Full duplex may be the next breakthrough in mobile networking

Stanford startup Kumu Networks didn’t receive much notice at Mobile World Congress this week as the giants of the mobile industry revealed their plans for 2015, but it did get the attention of two rather important mobile carriers. At their separate booths, Telefónica and SK Telecom were showing off a Kumu-built radio transmission system called full duplex, which both carriers said could eventually become one of the key technologies of any future 5G standard.

When the mobile companies pull out the 5G card, they’re usually trying to signal that something is a really big deal, and in the case of Kumu, they could very well be right. What full duplex does is solve a fundamental problem in wireless communications that limits a network’s full capacity potential: the inability to transmit and receive signals on a radio channel at the same time. The problem is known as self-interference, but the concept is not quite as complex as it sounds.


Imagine two people are having a conversation, which itself is one of the simplest two-way — or duplex — communication channels. If both people are talking at the same time, neither one can understand what the other is saying. The words one person speaks get drowned out by the other’s voice before it ever reaches his ears. The same principle holds for wireless transmissions. When a radio is transmitting its signals bleed over into its own receiver interfering with the signals it’s trying to listen for.

For that reason wireless networks have always been built in something called half-duplex mode, which basically prevents them from ever transmitting and receiving in the same channel at the same time. It’s why most mobile networks in the world today use different sets of frequencies for downlink and uplink transmissions (For instance in many U.S. LTE systems, our devices receive data from the tower in a 2100 MHz channel, but they send information back at 1700 MHz). And it’s why a Wi-Fi router flip-flops between transmitting and receiving when it talks to your laptop or smartphone. Half-duplex has served the wireless industry well, but using it means you’re only using half of the total capacity of your airwaves at any given time.

Kumu Networks is based in Santa Clara but its roots are in Stanford where its founders started their full duplex research.

Kumu Networks is based in Santa Clara but its roots are in Stanford where its founders started their full duplex research.


As my colleague Signe Brewster wrote in Gigaom’s first look at the Stanford startup in 2013, Kumu claims to have developed the mathematical breakthrough necessary to solve the problem of self-interference at a practical level. And now it’s claiming to have produced a commercially viable full-duplex radio system that can transmit and receive simultaneously without turning its connection to mush. According to Kumu VP of product development Joel Brand, the company accomplished this by becoming a very smart listener.

Essentially Kumu is constantly scanning the radio environment, gauging the exact state of the airwaves at any given time, Brand said. Using internally developed algorithms, Kumu can “hear” how the transmission the radio is pumping out is changing the signal environment a the receiver. It can then compensate for those changes as signals heading the opposite direction arrive. It’s like echo cancellation applied to radio waves instead of sound.

Full Duplex demo

Kumu supplied some photos of the full duplex rig it demoed at Mobile World Congress, and I’ll be the first to admit it doesn’t look very impressive. But at MWC I asked Vish Nandlall, CTO of Australian multinational mobile carrier [company]Telstra[/company], about the technology, and he said it was the real deal. Full duplex isn’t some crazy new concept Kumu just made up one day, he said. Full duplex is used today in regular phone lines, and its application to wireless has been kicking around scientific papers and academic research labs for some time. But what Kumu did was come up with a viable technology that could be applied to real world networks, Nandlall said.

The impact could be quite significant. If you remove the self-interference barrier, carriers could use all of their spectrum for both uplink and downlink at the same time, which would double the capacity or double the number of connections any network could support. Wi-Fi networks would no longer have to alternate between sending data and receiving it, thus dramatically improving their download and upload speeds. It might not solve the so-called spectrum crunch, but it would go a long way to making wireless networks a lot more efficient.

Right now Kumu is pitching the technology to carriers as a backhaul system, so they could use their 4G spectrum to concurrently communicate with phones and the core network. But Brand says in the future full duplex can easily be applied to the access network connecting our devices. In fact, Kumu’s MWC demos were using off-the-shelf radio smartphone chips from [company]Qualcomm[/company], just with the duplexer ripped out. That kind of change would require a redesign of both our networks and our devices, which isn’t going to happen overnight. That’s why Kumu and its carrier partners [company]Telefónica[/company] and [company]SK Telecom[/company] are looking ahead to 5G.


