Variable-rate data transmission with blind rate detection for coherent DS-CDMA mobile radio

Variable-rate data transmission with no rate indicator is described for direct sequence code division multiple access (DS-CDMA) mobile radio. The variable-rate data to be transmitted is block-encoded using a cyclic redundancy check (CRC) and then convolutionally encoded before being spread. The convolutionally encoded data is always brought to the zero state at the end of the data sequence within each frame. Blind rate detection is incorporated into the process of Viterbidecoding the received convolutional-coded frame data. At each possible end bit position (i.e., each possible transmission rate), the trellis path arriving at the zero-state is selected if its path metric satisfies a certain condition, and is then traced back to recover the frame data. CRC is used to determine whether the recovered data is correct or not. The path selection condition is described. The average frame error rate (FER) and average false detection rate (FDR) are evaluated by computer simulation under frequency selective multipath Rayleigh fading environments and the results are compared with another variable-rate transmission scheme using a rate indicator.