How Your Phone Works: a Quick Guide to Cellular Technology & Cell Towers

Mobile phones are pretty ubiquitous, but how do they work? They’ve been commonly called cell phones in the US, due to the cellular technology that they use. In most other ways they’re like other wireless devices, transmitting signals carrying voice, text and digital data via radio waves from one device to another between cell towers.

The Honeycomb of Cells 

Meanwhile the cellular technology means that instead of one big central hub transmitting data [as it is with Wi-Fi, 5], or transmitting directly from device to device [like Bluetooth, 4], the land area – now most of the populated world – is covered by multiple interconnected transmitters. Each tower transmits radio frequencies [RF] roughly in circles centred on the tower, with the edge of the next transmitter’s circle picking up as the connection from the first drops off. Transmitters, or base stations, are placed so that their transmitting circles overlap.

The most effective pattern can be pictured as connecting hexagons, with a basic design element of groups of seven cells, ensuring calls don’t drop out as users move between stations [known as handoffs]. Phone users are usually, and ideally, unaware of the move between stations, unlike for instance taxi company systems where drivers have to switch frequencies as they move areas.

The hexagonal cells form a pattern like a honeycomb over the earth [3]: cellular technology

Distances between cells depend on geographical and meteorological features [e.g. ducting, absorption by surrounding matter, 1] that affect transmission, as well as the type and height of the antenna, and the RF power level of the emissions.

Multiple Access

‘The other main concept of cellular technology was that they were multiple access, meaning that they placed multiple voice or data connections into a single radio channel’ [1]. Frequency re-use at geographical intervals is a central tenet that’s really allowed for the massive success of mobile phones by maximising coverage area and simultaneous conversations. ‘The concept goes beyond the number of antennas and deals with how the radio frequency [RF] itself is used and reused’ [1].
Building a network necessitates a lot of co-ordination between engineers over frequencies and distances to reuse RFs. They also need to avoid system interference and co-channel interference. Mobile phones use paired channels – one for transmitting and one for receiving [except with SMS or streaming]: they may or may not be the same frequency.

Low Power
Another big advantage of this cell technology is the low level of power needed. A typical phone ‘includes a dual-strength transmitter, capable of transmitting either 0.6-watt or 3-watt signals. In comparison, a larger AM radio station will typically broadcast a 50,000-watt signal; even smaller AM stations broadcast 5,000-watt signals. A cell phone’s 3-watt signal is puny in comparison.
The reason mobile phones can get by with such low-power transmitters is that they’re transmitting within a relatively limited range—within the current network cell. It’s not necessary or desirable for a phone’s signal to extend beyond the current cell; this way, the same broadcast frequencies can be used by multiple cells without danger of interference’ [3].

 

cell towers

The Cellular Technology Network Includes Cell Towers

There are five parts of a cellular network:
1. Mobile Unit [usually a phone, can be mounted in a vehicle like a GPS];
2. Cell Base Station comprising cell towers, antennas etc, land or rooftop based. May be called a Base Transceiver Station (BTS), it defines the coverage area and controls radio link protocols;
3. Fixed Network: base station controllers of numerous cell sites: connect to the outside world and allocate RFs;
4. Mobile Switching Centre: the brains of the network, responsible for call routing for roaming subscribers, registration and connection to the public network;
5. The interconnection to the Public Switched Telephone Network (PSTN, and the Integrated Services Digital Network, ISDN – Australia probably has a different system for phones and surveillance)[1]. There are also support services for all these operations.

Control channels collect information from all these elements, used for billing, for the provider’s records, and potentially for law enforcement. The SIM – Subscriber Identity Module – card also contains abundant retrievable information, such as location [in the USA: HLR – Home Location Register and VLR – Visitor Location Register], that users need to be aware of. In Europe some subscribers store their medical records on their SIM card.

Generation after Generation

GSM, the Global System for Mobile Communication was the main initial system, and standardized cellular communication thoughout Europe. GSM was rolled out in 1991 and its first iteration was analog based. 2G stands for ‘second generation’, and the G designation continues up to the current 4G. 2G was digital and introduced encryption, operating on 900 MHz, 1800 MHz and 1900 MHz and Digital Communication System 1800. The major advance of 4G is that mobile broadband internet services can be provided to external systems, such as laptops, wireless and modems [2].

Why is GSM called the first true intelligence and wireless network?
1. It has an open, distributed architecture;
2. The separation of switching and service control functions;
3. Full use of SS7 as the signalling infrastructure;
4. Its clearly defined and specified interfaces;
5. The nature of its IN structure [2].
Related Technologies

There are a few linked technologies and innovations that enhance cellular technology and our understanding of it. For instance, GSM introduced General Packet Radio Service (GPRS) and Enhanced Data Rates for Global Evolution (EDGE) in its 3G roll-out, which actually used the competing CDMA technology [below] and allows higher transfer rates.

CDMA: The USA also has Code Division Multiple Access or CDMA, with its roots in WWII era spread spectrum technology. Spread spectrum technology avoids some of the problems of interference caused when conventional mobiles only use a very narrow part of available RF bandwidth.

LTE stands for Long Term Evolution, often called 4G LTE. It increases bandwidth available for voice and data communications by using a different radio interface combined with a number of network improvements, and is used to upgrade both GSM and CDMA based networks. LTE brought very high bandwidth to mobile devices, hotspots, and peripherals, while XLTE is at least twice as fast.

VoLTE sends voice data over the data portion of the phone connection, and has incredible voice quality [like they’re right next to you, 2].

Summary

So this has been a quick skim through cellular technology – how it works with your mobile phone, using minimal power, and allowing seamless transitions between transmitters as you move around. It also has the potential to store huge amounts of information about you, with advantages and drawbacks that people are just starting to realise.

We’ve also explained how the technology has developed from the first generation to 4G, and some other improvements like LTE. Hoping this has been helpful!
1. https://www.eff.org/files/filenode/cellular_technology.pdf
2. https://danielmiessler.com/study/cellular/
3. http://www.quepublishing.com/articles/article.aspx?p=2021961
4. Bluetooth enables any electrical device to wirelessly communicate with another on the unlicensed 2.5MHz frequency. Other RF technologies are Software Defined Radio (SDR) and Cognitive Radio (CR) [1].
5. Wi-Fi calling lets you route regular phone calls over a wi-fi connection, and will let you swap back and forth between the internet and your phone network [2].

 

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  • martha carter
    Reply

    Where do I get a cell phone towers for a individual?

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