Hi Matthias,
for me it is not fully clear, what type of cable you plan to use. Do you just intend to use AWG22 cables as defined for PROFINET (or even thicker cables) or is the idea to also use thinner AWG26-AWG23 cables in office (IT) environments? Is it expected to also work for link segments up to 100 m using these thinner types of cable with the same immunity related to external noise?
What would be the expected noise immunity in office and especially also industrial/automotive/OT environments? Background of this question is, that using a single pair instead of 4 pairs, as e.g. for 1000BASE-T, leads to a significantly higher symbol rate (or alternatively number of needed PAM-levels, but this would likely not be the way to go) compared to 1000BASE-T. Consequently this leads to a significantly higher IL for a 100 m link segment using the same wire diameter (e.g. at half-Nyquist frequency) for a SPE solution, compared to 1000BASE-T and thus reduces the SNR at the receiver for a given external noise.
1000BASE-T1 supports 40 m based on the link segment delay spec, and based on the IL definitions the class B link segment allows for 17.21 dB @ 375 MHz (Nyquist) or 11.86 dB @ 187.5 MHz (half-Nyquist). Roughly extrapolating this to 100 m would lead to an IL of 43.03 dB (x 2.5) for 375 MHz and 29.65 dB for 187.5 MHz, which is already significant. Looking into presentation
https://www.ieee802.org/3/SPEP2P/public/ISOchannelsJune%2021-schicketanz.pdf, this presentation states about 20 dB @ 100 MHz for an AWG23 cable. At 375 MHz, just looking at the skin effect, this would roughly lead to an estimated IL of SQRT(375/100) * 20 dB = 38.8 dB and 27.4 dB @ 187.5 MHz, which is with some margin pretty close to the extrapolated link segment definition for a class B segment of Clause 97. For smaller diameters, the IL increases further. Having this said, this might/will lead into the room of technical feasibility, if the same (or similar) noise requirements than e.g. for a 1000BASE-T1 automotive or industrial segment are needed.
So when thinking about increasing the link segment length for e.g. a 1000BASE-T1 equivalent modulation, the expected noise environment would be one of the key points to initially answer. Alternatively having the need for larger diameter wires to bring the IL down, leads to higher cost and larger material requirements (especially copper) again and also makes installations more difficult as pretty strong cables must be handled, which would reduce the benefits compared to a 1000BASE-T implementation using 4-pairs. So for me it would be really interesting to know more about the technical feasibility related to noise immunity and the intended cable wire diameters/IL expectations. From my point of view this would also be important related to a good distinction to the already existing PHYs with a comparable 100 m reach.
Regards,
Steffen
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