Diversity-Oriented Grant-Free Transmissions for Underwater Wireless Networks

Grant-free (GF) transmission has received significant interests in the fifth generation (5G), that distributed transmission shows the potential of reducing the latency and overhead. In this paper, we introduce GF transmission into underwater wireless networks, and propose a diversity-oriented transmission scheme over doubly-selective underwater acoustic channels. In our design, the users can access the network only based on the channel estimation at the the PHY-layer without any grant. Meanwhile, the receiver can enjoy the enough diversity offered by the doubly-selective acoustic channels with low-complexity zero-forcing equalizers (ZFEs). Furthermore, the fairness control and energy-efficient transmission have been studied during the designing. In the experiment, we analyze the bit error rate (BER) at the receiver, the successful transmission rate of the underwater wireless networks and so on. The results exhibit the performance gains by the proposed grant-free transmission scheme in both the MAC-layer and the PHY-layer.