Communications

Beamforming for Wi-Fi, WiMAX and LTE

Concentrating a wireless signal in a tight beam has tremendous advantages. You need less power for equivalent distance, you create less interference to others and, if your receiving antenna is similarly directional, you avoid a lot of interference from others. Of course people have been using directional antennas to achieve narrow wireless beams for years. But a directional antenna has to be aimed and then it's fixed.

That's great for a point-to-point link but useless for someone on the move.

Beamforming creates a narrow wireless beam that can be steered in software. Suddenly the advantages of narrow beams can be applied to point-to-multi-point systems and in systems where one or both ends are in motion. Of course the process is quite sophisticated and, until recently, was very expensive. Luckily that is changing, rapidly!

This slide shows how, with beamforming, one Wi-Fi access point can communicate, in rapid succession, with three different clients.  And this can happen despite another access point using the same channel to talk with one of it's clients. Indeed, it all works despite the existence of a legacy Wi-Fi device that is broadcasting omni-directionally on the same channel.  Pretty powerful!

Think what something like this could do for tenants in a large apartment block. It no longer matters that 34 neighbors have nearby Wi-Fi access points.

Proprietary or "standard" ??

Based on questions I get, there appears to be quite a bit of confusion. The answer of course is we see both proprietary and standard implementations within the Wi-Fi market.

Beamforming is an optional part of the 802.11n standard and silicon support for this option is emerging (more on that in a moment). Beamforming is also part of the most recent revisions of WiMAX and LTE standards. Confusion arises because there are several different things which are legitimately called beamforming.  

The simplest is a switched beamformer in which there are multiple directional antenna elements and the radio or radios are connected to the appropriate elements as needed.  This is what Ruckus Wireless does today. It's what Vivato Networks did with 802.11g back in 2003. The Ruckus products have 12 or more fixed elements and, on a frame-by-frame basis (e.g. every 10 ms), they decide which two of those antenna elements to connect to the two terminals on an Atheros (2x2 MIMO) Wi-Fi chip, based which combination works best for the specific device the access point is communicating with.  Many people have patents here, but the ideas are very old, so the patents may not be very valuable.

Next are phased array beamformers.  Here multiple simple antenna elements, equally spaced, form an array.  Each element sends (or receives) the same signal but phase delays are introduced so, via constructive and destructive interference, the resulting wireless signal forms a narrow beam.  This beam can then be steered by varying the phase delays. Phased array beamformers are also well established with examples dating back to 1905 and widespread use in radars since World War II.

Finally, in MIMO systems, precoding is a mathematical generalization of beamforming that leverages antennas elements that may not be equi-spaced and deals with the fact that the other end has multiple receiving antennas. And at the receiver end, maximal-ratio-combining (MRC) optimizes decoding of the transmitted signals. Very roughly you can think of these MIMO computations as putting the maximum beam lobe as close as possible to the desired target while placing nulls (of the antenna pattern) as close as possible to the primary interferers.

Today's widely deployed Wi-Fi chips have two radio chains (2x2 MIMO) which are typically used for horizontal and vertical polarization, but 3x3 and 4x4 MIMO chips have come to market.  With 4x4 MIMO Wi-Fi chips we see transmit beamforming via precoding and receive beamforming via MRC.  Indeed, two silicon startups, Quantenna Communications in California and Celeno Wireless in Israel, have announced Wi-Fi chips that support 4x4 MIMO with transmit beamforming and both vendors' chips have shown up in consumer products, e.g., the Quantenna chip in the Netgear WNHDB3004.

The 802.11n standard specifies how the needed information is passed, so the computations that Quantenna and Celeno do (and others in the future) can be carried out at either end even though the devices are from different vendors.

 My interest

Beyond mentions in my speaking engagements and wireless tutorials, beamforming will be directly useful to netBlazr, our new (and radically different) wireless ISP.  netBlazr depends upon participants deploying network elements.  Today, these require aiming but, with beamforming, aiming won't matter and, if the unit is bumped later on, beamforming will compensate on-the-fly.

