FPGA平台srsUE无法连接srsRAN的技术排查请求

环境概述 #

• srsUE运行环境：搭载2核CPU、1G内存的Buildroot系统FPGA平台
• srsRAN(gNB)运行环境：Ubuntu 22系统笔记本
• 5GC部署方式：Docker化版本
• 通信链路：srsUE与srsRAN通过ZMQ在本地网络通信
• 核心问题：srsUE无法完成到srsRAN的附着流程

日志信息 #

UE日志 #

UE日志截图显示，设备处于小区搜索阶段，但未成功完成后续的同步、附着流程。

gNB日志 #

2025-03-07T20:05:40.500739 [zmq:tx:0:0] [I] Waiting for request.
2025-03-07T20:05:41.195026 [zmq:rx:0:0] [I] Waiting for data.
2025-03-07T20:05:41.196508 [zmq:rx:0:0] [I] Waiting for reading samples. Completed 300 of 11520 samples.
2025-03-07T20:05:41.500739 [zmq:tx:0:0] [I] Waiting for request.
2025-03-07T20:05:42.195028 [zmq:rx:0:0] [I] Waiting for data.
2025-03-07T20:05:42.196532 [zmq:rx:0:0] [I] Waiting for reading samples. Completed 300 of 11520 samples.
2025-03-07T20:05:42.500741 [zmq:tx:0:0] [I] Waiting for request.
2025-03-07T20:05:43.195030 [zmq:rx:0:0] [I] Waiting for data.
2025-03-07T20:05:43.196586 [zmq:rx:0:0] [I] Waiting for reading samples. Completed 300 of 11520 samples.

配置文件 #

UE配置文件 #

[rf]
freq_offset = 0
tx_gain = 50
rx_gain = 50
srate = 23.04e6
nof_antennas = 1

device_name = zmq
device_args = tx_port=tcp://[ue ip]:2002,rx_port=tcp://[gnb ip]:2001,base_srate=23.04e6

[rat.eutra]
dl_earfcn = 2850
nof_carriers = 0

[rat.nr]
bands = 3
nof_carriers = 1
max_nof_prb = 106
nof_prb = 106

[pcap]
enable = none
mac_filename = /tmp/ue_mac.pcap
mac_nr_filename = /tmp/ue_mac_nr.pcap
nas_filename = /tmp/ue_nas.pcap

[log]
all_level = debug    # Instead of info
phy_lib_level = debug
all_hex_limit = 32
filename = /usr/ue.log
file_max_size = -1

[usim]
mode = soft
algo = milenage
opc  = 63BFA50EE6523365FF14C1F45F88737D
k    = 00112233445566778899aabbccddeeff
imsi = 001010123456780
imei = 353490069873319

[rrc]
release = 15
ue_category = 4

[nas]
apn = srsapn
apn_protocol = ipv4

[gw]
#netns = ue1
ip_devname = tun_srsue
ip_netmask = 255.255.255.0

[gui]
enable = false

gNB配置文件 #

# This configuration file example shows how to configure the srsRAN Project gNB to allow srsUE to connect to it. 
# This specific example uses ZMQ in place of a USRP for the RF-frontend, and creates an FDD cell with 10 MHz bandwidth. 
# To run the srsRAN Project gNB with this config, use the following command: 
#   sudo ./gnb -c gnb_zmq.yaml

cu_cp:
  amf:
    addr: 10.53.1.2                 # The address or hostname of the AMF.
    port: 38412
    bind_addr: 10.53.1.1            # A local IP that the gNB binds to for traffic from the AMF.
    supported_tracking_areas:
      - tac: 7
        plmn_list:
          - plmn: "00101"
            tai_slice_support_list:
              - sst: 1
  inactivity_timer: 7200            # Sets the UE/PDU Session/DRB inactivity timer to 7200 seconds. Supported: [1 - 7200].

ru_sdr:
  device_driver: zmq                # The RF driver name.
  device_args: tx_port=tcp://[gnb ip]:2001,rx_port=tcp://[ue ip]:2002,base_srate=23.04e6 # Optionally pass arguments to the selected RF driver.
  srate: 23.04                      # RF sample rate might need to be adjusted according to selected bandwidth.
  tx_gain: 75                       # Transmit gain of the RF might need to adjusted to the given situation.
  rx_gain: 75                       # Receive gain of the RF might need to adjusted to the given situation.

cell_cfg:
  dl_arfcn: 368500                  # ARFCN of the downlink carrier (center frequency).
  band: 3                           # The NR band.
  channel_bandwidth_MHz: 20         # Bandwith in MHz. Number of PRBs will be automatically derived.
  common_scs: 15                    # Subcarrier spacing in kHz used for data.
  plmn: "00101"                     # PLMN broadcasted by the gNB.
  tac: 7                            # Tracking area code (needs to match the core configuration).
  pdcch:
    common:
      ss0_index: 0                  # Set search space zero index to match srsUE capabilities
      coreset0_index: 12            # Set search CORESET Zero index to match srsUE capabilities
    dedicated:
      ss2_type: common              # Search Space type, has to be set to common
      dci_format_0_1_and_1_1: false # Set correct DCI format (fallback)
  prach:
    prach_config_index: 1           # Sets PRACH config to match what is expected by srsUE                # Sets PDSCH MCS to 64 QAM                # Sets PUSCH MCS to 64 QAM
  pdsch:
    mcs_table: qam64
  pusch:
    mcs_table: qam64    

log:
  filename: /tmp/gnb.log            # Path of the log file.
  all_level: debug                   # Logging level applied to all layers.
  rrc_level: debug
  f1ap_level: debug
  f1ap_json_enabled: true
  hex_max_size: 0                   # Logging level applied to all layers

pcap:
  mac_enable: false                 # Set to true to enable MAC-layer PCAPs.
  mac_filename: /tmp/gnb_mac.pcap   # Path where the MAC PCAP is stored.
  ngap_enable: false                # Set to true to enable NGAP PCAPs.
  ngap_filename: /tmp/gnb_ngap.pcap # Path where the NGAP PCAP is stored.

诊断结论 #

1. 带宽与采样率配置验证 #

gNB配置20MHz带宽、15kHz子载波间隔，理论所需采样率为20MHz × 1.12（过采样因子）=22.4MHz，当前配置的23.04e6采样率符合要求，且UE与gNB的采样率、base_srate参数完全一致，因此带宽与采样率不匹配的可能性可以排除。

2. 资源限制分析 #

从gNB日志可见，ZMQ接收端仅收到部分采样数据（300/11520），说明UE无法生成或发送完整的基带样本。srsUE的PHY层对CPU计算能力要求较高，尤其是NR模式下，2核1G内存的FPGA平台资源严重不足，无法及时处理基带信号的编码、解码及ZMQ数据传输任务，导致UE无法完成小区同步、附着的关键流程。

3. 补充验证建议 #

• 查看UE端系统负载：执行top或sar -u 1命令，若CPU持续处于100%使用率，可明确资源不足的问题
• 检查ZMQ端口映射：当前UE与gNB的端口配置是对应的（UE rx_port对应gNB tx_port，UE tx_port对应gNB rx_port），链路配置无问题

解决方案建议 #

1. 降低UE配置负载：将带宽调整为10MHz，对应采样率改为11.52e6，减少PHY层计算量
2. 优化系统资源：关闭Buildroot系统中不必要的后台服务，释放内存和CPU资源
3. 调整进程优先级：给srsUE进程分配更高的CPU调度优先级，确保关键任务的执行资源

内容的提问来源于stack exchange，提问作者Shirin Ebadi