Multicarrier Faster-Than-Nyquist Based on Efficient Implementation and Probabilistic Shaping

Multicarrier faster-than-Nyquist (MFTN) signaling can improve spectral efficiency by reducing time interval and frequency spacing of the traditional Nyquist signaling. This deliberately introduces the intersymbol interference (ISI) and intercarrier interference (ICI), which makes the detection of MFTN signaling a challenging task. In this paper, we propose a low-complexity receiver to remove the ISI and ICI for MFTN signaling. A cycle-free factor graph is employed to represent the factorization of the joint posterior distribution of the transmitted symbols. Then, Gaussian message passing (GMP) is derived on the factor graph. Simulation results demonstrate that, the proposed low-complexity algorithm can perform close to the MAP receiver. The spectral efficiency can be improved by 56% with less than 0.4dB bit error rate performance loss.

Multicarrier faster-than-Nyquist (MFTN) is a spectral efficient transmission scheme for future communication systems. However, as one of the most important drawbacks of multicarrier transmission systems, the peak-to-average power ratio (PAPR) of MFTN signals is still not clear yet. In this paper, we investigate the PAPR of MFTN signals for nonlinear satellite communication systems. First of all, the PAPR distribution of MFTN signals under various practical situations is evaluated, and we show that the PAPR of MFTN signals is closely related to the number of subcarriers, the shaping pulse, and the time–frequency packing factors. Moreover, different from conventional Nyquist multicarrier signals, certain time–frequency packing in MFTN will however, improve the PAPR performance. Then, the PAPR of MFTN signals under the given spectral efficiency is considered. By jointly optimizing the time–frequency spacing to minimize the PAPR, we show that the MFTN combined with low-order modulation could be more energy efficient than the corresponding Nyquist high-order modulation signals. Finally, we investigate the PAPR reduction for MFTN signals. Specifically, a selective mapping-based alternative-signal scheme, which mainly intended for the conventional Nyquist multicarrier signals, is extended to the MFTN signaling system. It is shown that the PAPR reduction performance of the considered scheme is robust to the time–frequency packing, and even approaches the conventional orthogonal frequency-division multiplexing system. Our numerical results validate that besides the high spectral efficiency, the MFTN may be also an energy efficient transmission scheme for next-generation satellite communication systems.

These days we find an enormous growth in wireless communication technologies. The use of OFDM in wireless systems has created a way to provide high data rates, less intercarrier interference(ICI), and less intersymbol interference(ISI). OFDM has become the core of most 4G communication systems, a Long Term Evolution (LTE) system. OFDM system divides the available signal spectrum into smaller bandwidths and transmits them to the receiver without interference with each other by inserting the cyclic prefix in between the signals. LTE uses OFDM for downlink, SC-FDMA for uplink and MIMO for enhanced throughput. The OFDM uses inverse fast fourier transform(IFFT) and fast fourier transform(FFT) for conversion of data. The system performance is measured by correlating the signal to noise ratio to bit error rate. The system performance is evaluated to study the effect of various LTE design parameters by simulating in MATLAB

<p>Orthogonal frequency division multiplexing (OFDM) is a transmission system that uses multiple orthogonal carriers that are sent out at the same time. OFDM is a technique for mobile and wireless communication that has high-efficient frequency utilization, high data-rate transmission, simple and efficient implementation using the fast Fourier transform (FFT) and the inverse fast Fourier transform (IFFT), and reduces inter symbol interference (ISI) by inserting cyclic prefix (CP). One of the most important approaches in an OFDM system is channel estimation. In this paper, the orthogonal frequency division multiplexing system with the Rayleigh channel module is analyzed for different areas. The proposed approach used large numbers of subcarriers to transmit the signals over 64-QAM modulation with pilot add channel estimation. The accuracy of the OFDM system is shown in the measuring of the relationships of peak power to the noise ratio and bit error rate.</p>

