`Openness` and the Public Airwaves

`Openness` and the Public Airwaves
‘Openness’ and the Public
Airwaves
Victor Bahl
Microsoft Research
MobiHoc 2005
May 26, 2005
Do we have a problem?
Number of wireless data devices is increasing
Demand and expectation from wireless connectivity is increasing
Unlicensed bands are not sufficient to meet these demands
Intense lobbying by Microsoft & others to FCC for additional
unlicensed spectrum
Success! November 2003
• FCC opens up 255 MHz (5.470-5.725 GHz) for RLAN and U-NII
(with DFS and TPC)
In the meantime..WiFi is everywhere…
Wi-Fi Hits the Hinterlands, BusinessWeek Online, July 5, 2004
“Who needs DSL or cable? New “mesh” technology is turning entire small towns into
broadband hot spots”
Rio Rancho N.M., population 60,000, 500 routers covering 103 miles2
NYC wireless network will be unprecedented, Computerworld, June 18, 2004
“New York City plans to build a public safety wireless network of unprecedented
scale and scope, with a capacity to provide tens of thousands of mobile users”
Rural Areas need Internet too! Newsweek, June 7, 2004 Issue
“EZ Wireless built the country's largest regional wireless broadband network, a 600square-mile Wi-Fi blanket, and activated it this February”
Hermiston, Oregon, population 13,200, 35 routers with 75 antennas covering
600 miles2
Mesh Casts Its Net, Unstrung, January 23, 2004
“Providing 57 miles2 of wireless coverage for public safety personnel in Garland
Texas”
Question is….
Can you build robust wireless networks in unlicensed bands?
Unlicensed Bands: Colliding standards
Courtesy: Mobilian Corp.
Performance worsens when there are large number of
short-range radios in the vicinity
TCP Sequence Number
Following rules and regulations but….
Adding BT to
the mix
Time(second)
Two TCP Downloads From a 802.11 Access Point
The world if full of non-802.11 Devices
LUV-200MV
I-920X009
SDX-1
2.4 GHz FM Video Transmitters
http://www.rf-video.com/
I-520X007
2.4 GHz Spread Spectrum Data Transmitters
http://www.freewave.com/
Baby Monitor
WaveTV 100
VT2461
2.4 AGHz
WAVECOM Jr.
In the presence of other 2.4 GHz devices
Phone on
Panasonic 2.4GHz Spread Spectrum
Phone 5 m and 1 wall from receiver
Local behavior affects Global Performance!
Doesn’t care
120
Packets get dropped!
Normalized Percentage
100
80
60
40
20
0
Base
One TCP
10% Drop rate
Do we need Etiquettes?
Every “common” needs rules that apply to everyone
(Voluntary standards aren’t sufficient)
Etiquettes do not completely eliminate device interference
Etiquettes do not address the inevitable reduction of
throughput with increase in node density
Design Criteria for Regulations
1.
Allow continued innovation in the Physical (PHY) and
Medium Access Control (MAC) layers
2.
Minimize mutual interference between transmitters
3.
Allow all devices to contend and gain access to the
channel
4.
Maximize spectrum utilization and capacity
Note: goals 2 & 4 are related.
Promote harmonization of rules and regulations for spectrum
management around the world
Constraints (my opinion only)
1.
Make no assumptions about receivers or their
existence
Consider transmitters only
2.
Make no assumptions about the channel
3.
Make no assumptions about formats
Channel may be symmetric or asymmetric
Do not think in terms of bits, bytes, or frames – this is for
higher layer protocols (e.g. TCP/IP)
Work with time, frequency, and power
Now go figure it out ☺
But wait…what about connectivity?
5 GHz:
Bandwidth is good,
Published 802.11a ranges
(Yellow circles) decent
Measured range (red
circle) poor
Range is not sufficient to
bootstrap mesh until
installed % is quite high (in
this diagram ~50%)
0
20 40 60 80 100 120140 160
But….
What about lower frequencies?....
700 MHz:
Much better range:
about 7 times further
than 5 GHz at equal
power settings
Three 2 MHz
channels can
bootstrap a
neighbourhood with
~3-5 Mbps
0
20 40 60 80 100 120140 160
Dual Freq.
Network
As more clients come
online, links form in highfrequency range and more
of the mesh is connected
with high-bandwidth
0
20 40 60 80 100 120140 160
Government is trying to help…
May 2004 FCC issues NPRM (Notice of Proposed Rule Making):
• Proposal to allow operation of unlicensed device operation in
broadcast television spectrum (ET Docket No. 04-186)
• Establishes a Wireless Broadband Task Force to investigate
technological development, review wireless broadband
policies and research applications of technology
February 2005 Task force issues 8 key findings
…
•
•
…
Expedite transition of DTV spectrum for Wireless Broadband and
Public Safety
Best industry practice among unlicensed users to facilitate efficient
spectrum use
Broadband WiFi Debate
…there are always two sides to the coin
Proponents
•
•
Local and state government should provide WiFi access free
everywhere
Propel US from its 13th position among developed nations
– Lower cost, faster deployment (specially in rural areas)
– Stimulate competition by raising service standards
Detractors
•
•
•
Unfair to ask private sector to compete with local
government who have tax dollars
Not a utility, highly competitive enterprise
Continuously changing due to innovation
Now go get involved…..
Where do I stand?
Want to enable wireless broadband Internet access
Like both licensed and unlicensed spectrum (particularly below 1
GHz)
For Unlicensed spectrum:
Researching co-existence etiquettes (it’s a challenge)
• Regulations will be necessary; industry standards are not sufficient)
For Licensed spectrum:
Researching leasing options in licensed bands
Thanks!
For prior work & updates, check out:
http://research.microsoft.com/netres/
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