Ziyu Wang

A new family of 2-D optical orthogonal codes and analysis of its performance in optical CDMA access networks

A new family of two-dimensional optical orthogonal code (2-D OOC), one-coincidence frequency hop code (OCFHC)/OOC, which employs OCFHC and OOC as wavelength hopping and time-spreading patterns, respectively, is proposed in this paper. In contrary to previously constructed 2-D OOCs, OCFHC/OOC provides more choices on the number of available wavelengths and its cardinality achieves the upper bound in theory without sacrificing good auto-and-cross correlation properties, i.e., the correlation properties of the code is still ideal. Meanwhile, we utilize a new method, called effective normalized throughput, to compare the performance of diverse codes applicable to optical code division multiple access (OCDMA) systems besides conventional measure bit error rate, and the results indicate that our code performs better than obtained OCDMA codes and is truly applicable to OCDMA networks as multiaccess codes and will greatly facilitate the implementation of OCDMA access networks.

A new family of 2D variable-weight optical orthogonal codes for OCDMA systems supporting multiple QoS and analysis of its performance

A new family of two-dimensional variable-weight and constant-length optical orthogonal codes (2D VWOOCs) is proposed, and the code cardinality and BER performance for the corresponding OCDMA system are analyzed in this article. It is shown that the cardinality of 2D VWOOC is larger than that of constant-weight 2D OOC and close to the upper bound in theory. In an OCDMA network, the users employing 2D VWOOC codewords with larger Hamming weight outperform the users using 2D VWOOC codewords with smaller Hamming weight in bit-error-rate performance. Therefore, the OCDMA network employing 2D VWOOC can support diverse quality-of-services (QoS) classes and multimedia services, and make the better use of bandwidth resources in optical networks.

Security performance analysis of an M-code keying OCDMA system

In this article, an M-code keying OCDMA system with parallel encoders/decoders is presented and its security performance is quantitatively analyzed. Under brute-force searching techniques, the formula about the average searching time is derived. The bit-correct-interception possibilities for tapping individual and multiple users’ signals are calculated, respectively. By analysis, it is shown that the security performance of an OCDMA system can be enhanced by employing M-code keying.

Performance analysis of a new random access protocol for OCDMA networks

A New random access protocol for OC-DMA networks is proposed in this paper. Employing a new mathematical model, namely the processor-sharing system, steady-state throughput ratio and average delay of OCDMA networks are calculated. The results reveal that our protocol outperforms other existing protocols. Meanwhile, we investigate the performance of OCDMA networks by altering the code parameters, i.e., length and weight, and the maximum number of active users in the system, corresponding results are indeed consistent with the practical situation. In addition, the analysis is simplified compared with the conventional Markov chain model. Thus the processor-sharing system is truly applicable to model OCDMA networks.

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.

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.

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.

Analysis of Scale Factor Error for Open-loop Fiber Optic Gyroscope with A Digital Signal Processing System

We research the effect of the instability of the modulation depth and the nonlinearity of the modulating signal on the scale factor error for open-loop fiber optic gyroscope with a digital signal processing system.