SSB-carrier mismatch detection from speech characteristics: Extension beyond the range of uniqueness

In certain radio-surveillance applications, speech signals with uncertain carrier frequencies may be detected. Beyond other disturbances, carrier mismatches distort the demodulated SSB signals by frequency shifts Δ
_f
. Recently, a detection and correction of such errors was presented [1], exploiting the harmonic structure of voiced speech with a fundamental (or "pitch") frequency f
_p
. Noise-robust, modified pitch-detection methods [2, 3] were shown to be applicable, together with an iteratively corrected "coherentsuperposition" algorithm [4, 5]. Thereby, carrier errors are removed reliably [1] though only within an a-priori uniqueness range |Δ
_f
| <; f
_p
/2. In the following, the extension beyond this limitation is presented. It emerges from a closer, statistical analysis of the measurement errors: The measurement statistics within this range are interpreted as a conditional probability density function (pdf) p
_Δ
f
(x|y) conditioned on the actual pitch frequency, its combination with the (measurable) pitch-frequency pdf P
_fp
(y) yields the joint pdf P
_Δ
f
,
_fp
(x,y), and its integration gives the marginal pdf P
_Δ
f
(x). Its evaluation leads to an even narrower reliability range |Δ
_f
| <; f
_p
/23, first. The interpretation of the uniqueness range as one period of an Ip-periodic repetition of the measurement statistics, however, leads to the solution: After the same steps as sketched above, the marginal pdf P
_Δf
(x) shows a strong peak at the true value Δf without a (theoretical) restriction. The resulting algorithm was successfully tested with simulated and real data.