Keattisak Sripimanwat

Secret key reconciliation using BCH code in quantum key distribution

Due to imperfection in quantum key distribution (QKD) an uncorrected secret key transmitted via quantum channel exists at the receiver side. This paper presents an alternative method to recover those quantum key by using BCH codes - a class of error control coding (ECC). Application of BCH codes to source coding with side information is described for quantum key reconciliation. Unlikely to many previous protocols, the proposed scheme aims to reduce public communication with acceptable quantum bit error rate and a number of disclosed bits; therefore, it is suitable to applications of high speed QKD.

Cell selection schemes for femtocell-to-femtocell handover deploying mobility prediction and downlink capacity monitoring in cognitive femtocell networks

Femtocell networks have been proposed for indoor communications as the extension of cellular networks for enhancing coverage performance. Because femtocells have small coverage radius (15 to 30 meters), femtocell users (FU) walking at low speed still make frequent femtocell-to-femtocell handover. When performing a femtocell-to-femtocell handover procedure, a cell selection scheme, which is used to select the target handover femtocell, should be able to reduce unnecessary handovers. The cell selection scheme should also support FUs connection quality by not selecting an overloaded target femtocell. In this paper, we propose two new cell selection methods for femtocell-to-femtocell handover in which one is designed based on mobility prediction and another is based on femtocell capacity estimation. Simulation results show that each method provides different performance enhancement when comparing with the conventional RSS-based cell selection. It also shows that there is a trade-off between reducing unnecessary handover and avoiding overloaded femtocells which is the difficult and open challenge when designing an efficient cell selection scheme in future studies.

Secure and efficient key management technique in quantum cryptography network

In conventional security mechanism, security services based on symmetric key cryptography assume keys to be distributed prior to secure communications. The core function of exchanging and sharing a secret key between two endpoints are the secure key management methodology which is one of the most critical elements need to be more concerned when integrating cryptographic functions into the system. In case the key management mechanisms is weak can lead to the vulnerability holes or a potentially fatal outsider attacks as the harmful effects to the system. Since, there is still no standardized architecture or protocol that can provide cross application symmetric key management services. Therefore, this paper approaches a secure key management model and its custom protocols to build Thailand quantum trusted network with offers simultaneous quantum key distribution to multiple user overtime. Consequently, the proposed technique has also overcome the limitation of quantum point-to-point key sharing. Based on the discussion of key management security requirement, deal with generic key management concepts and designing the new custom protocols to close the possibility loopholes, to offers reliability and convenience of use, as well as to introduce a secure and efficient key management technique for quantum cryptography network in Thailand where any communication services can take place.

Design and simulation of a novel indoor mobile robot localization method using a light-emitting diode positioning system

A key problem of mobile robots is that of the positioning capability in order to detect their locations in the operating environment. A promising technology used in indoor localization recently is Visible Light Communication (VLC). In this paper, an integrated Angle of Arrival-Received Signal Strength (AOA-RSS) localization method using the VLC, which could get high accuracy with simple hardware, is proposed. In addition, the Extended Kalman Filter (EKF) and Particle Filter (PF) algorithms are combined with the proposed AOA-RSS localization method in order to achieve higher accuracy of the mobile robot positioning. By computer simulation, the performance of the proposed AOA-RSS localization method combined with the EKF and PF algorithms are compared. The combination scheme outperforms the individual VLC localization with small error approximation of a few centimetres.

Improved Gradient Descent Bit Flipping algorithms for LDPC decoding

For LDPC decoding, a class of weighted bit-flipping algorithms is much simpler than a belief propagation algorithm. This work proposes a modified Gradient Descent Bit-Flipping algorithm based on Reliability Ratio with an adaptive threshold to address trade-off between performance and latency. From numerical results, the proposed algorithm achieves lower latency without an expense of performance. It yields average iteration reduction of 15-27% over SNR range from 2.5 dB to 4.5 dB. In addition, it provides better decoding performance gains, i.e. 0.05-0.25 dB over low-to-medium SNR range between 1.5 dB and 4 dB comparing to previous schemes.

