Telecoms watchdog Ofcom has taken a step towards releasing more bandwidth capacity for ultra-fast broadband and 4G.Ofcom said it was inviting potential bidders to comment on proposals for its auction of so-called "spectrum" in the 2.3 GHz and 3.4 GHz bands, which is expected late next year or in early 2016.The regulator said it had not yet chosen specific uses for the capacity, but it is likely to interest mobile phone operators, which rely on spectrum to provide internet services on consumers' smartphones and tablets. The 2.3 GHz and 3.4 GHz spectrum bands are frequencies which could be suitable for providing very high data capacity. Many existing mobile handsets from major manufacturers including the Apple iPhone 5 and 6, HTC Desire and Samsung Galaxy are already compatible with the 2.3 GHz spectrum in other markets. The band is so far being used for high-speed 4G mobile broadband networks in 10 countries outside Europe, including China, India and Australia. The 3.4 GHz band is in use for 4G wireless broadband in six countries including the UK, Canada and Spain.Previous releases of extra spectrum sparked controversy because mobile operator EE was able to start 4G services earlier than rivals such as Telefonica's O2 and Vodafone.Ofcom said the latest auction was designed to be fair and transparent, enabling the spectrum to be awarded to those who can put it to the most efficient use and in the best interests of consumers.The consultation closes on 23 January 2015.Ofcom's spectrum director Philip Marnick said: "Today marks an important step in ensuring that the UK has sufficient spectrum to support our wireless economy."