11-10-2017, 09:51 AM
Zigbee also known as IEEE 802.15.4 is a communications standard designed for low-power short-range communications between wireless devices. It is classified as a wireless personal area network (WiPAN), a term that also includes the Bluetooth standard (IEEE 802.15.3).
The ZigBee standard has seen a growing interest in both the commercial and military markets for applications such as wireless sensor networks, home automation and industrial control. An interesting facet of the ZigBee standard is that it is designed in such a way that the devices can form self-training and self-healing ad hoc or mesh networks. In this scenario, a central "PAN coordinator" device monitors the status of the network configuration. In recent years, sensor networks have been the subject of much research in military and battlefield applications. Therefore, there is significant interest in using the ZigBee standard to define communications links in ad hoc battlefield intelligence scenarios.
A design decision of the ZigBee specification that makes it ideal for remote wireless sensors is the implementation of a low-power physical layer (PHY). As a summary, the PHY specifications allow ZigBee devices to operate in a three-band: 868 MHz (Europe), 915 MHz (North America) and 2.4 GHz (global). The 2.4 GHz band, in which the ZigBee transceivers are most commonly deployed, uses the Quadrature Phase Shift Quadrature Shift (OQPSK) modulation current.
This scheme is a derivation of the traditional QPSK and is used because it requires less energy than similar schemes, while achieving the same or better performance. OQPSK uses a maximum phase transition of 90 degrees from one symbol to another. This prevents overwriting of symbols and requires slightly lower transmission power than the traditional QPSK modulation scheme. This design decision, combined with the use of 5 MHz channel bandwidth, allows devices to achieve data rates of up to 250 kb / sec in a reasonably energy efficient manner.
Because ZigBee transceivers are designed for low power applications, the PHY is relatively tolerant of significant errors. In fact, the devices are able to tolerate an error vector magnitude (EVM) of up to 35% while maintaining reasonable bit error rate (BER) performance. Therefore, design validation and product ordering requires a variety of testing methodologies. In the following sections, we will explain why specific tests will be conducted and provide suggestions to enable more accurate testing methodologies.
The ZigBee standard has seen a growing interest in both the commercial and military markets for applications such as wireless sensor networks, home automation and industrial control. An interesting facet of the ZigBee standard is that it is designed in such a way that the devices can form self-training and self-healing ad hoc or mesh networks. In this scenario, a central "PAN coordinator" device monitors the status of the network configuration. In recent years, sensor networks have been the subject of much research in military and battlefield applications. Therefore, there is significant interest in using the ZigBee standard to define communications links in ad hoc battlefield intelligence scenarios.
A design decision of the ZigBee specification that makes it ideal for remote wireless sensors is the implementation of a low-power physical layer (PHY). As a summary, the PHY specifications allow ZigBee devices to operate in a three-band: 868 MHz (Europe), 915 MHz (North America) and 2.4 GHz (global). The 2.4 GHz band, in which the ZigBee transceivers are most commonly deployed, uses the Quadrature Phase Shift Quadrature Shift (OQPSK) modulation current.
This scheme is a derivation of the traditional QPSK and is used because it requires less energy than similar schemes, while achieving the same or better performance. OQPSK uses a maximum phase transition of 90 degrees from one symbol to another. This prevents overwriting of symbols and requires slightly lower transmission power than the traditional QPSK modulation scheme. This design decision, combined with the use of 5 MHz channel bandwidth, allows devices to achieve data rates of up to 250 kb / sec in a reasonably energy efficient manner.
Because ZigBee transceivers are designed for low power applications, the PHY is relatively tolerant of significant errors. In fact, the devices are able to tolerate an error vector magnitude (EVM) of up to 35% while maintaining reasonable bit error rate (BER) performance. Therefore, design validation and product ordering requires a variety of testing methodologies. In the following sections, we will explain why specific tests will be conducted and provide suggestions to enable more accurate testing methodologies.