The science behind bad mobile signal


There are many contributing factors to the deterioration of mobile telecommunications signals, that result in areas known as ‘blackspots’.

Blackspots cause significant disruptions for both the end-user and the carriers that are supplying the networks.

As opposed to simply being too far away from a telecommunications cell tower, blackspots are defined as due to other external factors.

Typical symptoms of mobile blackspots are call drop-outs, highly variating signal strength, internet timeouts, noise during calls, slow mobile internet, difficulty hearing other callers and increased battery usage of the mobile device.

These symptoms are usually caused by three main factors.

Natural Terrain Obstructions

The number one cause of mobile blackspots is due to the area of terrain between the cell tower that is sending out the signal and the mobile device that is receiving it.

Radio waves are part of the same electromagnetic spectrum as light waves and so it can be easier to understand the science behind mobile telecommunication signalling by visualising it in the same way.

A mobile device receives signal by connecting with a cell tower via radio waves. The behaviour of these waves as they travel to a mobile device is called propagation. Much-like a shadow that is cast by light hitting an object, when there are significant variations in the terrain that block the path between a cell tower and a device, much of the signal is unable to pass-through and reach it directly. Instead, through a process called diffraction, the waves bend inwards towards the ‘shadowed’ region. This process causes the areas of ‘strength’ and ‘weakness’ in a devices connectivity.

diagram-1-01-01

Example of terrain blocking signal and causing diffraction

Telecommunications network providers are able to improve the signal in these pockets of decreased signal strength with a number of technologies, including small cells (also known as femtocells) which work with the larger cell tower (macrocells) to redirect signal in refined areas.

diagram-2-small-cells-01-01

More recent developments have also included the use of drones and balloons to ‘bounce’ the signal from the cell tower and direct it at a specific point in space, such as a crowded event. These technologies are particularly promising for tackling bad mobile signal at large-scale events such as festivals and sporting fixtures.

Non-terrain Obstructions

Non-terrain obstructions work in a similar way to natural obstructions; however, it is dependent on the material that stands between the cell tower and the connecting device because the effect that an object has on signal strength depends on the materials penetrability. Not only that, but where objects cannot be penetrated by the radio-wave, they reflect, causing various other signal paths. This is known as a multipath environment.

The problem with a multipath environment is that, although you may eventually receive the signal from the cell tower, it will have taken a longer amount of time to reach the device. This can result in a delay.

Antenna Angle or Tilt

In some instances, you may not be far from the cell tower as well as have a clear path (i.e. no significant terrain or non-terrain obstructions) and still suffer from poor mobile telecommunications signal. This can be due to the angling of the broadcasting antenna on the cell tower.

Although in most densely populated areas, telecommunication service providers use three directional broadcasting antennas, with each focused to cover a sector of 120 degrees, some more basic towers only have one omnidirectional transmission antenna which cover the full 360-degree radius. The latter may sound preferable, but each transmitter has a capacity limit, so by only using one it means you are limiting the number of users and speed that is available.

Antennas may be tilted by the provider to focus their signal at a smaller coverage area that is favoured by the operator. Unfortunately, in these cases the areas that are on the edge or outside of the coverage sector will experience diminished signal strength.

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