## 5 Experimental Tests
### Communication Tests  
The communication tests in the model pool were performed using DSSS signals constructed of m-sequences, Kasami codes, and Gold codes. The parameters of the transmitted signals are presented in Table 1. For each signal parameter's configuration, 20 transmission tests were performed. During each test, a single transmission frame had a duration of 6 s and was constructed of a variable number of symbols, depending on the signal bandwidth (Table 1). The set of information bits sent in each transmission frame was different, generated as a pseudorandom sequence with uniform distribution. During each communication test, regardless of the bandwidth of the transmitted signal, the received signal-to-noise ratio was in the range of 15-17 dB. After performing the measurements and analysis of the obtained results, additional simulation tests were carried out to estimate how the obtained reliability can be increased using ECC coding. For this, sequences of correctly and incorrectly received bits were used, achieved during the processing of the recorded DSSS signals. The same BCH codes were used, as in the case of simulation tests performed in the Watermark simulator. Table 10 shows the BER results averaged over 20 transmission tests for each type of communication signal, determined by the spreading sequence and the bandwidth. Similar to the tests with the measurement pool simulator and Watermark software, the best BER  
Figure 14: The module of time-varying impulse response, measured using PRBS of a bandwidth equal to 5 kHz, and estimated power delay profile and space-frequency correlation function. Figure 15: The module of time-varying impulse response, measured using PRBS of a bandwidth equal to 8 kHz, and estimated power delay profile and space-frequency correlation function. results were obtained for the DSSS signal bandwidth equal to 1 kHz. In this case, the use of each of the spreading sequences makes it possible to achieve a BER less than 0.001. In the case of other bandwidth values, the best results were obtained using the m-sequence as the spreading sequence. The BER obtained for Kasami codes and Gold was several times higher than in the case of m-sequences. During the transmission of signals of bandwidth equal to 2 kHz, m-sequence could obtain a BER less than 0.001, while for Kasami codes the BER was equal to 0.06, and for Gold codes the BER was equal to 0.18. Using ECC encoding, it is possible to achieve an error rate of less than 0.01, with a code rate equal to 5/15 = 0.3333 in the case of transmission with Kasami codes. The transmission rate is then reduced from 7.84 bps to 2.61 bps. Moreover, a BER less than 0.001 can be achieved using a BCH code rate equal to 6/31 = 0.1935, which means a reduction in the transmission rate to 1.62 bps. In the case of transmission with Gold codes, achieving a BER lower than 0.01 would reduce the transmission rate to a value lower than 1 bps. In the bandwidth equal to 4 kHz, it is possible to transmit data with a rate equal to 5.23 bps (m-sequences) or 3.04 bps (Gold codes), with a BER less than 0.01. A BER less than 0.001 can be achieved in the case of transmission with m-sequences with a rate equal to 3.04 bps. During transmission in a bandwidth equal to 5 kHz, it is possible to obtain a BER of less than 0.01 using the m-sequences and BCH coding of code rate equal to 7/63 = 0.1111. The ECC coding reduces the transmission rate from 19.61 bps to 2.18 bps. In the bandwidth equal to 8 kHz, the highest reliable transmission rates using m-sequences were obtained, that is, 10.46 bps with a BER less than 0.01 and 6.07 bps with a BER less than 0.001.