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Error Vector Magnitude

    Last Modified: February 6, 2018

    Error Vector Magnitude (EVM) is a measure of demodulator performance in the presence of impairments. The demodulated symbols are compared against ideal symbol locations over the measurement window to measure EVM, magnitude error, and phase error.

    The following image shows the comparison of demodulated symbols against ideal symbol locations.

    where In+jQn is the vector representing the symbol being measured at index n

    is the ideal vector close to the actual symbol being measured

    N is the number of symbols to be measured

    • The EVM normalization parameter is supported only for QAM modulations.
    • EVM measured on OQPSK symbols uses two samples per symbol because the maximum instance of I and Q are separated by half the symbol duration.
    • Offset EVM in OQPSK is measured on symbols after aligning the I and Q channels by removing the half symbol duration in the Q channel.

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