Signal strength is measured in decibels (dB). The transmissions between mobile device and base station are of a relatively low power, so the figures you see are usually microvolts per metre; simply put, the greater the number of microvolts, the stronger the signal.
Unfortunately, the signal bars on a mobile phone do not accurately represent the true signal. The bars do not account equally for decibel loss – for instance, having two out of four bars does not mean that you are receiving at half power, as the smallest three bars together cover less power loss than the top single bar on its own. As you can see, this makes the system highly inaccurate and you could be classed as having a ‘low-strength’ signal even with three bars showing.
The mobile networks are constantly battling to improve coverage and they still use the same solutions they always have: more base stations, higher power transmissions, taller antenna masts and stronger antennas, and, more recently, femtocells to provide signal in high-traffic but low-coverage areas. As with all radio services, the higher the power, the further the signal will be transmitted – equally, the lower the frequency of the spectrum, the lower the power needed to achieve the same distance. A mobile operator with spectrum at 8ooMHz will need to broadcast at a lower signal strength than an operator with spectrum at 2.6GHz to achieve the same coverage, assuming an equivalent number and placement of base stations.
Network providers use coverage noticers to spot ‘dead zones’ – areas with no coverage -and these devices will emit a beep when within one. They can be used alongside tracking software in cars or on foot to build a map of general coverage over wide areas. Population density and dead zone data is used with destructive interference information to create a picture of where coverage is required most urgently. Destructive interference can be caused by large buildings constructed from metal, which can kill off a signal indoors, trees, terrain and many other obstacles. This makes the science behind coverage extremely complex but something networks continually use to improve signal strength for us all. On other blog – How Strong Is Your Wi-Fi Wireless Signal?