Zhongwei Tan

High Speed Band-Limited 850-nm VCSEL Link Based on Time-Domain Interference Elimination

Short-distance optical interconnection among servers in data centers has attracted the attentions of a multitude of researchers. The method to make the optical link with high transmission capacity and low cost becomes increasingly crucial. Considering these requirements, we propose a new equalization method for time-domain interference elimination in this letter, employed in a band-limited 850-nm vertical cavity surface-emitting laser (VCSEL) link. The method is named simplified maximum likelihood sequence estimation (MLSE), which reduces about 87.8% computational complexity in digital signal processing compared with the conventional MLSE. Based on the proposed simplified-MLSE and combined with the feed-forward equalizer (FFE), a 60-Gb/s non-return-to-zero (NRZ)-modulated VCSEL link could transmit via 56-m OM4 multimode fiber (MMF), and the bit error rate (BER) is still lower than the 7% hard-decision forward error correction (FEC) threshold. The 3-dB bandwidth of the employed 850-nm VCSEL in this transmission system is only 18 GHz, fulfilling the principle of cost-efficient optical interconnects and showing the enormous potential of our proposal in data centers.

A low-complexity sensor fusion algorithm based on a fiber-optic gyroscope aided camera pose estimation system

Visual tracking, as a popular computer vision technique, has a wide range of applications, such as camera pose estimation. Conventional methods for it are mostly based on vision only, which are complex for image processing due to the use of only one sensor. This paper proposes a novel sensor fusion algorithm fusing the data from the camera and the fiber-optic gyroscope. In this system, the camera acquires images and detects the object directly at the beginning of each tracking stage; while the relative motion between the camera and the object measured by the fiber-optic gyroscope can track the object coordinate so that it can improve the effectiveness of visual tracking. Therefore, the sensor fusion algorithm presented based on the tracking system can overcome the drawbacks of the two sensors and take advantage of the sensor fusion to track the object accurately. In addition, the computational complexity of our proposed algorithm is obviously lower compared with the existing approaches (86% reducing for a 0.5 min visual tracking). Experiment results show that this visual tracking system reduces the tracking error by 6.15% comparing with the conventional vision-only tracking scheme (edge detection), and our proposed sensor fusion algorithm can achieve a long-term tracking with the help of bias drift suppression calibration.

Energy consumption analysis of C-RAN architecture based on 10G EPON front-haul with daily user behaviour

Cloud Radio Access Network (C-RAN) is a novel network architecture, which can solve many challenges of operators when facing the ever-increasing user demands. Specially, the operating expense (OPEX) of C-RAN is an issue of common concern. In this paper, we evaluate the energy consumption of the architecture based on a 10G EPON front-haul considering the daily user behaviour. The simulation results present the energy consumption distributions of C-RAN with daily user behaviour and in different quality of service (QoS).

Energy Evaluation for Cloud RAN Employing TDM-PON as Front-Haul Based on a New Network Traffic Modeling

Cloud radio access network (C-RAN) is a novel network architecture to meet the ever-increasing user demands. Specially, the operating expense of C-RAN, including the energy consumption, is an issue of common concern. Former studies in energy consumption evaluation of C-RAN only considered the case of one virtual server and one remote radio head, which ignored the optical front-haul and cannot provide an overall analysis for the whole access network. In this paper, we analyze the energy consumption of the whole C-RAN architecture, employing Ethernet-based time division multiplexing passive optical network (TDM-PON) (i.e. 10G EPON) as the optical front-haul. Obviously, it becomes complex to analyze the energy problem for the whole network after bringing in the front-haul part. Based on queueing theory, this paper provides a new network traffic modeling for energy analysis in C-RAN. And, we propose a strategy to make the system work in the most energy-efficient state considering the quality of service. In addition, the comparison between C-RAN and 10G-EPON-LTE architecture has also been conducted. We analyze the power-delay tradeoff, the power changes along with request arrival rate, and the daily power distribution in the two networks. From the numerical results, C-RAN architecture can save more than 60% power in a typically low request arrival rate, and reduce about 40% energy for a whole day, considering the daily user behavior, which demonstrates its large potential in the next generation network.

