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    Last Modified: February 6, 2018

    Demodulated PSK and QAM signals are known to have ambiguity in phase if the transmitted signal is not known. If this phase ambiguity is not resolved, the hard decision of symbols returns in incorrect bits.

    Some communication schemes resolve the phase ambiguity issue by using differential mapping. Refer to PSK for more information about differential mapping.

    Another solution to the issue is to transmit a known bit pattern to the receiver. Such known bit patterns are called synchronization bits. When synchronization is enabled, the demodulator attempts to find the phase ambiguity using the known bits.

    If synchronization bits are found, the demodulator corrects for phase ambiguity, and then the signal from this location is used for the measurement. You can specify a measurement offset from this synchronized location. In this case, the number of symbols measured for transmit quality may be lesser than the specified number of symbols.

    If synchronization bits are not found in the measurement interval, the demodulator uses all the symbols acquired for measuring the transmit quality.

    In some communication schemes, synchronization bits are used to mark the start of message frame. Enable bit synchronization to measure only the signal corresponding to the message frame.

    Specify the synchronization bits, read from left to right, as shown below.

    {b0 ... b(log2M)-1}0 {b0 ... b(log2M)-1}1 ... {b0 ... b(log2M)-1}n-1

    where M is the M-ary and n is the number of symbols that form the synchronization pattern.

    The length of the synchronization bits are truncated to an integer multiple of log2M bits per symbol.


    In case of burst signals, the bits corresponding to the initial symbols of the burst may not be detected. These symbols correspond to the measurement filter transient. Refer to the Filters topic to know the length of the measurement filter. When providing synchronization bits, you must consider the filter length.

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