A standard Quadrature Amplitude Modulation constellation (non-gray code) diagram showing a demonstrative 4-bit binary code pattern. (Phase offset and amplitude values may not represent those used in real life) (Photo credit: Chris Watts via Wikipedia)
There’s a new arms race in the microwave industry, and it’s over who can claim support for the highest QAM level. Now two vendors are out in the market fighting it out over who had 2048QAM first, yet go back a little more than 12 months and 512 or 1024QAM had barely hit the market. We even are seeing mentions of 4096QAM in some conference presentations. We here at Aviat Networks view these advances as a good thing for our industry, but this heavy marketing of 2048QAM does no one any favors, as it focuses purely on only one aspect of high modulations—capacity—and ignores several other aspects that need to be understood, namely:
- Capacity improvement diminishes with every higher modulation step
- High modulations come with much lower radio system performance—requires shorter hops and/or larger antennas
- High modulations are much more sensitive to interference—makes link coordination difficult (if not impossible)
- High modulations need higher Tx power, increased phase noise and linearity—increases radio design complexity cost
So as with most things that are presented as a cureall, higher order modulations are a useful tool to help operators address their growing backhaul capacity needs, but the catch is in the fine print. Operators will need to look at all the tools at their disposal, of which 1024/2048QAM is a useful option, albeit one that will require very careful planning and strategic deployment. In general, operators need practical solutions for capacity increases, as detailed in “Improving Microwave Capacity“. In fact, speaking of practicalities, the real challenges with LTE backhaul has very little to do with capacity…as detailed by this article. For the complete “Modulations Arms Race” article, click here.
Director, Corporate Marketing