Fast Fourier Transform (FFT)/Inverse Fast Fourier Transform (IFFT) are the key computation block in Orthogonal Frequency Division Multiplexing (OFDM) system. They dominate most of the areas and power dissipation in implementation therefore efficient low-power and high-throughput implementation of FFT processor is essential for successful deployment of OFDM based system. High-throughput and Low-power 128-point FFT Processor is designed using Radix-25 algorithm to reduce computation complexity and the feedforward pipeline architecture [called Multipath Delay Commutator (MDC)] with four data path for providing higher throughput. This architecture is more hardware-efficient than Multipath parallel feedback (MDF) design, which makes them attractive for the computation of FFT in most demanding applications. The proposed FFT processor uses improved Digit slice multiplier for complex multiplication. This proposed FFT processor is designed using Verilog and implemented using 180 nm CMOS Technology with supply voltage of 1.8v. The result shows significant reduction in power consumption in comparison with existing design and increasing throughput with area trade off.

Ultra wideband (UWB) radio is a promising technology for short range wireless communications. It can be used for both high rate and low rate transmissions. High data rate can be achieved by using multiband (MB)-UWB approach whereas low data rate with robust system performance can be obtained by employing time hopping (TH)-UWB radio systems Majhi et al. (2006); Win & Scholtz (1998a). Nowadays, applications of UWB are spreading to various fields such as vehicle communications, wireless sensor networks, ad hoc wireless networks, and controller area networks. The most of the systems require low to moderate (1 kbs-100 mbs) data rates with an acceptable implementation cost. However, due to the presence of fast Fourier transform (FFT) and inverse FFT (IFFT), MB-UWB may not be a cost effective procedure for low data rate systems. Therefore, one needs an efficient system which adaptively changes the data rate from low to moderate with robust system performance. TH-UWB with OOK-PSM modulation provides low data rate with robust system performance Majhi, Madhukumar, Premkumar & Richardson (2008). However, it is possible to scale the TH-UWB radio system for low to moderate data rates by incorporating higher level modulation schemes with an adaptive method. For TH-UWB systems, various M-ary modulation schemes such as pulse positionmodulation (PPM), pulse amplitude modulation (PAM), pulse shape modulation (PSM), and their combined forms have been proposed to improve data rates and system performance with low complexities Bin et al. (2003); Durisi & Benedetto (2003); Ghavami et al. (2002); Michell et al. (2003); Usuda et al. (2004). However, due to the increase of inter symbol interference (ISI) in the presence of multipath channel, M-ary PPM or M-ary orthogonal PPM (OPPM) are not effective for TH-UWB systems with RAKE reception when M is high Foerster (2003); Win & Scholtz (1998b). High-level M-ary PAM is rarely used in short range and low power consumption communications systems Guvenc & Arslan (2003). This is because that the Euclidian distances between constellations become small with increase in M. Due to its robustness against ISI and multiple access interference (MAI), pulse-based modulation such as PSM has become an interesting research topic in TH-UWB, direct sequence UWB (DS-UWB) and transmitted referenceUWB (TR-UWB) radio systemsChu M de Abrue et al. (2003); Gezici et al. (2006); Hwang et al. (2007); Kim & Womack (2007); Parr et al. (2003). However, high-level M-ary PSM cannot be used due to the limited auto correlation properties 2

Software-defined radio (SDR) is a challenging domain for language designers. To be useful in the real world, radio protocol implementations must operate at high data rates with low latency, yet to be useful to implementers, a language should allow programmers to express algorithms at a high level of abstraction without having to worry about the very low-level details that are necessary for meeting performance requirements. Ziria demonstrated that a high-level language for writing wireless physical layer (PHY) protocols could be competitive with hand-written C++, but only in a context where performance-critical computations, such as FFT and Viterbi, were still written in C++ and accessed via a foreign function interface. We demonstrate that a new implementation of Ziria, embodied in the kzc compiler, allows even performance-critical blocks such as FFT and Viterbi to be written in a high-level language without sacrificing performance. Because kzc performs whole-program optimization, a radio protocol pipeline using an implementation of Viterbi written in Ziria can outperform an implementation that calls out to . The contributions of this paper fall into two categories. First, we describe two new optimizations in kzc, both of which are critical for wringing performance out of high-level code: an aggressive partial evaluator for Ziria programs, and an automatic lookup-table (LUT) generator. Second, we show how these optimizations allow the efficient implementation of three performance-critical blocks in Ziria: Viterbi decoding, the Fast Fourier Transform (FFT), and the inverse Fast Fourier Transform (IFFT).

