Extended reach OFDM-PON using super-Nyquist image induced aliasing.

We experimentally demonstrate the transmission of multi-order quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) millimeter wave signals at D-band. Meanwhile, the system nonlinearity analysis is also given, which is originated from the unsatisfactory optoelectronic devices, multi-order QAM and the high peak-to-average power ratio (PAPR) of OFDM signal. To alleviate the system nonlinearity, Volterra nonlinearity compensation (VNC) is adopted. Probabilistic shaping (PS) has been regarded as an effective approach to ensure the system robustness. By using the technologies of probabilistic shaping and Volterra nonlinearity compensation, 57.21-Gbit/s 4096-QAM OFDM signal at 117 GHz can be delivered over 13.42-m wireless distance in our experiment, achieving the normalized general mutual information (NGMI) threshold of 0.83 with 25% soft-decision forward-error correction (SD-FEC) overhead. In addition, we simulated the D-band millimeter wave simulation system in VPI software. The NGMI performance between conventional and discrete Fourier transform-spread (DFT-S) 16-QAM OFDM has been compared in simulation at the same optical signal-to-noise ratio (OSNR). The case of conventional 16-QAM OFDM has better performance. To the best of our knowledge, this is the first demonstration of transmission of multi-order QAM OFDM millimeter wave signal at D-band using PS and VNC methods.

Orthogonal frequency division multiplexing (OFDM) signals have a generic problem of high peak to average power ratio (PAPR) which is defined as the ratio of the peak power to the average power of the OFDM signal. The drawback of the high PAPR is that the dynamic range of the power amplifiers (PA) & digital-to-analog (D/A) converters required during the transmission and reception of the signal is higher. As a result, the total cost of the transceiver increases, with reduced efficiency. This paper includes an idea of the PAPR constraint, along with the implementation and analysis of some specific algorithms for PAPR reduction of the OFDM signals. All the PAPR reduction algorithms are implemented and tested in the OFDM transceiver designed using Matlab. Analyzing some specific algorithms, we propose a novel algorithm by combining the subcarrier phase adjustment and linear combination of the time domain OFDM signals. Simulation results for a OFDM system employing Quadrature Amplitude Shift Keying (QASK) symbols and Quadrature Amplitude Modulation (QAM) can achieve a PAPR reduction of 5 dB.

Multicarrier modulation technique also known as Orthogonal Frequency Division Multiplexing (OFDM) is considered to be the most rapidly growing technique for 4th Generation wireless communication system. Due to its high speed data rate and its ability of multipath fading channel robustness. OFDM becomes an attractive technique and it is widely adopted in many wireless communications system. OFDM signal carries its major drawback of high Peak to Average Power Ratio (PAPR) problem. Out of band radiation and in band distortion produced due to its high PAPR. Mobile phone communication suffer severe drawback during its amplification. When OFDM employed a non linear Power Amplifier (PA), it produces the fluctuation in amplitude of OFDM signal. This paper discusses the method to overcome PAPR in terms of its performance by using improved clipping technique for PAPR reduction. This method is easy to implement and reduces the amount of PAPR by clipping the peak of the maximum power signal. We present an improved method for PARR reduction for reducing peak magnitude of OFDM signal. This scheme simultaneously minimizes the peak magnitude of PAPR in OFDM signal.

Integration system of photon-assisted W-band millimeter wave wireless communication and free space optical communication based on OFDM signal transmission

Orthogonal frequency division multiplexing (OFDM) is an attractive and effective technique for wireless communications. However, an OFDM signal has a large peak-to-average power ratio (PAPR), which will cause serious nonlinear distortion especially when the signal passes through a nonlinear system. Adaptive symbol selection scheme (ASSS) is used to reduce the unwanted PAPR by selecting the adaptive OFDM signal with the smallest PAPR before transmitting. Because of the side information needed in ASSS, the effective data rate finally got in the receiver decreases. We develop a new modulation method using ASSS and channel estimation together, which can transmit the needed side information in the pilot tones made by channel estimation during the signal transmission. Our simulation results show that the method we proposed is a promising and valuable technique for reducing PAPR in OFDM signals.

