The transmission of duplicate packets provides a loss-resilience without undue time-delay in the video transmission over packet loss networks. However, this method generally deteriorates the problem of traffic congestion because of the increased bit-rate for duplicate packet transmission. In this paper, we propose a set of techniques for an efficient packetization and transmission of duplicate video packets. The proposed method transmits the duplicate packet containing high priority data that is quite small in volume but very important for the reconstruction of the video. This method significantly reduces the required bit-rate for duplicate transmission. An efficient packetization method is also proposed to reduce additional packet overhead which is required for transmitting the duplicate data. It is shown by simulations that the proposed method remarkably improves the packet loss-resilience for video transmission only with small increase of redundant duplicated data for each slice.

We present a low power architecture that dynamically controls wordlengths in a wireless OFDM demodulator. Finding the optimum wordlength for digital circuit systems is difficult because the trade-off between the hardware cost and system performance is not conclusive. Actual circuit systems have large wordlengths at the circuit design level to avoid calculation errors caused by a lack of dynamic range. This indicates that power dissipation can still be reduced under better conditions. We propose a tunable wordlength architecture that dynamically changes its own wordlength according to the communication environment. The proposed OFDM demodulator measures error vector magnitudes (EVMs) from de-modulated signals and tunes the wordlength to satisfy the required quality of communication by monitoring the EVM performance. The demodulator can reduce dissipated energy by a maximum of 32 and 24% in AWGN and multipath fading channels.

For point-to-point mobile visual communications, layered video has been utilized to adapt to time-varying channel capacity over noisy environments. From the perspective of the HVS (Human Visual System), it is necessary to minimize the loss of visual quality by specifically maintaining the throughput of visually important regions, objects and so on. Utilizing the prioritized bitstreams generated according to each layer, the throughput can be improved for given channel statistics. In this paper, we define the transmission gain and measure the improved performance when the throughput of ROI (Regions Of Interest) is increased relative to visually unimportant regions over a capacity limited mobile channel.

To support multimedia applications effectively in mobile networks, the handover latency or packet losses during handover should be very small. Addressing this issue, we present a cooperative mobile router-based handover (CoMoRoHo) scheme for long-vehicular multihomed mobile networks. The basic idea behind CoMoRoHo is to enable different mobile routers to access different subnets during a handover and cooperatively receive packets destined for each other. In general, packet losses are directly proportional to handover latency; however, the overlapped reception of packets from different subnets makes possible to minimize packet losses even without reducing handover latency. To evaluate the scheme, we carried out performance modeling of the CoMoRoHo scheme in comparison with the Fast Handover for Mobile IPv6 (FMIPv6) protocol in regard to the handover latency, packet loss, signaling overhead, and packet delivery overhead in access networks. The analysis results show that CoMoRoHo outperforms FMIPv6 by reducing the packet losses as well as signaling overheads by more than 50%. Moreover, CoMoRoHo imposes lower packet delivery overheads required for preventing packets from being dropped from access routers. We thus conclude that CoMoRoHo is a scalable scheme because its performance remains intact even when the access network is overloaded.

This paper proposes efficient DSP instructions and their hardware architecture for the Viterbi algorithm. The implementation of the Viterbi algorithm on a DSP chip has been attracting more interest for its flexibility, programmability, etc. The proposed architecture can reduce the Trace Back (TB) latency and can support various wireless communication standards. The proposed instructions perform the Add Compare Select (ACS) and TB operations in parallel and the architecture has special hardware, called the Offset Calculation Unit (OCU), which automatically calculates data addresses for acceleration of the trellis butterfly computations. When the constraint length K is 5, the proposed architecture can reduce the decoding cycles about 17% compared with Carmel DSP and about 45% compared with TMS320C55x.

In this paper, a novel location management scheme called Distributed Group Tracking (DGT) for group communications in Cellular IP networks is proposed. In DGT, Base stations track each member of a group and build a share multicast routing tree called DGT-Tree for the group in a distributed manner. Transmission of multicast packets among group members is along the group's DGT-Tree. Simulation study has demonstrated that a better performance can be achieved by DGT over the gateway-based counterpart in terms of transmission cost as well as link load balance. Moreover, the average number of DGT operations decreases as the group size increases, showing the good scalability of the DGT scheme, and the average number of control packets as well as the cache requirement for performing DGT operations demonstrate the moderate overhead introduced by DGT.

This paper studies a multiband mobile communication system to support both high data rate services and wide service coverage, using high and low frequency resources with different propagation characteristics. In the multiband system, multiple frequency bands are managed by a base station and one of the frequency bands is adaptively allocated to a terminal depending on his channel quality. By limiting the low frequency resources to a terminal not covered by the higher frequencies, the presented multiband system can accommodate many terminals providing wide coverage area, as if all radio resources have low frequency. From numerical results, the multiband system can provide wide service coverage area for much larger number of terminals than conventional systems. It is also found that an appropriate balance of multiple frequency resources is essential to achieve high capacity.

