China remains the key driver of the ecosystem, but new TDD spectrum will be allocated in most regions of the world during the current wave of 4G auctions, and carriers everywhere are considering how it could be harnessed to augment their capacity. For instance, some European operators expect to deploy TD-LTE as a second wave when their FDD capacity starts to get strained, or to use the TDD band for a separate layer of small cells, within a HetNet, or for a specific function such as machine-to-machine services.
Other operators, like Orange and AT&T, plan to use unpaired frequencies to add to their initial LTE network capacity, using supplemental downlink techniques. Then there are carriers which already have access to TDD bands, often because they have Wimax businesses, Clearwire being a famous example.
Most of this spectrum is in 2.3GHz or 2.5GHz, but some players, like UK Broadband, are even harnessing the 3.5GHz band.
This gained new prominence recently when the FCC talked about releasing 100MHz of spectrum here, possibly targeted at small cell networks with global roaming potential. The band is suited to small cells because it support base stations with limited range, and so is generally uneconomic for macrocell rollouts.
Doug Pulley, CTO wireless at chip provider Mindspeed, said in a recent interview with ThinkSmallCell: “This is really nice spectrum to use. Significantly, it is one of the few global bands – and it is TDD everywhere. While it's at the limit of what a macrocellular network could deploy, it's really good at short range/high bandwidth, it will go through walls a little better than the 5GHz used by Wi-Fi 802.11ac. There's also plenty of bandwidth available.