Packet Data

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.

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.