Mobile audio-visual terminal: system design and subjective testingin DECT and UMTS networks

摘要

It is anticipated that there will shortly be a requirement fornmultimedia terminals that operate via mobile communications systems.nThis paper presents a functional specification for such a terminalnoperating at 32 kb/s in a Digital European Cordless Telecommunicationsn(DECT) and Universal Mobile Telecommunications System (UMTS) radionnetwork. A terminal has been built, based on a PC with digital signalnprocessor (DSP) boards for audio and video coding and decoding. Speechncoding is by a phonetically driven code-excited linear prediction (CELP)nspeech coder and video coding by a block-oriented hybrid discrete cosinentransform (DCT) coder. Separate channel coding is provided for the audionand video data. The paper describes the techniques used for audio andnvideo coding, channel coding, and synchronization. Methods of subjectiventesting in a DECT network and in a UMTS network are also described.nThese consisted of subjective tests of first impressions of the mobilenaudio-visual terminal (MAVT) quality, interactive tests, and thencompletion of an exit questionnaire. The test results showed that thenquality of the audio was sufficiently good for comprehension and thenvideo was sufficiently good for following and repeating simplenmechanical tasks. However, the quality of the MAVT was not good enoughnfor general use where high-quality audio and video was needed,nespecially when transmission was in a noisy radio environment