Kai Sheng Chen

Radio Transmissions over Residue-Stuffed-QC-Coded Optical CDMA Network

Residue stuffed quadratic congruence (RSQC) codes are proposed for radio-over-fiber (RoF) scheme based on spectral-amplitude-coding (SAC) optical code-division multiple-access (OCDMA) networks. These new codes generated from residue method can enlarge the code space, and the decoder of this new code is cost-effective and suitable for realization. The error rate performance of the proposed RSQC code (two-code keying) and the original SQC code (on-off keying) are analyzed.

Securing Optical Network Access with Post-switching Coding Scheme of Signatures Reconfiguration

Optical code-division multiple-access (OCDMA) has been considered as a good candidate to provide optical layer security. In this paper, an enhanced OCDMA network security mechanism with pseudo-noise (PN) type of M-sequence coding switching is presented to against eavesdropping. Signature code unique to each OCDMA network user is reconfigured in accordance with the register state of a controlling electrical shift register. Examples of signature reconfiguration following state switching of controlling shift register for both network user and eavesdropper are numerically illustrated. It is shown that, by dynamically changing PN state of shift register to reconfigure user signature sequence, eavesdropper will encounter difficulty on decoding correct data sequences. The proposed scheme hence raises a high error probability for eavesdroppers. Accordingly, the degree of the proposed optical network confidentiality can be largely improved.

Using Stuffed Quadratic Congruence Codes for SAC Labels in Optical Packet Switching Network

While optical codes in optical code-division multiple access (OCDMA) has been extensively investigated, research of optical coding labels in optical multi-protocol label switching (MPLS) network is relatively unexplored. This paper studies optical labels with spectral-amplitude coding (SAC) for optical packet switching (OPS) network. The research focuses on implementing two different codes in optical labels: stuffed quadratic congruence (SQC) codes and M-sequence codes. Label-error rate (LER) is quantified to ascertain the influence of code pattern on system performance. The findings suggest that SQC coded label can support more numbers for label stacking, due to its very low cross-correlation value.

Using wavelength/time signatures scrambling to realize cryptographic coded-wdm data networks

Abstract To combat with multiple-users interference and malicious eavesdropping, this paper proposes a double scrambling scheme over time/wavelength for a cryptographic optical CDMA (OCDMA) data transmission. By using wavelength-spreading/time-hopping, data reliability in OCDMA network can be highly improved. On the transmitter side, data bits are sliced into spectral chips, coded into M-sequence codes, and conducted with different units of time-delay. In the receiver side, fiber-delay lines (FDLs) reverse the spectral chips back to the same time basis, and optical switches (OSWs) turn on-off spectral chips into balanced detector for the final data decoding. By changing signature code frequently, the eavesdroppers cannot catch on the changing code speed and have little chance to detect the channel waveform to solve the code. To against eavesdropping, we take advantages of linear cyclic, periodic, and nearly-orthogonal characteristics of M-sequence codes. OSWs and FDLs are added into the arrayed-waveguide grating (AWG) codecs. The spectral codes and the time-delay units will follow cell states of a controlling shift register. Different shift register states will reconfigure AWG light spectra into different coding sequences. After pass through the associated OSWs and FDLs, user signature code appears to be a two-dimensional code matrix. In perspective of eavesdropper, smooth eavesdropping presents difficulties due to signature codes’ frequent changing. The system can therefore achieve a high level of network confidentiality.

Experiments on using Spatial Light Modulators to realize optical CDMA network coder/decoders

We propose a new scheme in optical code-division multiple-access (OCDMA) system by using liquid crystal (LC) Spatial Light Modulators (SLMs) with programmable bipolar codes. The key to the system performance depends on constructing a decoder that implements a true bipolar correlation using only unipolar signals and intensity detection. In our optical access coding system, the power spectrum is coded with programmable LC-SLMs. The high polarization selectivity of these components coupled with the polarization rotation ability of liquid crystal elements makes access coding switching possible with high extinction ratio and low crosstalk.

