8 Assessment of equivalent qdu, Experiment 6

3GPP46.008Half rate speechPerformance Characterization of the GSM Half Rate speech codecRelease 17TS

The experiment on the assessment of qdu was designed to assess the half rate codec performance, in error free conditions, in terms of Equivalent Quantization Distortion Units (qdu) as defined by the ITU-T. Two laboratories performed the experiment (CSELT and DEUTSCHE TELEKOM) and the following conclusions were drawn from their results:

a) For single encoding, the half rate codec was judged to be statistically equivalent to the full rate. Similar planning rules could therefore be applied to both algorithms if the configuration is not mobile-to-mobile. The figure of equivalent qdu for the half rate codec was found to lie somewhere between 8 and 16 qdu. A more precise figure could not be determined due to differences in the results from the two laboratories.

(It is reminded that for the full rate an "average" figure of 7-8 qdu was indicated by SCEG to GSM, after considering test results showing values between a minimum of 4-5 qdu and a maximum of 21-22 qdu).

b) For tandemed conditions, a statistically significant difference in performance between the half and full rate codecs was detected in one of the two laboratories. The results confirmed that a noticeable degradation in speech quality in mobile-to-mobile connections is likely.

Generally, both the Half- and Full-Rate showed a worse performance than the other standards (ITU-T Recommendations G.711 [1], G.726 [2], at 32 kbit/s, and G.728 [3]) included in the experiment.