Unequal Error Protection by Source-Controlled Digital Modulation

In digital transmission systems for speech, audio, and video signals, the bits generated by the source can be subdivided into groups with different bit error sensitivities. If bits are inverted due to disturbed transmission, different intensities of distortion of the reconstructed signal occur. The transmission quality can be improved if the bit classes are unequally protected by channel coding. The objective of this thesis is the realization and optimization of an alternative concept of unequal error protection without channel coding: modulation with unequal power allocation (MUPA). The available power is unequally distributed
to the modulation symbols according to the individual bit error sensitivity and the channel quality. The power allocation at the transmitter is optimized in the sense of the minimum mean square error (MMSE). MUPA requires only negligible additional complexity. In accordance with information theory, the quality of audiovisual signals is improved, although the average bit error rate is increased. The proposed technique of modulation with unequal power allocation can be combined with soft demodulation and is especially suited for systems such as Bluetooth with weak or no channel coding. In comparison to conventional
modulation schemes, significant improvements of the transmission quality and the error robustness are achieved by MUPA.