64 QAM system phase noise?

[biff44]

Anyone know what total system local oscillator SSB phase noise a 64 QAM backhaul radio would need for good performance, OC3 data rate?

I have this in my notes, but want to confirm if it is in the right ballpark:

100 Hz -51 dbc/hz
1 KHz -73
10 KHz -82
100 KHz -101
1 Mhz -120
5 Mhz -132
>10 MHz -132

And spurious at 50 dBc +/- 25 Mhz from the carrier.

Look about right?

 

[tony_lth]

I had designed STM1 (i.e. 128QAM) microwave, 18G+ microwave point to point for more than 4 years.
The STM1 (128QAM) performance should be:
-62dBc/Hz@1KHz
-78dBc/Hz@10KHz
-101dBc/Hz@100KHz
-106dBc/Hz@1MHz
for 128QAM, the most important is 10K, 100K. The others is not important.
for QPSK, we also notice 1K besides 10K and 100K.
So your phase noise is very good for 64QAM.

About the spurious, you should check the spectrum according to the standards of Europe or US or local goverments.

And don't forget IM3. For 128QAM, at the specified power output, the IM3 should be greater than 40dBc.
For QPSK, the IM3 should be greater than 24dBc.

---------- Post added at 23:14 ---------- Previous post was at 23:03 ----------

The spectrum must pass the MASK of the local goverment, say EN 302 217.
The 128QAM for STM-1 bandwidth is 28MHz.
The QPSK bandwidth can be 3.5M, 7M, 14M, etc. The bandwidth smaller, the more strict specification about the 1K phase noise.

 

[Aladdin.CN]

Hi, tony_lth

For 128QAM, at the specified power output, the IM3 should be greater than 40dBc.
For QPSK, the IM3 should be greater than 24dBc.

Can you tell me how to get the IM3 requirement of 128QM?

tks

 

[tony_lth]

Hi, Aladdin,

I don't know what you mean. IM3 is determined by TX chain specifications. That's the basic concept. You should look up some textbook.

 

[Aladdin.CN]

Hi, tony_lth,

For Microwave PtP
As you said, For 128QAM, at the specified power output, the IM3 should be greater than 40dBc.

My question is "How to get the requirement of IM3 (40dBc@Pmax_128QAM, Pout of HPA) from the mask requirement "?
The 40dBc is a experiential value or coming from theory?

As I know, for different freq. band (such as 18G and 38G), the mask requirement from ETSI have something difference. Whether we can use the same standard of IM3 for 128QAM or not?

 

[tony_lth]

The value is firstly tested from some famous vendors' products. Maybe you can derive it from the MASK.
40dBc is at normal temperature, at high temp, it maybe degrade to 37dBc. But it still can support 128QAM at high temp.
Yes, there is a little difference between 18G and 38G.
But I still use 40dBc for 38G.
Good luck.