The analytic expression for the transmission spectrum of cascaded long-period fiber gratings is presented in a closed form. When several identical gratings are cascaded in-series with a regular distance, the transmission spectrum is revealed to have a series of regularly spaced peaks, suitable for multi-channel filters. The analytic solution is obtained by diagonalizing the transfer matrix of each grating unit that is composed of a single grating and a grating-free region between adjacent gratings. The spectrum of the device is simply described with the number of cascaded gratings and a single parameter that has the information of the phase difference between the modes. With the derived equation, the spectral behaviors of the proposed device are investigated. The intensity of each peak can be controlled by adjusting the strength of a single grating. The separation between adjacent gratings determines the spacing between the peaks. The finesse of the peaks can be increased by cascading more gratings. The derived analytic results are compared with the known results of paired gratings and phase-shifted gratings.

In an ideal fiber grating having a uniform refractive index modulation, the reflection or the transmission spectrum is symmetric with equal amount of side lobes on both sides of the resonant wavelength of the fiber grating. It is observed that a long-period fiber grating made by a non-uniform UV laser beam through a uniform amplitude mask has an asymmetric transmission spectrum. The asymmetric characteristic is explained with Mach-Zehnder effect in the long-period fiber grating. The non-uniform UV laser beam makes also a non-uniform index modulation along the fiber core. Therefore, a beam coupled to a cladding mode at a section of the grating can be re-coupled to the core mode after passing a certain distance. The re-coupled beam makes Mach-Zehnder-like interference with the un-coupled core mode. However, it is presented that the asymmetric phenomenon can be overcome by scanning the UV laser beam along the fiber over the mask. The beam scanning method is able to suffer the same fluence of the UV laser beam on the fiber. Finally, a linearly chirped long-period fiber grating was made using the non-uniform UV laser beam. Due to the asymmetricity the chirping effect was not clearly observed. It is also presented that the beam scanning method could remove the asymmetric problem and recover the typical spectrum of the linearly chirped fiber grating.

We demonstrate, through numerical simulations, the possibility of trans-oceanic single channel transmission at 160 Gbit/s with no active control. This was achieved using short period dispersion management, which supports short pulse propagation at practical map strengths. We demonstrate that through careful selection and optimisation of the system parameters the performance of this system can be extended. We also define the tolerable limits of the system to the residual dispersion slope and polarisation mode dispersion.

The effect of wavelength detuning on the device performance of identical-epitaxial-layer (IEL) electroabsorption (EA) modulator integrated distributed feedback (DFB) lasers is studied in detail. Based on the lasing behavior of integrated devices with different amount of wavelength detuning and the photocurrent spectra under different reverse biases, the optimal wavelength detuning is experimentally determined to be around 30-40 nm for our IEL integrated devices. By adopting gain-coupled DFB laser section, integrated devices with optimal wavelength detuning have demonstrated excellent single mode performances. The extinction ratio is measured to be greater than 15 dB at -3 V, and the modulation bandwidth is around 8 GHz.

A photonic crystal fibre has an array of microscopic air holes running along its length. The periodicity of the array is broken by a deliberate "defect" that acts as a waveguide core. Light is confined to this core by the holes. Although some designs of photonic crystal fibre guide light by total internal reflection and so can be considered analogues of conventional optical fibres, their properties can be strikingly different. Other designs guide light by photonic bandgap confinement and represent a totally new type of fibre.

Recent progress in ultrahigh bit rate optical transmission using time-division multiplexing and wavelength-division multiplexing is described. Latest over 1 Tbit/s transmission experiments are shown and the possibility of higher bit rate transmission is discussed.

We describe a control scheme for wireless-link layers and the TCP/IP layers in which wireless link states, such as signal strength and transmission rate, are transparent to the upper network layers and govern the behavior of the upper layers. Monitoring and notifying functions for wireless link states are incorporated into mobile hosts, and prefetching functions for the mobility agent lists are added to the present MobileIP functionalities of the network layers. In addition, we give the mobile hosts functions for controlling the TCP advertised windows in the transport layers and give the base-stations buffering functions to deal with the variable signal strength of the wireless links. A simulation (using ns-2) of this control scheme shows that mobile agent can be switched at the network layers soon after base-station hand-over and that errors in packet routing, packet loss and communication throughput reduction can be avoided. Moreover, communications can be interrupted without having to shrink the size of the congestion windows of the TCP senders, which improves overall throughput.

