 5 Gushan Node 9 Yancheng Google earth Imagery Date: 12/31/2005 22°38'52.95" N 120°14'01.11" E elev Oft eye alt 30956 ft Figure 1.11 Geographical locations of transceiver nodes. The GPS coordinates of nodes 4, 5, and 9 are (N22.66038, E120.21450), (N22.64844, E120.21405), and (N22.64169, E120.23450), respec- tively. Their relative distances are 1549.58 m (from node 4 to node 5), 2187.60 m (from node 5 to node 9), and 3377.72 m (from node 9 to node 4). Source: Map data: google, © Digital Globe, © Kingway Ltd, © GeoForce Technologies, © TerraMetrics. The sea depth is around 20 m and the node depth is around 10 )m. The transducer and the hydrophones may drift due to waves. During the sea test, the nodes transmitted with each other and the received data packets were recorded. The basic system parameters are provided in Table 1.1. The bandwidth of the system is 5.36 kHz. The total number of subcarriers is 1600, within which there are 1278 data sub- carriers, 214 pilot subcarriers, and 108 null subcarriers. The guard interval has a length of 50 ms, which is much longer than the maximum channel delay spread. The pilot subcarri- ers are used for channel estimation. For the ICI two-path cancellation schemes, the pilots are uniformly inserted among the data subcarriers. However, for the ICI self-cancellation schemes, to avoid loss of spectral efficiency, the mirror-mapped pilot structure has to be adopted. Thus, the ICI self-cancellation schemes do not facilitate OFDM system standard- ization. In addition, quadrature phase shift keying (QPSK) modulation is adopted for the mirror-mapping-based schemes. To demonstrate the performance of the mirror-mapping-based schemes, there are two benchmark candidates, both of which have the same spectral efficiency as the mirror-mapping-based schemes. The first one is the plain OFDM with BPSK modulation (OFDM-B). The second one is the OFDM scheme with half of the total subcarriers occupied by QPSK data symbols and each of the data symbols surrounded by two null subcarriers (OFDM-QH). For