In ZigBee (802.15.4), is there a preamble like WiFi (STS, LTS). I have not studied much details, but from first view it looks like there are sequence of zeros as preambles.
So when transmitted in air, is there any repetition of samples like WiFi preambles (STS 10 times and LTS 2 times).
ZigBee has preamble which consists of 8 zero symbol repetitions. In ZigBee symbols consists of 4 bits which are mapped to 32 chips. So basically you have 8 repetitions of 32 chips. If you have further questions shoot me, I just made an ZigBee Tx/Rx on FPGA.
So that means, a total of 256 bits for the preamble part. And since zigbee uses oqpsk, there will be total 256/2 = 128 complex symbols in the front of a zigbee frame. Is that calculation correct :)
Yes that is correct.
In the receiver side what is the Error threshold used chip errors. I mean when a symbol is decoded from 32 bit sequence, how many chip error could be tolerated.
PDU begins with a preamble sequence which is composed of 32 zeros (all bytes set to 0x00) and is used for chip and symbol synchronization at receiver part of transceiver. Start of frame delimiter (SFD) follows the preamble and is 8 bit field segregate between preamble and actual physical layer data. The SFD indicates the end of the SHR and the start of the packet data and is set to 0x7A. At the receiver side, an 802.15.4 radio synchronizes to incoming zero-symbols and searches for the SFD sequence to receive incoming packets. The PHR includes a 1-byte length field that describes the number of bytes in the packet’s payload, including the 2-byte CRC. PSDU field carries PHY packet but the payload is transferred from MAC sublayer. Its length is variable.