Issue with 4G LTE Signal Detection and Internet Connectivity in SRSRAN

[Andrysm]

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Hello, I am working on a 4G LTE project using SRSRAN and USRP B210 as the hardware. I have encountered an issue where the 4G LTE signal is detected intermittently. Sometimes the UE connects successfully, but most of the time it fails to detect the network, or the connection drops frequently. Additionally, the internet connection is not established, even though the 4G LTE signal appears on the UE.

Problem Details:

The 4G LTE signal is sometimes detected, but it keeps disconnecting and reconnecting intermittently. There is no internet connectivity even though the UE is connected to the network. I have checked the logs and seen messages about RRC Reestablishment and Tx while waiting for EOB timed out, but I am unable to identify the root cause. Steps I have tried:

I have adjusted tx_gain and rx_gain settings in the eNB configuration. I checked and ensured that the CPU Governor is set to performance mode. I tested the connectivity with different earfcn and RACH parameters. Despite these changes, the issue persists, and I am unsure why the internet connection is still not established.

Questions:

Can you help me understand why the 4G LTE signal is unstable and intermittently detected? Why am I unable to get internet connectivity despite the 4G LTE signal being available? Are there any other configuration parameters or steps I should check in the SRSRAN setup to resolve this issue? Any help or advice would be greatly appreciated! Thank you.

TOOLS USRP B210 UE REDMI 10C Ubuntu 22.04

EPC CONFIG [mme] mme_code = 0x1a mme_group = 0x0001 tac = 0x0007 mcc = 510 mnc = 77 mme_bind_addr = 127.0.1.100 apn = 12345 dns_addr = 8.8.8.8 encryption_algo = EEA0 integrity_algo = EIA1 paging_timer = 2 request_imeisv = false lac = 0x0006

[hss] db_file = /home/andry/.config/srsran/user_db.csv

[spgw] gtpu_bind_addr = 127.0.1.100 sgi_if_addr = 172.16.0.1 sgi_if_name = srs_spgw_sgi max_paging_queue = 100

[log] all_level = debug all_hex_limit = 32 filename = /tmp/epc.log

ENB Config [enb] enb_id = 0x18B mcc = 510 mnc = 77 mme_addr = 127.0.1.100 gtp_bind_addr = 127.0.1.1 s1c_bind_addr = 127.0.1.1 s1c_bind_port = 0 n_prb = 25 tm = 1 nof_ports = 1

[enb_files] sib_config = sib.conf rr_config = rr.conf rb_config = rb.conf

[rf] dl_earfcn = 500 tx_gain = 100 rx_gain = 50

device_name = uhd

[log] all_level = debug all_hex_limit = 32 filename = /tmp/enb.log file_max_size = -1

