Government consults on 3.5GHz 5G spectrum

RSM consults on preventing interference

Radio Spectrum Management (RSM) has initiated a consultation on technical principles to prevent interference between different mobile operators in the 3.5GHz band (3410 – 3800MHz) 5G band which it plans to auction in 2020.

5G in the band has been standardised internationally to use time division duplex technology (TDD), a system in which the same frequencies are used for both transmit and receive, but with the function alternating at a rate such that users are unaware of any break in a conversation.

RSM explains that where different operators are using different frequencies within the band there will still be potential for interference if their TDD timings are not synchronised.

Its consultation document proposes a scheme under which all future users of the 3.5 GHz band synchronise their transmissions to a set structure.

Users of the spectrum could opt not to synchronise as long as they did not cause harmful interference to other users with adjacent spectrum.

The recommended synchronisation scheme proposed in the consultation document is the outcome of a technical working group) comprising industry stakeholders with an interest in the 3.5 GHz band It included mobile network operators, fixed network providers, equipment manufacturers and the Wireless Internet Service Providers Association (WISPA).

The group proposed the whole 3.5 GHz band be synchronised to a 5G-specific frame structure and timing requirement, and  considered an enforcement mechanism for implementation of the scheme.

The proposed arrangements are independent of any variation of the 3.5GHz band plan and any allocation of the spectrum. Current usage rights expire in November 2022 and auctions of usage rights will be held prior to that date.

A paper discussing the allocation process was issued in April 2018.  In August of that year Spark published a briefing paper setting out its plans for 5G services, and criticising the government for what it says is policy inertia on 5G.

Managing director Simon Moutter said the company was already making decisions contingent on securing additional 5G spectrum, but there was no clear government policy on when spectrum would be available or in what bands.

If Spark’s recommendations were adopted they would make a shared TDD timing regime unnecessary. Spark floated the idea of a single 5G network saying: "The New Zealand market is, and is likely to remain, small compared to the level of investment required to roll out a national network. The question of whether there is ‘room’ in the New Zealand market for multiple 5G networks, or whether a single national 5G network would be more cost effective, has been raised in the media."

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