If it gets more money, Clearwire LLC (Nasdaq: CLWR) could be one of the first operators in the world to deploy Long Term Evolution Time Division Duplex (LTE TDD), so we thought it was a good time to remind you what this 4G technology is and how it is different from today’s Long Term Evolution (LTE) networks. (See Clearwire Goes It Alone With Faster 4G.)

The basics
The key difference between LTE TDD, sometimes also known as TD-LTE, and the frequency division duplex (FDD) version more common today is in what spectrum the technology is deployed in and how the signal is transmitted. TDD technology uses a single channel and a timed signal to separate uploads and downloads. FDD systems have two channels of paired spectrum separated with a guard band for uploads and downloads.

Advocates of TDD technology suggest that the single channel makes the network more bandwidth-efficient. In the real world, however, operators tend to deal with the spectrum they were dealt through acquisition or auction. Therefore, Verizon Wireless is running FDD LTE on its 700MHz holdings, whereas — as AnandTech points out — Clearwire has enough 2.5GHz spectrum to consider various TDD deployment tactics while continuing to run its existing WiMax network. (For some history on this, see McCaw’s Mystery Millions and A Clearwire Timeline .)

The devices
IP-based TDD devices are ideal for fast data downloads; indeed, Clearwire claims up to 120 Mbit/s down in tests in Phoenix. In the future, this will likely mean digital cameras, video recorders and MP3 players using the technology, as well as handsets, tablets and PCs. For now, vendors like Huawei Technologies Co. Ltd. are introducing multi-modal TD-LTE data cards that can support a variety of 3G and 4G technologies. (See Huawei Readies LTE TDD Device.)

The players
Huawei and other Asian vendors like Samsung Electronics Co. Ltd. (Korea: SEC) and ZTE Corp. (Shenzhen: 000063; Hong Kong: 0763) loom large as LTE TDD device suppliers now, largely because the technology has been spearheaded by China Mobile Communications Corp. and is being tested on the mainland and growing in popularity as a next-generation option in India. Alcatel-Lucent (NYSE: ALU), Ericsson AB (Nasdaq: ERIC) and Nokia Siemens Networks have all participated in various trials as well. (See China Mobile Trials LTE TDD With NSN and Market Spotlight: LTE TDD.)

The future
If it raises the $600 million it needs to deploy a TDD LTE overlay in the U.S., Clearwire could be among the first operators to bring the technology online in the world. ABI Research currently tracks 28 commercial FD-LTE networks, but says that no TD-LTE network has yet gone live. (See No TD-LTE Network has Gone Live Yet.)

Clearwire’s shift to LTE is not just a move away from WiMAX, but it cements Clearwire’s shift in strategy from being a retail operator to a wholesale provider — a shift that has been coming for a while. In this week’s announcement Clearwire said that it would sell its LTE network not just to partners such as Sprint, but also to anyone that wants such service.

This isn’t a new field for Clearwire, which has sold wholesale WiMAX access to the cable providers that funded it and to retailers such as Best Buy, but as it moves to LTE and closes down retail locations this wholesale strategy is becoming more clear. And it’s also setting Clearwire up as an odd operator out in the industry as many other cellular companies try to sell services as opposed to pure capacity. However, in Clearwire CTO John Saw’s view “LTE is all about capacity.”

Building the LTE wholesale network.
During the call to discuss the transition to LTE, Clearwire emphasized that it would employ a version of LTE known as LTE-Advanced. This refers to releases 10 and 11 of the LTE technology, but Release 10 was just frozen in March and the gear isn’t out yet for it. What Clearwire hopes to deploy if it gets $600 million or so from investors, is LTE Release version 8, and will be upgradable to later releases that are actually LTE-Advanced. The key elements for Clearwire, and the reason it’s using the LTE-Advanced lingo is because it’s using some features built into the version of the standard that are associated with LTE-Advanced. Plus, since LTE-Advanced was the “real 4G” according to the ITU, I’m sure there will be some marketing spin on this later.

Saw says that Clearwire plans to take advantage of features that allow an operator to group different spectrum bands together to create a virtual pipe as well as features known as MIMO that allow multiple antennas on the device and base stations to boost upload speeds. Those two things are the most important reasons Clearwire has switched to LTE.

