5G/NR - Initial Access/RACH                                           Home : www.sharetechnote.com

 

 

 

 

Initial Access means a sequence of process between UE and gNB(Network) in order for UE to aquire Uplink Synchronization and obtain specified ID for the radio access communication. In more familiar terms, this Initial Access is refered to be 'RACH process'. Depending on the document, the term Initial Access may mean 'Downlink Synchronization + RACH'. But in my case, Initial Access usually refer to RACH process and I wrote a separate page for downlink synchronization.

 

Even though the detailed parameter is not determined (as of Apr 2017), the overal logic of NR RACH will be very similar to LTE RACH process (Based on TR 38.804 v1.0.0 - Ref [32]). So if you are already familiar with LTE RACH process, it would easily pick up NR RACH process. If you are not familiar with LTE RACH process, I would strongly recommend to go through LTE RACH page and try to get familiar with the procedure.

 

 

 

 

Why RACH ?

 

The first question poping up in your mind when you first hear about the word RACH or RACH Process would be 'Why RACH ?', 'What is the functionality/purpose of RACH process ?', "Why we need this kind of complicated (looks over-complicated) ?'.

For sure, it is not for confusing you :), RACH has very important functionality especially in LTE (and in WCDMA as well). The main purpose of RACH can be described as follows.

    i) Achieve UP link synchronization between UE and eNB

    ii) Obtain the resource for Message 3 (e.g, RRC Connection Request)

In most of the communication (especially digital comunication regardless of whether it is wired or wireless), the most important precondition is to establish the timing synchronization between the reciever and transmitter. So whatever communication technology you would study, you would see some kind of synchronization mechanism that is specially designed for the specific communication.

 

In NR (in LTE and WCDMA as well), the synchronization in downlink (Transmitter = gNB, Reciever = UE), this synchronization is achieved by the special synchronization channel (special physical signal pattern). Refer to Synchronization page for the details.

This downlink sync signal gets broadcasted to everybody and it is get transmitted all the time with a certain interval.

However in Uplink(Transmitter = UE, Reciever = gNB), it is not efficient (actually waste of energy and causing a lot of interference to other UEs) if UE is using this kind of broadcasting/always-on synchronization mechanism. You may easily understand this kind of problem. In case of uplink, this synchronization process should meet following criteria

    i) The synchronization process should happen only when there is immediate necessity

    ii) The synchronization should be dedicated to only a specific UE

All the complicated/confusing stories in this page is mostly about the process specially designed mechanism to meet these criteria.

 

Another purpose of RACH process is to obtain the resource for Msg3 (Message 3). RRC Connection Request is one example of Msg3 and there are several different types of Msg3 depending on situation. You would figure out this part in reading through this page and this is not very complicated to understand.

 

 

 

When we need RACH  ?

 

There are many situation that triggers RACH process. The list of cases are summarized in 38.300-9.2.6 as follows. The first half of the list(i~iv) is same as in LTE case.  The second half of the list would be NR specific. We don't have RRC_INACTIVE state (item v), On-Demand SIB transmition(item vii) in LTE, we have a primitive types of BeamFormaing / BeamManagement in LTE but not as sophisticated as in NR(item viii). We do have CA(SCell addition) in LTE but we don't trigger RACH in any of CA activity in LTE(item vi).

 

    i) Initial access from RRC_IDLE;

    ii) RRC Connection Re-establishment procedure;

    iii) Handover;

    iv) DL or UL data arrival during RRC_CONNECTED when UL synchronisation status is "non-synchronised";

    v) Transition from RRC_INACTIVE;

    vi) To establish time alignment at SCell addition;

    vii) Request for Other SI

    viii) Beam failure recovery.

 

 

 

Two types of RACH : Contention Based and NonContention Based

 

This is also almost same as in LTE as described below.

 

When a UE transmit a PRACH Preamble, it transmits with a specific pattern and this specific pattern is called a "Signature". In each LTE cell, total 64 preamble signatures are available and UE select randomly one of these signatures.

 

UE select "Randomly" one of these signatures ?

 

Does this mean that there is some possibility that multiple UEs send PRACH with identical signatures ?