A definition of least cyclostationary order (LCO) is proposed based on the inner cyclic period of single carrier and orthogonal frequency division multiplexing (OFDM) signals. The LCOs of single carrier and OFDM signals are derived. Since the LCO has a relationship with the carrier frequency offset (CFO), a blind CFO estimation scheme for single carrier and OFDM signals can be proposed. The novel scheme is entirely blind without any priori information and is proved to be the same as cumulants estimation when the LCO is known. However, the new scheme is superior to the estimation based on cumulant when the LCO is unknown. The mean-square error of M-phase shift keying signals approaches the Cramer–Rao bound in additive white Gaussian noise (AWGN) channel. Simulation results are given to verify the effectiveness of the proposed blind estimation scheme in Rician fading channel and in AWGN channel.

Recently many researchers have turned their interests to Orthogonal Frequency Division Multiplexing (OFDM) signal since its promising features in radar. This paper concerns a novel Synthetic Aperture Radar (SAR) system which employs this OFDM signal. Though the OFDM will bring lots of advantages, the performance may be changed since the signal of SAR is different from conventional ones. To evaluate the change, this paper will give a theoretical analysis and the corresponding simulation results from the viewpoint of ambiguity function. This ambiguity function is equivalent to the role of Point Spread Function (PSF) which is often used in SAR for evaluating resolutions. Comparing to the conventional SAR with LFM signal, it is proved that the resolution of SAR based on OFDM is equivalent to the conventional one or even better. This ambiguity function also provides a principle for selecting various OFDM signals as the transmit signal of SAR.

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique that has been widely applied in wireless broadband communications such as the fourth-generation (4G) and supports the development of the fifth-generation (5G) technology because it is efficient and effective. However, OFDM has a high Peak to Average Power Ratio (PAPR) value where the system must use a Power Amplifier (PA) with a high linear range so that the signal can work on PA. Whereas, PA is a nonlinear component that has limited linear region according to the component specifications. If an OFDM signal with high PAPR passes through the nonlinear region of PA, the signal will be distorted nonlinearly and ultimately worsen the OFDM performance. Although many researchers are interested in studying this issue, several scenarios are still not explored. This work investigates a way to mitigate nonlinear distortion by a combination of PAPR reduction and PA linearization with predistortion. Memory-Hammerstein has been suggested as a model for predistorter and PA. The input of the predistorter is the PAPR reduced signal with companding technique, which is a simple and effective PAPR reduction technique for OFDM. The system performance will be evaluated using signal spectrum, PAPR, and Bit Error Rate (BER). The simulation results obtained are that the performance drops dramatically to more than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> for the BER value when a nonlinear disturbance is given and the performance improves after a predistorter is applied. The combination of hybrid companding and predistorter offers better performance, it can reduce PAPR and compensating for nonlinear distortions caused by the PA. Hence, this combined scheme can be considered and adopted in future wireless communications systems including 5G.

We propose a power-efficient method for transmitting multiple frequency-division multiplexed (FDM) orthogonal frequency-division multiplexing (OFDM) signals in intensity-modulation direct-detection (IM-DD) optical systems. This method is based on quadratic soft clipping in combination with odd-only channel mapping. We show, both analytically and experimentally, that the proposed approach is capable of improving the power efficiency by about 3 dB as compared to conventional FDM OFDM signals under practical bias conditions, making it a viable solution in applications such as optical fiber-wireless integrated systems where both IM-DD optical transmission and OFDM signaling are important.

Clipping is an efficient and simple method to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. However, clipping causes distortion and out-of-band radiation. In this letter, a novel iterative receiver is proposed to estimate and cancel the distortion caused by clipping noise. The proposed method is applied to clipped and filtered OFDM signals. It is shown by simulation that for an IEEE 802.11a typical scenario the system performance can be restored to within 1 dB of the nonclipped case with only moderate complexity increase and with no bandwidth expansion.