For the deeply nerdy, it’s using TDD-LTE (GigaOM Pro sub req’d), a different variation from Verizon and AT&T, which are deploying FDD-LTE. The difference is that Verizon and AT&T must deploy their spectrum in equal clumps going upstream and downstream, but Clearwire (and anyone using TDD-LTE) can allocate their spectrum unevenly, with a greater proportion going to downstream and less for upstream use.

Upgrading the existing infrastructure will be easier in cities where Clearwire has recently deployed WiMAX said Saw: “Adding LTE to those markets is as simple as plugging in another line card on the cell site.” In some areas Clearwire may have to install new radios and in general it will upgrade the core network and backhaul networks, all for that estimated $600 million mentioned.

What happens to WiMAX?
But amid the Clearwire move to LTE, what happens to the existing WiMAX network? Saw says it will remain intact. The company will use 20 MHz of spectrum for LTE and reserve 10 MHz for WiMAx and operate both networks side-by-side. In most cases the equipment is designed to do just that.

It all depends on devices.
By managing multiple networks, even if it can reuse some of the same equipment, Clearwire avoids the challenge of clearing spectrum and getting people to transition to new devices. But devices will still be a key element in Clearwire’s success with LTE. Because it plans to offer wholesale access, Clearwire will have to rely on device makers to put radios into their products that are TDD-LTE compliant and that work in the 2.3 to 2.7 GHz spectrum band that Clearwire is using. Wireless radios, with their associated IP aren’t cheap, so the key is getting them both inexpensive, but also small enough and power efficient enough that a tablet using Clearwire’s LTE won’t cost a lot more and will still have decent battery life.

Clearwire has teamed up with China Mobile and Vodafone to promote a world band in its spectrum for TDD-LTE as part of the Global TD-LTE Initiative. Saw claims that the members of the GTI represent hundreds of millions of potential subscribers and members are deploying networks this year. He didn’t provide details but said Qualcomm, Broadcom and others are planning chips for the band. When I asked if the chips were sample and if we could expect a 12-18 month time frame before such devices hit the market, he said pre-commercial devices are already available. That’s not a clear answer so figuring out when devices that could use the network will arrive is still an open question. Qualcomm recently made its own spectrum play in India in the 2.3 GHz band suggesting it does have plans to support it with radios.

Clearwire’s gamble may all depend on cheap chips
Clearing up Clearwire’s business model.
With its plans to deploy LTE only in areas with high demand, Saw explains that Clearwire’s business model will be built around providing capacity offload. This is something other carriers are doing with Wi-Fi today, but having a more mobile option clearly has benefits in areas where one can’t find a hot spot. By offering LTE it would compete against the planned wholesale LTE network from LightSquared, which wants to use a mix of satellite and terrestrial capacity from Sprint to offer service.

Clearwire is up against LightSquared’s planned satellite network.
Saw bristled when compared with LightSquared pointing out that the company is not only in a fight with the GPS industry over interference, but it also doesn’t have a network. “It’s hard to speculate about LightSquared. It has zero spectrum and no network, and even if they, by some miracle, get their lower 10 MHz approved, that’s a very thin network compared to having 160 MHz in the top 100 markets,” Saw said.

And once again we’re back to capacity, which is what Clearwire has to hope matters. Even with its WiMAX network, Clearwire was hitting the capacity angle hard, because it had those vast spectrum reserves. And while technologists will argue about the poorer spectrum propogation characteristics of the 2.3 and 2.7 bands (they don’t go through buildings easily), that’s the cards Clearwire was dealt (or bought, cheap at auction actually). So the question for Clearwire investors and partners becomes whether or not Clearwire can build out an LTE network designed to offer mobile broadband in areas where carriers and other providers need service and whether that business is big enough to support the costs of building and running such a network.

Sales of HTC’s LTE-enabled smartphone, the HTC ThunderBolt, have been strong since the device was launched by Verizon Wireless in the US in mid-March, positioning HTC ahead of its major rivals in the development of LTE phones, according to industry sources.

Sales of the HTC ThunderBolt reached about 260,000 units in the first two weeks after the launch of the gadget, according to an estimate of sources at the supply chain in Taiwan.

Although Verizon has also signed cooperation agreements with Samsung Electronics, LG Electronics (LGE) and Motorola Mobility for the launch of other LTE phones, Samsung’s model, the Droid Charge, will not be launched until the end of this month, before LGE launches its LG Revolution.

Motorola’s LTE phone, the Droid Bionic, is reportedly to be available in the second quarter but could be delayed to the third, the sources indicated.

