Communications

Wi-Fi offload, not Femtocells

Mobile operators face soaring data demand (~18x in less than 30 months according to slide 10 here). The natural evolution of 2G/3G/4G infrastructure delivers about 2X additional capacity every 24 months (see slide 11, ibid).  That's a major disconnect!

(At least) two solutions are on the table, Femtocells and Wi-Fi offload.  Both approaches solve the backhaul issue by using customer or 3rd party links (DSL, DOCSIS, T1/E1, WISP or otherwise).

Femtocells are tiny mobile cellsites using the mobile operators' licensed spectrum, supporting all handsets and all services.  Thus femtocells are a great way to extend coverage.  If you want mobile voice service in a place where macrocell coverage is poor, a femtocell could be ideal.  However, that's the only place where femtocell's have the advantage.

As a solution for mobile data capacity, Wi-Fi wins, for many reasons.

First, most mobile data is destined for the open Internet, not for someplace on the mobile operator's network.  Multiple actual measurements of live traffic in different countries show 96%-99% of all bytes passed over the mobile data channel are destined for the Internet.

The mobile operator's NGN mobile core network is a complex network designed to support differential services, fine-grained billing and so forth. This makes it significantly more expensive than a best efforts network like the Internet and yet, no operator has found a way to charge for this extra capability — people just want to get to the Internet.

Femtocells are part of this complexity, and cost.

Second, the primary sources of mobile data demand are laptops, notebooks and smart phones. Laptops and notebooks have Wi-Fi connectivity. Half of smart phones have Wi-Fi already and the percentage is rising rapidly.  So the major demand comes from devices that can connect to either femtocells or Wi-Fi hotspots. Thus the only potential disadvantage of Wi-Fi hotspots is gone or rapidly vanishing.

Third, Wi-Fi access points cost less than femtocells.  Besides being somewhat simpler, they are being produced in very high volumes, far higher than the mobile operators are likely to achieve with femtocells. Femtocells might have made sense when they were first conceived, but today Wi-Fi has changed the landscape which leads us to...

Fourth, Wi-Fi access points are showing up everywhere.  People are installing them in their homes but we also see Wi-Fi coverage in enterprises, in retail establishments and in public places. 

Individuals spend most of their online time in just two locations: home and the office. Enterprises will not install Femtocells as the IT department can't control them.  Consumers, retail and public locations have already done or are doing Wi-Fi.  They won't install femtocells unless there is some form of subsidy from the operator — another cost with no net benefit. 

Summary: 

 Femtocells will flop. They do provide a way to extend voice coverage into homes that macro cells don’t reach, but they are not efficient for data offload. Since Wi-Fi is efficient for data offload, and it costs less to buy and less to operate, Wi-Fi will trump Femtocells.

What should an operator do?

Mobile operators need to focus on providing bundles of connectivity, not on whether its 3G/4G or Wi-Fi. They should be encouraging Wi-Fi offload by bundling "free" public Wi-Fi access with their mobile data plans.

In the long term, it's likely most mobile data bytes will go over Wi-Fi.  The 3G/4G network is still necessary to provide a backup path when no Wi-Fi is available. Mobile operators who recognizes this can still come out on top, if they focus on facilitating connectivity for their customers regardless of the technology involved.

Broadband Wireless — the future is 5 GHz

and eventually, spectrum from 4 GHz to 10 GHz.  

Unfortunately, the mobile industry doesn't understand the implications of MIMO or beamforming, so they are asking for the wrong thing.  They are asking for more spectrum near their current bands (below 2.1 GHz) or lower, e.g. in former TV bands below 700 MHz.  This is all wrong.

Until recently you could say: lower frequencies "work better" meaning they go farther.  But this was a technology limitation, not something in the physics. From a physical point of view, 5 GHz photons pass through the atmosphere just as well as 700 MHz photons. Today, MIMO and beamforming are correcting some of these historic technology limitations and changing everything.

• MIMO not only delivers significant performance improvement, it makes 5 GHz spectrum as useful as lower frequency spectrum for all sorts of applications.
• Beamforming delivers the next performance increment (20x and up), and it's actually easier to implement at higher frequencies.

Addressing mobile data demand

There is no doubt data consumption is growing more rapidly than mobile operators' data capacity (see slides 10 and 11 of my presentation at 4GWE). Unfortunately, US cellular operators are pressing for more low frequency radio spectrum and they are being heard in Washington. In his keynote at this year's Consumer Electronics Show, FCC Chairman Julius Genachowski said an impending shortage of wireless spectrum in the U.S. will dampen future economic growth unless action is taken to fix the problem. 

However, the short term issue is investment dollars not spectrum and the long term solution is new technology at much higher frequencies (above 4 GHz) rather than more spectrum for existing technology near existing bands.

Why 5 GHz spectrum is more useful than TV frequencies

Everyone know TV signals go long distances but remember than TV broadcasters use from 100 Kilowatts to 5 Megawatts ERP.  That's a million to a hundred million times more signal than your mobile handset puts out.  No wonder it covers a lot of distance.

There's also an equation most wireless engineers use in one form or another to calculate free space path loss which says higher frequencies have more loss. But this equation encapsulates two factors:  the true path loss and the size of the antenna.  It assumes a 1/2 wavelength antenna. Higher frequencies have shorter wavelengths, so it assumes the antenna gets smaller as the frequency goes up. Smaller antenna, less signal. With comparable antenna apertures, path loss in the atmosphere is the same from below 50 MHz to nearly 10 GHz. Thus in open air, 5 GHz photons go just as far as 500 MHz (US channel 19) photons or indeed photons for Channel 2 or Channel 50.

Multi-path and MIMO

The reason people have had trouble with higher frequencies for the past 100+ years is "multi-path" propagation.  As a signal radiates from a source, some of it goes directly to the receiving antenna but some of it goes in other directions where it may be reflected or refracted by objects it encounters. When reflected signals also reach the receiving antenna, they are slightly delayed because they traveled a slightly longer distance.  In the days of over-the-air analog TV, we saw these delayed signals as "ghosts" or shadows around images on our TV screens.  For digital data transmission, multi-path contributes to the "noise" in the signal-to-noise ratio. The historic problem with higher frequencies is their shorter wavelengths made it easier for them to be reflected and refracted by man-made objects like buildings, window frames and even closely spaced double pane glass surfaces.

 

But with MIMO, all this changes. With MIMO's multiple antennas and multiple radio front ends, it's possible to separately decode and make use of the multi-path signals.  Now "multi-path" is not only removed as a source of "noise," it adds additional signal and helps carry more data.

Beamforming

A beamformer uses signal processing to control the phase and relative amplitude of the signal at each of a group of independent antenna elements.  Radiation from multiple antenna elements causes a pattern of constructive and destructive interference in the resulting wavefront.  This can produce a tight beam just like one from a highly directional antenna.  But with beamforming, the antenna beam can be steered in software on a packet-by-packet basis.

With eight antenna elements spaced 1/2 wavelength apart (total 3.5 wavelengths), you can create a beam like this:

 

Highly directional beams significantly extend the usable range of a wireless system. And since the beam is computed with digital signal processing software, it can be steered to different directions in microseconds. What's more, the benefits of beamforming apply both while transmitting and while receiving. Either way, the beamformer accentuates the signal in the desired direction while surpressing signals to/from other directions.

But what about wavelength?  To obtain this narrow beam, the outer antenna elements are 3.5 wavelengths apart.  At 5.8 GHz, that's less than 7.5" so the whole antenna array easily fits in a ceiling mounted access point just 8" x 3" by 2".  At 700 MHz, that degree of beamforming still requires 3.5 wavelengths, but wavelengths are longer so now we need 5 feet of separation — something that may fit on a cell tower, but is difficult for a microcell and impossible for a femtocell.  For beamforming, higher frequencies are an advantage.

More spectrum at higher frequencies

Finally, there's a lot more spectrum potentially available at higher frequencies and, today, in the 5GHz band, there is over 555 MHz of license-exempt spectrum already available for applications like Wi-Fi. That's more spectrum than Verizon Wireless, AT&T Wireless, Sprint PCS and T-Mobile USA have, combined!

Wi-Fi blazes the trail

The Wi-Fi market place is vastly more diverse than the 3G/4G mobile operator market place, which means many new technologies show up in Wi-Fi years before they are deployed in mobile networks.  That is certainly true of so-called 4G modulation (OFDM) which was deployed for Wi-Fi with 802.11a (1999) and 802.11g (2003), years ahead of WiMAX (2005) or LTE (2010).

