cos(45deg) = 707kph, agree?

in that case it could not communicate with the cell due to the high Doppler shift.

to get a closing speed less than 500kph, angle is >60deg.

the number of cells required will be huge if that is the only way of addressing the Doppler shift problem.

do the trigonometry, speed is a problem.

Mirza said...

Anonymous comment looks logical.