E-UTRA Synchronized Random Access
Before the random access procedure can be initiated, the following information is assumed to be available:
- the available set of PRACH resources for the transmission of the Random Access Preamble and their corresponding RA-RNTIs.
- the groups of Random Access Preambles and the set of available Random Access Preambles in each
group.
- There are 64 preambles available in each cell.
- the thresholds required for selecting one of the two groups of Random Access Preambles.
- the parameters required to derive the TTI window [RA_Window_Begin – RA_Window_End].
- the power-ramping factor POWER_RAMP_STEP.
- the parameter PREAMBLE_TRANS_MAX [integer > 0].
- the initial preamble power PREAMBLE_ INITIAL_RECEIVED_TARGET_POWER.
- the parameter Maximum number of Message3 HARQ transmissions.
Note that the diagram above is only for illustration of the random access sequence, and the exact transmission timing of the random access preamble should be determined according to the selection of the PRACH resources (specified in time and frequency domain) as per TS36.321 Section 5.1.2.
E-UTRA Random Access Response
More information can be found in TS36.321 Section 5.1.4. Once the Random Access Preamble is transmitted, the UE shall monitor the PDCCH associated with the RA-RNTI
defined below in the TTI window [RA_WINDOW_BEGIN—RA_WINDOW_END] for Random Access Responses identified by the RA-RNTI.