Optus mounts 4G challenge Optus says its 4G signals will reach 70 per cent of Australia "metropolitan population" by the end of 2014. Telstra's primacy in the 4G mobile race is about to be seriously challenged by Optus, with the country's second largest carrier promising to have 70 per cent of Australia's metropolitan population covered in the next year. Optus says it is expanding 4G mobile coverage to match its key competitor in an increasingly intense battle for customers. Meanwhile, carriers are bracing for explosive growth in data traffic in the coming years. In comparison, Telstra will extend its 4G network to about two thirds of Australia's land mass at the end of the next month and already has more than 2 million 4G devices connected to its network. Optus' managing director for network, Günther Ottendorfer said it was "aggressively" expanding its 4G coverage, but refused to divulge the current extent of 4G coverage in Australia. Andrew Smith, Optus' vice president of mobile engineering team, said the telco had 700 4G mobile sites across the country and about two third of these sites were located in Melbourne and Sydney. It is believed that Telstra has twice as many 4G mobile transmission sites as Optus. Mr Ottendorfer was also evasive on the scale of Optus' investment in the network. He said "for the past three years, we invested two billion [dollars] in our network." The carrier has also launched what is known as TD-LTE in its network, a variant of the prevailing 4G network technology. Currently, 4G networks in Australia run on FD-LTE, which uses two separate frequency channels, one for data travelling in each direction. TD-LTE is a new type of technology where data uploads and downloads occur on the same frequency, but at different times.