it is only with the MIB
are in the QPSK
mapped to six resource blocks (72 sub-carriers), sub-frame 0 is the center of the DC subcarrier
is mapped to a resource element, which does not reserved for transmitting reference signals, PDCCH or PHICH
UE by detecting the PBCH, the following information can be obtained:
(1) received by the downlink system bandwidth can know MasterInformationBlock cell, a PHICH configuration (see "LTE: PHICH (a)"), a system frame number (System Frame Number, SFN more precisely, acquired Yes. SFN high eight, the lowest two need to get in the PBCH blind detection, which will be described later).
(2) the number of antenna ports cell-specific (cell-specific antenna port): 1 or 2 or 4.
(3) for the L1 / L2 control signal (including PCFICH, PHICH, PDCCH) transmission diversity mode (transmit-diversity scheme): PBCH and L1 / L2 control signal can only use a single antenna transmission or transmission diversity, if using a transmission diversity, PBCH and L1 / L2 control signal use the same multi-antenna transmission diversity mode.
----------------
After the cell search procedure, UE already knows a 10ms timing, i.e. know the location of the sub-frame 0 is located.
Located on the PBCH in subframe 0 of the second slot of the time domain of the first four OFDM symbol, occupying the central 72 subcarriers (excluding DC) on the frequency domain.
PBCH within 40ms cycle is repeated four times, and each time PBCH sent all carry the same coded bit, that is to say, every time can be decoded alone. Thus, in the channel quality (SIR) is good enough, the UE may receive only one, it is possible to successfully decode the contents of the PBCH that 40ms in; if not, for soft combining with the contents of the next 10ms the PBCH transmission and then decodes, until we have decoded the PBCH.
As already mentioned, by MIB, UE SFN can only get to a high of 8, the lowest two (ie, 40ms timing) is obtained by a blind detection PBCH. PBCH transmitted per 40ms will be provided with a different scrambling and bit position (i.e., a total of four different phase of the PBCH scrambling code), and will be reset every 40ms.
Each UE may of the PBCH scrambling code is used to try decoding the four possible phase PBCH, if the decoding is successful, the cell is also known in the 40ms frame transmission of the MIB number system, i.e., to know the SFN minimum two. ([2] and [6] introduces minimum SFN 2-bit detection several strategies, are interested can find out)
Multi-antenna transmission of the PBCH can transmit diversity, and when the second antenna port transmission, only using the SFBC; 4 antenna port transmission, only combined SFBC / FSTD. UE using three different CRC mask (see particularly Section 5.3.1.1 of 36.212) to blind detection PBCH, available number of antenna ports, the number of antenna ports and a transmission diversity mode correspondence (antenna port 1 <-> No; 2 antenna port <-> SFBC; 4 antenna ports <-> combined SFBC / FSTD), and therefore when the UE successfully decoded PBCH, to know the cell-specific number of antenna ports and a transmission for the L1 / L2 control signal diversity mode. (Description of SFBC, FSTD and see [1] Section 5.4.1.4 and Section 10.3.1.2)
There are three combinations PBCH antenna port (1/2/4) and (Phase) combination of four different scrambling codes, so do blind detection PBCH up to 12 possible combinations.
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5G
in
PBCH
the
payload
length is
24
bits, the
LTE
the
PBCH POH The payload
is the same length.
2
,
. 5G
in the
24
-bit
payload
details: see
38.331
Protocol:
MIB ::= SEQUENCE {
systemFrameNumber BIT STRING (SIZE (6)),
subCarrierSpacingCommon ENUMERATED {scs15or60, scs30or120},
ssb-SubcarrierOffset INTEGER (0..15),
dmrs-TypeA-Position ENUMERATED {pos2, pos3},
pdcch-ConfigSIB1 INTEGER (0..255),
cellBarred ENUMERATED {barred, notBarred},
intraFreqReselection ENUMERATED {allowed, notAllowed},
spare BIT STRING (SIZE (1))
}
Which
5G
leaving only the domain:
systemFrameNumber
.
Here:
the SFN
higher
6
bits in
PBCH payload
, the lower
4
bits of the channel coding for a part of, the
PBCH
transmission of a transport block.
Next look
SFN
this lower
4
bits
PBCH
which position the transport block
-PBCH payload
generated at
. 3
,
the PBCH payload
generated
See
38.212 7.1.1
section describes the following summary of the festival is to understand.
As can be seen from the figure:
the SFN
lower
4
bits are generated immediately high
the PBCH payload
(
24
bits) after.
38.212 7.1.1
section is dealt equivalent
PBCH
transport block
(TB)
, and of length from the input
24
into a bit
24 + 8 = 32
bits of.
. 4
,
the PBCH
in the subsequent processes bit level Introduction
PBCH Payload
after generating
(32
bits
) ->
scrambled
-> the CRC
added
-> the Polar
coding
->
rate matching.
Wherein a scrambled output data of the same length, or
32
bits.
The CRC (24
bits
)
after addition of the output data length is
32 + 24 = 56
bits.
Polar
coding, the output bit length of
N = 2 ^ 9 = 512
bits.
Rate matching the output data length is
E = 864
bits.
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