 

Yes.

 

There is such a possibility. It means the same PRACH preamble from multipe UE reaches the NW at the same time.. this kind of PRACH collision is called "Contention" and the RACH process that allows this type of "Contention" is called "Contention based" RACH Process. In this kind of contention based RACH process, Network would go through additional process at later step to resolve these contention and this process is called "Contention Resolution" step.

 

But there is some cases that these kind of contention is not acceptable due to some reason (e.g, timing restriction) and these contention can be prevented. Usually in this case, the Network informs each of the UE of exactly when and which preamble signature it has to use. Of course, in this case Network will allocate these preamble signature so that it would not collide. This kind of RACH process is called "Contention Free" RACH procedure. To initiate the "Contention Free" RACH process, UE should be in Connected Mode before the RACH process as in Handover case.

 

Typical 'Contention Based' RACH Procedure is as follows :

 

i) UE --> NW : RACH Preamble (RA-RNTI, indication for L2/L3 message size)

ii) UE <-- NW : Random Access Response (Timing Advance, T_C-RNTI, UL grant for L2/L3 message)

iii) UE --> NW : L2/L3 message

iv) Message for early contention resolution

 

Now let's assume that a contention happened at step i). For example, two UEs sent PRACH. In this case, both of the UE will recieve the same T_C-RNTI and resource allocation at step ii). And as a result, both UE would send L2/L3 message through the same resource allocation(meaning with the same time/frequency location) to NW at step iii). What would happen when both UE transmit the exact same information on the exact same time/frequency location ? One possibility is that these two signal act as interference to each other and NW decode neither of them. In this case, none of the UE would have any response (HARQ ACK) from NW and they all think that RACH process has failed and go back to step i). The other possibility would be that NW could successfully decode the message from only one UE and failed to decode it from the other UE. In this case, the UE with the successful L2/L3 decoding on NW side will get the HARQ ACK from Network. This HARQ ACK process for step iii) message is called "contention resolution" process.

 

Typical 'Contention Free' RACH Procedure is as follows :

 

i) UE <--NW : RACH Preamble (PRACH) Assignment

ii) UE --> NW : RACH Preamble (RA-RNTI, indication for L2/L3 message size)

iii) UE <--NW : Random Access Response (Timing Advance, C-RNTI, UL grant for L2/L3 message)

 

 

 

Two Types of Sequence : Short Sequence and Long Sequence

 

 

 

 

Fundamental Difference from LTE RACH

 

As I mentioned above, the overall protocol sequence would be almost same in LTE and NR. The major difference between LTE RACH and NR RACH would lie just before RACH Preamble gets transmitted.  It is due to BeamForming which would be supported by default (especially in mmWave) in NR. So in case when NR is operating in Beamforming mode, UE need to detect and select a best beam for RACH process. This beam selection process would be the fundamental difference between LTE RACH and NR RACH process.

 

 

 

Preamble Sequence Generation

 

Like LTE Preamble Sequence, NR Preamble sequence is also based on Zadoff Chu based sequence. Overall sequence generation is as follows.

 

 

 

The detailed base sequence generation algorithm can be summarized as follows. Even though the details are different, basically this is similar to LTE as well. There are two types of sequence in terms of sequence length(L_RA = 139 and 839).

 

 

< Frequency Domain Sequence Generation >

 

Following is the equation to generate PRACH sequence in frequency domain based on 36.211-6.3.3.1.

 

 

 

 

<Time Domain Sequence Generation >

 

Following is the equation to generate the time domain sequence for PRACH. Basically the big picture is to do IFFT to the frequency domain data generated above.

 

 

 

 

zeroCorrelationZoneConfig and Ncs

 

The Ncs in the above equation is determined by zeroCorrelationZoneConfig in RRC message and the value is determined by the following mapping table.

