PTP820 2+0 Configuration

Products PTP
1

Let's talk about 2+0 configuration here and clarify a few concept and restrictions you may face when you planning a 2+0 link. 

People will like to use 2+0 configuration to achieve high capacity. In addition, it also provide some level of redundancy. if one of the link fail, all traffic will be routed through the other link.

Normally we talk about three configurations:

  1. ACCP - Adjacent Channel Co Polarization
  2. ACAP - Adjacent Channel Alternate Polarization
  3. CCDP - Co Channel Dual Polarization (or people call it XPIC

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You can achieve a 2+0 configuration with:

- 2 x PTP820S

- 1 x PTP820C with 2nd core activated

- 1 x PTP820G dual modem with 2nd modem activated

If the 2+0 link has seperate antenna, then there is no restrictions. 

But when you plan a 2+0 configuration share a common antenna, both channel must be covered by the same sub-band radio.


Let's take an example - 2+0 11 GHz with 40 MHz channel share a common antenna using PTP820S

Following configuration is supported as they are covered by same sub-band (Ch1w6)

Picture1.jpg 

Following configuration is not supported as they can NOT covered by same sub-band (Ch1w6 vs. Ch7w13)

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Commonly in a 2+0 configuration, both channel are using the same channel size. In the cases you need different channel size, it is ok as long as both channel also covered by same sub-band.  For example, you could have one channel using 40 MHz channel and the other use 30 MHz channel, itis supported.

The only exception is 80MHz. in a 2+0 configuratoin, if you have one channel using 80MHz, the other channel must be 80 Mhz as well.

thanks

Allen

4 Likes
2

I'm wondering what is the reason for the requirement to use the same sub-band radios when using a single antenna?  We recently installed a new 2+0 link with PTP820S radios.  We needed to use a single antenna due to space on the tower.  However, the only two available channels were in separate sub-bands.  These two channels are 80 MHz, on opposite polarities in the 11 GHz band.  We installed the radios and antennas, never realizing that this was not recommended.  Our vendor never mentioned that this would be a problem (we sent them the frequencies prior to ordering the equipment), and I know that they worked closely with Cambium before they ever sent us a BOM.  I just happened to stumble upon this post tonight, and realized our configuration is not in compliance.  We have traffic on it, but not much at this point.  On one side, we have a 2 foot dish with an OMT combining the two radios on opposite polarities.  On the other side, we have an 8 foot dual-pol dish with the radios on remote mounts and flexible waveguides connecting the radios to the dish.   At this point, the link is operating on both channels at full signal, and modulation does not appear to be suffering.

So are the implications here?  What sort of problems is this going to create?

Craig

3

Hi, Craig,

The rule we put together is guidance to provide guaranteed perfomrance in 2+0. The reason is when both channel fall to same sub-band, the filter at depliexer provide further help on radio MSE (Mean Square Error Rate).

In the cases when you don't have the radio covers by same radio, the 2+0 may still work, but we can't guaranteed in each case it will work. 

It is good to know your links works, can you send me a screen short for MSE stats?

thanks

Allen

4

Allen,

Here are the screenshots from all four radios comprising this 2+0.  Please note that the time/date on the radios is not synchronized with any NTP server, and the dates are currently all different.  However, these screenshots were all taken within about 10 minutes of each other.  Please let me know your thoughts  based on this information.

Craig

5

I'm new to the PTP820s, and am configuring a link for 2+0 ACAP using the OMT and 2 radios on each side.  Do the radios get setup as though they are 2 seperate 1+0 links?  I assume that that need to setup LAG as well?

6

What would you like to do?

Have you read this post?

http://community.cambiumnetworks.com/t5/Licensed-Microwave/LAG-options-for-PTP-820S/m-p/72222#M559

You can use external switches to do the traffic combining, you can use internal LAG, or you can use MC-ABC.

Each of these options has tradeoffs:

MC-ABC combines the traffic at Layer 1 and is the most efficient way to use the channels. (Depending upon the configuration and the traffic, LAG may allow one link to be fully utilized while the other link is under utilized. LAG doesn't necessarily guarantee even traffic distribution.)

There's no additional cost with internal LAG. External LAG requires two drop cables per end, one for each link.

I hope this helps!