The 802.11n specification includes MIMO and optional beamforming and silicon technology is appearing to support 4x4 MIMO with beamforming.  MIMO products (2x2) have been shipping since 2007 and 4x4 MIMO in consumer products expected in the next six months. Meanwhile, many players are scrambling to deliver 11n options, including beamforming. Early systems are already deployed.

Mobile operators, please pay attention

The technology benefits of MIMO and beamforming apply to the mobile phone industry, it will just take a few years for the deliberate pace of the industry to catch up.  Meanwhile, mobile phone operators should be tracking real world measurements of Wi-Fi performance to understand what spectrum they will really need five to eight years hence.

Wi-Fi's likely impact on 3G/4G services and operators

This morning at the 4G Wireless Evolution conference in Miami, I gave a talk about how Wi-Fi is going to impact both 3G/4G operators and fixed line operators over the next 2-4 years.  The slides are on SlideShare, and here:

Wi-Fi Opportunities In A 4G World

View more documents from Brough Turner.

I think the reason I’m invited back is I manage to be controversial and since, today, I was given more than an hour all for myself, I attempted to make at least a few provocative points:

• We’re at a wireless tipping point that will dramatically drive up performance of all wireless systems, but Wi-Fi is way ahead of WiMAX or 3G/4G mobile, thus Wi-Fi is where the excitement will be over the next 2-5 years.

• Femtocells will flop.  They do provide a way to extend voice coverage into homes that macro cells don’t reach, but they are not efficient for data offload.  Since Wi-Fi is efficient for data offload, and it costs less to buy and less to operate, Wi-Fi is will trump Femtocells.

• Wi-Fi is consistently ahead of the 4G community in commercial deployments of “4G technologies.”  Specific 4G technologies that Wi-Fi has pioneered include OFDM modulation (802.11a, 802.11g, 802.11n), MIMO (802.11n) and beam forming (done via antenna element selection as early as 2002;  and done via antenna arrays with on-silicon signal processing under 802.11n, coming to market right now).

• MIMO makes 5 GHz spectrum as useful as 2.4 GHz spectrum or TV spectrum. 

• Beam forming via adaptive antenna arrays will dramatically drive up performance (for Wi-Fi beginning now and for WiMAX and LTE some years from now).  Beam forming increases range, reduces interference and allows spectrum reuse even in confined areas.

• But with beam forming 5 GHz spectrum becomes more valuable than 2.4 GHz or TV spectrum as shorter wavelengths (at higher frequencies) allow tighter beams.

• As Wi-Fi performance and range increase, it’s becoming useful for broadband wireless service delivery, thus driving down costs and helping fuel rapid growth in the Wireless ISP community.  (There are over 2000 WISPs in the US today.)

In my talk, I backed up these statements with data and arguments that may not be clear from the slides alone.  If there is any point you don’t agree with or don’t understand, fire away in the comments below and I’ll endeavor to answer within a day or two, or elaborate in a separate blog post.

Off to 4G Wireless Evolution in Miami

I'm off to Miami to attend (and speak) at the 4G Wireless Evolution conference.  Although I spent most of 2002-2008 providing technology and applications for mobile networks, my current interest is Wi-Fi, so I'm going to try and shake people up with a talk on Wi-Fi in a 4G world.  

Of course, I'll also peruse IT Expo that's co-located but, even through I spent two decades in computer telephony and have promoted Internet Telephony since 1996, it's now a distraction from all things wireless!

More explanation at some point.  Meanwhile, if you will be at 4GWE or IT Expo, please say hello.  I'll be there Wednesday morning until mid-day Friday.

Wi-Fi in the TV White Spaces - 802.11af task group underway

The commercial success of unlicensed devices in TV whites spaces remains an open question, but Wi-Fi support could tip the balance, so it's good the IEEE standards association has officially chartered an 802.11 task group to:

... create an amendment whose implementation in solutions is likely to receive FCC approval for operation in the TV White Spaces under the 47 CFR Part 15 subpart H rules.

The group is 802.11 "TGaf." Their first meeting will be in Los Angeles the week of January 18th and their initial schedule calls for final votes on a new spec by the summer of 2011. My guess is they'll hit that 2011 date since many of the more difficult white space issues were figured out for 802.11y. In particular, 802.11y specifies "dependent station enablement (DSE)" where low cost devices (clients or access points) can operate under the supervision of a more intelligent (e.g. more expensive) device that actually consults FCC-mandated databases and provides sophisticated sensing.

TV White Spaces may yet be a commercial failure

At least as defined so far, TV white space rules are so restrictive that a market may never emerge. Indeed TV white spaces could follow the same path as Ultra Wide Band (UWB) - much hoopla, some significant investments, but no significant commercial success.  As specified so far, the only places where meaningful amounts of white space spectrum are available are rural areas where the population is small. This means sales volumes will be small and prices will be high - not exactly a formula for commercial success.

The good news is Wi-Fi operation will inherit much of the high volume silicon advantages created for other bands; only the actual RF amplifiers and antennas are specific to TV frequencies. If anything can succeed, Wi-Fi should be it.

Applications that could benefit from white spaces operation

Wi-Fi at TV frequencies could be useful for:

1. Rural broadband access for subscribers in densely forested areas.  If there is a line of sight, Wi-Fi at 5 GHz is more useful (and has more capacity and low cost) but when subscribers are hidden by trees, TV frequencies are scattered less.
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2. Wireless LANs inside heavy masonry buildings or those with plaster on metal wire lath.

In most other applications, 5 GHz is preferable to TV frequencies.  That may sound nuts to wireless engineers used to free space path loss calculations, but those calculations assume the antenna gets smaller as the frequency goes up.  With comparable antenna apertures, path loss in the atmosphere is roughly flat from 50 MHz to nearly 10 GHz.  Thus in open air, 5 GHz photons go just as far as 500 MHz (US channel 19) photons or indeed photons for Channel 2 or Channel 50. 

There's also a lot more spectrum available at 5 GHz.  What's more it's easier to form highly directional radio beams at 5 GHz than it is at TV frequencies.  Finally, at 5 GHz you need less open area around a line-of-sight transmission path, i.e. the Fresnel zone is smaller.

The primary place where 500 MHz does better than 5 GHz is going through heavy masonry.  The US National Institute of Standards and Technology (NIST) has done detailed measurements of how radio waves are attenuated as they pass through various building materials.  Their report is here.  Masonry significantly obstructs radio signals but it's much worse at 5 GHz than it is at 500 MHz.

Dense forests also obstruct radio waves.  The situation is a lot more complex as the randomly distributed leaves, twigs, branches and tree trunks cause attenuation, scattering, diffraction and absorption. There's been quite a bit of study of radio in forests, both for radio communication and for satellite observation of natural resources.  A good summary is here.  In short, wet forests are more of a problem than dry forests and lower frequencies do better than higher frequencies.

Wi-Fi:  the best bet for commercial success with TV white space

Wi-Fi has several years lead over WiMAX or LTE in deployment of so-called 4G technology.  In addition, the Wi-Fi market is large so prices are low (versus WiMAX or LTE where handsets may eventually be low cost, but infrastructure is expensive).  If there there is commercial success in the TV white spaces, it's most likely to be with Wi-Fi, in the 2012-2014 time frame.

Broadband capacity - the impact of averaging many subscribers

The fundamental idea of packet networks like the Internet is to transport variable rate data flows over a shared infrastructure.  Individual end points may generate little or no traffic for minutes or hours on end and then suddenly want to send or receive a large data set as quickly as possible.  Packet networks efficiently share common transport facilities among multiple users but how does this sharing actually work?  Yesterday I posted some actual, relatively current data from three small ISPs.  Today, let me show you how averaging traffic from many individual end points produces a completely stable core network flow.

Each of the graphs below shows successive five minutes measurements during a 24 hour period, but the first graph reflects a few hundred subscribers while the final graph represents the average of many, many millions of subscribers.

In the first graph, the blue line reflects outbound traffic from a few hundred subscribers.  While the average is just over 1 Mbps, the peak (at ~1615 hrs) is 6.9 Mbps for a peak-to-average of nearly 7-to-1.  The green bars represent inbound traffic with an average of 5.6 Mbps and a peak of nearly 16.8 Mbps for a peak-to-average of 3-to-1.  Some of this is time-of-day dependency but a lot of it, particularly the 6.91 Mbps spike at 1615 hrs, is the result of averaging only a few hundred subscribers.

 

Here's a traffic measurement at AMS-IX, the largest Internet Exchange in the world.  With an average of nearly 1 Gbps, the peak-to-average is a modest 1.43-to-1 and it's almost entirely due to time of day.  The largest change from one 5 minute measurement to the next appears to be about 140 Mbps so the short term peak-to-average is perhaps 1.1-to-1.

