Pilot Tones Research Articles

An efficient technique based on firefly algorithm for pilot design process in OFDM-IDMA systems

Accurate placement of pilot tones has been a crucial task in multicarrier transmission technologies since there is a strong relation between pilot positions and channel estimation performance. Therefore, the firefly algorithm (FA) is proposed for achieving the optimal pilot distribution by optimizing the pilot positions in order to minimize the estimation errors of the least squares algorithm employed in orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems. According to the simulation results, our proposed FA-based pilot optimizer provides a great performance increase in OFDM-IDMA systems by obtaining the most appropriate pilot distribution pattern among the considered pilot placement strategies. The upper bound of mean square error (MSE) is used as the fitness function in the optimization process for avoiding the matrix inversion operation that is needed when calculating MSE itself.

10 Tb/s PM-64QAM Self-Homodyne Comb-Based Superchannel Transmission With 4% Shared Pilot Tone Overhead

We demonstrate transmission of a comb-based 10 Tb/s 50 $\times$ 20 Gbaud PM-64QAM superchannel using frequency comb regeneration to reduce carrier offsets and allow for self-homodyne detection. The regeneration is enabled by transmitting two optical pilot tones which are filtered and recovered in the receiver using optical injection locking and an electrical phase-locked loop. We show that by utilizing frequency combs together with optical pilot tones, self-homodyne detection similar to systems using one pilot tone per wavelength channel, can be achieved. Sharing the overhead for pilot tones reduces the complexity and limits the overhead to 4%. This enabled a total superchannel spectral efficiency of 7.7 b/s/Hz. To evaluate the performance, we perform both back-to-back measurements and transmission over 80 km of standard single-mode fiber. Successful self-homodyne detection of all 50 data channels in the 10-nm-wide superchannel demonstrates that the spectral coherence from frequency combs, combined with the use of optical pilots, can overcome limitations arising from frequency offset and phase noise in high-order QAM transmission while keeping the pilot overhead low.

Photonic Microwave Frequency Measurement Based on Frequency-Configurable Pilot Tones

A photonic technique for microwave frequency measurement with flexible range and high resolution is proposed based on frequency-configurable pilot tones. The method extracts the remote unknown microwave frequency by measuring electrical power at two known pilot frequencies, avoiding dual-channel photodetection and broadband microwave power measurement over the whole interested frequency range. Moreover, it enables flexible measurement range by configuring two pilot frequencies. A proof-of-concept experiment is successfully demonstrated with the frequency range of 6–18.9 GHz and the resolution of 0.1 GHz.

Pilot tones design using particle swarm optimization for OFDM–IDMA system

Since the channel estimation performance is directly affected by the pilot positions, it has been a major task in multicarrier transmission schemes to adjust the pattern of pilot distribution for the purpose of minimizing the estimation errors. Therefore, in this paper, we utilize particle swarm optimization (PSO) algorithm for pilot design process in orthogonal frequency division multiplexing–interleave division multiple access (OFDM–IDMA) system. The main contributions of the paper are: (1) increasing the performance of least squares (LS) algorithm used for channel estimation in OFDM–IDMA system by optimizing the pilot positions using PSO algorithm, (2) instead of using MSE itself in which the matrix inversion process is required as the fitness function of PSO, using the upper bound of mean square error (MSE) in order to decrease the system complexity, (3) using two types of channel models known as COST 207 Rural Area and COST 207 Typical Urban in the simulations to be able to support the reliability and stability of the proposed method in different conditions. In the simulations, it is observed from the bit error rate (BER) and MSE graphs that optimizing the placement of pilot tones using our proposed method demonstrates a superior performance compared to the other considered pilot placement strategies by providing a significant increase in the performance of LS algorithm.

High Spectral Efficiency PM-128QAM Comb-Based Superchannel Transmission Enabled by a Single Shared Optical Pilot Tone

We exploit the coherence of frequency combs for high spectral efficiency superchannel transmission via effective sharing of a single pilot tone. By phase-locking the receiver comb to the transmitted pilot tone, carrier offsets are suppressed while both the overhead and complexity associated with the pilot tone are reduced. We form a 55 carrier superchannel using a 25-GHz spaced electro-optic frequency comb seeded by a 100-kHz linewidth laser. At a pilot tone overhead of $ 2%, the reduction in carrier offsets is shown to facilitate blind DSP-based carrier recovery of all 54 $\times$ 24 Gbaud PM-128QAM data channels. The resulting superchannel spectral efficiency is 10.3 bits/s/Hz assuming a 28% overhead for forward error correction. Our results show the potential for optical pilot tones to reduce both overhead and complexity in systems using comb-based superchannels together with high-order modulation formats.

