In this paper, a practical adaptive TuCM scheme is proposed, and its adaptive method is described. With some hardware considerations, a suboptimal optimization algorithm which shows that the number of fading regions is variable is put forward. The proposed adaptive TuCM comes within 3 dB of fading channel capacity, exhibits about 3 dB power gain over conventional adaptive TCM, and is easy to realize by hardware. Considering delay and channel estimation error, the BER performance of adaptive TuCM is analyzed and simulated. In the performance analysis, the method of data fitting is applied to obtain the BER expression for TuCM, and a fitting mathematical model is proposed. Results show that adaptive TuCM is very sensitive to delay and channel estimation error. To alleviate these problems, we proposed an improved power adaptation that can make adaptive TuCM practical.

In this letter, the effect of an imperfect channel estimation and carrier frequency offset on the performance of transmit diversity OFDM systems is investigated. For the performance evaluation, the average bit error rate (BER) expression is derived in the presence of the imperfect channel information including both the inherent estimation error and the imperfect windowing error derived in a mismatched channel separation.

Carrier frequency and symbol timing errors may greatly degrade the performance of the orthogonal frequency division mulitplexing (OFDM) system, especially in multipath environment. In this paper, we explore the cyclostationarity of OFDM signals, which only relies on second order statistics, to estimate the synchronization offset. First, a coarse carrier frequency offset estimator for multipath environment is developed using the second order statistics of the received OFDM signal. It has a wide capture range though not accurate. Second, we introduce a new synchronization algorithm based on cyclostationarity and matched filter theories, which can get the maximal estimation SNR in multipath environment. Both estimators utilize channel state information to achieve better estimation performance and are non-pilot aided. They can be combined to form a whole OFDM synchronizer for multipath environment. Finally, simulations confirm the performance of the estimation algorithm.

A technique for the design of circular- and racetrack-shaped NRD guide ring resonators was developed based on the mode coupling theory. Besides the operating mode, a parasitic mode is generated at curved sections of the resonator as a result of the mode conversion. Resonance of the NRD guide ring resonator is derived by characteristic equations of the coupled modes and then employed in making the design diagrams, which are useful for determining the dimensions of the ring resonators. It is shown that the discrepancy between the experimental results and previous theory can be resolved by using the present theory. Low loss, small-sized ring resonators with curvature radii of less than 5.3 mm were fabricated at 60 GHz and a band rejection performance of more than 30 dB was observed. Moreover, a procedure for the design of the channel dropping filter was developed and a 2-pole filter, which has great advantages such as a low insertion loss of 1.2 dB and a compact size smaller than that of a golf ball, was successfully developed by using two racetrack-shaped ring resonators.

Frequency channel allocation according to the interference among links is important in autonomous distributed control wireless base station networks from the viewpoint of efficient frequency utilization. It is generally difficult to estimate the interference imposed on other links in a distributed control scheme. This paper proposes a novel frequency channel allocation scheme employing distributed control utilizing broadcast signals to estimate the intensities and frequencies of the interference to other links. The frequency channel, which can be allocated to a link from the viewpoint of the degree of the interference imposed on other links, can be found by receiving broadcast signals. Simulation results show that the proposed scheme efficiently allocates frequency channels to each link to avoid the interference.

The use of concatenated codes in non-coherent synchronous optical fiber CDMA networks is proposed. The concatenated code sequences are generated using Walsh code sequences and balanced Walsh code sequences, which are selected from Walsh code sequences. The selection of balanced Walsh code sequences is presented and the design of fully programmable electro-optical transmitter and receiver is reported. In the proposed network, sequence-inversion keying of intensity modulated unipolar concatenated code sequences is employed at the transmitter and unipolar-bipolar correlation is implemented at the receiver. The analysis of the system BER performance is presented and it is proved that multiple-access interference is completely eliminated. It is also shown that the BER performance of the proposed system is better than that of non-coherent synchronous optical fiber CDMA system using optical orthogonal codes with double hard-limiters.

This paper presents laboratory experimental results on the throughput performance when key techniques such as adaptive modulation and channel coding (AMC) and hybrid automatic repeat request (ARQ) with packet combining are employed by an implemented transceiver based on the High-Speed Downlink Packet Access (HSDPA) air interface in a multipath fading channel. In AMC operation, we applied four modulation and coding schemes (MCSs): MCS1 (QPSK data modulation with the channel coding rate of R = 1/2, hereafter simply referred to as QPSK with R = 1/2), MCS2 (QPSK with R = 3/4), MCS3 (16 QAM with R = 1/2), and MCS4 (16 QAM with R = 3/4). The results elucidate that a peak average throughput above 5.0 Mbps is achieved at the average received signal energy per chip-to-background noise power spectrum density ratio (Ec/N0) of more than approximately 20 dB in a one-path fading channel; nevertheless, the achievable peak throughput becomes approximately 2.9 (2.6) Mbps due to severe multipath interference (MPI) in a two-path fading channel where the average signal power of the second path is 6 (3) dB lower than that of the first path, assuming nine-code-channel multiplexing with the fading maximum Doppler frequency of fD = 5 Hz. Furthermore, we clarify that although the throughput performance employing Type-II hybrid ARQ (i.e., Incremental redundancy) is almost the same as that employing Type-I hybrid ARQ with packet combining (i.e., Chase combining) in a two-path fading channel, Incremental redundancy exhibits superiority over Chase combing in a one-path fading channel for a high Doppler frequency channel such as fD = 80 Hz.

