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  • #13690
    Tolga Girici

    Dear all,

    In the version 1.2 of the simulator, multi user MIMO is done by techniques such as zero forcing and block diagonalization at the base station.

    In the mu-mimo case, the PMI is disabled. As far as I understand the base station needs the detailed channel information in order to do ZF or BD.

    How does the BS obtain this channel information from all of the users?

    Base station can send pilot signals and users can estimate the channel and send feedback. However, for a large number of users , this would create a large overhead.


    Dear Tolga,

    exactly, the BS does multiplex pilots for the users in the downlink which indeed results in a large overhead. To avoid this, a scheme where orthogonal pilot sequences are employed helps in this case. This is implemented via the LTE Uplink pilot pattern. Here, pilot symbols for users are allocated overlapping in the time-frequency resource grid and orthogonal sequences are used for channel estimation. This reduces the overhead significantly.

    When doing so, the orthogonal pilot sequence length has to be longer than the number of scheduled users in the multi-user MIMO cell to ensure orthogonality in between the user pilot symbols.

    best regards
    Stefan Pratschner

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