Finding sites for new infrastructure in a city is difficult and expensive. This is particularly true when there are tight restrictions on where equipment can be located in order to function. This location restriction applies to both local air pollution monitoring and high capacity wireless communications equipment and as increasing demand for data drives the introduction of 5G wireless communication the expected deployment densities of 5G networks start to look similar to the spatial variation of urban pollution (see figure 1).
The issue of securing enough cell sites has been a problem for wireless operators since GSM was rolled out in the mid 1990s and operators have become skilled at finding sites for their basestations. However, at the same time, land owners have realised the value of their buildings, bridges, poles and even oil company advertising signs at petrol stations. This has led to a steady rise in the cost of site rental as a proportion of a network’s operating costs; to the point where they now constitute between 40% and 50% of total operating costs. For comparison, the cost of the network equipment itself is only about 10% of operating costs. The same economic drivers are likely to apply to air quality monitoring networks so they will need to continually innovate to prevent site rental costs becoming unmanageable as sensor networks get denser to police increasingly ambitious urban air quality standards.
Shrinking and remoting controls costs
One line of innovation that has worked well for wireless networks is to reduce the physical size of basestations and combine multiple network functions into a single physical package. Another has been to enable the electronics of the basestation to be located some distance from the antenna. This works because the antenna, like the air sampling point, is the only part of a network that must be located in a specific place (to control how the wireless energy propagates across a city). Historically, the antenna could only be connected to the transmitter/receiver by coax cables that were short, bulky and expensive – rather like air sample tubes today – but heavy investment enabled a digital image of the signal to be sent 10s or 100s of meters over optic fibre with a minimum of conversion and amplification equipment located inside the antenna raydome. Similar innovations in sample tube design, including surface coatings and reliable characterisation of the tube, could enable actual air analysis to be performed where rental costs are lower, visual intrusion less, and maintenance access easier.