## 5 Pool Experiment  
We conducted a non-reflective pool experiment to validate our proposed method. Figure 13 shows a pool experiment assuming a reverse two-path multipath condition. This pool's dimensions are 5.0 m by 2.5 m and the depth is 2.5 m. Two transmitting transducers TX1 and TX2, about 3.2 m apart, are used to model the multipath environment. While TX1 and TX2 send signals at the same power, a receiving transducer RX moves 0.75 m from  
Figure 11: Comparison of simulated BER.  
Figure 12: BER vs. CNR of conventional and iterative mDDP on NumCOL = 21.  
0.5 m from TX1 in the direction of TX2 with a speed of 0.25 m/s. All transducers were installed at the same depth, 1.8 m.  
Using time domain signals obtained through the RX transducer in the non-reflective pool environment, BER measurements were made using the computer simulations of the conventional and proposed methods. Figure 14 shows the spectrum of the received advance signal of the RX transducer. An 8 kHz bandwidth between 20 kHz and 28 kHz with a center frequency of 24 kHz can be seen in the received spectrum. The reason why the power spectrum is rising steadily to the right is due to the frequency characteristics of the transducer used. A low pass filter was inserted to flatten the power spectrum in order to cancel the frequency response of the receiving transducer when the received signal is used in a computer simulation.  
For the signals sent out from TX1 and TX2, we used the 400 OFDM symbols (about 10.0 s) used in the computer simulation presented in Table 1. Figure 15 shows the BER for approximately 3 s during which the RX transducer is being moved out of approximately  
Figure 14: The received spectrum on RX transducer.  
Figure 13: Non-reflective pool experiment environment.  
10 s of signal transmission from TX1 and TX2. In Figure 15, the word \"Moving\" is shown in red in the graph of the time dependence of the bit error rate when the RX transducer is moving. It can be seen that the BER is degraded for NumCOL = 1 for the iterative mDDP of the proposed method compared to the BER of the conventional method, but as the value of NumCOL is increased, the BER improves. At NumCOL = 51, the error rate is a factor of approximately 45 of the conventional method. Figure 16 is a graph of NumCOL vs. BER for the non-reflective pool experiment. The one-step mDDP shows that BER saturates at NumCOL = 31, but the iterative two-step mDDP shows that BER improves even when NumCOL is 31 or higher. This may be due to the fact that the effect of ICI becomes smaller as the carriers subject to ICI cancellation move further away.  
Figure 15: Results of pool experiment environment time dependencies of measured BER and constellation (real part of complex).  
One of the reasons for the slight degradation of BER compared to the two-wave multipath environment subjected to the Doppler shift created in the simulation is the non-reflective pool environment, but signal reflection from the pool surface is considered to exist because the experiment is conducted with the transducer suspended above the water surface. Therefore, the possibility of a two or more-wave multipath environment and noise superimposition from the acoustic device of the signal receiver are also possible.