Dr Doug Pulley, CTO Mindspeed, highlights progress on TDD mode for small cells

Dr Doug PulleyI met with "Dr Doug" at LTE World Summit last month where Mindspeed were demonstrating their high performance LTE chipset working with commercially available LTE USB dongles. He highlighted a lot of recent activity in the TDD mode for LTE, which he believes will be adopted as a truly global standard. He explained the current market status, how Mindspeed is involved and is excited about a potential new opportunity in the US.

A quick recap on TDD

Up to now, TDD mode has been associated with China. TDD mode uses only a single spectrum band rather than requiring a paired frequency band, and can operate asymmetrically with a higher proportion of downlink traffic – ideal for today's web traffic and cloud services.

There are two different TD standards:

  • For 3G, the TD-SCDMA mode is used by China Mobile but is not used outside China.
  • For LTE, the TD-LTE mode is firmly embedded in the LTE specifications and has already been deployed outside China and, as Doug explains, has a growing importance.

A lot of TDD market activity

"Although 3G TD-SCDMA is not used outside China, we're seeing wider take-up for TD-LTE. Softbank in Japan are actively deploying it on a large scale for capacity offload. It's also being used in India, where there is a strong expectation that WiMAX carriers will migrate to it and so it will become a truly global standard. We expect the same for Clearwire in USA. In Europe the 2.6GHz licenses allocate a chunk specifically for TD. Indeed, it seems to be already more widespread outside China where it is in a trial stage.

"Part of the reason for this is that the TDD mode has already been incorporated into the chipsets for LTE devices, from USB sticks to smartphones and tablets. The services, protocols and standards above the physical layer are as similar as practical for TDD and FDD modes. As always, device availability is key.

"In many ways, LTE is not as big a jump from 3G as was the migration from 2G through GPRS to 3G. The many challenges for component technologies for RF and baseband had been tackled for WiMAX. Network operators are already familiar with running data networks, where LTE provides faster speeds and higher spectrum efficiency."

How is Mindspeed involved in TD-SCDMA?

"Picochip (now part of Mindspeed) was involved at an early stage to define TD-SCDMA specifications for femtocells . We continue to be involved in ongoing activities to refine the standard commercial product requirements, such as the number of users, throughput etc."

"Our chipset reference design has been incorporated into the majority of the eight or so commercial TD-SCDMA products available today. It remains to be seen in what form China Mobile will deploy TD-SCDMA femtocells, but the technology has already been through a successful trial period and is commercially available in the Suzhou region.

"Device availability is critical. Apple's rumoured decision to incorporate TD-SCDMA into the next iPhone 5 together with Samsung's wide range of TD-SCDMA devices will dramatically increase consumer interest. TD-SCDMA femtocells would surely have a role to play in customer satisfaction too.

How does that affect TDD-LTE?

"A combination of Mindspeed's market leading LTE baseband chipset and Picochip's TDD expertise has allowed us to offer a robust TDD-LTE reference design to the market. Our chipset can support both modes (FDD and TDD).

"Our recent press release announced a join development lab with China Mobile that covers several wireless technologies including both 3G and LTE. Mindspeed continue to retain a development centre in Beijing which will be closely linked to this partnership.

How does the wide choice of spectrum for TDD affect the solution?

"Small cells require an RF transceiver to convert the baseband signal to and from the RF antenna. The same suppliers and often the same components can be used for TDD mode, albeit with a different hardware configuration. (The point here is TDD is actually loads easier than FDD to put anywhere) I don't see any problem with small cell technology (including TDD mode) being adapted for use anywhere in the common wireless frequency bands from 400MHz through 4GHz.

"We've worked more closely with a small number to create a more tightly integrated and tested solution which form part of our reference designs, such as the one we are demonstrating here today. The wide choice of spectrum allocated for TDD mode will require more adaptable RF products, and we've seen further developments of those to meet these needs.

Do you see other opportunities for TDD elsewhere in the world?

"The recent FCC announcement in the US about releasing 100MHz of spectrum at 3.5GHz is very interesting. 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.

"The rules about how this spectrum could be allocated and used aren't yet clear. It could be standalone or possibly use carrier aggregation with other bands which could be quite interesting to existing spectrum holders. Perhaps it will be positioned somewhere between the "free for all" Wi-Fi and completely independent cellular networks."

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