 

Finally, here a measurement of all the traffic flowing through AMS-IX – over 822 Gbps peak.  Here the time-of-day variation remains but there are virtually no statistical fluctuations.  The short term peak-to-average is almost 1-to-1.

 

To put this in economic terms, for an Internet backbone link that runs at many Gbps your daily traffic profile is completely stable and you can guarantee zero packet loss merely by providing 10%-20% extra capacity above your daily peak.  

But if you are running a small ISP, both the capacity you need per subscriber and the extra "headroom" for unanticipated peaks must be substantially larger.  To get a handle on what is required we also need to look at shorter intervals (shorter than five minutes).  But more on that in a subsequent post.

ISP Contention Ratios and average traffic per user – some data points

Recently there’s been a flurry of discussions about bandwidth shortages, not to mention bandwidth hogs, bandwidth caps, network neutrality and what constitutes fair practices by ISPs. But there is very little public data and no transparency! 

So let me offer a (very) few actual data points, one from a few years ago and three fairly current. These come from friends who are operators and from emails shared on trade association mail lists. Since some of it was not intended for publication, I have withheld specific names. 

Notice contention ratios vary widely and yet each of these operators has enough extra capacity that they claim to avoid link saturation and its impacts, like packet loss and excessive ping times. It’s true these are all small operators (280-1200 customers) so this data lacks the statistical smoothness one would expect when aggregating traffic from thousands or millions of subscribers. 

I also have some data on traffic averages by time and by number of subscribers that I’ll share in a subsequent blog post. 

Mar 2006 – Rural ISP (Dialup, DSL & Wireless)
130 Motorola Canopy subscribers (with 512 Kbps service)
150 DSL subscribers (110 with 512 Kbps service; 40 at 1 Mbps)
100 dialup lines serving 800 customers (average 40 Kbps)
Daily traffic was saturating 4.5 Mbps (3 T1s) for an hour per day but not with 6 Mbps.
Contention ratio: 164Mbps / 6 Mbps -> 27:1
Traffic per BB user: 6 Mbps / 280 subscribers -> 21 Kbps 

Sep 2009 – Rural ISP (DSL & Wireless)
1200 customers, DSL subs at 1.5, 3 or 6 Mbps; wireless subs at 384 Kbps, 768 Kbps, 1 Mbps or 3 Mbps. I don’t have the mix, so I'm guessing the contention ratio.
Daily traffic peaks at around 35-40 Mbps; up to 150 Mbps Internet transit available.
Contention ratio: 2400 Mbps(?) / 150 Mbps -> 16:1
Traffic per BB user: 40 Mbps / 1200 subscribers -> 33 Kbps 

Sep 2009 – Community-run WISP
340 customers, mostly on 3-4 Mbps service
Daily traffic peaks around 17 Mbps; 45 Mbps of Internet transit available.
Contention ratio: 1190 Mbps / 45 Mbps -> 26:1
Traffic per BB user: 17 Mbps / 340 members -> 50 Kbps 

Sep 2009 – Rural ISP
370 customers: 300 Customers on wireless (1-3 Mbps) and 70 customers with FTTH (10/100 & up, but most have 10 Mbps peak). Monthly fees based on a 10 or 20 GB cap with extra charges for heavier use.
Daily traffic peaks at 13-14 Mbps; 20 Mbps of Internet transit available.
Contention ratio: 1200 Mbps (?) / 20 Mbps -> 60:1
Traffic per BB user: 14 Mbps / 370 subscribers -> 37 Kbps

White spaces could be the broadcasters best hope

For years, the National Association of Broadcasters (NAB) fought the White Spaces Coalition and others interested in making US "TV white spaces" available for broadband, Wi-Fi or indeed, any new purpose. When the FCC voted 5-0 to permit license exempt use of TV White Spaces, the industry brought suit in Federal court. And they did this, despite rules in the FCC's decision that are so restrictive that, for now, white spaces devices are doomed to commercial failure. The NAB are savvy in the ways of Washington

But fighting the White Space Coalition is short sighted. The NAB faces a much bigger and more powerful enemy — mobile operators.

The White Spaces Coalition merely seeks permission to use spectrum where NAB members are not using it, i.e. on a non-interference basis as "secondary users" with purely secondary rights.  

The mobile industry wants it all.  They'd prefer that broadcast spectrum be taken back and auctioned off for mobile use. Discussions on recapturing broadcast spectrum ramped up after an October comment by FCC broadband czar Blair Levin. For example see the transcript of this December 1st panel discussion. Or consider last week's appointment of Duke Law Professor Stuart Benjamin as the FCC's first Distinguished Scholar in Residence. Benjamin is a vocal proponent of reclaiming the TV broadcast spectrum!

Broadcasters beware!  

Unlike the White Spaces Coalition, the mobile operators are political experts. They are part of a 100+ year telecom lobbying heritage. The Bell System was lobbying government agencies before the broadcast industry existed. Now Congress is considering spectrum policy. The FCC is considering spectrum policy.  

Broadcasters may eventually extort large sums of money out of the public, but over the next decade they will lose more and more of their spectrum.  I am no fan of the broadcast industry. Even after converting to more modern "digital" broadcasting, they are sitting on spectrum they don't need in order to deliver a limited number of channels of broadcast TV to the 14% of households who don't subscribe to cable. I'm one of those 14% and I don't even watch TV, so I have no interest in broadcasters' survival. But I can't help noticing there is one thing broadcasters could do that would block mobile operators from taking over broadcast spectrum.

White spaces can save broadcasters' spectrum rights

If license exempt white space devices are commercially successful, it will become increasingly difficult and then politically impossible for Congress or the FCC to recapture TV spectrum for exclusive use by the mobile industry. If Wi-Fi, WiMAX and other consumer devices appear using TV frequencies, it will become harder and harder to displace these consumer uses and recapture the exclusive use the mobile industry requires.  

So, if the broadcast industry really wants to hold onto their current spectrum rights, they should get as many non-interfering "secondary users" into their band as possible.  Otherwise, they will eventually lose their primary rights to the quest for more mobile broadband.

Wireless tipping point! My presentation at EU eComm today

My presentation this morning was entitled "A Wireless Tipping Point, Open Spectrum Implications."

A Wireless Tipping Point, Open Spectrum Implications

View more documents from Brough Turner.

The abstract:

Are we using radio spectrum efficiently? No.

Is this likely to change? Not soon.

"Smart" radios have the potential to support much more efficient and productive use of spectrum, but spectrum regulation is a political issue with well established stakeholders. What's more, our limited experiments with commons-based spectrum management have had widely differing results: WiFi, enormous success; UltraWideBand, disappointment. WiFi's success happened in "junk" spectral bands where established players weren't interested. That will be difficult to repeat, but Brough will describe some very simple physical principals of radio propagation which, when combined with the next five years of Moore's law progress in semiconductors, suggest a path forward that's very different from TV white spaces. Indeed, the most important result of regulatory decisions on UltraWideBand and TV white spaces is they validate the concept of secondary access.

24K hits - the Impact of Slashdot

Many thanks to timothy for getting my Sunday post about AT&T Wireless onto Slashdot on Sunday evening at 9:58PM.  I normally get 1800-2000 page views per week.  The impact of the Slashdot mention was 24K page views in the next 30 hours.

I will reply to all comments, hopefully before the end of next weekend.  Thanks.

Leaving for eComm in Amsterdam - Will tweet conference talks

I'll be leaving for Amsterdam this afternoon to attend Fall eComm 2009. 

I plan to record my notes as I did at the HD Communications summit in NYC in September, i.e. I'll write my notes on Twitter in real time and then, after the conference, collate the results into one giant blog post (for my own sake as much as for yours, esteemed reader).

If you're interested in live coverage, follow my tweets at: http://twitter.com/brough

Whoever and whatever you follow, I assume the common tag people will be using (as before) will be "eComm" so that's another approach...

Shameless self-promotion:  My part in the conference:

On Wednesday morning, I'm speaking on Open Spectrum issues.  I will point out some laws of physics and emerging technology changes that, together, suggest a new, better focus for open spectrum efforts.

On Wednesday afternoon, I'm a panelist on Andy Abramson's panel, "Are current wireline and wireless eco-systems still relevant?."

And then on Friday afternoon, I'm moderating a panel that I've organized on "Spectrum 2.0 - What's really happening?"

Has AT&T Wireless data congestion been self-inflicted?

We've all heard or read stories about how iPhone usage has overloaded the AT&T Wireless network but it's likely at least some of their problems are the result of configuration errors ― specifically, congestion collapse induced by misconfigured buffers in their mobile core network.

