Half Subcarrier Shift (LTE)
Selected
When is selected, the demodulator expects the uplink signal to comply with the LTE Long Term Evolution standard regarding subcarrier shift and phase reset. The LTE standard requires that the uplink subcarriers be spaced on either side of DC by half the subcarrier spacing. When this is done, a phase reset is also needed after each symbol.
To demodulate a signal that does not shift the subcarriers by half the subcarrier spacing (and therefore does not need a phase reset), clear the parameter.
To demodulate a signal that conforms to the half subcarrier shift, but does not reset the phase each symbol, clear this parameter. The signal will then be demodulated correctly, but will show a frequency offset error of 7.5 KHz.
Background
Downlink signals have an odd number of subcarriers, and the middle subcarrier, located at DC, is discarded, since recovering the data from a DC subcarrier In an orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) signal, the subcarrier whose frequency would be equal to the RF center frequency of the station. is generally difficult. In contrast, uplink signals have one less subcarrier than the corresponding downlink signal and are shifted down in frequency by half the subcarrier spacing such that the subcarriers are symmetric about DC, causing less bandwidth to be wasted.
See Also
