Carrier Recovery Method Research Articles

Efficient carrier-recovery method for simple self-referenced continuous-variable quantum key distribution with a long-short-term memory network

Efficient carrier-recovery method for simple self-referenced continuous-variable quantum key distribution with a long-short-term memory network

Enhanced frame synchronization and carrier recovery in coherent FSO communication: a pseudo-random and cyclic QPSK approach.

To alleviate the impact of atmospheric turbulence on receiver carrier recovery in free-space optical communication, this study introduces a novel frame synchronization and carrier recovery method. This method employs a blend of pseudorandom sequences and specific cyclic quadrature phase shift keying (QPSK) training sequences, facilitating frame synchronization and frequency offset (FO) estimation. The research designs a time-series metric curve to counteract the effect of side peaks, enhancing the accuracy of frequency offset estimation via QPSK spectrum features. Furthermore, the method incorporates a two-stage frequency offset estimation process, utilizing the inherent sign characteristics of the x and y polarization states. Applied to the quadrature amplitude modulation system under atmospheric turbulence conditions, the proposed algorithm demonstrates high precision under both strong and weak turbulence conditions. Furthermore, we confirmed the universality of the algorithm across multiple modulation formats.

Design of feedforward master–slave carrier phase recovery in frequency comb-based superchannel coherent transmission systems with nonlinear phase noise

Master–slave common carrier phase recovery (MS-CCPR) is a method for reducing computational complexity of the phase recovery in multi-channel systems where the channels have correlated phase noise. However, these systems will suffer performance penalties if there are phase-noise differences between the channels. Since MS-CCPR schemes rely on phases of the subchannels being same, the intra-channel phase-drift will inevitably influence the design and performance of such schemes. In addition, fiber nonlinearities may introduce further different phase perturbations on the subchannels of a superchannel. This paper presents a master–slave carrier recovery method with compensation of the phase-noise differences based on the blind phase search method for optical frequency comb-based WDM systems. Specifically, we investigated in details using simulations, for the first time, the impact of this phase-noise differences on the performance of master–slave scheme in long-haul transmission systems with laser and nonlinear phase noise effects. In the MS-CCPR strategy used, the slave subchannels are preprocessed with the master–slave scheme, then a low-complexity slave phase-tracker is used to correct the phase-noise differences remaining on them. The concept has been numerically verified in simulations for square 16-QAM format, where the BER limit for soft-decision FEC could still be achieved in a link of 3000 km.

Twin-SSB-OFDM Transmission Over Heterodyne W-Band Fiber-Wireless System With Real-Time Implementable Blind Carrier Recovery

We experimentally demonstrate a heterodyne W-band fiber-wireless system using a twin single-side-band orthogonal frequency division multiplexing (Twin-SSB-OFDM) transmission scheme with low-cost electrical filters. The transmission scheme is proposed to halve the required sampling rate of the baseband receiver. Moreover, since the W-band signal generation is based on optical heterodyne with nonideal laser sources, there is a time-varying carrier frequency offset (CFO) in the system. To mitigate the CFO effect and simultaneously realize down-conversion, a blind carrier recovery method is proposed and validated in the system. The experimental results show that after 22-km SSMF transmission and 1-m wireless transmission, the system can achieve a 40.07 Gb/s data rate with a bit-error-ratio (BER) below 3.8 × 10−3 when using a two-channel 12-GSa/s arbitrary waveform generator (AWG) as transmitter and two emulated 12-GSa/s baseband receivers. In addition, by setting the AWG at 5-GSa/s and using a 5-GSa/s real-time field programmable gate array (FPGA)-based receiver, an additional experiment is carried out by implementing the proposed method in the real-time receiver. Although the frequency swing of the intermediate frequency (IF) carrier of the received signal is up to ∼300 MHz, the system can also achieve a relatively stable transmission performance. The additional experiment further verifies the effectiveness and practical feasibility of the proposed carrier recovery method and the Twin-SSB-OFDM transmission scheme.

A 15-Gb/s 8-PSK Demodulator With Comparator-Based Carrier Synchronization

In this paper, a novel 8-phase-shift-keying (8-PSK) carrier recovery and demodulation method using a comparator and frequency divider is proposed. A proof-of-concept 8-PSK demodulator for high-data-rate millimeter-wave communication systems is designed and tested, which can support 8-PSK transmission up to 15 Gb/s with a bit error rate less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> .

Moving Target Detection and Doppler Extraction Using Digital Spread Spectrum Radar

In this paper, we discuss a Spread Spectrum based radar system for car detection in the road and autonomous guidance of vehicles. An autonomous intelligent vehicle has to perform a number of functionalities. Segmentation of the road, determining the boundaries to drive in and recognizing the vehicles and obstacles around are the main tasks for vision guided vehicle navigation. In this article we propose a set of algorithms which lead to the solution of road and vehicle collision using carrier recovery method from car velocity using DSSS RADAR. In such a spread spectrum system, the transmitted signal is spread over a larger bandwidth, which is much wider than the minimum bandwidth required to transmit the information. Automotive radar systems can take advantage of spread spectrum techniques because of their interference rejection, immunity from noise and multipath distortion, and high resolution ranging properties. In addition, there is no need for high-speed, fast-settling frequency synthesizers. Moreover, spread spectrum techniques can improve the reliability of automotive radars. The data from different sensors on different cars can be combined in order to observe the complete car environment. Thus a spread spectrum radar system will allow sharing the same bandwidth also for data link needed by car-to- car communication systems. The algorithm described here is to recover Doppler frequency using 2P power method from which we are able to detect the vehicle condition in road.