 

Following two tables (Table 6.3.3.1-5, Table 6.3.3.1-6) are applicable for Long Sequence RACH Preambles

 

<  38.211-Table 6.3.3.1-5:  Ncs for preamble formats with   >

 

 

<  38.211-Table 6.3.3.1-6:  Ncs for preamble formats with   >

 

 

Following tables (Table 6.3.3.1-7) are applicable for Short Sequence RACH Preambles

 

<  38.211-Table 6.3.3.1-7:  Ncs for preamble formats with   >

 

 

 

Root Sequence Index

 

Like LTE Root Sequence Index, NR use different numbering system at RRC layer and Physical Layer for Root Sequence Index and the mapping between these two are defined as in following tables.

 

 

< 38.211-Table 6.3.3.1-3: Mapping from PRACHRootSequenceIndex  i to sequence number u  for preamble formats with L_RA = 839 >

 

 

< 38.211-Table 6.3.3.1-4: Mapping from PRACHRootSequenceIndex  i to sequence number u  for preamble formats with L_RA = 139 >

 

 

 

Preamble Format

 

NR also use various types of Preamble Format as shown below. You would notice that NR PRACH preamble format is much more diverse than LTE Preamble Format

 

As you see in the following tables, two different length (L_RA) of PRACH preamble is used depending on subcarrier spacing of the preamble.

 

When the subcarrier spacing of PRACH preamble is 1.25 or 5 Khz, long sequence (L_RA = 839) is used as in the following table. (NOTE : Regarding 'Restricted sets', refer to zeroCorrelationZoneConfig and Ncs)

 

< 38.211 - Table 6.3.3.1-1: PRACH preamble formats for   and    >

 

When the subcarrier spacing of PRACH preamble is 15,30,60 or 120 Khz, short sequence (L_RA = 139) is used as in the following table. (NOTE : Regarding 'Restricted sets', refer to zeroCorrelationZoneConfig and Ncs)

 

< 38.211 - Table 6.3.3.1-2: Preamble formats for   and   where   >

 

NOTE : Kappa is defined as 64 in 38.211-4.1 as below. (Refer to Timing Unit page for the details)

 

Followings are the illustration of RACH Preamble Time domain structure. GP(GAP) length in this illustration are from Ref 36. The number 0.509 ns(0.509 x 10^-6 ms) is the value of the parameter Tc and 64 is the value of the paramter K(Kappa).

 

 

< Preamble Format 0 >

 

 

 

< Preamble Format 1 >

 

 

 

< Preamble Format 2 >

 

 

 

< Preamble Format 3 >

 

 

 

Following illustration shows the short sequence A,B,C. The length calculated here is based on 15 Khz frequency(u=0) interval. As this interval goes higher (e.g, 30, 60, 120, 240 Khz), the length gets shorter.

 

 

< Preamble Format A1 >

 

 

 

< Preamble Format A2 >

 

 

 

< Preamble Format A3 >

 

 

 

< Preamble Format B1 >

 

 

 

< Preamble Format B2 >

 

 

 

< Preamble Format B3 >

 

 

 

< Preamble Format B4 >

 

 

 

< Preamble Format C0 >

 

 

 

< Preamble Format C2 >

 

 

 

 

Random Access Configuration

 

As in LTE, NR Random Access Configuration is the parameter that determine when (i.e, which radio frame and which subframe) UE is allowed to transmit PRACH Preamble and what kind of Preamble format it should transmit. If you are familiar with the interpretation of LTE RACH configuration table , you would easily understand this table as well. Except n_SFN mod x = y part, everything is same as in LTE case.

 

 

< 38.211 v15.1.0-Table 6.3.3.2-2: Random access configurations for FR1 and paired spectrum/supplementary uplink >

 