A bi-directional and multi-channel wireless telemetry capsule, 11 mm in diameter, is presented that can transmit video images from inside the human body and receive a control signal from an external control unit. The proposed telemetry capsule includes transmitting and receiving antennas, a demodulator, decoder, four LEDs, and CMOS image sensor, along with their driving circuits. The receiver demodulates the received signal radiated from the external control unit. Next, the decoder receives the stream of control signals and interprets five of the binary digits as an address code. Thereafter, the remaining signal is interpreted as four bits of binary data. Consequently, the proposed telemetry module can demodulate external signals so as to control the behavior of the camera and four LEDs during the transmission of video images. The proposed telemetry capsule can simultaneously transmit a video signal and receive a control signal determining the behavior of the capsule itself. As a result, the total power consumption of the telemetry capsule can be reduced by turning off the camera power during dead time and separately controlling the LEDs for proper illumination of the intestine.

An important area in visual communications is the restoration of image sequences degraded by channel and noise. Since a nonlinearity is commonly involved in image transmitting procedure, an adaptive nonlinear equalizer is required. In this paper we address this problem by proposing a 3D adaptive nonlinear filter, namely the 3D adaptive Volterra filter with an LMS type of adaptation algorithm. This adaptive filter is used for equalizing an unknown 2-D channel with some point-wise nonlinearity and restoring image sequences degraded by this channel. Prior to filtering, motion is estimated from the sequence and compensated for. For this purpose, a robust region-recursive Higher Order Statistics (HOS) based motion estimation method is employed. The overall combination is able to adequately remove undesired effects of communication channel and noise. The performance of this algorithm is examined using real image sequences demonstrated by experimental results.

A new power and bandwidth efficient modulation technique - Superposed Quadrature Quadrature Amplitude Modulation (SQ2AM) - for use in nonlinear satellite channel is presented. SQ2AM technique expands 2-dimensional SQAM signals into 4-dimensional quadrature modulated signals by using orthogonal baseband waveforms and carriers. The power spectrum and BER performance of SQ2AM are analyzed and compared with those of QPSK, SQAM and Q2PSK in a nonlinearly amplified multi-channel environment.

We show that a randomized addition-sub-traction chains countermeasure against side channel attacks is vulnerable to an SPA attack, which is a kind of side channel attack, under distinguishability between addition and doubling. The side channel attack takes advantage of information leaked during execution of a cryptographic procedure. The randomized addition-subtraction chains countermeasure was proposed by Oswald-Aigner, and is based on a random decision inserted into computations. However, the question of its immunity to side channel attacks is still controversial. The randomized addition-subtraction chains countermeasure has security flaw in timing attacks, another kind of side channel attack. We have implemented the proposed attack algorithm, whose input is a set of AD sequences, which consist of the characters "A" and "D" to indicate addition and doubling, respectively. Our program has clarified the effectiveness of the attack. The attack algorithm could actually detect secret scalars for given AD sequences. The average time to detect a 160-bit scalar was about 6 milliseconds, and only 30 AD sequences were enough to detect such a scalar. Compared with other countermeasures against side channel attacks, the randomized addition-subtraction chains countermeasure is much slower.

Multi-channel arrayed waveguide devices are crucial for WDM optical communication systems. Multi-channel arrayed polymer-based waveguide devices have been important for reducing cost and size. This paper introduces two types of multi-channel arrayed polymer-based waveguide devices. We designed and fabricated a four-channel arrayed 22 thermo-optic switch using a low-loss polymer and a four-channel arrayed electro-optic Mach-Zehnder modulator using an electro-optic polymer. The four-channel arrayed 22 thermo-optic switch has very low power consumption and uniform performance. The switching time of the four-channel arrayed EO Mach-Zehnder modulator operating with just lumped electrodes is less than a few nanoseconds.

One of the difficulties in routing problem is in wirability which is to guarantee a physical connection of a given topological route. Wirability often fails since the width of a wire is relatively large compared with the size of modules. As a possible solution, this paper proposes an incremental wiring algorithm which generates wires net-by-net without overlapping other pre-placed circuit elements. The idea is to divide a wire into a series of rectangles and handles them as modules with additional constraints to keep the shape of the wire. The algorithm was implemented and experimented on a small instance to show its promising performance.

