The Baseband Section

In Chapter 3 we discussed code generation requirements and root raised cosine filter
implementation, and we introduced digital processing methods of producing these
functions in the handset. These same functions are required in the Node B transmitter,
but given less restriction on power consumption, different trade-offs of software
against configured silicon may be made. Also, in the handset it was seen that after the
RRC filter implementation, the signals (I and Q) were passed to matched DACs for
conversion into the analog domain. An analog-modulated IF was produced that was
then upconverted to final transmit frequency. Again, in the Node B, the signal can
remain in the digital domain—to produce a modulated IF and only be converted to
analog form prior to upconversion. This approach comes nearer to the software radio
concept and so provides greater flexibility.