PRACH

Configuration

Index

Preamble

Format

n_SFN mode x= y

Subframe

number

Starting

Symbol

Number

of

PRACH

slots

within a

subframe

number of

time -

domain

PRACH

occassions

within a

RACH slots

PRACH

duration

x

y

0

0

16

1

1

0

-

-

0

1

0

16

1

4

0

-

-

0

2

0

16

1

7

0

-

-

0

3

0

16

1

9

0

-

-

0

4

0

8

1

1

0

-

-

0

5

0

8

1

4

0

-

-

0

6

0

8

1

7

0

-

-

0

7

0

8

1

9

0

-

-

0

8

0

4

1

1

0

-

-

0

9

0

4

1

4

0

-

-

0

10

0

4

1

7

0

-

-

0

11

0

4

1

9

0

-

-

0

12

0

2

1

1

0

-

-

0

13

0

2

1

4

0

-

-

0

14

0

2

1

7

0

-

-

0

15

0

2

1

9

0

-

-

0

16

0

1

0

1

0

-

-

0

17

0

1

0

4

0

-

-

0

18

0

1

0

7

0

-

-

0

19

0

1

0

1,6

0

-

-

0

20

0

1

0

2,7

0

-

-

0

21

0

1

0

3,8

0

-

-

0

22

0

1

0

1,4,7

0

-

-

0

23

0

1

0

2,5,8

0

-

-

0

24

0

1

0

3, 6, 9

0

-

-

0

25

0

1

0

0,2,4,6,8

0

-

-

0

26

0

1

0

1,3,5,7,9

0

-

-

0

27

0

1

0

0,1,2,3,4,5,6,7,8,9

0

-

-

0

28

1

16

1

1

0

-

-

0

29

1

16

1

4

0

-

-

0

30

1

16

1

7

0

-

-

0

31

1

16

1

9

0

-

-

0

32

1

8

1

1

0

-

-

0

33

1

8

1

4

0

-

-

0

34

1

8

1

7

0

-

-

0

35

1

8

1

9

0

-

-

0

36

1

4

1

1

0

-

-

0

37

1

4

1

4

0

-

-

0

38

1

4

1

7

0

-

-

0

39

1

4

1

9

0

-

-

0

40

1

2

1

1

0

-

-

0

41

1

2

1

4

0

-

-

0

42

1

2

1

7

0

-

-

0

43

1

2

1

9

0

-

-

0

44

1

1

0

1

0

-

-

0

45

1

1

0

4

0

-

-

0

46

1

1

0

7

0

-

-

0

47

1

1

0

1,6

0

-

-

0

48

1

1

0

2,7

0

-

-

0

49

1

1

0

3,8

0

-

-

0

50

1

1

0

1,4,7

0

-

-

0

51

1

1

0

2,5,8

0

-

-

0

52

1

1

0

3,6,9

0

-

-

0

53

2

16

1

1

0

-

-

0

54

2

8

1

1

0

-

-

0

55

2

4

0

1

0

-

-

0

56

2

2

0

1

0

-

-

0

57

2

2

0

5

0

-

-

0

58

2

1

0

1

0

-

-

0

59

2

1

0

5

0

-

-

0

60

3

16

1

1

0

-

-

0

61

3

16

1

4

0

-

-

0

62

3

16

1

7

0

-

-

0

63

3

16

1

9

0

-

-

0

64

3

8

1

1

0

-

-

0

65

3

8

1

4

0

-

-

0

66

3

8

1

7

0

-

-

0

67

3

4

1

1

0

-

-

0

68

3

4

1

4

0

-

-

0

69

3

4

1

7

0

-

-

0

70

3

4

1

9

0

-

-

0

71

3

2

1

1

0

-

-

0

72

3

2

1

4

0

-

-

0

