The underwater acoustic channel (UAC) is known to offer poor communication channel and very limited transmission bandwidth. The channel is highly frequency selective and the channel response changes over time due to variations in channel conditions. Designing a system to deal with the frequency and time selective channel in UAC, therefore, becomes very challenging. Attempts were made to solve t...

Frequency-domain pre-equalization (pre-FDE) transmission can be used instead of FDE reception for improving the transmission performance in a severe frequency-selective fading channel. Antenna diversity technique is also a well-known technique for improving the transmission performance, especially, transmit antenna diversity technique has been attracting much attention. In this paper, we propos...

Multi-access interference (MAI) limits the transmission performance of the DS-CDMA uplink. In this paper, we propose 2-dimensional (2D)-OVSF spreading for chip-interleaved DS-CDMA uplink transmission. By adopting 2D-OVSF spreading, the multiuser channel is transformed into orthogonal single-user channels irrespective of users’ data rates. Thus, single-user frequency-domain MMSE equalization can...

Similar to the single-carrier transmission [1], the bit error rate (BER) performance of DS-CDMA in a frequency-selective fading channel can be significantly improved with coherent frequency-domain equalization (FDE) instead of using Rake combining [2][3]. However, coherent FDE requires accurate channel estimation and the imperfect channel estimation results in the performance degradation. For p...

In this paper, we propose a novel concept of differentially encoded multi-carrier faster-than-Nyquist (DMFTN) signaling with noncoherent detection, which is robust against detrimental doubly selective fading channel. the proposed scheme, by approximately diagonalizing FTN-specific ISI and noise correlation matrices, traditional differential encoding detection algorithm directly applied to MFTN ...

Most transmission schemes for MIMO channels assume (i) a block fading channel without delay spread and (ii) availability of channel state information at the receiver. Here, we extend the space-time motrir modulation (STMMj scheme and the iterative demodulation algorithm that we introduced previously to unknown, doubly selective MlMO channels, i.e., delayDoppler-spread MlMO channels that are unk...

In previous work, we presented a receiver to detect and decode parallel concatenated convolutional (PCC) coded transmissions over a frequency selective Rayleigh fading channel. This scheme generalized work by Valenti and Woerner to frequency selective channels. It was shown that re-estimation of the channel after each PCC decoding iteration yields significant gain. In this paper we present a de...

Recently it has been shown that by exploiting the fading properties of the wireless environment, a communication structure with multiple transmit/receive antennas can deliver enormous capacities [1]. Several architectures have been proposed to implement space-time systems for the narrowband flat fading wireless environment [2,3]. However, in order to support higher data rates, the concept of sp...