The Global Mobile Suppliers Association (GSA) expects 234 LTE networks will be commercially launched in 83 countries by the end of 2013. The technology is now central to operators’ plans to bring ever more bandwidth-intensive and, hopefully, profitable services to their users.
Initially pitched as a simple software upgrade to existing 3G or UMTS equipment, it’s now apparent that LTE is only a software upgrade for those operators that have deployed the most recent versions of UMTS equipment. All the others will face at least some form of hardware upgrade. Not such a smooth transition after all.
Add to that the fragmentation of approaches to the standard caused by the differences in spectrum allocation in individual countries, and there are several flavours of LTE to consider. In fact, there are now 44 different bands in which LTE is being deployed.
Far from being a unified technology with a standardised global approach to deployment, LTE has become more of a foundation technology that is being rolled out in a series of variants according to spectrum availability and the business model of the deploying operator.
Perhaps the idea of a unified, global standard only exists in the theoretical minds of standards bodies but, as LTE deploys, it seems to be moving further and further from that ideal. That erosion of standardisation has radically altered the business case for LTE and severe challenges now go hand in hand with deployment.
‘LTE is such a complicated thing now because of the way it has been deployed,’ says Stirling Essex, a director of Cambridge Wireless and Espansivo. ‘It is a world system but that makes it harder for smaller companies to enter the market. If you didn’t want to compete with GSM, you could compete in CDMA or TETRA or something else, but LTE is a big guy’s game.’
Allan Oakman, services and solutions director at Huawei, would prefer to see spectrum standardisation in at least some of the bands and sees 1800MHz as the most likely band for supporting roaming. ‘So far, Japan, South Korea and the US lead the market, accounting for about 80%-90% of global LTE users,’ he says.
‘However, the LTE markets in Europe and Asia, as well as the Middle East, are starting to rise up the ranks. Also, nearly 38% of commercial LTE networks have been launched on 1800MHz spectrum. Almost all regions of the world are considering 1800MHz as the prime spectrum for LTE deployments, which is important for international LTE roaming.’
If that continues, much of the concern regarding roaming capability will be addressed, with 1800MHz becoming a standard roaming band and the array of other spectrum used to support domestic users.
Absence of voice support also presents operators with challenges. VoLTE (Voice over LTE), the technology that will enable voice for LTE, is still almost a year away from commercial deployment in even the most advanced LTE markets. LTE was conceived to be an all-IP data bearer but standards writers seem to have forgotten that voice, while commoditised, remains the killer app for users.
‘From a data standpoint, roll-outs are well underway,’ says Leslie Ferry, vice president of marketing at Broadsoft. ‘From a communications standpoint, VoLTE in late 2013 or 2014 is the expectation.’
Essex thinks that has been a glaring omission. ‘I was very surprised that voice hadn’t been taken on board in the standards,’ he adds. ‘The error was assuming LTE was just going to be about data because voice will always be important. That caught specification writers on the back foot.
‘VoLTE is the obvious thing but bandwidth efficiency isn’t as good as GSM, so it’s not a bandwidth efficient way of introducing voice. Something has gone wrong there and not been very helpful. Companies urgently need to resolve this and semi-temporary solutions are being deployed, urgent need is driving expedient solutions but the industry needs proper solutions,’ says Essex.
FDD vs TDD
All isn’t perfect on the data side either. At the most simple level, basic decisions such as what type of LTE to deploy need to be made. Broadly, there are three choices: frequency division duplexing (FDD), time division duplexing (TDD) and the converged FDD/TDD version.
‘F is for frequency and T is for time,’ explains Steve Bowker, CTO of Aircom International. ‘It’s about the way you divide spectrum for the uplink and downlink. With FDD you have different bands done in pairs dedicated for uplink or downlink transmission. TDD is just a single band of spectrum and at one instant in time transports uplink and at another transports downlink traffic.
‘There are a number of reasons for each approach. TDD is also interesting where the environment has more downlink than uplink. Unbalanced spectrum can only be used for TDD and it is usually cheaper [to acquire],’ he says.
Mark Altshuller, CTO of the broadband wireless access division at Alvarion, thinks the market is less starkly divided. ‘The majority of the LTE industry is focused on the mainstream cellular market, where big early comer operators such as AT&T, Verizon Wireless (USA) and KDDI (Japan) have deployed LTE networks since 2011. This market is FDD,’ he says.
‘However, most operators worldwide are only doing trials with LTE and continue to invest in HSPA (high-speed packet access). The leading vendors are big giants: Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Huawei and ZTE. In parallel, China Mobile is leading a TDD-LTE version of LTE.
‘However, the real commercial deployment is delayed,’ continues Altshuller. ‘China Mobile is continuing in wide pre-commercial deployments in China. In this TDD-LTE China Mobile activity all the Chinese vendors are involved – Huawei, ZTE, Datang, Potevio – as well as international companies including NEC and all the giant vendors.’
The technologies serve different operator requirements, but manufacturers are building reference designs that address both. ‘There are notable differences between TDD-LTE and FDD-LTE; particularly in terms of uplink and downlink transmission,’ explains Paul Beaver, products director at Anite.
‘FDD-LTE makes use of two carrier frequencies, assigning an individual frequency for uplink and downlink respectively, transmitting and receiving data simultaneously. Conversely, TDD-LTE makes use of a single carrier frequency to support uplink and downlink transmission, but the time for transmitting and receiving is always different. However, TDD-LTE is not a technology that is superseding FDD-LTE. Each technology has its own unique set of advantages,’ says Beaver.