73

3

2

1

7

0

-

-

0

74

3

2

1

9

0

-

-

0

75

3

1

0

1

0

-

-

0

76

3

1

0

4

0

-

-

0

77

3

1

0

7

0

-

-

0

78

3

1

0

1,6

0

-

-

0

79

3

1

0

2,7

0

-

-

0

80

3

1

0

3,8

0

-

-

0

81

3

1

0

1,4,7

0

-

-

0

82

3

1

0

2,5,8

0

-

-

0

83

3

1

0

3, 6, 9

0

-

-

0

84

3

1

0

0,2,4,6,8

0

-

-

0

85

3

1

0

1,3,5,7,9

0

-

-

0

86

3

1

0

0,1,2,3,4,5,6,7,8,9

0

-

-

0

87

A1

16

0

4,9

0

1

6

2

88

A1

16

1

4

0

2

6

2

89

A1

8

0

4,9

0

1

6

2

90

A1

8

1

4

0

2

6

2

91

A1

4

0

4,9

0

1

6

2

92

A1

4

1

4,9

0

1

6

2

93

A1

4

0

4

0

2

6

2

94

A1

2

0

4,9

0

1

6

2

95

A1

2

0

1

0

2

6

2

96

A1

2

0

4

0

2

6

2

97

A1

2

0

7

0

2

6

2

98

A1

1

0

4

0

1

6

2

99

A1

1

0

1,6

0

1

6

2

100

A1

1

0

4,9

0

1

6

2

101

A1

1

0

1

0

2

6

2

102

A1

1

0

7

0

2

6

2

103

A1

1

0

2,7

0

2

6

2

104

A1

1

0

1,4,7

0

2

6

2

105

A1

1

0

0,2,4,6,8

0

2

6

2

106

A1

1

0

0,1,2,3,4,5,6,7,8,9

0

2

6

2

107

A1

1

0

1,3,5,7,9

0

2

6

2

108

A1/B1

2

0

4,9

0

1

7

2

109

A1/B1

2

0

4

0

2

7

2

110

A1/B1

1

0

4

0

1

7

2

111

A1/B1

1

0

1,6

0

1

7

2

112

A1/B1

1

0

4,9

0

1

7

2

113

A1/B1

1

0

1

0

2

7

2

114

A1/B1

1

0

7

0

2

7

2

115

A1/B1

1

0

1,4,7

0

2

7

2

116

A1/B1

1

0

0,2,4,6,8

0

2

7

2

117

A2

16

1

2,6,9

0

1

3

4

118

A2

16

1

4

0

2

3

4

119

A2

8

1

2,6,9

0

1

3

4

120

A2

8

1

4

0

2

3

4

121

A2

4

0

2,6,9

0

1

3

4

122

A2

4

0

4

0

2

3

4

123

A2

2

1

2,6,9

0

1

3

4

124

A2

2

0

1

0

2

3

4

125

A2

2

0

4

0

2

3

4

126

A2

2

0

7

0

2

3

4

127

A2

1

0

4

0

1

3

4

128

A2

1

0

1,6

0

1

3

4

129

A2

1

0

4,9

0

1

3

4

130

A2

1

0

1

0

2

3

4

131

A2

1

0

7

0

2

3

4

132

A2

1

0

2,7

0

2

3

4

133

A2

1

0

1,4,7

0

2

3

4

134

A2

1

0

0,2,4,6,8

0

2

3

4

135

A2

1

0

0,1,2,3,4,5,6,7,8,9

0

2

3

4

136

A2

1

0

1,3,5,7,9

0

2

3

4

137

A2/B2

2

1

2,6,9

0

1

3

4

138

A2/B2

2

0

4

0

2

3

4

139

A2/B2

1

0

4

0

1

3

4

140

A2/B2

1

0

1,6

0

1

3

4

141

A2/B2

1

0

4,9

0

1

3

4

142

A2/B2

1

0

1

0

2

3

4

143

A2/B2

1

0

7

0

2

3

4

144

A2/B2

1

0