In early September, David Reed sent this interesting message to the IRTF's "end-to-end" email list.  List members include some world experts on Internet protocols.  During the next couple of days, there were over 40 messages in related threads.  While some of these experts were over-thinking the problem, if you are patient enough to read through the many messages, what emerges is clear.  At least in the case David measured (from a hotel room in Chicago, while he had 5 bars of signal strength, using an AT&T Mercury 3G data modem in his laptop), the terrible throughput and extreme delays he experienced appear to result from overly large buffers in the routers &/or switches in AT&T's core network.  Note:  if you don't want to read all the list messages the short summary is:  >8 second pings times!  What's more the effect was bymodal:  either ping times under 200 ms, or over 5 seconds.

Recently I was talking with a friend whose company continuously operates (and monitors) multiple 3G data links on the Verizon Wireless, AT&T Wireless and Sprint  PCS networks.  His data shows periods when the round trip time for http requests goes over 8 seconds, on the AT&T Wireless network only!  I don't have a copy of his data that I can examine in detail, but when combined with David Reeds report, it certainly appears AT&T Wireless has configuration problems.  If you read on you'll see this may not be the result of gross stupidity, but someone at AT&T Wireless should be a little embarrassed.

My (techie outsider's) Analysis of What's Happening

Buffers in Packet Networks

Routers (& switches) in a packet network have to include buffering in order to absorb transient traffic bursts.  Unfortunately, despite decades of research and operational experience, there is no simple formula for how much buffering is optimal at any given location in a network.  If you're interested in more detail, Ravi Prasad has a good review of the literature on pages 10 & 11 of his (April 2008) PhD thesis.  But decades of operational experience have yielded some basic precepts and it appears AT&T Wireless is violating at least one basic precept.

The buffer in front of a congested link must induce some packet loss.  TCP (the dominant Internet protocol) continuously increases it's transmit rate until it experiences packet loss, then it cuts its rate in half and enters a congestion avoidance mode.  If the network becomes full but there is no packet loss, each TCP sender will keep increasing it's rate causing the network to suffer a congestion collapse.

In the case of a mobile network, the limited resource is over-the-air capacity.  Backhaul may also be expensive, but it's relatively easy to over provision anything else in the operator's network.  So the issue is, how big should the buffer be in the last router between the high capacity core network and the actual over-the-air data path to a subscriber?  Ideally we'd like enough buffer to absorb momentary packet bursts that, averaged out, don't exceed the available over-the-air capacity.  But as soon as the offered traffic exceeds the available over-the-air capacity, we want some packet loss.  The complicating factor is the way 3G wireless networks schedule over-the-air traffic.

Jitter in 3G radio networks

One cellular base station serves multiple users and the quality of the connection to any specific user depends upon instantaneous wireless propagation characteristics.  These can vary second by second and even millisecond by millisecond when a user is moving.  To deal with over-the-air losses, the basestation (the "Node-B" in a 3G network) keeps copies of each packet until a positive acknowledgement (ACK) is received, retransmitting the packet if the ACK is not received in time. Of course retransmissions introduce delay and jitter.  Furthermore, at any given instant, some users wireless links are better than others.  In order to maximize the total traffic in a cell, the 3G MAC layer schedules transmissions to individual users based on who has the best instantaneous throughput.  This is an efficient solution but it also introduces different amounts of jitter into each user's data path.  Luckily these effects are well understood and not that severe.  With HSDPA, the basic transmission time interval is 2ms so total delay variation is relatively small.  This graph from Jang et al (1) is typical of measured values in an HSDPA network.

Most jitter is below 15 ms.  Measurements of ping latency between 3G wireless devices and the first IP server at the edge of the mobile core network (typically the GGSN) can extend out to over a second as this graph from Mun Choon Chan and R. Ramjee (2) shows:

but most of the time, total IP latency is a few hundred milliseconds. As mentioned earlier, David Reed reported bimodal operation on the AT&T Wireless network with normal behavior yielding ping times under 200 ms.

Likely cause of AT&T's problems

So what is happening in the AT&T Wireless network when ping times go over 8 seconds?  We know how a customer's IP packets are passed through an operator's mobile core network.  They are tunneled all the way from the handset to the Gateway GPRS Signaling Node (GGSN), i.e. to the router where the mobile core network connects to other networks.  The protocol stacks for this tunneling look like this:

More recent versions replace the ATM and AAL5 with Ethernet and IP, but the user never sees this as user IP data is tunneled across the top of the diagram (carried by PDCP and GTP-U).  As a result, user traceroutes can't reveal the detail of what's happening in the core network.  The first thing the user can see is the GGSN (the gateway to the next network).  So we can't make conclusive measurements from outside the network, but we do know a few more things.

The bottleneck link is the over-the-air link, i.e. the connection from radio access network or UTRAN to the Mobile Statation (MS) in the above diagram, therefore the critical buffers are those at the UTRAN.  In practice the UTRAN includes both the basestations (called Node-Bs) and the Radio Network Controllers (RNCs) which coordinate handovers between basestations (among other things).  Because of hand-overs, the amount of data buffered at the Node-B is relatively small. It's the buffers at the RNC that must be large enough to deal with the delay variations in the radio network and yet small enough to induce packet loss when the network gets congested.

While I don't personally have experience managing a 3G HSDPA network, my impression is UTRAN buffers are normally less than 200 ms.  Recently Yerima and Al-Begain presented an interesting paper (3) on buffer management in 3.5G wireless networks in which they concluded that 120 ms buffers were ideal for downlink traffic in a specific UMTS-HSDPA configuration.

Zero Packet Loss

It appears AT&T Wireless has configured their RNC buffers so there is no packet loss, i.e. with buffers capable of holding more than ten seconds of data.  Zero packet loss may sound impressive to a telephone guy, but it causes TCP congestion collapse and thus doesn't work for the mobile Internet!

=================================================

References

(1) 3G and 3.5G Wireless Network Performance Measured from Moving Cars and High-Speed Trains, by Keon Jang† (keonjang@an.kaist.ac.kr), Mongnam Han† (hgma11@gmail.com), Soohyun Cho∗ (shcho1@kt.com), Hyung-Keun Ryu∗ (hkryu@kt.com), Jaehwa Lee∗ (jhlee@koren21.net), Youngseok Lee‡ (lee@cnu.ac.kr), Sue Moon† (sbmoon@kaist.edu)

  † Computer Science Department, KAIST

  ‡ School of Computer Science & Engineering, Chungnam National University

  ∗ KT Central R&D Laboratory
http://an.kaist.ac.kr/~sbmoon/paper/intl-conf/2009-micnet-3g.pdf

(2) TCP/IP performance over 3G wireless links with rate and delay variation,

by Mun Choon Chan and R. Ramjee, Bell Labs  (presented by Jinqiang Yang)
http://wwwcsif.cs.ucdavis.edu/~ghosal/Teaching/ECS289I/Lectures/jinqiang-yang-wirelessTCP.pdf

(3) Dynamic Buffer Management for Multimedia Services in 3.5G Wireless Networks,

by Suleiman Y. Yerima and Khalid Al-Begain

Proceedings of the World Congress on Engineering 2009 Vol I

WCE 2009, July 1 - 3, 2009, London, U.K.
http://www.iaeng.org/publication/WCE2009/WCE2009_pp857-862.pdf

MassTLC Innovation Un-Conference

I'm at the Massachusetts Technology Leadership Council's Innovation Un-Conference today, because the previous such conferences were clearly worth it.  This unconference series was the personal mission of Bill Warner and, as of today, it's grown extra layers beyond a straight unconference, including one-on-one mentoring sessions for entrepreneurs and a social networking site run by Eventvue.

Not surprisingly, my interactions have been all over the block, as there are plenty of interesting people here and zillions of ideas, entrepreneurs and those that cater to start ups (lawyers, investors, marketing and PR, consultants of every stripe).  There does seem to be a preponderance of social networking businesses and/or advice on using social networking to support whatever else you are doing.  While I use a variety of social networking tools, I'm more interested in infrastructure for my next company, so this is interesting but distracting.

At the last moment I decided to host a session myself (on potential business models for services delivered via wireless mesh technology).  We ended up in very far away room and the session was lightly attended (5 people total) but still a good discussion.  Other highlights of the day include hearing Donald Eastlake's pitch for Stellar Switches and talking with him about his recent standards work (Donald chaired the IEEE's 802.11s while at Motorola and still chair's the IETF's TRILL working group).  Later sessions included two on networking ideas and entrepreneurs and networking students who want to be entrepreneurs or want to work at startups. (I expect to need partners for 1-3 different businesses by early next year...).  Two people to track are Bobbie Carlton who has been running Mass Innovation Nights and Lauren Celano who is launching a biotech careers site, Propel Carrers, but is thinking more generally.  At Lauren's session I also met Rick Eichhorn, a recent Babson MBA graduate.  Rick appeared to have evaluated all of the potential career networking sites and several of us urged him to write a white paper or consumer reports like summary.  If he does, I'll certainly point to it. Unfortunately, I missed the session where Scott Kirsner apparently listed 40+ innovation networking events that happen in and around Boston.

