This work presents a frequency-scaling low-power (FSLP) design methodology for managing power consumption of cores in the tile-based network-on-chip (NOC) architecture. A moving picture experts group (MPEG) core is tested using the field-programmable gate array (FPGA) implementation to verify the feasibility of the proposed method. Measurement results show that about 30% power consumption can be saved in the MPEG core and reveal that the proposed FSLP design method can be suitable for cores in the tile-based NOC applications.

In this letter, a new channel-adaptive beamforming method is proposed for OFDMA systems with smart antennas. In the method, the size of a cluster for resource unit is determined adaptively according to a region-splitting criterion. It is shown by simulations that the proposed method shows good performance in both frequency-flat and frequency-selective channels.

This letter describes an efficient architecture for a Software Defined Radio (SDR) Wideband Code Division Multiple Access (WCDMA) receiver using for high performance wireless communication systems. The architecture is composed of a Radio Frequency (RF) front-end, an Analog-to-Digital Converter (ADC), and a Quadrature Amplitude Modulation (QAM) demodulator. A coherent demodulator, with a complete digital synchronization scheme, achieves the bit-error rate (BER) of 10-6 with the implementation loss of 0.5 dB for a raw Quadrature Phase Shift King (QPSK) signal.

Orthogonal frequency division multiplexing (OFDM) has been adopted in the physical layer of IEEE802.11a WLAN standard. In this Letter, a high-resolution frequency-offset estimation scheme is presented for the OFDM-based WLAN. The scheme efficiently exploits the features of the 802.11a preamble for high-resolution estimation of frequency-offset. Simulation results indicate that the algorithm is much superior to the conventional scheme for frequency-offset estimation in the 802.11a WLAN.

A new channel estimator that does not require a separate frequency offset estimator is proposed. The new algorithm has low complexity and low latency compared to the well-known weighted multi-slot averaging algorithm. The simulation results demonstrate the improved resistance to high Doppler frequency and high frequency offset.

Coupling between resonators are analyzed theoretically on basis of the coupled mode theory. New and basic equations for the coupling coefficient are derived and compared with those of waveguides. They should be useful for understanding the physical background of coupling and designing a new coupling scheme.

We propose utilizing subband-based blind source separation (BSS) for convolutive mixtures of speech. This is motivated by the drawback of frequency-domain BSS, i.e., when a long frame with a fixed long frame-shift is used to cover reverberation, the number of samples in each frequency decreases and the separation performance is degraded. In subband BSS, (1) by using a moderate number of subbands, a sufficient number of samples can be held in each subband, and (2) by using FIR filters in each subband, we can manage long reverberation. We confirm that subband BSS achieves better performance than frequency-domain BSS. Moreover, subband BSS allows us to select a separation method suited to each subband. Using this advantage, we propose efficient separation procedures that consider the frequency characteristics of room reverberation and speech signals (3) by using longer unmixing filters in low frequency bands and (4) by adopting an overlap-blockshift in BSS's batch adaptation in low frequency bands. Consequently, frequency-dependent subband processing is successfully realized with the proposed subband BSS.

To achieve both of a high peak performance and low average power characteristics, frequency-voltage cooperative control processor has been proposed. The processor schedules its operating frequency according to the required computation power. Its operating voltage or body bias voltage is adequately modulated simultaneously to effectively cut down either switching current or leakage current, and it results in reduction of total power dissipation of the processor. Since a frequency-voltage cooperative control processor has two or more operating frequencies, there are countless scheduling methods exist to realize a certain number of cycles by deadline time. This proposition is frequently appears in a hard real-time system. This paper proves two important theorems, which give the power-minimum frequency scheduling method for any types of frequency-voltage cooperative control processor, such as Vdd-control type, Vth-control type and Vdd-Vth-control type processors.

Frequency-domain and time-domain novel uniform asymptotic solutions for the scattered fields by an impedance cylinder and a dielectric cylinder, with a radius of curvature sufficiently larger than the wavelength, are presented in this paper. The frequency-domain novel extended UTD and the modified UTD solutions, derived by retaining the higher-order terms in the integrals for the scattered fields, may be applied in the deep shadow region in which the conventional UTD solutions produce the substantial errors. The novel time-domain uniform asymptotic solutions are derived by applying the saddle point technique in evaluating the inverse Fourier transform. We have confirmed the accuracy and validity of the uniform asymptotic solutions both in the frequency-domain and in the time-domain by comparing those solutions with the reference solutions calculated from the eigenfunction expansion (frequency-domain) and from the hybrid eigenfunction expansion and fast Fourier transform (FFT) method (time-domain).

