Illuminated thinking

This article is from the CW Journal archive.

The Guardian recently claimed “The rollout of the 5G network is being stalled by at least two years over legal wrangling about the control of millions of lampposts.”

Are lampposts really that important?

Radio engineers have noted the usefulness of lampposts as radio masts for decades. They are perfect in so many ways - spaced at nice consistent intervals, about the right height, easy to attach equipment to, and with power already available. And yet, they have been little used. Partly this is because of the difficulty in gaining the rights to access them, as the Guardian reports, but mostly it is because lampost cells are of limited value to mobile networks.

The only reason for outdoor small cells is to add capacity to the network. But mobile operators have found, and some modelling I did, has shown, that typically gains are only realised up to three small cells per sector of a macrocell. Small cells need to “borrow” radio frequencies from the macrocell and doing so reduces its capacity. They can only add more than this capacity if there is substantial mobile traffic within their coverage area. In any sector there tend to be a few hot-spot locations such as stations or shopping malls that have sufficient density of users, but once these have coverage, there is little benefit in more small cells. The situation is getting worse as mobile usage increasingly occurs indoors. Small cells can be poor at penetrating buildings as they tend to be low down so cannot see into the upper floors of the tall buildings, and radiate signal down streets, tangentially to windows, making it harder for the signal to get inside. Most operators already have around three small cells per city sector and have reached a natural limit, regardless of lampposts availability.

Does 5G change this situation at all? A rationale for 5G was that traffic would grow massively; perhaps a thousand fold. If this happens there will be enough traffic to justify small cells, indeed, they would be the only way to deliver enough capacity. But such levels of traffic seem unlikely. What we have seen is that growth levels are slowing, falling from around 50 per cent a year. In the US last year growth was only 11 per cent and many other countries are also tending downwards and may soon reach single-digit annual growth rates. Networks might only need two to three times capacity increases for the next four or more years. The frequencies that come with 5G should deliver these sorts of gains, especially if 5G can deliver the spectrum efficiency proponents promise due to its beam-forming antennas.

So for a few years lampposts would not seem to have much of a role to play. It is too early, and too uncertain, to start planning now for what might come beyond that. Lamppost access is definitely not holding up 5G.  Indeed 5G is now being deployed across a number of cities.

This leads to a number of other conclusions.

Firstly, outdoor small cells would not seem to have a significant role for the immediately foreseeable future.

Secondly, even if access might have limited value for a few years, lampposts are unique and with exclusive access might gain some advantage. Given that countries aim for a competitive market, allowing any one player exclusivity does not seem sensible. Multiple mobile operators cannot deploy on the same lamppost as the amount of equipment exceeds the safe loading limits, so deployments might have to be built by a neutral host with one set of equipment that can provide service to all mobile operators. Such a concept is being considered in rural areas for cost reasons.

This raises the broader question as to why not collapse to a single mobile network across the country that all operators can share.

Finally, the role of the lamppost as a radio mast may not be in cities. It could be more valuable in suburbs for short-range, high-capacity broadband-to-the-home. Such deployments cannot use larger cells as the frequencies needed for gigabit data rates have too short a range. If Governmental attention is to be given to lampposts, it is in suburbia where it should be focused.