If you live within reach of Burlington Massachusetts, I highly recommend future Mass TLC Innovation conferences.

eComm agenda is on-line ―Check out the speakers!

There's a fascinating agenda building for eComm in Amsterdam in October.  Here's the latest list of talks, but what's best is the set of speakers who are giving these talks.  I personally know quite a few and know of many more (who I look forward to meeting).  The group includes a preponderance of innovators -- new views on what's happening, new ideas for how to drive change.  If you don't read through this list of talks, look at the speakers list here.  Then come to Amsterdam and meet these people.

21st Century Economics: Lessons for Telcos - Umair Haque (Havas Media Lab)

Advances In Spectrum Transparency, Software Defined Radio/Cognitive Radio - Darrin M Mylet (Spectru-Station)

Almost all Marketing & Product Management of Telco Services is Wrong - Rudolf van der Berg (Logica)

Current Trends in Community Wireless Networks and Beyond - Aaron Kaplan (FunkFeuer)

Death of the Handset: Evolving from Mobile Devices to the Mobile Digital Life - Mark Rolston (frog Design)

Edge As Value - Value As Edge - Graham Brierton (Voicesage)

Enslaving Humans using Communications Technology for Fun and Profit - Thomas McCarthy-Howe (Jaduka)

Entrepreneurial Advantages with New Open-Source Technologies - Jay Phillips (Voxeo)

European Telecoms 2015: Silent Death or Generative Bazaar? - Julien Salanave (IDATE Telecoms)

Finding Disruption - Michael Jackson (Mangrove Capital)

Goodbye Minutes, Hello Moments - Martin Geddes (BT)

Google Wave - David Wang (Google)

How the "Internet of Things" will Change the Way we Connect - Alexandra Deschamps-Sonsino (Tinker.it)

How to get More Value out of Customer Interactions by Blending Online with Voice - Stefan Hopmann (Swisscom)

Humans as a Service: Abstracting Communications to Reach New Applications - Todd Landry (NEC Sphere)

Is LTE being Held Hostage by Ordinary Voice Telephony? - Dean Bubley (Disruptive Analysis)

Lifestyle Segmentation from Carrier Location and Call Data - Greg Skibiski (Sense Networks)

Lifestyle Segmentation from Carrier Location and Call Data - Tony Jebara (Sense Networks)

LTE - Long Term Employment or Less Than Expected? - Moray Rumney (Agilent)

Open Access Makes Economic Sense - Benoît Felten (Yankee Group)

Open Screen Project: Next Generation Contextual Applications - Andrew Shorten (Adobe)

Opening of the Terahertz Region - Robert Horvitz (Open Spectrum Foundation)

Opportunities in Post-Telecom Connectivity - Bob Frankston (Frankston Innovating)

Post Financial Trauma - How is the Telecom Value Chain Now Positioned? - James Enck (mCapital)

Redefining Gifts in the Digital Space - Katie Lips (Little World Gifts)

Slowing Down Communication: Designs Inspired by Quality, Intimacy, and Humanity - Stefan Agamanolis (Distance Lab)

Spectrum 2.0 – What's Really Happening? - Brough Turner (Ashtonbrooke)

Stealth Approaches to Legislating Open Spectrum - Brough Turner (Ashtonbrooke)

Technology and Biological Evolution: What This Means for Media and Communications Technologies - Tomas Rawlings (University of the West of England)

Telemedia Futures - Gerd Leonhard (MediaFuturist.com)

The Emerging Telecology of Social Networks and the Status Update - Stuart Henshall (Phweet)

The Future of Interconnection - Rudolf van der Berg (Logica)

The Global Battle for Communications Justice: An Open Spectrum Manifesto - Sascha Meinrath (New America Foundation)

The Next Wave of Communications Applications - Cullen Jennings (Cisco)

The Practical Edge of Speech Technology - Moshe Yudkowsky (Disaggregate)

Ubiquitous Voice over Broadband - is There a Future Role for the Smart Pipe? - Martin Taylor (MetaSwitch)

Unlicensed Spectrum: Future Regulation - Prof. William Webb (Ofcom)

Video Killed the Telephone Czar? - Jan Linden (Global IP Solutions)

When Will HD Voice Become a Reality? - Martyn Davies (Dialogic)

What Would Telephony be Like if we Designed it Today? - Matt Ranney (RebelVox)

If you've read this far, there's a 10% discount via this registration link - register here.  And for more information, visit http://eComm.ec.  This one conference is at the top of my list for:  interesting, productive and an excellent set of contacts.

LTE: another way to estimate when it will be real

Hardly a week goes by without a press release touting how soon we'll be using a Long Term Evolution (LTE) wireless network.  Verizon has promised a major commercial launch in 2010 and a two-city trial before the end of 2009.

Let me show you a little chart I put together for my 3G Tutorial and have repeatedly updated (e.g for my 3G / 4G Tutorial and for the cellular wireless history "Our G-enealogy" presented at 4G Wireless Evolution.  This tracks the different releases of wireless specifications by the 3rd Generation Partnership Project (3GPP), the body that controls the GSM family of wireless specifications.

Release	Specs complete	Commercial deployments	Major new features defined
98	1998		Last purely GSM release
99	1Q2000	2003	W-CDMA (UMTS) air interface
4	2Q2001	2004	Softswitching & IP in core network
5	1Q2002	2006	HSDPA and IMS
6	4Q2004	2007	HSUPA, MBMS, GAN, PoC & WLAN integration
7	4Q2007	Future (2010 seems likely)	HSPA+, Better latency & QoS for VoIP
8	4Q2008	Future	LTE, All-IP

If every other release has taken ~3 years from specs complete to commercial deployments, why is LTE going to be so much faster?  Especially when we remember the 3GPP Release 8 specification freeze was ahead of schedule only because parts were delayed until March 2009.

Based on this chart, an sane person would project LTE in 2011 and wouldn't be surprised if substantial deployments didn't begin until 2012.

Now it's true, I define commercial deployments as at least two operators (somewhere in the world) selling commercial services to the general public who also have access to an assortment of compatible mobile devices.  On the other hand, if Verizon has just one or two USB modems that receive data from the LTE network and they deploy that LTE network beyond their first two cities, Verizon will declare they've met their plan.  So most likely we'll both be "right."

Speaking at 4G Wireless Evolution conference next week

I'll be at 4G Wireless Evolution next week.  It's being held in Los Angeles, co-located with Internet Telephony Expo (ITEXPO West 2009).

My first session is:

TUE 9/1 - 9:00-10:15am

"Mobile Broadband- New Applications and New Business Models” (4G1-01)

ROOM #: 501A

Whether it's LTE or WiMAX or local WISPs using combinations of Wi-Fi, WiMAX and other technologies, we are on the verge of having affordable mobile broadband in the US (it's already available in the UK and Scandinavia and becoming available elsewhere in the EU). What services can be provided over the top and what services need or can benefit from operator capabilities (QoS, security, ...)? The iPhone store, Android store and similar initiatives suggest power is shifting away from the operators and into the hands of application developers and the end user. How can operators leverage their core capabilities (QoS, security, billing, customer relationships, call detail, ...) to provide applications and remain relevant to their customers?

And the second session a day later:

WED 9/2 - 8:30-9:45am

"Our G-enealogy” (4G3-01)

ROOM #: 501A

The Generations do not flash cut from one version to another so 4G should not be considered an end point, but a process. Looking at the history of cellular technology helps us gain an understanding of the converging 4G model of the world. Based on cellular technology, and the progress to date, how long will it take for Long Term Evolution (LTE) to be delivered? Where do we stand in the process of delivering wireless broadband services?

If you will be at 4GWE or ITEXPO, please say hello.

Ofcom goes nuts - will they regulate visible light next?

Ofcom, the UK regulator, has deigned to allow UK citizens license-exempt use of the 275-3000 GHz band.  These are freqencies have historically been lumped in with Infrared.  Of course, these are temporary regulations while they await an international decision at the World Radio Conference in 2011 (WRC-2011).  So it's not just Ofcom that troubles me, but spectrum regulator's in general.  Best bets are, after 2011, everyone will be regulating 275-3000 GHz, but why jump the gun?  As for light, there will also be a discussion at WRC-2011 about regulating "free-space optical" communication.  At least the US is on record as opposed to regulating free-space optical links.

