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In this tutorial paper we present equalization techniques to mitigate inter-symbol interference (ISI) in high-speed communication links. Both transmit and receive equalizers are analyzed and high-speed circuits implementing them are presented. It is shown that a digital transmit equalizer is the simplest to design, while a continuous-time receive equalizer generally provides better performance. Decision feedback equalizer (DFE) is described and the loop latency problem is addressed. Finally, techniques to set the equalizer parameters adaptively are presented.

The watermark embedded by traditional methods is easy to be lost under some attacks. To overcome this problem, this study proposes a novel method based on DWT. It adopts a digital audio watermarking state-switching system which optimizes DWT coefficients doubly. Firstly, it combines the quantization-embedding system and the weights of DWT coefficients with SNR to obtain an optimization model for watermarking. Next, the Lagrange principle, Hessian matrix, and minimum energy play three essential roles to obtain the optimal DWT coefficients and weights. Moreover, the almost invariant feature of the optimal weights holds demonstrating resistance to amplitude scaling. Compared with similar algorithms, the experimental results verify that the embedded audio in the proposed method has higher signal-to-noise ratio (SNR) and lower bit error rate (BER). At the same time, it indicates stronger robustness against various attacks, such as re-sampling, amplitude scaling, and mp3 compression.

This paper addresses the reduction of peak-to-average power ratio (PAPR) and synchronization errors of an orthogonal frequency division multiplexing (OFDM) for Mobile-WiMAX physical layer (PHY) standard. In the process, the best achievable PAPR of 0 dB with efficient power amplification is found for the OFDM signal using phase modulation technique, which avoids the nonlinear distortion. Further, the constant modulus algorithm (CMA) and sign kurtosis maximization adaptive algorithm (SKMAA) equalizers are used in the system to reduce the synchronization errors. However, the experimental study is performed on a test platform for a practical proof of the concept. The test platform is based on the Ettus universal software radio peripheral (USRP) N210 hardware and the GNU Radio open source software. Several tests are carried out to observe the effect of equalizers on the system. The performance comparison of bit error rate/symbol error rate (BER/SER) values are tabulated for the system with and without equalization.

Nonorthogonal multiple access (NOMA) waveforms need to be tested for their performance and effectiveness using partial transmit sequence (PTS) techniques and peak-to-average power ratio (PAPR) analysis. This is an important part of the advanced radio framework. This paper examines the PAPR features of NOMA systems using PTS with different sub-carrier configurations (64, 256, and 512). We examine BER, PSD, and PAPR distributions by modeling NOMA waveforms with PTS to understand the impact of different sub-carrier counts on signal complexity and efficiency. The findings shed light on how sub-carrier quantity affects PAPR statistics and offer guidance on the best way to design NOMA waveforms for improved spectral efficiency and reduced signal distortion. The simulation results show that by lowering the PAPR while maintaining the BER performance, the suggested system performs better than the traditional PAPR algorithm.

Optical orthogonal time frequency space (OTFS) is better at handling Doppler shifts and multipath fading, making signals more reliable and valuable in places with much movement beyond the fifth generation (B5G). Using practical power amplifiers at the transmitter causes power inefficiency and signal distortion because of the OTFS system’s high peak-to-average power ratio (PAPR), severely reducing system efficiency. Combining partial transmit sequence (PTS) and selective mapping (SLM), a technique known as PTS+SLM, reduces peak power. While SLM generates numerous phase-modulated signal candidates and chooses the one with the lowest PAPR, PTS separates the signal into sub-blocks and optimizes their phases to decrease peak power. With few changes to the signal structure, this dual strategy effectively reduces PAPR while improving power spectral density (PSD) efficiency. As a result, we ensure the accuracy and dependability of the transferred data by maintaining the bit error rate (BER). Fractal optimization methods could be applied to these algorithms. For example, fractal-inspired optimization techniques might be used to explore the phase space more effectively or to discover new phase sequences that result in lower PAPR. According to the simulation findings, the suggested PTS+SLM method works better than the traditional PTS and SLM methods.