Error concealment is an essential part of reliable video communication systems because transmission errors are inevitable even when the coded bitstream is highly protected. The problem of temporal EC can be factored into two parts regarding candidate motion vectors (MVs) employed and the matching criterion to evaluate the fitness of each candidate MV. In order to obtain more faithful EC results, this paper proposes a novel iterative EC algorithm, in which an efficient way to provide candidate MVs and a new fitness measure are presented. The proposed approach for candidate MVs systematically utilizes all the available neighboring MVs by exploiting a well-known spatiotemporal correlation of block MVs. Also, in order to remove the dependency of a damaged block's quality of concealment on the already concealed adjacent blocks, we develope a new matching criterion. The objective of the proposed fitness measure is to minimize the total boundary matching errors induced by the whole corrupted blocks. Simulations performed using an H.263 codec demonstrate a significant improvement on the subjective and objective concealed video qualities, especially when the corrupted area is wider than a single row of coding blocks.

In quantum communication theory, a realization of the optimum quantum receiver that minimizes the error probability is one of fundamental problems. A quantum receiver is described by detection operators. Therefore, it is very important to derive the optimum detection operators for a realization of the optimum quantum receiver. In general, it is difficult to derive the optimum detection operators, except for some simple cases. In addition, even if we could derive the optimum detection operators, it is not trivial what device corresponds to the operators. In this paper, we show a realization method of a quantum receiver which is described by a projection-valued measure (PVM) and apply the method to 3-ary phase-shift-keyed (3PSK) coherent-state signals.

Understanding traffic characteristics in mobile communications is invaluable for planning, designing, and operating cellular networks, and various mobility models have therefore come to be developed to predict traffic characteristics. In this paper, cell-dwell-time distribution and transition probability in a virtual cellular system are first estimated from the results of measuring taxi motion using the Global Positioning System (GPS) for large-city and small-city ranges of motion. Then, on the basis of simulations using these estimations, traffic characteristics like handoff rate and channel blocking probability in a cellular system are evaluated. It was found that a difference between large and small cities could be observed in speed distribution and direction-of-travel probability, but only a slight difference in cell-dwell-time distribution.

In this paper, we propose a new location tracking method for pointer forwarding with distributed HLRs schemes to decrease the location tracking cost. Similar to the distributed HLR schemes, the location information is replicated on all HLRs in our scheme. However, unlike the traditional distributed HLR schemes, we propagate the most recent location changes from an HLR to reset the forwarding pointers in other HLRs, and thus reduce the cost of location tracking for call deliveries. The signaling cost of location propagation may be too costly to be practical. Therefore, we allow some inconsistency to exist among the location data of HLRs and defer the propagation of location changes to reduce the propagation cost. Three delay propagation policies are also proposed and analyzed using simulation. The performance result shows that the delay propagation policies reduce the propagation cost and the propagation resetting process degrades the location tracking cost. Our method preserves a low total cost for call deliveries, registrations and propagations in distributed HLRs.

We have proposed and implemented a spread spectrum (SS) wireless switch using 2.4 GHz front-end AlN/Al2O3 surface acoustic wave (SAW) matched filter (MF). Since the SAW MF has radio frequency (RF) front-end operation, RF components are not needed in the received circuit. High impedance in the peripheral circuit using passive devices has been employed for low current consumption. The SS wireless switches have been designed with the power consumption of less than 100 µW by using the SAW MF. It is confirmed that implemented SS wireless switch has a long battery life of 10 years and communication range of 30 m.

This paper proposes a new satellite communication system that enables high-speed communication in a mobile environment. The system configuration combines a terrestrial mobile network and an existing satellite system, and includes a tracking antenna that was newly developed to receive 30 Mbit/s signals from commercial communication satellites. A prototype system comprising the mobile network, the satellite system and a vehicle in which the tracking antenna is installed was constructed for purposes of evaluation and demonstration. A LAN system was incorporated in the experimental vehicle by using the tracking antenna, a satellite router and a Personal Digital Cellular phone. The validity of the proposed system was verified by the tracking antenna driving tests, system UDP tests and FTP throughput tests in a mobile environment.

To satisfy huge service demand and multi-traffic requirements with limited bandwidth, this paper proposes two different procedures of multi-channel multiple access schemes with the slotted ALOHA operation for both data and voice traffic and presents an exact analysis to numerically evaluate the performance of the systems. In scheme I, there is no limitation on access between data transmissions and voice transmissions, i.e., all channels can be accessed by all transmissions. In scheme II, a channel reservation policy is applied, where a number of channels are used exclusively for voice packets while the remaining channels are used for both data packets and voice packets. We call the system using scheme I "Non-reservation system" and call the system using scheme II "Reservation system. " Performance characteristics we obtained include loss probability for voice traffic, average packet delay for data traffic and channel utilization for both traffic. The performance of the schemes and the effects of the design parameters are numerically evaluated and compared to a wide-bandwidth conventional single-channel slotted ALOHA system with single data traffic. The analysis presented in this paper will be not only useful for the performance evaluation and the optimum design of multi-channel multi-traffic systems in wireless environments, but also applicable to evaluate other performance measures in priority networks, cellular mobile radio networks or multi-hop wireless networks.

