A smartphone needs a unique identity to use a cellular network. A SIM (Subscriber Identity Module) securely stores this identity (the IMSI: International Mobile Subscriber Identity). For a CDMA phone, the identity is stored in the phone. If you have a CDMA phone with a SIM, then this is most likely to allow the use of an LTE network (non-CDMA). Your SIM is provided by your cellular network operator.
There are a number of common network types. 4G LTE is currently the newest and fastest, 3G being slower. Airplane mode suspends radio-frequency signal transmission.
The cellular network is a communications network where a cell phone wirelessly connects using radio waves. The geographic area is divided into cells with each cell tower using a certain frequency (band). Neighboring cells use different frequencies to reduce radio interference. A cell phone registers to a cell, but constantly checks for nearby (detected) cell tower signals and uses this information (such as nearby cell tower signal strength and interference) to determine whether the phone should change to a cell tower with a better signal.
If you are buying a used phone, you should note the IMEI number (or MEID/ESN) and use it to check whether the phone is blocked in your country. This is normally an indication that the phone was lost, stolen or payments have not been made. You can find the IMEI for your phone with my Phone Check and Test app (Report option, Telephony network).
Phones transmit radio waves to cell towers and receive radio signals from the cell towers. The power used to transmit is managed by the phone and the cell tower (base station) and is based on a number of factors, such as distance to the cell tower (the further you are from a cell tower, the more power will be used to transmit). The maximum amount of energy a phone can emit is regulated by governments for public safety. All phones should be tested by the phone manufacturer for compliance and report this as a SAR (Specific Absorption Rate) value. This is the rate at which energy is absorbed by the body when exposed to a radio frequency at a defined distance from the body (e.g. 2 cm).
The app store has a number of signal boosters. Logically, if an app could change radio parameter limits to allow the transmit power to be boosted, then you would have to expect the phone would no longer comply with it’s SAR rating (i.e. it would emit more energy that allowed – and your body would absorb this). Of course, manufacturers do not allow this. So, it would seem that signal booster apps disconnect from the network and allow the phone to reconnect – in some cases this may provide a better signal (like turning a device off and back on).
A poor signal (e.g. 1 bar) can cause a number of problems, like call dropouts and increased battery usage. The main things you can do to improve your signal are:
- Monitor your signal: get a Phone signal app to monitor your signal strength (in dBm) over time and check how much of a problem it really is;
- Location: move to a different position in your house to get a better line of site with the cell tower your phone is registered with;
- It may be possible that the way you hold your phone and even the case can slightly block the signal. You could try holding the phone at a different position;
- Try a different phone model: not all phones are created equally;
- Purchase signal booster hardware. This equipment receives a signal and retransmits it. This can work because the equipment will have better antennas and higher power than your phone (as it does not need to work 2cm from your head);
- Change to a different network operator;
- But start by asking your cell phone operator what they recommend.