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This paper compares the effectiveness of different spread OFDM techniques with transmit diversity used for underwater acoustic communications. Spreading by Walsh-Hadamard codes, discrete Fourier transform, discrete cosine transform and carrier interferometry (CI) codes have been combined with the application of space-time and space-frequency transmit diversity in OFDM for underwater acoustic communication...
Conventional orthogonal frequency division multiplexing (OFDM) can reduce errors in underwater channels but frequency selective fading can still degrade the data on carriers near deep fade regions. Recently spread-OFDM (SOFDM) which combines the properties of spread spectrum with multicarrier communication has become popular. In this paper spreading by Walsh-Hadamard (WH) codes, discrete Fourier transform...
Discrete Cosine Transform based Orthogonal Frequency Division Multiplexing (DCT-OFDM) is proposed for the first time for Underwater Acoustic Communication. Underwater acoustic channels are characterized as doubly spread channels in time and frequency. The orthogonality feature of conventional OFDM is also provided by inverse DCT (IDCT)-DCT structure with the added advantages of reduced implementation...
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