MODEM Design And Implementation Of Underwater Acoustic Communication Based On Direct Sequence Spread Spectrum

Direct Sequence Spread Spectrum technology is one extended underwater acoustic communication networks commonly used techniques. However,unlike traditional radio communication network system, the sound of water in the channel conditions due to multi-path channel, time-varying, fading and other factors, the signal during transmission is easy to produce inter-symbol interference,bit error rate, the communication quality not ideal.In response, American scientists M. Stojanovic hypothesis proposed chip feedback equalization (CHF), through the chip level equalization and adaptive decision-feedback hypothesis transmission sequence, can effectively compensate for the phase error tracking fast time-varying channel caused and reduce code interference between relatively conventional decision feedback equalization techniques have greatly improved in performance. On the other hand, in the conventional construction of underwater acoustic communication network node, the sound of water used in networking MODEM due to processor performance, size,power consumption, and many other factors, there are many constraints in the actual development of the finished project.For the development of a water sound direct sequence spread spectrum technology as a means of communication, to achieve low error, miniaturization and efficient real-time,high-speed, low-power type hydroacoustic MODEM. Firstly, in CHF algorithm proposed on the basis of M. Stojanovic, with Gold code and Chaotic code for spreading code, combined with coding, matched filtering, synchronization, CFAR detection techniques to establish a direct comparison of the sequence of the sound of water spread spectrum communication simulation platform, and secondly, to select the United States TI introduced a new generation of dual-core (DSP C6748 + ARM926EJ-STM), high efficiency, low-power processors OMAPL138 applies MODEM design, through the design of functional requirements analysis MODEM located in meet the communication transmitting and receiving on the basis of high-precision, high-precision timing synchronization design, reducing system design errors.Finally, to improve the MODEM real-time, reducing the amount of system operations in real-time convolution algorithm design involves partially overlapping reservations and ingenious method to allocate system memory, reduce resource redundancy. Experimental results show that the channel pool: on the one hand, we design MODEM to stabilize, more efficient way to work in fading underwater acoustic channel environment, high-precision clock synchronization errors on the way to reduce the system's interference algorithm,CHF algorithm should MODEM receive real-time solution of calculation, equalization process significantly reduces multipath fading conditions of transmission error. On the other hand,comparison of the data communication via MODEM Gold Chaotic code spreading code and under the spreading code obtained Chaotic average mean square error (MSE) Gold code spreading relatively low about 7dB, equilibrium can be applied to obtain faster CHF adaptive recursive convergence speed, lower equilibrium feedforward / feedback filter tap length experimental results demand for real-time optimization MODEM give guidance and advice.