Orthogonal Frequency Division Multiplexing (OFDM) is an attractive technique for wireless communications applications. However, one of the main disadvantages of OFDM is its high Peak to Average Power Ratio (PAPR) that limits transmitter power efficiency. Without any measures, the OFDM signal is limited by the power amplifier (in the transmitter) what causes interference both on the signal itself and in adjacent frequency bands. In this paper we formulate the reduction of the PAPR problem as a Second Order Cone Programming problem (convex optimization). We extend two known methods by choosing unused carriers in standards to minimize PAPR. The results are presented for the 802.11a standard. The proposed method induces no in-band distortion and stay compatible towards the IEEE 802.11a spectrum masking. Moreover, they don't need any side information and can be applied for real or complex OFDM baseband.

Orthogonal Frequency Division Multiplexing (OFDM) has several desirable attributes, such as high immunity to inter-symbol interference, robustness with respect to multi-path fading, and ability for high data rates, all of which are making OFDM to be incorporated in wireless standards like IEEE 802.11a/g/n WLAN and ETSI terrestrial broadcasting. However one of the major problems posed by OFDM is its high Peak-to-Average-Power Ratio (PAPR), which seriously limits the power efficiency of the transmitter’s High Power Amplifier (HPA). This is because PAPR forces the HPA to operate beyond its linear range with a consequent nonlinear distortion in the transmitted signal. One of good solutions to mitigate this nonlinear distortion is put a Pre-Distorter before the High Power Amplifier and increase linear dynamic range up to a saturation region (1) (2) (3). However, the main disadvantage of Pre-Distorter technique is that these PD techniques only work in a limited range, that is, up to the saturation region of the amplifier. In this situation, Peak-to-Average Power Ratio (PAPR) reduction techniques which pull down high PAPR of OFDM signal to an acceptable range can be a good complementary solution. Due to practical importance of this, there are various PAPR reduction techniques for OFDM signals (4) (5) (6) (7) (8) (9). Among them, the PTS (Partial Transmit Sequence) technique is very promising because it does not give rise to any signal distortion (9). However, its high complexity makes it difficult to use in a practical system. To solve the complexity problem of the PTS technique, Cimini and Sollenberger proposed an iterative flipping algorithm (10). Even though the iterative flipping algorithm greatly reduces the complexity of the PTS technique, there is still some performance gap between the ordinary PTS and the iterative flipping algorithm. In this chapter, we propose an enhanced version of the iterative flipping algorithm to reduce the performance gap between the iterative flipping algorithm and the ordinary PTS technique. In the proposed algorithm, there is an adjustable parameter to allow a performance/complexity trade-off.

This paper presents an analysis of amplitude distortions happening in an orthogonal frequency division multiplexing (OFDM) signal at communication receivers. It is shown in this paper that the amplitude distortion causes inter-carrier interference (ICI) in an OFDM system. Simple but efficient solutions are proposed for combating different amplitude distortions and subsequent ICI cancellation. Simulation results in typical urban channel and Gaussian channel show that extra gains are obtained by introducing these techniques into an existing OFDM receiver system.

This paper studies different coarse positioning techniques for wireless networks using orthogonal frequency division multiplexing (OFDM) signals. The methods under study are based on timing synchronization algorithms and various preambles embedded in the OFDM signal. Also correlation-based approaches and Multiple Signal Classification (MUSIC) approaches are investigated. The performance of the studied estimation algorithms is analyzed in terms of root mean square error (RMSE), obtained from computer simulation results and the aim is to provide a detailed comparison of various OFDM preamble-based timing estimators.

In this paper, a linear moving average recursive filtering technique is proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing (OFDM) signals. The proposed low complexity technique is analyzed in an oversampled OFDM system and a simple distribution approximation of the oversampled and linearly filtered OFDM signals is also proposed. Corresponding time domain linear equalizers are developed to recover originally transmitted data symbols. Through extensive computer simulations, effects of the new filtering technique on the oversampled OFDM peak-to-average power ratio (PAR), power spectral density (PSD) and corresponding linear equalizers on the frequency selective Rayleigh fading channel transmission symbol-error-rate (SER) performance are investigated. The newly proposed recursive filtering scheme results in attractive PAR reduction, requires no extra fast Fourier transform/inverse fast Fourier transform (FFT/IFFT) operations, refrains from transmitting any side information, and reduces out-of-band radiation. Also, corresponding linear receivers are shown to perform very close to their frequency domain counterparts.