“…Although PRWs have been available for over two decades, the earliest research on different signal transmission on PRWs was published in 2010 [107], and the majority of studies were conducted (61/63, 96.8 per cent) after 2015. As shown in Figure 3, most of the studies belonged to China (38) [7,15,28,[30][31][32][33][34]37,38,40,[44][45][46][47][48][49][50][51][52][53][54]56,60,61,63,65,73,81,104,106,[108][109][110][111][112][113] followed by the U.S. ( 9) [4,5,14,34,35,67,78,99,…”