Using Genetic Algorithms to Approximate Weighted Geometric Dilution of Precision

As the Internet and mobile device get universal, mobile positioning in wireless communication becomes an important application. The wireless signal is influenced by many factors. Fading effect and multipath propagation increase the signal propagation time and change the angle of the received signal. All of these reduce mobile positioning accuracy. In line-of-sight (LOS) system, a signal can be measured precisely. However, there are many obstacles between a mobile station (MS) and a base station (BS) in the real environment. It causes non-line-of-sight (NLOS) effect. NLOS is a major factor that causes errors in mobile positioning. Although NLOS influences the signal propagation, these effects can be reduced. To enhance positioning accuracy, we choose the BS with the least error to estimate the mobile position by calculating the geometric dilution of precision (WGDOP), which is a value to quantify positioning performance. A WGDOP small value represents high accuracy. Using WGDOP to select the best combination of BSs improves MS positioning accuracy. Because the calculation of WGDOP is complex, it is a great burden on a device and spends lots of time. To reduce the load of devices, an approximation method based on genetic algorithm (GA) is proposed to derive WGDOP value efficiently.

Illustrative Signature Keys Reconfiguration to Combat with Eavesdroppers in Wavelength-coded Optical Access Networks☆

Abstract In order to enhance data transmission security within internet network, this paper consider a signature reconfiguration scheme over wavelength-coded network coder/decoders (codecs). We propose the reconfiguration scheme of composite signatures in which optical network codecs reconfigure their signature keys in a tractable way to enhance system confidentiality for coded wavelength-division multiplexing (WDM) transmissions. Based on conventional maximal-length sequence (M-sequence) codes over arrayed-waveguide-grating (AWG) codecs, composite signatures of relative prime-length M-sequence codes are structured to identify network node users. Network codecs change their signatures dynamically such that eavesdroppers cannot keep up with the speed of code changing, and thus unable to detect the channel waveform to descramble the code. Evaluated results show the effectiveness of the proposed approach via composite signatures reconfiguration against practical eavesdropping.

Error performance of BPSK-modulated radio transmissions over SQC-coded optical CDMA network

Stuffed quadratic congruence (SQC) codes are used for radio-over-fiber (RoF) scheme based on spectral-amplitude-coding (SAC) optical CDMA network for interference elimination. The binary phase-shift keying (BPSK) signal is modulated on a radio frequency (RF) carrier. And the system is simulated by the software of Opti-system. The simulated error rate performance of SQC codes is compared with former M-sequence codes. Otherwise, several conditions are analyzed whether it will influence the system performance in the receiver.

Orthogonal stacked composite M-sequence labels for quick packet routing over optical MPLS network

In this paper, we construct a composite label sets for optical multi-protocol label switching (MPLS) network. Relatively prime lengths maximal-length (M-sequence) codes are taken to compose into spectral-amplitude coding (SAC) labels. These composite M-labels possess good orthogonality and are compatible with packet labels stacking. With correlation subtraction scheme in packet routing node, local node label can be identified from the stacked labels. The composite M-labels are coded with arrayed-waveguide gratings (AWGs) with small number of input-output ports to reduce hardware requirement. Compared with conventional M-sequence labels, composite M-labels behave more flexibility on routing data packets. The proposed composite M-labels coding can support optical packet switching network (OPS) with fast label processing.

BPSK-modulated radio transmissions over optical CDMA network for MAI elimination

We describe the implementation of radio-over-fiber (ROF) techniques with a combination of spectral-amplitude-coding optical code-division-multiple-access (SAC-OCDMA). The architecture of proposed fiber-radio network is presented in details where the radio frequency (RF) modulated signal is up-converted to the spectrum-coded optical carriers. System evaluation is analyzed by deriving the average bit error rate (BER) expression. Gaussian approximation is applied for the noise distribution, taking into account the thermal and phase-induced intensity noise (PIIN) in the receiver. The binary phase-shift keying (BPSK) signal is modulated on a radio frequency (RF) carrier. System evaluations are performed under the condition of different code-types (m-sequence code and SQC code) and code-lengths.