Today comes the well-trailed news that Nextel are deploying a high-speed wireless WAN network, presumably based on Flarion’s FLASH-OFDM technology. (Nods to /. and Techdirt. More analysis also at Reiter’s weblog.)
As I said last week, 802.20 will be really important. Why? Well, as one well-informed colleage reminds me, 802.16 (aka WiMax) doesn’t have doppler tolerance built in from the start. That means it stops working when you start moving. It is essentially impossible to build this capability in later without starting again from scratch on new coding, silicon, FPGAs etc. Some limited hacks may enable a bit of motion tolerance. Flarion’s technology is converging with the 802.20 standard, which does have doppler tolerance from the beginning.
I’ve had a demo of a Flarion network. I sat in the back of a van driving at 70mph down the I435 watching someone play networked Quake. I’ve never felt such intense motion sickness so quickly! But the demo didn’t just make me want to reach for the barf-bag — it blew my socks off too. They built a low-latency push-to-talk application in … 2 days. Most carriers have taken years to achieve this. Nextel’s 2G Direct Connect technology, which is wildly successful in the US, took years to perfect. New competitors still haven’t reached that bar. With Flarion, it’s a few hours playing with your SIP toolkit in your favorite IDE.
This announcement is interesting for other reasons. The acronym gives it away: FLASH-OFDM stands for Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing. Let’s digest that piece at a time, and not eat the whole cow at once.
The “fast” bit is the easy one. Some modest knowledge of information theory and physics tell you how much you can pump through a slice of spectrum between two points. FLASH-OFDM is efficient in its encoding and handling of multi-path issues, so it comes out well on any speed test.
Traditional 3G cellular networks establish a virtual circuit to each handset. To communicate, a signalling channel is used to bring the circuit up and tear it down. This can take a long time — 10 seconds or more under load. The channel is also typically torn down after a timeout following a period of inactivity. So there is a lot of latency in establishing and re-establishing a channel. Then even once you have a channel, a queueing algorithm determines who gets to speak when. The distance you lie from the tower and amount of interference can affect how often you get a chance to speak. If you’re unlucky, it might be too long for you to win at Quake against wired competitors. FLASH-OFDM is pretty smart about queueing and also enables QoS for IP communications. (I’ll write about QoS another day and when and why it matters.)
As the Flarion marketing department puts it:
Third generation (3G) mobile networks, on the other hand, retain a circuit-switched, hierarchical architecture. Consequently there is tension between the design objectives and the current environment of the wired Internet and mobile voice networks. The resulting design compromises of circuit-switched networks, which are optimized for voice, impair their ability to deliver high-speed, low-latency data cost effectively. The resulting high cost-per-megabyte of data delivery over circuit-switched based networks will prevent the emergence of mass-market wireless Internet access. An alternative approach, focusing directly on high speed, low cost and low latency wireless data delivery is required. Flarion, through its innovative FLASH-OFDM airlink, addresses the challenge of delivering affordable mobile broadband.
The worst-case latency for a packet transmission on a Flarion network is about 5ms. In other words, about 200 times better than a CDMA 1xRTT network, typically found in the US, Korea or Japan.
The usual figures for data throughput you see for a CDMA or GSM/EDGE/UMTS network are maximum burst or sustained throughput. But most people don’t spend their lives doing FTPs. Instead they are using chatty, bursty applications. So the apparent spectral efficiency of 3G networks is a mirage. Your true throughput is terrible, because you spend all your life setting up and tearing down channels, and waiting for your one time-critical ACK packet to be sent. For instance, see this paper on page 5 for how throughput of a TCP/IP links varies with latency.
It’s the throughput of the complete system loaded with users that counts, not an artificial network test with a single laptop under the tower at 3am. Peak throughput is irrelevant.
You don’t have to be a genius to see that low-latency plus high-bandwidth looks like a tasty recipe for next-generation IP-based voice apps. Voice is still the “killer app”. But it is evolving once freed from the clammy dead hand of circuit telephony. Should enterprises start demanding end-to-end encypted voice, then Flarion can deliver it using off-the-shelf technology. Integrate presence, IM and voice a-la Skype? No problem. Anyone left with a faux-circuit network will be left spluttering.
Seamless hand-off matters for voice calls. WiFi is weak in this respect (today) because authentication and hand-off is slow. Plenty of people are working on fixing this. Dropped calls (or the perception of a dropped call) are the #1 driver of customer (dis)satisfaction with wireless networks. This is a “must-have” non-trivial feature.
So that was low latency and seamless hand-off. There was a bit more to the acronym soup, though. That OFDM stuff — what does it mean? Well, CDMA (the basis for 3G) has some unfortunate disadvantages. It needs complex and expensive power modulation circuitry to keep everyone shouting at the same volume. The cell site coverage shrinks as the system becomes loaded (called “cell breathing”). The coding isn’t built for IP communications — it was all done for voice, with packet as an afterthought.
