A novel compact T/R (Transmit/Receive) switching circuit for wideband T/R modules has been proposed. It employs quadrature couplers and gate-and-drain-driven HPAs to remove circulators or T/R switches from a conventional T/R module, and T/R switching is made with controlling biasing conditions of the FETs in HPAs. Furthermore, an optimum biasing condition and design of output matching circuit of the HPA have been studied to reduce loss in RX-mode, and the validity of the method has been confirmed by measurements.

A new modulation technique for "LInear modulation with Nonlinear Translation" (LINT) is proposed. The new LINT technique is an extension of the popular LINC (LInear amplification with Nonlinear Components) technique for power efficient transmitter operation with spectrally efficient linear modulations. While providing this advantage, the LINT technique also incorporates the principles of direct modulation and provides frequency translation without the use of multiple stages of bulky upconversion circuitry. These features make the LINT method especially suitable for high frequency applications emerging at upper microwave and millimeter-wave frequencies. A two-stage 12 frequency multiplier chain is employed for frequency translation, to evaluate the feasibility of the LINT architecture for generating 16-QAM modulation at 28 GHz. The effect of imperfections on modulator performance is also considered.

In OFDM-CDMA down link (base-to-mobile) transmissions, each user's transmit data symbol is spread over a number of orthogonal sub-carriers using an orthogonal spreading sequence defined in the frequency-domain. The radio propagation channel is characterized by a frequency- and time-selective multipath fading channel (which is called a doubly selective multipath fading channel in this paper). Frequency-domain equalization is necessary at the receiver to restore orthogonality among different users. This requires accurate estimation of the time varying transfer function of the multipath channel. Furthermore, the noise enhancement due to orthogonality restoration degrades transmission performance. In this paper, pilot-aided threshold detection combining (TDC) is presented that can effectively suppress the noise enhancement. If the estimated channel gain is smaller than the detection threshold, it is replaced with the detection threshold in the frequency equalization. There exists an optimal threshold that can minimize the bit error rate (BER) for a given received Eb/N0. The average BER performance of OFDM-CDMA down link transmissions using the TDC is evaluated by computer simulations. It is found that TDC using optimum detection threshold can significantly reduce the BER floor and outperforms DS-CDMA with ideal rake combining.

A simple and practical methodology to make microwave voltage-controlled oscillators (VCOs) very linear is presented. Incorporating a very short microstrip line ( λg/4) for varactor's bias feed, the C-V curve was shifted by a constant -Δ C and performed a capacitance tailored nearly proportional to VCONT-2. This modification featured very linear VCO implementation at no expense of housing and phase noise performance. Ka- and Ku-band VCOs fabricated with this new technique exhibited a constant tuning sensitivity in a wide control voltage range (2-10 V). The phase noise level at 100 kHz offset was as low as -107 dBc/Hz for a 13 GHz-band VCO and better than -85 dBc/Hz for a 38 GHz-band VCO, due to combination of capacitor-coupled high-Q resonator and multiplier. This technology is very effective for quasi-millimeter-wave and millimeter-wave FM/FSK modulation and FMCW radar applications.

This letter derives low-complexity frame and coarse frequency-offset synchronization techniques for orthogonal frequency division multiplexing (OFDM)-based HIPERLAN (HIgh PErformance Radio LAN) system. We first propose a frame detector structure directly based on the correlation method and a reduced complexity structure having the similar performance compared with conventional correlation method. We then propose a coarse frequency-offset synchronization technique and show the performance of the proposed techniques by simulation.

A broadband RF front-end having a direct conversion architecture has been developed. The RF front-end consists of two broadband quadrature mixers, a multi-band local oscillator, and a broadband low-noise variable gain amplifier (LNVGA). The mixer achieves broadband characteristics through the incorporation of an in-phase power divider and a 45-degree power divider. The in-phase power divider achieves broadband characteristics through the addition of a compensation capacitor. The 45-degree power divider achieves broadband phase characteristics through the addition of a compensation capacitor and a compensation resistor. The local oscillator, which is composed of two VCOs, two frequency dividers, and four switches, can cover three systems including one FDD system. The LNVGA achieves its broadband characteristics without the use of reactance elements, such as inductors or capacitors. In a trial demonstration, when the RF frequency was between 900 MHz and 2.5 GHz, the mixer for a demodulator experimentally demonstrated an amplitude balance of less than 1.6 dB and a quadrature phase error of less than 3 degrees. When the RF frequency was between 900 MHz and 2.5 GHz, the mixer for a modulator demonstrated an image ratio of less than -30 dBc. The local oscillator demonstrated multi-band characteristics, which are able to cover the target frequencies for three systems (PDC, PHS, 2.4 GHz WLAN). From 900 MHz to 2.5 GHz, the amplifier shows a noise figure of less than 2.1 dB and a gain of 28 1.6 dB.

