What are the reasons for the limited range of 802.11 technology (AKA
WLAN or WiFi)? Are there any know methods to extend the range beyond a
few hundreds feet? Is there any method that does not require changes
in the terminal equipment?
One of the methods I heard of, is using a phased array antenna. A
company named Vivato claims they have such a technology.
I want links to relevant researches conducted by academic
organizations or by companies, as well as links to patents regarding
this issue.

According to the sources I have researched below, the main limiter of
802.11 range is interference. Metal objects (filing cabinets, nails,
beams, lead paint) in a wireless-networked area, and dense materials,
like concrete, are obstacles for radio waves and can cut down range.

Based on all the research I've done, the extra phased-array antenna is
one solution offered. There are many kinds of extender antennas, and I
list websites showing different kinds below (under the PRODUCTS
heading). An omni-directional antenna is recommended.

Another device I learned of is a repeater. It regenerates a network
signal to extend the range of an existing network.

Another solution is to replace stock antennas of access points with
more powerful antennas.

Last, there is a new access point kind of access point that plugs into
the AC power lines and uses them to transfer data. The first mentioned
link below gives more details on all these that I mentioned.


ARTICLES, DOCUMENTS AND RESEARCHES

802.11 Planet - Wireless Home Networking, Part V - Interference and
Range Extension
http://www.80211-planet.com/tutorials/article.php/1497111
- This site, 802.11 Planet, seems to be the best source today for
802.11 solutions and researches.

802.11 Planet - Wireless Networking Reference - Antennas / Range
Boosting
http://www.practicallynetworked.com/tools/wireless_articles_range.htm

802.11 Planet - Extending WLAN Range with Repeaters
http://www.80211-planet.com/tutorials/article.php/1571601

802.11 Planet Webopedia – entry “Repeater”
http://80211-planet.webopedia.com/TERM/r/repeater.html

Practially Networked - Solving Wireless Range Problems
http://www.practicallynetworked.com/support/wireless_range_probs.htm

Radioactive Networks: Distance Limits for 802.11
http://www.radio-active.net.au/web/80211/distance.html

Slashdot - 802.11, Horizon Drop-Off And Range
http://slashdot.org/articles/01/04/02/1323221.shtml

RF Design: 802.11b/a - A physical medium comparison
http://rfdesign.com/ar/radio_ba_physical_medium/

TechTV | Extend Your Wi-Fi Range by Patrick Norton, April 4, 2002 
http://www.techtv.com/screensavers/answerstips/story/0,24330,3306273,00.html

IEEE 802.11 Wireless LAN Presentation 
http://www.cs.unibo.it/~bononi/Sim2003/lezione5.pdf


PRODUCTS

802.11 Product Guide – starting page
http://products.80211-planet.com/802.11_products/

802.11 Product Guide - Category antenna - Latest Updates (1)
http://products.80211-planet.com/802.11_products/antenna/recent1.html

Sades J720 - Antenna stuff
http://www.shadesj720.com/antenna_stuff.htm

VOCAL LDPC Codes Extend IEEE 802.11a, 802.11b and 802.11g Wireless LAN
Range - press release by Vocal Technologies, Ltd.
http://www.vocal.com/press_release/020212bpr.htm

Low Cost 802.11A Directional Antenna using obsolete PrimeStar Dish
http://www5.cs.cornell.edu/~eckstrom/802.11a/primestar/

Windows for Devices - Phased-array antenna to extend 802.11b range -
Nov. 4, 2002 (The Vivatco product)
http://windowsfordevices.deviceforge.com/sponsors/SP7337459028-NS9147886209.html


Google search strings:
802.11 range extend
802.11 range extension
802.11 range limits
802.11 range problems
802.11 directional antenna
802.11 range improvement/improve
802.11 range increase

May this give you the resources and information you need.

---

Request for Answer Clarification by guy_y-ga on 09 Mar 2003 10:30 PST

Techtor, thanks for the answer. Most of the links you found provide
high level information, while I'm interested in the physical layers.
What i really need is an extensive explanation regarding the physics
of 802.11 RF limitations and the impact on the MAC layers.
The article on RF design web site was a good start. Some links to
academic researches and patents in the subject are welcome.

---

Clarification of Answer by techtor-ga on 09 Mar 2003 21:47 PST

Thanks for clarifying what you need. Please hold on while I search for
the requested information.

---

Clarification of Answer by techtor-ga on 12 Mar 2003 01:43 PST

There are the easiest links to find to documents that might touch on
your topic of RF interference and MAC layers. I couldn’t find any
patents posted though, but maybe the IEEE website may have a clue as
to acquiring some. I hope they will do. If not, do inform me. Thanks.