T-Mobile will launch LTE in the Wi-Fi airwaves in 2016

T-Mobile came up short compared to Verizon and AT&T in the last 4G spectrum auction, but it looks like it’s found another source of airwaves, and these won’t cost it anything. At Mobile World Congress on Monday, T-Mo revealed that in 2016 it plans to deploy LTE in the unlicensed 5 GHz bands, the traditional home of Wi-Fi, and it’s likely the Wi-Fi industry isn’t going to be very happy about it.

[company]T-Mobile US[/company] has never made a secret of its interest in operating in the unlicensed bands, but until now we’ve never had a firm deployment date, and that date is actually pretty darn close.

The country’s fourth largest carrier will use [company]Alcatel-Lucent[/company] small cells – which are like big tower-mounted cells, just tinier – embedded with [company]Qualcomm[/company]’s radio processing chips and LTE-Unlicensed technology (T-Mobile has tested similar systems from [company]Nokia[/company] and [company]Ericsson[/company] as well). The carrier plans to start a trial of LTE-Unlicensed this year and then adopt LTE-U’s more technically sophisticated brother LTE-License Assisted Access (LTE-LAA) when it takes that network commercial next year.

I just spouted off a lot of acronyms there, but the key thing you need to know about LTE in the unlicensed bands is it will share the 5 GHz airwaves with Wi-Fi, moving from channel to channel to find a clear path for its 4G transmissions, just as Wi-Fi networks coexist with another in the same spectrum today. The problem is, according to the Wi-Fi industry, LTE won’t necessarily play nicely with the other Wi-Fi networks in the band, potentially forcing Wi-Fi users off of their own spectrum.

This issue is going to come to a head over the next year – it’s already becoming a major topic at MWC this year – as more carriers announce their unlicensed intentions. Basically the mobile and Wi-Fi industry are engaging in an old-fashioned turf war. It’s easy to see why carriers are interested in the unlicensed bands. They have hundreds of megahertz of airwaves they could potentially tap for their 4G networks, which could translate into faster speeds and more capacity for their customers.

But it’s also clear why the Wi-Fi industry isn’t exactly welcoming the carriers with open arms. The unlicensed band is meant to be open and shared, but carriers traditionally aren’t the open and sharing types. They’re accustomed to owning their airwaves and doing with them whatever they please.


White space broadband gets green light in UK

The British telecoms regulator Ofcom has formally approved the deployment of white-space broadband technology in the U.K., following trials.

White space broadband uses the empty buffer zones that are placed between TV channels to stop them bleeding into one another. The broadband technology glues together these patches of spectrum and, as pilots around the world have shown, it can do so without interfering with the TV transmissions. This is achieved through the use of databases that tell the client device which spectrum it can use in which location and at which time.

Ofcom said on Thursday that it hopes the technology can be deployed in the U.K. by the end of this year.

“This decision helps ensure the U.K. takes a leading role in the development of innovative new wireless technology,” acting Ofcom CEO Steve Unger said in a statement. “It is also an important step in helping the U.K.’s wireless infrastructure evolve effectively and efficiently.”

White space technology may work, but few countries have thus far authorized its use due to concerns over interference. The only commercial deployment I have so far seen was that of a student-oriented network in Ghana, with [company]Microsoft[/company]’s involvement, which went live last month after an on-campus pilot.

The lack of widespread regulatory movement on white space broadband has already forced some in the industry to look to different spectrum for supporting their new internet-of-things networks. That’s a pity, as it works very well for sensor networks, and indeed it’s being tested out in the U.K. for flood defenses and smart city webcams and sensors.

Apart from that, the technology is also good at delivering web access over long distances and into buildings — just like TV broadcasts, funnily enough — and therefore has a lot of potential for both urban and rural broadband provision. As I saw for myself at a [company]Google[/company] trial in my native Cape Town, it’s no fiber competitor but it can make a real difference in areas where fixed-line providers are loath to roll out decent infrastructure.

Car makers clash with Congress over Wi-Fi

Congress wants U.S. regulators to hurry up and open a chunk of federal 5.9 GHz airwaves for commercial Wi-Fi, which would let more smartphones, tablets and laptops milk faster speeds out of wireless routers and hotspots. But the automotive industry, which has designs on the same frequencies, really wants the government to slow down.