With Verizon having a total of 565,000 LTE subscribers at the end of the first quarter, sales of the ThunderBolt accounted for nearly 50% of all LTE-enabled devices, which also included tablet PCs, notebooks and broadband routers sold through Verizon networks in the quarter, indicated the sources.

However, the sources also noted that Samsung was ahead of HTC with regards to the number of LTE phones that have been launched. In addition to the forthcoming Droid Charge, Samsung have already launched two LTE phones, the Craft and Galaxy Indulge, in cooperation with US-based carrier MetroPCS.

Verizon Wireless will redouble its Long Term Evolution (LTE) efforts in 2011 as it reveals that its first 4G smartphone — the High Tech Computer Corp. (HTC) (Taiwan: 2498) Thunderbolt — was a best seller in the first quarter of 2010. (See Verizon Reports Q1.)

The carrier plans to cover more than 185 million potential subscribers with its LTE deployment by the end of the year. The network already offers consumers average download speeds of 5 Mbit/s to 12 Mbit/s over the air in many major U.S. cities.

“By the end of the year we plan to be in about 175 markets,” Verizon Communications Inc. (NYSE: VZ) CFO Fran Shammo said in the first-quarter earnings call. Verizon had previously said that it expects to be in around 147 metropolitan markets by the end of the year. (See Verizon Sets More LTE Launches.)

One of the motivating factors may be the success of the operator’s first 4G phone, the HTC Thunderbolt. The company sold 260,000 Thunderbolts in two weeks when it went on sale, with more than 500,000 4G devices, such as data cards, activated overall during the quarter.

Verizon sold 2.2 million Apple Inc. (Nasdaq: AAPL) iPhone 4s for the two months it was available on the Verizon network during the first quarter. Rival AT&T Inc. (NYSE: T) activated 3.6 million iPhones in the first quarter, 33 percent more than this time last year. (See AT&T’s iPhone Growth Continues.)

Overall, Verizon added 1.8 million total new connections, including 906,000 retail customers on monthly contracts and 897,000 wholesale and other connections. The operator now has 88.4 million retail customers and 15.6 million wholesale and other connections in total, including machine-to-machine (M2M) links.

The influx of new smartphones onto the Verizon network has once again boosted its wireless data revenues. Data revenues for the quarter were US$5.5 billion, up $1 billion or 22.3 percent year-on-year, which represents 38.1 percent of all service revenues. Total wireless revenues were $16.9 billion, up 10.2 percent year-on-year.

The company revealed its plan while announcing the first demonstration of its LTE network, scheduled to launch in July.

SK Telecom also said it would apply Coordinated Multi-Point technology to the network when up and running in a bid to prevent base station interference, and “pursue early development” of LTE femtocells.

A pre-existing network of 2G 800MHz repeaters will also be used to boost the new network’s signals.

SK Telecom in January chose Samsung, LG-Ericsson and NSN as its LTE vendor partners, and earlier that month revealed the results of field trials with China Mobile.

SK Telecom is South Korea’s largest mobile operator. The company will be going head to head against LG U+ – which also plans to launch LTE in July – and KT, which has its own LTE ambitions.

Hi3G Access AB ’s plan to roll out dual-mode Long Term Evolution (LTE)/Long Term Evolution Time Division Duplex (LTE TDD) networks in Sweden and Denmark signals the rise of a hybrid deployment model using both flavors of the next-generation mobile technology. (See ZTE Scores LTE TDD/FDD Deal .)

The dual-mode development in the Nordics using LTE’s kissin’ cousin technologies — FDD and TDD — also provides further confirmation that LTE TDD is not only for the Chinese and Indian markets. Rather, Hi3G’s announcement shows that LTE TDD can be used to complement the FDD flavor of LTE in a hybrid model in regions outside the Asia/Pacific to meet capacity and coverage requirements in 4G networks. (See Europe’s LTE TDD Creep, Global TDD Initiative Launched at MWC 2011, China Mobile Opens Up on LTE TDD Trials and Analyst: LTE TDD Will Reach India in 2011.)

And Hi3G is not alone. Polish operator Aero 2 Sp. z o. o. could actually be the first mobile operator to launch a dual-mode FDD/TDD network using 2.5GHz TDD spectrum, which is expected to become operational this year, according to Heavy Reading Senior Consultant Berge Ayvazian.

