【求助】空口没有解码到PBCH信号
分支：ngap-wf-1120-srb-gtp环境：Ubuntu 18.04.3 LTS X86_64
命令：
GNB侧：./targets/bin/nr-softmodem.Rel15 -E-O ./gnb.conf --do-ra
GNB配置：
absoluteFrequencySSB = 500208;
dl_frequencyBand = 41;
dl_absoluteFrequencyPointA = 499200;
dl_offstToCarrier = 0;
dl_subcarrierSpacing = 1;
dl_carrierBandwidth = 106;
initialDLBWPlocationAndBandwidth = 13475;
initialDLBWPsubcarrierSpacing = 1;
initialDLBWPcontrolResourceSetZero = 12;
initialDLBWPsearchSpaceZero = 0;
ul_frequencyBand = 41;
ul_offstToCarrier = 0;
ul_subcarrierSpacing = 1;
ul_carrierBandwidth = 106;
initialULBWPlocationAndBandwidth = 13475;
initialULBWPsubcarrierSpacing = 1;
nrUE侧: ./targets/bin/nr-uesoftmodem.Rel15--numerology 1 -r 106-C 2501040000 --ue-scan-carrier --ue-txgain 70 --ue-rxgain 90-E --usrp-args type=b200 --do-ra -T -U 1
运行结果：
GNB侧：
RX Gain 0 114.000000 (49.800000) => 64.200000 (max 76.000000)
USRP TX_GAIN:89.75 gain_range:89.75 tx_gain:0.00
...
TYPE <CTRL-C> TO TERMINATE
Entering ITTI signals handler
ru_thread_prach() RACH waiting for RU to be configured
ru_thread_prach() RU configured - RACH processing thread running
RU 0 rf device ready
RU 0 no asynch_south interface
ru_thread_tx ready
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
gNB 0 frame 0, subframe 0 : previous information from RU tx 0 (num_RU 1,mask 1) has not been served yet!
Frame 8 : MIB->BCHCC_id 0, Received 3 bytes
Frame 16 : MIB->BCHCC_id 0, Received 3 bytes
Frame 24 : MIB->BCHCC_id 0, Received 3 bytes
Frame 32 : MIB->BCHCC_id 0, Received 3 bytes
nrUE侧:
RX Gain 0 90.000000 (49.800000) => 40.200000 (max 76.000000)
USRP TX_GAIN:19.75 gain_range:89.75 tx_gain:70.00
Actual master clock: 46.080000MHz...
Actual clock source internal...
Actual time source internal...
RF board max packet size 1916, size for 100µs jitter 4608
rx_max_num_samps 1916
RX Channel 0
Actual RX sample rate: 46.080000MSps...
Actual RX frequency: 2.501040GHz...
Actual RX gain: 40.000000...
Actual RX bandwidth: 40.000000M...
Actual RX antenna: RX2...
TX Channel 0
Actual TX sample rate: 46.080000MSps...
Actual TX frequency: 2.501040GHz...
Actual TX gain: 19.750000...
Actual TX bandwidth: 40.000000M...
Actual TX antenna: TX/RX...
Actual TX packet size: 1916
Device timestamp: 2.359897...
has loaded USRP B200 device.
10 Dec 16:30:55 ntpdate: adjust time server 172.19.1.64 offset 0.014141 sec
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
sleep...
Check absolute frequency DL 2501040000, UL 2501040000 (oai_exit 0, rx_num_channels 1)
Starting sync detection
Running Initial Synch (mode 0)
nr_synchro_time: Sync source = 2, Peak found at pos 305244, val = 7537049 (69 dB) avg 61 dB, ffo 0.000000
PSS execution duration 155128 microseconds
Initial sync : Estimated PSS position 305244, Nid2 2
sync_pos 305244 ssb_offset 305136
Calling sss detection (normal CP)
Initial sync: starting PBCH detection (rx_offset 0)
TDD Normal prefix: CellId 881 metric 1089, phase 1, pbch -1
nr_synchro_time: Sync source = 0, Peak found at pos 17512, val = 8553649 (69 dB) avg 61 dB, ffo 0.000000
PSS execution duration 154172 microseconds
Initial sync : Estimated PSS position 17512, Nid2 0
sync_pos 17512 ssb_offset 17404
Calling sss detection (normal CP)
Initial sync: starting PBCH detection (rx_offset 0)
TDD Normal prefix: CellId 627 metric 1290, phase 5, pbch -1
Initial sync : Estimated power: 0 dB
trying carrier off -100 Hz, rxgain 90 (DL 2501039900, UL 2501039900)
Setting USRP TX Freq 2501039900.000000, RX Freq 2501039900.000000
Check absolute frequency DL 2501040000, UL 2501040000 (oai_exit 0, rx_num_channels 1)
Starting sync detection
问题：
都是do-ra, 走射频板，UE 没有成功解码PBCH，可能是UE和GNB频率没有对应上。另外GNB侧tx-gain配置读取值为0，不太正常。GNB怎么配置tx-gain?
射频线直连，10db衰减，ue和gnb都不设置gain的值。可以试一下。
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