MULTI-CHANNEL, EMBEDDED PILOT SIGNAL QUALITY MEASUREMENT ALGORITHM

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MOTOROLA INC. Technical Developments Volume 12 April 1991

MULTI-CHANNEL, EMBEDDED PILOT SIGNAL QUALITY MEASUREMENT ALGORITHM

by Mark Birchler

  Multi-Channel digital communication systems employ multiple independent sub-channels, each of which is modulated to a unique sub-carrier frequency. Each of these sob-channel signals may contain embedded TDM pilots for channel magnitude and phase correction.

  Frequency selective transmission channels cause IS1 in the received sub-channel symbol estimates. The magnitude of the ISI increases proportionally with the delay spread. Thus for a given C/(I+N), a normal mean square error (MSE) signal quality estimator can give results that vary an order of magnitude, depending on the delay spread of the channel (see Figure 1).

  If a more accurate measure of C/(I+N) is needed, then it is desirable to reduce the effect of delay spread on the signal quality estimate. This can be accomplished by weighting the raw squared error estimates by values derived from the embedded pilots.

  The basic idea is fairly simple. Each of the sub- channels has a channel estimator based on TDM embedded pilots. This system effectively samples the

magnitude and phase of each transmission channel at the sub-channel center frequency. Large squared error values occur in a sub-channel with a fade notch in band. In this case, the channel estimator magnitude will be relatively small for the in band notch sub- channel and relatively large for the others. This effe...