A reduction in the intensity deviation of a nine-channel optical frequency comb block (OFCB) is demonstrated, by adopting an asymmetric differential drive method for an InP-based dual drive Mach-Zehnder modulator. The generation of a tailored OFCB with an intensity deviation of less than 0.8dB is confirmed by using the modulator.

Broadband wireless channels are frequency selective in nature. In this paper, a novel precoder with finite impulse response (FIR) structure is proposed to maximize the throughput of the multiple-input multiple-output (MIMO) frequency-selective multicast channel. An iteration mechanism is investigated to obtain the desired FIR precoding matrix. In the iterative process, two associated parameters, namely the innovation orientation and the iteration step size, are jointly derived by the convex optimization program and the traditional Gauss-Newton algorithm. Convergence and complexity analyses are presented, and the numerical simulations indicate that the proposed method outperforms the existing schemes in the moderate to high signal to noise ratio (SNR) regime.

Space diversity reception is well known as a technique that can improve the performance of wireless communication systems without any temporal and spectral resource expansion. Implant body area networks (BANs) require high-speed transmission and low energy consumption. Therefore, applying spatial diversity reception to implant BANs can be expected to fulfill these requirements. For this purpose, this paper presents a local frequency offset diversity system with π/4-differential quadrature phase shift keying (DQPSK) for implant BANs that offer improved communication performance with a simpler receiver structure, and evaluates the proposal's bit error rate (BER) performance by theoretical analysis. In the theoretical analysis, it is difficult to analytically derive the probability density function (pdf) on the combined signal-to-noise power ratio (SNR) at the local offset frequency diversity receiver output. Therefore, this paper adopts the moment generating function approximation method and demonstrates that the resulting theoretical analyses yield performances that basically match the results of computer simulations. We first confirm that the local frequency offset diversity reception can effectively improve the communication performance of implant BANs. Next, we perform an analysis of a realistic communication performance, namely, a link budget analysis based on derived BER performance and evaluate the link parameters including system margin, maximum link distance and required transmit power. These analyses demonstrate that the local frequency offset diversity system can realize a reliable communication link in a realistic implant BAN scenario.

A body bias generator (BBG) for fine-grained body biasing (FGBB) is proposed. The FGBB is effective to reduce variability and power consumption in a system-on-chip (SoC). Since FGBB needs a number of BBGs, the BBG is preferred to be implemented in cell-based design procedure. In the cell-based design, it is inefficient to provide an extra supply voltage for BBGs. We invented a BBG with switched capacitor configuration and it enables BBG to operate with wide range of the supply voltage from 0.6V to 1.2V. We fabricated the BBG in a 65nm CMOS process to control 0.1mm2 of core circuit with the area overhead of 1.4% for the BBG.

In this paper, we present a new four parameter estimator of sampled sinusoidal signals that does not require iteration. Mathematically, the four parameters (frequency, phase, magnitude, and dc offset) of sinusoidal signals can be obtained when four data points are given. In general, the parameters have to be calculated with iteration since the equations are nonlinear. In this paper, we point out that the four parameters can be obtained analytically if the four data points given are measured using a fixed sampling interval. Analytical expressions for the four parameters are derived using the signal differences. Based on this analysis, we suggest an algorithm of estimating the four parameters from N data samples corrupted by noise without iteration. When comparing with the IEEE-1057 method which is based on the least-square method, the proposed algorithm does not require the initial guess of the parameters for iteration and avoid the convergence problem. Also, the number of required numerical operations for estimation is fixed if N is determined. As a result, the processing time of parameter estimation is much faster than the least-square method which has been confirmed by numerical simulations. Simulation results and the quantitative analysis show that the estimation error of the estimated parameters is less than 1.2 times the square root of the Cramer-Rao bounds when the signal to noise ratio is larger than 20dB.

Orthogonal frequency division multiplexing (OFDM) has been attracting much attention because of its robustness against frequency selective fading. Instead of well-known cyclic prefix (CP) insertion, known training sequence (TS) insertion can be used for OFDM block transmission (called TS-OFDM). In this paper, we propose a new receiver design, which can obtain the frequency diversity gain through the use of frequency-domain equalization (FDE) for TS-OFDM. A conditional bit error rate (BER) analysis of the proposed FDE is presented. The average BER performance of the TS-OFDM signal transmission in a frequency-selective Rayleigh fading channel is evaluated by the Monte-Carlo numerical computation method using the derived conditional BER and is confirmed by computer simulation. Numerical and computer simulation results show the proposed TS-OFDM with FDE improves BER and throughput performance of TS-OFDM compared to the conventional TS-OFDM receiver due to the frequency diversity gain. It is also shown that the proposed TS-OFDM with FDE is more robust against imperfect channel estimation than the conventional TS-OFDM receiver.

