Youngil Park

Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access: a review (Invited)

Feature Issue on Optical Access Networks (OAN) The passive optical network (PON) is an optical fiber based network architecture, which can provide much higher bandwidth in the access network compared to traditional copper-based networks. Incorporating wavelength-division multiplexing (WDM) in a PON allows one to support much higher bandwidth compared to the standard PON, which operates in the

A symmetric-structure CDMA-PON system and its implementation

A code-division multiple-access (CDMA) passive optical network is proposed as an optical access network system to satisfy the subscribers increasing data traffic. A CDMA scheme is used not only for delivering multiple channels to as many remote units, but also for suppressing optical beat noise. In this study, a beat noise environment is analyzed and a transceiver structure to efficiently increase the reverse link rate is suggested. Fundamental experimental results are provided to show its validity.

Localization of Wireless Sensor Network using artificial neural network

In Wireless Sensor Networks (WSN), location estimation is important for routing efficiency and location-aware services. Traditional received signal strength based localizations using propagation-loss model are often erroneous for the low-cost WSN devices. The reason is that the wireless channel is vulnerable to so many factors that deriving the appropriate propagation-loss model for the low cost WSN devices is not possible. Hence, we propose a flexible model based on neural network and grid sensor training phase for accurate localization of sensors. Simulation results show that the location accuracy can be increased by increasing the grid sensor density and the number of access points.

Shared-wavelength WDM-PON access network for supporting downstream traffic with QoS

We propose a novel shared-wavelength WDM-PON architecture to accommodate downstream bursty traffic, and provide architectural support for different QoS to users. Downstream wavelength-allocation algorithm is proposed and its properties are evaluated.

Performance improvement of indoor positioning using light-emitting diodes and an image sensor for light-emitting diode communication

Abstract. Light-emitting diodes (LEDs) are expected to replace existing lighting technologies in the near future because of the potential dual function of LED light (i.e., wireless communication and lighting) in the context of visible light communication (VLC). We propose a highly precise indoor positioning algorithm using lighting LEDs, an image sensor, and VLC. In the proposed algorithm, three LEDs transmit their three-dimensional coordinate information, which is received and demodulated by a single image sensor at an unknown position. The unknown position is then calculated from the geometrical relations of the LED images created on the image sensor plane. We describe the algorithm in detail. A simulation of the proposed algorithm is presented in this paper. We also compare the performance of this algorithm with that of our previously proposed algorithm. The comparison indicates significant improvement in positioning accuracy because of the simple algorithmic structure and low computational complexity. This technique does not require any angular measurement, which is needed in the contemporary positioning algorithms using LEDs and image sensor. The simulation results show that the proposed system can estimate the unknown position to an accuracy of 0.001 m inside the approximate positioning area when the pixel value is >3000.

Color-Space-Based Visual-MIMO for V2X Communication

In this paper, we analyze the applicability of color-space-based, color-independent visual-MIMO for V2X. We aim to achieve a visual-MIMO scheme that can maintain the original color and brightness while performing seamless communication. We consider two scenarios of GCM based visual-MIMO for V2X. One is a multipath transmission using visual-MIMO networking and the other is multi-node V2X communication. In the scenario of multipath transmission, we analyze the channel capacity numerically and we illustrate the significance of networking information such as distance, reference color (symbol), and multiplexing-diversity mode transitions. In addition, in the V2X scenario of multiple access, we may achieve the simultaneous multiple access communication without node interferences by dividing the communication area using image processing. Finally, through numerical simulation, we show the superior SER performance of the visual-MIMO scheme compared with LED-PD communication and show the numerical result of the GCM based visual-MIMO channel capacity versus distance.

Visible light communications with color and dimming control by employing VPPM coding

We propose a data transmission scheme using visible light LEDs with color and dimming control. PWM and VPPM coding schemes are used for the control of color and dimming, respectively. The coding procedures and the test results are provided.

ONU power equalization of ethernet PON systems

Power differences among optical network unit (ONU) channels received at an optical line terminal (OLT) of ethernet passive optical network systems are minimized to increase burst-mode receiver performance and acquire reliable ONU operation. The OLT measures each ONU power and sends control messages back to ONUs during registration stage. The ONU is designed to change its modulation depth using received control bits. A digital automatic power control circuit is used at the ONU site to help this process. Proposed schemes are implemented and test results are provided.

Hybrid optical star coupler suitable for wavelength reuse

A hybrid optical star coupler is proposed for wavelength-division multiplexed (WDM) star networks where a portion of wavelengths are reused. Local star couplers of n/sup 2//spl times/n/sup 2/ type are adopted to prevent ghost signals from being generated. An arrayed waveguide grating is also utilized to interconnect these couplers with low loss and for partial security. We experimentally investigated transmission performance and the result showed that interconnecting links require more power penalty than local links by 0.23 dB.

Efficient clustering algorithm for delay sensitive PON-based wireless sensor network

To maintain the latency and energy secured data transmission, super frame structure is important with MAC protocol. We propose a new clustering algorithm and PON-based structure to balance the network traffic and limit the network size. We also analyze effect of super frame size on network delay and energy consumption.