Optical near-field distributions of planar dielectric and metallic objects placed on a large dielectric substrate plate have been calculated by the volume integral equation using an iterative method called generalized minimal residual method with the fast Fourier transform technique. The basic characteristics of the near-field have been investigated in detail for large and small objects, dielectric and metallic objects and incident p-polarized and s-polarized evanescent fields.

This paper presents a novel system-level design methodology, called quality-driven design, by which application-specific optimization can be achieved; furthermore the entire functionality can be shared to maximize design reuse. As a case of study, this paper focuses on quality-driven design for video applications and introduces an output quality adaptive approach based on variable bitwidth optimization to explore a new design space. MPEG2 video is used as the driver application to illustrate the potential of the presented methodology. Experimental results show the effectiveness of the methodology.

To design a high-speed m-bit parallel inversion circuit over GF(2m), we study two variations for the repetition-operation of the numerical formula, AB2, in employing square-first and multiply-first type operations. From the proposed two variations, we propose four inversion architectures, adopting the multiplier and square in [10], as follows: simple duplication semi-systolic architecture for multiply-first inversion circuit (MFIC), m-bit parallel semi-systolic architecture for MFIC, simple duplication semi-systolic architecture for square-first inversion circuit (SFIC), and simplified m-bit parallel semi-systolic architecture for SFIC. Among them, performance of the simplified m-bit parallel semi-systolic architecture for SFIC is recommended for a high-speed applications to get a maximum throughput in the sense of small hardware-complexity, and low latency. When we implement the simplified 8-bit parallel semi-systolic architecture for SFIC over GF(28) by using 0.25 µm CMOS library, necessary are 2495 logic-gates and 1848 latches, and the latency is 56 and the estimated clock-rate is 580 MHz at 100% throughput.

Finite-state vector quantization (FSVQ) is a well-known block encoding technique for digital image compression at low bit rate application. In this paper, an improved feature map finite-state vector quantization (IFMFSVQ) algorithm using three-sided side-match prediction is proposed for image coding. The new three-sided side-match improves the prediction quality of input blocks. Precoded blocks are used to alleviate the error propagation of side-match. An edge threshold is used to classify the blocks into nonedge or edge blocks to improve bit rate performance. Furthermore, an adaptive method is also obtained. Experimental results reveal that the new IFMFSVQ reduces bit rate significantly maintaining the same subjective quality, as compared to the basic FMFSVQ method.

DS/CDMA systems employing long-period PN sequences are becoming a widespread standard of wireless communication systems. However, fast acquisition of long-period PN sequences at a low hardware cost is conventionally a difficult problem. This paper proposes a new fast acquisition algorithm for a class of PN sequences, which includes m- and GMW sequences as special cases, and shows that the mean (correct) acquisition time can be considerably reduced under input SNR values well below those used in modern DS/CDMA systems. Its fast acquisition capability is based on a decomposition of long PN sequences into a number of short ones and achieves a significantly reduced code phase uncertainty of acquisition at relatively small hardware cost. It can be applied as a (part of) acquisition system of a DS/CDMA system instead of a slow sliding correlator or a costly matched filter.

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 development of efficient quality of service (QoS) routing algorithms in a high-speed network environment is a very important and at the same time very difficult task due to the need to provide divergent services with multiple QoS requirements. Recently heuristic algorithms based on Lagrange relaxation techniques have been proposed to resolve the contradiction between the time complexity and the quality of solution. In this paper, we investigate the performance of two heuristic algorithms, LR_DCLC and NR_DCLC, for the delay-constrained least-cost (DCLC) routing problem. Algorithm LR_DCLC is based on linear relaxation, while algorithm NR_DCLC, which is proposed in this paper, is based on nonlinear relaxation. A large number of simulations demonstrate that even though both algorithms have very good performance, NR_DCLC can obtain much better solutions than LR_DCLC by running Dijkstra's algorithm on average a few more times, especially in the case when the optimal solutions are hard to find.