 

My notes from the Community Wireless Networks Summit in Vienna

As with most conferences I attend, I took most of my notes using Twitter.  Since I can't always depend on accessing old tweets, here is the entire tweet stream from the conference in one blog post.  I don't know if this is of use to anyone else, but at least I know I'll have a record of my notes that I can refer back to.

The full name of the conference was The International Summit for Community Wireless Networks (ISCWN) and it was held in Vienna on August 12-15, 2010.  See the conference website.

International Summit for Community Wireless Networks http://bit.ly/9Lp41p
Good conference Wi-Fi http://bit.ly/dkwUh2
OK, I'm finally set up to Tweet &/or blog the International Summit for Community Wireless Networks http://wirelesssummit.org
While there's plenty of broadband behind the Wi-Fi, there are very few power outlets, at least as yet.
Community Wireless conf finally getting underway
Sascha Meinwrath opening: 1/2 the participants are missing, even some who were here an hour ago, so expect stragglers, but we start.
Sascha: 80% of cash raised goes to travel allowances; 10% everything else; plus donations.
Aaron Kaplan, Funkfeuer, on TechGate facility science park estbsh'd 2001 by City; conf venue; also supports Funkfeuer
Aaron there is swimming in the old Danube - it's clean now! Also boat rental nearby!
Aaron: Funkfeuer hotspots since 2003, now reaching almost to Bratislava. Mixed mesh and P2P backbone
Sascha on previous feedback - social time is key
Jim Baller: America at the Crossroads: Greatness or Mediocrity. 15+ yrs fighting ILECs on behalf of muni's - mostly successful!
Baller: credits Broadband Coalition http://bb4us.net/  Also as key to Congress requiring FCC to do a BB Plan
Baller on the US national BB plan: We need big goals, the BB plan didn't deliver! It's goals for 2020 happening elsewhere today.
Baller: US BB Plan focuses on inches, not yards and miles.
Baller: US BB Stimulus: Awards coming quickly (9/2010 deadline): middle mile, rural first mile
Baller on Google gigabit initiative yielded 1100 muni applications and showed pent up demand
Baller: Ugly side - incumbents bigger, stronger & nastier than five yrs ago. Cable industry even nastier. Now Google is in question.
Baller: But btwn BB Plan (it's a plan), Google fiber init., $7B Stimulus goes to new parties, community BB efforts
Baller responding to Q about wireless: I'm a fiber guy, then disappointing comments on FCC being pro-wireless. Misses FCC focus :(
Baller responding to Q about Australia admits that most in US don't know what's happening in the rest of the world.  US always has excuses - "we're different."
Sascha introducing Ramon Roca, President, guifi.net Foundation, a fantastic alternative that's happening in Spain. 
Guifi runs a very large network across rural (and urban) Catalonia in Spain. http://guifi.net/
Ramon Roca: Vision for the Future. Will talk about: Why scale? and their sustainable economic model!
Ramon: Guifi has 10K+ nodes and 15 Km of networks, but still tiny compared to telco. Scale as a goal. Need growth to be sustainable.
Ramon: need sustainable model - critical mass; org issues; legal; partners. Non-profit core w/biz around.
Ramon: Demand is there; also incumbent not interested in low 40%.
Ramon on mgmt: horizontal, bi-directional & collaborative - examples from their website. Website appears to be key for communit.
Ramon on public/private: public requirements must be written: contracts, license, P2P agreements. Must be clear, and legal.
Ramon on public/private - like OS licenses, the network is considered private by govnmt. Need documents just as open src does.
Ramon facilitates integration and cooperation between diverse groups, e.g. need churches for their steeples! need public ROW access.
Ramon: Guifi license is required if you want to participate! Like GNU license, Guifi license even deals with revisions.
Ramon: Guifi license defines everything
Ramon: Guifi is also a ""public"" network in the legal sense in Spain because they had to in order to deploy some fiber.
Ramon: Guifi ROI for many: supply chain dlrs/shops, prof svcs and svc provdrs who mediate wholesale mkts.
Ramon: Catalonia is a bit ahead of Spain but w/o Guifi Osona (rural Catalonia) way behind. Now Osona ahead of rest of Spain & even the UK.