ODFM is generally a more tolerant technology, even if it is a bit heavy on the signal processing (lots of matrix algebra, folks!). For instance, those orthogonal frequencies make power management of adjacent multi-path signals less of an issue. To quote the Flarion marketroids again:
Since all conventional cellular wireless systems, including 3G, were fundamentally designed for circuit switched voice, they were designed and optimized primarily at the physical layer. The choice of CDMA as the physical layer multiple access technology was also dictated by voice requirements. FLASH-OFDM, on the other hand, is a packet switched designed for data and is optimized across the physical, MAC, link and network layers. The choice of OFDM as the multiple access technology is based not just on physical layer considerations but also on MAC, link and network layer requirements.
So we have here a co-ordinated set of changes at layers 1 and 2 of the protocol stack. What’s fascinating is that this destroys the last refuge of the circuit carriers from business model change. Changes at the lowest technology levels ripple all the way up to the business model for the application layer. Wireless is not a safe harbor.
Thus far we have seen gradual but unstoppable substitution of wireless minutes for wired calling. Within a decade, Flarion and its competitors could potentially drive carriers out of the voice service business entirely. Cable companies and wireless ISPs will be able to give away voice to get you to buy into their pipe. Why? Because an ever-larger proportion of calls become VoIP, and the only significant direct cost is a remote directory look-up for a SIP routing function. Off-net PSTN interconnect shrinks to zero.
If Flarion tweaked their technology to lower the peak throughput and instead give a predictable low-latency 100-200kbps to more users at a lower unit cost, you would have the killer transport for a wireless successor to Skype. Now that would be interesting. Any VCs out there wanting to fund some market disruption?
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Great article and great analysis - came here from GigaOm and plan on reading more...
Here's some questions back to you - and I realize some of these may be stupid as I really don't know that much about the emerging wireless technology - so forgive me if I'm missing something really basic!
1. Would it be possible for a mobile phone to be able to use a Flarion-powered network and VOIP to both reduce the cost of running a cell phone network, and potentially open up the cell phone to broader applications such as real-time video?
2. Nextel has MMDS frequencies - but is the Flarion technology deployable on other frequencies - I'm specifically curious about XO Communication: they have LMDS frequencies and was curious if they could deploy the Flarion tech? Would it just have shorter range?
3. My understanding is that MMDS and LMDS both had line-of-sight requirements when they first came out and that was a significant limitation. My understanding of the Flarion tech is that it specifically does not require this - as your example of speeding down a road in a car would imply. Am I reading this right?
4. Lastly, who's really going to benefit from this tech? From Nextel's point of view, I could see that they could over broadband to the house, and VOIP to provide phone service. Seems like this will allow the wireless companies to become full-service telecomm providers.
I could also see them partnering with satellite tv providers (DirecTV) to have a full offering to compete with cable. Cable seems the most vulnerable here - they've been making fat margin on broadband connections that has helped us ignore the slower growth of basic cable connections. Take that away and they could be hurting.
Thoughts appreciated!
Damian
Posted by: at February 8, 2004 01:56 PM> Would it be possible for a mobile phone to be
> able to use a Flarion-powered network and VOIP
> to both reduce the cost of running a cell phone
> network, and potentially open up the cell phone
> to broader applications such as real-time video?
VoIP isn't necessarily a good way of reducing the cost of delivering vanilla POTS voice calls. There's a horrendous overhead -- about 80% of the data in an unoptimized WiFi VoIP call is headers from the many layers of the protocol stack. As long as spectrum is a scarce resource, some form of vertical integration of WWANs to support mass-market voice service is likely to be desirable.
On the other hand, the lack of a dedicated channel in F-OFDM can make things a lot more efficient, such as push-to-talk. And clearly, the moment you start to do serious service innovation, the "stupid network" wins out every time, "inefficiency" notwithstanding.
> Nextel has MMDS frequencies - but is the Flarion
> technology deployable on other frequencies
Yes and no. I'm not an RF or coding expert, but I believe the ASICs and signal coding are customized for specific frequencies. (Anyone know what they're talking about here - please enlighten us all!) But AFAIK the F-OFDM approach is not tied to any one freqency band (but neither are analog, TDMA, or CDMA.) The main innovation is really one of mathematics and coding theory, not physics.
> My understanding is that MMDS and LMDS both had
> line-of-sight requirements when they first came
> out and that was a significant limitation. My
> understanding of the Flarion tech is that it
> specifically does not require this - as your
> example of speeding down a road in a car would
> imply. Am I reading this right?
Yes and yes.
> Lastly, who's really going to benefit from this
> tech? From Nextel's point of view, I could see
> that they could over broadband to the house, and
> VOIP to provide phone service. Seems like this
> will allow the wireless companies to become
> full-service telecomm providers.
Google for "investor in Flarion". Those are your winners. Nextel is an investor. Some of the other investors give you eye-opening insights as to where the operators' true allegiances are (hint: watch the money, not the mouth). If I was Qualcomm, I'd be worried. CDMA's days might be numbered. (I saw a recent private demo of a next-generation CDMA network, and it was feeble compared to Flarion.)
