Section: 5.7.2 Preamble sequence generation
Content: The random access preambles are generated from Zadoff-Chu sequences with zero correlation zone, generated from one or several root Zadoff-Chu sequences. The network configures the set of preamble sequences the UE is allowed to use. There are up to two sets of 64 preambles available in a cell where Set 1 corresponds to higher layer PRACH configuration using prach-ConfigurationIndex and prach-FrequencyOffset and Set 2, if configured, corresponds to higher layer PRACH configuration using prach-ConfigurationIndexHighSpeed and prach-FrequencyOffsetHighSpeed. The set of 64 preamble sequences in a cell is found by including first, in the order of increasing cyclic shift, all the available cyclic shifts of a root Zadoff-Chu sequence with the logical index rootSequenceIndexHighSpeed (for Set 2, if configured) or with the logical index RACH_ROOT_SEQUENCE (for Set 1), where both rootSequenceIndexHighSpeed (if configured) and RACH_ROOT_SEQUENCE are broadcasted as part of the System Information. Additional preamble sequences, in case 64 preambles cannot be generated from a single root Zadoff-Chu sequence, are obtained from the root sequences with the consecutive logical indexes until all the 64 sequences are found. The logical root sequence order is cyclic: the logical index 0 is consecutive to 837. The relation between a logical root sequence index and physical root sequence index is given by Tables 5.7.2-4 and 5.7.2-5 for preamble formats 0 – 3 and 4, respectively. The root Zadoff-Chu sequence is defined by where the length of the Zadoff-Chu sequence is given by Table 5.7.2-1. From the root Zadoff-Chu sequence, random access preambles with zero correlation zones of length are defined by cyclic shifts according to where the cyclic shift is given by and is given by Tables 5.7.2-2 and 5.7.2-3 for preamble formats 0-3 and 4, respectively, where the higher-layer parameters zeroCorrelationZoneConfig and zeroCorrelationZoneConfigHighSpeed shall be used for PRACH preamble Set 1 and Set 2 (if configured), respectively. Restricted set type B shall be used for PRACH preamble Set 2 (if configured), and the parameter High-speed-flag provided by higher layers determines if unrestricted set or restricted set type A shall be used for PRACH preamble Set 1. The variable is the cyclic shift corresponding to a Doppler shift of magnitude and is given by where is the smallest non-negative integer that fulfils . The parameters for restricted sets of cyclic shifts depend on . For restricted set type A and , the parameters are given by For restricted set type A and , the parameters are given by For restricted set type B and , the parameters are given by For restricted set type B and , the parameters are given by For restricted set type B and , the parameters are given by For restricted set type B and , the parameters are given by For restricted set type B and , the parameters are given by For restricted set type B and , the parameters are given by For all other values of , there are no cyclic shifts in the restricted set. Table 5.7.2-1: Random access preamble sequence length Table 5.7.2-2: for preamble generation (preamble formats 0-3) Table 5.7.2-3: for preamble generation (preamble format 4) Table 5.7.2-4: Root Zadoff-Chu sequence order for preamble formats 0 – 3 Table 5.7.2-5: Root Zadoff-Chu sequence order for preamble format 4