[gui] enable = false

LOG EPC Attach request -- Attach type: 2 Attach Request -- UE Network Capabilities EEA: 11110000 Attach Request -- UE Network Capabilities EIA: 01110000 Attach Request -- MS Network Capabilities Present: true PDN Connectivity Request -- EPS Bearer Identity requested: 0 PDN Connectivity Request -- Procedure Transaction Id: 86 PDN Connectivity Request -- ESM Information Transfer requested: true Attach Request -- Found previously attach UE. Received GTP-C PDU. Message type: GTPC_MSG_TYPE_DELETE_SESSION_REQUEST Downlink NAS: Sending Authentication Request UL NAS: Received Authentication Response Authentication Response -- IMSI 510770123456781 UE Authentication Accepted. Generating KeNB with UL NAS COUNT: 0 Downlink NAS: Sending NAS Security Mode Command. UL NAS: Received Security Mode Complete Security Mode Command Complete -- IMSI: 510770123456781 Sending ESM information request UL NAS: Received ESM Information Response ESM Info: APN 12345 Getting subscription information -- QCI 7 Sending Create Session Request. Creating Session Response -- IMSI: 510770123456781 Creating Session Response -- MME control TEID: 3 Received GTP-C PDU. Message type: GTPC_MSG_TYPE_CREATE_SESSION_REQUEST SPGW: Allocated Ctrl TEID 3 SPGW: Allocated User TEID 3 SPGW: Allocate UE IP 172.16.0.4 Received Create Session Response Create Session Response -- SPGW control TEID 3 Create Session Response -- SPGW S1-U Address: 127.0.1.100 SPGW Allocated IP 172.16.0.4 to IMSI 510770123456781 Adding attach accept to Initial Context Setup Request Sent Initial Context Setup Request. E-RAB id 5 Received Initial Context Setup Response E-RAB Context Setup. E-RAB id 5 E-RAB Context -- eNB TEID 0x3; eNB GTP-U Address 127.0.1.1 UL NAS: Received Attach Complete Unpacked Attached Complete Message. IMSI 510770123456781 Unpacked Activate Default EPS Bearer message. EPS Bearer id 5 Received GTP-C PDU. Message type: GTPC_MSG_TYPE_MODIFY_BEARER_REQUEST Sending EMM Information UL NAS: PDN Connectivity Request DL NAS: Sending PDN Connectivity Reject UL NAS: PDN Connectivity Request DL NAS: Sending PDN Connectivity Reject Received UE Context Release Request. MME-UE S1AP Id 6 There are active E-RABs, send release access bearers request Received GTP-C PDU. Message type: GTPC_MSG_TYPE_RELEASE_ACCESS_BEARERS_REQUEST Received UE Context Release Complete. MME-UE S1AP Id 6 UE Context Release Completed. Initial UE message: LIBLTE_MME_MSG_TYPE_TRACKING_AREA_UPDATE_REQUEST Received Initial UE message -- Tracking Area Update Request Tracking Area Update Request -- S-TMSI 0x5e14d1a8 Tracking Area Update Request -- eNB UE S1AP Id 6 Warning: Tracking area update requests are not handled yet. Initial UE message: LIBLTE_MME_MSG_TYPE_ATTACH_REQUEST Received Initial UE message -- Attach Request Attach request -- M-TMSI: 0x5e14d1a8 Attach request -- eNB-UE S1AP Id: 7 Attach request -- Attach type: 2 Attach Request -- UE Network Capabilities EEA: 11110000 Attach Request -- UE Network Capabilities EIA: 01110000 Attach Request -- MS Network Capabilities Present: true PDN Connectivity Request -- EPS Bearer Identity requested: 0 PDN Connectivity Request -- Procedure Transaction Id: 88 PDN Connectivity Request -- ESM Information Transfer requested: true Attach Request -- Found previously attach UE. Found UE context. IMSI: 510770123456781, old eNB UE S1ap Id 0, old MME UE S1AP Id 0 Received GUTI-Attach Request from attached user. GUTI Attach request NAS integrity failed. RE-starting authentication procedure. Received GTP-C PDU. Message type: GTPC_MSG_TYPE_DELETE_SESSION_REQUEST Downlink NAS: Sent Authentication Request UL NAS: Authentication Failure Authentication Failure -- Synchronization Failure Downlink NAS: Sent Authentication Request UL NAS: Received Authentication Response Authentication Response -- IMSI 510770123456781 UE Authentication Accepted. Generating KeNB with UL NAS COUNT: 0 Downlink NAS: Sending NAS Security Mode Command. UL NAS: Received Security Mode Complete Security Mode Command Complete -- IMSI: 510770123456781 Sending ESM information request Unhandled NAS integrity protected message LIBLTE_MME_MSG_TYPE_ESM_STATUS Received UE Context Release Request. MME-UE S1AP Id 7 No UE context to release found. MME-UE S1AP Id: 7 Received UE Context Release Request. MME-UE S1AP Id 9 Initial UE message: LIBLTE_MME_MSG_TYPE_ATTACH_REQUEST Received Initial UE message -- Attach Request Attach request -- M-TMSI: 0x5e14d1a8 Attach request -- eNB-UE S1AP Id: 8 Attach request -- Attach type: 2 Attach Request -- UE Network Capabilities EEA: 11110000 Attach Request -- UE Network Capabilities EIA: 01110000 Attach Request -- MS Network Capabilities Present: true PDN Connectivity Request -- EPS Bearer Identity requested: 0 PDN Connectivity Request -- Procedure Transaction Id: 89 PDN Connectivity Request -- ESM Information Transfer requested:

LOG ENB Disconnecting rnti=0xb40. Disconnecting rnti=0xb3f. Disconnecting rnti=0xb3e. Disconnecting rnti=0xb3d. Disconnecting rnti=0xb3c. RACH: tti=2921, cc=0, pci=1, preamble=40, offset=14, temp_crnti=0xb51 RACH: tti=2921, cc=0, pci=1, preamble=43, offset=20, temp_crnti=0xb52 RACH: tti=2921, cc=0, pci=1, preamble=46, offset=25, temp_crnti=0xb53 RACH: tti=2921, cc=0, pci=1, preamble=49, offset=31, temp_crnti=0xb54 Disconnecting rnti=0xb45. Disconnecting rnti=0xb44. Disconnecting rnti=0xb43. Disconnecting rnti=0xb42. Disconnecting rnti=0xb41. RACH: tti=2941, cc=0, pci=1, preamble=1, offset=9, temp_crnti=0xb55 RACH: tti=2941, cc=0, pci=1, preamble=4, offset=14, temp_crnti=0xb56 RACH: tti=2941, cc=0, pci=1, preamble=7, offset=20, temp_crnti=0xb57 RACH: tti=2941, cc=0, pci=1, preamble=10, offset=25, temp_crnti=0xb58 RACH: tti=2941, cc=0, pci=1, preamble=13, offset=31, temp_crnti=0xb59 RACH: tti=2961, cc=0, pci=1, preamble=1, offset=25, temp_crnti=0xb5a Disconnecting rnti=0xb4a. Disconnecting rnti=0xb49. Disconnecting rnti=0xb48. Disconnecting rnti=0xb47. Disconnecting rnti=0xb46. RACH: tti=2961, cc=0, pci=1, preamble=4, offset=31, temp_crnti=0xb5b RACH: tti=2961, cc=0, pci=1, preamble=25, offset=43, temp_crnti=0xb5c RACH: tti=2961, cc=0, pci=1, preamble=27, offset=1, temp_crnti=0xb5d RACH: tti=2961, cc=0, pci=1, preamble=30, offset=7, temp_crnti=0xb5e