Linear chirp-based underwater acoustic communication has been widely used due to its reliability and long-range transmission capability. However, unlike the counterpart chirp technology in wireless -- LoRa, its throughput is severely limited by the number of modulated chirps in a symbol. The fundamental challenge lies in the underwater multi-path channel, where the delayed copied of one symbol may cause inter-symbol and intra-symbol interfere. In this paper, we present UWLoRa+, a system that realizes the same chirp modulation as LoRa with higher data rate, and enhances LoRa's design to address the multi-path challenge via the following designs: a) we replace the linear chirp used by LoRa with the non-linear chirp to reduce the signal interference range and the collision probability; b) we design an algorithm that first demodulates each path and then combines the demodulation results of detected paths; and c) we replace the Hamming codes used by LoRa with the non-binary LDPC codes to mitigate the impact of the inevitable collision.Experiment results show that the new designs improve the bit error rate (BER) by 3x, and the packet error rate (PER) significantly, compared with the LoRa's naive design. Compared with an state-of-the-art system for decoding underwater LoRa chirp signal, UWLoRa+ improves the throughput by up to 50 times.

翻译：基于线性调频的水声通信因其可靠性和远距离传输能力而被广泛应用。然而，与无线领域的对应调频技术LoRa不同，其吞吐量严重受限于符号中调制调频的数量。根本挑战在于水下的多径信道，其中同一符号的延迟副本可能导致符号间和符号内干扰。在本文中，我们提出UWLoRa+系统，该系统实现了与LoRa相同的调频调制但具有更高数据速率，并通过以下设计增强LoRa的方案以应对多径挑战：a) 将LoRa使用的线性调频替换为非线性调频，以减少信号干扰范围和碰撞概率；b) 设计一种算法，首先对每条路径进行解调，然后结合检测路径的解调结果；c) 将LoRa使用的汉明码替换为非二进制LDPC码，以减轻不可避免碰撞的影响。实验结果表明，与LoRa的原始设计相比，新设计将误码率（BER）提高了3倍，并显著降低了误包率（PER）。与最先进的解码水下LoRa调频信号系统相比，UWLoRa+的吞吐量提升了高达50倍。