1 ppm for the UE) before transmission on the uplink can occur. Lastly, analog components tend
to have DC drifting issues which basically shifts the information bearing signal. However, the baseband
signal processing algorithms typically operate under the impression that the origin is located at
(0, 0). Moving the origin to another location will degrade performance unless this DC offset is estimated
and removed [41].
The quadrature demodulation requires the use of the LPF to filter out the spectral components at
twice the input frequency. Recalling our earlier discussion on pulse shaping, this LPF can, in fact,
have a response that this is matched to the transmitted waveform.
6.7.2 Software Defined Radio (SDR) Evolution
In this section, we will present some comments on the notation of having a radio (MS or UE) be completely
programmable through software changes [42]. The present day approach is to optimize the
design with respect to cost, size, power, and overall performance. Much effort is placed in performing
functionality partitioning of the signal processing algorithms to achieve a competitive consumer
product.
The current state of the art in digital signal processors (DSPs) preclude performing all the baseband
tasks within the DSP.
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