Ramon: Guifi network now 15% of BB links in Osona; and yet DSL subscription haven't dropped.
An English version of the Guifi Wireless commons license is here: http://guifi.net/WCL_EN
Ramon futures: working on fiber from farms (FFtF) cheap & easy & Gbps; always a combination.
Ramon has had fights with incumbent about ROW (even when on private property) and about access to poles. Ramon - do it! then fight.
Ramon - their main focus is to stay on private ROW, but as a public carrier they can now go after public ROW.
Ramon: stories about fights over public fiber & public ROW - everything you expect, except Guifi seems to win, espc. in rural area.
Ramon: Guifi participants getting access to public fibers laid for cameras after threaten authorities - tractor might hit camera...
Ramon concludes by emphasizing need to enlist service businesses and computer shops, e.g. 3rd party for profit businesses.
Lightning talks where individuals describe their networks.
Austin (TX) Wireless - hotspot service; wanted free Wi-Fi; customers incl coffee shops that compete with Starbucks.
Austin Wireless - other things to help venues, e.g. splash pages
Austin Wireless: splash pages useless if not totally relevant for the customer: Weather, sports, local info, Facebook links, venue.
Austin Wireless: Now making $ by providing marketing services to their venues, restaurants, coffee shops, etc.
Austin Wireless: Also does Chimpit which brings venue portal even if you're on another network.
Chambana.net joint project of IMC and Acorn IT collaborative - ~6 active people and 9 servers. Walk-in computers, media prod. lab.
Chambana.net host websites, many other IT services, but also some wireless! Small network, switching from NetBSD to OpenWRT.
Chambana.net: It sounds like their wireless net is secondary to what they do, and is currently down and being reworked.
Chambana.net: Wireless network is completely open, no splash page. Runs on donated hardware
Chambana.net runs on donations, but entire uplink is one Comcast business service. But part of a stimulus grant, so near future good
Tribal Digital Village: 19 tribes HQ in San Diego CA, only way to get Internet to reservations. sovereign nations within US, but...
Tribal Digital Village: 350 miles of P2P and P2MP links mostly license exempt; 18 bldgs
Tribal: Paid NW in parallel reaches 200 individual homes. 2/2 Mbps for $34.95 per month. Hope to reach 2000 of 2700 homes.
Tribal: 1K devices connected to net. Fiber at headend feeds an arc of P2P links. Now many gamers accessing via local centers.
Tribal: Too small and separate to think about running their own radio regulatory regimes. But not too worried about conforming :)
Djursland http://www.diirwb.net/ Rural area in Denmark; 95% can get DSL (fr 1600 exchgs). Last 5% not svc'd.
Djursland P2MP design
Djursland: NW built by volunteers
Djursland gets favorable Interent transit because the farmers drove (& control) the fiber backbone deployment.
Funkfeuer: mesh using OSLR; got help from jaap@scii.nl & friends in Berlin.
Funkfeuer: 240 roofs; financial sustainability based on hosting center revenues; Gbps uplink
Funkfeuer: slightly below mkt for hosting; TV streaming experiments; running Wi-Fi for events.
Funkfeuer: Fiber splicing is easy, if you have the expensive machine (~6000 Euros). Basically welding glass.
Funkfeuer is a closed user group. This is important for VoIP and other regulatory issues, including streaming TV to you members!
Funkfeuer Graz: like NW in Vienna; Technical Univ in Graz helped them grow fast; slower growth >2007 as 3G faster.
Funkfeuer Graz: now working to link with Bratislava (Slovokia) which could be the first international community network in EU.
Funkfeuer Graz: longest link today is 30 km which gets them 1/2 way to Bratislava (Ubiquiti radios)
Malcolm Matson knows of two networks connected (quietly) btwn Solovakia and Hungary.
Belgrade Wireless: up to 20 km links (> 50 Mbps) using corner antennas as shown in previous conf. NW now extends over 100 Km.
Belgrade: 3D corner antennas invented by Prof in Belgrade. Big focus on community events.
Belgrade: 3D Corner Antennas http://su.pr/AjXm1p - feeder for dish reflector - mixed polarization
More 3D corner antenna info here  http://su.pr/7t9990 Need to follow up on whether this remains relevant w/ MIMO using polarization.
