传输地震数据的CDDM-1A数传电台采用GMSK调制与Viterbi译码，Viterbi译码是一种最大似然译码算法，译码复杂度与信道质量无关，GMSK调制方式广泛用于无线通信系统中。通过研究译码软、硬判决实现理论，比较在GMSK系统中两种判决对误码率的差别，在Simulink中设计了基于GMSK调制方式、卷积编码、软判决与硬判决译码相对比的通信仿真系统，分析不同信噪比对误码率的影响。仿真结果证明了所建立的系统的正确性，说明使用GMSK调制方式，在误码率为10-3—10-2的区间内，使用软判决要比硬判决译码提升信噪比约3dB。因此数传电台采用Viterbi译码是有效保证地震信号传输质量的方法。
GMSK modulation and Viterbi decoding are generally applied in the CDDM-1A data radio used to transmit seismic data. Viterbi decoding is a maximum likelihood decode algorithm, the complexity of which is independent of channel quality. GMSK is a widely applied modulation mode in radio systems. By studying the implementation theory of the soft and hard decision algorithms of the Viterbi decoding, and comparing the error rates of the two decisions in the GMSK system, this paper establishes a complete communication simulation system based on GMSK modulation, convolutional code and comparing of the soft and hard decision algorithms of the Viterbi decoder in the Simulink, to analysis the impact of different SNRs on error rates. The simulation results prove the validity of the system established, and demonstrate that using GMSK modulation, at error rates ranging from 10-3 to 10-2, the soft decision improves SNR by 3dB than that of the hard decision. Therefore, Viterbi decoding can be used by the radio system to ensure the transmission quality of seismic data.
