Ever since the International Telecommunication Union created its IMT-2000 family of 3G technologies ten years ago, 3G has come in two basic forms: FDD and TDD. FDD offered separate spectrum bands for uplink and downlink traffic, while TDD offered upstream and downstream traffic on the same band.
But while FDD-based technologies like W-CDMA and CDMA2000 dominated 3G rollouts (the former more so than the latter), TDD-based TD-CDMA remained generally unloved except by vendor IPWireless and its small customer base, while the other TDD option, TD-SCDMA, was China's homegrown technology that most industry players regarded as a China-only technology with no realistic chance of ever seeing deployment outside of China, although Taiwanese operators FarEasTone and Vibo Telecom began small-scale trials of TD-SCDMA late last year.
However, TD-SCDMA - which went fully commercial in China last year and is now available in 238 cities from China Mobile - is suddenly looking primed to go international in the form of its next-gen version, TD-LTE, which has the full backing of the 3GPP as part of its overall LTE standards effort. That doesn't automatically guarantee greater operator interest in TDD outside of China - where, like its 3G predecessor, TD-LTE is guaranteed a home. But the past couple of months have seen a flurry of announcements around Asia regarding TD-LTE's viability.
Not unexpectedly, China Mobile signed a deal in April with FarEasTone to jointly develop a TD-LTE trial in Taipei. Much more surprising was Qualcomm's announcement last month that it would enter the long-awaited spectrum auctions in India to bid for broadband wireless access (BWA) spectrum in the unpaired 2.3-GHz band, with the intention of using it for TD-LTE, rather than Wimax. Later that month, Japan's Softbank Mobile - which gained access to 2.5GHz TDD spectrum in March after acquiring a stake in failing PHS operator Willcom - said TD-LTE was definitely on the table as an option. And perhaps tellingly, as TDD vets like Huawei, ZTE, Motorola and Nokia Siemens Networks have been issuing progress reports on TD-LTE developments, Ericsson announced a tie-up with Datang Telecom to integrate Datang's TD-SCDMA RAN gear into its 3G portfolio, ostensibly to beef up its China business, but also to develop TD-LTE solutions.
Such is the sudden excitement over TD-LTE that it's not only expected to see rapid take-up once commercial deployments starting next year, but will also comprise a sizable chunk of the entire LTE market by 2014, says Mike Wang, NSN's general manager for Taiwan, Hong Kong and Macau.
"It took W-CDMA six years to reach 100 million subscribers, but LTE will hit that in four years, and we project that TD-LTE will account for 40% of LTE subscribers by that time," he told Wireless Asia.
What's going on here? What's TD-LTE got that its TDD ancestors didn't? Part of the answer lies in spectrum availability and changing market dynamics. However, a major key to the puzzle is, ironically, LTE's arch rival Wimax, which is not only helping make the business case for TDD in general, but - even more ironically - could serve as the platform for future TD-LTE deployments.