The IEEE 802.15.4 standard was released in 2003 and adopted by the ZigBee Alliance. This standard provides guidance upon which the ZigBee networking and applications are constructed. The standards were revised in 2006 that among other items added the bit rates of 100 and 250 kb/s to the PHY (physical layer) 868/915 MHZ bands. ZigBee employs carrier sense multiple access with collision avoidance (CMSA/CA). This enables the signal to sense when a channel is idle before transmitting. The 2.4 GHz band uses the direct sequence spread spectrum (DSSS) modulation technique. This technique spreads the signal over the entire bandwidth. ZigBee operates within a range of 10 to 75 meters. The environment in which it is deployed, may affect the range. The following table provides more detail on ZigBee.
|
PHY (MHz) |
Frequency Band (MHz) |
Spreading Parameters |
Data Parameters |
Channel Spacing (MHz) |
||
|---|---|---|---|---|---|---|
|
Chip Rate (kchips/s) |
Modulation |
Bit Rate (kb/s) |
Symbol Rate (ksymbol/s) |
|||
|
868/915 |
868–868.6 |
300/400/400 |
BPSK/ASK/O-QPSK |
20/250/100 |
20/12.5/25 |
— |
|
902–928 |
600/1600/1000 |
BPSK/ASK/O-QPSK |
40/250/25 |
40/50/62.5 |
2 | |
|
2450 |
2400–2483.5 |
2000 |
O-QPSK |
250 |
62.5 |
5 |
The software selection for ZigBee is 802.15.4 and as the name implies, operates in the 2.4 GHz band using offset QPSK.. Optionally it can also operate in the 868/915 MHz bands.