The transmission of the earth wave is stable, hardly influenced by climate and its channelparameter does not change with time basically, it is ConstantParameterChannel.
地波传播受天气的影响较小，比较稳定，信道参数基本上不随时间的变化而变化，是恒参信道。
2
In the channel output, subspace decomposition is employed. If the signal subspace can be exclusively decided by the channel, the parameter of the channel can be estimated by a constant.