In his recent White Paper, “LTE TDD Operator Business Case & Adoption Forecast,” Ayvazian analyzes this hybrid deployment scenario for operators that already have, or plan to acquire, TDD spectrum.

“With a limited supply of appropriate LTE FDD spectrum, mobile operators with access to TDD spectrum are driving hybrid LTE FDD/TDD network development in Europe, Eastern Europe/CIS, and Middle East/ Africa beginning in 2012,” said Ayvazian.

He notes that a practical scenario for a country such as Germany would be to use LTE FDD for national and outdoor coverage and then use LTE TDD in urban and densely populated suburban areas where high capacity is needed. German operator E-Plus Service GmbH & Co. KG will look at the use of LTE TDD in an upcoming trial with equipment from ZTE Corp. (Shenzhen: 000063; Hong Kong: 0763). (See E-Plus to Trial LTE With ZTE .)

The “ideal” scenario from a cost point of view, according to Ayvazian’s White Paper, is for an operator to use LTE TDD to deploy picocells and femtocells to add capacity and boost indoor coverage, complementing LTE FDD macrocells in high-traffic urban areas.

Vodafone Group plc (NYSE: VOD) showed another use for the TDD-based technology at the Mobile World Congress in February with a demo showing LTE TDD used for backhaul for an LTE small cell deployment. (See MWC 2011: Vodafone Demos LTE TDD for Backhaul .)

Why this matters
While China and India will likely drive the biggest volumes of LTE TDD, its emergence on the mobile infrastructure technology scene presents many opportunities for operators worldwide to use their TDD spectrum (normally used for WiMax deployments). The hybrid models noted here show that operators are already starting to think about how to take advantage of this new option for adding 4G coverage and capacity.

China’s telecom ministry has stated that large-scale commercial deployment of LTE in the country will take between 3- 5 years.

This is the first time the ministry of industry and information technology (MIIT) has provided an official timeline for the country’s move to LTE.

Minister Miao Wei further told China Daily that significant rollouts were not to be expected until 2014.

China has been actively campaigning to have its homegrown LTE standard, TD-LTE, accepted globally. But most mature markets are supporting the more common FDD-LTE.

Miao declined comment on whether China would allow multiple LTE standards.

But 3G now looks set to remain the staple for China’s carriers until 2014.

The potential for 3G in China may not yet have been reached, according to figures from the MIIT. The ministry had anticipated 60 million 3G users in the country by the end of last year, but numbers stood at 47 million. Growth in 3G subscribers had largely been hampered by the lack of affordable 3G-compliant handsets.

Kevin Wang, an analyst at IHS iSuppli, told Telecom Asia that China’s carriers were likely to continue investing in 3G in order to attract users and improve ARPU.

“Today, there is no strong need for LTE networks. LTE devices are extremely limited in availability and 3G and 3.5G networks are capable of supporting most mobile applications,” says Wang.

Research from IHS iSuppli indicated China Mobile, which helped develop TD-LTE, would be likely be the first carrier to go forth with 4G, followed by China Telecom and China Unicom. According to Wang, China Unicom had the least incentive for LTE due to its status as China’s sole retailer of Apple’s iPhone.

TD-LTE trials are now underway in six cities in China.

NEW YORK (TheStreet) — Apple’s(AAPL) Verizon iPhone — the one you’ve been waiting for — will keep you waiting another year.

The iPhone 5, due out sometime this summer, will not be an LTE 4G phone, says Telecom Pragmatics analyst Sam Greenholtz, who has talked with people close to the matter.

“The next iPhone — the iPhone 6 — is an LTE version under development now with production aimed for a June/July launch next year,” Greenholtz said, citing his sources. Checks with several industry insiders and analysts also support Greenholtz’ information. Apple did not comment, and Verizon(VZ) said it had “nothing to announce.”

Not only will the lack of a 4G Verizon iPhone likely disappoint everyone who passed on the iPhone 4 in hopes of buying one that would run on Verizon’s fastest network, it also keeps Apple in the middle of the pack behind more muscular Google(GOOG) Android phones. Motorola(MMI), HTC and LG are all prepping 4G LTE Android phones, which are among the 10 LTE devices coming to Verizon as early as this spring.

“I don’t think Apple saw this level of hardware competition when they locked in iPhone 5 specs,” says MKM Partners analyst Tero Kuittinen, referring to Apple’s component decisions.

The iPhone 5 is expected to be a world phone designed to work on European networks, the HSDPA-Plus network that AT&T(T) has dubbed 4G, and on Verizon’s 3G network.

