Paramin Sangwongngam

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.

System demonstration for visible light communication using adaptive threshold detection for low data rate applications

With the materialization of light emitting devices for solid state lighting, visible light communication (VLC) has provided a prospect to realize low cost, high speed, power efficient and secure data transmission in addition to lighting. Incandescent and fluorescent light sources are being replaced by light emitting diodes (LED) which are not only energy efficient but also help in reducing carbon dioxide CO2 emission. In this paper, experimental results are being presented using a new protocol for VLC and the optimum placement of the LEDs within the transmitter to maximize the transmitter foot prints.

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.

APP demodulator for turbo coded differential unitary space-time modulation

In this paper, an iterative multiple symbol differential detection (MSDD) for turbo coded differential unitary space-time modulation (DUSTM) is developed by using an a posteriori probability (APP) demodulator under correlated slow and fast Rayleigh flat fading channels. The metric function necessary for the detection operates based on linear prediction. Two approaches are presented to utilize the metric. In the first approach, the BCJR algorithm is modified to deal with the increased-state trellis of the differential modulation. In the second approach, the VA is modified to find the symbol sequences associated with the survivors for the BCJR algorithm.

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.

Iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation

In this paper, an iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation using a posteriori probability (APP) demodulator is investigated. Two approaches of different complexity based on linear prediction are presented to utilize the temporal correlation of fading for the APP demodulator. The first approach intends to take account of all possible previous symbols for linear prediction, thus requiring an increase of the number of trellis states of the APP demodulator. In contrast, the second approach applies Viterbi algorithm to assist the APP demodulator in estimating the previous symbols, hence allowing much reduced decoding complexity. These two approaches are found to provide a trade-off between performance and complexity. It is shown through simulation that both approaches can offer significant BER performance improvement over the conventional differential detection under both correlated slow and fast Rayleigh flat-fading channels. In addition, when comparing the first approach to a modified bit-interleaved turbo coded differential space-time modulation counterpart of comparable decoding complexity, the proposed decoding structure can offer performance gain over 3 dB at BER of 10−5.

An app demodulator for iterative decoding of turbo coded differential space-time modulation with unitary group codes

A modified technique for joint iterative decoding of serial concatenation of turbo code and unitary space-time group code is proposed and evaluated under temporally correlated fading channels. This approach further takes advantage of the system by exploiting the unitary space-time group code which possesses trellis structure of differential modulation. The extrinsic information of modulation symbols is calculated from this trellis structure by using a detector called an a posteriori probability (APP) demodulator. The simulation results show that our modified method is superior to the conventional one at the expense of more complexity.