To secure the interactive multimedia applications in WLANs (wireless local area networks), it is pertinent to implement a number of security services such as authentication, key exchange and real-time encryption/decryption. The implementation of those security services in WLANs presents a complex and challenging environment because these services may deplete the limited network resources and increases the burden of supporting the quality of service for multimedia applications. As an alternative solution, we thus introduce a new security system, which is based on RCNC (Random Connection Node Convolutional) code and M-sequence. The architecture of RCNC code formed by developing the conventional convolutional code structure has an excellent security operation as well as an error correction function. To verify the performance of our proposed system, the computer simulations have been performed in IEEE 802.11b environment.

The implementation of conventional Multi-Code Code Division Multiple Access (MC-CDMA) system needs many orthogonal codes (OCs) compared to traditional Direct Sequence-CDMA (DS-CDMA) systems. To reduce the number of OCs in MC-CDMA for multi-media services, we propose a new scheme in which a sub-orthogonal code (SOC) technique is adopted. To clarify the validity of our proposed system, the computational simulations have performed.

We propose a MC-CDMA (Multi-Carrier CDMA) system with MD (multi-detector). Due to unknown functional form of noise in wireless channel environments, it is not easy to design a detector through estimating the functional form of noise. Instead, we design a MD, which is based on DGT (Data Grouping Technique) and quantiles estimated through RMSA (Robbins-Monro Stochastic Approximation) algorithm. The system suggested here, MC-CDMA with MD, has the ability to alleviate problems associated with various noise components. To clarify the validity of our proposed system, the computer simulations have been performed under various channel environments.

The field supported by multilayered periodic waveguides is well characterized by only one or two discrete leaky waves, rather than by a more complicated field representation that includes continuous spectra. The rigorous leaky-modes coupled in multilayered geometry can be then treated by relatively simpler and analytic model that describes the operation of practical optoelectronic devices in terms of leakage effects. To complement our modeling, we discuss and emphasize novel mathematical formulations based on the field orthogonality conditions of TE and TM modes coupled in multilayered periodic structures. In addition, to show the validity of our approach we numerically evaluate new physical meanings to illustrate quantitatively and rigorously the coupling efficiency of grating-assisted directional couplers (GADCs). The results reveal that the systematic and effective technique yields phenomenologically useful interpretations.

We apply newly developed rigorous modal transmission-line theory (MTLT) to evaluate optimal design conditions on optical power coupling in grating-assisted directional couplers (GADCs) with two or three guiding channels. By defining a power distribution ratio (PDR) and coupling efficiency (CE) amenable to the rigorous analytical solutions of MTLT, we explicitly analyze the power coupling characteristics of TE modes propagating in GADCs. The numerical results reveal that the incident power is optimally coupled into the desired guiding channel if the powers of rigorous modes excited at the input boundary of grating-assisted coupler are equally partitioned.

Power distribution in multilayered periodic waveguides is first analyzed by longitudinal modal transmission-line theory (L-MTLT). Novel effective characteristic impedances of the equivalent network for TE and TM modes are then derived, and a symmetrical grating guide with three layers is rigorously evaluated to clarify the validity of our approach. Excellent agreement between our results and the results due to other methods indicates that our approach is able to not only reveal all the physical meaning embedded in the multilayered and multi-sectional periodic waveguides, but also predict various possible Bragg regimes rigorously and simply.

A rigorous modal approach based on the transmission-line description has developed to explore effectively the filtering characteristics of planar optical DFB guiding structures. Using the modal transmission-line theory, the leakage and filtering characteristics of metal-strip gratings and dielectric gratings with gain or loss are first evaluated in details at the first- and third-order Bragg regimes. It can thus serve as a powerful template for computational algorithms to determine systematically and rigorously the optical effects of multilayered periodic guiding structures, which are not readily obtained by other methods.