Updates from the OLSR-NG Project - Henning Rogge (FKIE) & Aaron Kaplan (Funkfeuer.at) - history, today & futures.
OLSR-NG: 1 of 2 major mesh stds (other AODV). RFC 3626. Tonnesen PhD, Lopatic LQ & Fisheye extensions
OLSR-NG working on OLSR. Guys in Berlin starting over (BATMAN); HSLS hazy sighted link state (CUWin).
OLSR-NG session: CUWin HSLS didn't get beyond simulations
OLSR-NG: OLSR is link state - every node knows whole graph (100K entries = 4.8 MB); but MPR now off
OLSR-NG: MPRs only matter with really dense NWs, but with only 2-3 links per node, they don't pay.
OLSR-NG: ETX link quality metric used instead of basic hop count, i.e. sum of ETXs not sum of hops. But heavy compute load!
OLSR-NG bringing down compute load (now linear not exponential). 100-to-1 benefit with 400 nodes. Still Dijkstra, but optimize data.
OLSR-NG: malloc() thrashing fixed
OLSR-NG futures: soft refresh (CSN), better metrics (ETT, MIC), multipath routing (experimental), Q of layer 2 capabilities.
OLSR-NG: Henning comments on how few multi-path routing projects have made any progress... Problem: must choose whole path. very hrd
OLSR Henning: OLSRd 0.6.0 is current. Clean rewrite of routing code; smarter gateways to reduce thrashing btwn GWs.
Henning: 0.6.0 has very few (& only site-specific) bugs - very stable!
Henning on future plans: telnet/http server (done); config mgmt (stability, flexiblty.
Henning also thinking about better metrics but limited by packet format prior to OSLR v2. Many metrics in discussion in academia.
Henning responding to Q: negative about dual protocol mode to support migrations. Thinks it wold be very hard.
Henning - active developers= ~1.5 people
Henning complaining about academics who've made patches w/o consulting (thus doing stupid things) and without plans to give back.
Henning & Aaron on how plugin system makes it easy to try new things in a clean fashion.
Freifunk Berlin started 2002; then OSLR in 2003-04; 28 devices @ 2004 OS conf; PC to openWRT for embedded.
Freifunk took off in 2005 despite labeling website ""OSLR experiment"" but users wanted reliability
Freifunk can't even switch to B.A.T.M.A.N. because OSLR widely deployed
Freifunk net is now shrinking, as people who came only for bandwidth are getting DSL and 3G mobile.
Freifunk has issue of switching gateways which doesn't affect Frunkfeuer with their fixed gateways and public IPs.
guifi.net is a bunch of communities, not all interconnected. 10,300 nodes using same software, same tools and same license.
guifi.net is showing off an impressive set of tools for examining nodes, plus there's extra data that the node owner can access.
guifi.net Using MRTG http://oss.oetiker.ch/mrtg/
guifi.net is a large wireless LAN. Must search for & connect to services, like Internet access. Libraries & other offer Inet-GWs.
Île sans fil network in Montreal  http://www.ilesansfil.org/  Now 200 hotspots installed, free Internet thru portal page.
Île sans fil limits users to 7 GB/wk. 150K users registered. Each hotspot has own page. Projects: Authpuppy, WiFiDog
Wireless Toronto - captive Wi-Fi portals, started with Wifidog from ◊le sans fil.
Wireless Toronto has struggled compared to Montreal. All volunteers. Hotspots, but now adding mesh, e.g. in parks.
Wireless Toronto - no spt fr Government who started and sold a parallel NW. Hard to find location-based content for portal pages.
Wireless Toronto survives on annual fees from businesses with portals; organized as a club, not a nonprft
Wireless Toronto new mesh started with BATMAN but found OSLR more reliable. Using Open-mesh but moving to Authpuppy.
Wireless Toronto - the less you talk about Wi-Fi and the more you talk about mktg, the better you do selling business hotspots.
Wireless Toronto using AutoAP in part to just monitor what's going on, wirelessly, in their neighborhoods.
Open Wireless Networks http://consume.net in London
Consume fell out of use ~2003
OWN: nodes all clustered in London near Greenwich Park. Not 400 nodes
Good line-of-sight planning tool:  http://www.heywhatsthat.com/
Village Telco http://www.villagetelco.org/about/mobiles have brought telecom to Africa, but not Internet, yet...
Village Telco: it didn't take off
Village Telco: Built ""mesh potato"" - solar mesh device w/analog phone adapter; production units next month.
