Low-cost Access Networks Research Articles

Low-cost WDM-PON supporting flexible point-to-point communication between any two ONUs for data centers

This paper proposes a low-cost access network architecture supporting flexible point-to-point communication between any optical network units (ONUs). By sharing transceivers between upstream/downstream communication and ONU communication, the number of transceivers required in ONU can be decreased. Coupled with using passive components instead of active transmitters and adopting modular design of nodes for integration, the cost of manufacturing and maintenance of network equipment can be significantly reduced. In addition, by skillfully allocating wavelengths, not only wavelength multiplexing can be realized and thereby improving the utilization of network wavelength resources, but also the Rayleigh backscattering (RB) in signal transmission can be effectively weakened. Finally, by the simulation experiment, the effectiveness of the proposed architecture is demonstrated.

An Opportunistic Push Scheme for Online Social Networking Services in Heterogeneous Wireless Networks

Article synchronization is one of the most fundamental issues in online social networking services (SNSs). In particular, when deploying multiple access networks with different transmission costs, an efficient synchronization scheme should be devised for users to enjoy SNSs in heterogeneous wireless networks. In this paper, we propose an opportunistic push scheme (OPS) that aggregates published articles, opportunistically pushing them through low-cost access networks (e.g., open Wi-Fi networks). To balance the reduced transmission costs and the increased page loading time, we formulate a Markov decision process problem that considers a mobility model based on the users’ social contact pattern. Evaluation results demonstrate that OPS with the optimal policy can reduce the number of transmissions in high-cost access networks, while satisfying users’ quality of experience in terms of the page loading time.

High-speed quasi-balanced detection OFDM in visible light communication

In this paper, we proposed and experimentally demonstrated a novel quasi-balanced detection (QBD) technique in orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) system. By employing opposite signals to odd and even consecutive symbols, the nonlinearity distortion, and direct current can be eliminated efficiently. Additionally, the sensitivity of receiver can also be improved by 3dB, thus a longer transmission distance and high-order modulation formats can be received. We achieved physical data rate of 2.1-Gb/s enabled by wavelength-division-multiplexing (WDM), pre- and post-equalization, and the resulting bit error ratios (BERs) were below the FEC limit of 3.8x10(-3). The distance was above 2.5 meters that was long enough for indoor communication. Compared with conventional direct-detection optical (DDO-OFDM) and asymmetrically-clipped optical (ACO-OFDM), the BER can be enhanced by 22.2dB and 20.8dB, respectively, which shows great potential in short range and low cost access network.

Routing Metrics and Protocols for Wireless Mesh Networks

WMNs are low-cost access networks built on cooperative routing over a backbone composed of stationary wireless routers. WMNs must deal with the highly unstable wireless medium. Therefore, the design of algorithms that consider link quality to choose the best routes are enabling routing metrics and protocols to evolve. In this work, we analyze the state of the art in WMN metrics and propose a taxonomy for WMN routing protocols. Performance measurements for a WMN, deployed using various routing metrics, are presented and corroborate our analysis.

Pulse Position Modulation for Spectrum-Sliced Transmission

An original analysis is presented for spectrum-sliced (SS) transmission employing digital pulse position modulation (PPM) and maximum likelihood detection. The treatment is placed within the context of low-cost access networks, where system parameters allow employment of the Gaussian approximation. SS-PPM is compared to on-off keying (SS-OOK) in the presence of dispersion and found to be typically some 2-4 dB more sensitive. In addition, comparison is made with laser-based OOK where the optimum SS-PPM configuration reduces or eliminates the SS power penalty.

High-performance 1.3-μm InAsP strained-layer quantum-well ACIS (Al-oxide confined inner stripe) lasers

We have demonstrated high-performance 1.3-/spl mu/m InAsP strained-layer quantum-well lasers with Al-oxide confined inner stripe (ACIS) structure. The oxidized layers are consisted of strain-compensated AlAs-InP-AlInAs (6 nm/2 ML/3 nm) superlattice (SAS) layers and grown on InP substrate using gas-source molecular beam epitaxy (GS-MBE). For the structural optimization of the ACIS laser, the dependence of quantum efficiency, threshold current and lateral mode characteristics on the initial ridge width and the current aperture width have been investigated. A very low-threshold current of 2.0 mA, a high differential quantum efficiency of 67% and stable single lateral mode operation of over 40 mW were obtained for the optimized ACIS lasers. The excellent characteristics obtained in the ACIS lasers are attributed to both the current and the optical confinements by the Al-oxide layer. In addition, we confirmed high uniformity of the threshold current and the oxidized width. This device is very promising candidate for low-cost access networks and optical interconnects.

Integrated GaInAsP laser diodes with monitoring photodiodes through semiconductor/air Bragg reflector (SABAR)

A 1.3-/spl mu/m GaInAsP laser diode (LD) is integrated with a monitoring photodiode (M-PD) through a semiconductor/air Bragg reflector (SABAR). Instead of conventional cleavage, the SABAR can provide not only Fabry-Perot resonance with high reflectivity, but also possibility of integration of laser with other functional devices. The design, fabrication, and some characteristics including threshold current, monitoring photocurrent, SABAR reflectivity as a function of the number of semiconductor/air pairs N are reported. The threshold current of ridge waveguide laser with SABAR (cavity length L=160 /spl mu/m, ridge width W=7 /spl mu/m, SABAR pairs N=3) is 20 mA. The threshold current is reduced by improving butt-coupled interface between active and passive waveguides employed in this laser and is expected 2 mA//spl mu/m. The monitoring photocurrent responds linearly with output power from the laser and 0.024 mA at laser output power of 5 mW. From the threshold characteristics, SABAR reflectivity is determined to >80%. The increase of photocurrent can be achieved by optimizing the number of SABAR pairs to N=1. We have obtained threshold current of 22 mA in the followed laser structure (L=270 /spl mu/m, W=7 /spl mu/m, N=1), and detector photocurrent of 1.13 mA (@5 mW). The experimental SABAR reflectivity is /spl sim/50%, which is estimated by threshold characteristics and efficiency of light output power. The laser has a mode field converter section, resulting in narrow beam divergence 11/spl deg/ along vertical axis. This integrated laser is very promising candidate for coming optical module in low-power consumption and low-cost access network systems.