JVC TDR6 Eb/N0 Estimation Algorithm, Estimating Eb/N0 Using a Spectrum Analyzer

Eb/N0 Estimation Algorithm

Within the FEC decoder IC, the Viterbi decoder output is re-encoded and compared to a delayed version of the original encoder input. Incoming bit errors that are corrected will result in a difference between original input and the encoded output. These differences are accumulated for a fixed amount of time. This accumulation register can be read by the TDR6 microprocessor and gives an approximation of the signal to noise level of the input signal. Once these reading have been calibrated using an input with a known Eb/N0, they are used by the TDR6 to accurately estimate the Eb/N0 of the incoming signal.

Note that the estimated Eb/N0 reading is accurate only for relatively low Eb/N0 readings (less than 10). This is because there are not enough bit errors at higher Eb/N0 to generate an accurate estimation.

Estimating Eb/N0 Using a Spectrum Analyzer

Sometimes it is desirable to be able to estimate the Eb/N0 of an input signal using a spectrum analyzer. The following equation will provide a reasonable approximation.

Eb / N0 = 10 log10 [(10D/10 - 1)(SR/IR)] where:

■D = Distance in dB from top of spectrum to noise floor

■SR = Symbol Rate (symbols/sec)

■IR = Information Rate (bits/sec)

To determine the symbol rate issue the command DMD.x SR. The symbol rate is not available from the front panel.

The information rate is the TDR6 data rate parameter. To determine the data rate:

■Using the front panel, select Details>Input>Demod>RF_x>Data Rate where x = A, B, C, or D

■Using a remote unit, issue the command DMD.x DR

Demodulator Low Eb/N0 Alarm

The TDR6 issues a “low Eb/N0” fault if the Eb/N0 is ever 1 dB lower than the DVB specification. You should operate with at least a 2 dB margin to allow for rain-fade and other conditions.

Troubleshooting This section provides information that may be helpful in troubleshooting including:

■Using a spectrum analyzer to check the configuration

■Troubleshooting commands

Spectrum Analyzer

Following are ways you can use a spectrum analyzer to check the configuration of the QPSK demodulator:

■Confirm that an input signal is present

■Confirm that spectrum is flat

■Confirm that width conforms to (1.35 * symbol rate)

84 01-0870-401B 01/03 Demodulator Application Notes