In This article I write about step of Physical random access procedure in umts. As shown in below figure steps is as below.

  • Derive the available uplink access slots, in the next full access slot set, for the set of available UMTS RACH sub-channels within the given ASC. Randomly select one access slot among the ones previously determined. If there is no access slot available in the selected set, randomly select one uplink access slot corresponding to the set of available UMTS RACH sub-channels within the given ASC from the next access slot set. The random function shall be such that each of the allowed selections is chosen with equal probability.
  • Randomly select a signature from the set of available signatures within the given ASC.
  • Set the Preamble Retransmission Counter to Preamble_ Retrans_ Max
  • Set the parameter Commanded Preamble Power to Preamble_Initial_Power
  • Transmit a preamble using the selected uplink access slot, signature, and preamble transmission power.
  • If no positive or negative acquisition indicator (AI neither 1 nor 1) corresponding to the selected signature is detected in the downlink access slot corresponding to the selected uplink access slot.
  • Select the next available access slot in the set of available UMTS RACH sub-channels within the given ASC.
  • Select a signature.
  • Increase the Commanded Preamble Power.
  • Decrease the Preamble Retransmission Counter by one. If the Preamble
  • Retransmission Counter > 0 then repeat from step 6. Otherwise exit the physical random access procedure.
  • If a negative acquisition indicator corresponding to the selected signature is detected in the UMTS downlink access slot corresponding to the selected UMTS uplink access slot, exit the physical random access procedure Signature
  • If a positive acquisition indicator corresponding to the selected signature is detected , Transmit the random access message three or four UMTS uplink access slots after the uplink access slot of the last transmitted preamble
  • exit the physical random access procedure

Random Access Procedure in umts