Over the decades, government regulators have gradually expanded the range of frequencies they consider to be the radio spectrum subject to their regulation.  But until recently the highest frequency that anyone considered "radio" has been 300 GHz.  See for example this excerpt from a US Department of Commerce chart in 2003 (full chart here).

Very little use has been made of any spectrum above 60 GHz although there are commercial products in development in various bands between 60 GHz and 100 GHz.  The problem is, at higher and higher frequencies, absorption due to oxygen molecules and water vapor increases until you reach a "window" that we know as the visible light portion of the spectrum.  Since the atmosphere contains oxygen, not to mention water vapor (yes, even in desert areas), transmissions above 300 GHz are severely attenuated.

So whatever happened to the principal that you leave things unregulated until and unless it becomes clear that regulation is required?

WiMAX to be a fringe technology by 2015

Recently I was interviewed by the folks at TMC because I'm giving two presentations, “Mobile Broadband – New Applications and New Business Models” and “Our G-enealogy” at the upcoming 4G Wireless Evolution conference in Los Angeles September 1st-3rd.  The first talk's subject should be clear. The second talk, "Our G-enealogy," is a high level version of my 3G-4G wireless tutorial.

In any event, they asked a bunch of questions, including my thoughts on WiMAX and I answered.  For all the Q&A see the interview, here.

eComm in Amsterdam ― shameless self promotion

I've just wrapped up a focused effort that delayed blogging and many other things.  As a result, I finally submitted the detailed description for my plenary slot at eComm Fall 2009 which will be happening in Amsterdam October 28th-30th.  My abstract is not up on the website yet, but hopefully the next few weeks will bring details on my talk and many others.  For now, let me just say my title is
   Stealth Approaches to Legislating Open Spectrum
in which I propose what I hope is a novel approach to dramatically expanding the capabilities and commercial success of license-exempt consumer devices.

This will be the first time eComm has been held in Europe but, based on the first two eComm conferences (2008 and Spring 2009), this is the meeting for the future of communications.  It's not a trade show and it's not a mass event.  Instead, it's three days of rapid paced information ― high level, insightful and non-commercial.  Even more important, the people are very, very interesting.  It's not cheap, but it costs less if you sign up now (especially if you sign up before July 21st).  What's more, because I'm such an enthusiast, and I'm on the conference's advisory board, I've been given a discount code.  For an additional 20% off type in "BroughTurner" as the eComm discount code, i.e. where the registration form says "Click here to enter a promotional code."

I hope to see you in Amsterdam in October.

Opportunity Doesn't Always Knock. Sometimes It Calls.

The mammoth telecom industry ― fixed and cellular ― is in the process of being re-written. You can stand on the side and be written into history or join with the growing community that's writing the future. Opportunities have never been so great ― to influence how humanity connects, communicates and collaborates and to profit from radical restructuring.

Open Spectrum slide deck is now on-line

Here's the slide deck I used at last Thursday's meeting of the Boston section of the IEEE Communications Society.

Open Spectrum - Physics, Engineering, Commerce and Politics

View more presentations from Brough Turner.

Among other things, I debunk the following spectrum myths:

• Spectrum is scarce
• 4G is the future of wireless
• Auctions drive efficient use of spectrum
• Spectrum utilization requires massive investments
• TV spectrum is “beach front” property

The full write up from the IEEE announcement:

Communications Society

7:00 PM, Thursday, May 14

The Open Spectrum Potential for Evolutionary and Revolutionary Technology and Business Solutions

Brough Turner; Founder and CTO at Ashtonbrooke and Chief Strategy Officer at Dialogic

In November 2008, the FCC voted unanimously to permit unlicensed wireless devices that operate in the empty "white space" between TV channels. Their “TV White Spaces” decision was the culmination of many years of proceedings, but it's just one step in a much larger discussion, commonly referred to as “Open Spectrum.”

Our use of radio spectrum is regulated under principles that were established in the 1920s, when radio spectrum appeared to be a scarce resource and frequency was the only reasonable basis for allocation. Today’s wireless technology vastly exceeds anything imagined in the 1920s and from physical principles we know that many, many orders of magnitude further improvement are possible. Already the application of new approaches in just a few slivers of spectrum has fostered new industries – WiFi, Bluetooth and more.

The presentation discusses the predecessors, potentiality, and directions for Open Spectrum, including:

• A brief history spectrum regulation from before the Radio Act of 1927 to today.
• Results from measurements of actual spectrum utilization in New York and Washington DC.
• An overview of "Open Spectrum" experiments to date, including “license exempt sharing” in the 900 MHz, 2.4 GHz and 5 GHz bands and different forms of "secondary use" including UWB, 3650 MHz and now TV White Spaces.
• The physics of propagation and its impact on the range of White Spaces services vs. WiFi, WiMAX, 3GSM and LTE.
• IEEE 802.11y protocols and the prospects for expanding secondary use beyond TV White Spaces.

Brough Turner is founder and CTO at Ashtonbrooke and Chief Strategy Officer at Dialogic. Formerly he was founder and CTO at Natural MicroSystems and NMS Communications. He speaks and writes on a variety of communications topics including 3G and 4G wireless tutorials. He presented most recently at the 4G Wireless Evolution conference in February. Brough is an electrical engineering graduate of MIT and has 25 years experience in telecommunications.

Open Spectrum ― I'm presenting at an IEEE meeting this Thursday

This Thursday evening (May 14th), I'll be discussing Open Spectrum at the May meeting of the Boston chapter of the IEEE Communications Society.  My working title:  Open Spectrum ― Physics, Engineering, Commerce and Politics.  This is a technical audience, so we'll touch the physics of electromagnetic propagation and examine radio engineering solutions as they stood in the 1920s, as they are today and where they're likely to take us in the coming decade.  But we'll also look at the politics of spectrum regulation and the commercial implications of recent developments.

Just to get your attention:

• We'll explain why the TV White Spaces (TVWS) won't be considered  "beach front spectrum" in the future, and
• Why the lasting impact of the FCC's recent TVWS decision may be what it does for "secondary access"

If you're in the greater Boston area and at all interested in spectrum policy or the commercial evolution of WiFi and other unlicensed technologies, please stop by. 

The meeting begins at 7 p.m. and the presentation soon after at the Verizon Labs, 117 West Street, Waltham. The meeting is preceded by an optional dinner at Bertucci's, Winter St, Waltham, at 5:30 p.m.  The meeting is open to all, but please let Paul Zorfass know if you plan to attend the dinner at Bertucci’s. Paul can be contacted at paul.zorfass@embeddedtrade.com.  More directions and details here.

Spectrum Transparency: Can the US catch up with France?

Richard Whitt has a good article, Taking stock of the nations airwaves, on the Google Public Policy Blog.  He focuses on the Radio Spectrum Inventory Act, a bill introduced in the US Senate by Senators John Kerry (D-MA) and Olivia Snowe (R-ME).

It's hard to argue spectrum policy if you can't actually determine who has what rights in which parts of the radio spectrum.  This bill is a start.

For a first cut at what we should aspire to, look at this site by the Autorité de Régulation des Communications électroniques et des Postes - the French equivalent of the US FCC.  Try typing in a frequency or a frequency range; then hit "Rechercher."

I haven't figured out how to determine who owns individual licenses to spectrum in France and, of course, that is critical.  The proposed US law, S.649, explicitly calls for such information to be gathered and made available to the public on a website.  Let's hope this passes.

I'm off to the Emerging Communications Conference in San Francisco

It's snowing in Boston and my American flight has been cancelled but Virgin America claims their 8:35am flight is going to leave on time.  So here I am in the Virgin gate area.  Wish me luck.

At this point there are a ton of people I'm hoping to hook up with at eComm 2009.  The agenda looks really good.  And, of course I'm looking forward to good discussions around two favorite policy topics: broadband access and wireless spectrum.

My talk on Wednesday is: Structural Bypass: A simple, proven path to “Real Broadband.”

While the US struggles to define "broadband," high speed Internet access (100 Mbps & above) is widely available at modest cost in several countries and quite a few more cities. So far, US political discussion has largely neglected these successes. Brough will point out what's common among diverse international success stories and propose a path for the US that has proven to work elsewhere, despite established monopolies and political processes dominated by vested interests.

On Thursday, I've organized a panel entitled:  Spectrum 2.0 - What's really happening?

WiFi, UltraWideBand and now TV White Spaces represent new commons-based approaches to radio spectrum regulation. While some advocate commons-based approaches for all wireless spectrum, that's hardly acceptable to broadcasters or the mobile phone industry. By questioning a diverse panel of industry experts, we will expose the roots of today's controversy - technical, commercial and political - and see what's likely to occur over the next two to five years and in the long term.