Based on the Khatri-Rao matrix product, we propose a novel unitary space-time modulation design called KR-USTM in this paper. Different from existing USTM schemes, such as the systematic approach and space-time frequency-shift keying (ST-FSK), KR-USTM does not require any computer search and can be applied to any number of transmit antennas. Moreover, the special structure of KR-USTM also makes it a high-rate scheme and achieve full antenna diversity as well as lower decoding complexity. Simulation results show that the proposed KR-USTM constellation achieves error performance comparable to existing USTM designs at low rates, while it outperforms them at high rates.

A compact open-loop resonator bandpass filter is presented to suppress the spurious passband using compensated compact microstrip resonant cell (C-CMRC) feeding structure. Based on the inherently compact and stopband characteristics of the C-CMRC feeding, the proposed filters shows a better spurious rejection performance than the only open-loop resonator filter. The suppression is -57.4 dB, -49.5 dB, and -43.9 dB at the 2nd, 3rd and 4th harmonic signal separately. All the performance of proposed filters have been verified by the measured results.

Efficient group rekeying is an important issue for secure group communications. Most of the proposed group rekeying methods require expensive encryption and decryption operations to rekey the group. However, in a model where a trusted server is used to distribute group keys, the trusted server may become a bottleneck because of the expensive computation operations, such as encryption, that it has to perform. In this paper, we propose a new stateless group rekeying scheme to solve the multicast group rekeying problem. In our proposed scheme, the trusted server combines mask-based key-location hiding with the simple XOR-encryption using secret hash values to rekey the group. Without affecting the system security, our approach reduces the processing cost of the trusted server by eliminating the need to encrypt the group key. Moreover, to acquire the group key, the computational cost of the group members is low and stable regardless of the rekeying message size.

This paper presents constructions of two kinds of sets of sequences with a zero correlation zone, called ZCZ code, which can reach the upper bound of the member size of the sequence set. One is a ZCZ code which can be constructed by a unitary matrix and a perfect sequence. Especially, a ternary perfect sequence with elements 1 and zero can be used to construct the proposed ZCZ code. The other is a ZCZ code of pairs of ternary sequences and binary sequences which can be constructed by an orthogonal matrix that includes a Hadamard matrix and an orthogonal sequence pair. As a special case, an orthogonal sequence pair, which consists of a ternary sequence and a binary sequence, can be used to construct the proposed ZCZ code. These codes can provide CDMA systems without co-channel interference.

We extend the sliding block code in symbolic dynamics to transform J (≥2) sequences of Markov chains with time delays. Under the assumption that the chains are irreducible and aperiodic, we prove the central limit theorem (CLT) for the normalized sums of extended sliding block codes from J sequences of Markov chains. We apply the theorem to the system analysis of asynchronous spread spectrum multiple access (SSMA) communication systems using spreading sequences of Markov chains. We find that the standard Gaussian approximation (SGA) for estimations of bit error probabilities in such systems is the 0-th order approximation of the evaluation based on the CLT. We also provide a simple theoretical evaluation of bit error probabilities in such systems, which agrees properly with the experimental results even for the systems with small number of users and low length of spreading sequences.

Secure communication in Mobile Ad Hoc Networks (MANETs) is important as nodes communicate over the wireless medium, which can be easily eavesdropped. Currently, the literature of secure IP address autoconfiguration in MANETs is extremely rare. In this paper, we propose five protocols that provide both secure IP address autoconfiguration and authenticated group key agreement (GKA) to give a more efficient and secure solution for MANET communications. Whenever a dynamic group membership event such as node join, node leave, network merge and network partition occurs, our protocols ensure that the IP address allocation table and group key are updated so that there are no address conflicts and leaving and joining users cannot decrypt future and previous communications respectively. A complexity analysis shows that despite having additional capabilities such as IP address autoconfiguration and key authentication, our protocols are still efficient when compared to other GKA protocols.

The optical ZCZ code is a set of pairs of binary and bi-phase sequences with zero correlation zone. An optical M-ary direct sequence spread spectrum (M-ary/DS-SS) system using this code can detect a desired sequence without interference of undesired sequences. However, the bank of matched filters in a receiver circuit may fall into large scale. In this paper, we propose the compact construction of a bank of matched filters for an M-ary/DS-SS system using an optical ZCZ code. This filter bank can decrease the number of 2-input adders from O(N2) to O(N) and delay circuits from O(N2) to O(Nlog 2 N), respectively, and is implemented on a field programmable gate array (FPGA) corresponding to 400,000 logic gates.

