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OpenAirInterface LTE

This tutorial also assumes basic familiarity with LTE standard. It uses OpenAirInterface open source software implementation of LTE basestation (eNodeB or eNB) and modem (user equipment or UE) developed at Eurecom. The tutorial given here is based on the OAI_real-time_LTEsoftmodem tutorial.

The image used for this experiment is oai-trunk-head.ndz. Image uses Ubunutu 14.04 and has low-latency 3.19 kernel install and UHD drivers needed for B210/X310 USRPs (UHD 3.8.2)). This image was derived from vanilla image ubuntu-14-04-64bit-3.19-lowlatency.ndz (that was created based on OpenAir instructions) from ubutbu-14-04-64bit.ndz (baseline.ndz). In addition to installation steps in OpenAir documentation, once low latency kernel was installed, drivers for Broadcom and Netgear devices? had to be manually re-installed.

Two images were created based on git cloning instructions and compiling instructions:

  • oai-master.ndz - master branch clone from git in /root
  • oai-develop.ndz - develop branch clone from git in /root

The openair-cn (EPC) was installed with default passwords of oai and default choice of "N" for optional packages (freeDiameter, asn1c pach and xtables_addons_oai). xtables_addons_oai was pulled out of git but not installed.

Update for oai-develop.ndz: The openair-cn (EPC) was installed with default passwords of oai and default choice of "Y" for optional packages (freeDiameter, asn1c pach and xtables_addons_oai). xtables_addons_oai was pulled out of git and installed.

Note If you intend to use graphical user interface please make sure to install appropriate tools on your local machine and configure X11 forwarding

Quickstart Option

We have an image available, named oai-dev.ndz. It has all the necessary driver and software pre-installed, and two scripts available to immediately boot up the eNB and UE. This quickstart assumes use of Sandbox1, nodes 1-1, and 1-2.

  1. To proceed, after having a reservation, load the following image.
    • omf load -t node1-1,node1-2 -i oai-dev.ndz
    • The nodes will automatically turn off when imaging is completed.
  2. Turn the nodes on.
    • omf tell -a on -t node1-1,node1-2
  3. Open a terminal to each node. You must enable X11 Forwarding to see the GUI and statistics screens.
  4. On the first node, execute script ./CompandRuneNB
  5. On the second node, execute script ./CompandRunUE
  6. For subsequent runs, execute ./runeNB or ./runUE instead, to avoid recompiling.
  7. These scripts will create interface oai0 and assign an address.
    1. Use ifconfig or ip a to see the address assigned.
    2. By default the eNB has address, and the UE has addresss, but you should double check.
  8. You should be able to ping from one node to the other on these addresses.
    1. From UE, ping or to see live statistics mtr
  9. For throughput testing
    1. On the eNB, execute iperf -s
    2. On the UE, execute iperf -c

The code was compiled with USRP support i.e. with:

cd trunk/targets/bin; build_oai.bash -l ENB -c -w USRP

More details on various build options are available on OpenAirInterface build page.

In this tutorial we will use nodes with USRP b310 and have the basestation on node9-1 and modem on node6-20.

Prepare the nodes

  1. Load the image with the OpenAirInterface code on the nodes that have USRP B210 attached. After imaging the nodes are turned off automatically.

omf load -t inventory:topo:B210 -i oai-master.ndz

  1. Turn ON the nodes that successfully imaged (give them some time and check their status with omf stat before proceeding).

omf tell -a on -t system:topo:imaged

Execute the experiment

Primary objective is to establish the LTE connection between the UE and eNB. In order to that we need to prepare configuration files on two nodes: node9-1 and node6-20.

  1. ssh into nodes: Open the two ssh sessions from the console to the two nodes
  1. Prepare configuration files: Make sure to have correct parameters in oai.conf file in roots home directory on the node (/root) as follows:
    1. Operating frequency band parameters:
      1. E-UTRA band
      2. Corresponding duplex mode (e.g. FDD/TDD),
      3. Downlink frequency [Hz], uplink frequency offset [Hz] (which is given in reference to the downlink frequency).
      4. LTE bandwidth: N_RB_DL = {6,15,25,50,75,100} corresponding to bandwidth = {1.4,3,5,10,15,20} MHz For example:
            ////////// Physical parameters:
            component_carriers = (
                                   frame_type                                         = "FDD";
                                   eutra_band                                         = 7;
                                   downlink_frequency                                 = 2660000000L;
                                   uplink_frequency_offset                            = -120000000;
                                   N_RB_DL                                            = 25; #N_RB_DL choice: 6,15,25,50,75,100
        In this example, LTE operates in E-UTRA band 7 which allows the FDD mode. LTE operates at 5 MHz bandwidth around downlink and uplink center frequencies which are at 2660 MHz and 2540 MHz, respectively.

