Jiro Yamakita

Analysis of diffraction in periodic liquid crystals: the optics of the chiral smectic C phase

A method for analyzing diffraction properties of periodic liquid crystals is presented that uses the previous theory for anisotropic dielectric gratings [ J. Opt. Soc. Am.73, 901 ( 1983)]. The method applies to any type of periodic liquid-crystal structure with arbitrary orientation of the helical axes. As an example of the present analysis, both forward and backward diffraction properties of a chiral smectic C phase are given for the incidence of linearly polarized and circularly polarized waves. An approximate two-wave analysis is also derived and is compared with the rigorous results.

Effect of exponential backoff scheme and retransmission cutoff on the stability of frequency-hopping slotted ALOHA systems

The combinatorial effect of an exponential backoff scheme and retransmission cutoff on the stability of frequency-hopping slotted ALOHA systems with finite population is investigated in terms of the catastrophe theory. In the systems, the packet retransmission probabilities are geometrically distributed with respect to the number of experienced unsuccessful transmissions and a packet will be discarded after a certain number of unsuccessful transmissions. Expressions which should be satisfied at equilibrium points are first derived. Then, the cusp point and the bifurcation sets are numerically evaluated. Finally, we visualize how the exponential backoff scheme and retransmission cutoff effect depends on the bistable region. Numerical results show that the exponential backoff scheme can mitigate bistable behavior of the system with finite population. However, it is also revealed that there is asymptotically no effect of the exponential backoff scheme on the stability of the system with infinite population.

Backfire-to-endfire radiation characteristics of CRLH-TL using substrate integrated waveguide and metal-patches

We have proposed a new type of the CRLH-TL consisting of two-layer planar substrates recently. It consists of a base waveguide of a substrate integrated waveguide (SIW), and series capacitances realized by slit apertures and metal patchs arranged on the upper conductor of the SIW. It is expected to become one of the basic CRLH-TL structures over 10 GHz or millimeter-wave. However radiation from the metal-patchs cannot neglect in this structure. Then we proposed a leaky-wave antenna using the SIW metal-patch type CRLH-TL. In this paper, beam scan characteristics as a function of driving frequency are confirmed theoretically and experimentally. A SIW metal-patch type CRLH-TL with transition frequency of 16 GHz is designed for a leaky-wave antenna and fabricated. Measured results agree well with theoretical and numerical results.

Analysis of unsaturation throughput of IEEE 802.11 DCF

Most analytical models proposed so far for IEEE 802.11 distributed coordination function (DCF) focus on saturation performance. In this paper, we develop an analytic model for unsaturation throughput evaluation of IEEE 802.11 DCF, based on Bianchis model (2000). The model explicitly takes into account both the carrier sensing mechanism and an additional backoff interval after successful frame transmission, which can be ignored under saturation conditions. Expressions are derived by means of the equilibrium point analysis. The accuracy of our model is validated through computer simulation.

New composite right/left-handed transmission line using substrate integrated waveguide and metal-patches

A new Composite Right/Left-Handed Transmission Line (CRLH-TL) for millimeter wave frequency is proposed and investigated theoretically and experimentally. It consists of a Substrate Integrated Waveguide (SIW) with slit apertures and a dielectric film with metal patches. A prototype of SIW Metal-patch type CRLH-TL that satisfies the balance condition is designed. Dispersion diagram and S-parameters are derived numerically, and typical field distributions of RH and LH transmission and the zero-order resonance are shown. The experimental results of the proposed SIW Metal-patch type CRLH-TL agree the analytical results well. Because both the layers of the SIW and the metal-patched dielectric film compose simple planar periodic structure, the SIW Metal-patch type CRLH-TL has advantage of simple manufacturing. It is expected to be one of the basic structure of CRLH-TL or components such as leaky wave antenna and LH coupler above 10 GHz or millimeter wave frequency.