Eigenvector Basis Expansion-Based Phase Noise Suppression Method for CO-OFDM Systems

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) system is known vulnerable to the laser phase noise. In this letter, we propose a novel phase noise suppression method based on eigenvector basis expansion (EBE) for CO-OFDM systems. With the help of the proposed method, the induced phase noise effects can be mitigated efficiently. Numerical results show that compared with the orthogonal basis expansion-based phase noise suppression method, by performing an EBE to the phase noise, a more accurate description of the phase noise can be achieved, and hence leads to a better system performance. Besides, the additional computational complexity is limited, since the eigenvector basis only depends on the laser linewidth.

A 70 Gbps NRZ optical link based on 850 nm band-limited VCSEL for data-center intra-connects

Short-reach optical interconnects among servers in data centers have attracted extensive studies recently. High capacity and low cost are two key problems for optical link. In this paper, we demonstrate a band-limited 850 nm vertical cavity surface emitting laser (VCSEL) based optical transmission system. The optical link realizes 70 Gb/s (65 Gb/s net rate) non-return-to-zero (NRZ) signal transmission over 11 m and 20 m OM4 multimode fiber (MMF), with the help of equalization for time domain interference elimination. The utilized VCSEL has a bandwidth of only 18 GHz, meeting the principle of low cost. The data baud rate in this paper reaches the highest value for an 18-GHz-class 850 nm VCSEL based optical link, to our best knowledge.

Linearly interpolation-based almost blind phase noise suppression method for CO-OFDM systems

In this paper, we improve the pseudo pilot-aided orthogonal basis expansion based (PS-OBE) phase noise suppression method proposed in our recent work by linearly interpolation (LI). The LI-PS-OBE method provides a more accurate detection of the pseudo pilots and hence the system performance can be improved significantly.

Energy Consume Analysis for Ring-Topology TWDM-PON Front-Haul Enabled Cloud RAN

Cloud radio access network (C-RAN) is a new architecture to meet the ever increasing internet data traffic. In particular, the operating expense (OPEX), mainly the energy consumption, of C-RAN is an issue of common concern. Several former works in this area lacked the essential consideration for the optical front-haul part, as a result that it cannot provide overall energy consumption study for the whole system. In this paper, we analyze the energy consume problem in a new C-RAN architecture, i.e., the ring-topology time-wavelength division multiplexing (TWDM) passive optical network (PON) front-haul enabled C-RAN, considering the requirements for large transmission capacity, high energy efficiency, and the appropriate utilization in the large-scale and densely populated cities. After bringing in this optical front-haul and considering the quality of service, a network traffic modeling is provided to analyze the energy problem based on queueing theory. We also conduct the network optimization to ensure that the system works in the most energy-efficient state. Besides, the energy comparisons among the ring-topology TWDM-PON front-haul enabled C-RAN, the time division multiplexing (TDM) PON enabled C-RAN and the ring-topology TWDM-PON-LTE architecture have also been made. According to the numerical results, the new C-RAN, after energy optimization, can save up to 58.1% energy compared with the TWDM-PON-LTE architecture, and also has a slight advantage over the TDM-PON enabled C-RAN (saving more than 2% energy), demonstrating its broad application prospects and large potential in the future.

Experimental analysis of the dynamic north-finding method based on a fiber optic gyroscope: erratum

This paper demonstrates the principles of static and dynamic north-finding methods by measuring the projection of the Earths rotation rate with a fiber optic gyroscope. For a comprehensive comparison of the two methods, the influence of a closed-loop feedback mechanism of a servo motor in a turntable is taken into consideration. Thus, we proposed the static and dynamic north-finding experimental implementations according to the different impact of the motor jitters and the different seeking times. Experimental results show that the dynamic method can reduce the north-finding bias error and instability by 60.1% and 54.6%, respectively, in the seeking time of 360 s, while the reduced proportions are 81.3% and 82.5%, respectively, in the seeking time of 120 s, compared with the static method under the jittering effect of the turntable. Therefore, it can be concluded that the dynamic method is more accurate and robust to the jittering effect.

Research on performances of coherent Nyquist-WDM-PON and WDM-OFDM-PON using effective phase noise suppression methods

In this paper, we research on performances of coherent Nyquist-WDM-PON and WDM-OFDM-PON using effective phase noise suppression methods. We find that WDM-OFDM-PON achieves better performance with the help of effective phase noise compensation.