Method for cross-correlation-free bit error rate measurement in quadrature-modulation systems by means of a pseudo-random binary signal string

摘要

In pseudo-random binary signal strings (PRBS) which are split in quadrature amplitude modulation (QAM) into two binary sub-streams, the cross-correlation components unexpectedly occurring there which render correct bit error rate measurement impossible are already eliminated at the output of the pseudo-random binary signal generator. For this purpose, the PRBS to be fed to the QAM system is first split into two binary sub-strings with double the pulse period 2 T, the sub-strings are scrambled differently from one another and then re-combined to form a new PRBS before being split once more in the known quadrature amplitude modulation. A PRBS pre-processed to this extent has the statistical independence required for bit error rate measurement. The scrambling at the transmitting end is reversed once more at the receiving end by two corresponding descramblers. For correct synchronisation of the descramblers, the descramblers are switched via a changeover switch to the respective other output of a series-to-parallel converter connected upstream in the bit error rate measuring device at the receiving end if a bit error rate is indicated at the receiving end which is clearly too high (Fig. 3). <IMAGE>