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IEEE 802.15.4 |
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Description
Specifications
Options
The IEEE 802.15.4 compliant XBee OEM RF module is a solution that satisfies the unique needs of low-cost,
low-power wireless sensor networks. The modules are easy-to-use, require minimal power and provide reliable delivery of critical data between
devices. Its small form factor saves valuable board space.
The XBee module operates within the ISM 2.4 GHz frequency band and is pin-for-pin compatible with MaxStream's XBee-PRO (60 mW)
Modules. The modules are optimized for use in US, Canada, Australia, Israel and Europe.
No configuration is necessary for out-of-box RF communications. The module’s default configuration supports a wide range of data system
applications. Advanced configurations can be implemented using simple AT commands.
802.15.4 is a standard for wireless communication put out by the IEEE (Institute for Electrical and Electronics Engineers). The IEEE is a
technical professional association that has put out numerous standards to promote growth and interoperability of existing and emerging
technologies. IEEE has published the standards that define communication in areas such as the Internet, PC peripherals, industrial communication
and wireless technology. As a few examples, the IEEE 802.11 standard defines communication for wireless LAN and 802.16 defines communication for
broadband wireless Metropolitan Area Networks.
While both of those wireless standards are concerned with higher bandwidth Internet access applications, 802.15.4 was developed with lower data
rate, simple connectivity and battery application in mind. The 802.15.4 standard specifies that communication can occur in the 868- 868.8MHz, the
902-928 MHz or the 2.400-2.4835 GHz Industrial Scientific and Medical (ISM) bands. While any of these bands can technically be used by 802.15.4
devices, the 2.4 GHz band is more popular as it is open in most of the countries worldwide. The 868 MHz band is specified primarily for European
use, whereas the 902-928 MHz band can only be used in the United States, Canada and a few other countries and territories that accept the FCC
regulations.
The 802.15.4 standard specifies that communication should occur in 5 MHz channels ranging from 2.405 to 2.480 GHz. In the 2.4 GHz band, a
maximum over-the-air data rate of 250 kbps is specified, but due to the overhead of the protocol the actual theoretical maximum data rate is
approximately half of that. While the standard specifies 5 MHz channels, only approximately 2 MHz of the channel is consumed with the occupied
bandwidth. At 2.4 GHz, 802.15.4 specifies the use of Direct Sequence Spread Spectrum and uses an Offset Quadrature Phase Shift Keying (O-QPSK) with half-sine pulse shaping to modulate the RF carrier. The graph below shows the various channels at the spacing specified by 802.15.4.
The 802.15.4 standard allows for communication in a point-to-point or a point-to-multipoint configuration. A typical application involves a
central coordinator with multiple remote nodes connecting back to this central host.
MaxStream’s XBee Series 1 family of radios can be set up to operate in a point-to-point, point-to-multipoint or a peer-to-peer configuration.
While standard 802.15.4 always requires a coordinator, the MaxStream radios are set up so that a coordinator is not required.
© 2007 MaxStream, Inc.
RF Protocol: 802.15.4
XBee
XBee-PRO
Indoor/urban Range:
Outdoor line-of-sight Range:
Transmit Power Output:
Power-down Current:
Operating Frequency:
RF Data Rate:
up to 100’ (30 m)
up to 300’ (100 m)
1 mW (0 dBm)
<10 µA
2.4 GHz
250,000 bps
up to 300’ (100 m)
up to 1 mile (1.6 km)
60 mW (20 dBm) EIRP
<10 µA
2.4 GHz
250,000 bps
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Should I purchase the XBee or the XBee-PRO?
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The XBee and XBee-PRO are drop-in compatible equivalent products, with
a few exceptions. The XBee-PRO module includes RF signal amplifiers
to provide a higher transmit power and better receive sensitivity than
the XBee module, providing longer range, but requiring more electrical
current. For battery-powered devices, the XBee is often a better
choice due to the lower power requirements, when reduced range is
acceptable.
Both the XBee and XBee-PRO provide a 250 kbps over-the-air data rate,
but for practical purposes, any one module can sustain 50 - 100 kbps
in an application. In addition to the serial interface, the modules
include the ability to perform I/O line passing, meaning that basic
control signals (on/off) can be passed between modules, enabling very
easy systems integration in basic control systems.
The higher transmit power of the
XBee-PRO supports fewer RF channels due to FCC restrictions, so for
best interoperability, it is recommended to use RF channels supported
by both the XBee and the XBee-PRO. The X-CTU configuration program is
an excellent tool for evaluating compatibility of settings between the
two modules.
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What type of antenna should I get?
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XBee modules are available with a PCB chip antenna, a ¼ monopole integrated whip antenna, or a U.FL antenna connector that allows for
connection to a dipole or other external antenna.
The chip and integrated whip antennas are suited for any application, but are especially useful in embedded applications. Since the
radios do not have any issue radiating through plastic cases or housings, the antennas can be completely enclosed in those types of
applications.
The U.FL connector is used in conjunction with an adapter cable that can be connected to a dipole or gain antenna if the housing is
metal or if that solution is more desirable mechanically. Range can differ somewhat with different antenna types, so that should be a
consideration when choosing what type of antenna you want to use.
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