Lan Rao

Optical millimeter wave generated by octupling the frequency of the local oscillator

What we believe to be a new scheme to generate an optical millimeter wave with octupling of the local oscillator via a nested LiNbO3 Mach-Zehnder modulator (MZM) is proposed and implemented by numerical simulation. Since the response frequency of the modulator and the local frequency are largely reduced, the bandwidth requirement of the transmitter to the optical and electrical components is reduced greatly. Then, the parameters of the nested modulator are analyzed theoretically, and we find that both the extinction ratio of the MZM and the phase imbalance between its two arms have influence on the performance of the generated optical millimeter wave.

Transmission performance of quadruple frequency optical millimeter-wave with single and dual carrier data modulations

We have demonstrated generation and transmission of the 40GHz dual-tone optical millimeter (mm)-wave by quadrupling the 10GHz radio frequency local oscillator via a single dual-electrode 10GHz Mach-Zehnder modulator. The transmission performance of two different data modulation formats are discussed based on the transmission function of the dispersive fiber theoretically and then verified by simulation. Conclusion is given that, the transmission distance with dual tone data modulation is limited because of the sidebands walk off effect caused by the fiber dispersion. The bit walk off effect can be eliminated and transmission distance can be extended greatly for single tone data modulation.

Mitigation of nonlinear interference noise introduced by cross-phase modulation in the dual-polarization 16 QAM wavelength-division multiplexing coherent optical system

Abstract. A complex adaptive equalizer using a least-mean-square (LMS) algorithm is proposed to mitigate the effect of nonlinear interference induced by cross-phase modulation in wavelength-division multiplexing (WDM) coherent optical systems. We show the effect of nonlinear interference is equivalent to slow time-varying intersymbol interference. Simulations of dual-polarization 16 quadrature amplitude modulation (QAM) WDM systems are conducted to test the effectiveness of our proposed compensation method. The consequences show that significant improvement in system performance can be achieved by using the adaptive LMS equalization method.

Two-dimensional priority-based dynamic resource allocation algorithm for QoS in WDM/TDM PON networks

Wavelength division multiplexing/time division multiplexing (WDM/TDM) passive optical networks (PON) is being viewed as a promising solution for delivering multiple services and applications. The hybrid WDM / TDM PON uses the wavelength and bandwidth allocation strategy to control the distribution of the wavelength channels in the uplink direction, so that it can ensure the high bandwidth requirements of multiple Optical Network Units (ONUs) while improving the wavelength resource utilization. Through the investigation of the presented dynamic bandwidth allocation algorithms, these algorithms can’t satisfy the requirements of different levels of service very well while adapting to the structural characteristics of mixed WDM / TDM PON system. This paper introduces a novel wavelength and bandwidth allocation algorithm to efficiently utilize the bandwidth and support QoS (Quality of Service) guarantees in WDM/TDM PON. Two priority based polling subcycles are introduced in order to increase system efficiency and improve system performance. The fixed priority polling subcycle and dynamic priority polling subcycle follow different principles to implement wavelength and bandwidth allocation according to the priority of different levels of service. A simulation was conducted to study the performance of the priority based polling in dynamic resource allocation algorithm in WDM/TDM PON. The results show that the performance of delay-sensitive services is greatly improved without degrading QoS guarantees for other services. Compared with the traditional dynamic bandwidth allocation algorithms, this algorithm can meet bandwidth needs of different priority traffic class, achieve low loss rate performance, and ensure real-time of high priority traffic class in terms of overall traffic on the network.

Study on a low complexity adaptive modulation algorithm in OFDM-ROF system with sub-carrier grouping technology

During the last decade, the orthogonal frequency division multiplexing radio-over-fiber (OFDM-ROF) system with adaptive modulation technology is of great interest due to its capability of raising the spectral efficiency dramatically, reducing the effects of fiber link or wireless channel, and improving the communication quality. In this study, according to theoretical analysis of nonlinear distortion and frequency selective fading on the transmitted signal, a low-complexity adaptive modulation algorithm is proposed in combination with sub-carrier grouping technology. This algorithm achieves the optimal performance of the system by calculating the average combined signal-to-noise ratio of each group and dynamically adjusting the origination modulation format according to the preset threshold and user’s requirements. At the same time, this algorithm takes the sub-carrier group as the smallest unit in the initial bit allocation and the subsequent bit adjustment. So, the algorithm complexity is only 1 /M (M is the number of sub-carriers in each group) of Fischer algorithm, which is much smaller than many classic adaptive modulation algorithms, such as Hughes-Hartogs algorithm, Chow algorithm, and is in line with the development direction of green and high speed communication. Simulation results show that the performance of OFDM-ROF system with the improved algorithm is much better than those without adaptive modulation, and the BER of the former achieves 10e1 to 10e2 times lower than the latter when SNR values gets larger. We can obtain that this low complexity adaptive modulation algorithm is extremely useful for the OFDM-ROF system.

