2.4GHz 11Mbps unlicensed wireless computer networking and the IEEE 802.11 standard from the UARC perspective in the year 2003

http://www.xmission.com/~c/uarc/ieee802
or http://www.qsl.net/kk7dv/uarc/ieee802
by Gary Crum, [email protected]
last modified on January 28, 2003

Introduction

This article is about the radio-based wireless computer networking system defined by the IEEE 802.11 standard.  IEEE is the Institute for Electrical and Electronics Engineers, and the use of equipment based on the 802.11b standard is becoming a very inexpensive and popular way for computers to communicate over radio, especially over short distances such as within an office building.  Access point routers and PCMCIA cards with 2.4GHz transceivers cost under $100 now.  Data rates of wireless 802.11b networking can be 11Mbps (11000000 bits per second), which is approximately that of the original wired ethernet 802.3 specification.  These rates are a good match for current use of Internet protocols for computer networking.

IEEE 802.11b RF transmission conforms to FCC Part 15 rules for unlicensed operation of low-power devices, so this topic is somewhat analogous to discussing the design and usage of cordless telephones.  But, 802.11 allows large numbers of computers to participate in a network, at data rates over a megabit per second, so hopefully this topic is a little more interesting than discussing cordless telephones.

The 802.11 standards are also given names such as Wi-Fi and AirPort.  Existing 802.11b products use 2.4GHz spread-spectrum transceivers at power levels less than 100 milliwatts for computer networking at data rates from 1 to 11 megabits per second.  Newer specifications such as 802.11g introduce higher data rates such as 54Mbps, and the use of radio spectrum at 5GHz.  Because of the popularity of 802.11 equipment, the FCC is soliciting comments for future spectrum allocation for similar specifications, and the ARRL has formed a working group for the use of 802.11 specifications under Part 97 rules (with corresponding modifications such as the possible use of higher power).

The timely topics discussed below include:
- Links to web pages with more information including specifications, reviews and analysis, and engineering work in progress.  This is the "core" content of this article, since there is a great deal of information about 802.11 in web pages.
- Internet access from laptop computers at UARC meetings.
- A firsthand throughput test result: 5Mbps FTP throughput using 802.11b -- 45% efficiency.

Links

This is the core content of this article;  Computer networking, including 802.11, is one topic on which there is a great deal of good information in web pages.

http://www.palowireless.com/i802_11/tutorials.asp
    A great collection of links, including tutorials on the subject of 802.11.

http://grouper.ieee.org/groups/802/11/
    The IEEE site for 802.11, including standards documents.

http://www.intelligraphics.com/articles/80211_article.html
    "Introduction to IEEE 802.11."

http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html
    "Security of the WEP algorithm."

http://www2.arrl.org/hsmm/
    An ARRL group working on 802.11 projects using Amateur Radio Part 97 rules.

http://home.satx.rr.com/wdubose/
    A San Antonio radio club working on 802.11 projects.

http://www.turnpoint.net/wireless/has.html
http://www.oreillynet.com/cs/weblog/view/wlg/448
    Homebrew 2.4GHz antennas used for 802.11, including the "Pringle's Can Antenna."

http://slashdot.org/article.pl?sid=02/12/31/1943224&mode=thread
http://www.apple.com/airport/
    New 802.11g hardware, with data rate of 54Mbps.

http://slashdot.org/article.pl?sid=02/12/22/2115207&mode=thread
http://www.linksys.com/splash/wsb24_splash.asp
http://www.hyperlinktech.com/web/amplifiers_2400.html
http://www.ydi.com/products/amp2441-amplifier.php
    802.11b RF amplifier products.

http://www.tomshardware.com/network/20030117/index.html
http://www.techtv.com/freshgear/products/jump/0,23009,3395028,00.html
http://www.timhiggins.com/ProductGuides-Wireless.php
http://www.oreillynet.com/pub/a/wireless/2001/03/29/microwave.html
    Some discussion of performance, price and interference issues.

http://slashdot.org/article.pl?sid=02/12/12/1336258&mode=thread
http://hraunfoss.fcc.gov/edocs_public/attachmatch/DOC-229400A1.doc
    "FCC BEGINS INQUIRY REGARDING ADDITIONAL SPECTRUM FOR UNLICENSED DEVICES."

Internet access at UARC meetings

One fun practical use of 802.11b wireless computer networking is the availability of Internet access at UARC meetings, using laptop computers.  The University of Utah does have some 802.11b coverage on campus, but it does not normally include the UARC meeting room, EMCB 101.  Since there is a 10BaseT (wired) ethernet connection to the campus network in the room, I have setup a temporary access point during the last two UARC meetings, and I will probably continue to do so at the UARC meetings I attend.

Since I configure the network to be "public" and broadcast the W7SP network name, the use of this network should be trivial;  The setup can even be completely automatic depending on network device driver configuration.  DHCP is used to assign a dynamic IP address along with default gateway and nameserver information.  These standards are independent of operating system type, so this should certainly work with common operating systems such as Linux, Windows, OS X and FreeBSD.  If there are any problems using the network, you are welcome to contact me, Gary Crum, [email protected].

Throughput test

Here is the result of a firsthand test of 802.11b throughput.  I transferred a 10MB file from one computer named "d" to another named "b", in both directions and over both an 802.11b wireless connection as well as a 10BaseT (wire) ethernet connection.  The result was a throughput of around 5Mbps over 802.11b, and a throughput of around 9Mbps over 10BaseT.  This shows a much lower efficiency over 802.11b than over ethernet (45% versus 90%), but the 5Mbps throughput over 802.11b is still quite fast.  In the case where the global Internet is being accessed, the bottleneck limiting data throughput can often be a lower speed link such as a 640Kbps DSL connection.

Incidently, another aspect of network performance is latency, and in this area I have observed "ping" ICMP round-trip times down around 2 milliseconds, which is comparable to 10BaseT ethernet.  Of course, there are faster versions of wired ethernet;  100BaseT is a very common standard providing 100Mbps data rates, and 1Gbps and 10Gbps ethernet standards also exist.  So, computer networking over copper and fiber can be much faster than 802.11 RF data rates, but the original 10Mbps ethernet standard serves as a good baseline for performance comparison.

Here is the raw data from my firsthand test:

wireless (11Mbps 802.11b link):
d->b
629 KB/s, 5.03 Mbps throughput, 45.7% efficiency
b->d
610 KB/s, 4.88 Mbps throughput, 44.4% efficiency

10BaseT ethernet:
d->b
1126 KB/s, 9.01 Mbps throughput, 90.1% efficiency
b->d
1117 KB/s, 8.94 Mbps throughput, 89.4% efficiency

Conclusion

IEEE 802.11 is a popular specification for unlicensed wireless computer networking.  Whereas the bulk of amateur "packet" radio involved data rates of 1200 bits per second in the 2-meter band, 802.11 involves data rates over 1000 times that in the 13-centimeter band.  There is a lot of online information about 802.11, and I hope this article is a convenient survey of some current links.  Certainly search engines such as http://www.google.com can be used to find information with appropriate keywords such as "802.11" and "Wi-Fi".