ort channel is mapped and a control part that carries Layer 1 control information; they are transmitted in parallel. Ndata bits Pilot Npilot bits NTFCI bits Control Tslot = 2560 chips, 10*2k bits (k=0..3) Slot #0 Slot #1 Slot #i Slot #14 Message part radio frame TRACH = 10 ms Figure 4.7 Random-access message part radio frame structure. The UMTS Network and Radio Access Technology A 10 ms message part consists of one message part radio frame, while a 20 ms message part consists of two consecutive 10 ms message part radio frames. The message part length can be determined from the used signature and/or access slot, as configured by higher layers. Table 4.10 illustrates data and control fields of the random access mes- sage. Table 4.10 Random Access Message Data and Control Fields Channel bit Channel symbol Bits/ Bits/ Npilot Ndata format #i rate (kbps) rate (ksps) frame Control fields NTFCI The data part consists of 10 X 2k bits, where k = 0,1,2,3. This corresponds to a spreading factor of 256, 128, 64, and 32 for the message data part, respectively. The control part consists of 8 known pilot bits to support channel estimation for coher- ent detection and 2 TFCI bits. This corresponds to a spreading factor of 256 for the message control part. The pilot bit pattern is described in Table 4.11. The total number of TFCI bits in the random-access message is 15 X 2 = 30. The TFCI of a radio frame indicates the transport format of the RACH transport channel mapped to the simultaneously transmitted message part radio frame. In the case of a 20 ms PRACH message part, the TFCI is repeated in the second radio frame. Table 4.11 Pilot Bit Patterns for RACH Message Part with Npilot = 8 Slot # Npilot = 8 Bit # The UTRA Physical Layer Design 4.3.3.2 Physical Common Packet Channel (PCPCH) The Physical Common Packet Channel (PCPCH) carries the CPCH. The CPCH trans- mission is based on the Digital Sense Multiple Access - Collision Detection (DSMA- CD) technique with fast acquisition indication. The UE can start transmission at the beg