There are two dedicated channels
and one common channel for the uplink. User data is transmitted
on one of these channels, the Dedicated Physical Data Channel
(DPDCH), as is the control information. The Random Access Channel
is a common access channel.
The Dedicated Physical Control Channel (DPCCH) is needed to transmit
pilot symbols for coherent reception, power signaling bits, and
rate information for rate detection. The two basic solutions
for multiplexing physical control and data channels are time
multiplexing and code multiplexing. A combined IQ and code multiplexing
solution (dual-channel QPSK) is used in the WCDMA uplink and
to avoid Electromagnetic Compatibility (EMC) problems with Discontinuous
Transmission (DTX).
There is a major drawback of a time multiplexed control channel,
that is where there are EMC problems that arise when DTX is used
for data transmission. Figure 31 shows an example of DTX during
normal speech transmission. During periods when there is silence
there is no need for information bits to be transmitted. This
results in pulsed transmission of the of the control data that
has to be transmitted.
