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It is tough to achieve higher transmit speed and lower bit error rate(BER) because of the complexity of the underwater acoustic channel. This paper proposes a method of orthogonal frequency division multiplexing (OFDM) modulation technique for improving the situation. It can reduce BER with the ability of resisting multi-path interference and can increase communication rate with the characteristic...
This paper proposes a basic MC-CMDA. via carrier interferometry Codes (CI codes) in an Underwater Acoustic(UWA) Channel. Compared with OFDM in UWAC, it can allow a number of users simultaneously and asynchronously accessing the UWA channel. A trade off relation exists between diversity gain and user capacity as well as between spread spectrum gain and system efficiency. Then diversity combining scheme...
According to the feature of underwater acoustic channel (UWA), the implementation of time and frequency synchronization is introduced. In the sea area, the experiment result show that the synchronization method of OFDM system has the better performance.
Based on characteristics of Underwater Acoustic Channel and LFM (Linear Frequency Modulation) signal, LFM signal is adopted for timing synchronization signal of OFDM Underwater Communication System. The generation and detection principle of LFM signal are summed up. Then the scheme based on the theory above is implemented on FPGA (Field Programmable Gate Array). Finally, the result of a pool test...
Considering the features of Underwater Acoustic channel and the sensitivity versus synchronization for CI/OFDM system, A time and frequency synchronization method based on Constant Amplitude Zero Auto-Correlation(CAZAC) sequence is presented. The time offset estimation and carrier frequency offset estimation can be achieved simultaneously. The fractional part and integral part of carrier offset estimation...
In this paper, multiple access technique for the physical layer of underwater acoustic (UWA) networks is discussed. Considering the characteristics of acoustical channel and UWA networks, multi-carrier code division multiple access(MC-CDMA) method is chosen as the multiple access strategy in the design of an UWA network. On this basis, a MC-CDMA multiple access scheme is proposed. The preliminary...
Underwater acoustic (UWA) channel is a time-space-frequency varying channel. Coherent detection requires channel estimation in Orthogonal Frequency Division Multiplexing (OFDM) system. In this paper, the channel estimation methods based on pilot for OFDM UWA system are investigated. Through analysis and testing about two channel estimation performance, the adaptability based on Pilot Symbol Assisted...
Bused on the features of underwater acoustic channel, a novel scheme of timing synchronization for OFDM systems is proposed. An adaptive pilot coarse timing synchronization method is used for established synchronization rapidly. For getting the accuracy timing position, CAZAC sequence is used as fine timing synchronization. Both the computer simulation results and laboratory pool tests show that the...
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