In orthogonal frequency-division multiplexing (OFDM)-based wireless local area networks (WLANs), phase noise (PHN) and residual frequency offset (RFO) can cause the common phase error (CPE) and the inter-carrier interferences (ICI), which seriously degrade the performance of systems. In this letter, we propose a combined pilot symbol assisted and decision-directed channel estimation scheme based on the least-squares (LS) and the maximum-likelihood (ML) algorithms. Simulation results present that the proposed scheme significantly improves the performance of OFDM-based WLANs.

A novel blind channel estimation scheme is proposed for OFDM systems employing PSK modulation. This scheme minimizes the number of possible channels by exploiting the constant modulus property, chooses a best fit over the possible channels by exploiting the finite alphabet property of information signals, and achieves competitive performance with low computational complexity. Results comparing the new scheme with the finite-alphabet based channel estimation are presented.

In this paper, the magnetic field properties and the dosimetry at intermediate frequency (21 kHz) for an induction heater are investigated with the coil model, which is prescribed as substitute source model in the European standard EN50366 (CENELEC). The accuracy of the magnetic field vectors and the values of the induced current density, which are achieved with the coil model, are compared with the results of a realistic model of the induction heater obtained from the equivalent source model. It is shown that the coil model coincides well for the magnitude of the magnetic field strength around the induction heater. On the other hand, the dominant field vector of the coil model differs significantly from the real induction heater, which leads to induced current densities in the body model which are three time larger. Owing to these results, the applicability of the coil model prescribed in the EN50366 is confirmed for the induction heater.

The analog IC technology, might sound old-fashioned, is still important for the future wireless systems such as 4G cellular phone systems, broadband wireless networkings, and wireless sensor networkings. The analog features and issues of the scaled CMOS transistor, the basic issue and the technology trend for the ADC as an important building block of wires systems, and the feature of the digital RF architecture proposed recently are reviewed and discussed. Higher speed and lower power consumption are expected for low SNR systems along with the further technology scaling. However, the high SNR system is not realized easily due to a decrease of signal voltage. One of the important technology trends is the digitalization of RF signal to realize the system flexibility, robustness, area shrinking, and TAT shortening.

For multilevel-coded modulation, the cut-off rate of multiple antenna systems over frequency-flat, fast fading channels is derived. Following Wozencraft's approach, a closed-form expression for the cut-off rate is obtained as a function of energy ratio per dimension It is shown that the maximum value of cut-off rate increases linearly with the number of transmit antennas.

We theoretically analyze the performance of coherent ultrashort light pulse code-division multiple-access (CDMA) communication systems with a nonlinear optical thresholder. The coherent ultrashort light pulse CDMA is a promising system for an optical local area network (LAN) due to its advantages of asynchronous transmission, high information security, multiple access capability, and optical processing. The nonlinear optical thresholder is based on frequency chirping induced by self-phase modulation (SPM) in optical fiber, and discriminates an ultrashort pulse from multiple access interference (MAI) with picosecond duration. The numerical results show that the thermal noise caused in a photodetector dominates the bit error rate (BER). BER decreases as the fiber length in the nonlinear thresholder and the photocurrent difference in the photodetector increase. Using the nonlinear optical thresholder allows for the response time of the photodetector to be at least 100 times the duration of the ultrashort pulses. We also show that the optimum cut-off frequency at the nonlinear thresholder to achieve the minimum BER increases with fiber length, the total number of users, and the load resistance in the photodetector.

The speech noise reduction system based on the frequency domain adaptive line enhancer using a windowed modified DFT (MDFT) pair is presented. The adaptive line enhancer (ALE) is effective for extracting sinusoidal signals blurred by a broadband noise. In addition, it utilizes only one microphone. Therefore, it is suitable for the realization of speech noise reduction in portable electronic devices. In the ALE, an input signal is generated by delaying a desired signal using the decorrelation parameter, which makes the noise in the input signal decorrelated with that in the desired one. In the present paper, we propose to set decorrelation parameters in the frequency domain and adjust them to optimal values according to the relationship between speech and noise. Such frequency domain decorrelation parameters enable the reduction of the computational complexity of the proposed system. Also, we introduce the window function into MDFT for suppressing spectral leakage. The performance of the proposed noise reduction system is examined through computer simulations.