The panelists are top notch:  Richard Bennett, Maura Corbett, Peter Ecclesine, Darrin Mylet and Richard Whitt.

If you're attending, please say hello.

Wireless Tutorial slides posted

The slides we used for our four part Wireless Tutorial at the 4G Wireless Evolution conference in Miami last week are now up on the web.

History and Evolution of Mobile Radio

Part One covers the history of mobile wireless from the earliest days

to the latest 4G technology.

Part one is also available as a webinar recorded in 3 sections last fall.

IEEE Wireless Ethernet Keeps Going and Growing

Part two covers the IEEE wireless systems:  WiFi, WiMAX and more...

Mobile Broadband: New Applications and New Business Models

Part three covers emerging world of mobile broadband access and some of the applications it enables.

White Spaces and Open spectrum Issues

Finally, part four focuses on Open spectrum and the recent decision by the FCC to permit unlicensed devices to operate on unoccupied TV channels - the so called TV White Spaces.  In the end, there's alot more that will be possible eventually...

Wireless Tutorial - 2G, 3G, 4G and beyond - in Miami today

I'm in Miami for the 4G Wireless Evolution conference which is being held in conjunction with Internet Telephony Expo.  Fanny Mlinarsky and I are kicking off the conference with a comprehensive wireless tutorial starting at 10:30 this morning.  So no pictures of Miami Beach or warm weather until after our all day event is complete.

Best conference bet for 2009 ― eComm 2009, March 3-5, San Francisco

I attended a number of conferences in 2008, both interesting and not so interesting.  One conference stands out, for the range of interesting speakers and the variety of interesting people I met.  That was the first Emerging Communications Conference, eComm 2008, organized by Lee Dryburgh.  Many of talks from this conference are available on Slideshare and as podcasts on IT Conversations.

eComm 2009 is scheduled to take place at the San Fransico Airport Marriott, March 3-5, 2009.  I highly recommend you check it out.

This is not a trade show with vendors hawking today's products and multiple tracks full of vendor product pitches. 

Presenters have been chosen for the quality of their proposals:  is it new?  is it disruptive?  what will the audience learn?  (As an adviser, I've been in on those discussions).  Like last year, the format is one track spread over three days, with 15 minute presentations, 5 minute lightning presentations, panel discussions and social time.  It all adds up to a veritable fire hose of information.

There's a list of speakers here.  Major topics for 2009 (so far) include:

* Mobile Social Networking (MoSoSo)
* Open Handsets & the Open Ecosystem
* Both Voice and Video Evolution
* Convergence of Media with Personal Communications
* Open Spectrum
* Open Communication Platforms
* Leveraging Cloud Computing
* Social Computing
* Towards 4G Wireless
* P2P and Decentralization of Telecoms
* Communications enabling business processes, especially B2C
* New Forms of Contactability and Connectability
* Emerging Markets

And last, but by no means least, if you mention my name you get 20% off.  More specifically, if you enter the promo code "BroughTurner" (case-sensitive) at the appropriate point during registration, you'll get 20% off the registration fee.  This works now, while early bird rates are in effect, and I'm told it will also work right up to the last minute ("late", not on-site registration), although then it's 20% off the full conference rate, and only if the event is not sold out!

I hope to see you there.

TV White Spaces - Fundamentals misunderstood

The FCC's recent decision to allow secondary use of the TV bands by license-exempt devices is a political breakthrough we can all rejoice in, but the widely claimed technology benefits are at least partly bogus.

Here's a typical claim:

This is the same spectrum we have referred to as "prime beachfront property."  < ... >  These lower frequency signals lose less power as they travel, hence requiring fewer base stations to cover an area. They also feature far better penetration characteristics, which is key to improving indoor operation.

This is true of deployed systems today, but for engineering reasons, not due to the physics of electromagnetic waves.

Today, wireless technology is advancing at such a pace that higher frequencies, for example at 5 GHz, will be more useful than TV White Space, perhaps within the time it takes TVWS equipment to get widely deployed -- certainly within 5-10 years.  What's happening is MIMO and advanced MIMO driven by emerging WiFi (802.11n), WiMAX and LTE systems.  As these systems get developed and deployed, signals at 5 GHz will achieve similar or greater range than TVWS, similar or better building penetration, lower costs and substantially higher carrying capacity.

The reason buildings appear to attenuate high frequency signals (like 5 GHz) more than those in the TVWS bands is, as radio signals hit the different materials that make up walls, windows, furniture, and other building elements, they scatter (due to diffraction and reflection).  With conventional receivers, only the primary signal is detected while scattered signals appear as noise, degrading the received signal.  Shorter wavelength signals are scattered by smaller objects and thus by more of the building's elements.  The higher the frequency the shorter the wavelength, so it's higher frequencies that experience more scattering.  But if you have multiple antennas and multiple receiver channels (MIMO), you overcome scattering.

Indeed with MIMO, the tables are turned.  MIMO systems use multiple antennas, typically separated by several wavelengths, or beamforming with many antenna elements each separated by 1/2 wavelength, but that's a problem for TVWS sysems.  At 5 GHz, a wavelength is 6 cm or just over 2 inches, but TVWS wavelengths range from 1.4 meters (55 inches) to 5.6 meters (over 18 feet).  Separating multiple antennas by several wavelengths is a problem at TVWS frequencies.  It might be feasible at a fixed base station but it's too bulky for a residential device and completely nuts for a laptop computer or a mobile phone.  So expect MIMO to be widely deployed at 5 GHz, but not so widely or not at all in the TVWS bands.

There are many other reasons why physics favors 5 GHz over the TVWS bands, but MIMO is the one place where engineering is catching up with physics as we speak.

Secondary Use of spectrum ― TV White Spaces just the beginning

Yesterday, the US Federal Communications Commission voted to allow qualified devices to operate on a license-exempt basis in unused portions of TV channels 2-51, spectrum commonly referred to as "TV white spaces."  A lot has already been written about this move which was supported by Intel, Google and others in the White Spaces Coalition, but vilified by TV broadcasters.

What missing in these discussions is the bigger picture.  Almost all radio spectrum is under-utilized and yet, except for a few slivers, it's all been assigned to someone. Meanwhile today's radio technology is vastly more efficient than most of what has been licensed.  What's more, we now have the potential to share wireless spectrum in ways that potentially render the whole idea of fixed frequency assignments obsolete.  But those who have licenses under the existing regime represent strong vested interests.  The only politically acceptable approach is to open up "secondary use" while protecting legacy licensees.

The first step was getting access to the 3650-3700 MHz spectrum, something that happened last year.  Yesterday's move was a much bigger step, because the legacy licensees in the TV bands are so vocal and so well connected in Congress.

Now we need similar access to all the rest of the spectrum!

To elaborate...

Am I too optimistic about TV White Spaces?

Some have complained the white space rules are too restrictive and will never allow the technology to reach it's promise.  But these rules are subject to change as technology improves, as initial fears are overcome and as the growing "secondary use" community gains critical mass and political clout.  Such FCC rule changes are routine and are normally completed without the mass of publicity that surrounded yesterday's decision.

Spectrum under-utilized

Today, almost all radio spectrum has been licensed to someone although most spectrum is unused most of the time, even in major metropolitan areas.  Obviously there are a lot of unused TV channels in any one city, as illustrated by these energy measurements in Washington DC's Dupont Circle:

but most spectrum, particularly from 1 GHz to 10 GHz is under-utilized:

Radio technology has been improving at least as rapidly other electronic technology and yet most spectral assignments were made decades ago and mandate the use of specific technologies that are completely obsolete.  What's worse, it now appears that the whole concept of assigning specific frequencies to specific users was just a result of limitations of early- and mid-20th century technology.  Today, and more so in the future, there are orders of magnitude of additional performance that can be obtained from wireless technology.  But in almost all cases, new technologies are blocked by existing assignments and their associated vested interests (like the National Association of Broadcasters in the case of TV white spaces).

The Visual Analogy

To get a sense of the potential, consider the visual spectrum (light waves are just very, very high frequency radio waves).  I don't need a license to turn on a light bulb.  No one has licensed the sun.  And no one has licensed the lightwave receivers that are our eyes together with our visual cortices.  And yet we receive an enormous amount of information visually and we do so despite others in our immediate vicinity operating with exactly the same frequencies.  Today's radio receivers don't approach the efficiency of the human vision system but we now understand that they could, and presumably will, in due course.