In this paper, we present a new all-digital carrier recovery loop for high-order quadrature amplitude modulation (QAM) signal constellations. The proposed approach is a blind phase-frequency detector structure that consists of a phase detector, a phase offset estimator, a frequency offset estimator, and a digital control oscillator. Compared to previous related approaches, the proposed algorithm provides a wider acquisition range and a more accurate estimation of frequency and phase offsets. These features are demonstrated by simulation results of the DOCSIS (Data-Over-Cable Service Interface Specifications) cable modem system.

This paper considers the low-frequency scattering by a circular dielectric cylinder and modifies the exact polarizability tensor to extend the valid region of the known low-frequency solution. When compared to the traditional formulation, the proposed solution is shown to be valid for cylinders with a higher dielectric constant and larger radius.

A robust joint symbol timing and fractional frequency offset estimator for OFDM systems in multipath fading channels is proposed based on cyclic shifting and autocorrelation properties of PN codes. A new timing metric is also introduced by considering the delay spread to improve the robustness of the estimator in the multipath fading channels.

In this letter, a joint estimation algorithm of Doppler spread and frequency offset for OFDM systems in Rayleigh fading channels is proposed based on the autocorrelation function between the last part of the received OFDM signal and its copy in guard interval. It is shown by computer simulations that the proposed algorithm performs well for different Doppler spread values and carrier frequency offsets.

In software defined radio systems, placing the analog-to-digital converter (ADC) near the antenna part in the block diagram of the receiver is desired to improve the flexibility of the system. The radio frequency (RF) sampling method, in which the received signal is sampled at the RF stage, realizes such structure. The undersampling is a potential method to sample the RF signal using the existing consumer ADCs because high speed ADCs are required in the traditional methods, such as Nyquist sampling or the oversampling of the RF signal. This paper presents a technique to determine the minimum sampling frequency to undersample the separated multiple wireless systems simultaneously. In addition, this paper proposes a frequency selecting scheme that enables selection of a lower sampling frequency by receiving at least the desired transmission channels in the wireless system signals. This paper also provides a result of performance analysis of the proposed scheme.

In order to simultaneously combat both of the inter-carrier interferences (ICIs) and multiple access interferences (MAIs) to achieve reliable performance in multi-carrier code division multiple access (MC-CDMA) systems, this letter proposes a maximum likelihood based scheme for joint frequency offset estimation and multiuser symbol detection. To reduce the computational complexity called for by the joint decision statistic without extra mechanisms, the genetic algorithm (GA) is employed to solve the nonlinear optimization involved. Due to the robustness of the GA, the joint decision statistic can be efficiently solved, and, as shown by furnished simulation results, the proposed approach can offer satisfactory performance in various scenarios.

This letter proposes a modified orthogonal frequency division multiplexing (OFDM) system with low peak-to-average power ratio (PAPR) and reduced complexity. To do this, OFDM system exploits a frequency diversity equipped with a simple symbol repetition. From the presented results, we can see that the investigated OFDM system with one transmit antenna gives the same diversity gain to two-branch transmit diversity and can be implemented with reduced transmitter complexity and low peak power at the cost of decoding delay.

A sampling frequency offset estimation scheme for MB-OFDM UWB systems is proposed based on technical specification and multi-band utilization of the MB-OFDM. An estimation scheme using simple weighting factor based on the received signal power of each sub-channel is also introduced to efficiently combine estimates obtained from all the sub-carriers and to improve the estimation performance.

This letter deals with our investigations into improving the performance of a wireless uplink system when an orthogonal frequency-division multiple access (OFDMA) is used as an access scheme. To do this, the OFDMA-based uplink system adopts a frequency diversity coupled with a cyclic time shift (CTS) at the transmitter, which is named as the FD-OFDMA system with CTS. It is found that the multi-user FD-OFDMA system equipping with CTS can decrease the probability of destroying the orthogonality among the users and provide the MAI-robust reception without decreasing the bandwidth efficiency of the system.

We propose an accurate and efficient model of having an unbalanced differential line structure, where mode-conversion and frequency dependent loss effects are considered in above the GHz frequency range. To extract model parameters of the proposed unbalanced differential line model, we measured s-parameters of test patterns using a 2-port VNA and defined a new type of mixed-mode s-parameter. The model parameters were obtained and are described for various types of the unbalanced differential line structures. Finally, the validity of the proposed model and the model parameters were successfully confirmed by a series of time-domain measurements and a lattice diagram analysis.

In this paper, we propose and investigate space-time-frequency turbo coded OFDM transmissions through time-varying and frequency-selective fading channel. The proposed turbo code is a serial concatenated convolutional code which consists of space-frequency and time-frequency domain codes. The aim of the proposed turbo code is to obtain both diversity and coding gains over space-time-frequency domain. Using computer simulations and EXtrinsic Information Transfer (EXIT) charts, we investigate the optimum structure of inner and outer codes. Simulations demonstrate that the proposed system leads to significantly enhanced performance. Moreover, we analyze the computational complexity.