A two-layer queueing model to predict performance of packet transfer in broadband networks

In this paper, we propose an approximate analytical method to predict the performance of packet transfer in broadband networks. Since the ATM is a promising way to achieve a multimedia data transmission in broadband networks, the underlying network is assumed to be an ATM network. To represent the packet-level and the cell-level data transfers, we introduce a two-layer queueing network model. In the higher layer of the model, the source node (the sender) generates packets and then segments the packets into cells, while the destination node (the receiver) reassembles the arriving cells into the packets. The lower layer model is a tandem queueing network in which each queue corresponds to an ATM switch. We employ a discrete-time analysis of the queueing network model to obtain the packet-level performance measures, such as the end-to-end packet transfer delay, the packet loss probability, and the throughput. In numerical examples, we show some packet transfer delay distributions and effects of the packet size on the packet loss probability.

Analysis of Unsaturation Performance of IEEE 802.11 DCF with and without Slow Contention Window Decrease*A part of this work was supported by Japan Society of the Promotion of Science (Grants-in-Aid for Scientific Research (c)) and by Okayama Multimedia Forum.

Most of analytical models proposed so far for the IEEE 802.11 distributed coordination function (DCF) focus on saturation performance. In this paper, we develop an analytic model for unsaturation performance evaluation of the IEEE 802.11 DCF with and without slow contention window decrease (SCWD). The model explicitly takes into account the carrier sensing mechanism and an additional backoff interval after successful frame transmission, both of which can be ignored under saturation conditions. Expressions are derived for throughput and delay characteristics by means of the equilibrium point analysis. The accuracy of our model is validated through computer simulation. Numerical results based on the IEEE 802.11b with CCK show that the SCWD can stably achieve approximately 20% performance gain over the normal 802.11 DCF under unsaturation conditions as well as saturation ones.

Performance comparison of imperfect symbol- and bit-interleaving of block codes over GF(2/sup m/) on a Markovian channel

We analytically compare the performance of imperfectly symbol- and bit-interleaved block codes over GF(2/sup m/) on a first-order Markovian channel in terms of the error probability of a received word. The analytical method developed in Sakakibara (2000) is extended, so that binary transmission of block codes over GF(2/sup m/) can be incorporated with the assumption of negligible probabilities of decoding error. Expressions are derived for two decoding strategies; independent bounded-distance (IBD) decoding and error-forecasting (EF) decoding. In the IBD decoding, channel errors up to half of the minimum distance can be decoded in each received word. On the other hand, combining an erasures-and-errors decoding algorithm, more errors may be corrected in the EF decoding. The derived expressions are examined on two typical classes of two-state Markovian channels. Numerical results indicate that a combination of symbol-interleaving and the EF decoding offers the best performance even for imperfect interleaving. This can compensate for the superiority of perfect symbol-interleaving to perfect bit-interleaving addressed by Wicker (1992). It is also found that the optimum depths of symbol- and bit-interleaver is approximately given by 2b and 4b, respectively, where b is the average length of burst errors in bits.

An incremental redundancy hybrid ARQ scheme using punctured MDS codes for frequency-hopping channels

An analytical method is developed for an incremental redundancy hybrid ARQ scheme using punctured MDS codes, which was originally proposed by Mandelbaum, on frequency-hopping channels. We derive expressions for throughput and the average number of packet transmissions required to be received correctly. The effect of a header in a packet is also taken into account. The derived expressions are examined for two types of redundancy partitioning: (i) equal-packet-length, and (ii) homogeneous-redundancy. It is shown from numerical results that the homogeneous-redundancy partitioning with appropriate parameters slightly outperforms the equal-packet-length partitioning.

Analysis of wave diffraction in a periodically bent nematic liquid crystal

Diffraction properties of a periodically bent nematic liquid crystal (PBNLC) are analyzed by using the previous theory for periodic liquid crystals [ J. Opt. Soc. Am. A4, 27 ( 1987)]. Wave propagation in the PBNLC is described by coupled-wave equations in a matrix form, and the diffraction and dispersion properties of the PBNLC are given. Approximate two-wave analysis taking into account the boundary effect is also derived, and good agreements between the approximate and rigorous solutions are shown.