AMSI technology, developed by the Reliaspeak Information Technology Co., Ltd, is an abbreviation of “the advanced signal modulation and demodulation algorithm resistant the audio compression algorithm interference with voice incentive mechanism.” AMSI incorporates technology of voice coding, signal modulation, signal synchronization, frequency domain/time domain compensation, signal deformation correction, error correction algorithm and so on, and is mainly applied to achieve high reliability data transmission in the lossy voice channels.
AMSI works like a traditional telephone Modem. At the sending end, the digital signal is converted to analog modulation tone which is modulated by AMSI, and transmits through landline telephone, mobile phone, VoIP link like the ordinary audio signal; while at the receiving end, AMSI demodulate the analog modulation tone to a digital signal.
The difference between AMSI and traditional telephone Modem is: the audio signal modulated by AMSI can still be demodulated accurately after being compressed and reduced by medium-low rate vocoder, that is, AMSI has sufficient penetration capability for medium and low rate vocoders, thereby provides a reliable base data channel for digital voice encryption through standard voice channels such as mobile phones.
Voice analog encryption is the earliest developed voice security technology since World War II, the advantage is that the algorithm is simple enough to encrypt the speech source. It can achieve an end-to-end encryption communication, and can be used in a variety of voice channels. However the fatal flaw is that it cannot completely disrupt the speech features, there is an obvious intelligibility residue in the encryption communication that can be easily analyzed and cracked. There is no security at all, especially in the face of strong computer processing power, and has gradually out of the market since the 90s of last century.
Digital encryption is currently the most secure information security technology that has been proven, and is also true for voice communications. With the development of communication technology, the telephone has been developed from a single analog phone to mobile phones, IP phones, satellite phones, and can interconnecting and intercommunicating based on unified IP network. However there is a huge technical hurdle to make an encrypted call using digital encryption technique between different types of phone equipment. At present, there is no such a technology can establish a basic data channel between different telephone networks, operators, and various telephone terminals, which supports the reliable transmission of encrypted data. Its root cause is that the only intercommunication element between the various types of phone terminals is audio signals, which are compressed by vocoders. The existing Modem technology cannot do a reliable data transmission based on the lossy of voice channels. This is the problem we develop AMSI to solve.
It is well known that the larger the compression ratio of the vocoder, the greater the distortion of the processed audio signal, which means that the modulation signal is more difficult to be correctly demodulated. The goal of AMSI is to provide high communication bandwidth in a common medium and low rate vocoder application environment (eg, cellular voice communication) while ensuring that the bit error rate is within acceptable limits.
AMSI modulation technology performance:
|Supportable speech coding rate||> 8kbps|
|Supportable universal speech codecs||AMR,SPEEX,SILK,G.711,G.72,GSM EFR|
|Available data communication bandwidth||2.4kbps(for above 12kbps rate vocoder)；
1.2kbps(for 8kbp to 12kbps rate vocdoer)
|Error rate of data transmission||<0.3% (for above 12kbps rate vocoder)
<1% (for 8kbp to 12kbps rate vocoder)
Data transmission error rate of AMSI modulation technology in actual communication environment:
|Communication Mode||Speech codec of voice channel||Bit error rate|
|GSM||EFR, AMR FR||0.2%~0.7%(Good signal),|
1%~2% (Normal Signal)
|UMTS||AMR NB, AMR WB||0.2%~0.7%(Good signal),|
1%~2% (Normal signal)
|VoLTE||AMR NB, AMR WB||0.02%~0.5%|
0.5%~1% (Small signal line condition)