Abstract
In UWAC (underwater acoustic communication), UWA (underwater acoustic) channels change rapidly due to varying environment conditions. AMC (adaptive modulation and coding) is an efficient technique to improve system efficiency by changing transmission parameters according to channel conditions in UWA channels. In this paper, we propose an environmental cognition orthogonal frequency division multiplexing (OFDM) UWAC system and compare it with AMC algorithm with six transmission modes together with three threshold detection algorithms. Simulation and experimental results show the effectiveness of the proposed system. The system will play an important role in future communication networks which can significantly improve the efficiency of the system.
Highlights
E UWA channel is one of the most complex wireless channels whose characteristics are affected by various parameters, such as the propagation distance of the acoustic signal, the interference signal caused by multipath propagation, the environmental noise, and the Doppler shift caused by movement or the roughness of the sea surface. [19, 20] Adaptive modulation and coding (AMC) technology can change transmission parameters, according to the changes in underwater acoustic channels to improve the efficiency of the communication system. is algorithm will further promote the development of the networking technology
In [24], the effective signal-to-noise ratio (ESNR) is calculated using the Acknowledge Character (ACK), which does adequately reflect channel characters because of the limited length of the ACK. erefore, we propose an improved ESNR (IESNR) criterion which is shown as follows: Ek∈SH cs[k]s[k]2
In other research studies that adopt the CS channel estimation algorithms, there are no prior information regarding the channel multipaths’ number, which will waste computing time and cause inaccurate estimation. e algorithm flow proposed in this paper is shown in Figure 3; it is suitable for real-time duplex communication systems. e channel tap coefficients obtained by preamble sequence (PS) are fed back to the CS algorithm so that the system can complete more accurate channel estimation in a shorter time. en, during the CS channel estimation procedure, Xp and Yp are signals obtained from the whole transmitting orthogonal frequency division multiplexing (OFDM) signal, which will mainly be pilot signals. is CS algorithm is adopted in the ESNR channel quality assessment criterion known as the IESNR criterion
Summary
Several studies have focused on UWAC in recent years, with both multicarrier transmissions [1,2,3,4,5,6,7,8,9,10,11] and single carrier transmissions. [12,13,14,15] In an UWAC system, the rapidly varying multipath channel and the limitation of the bandwidth are major constraints [16,17,18]. [19, 20] Adaptive modulation and coding (AMC) technology can change transmission parameters, according to the changes in underwater acoustic channels to improve the efficiency of the communication system. [24] e transmission of RTS and CTS signals will waste the limited energy, but will be unable to adjust the transmission mode during transmission These kinds of procedures estimate channel condition only once and do not permit sensing of the channel in real time. Unless the RTS and CTS signals transmit before each communication, the system can adopt its transmitting mode according to the channel condition involved in the CTS signal This will waste a lot of time and affect the transmission efficiency.
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