Section: 10.1.6.1 Time and frequency structure
Content: The physical layer random access preamble is based on single-subcarrier frequency-hopping symbol groups. A symbol group is illustrated in Figure 10.1.6.1-1, consisting of a cyclic prefix of length and a sequence of identical symbols with total length. The total number of symbol groups in a preamble repetition unit is denoted by . The number of time-contiguous symbol groups is given by . The parameter values for frame structures 1 and 2 are listed in Tables 10.1.6.1-1 and 10.1.6.1-2, respectively. Figure 10.1.6.1-1: Random access symbol group Table 10.1.6.1-1: Random access preamble parameters for frame structure type 1 Table 10.1.6.1-2: Random access preamble parameters for frame structure type 2 The preamble consisting of symbol groups shall be transmitted times. For frame structure type 2, when an invalid uplink subframe overlaps the transmission of symbol groups without a gap, the symbol groups are dropped. For frame structure type 2, the transmission of symbol groups are aligned with the subframe boundary. The transmission of a random-access preamble, if triggered by the MAC layer, is restricted to certain time and frequency resources. A NPRACH configuration provided by higher layers contains the following: - NPRACH resource periodicity (nprach-Periodicity), - frequency location of the first subcarrier allocated to NPRACH (nprach-SubcarrierOffset), - number of subcarriers allocated to NPRACH (nprach-NumSubcarriers), - number of starting sub-carriers allocated to UE initiated random access (nprach-NumCBRA-StartSubcarriers), - number of NPRACH repetitions per attempt (numRepetitionsPerPreambleAttempt), - NPRACH starting time (nprach-StartTime), - Fraction for calculating starting subcarrier index for the range of NPRACH subcarriers reserved for indication of UE support for multi-tone msg3 transmission (nprach-SubcarrierMSG3-RangeStart). NPRACH transmission can start only time units after the start of a radio frame fulfilling . For frame structure type 1, after transmissions of time units for preamble formats 0 and 1, or time units for preamble format 2, a gap of time units shall be inserted. NPRACH configurations where are invalid. The NPRACH starting subcarriers allocated to UE initiated random access are split in two sets of subcarriers, and , where the second set, if present, indicate UE support for multi-tone msg3 transmission. The frequency location of the NPRACH transmission is constrained within sub-carriers, and within subcarriers when preamble format 2 as described in Table 10.1.6.1-1 is configured. Frequency hopping shall be used within the 12 subcarriers and 36 subcarriers when preamble format 2 as described in Table 10.1.6.1-1 is configured, where the frequency location of the ith symbol group is given by where . The quantity depends on the frame structure. For frame structure type 1: - if , for preamble formats 0 and 1 as described in Table 10.1.6.1-1: where with being the subcarrier selected by the MAC layer from , and the pseudo random sequence is given by clause 7.2. The pseudo random sequence generator shall be initialised with . - if , for preamble format 2 as described in Table 10.1.6.1-1: where with being the subcarrier selected by the MAC layer from , and the pseudo random sequence is given by clause 7.2. The pseudo random sequence generator shall be initialised with . For frame structure type 2: - if , for preamble formats 0, 1, and 2 as described in Table 10.1.6.1-2: where with being the subcarrier selected by the MAC layer from , and the pseudo random sequence is given by clause 7.2. The pseudo random sequence generator shall be initialised with . - if , for preamble formats 0-a, 1-a, as described in Table 10.1.6.1-2: where with being the subcarrier selected by the MAC layer from , and the pseudo random sequence is given by clause 7.2. The pseudo random sequence generator shall be initialised with .