A R-ASK OFDM Modulation and Demodulation Scheme Against Vocoder Compression

Resisting the compression on signals by the vocoder of the network is a difficult point to achieve end-to-end secure voice communication. However, only the modulation algorithms for traditional GSM voice channels are available in the relevant fields. Most of these algorithms only pass simulation and cannot be applied to actual scenes. This paper proposes an anti-vocoder compression modulation algorithm that combines relative amplitude shift keying with orthogonal frequency division multiple. The data is modulated by the difference of the frequency domain amplitudes of adjacent subcarriers, with a modulation rate of up to 1.5 Kbps and good anti-compression performance. A synchronization frame header is also designed, which has good anti-vocoder suppression characteristics. After the actual network voice channel transmission test, the algorithm modulation error rate is less than 0.5%, and the restored voice has high intelligibility. The overall scheme can be applied to the instant messaging of mainstream network voice software and has practical application value.