1 SS/PBCH block的时频结构

1个SSB在时域包含4个OFDM符号，在频域上包含240个连续子载波。时频结构如下图所示。

在SSB的时频结构上，PSS、SSS、PBCH和PBCH DMRS资源分配如下图所示。

对于1个SSB，UE假设：

• Antenna port 4000用于传输PSS、SSS、PBCH和PBCH DMRS。
• PSS、SSS、PBCH和PBCH DMRS使用相同的CP(cyclic prefix)和SCS(subcarrier spacing)。
• 对于SSB type A，u=0,1 k_SSB={0,1,…,23}，N_CRB^SSB根据15kHz子载波间隔计算。
• 对于SSB type B，u=3,4 k_SSB={0,1,…,11}，N_CRB^SSB根据60kHz子载波间隔计算。
• The centre of subcarrier 0 of resource block N_CRB^SSB coincides with the centre of subcarrier 0 of a common resource block with the subcarrier spacing provided by the higher-layer parameter subCarrierSpacingCommon. This common resource block overlaps with subcarrier 0 of the first resource block of the SS/PBCH block.

The UE may assume that SS/PBCH blocks transmitted with the same block index on the same center frequency location are quasi co-located with respect to Doppler spread, Doppler shift, average gain, average delay, delay spread, and, when applicable, spatial Rx parameters. The UE shall not assume quasi co-location for any other SS/PBCH block transmissions.

2 PSS/SSS

PSS序列生成，由NID(2)决定。N_ID2 = {0,1,2}

SSS序列生成，由NID(1)和NID(2)决定。N_ID1 = {0,1,…,335}

UE通过解PSS和SSS，可以获得NID(1)和NID(2)，通过下式可计算小区ID(0-1007)。

3 PBCH

3.1 PBCH DMRS

LTE利用CRS(Cell Specific Reference Signal)解码PBCH，而5G中没有CRS，故需要DMRS来解码PBCH。

PBCH DMRS序列生成 PBCH DMRS序列由Pseudo Random序列生成，UE通过解码PBCH DMRS，UE可以知道如何解PBCH，同时也会得到SSB index和Half Frame Number。

遗留问题：DMRS如何解调的？

3.2 PBCH payload

PBCH Payload包含系统帧号的低四位、半帧号(half frame bit)、k_ssb的高1位、SSB index的高3位。具体生成如下图所示。

4 MIB

BCCH-BCH-Message ::=            SEQUENCE {
    message                         BCCH-BCH-MessageType
}

// bit length of BCCH-BCH = bit length of mib + 1

// bit length of BCCH-BCH = messageClassExtension + 1

BCCH-BCH-MessageType ::=        CHOICE {
    mib                             MIB,
    messageClassExtension           SEQUENCE {}
}

// Size = 6+1+4+1+8+1+1+1 = 23bits

MIB ::=                             SEQUENCE {
    systemFrameNumber                   BIT STRING (SIZE (6)),
    subCarrierSpacingCommon             ENUMERATED {scs15or60, scs30or120},
    ssb-SubcarrierOffset                INTEGER (0..15),
    dmrs-TypeA-Position                 ENUMERATED {pos2, pos3},
    pdcch-ConfigSIB1                    PDCCH-ConfigSIB1,
    cellBarred                          ENUMERATED {barred, notBarred},
    intraFreqReselection                ENUMERATED {allowed, notAllowed},
    spare                               BIT STRING (SIZE (1))
}

5 SSB的调度

http://www.sharetechnote.com/html/5G/5G_FrameStructure.html#SS_PBCH_TimeDomainResourceAllocation

ServingCellConfigCommon ::= SEQUENCE {
    ...
    ssb-PositionsInBurst CHOICE {
        shortBitmap                  BIT STRING (SIZE (4)),
        mediumBitmap                 BIT STRING (SIZE (8)),
        longBitmap                   BIT STRING (SIZE (64))
    },
    ssb-periodicityServingCell       ENUMERATED { ms5, ms10, ms20, ms40, ms80, ms160, spare2, spare1 }         
    dmrs-TypeA-Position              ENUMERATED {pos2, pos3},
    ...
}

问题： L = 8 11011000 ssbIndex怎么编号？

SSB Matlab 仿真

http://www.sharetechnote.com/html/lte_toolbox/Matlab_LteToolbox_5G_SS_PBCH.html