Performance of Coherent OFDM and Differentially Coherent OFDM Communication Systems in Water Pipeline Channels

In this work we describe our investigation into the performance of coherent orthogonal frequency division multiplexing (OFDM) and differentially coherent OFDM communication systems in a wideband waveguide channel consisting of a steel pipe filled with static water. The channel transfer function was measured by a vector network analyzer, and the channel noise (found to be normally distributed above 10 kHz) was measured by a hydrophone connected to a data acquisition device. The measured steel-pipe water channel together with additive complex Gaussian noise is used as the communication channel. Bit error rate (BER) simulation results show that coherent OFDM outperforms differentially coherent OFDM because it takes advantage of accurate channel estimation. Nonetheless, differentially coherent OFDM detection performs well when the sub-carrier separation is less than the coherence bandwidth, offering the benefit of lower system complexity and increased throughput efficiency.