Transmission of SBC speech via 16-level QAM over mobile radio channels

The transmission of 16-kb/s subband-coded (SBC) speech via Reed-Solomon (RS) coding and 16-level QAM (quadrature amplitude modulation) modulation over Rayleigh fading channels is addressed. An average locking AGC (automatic gain control) method is described which requires no side information to be transmitted. Different RS coders were used to code the SBC bits, depending on their perceptual significance and their position in the Gray-coded QAM words. Proposed schemes operating at 5.3 and 6.7 kbaud yielded near-toll-quality speech for channel signal/noise ratios in excess of 29 and 22 dB, and delays of 180 and 144 ms, respectively, for vehicular speeds of 30 and 60 mph. Results indicate that near-toll-quality speech from a relatively simple SBC codec can be transmitted over mobile radio channels within a bandwidth of 10 kHz