10.1.6 Narrowband physical random-access channel
36.2113GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Physical channels and modulationRelease 17TS
10.1.6.1 Time and frequency structure
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
|
Preamble format |
|
|
|
|
|
|
0 |
4 |
4 |
5 |
|
|
|
1 |
4 |
4 |
5 |
|
|
|
2 |
6 |
6 |
3 |
|
3 |
Table 10.1.6.1-2: Random access preamble parameters for frame structure type 2
|
Preamble format |
Supported uplink-downlink configurations |
|
|
|
|
|
|
0 |
1, 2, 3, 4, 5 |
2 |
4 |
1 |
|
|
|
1 |
1, 4 |
2 |
4 |
2 |
|
|
|
2 |
3 |
2 |
4 |
4 |
|
|
|
0-a |
1, 2, 3, 4, 5 |
3 |
6 |
1 |
|
|
|
1-a |
1, 4 |
3 |
6 |
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 
.
10.1.6.2 Baseband signal generation
The time-continuous random-access signal 
for symbol group 
is defined by
where , 
is an amplitude scaling factor in order to conform to the transmit power 
specified in clause 16.3.1 in TS 36.213 [4], 
, 
accounts for the difference in subcarrier spacing between the random access preamble and uplink data transmission, and the location in the frequency domain controlled by the parameter 
is derived from clause 10.1.6.1. The variable
is given by Table 10.1.6.2-1.
Table 10.1.6.2-1: Random access baseband parameters
|
Preamble format |
|
|
|
Frame Structure Type 1 |
Frame Structure Type 2 |
|
|
0, 1 |
3.75 kHz |
|
|
0-a, 1-a |
3.75 kHz |
|
|
2 |
1.25 kHz |
3.75 kHz |