Dynamic bandwidth allocation based on multiservice in software-defined wavelength-division multiplexing time-division multiplexing passive optical network

Abstract. The wavelength-division multiplexing passive optical network (WDM-PON) is a potential technology to carry multiple services in an optical access network. However, it has the disadvantages of high cost and an immature technique for users. A software-defined WDM/time-division multiplexing PON was proposed to meet the requirements of high bandwidth, high performance, and multiple services. A reasonable and effective uplink dynamic bandwidth allocation algorithm was proposed. A controller with dynamic wavelength and slot assignment was introduced, and a different optical dynamic bandwidth management strategy was formulated flexibly for services of different priorities according to the network loading. The simulation compares the proposed algorithm with the interleaved polling with adaptive cycle time algorithm. The algorithm shows better performance in average delay, throughput, and bandwidth utilization. The results show that the delay is reduced to 62% and the throughput is improved by 35%.

Dynamic routing and spectrum assignment based on multilayer virtual topology and ant colony optimization in elastic software-defined optical networks

Abstract. Elastic software-defined optical networks greatly improve the flexibility of the optical switching network while it has brought challenges to the routing and spectrum assignment (RSA). A multilayer virtual topology model is proposed to solve RSA problems. Two RSA algorithms based on the virtual topology are proposed, which are the ant colony optimization (ACO) algorithm of minimum consecutiveness loss and the ACO algorithm of maximum spectrum consecutiveness. Due to the computing power of the control layer in the software-defined network, the routing algorithm avoids the frequent link-state information between routers. Based on the effect of the spectrum consecutiveness loss on the pheromone in the ACO, the path and spectrum of the minimal impact on the network are selected for the service request. The proposed algorithms have been compared with other algorithms. The results show that the proposed algorithms can reduce the blocking rate by at least 5% and perform better in spectrum efficiency. Moreover, the proposed algorithms can effectively decrease spectrum fragmentation and enhance available spectrum consecutiveness.

Polarization Mode Dispersion monitoring for phase-modulated optical signals utilizing parallel cross-phase modulation in a highly nonlinear fiber

We propose a first-order Polarization Mode Dispersion (PMD) monitoring technique for phase-modulated optical signals utilizing the cross-phase modulation (XPM) effect between the input signal and the inserted continuous-wave probe in parallel connection. Because of accumulation of PMD, the XPM effect in nonlinear fiber leads to variation of pump phase. This can cause spectrum broadening resulting in variation of pump power. The technique can suppress the influence of PMD in one branch of the two signals in parallel connection then use the difference of the two pump power at the same band to monitor PMD. The simulation shows that the technique can monitor PMD of 40-Gb/s non-return-to-zero differential quadrature phase-shift keying (NRZ-DQPSK) from 0–30ps.The dynamic range over 3dB can be used in accurate monitoring compared to existing methods. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s NRZ-DQPSK, is also investigated via simulation.

Direct-modulated multiple formats optical OFDM system based on Discrete Wavelet Transform

We demonstrated a direct-modulated multiple formats optical OFDM system based on Discrete Wavelet Transform by using MATLAB software. The simulation results indicated that DWT-OFDM has a good advantage over FFT-OFDM, and the signals at a bit rate 5Gbit/s have a good performance which is nearly equal to 10−3 when OSNR is equal to 25dB over 300km optical fiber channel which only concerns the influence of chromatic dispersion.

A Software Defined Radio Access Network based on inter-cell interference suppression

The convergence of optical and wireless network has led to the trend of future access network . Under the study of Software Defined Radio Access Network(SD-RA) and Soft Frequency Reuse(SFR) system model, this paper presents a new inter-cell interference suppression algorithm of SD-RA network. The paper also summarizes and analyses the difference between the SFR based on coordinate multi-point transmission (CoMP) and SD-RA. The computer simulation results show that the inter-cell interference suppression algorithm can bring about 5dB SINR (Signal to Interference plus Noise Ratio) gain.