Refarm 2G Spectrum for IoT?

#Discussion(IoTStack) [ via IoTForIndiaGroup ]

[ IoTForum has advocated dedicated IoT allocation of expiring 2G licenses in India ]

What is spectrum refarming?
Each newer generation of mobile network introduced significantly improved radio technology, increasing capacity, data speeds and performance. 4G/LTE can penetrate further indoors than 2G, achieving 100x data rates with high definition voice. Often each new generation comes with its own dedicated spectrum, 2G at 900MHz, 3G at 2100MHz and 4G at 700/800MHz.

4G also opened up many new bands such as 2.3GHz and 2.6GHz, offering both TDD and FDD mode that means it can be assigned to many more dormant bits of spectrum. We’ll even see it introduced into 3.5GHz this year and 5GHz thereafter.

But for existing networks it can be attractive to reassign frequencies previously used for 2G or 3G and operate them with 4G/LTE. You would normally expect new LTE spectrum to be used first, expanding the capacity of each existing cellsite. Higher frequencies (say 2.6GHz) are most useful to add capacity in dense/busy areas where shorter range and spectrum reuse is important, whereas lower frequencies (900MHz) are more relevant in sparsely populated areas requiring larger coverage and in-building penetration.

Refarming isn’t so worthwhile until a substantial proportion of the user smartphones are compatible, so there is a market timing issue where operators would want to monitor and even encourage upgrades while matching infrastructure progress to take advantage of it.

Technical Implementation
Mobile operators have been looking ahead at this issue for several years, and most have re-equipped their entire basestation inventory with software configurable radios from Ericsson, Huawei and Nokia. These can be remotely assigned to 2G, 3G or 4G as required, although major band changes (e.g. from 2100MHz to 800MHz) would require antenna replacement. There may also be some physical adjustment to antenna tilt because of the longer range of 4G.

Examples of refarming to date
We’ve previously reported that several leading operators planned to switch off their 2G service altogether. Japan had done this some years ago (their proprietary PDC system was similar to but incompatible with GSM). After many years of advanced notice on 1st January 2017, AT&T started turning it off across the USA. There had been many years of advanced notice (and a quiet backroom deal with T-Mobile to take over some machine-to-machine contracts), so it was relatively painless. Nonetheless, one San Francisco bus company suffered problems with it’s traffic information App – some of their buses with outdated GSM trackers “disappeared” and so the App gave incorrect information about when the next bus was due. They may also be losing out on some potentially lucrative inbound roaming visitors, where their home networks smartphones don’t support AT&T’s 3G or 4G bands.

Most of the European operators I’ve spoken to are quite keen to retain a sliver of GSM coverage, even if just a few hundred kHz, because virtually every mobile phone has this baseline capability to fall back to. Some M2M systems would be quite costly to upgrade.

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