Other improvements include a possibly bigger 4-inch screen, a dual-core processor and, as we first reported last year, an 8-megapixel Sony(SNE) camera.

“They are basically playing catch up,” says Rodman Renshaw analyst Ashok Kumar, referring to the features that are, or have been, common to phones from top-tier rivals.

The news comes as Apple prepares to launch a new version of its tablet, the iPad 2, next week. CEO Steve Jobs, who is out indefinitely due to illness, is not likely to be the master of ceremonies. And his absence from the event will once again revive questions of how the company can continue its phenomenal success streak without him.

The delayed LTE iPhone may be the first big test of acting-chief COO Tim Cook’s persuasiveness.
To some analysts, though, the lack of LTE in the iPhone 5 isn’t a huge problem.

“It’s too early to push LTE now; it’s too much cost and too much of a sacrifice on battery life and it doesn’t give you any great advantage at this point,” says independent analyst Chris Umiastowski, formerly with TD Newcrest.

Still, for Apple fans who must have the latest and greatest, the LTE 4G delay will not come as pleasant news. And unlike Jobs, who would somehow find a way to turn this news positive, Cook could have a harder time smoothing it over.

Despite the much-hyped higher surfing speeds that LTE looks set to bring, the clear case for the technology from an operators’ point of view lies in the potential opportunity to reduce the cost per bit.

The LTE wave in the Asia Pacific is being led by Japan, Hong Kong, South Korea and Australia, which will each see at least one commercial LTE rollout by year-end.

However, the technology’s progress in the rest of the region could be hampered by simple economics, says Foong King Yew, a principal analyst at Gartner.

“The pace of change is very rapid, with carriers expected to deploy new technologies within a shorter span of time. Think the early transitions from WAP to GRPS to EDGE to 3G and now, LTE,” says Foong. “Each change involves investment. How can they ensure they get reasonable returns?”

Carriers’ potential LTE woes could also stem from the ‘uncertainty of the charging mechanism’, says Foong. “With many carriers now expected to give away more for less due to competition, many may have to take another look at flat rate data plans for mobile broadband, as this will have a direct impact on the decision to invest in LTE.”

While much of an operator’s existing infrastructure can be reused in the move to LTE, technical challenges exist for 2G/2.5G/3G providers to maintain the quality of service on their networks while the LTE upgrade goes on.

“Carriers need to put in place the necessary bandwidth in the backhaul, with the high data usage expected from LTE networks,” says IDC’s senior research manager Alex Chau.

Long-Term Evolution (LTE), the wireless broadband technology that is being rolled out on networks around the world, is heading past 1 Gbps speeds, thanks to Japanese carrier, NTT DoCoMo. They have recently received spectrum in the cities of Yokosuka and Sagamihara to start testing what they call a 4G LTE Advanced network.

LTE Advanced gets 1 Gbps on the downlink and 200 Mbps on the uplink. In March 2010, Chinese equipment maker Huawei showed off 1.2 Gbps LTE Advanced. In December, NTT DoCoMo launched its LTE network, which currently offers download speeds of 37.5 Mbps and upload speeds of 12.5 Mbps.

As a technology, LTE is likely to replace the HSPA set of technologies, though many network operators (including T-Mobile USA) believe that, for now, HSPA has enough headroom to keep up with LTE. Today, Ericsson announced that it had come up with a new HSPA technology that allows for 168 Mbps downlink and 24 Mbps uplink speeds.

Ericsson claims that we are seeing speeds go up on HSPA because of the combination of three different technologies: 64 quadrature amplitude modulation (QAM) or higher order modulation, MIMO dual-antenna technology and multi-carrier technology. (Learn more about how Ericsson does it.)

Ericsson claims that it has set a new world record using commercial network equipment, and the company has been pushing the envelope on HSPA technology over the past few years. In 2009, Ericsson launched 42 Mbps (downlink) HSPA in trials, and we saw the commercial deployment of that technology in 2010. Last year it trialed 84 Mbps downlink speeds and expects commercial upgrades in 2011. By 2012 it won’t come as a surprise to me when we see 168 Mbps downlink speeds hit the HSPA networks.

In December 2010, Ericsson’s long-time rival, Nokia Siemens Networks announced that it had come up with a way to give HSPA even more of a boost. They proposed a new wireless broadband standard that could offer peak download speeds of 672 Mbps.