For many years, research and teaching at the IKS have been focused on speech and audio communication as well as specific aspects of mobile communication. The main field is the digital processing of speech and audio signals for mobile telephony.
The block diagram below describes the signal processing components of a typical mobile phone. The components are classified into three categories: Signal Enhancement, Coding, and Modulation. Further information can be obtained by following the links below.
- The beamformer makes use of a microphone array in order to amplify speech from the direction of the speaker and attenuate interfering sounds from other directions.
- The echo canceller reduces acoustical echoes from the loudspeaker.
- Noise reduction attenuates the recorded background noise.
- Dereverberation removes unwanted reverberation from the recorded speech.
- Far-end noise reduction attenuates background noise from the other side.
- Artificial bandwidth extension converts a received narrow-band signal into a wide-band signal by estimating missing parts of the spectrum.
- Intelligibility enhancement adapts the received speech based on the local noise characteristics such that it becomes more intelligible.
Coding and Modulation
- The source encoder compresses the speech signal and therefore reduces the data rate necessary for the transmission.
- The channel encoder adds redundancy in order to make the signal robust with respect to possible transmission errors.
- The signal is modulated onto the carrier frequency.
- The channel decoder exploits the redundancy added by the channel encoder in order to detect and correct transmission errors.
- The source decoder retrieves the waveform of the speech signal.
- Error concealment: In case of uncorrectable transmission errors, the affected signal frames are replaced by a repetition of previous signal frames.
Kwa miaka mingi, utafiti na kufundisha katika ICS imekuwa ililenga hotuba na mawasiliano ya sauti kama vile masuala maalum ya mawasiliano ya simu. Sehemu kuu ni usindikaji wa dijiti wa hotuba na ishara za sauti kwa ajili ya simu za mkononi. Mchoro wa block hapa chini unaelezea vipengele vya usindikaji wa ishara ya simu ya mkononi ya kawaida. Vipengele ni classified katika makundi matatu: Signal Enhancement, Coding, na Modulation. Habari zaidi inaweza kupatikana kwa kufuata viungo hapa chini. - Beamformer hutumia safu ya kipaza sauti ili kuimarisha hotuba kutoka kwa mwelekeo wa msemaji na kupunguza sauti za kuingiliana kutoka kwa mwelekeo mwingine. - Echo canceller hupunguza echoes acoustic kutoka kwa msemaji. - Kupunguza kelele attenuates kumbukumbu kelele ya nyuma. - Dereverberation huondoa reverberation zisizohitajika kutoka hotuba kumbukumbu. - Far-mwisho kelele kupunguza attenuates kelele ya nyuma kutoka upande mwingine. - Artificial bandwidth extension hubadilisha kupokea nyembamba-band ishara katika pana-band ishara kwa kukadiria sehemu kukosa ya wigo. - Kuongeza uelewevu hubadilisha hotuba iliyopokelewa kulingana na sifa za kelele za mahali hapo ili iwe rahisi zaidi kuelewa. Coding na Modulation - chanzo encoder compresses sauti ishara na hivyo hupunguza kiwango cha data muhimu kwa ajili ya maambukizi. - encoder channel anaongeza redundancy ili kufanya ishara imara kuhusiana na makosa ya uwezekano wa maambukizi. - Ishara ni modulated juu ya mzunguko carrier. - decoder channel exploits redundancy aliongeza na encoder channel ili kugundua na kurekebisha makosa ya maambukizi. - decoder chanzo hupata waveform ya ishara ya hotuba. - makosa kufichwa: Katika kesi ya makosa ya maambukizi uncorrectable, kuathirika ishara frames ni kubadilishwa na kurudia ya ishara frames awali.