Parameters in oai.conf can be varied as long as they are within predefined set of values which can be found in file ~/rel_0.1_26.10.2014/openair2/ENB_APP/enb_config.c or ~/trunk/openair2/ENB_APP/enb_config.c

  1. Make sure to have correct IP address configuration for parameters "ENB_IPV4_ADDRESS_FOR_S1_MME" and "ENB_IPV4_ADDRESS_FOR_S1U" to match node numbers. For example, for nodeX-Y, these IP address parameters become as "10.10.X.Y/16". So for our basestation node the relevant sections in the oai.conf file in /root directory on the nodes we should look like (we don't want MME support and have to adjust the ip addresses to match what we have on the control interface of the node):
        ////////// MME parameters:
        mme_ip_address      = ( { ipv4       = "";
                                  ipv6       = "10:10:0::100";
                                  active     = "no";
                                  preference = "ipv4";
            ENB_INTERFACE_NAME_FOR_S1_MME            = "eth1";
            ENB_IPV4_ADDRESS_FOR_S1_MME              = "";
            ENB_INTERFACE_NAME_FOR_S1U               = "eth1";
            ENB_IPV4_ADDRESS_FOR_S1U                 = "";
            ENB_PORT_FOR_S1U                         = 2152; # Spec 2152
  1. Run the lte-softmodem: Depending on whether you want to run it with or without mme, execute lte-softmodem on corresponding nodes:
On the eNB node (node9-1) On the UE node (node6-20)
w/o MME lte-softmodem-nomme -Ooai.conf -V lte-softmodem -U -Ooai.conf -C 2660000000 -V
w MME lte-softmodem -Ooai.conf -V lte-softmodem -U -Ooai.conf -C 2660000000 -V

If the above commands are executed with the "-d" flag and if X11 forwarding is enabled for the current ssh session, the signal tracer will pop out as shown in Figure 1 (not that this requires relatively high bandwidth).

The output on both consoles should look something like this:

