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.

Sprint Nextel Corp. (S) Chief Executive Officer Dan Hesse said the company remains committed to partner Clearwire Corp. (CLWR) and “every option” for its future involves the wholesaler and its fourth-generation WiMax technology.

Hesse said he’d like to see Sprint do more network sharing with Clearwire, which sells capacity from its own network to Sprint and other carriers. He spoke today at the Deutsche Bank AG Media & Telecom Conference in Palm Beach, Florida.

Deutsche Telekom AG (DTE) has held talks to sell its T-Mobile USA unit to Sprint in exchange for a major stake in the combined entity, according to people with knowledge of the discussions.

Hesse declined to comment on speculation about any such transactions.

Clearwire Corp. has abandoned its retail strategy to focus on being a wholesale network provider of fast wireless service, said people familiar with the matter, opening the door for additional investment in the struggling company by Sprint Nextel Corp.

The shift represents a victory for Sprint Nextel, the No. 3 U.S. wireless carrier by subscribers, which owns a non-controlling majority stake in the next-generation wireless-service provider and relies on the company’s 4G network to service its customers.

Sprint has long argued that Clearwire should spend its limited capital on finishing the expansion of its network, but Clearwire has insisted on maintaining an independent retail strategy that competes with the Sprint brand.

That strategy has been increasingly difficult to maintain as cash-strapped Clearwire has struggled to raise additional funds to finance the completion of its 4G wireless network. Now, Clearwire’s goal is to get the company cash flow positive as quickly as possible, said one person familiar with its thinking. The person added it could take 12 to 18 months to achieve that goal.

The company, which was founded by cellular pioneer Craig McCaw, currently has enough funds to continue operating through the end of the year, but that forecast depends on how quickly it is able to build out its network.

At the end of the third quarter in 2010, Clearwire said its network covered 100 million potential customers, and that it planned to cover 120 million people by the end of 2010. Credit Suisse analyst Jonathan Chaplin said Clearwire promised to reach 200 million people in its original plan. “Everyone always expected them to go to 200 million,” said Mr. Chaplin.

Clearwire will continue to maintain its current retail operations and has no plans to shut down its 140 stores at the moment, said a person familiar with the matter.

The strategic shift could lay the groundwork for an infusion of cash from Sprint into Clearwire down the line, although there are currently no plans to do so, said people familiar with the matter. Clearwire needs billions of dollars to finish building its nationwide wireless network.

Clearwire’s change of course “gives Sprint a lot more choices to make in the future” about additional Clearwire investments, another person familiar with the situation observed. And the move is good for Clearwire “because they now have a better chance for survival.”

To raise more money in the near term, Clearwire executives have said that the company is talking to a number of potential investors and considering the sale of roughly 20%, or $2 billion worth, of its wireless spectrum.

In November, the company said it was taking drastic actions to conserve cash, including cutting 15% of its work force, or 630 jobs, as well as suspending some of its commercial and retail operations. Then, in December the company announced that it planned to raise $1.1 billion by issuing debt. Sprint declined to take part in the debt offering.

But the abandonment of the retail strategy suggests that relations between the two companies are finally on the mend after months of feuding.

Clearwire’s retail strategy was viewed by some as an attempt by Clearwire to pressure Sprint to purchase the company in its entirety. But Sprint executives never took the bait, stating publicly that they had no plans to purchase Clearwire. Last fall, Sprint’s then chief financial officer Robert H. Brust dismissed an acquisition, arguing it would be very expensive and too dilutive to Sprint shareholders.

The thaw in relations started in late December when Mr. McCaw stepped down as chairman of Clearwire’s board. He was replaced by John Stanton, who served as a director of Clearwire since November 2008. Benjamin Wolff, a former Clearwire chief executive, was also brought onto the board of directors to replace Mr. McCaw.

Sprint’s network operations and wholesale president Steven Elfman reiterated Sprint’s committment to Clearwire, downplaying speculation that the company might abandon its support for the WiMax network builde

r.

Sprint’s network operations and wholesale president Steven Elfman recently discussed the company’s latest network upgrades while committing to its 4G partner, Clearwire.

Samsung”Our 4G is with Clearwire,” Elfman said, while adding there were no plans otherwise. Clearwire, a Kirkland, Wash. based wireless service provider, has recently secured $1.3 billion in debt financing. It is also undergoing arbitration proceedings against Sprint in a dispute over fees for network use, according to Securities and Exchange Commission filings. Elfman would not comment on the arbitration.

He said Clearwire is a part of the plan for Sprint to roll out multimode technologies, which will allow Sprint bring together multiple spectrum bands on one device.

Sprint’s recently announced deal with Alcatel-Lucent, Ericsson and Samsung includes a $4-5 billion investment will allow for network flexibility and have a net benefit of $10-11 billion. “This will allow us to support devices with multimode chipsets,” Elfman said. Currently, Sprint has 800MHz spectrum, 1.9GHz spectrum and, through its relationship with Clearwire, 2.5GHz spectrum.

The new multimode technology will reduce operating costs by increasing efficiency, reduce Sprint’s carbon footprint and ensure the most effective expansion of 4G. This expansion could mean a shift to LTE, which uses WiMax technology for 4G.

