Mobile signal problems have several distinct causes that get described with the same word.
Coverage
Whether a signal reaches you at all.
Which depends on transmitter placement and terrain.
Capacity
Whether the cell can handle everyone using it.
Which is why signal is strong and data is slow at busy times.
Spectrum
Frequency bands with different range and capacity characteristics.
Which is why lower bands cover further and carry less.
Indoor signal
Building materials attenuating signal substantially.
Why signal bars mislead
The indicator shows signal strength from the nearest cell, which says nothing about how many other people are using it.
Which is why full bars and unusable data happen together at concerts, stations and city centres at peak times.
Those are capacity problems rather than coverage problems, and no amount of moving towards a window will fix them.
Frequency trade-offs
Low bands travelling further and carrying less data.
Which is why rural coverage and urban speed use different spectrum.
Network sharing
Operators sharing infrastructure.
Which means coverage differences may be smaller than marketing implies.
Wifi calling
Routing calls over broadband where signal is poor.
Checking coverage
Operator maps and independent crowd-sourced measurements.
What actually improves a poor signal
Moving towards a window, using wifi calling, or in some cases a small indoor cell provided by the operator.
Which addresses coverage problems and does nothing for capacity ones.
Understanding which problem you have determines whether any of it will help, and the distinction is straightforward once you know to make it.
Generational technology
Successive standards adding capacity and reducing latency.
Which delivers benefits unevenly depending on deployment.
Roaming
Using other operators' networks abroad.
Which is regulated in some regions and expensive elsewhere.
Emergency calls
Connecting through any available network.
Which works when your own operator has no coverage.
Checking before you commit
Independent coverage measurements rather than operator maps alone.
Choosing a provider sensibly
Coverage where you actually spend time matters more than headline network claims, and independent measurement data is better than operator maps.
Which is available free from several sources that collect real device measurements.
Network sharing arrangements also mean that operators marketed as different frequently use the same masts in many areas.
Data allowances
Usage patterns varying enormously between people.
Which makes checking your own actual use worthwhile before choosing a plan.
Rural coverage obligations
Regulators requiring geographic coverage.
Which has improved rural service.
Battery and signal
Devices using more power in weak signal areas.
If coverage is poor at home
Wifi calling and operator femtocells as practical options.
Why it is worth knowing how these things work
Most of the systems that shape ordinary life are invisible by design. Nobody explains why a parcel took an odd route, why a film left a streaming service, why a wait extended, or why a price changed between two searches.
The absence of explanation is rarely deliberate concealment. It is that the people running these systems are solving their own problems, and the reasoning behind their decisions is obvious to them and completely opaque from outside.
Understanding the mechanism does not always change what you can do about it. It does remove a category of low-grade frustration that comes from assuming something is arbitrary, unfair or aimed at you personally when it is usually none of those things.
The pattern that recurs
Across almost all of these systems, the same three things turn out to be true. The behaviour that looks irrational from outside is optimising for something the observer cannot see. The cost that seems unexplained is usually concentrated in one specific stage of the process. And the information that would resolve the confusion is generally published somewhere and read by nobody.
That last point is the most useful. Regulators, operators and industry bodies publish an enormous amount of explanatory material that answers exactly the questions people complain about not being able to get answers to. It is dry, it is not promoted, and it is free.
A note on sources
Where regulation is involved, national regulators publish the actual rules and they are generally clearer than press coverage of them. Where an industry is involved, trade publications aimed at people working in it are considerably more informative than consumer coverage.
Practices described here vary substantially between countries, and anything with legal, financial or medical consequences warrants checking against the rules that apply where you are.
The pattern that recurs
Across almost all of these systems, the same three things turn out to be true. The behaviour that looks irrational from outside is optimising for something the observer cannot see. The cost that seems unexplained is usually concentrated in one specific stage of the process. And the information that would resolve the confusion is generally published somewhere and read by nobody.
That last point is the most useful. Regulators, operators and industry bodies publish an enormous amount of explanatory material that answers exactly the questions people complain about not being able to get answers to. It is dry, it is not promoted, and it is free.