[RRC][I][eNB 0] Init (UE State = RRC_IDLE)...
[RRC][I][eNB 0] Checking release 
[RRC][I][eNB 0] Rel8 RRC
[RRC][I][eNB 0] Configuration SIB2/3
[MAC][I][rrc_mac_config_req] [CONFIG][eNB 0] Configuring MAC/PHY
[MAC][I][rrc_mac_config_req] [CONFIG]SIB2/3 Contents (partial)
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.n_SB = 1
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.hoppingMode = 0
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.pusch_HoppingOffset = 0
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.enable64QAM = 0
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.groupHoppingEnabled = 1
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.groupAssignmentPUSCH = 0
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.sequenceHoppingEnabled = 0
[MAC][I][rrc_mac_config_req] [CONFIG]pusch_config_common.cyclicShift  = 1
[SCTP][I][sctp_handle_new_association_req] Setsockopt SOL_SOCKET socket bound to : eth1
[SCTP][I][sctp_handle_new_association_req] Converted ipv4 address to network type
[SCTP][I][sctp_handle_new_association_req] connectx assoc_id  1 in progress..., used 1 addresses
[SCTP][I][sctp_handle_new_association_req] Inserted new descriptor for sd 56 in list, nb elements 1, assoc_id 1
[SCTP][I][sctp_eNB_flush_sockets] Found data for descriptor 56
[SCTP][I][sctp_eNB_read_from_socket] Received notification for sd 56, type 32769
[SCTP][I][sctp_eNB_read_from_socket] Client association changed: 0
[SCTP][I][sctp_get_peeraddresses] ----------------------
[SCTP][I][sctp_get_peeraddresses] Peer addresses:
[SCTP][I][sctp_get_peeraddresses]     - []
[SCTP][I][sctp_get_peeraddresses] ----------------------
[SCTP][I][sctp_get_sockinfo] ----------------------
[SCTP][I][sctp_get_sockinfo] SCTP Status:
[SCTP][I][sctp_get_sockinfo] assoc id .....: 1
[SCTP][I][sctp_get_sockinfo] state ........: 3
[SCTP][I][sctp_get_sockinfo] instrms ......: 8
[SCTP][I][sctp_get_sockinfo] outstrms .....: 64
[SCTP][I][sctp_get_sockinfo] fragmentation : 1452
[SCTP][I][sctp_get_sockinfo] pending data .: 0
[SCTP][I][sctp_get_sockinfo] unack data ...: 0
[SCTP][I][sctp_get_sockinfo] rwnd .........: 106496
[SCTP][I][sctp_get_sockinfo] peer info     :
[SCTP][I][sctp_get_sockinfo]     state ....: 2
[SCTP][I][sctp_get_sockinfo]     cwnd .....: 4380
[SCTP][I][sctp_get_sockinfo]     srtt .....: 0
[SCTP][I][sctp_get_sockinfo]     rto ......: 3000
[SCTP][I][sctp_get_sockinfo]     mtu ......: 1500
[SCTP][I][sctp_get_sockinfo] ----------------------
[SCTP][I][sctp_eNB_read_from_socket] Comm up notified for sd 56, assigned assoc_id 1
[S1AP][I][s1ap_eNB_generate_s1_setup_request] 3584 -> 00e000
[SCTP][I][sctp_send_data] Successfully sent 53 bytes on stream 0 for assoc_id 1
[SCTP][I][sctp_eNB_flush_sockets] Found data for descriptor 56
[SCTP][I][sctp_eNB_read_from_socket] Received notification for sd 56, type 32777
[SCTP][I][sctp_eNB_flush_sockets] Found data for descriptor 56
[SCTP][I][sctp_eNB_read_from_socket] [1][56] Msg of length 27 received from port 36412, on stream 0, PPID 18
[S1AP][I][s1ap_decode_s1ap_s1setupresponseies] Decoding message S1ap_S1SetupResponseIEs (/root/trunk/targets/RT/USER/objs/openair-cn/S1AP/s1ap_decoder.c:3544)
[ENB_APP][I][eNB_app_task] [eNB 0] Received S1AP_REGISTER_ENB_CNF: associated MME 1
Waiting for eNB application to be ready
[HW][I][SCHED] eNB TX thread 0 started on CPU 5
[HW][I][SCHED][eNB] eNB RX thread 0 started on CPU 0
[HW][I][SCHED] eNB TX thread 1 started on CPU 0
[HW][I][SCHED][eNB] eNB RX thread 1 started on CPU 5
[HW][I][SCHED] eNB TX thread 2 started on CPU 2
[HW][I][SCHED][eNB] eNB RX thread 2 started on CPU 0
[HW][I][SCHED] eNB TX thread 3 started on CPU 5
[HW][I][SCHED][eNB] eNB RX thread 3 started on CPU 5
[HW][I][SCHED] eNB TX thread 4 started on CPU 4
[HW][I][SCHED][eNB] eNB RX thread 4 started on CPU 1
[HW][I][SCHED] eNB TX thread 5 started on CPU 4
[HW][I][SCHED][eNB] eNB RX thread 5 started on CPU 4
[HW][I][SCHED] eNB TX thread 6 started on CPU 0
[HW][I][SCHED][eNB] eNB RX thread 6 started on CPU 1
[HW][I][SCHED] eNB TX thread 7 started on CPU 1
[HW][I][SCHED][eNB] eNB RX thread 7 started on CPU 0
[HW][I][SCHED] eNB TX thread 8 started on CPU 1
[HW][I][SCHED][eNB] eNB RX thread 8 started on CPU 0
[HW][I][SCHED] eNB TX thread 9 started on CPU 0
[HW][I][SCHED][eNB] eNB RX thread 9 started on CPU 1
Creating main eNB_thread 
[SCHED][eNB] Started eNB main thread on CPU 4
eNB_thread: mlockall in ...
eNB_thread: mlockall out ...
waiting for sync (eNB_thread)
Entering ITTI signals handler

The command line parameters of lte-softmodem

Relevant (i.e. for USRP command line parameters for the lte-softmodem command are:

  • -O file: eNB configuration file (this is the preferred way to pass basic parameters and there are several examples in $OPENAIR_TARGETS/PROJECTS/GENERIC-LTE_EPC/CONF/
  • -g LEVEL: set the level of debug for the log generation (-g7 is quite high and useful to trace bugs in the procedures/protocols, -g9 even dumps packets at all levels of the protocol stack)
  • -d: enables xforms signal tracer
  • -U: start as UE (default: eNB)
  • -C freq: set carrier frequency to f0 for all chains (extension to independent frequencies trivial)
  • -V: enables the VCD debugging tool (this is a temporal event tracer, which is useful for real-time debugging using GTKWave)
  • -K file: ITTI logfile. ITTI is an intertask tracing utility which helps debugging with an EPC. It can traces all exchanges between RRC<->S1AP, RRC<->PDCP, PDCP<->S1
  • -S: do not exit for the missing slots, instead increment the counter.
  • --debug-ue-prach: only send prach but do not connect
  • --no-L2-connect: only runs rx, does not send prach

More details on running lte-softmodem are available on OpenAirInterface real-time LTE softmodem page.

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