Beat Noise Suppression Research Articles

Beat Noise Suppression Using Adaptive Line Enhancers for FM Radio in Motor Vehicles

There exists interference in a frequency modulation (FM) radio wave in a motor vehicle. The interference is called as a beat noise which is an electromagnetic radiation caused from electronic devices equipped on the motor vehicle. The beat noise becomes a perceptual sinusoidal noise and/or breaks a spectral structure of a broadcasting sound. It is required to suppress the beat noise by using a low cost device such as a DSP with a low-clock frequency. This paper proposes a noise suppressor employing two adaptive line enhancers as a promising method to be implementable on a DSP with low-clock frequency. We apply the proposed noise suppressor to signals obtained in the middle of the demodulation process. Simulation results show that the proposed method effectively suppresses the beat noise and extracts the broadcasting sound with high accuracy.

Variable-frequency lock-in detection for the suppression of beat noise in Brillouin optical correlation domain analysis

We propose and experimentally demonstrate a novel lock-in detection method to avoid a beat noise in Brillouin optical correlation domain analysis (BOCDA) which appears in the sweep of the sensing position and deteriorates the measurement accuracy by distorting the acquired Brillouin gain spectrum. In our analysis, the origin of the beat noise is shown to be the fluctuation of the Brillouin gain induced by the chopping of the intensity-modulated pump wave, and the optimal relation between the modulation and the lock-in frequencies is developed as an effective solution to circumvent the beat noise.

A novel beat-noise-reducing en/decoding technology for a coherent 2-D OCDMA system

A novel fiber Bragg grating (FBG)-based en/decoder for a coherent two-dimensional (2-D) wavelength-time (WT) optical code-division multiple-access (OCDMA) system is proposed to suppress the beat noise (BN). The feasibility of en/decoding function and the effectiveness of BN suppression are demonstrated by the simulation comparison between the conventional and proposed scheme, which are also further validated by en/decoding experiments with two users at a data rate of 2.5, 5 and 10 Gb/s respectively. The further numerical performance analysis of the proposed en/decoding method reveals the BER improvement compared with the conventional system.

Reducing the backreflection impact by using homodyne detection in WDM single-fiber loopback access networks

This paper uses homodyne detection to reduce the impact of backreflections in wavelength division multiplexing (WDM) single-fiber loopback access networks. We present the principle of our beat noise suppression scheme and the configuration of upstream signal transmission that enhances the effectiveness of the proposed technique. We also experimentally confirm that beat noises can be eliminated within the signal bandwidth with no significant waveform distortion.

Reconfigurable Multiport Optical Encoder/Decoder With Enhanced Auto-Correlation

A novel planar configuration of a multiport encoder/decoder (E/D) is presented that has enhanced performance in terms of beat-noise suppression and network confidentiality. We insert a splitter and a set of phase shifters in front of a standard arrayed-waveguide-grating-based multiport E/D to generate spectral-phase codes. The new configuration keeps the same key features and it is able to generate/process a set of different codes simultaneously; at the same time, the network confidentiality is enhanced, because only the intended receiver, which knows the phase-shifter values, is able to recognize the code. Furthermore, whereas the auto-correlation function of the previous E/D has a triangular shape, in this case it is similar to the input pulse, enhancing the system cascadability and reducing the beat noise.

Noise and Intersymbol-Interference Properties of OTDM and ETDM Receivers

We experimentally and theoretically confirm the similar performance of optical time-division demultiplexing (OTDM) and electrical time-division demultiplexing (ETDM) receivers for beat-noise limited return-to-zero signal detection. OTDM receivers show a slight sensitivity advantage, largely independent of parameters like the receiver's optical filter bandwidth or center frequency. The OTDM sensitivity benefit is caused by reduced intersymbol-interference properties of the OTDM receiver, as well as by the suppression of beat noise by the temporal demultiplexing window. The latter effect can be captured by extended expressions for the beat-noise variances presented in this letter.

Optical beat noise suppression and power equalization in subcarrier multiple access passive optical networks by downstream feedback

This paper describes a cost-effective method of suppressing optical beat noise in subcarrier multiple access passive optical networks. The method is based on initial power equalization followed by automatic fine tuning of laser wavelengths, via downstream feedback control of their mean powers, so that the receiver noise floor level is continuously minimized. Application and performance of the method is demonstrated for a low-cost 16-channel system with uncooled Fabry-Perot lasers, utilizing narrow-band QPSK modulated subcarrier frequencies over more than one octave. In static and dynamic temperature worst-case situations a considerable reduction in the number of transmission errors caused by optical beat noise is observed, depending on the temperature change rate.

Suppression of beat noise from optical amplifiers using coherent receivers

Coherent optical fiber communications have been studied intensively because of their high receiver sensitivity and high-frequency selectivity. With the advent of an erbium-doped fiber amplifier (EDFA), however, the first advantage seems to have become less attractive. Nevertheless, the combination of the EDFA and coherent techniques offers a number of attractive features. In this paper, we show both theoretically and experimentally that the excess beat noises (common-mode and image-band beat noises) from optical amplifiers can be suppressed by using coherent receivers such as a balanced receiver and a double-stage phase-diversity (DSPD) receiver. The noise figure (NF) of the excess-noise-suppressed coherent receivers with an optical preamplifier is shown to be 0 dB. Bit-error-rate (BER) formulas are also discussed. >