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Hi Bill,
I only have superficial understanding of radio so can’t comment on the appropriateness of the analogies you are making. However, be careful in making them because the radio channel is very different, and polarizations are typically not used as orthogonal channels to double capacity. There are many embarrassing examples of wireless envy in optics, including by esteemed academics. Two examples are CDMA and OFDM.
Transmitter loss is defined as total power loss from chip input to output, or it can be defined as per channel loss from input to output, which is the same number, except the range is shifted by 6dB.
Thank you
Chris
Coming from a cellular radio back ground, which has been “coherent” for ages, I have never heard of “transmitter loss”.
Is there a definition somewhere?
From the slide you reference Chris, this looks like what we would call in radio “PA efficiency”.
Perhaps in this case, “Modulator Efficiency”e.g. Basestations would be required to transmit, say 40 watts (at BTS antenna port), however historical PA efficiencies were say ~25% (at one time).
Meaning we had to build a 160 Watt system @ 25% efficiency.
The PA efficiency never entered the link budget however when you have 6 160 watt PA’s you can bet the ~1Kw entered into other calculations.
(6 being 3 sectors with 2x2 MIMO) which affected over all costs.
From: Chris Cole <chris@xxxxxxxxxxxxxxx>
Sent: Thursday, October 13, 2022 2:38 PM
To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_B400G] Oct 2022 Session Webpage Update
Warning - External Email
Dear 802.3df participants,
I received several private emails asking about my Coherent receiver sensitivity comment during yesterday's call. In a previous reflector thread, I used a simple link budget analysis but it looks like further explanation is in order.
The statement that Coherent detection provides 12-13 dB sensitivity gain over IMDD is correct, however in datacenter context is only half the story.
In Telecom, this is a tremendous advantage because to first order it can double span reach. It is therefore understandable that it's brought up in discussion of datacom giving the impression of similar advantage. The opposite is true. For typical SiPh implementations the huge Coherent transmitter loss results in overall link budget loss over IMDD. As commented previously, Eric deserves credit for being transparent about this, as the more typical approach by proponents has been to hide it.
The better absolute Coherent receiver sensitivity is more than cancelled out by lower coherent transmitter output power, for example -10dBm in TF proposals. IMDD EML transmitter output power can be well above 0dBm. Unlike in Telecom, there are no EDFAs to increase the optical power.
Thank you
Chris
On Thu, Oct 13, 2022 at 8:50 AM John D'Ambrosia <jdambrosia@xxxxxxxxx> wrote:
All,
Updates to presentations at the 12 Oct meeting have been uploaded to the October 2022 Session webpage – https://www.ieee802.org/3/df/public/22_10/index.html.
I am working with Kent Lusted on the minutes for the meeting. Further updates may be made during this time. If any are made, this will be noted when the Task Force is notified of the uploading of the unapproved minutes.
Regards,
John D’Ambrosia
Chair, IEEE P802.df Task Force
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