Simple Carrier Recovery Approach for RF-Pilot-Assisted PDM-CO-OFDM Systems

For RF-pilot-assisted PDM-CO-OFDM systems, we propose and demonstrate a carrier recovery method applying a simple moving average filter (MAF) to extract the central RF-pilot for phase noise compensation. Because only two additions per output sample would be required to implement such a MAF, its computational complexity is rather simple compared to any other direct-form finite impulse response (FIR) filter. To handle its weak side-lobe attenuation, which would cause the spectrally nearby OFDM signal to interfere with the extracted pilot signal, we further propose using multiple MAFs in cascade to enhance the side-lobe attenuation. We evaluate the performance of a 16-QAM and 40-Gbps PDM-CO-OFDM signal, in terms of the bandwidth tolerance, optical signal to noise ratio (OSNR) tolerance, nonlinear tolerance, linewidth tolerance, and residual carrier frequency offset (RFO) tolerance, with different filters including the simple MAF, cascaded MAFs, and the previously-demonstrated multi-stage decimation and interpolation filter (MDIF). We've found that 1) all the filters exhibit similar performance to the ideal brick-wall filter in terms of noise and nonlinear tolerances, 2) the MAF1 exhibits the worse tolerances against linewidth and RFO, and 3) the MDIF has to be carefully designed to enhance its tolerances against both the linewidth and RFO.

A Novel Code-Aided Carrier Recovery Algorithm for Coded Systems

We present a novel code-aided carrier recovery method for low-density parity-check (LDPC) coded systems, which comprises two supporting algorithms: 1) a coarse synchronization by maximizing a cost function, the mean absolute value of the soft outputs of the LDPC decoder, followed by a simple interpolation operation to improve the estimation accuracy and 2) a fine synchronization based on the soft decisions produced by the LDPC decoder. With moderate computational complexity, this proposed algorithm is designed to synchronize signals with large carrier frequency offset and phase offset at low signal-to-noise ratio (SNR). When applied to the case of an 8-PSK system with (1944,972) LDPC code, the performance loss compared to the case of ideal synchronization is negligible.

Initial-Estimation-Based Adaptive Carrier Recovery Scheme for DVB-S2 System

A data-aided (DA) carrier recovery (CR) method, which can select different coarse frequency estimation (CFE) paths adaptively according to the initial-estimation of frequency offset, is proposed for the 2nd Generation Digital Video Broadcasting Satellite (DVB-S2) system to accomplish the convergence within at most 400 pilot blocks. The well-known two-step CR scheme is used for the consideration of precision and speed, whereas both the CFE and the fine frequency estimation (FFE) adopt L&R algorithm as their basic frequency estimator so that the same correlation operation can be used by both of them to decrease the realization complexity. Optimum threshold values for different CFE paths are determined by analyzing the ill-selection probability and robust Root Mean Square Error (RMSE) performance has been confirmed by our simulations.

Feed-Forward Optical Carrier Recovery for QAM Coherent Optical Receivers

We numerically investigate a feed-forward optical carrier recovery method for quadrature amplitude modulation (QAM) signals, which includes fast Fourier transformation (FFT) method for carrier frequency estimation (CFE) and blind phase search (BPS) algorithm for carrier phase estimation (CPE), respectively. Simulation results for 16- and 64-QAM systems verify the good performance of this carrier recovery method. For 10 Gbaud 16- and 64-QAM systems, any frequency offset between −1.25 and 1.25 GHz can be estimated using FFT method with maximum errors of several MHz. Through further CPE by BPS algorithm, the optical signal to noise ratio (OSNR) penalties at BER of 1·10−3 for 16-QAM system with linewidth times symbol period product of 2·10−4 and for 64-QAM system with linewidth times symbol period product of 5·10−5 are 1.2 and 1.1 dB, respectively.

A Robust and Adaptive Carrier Recovery Method for Chinese DTTB Receiver

This paper presents a robust and adaptive carrier recovery method for Chinese digital terrestrial television broadcasting (DTTB) system in which pilot signal and pseudonoise (PN) sequence are adopted to help carrier recovery. The conventional methods utilize pilot or PN sequence respectively. In this paper, we try to combine the advantage of each method together and propose a well designed state machine to control system state automatically. Moreover, as for using PN sequence, a fine PN tracking state is introduced to ensure the robustness of the proposed method. Software simulations show that the proposed method can provide large acquisition range, short acquisition time and small tracking jitter in severely distorted static and dynamic channels. Lab tests and field trials also prove its good performance in real propagation environments.

An ultra-fast carrier recovery versus traditional synchronizers

A new ultra fast carrier recovery (CR) method based on adaptive phase tracking (APT) and frequency control (FC) is disclosed for a large class of digitally modulated system. The new digital signal processing (DSP) based methodology is demonstrated by hardware experiment for coherent demodulation. In addition, our comparative study with more conventional synchronization techniques indicate that the synchronization speed of our APT is reduced from the present state of the art (20 bits) to 4 bits. The tremendous synchronization advantage combined with robust error rate performance leads to increased spectral efficiency, power efficiency and larger capacity.