1,4,7

0

2

3

4

145

A2/B2

1

0

0,2,4,6,8

0

2

3

4

146

A2/B2

1

0

0,1,2,3,4,5,6,7,8,9

0

2

3

4

147

A3

16

1

4,9

0

1

2

6

148

A3

16

1

4

0

2

2

6

149

A3

8

1

4,9

0

1

2

6

150

A3

8

1

4

0

2

2

6

151

A3

4

0

4,9

0

1

2

6

152

A3

4

0

4

0

2

2

6

153

A3

2

1

2,6,9

0

2

2

6

154

A3

2

0

1

0

2

2

6

155

A3

2

0

4

0

2

2

6

156

A3

2

0

7

0

2

2

6

157

A3

1

0

4

0

1

2

6

158

A3

1

0

1,6

0

1

2

6

159

A3

1

0

4,9

0

1

2

6

160

A3

1

0

1

0

2

2

6

161

A3

1

0

7

0

2

2

6

162

A3

1

0

2,7

0

2

2

6

163

A3

1

0

1,4,7

0

2

2

6

164

A3

1

0

0,2,4,6,8

0

2

2

6

165

A3

1

0

0,1,2,3,4,5,6,7,8,9

0

2

2

6

166

A3

1

0

1,3,5,7,9

0

2

2

6

167

A3/B3

2

1

2,6,9

0

2

2

6

168

A3/B3

2

0

4

0

2

2

6

169

A3/B3

1

0

4

0

1

2

6

170

A3/B3

1

0

1,6

0

1

2

6

171

A3/B3

1

0

4,9

0

1

2

6

172

A3/B3

1

0

1

0

2

2

6

173

A3/B3

1

0

7

0

2

2

6

174

A3/B3

1

0

1,4,7

0

2

2

6

175

A3/B3

1

0

0,2,4,6,8

0

2

2

6

176

A3/B3

1

0

0,1,2,3,4,5,6,7,8,9

0

2

2

6

177

B1

16

0

4,9

0

1

7

2

178

B1

16

1

4

0

2

7

2

179

B1

8

0

4,9

0

1

7

2

180

B1

8

1

4

0

2

7

2

181

B1

4

0

4,9

0

1

7

2

182

B1

4

1

4,9

0

1

7

2

183

B1

4

0

4

0

2

7

2

184

B1

2

0

4,9

0

1

7

2

185

B1

2

0

1

0

2

7

2

186

B1

2

0

4

0

2

7

2

187

B1

2

0

7

0

2

7

2

188

B1

1

0

4

0

1

7

2

189

B1

1

0

1,6

0

1

7

2

190

B1

1

0

4,9

0

1

7

2

191

B1

1

0

1

0

2

7

2

192

B1

1

0

7

0

2

7

2

193

B1

1

0

2,7

0

2

7

2

194

B1

1

0

1,4,7

0

2

7

2

195

B1

1

0

0,2,4,6,8

0

2

7

2

196

B1

1

0

0,1,2,3,4,5,6,7,8,9

0

2

7

2

197

B1

1

0

1,3,5,7,9

0

2

7

2

198

B4

16

0

4,9

0

2

1

12

199

B4

16

1

4

0

2

1

12

200

B4

8

0

4,9

0

2

1

12

201

B4

8

1

4

0

2

1

12

202

B4

4

0

4,9

0

2

1

12

203

B4

4

0

4

0

2

1

12

204

B4

4

1

4,9

0

2

1

12

205

B4

2

0

4,9

0

2

1

12

206

B4

2

0

1

0

2

1

12

207

B4

2

0

4

0

2

1

12

208

B4

2

0

7

0

2

1

12

209

B4

1

0

1

0

2

1

12

210

B4

1

0

4

0

2

1

12

211

B4

1

0

7

0

2

1

12

212

B4

1

0

1,6

0

2

1

12

213

B4

1

0

2,7

0

2

1

12

214

B4

1

0

4,9

0

2

