Chromatic dispersion (CD) is one of the main limitations for high speed intensity modulation and direct-detection transmission system. Electrical dispersion compensation is a cheaper and easier way to compensate CD. In this paper, we compare the performance of chromatic dispersion pre- and post-compensation for optical single side-band (SSB) 4-level pulse amplitude modulation (PAM4) signal with Kramers-Kronig (KK) receiver by simulation and experiment. We put the pre-compensation after Hilbert transform at the transmitter side and the CD post-compensation after KK receiver at the receiver side. The results show that CD tolerance of the dual-drivel Mach-Zehnder modulator (DDMZM) based SSB signal is related to the optical modulation index (OMI) of the modulator in CD pre- and post-compensation scenarios. When the optical signal-to-noise ratio (OSNR) is relatively large, CD post-compensation is more sensitive to OMI than precompensation with KK receiver. We also explore the impact of signal peak-to-average power ratio (PAPR) on the precompensation system by simulation.
As an alternate to fast Fourier transform-based orthogonal frequency-division multiplexing (OFDM), wavelet packet transform (WPT)-based OFDM (WPT-OFDM) does not require cyclic prefix to avoid inter-symbol-interference. The wavelet has many varieties and therefore, it can provide more freedom for system design to suit different applications. We propose a real-valued WPT-OFDM that uses intensity modulation/direct detection. We also conduct an experiment to verify its performance through a 75-km standard single-mode fiber.
In this paper, we conduct a simulation for WDM-PON with coherent optical OFDM using partial carrier filling (PCF)
configuration. The impact of PCF patterns and PCF factor on transmission performance at 40-Gb/s over 100 km are
studied and simulated. The influence of power into fiber is examined to obtain the optimal value corresponding to the
expected transmission distance.
The introduction of OFDM into PON networks is to leverage the merits of OFDM to provide the flexibility and reduce
the cost. In this paper, we present our latest works on OFDM-PON. Firstly, we propose and demonstrate a novel OFDMPON
upstream transmission architecture with traffic aggregation by orthogonal band multiplexing. The multiplexed 10-
Gb/s OFDM signal is collectively received. We also conduct a proof-of-concept experiment to verify the architecture.
Secondly, we propose and experimentally demonstrate wavelet packet transform based OFDM (WPT-OFDM) using
real-valued transforms, which enables the cost-effective intensity modulation/direct detection (IM/DD). Unlike
conventional FFT-based OFDM, the need for cyclic prefix is eliminated due to the time-frequency localization properties
of the wavelet.
The channel estimation result of non-pilot subcarriers mainly depends on adjacent pilot subcarriers. A linear
interpolation algorithm has been applied to the channel estimation of non-pilot subcarriers. The performance of
interpolation algorithm has been simulated in a 10Gb/s direct-detection optical orthogonal frequency division
multiplexing (DDO-OFDM) communication system. Constellation convergence is greatly improved.
To achieve adaptive modulation technology in Optical Orthogonal Frequency Division Multiplexing
(OOFDM) system, the channel estimation has to be made first and foremost. By imposing a symbol of
pilot signals after a certain amount symbols, the frequency response of a given transmission link can be
given out. The modulation format can be determined according to the frequency response. A high (low)
modulation format is used on a sub-carrier suffering a low (high) transmission loss. The modulation
format can be adjusted adaptively.
Different operation models of joint optical multi-band detection systems are provided here, corresponding to the different
characters of detecting probabilities of subsystems. It leads to a higher over-all detecting probability. The joint optical
detection system is able to be operated under different models when detection probabilities of subsystems are low or
there is big difference among the probabilities. When all the probabilities of subsystems are low, the joint optical
detection system directly conducts data fusing. If there is big difference among the probabilities of subsystems,
information from the subsystems is chosen before entering the fusion center. In this way, the false-alarm probability of
the joint optical detection system reduces obviously comparing with direct data fusion. So it also can reduce the
calculation of system and improve the competence of system.
Within the realm of OFDM research, (peak-to-average power ratio)PAPR is an important object to be considered.
Overlarge PAPR can deteriorate the linearity of the wireless systems. In this paper, we interpret the concept of PAPR in
optical OFDM system and testify that the modulation method in sub-carriers and nonlinear effects can affect PAPR in
the optical OFDM system. Through simulation, PAPR problem stand out while considering OFDM in optical
transmission technology, so reducing it has become an important subject in optical OFDM system.
Camera calibration is an important step for vision-based measurement applications. A well-known flexible camera calibration method is analyzed that uses the checkerboard pattern plane and in which the camera can be moved freely. When using a perspective projection camera model, characteristics of both the objective plane and the image plane are utilized and accurate results can be obtained. However, the method's results may fail when the rotation angles of the planar pattern are small, and the distortion coefficients obtained under the perspective projection model can not be used for a real-time vision application. We solve the ill-conditioned equations using the genetic algorithm, and the correct camera parameters are always obtained. We compute the distortion coefficients of the inverse projection model, which can be used for general vision applications. The influence of the corner detection precision is taken into consideration. Simulation shows that the best results may be obtained when the planar pattern is placed in a close range and its rotation angle is small. Simulations and real-world experiments illustrate that the improved calibration algorithm can always obtain robust and accurate results.
In a real-time vision navigation system, an accurate and fast convergent pose estimation algorithm is required for the video guidance sensor. The orthogonal iteration (OI) algorithm is fast and globally convergent, but its results have a large translation error at a close range, and sometimes it fails to give a correct rotation matrix when the data are severely corrupted, when using the 3-D feature points. When the rotation matrix solution in the OI algorithm has been refined, an efficient pose estimation algorithm is derived. Simulation of the improved algorithm shows that the rotation matrix is always proper, which in turn improves the accuracy of the translation vector. The noise resistance and the outlier tolerance are enhanced by using the improved algorithm. The two algorithms are applied to our experimental system for an unmanned vehicle rendezvous and docking simulation separately. The comparison experiments show that the relative distance error is less than 0.28% from 1.5 to 5 m, and the rotation angle error is within ±0.7 deg in 5 m using the improved algorithm. These are better than the results using the OI algorithm.