While at the ISCWN in Vienna, I met Ben West of WasabiNet in St. Louis. He’s provided excellent coverage of the sessions he attended in his day-by-day posts here:
August 17, 2010
August 10, 2010
August 04, 2010
AT&T Wireless still struggling with the basics
Has AT&T gotten better since I last wrote about their network performance at some length? Maybe not ...
July 27, 2010
July 23, 2010
July 22, 2010
July 20, 2010
June 14, 2010
April 06, 2010
One free ticket to eComm
Also, one 50% off ticket...
I'll be at the Emerging Communications Conference, eComm Americas, beginning Monday April 19th at the San Francisco Airport Marriott. If you're not familiar with eComm, I highly recommend it. Interesting people, fascinating presentations, none of those trade show pitches... Check it out.
And, as organizer and moderator of Tuesday's panel discussion on the US Broadband Plan, I get one free ticket and one 50% off ticket that I can give to a friend or colleague. If you're reading my blog, you clearly qualify. If you are interested, send me an email - send it to my initials "rbt" at my personal domain, i.e. broughturner.com.
March 31, 2010
March 20, 2010
March 06, 2010
February 20, 2010
A directional antenna for VHF TV — it's Large!
A potential limitation of TV "white spaces" arises from the relatively large wavelengths associated with these lower frequencies (lower than mobile or Wi-Fi). At cellular frequencies, and even better at Wi-Fi frequencies, wavelengths are quite short (at 5.8 GHz, a half wavelength is 2.5 cm, i.e. 1 inch), so it becomes relatively easy to build highly directional antennas. Not so with TV frequencies.
Here's a picture from a wonderful article by Neal McLain about highly directional VHF TV antennas in the CATV industry.
Quoting Frank Baxter, formerly Vice President of Engineering for GE Cablevision:
[This] antenna was erected in about 1965 [near] Merced, California, [for] a CATV system owned and operated by General Electric Cablevision until 1986. The screen was about 90 feet high and 360 feet long. The radius of the torus was about 100 feet. The screen was centered on San Francisco and several antennas were placed along the locus of feed positions to cover all the Bay Area signals. The support structure consisted of steel towers with the appropriate curvature and the screen was constructed using horizontal, stretched steel wire.
This is an extreme case, but it's worth remembering. Today, semiconductor technology makes it possible to do MIMO and, in the very near future, adaptive beam forming, in silicon at consumer price points. As a result, we're on the verge of major performance gains for wireless, at short wavelengths. That's 2 GHz and 5 GHz, but much less so TV white spaces.
TV white spaces will be useful for applications that must penetrate trees or heavy masonry but, as I commented earlier, the real action over the next 2-5 years (and beyond) will be at frequencies, like 5 GHz, where highly directional antennas can be built in small spaces.
February 16, 2010
February 13, 2010
Overestimating mobile data growth
Cisco has recently updated their forecast of mobile data growth. The good news is their forecast compound annual growth rate (CAGR) is down, from last year's forecast of 131% to their current forecast of 108% growth per year.
Unfortunately, when you look over the past 15 years of Internet traffic growth, the idea that any specific sector could exceed 100% growth for more than 1-2 years just isn't credible.
In the early days of the Internet (prior to 1994) traffic did approximately double each year. And, as Andrew Odlyzko points out in his classic study, there was a period of perhaps 18 months in 1995-1996 when US traffic grew much more rapidly, however growth reverted to 100% per year in 1997. And since then, Internet traffic growth has been slowing.
The most comprehensive data I am aware of is from Minnesota Internet Traffic Studies (MINTS) which shows the rate of Internet backbone traffic growth slowing so that in recent years (2008-2009) it has been in the range 40%-50%. For a good discussion of long term trends see Internet Growth Trends & Moore's Law.
Mobile network traffic growth
It's interesting to look back on the growth of mobile networks so far. Here are some numbers on cell sites, subscribers and voice minutes of use, extracted from CTIA data by Andrew Odlyzko.
1991 2006
subscribers 6.38 M 219.7 M
cell sites 6,685 197,576
MOUs 5.2 B 858 B
Over 15 years, voice traffic grew 165x which is 41% CAGR.
As an aside, it's interesting is to separate the growth in capacity due to more cell sites from the growth due to better wireless technology. Over the 15 year period 1991-2006, we got a 30x growth in the number of cell sites, or 25% CAGR. That suggests improvements in wireless technology (the transition from 1G AMPS to 2G and 3G systems) provided for only 5.58x of the increased traffic, or 12% CAGR. This surprised me. It can't be due to uncounted data traffic as data traffic was a small percentage of the mix in 2006. If true, it's rather embarrassing for the 2G and 3G equipment providers. Any suggestions?
There's a different view in this study of available mobile data download speeds done by Novarum Inc.
This shows available download data rates doubling in a little less than 24 months, or ~45% CAGR. However, this is measuring available bandwidth, not actual traffic. None-the-less, it's suggestive of capacity as these measurements were made on live networks during business hours.
A More Reasonable Projection
Given both Internet and wireless history, I suggest mobile Internet traffic growth over the next 5 years is more likely to be in the range 50% to 100% CAGR. There may be a 12-18 month period when it grows more than 100% per year, but only for 12-18 months and only if some alternate technology enters the mix (for example, widespread use of Wi-Fi hotspots as I suggested a few weeks ago).
February 04, 2010
February 02, 2010
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.
January 22, 2010
January 19, 2010
January 09, 2010
December 15, 2009
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.
December 14, 2009
December 13, 2009
October 28, 2009
October 26, 2009
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?"
October 25, 2009
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 networksOne 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/~
(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.
(3) Dynamic Buffer Management for Multimedia Services in 3.5G Wireless Networks, by Suleiman Y. Yerima and Khalid Al-BegainProceedings of the World Congress on Engineering 2009 Vol I
WCE 2009, July 1 - 3, 2009, London, U.K.
http://www.iaeng.org/
October 01, 2009
September 22, 2009
August 31, 2009
August 25, 2009
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.
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July 19, 2009
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?
July 18, 2009
July 16, 2009
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.
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May 16, 2009
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.
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May 11, 2009
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.
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May 05, 2009
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.
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March 02, 2009
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.
February 10, 2009
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...
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February 02, 2009
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.
December 03, 2008
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.
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November 16, 2008
November 05, 2008
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.
October 20, 2008
October 16, 2008
August 20, 2008
August 08, 2008
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!
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Recent Posts
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- Commercial use of TV White Spaces in 2 years?
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