We present a novel decision-aided algorithm in this paper for orthogonal frequency division multiplexing (OFDM) systems to eliminate the residual intersymbol interference (ISI) introduced by the channel impulse response that exceeds the length of the guard interval. The algorithm uses decisions to estimate the residual ISI by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) with a very low computational complexity. This method can be applied for non-sample spaced channel. Simulations for the application of the residual LSI cancellation algorithm to the wireless LAN system (WLAN) are performed. The simulation results show that the residual LSI cancellation algorithm presented in this paper provides good performance improvements on static fading LSI channels

This paper describes a correlation-based watermarking technique with the fast Fourier transforms (FFTs) for three-dimensional (3-D) mesh models. For generating a watermark with desirable properties, similar to a pseudonoise (PN) signal, an impulse signal on a two-dimensional (2-D) space is spread through the FFT, multiplications of a complex sinusoid signal, and the inverse FFT. This system easily incorporate a frequency selectivity property, because zero-valued components in the multiplication block prevent the energy of the impulse signal at appropriate frequencies. As a result, the proposed approach requires no additional transform, such as the discrete cosine transform and wavelet transform. Since the amount of information that can be stored in the watermark depends on the size of a spread space, the elimination of the subband transform increases a payload of the watermark in a previous paper. The watermark, i.e., spread impulse signal, is embedded into 3-D data aligned by the principle component analysis (PCA). In the detection procedure, after realigning the watermarked mesh model through the PCA, we map the 3-D data on the 2-D space via block segmentation and averaging operation. The 2-D data are processed by the inverse system, i.e., the FFT, the division of the complex sinusoid signal, and the inverse FFT. From the resulting 2-D signal, we detect the position of the maximum value as a signature.

In recent years, target detection has drawn increasing attention in the field of radar signal processing. In this paper, we address the problem of coherent integration for detecting high-speed maneuvering targets, involving range migration (RM), quadratic RM (QRM), and Doppler frequency migration (DFM) within the coherent processing interval. We propose a novel coherent integration algorithm based on the frequency-domain second-order phase difference (FD-SoPD) approach. First, we use the FD-SoPD operation to reduce the signal from three to two dimensions and simultaneously eliminate the effects of QRM and DFM, which leads to signal-to-noise ratio improvement in the velocity-acceleration domain. Next, we estimate the target motion parameters from the peak position without the need for a search procedure. We show that this algorithm can be easily implemented by using complex multiplications combined with fast Fourier transform (FFT) and inverse FFT (IFFT) operations. We perform comparisons with several representative algorithms and show that the proposed technique can be used to achieve a good trade-off between computational complexity and detection performance. We present both simulated and experimental data to demonstrate the effectiveness of the proposed method.

Summary Numerical simulations of elastic wave propagations are the critical components for seismic imaging and inversion. Finite-difference schemes yield high efficiency but fail to ensure the accuracy of the high wavenumber components. The pseudo-spectral algorithm is accurate up to the Nyquist frequency, and it is efficient because of the high level optimization of the fast Fourier transform (FFT) algorithm. The calculation of derivatives in elastic wave propagation could employ the success of FFT optimization. A conventional spectral method consists of three procedures: a forward real to complex (R2C) FFT, a multiplication of the derivative term, such as a for first derivatives, and a complex to real (C2R) inverse FFT. For any even number, the R2C FFT is actually utilizing a half-sized C2C FFT, and then a further spectral manipulation is employed to obtain the spectrum. We propose an efficient scheme to calculate the derivatives for elastic wave propagation in which we apply a forward C2C FFT, and then multiply it with a set of coefficients, and finally a C2C inverse FFT is applied to complete the calculations. With such scheme, a 30% of efficiency has been achieved. In the end, we demonstrate the accuracy and efficiency on a seismic imaging project.

