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why QPSK modulation scheme is used for all control channels in LTE ?

+1 vote

why QPSK modulation scheme is used for all control channels in LTE ?

posted May 27, 2017 by anonymous

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2 Answers

+1 vote


control channels are common in LTE, To decode control channel we need modulation type used by ENB but this is not conveyed by ENB ,so to make it common modulation type they come up with QPSK. Why QPSK is it is effective among other modulation type.

answer May 29, 2017 by Jaganathan
Is it possible to use 16QAM,  64QAM modulation for control channels,  Which modulation scheme is used for PBCH.
PBCH is QPSK modulated. No if you change 16QAM or 64 QAM then UE side and ENB PHY side we need changes , it is not possible now. 16,64QAM is good modulation type if channel quality is better  but for all condition QPSK will be effective.
    If we are near to eNodeB , we use 64 QAM or 16 QAM in this situation PBCH will use QPSK or 16,64 QAM,
0 votes

I think reasons to use qpsk modulation scheme for signalling in LTE could be...
1. Qpsk is most robust modulation scheme in LTE. So any ue cell edge or cell center, can decode the signalling.
2. To reduce complexity at eNb , only one qpsk modulation scheme used for signalling.

answer May 30, 2017 by Veer Pal Singh Yadav
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0 votes

Many values for the MCS index have been defined in the specification. Value ranges from 0 to 31.
Each MCS index values corresponds to different combination of "number of spatial streams + modulation type + Coding rate" .
In case of PDSCH resource allocation, eNodeB considers feedback from the UE but in case of PMCH where data is transmitted only at downlink. How a particular MCS index would be chosen for multimedia multicast broadcast data transmission ?
If I am correct, selection of MCS index is done at MCE and sends to eNodeBs/cells belong to the same MBSFN area ?
In this case when MCS index is selected by MCE, how MCE take decision on this factor ?
I am also looking for set of MCS index values which can be used for MBMS transmission ?

+5 votes

What calculation or logic behind to derive this 64 ?

+4 votes

Actually there are three resource allocation types being used to allocate resources to UE(s) in downlink and uplink. For downlink all three (Type 0, 1 and 2) used but for uplink only resource allocation type 2 is being used.