Performance evaluation criterion is one of the most important issues for design of network traffic control mechanisms and algorithms. Due to multiple performance objectives of network traffic control, performance evaluation criteria must include multiple performance metrics executed simultaneously, which is called integrated performance evaluation criteria. In this paper, we analyze various performance metrics of network traffic control, and propose three integrated performance evaluation criteria. One is the improvement on original Power formula; our new Power formula is based on the multi-service-class model. Another is about the fairness of user's QoS (Quality of Service) requirements (queuing delay and loss rate); especially the detailed discussion on Proportional Fairness Principle is given. And the third one is the integration of preceding two, in which the throughput, queuing delay, packet loss rate, and the fairness are considered simultaneously.

A new iterative algorithm based on the Gauss-Seidel iteration method is proposed to solve the matrix equation in the MoM analysis of the array antennas. In the new algorithm, the impedance matrix is decomposed into a number of sub matrices, which describe the self and mutual impedance between the groups of the array, and each sub matrix is regarded as a basic iteration unit rather than the matrix element in the ordinary Gauss-Seidel iteration method. It is found that the convergence condition of the ordinary Gauss-Seidel iteration scheme is very strict for the practical use, while the convergence characteristics of the present algorithm are greatly improved. The new algorithm can be applied to the sub domain MoM with a fast convergence if the grouping technique is properly used. The computation time for solving the matrix equation is reduced to be almost proportional to the square of the number of the array elements. The present method is effective in MoM analysis of solving large-scale array antennas.

When M-ary QAM (MQAM) signals experience the Rician fading channels, diversity schemes can minimize the effects of these fadings since deep fades seldom occur simultaneously during the same time intervals on two or more paths. The symbol error probability of MQAM systems using L-branch maximum ratio combining (MRC) diversity reception is derived theoretically over frequency-nonselective slow Rician fading channels with an additive white Gaussian noise (AWGN). This derived evaluation is expressed as the infinite series composed of hypergeometric and gamma functions. These performance evaluations allow designers to determine M-ary modulation methods for Rician fading environments.

This letter presents text-independent speaker identification results for telephone speech. A speaker identification system based on Karhunen-Loeve transform (KLT) derived from codebook design using genetic algorithm (GA) is proposed. We have combined genetic algorithm (GA) and the vector quantization (VQ) algorithm to avoid typical local minima for speaker data compression. Identification accuracies of 91% were achieved for 100 Mandarin speakers.

This paper describes our vehicle classification system, which is based on local-feature configuration. We have already demonstrated that our system works very well for vehicle recognition in outdoor environments. The algorithm is based on our previous work, which is a generalization of the eigen-window method. This method has the following three advantages: (1) It can detect even if parts of the vehicles are occluded. (2) It can detect even if vehicles are translated due to veering out of the lanes. (3) It does not require segmentation of vehicle areas from input images. However, this method does have a problem. Because it is view-based, our system requires model images of the target vehicles. Collecting real images of the target vehicles is generally a time consuming and difficult task. To ease the task of collecting images of all target vehicles, we apply our system to computer graphics (CG) models to recognize vehicles in real images. Through outdoor experiments, we have confirmed that using CG models is effective than collecting real images of vehicles for our system. Experimental results show that CG models can recognize vehicles in real images, and confirm that our system can classify vehicles.

This paper proposes a channel monitor-based unequal error protection scheme using a dynamic OFDM subcarrier assignment technique for broadband video transmission systems in frequency selective fading environments. In the proposed system, to achieve stable regeneration of the received video, subcarriers with relatively high channel gain are assigned to the high priority data (HPD) in the MPEG data. To further guarantee a required transmission quality of the HPD, the proposed system also employs subcarrier transmission power control with delay profile information (DPI) feedback-type channel estimation technique. Computer simulation confirms that the proposed technique is effective in preventing quality degradation with about 20 dB lower transmission power than the conventional systems in frequency selective fading environments.

The UCHT (Unified Complex Hadamard Transform) has been proposed as a new family of spreading sequences for DS-SSMA systems recently. In this Letter, the periodic autocorrelation (PAC) properties of the Unified Complex Hadamard Transform (UCHT) sequences are analyzed. Upper bounds for the out-of-phase PAC are derived for two groups of the UCHT sequences, namely the HSP-UCHT and the NHSP-UCHT sequences (the later is a more general representation of the well-known Walsh-Hadamard (WH) sequences). A comparison of the two bounds is performed. It turns out that the HSP-UCHT sequences have a lower upper bound for the out-of-phase PAC. This makes the HSP-UCHT sequences more effective than the WH sequences in combating multipath effect for DS-SSMA systems.