  Communication in extreme environments is an important research topic for
various use cases including environmental monitoring. A typical example is
underwater acoustic communication for 6G mobile networks. The major challenges
in such environments are extremely high-latency and high-error rate. They make
real-time image transmission difficult using existing communication protocols.
This is partly because frequent retransmission in noisy networks increases
latency and leads to serious deterioration of real-timeness. To address this
problem, this paper proposes a stochastic image transmission with Constrained
Application Protocol (CoAP) for extreme environments. The goal of the proposed
idea is to achieve approximate real-time image transmission without
retransmission using CoAP over UDP. To this end, an image is divided into
blocks, and value is assigned for each block based on the requirement. By the
stochastic transmission of blocks, the reception probability is guaranteed
without retransmission even when packets are lost in networks. We implemented
the proposed scheme using Raspberry Pi 4 to demonstrate the feasibility. The
performance of the proposed image transmission was confirmed from the
experimental results.
