Setting value of "feedback_channel_delay"

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  • #10739

    Hello all,

    I have two questions about the parameter “LTE_config.feedback_channel_delay”.

    Questions 1. The LTEsystemDoc indicates “LTE_config.feedback_channel_delay” can be set to 0. If it is set to 0, does that means the current channel state information can be used immediately to generate the modulation and coding scheme (MCS), resource block assignment, etc? In other words, we do not need channel prediction in this case?

    Questions 2. When I set LTE_config.feedback_channel_delay=0, simulation_type = ‘omnidirectional_eNodeBs’, some error occurs. The launch file I used is “LTE_sim_main_launcher_demo_basic”. And the error profile is attached as follows. Thanks.

    Index exceeds matrix dimensions.

    Error in network_elements.UE/set_SINRs_according_to_schedule (line 570)

    Error in LTE_sim_main (line 466)

    Error in LTE_sim_main_launcher_demo_basic (line 64)
    output_results_file = LTE_sim_main(LTE_config);


    About Questions 2, it seems that I find the problem.

    I am using version “System-Level-Simulator-Rel-v1-9-Q2-2016”. And I change line 414 of LTE_sim_main.m from “if (LTE_config.feedback_channel_delay==0 && LTE_config.runtime_precoding)” to “if (LTE_config.feedback_channel_delay==0 && ~LTE_config.runtime_precoding)”, then the error does not occur.

    However, I am not sure whether my modification is right, or whether this modification breaks the function of this Simulator. Looking forward to discussion and help. Thanks


    Dear Yvan,

    1. For the zero feedback delay, in the first TTI there is no feedback, as no ACKs are available. For the rest of the TTIs, the feedback is equal to the current channel state information already stored at the UE object (see function receive_UE_feedback(obj) stored at +network_elements/eNodeB_sector.m.)

    2. There was a bug in the LTE_sim_main.m file. The error occurred in your case because the link quality model was not called before calling the function set_SINRs_according_to_schedule(). Replace the lines 414 to 470 with the code available in this link:
    password: vienna.

    In the launcher file it is important to also specify the trace version which directly relates to the precoding mode:
    a) trace version ‘v1’ – non runtime precoding
    b) trace version ‘v2’- runtime precoding
    since the two modes are treated differently, and also note that only some transmission modes are supported by trace version ‘v2’.

    Thanks for the bug report and let us know if you further encounter any problems.
    Best regards,

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