Dave

7

Good evening,

my ptp820s goes into "alert" mode upon activation of the modulation; can you help me

8

That doesn't sound good. I suggest that you contact customer support!

https://www.cambiumnetworks.com/support/contact-support/

9

Dear Allen,

What is the minimum frequency distance to consider in ACAP? Can they really be next to each other?

Taking your example: 10735/11225 and the next pair to it 10775/11265 would work fine?

Eventually they can even somewhat overlap? What is the rule to follow?

Thanks,
Marton

10

Adjacent channels are allowed; overlapping channels are not allowed.

Have you tried this in LINKPlanner?

Set up an 11 GHz 40 MHz PTP 820S 2+0 link.

The "Select" button under "Configuration at Each End" has a marvelous frequency selection tool that shows you the channels that will work. This tool will prevent you from choosing channels that are in different sub-bands, and it will prevent you from using overlapping channels as well.

Give it a try, I'm sure you'll like it.

Dave

1 Like
11

P.S. Download LINKPlanner (for free!) here:https://support.cambiumnetworks.com/files/linkplanner/

12

Is there an order of preference for the 3 modes?  Based on performance, or cost due to required license keys?  I see for example that there is a license key to enable XPIC.

Should we tell our frequency coordinator to try and find available channels starting with a certain preferred mode, then the second best, etc.?  And then order equipment and license keys accordingly?  I don't want to dictate a certain mode to them and reduce the chances of successfully coordinating the link.  But if a certain mode will perform better or cost less, then I should give them some priorities.

13

This depends upon the part of the world the link is to be installed.

If there's lots of congestion (i.e., not very many channels available for ACCP--two channels with the same polarity), then you may need to consider Cross-Polar (ACAP) (two channels, one V and one H) or XPIC (CCDP) (one channel--V and H polarity).

You're right, though, XPIC is an additional equipment cost--you'll need to purcchase feature activation keys for each transmitter. (In this case, you'll need four feature activation keys.)

You should be able to work with your frequency coordinator--start with 2+0, Co-Polar, both Vertical. If they can't find that, try 2+0 Cross-Polar, and finally, 2+0 XPIC.

Only consider 2+0 Co-Polar with both Horizontal if you know the link can tolerate rain fading and you don't want to purchase the XPIC feature activation keys.

Of course, do not order the equipment until you have the frequencies.

If you do get two frequencies (ACCP or ACAP), and if your ODUs share the same antenna, be sure that the coordinator puts both frequencies into the same ODU sub-band.

LINKPlanner will prevent you from selecting two frequencies from different sub-bands--coordinators are usually aware of this limit, and they usually know how to use LINKPlanner to determine what works and what doesn't work.

I hope this helps!

Dave

14
@allenyu wrote:

Hi, Craig,

The rule we put together is guidance to provide guaranteed perfomrance in 2+0. The reason is when both channel fall to same sub-band, the filter at depliexer provide further help on radio MSE (Mean Square Error Rate).

Allen

What do you mean when you say the filter at depliexer provide further help on radio MSE?  I assume you mean diplexer.  Is there a filter on the diplexer of each radio or are you talking about the splitter/combiner that the radios mount to?  I only seen a single part number for the splitter/combiner?

15

Okay, I'm assuming you mean the diplexer on the radio.    This stuff is above my head so I have a few questions.  When running 2+0 ACCP you say to be guaranteed to work well the radios need to be from the same sub-band.  What are the chances of things working using 2 radios from different sub bands?  It would seem to me the higher channel separation would benefit, not hinder performance?

16

Have a look at this article: http://community.cambiumnetworks.com/t5/Licensed-Microwave/Hey-Why-do-I-have-to-use-the-same-sub-band/m-p/71532

Please let us know if you have further questions.

Self-interference is not always obvious; it is usually quite nasty.

I hope this helps!

Dave

17

~8 months late to the discussion, but the whole mixing sub-bands topic is an interesting one.  It might seem intuitive that the further the channel separation the better, but as you increase the channel separation the TxL frequencies from Band 1 may approach the TxH frequenices of Band 2, for example.

See attached example, where choosing two 40 MHz channels at the opposite ends of the available spectrum (CH1 and CH12) results in the OMT/Splitter mixing transmitting and receiving frequencies that are only 50 MHz apart.  Radio A is transmitting 11175 MHz while Radio B is receiving 11225 MHz, which may cause issues!

The degree to which the diplexers can handle this will vary based on that specific level of separation, but as a best practice/rule, it's best not to mix sub-bands.