We investigate the use of differential spacefrequencyblock codes (SFBCs) with orthogonal frequency division multiplexing (OFDM) over underwater acoustic channels. While SFBC efficiently exploits spatial transmit div...
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ISBN:
(纸本)9781479928941
We investigate the use of differential spacefrequencyblock codes (SFBCs) with orthogonal frequency division multiplexing (OFDM) over underwater acoustic channels. While SFBC efficiently exploits spatial transmit diversity, differentially coherent detection eliminates the need for extensive signal processing required for channel tracking. System performance is demonstrated using real data transmitted in the 12-26 kHz acoustic band from a vehicle moving at 0.5-2 m/s and received over a 100 m shallow water channel, using 4-QAM and a varying number of carriers ranging from 128 to 2048. Performance results demonstrate the advantage of the differentially coherent SFBC detection over the conventional, coherent SFBC detection which suffers from imperfect channel estimation.
The orthogonal frequency-division-multiplexing(OFDM) scheme has been adopted in many applications such as the digital broadcast television, the wireless communications, and the high-bit-rate communications over the ex...
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ISBN:
(纸本)9781634396226
The orthogonal frequency-division-multiplexing(OFDM) scheme has been adopted in many applications such as the digital broadcast television, the wireless communications, and the high-bit-rate communications over the existing copper networks. OFDM has found the applications in several mobile radio communication systems, such as the European DAB (digital audio broadcasting) system and the DVB (digital video broadcasting) system. The basic concept of OFDM is to sub-divide the information bit stream into a large number of bit streams, each with low individual bit rates, which are then carried on individual orthogonal subcarriers. This transmission technique is especially suited for mitigating the effect of the multipath fading channel. Multicarrier systems such as OFDM are well known to allow a bandwidth efficient transmission over strongly frequency selective channels at a moderate implementation effort. OFDM link the subcarriers are perfectly orthogonal only if transmitter and receiver use exactly the same frequencies. The overall performance of OFDM systems is very sensitive to time and frequency synchronization offsets. It is therefore important to design stable synchronization blocks in order to guarantee the proper orientation of the receiver. The OFDM systems however are highly sensitive to the frequency offset. Therefore, an accurate estimation of the frequency offset is critical. A false estimate leads to ISI which may disturb the orthogonality of the system and cause essential degradation due to *** is sensitivity to frequency offset in the channel, immediately results in inter carrier interference(ICI). One of the drawbacks of OFDM has been proved to be its high sensitivity to frequency offset. This frequency offset is usually divided into an integral part, which is a multiple of the subcarrier spacing, and a fractional part which is less than one half of the subcarrier spacing, Which results in inter-carrier interference (ICI).The undesired ICI degrades
In this paper, we consider the problem of the spacefrequencyblock Codes (SFBC) decoding, according to the Maximum A Posteriori (MAP) criterion when the channel is not perfectly known at the receiver. We propose to u...
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ISBN:
(纸本)9781424457939
In this paper, we consider the problem of the spacefrequencyblock Codes (SFBC) decoding, according to the Maximum A Posteriori (MAP) criterion when the channel is not perfectly known at the receiver. We propose to use the Expectation Maximization (EM) algorithm to solve this problem. Simulation results show that the performance of our iterative decoder using the EM algorithm is very close to the performance obtained when the channel is perfectly known. We also propose an efficient implementation of the iterative decoder (based on the EM algorithm) on FPGA.
In a high mobility environment, single-carrier (SC) space-frequency block coding (SFBC) diversity achieves better bit error rate (BER) performance than SC space-time blockcoding (STBC) diversity. However, in a strong...
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ISBN:
(纸本)9781479980925
In a high mobility environment, single-carrier (SC) space-frequency block coding (SFBC) diversity achieves better bit error rate (BER) performance than SC space-time blockcoding (STBC) diversity. However, in a strong frequency-selective fading channel, the BER performance degrades due to the orthogonality distortion of SFBC codeword. In this paper, we propose a frequency-domain equalization (called robust FDE) suitable for SC-SFBC diversity in a frequency-selective fading. The robust FDE weights are jointly optimized based on minimum mean square error (MMSE) criterion taking into account channel variation within a SFBC codeword caused by frequency-selective fading. It is shown by computer simulation that proposed robust FDE always achieves BER performance superior to conventional FDE whose weights are determined without considering the channel frequency variation within a SFBC codeword.
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