在現(xiàn)代通信系統(tǒng)中，電話語音的頻帶被限制在300 Hz～4 kHz的范圍內(nèi)，帶來了語音可懂度和自然度的降低。為了在不增加額外成本的前提下提高語音的可懂度和自然度，進(jìn)行了電話語音頻帶擴(kuò)展的研究。提出了一種改進(jìn)的基于碼本映射的語音帶寬擴(kuò)展算法：在碼本映射的過程中，使用加權(quán)系數(shù)來得到映射碼本。客觀測試結(jié)果表明，用此算法得到的寬帶語音的譜失真度比用一般的碼本映射降低至少2%。主觀測試結(jié)果表明，用此算法得到的寬帶語音具有更好的可懂度和自然度。
Abstract:
In modern communication systems， the bandwidth of telephone speech is limited from 300Hz to 4 kHz， which reduces the intelligibility and naturalness of speech. Telephone speech bandwidth extension is researched to get wideband speech and to improve its intelligibility and naturalness， without increasing extra costs. This paper put forward an improved algorithm of speech bandwidth extension based on codebook mapping. In the process of codebook mapping， weighted coefficients were used to get mapping codebook. Objective tests show that spectral distortion of wideband speech obtained by this algorithm reduces at least 2%， comparing to conditional codebook mapping. Subjective tests show that the wideband speech obtained by this algorithm has better intelligibility and naturalness.
在LDPC譯碼時，使用LLR BP算法其校驗(yàn)節(jié)點(diǎn)的計(jì)算復(fù)雜度十分高，而且當(dāng)LDPC碼中有許多的短環(huán)時，譯碼性能也會降低。基于以上的這些問題提出了一個新的混合校驗(yàn)變量過程，通過調(diào)整校驗(yàn)節(jié)點(diǎn)的處理振幅和變量節(jié)點(diǎn)的信息相關(guān)性來降低計(jì)算復(fù)雜度，其仿真過程表明在譯碼性能和運(yùn)算復(fù)雜度上與LLR BP 算法都有較大的提高。