Combining the strong anti-interference advantages of OFDM technology and the time-frequency analysis features of fractional Fourier transform (FFT), we apply OFDM as the coding modulation technology for digital watermarking. Based on the Arnold scrambling and OFDM coding, an innovative DFRFT digital watermarking algorithm is proposed. First, the watermark information is subjected to the Arnold scrambling encryption and OFDM coding transform. Then it is embedded into the FFT domain amplitude. The three parameters of scrambling iterations number, t, FFT order, p, and the watermark information embedded position, L, are used as keys, so that the algorithm has high safety. A simulation shows that the algorithm is highly robust against noise, filtering, compression, and other general attacks. The algorithm not only has strong security, but also makes a good balance between invisibility and robustness. But the possibility of using OFDM technique in robust image watermarking has drawn a very little attention.

We propose a novel approach to the target localization problem using Doppler frequency shift measurements. We first reformulate the maximum likelihood estimation (MLE) as a constrained weighted least squares (CWLS) estimation, and then perform the semidefinite relaxation to relax the CWLS problem as a convex semidefinite programming (SDP) problem, which can be efficiently solved using modern convex optimization methods. Finally, the SDP solution can be used to initialize the original MLE which can provide estimates achieve the Cramer-Rao lower bound accuracy. Simulations corroborate the good performance of the proposed method.

We propose an adaptive reversible data hiding method with superior visual quality and capacity in which an adaptive generalized difference expansion (AGDE) method is applied to an integer-to-integer subband transform (I2I-ST). I2I-ST performs the reversible subband transform and the AGDE method is a state-of-the-art method of reversible data hiding. The results of experiments we performed objectively and perceptually show that the proposed method has better visual quality than conventional methods at the same embedding rate due to low variance in the frequency domain.

This paper presents frequency diversity effects of localized transmission, clustered transmission, and intra-subframe frequency hopping (FH) using a frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). In the evaluations, we employ the normalized frequency mean square covariance (NFMSV) as a measure of the frequency diversity effect, i.e., randomization level of the frequency domain interleaving associated with turbo coding. Link-level computer simulation results show that frequency diversity is very effective in decreasing the required average received signal-to-noise power ratio (SNR) at the target average block error rate (BLER) using a linear minimum mean-square error (LMMSE) based FDE according to the increase in the entire transmission bandwidth for DFT-precoded OFDMA. Moreover, we show that the NFMSV is an accurate measure of the frequency diversity effect for the 3 transmission schemes for DFT-precoded OFDMA. We also clarify the frequency diversity effects of the 3 transmission schemes from the viewpoint of the required average received SNR satisfying the target average BLER for the various key radio parameters for DFT-precoded OFDMA in frequency-selective Rayleigh fading channels.

In this paper, we propose a time and memory efficient Ultra Wide Band Short Range Radar (UWB SRR) system for measuring relative target velocities of up to 150km/hr. First, for the proposed detector, we select the required design parameters for good performance. The parameters are the number of coherent integrations, non-coherent integrations, and FFT points. The conventional detector uses a Fast Fourier Transform (FFT) to extract the range and velocity of the target simultaneously. Therefore, it requires high computation effort, high FFT processing time, and a huge amount of memory. However, the proposed pulse radar detector first decides the target range and then computes the target velocity using FFT sequentially for the decided range index. According to our theoretical and simulation analyses, the FFT processing time and the memory requirement are reduced compared to those of the conventional method. Finally, we show that the detection performance of the proposed detector is superior to that of the conventional detector in a background of Additive White Gaussian Noise (AWGN).

In this paper, we propose a spectrally efficient frequency-domain channel estimation scheme suitable for training sequence inserted single-carrier (TS-SC) block transmission using frequency-domain equalization (FDE). The proposed scheme performs the channel estimation in two steps and allows the use of shorter TS (but, longer than the channel length) than the conventional channel estimation schemes. In the first step, the received TS having cyclic property is constructed for performing frequency-domain channel estimation and the improved channel estimate is obtained by using simple averaging of noisy channel estimates. In the second step, the maximum likelihood channel estimation is carried out iteratively by using both the TS and the estimated symbol sequence obtained in the first step. It is shown by computer simulation that the proposed 2-step frequency-domain iterative channel estimation scheme achieves a bit error rate (BER) performance close to perfect channel estimation even in a relatively fast fading environment.

The second generation digital terrestrial broadcasting system (DVB-T2) is the first broadcasting system employing MISO (Multiple-Input Single-Output) algorithms. The potential MISO gain of this system has been roughly predicted through simulations and field tests. Of course, the potential MISO SFN gain (MISO-SFNG) differs according to the simulation conditions, test methods, and measurement environments. In this paper, network gains of SISO-SFN and MISO-SFN are theoretically derived. Such network gains are also analyzed with respect to the receive power imbalance and coverage distances of SISO and MISO SFN. From the analysis, it is proven that MISO-SFNG is always larger than SISO SFN gain (SISO-SFNG) in terms of the achievable SNR. Further, both MISO-SFNG and SISO-SFNG depend on the power imbalance, but the network gains are constant regardless of the modulation order. Once the field strength of the complete SFN is obtained by coverage planning tools or field measurements, the SFN service coverage can be precisely calibrated by applying the closed-form SFNG formula.