Village Telco: Mozilla is filming the project.
Village Telco: Retail cost $119
Wlan Ljubljana: http://wlan-lj.net Can't beat widespread fiber at $14/month, but each has excess capacity and willing to share.
Wlan Lj now up to 50 nodes & adding rural areas - now wlanslovenija! http://wlan-si.net entirely volunteers
Wlan Lj is clearly a group of hackers having fun, but it's not clear to me if they are really serving a need. Sustainability???
Wlan Lj has done solar nodes - 24 hr reliability but froze during the winter and wasn't restored until spring (cold on roof!).
Athen Wireless Metropolitan Network (AWMN) strtd 2002 because no DSL; open experimentat WLAN.
AWMN has some people who offer Internet access, but it's not the primary goal. Participants tend to be Univ types - young, educated.
AWMN mostly at 5.4 GHz with Linux and MikroTik routers. Islands of OSLR connected by BGP; 2505 nodes; 1100 backbone nodes.
AWMN speeds vary 11 Mbps to 150 Mbps. 730 access points. Organized by an association; events; community; no grants.
AWMN Recently, large deployments of 11n
AWMN As a local LAN, they have mirrors of many Internet services, also transliterated version of Google (Woogle), Yahoo, etc.
Richard MacKinnon of Austin Wireless follows me in the Freemium session. AW strt'd as all free, but wasn't sustainable.
MacKinnon: Austin Wireless used automation to replace 50 volunteers with 2 fulltime staff. Merchants pay to provide free access.
MacKinnon: Pull together local news for hotspot portal pages
MacKinnon: Used to charge $5/mo
MacKinnon: Integrate Facebook into portals, incent patron's to talk about the business they're visiting on their FB page. Biz value!
MacKinnon: installations were fun at 1st
MacKinnon: $55/mo buys support. Restaurants hate Wi-Fi but have to have it to be competitive. So support is key - ""power cycle box!
MacKinnon: deals with cable company; POS crdit crd installers.
MacKinnon: Ads didn't work but local ads may be coming back.
Nemanja Topovic, Belgrade Wireless, Serbia started as all volunteers. Had problems with Government (spectrum laws).
Topovic low cost svc didn't work (1 Euro/mo) as people expect full svc. Discusses many paths they've tried, unsuccessfully...
Topovic - network grew rapidly 2004-2006 but growth has stopped. Looking for a program that could restart their network.
Topovic: BGWireless not a mesh, uses high speed P2P and P2MP. Closed network.
MacKinnon suggests his biz mode for Topovic. Key is offering free svc to avoid spt issues and then find a premium svc to cover costs
MacKinnon - important to offer new paid service as something new, not as a price increase on old service.
MacKinnon: 200 customers today (and 1 & 2 yrs ago) but different group & paying more & more loyal. Free customers were least loyal.
MacKinnon user community divided: some just want Internet
Paul from NFP? talking about SW defined GNU radio work going on in the building. Available for discussions later...
Robin Chase, Meadow Networks (previously founder of Zipcar) will be evening keynote spkr - next up.
Robin Chase on tie-in of transportation and networks: financing (fuel tax moving to road tax eventually - per km!).
Chase Auto density in cities (congestion) but expense of rural rds. Moving to congestion pricing. Will need more technology...
Chase on transport costs not reflecting true costs (fuel/environment, etc.)
Chase Public-Private Partnership discussions are missing the individual. Transport tech has decided they need their own stuff.
Chase: transportation guy gets his spectrum; EMS/medical types need their own stuff- it's just comms
Chase: Transport problems: Lumpy density, congestion, financing, right pricing same problems as in comms infrastructure -> dist. NW
Chase: future for transport and comms is distributed networks
Chase focus on distributed and collaborative inputs as a path to innovation.
Chase: words to use when talking about Gov. spending: open data; open standards; open source
Chase talking about Comuto (ride sharing in France)  http://www.comuto.fr/ now has more unique users than ZipCar (& just in France).
Chase: talking about CouchSurfing: 7 yrs old; 200 countries, 71K cities; more ""beds"" than major hotel chains.
Chase on Chatroulette - built it in 3 days; but in 6 months it now gets 30M unique visitors - mindboggling!
