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
- March 1, 2012
- 1024QAM, 3GPP Long Term Evolution, Aviat Networks, backhaul, Barcelona, Base station, Mobile World Congress, modulation, small cell backhaul, small cells, Wi-Fi, wtm 3200
¡Hola! again from the final day at Barcelona, where close to 1500 companies have been busily showcasing their products and services since Monday.
Once again microwave backhaul has featured highly with the main development being the widespread adoption of 1024QAM modulation. At least half a dozen new products now support this higher modulation level. Of course we are one of them, showing our new WTM 3200 all-outdoor radio. 1024QAM supports about 25 percent more throughput over the radio path compared to 256QAM, but it does come with a tradeoff in reduced system performance and increased interference sensitivity. These can be somewhat offset by using Adaptive Modulation, so if the link starts to struggle at 1024QAM it can drop back to a lower modulation until conditions improve.
Small cell backhaul has also been a hot topic, with many vendors jockeying for position in this emerging application. Small cells are tiny base stations that can be fitted to lamp posts or the sides of buildings, covering just a few hundred square yards/meters and would provide enhanced coverage and capacity to the network. There is talk of there being literally millions of these small cells being deployed over the next five years, starting in 2014 or so, and the big challenge will be backhauling all that traffic.
Multi-technology small cells (WiFi + LTE) are emerging to enable mobile offload directly at the outdoor mounted small cell. Offload solutions that offload traffic at the building and onto fiber/DSL are designed to relieve the RAN and backhaul networks. This approach however is designed to provide capacity relief to the RAN part of the network only and will use the same backhaul as LTE traffic. The intersection of mobile offload and outdoor mounted small cells will mean backhaul remains a critical part of the offload solution for some time to come.
As with last year, there is still a huge proliferation of new LTE-enabled smartphone and tablet devices. More connections bring more opportunities. This is good for our business as mobile operators will need to upgrade their networks.
Until next year!