6.11 Synchronization signals
36.2113GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Physical channels and modulationRelease 17TS
There are 504 unique physical-layer cell identities. The physical-layer cell identities are grouped into 168 unique physical-layer cell-identity groups, each group containing three unique identities. The grouping is such that each physical-layer cell identity is part of one and only one physical-layer cell-identity group. A physical-layer cell identity 
is thus uniquely defined by a number
in the range of 0 to 167, representing the physical-layer cell-identity group, and a number
in the range of 0 to 2, representing the physical-layer identity within the physical-layer cell-identity group.
6.11.1 Primary synchronization signal (PSS)
6.11.1.1 Sequence generation
The sequence 
used for the primary synchronization signal is generated from a frequency-domain Zadoff-Chu sequence according to
where the Zadoff-Chu root sequence index 
is given by Table 6.11.1.1-1.
Table 6.11.1.1-1: Root indices for the primary synchronization signal
|
|
Root index |
|
0 |
25 |
|
1 |
29 |
|
2 |
34 |
6.11.1.2 Mapping to resource elements
The mapping of the sequence to resource elements depends on the frame structure. The UE shall not assume that the primary synchronization signal is transmitted on the same antenna port as any of the downlink reference signals. The UE shall not assume that any transmission instance of the primary synchronization signal is transmitted on the same antenna port, or ports, used for any other transmission instance of the primary synchronization signal.
The sequence 
shall be mapped to the resource elements according to
For frame structure type 1, the primary synchronization signal shall be mapped to the last OFDM symbol in slots 0 and 10.
For frame structure type 2, the primary synchronization signal shall be mapped to the third OFDM symbol in subframes 1 and 6. Resource elements 
in the OFDM symbols used for transmission of the primary synchronization signal where
are reserved and not used for transmission of the primary synchronization signal.
For frame structure type 3, the primary synchronization signal shall be mapped according to frame structure type 1 with the following exceptions:
– the primary synchronization signal shall be transmitted only if the corresponding subframe is non-empty and at least 12 OFDM symbols are transmitted,
– a primary synchronization signal being part of a discovery signal shall be transmitted in the last OFDM symbol of the first slot of a discovery signal occasion.
For an MBMS-dedicated cell, the primary synchronization signal shall be mapped according to frame structure type 1 with following exception:
– the primary synchronization signal shall be transmitted in slot 0 in subframes fulfilling 
only,
6.11.2 Secondary synchronization signal (SSS)
6.11.2.1 Sequence generation
The sequence 
used for the second synchronization signal is an interleaved concatenation of two length-31 binary sequences. The concatenated sequence is scrambled with a scrambling sequence given by the primary synchronization signal.
The combination of two length-31 sequences defining the secondary synchronization signal differs between subframes according to
where 
. The indices 
and 
are derived from the physical-layer cell-identity group 
according to
where the output of the above expression is listed in Table 6.11.2.1-1.
The two sequences 
and 
are defined as two different cyclic shifts of the m-sequence 
according to
where
, 
, is defined by
with initial conditions
.
The two scrambling sequences 
and 
depend on the primary synchronization signal and are defined by two different cyclic shifts of the m-sequence 
according to
where 
is the physical-layer identity within the physical-layer cell identity group 
and 
, 
, is defined by
with initial conditions 
.
The scrambling sequences 
and 
are defined by a cyclic shift of the m-sequence 
according to
where 
and 
are obtained from Table 6.11.2.1-1 and 
, 
, is defined by
with initial conditions 
.