Chase: Andrey could do ChatRoulette because platform (Pcs, Internet) was there and there was excess capacity available.
Chase on all the crazy ideas that are now iPhone apps and yet the excess capacity has fostered some incredible innovations.
Chase: People & Platforms -> Speed & Scale
Chase wants open mesh device in every car that will have to be paying congestion fees, getting traffic data
Chase wants an open platform in cars so we foster new apps we can't can't even envision now.
Chase: what if all nodes (smart grid, smart cars, smart infrastructure) were peers? and open platforms!
Chase: www.networkmusings.blogspot.com & @rmchase & rchase@alum.mit.edu
Vic Hayes of TU Delft University: Spectrum Assessment for Wi-Fi. History of FCC & license exempt spectrum and Wi-Fi market.
Hayes: FCC landmark decision 1985- license exempt; use more spectrum than required; spread spectrum tech.
Hayes: Standard CDMA history including Hedy Lamar's patent, but I learned something new - she was born in Vienna!
Hayes has some good slides to explain CDMA. I'll probably stick with my standard slides http://su.pr/1LMCYl
Hayes: FCC wanted to allow spread spectrum over wider bands but got objections so they settled on ISM because no one cared.
Hayes on attempts to get similar rules thru CEPT - succeeded in 1991 for 2.4 GHz band only and with slightly different rules.
Hayes: CEPT said only -10 dBW ERP (100 mw) and 10 mw per MHz
Hayes: because of cost of electronics, 900 MHz took off 1st (in 1989)
Hayes on how Wi-Fi 11 Mbps beat HomeRF even though the FCC permitted wideband hoppers (1998-2000). Wi-Fi faster
Hayes: 2002 FCC permits intelligent hoppers (reduce blutooth intf) & power spectral density rule (opens the way for OFDM, i.e. 11g).
Hayes: Now 5 GHz - FCC NII proceeding - Apple, Lucent, etc. release 1997. Adds 5 GHz spectrum.
Hayes: meanwhile CEPT yielded to Satellite industry and reduces pwr at 5 GHz, but add more spectrum for HIPERLANS (455 MHz).
Hayes: CEPT decides to go to WRC 2003 to make 5 GHz primary and global. US problem because NTIA refused. Took until Jan2003 to win.
Hayes: In June03 WRC 2003 allocates 455 MHz co-primary in 5 GHz band. Accepted in US & EU - still in flux in many countries.
Hayes: Once spectrum is allocated, it still must be defended (find reasons in style with current political agenda).
Hayes promoting his upcoming book: The Innovation Journey of Wi-Fi, Edited by Vic Hayes et al. to be published by Dec2010.
Clarification of 1st unlicensed spectrum was 1937 for baby monitors, etc.
Hayes: Questions about Ad Hoc mode
Rabi Karmacharya & Basanta Shrestha of OLE Nepal using wireless to deliver Internet connectivity to schools in Nepal
OLE Nepal: Initial focus (2006) was OLPC, but if you got PCs, there was still no Internet
OLE Nepal: Don't have to teach kids how to use computers - that comes naturally - but need to create content in local language.
OLE Nepal: Teachers have to be retrained, and need to realize the kids may know more about the PCs that they do.
OLE Nepal: Need network infrastructure, in schools and between schools and the Internet.
OLE Nepal: Open source, open content
OLE Nepal: 28 people on staff
OLE Nepal: First priority is a network to and btwn schools as Internet upstream is very expensive in Nepal.
OLE Nepal: One highway with fiber runs length of country in the southern lowlands (near India border). Northern areas to 8K meters!
OLE Nepal: fiber line is connected to India so Internet transit pricing has come down substantially, but still very expensive.
OLE Nepal: approaching 38 schools in six districts & 4K students connected. P2P WLAN w/ typ. 5-10 Km distances
OLE Nepal: ADSL where available, used with VLAN.
OLE Nepal: On the plains, need to find a hill to act as relay point. Sometimes >20 km links needed (example 26km).
OLE Nepal: In hilly areas, may need 3-4 relay points at remote sites (4 hr walk)
OLE Nepal: School NW have: radio; switch; & 2-3 Wi-Fi Aps; all w/UPS. Select equip. for low power! Linksys WRT54GL w/DDWRT.
OLE Nepal: MikroTik 433 AH & 411 CPE - have used this up to 26 km. Also EnGenius radios, but not reliable.
OLE Nepal: SW tools: Google Earth, Radio Mobile, mirror tst'g. Use trees as towers (cut away foliage).
Ben West of Wasabi Networks (St. Louis) has posted his Community Wireless Day 1 notes here:http://su.pr/3FG39a
