RF And Optical Network Integration with Geoff Varrall

One of the benefits of doing a blog each month, apart from helping to sell a few books is that it helps identify areas where technology is changing in interesting ways.

The impact of optical technologies on radio networks is a case in point. A modern telecoms network is a complex mix of radio and optical systems. 50 years ago, fibre optic cable had a loss of 20 dB per kilometre. Today optical fibre has a loss of 0.2 dB per kilometre. Free space optical links in clear conditions have a similar loss, are faster than fibre and work extremely well in space.

It could be argued that radio systems have realised similar improvements over the past fifty years. Part of the efficiency gain has been realised from the transition from analogue to digital signal processing. Additional capacity has been realised from moving to higher frequencies. 5G networks implemented in C Band at 3.5 GHz are a present example.

Optical links have similarly benefited from the analogue to digital transition but digital signal processing has also made it easier to work across multiple optical frequency bands including optical C band.

Earlier this year US telecom operators spent $80 billion dollars buying 100 MHz of C band radio spectrum. Optical C band (from 191 to 195 THz) can be used in terrestrial fibre and for free space point to point links in terrestrial systems, space systems, sub orbital systems and below the cloud and above the cloud communication platforms.

RF spectrum is becoming more expensive over time and opportunities to increase throughput are reducing as systems get close to the Shannon limit. Optical spectrum is free and unregulated and supports tens of Terahertz of bandwidth. Coherent modulation and improved channel stability means that steady improvements in throughput and power efficiency are realisable for the foreseeable future. The implication is that over the next fifty years (from now to the 2070’s), optical assets will appreciate faster than RF assets and space and aerial assets will appreciate faster than terrestrial assets.

The rate and scale of this emerging difference in asset value over time is open to debate but you can find out more by reading this month’s posting.


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