Vividwireless 4G a backup: Telstra

High-end spectrum, such as that obtained by Optus in its Vividwireless buy, will be useful to support long-term evolution (LTE) services in lower-end spectrum bands, according to Telstra's chief technology officer Dr Hugh Bradlow.

Speaking at the Communications Alliance's Broadband and Beyond 2012 conference in Sydney today, Bradlow said that telcos realistically only have approximately 3GHz of spectrum in total available for the deployment of mobile networks. He said that as demands on networks rise and more spectrum is required, telcos will be forced to find a way to maximise the available spectrum, and to use all the spectrum they can.

In addition to technologies such as femtocells, Bradlow said that telcos would move into high-end spectrum bands, such as the 2.3GHz band, and deploy time-division duplex LTE (TD-LTE) to supplement the frequency-division duplex LTE (FD-LTE) networks.

"By the laws of physics, we only have about 3 Gigahertz of spectrum available to us. There's going to be huge pressure on utilising that spectrum as efficiently as possible, which is one of the reasons why people are interested in TD-LTE, which will be built in to LTE systems," he said.

"It's not that [it] is a better technology; in fact, it is inferior to FD-LTE, but it actually is just a way of utilising every scrap of spectrum you can get a hold of."

FD has been the preferred LTE type for telco networks in Australia, with both Telstra and Optus deploying FD-LTE in the 1800MHz spectrum. It works by separating uplink and downlink into separate blocks in the spectrum band. However, while this provides greater uplink speeds, it uses more spectrum.

For TD-LTE, the transmission is done in a single block of spectrum, but uplink and downlink transmissions are timed between one another. This means that download speeds can be brought up, but it is at the expense of the upload.

Both NBN Co and Vividwireless have high-end spectrum bands reserved for the deployment of TD-LTE networks. Earlier this week, Optus announced that it would buy Vividwireless and secure its 2.3GHZ spectrum licences for the deployment of a TD-LTE network that would let Optus build a hybrid FD-LTE and TD-LTE network.

Bradlow said today that although 2.3GHz is "not the world's most efficient spectrum", it is still useful for a TD-LTE network.

"You can offer LTE services in it," he said. "You could use it as a customer-access technology. You've seen the Chinese push hard on it."

Bradlow also said that high-end spectrum bands would be useful for backhaul for mobile networks.

The chief technology officer told the audience that as demand for mobile network services grows, latency will be key to ensuring that customers are able to use their mobile services. He said that although there has been a push for more public Wi-Fi access points used to offload network traffic, he doesn't think that this is the solution.

"Unfortunately, Wi-Fi still suffers from the problem of being public spectrum and not having interference management," he said. "Your latencies are pushing up due to the lack of interference management. Wi-Fi is quite popular as an offload system ... but having access to a signal is not good enough. You need signal with throughput."