A Blind Side Information Detection Method for Partial Transmitted Sequence Peak-to-Average Power Reduction Scheme in OFDM Underwater Acoustic Communication System

In this paper, we propose a blind side information detection scheme for partial transmitted sequence (PTS) peak-to-average power ratio reduction (PAPR) method in underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) communication systems. The proposed scheme employs a corresponding table between the distributions of pilot tones and the phase rotation candidates to obtain a pseudo-optimum PTS PAPR reduction performance and a dramatic reduction of the total calculation cost. Meanwhile, predefined distributions of pilot tones are used to identify the phase rotation factor combination that has been selected and used at the transmitter. The spectral efficiency and data rate remain unaffected as the proposed PTS technique requires no additional pilot tones except for the tones used for channel estimation. Due to the sparse characteristic of the underwater acoustic channel, compressed sensing is adopted to complete the channel estimation and the phase rotation detection. The basis pursuit denoising algorithm employed here reduces the number of pilot tones as compared with linear channel estimation method. Simulation results show that the proposed scheme has better PAPR reduction performance compared to the conventional PTS scheme and the performance gap increases with the number of subblocks. Simulation and field experimental results demonstrate that the proposed scheme can differentiate the phase rotation factor. Therefore, the quality of the UWA OFDM communication system is significantly enhanced.

ANALISA AUDIO STEREO DECODER UNTUK RADIO PENERIMA FM BERBASIS IC AN7410N

A stereo decoder is enabled to separate information and modulated signal by recovering the previous information signal come as one with the carrier signal using a varying frequency according to the amplitude change value that becomes the same information signal as the original signal or as stereo audio. Inside a stereo audio, there is a component which each functions to get the required signal results in the stereo decoder. The designed stereo decoder uses a single IC; IC AN7410N as a demodulator that is designed to demodulate the signal from the stereo encoder to the L and R audio signals. The result of the test shows that stereo decoder can detect the 19 kHz pilot tone frequency and stereo decoder can also receive FM radio broadcast from the sender and output audio results in the form of stereo L and R, even though the sideband frequency output measurement from each channel L and R, shows the frequency difference (Hz) of expected output frequency.Keywords: audio, stereo, decoder, AN7410N

Channel Estimation for Optical-OFDM-Based Multiuser MISO Visible Light Communication

A least squares-based channel estimation algorithm is proposed for optical orthogonal frequency division multiplexing-based multiuser multiple input single output visible light communications. The pilot sequence and pilot tones are optimized to derive the minimum-mean-square error of the channel estimation. Each user estimates the channel independently, and sends the estimates of the channels to the transmitter. Based on the estimated channels, zero-forcing precoding is applied at the transmitter to achieve the spatial multiplexing gain. The simulated performances of channel estimation and data detection are provided.

Channel Equalization and Phase Noise Compensation Free DAPSK-OFDM Transmission for Coherent PON System

Channel equalization and phase noise compensation are required in coherent optical orthogonal frequency-division multiplexing (CO-OFDM) transmission systems for reliable performance. In general, redundant data such as training symbols and pilot tones are necessary for channel and phase noise estimation in quadrature amplitude modulation (QAM) based CO-OFDM systems, which reduces the spectral efficiency of the system. Especially, in the coherent passive optical network (PON), the redundancy increases as the number of subscribers increases. In this letter, we propose a differential amplitude shift keying (DAPSK)-based CO-OFDM transmission for PON system, which does not require channel equalization and phase noise compensation processes. The proposed DAPSK-based CO-OFDM transmission was experimentally demonstrated, and the performance according to receiver launched power and the number of subcarriers was compared with QAM-based CO-OFDM.

Dynamic wavelet-based pilot allocation algorithm for OFDM-based cognitive radio systems

In a cognitive radio system, the goal is to make better use of the radio electric spectrum, allowing non-licensed users access to those currently unused electromagnetic bands assigned to licensed users (LUs). This can be achieved using OFDM, where the non-licensed users must select the temporarily available subcarriers and turn off those subcarriers used by LUs in order to avoid interference. Hence, only a subset of the subcarriers can be used for data or pilot tone transmission. To this end, some pilot allocation algorithms have been proposed for this dynamic scenario, but they are designed in such away that an equispaced pilot placement is respected (as much as possible) while minimizing the mean squared error of the channel estimate. Nevertheless, this equispaced placement can lead to the use of an increased number of pilots in order to achieve a good channel estimation. In this work, a new pilot allocation algorithm based on wavelet transform is presented. The proposed algorithm uses the discrete wavelet transform to analyze the previous channel state information, taking the knowledge of the available subcarriers into account to provide a suboptimal solution for the pilot positions. This solution leads to a non-equispaced pilot placement, which improves the channel estimation and consequently, the system performance. Likewise, the introduced algorithm allows a reduction of the number of necessary pilots, which aids in increasing the data rate. Finally, simulation results corroborate the effectiveness of the algorithm in dynamic channel scenarios.