A new pilot-aided multiuser detection scheme, single code cyclic shift (SCCS) detector, is proposed in this paper for synchronous CDMA multiuser signal reception. The unique feature of the proposed detector is that a receiver can decode multiuser signals even without explicit knowledge of all signature codes active in the system. The transmitting signal from a base station to a mobile contains two separated channels: the pilot and data channels; the former consists of periodically repeated pilot symbols encoded by the same signature codes as the one spreading the latter. Both pilot and data signals for a specific mobile are sent by a base-station using quadrature and in-phase carriers at the same frequency with QPSK modulation. A matched filter bank, consisting of M correlators that match to distinct cyclic-shifted versions of a "single" signature code, is employed for "channel cyclic shift correlation function" estimation, followed by the multiuser detection algorithm based on the channel information obtained earlier. The performance of the proposed SCCS detector is evaluated and compared to decorrelating detector by computer simulations considering various multipath channels with different profiles. The results demonstrate that a synchronous CDMA joint detection can be implemented successfully without necessarily knowing all signature codes of the system.

A linear voltage-to-current convertor without current mirror circuit is proposed for low distortion applications employing short channel MOSFET's. Twin current sources and current sinks pair of MOSFET's having the same drain-source voltage are employed for a substitute of the current mirror circuits, in order to eliminate the channel length modulation factor of the short channel MOSFET's. HSPICE simulation is shown in order to evaluate the proposed circuits. As an application, a low distortion OTA is realized by employing the proposed linear voltage-to-current convertor with short channel MOSFET's.

In Ad Hoc networks, communication between a pair of hosts uses channel resources, such that the channel cannot be used by the neighboring hosts. A channel used by one pair of hosts can be reused by another pair of hosts only if their communication ranges do not overlap. Channels are limited resources, accounting for why exploiting channel reuse opportunities and enhancing the channel utilization is essential to increasing system capacity. However, exploiting channel reuse opportunities may cause a co-channel interference problem. Two pairs of communicating hosts that use the same channel may gradually move toward to each other. A channel reassignment operation must be applied to these hosts to maintain their communication. This investigation presents a channel assignment protocol that enables the channel resources to be highly utilized. Following this protocol, a channel reassignment protocol is also proposed to protect the communicating hosts from co-channel interference caused by mobility. The proposed reassignment protocol efficiently reassigns a new available channel to a pair of hosts that suffers from co-channel interference. The performance of the proposed protocols is also examined. Experimental results reveal that the proposed protocols enable more hosts to communicate simultaneously and prevent their communication from failing.

In this paper, we propose a new IEEE 802.11 based multichannel MAC protocol, which satisfies a single transceiver constraint and which is still compatible with the IEEE 802.11 standard. Our proposed protocol does not need any additional transceivers, and we can make use of the current IEEE 802.11 hardware for the implementation of our multichannel protocol. We propose and investigate two kinds of channel selection algorithms, these are, the sender based channel selection scheme and the receiver based channel selection scheme. We evaluate the TCP performance over our proposed multichannel MAC protocol by the simulations taking account of the overhead, the time taken by changing the frequency channel and the time taken by the carrier sense in each channel. It is shown that our proposed scheme improves the performance significantly with a single transceiver. It is shown that the overhead costs are quite large in the multichannel MAC protocol, and the sender based channel selection scheme achieves better performance than that of the receiver based channel selection scheme in most cases. It is also shown that there exists a break-even value of the PLL synthesizer lockup time if we compare with the single channel IEEE 802.11 MAC protocol.

CPCH is an uplink common channel that is used by 3GPP to support reliable packet transport. In this paper, we propose a new access scheme by using the discrimination of backoff timer for providing a prioritized service. We also present a simple system model of CPCH for EPA and use it to derive mathematical results. The results show that multi-class services with different priorities can be served effectively and easily by the proposed scheme.

This study is a detailed numerical investigation on the relations between the performance of the RZ format single-channel transmission, and the chromatic dispersion of transmission fiber and pre-compensation ratio. We observed the transition from the SPM dominant low dispersion region to the intra-channel nonlinearities dominant high dispersion region, and found that the EOP is very sensitive to the pre-compensation ratio when the dispersion assumes a intermediate value. Furthermore, by analyzing the optical power-dependence of the EOP and other nonlinear impairments, we found that the amplitude fluctuation resulting from IFWM is dominant in determining the EOP in the transmission systems employing highly dispersed pulses.

A new pilot-aided channel estimation technique is proposed and applied to wideband CDMA (WCDMA) systems. This technique is based on conventional pilot-aided decision directed (PADD) algorithms. In this letter, conventional PADD algorithms are studied extensively and a modified PADD algorithm is presented. The performance of the proposed algorithm is compared with that of conventional PADD algorithms through computer simulations in Rayleigh fading environments.