F-OFDM probably isn't a good solution for fixed wireless. Why pay the penalty for doppler tolerance when you don't need it? WiMax is a better solution in that case. (And optically-switched fiber is probably the holy grail, anyway -- the wireless last mile is probably a stepping-stone technology for urban areas wanting to evolve beyond copper.)
Martin
Speaking of OFDM, doppler tolerance, and NLOS, ever hear of a company called NextNet Wireless?
Posted by: at February 10, 2004 10:44 PMHadn't heard of them until a few days ago. Will have to see what my contacts turn up! They seem pretty similar to Flarion.
There's usually some gotcha in each of these solutions that narrows their scope or suggests immature technolgy. Flarion, for example, took a while to perfect hand-offs, from what I hear. There's quite a laundry list of awkward questions you need to ask to cut through the marketing BS about each wireless technology. (For instance, the lack of power modulation in WiFi and intelligent channel selection really hamper the technology in very dense installations like conferences and apartment blocks.)
A VC acquaintance recently asked my opinion on another OFDM start-up in stealth mode, so I think this market is going to be interesting.
At the moment there's a bit of a chicken-and-egg problem with OFDM: without volume, the chipset costs are high, and high prices discourage adoption. As we've seen with WiFi, mass markets drive ridiculously low prices. It just takes someone brave with deep pockets to come in and give the market a kick. Anyone been watching where Craig McCaw's jet has been landing recently?
Martin
Thanks for the follow-up to my questions.
Does anyone know of a wireless tech which provides enough bandwidth for video? I'm thinking about two levels of video here - normal TV quality and HDTV quality. I don't believe there is any tech out there at the moment that has the bandwidth and can be deployed cheaply, but I was interested to see what you guys knew about it...
Thanks..
Posted by: at February 11, 2004 01:52 PMJust to point out a small problem in your opening paragraph: "WiMax" can work at speed. Check out the Canadian company Wi-Lan, who makes prestandard 802.16 gear, and claims a patent on the underlying OFDM variant that they call W-OFDM ("Basic OFDM" has been in the public domain for a while....). If you look at info they've published, they've been claiming operation at 70mph speeds for years, and they're working with the Korean ETRI to develop a 4G spec.
Hand-off still presents a problem, and I don't dismiss the fact that latency is important for particular applications. But with Intel, Fujitsu and others aiming for ASICs late this year, the deployment cost of WiMax will fal *much* faster than 802.20.
Posted by: at February 15, 2004 10:09 AMThis may lead to famous switch predicted by Negreponte in his book "being digital" where what communication services provided by wire move to wireless and the wireless communication services move to wired meadium.
Posted by: at February 15, 2004 08:29 PMI understand that doppler interference can be a factor, but this is only for higher speed applications (i.e. aircraft). I've run both 802.11 and 802.16-like radios in prototype environments. Most of the difficulty with 802.11 came into play with interference due to the CSMA/CA MAC (and the RTS/CTS NAV). I've seen 802.11 work on some airborne applications, and the doppler shift probably won't be an issue until speeds exceed 300 mph or so.
Are there any other differences you would use to recommend 802.20 over 802.16? I've seen preliminary 802.16 applications with a spectral efficiency of 3.1 bps/hz, which is currently beyond Flarion's performance. I'm not an advocate of any particular technology, I just think it is important to make relevant comparisons.
Posted by: at July 10, 2004 04:44 PMThat's because bits per second Hertz is a terrible metric. It is the local optimization of transmission through an already established channel. It isn't a global optimization of system throughput. Flarion's claim to fame is low latency (just check the acronym: FLASH-OFDM). You can economically send a single bit message. Chatty internet-type applications work and scale. That isn't the case for the CDMA competitors, and the jury is out on WiMax. They all spend too long negotiating at the MAC layer.
Which airline would you prefer to hold stock in: one which flew half-empty jumbo jets, or one which flew completely full 737s? The former is the "high capacity" (high bps/Hz) option -- lots of capacity that never gets filled because of the latency in the MAC.
Posted by: at July 10, 2004 11:06 PMThe mein problems of futures wireless sytems including OFDMA are frequency efficiemcy and Doppler Shift influence.
Maybe FBS method can help to avoide collision.
The main FBS advantages are:
• A significant decrease of the Doppler shift effects, as well as the time delays, frequency changing and orthogonality degradation.
• FBS removes the need for conducting tests or using pilot signals and/or equalizing processes. Eliminating prolonged selective fading by means of randomly shifting sub-carriers frequencies.
• The FBS method can be implemented in different wireless communication systems. FBS system will result in a significant increase systems throughput owing to pilot signals absence.
References:
M. Bank, "On increasing OFDM method frequency efficiency opportunity", IEEE Transactions on Broadcasting, 50(2), 2004 (165-171)
M. Bank, "System free of channel problems inherent in changing mobile communication systems",
Electronics Letters, 43(7), 2007 (401-402)