This paper studies channel sounding for selfish dynamic spectrum control (S-DSC) in which each link dynamically maps its spectral components onto a necessary amount of discrete frequencies having the highest channel gain of the common system band. In S-DSC, it is compulsory to conduct channel sounding for the entire system band by using a reference signal whose spectral components are sparsely allocated by S-DSC. Using nonuniform sampling theory, this paper exploits the finite impulse response characteristic of frequency selective fading channels to carry out the channel sounding. However, when the number of spectral components is relatively small compared to the number of discrete frequencies of the system band, reliability of the channel sounding deteriorates severely due to the ill-conditioned problem and degradation in channel capacity of the next frame occurs as a result. Aiming at balancing frequency selection diversity effect and reliability of channel sounding, this paper proposes an S-DSC which allocates an appropriate number of spectral components onto discrete frequencies with low predicted channel gain besides mapping the rest onto those with high predicted channel gain. A numerical analysis confirms that the proposed S-DSC gives significant enhancement in channel capacity performance.

In the literature, many resource allocation schemes have been proposed for multi-hop networks. However, the analyses provided focus mainly on the single cell case. Inter-cell interference severely degrades the performance of a wireless mobile network. Therefore, incorporating the analysis of inter-cell interference into the study of a scheme is required to more fully understand the performance of that scheme. The authors of this paper have proposed a parallel relaying scheme for a 2-hop OFDMA virtual cellular network (VCN). The purpose of this paper is to study a new version of that scheme which considers a multi-cell environment and evaluate the performance of the VCN. The ergodic channel capacity and outage capacity of the VCN in the presence of inter-cell interference are evaluated, and the results are compared to those of the single hop network (SHN). Furthermore, the effect of the location and number of wireless ports in the VCN on the channel capacity of the VCN is investigated, and the degree of fairness of the VCN relative to that of the SHN is compared. Using computer simulations, it is found that in the presence of inter-cell interference, a) the VCN outperforms the SHN even in the interference dominant transmission power region (when a single cell is considered, the VCN is better than the SHN only in the noise dominant transmission power region), b) the channel capacity of the VCN remains greater than that of the SHN even if the VCN is fully loaded, c) an optimal distance ratio for the location of the wireless ports can be found in the interval 0.2∼0.4, d) increasing the number of wireless ports from 3 to 6 can increase the channel capacity of the VCN, and e) the VCN can achieve better outage capacity than the SHN.

In this paper, joint transmit/receive frequency-domain equalization (FDE) is proposed for analog network coded (ANC) single-carrier (SC) bi-directional multi-antenna relay. In the proposed scheme, diversity transmission using transmit FDE is performed at relay station (RS) equipped with multiple antennas while receive FDE is carried out at base station (BS) and mobile terminal (MT) both equipped with single antenna. The transmit and receive FDE weights are jointly optimized so as to minimize the end-to-end mean square error (MSE). We evaluate, by computer simulation, the throughput performance and show that the joint transmit/receive FDE obtains the spatial and frequency diversity gains and accordingly achieve better throughput performance compared to either the transmit FDE only or the receive FDE only. It is also shown that ANC SC bi-directional multi-antenna relay can extend the communication coverage area for the given required throughput compared to conventional direct transmission.

To mitigate the impact of the frequency selectivity of the wireless channel on the initial ranging (IR) process in 802.16 based WiMax systems, several well known pre-equalization techniques applied in the IR are first analyzed in detail, and the optimal pre-equalization scheme is further improved for the IR by overcoming its weaknesses. A numerical simulation shows that the proposed pre-equalization scheme significantly improves the performance of multiuser detection and parameter estimation in the IR process.

The linearity analysis of a passive mixer is presented. The distortion mechanism caused by switching operation of a MOS transistor is elucidated from the static and dynamic analysis of passive mixers. Furthermore, the maximum input and output level to keep linear operation and its required bias conditions are expressed by simple equations. The maximum linear output amplitude of the passive mixer is determined only by the local signal amplitude and it does not depend on input and output impedance. The calculated linearity performances agree well with simulated and measured results.

This letter deals with blind carrier frequency offset estimation by exploiting the minimum variance distortionless response (MVDR) criterion for interleaved uplink orthogonal frequency division multiple access (OFDMA). It has been shown that the complexity and estimation accuracy of MVDR strictly depend on the grid size used during the search. For the purpose of efficient estimation, we present an improved polynomial rooting estimator that is robust in low signal-to-noise ratio scenario. Simulation results are provided for illustrating the effectiveness of the proposed estimator.

This paper introduces a radio frequency identification (RFID) tag for urination detection. The proposed tag is embedded into paper diapers in order to detect the patient's urination immediately. For this tag, we designed an RFID tag antenna at 950MHz, which matches the impedance of the associated integrated circuit (IC) chip. In addition, we calculate the antenna characteristics and measure the reflection coefficient (S11) and radiation pattern of the antenna. The results show that this system can be used to detect urination.