It was previously shown that the number of array elements must exceed the number of sources for multiple target direction of arrival (DOA) tracking. This is clearly not practical for code-division multiple access (CDMA) communications since the number of mobile users is very large. To overcome the restriction, adaptive angle tracking approaches employing the code-matched filters and parallel Kalman/H∞ algorithms are presented in this paper. The proposed approaches are applied to the base station of a mobile communication system. Different from Kalman prediction algorithm which minimize the squared tracking error, the adaptive H∞ filtering algorithm is a worst case optimization. It minimizes the effect of the worst disturbances (including modeling error of direction matrix models and array structure imperfection, process noise, and measurement noise). Hence, the difficult problem of tracking the crossing mobiles can be successfully handled by using the code-matched filters. Computer simulation is provided for illustrating the effectiveness of the adaptive angle tracking approaches.

We proposed a method for suppressing arc ignition in mechanical contact devices using a transient current switch and a capacitor. We applied the method to conventional reed switches. For the electric circuit analysis, we clarified the momentary voltage-current characteristics at breaking operation of reed switches by FEM analysis. We could also estimate the capacitance of the contact electrodes at the metal bridge rupture by FEM analysis, and would derive the non-arcing condition using SPICE simulation. The suitable capacitor value in the transient current circuit for arc ignition suppression would be depend on the load impedance, the power supply, the time depending contact resistance R(t)s, the contact capacitance, and the minimum arc voltage and current.

The main factor determining for both friction and contact resistance is the true contact area in the contact interface. Contact resistance depends on the size of the true contact area and contaminant films interposed between the contact areas of the interface. Moreover, friction force also depends on the true contact area. In particular, the formation of metallic junctions in the true contact area strongly effects the friction force. Therefore, since both electrical contact and friction force are related to the size of the true contact area, the contact resistance and friction force are considered to be interrelated through true contact areas. For electromechanical devices with sliding contacts such as connector and sliding switches, the contact resistance and friction are important characteristics. In order to obtain low contact resistance, contact load should be higher, but the friction force increases. These are opposite-side problems. In this study, as the contact resistance and friction occur in the same true contact area, the relationship between the contact resistance and friction was expressed in an equation. Moreover, this relationship was examined experimentally on a variety of contact surfaces under different surface conditions.

In this study, we propose an adaptive handoff scheme with dynamic hysteresis value for cellular communications, which is based on distance between the mobile station and the serving base station. Performance is evaluated in terms of the expected number of handoffs, the expected handoff delay, standard deviation of handoff location, and the expected link degradation probability as well. Numerical results and simulations show that the proposed scheme outperforms the handoff schemes with static hysteresis levels. The effect of distance error is also discussed.

This paper proposes a calibration method for catadioptric camera systems consisting of a mirror whose reflecting surface is the surface of revolution and a perspective camera as typified by HyperOmni Vision. The proposed method is based on conventional camera calibration and mirror posture estimation. Many methods for camera calibration have been proposed and during the last decade, methods for catadioptric camera calibration have also been proposed. The main problem with catadioptric camera calibration is that the degree of freedom of mirror posture is limited or the accuracy of the estimated parameters is inadequate due to nonlinear optimization. On the other hand, our method can estimate five degrees of freedom of mirror posture and is free from the volatility of nonlinear optimization. The mirror posture has five degrees of freedom, because the mirror surface has a surface of revolution. Our method uses the mirror boundary and can estimate up to four mirror postures. We apply an extrinsic parameter calibration method based on conic fitting for this estimation method. Because an estimate of the mirror posture is not unique, we also propose a selection method for finding the best one. By using the conic-based analytical method we can avoid the initial value problem arising from nonlinear optimization. We conducted experiments on synthesized images and real images to evaluate the performance of our method, and discuss its accuracy.

We achieved first dynamic all-optical signal processing with a bandgap-engineered MZI SOA all-optical switch. The wide-gap Selective Area Growth (SAG) technique was used to provide multi-bandgap materials with a single step epitaxy. The maximum photoluminescence (PL) peak shift obtained between the active region and the passive region was 192 nm. The static current switching with the fabricated switch indicated a large carrier induced refractive index change; up to 14 π phase shift was obtained with 60 mA injection in the SOA. The carrier recovery time of the SOA for obtaining a phase shift of π was estimated to be 250-300 ps. A clear eye pattern was obtained in 2.5 Gbps all-optical wavelength conversion. This is the first all-optical wavelength conversion demonstration with a bandgap-engineered PIC with either selective area growth or quantum-well intermixing techniques.