Table 6.11.2.1-1: Mapping between physical-layer cell-identity group 
and the indices 
and 
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0 |
0 |
1 |
34 |
4 |
6 |
68 |
9 |
12 |
102 |
15 |
19 |
136 |
22 |
27 |
|
1 |
1 |
2 |
35 |
5 |
7 |
69 |
10 |
13 |
103 |
16 |
20 |
137 |
23 |
28 |
|
2 |
2 |
3 |
36 |
6 |
8 |
70 |
11 |
14 |
104 |
17 |
21 |
138 |
24 |
29 |
|
3 |
3 |
4 |
37 |
7 |
9 |
71 |
12 |
15 |
105 |
18 |
22 |
139 |
25 |
30 |
|
4 |
4 |
5 |
38 |
8 |
10 |
72 |
13 |
16 |
106 |
19 |
23 |
140 |
0 |
6 |
|
5 |
5 |
6 |
39 |
9 |
11 |
73 |
14 |
17 |
107 |
20 |
24 |
141 |
1 |
7 |
|
6 |
6 |
7 |
40 |
10 |
12 |
74 |
15 |
18 |
108 |
21 |
25 |
142 |
2 |
8 |
|
7 |
7 |
8 |
41 |
11 |
13 |
75 |
16 |
19 |
109 |
22 |
26 |
143 |
3 |
9 |
|
8 |
8 |
9 |
42 |
12 |
14 |
76 |
17 |
20 |
110 |
23 |
27 |
144 |
4 |
10 |
|
9 |
9 |
10 |
43 |
13 |
15 |
77 |
18 |
21 |
111 |
24 |
28 |
145 |
5 |
11 |
|
10 |
10 |
11 |
44 |
14 |
16 |
78 |
19 |
22 |
112 |
25 |
29 |
146 |
6 |
12 |
|
11 |
11 |
12 |
45 |
15 |
17 |
79 |
20 |
23 |
113 |
26 |
30 |
147 |
7 |
13 |
|
12 |
12 |
13 |
46 |
16 |
18 |
80 |
21 |
24 |
114 |
0 |
5 |
148 |
8 |
14 |
|
13 |
13 |
14 |
47 |
17 |
19 |
81 |
22 |
25 |
115 |
1 |
6 |
149 |
9 |
15 |
|
14 |
14 |
15 |
48 |
18 |
20 |
82 |
23 |
26 |
116 |
2 |
7 |
150 |
10 |
16 |
|
15 |
15 |
16 |
49 |
19 |
21 |
83 |
24 |
27 |
117 |
3 |
8 |
151 |
11 |
17 |
|
16 |
16 |
17 |
50 |
20 |
22 |
84 |
25 |
28 |
118 |
4 |
9 |
152 |
12 |
18 |
|
17 |
17 |
18 |
51 |
21 |
23 |
85 |
26 |
29 |
119 |
5 |
10 |
153 |
13 |
19 |
|
18 |
18 |
19 |
52 |
22 |
24 |
86 |
27 |
30 |
120 |
6 |
11 |
154 |
14 |
20 |
|
19 |
19 |
20 |
53 |
23 |
25 |
87 |
0 |
4 |
121 |
7 |
12 |
155 |
15 |
21 |
|
20 |
20 |
21 |
54 |
24 |
26 |
88 |
1 |
5 |
122 |
8 |
13 |
156 |
16 |
22 |
|
21 |
21 |
22 |
55 |
25 |
27 |
89 |
2 |
6 |
123 |
9 |
14 |
157 |
17 |
23 |
|
22 |
22 |
23 |
56 |
26 |
28 |
90 |
3 |
7 |
124 |
10 |
15 |
158 |
18 |
24 |
|
23 |
23 |
24 |
57 |
27 |
29 |
91 |
4 |
8 |
125 |
11 |
16 |
159 |
19 |
25 |
|
24 |
24 |
25 |
58 |
28 |
30 |
92 |
5 |
9 |
126 |
12 |
17 |
160 |
20 |
26 |
|
25 |
25 |
26 |
59 |
0 |
3 |
93 |
6 |
10 |
127 |
13 |
18 |
161 |
21 |
27 |
|
26 |
26 |
27 |
60 |
1 |
4 |
94 |
7 |
11 |
128 |
14 |
19 |
162 |
22 |
28 |
|
27 |
27 |
28 |
61 |
2 |
5 |
95 |
8 |
12 |
129 |
15 |
20 |
163 |
23 |
29 |
|
28 |
28 |
29 |
62 |
3 |
6 |
96 |
9 |
13 |
130 |
16 |
21 |
164 |
24 |
30 |
|
29 |
29 |
30 |
63 |
4 |
7 |
97 |
10 |
14 |
131 |
17 |
22 |
165 |
0 |
7 |
|
30 |
0 |
2 |
64 |
5 |
8 |
98 |
11 |
15 |
132 |
18 |
23 |
166 |
1 |
8 |
|
31 |
1 |
3 |
65 |
6 |
9 |
99 |
12 |
16 |
133 |
19 |
24 |
167 |
2 |
9 |
|
32 |
2 |
4 |
66 |
7 |
10 |
100 |
13 |
17 |
134 |
20 |
25 |
– |
– |
– |
|
33 |
3 |
5 |
67 |
8 |
11 |
101 |
14 |
18 |
135 |
21 |
26 |
– |
– |
– |
6.11.2.2 Mapping to resource elements