To develop a smoothing method for speckle reduction is a significant problem, because of the complex ultrasonic characteristics and the obscurity of the tissue image. This paper presents a new method for speckle reduction from medical ultrasonic image by using fuzzy morphological speckle reduction algorithm (FMSR) that preserves resolvable details while removing speckle in order to cope with the ambiguous and obscure ultrasonic images. FMSR creates a cleaned image by recombining the processed residual images with a smoothed version of an original image. Performance of the proposed method has been tested on the phantom and tissue images. The results show that the method effectively reduces the speckle while preserving the resolvable details.

A K-band MMIC subharmonically pumped mixer integrating local oscillator (LO) amplifier has been developed. For up-converter application, it is necessary to reduce the leakage of second harmonic component of LO frequency to RF port, which is generated by nonlinear operation of LO amplifier. A quasi-lumped short-circuited stub using microstrip structure has been successfully applied to the MMIC mixer to enhance 2fLO-suppression. We propose a new configuration of a quasi-lumped short-circuited stub, which reduces the influence of parasitic elements of via-holes. The developed MMIC has a one-stage LO amplifier and it has shown about 10 dB-improvement of 2fLO-suppression compared to conventional configuration using a quarter-wavelength short-circuited stub.

The cellular-communication systems of the future will be required to provide multimedia services to users moving about in a variety of ways (on foot, in automobiles etc.). Different forms of motion have different characteristics. The characterization of the different forms of motion and their effects on telecommunications traffic is important in the planning, design and operation of mobile communication networks. The characterization of the motion of various platform types (inter-city buses, recreational vehicles, freight trucks, and taxis) based on measurements using Global Positioning System is presented in this paper. The measured characteristics of motion are then used to evaluate teletraffic statistics such as cell cross-over rate and cell dwell time by overlaying hypothetical cell systems on the measured loci of vehicles. Self-similarity was discovered in the cell dwell time characteristic of the taxis.

This paper experimentally evaluates the bit error rate (BER) performance of single-carrier broadband DS-CDMA (B-CDMA) scheme using a 100-MHz bandwidth (chip rate of 81.92 Mcps) in frequency-selective multipath fading channels. The achievable information bit rate is 20.36 (2.5) Mbps when the spreading factor (SF) is SF = 4 (32). In order to achieve a high data-rate transmission with high quality (i.e., average BER is below 10-6), we apply pilot symbol-assisted coherent Rake receiving with a large number of Rake fingers (maximum number of Rake fingers is SF2), 2-branch antenna diversity reception, convolutional coding, and signal-to-interference power ratio (SIR) measurement-based fast closed-loop transmit power control (TPC). Experimental results show that the average BER of 10-6 for the 20.36 (2.5)-Mbps transmission is achieved at the required average transmit Eb/N0 of approximately 6.7 (5.0) dB when the number of multipaths is L = 2 and the maximum fading Doppler frequency is fD = 20 Hz. We also show that Rake time diversity and fast TPC are effective in a broadband propagation channel where many resolvable paths (such as 12 paths) are observed.

As noncoherent direct sequence code-division multiple-access (DS-CDMA) mobile satellite communications, two typical transmission schemes are compared; one is a quasi-synchronous differential BPSK (QS-DBPSK) where orthogonal signals are used for reducing the multiple access interference and the other is M-ary orthogonal signaling (MOS) scheme where orthogonal signals are used for exploiting more efficient modulation. The performances are evaluated in additive white Gaussian noise (AWGN) and shadowed Rician fading (SRF) channels and the effects of timing misalignments in the QS-DBPSK system and the amount of Doppler shifts of a SRF channel are investigated. The results show that MOS much outperforms QS-DBPSK in the region of low system loading up to about 50% and a precise chip synchronization is required for QS-DBPSK. In a SRF channel, it is also shown that QS-DBPSK much outperforms MOS in a slow fading channel but MOS has a performance gain against the large Doppler shift.

This paper proposes an autonomous relay access algorithm that provides an intelligent wireless network structure for inter-vehicle communication systems. The proposed algorithm introduces a special classification among mobile terminals and assigns terminals to one of several terminal groups, which are adaptively and autonomously constructed according to traffic conditions. The proposed algorithm uses the terminal groups to conduct relay access transmission among terminals, and achieves a high rate of successful inter-terminal transmission. Computer simulation confirms that the proposed algorithm can achieve a lower blocking probability than that without a relay access scheme.