Error in Modulator 'symbolSpreading'

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  • #11489
    Imen Mrissa
    Participant

    Hi everyone,
    I tried to set ‘symbolSpreading’ of Modulator object to ‘DFT’ instead of ‘none’ but there is an error when reshaping ‘dataSymbols’ because size(dataSymbols) is not a multiple of nScheduledSubcarriers.

    Here is the error.
    Error using Modulation.Modulator/spreadingTransform (line 103)
    Product of known dimensions, 72, not divisible into total number of elements, 912.

    Error in Elements.BaseStation/generateTransmitSignal (line 77)
    spreadSymbols = currentMod.spreadingTransform(dataSymbols,
    currentLink.scheduledSubcarriers);

    Error in main (line 45)
    parfor iSweep = 1:length(simParams.simulation.sweepValue) % this may be ‘for’ or ‘parfor’

    Thank you for yo assistance.

    #11579

    Hi,

    since the spreading algorithm is performed per OFDM symbol, for example, 14 times per subframe (TTI) in an LTE system, the number of QAM symbols per OFDM symbols has to be always the same. Unfortunately, this requirement is not satisfied when the LTE downlink pilot pattern is employed as the pilots are mapped in a diamond shape within the resource grid. To enable the symbol spreading, suited pilot pattern needs to be implemented, such as the pattern for the LTE uplink, which employs DFT spreading. In this case, there are either no pilots in an OFDM symbol, or an OFDM symbol consists exclusively of pilot symbols. This enables to employ spreading, but is unfortunately not implemented yet. Please compare the LTE uplink and downlink pilot allocation schemes for clarification.

    best
    Stefan

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