This article is from the Robotics FAQ, by Kevin Dowling firstname.lastname@example.org with numerous contributions by others.
Tethers for supplying power and communication are sometimes
impractical and at best an annoyance. Digital communication via RF
and IR links is becoming cheaper and a number of companies are
providing off-the-shelf solutions. For basic serial line
communication a wide variety of radio modems are available that use
fixed frequencies or spread spectrum techniques. In many cases they
are also transparent. That is, you plug them directly into serial
ports on the robot and off-board computing directly. Higher
bandwidths such as Ethernet or high speed synchronous serial require
different hardware. However, with high speed serial communication
you may even be able to SLIP (Serial Line Internet Protocal) or PPP
(Point-to-Point Protocol) instead of using a LAN-based device.
This area of communication is changing very quickly and new products
and companies are appearing every day.
See also a nice list at: [LIST IS NO LONGER THERE - AWAITING NEW
or gopher://csd4.csd.uwm.edu List Maintained by David Kent,
10.4.1 RF Modems (Robotics related products)
[David Kent] RF or wireless modems provide data communication
without tethers and cables. Wireless systems can be susceptible to
noise, and multipathing (echos) which will result in tranmission
errors. A smart wireless modem will guarantee error free data gets
from one end to the other. This is accomplished by an internal
microprocessor which packetizes and addresses data. It also checks
received packets for errors and automatically requests a
retransmission from the sending modem if there is an error. All this
occurs transparently to the user. The users' RS-232 data stream goes
in one modem and comes out the other. Another advantage of this
method is that since packets are addressed, more than two modems can
share a single frequency without interference, however throughput
goes down accordingly. These work well with RS-232 devices that you
cannot run custom software on, eg. printers, plotters, bar code
scanners, as well as computers. Dumb modems on the other hand simply
transmit the data and hope it gets to the other end. Since there is
no addressing, any modems on the same frequency and in range will
receive all transmissions. Dumb modems are often used where the
equipment connected to the modem handles error detection/ correction
and addressing. Software libraries are available that work with
specific dumb modems to provide smart functionality. If you are
connecting a computer running custom software to the wireless modem
anyway, this may be the most cost effective solution. There are also
two main categories relating to the radio frequency (RF) portion of
the wireless modem. These are spread spectrum (unlicensed) and
VHF/UHF (licensed). Licensed means you need an FCC license. Costs a
couple hundred dollars to process the paperwork. Generally not a
problem getting one unless you live in some urban areas. Nice
collections of information and vendors of wireless modems are at
Wireless. and http://hydra.carleton.ca/info/wlan.html
"Comrad, Communications Research and Development Corporation"
7210 Georgetown Road, Suite 300
Indianapolis, IN 46268
fax: 317.291.3093 Comrad CCL901-DP 900 MHz Wireless Data Link. 500
meter range can be extended through additional transponders. RS232 -
38Kbaud. Battery pack available for portable applications. Two
transceiver units, software, power adapter, serial cables for
$449.95. Modems. Two channels: 1200-38,400 baud, 100m range, 20m
range through two walls. Easy to set up.
310 N. Mary Avenue
Sunnyvale, CA 94086
fax: 408.735.6643 AirLink - series of highspeed synch or async
modems to 256kb/s. Interfaces include V.11, RS-232, EIA-530. Spread
spectrum device operating in 902-928Mhz range.
"GRE America, "
tel: 800.233.5973 GINA 6000, spread spectrum, smart wireless modem,
up to 128 Kbps, 902MHz, 1 watt
"Hamtronics, Inc. "
65-D Moul Rd.
Hilton, NY 14468-9535
fax: 716.392.9420 1200 and 9600 baud units/modules for a few hundred
"Micrilor Inc "
17 Lakeside Park,
Wakefield, MA 01880
fax: 617.246.0157 RS-232, T1221 and R1221 transmitters. 902-928MHz,
no FCC license required. Data rates to 64k-baud. >100m range. Power
35mA@3VDC, Antenna is 60cm RG174 coax. Price: $550 ea.
"Monicor Electronics "
Fort Lauderdale, FL
fax: 305.979.2611 System 310 two-card OEM set for use in palmtops
and handheld computing. System 310 board set transmits at 1mW to 2W
for a range of 3 to 3km range. Priced at $660 in quantity. Model
IC-15-48 - rugged RS232 4800 baud modem. Can network a number of
these portables. $1630.
"Motorola Radio-Telephone Systems Group "
Arlington Heights, ILL
tel: 708.632.5000 AltairNet: 18GHz-based system design for wireless,
indoors networking. The boxes are fairly large, about the size of a
shoebox, and are relocatable but not portable. Problem is that is
that they really aren't for mobile applications. The reception area
has holes like swiss cheese. Not a problem with some fine adjustment
in stationary applications but a big problem for mobile devices.
"Pacific Crest Corporation"
1190 Miraloma ay, Suite W
Sunnyvale, CA 94086-4607
fax: 408.730.5640 DDR-96 and RDDR-96 Radio modems. To 9600 baud. 2W.
Point-to-point communcations. Uses standard RS-232 9pin DB style
connectors. Can also be used in packet switching networks. Forward
error correction techniques and PLL synchronization. The RDDR is a
ruggedized version. Cost is about $1100 and $1230 respectively. FCC
"Proxim, Inc. "
Mountain View, CA,
tel: 800-229-1630 Proxlink XR, spread spectrum, smart wireless
modem, up to 256 Kbps, 902MHz, 500mW, 800 ft range. "Scientific
31069 Genstar Road
Hayward, CA 94544 SpectraData 551 radio data link. Spread spectrum.
Range to 1.5miles (repeater for longer distances) RS232 to
38.4Kbaud. (900MHz or 2.4GHz).
A number of articles have also been posted about the modification of
inexpensive walkie-talkies for wireless communication. Typical
bandwidths are limited to about 1200 baud. This may be sufficient
for simple command-level control of a mobile mechanism. See the
[10.4.2] RF Video
For regular frame rate video over relatively short distances it's
hard to beat the price and availability of several consumer products
in the $100 range. Check local stores or place like the Sharper
Image (Gemini Rabbit is one of the companies making these units)
Microwave systems require line-of-site communication, licensing, and
[10.4.3] RF Ethernet (Robotics related products)
"Aironet Wireless Communications"
367 Ghent Road, Suite 300
Akron, OH 44334-0292
fax: 216.665.7922 ARLAN series of wireless products. Aironet has the
largest installed base of spread spectrum radios (>200,000) Up to
1Mbps at 900MHz and 2Mbps at 2.4Ghz. Ethernet and Token rings access
points (630 and 631 series), wireless multipoint bridges (640 series
ARLAN products), wireless network adapter cards, PCMCIA cards and
numerous software and network management tools.
They are distributed through Anixter. For local Anixter offices call
708.677.2600. We've used a number of the ARLAN products for years at
CMU and it's been plug and play.
"Proxim Inc. "
295 North Barnardo Ave.
Mountain View, CA 94043
fax: 415.964.5181 A product announcement for wireless LAN board on
p.68 in May/92 Byte Magazine Price: $495, Range: 800 ft. Data Rate:
242 Kbps Channels: 3
Grouper wireless networks. Spread-spectrum (no FCC license)
902-928MHz. Several products for Macintosh computer.