While most mobile phones in use are on 4G/LTE networks and the world is moving to 5G, more than 10 million smartphones in the U.S. still depend on 3G. Additionally, older devices such as Chromebooks, iPads, and Kindles are connected to 3G networks for their cellular network functions. Some older internet-connected systems, such as home security, car navigation and entertainment systems and solar panel modems, are also 3G-specific. These systems will need to be replaced or upgraded by consumers.
Why are telecommunications companies turning off their 3G networks? I can help you understand as an electrical engineer who studies wireless communication. This is the difference between 3G and later technology, such as 4G/LTE or 5G.
Imagine a family vacation. Imagine your spouse on the phone organizing activities at the destination. Your teenage daughter is streaming music and talking with friends while her younger brother is playing online games with his friends. These conversations and data streams can be communicated via the cellular network simultaneously. This is something you probably take for granted. But have you ever thought about how the cellular network can simultaneously handle all these activities from one car?
All those messages must be communicated.
It is a technical trick called multiple accessibilities. Imagine writing messages to 100 friends using one sheet of paper. Each person will receive one private message. Multiple access technology in 3G networks allows you to write every message to your friends on one sheet of paper. All messages are then written on top of each other. You have a set of special pens in different colours so you can uniquely write every message. Each friend also has glasses that only show the intended colour.
The number of colours you can use to send messages is limited. If you wish to send more messages than you have coloured pens, you’ll need to mix them. When friends apply their special lens, they can see some of the messages sent. Although they won’t be able to see all the messages, the overlap may cause the message to become blurred, making it more difficult to read.
Code Division Multiple Access (or CDMA) is the multiple access technology used in 3G networks. It was created by Qualcomm founder Irwin M. Jacobs and several other notable electrical engineers. It is based upon the idea of a spread spectrum, which can be traced back to the early 20th century. Jacobs’ 1991 paper demonstrated that CDMA could significantly increase cellular capacity over other systems.
CDMA allows all cellular users to send and receive signals at any time and on all frequencies. If 100 people want to make a call or use a service, their 100 signals will overlap over the entire cellular spectrum.
Overlapping signals create interference. CDMA eliminates interference by giving each user a unique signature. This code sequence can be used to retrieve each user’s signal. The code corresponds with the colour of our paper analogy. The codes may overlap if too many people use the system at once. Interference can result, and this problem worsens with increasing numbers of users.
Slices of time and spectrum
Other multiple access techniques allow users to access the whole spectrum of cellular frequencies simultaneously but do not permit them to share it all. Time slots are created by division over time. Although each connection can last for multiple time slots, they are so brief – only matter milliseconds – that the cellphone user does not notice interruptions from the alternating time slots. It appears that the connection is continuous. This time-slicing technique uses time-division multiple access (TDMA).
You can also divide in frequency. Each connection has its frequency band in the cellular spectrum. The connection is continuous throughout its duration. Frequency division multiple access (FDMA) is the frequency slicing method.
FDMA or TDMA, in paper terms, is like dividing 100 sheets of paper in any dimension and writing every private message on one sheet. TDMA, on the other hand, would be horizontal strips. All messages can be separated into individual strips.