essage part. These is also an offset given in between the last preamble Parameter Planning Access slot Uplink Power ramp-up preamble to message Power ramp-up step PRACH frame 15 access slots 1st Preamble 2nd Preamble RACH Message Downlink Access slot AICH frame 15 access slots Acquisition Indication Figure 2.42 Power ramp-up process sent and the message part to guarantee reception of the message. As the RACH message is short no power control is used. The mobile sends a predefined number of preambles, ramping up power in between every step. If the mobile has ramped up the power a predefined number of times and receives no confirmation from the base station, if starts the sequence from the begining and repeats it, but the sequence of ramping up the TX power is repeated only a predefined number of times. The UE will exit the random access procedure if it does not receive a response from the base station before it runs out the maximum number of times it is allowed to repeat the power ramp-up procedure. PRACH and AICH channels are structured to a 20 ms frame with 15 access slots. The PRACH frame is divided into two access slot sets: access slot set 1 (access slots 0 to 7) and access slot set 2 (access slots 8 to 14). Random Access Procedure: Preamble and Message The preamble is 4096 chips long. It consists of 256 X 16 chip signatures. There are 16 possible signatures in each cell. The uplink scrambling code of a cell is selected from 16 dedicated UL scrambling codes. The RACH message consists of one or two radio frames (10-20 ms). The scrambling code number is the same as that used for the preamble. The message part can have different spreading factors. The spreading factor is based on a selected signature and spreading factors between 256 and 32 can be used. Random Access Procedure: AICH Each acquisition indication channel (AICH) slot carries a separate acquisition indication for each signature (total 16). The acquisition indication has three different values: 0, no indication the BTS has not received this signature;