z-wave physical layer | zwave PHY layer basics
This page on z-wave physical layer(PHY) covers basic features of zwave physical layer and mention z-wave PHY transmitter block diagram.
The following are the functions performed at z-wave physical layer(zwave PHY).
• to assign RF profile to the zwave physical channel
• to activate and deactivate RF transceiver
• Transmission and reception of data frames i.e. payload
• clear channel assessment
• radio frequency selection
• link quality check based on received frames
There are three different data rates supported in z-wave Physical layer. They are 9.6 kbps(designated as 'R1'), 40 Kbps(designated as 'R2') and 100 Kbps(designated as 'R3'). Based on this data rate different physical layer configuration is made.
As shown in the figure-1 z-wave physical layer consists of modulation and coding blocks. Based on the data rates R1, R2 or R3 different configurations of the z-wave PHY is made as mentioned in the table below.
|Data Rate Designation||Bit Rate||Symbol Rate||Accuracy|
|R1||9.6 Kbps||19.2 Kbaud||+/- 27 ppm|
|R2||40 Kbps||40 Kbaud||+/-27 ppm|
|R3||100 Kbps||100 Kbaud||+/-27 ppm|
Table-1: z-wave Data Rate and Accuracy
After the modulation and coding of the input MAC layer data, frame is formed as per format outlined in z-wave tutorial. In order to do this at physical layer preamble is inserted before 'SOF' field.
|Data Rate Designation||Modulation||Coding||separation||Symbols|
|R3||GFSK (BT=0.6)||NRZ||58 KHz+/-10%||Binary|
Table-2:Modulation and coding format in z-wave Physical Layer
As mentioned in the table-2 FSK modulation is employed for R1 and R2 rates while GFSK is used for R3 data rate. For R1 manchester coding is used while for R2/R3 NRZ coding types is used.
All the data is transmitted in little endian format. They are transmitted in blocks of 8 bit with MSB is sent first after manchester coding. Manchester coding will help in obtaining DC free signal.
At the z-wave physical layer receiver, preamble is used for synchronization before decoding and demodulation is carried out to retrieve the MAC layer data. After the decoding of the data, they will be passed to the upper layers for further processing.
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