An Underwater Acoustic Implementation of DFT-Spread OFDM

Abstract

This paper presents a design of DFT-spread OFDM system applied to an underwater acoustic channel. It does not only combine all the advantages of a conventional OFDM system but also reduces the peak-to-average power ratio of the transmit signal. Besides, the scheme spreads the information over several subcarriers as a result of the application of an additional DFT operation and leads to a diversity gain in a frequency-selective fading channel, which is one of the many challenges of communicating data through an underwater acoustic channel. Simulation results show that our proposal possesses good bit-error-rate performance. The system has been tested in a real underwater acoustic channel-the experimental pool in Xiamen University. The experimental results show that the DFT-spread OFDM system can achieve better results than a simple OFDM system in a benign underwater channel.

Performance Evaluation of DFT-Spread OFDM and DCT-Spread OFDM for Underwater Acoustic Communication

“…For ordinary OFDM, the BER at 15dB is as high as 4.5e-4 and that of DFT-SOFDM is 1e-4. Result for DFTSOFDM matches with the existing result of [9] which validates the simulation. At a BER of 1e-4 DCTSOFDM has a SNR gain of about 1dB over DFTSOFDM.…”

“…DCT spread OFDM with repetitive code with code ratio ¼ is evaluated. The scheme is shown in figure 5 and is compared with the localized DFTSOFDM scheme proposed in [9] as shown in figure 6. At a SNR of 15dB the proposed scheme has a BER of 4.5e-5 where as DFTSOFDM has that of 1e-4.…”

“…Figure 11 shows the complementary cumulative distribution (CCDF) versus PAPR plot for both DFTSOFDM and DCTSOFDM with respect to OFDM, which confirms that the latter has a slightly better performance. [9] VI. CONCLUSION This paper evaluated the DCT spread OFDM system, a technique that overcomes the fading effects of underwater acoustic channel nulls by spreading the modulated symbols across the bandwidth before OFDM.…”

“…In [8] it is mathematically proved that this method is effective in reducing the PAPR. In this paper the use of DCT spread OFDM for UWA communication is proposed and its performance is compared with the already existing results of DFTSOFDM [9] under similar conditions. A novel scheme of using the null subcarriers to implement complex field repetitive coding in case of DCTSOFDM is proposed to further reduce the BER.…”

Recent trends in multicarrier underwater acoustic communications

“…This technique is called code spread (CS) OFDM. CSOFDM or simply SOFDM enjoys the spreading gain of code division multiple access (CDMA) along with multicarrier transmission [35], [36], [51], [52]. Such a system is shown in figure 2.…”