Modeling Wireless MAC Layer Protocols using STRESS 
Shamim Begum, EE599, Fall 2000
http://www-scf.usc.edu/~sbegum/wl-mac-2.ppt

Mac Layer Broadcast Support In 802.11 Wireless Networks
www.ics.uci.edu/~lzan/adhoc/ktang2.pdf
- It’s about MAC layers, though not about range extension, but could
have some useful info

A Detailed Study on Wireless LAN Technologies
http://crystal.uta.edu/~kumar/cse6392/termpapers/Vijay_paper.pdf

Performance study of access control in wireless LANs – IEEE
802.11 DFWMAC and ETSI RES 10 Hiperlan
http://delivery.acm.org/10.1145/280000/272168/p55-weinmiller.pdf?key1=272168&key2=0017174401&coll=portal&dl=ACM&CFID=11111111&CFTOKEN=2222222

A Comparison Study of Omnidirectional and Directional MAC Protocols
for Ad Hoc networks.
http://alfalfa.cis.udel.edu:8080/refs/papers/huang02comparison.pdf

802.11a: Higher Range and Rate
http://www.winlab.rutgers.edu/~praveen/personal_files/80211a.ppt

Outdoor IEEE 802.11 Cellular Networks: Radio Link Performance
http://www.bell-labs.com/user/kin/papers/802.11.radio.pdf

Outdoor IEEE 802.11 Cellular Networks: MAC Protocol Design and
Performance
http://www.bell-labs.com/user/kin/papers/802.11.mac2.pdf

Reliable MAC Layer Multicast in IEEE 802.11 Wireless Networks
http://www.cis.ohio-state.edu/siefast/group/publications/sun2002reliablemac.pdf

Wireless Personal Area Networks and Home RF
http://dessr2m.adm-eu.uvsq.fr/wpan.pdf

A Novel MAC Layer Protocol for Space Division Multiple Access in
Wireless Ad (ResearchIndex)
http://citeseer.nj.nec.com/552046.html

Excerpts from a 2002 Wireless ISP Feasibility Study
http://www.webeyetech.com/White_papers/WirelessLAN.pdf


OTHER ARTICLES:

802.11 Planet - EIRP Limitations for 802.11 WLANs by Jim Geier
http://www.80211-planet.com/tutorials/article.php/1428941

Minimizing 802.11 Interference Issues by Jim Geier
http://www.80211-planet.com/tutorials/article.php/953511

802.11 Articles & Tutorials - TrooBloo - Technology Articles &
Tutorials (some point to the 802.11 Planet articles)
http://www.troobloo.com/tech/80211.1.shtml
Business 2.0 - Magazine Article - Do-It-Yourself Wi-Fi by Owen Thomas,
May 2002
http://www.business2.com/articles/mag/0,1640,39276%7C2,FF.html

Document list from IEEE
http://grouper.ieee.org/groups/802/11/Documents


SPECIFIC SOURCE SITES (just in case they might help):

Bitpipe: White Papers, Webcasts and Case studies
http://www.bitpipe.com

The 802.11 Report - email list
http://www.80211report.com

Search strings:
802.11 range extension mac study
802.11 range improve study
802.11 rf interference
802.11 mac layer interference

there are several reasons for the limited range of 802.11

1: The frequency used is reletively high (2.4ghz) and is readily
absorbed by trees and moisture

2: the fcc maximum power output is limited to 1 watt eirp when
transmitting omnidirectionally (in all directions), however, most wifi
equipment transmits between 1/30 watt and 1/10 watt.

3: antennas used transmit in all directions, which reduces range

Ways to improve range:

1: use a directional antenna. There are several kinds. Phased array is
one kind of antenna that provides directional gain, and in some
configurations may be reconfigured to aim in different directions
without human intervention. Other types of antennas are parabolic dish
(satellite dish style) antennas, yagi, waveguide, etc.

2: increase power output using an amp. If you make sure you are within
fcc limits, this is another valid way to increase range.

For more information, I recommend reading the following links:

http://seattlewireless.net/
http://www.turnpoint.net/wireless/cantennahowto.html
http://www.wwc.edu/~frohro/Airport/Primestar/Primestar.html
http://www.turnpoint.net/wireless/has.html

It should be noted that with proper line of sight, no interference, a
correctly constructed antenna, sufficient power and good cabling, a
point to point link using 802.11 technology is possible at distances
exceeding 10 miles using methods described in the above links.

Thanks funkywizard for the useful comment. I'm still looking for
information regarding commercial products to extand the range of WLAN.
Patents and researches are welcomed as well

Guy_V, if there is any problem with my answer, please do not hesitate
to ask for a clarification.

Again, I encourage you to post a clarification if you find any problem
with the additions to my answer. Thank you.

I am glad you found no problem with my answer. Thank you for the
five-star rating! :)