Broadband internet: Copper telephone wire could be almost as fast as fibre

Many homes in the UK rely on repurposed phone lines for internet access, leading to slow download speeds, but there may be a solution

By Matthew Sparkes

Fibre-optic cable is being laid across the UK at great expense to speed up people’s internet connections, but researchers claim that the copper telephone wire already in use across the country can achieve data rates three times higher than currently seen at a fraction of the price, at least over short distances. Their technique to boost speeds may help to ease the transition to nationwide fibre optic, and may also be of use in countries that use similar twisted-pair copper wire.

Ergin Dinc at the University of Cambridge and his colleagues say that twisted pairs of copper wire, of the type used for decades as telephone lines and now repurposed for broadband internet, can support a frequency fives times higher than is currently used, which would dramatically improve data transmission rates. Above that limit, the researchers found that the wire essentially acts as an aerial and transforms any signal sent along it into radio waves that dissipate before reaching their destination.

“These cables are actually very old, invented by Alexander Graham Bell, and since then no one has looked into the theoretical limits,” says Dinc.

He and his colleagues say that their findings may allow houses near fibre-optic cables to achieve higher speeds than they currently enjoy without the expense of running fibre all the way to their home.

Fibre-optic cables carry groups of photons to represent data, and huge numbers of these groups can be sent along the line one after another without waiting for the first to arrive. Fibre connections in use today typically operate at 1 gigabit per second, but theoretical speeds could be many thousands of times higher.

But in copper wiring, the signal is sent by an electrical current running along the entire length of cable, and the data transmission rate is limited by how quickly the current can be changed.

Existing copper broadband connections operate at a frequency below 1 gigahertz, where the current is changed a billion times a second, but the researchers discovered that this can theoretically be raised to 5 gigahertz using a small and cheap component called a balun.

Dinc doesn’t believe this will translate directly to a fivefold increase in data transmission, because the error rate increases at higher frequencies. Further research is needed to determine how much of a boost is really possible, but Dinc estimates that 3 gigabits per second is feasible. That is triple the current theoretical maximum, although in practice, most people with copper wire broadband in the UK only achieve speeds of at most 80 megabits per second.

Journal reference: Nature Communications, DOI: 10.1038/s41467-022-29631-8