Turbo-coded Orthogonal Frequency Division Multiplex transmission of 8 kbps encoded speech

Abstract

In this paper we have considered using turbo channel coding to encode the 8 kbits/s output from the G.729 speech codec. The source and channel coded bits are then transmitted using a wideband Orthogonal Frequency Division Multiplexing (OFDM) system in the framework of the Mode-I FRAMES proposals [I]. We illustrate the benefits of using OFDM with channel coding to alleviate some of the problems associated with wideband fading channels. Furthermore, we discuss how OFDM can be used in conjunction with the G.729 speech codec and half rate channel coding in order to utilise one speech/data FRAMES sub-burst. Finally some of the issues and problems associated with using turbo coded OFDM in speech transmission systems are considered using the system characterised in Table 1. In Figure 6 a channel SNR of 6dB appears sufficiently high under the stipulated system conditions for near-unimpaired speech transmission.