EnOcean Physical Layer / Radio Interface
- the physical layer of the EnOcean system defines the performance of the communications between the different nodes..
The EnOcean physical layer defines the performance of the radio interface.
Parameters including the radio signal definition, modulation, etc.
EnOcean physical layer basics
EnOcean uses a very simple radio transmission system. Not only is this easy to encode, but also receive. This ensures that low power operation is possible because of the low levels of processing required. Also it is possible to achieve high levels of efficiency ion the RF amplifier because it can be run in compression.
There are several key aspects for the physical layer:
- GFSK modulation: The EnOcean radio interface uses a form of modulation known as GFSK: Gaussian Frequency Shift Keying. Frequency Shift Keying is a form of frequency modulation where the signal frequency is changed between two frequencies dependent upon the modulation. In the case of the EnOcean radio signal the sift is ±62.5kHz of the central carrier position. The +62.5 kHz position is for the code used to indicate logical "1" and the -62.5 kHz position is the code used to indicate a logical "0".
As with any signal, sidebands spread out either side when modulation is applied. In the case of a frequency shift keyed signal with sharp switching edges, sidebands could spread out over a wide bandwidth and therefore the signal is filtered at the transmitter to ensure only a narrow bandwidth is occupied. A Gaussian filter is used for this - hence the name Gaussian Filtered Frequency Shift Keying, GFSK.
The EnOcean standard allows for the use of different GFSK filter parameters dependent upon the required national regulation requirements.
- EnOcean Frequencies: The EnOcean radio interface specification states that the system can operate within a variety of ISM bands. However the individual frequencies are specified for which the system is to be used are specified within the standard. Currently two frequencies are specified: 902.875MHz which is aimed at the North American market and 928.35MHz which is aimed at the Japanese market. The standard states that the aim of the specification is to be frequency independent and therefore additional frequencies may be introduced as new markets or requirements arise.
- EnOcean Frame: Data to be transmitted is assembled into frames. This enables synchronisation, and the correct reception of the data, etc. Read more details about the EnOcean Radio Protocol.
Frequency shift keying is used as the modulation as this has no amplitude content and the transmitting amplifier can be run into compression where it operates far more efficiently.
|EnOcean Physical Layer Parameters Summary|
|Data rate tolerance||-30||+30||ppm|
|PA ramp on time||40||µs|
|PA ramp off time||40||µs|
|Code for 1||+62.5||kHz|
|Code for 0||-62.5||kHz|
By Ian Poole
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