The airwaves in question are part of a big spectrum package the White House wants to put to shared use, allowing government and military agencies and the private sector to split time over the airwaves. The Federal Communications itself has been searching for more spectral real estate for Wi-Fi. It seems that everyone is on the same page – well almost everyone.

Automakers plan to use one of those spectrum bands (5850-5925 MHz to be exact) for new automotive networks that would connect cars to each other on the highway and to roadside infrastructure, creating the first smart transportation grids. Talking vehicles could coordinate highway navigation, thereby preventing accidents and easing the flow traffic as well as bringing us one step closer to the autonomous car.

This kind of vehicle-to-vehicle communication, as its called, is another priority of the Obama Administration, but the automotive industry has asked the government to apply the brakes on the Wi-Fi plan until the proper safeguards are in place to make sure commercial and vehicle networks can play nice in the 5.9 GHz band. Backers of the plan, however, think the automakers are stalling, and they’ve gotten their representatives in Congress to apply a little political heat.

U.S. Senators Marco Rubio (R-Fla.) and Cory Booker (D-N.J.) revived legislation from last session called the Wi-Fi Innovation Act, which sounds a lot more impressive than what the legislation would actually accomplish. Specifically the bill would require the FCC to “move swiftly” in conducting a feasibility study on the 5.9 GHz band while balancing the need of the automotive industry with those of commercial users. The bill also calls for a study on how Wi-Fi could be used in low-income areas for internet access. Representative Bob Latta (R-Ohio) introduced companion legislation in the U.S. House.

Big automotive is not happy. AAA and all of the big car manufacturing lobbying groups sent a letter to Congressional bigwigs asking them to oppose the legislation. In a statement, the Intelligent Transportation Society of America said that the automotive and Wi-Fi industries are already working together to see if sharing in the 5.9 GHz band is feasible.

“This collaborative process should continue without Congressionally-imposed deadlines, restrictive parameters or political pressure that creates regulatory uncertainty and could delay bringing these life-saving crash prevention technologies to consumers,” ITS-America CEO and President Thomas Kern said.

But the automotive industry is pretty lonely in its stance. [company]Google[/company], [company]Microsoft[/company], the Consumer Electronics Association, [company]Comcast[/company] and [company]Time Warner Cable[/company] (through their wireless lobbying group WiFiForward), the Wi-Fi Alliance, the Telecom Industry Association and consumer advocates Public Knowledge all applauded the legislation.

AT&T, Verizon, Dish were the big 4G auction spenders

If you were looking for surprise winners out of the blockbuster 4G spectrum auction that ended Thursday, then you’ll likely be disappointed. Only four operators paid more the $1 billion for their licenses and they’re the ones everyone expected to win: AT&T, Verizon, Dish Network and T-Mobile.

According to the auction results released by the FCC on Friday, [company]AT&T[/company] spent the most racking up $18.19 in bids for these Advanced Wireless Services (AWS) airwaves, while [company]Verizon[/company] came in second, spending $10.43 billion. The upstart in the auction, [company]Dish Network[/company], bid $9.99 billion through its two auction entities SNR Wireless and NorthStar Wireless. If there was a surprise in this auction, it was how little [company]T-Mobile[/company] spent: only $1.77 billion.

[dataset id=”911272″]

Though the auction closed with $44.9 billion in total bids, that overall amount was adjusted to $41.3 billion because of discounts applied mainly to Dish Networks’ bids.

AT&T took the most expense license for $2.77 billion in metro New York and Verizon grabbing its Los Angeles equivalent for $2.06 billion. After those top two markets though, you see a three-way race for airwaves between Ma Bell, Big Red and Dish, as all three aggressively went after in the big metropolises like Chicago, San Francisco, Boston and Washington, D.C., as well as the remaining licenses in NYC and LA. Half of the total spending in the auction went to 15 individual licenses even though there were 1,611 total licenses on the block.

Meanwhile T-Mobile seem far more targeted in its license selections – or it just wasn’t ready to pay the high prices asked. Its most expensive license was for the Houston area, costing $263 million. It also picked up strategic licenses in places like Miami, Phoenix, San Antonio, Austin, Indianapolis, Cleveland and New Orleans.

