ZigBee Overview
ZigBee adds the network (NWK) layer and the framework for an
application layer to the physical (PHY) layer and the media
access control (MAC) sub-layer that are defined in
IEEE 802.15.4-2003.
The IEEE 802.15.4-2003 has two PHY layers that operate in two separate
frequency ranges: 868/915MHz and 2.4GHz. The 868MHz band is used
in Europe, the 915MHz band is used in North America.
The 2.4GHz range is used virtually worldwide.
The IEEE 802.15.4-2003 MAC layer controls access to the radio
channel. Its responsibilities include transmitting beacon frames,
synchronization, and providing a reliable transmission mechanism.
The ZigBee network layer (NWK) supports star, tree, and mesh
topologies. In a star topology the network consists of a ZigBee
coordinator and end devices. The ZigBee coordinator is responsible
for initiating and maintaining the devices on the network.
In mesh and tree topologies the ZigBee coordinator is responsible for
staring the network and for choosing certain key network parameters,
but the network may be extended through the use of ZigBee routers.
In tree networks, routers move data and control messages through the
network. Tree networks may employ beacon-oriented communication as
described in IEEE 802.15.4-2003.
Mesh networks allow full peer-to-peer communication. ZigBee routers in
mesh networks do not currently emit regular IEEE 802.15.4-2003
beacons. The ZigBee specification only describes networks where
communications begin and terminate within the same network. Device
discovery and service discovery enable the creation of self-organizing
ad-hoc networks.
- The raw, over-the-air data rate is 250 kbit/s per channel (2.4
GHz band), 100 kbit/s per channel in the 915 MHz band, and 20 kbit/s
in the 868 MHz band.
- Transmission range is rougly 300ft (1mW) and 4000ft (60mW).
- The basic channel access mode is "carrier sense, multiple
access/collision avoidance" (CSMA/CA).
- In the 2.4GHz band there are 16 channels each requiring 5MHz
of bandwidth.
- IEEE 802.15.4-2003 short (16-bit) and long (64-bit) address modes supported.
Applications
The majority of the ZigBee application initiatives listed on the
ZigBee Alliance website involve the integration and central management
of lighting, heating, cooling and security systems in home and
industrial environments. An integrated system enables conservation
through optimized HVAC management and communication of usage
information to the consumer. For lighting systems ZigBee provides an
opportunity to quickly create adaptable workspaces and upgrade
building infrastructure with minimal effort.
- ZigBee Smart Energy Smart Energy enables both wired and
wireless communications between utility companies and home area
networks (HANs). A HAN can consist of everyday household devices
such as thermostats and appliances as well as Pluggable-Electric
Vehicles (PEVs),
- ZigBee Home Automation ZigBee Home Automation is the global
standard for the control of appliances, lighting, environment,
energy management, safety, and security.
- ZigBee Building Automation Integrate and centralize the
management for lighting, heating, cooling and security systems.
- ZigBee Health Care ZigBee Health Care provides a global
standard for interoperable wireless devices enabling secure and
reliable monitoring and management of noncritical, low-acuity
healthcare services targeted at chronic disease.
- Retail Services Collection, delivery, selection, data sharing
with customers, in-store and mobile retail applications.
Supply chain management, regulatory management. energy management
- ZigBee Remote Control Standard for RF control of
consumer electronic devices. Offers non-line-of-sight
operation, two-way communication and longer range than
IR solutions. ZigBee Remote Control is the public application
profile for the ZigBee RF4CE specification.
Additional applications ---
- Inertial Measurement Systems MEMs sensors integrated in industrial,
automotive, military, aviation and marine environments.
- Environmental Data Collection Agricultural, environmental and
conservation studies.
- Arts and Education Interactive exhibits, games, robotics.
MaxStream XBee Modules
| Wireless Performance (99% Throughput)
|
| Module
| Antenna
| Distance
|
|
|
| Outdoor
| Indoor
|
| | | Line-of-Sight | Office
|
| XBee | Chip | 470 ft. | 80 ft.
|
| | Whip | 845 ft. | 80 ft.
|
| XBee-Pro | Chip | 1690 ft. | 140 ft.
|
| | Whip | 4382 ft. | 140 ft.
|
The MaxStream XBee modules are fully integrated modules designed to
meet IEEE 802.15.4-2003. The XBee integrates a microcontroller
(with ADC and digital I/O), radio and antenna into a 1"x1" module.
The modules operate within the ISM 2.4GHz frequency range and can be
configured with different antenna and transmitter amplifier
options. For outdoor line-of-sight transmissions the range of the 1mW
transmitter is over 400feet with a chip antenna. The 60mW
transmitter with a whip antenna has a range of over 4000ft.
Sensor Node
| XBee Average Current (Vcc=3V)
|
| Duty Cycle | Cyclic Sleep | Hibernate
|
| 10% | 6.22mA | 6.20mA
|
| 1% | 0.67mA | 0.64mA
|
| 0.1% | 0.12mA | 0.09mA
|
The XBee can be used to create a low cost, low power ZigBee sensor
node. Properly conditioned sensors can be connected to the ADC inputs
and the XBee can be programmed to periodically alternate between sleep
and operate modes. At a Vcc of 3V the maximum sleep current
for a cyclic sleep mode is 34uA. The cyclic sleep mode is software
controlled using the XBee microcontroller. With external hardware
control the XBee can be put in hibernate mode which has a maximum
current of 3uA. These low currents are only achieved with a Vcc
of 3V. At a Vcc of 3.3V both sleep currents have
typical values of 100uA.
Operating Currents
The operating current for an XBee is 50mA. Conservative efficiency
and quiescent current estimates for a DC-DC converter to boost two AA
cells to 3V would be efficiency > 90% and Iq < 20uA. When the
XBee is in operating mode the current drawn from the battery is 62mA.
The sleep mode currents drawn from the battery for hibernate mode
(SM1) and cyclic sleep mode (SM4) are 23uA and 54uA respectively.
Battery Life
Using 2-AA cells yields a battery life of over 2 1/2 years is possible
using cyclic sleep mode (SM4) and a 0.1% duty cycle.
Improvements
- For duty-cycles below 1% the average current can be reduced by
another 30-40% by changing from cyclic sleep (SM4) to hybernate
mode (SM1). This involves additional hardware (which will increase
the required current).
- The DC/DC converter Iq specification is conservative. With a
small amount of additional design work it is not unreasonable to
expect a 50% reduction in Iq.
- Change the battery chemistry. Using a Li-ion battery and a 3V
regulator yields an efficiency of ≈ 80% but an Iq of a few
micro-amps. For low duty-cycle systems this would provide a major
reduction in current consumption.
- Use a system-on-chip solution that enables a lower current
cyclic sleep mode. This requires more engineering and possibly
RF PCB layout.
References
Freaklabs
wikipedia ZigBee
ZigBee Alliance
MaxStream (2005)
XBee/XBee-PRO OEM RF Module Antenna Considerations
Retrieved August 12, 2008, from
here
MaxStream (2007)
XBee/XBee-PRO Product Manual v1.xAx - 802.15.4 Protocol}
Retrieved April 30, 2008, from
here
ZigBee Smart Energy Profile Marketing Requirements Document (2009)
Retrieved Jan 28, 2010 from
here
ZigBee Specification (2008) Retrieved Jan 28, 2010 from
here
Educational Kits and Rapid Prototyping Tools