Ben West's Day 2 notes include notes from the session I spoke in: http://su.pr/1DHUFi
There's a big EU network that's not here. It's Czech Freenet: http://su.pr/2qMyeE 
Whoops - and this Czech Freenet: http://su.pr/24yYU8
Future for Community Wireless Networks session lead by Aaron Kaplan and Vic Hayes. EU wired net getting better and CWN shrinking...
Future of CWN: ideas fr. grp: underserved rural areas; hacker grps want to stay that way.
CWN futures: my categories: hacker comm, social comm & svc provider. All NWs have some of each, but one tends to be primary.
CWN futures: several people object to categorizations (in general?)
CWN futures: Movement to integrate node databases fr. many diff. networks. Exchange knowledge on making node db's. Mtg in <6 mo.
CWN futures: A world node database would create a larger vision of the movement, espc. for members in individual networks.
CWN futures: some desire for turnkey node solution prompts objection from Berlin hacker community that people would stop learning.
CWN futures: Ramon (guifi) sees evolution in the discussions over past 4 yrs: more consensus, meta focus (e.g. world db).
Networking rural areas: Rantanen - Tribal NW mostly done with grant money.
Networking rural areas: Rantanen offerring his cast off equipment to Krusevac Open
Networking rural areas: Krusevac network is technically illegal under Serbian law (ISPs must be licensed w/many problems & cost).
Telecom for disaster relief - Mark Summer of Inveneo talking about wireless in Haiti after the earthquake -http://www.inveneo.org/
Mark Summer: Mountain range around Port au Prince was key
Mark Summer: so many Sat Phones came into Haiti that satellite capacity was saturated.
Mark Summer: got Ubiquiti to get stuff from distributors (in 3 days)
Summer: Kitted everything over a weekend; VSAT vendor committed 5 Mbps link if dish fixed.
Summer: Google got very high res imagery on-line within 48 hrs and updated it every few days. Open Street Maps for former streets.
Summer: got VSAT up in <24hrs
Summer: Got 3-4 radios in per day
Summer: Linked 18 NGOs at 23 locations in 3 wks; NGOs didn't want it turned off, as better than pre-disaster.
Closing keynotes just starting. Tomorrow: open spectrum alliance
Aaron Kaplan thanking many, many. Node DB SIG being set up for this coming winter.
Sascha Meinrath asking for ideas we should ponder over next yr. Answers: 1. OS physical layer (GNU radio?) - seeking FPGA designers.
Answers 2) Allison Powell (@postdocal) learned we're still not good at telling stories. She's seeking people to interview.
Answers - Rabi Karmacharya (OLE Nepal) very struck by the discussions of biz models and how NW can help in disaster recovery.
Audience comments: worried that several major networks are loosing nodes
Audience comments: Session on splicing fiber was exciting. Community radio + community fiber (+ community satellite?) !
Audience comments: Credit to Matt Rentenen for offerring to pass on older equipment. Sascha suggests an email to CWN list.
Audience comments reinforcing idea of using Wikipedia as the master list of Comm Wireless NWs + spectrum laws http://su.pr/2C3YFz
At OSA Mtg http://su.pr/2AtH5O 1st formal mtg took 1.5 hrs as bylaws are in German & English. Hopefully we'll talk spectrum soon.
OSA Mtg: @postdocal asks OSA view on net neut & suggests links with other advocacy grps. Open a rathole? Sent for email discussion.
Now in GNU radio discussion. Ah techies, > interesting than policy talk.. Getting into to USRP http://www.ettus.com/ which I already know of.
Paul Fuxjaeger on GNU radio: OFDM for 11a, 11g required substantial mods to GNU radio blocks. Also hard meet IEEE timing req.
Fuxjaeger, GNU: For 2x2 MIMO, externally sync 2 USRP2s (not w/Ettus cable!) so as to maintain 2 Gig data streams, vs 1 w/Ettus cable
Fuxjaeger: http://www.oz9aec.net has interesting GNU radio stuff, also an update on Gumstix & GNU radio! More shortly...
Fuxjaeger: http://su.pr/A899kx has the pointers for Gumstix and GNU radio
Fuxjaeger: http://su.pr/1TZZeQ is the PR for Gumstix's product Stagecoach which packages TI OMAP processors that may be used w/Ettus
Kaplan wraps up the GNU radio session w/demo pasting macro blks & receiving signal from a Ham radio in 70cm band, i.e. 420-450 MHz.