A new interspersed orthogonal frequency division multiplexing (OFDM) based on Hadamard coded Discrete Harmonic wavelet transform (DHWT), is proposed for complex modulation under exponential channel model. In this method, real part of complex signal is transformed by DCHWT and imaginary part by DSHWT and summed to form interspersed harmonic wavelet based OFDM (IHWT OFDM). DHWT exploits the useful properties of DCT and DST viz., energy compaction/low leakage, frequency resolution and its real nature, compared to DFT. This wavelet is simple as it has reduced processing due to its harmonic wavelet nature. The harmonic nature has built in decimation, easy interpolation by concatenation of different scales in frequency (DCT and DST) domain without associated anti-aliasing filters for analysis, image rejection filters and complicated delay compensation for synthesis. In this work, we have explored advantages of DHWT to implement IHWP-OFDM for QPSK modulated signals. Hadamard codes are employed in proposed method to further improve BER and PAPR performance. New OFDM provides PAPR reduction of 2.6, 3.8 and 1.4 dB as compared to Haar, Daubechies WT OFDM and DFT, respectively.

In this paper, we address the error probability performance of space-time block coded system (STBC) in multipath Rayleigh fading channel. We consider STBC with rate one for two transmit antennae and rate half for three transmit antennae, and present an optimal maximum-likelihood-sequence-estimation (MLSE) and a block-by-block suboptimum decoding receiver structures. The proposed receiver schemes are suitable for short-range wireless communication or wireless personal area network (WPAN), where the delay spread is usually smaller than one symbol period. A reduced-state MLSE receiver with new trellis structure is first developed for the multiple-input multiple-output (MIMO) scenario assuming availability of ideal channel state information (CSI). Then a less complex block-by-block suboptimum decoding algorithm is also developed for the unequalized multipath fading channel, as an alternative to the computationally intensive MLSE. The suboptimum receiver symbol timing is optimized in order to obtain minimum error probability for the general multipath power delay profiles. From our simulation results, we show that our proposed MLSE receiver can mitigate the multipath induced intersymbol interference (ISI) effectively and at bit error rate (BER) of 10^-3, a two-transmit and two-receive (2, 2) STBC system gains as much as 11.5 dB in SNR over a single-antenna uncoded system. We also verify that the MLSE receiver always outperforms the suboptimum receiver, as expected. Error floors appear in the BER performance curves of the suboptimum receiver because ISI is not equalized, whereas no such floors appear with the MLSE receiver.

In this tutorial paper we present equalization techniques to mitigate inter-symbol interference (ISI) in high-speed communication links. Both transmit and receive equalizers are analyzed and high-speed circuits implementing them are presented. It is shown that a digital transmit equalizer is the simplest to design, while a continuous-time receive equalizer generally provides better performance. Decision feedback equalizer (DFE) is described and the loop latency problem is addressed. Finally, techniques to set the equalizer parameters adaptively are presented.

In this paper, a Tactical Data Link Communication System (TDLCS) simulation model mainly consisted of frequency-hopping spread spectrum (FHSS) module has been built by using the Simulink platform in Matlab. The single tone interference signal was added into this simulator. Frequency spectrogram figures and Bit error rate (BER) curves are obtained after simulations, which indicate that the frequency-hopping (FH) module of the TDLCS has a good ability to resist single tone interference.

Data transmission is affected by factors such as multipath effect, noise, time varying and Doppler effect in HF channel. In comparison with traditional equalization, turbo equalization is a better approach to these problems. In this paper, we build a simulation model of turbo equalization in HF communication system based on the characteristics of HF channel, comparatively analyze of the effect of some parameters such as length of interleaver, number of iterations and convolutional encoder. Subsequently the burst waveform in MIL-STD-188-141b and the MMSE-based turbo equalizer was developed, thus providing a reliable basis for the application of Turbo equalization in HF channel. The simulation illustrates that the MMSE-based Turbo equalization can reduce the gap between the simulation BER curve and theoretical curve, alleviating the impact of multipath fading, noise and Doppler effect; providing a high value and extensive application prospect.