1

12

215

B4

1

0

1,4,7

0

2

1

12

216

B4

1

0

0,2,4,6,8

0

2

1

12

217

B4

1

0

0,1,2,3,4,5,6,7,8,9

0

2

1

12

218

B4

1

0

1,3,5,7,9

0

2

1

12

219

C0

8

1

4

0

2

7

2

220

C0

4

1

4,9

0

1

7

2

221

C0

4

0

4

0

2

7

2

222

C0

2

0

4,9

0

1

7

2

223

C0

2

0

1

0

2

7

2

224

C0

2

0

4

0

2

7

2

225

C0

2

0

7

0

2

7

2

226

C0

1

0

4

0

1

7

2

227

C0

1

0

1,6

0

1

7

2

228

C0

1

0

4,9

0

1

7

2

229

C0

1

0

1

0

2

7

2

230

C0

1

0

7

0

2

7

2

231

C0

1

0

2,7

0

2

7

2

232

C0

1

0

1,4,7

0

2

7

2

233

C0

1

0

0,2,4,6,8

0

2

7

2

234

C0

1

0

0,1,2,3,4,5,6,7,8,9

0

2

7

2

235

C0

1

0

1,3,5,7,9

0

2

7

2

236

C2

16

1

4,9

0

1

2

6

237

C2

16

1

4

0

2

2

6

238

C2

8

1

4,9

0

1

2

6

239

C2

8

1

4

0

2

2

6

240

C2

4

0

4,9

0

1

2

6

241

C2

4

0

4

0

2

2

6

242

C2

2

1

2,6,9

0

2

2

6

243

C2

2

0

1

0

2

2

6

244

C2

2

0

4

0

2

2

6

245

C2

2

0

7

0

2

2

6

246

C2

1

0

4

0

1

2

6

247

C2

1

0

1,6

0

1

2

6

248

C2

1

0

4,9

0

1

2

6

249

C2

1

0

1

0

2

2

6

250

C2

1

0

7

0

2

2

6

251

C2

1

0

2,7

0

2

2

6

252

C2

1

0

1,4,7

0

2

2

6

253

C2

1

0

0,2,4,6,8

0

2

2

6

254

C2

1

0

0,1,2,3,4,5,6,7,8,9

0

2

2

6

255

C2

1

0

1,3,5,7,9

0

2

2

6

 

 

 

Just for clarity, let me give you a couple of examples.

 

Example 1 > PRACH Configuration Index = 0

    In this case, x is 16 and y = 1. It means UE is allowed to transmit PRACH in every odd radio frame (i.e, the radio frame meeting n_SFN mod 16 = 1).  UE is allowed to transmit the PRACH at SFN = 1, 17, 33, ....

    In this case, Subframe number is set to 1. It means that UE can transmit PRACH at the subframe 1 within the radio frame determined as above.

 

 

Example 2 > PRACH Configuration Index = 27

    In this case, x = 1 and y = 0. It means UE is allowed to transmit PRACH in radio frame (i.e, the radio frame meeting n_SFN mod 1 = 0). UE is allowed to transmit at every SFN.

    In this case, Subframe number is set to 0,1,2,3,4,5,6,7,8,9. It means that UE can transmit PRACH at any subframe within the radio frame determined as above.

 

 

 

< 38.211 v15.1.0-Table 6.3.3.2-3: Random access configurations for FR1 and unpaired spectrum >

 

