LTE PRACH Measurement
R&S
®
CMW-KM5xx/-KS5xx
746
User Manual 1173.9628.02 ─ 16
Channel Bandwidth [MHz]
1.4
3
5
10
15
20
Resource Blocks (RB)
6
15
25
50
75
100
4.2.7.2
Preambles in the Time Domain
In the time domain a preamble consists of a Cyclic Prefix (CP) and the preamble
sequence.
Fig. 4-4: Preamble structure
The length of CP and preamble sequence depend on the preamble format as shown in
the following table, where T
s
is the basic LTE time unit (1 T
s
= 1/30.72 MHz
≈
32.55
ns).
Table 4-2: Preambles in the time domain
Preamble format
CP length [T
s
]
Sequence length [T
s
]
Preamble length [T
s
]
0
3168
24576
27744
1
21024
24576
45600
2
6240
2*24576
55392
3
21024
2*24576
70176
4
448
4096
4544
Thus a preamble with format 0 to 3 requires between 2 and 6 UL timeslots for trans-
mission. A preamble with format 4 is only relevant for TDD and is transmitted in uplink
pilot timeslots (UpPTS).
The time resources allowed for transmission of preambles are restricted by 3GPP.
There are 64 configurations for FDD and 58 configurations for TDD, identified via the
PRACH configuration index. The index defines which radio frames, subframes etc. can
be used and which preamble format is used. For details refer to 3GPP TS 36.211 sec-
tion 5.7.1.
4.2.7.3
Preamble Sequences
Random access preambles are generated from Zadoff-Chu sequences with zero corre-
lation zone. For each cell a set of 64 preamble sequences is generated from one or
several root Zadoff-Chu sequences via cyclic shift. The UE decides which of these 64
preamble sequences it uses for the PRACH procedure.
A logical root sequence index is broadcasted within the system information as
RACH_ROOT_SEQUENCE. The UE uses the logical root sequence index to deter-
General Description
深圳德标仪器
135-1095-0799