Adaptive Modulation And Power Allocation For OFDM Underwater Acoustic Communication

Orthogonal frequency division multiplexing(OFDM)can effectively eliminate frequency selective fading,which is suitable for underwater acoustic(UWA)communication systems with severe multipath expansion and limited bandwidth resources.Adaptive modulation and power allocation techniques are key technologies in UWA communication,which can adapt to complex channels and improve communication efficiency.However,since the adaptive technology adjusts the transmission parameters according to the real-time channel state information(CSI),the performance is severely degraded in the time-varying channel.Thus we introduce the channel prediction method,making it suitable for UWA channels with long-term propagation delay and fast time-varying.This paper studies the adaptive modulation and power allocation OFDM UWA communication system based on channel prediction technology,realizing high-speed,low-energy,robust and reliable OFDM communication under time-varying channel.Firstly,the physical characteristics of the time-varying UWA channel are discussed.Using the sparseness feature,channel prediction is conducted in a simpler time domain in a simpler time domain using the pre-estimated channel,which reduces the computational complexity and improves the prediction accuracy by removing most noise effects.In this paper,the minimum mean square error(MMSE),the least mean square(LMS)and the recursive least squares(RLS)algorithms are studied,with whose complexity and applicability compared.Then,this paper studies the adaptive modulation and power allocation techniques in OFDM systems.Firstly,the OFDM adaptive communication model is presented.The iterative water-filling power allocation(IWFP)algorithm is studied according to the water filling principle.it and power allocation algorithms are studied separately based on the principle of maximum bit rate,power minimization and optimal performance of bit error rate.The Hughes-Hartogs algorithm,Chow algorithm and Fischer algorithm are introduced,which eliminate the steps of measuring the communication water environment in advance and artificially setting the switching threshold,so that the adaptive system communication is more flexible.The transmission performance of OFDM adaptive systems with coded channel and uncoded channel are compared by simulation.Finally,experimental data is used to validate the proposed algorithms.The channel prediction errors are all within 10~-22 in slow,fast and under-ice acoustic channel environments,which proves that the adaptive channel prediction algorithms can be effective in several different environments.The pool test this paper can guaranteed the communication stability while improving the frequency band utilization.The performance of the adaptive communication system combining the channel prediction method is analyzed.The simulation results show that the channel prediction technology can provide reliable CSI for the adaptive communication system,which provides technical support for the realization of the future OFDM adaptive UWA communication system.The research results of this paper are expected to provide an important technical basis for future realization of adaptive underwater acoustic communication based on environmental awareness.