PRACH

Configuration

Index

Preamble

Format

n_SFN mode x= y

Subframe

number

Starting

Symbol

Number

of

PRACH

slots

within a

subframe

number of

time -

domain

PRACH

occassions

within a

RACH slots

PRACH

duration

x

y

0

0

16

1

9

0

-

-

0

1

0

8

1

9

0

-

-

0

2

0

4

1

9

0

-

-

0

3

0

2

0

9

0

-

-

0

4

0

2

1

9

0

-

-

0

5

0

2

0

4

0

-

-

0

6

0

2

1

4

0

-

-

0

7

0

1

0

9

0

-

-

0

8

0

1

0

8

0

-

-

0

9

0

1

0

7

0

-

-

0

10

0

1

0

6

0

-

-

0

11

0

1

0

5

0

-

-

0

12

0

1

0

4

0

-

-

0

13

0

1

0

3

0

-

-

0

14

0

1

0

2

0

-

-

0

15

0

1

0

1

0

-

-

0

16

0

1

0

4,9

0

-

-

0

17

0

1

0

3,8

0

-

-

0

18

0

1

0

2,7

0

-

-

0

19

0

1

0

8,9

0

-

-

0

20

0

1

0

4,8,9

0

-

-

0

21

0

1

0

3,4,9

0

-

-

0

22

0

1

0

3,4,8

0

-

-

0

23

0

1

0

7,8,9

0

-

-

0

24

0

1

0

3,4,8,9

0

-

-

0

25

0

1

0

6,7,8,9

0

-

-

0

26

0

1

0

1,4,6,9

0

-

-

0

27

0

1

0

1,6

0

0

28

0

1

0

1,6

7

-

-

0

29

0

1

0

1,3,5,7,9

0

-

-

0

30

1

16

1

7

0

-

-

0

31

1

8

1

7

0

-

-

0

32

1

4

1

7

0

-

-

0

33

1

2

0

7

0

-

-

0

34

1

2

1

7

0

-

-

0

35

1

1

0

7

0

-

-

0

36

2

16

1

6

0

-

-

0

37

2

8

1

6

0

-

-

0

38

2

4

1

6

0

-

-

0

39

2

2

0

6

7

-

-

0

40

2

2

1

6

7

-

-

0

41

2

1

0

6

7

-

-

0

42

3

16

1

9

0

-

-

0

43

3

8

1

9

0

-

-

0

44

3

4

1

9

0

-

-

0

45

3

2

0

9

0

-

-

0

46

3

2

1

9

0

-

-

0

47

3

2

0

4

0

-

-

0

48

3

2

1

4

0

-

-

0

49

3

1

0

9

0

-

-

0

50

3

1

0

8

0

-

-

0

51

3

1

0

7

0

-

-

0

52

3

1

0

6

0

-

-

0

53

3

1

0

5

0

-

-

0

54

3

1

0

4

0

-

-

0

55

3

1

0

3

0

-

-

0

56

3

1

0

2

0

-

-

0

57

3

1

0

1

0

-

-

0

58

3

1

0

1,6

0

-

-

0

59

3

1

0

1,6

7

-

-

0

60

3

1

0

4,9

0

-

-

0

61

3

1

0

3,8

0

-

-

0

62

3

1

0

2,7

0

-

-

0

63

3

1

0

8,9

0

-

-

0

64

3

1

0

4,8,9

0

-

-

0

65

3

1

0

3,4,9

0

-

-

0

66

3

1

0

7,8,9

0

-

-

0

67

3

1

0

3,4,8,9

0

-

-

0

68

3

1

0

6,7,8,9

0

-

-

0

69

3

1

0

1,4,6,9

0

-

-

0

70

3

1

0

1,3,5,7,9

0

-

-

0

71

A1

16

1

9

0

2

6

2

72

A1

8

1

9

0

2

6

2

73

A1

4

1

9

0

1

6

2

74

A1

2

1

2,3,4,7,8,9

0

1

6

2

75

A1

2

1

8,9

0

2

6

2

76

A1

2

1

7,9

0

1

6

2

77

A1

2

1

7,9

7

1

3

2

78

A1

2

1

4,9

7

1

3

2

79

A1

2

1

4,9

0

2

6

2

80

A1

2

1

9

0

1

6

2

81

A1

1

0

9

0

2

6

2

82

A1

1

0

9

7

1

3

2

83

A1

1

0

9

0

1

6

2

84

A1

1

0

8,9

0

2

6

2

85

A1

1

0

4,9

0

1

6

2

86

A1

1

0

7,9

7

1

3

2

87

A1

1

0

3,4,8,9

0

1

6

2

88

A1

1

0

3,4,8,9

0

2

6

2

89

A1

1

0

0,1,2,3,4,5,6,7,8,9

7

1

3

2

90

A1

1

0

1,3,5,7,9

0

1

6

2

91

A2

16

1

9

0

2

3

4

92

A2

16

1

4,9

0

2

3

4

93

A2

8

1

9

0

2

3

4

94

A2

8

1

4,9

0

2

3

4

95

A2

4

1

9

0

1

3

4

96

A2

2

1

8,9

0

2

3

4

97

A2

2

1

7,9

9

1

1

4

98

A2

2

1

4,9

9

1

1

4

99

A2

2

1

4,9

0

2

3

4

100

A2

2

1

9

0

1

3

4

101

A2

1

0

9

0

2

3

4

102

A2

1

0

9

9

1

1

4

103

A2

1

0

9

0

1

3

4

104

A2

1

0

8,9

0

2

3

4

105

A2

1

0

4,9

0

1

3

4

106

A2

1

0

7,9

9

1

1

4

107

A2

1

0

3,4,8,9

0

1

3

4

108

A2

1

0

3,4,8,9

0

2

3

4

109

A2

1

0

0,1,2,3,4,5,6,7,8,9

9

1

1

4

110

A2

1

0

1,3,5,7,9

0

1

3

4

111

A3

16

1

9

0

2

2

6

112

A3

8

1

9

0

2

2

6

113

A3

4

1

9

0

1

2

6

114

A3

2

1

2,3,4,7,8,9

0

1

2

6

115

A3

2

1

8,9

0

2

2

6

116

A3

2

1