AT&T, Verizon and T-Mobile already have LTE networks in the AWS band so they’re likely planning to use that spectrum to augment their current networks. Dish, on the other hand, has no network at all. It plans to repurpose some of its satellite spectrum for 4G use, and its auction winnings will complement those holdings nicely. The question is whether Dish really plans to become a carrier. It could partner with another carrier like Sprint or T-Mobile to build a network, sell its spectrum or just squat on it to see if it increases in value.

If Dish does choose to squat on its airwaves, it would be particularly shameless considering it just got a steep discount at the auction. As BTIG wireless analyst Walter Piecyk points out, Dish won all of its licenses through its two affiliates NorthStar and SNR, both of which qualify for what’s known as designated entity status. DE status is a kind of “poor carrier” classification that gives a bidder a 25 percent discount on any winning bid. If Dish had bid on its these licenses directly it would have wound up paying $13.3 billion, not $10 billion.

This post was updated several times Friday with more auction details and analysis.


4G spectrum auction ends, raising a record $45B

It took a grueling two and half months, but the Federal Communications Commission auction of new 4G airwaves is finally over. The provisional winning bids totaled $44.9 billion for 65 MHz of airwaves, the most the FCC has ever raised at an auction, but we won’t know that actual winners for a few days when the commission releases the official results.

The contest came to a close Thursday morning at the end of 341st round when no new bids were submitted. As you might expect the heftiest prices accrued to the big cities: A single 20 MHz license in New York City metro region went for $2.8 billion, while the same license in Los Angeles went for $2.1 billion. Once you got past the third largest metro area, Chicago, winning bids fell under $1 billion. The cheapest license? That would be a 5 MHz block in the territory of American Somoa, which cost just $2,800.

Unlike previous auctions, which opened up new spectrum bands for 3G and 4G services, Auction 97 centered on a band already widely used for LTE: the Advanced Wireless Service (AWS) band. It’s where [company]T-Mobile[/company]’s main LTE network lies as well as the new LTE overlays built by [company]Verizon[/company] and [company]AT&T[/company]. All three of those carriers participated in the auction, as they can easily add capacity to their networks with these new licenses.

The big question mobile industry wonks are debating, though, is just how heavily [company]Dish Network[/company] bid in the auction. These AWS airwaves complement the satellite spectrum it recently repurposed for 4G use, but the wily satellite TV operator may have had other goals in the auction. Analysts have suggested that Dish might be driving up bid prices for its competitors or gathering a stockpile of spectrum it can use for future leverage over the carriers.

The auction more than quadupled the $10 billion reserve price the FCC set, producing far more interest than anyone in the industry predicted. There are a lot of different opinions on what the record-busting conclusion of the auction means, though. My colleague Jeff John Roberts recently pointed out it’s a victory for net neutrality, as the high prices paid show that the carriers were bluffing when they claimed that Obama’s net neutrality plan would stifle investment.

Gigaom contributor Peter Rysavy said that the participation in the auction shows that the “spectrum crisis” is very real. If carriers could add more capacity and speed to their networks through technology upgrades and more cell towers, then they wouldn’t be paying such ridiculous prices for new airwaves, he wrote in a recent Gigaom post.

The mobile industry’s lobbying group CTIA tends to agree with Rysavy’s conclusion. CTIA’s new President Meredith Atwell Baker issued this statement:

The AWS-3 auction is the highest-revenue generating auction in the 20 year history of FCC spectrum auctions, and with the last major auction six years ago, this reflects wireless companies’ demand for this finite resource to meet Americans’ growing mobile broadband usage. With nearly $45 billion in bids – and billions more in capex – this auction is yet another illustration of the significant economic impact that exclusive, licensed use spectrum provides taxpayers and the U.S. economy. ?

Latest FCC auction shatters spectrum myths

The FCC’s Advanced Wireless Services-3 (AWS-3) auction, which is in its final rounds, has harvested close to $45 billion for the U.S. Treasury, more than twice the amount of any previous auction. It’s also shattered prevailing myths about the value of mid-band and high-band spectrum.

