O2 is spending £80 million to install 1,400 small cells in London by the end of this year, as it looks to improve coverage in the UK's capital.
The operator is working with Cisco on the project, with the vendor providing integration services.
O2 said it wants to deliver better mobile signal for businesses and consumers both indoor and outdoor, as well as pave the way for 5G.
The announcement is in addition to O2's project with Vodafone to improve coverage within the City of London.
Both companies announced last month that they would deploy a mix of small cells and Wi-Fi. The new network will be operational by the autumn of this year.
Derek McManus, COO of O2, said: “We recognise that customers’ need for mobile data in London and other urban areas continues to grow at a rapid pace. We understand the importance of digital connectivity in terms of driving the economy and ensuring that London can continue to compete on a global scale.
"This is why we’re investing in a range of innovative measures from small cells to macro masts in order to ensure we continue to give customers what they need; reliability and coverage wherever they go.”
According to the latest research from Ofcom, which tracked network quality in UK cities across 2016, O2 had the lowest average download speeds in London at 8MBps.
O2 was also in fourth place for average upload speeds.