Fixed-point arithmetic is used to provide faster and smaller implementations in many digital signal processing applications, including medical imaging, at the expense of decreased accuracy. In particular, when a Fast Fourier Transform (FFT)-Inverse Fast Fourier Transform (IFFT) pair are required as part of the calculation, the error introduced into the calculations can be significant. For some applications, such as Fourier Domain Optical Coherence Tomography (FD-OCT), this degradation is unacceptable. Our study shows that using a conventional fixed-point FFT-IFFT pair, such as Xilinx's FFT core, can produce an average 6-bit error for a 1024-point FFT using 12-bit input data in a 32-bit arithmetic system. The majority of the error is caused by quantization effects, particularly on the phase information of input signal. For this reason, in phase sensitive applications such as FD-OCT, the error dominates the fixed-point calculation: 78% in 16-bit and 51% in 32-bit systems. This work presents a parameterized 32 to 4096-point integer FFT implementation for FPGAs that uses a Split-Radix algorithm to reduce the number of multiplies and improve latency. Integer FFTs are perfectly reconstructible, with zero reconstruction error. Here, we specifically analyze a 1024-point Integer Split-Radix FFT (Int-SRFFT) and IFFT pair that perfectly reconstructs the original 12-bit input data using 22-bit arithmetic, compared to the average 6-bit error for a 1024-point FFT using 32-bit fixed-point arithmetic. The pipelined architecture of this design has a latency of 29.06us for a 1024-point FFT, and a throughput of more than 34 thousand 1024-point FFTs/second for a 22-bit datapath at an operating frequency of 274MHz. Although our Int-SRFFT is perfectly reconstructible, compared to Xilinx's fixed-point FFT, it has ~6% more flipflops, ~63% more LUTs, 5.3x more BRAMs, and a ~44% increase in latency. However, compared to a previous fixed-point SRFFT design on an FPGA, our throughput is 15.5x greater.

Optical Orthogonal Frequency Division Multiplexing (O-OFDM) is now used by a number of researchers because it provides major advantages in mitigating Group-Velocity Dispersion (GVD) in Single Mode Fiber (SMF). Unfortunately, when the uncompensated long-haul transmission ranges become very large, substantial dispersion is accumulated. Due to the large accumulated dispersion, the Cyclic Prefix (CP) duration will occupy a substantial fraction of the OFDM frame. This effect sets some limitations on the overall throughput and the spectral efficiency. Moreover, the transmission is inefficient because of the energy wastage contained within the CP. In the case where the Channel Impulse Response (CIR) is larger than the CP, the system performance is limited by the Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI). In this paper, we propose a Least Mean Square Time Domain Equalizer (LMS-TEQ) immediately after the channel. It can cancel the residual ISI and ICI caused by both the GVD and the CP length being shorter than the CIR.

Discrete multitone modulation allows for a simple receiver structure if the impulse response of the communication channel is shorter than the cyclic prefix. In ADSL, a time-domain equalizer (TEQ) is used to fulfil this requirement. Without a TEQ, unwanted intercarrier interference (ICI) and intersymbol interference (ISI) occur. In this paper, quadratic forms are developed to calculate the contributions of ICI and ISI to the desired signal. Based on these expressions, a new method for calculating the TEQ coefficients, which minimizes the effects of ICI, ISI, and additive noise, is derived. Simulations in the context of ADSL compare the performance of this new algorithm with one that is state of the art.

Recent research presents a technique to enumerate all valid assignments of “twiddle factors” for power-of-two fast Fourier transform (FFT) flow graphs. Brute-force search employing state-of-the-art Boolean satisfiability (SAT) solvers can then be used to find FFT algorithms within this large solution space which have desirable characteristics. Surprisingly, this approach has discovered FFT algorithms requiring fewer operations than the split-radix algorithm even when all twiddle factors are nth roots of unity. This paper reviews and then extends this prior research to examine fast discrete convolution algorithms when implemented via FFT and inverse FFT (IFFT) algorithms. In particular, we find that the combination of FFT and IFFT algorithms in fast convolution permits greater freedom when selecting valid twiddle factor assignments. We exploit this freedom and use SAT solvers to find new fast convolution algorithms with the lowest operation counts known.