First, the record sums that are being paid for relatively high-band spectrum at 1.7 and 2.1 GHz obliterate the notion that low-band spectrum below 1 GHz is the holy grail. Second, the mountain of dollars carriers are willing to spend to obtain more of the precious asset proves that more infrastructure or more efficient technology cannot be the sole solution for adding capacity to wireless networks.

In a piece I wrote for Gigaom in 2013, “Learn how technology will turn less desirable airwaves into ‘beachfront’ spectrum,” I argued that the benefits of lower frequencies are overstated and that higher frequency bands will provide the most capacity. The AWS-3 auction confirms the capacity benefit, as this spectrum is the capacity play, a critical component for many carriers to bolster their networks, at a time that the industry needs capacity like a person dying of thirst needs water. For example, Cisco predicted in its oft-cited “Global Mobile Data Traffic Forecast Update” a compound annual growth rate of 61 percent through 2018 for global mobile data traffic.

I’m not denying that lower frequencies are important and valuable. They absolutely reduce a company’s cost to deploy since the low-band frequencies penetrate better and propagate further, dropping the number of sites a company has to deploy to provide good coverage, particularly in rural areas. But most data is consumed in denser population areas, where cell sites are more packed so operators don’t need lower frequencies for propagation and can use higher frequencies that are actually better for capacity. For instance, higher frequencies permit denser antenna arrays, enabling higher spectral efficiency.

Beyond AWS, the next high-frequency band creeping toward auction is the 3.5 GHz small-cell band, followed by bands above 10 GHz for 5G, an area that the FCC is actively pursuing. The march to higher frequencies will continue inexorably, as radio does extend to 300 GHz before electromagnetic radiation becomes infrared. Although I anticipate that most development in the next decade will be sub–100 GHz,scientists are simulating systems that can transmit a terabit per second in optical bands. For now, AWS-3 spectrum represents a sweet spot that combines a large amount of spectrum (90 MHz previously in AWS-1 plus 65 MHz added in this auction), readily available technology on which the spectrum can be deployed, and international harmonization. So much for low band being all that matters.

The second myth is that operators don’t need spectrum and only need to invest more in their infrastructure. A corollary to this myth is that by using more efficient technology, such as smarter antennas, operators could extract much greater capacity from existing spectrum, as high as 100 times greater than the current system — a nonsensical pipe dream. In an auction, operators are driven by economics to bid for spectrum up to the amount that matches an equivalent capacity gain by investing the same amount in infrastructure or technology.

$45 billion proves that no silver bullets exist to boost capacity. Small cells are promising and will eventually become prevalent, but logistical issues such as backhaul, site access, lack of neutral-host solutions, are currently creating a lot of friction. As for smart antennas, both LTE and preliminary 5G roadmaps have no shortage of planned smart-antenna approaches, including massive MIMO, but none of these are smart enough to easily attach themselves to today’s network and produce huge gains. The industry is in the midst of transitioning from 2X2 MIMO to 4X2 MIMO on LTE downlinks, but even this investment only produces a 20 percent capacity gain (see page 71 of the linked report).

In a multi-decade analysis I recently completed, capacity has doubled every three years for the last two decades and is likely to continue to do so, using a combination of better technology, more sites, and more spectrum. The AWS-3 auction has shown us how important the spectrum component remains.

Peter Rysavy, president of Rysavy Research, has specialized in wireless technology for over twenty years.

With $45B in the bids, FCC 4G auction goes on holiday hiatus

It’s been more than a month, but the FCC’s auction of 4G airwaves is still chugging along to the surprise of many mobile industry watchers. With $44.5 billion in bids in 139 rounds so far submitted, the Federal Communications Commission is shutting the auction down for the holidays, with plans to pick back up on January 5.

The auction has already raised many multiples of its reserve price and gone on far longer than expected, though to be honest there hasn’t been much actual activity for some time. The competition for the big metro city licenses is over (though we won’t know who the actual high bidders are until the auction concludes), leaving carriers to fight over airwaves in smaller markets.

“The auction has basically ended, rising less than $10 million per round in primarily small markets as no top 25 market has received a new bid in over 20 rounds,” BTIG Research analyst Walter Piecyk said.

