We are pleased to share with you all an interesting article contributed by Mohamed Abdel Monem.
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Mohamed Abdel Monem Radio Optimization Senior Engineer at Vodafone Egypt
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Each symbol represents bits depending on the modulation technique, Each data point represents a different bit pattern. LTE devices use QPSK, 16QAM and 64QAM to modulate data and control information. The eNodeB supports all of these modulation techniques for the Down Link direction. However, 64QAM is optional in the Uplink direction.
Measuring Signal Quality
Both the eNodeB and the UE measure signal quality using Reference Signals.
The Reference Signals carry a known (pseudo-noise) bit pattern at a boosted power level.
The receiver performs channel equalization based on the received Reference Signals.
The eNodeB calculates the UE-transmitted signal quality by measuring UE Reference Signals, and by requesting Channel Quality Indication (CQI) feedback from the UE.
The eNodeB always controls and selects the modulation and coding scheme for both the Downlink and Uplink. |
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Good article , thanks
Thank you for sharing this interessting article.
I want to know if in theory we can estimate the CQI by estimating the SNR, can we do it just with the distance between the user and the eNodeB.
Best Regards.
Quite a refresher but I don't see the mention of 256 QAM.
Knowledgable!
What's the likelihood 256QAM can be deployed?
@Mr. Raj, if we based description post from Mr Yoo, for 256QAM you need to add 10db for reach Max SNR related 256QAM, this means Dmax(256 QAM)= Dmax(64 QAM) /3 if I m not wrong. But if we have bad QoS on the link , system will switch you directly for an less modulation for adapte you on best QoS. For have 256QAM you need to best QoS at the right distance.
Oh excuse of course not forget the load, if you don't have x2 interface need Master SON for offload the maximum of user during Busy hour period for keep Max user on right distance with Max modulation.
Dear Expert,
From a field,We have 63% QPSK utilisation in a customer network here in france and the CQI-modulation 3GPP mapping not matched as with CQI 15,we have QPSK which is strange.
SNR vs Modulation correlation shows for SNR<=2.5db we have 64QAM,else QPSK and 16QAM
do you know if there is any internal SNR-Modulation mapping table in ericsson ?because no parameters found or do you have any explaination about this behavior?
Thanks for your support
Tq. Nice as a Refresher...
You can find 256QAM in DL as additional options too:)
Too basic , 256 Qam already deployed in our network and not consider how Ues sending CQI information. PUCCH.. Thanks for the effort.
Tq. Nice as a Refresher...
Good
Thanks Very Good
Thanks. We need to equate this also to category of UE being used whether can support the modulation technique.