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Thread: Multi-Carrier IM measurement


Permlink Replies: 2 - Pages: 1 - Last Post: Nov 9, 2010 1:59 PM Last Post By: Leyo
Leyo

Posts: 63
Registered: 04/17/07
Multi-Carrier IM measurement
Posted: Nov 8, 2010 9:45 AM
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Hello,
This is regarding Multi-crrier IM measurement for GSM Base station.
I am using MXA (N9020A) for this measurement. ACP mode under spectrum Analyzer is used for this measurement. Noticed thata there two methods for the ACP measurment, IBW method and RBW method. What are the differnce between them. Can somebody point me some literature on this?. Is this ACP method valid only for WCDMA and LTE?. I mean is this ACP screen is valid for measuring GSM multi-carrier IM?.
For the following configuration
6 GSM carriers and the offset is 2.8 MHz. IBW method with IBW of 100 KHz, RBW/VBW 100 KHz Span 25 MHz.
I am sseeing a spike in the 2.8 MHz offset (around 5 dB higher than nornal IM signal) with ACP screen. But with normal swept SA method with above seetings, the spike is not there. Just wondering is this ACP method adding anything.
tabbott


Posts: 1,483
Registered: 07/24/09
Re: Multi-Carrier IM measurement
Posted: Nov 8, 2010 3:37 PM   in response to: Leyo in response to: Leyo
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Hello -

The difference between the Resolution Bandwidth (RBW) method and Integrated Bandwidth (IBW) method is that the RBW method tunes to each offset and sets the resolution bandwidth to a value close to the bandwidth of the offset and sweeps the offset in zero span. The average power is then computed from the time domain trace and the relative power to the carrier is calculated.

The integrated bandwidth method integrates the power in each of the offsets and calculates the relative power to the carrier. The integration technique is discussed in detail in App Note 1303.

This RBW method is primarily used for cdmaOne and cdma2k where there is a 30 kHz offset close to the carrier. This offset is small relative to the span so the IBW method variance is large due to the small number of trace points in this narrow offset. The IBW method is recommended in almost all other cases including WCDMA and LTE.

I would also recommend the N9071A GSM/Edge application which has been updated to handle multi-carrier signals and automates these measurement. More information is available here:

http://cp.literature.agilent.com/litweb ... 6532EN.pdf

You can also get a 14 day trial license you can use to get a better understanding of the algorithm used.

Regards -
Leyo

Posts: 63
Registered: 04/17/07
Re: Multi-Carrier IM measurement
Posted: Nov 9, 2010 1:59 PM   in response to: Leyo in response to: Leyo
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Hello,
Thanks for the reply.
I do have N9071A-3FP installed in my MXA. The version is 1.3.48804.23899. Is it latest?

Regarding the Multi-Carrier IM measurement, I am using the ACP screen in the SA mode. I have 6 GSM carriers spaced at 2.8 MHz. In the "offset limits" tab, I am entering offset freq as 2.8 MHz (I am interested only for offset A=2.8 MHz). There are two options for measuremnt, IBW and RRC Weighted. What is the "RRC Weighted method"?
As per 3GPP method, The IM productes should be measured in 100 KHz RBW and the carrier also at 100 KHZ RBW. So, I am selecting 100 KHz as IBW. Under the offset BW, I am selecting RBW=100 KHz and VBW=100 KHz. Is this set up correct?. I am confused about the IBW and RBW settings here.
Appreciate your help.

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