Improvement of the VLC localization method using the Extended Kalman Filter

This paper deals with localization problem of mobile robots in indoor environment based on Visible Light Communications (VLC). We propose an integrated AOA-RSS localization method of Angle of Arrival (AOA) and Received Signal Strength (RSS) methods to find out position of a mobile robot using an array of photodiodes (PDs). Performance of the integrated localization method depends on the number of PDs mounted on the mobile robot. In order to achieve more accurately in positioning the mobile robots location, we propose a combination of the proposed AOA-RSS localization method and the Extended Kalman Filter (EKF) algorithm. The efficiency of this combination is proved through computer simulation. The EKF also addresses a significant problem in robot navigation that is to control the mobile robot moving on the specified path in a certain activity.

Performance of ½-rate convolutional code on Winnow protocol for quantum key reconciliation

The quantum key reconciliation is an essential step of Quantum Key Distribution (QKD) systems for correcting error in the raw keys which happens after the transmission over a quantum channel, where two legitimate parties make their correlated bits identical by exchanging messages over the public channel. This paper presents an alternative method for error correction of quantum key reconciliation by using ½-rate convolutional code, a class of forward error correcting (FEC) on Winnow for discrete-variable QKD protocol. The convolutional code can be applied to source coding with a side information problem which uses to describe quantum key reconciliation process. In the proposed scheme, it focuses on the performance evaluation of ½-rate convolutional code in quantum key reconciliation. In order to reduce an amount of interactive communication via error-free public channel for high-speed QKD applications, this proposed method is that the suitable solution.

A Comprehensive Lighting Configuration for Efficient Indoor Visible Light Communication Networks

Design of an efficient indoor visible light communication (VLC) system requires careful considerations on both illumination and communication aspects. Besides fundamental factors such as received power and signal-to-noise ratio (SNR) level, studies on mobility scenarios and link switching process must be done in order to achieve good communication link quality in such systems. In this paper, a comprehensive lighting configuration for efficient indoor VLC systems for supporting mobility and link switching with constraint on illumination, received power, and SNR is proposed. Full connectivity in mobility scenarios is required to make the system more practical. However, different from other literatures, our work highlights the significance of recognizing the main influences of field of view angle on the connectivity performance in the practical indoor scenarios. A flexible link switching initiation algorithm based on the consideration of relative received power with adaptive hysteresis margin is demonstrated. In this regard, we investigate the effect of the overlap area between two light sources with respect to the point view of the receiver on the link switching performance. The simulation results show that an indoor VLC system with sufficient illumination level and high communication link quality as well as full mobility and support link switching can be achieved using our approach.

Performance analysis of partial pre-equalization for ACO-OFDM indoor optical wireless transmissions

We propose partial pre-equalization for indoor optical wireless transmissions based on asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) with intensity modulation and direct detection (IM/DD). Bit loading is applied to minimize the transmit optical power for a fixed target BER. Similar to pre-equalization, for diffuse indoor optical wireless channels, partial pre-equalization can reduce the transmit optical power over post-equalization for point-to-point transmissions. In addition, we consider broadcast transmissions to multiple users with possibly different channel qualities, where pre-equalization is not applicable. Finally, we specify an appropriate channel estimate at the transmitter for such broadcast transmissions.

MISO mixed phase precoding and its applications with turbo coding schemes

This paper proposes an application of mixed phase precoding in the MISO (multiple-input, single-output) wireless communications and its concatenation with turbo coding schemes. The principle of this phase precoding is rearranged in the manner of the closed-loop transmitted diversity to reduce the frequency-selective Rayleigh fading channel. Results show that the use of mixed phase precoding in the MISO wireless communication retrieves a lower bit error rate compared to those of related cases of wireless communications.