Obtaining secondary access to more spectrum

The technology that has been developed for the 3650 MHz band (see IEEE 802.11y for example) and the technology that is developed for the TV White Spaces, can be reused in other bands.  Already there are advocates for license-exempt access (as a secondary use) to the 800 MHz stretch of spectrum from 3400 MHz to 4200 MHz.  And, many other bands are candidates for license-exempt secondary use.

Let's take pleasure in the success in the TV white spaces, but resolve to go after all the white space across all the spectrum.

Coverage comparison for wireless systems at various frequencies

One of the items I've been meaning to add to my wireless tutorial is a discussion of actual coverage areas for different frequency bands.  This matters because, with today's mobile radio technology, lower frequencies cover more distance and do better at penetrating buildings.  That means fewer cell sites for equivalent coverage and thus lower infrastructure costs.

Indeed, a little discussed issue in the US is that Verizon and AT&T own the 850 MHz cellular spectrum and they were the big winners in the recent 700 MHz auctions.  Sprint PCS and T-Mobile USA use spectrum at 1900 MHz or 1700 MHz, so they need more cell sites to achieve similar coverage.  They are at a cost disadvantage.

Signals go even further using the 450 MHz spectrum that's available in some countries.  I've argued publicly that the best thing developing countries can do to bring mobile coverage to rural areas (for example in India), or to remote areas in general, is to make 450 MHz spectrum available to mobile operators.

To get a sense of how significant these effects are, here's a table that Qualcomm submitted to the ITU's Working Party 8F several years ago.  (Thanks to Joe Nordgaard for the pointer).

Frequency (MHz)	Cell radius (Km)	Cell area (Km2)	Relative cell count
450	48.9	7521	1
850	29.4	2712	2
950	26.9	2269	3.3
1800	14	618	12.2
1900	13.3	553	13.6
2500	10	312	24.1

Source: Qualcomm ITU 8/F Submission, June 11, 2001, “Coverage comparison of systems at various frequency ranges, including 450 MHz”

2G, 3G, 4G Wireless Tutorial

Recently I put a lot of effort into updating an earlier wireless tutorial.  Part of the resulting material was presented at the Communications Developer Conference in Los Angeles in September 2008.  Other versions have been used internally at NMS Communications.  Last week our marketing team recorded me presenting the tutorial and, today, the complete Wireless Tutorial:  2G, 3G, 4G and beyond became available as a slide deck and as three recorded segments of audio with slides (.wmv files).  Here's the abstract:

This comprehensive tutorial is designed to benefit both the technical and general telecom audience. Brough Turner reviews the history and evolution of mobile radio, evolving network architectures, services, applications, and business models; considers alternative 4G paths and the potential for convergence of GSM/LTE and WiMAX; and discusses the longer term impact of new WiFi standards on fixed and mobile wireless services. In this wireless tutorial, Brough also covers core network architectures and their evolution to all-IP, new wireless applications and application frameworks, spectrum licensing and more.

This work started as a 3G Tutorial that Marc Orange and I put together back in 2002.  Although the 3G Tutorial has not been updated since early 2003, it has remained one of the most frequently accessed pages on the NMS website.  So clearly there's interest.  Hopefully this new version will be even more useful as it covers the whole range from pre-mobile radio days to the latest 4G proposals.  Here's the outline:

• History and evolution of mobile radio

• Brief history of cellular wireless telephony
• Radio technology today: TDMA, CDMA, OFDMA
• Demographics and market trends today
• 3G, 3.5G, WiMAX, LTE and 4G migration paths

• Evolving network architectures

• GSM-MAP (EU) and IS-41 (US) origins
• Softswitches, VoIP and SIP in NextGen Networks (NGN)
• 3GPP and NGN convergence: releases, features and schedules

• Evolving services

• SMS, MMS, location, rich presence, video
• IP multimedia subsystem (IMS) vs. “dumb pipe”

• Applications and business models

• Killer applications & killer platforms
• 2-sided business models

• Related technology, Issues and Futures

• WiMAX, Backhaul, Bluetooth, NextGen WiFi
• Mobile device diversity / application environments

But there's still more needed...

There is much more I could add.  The current tutorial barely touches on mobile handsets, handset software and handset applications frameworks.  There's also a lot more to say about WiFi evolution, but I don't want to promise an update that could be significantly delayed.  After all, it did take me five years to get around to updating the original 3G Tutorial.   :-)

WiMAX will be successful, as a fringe technology

A recent Infonetics press release says “WiMAX has gained such momentum across so many regions that it is no longer sensible to suggest that WiMAX growth will be flattened by the emergence of LTE in the next few years."

Probably true, but it's also clear WiMAX will never reach the scale of either mainstream wireless family, i.e., WiFi or GSM/3GSM.  By comparison with these giants, WiMAX will be a fringe operation.  The critical issue is volume, and what counts is the wireless technology brand, not the technology itself.

Both WiFi and GSM/3GSM have already evolved through multiple generations of technology while maintaining backwards compatibility and thus interoperability.  Within the GSM community, there may be no commercial LTE subscribers as yet and relatively few HSPA subscribers, but more than a billion GSM/3GSM devices are manufactured each year with individual chip set product lines running multi-hundred million units per year.  WiFi chipsets also run at hundred-million units per year rates.  These volumes (and the guarantee of interoperability) mean GSM/3GSM and WiFi devices will always be substantially lower cost than anything WiMAX aspires to.  [Note:  today there are slightly less the 2 million WiMAX subscribers while optimistic projections suggest there will be more than 100 million in 2012.]  WiMAX may have technology leadership, but it can't catch up.  WiFi and GSM are the wireless families that will prosper, each in it's sphere – WiFi for unlicensed, GSM for licensed spectrum.

WiMAX will benefit from technology specific licensing in some emerging markets, i.e., valuable spectrum tied to specific technologies,  So WiMAX will survive, even while it's more expensive than LTE or WiFi.  As for market share, the optimistic parallel is "CDMA cellular", i.e. IS-95/ CDMA One/ CDMA 2000.  CDMA had technology leadership and it managed to capture nearly 20% of the 2G cellular market at it's peak, but it could never overtake GSM and, today, major operators are jumping ship to join the 3GSM crowd.

There may be a decade of contention, but in the end, WiMAX will die or be absorbed into the GSM brand.

Fascinating potential increment in WiFi & WiFi mesh performance

I just stumbled on an interesting paper by Shyamnath Gollakota and Dina Katabi at MIT describing ZigZag decoding.  They will be talking about their work at SIGCOMM later this month.

The problem they've addressed is that of hidden terminals competing in a shared medium, in this case 802.11 WiFi.  This diagram shows the problem:

Alice's radio can "hear" the base station (the access point of AP above) and can transmit to it, but her radio can't hear Bob's radio so, while Bob is transmitting, Alice starts transmitting.  Their transmissions interfere, neither is acknowledged, both retry and even though they each delay a random interval, it's highly likely that at least part of their retransmissions again interfere.  Alice's and Bob's radios are said to be hidden from each other.  The critical issue is, since they can't hear each other the normal "listen before transmit" algorithm doesn't help.

ZigZag allows the base station to decode both of the colliding packets with an efficiency as good as if they had been sent in separate timeslots.  What's more ZigZag is compatible with all the various WiFi modulations and works with existing terminals, i.e., only the base station (the AP) requires an upgrade.

So far they've only implemented a prototype in software using GNU radio, so we're unlikely to see this in commercial products for a year or two.  But their results are impressive:

We have implemented a ZigZag prototype in GNU Radio, and evaluated it in a 14-node testbed, where 12% of the sender-receiver pairs are hidden terminals, 8% sense each other partially, and 80% sense each other perfectly. Our results reveal the following findings.

• The loss rate averaged over scenarios with partial or perfect hidden terminals decreases from 82.3% to less than 0.7%, with some severe cases where the loss rate goes down from 100% to zero.
• Averaging over all sender-receiver pairs, including those that do not suffer from hidden terminals, we find that ZigZag improves the average throughput by 31% when compared to current 802.11.
• At all SNRs, ZigZag’s bit error rate (BER) is lower than if the colliding packets were scheduled in separate time slots. The average reduction in bit error in comparison to scheduling packets separately is 1.4x.

They've invented a straight forward approach to decoding colliding packets.  It seems obvious now that I read it and yet I've been interested in this subject for 25 years and their approach never occurred to me.  :(   If you are at all interested, read just the introduction to their paper.

Why does it matter?

First, it's another increment in the continuing exponential improvement in radio performance

Second, it helps IT directors get more capacity on wireless LANs.

But most important for the long term, it improves the prospects for mesh networks.  While I can't predict specifics for how it will happen, mesh networks have the potential to create capacity from the edge!  No operators, just individuals and enterprises purchasing devices for other reasons.  Now that will be significant!