  In this paper, we propose a physical-layer rateless code for wireless
channels. A novel rateless encoding scheme is developed to overcome the high
error floor problem caused by the low-density generator matrix (LDGM)-like
encoding scheme in conventional rateless codes. This is achieved by providing
each symbol with approximately equal protection in the encoding process. An
extrinsic information transfer (EXIT) chart based optimization approach is
proposed to obtain a robust check node degree distribution, which can achieve
near-capacity performances for a wide range of signal to noise ratios (SNR).
Simulation results show that, under the same channel conditions and
transmission overheads, the bit-error-rate (BER) performance of the proposed
scheme considerably outperforms the existing rateless codes in additive white
Gaussian noise (AWGN) channels, particularly at low BER regions.