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.

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.

Vladimir Kotelnikov – Father of Sampling Theory

Actually one of several "fathers."  Caution: the following is for the DSP engineers among you.  :-)

When I learned communications theory it was attributed to Claude Shannon (his 1948 paper) and sampling theory to Nyquist.  I do remember my father once telling me that E. T. Whittaker had published the relevant mathematics long before Shannon, but I never looked up the history.  And I never asked my father to elaborate as he was pushing his copy of Whittaker and Watson at the time, together with the idea I should be a mathematician or a physicist – not an engineer!

But on the plane back from Paris I read the June issue of Communications Engineer from The Institution of Engineering and Technology which included an interesting article on V. A. Kotelnikov by Professor Chris Bissell. 

... in the late 1940s <Shannon> wrote that the sampling theorem was “common knowledge in the communication art, but in spite of its evident importance it seems not to have appeared explicitly in the literature of communication theory.”  But Shannon was only partly correct. Ideas about sampling were indeed common knowledge in the late 1940s, and the theorem in various forms had appeared in the mathematical literature. But the theorem had also been published in the ‘literature of communication theory’ as early as 1933. Trouble was, it was published in the proceedings of a conference in Stalinist Russia – and in Russian.

The article goes on to give Kotelnikov credit for putting the problem of sampling a continuous, band-limited signal into an engineering context. Now that I'm back home and on-line again, I've been able to track down more of the story and access an English translation of Kotelnikov's seminal 1933 paper, On the capacity of the 'ether' and cables in electrical communication.  Not surprisingly, Wikipedia has an even more complete historical background on sampling theory in communications.

Suffice it to say, "Whittaker-Kotelnikov-Raabe-Shannon-Someya sampling theorem" would be a better name, as many people reached similar conclusions with varying degrees of parallelism.  Kotelnikov suffered from writing in Russian under Stalin and before the west started tracking Russian science.

Even with the English translation of Kotelnikov now available, Shannon's 1948 paper remains the best and most complete source for me.  I think it's only available in hardcopy forms, but other URLs of possible interest are here.