26-Gb/s DMT Transmission Using Full $C$ -Band Tunable VCSEL for Converged PONs

Wavelength division multiplex (WDM) passive optical network (PON) is considered for converged fixed mobile broadband access networking. We propose to utilize low-cost tunable lasers at the remote sites, together with a centralized wavelength locker. Practical implementations require a transparently added downstream signaling channel and upstream per-channel pilot tones for channel tagging and remote wavelength control. We demonstrate, for the first time, 26-Gbps discrete multitone transmission modulated on a low-cost wide tunable vertical surface emitting laser over up to 40 km of standard single-mode fiber. The results confirm that converged fixed mobile WDM-PON systems based on low-cost lasers carrying discrete multitone modulation are a technically viable approach.

Analysis of self-homodyne detection for 6-mode fiber with low-modal crosstalk

In this paper, we present an appropriate analysis on self-homodyne coherent system with 56×5×3Gb∕s WDM–PDM–MDM quadrature phase-shift keying (QPSK) signals using 6-mode weakly coupled few mode fiber. The mode division technology can effectively improve the spectral efficiency (SE) of self-homodyne detection. Of all the LP modes, LP01 mode is used to transmit the pilot tone (PT), while the others for signal channels. The influence of inter-mode crosstalk is analyzed. The proposed frequency domain MMA shows a better BER performance for intra-mode crosstalk elimination. The path-length misalignment’s influence caused by mode differential group delay (MDGD) is also investigated. The system tolerance for different laser’s line-width is compared as well as the influence of PT filter’s bandwidth.

Pilot tones design using Grey Wolf Optimizer for OFDM–IDMA system

Since the channel estimation performance is affected directly by the positions of pilot tones, the optimization of pilot placement process known as having quite important role on minimizing the estimation errors has become a significant task for the multicarrier transmission technologies. Therefore, we propose Grey Wolf Optimizer (GWO) for pilot tones optimization to enhance the performance of Least Squares (LS) algorithm employed for channel estimation in Orthogonal Frequency Division Multiplexing – Interleave Division Multiple Access (OFDM–IDMA) system. Besides, the upper bound of Mean Square Error (MSE) which can be derived through Gershgorin disc theorem is used as an objective function of GWO to get rid of computing matrix inversion that is indispensable when computing MSE. In the simulations, our proposed GWO based pilot design method is compared to random, equispaced, Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) based pilot placement strategies in terms of MSE and bit error rate (BER) criteria. The simulation results in which our proposed technique leaves behind the other considered strategies demonstrates that GWO based pilot design method is a promising pilot placement strategy for OFDM–IDMA system because of its high performance and low computational complexity.

Pilot-tone-based self-homodyne detection using optical nonlinear wave mixing.

An all-optical pilot-tone-based self-homodyne detection scheme using nonlinear wave mixing is experimentally demonstrated. Two scenarios are investigated using (1) multiple wavelength-division-multiplexed channels with sufficient power of the pilot tones and (2) a single channel with a low-power pilot tone. The eye diagram and bit error rate of the system are studied by tuning various parameters such as pump power, relative phase, and pilot-to-signal ratio.

Experimental Demonstration of Ultra-Dense WDM-PON With Seven-Core MCF-Enabled Self-Homodyne Coherent Detection

We demonstrate an ultra-dense wavelength-division-multiplexing (UDWDM) passive optical network (PON) in a spatial-division-multiplexing system utilizing our home-made seven-core multicore fiber (MCF) with a self-homodyne coherent detection (SHCD) scheme. In the SHCD system, we transmit 12 channels of 40-Gb/s UDWDM-PON signals using polarization-division-multiplexing quadrature phase-shift keying (PDM-QPSK) with a 12-GHz grid through the six outer cores of the seven-core MCF with the central core used to transmit the pilot tone. An optical frequency comb generator is employed to supply the multi-carriers for cost saving. After 37-km low-crosstalk seven-core MCF long-reach transmission with compact fan-in/fan-out multiplexers, a large transmission capacity of 2.88 Tb/s and a power budget of 26 dB are obtained. At the optical network unit side, a narrow linewidth local oscillator laser is no longer necessary since SHCD is adopted in our system. The complexity of the digital signal processing procedure at the coherent receiver is also greatly reduced as the carrier phase recovery and carrier frequency offset estimation are not needed.

