Backhaul bandwidth across the spectrum
I was recently pondering on the amount of spectrum available for the different types of small cell backhaul, when I came across a table of the UK spectrum allocations in the "Frequency Band Review for Fixed Wireless Service" for Ofcom.
Plotting the available bandwidths on a graph alongside sub-6GHz allocations for mobile access makes for an interesting comparison:
Starting at the bottom, we see that around 1.5GHz - a quarter of all spectrum below 6GHz - is available for mobile access of one sort or another.
This includes licenced cellular 2G, 3G and the forthcoming LTE allocations, as well as the 2.4 and 5GHz unlicensed bands for Wi-Fi etc.
In comparison, allocations for ‘microwave’ links between 6 and 60GHz are over ten times the size, with over 16GHz available.
Adding to this the 18GHz or so available for ‘millimetre wave’ between 60 and 80GHz, we see an enormous potential for high capacity transport.
Not only is there more spectral bandwidth, but the spectral efficiency is generally much higher for fixed Line-of-Sight (LoS) microwave links than for Non-Line-of-Sight (NLoS) mobile access.
The end result is significantly more capacity for microwave.
This analysis helps quantify the scarcity of NLoS spectrum below 6GHz and the need to reserve it for mobile access.
On the other hand, LoS spectrum above 6GHz is relatively abundant and is well suited to fixed backhaul links.
For small cell backhaul, we see microwave and millimetre wave LoS links doing the heavy lifting and backhauling the bulk of the capacity, whilst the NLoS solutions will address special situations that cannot be reached any other way.