The mapping of the sequence to resource elements depends on the frame structure. In a subframe for frame structure type 1 and 3 and in a half-frame for frame structure type 2, the same antenna port as for the primary synchronization signal shall be used for the secondary synchronization signal.
The sequence 
shall be mapped to resource elements according to
Resource elements 
where
are reserved and not used for transmission of the secondary synchronization signal.
6.11.3 Resynchronization signal (RSS)
6.11.3.1 Sequence generation
The resynchronization signal (RSS) is transmitted in subframes numbered , where the RSS duration is configured by higher layers. The sequence used for the th RSS subframe is generated according to
where the pseudo-random sequence is defined in clause 7.2. The pseudo-random sequence generator shall be initialised each subframe with , where u equals the value of the higher-layer parameter systemInfoUnchanged-BR-r15 as set in subframe . is given by Table 6.11.3.1-1.
Table 6.11.3.1-1: Definition of .
|
8 |
[ 1, 1, -1, 1, -1, -1, 1, 1 ] |
|
16 |
[ 1, 1, -1, -1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1 ] |
|
32 |
[ -1, -1, 1, 1, -1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, -1, 1, -1, 1, 1, -1, 1, 1, 1, -1, -1, 1, -1 ] |
|
40 |
[ 1, -1, -1, 1, -1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, 1, -1, 1, 1, -1, -1, 1, -1, 1, -1, -1, 1 ] |
6.11.3.2 Mapping to resource elements
If only one CRS port is configured in a cell, the UE may assume that the same antenna port is used for all subframes in an RSS transmission in the cell. Otherwise, the UE may assume that the same antenna port is used for RSS transmission in absolute subframes and and .
An RSS is transmitted in consecutive BL/CE DL subframes, starting in the first BL/CE DL subframe in a radio frame satisfying
where the RSS periodicity and the RSS time offset are configured by higher layers. In frequency domain, the RSS frequency location is assigned to the 24 subcarriers in the physical resource blocks numbers and , as configured by higher layers.
In each subframe used for RSS transmission, the RSS sequence shall be mapped to resource elements in sequence, starting with in increasing order of first the index , over the 24 assigned subcarriers and then the index .
A resource element overlapping with resource elements where cell-specific reference signals according to clause 6.10 are transmitted shall not be used for RSS transmission but is counted in the mapping process. Additionally, an RSS subframe is dropped if any RSS PRB pair overlaps with any PRB pair carrying PSS, SSS, PBCH or PDSCH associated with SI-RNTI. In frame structure type 2, those special subframes, indicated as BL/CE DL subframes by higher layer fdd-DownlinkOrTddSubframeBitmapBR, are not counted in RSS mapping and are not used for transmission of RSS.