Richard Siderman, managing director at Standard and Poor’s, said during a telecom panel that Clearwire and Sprint were two parties that need one another, as the former takes pressure of the former from a network standpoint.

For the multimode technology, Elfman said Sprint chose Alcatel-Lucent, Ericsson and Samsung based on price, technological capabilities and service. He said they used a reverse auction process.

The new network vision also includes the implementation of push to talk services. The plan, which is slated to roll out in 2011, will roll out on Qualcomm’s CDMA network. It will be more data centric than previous generations, notably the Nextel network, which will be phased out.

He said while no other wireless service providers offer this multimode technology, it’s likely they will all adopt it at some point. “This is not a custom Sprint technology, vendors are offering it everywhere,” Elfman said.

Sprint’s network operations and wholesale president Steven Elfman recently discussed the company’s latest network upgrades while committing to its 4G partner, Clearwire.

Clearwire is launching its 4G WiMax network in New York, San Francisco and Los Angeles before the end of the year, it said Monday.

The service offers speeds similar to Wi-Fi but without the short-range limitations and is already available in 56 markets across the U.S. The upcoming launch will strengthen the network’s reach into America’s largest cities and will likely make the service more attractive to business users who are often on the road.

New York will be get service from Nov. 1, Los Angeles on Dec. 1, and San Francisco in late December, the company said.

Services will be launched by Clearwire under its “Clear” brand and by Sprint, which owns a majority stake in Clearwire. In New York service will also be offered by Time Warner Cable and in San Francisco by Comcast.

Networks in the three cities have been under test for several weeks and last month PC World reported on initial service in San Francisco. The magazine found download speeds of almost 3Mbps and upload speeds of 1Mbps on the test network.

When full service begins users should see download speeds of between 3Mbps and 6Mbps, PC World said.

Clearwire also said it plans to launch 4G service in Denver, Miami, Cincinnati and Cleveland before the end of 2010.

The additional launches means Phoenix will become the largest U.S. city without 4G service from Clearwire/Sprint.

US operator Clearwire has put its spectrum on the auction block as it seeks funding to build out its 4G business.

Aiming to raise $2.5 billion to $5 billion, it has already attracted the interest of rival mobile operators and cable giant Time Warner, Bloomberg reports.

The auction, run by Deutsche Bank, is now in its second round. Clearwire’s majority shareholder, Sprint Nextel, is among potential buyers, along with AT&T, T-Mobile parent Deutsche Telekom and Verizon.

Clearwire’s plans to roll out a nationwide mobile Wimax network have stalled because of a lack of funding. Investors have cooled on the stock because of the imminent launch of LTE.

It said last month it was looking for additional funds to fuel expansion, and has had discussions with potential investors, including T- Mobile, Bloomberg said. The company would need $2 billion by the fourth quarter to fund its network construction.

Clearwire has an average of 120 MHz of spectrum in each market across the US, and is offering to sell 40 MHz. A price of 20-40 cents per MHz per US resident would reach the $2.5 billion to $5 billion mark, according to by Wells Fargo Securities.

The operator received $1.6 billion from investors last year to fund network expansion.

Clearwire Corp. said the three Sprint Nextel Corp. executives serving on its board have stepped down, potentially clearing the path for Clearwire to strike a deal.

Clearwire said Sprint Chief Executive Dan Hesse and fellow executives Keith Cowan and Steven Elfman have resigned from the Clearwire board. A spokeswoman for Sprint said the company plans to appoint independent successor directors in the next few months. In the meantime, Sprint has named its general counsel, Charles Wunsch, as an independent observer to the Clearwire board, the spokeswoman said.

The shift in the board comes as Sprint and Clearwire wrestle the timing and strategy of the deployment of Clearwire’s fourth-generation wireless network, as well as a looming need for additional funding. Clearwire said that the resignations relate to addressing recent changes in antitrust laws, but the move could provide Clearwire added flexibility to pursue a deal.

Sprint, which owns owns 54% of Clearwire, has positioned the 4G network as its primary weapon for attracting and retaining its highest-value customers. Sprint could buy out the remaining stake in the company, because other shareholders such as Comcast Corp. have signaled they are unwilling to provide additional funding.

Clearwire could also pursue a deal with T-Mobile USA, the U.S. wireless arm of Deutsche Telekom AG. Clearwire CEO Bill Morrow has said he was in talks with T-Mobile about a potential resale or investment partnership.

Spokeswomen from Sprint, based in Overland Park, Kans., and Clearwire, based in Kirkland, Wash., both declined to comment on speculation over a potential deal.

Clearwire said the move came “out of an abundance of caution to address questions raised by Clearwire regarding new developments in antitrust law,” such as a recent decision involving the National Football League and how it relates to the Clayton Act. That law bars so-called interlocking directorships in order to preserve competition and avoid possible collusion or exchange of sensitive pricing information between rivals.

Sprint and Clearwire both compete and partner up in the wireless business. Clearwire has launched the first 4G wireless network in the U.S., and Sprint is offering its own service on that network. But the cable companies also resell the service, which competes against Sprint. Clearwire also sells its own 4G services under its Clear brand.