The FCC has been trying to hurry the final bidders along by quickening the pace of the rounds. We’re now seeing eight rounds a day, and starting next year it may add even more. When the last bid is placed, the FCC will finally reveal the provisional winning bidders and they’re likely to be some familiar names: [company]AT&T[/company], [company]Verizon[/company] and [company]T-Mobile[/company]. Still there are 70 total bidders, including [company]Dish Network[/company], so we may see some surprises.

T-Mobile pushes LTE to the outskirts of 4 cities

T-Mobile’s 4G network may not have the geographical reach of Verizon’s, but T-Mobile has started taking the first steps to get there. In conjunction with its big rollover data announcement on Tuesday, T-Mobile revealed that its new LTE network on the 700 MHz band is now live in and outside of Cleveland, Colorado Springs, Minneapolis and Washington, D.C.

[company]T-Mobile[/company] has offered LTE services in those cities since 2013, but by tapping into new 700 MHz frequencies it bought from Verizon, it’s been able to create a higher-coverage, better-performing network. T-Mobile’s main LTE network is up in the 1700 MHz/2100 MHz band, but lower bands can propagate further, letting signals punch through walls and travel further in suburban and rural areas.

The big knock on T-Mobile is that its coverage has always been so poor compared to [company]AT&T[/company] and [company]Verizon[/company]. That’s a comparison T-Mobile wants to nullify as this new network gets rolled out, T-Mobile CEO John Legere said in a call with media Tuesday.

“I can’t tell you the exact month, but I can tell you that we won’t stop until we have a complete network,” Legere said.

CTO Neville Ray said that T-Mobile is using the spectrum to build an overlay in metro areas as well as expand the edges of its 4G coverage much further outside of cities than it has in the past. For example, in Washington, D.C., T-Mobile has used 700 MHz to go well beyond the Beltway, expanding into western suburbs and even outlying rural areas. Ray estimated that the upgrade has increased T-Mo’s LTE coverage by 30 to 40 percent in the D.C. region alone.

Today T-Mobile’s LTE systems cover 260 million people, but the 700 MHz upgrade will put 300 million people under its 4G umbrella. Most of that will be accomplished by bringing mobile broadband to the regions between cities it’s typically served only with 2G networks, Ray added.

Ray also said that T-Mobile’s new higher-capacity wideband LTE network is now available in 121 cities, including the newly launched New York City network. Wideband LTE T-Mobile increases 4G speeds and capacity by 50 percent in most cases, and in some cities it’s doubling bandwidth.

Tech firms say schools need more spectrum

If President Obama really wants to put Wi-Fi in every U.S. classroom, then the government will need to release more unlicensed spectrum for public use — or so says WifiForward, a spectrum lobbying group backed by Google, Microsoft, the cable companies and the Consumer Electronics Association.

WifiForward prepared a paper this week that calls for regulators to open up or lift restrictions on big swathes of the 5 GHz band so it can be used to build bigger, badder gigabit Wi-Fi networks. It also calls for the government to open up more white space spectrum and move forward with its plans to create a shared public-private band at 3.5 GHz, which could be used to link those Wi-Fi networks to the internet proper without using wires or fiber.

Obama is pushing an ambitious plan called ConnectEd to link 99 percent of all U.S. schools with high-speed broadband, and many tech companies like Apple and Microsoft and carriers like AT&T and Verizon have signed on as partners, pledging money, services and equipment to the effort. But WifiForward claims that if the administration wants to ConnectEd right, it needs to think in terms of very fat pipes.

A school of 1,000 students and staff needs at least a 1 Gbps broadband link to ensure every pupil and teacher has access to a 1 Mbps connection, according to a study by the State Educational Technology Directors Association that the paper cited. By 2018, there will be an estimated 56.5 million K-12 students in the U.S., and they will need a combined 56.5 Tbps of bandwidth. Those kind of capacities will require more spectrum than available today, WifiForward claims.

Of course, opening up more unlicensed spectrum wouldn’t just benefit schools, since that new capacity would be available to any company, organization or consumer using a Wi-Fi router. Emphasizing schools is a good way to pull on the public’s heartstrings, but WifiForward’s arguments are still valid. Unlicensed airwaves produced a tremendous amount of innovation around the world. Investing in more unlicensed technologies will keep that innovation going.