Experimental Analysis of LTE Signals in WDM-PON Managed by Embedded Pilot Tone

Dense deployment of many small cells is one promising solution to cope with mobile traffic increases. However, the deployment needs many optical fibers and network operators require efficient management for these cells. To overcome these issues, we have proposed a WDM-PON system managed by an electrically embedded pilot tone and confirmed its feasibility. In this letter, we compare management methods and clarify 128-kb/s pilot tone parameters that negligibly affect LTE signals transported by CPRI option seven experimentally. The results show that the modulation index as high as 20% and carrier frequency as high as 5 MHz are suitable under 1.0-dB optical power penalty.

A novel algorithm to mitigate the effect of clipping in orthogonal frequency division multiplexing underwater communication acoustic sensor system

Distinctive features of underwater communication channel pose significant challenges to effective underwater acoustic communication. Due to bandwidth limitation, orthogonal frequency division multiplexing is widely used for its high spectrum efficiency. However, orthogonal frequency division multiplexing also has its shortcomings, one of which is the relatively high peak-to-average power ratio, which leads to saturation in the power amplifier and consequent distortion of the signal. Clipping is the most commonly used method to address the high peak-to-average power ratio; however, it introduces additional noise resulting in degradation of the system’s performance. This article proposes a compressed sensing technique for mitigation of the clipping noise, which exploits pilot and data tones instead of reserved tones, thus making it distinct from the previous works and improves data rate. Moreover, in contrast with previous works, the channel is also estimated using compressed sensing technique, which provides more accurate channel characteristics for estimating the clipping noise than traditional methods like least square or minimum mean squared error. The better performance of the proposed Iterative compressed sensing algorithm is proved in simulations as well as in a pool experiment using acoustic wave sensors.

Frequency Acquisition Algorithm for DRM Receiver

In this paper we propose a frequency acquisition algorithm for DRM receiver . Given the parameters of the DRM system and the properties of PC hardware, the requirements for the frequency acquisition are analyzed. Following these requirements an acquisition algorithm using the FFT based on pilot is proposed. This algorithms utilize the continuous frequency correction pilot tones in the DRM signal. Simulation results on different fading channels show that the synchronization scheme suits our needs.

Self-coherent phase reference sharing for continuous-variable quantum key distribution

Generating "locally" the local oscillator is a fundamental requirement for continous-variable quantum key distribution (CV-QKD), both for performance and security reasons. As a consequence, next-generation CV- QKD systems will have to be implemented with a local local oscillator (LLO). This issue has been explicitly tackled in recent works, where the proposed and implemented approach, that we call LLO-sequential, consists in sequentially (temporally) multiplexing quantum signal optical pulses with phase reference pilot tones optical pulses. We develop a comprehensive analysis of the noise model and the hardware requirements in order to perform LLO CV-QKD. This analysis allows to quantitatively understand one of the limits of CV-QKD implemented with the LLO-sequential approach: such systems, unless operated at very high speed, have very strong requirements in terms of tolerable laser phase noise. LLO-sequential CV-QKD can thus in practice only be implemented with expensive, low phase noise lasers, such as ECL lasers. The main contribution of this work is to introduce designs for LLO CV-QKD based on self-coherence phase sharing, in which the phase reference information and the quantum information are coherently obtained from a single optical wavefront. We propose in particular a design, called LLO-displacement, where the phase reference information is encoded in the displacement of the standard CV-QKD Gaussian modulated coherent state (GMCS) protocol. We analyze the performance and the hardware requirements of the LLO-displacement design and our results indicate that it can be used to perform CV-QKD over distances up to 100 km with realistic and affordable hardware, in particular with standard telecom equipment and low cost DFB lasers. This opens a practical path towards the development of coherent quantum communications systems compatible with next-generation networks requirements.

Channel estimation using an adaptive neuro fuzzy inference system in the OFDM-IDMA system

In this paper, a channel estimator based on an adaptive neuro fuzzy inference system (ANFIS) is proposed for the purpose of estimating channel frequency responses in orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems. To see the performance of our proposed channel estimation method, five different techniques including well-known pilot-based estimation algorithms such as least squares (LS) and minimum mean square error (MMSE) with other heuristic methods like multilayered perceptron (MLP) trained by a backpropagation (BP) algorithm (MLP-BP), MLP trained by the Levenberg--Marquardt (LM) algorithm (MLP-LM), and radial basis function neural network (RBFNN) are compared with our proposed method by computer simulations. The comparisons are made with the aid of bit error rate and mean square error graphs. According to the simulation results, our proposed channel estimator based on ANFIS shows better performance than both the LS algorithm and the other considered heuristic methods like MLP-BP, MLP-LM, and RBFNN, whereas the MMSE algorithm still shows the best performance as expected because of exploiting channel statistics and noise information, which makes it very complex to be used in any system. As well as being less complex compared to the MMSE algorithm, the estimator based on ANFIS does not need pilot tones for channel estimation. These properties bring our proposed method to an advantageous position among the other estimation techniques.