Clearwire’s board structure allows for 13 members, seven of which Sprint has the right to appoint. The remaining four independent Sprint appointees to the Clearwire board remain.

The complex relationship has made for awkward moments for the two companies.

Because Sprint lacks board control, its Clearwire representatives “are often invited out of the room when key decisions are made because of potential conflicts,” said a person familiar with the matter. “It’s more than frustrating.”

Clearwire shares were up 5.9%, or 47 cents, at $8.47 on the Nasdaq Stock Market on Thursday morning. Sprint shares were down one cent at $4.59 on the New York Stock Exchange.

Clearwire (NASDAQ:CLWR) is going to launch a home router product that will allow users capture the company’s mobile WiMAX service and then transfer it to other devices in their home via WiFi, according to FCC documents.

The documents, unearthed by the blog Boy Genius Report, point to a device referred to as the Clear Modem with WiFi. The device, which looks similar to a standard cable modem, also has a phone jack, which could indicate that VoIP service will be included with the router.

A Clearwire spokeswoman declined to comment.

Lately, Clearwire has turned its attention to consumer-facing devices and services. In August, Clearwire launched a new, prepaid mobile hotspot that allows Apple’s (NASDAQ:AAPL) mobile devices to access its WiMAX network. The iSpot allows users to share the connection among up to eight WiFi-enabled Apple mobile devices.

Clearwire also recently introduced a new prepaid brand called Rover, which is currently only available in select markets. The Rover brand features two devices: The Puck, a portable WiFi hotspot that connects up to eight devices at one time; and the Stick, a personal USB modem that connects to a notebook, laptop or desktop. Both are WiMAX-only; the Puck costs $149.99 and the Stick costs $99.99.

The company is in the midst of a network buildout and plans to cover 80 markets and 120 million POPs by year-end. Though the company has been aggressive in its expansion, it still has not officially launched in large markets such as Los Angeles, New York City and San Francisco.

Philip Falcone has endured a lot of skepticism since announcing his intention to build a high-speed, fourth-generation (4G) wireless broadband network across the U.S. One oft-cited criticism–posed by analysts and other industry observers–is that Clearwire Corp. is already doing something similar and hasn’t yet succeeded at it.

The Clearwire comparison doesn’t sit well with Falcone, the founder of New York-based private investment firm Harbinger Capital. Falcone believes his venture, called LightSquared, possesses wireless spectrum that gives the startup an advantage over Clearwire.

In a profile in the latest issue of Forbes, Falcone speaks out against analysts that equate Clearwire and LightSquared. Citing the “physics” between LightSquared’s spectrum, which is located at 1.6 gigahertz (GHz) and Clearwire’s spectrum, which is located at 2.5 GHz, Falcone retorts, “Get a one-on-one with one of Clearwire’s investors and give them a few beers and you will get the skinny on how 2.5 GHz works with mobility. Or should I say doesn’t work…Too many dead spots.”

Clearwire, in turn, refutes Falcone’s remarks. The company’s Chief Technology Officer, John Saw, tells Forbes that Clearwire trumps LightSquared when it comes to the amount of spectrum it owns, the readiness of that spectrum and the ability to convince manufacturers to produce devices that work on its network.

First, a look at the spectrum. Clearwire holds 120 megahertz of spectrum in most of the cities it plans to cover in the U.S. LightSquared, which will use a combination of satellite and terrestrial spectrum for its network, has smaller “bands” of spectrum that measure five or 10 megahertz each. Clearwire says its “wide channels” mean it is better suited to “support the demands of high data consumption.”

Spectrum can be assessed both by quantity and quality. Clearwire doesn’t deny that LightSquared possesses spectrum in a lower frequency and that most people in the telecom industry believe lower-frequency spectrum offers better coverage at a more affordable price. However, Saw says that coverage matters primarily for voice service and rural markets. For mobile data, which is 4G’s main selling point, capacity is the more important factor, he says.

In cities, in particular, the need to deploy multiple cell sites to cover a high density of people means that LightSquared likely won’t see much cost savings over Clearwire despite its lower-frequency spectrum, Saw contends. “Within months [of its buildout], LightSquared will end up with the same number of cell sites as us if it wants to provide the same level of service,” he says.

Clearwire’s other defense is one it marshals frequently: that its early start with 4G gives it a timing advantage over other companies. LightSquared, for instance, must clear some of its spectrum before it can use it. “By the time they get [their spectrum] together, the competition will have blown past them,” says Saw. “LightSquared is still quite a ways from building anything.”

Saw’s final rallying point is that LightSquared will need to persuade device manufacturers and chipmakers to produce gadgets and silicon that supports its specific flavor of spectrum, known as the L-band. “To get manufacturers excited about your network, you need to show the potential for high volumes of users,” says Saw. “That seems like an oxymoron when you have a proprietary channel [like LightSquared].”

Regarding Falcone’s statement about “dead spots”, Saw says patches should disappear as Clearwire turns on more markets. He also says Clearwire tests users’ ability to log onto its network at highway speeds and considers the network to be “fully mobile.”