Wednesday, September 19, 2012

Ka Band - Will it ever escape domestic broadband and become a real contender competing with Ku?

Post IBC 2012, it seems that Ka is once again the talk of Amsterdam. But having experience this 'buzz' at the last 5 IBCs is Ka ever going to be something more meaty?
In my opinion I don't see that there is a replacement issue under all conditions. We have a continuing appetite for capacity, protection, and mobility from space that only add Ka spectrum to existing C/Ku.
I will contend that each band and each system has unique pros and cons. Aside from cost/byte, users must account for the supportability of their current C/Ku terminals and infrastructure, the application at hand, rain and overall weather conditions, and constraints (or not) to real estate for terminals (aperture size).
The problem is achieving a SLA with the deep fade margins associated with Ka band.When the first trials were done at Ka Band on the ACT and Olympus satellites back in the late 80's, the traffic was still serial; since then, powerful FEC codes have permitted the use of packet based traffic and this in turn has permitted the use of ACM. It is the sum of all these technologies that has finally permitted Ka band to be of commercial value. (obviously the drop in the price of 30GHz FETs has also helped).
Now during the fade, the ACM automatically downscales the MODCOD values so maintaining the availability (albeit at a reduced information rate). Even though the information rate is reduced during the fade, the use of packet shaping can enable a CIR to be maintained for specific traffic profiles within the stream.
The point that needs to be made is that there are variety of downlink bands being used with Ka-Band uplinks. (C, Ku and K), to my knowledge there isn't actually a communication satellite that supports both uplink and downlink in Ka band (please feel free to correct me if I am wrong).
At the higher end of K band (e.g. 21 GHz) the water absorption point starts to have a more pronounced affect, so applications using this cannot be directly compared to a downlink operating in Ku band (as we say in the UK, you have to "compare apples with apples").
A high performance hub earth station can be built that overcomes many of the "perceived" issues associated with Ka band and if grouped with a downlink in the lower part of K band (or Ku band) there is no reason why performance not too dissimilar to Ku band cannot be achieved.
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