There are two very different
types of packet data transmission within the WCDMA system. Short
data packets can be added to the random access bursts and this
method is called Common Channel Packet Transmission (CCPT). CCPT
is most commonly used for short infrequent packets, where link
maintenance needed for a dedicated channel would lead to an unacceptable
overhead. Another factor for the use of CCPT cuts out the delay
that can be associated with a dedicated channel. It should also
be noted that for common channel packet transmission only open
loop power control is in operation (Open Loop Power control measures
the interference conditions from the channel, and adjusts the
transmission power adoringly to meet the desired frame error
rate (Ojanpera, T etal. 1998)). CCPT should therefore be limited
to short packets that only use a limited capacity. This is shown
in Figure 33.
Figure 33 Packet Transmission
on the Common Channel
For larger or more frequent packets transmitted on a dedicated channel, a large single packet is transmitted using a single packet system, where a dedicated channel is released immediately after the packet has been transmitted. In a multipacket system the dedicate channel is maintained by transmitting power control and synchronization information between subsequent packets.