A novel frequency domain training sequence and the corresponding carrier frequency offset (CFO) estimator are proposed for orthogonal frequency division multiplexing (OFDM) systems over frequency-selective fading channels. The proposed frequency domain training sequence comprises two types of pilot tones, namely distinctively spaced pilot tones with high energies and uniformly spaced ones with low energies. Based on the distinctively spaced pilot tones, integer CFO estimation is accomplished. After the subcarriers occupied by the distinctively spaced pilot tones and their adjacent subcarriers are nulled for the sake of interference cancellation, fractional CFO estimation is executed according to the uniformly spaced pilot tones. By exploiting a predefined lookup table making the best of the structure of the distinctively spaced pilot tones, computational complexity of the proposed CFO estimator can be decreased considerably. With the aid of the uniformly spaced pilot tones generated from Chu sequence with cyclically orthogonal property, the ability of the proposed estimator to combat multipath effect is enhanced to a great extent. Simulation results illustrate the good performance of the proposed CFO estimator.

A novel method is proposed to synthesize dual-band bandpass filters (BPFs) from a prototype lowpass filter. By implementing successive frequency transformations and circuit conversions, a new filter topology is obtained which consists of only admittance inverters and series or shunt resonators, and is thereby easy to be realized by using conventional distributed elements. A microstrip dual-band BPF with central frequencies of 1.8 GHz and 2.4 GHz is designed and fabricated using microstrip lines and stubs. The simulated and measured results show a good agreement and validate thereby the proposed theory.

This letter evaluates the performance of an uplink multicarrier-code division multiple access (MC-CDMA) system when the frequency offsets of all users are random variables and the frequency offset for the desired user is compensated. The analysis confirms that performance degradation due to frequency offset is negligible if the estimation error of normalized frequency offset for the desired user is less than 10-1.

An LDPC-coded FH-OFDMA system is proposed for the uplink of a packet-based cellular system, where the frequency hopping (FH) is based on a resource block (RB) for coherent demodulation. For the system, different RB types are employed either for better intercell interference (ICI) averaging capability or for better channel estimation performance. For the receiver, practical iterative channel estimation and decoding methods are proposed to improve the channel estimation performance without boosting the pilot power and to mitigate the adverse effects of the ICI. Extensive simulation results are provided to show the effect of the RB size on the channel estimation and ICI averaging performance as well as possible application of the proposed receiver in harsh mobile environments with dynamic packet allocation.

In this letter, we investigate ESPRIT-based approaches for blind frequency offset estimation on MC-CDMA downlink. By analyzing the signal subspace structures of the MC-CDMA signals, the natures of the spreading codes and the number of users determine the feasibility of the ESPRIT-based approaches for the blind estimation task.

The spatial distribution of the electric field in the low to high frequency bands radiated from printed circuit board (PCB) should be estimated continuously from near to far field. The characteristic of the electric field distribution is analyzed by the FDTD-multiple analysis space (FDTD-MAS) method, which can analyze from near to far field continuously, and compared with measured results. Since the analyzed electric field distribution is good agreement with measured results, it is suggested that the continuous distribution for electric field from near to far field can be calculated by the FDTD-MAS method. The electric field at low frequency is larger than that at high frequency within 1 m.

In this letter, a hybrid selection combining (SC) and maximal ratio receive combining (MRRC) technique is proposed for orthogonal frequency-division multiplexing (OFDM) systems with multiple receive antennas. The proposed technique still uses multiple receive antennas, but it has just a single RF front-end and a single baseband demodulator. In comparison with the OFDM system with no diversity, we can achieve superior gain irrespective of bandwidth efficiency, and also in comparison with the MRRC OFDM, we can achieve better gain under the bandwidth efficiency of 3 bps/Hz at the bit error rate of 10-6.

The module-wise dynamic voltage and frequency scaling (MDVFS) scheme is applied to a single-chip H.264/MPEG-4 audio/visual codec LSI. The power consumption of the target module with controlled supply voltage and frequency is reduced by 40% in comparison with the operation without voltage or frequency scaling. The consumed power of the chip is 63 mW in decoding QVGA H.264 video at 15 fps and MPEG-4 AAC LC audio simultaneously. This LSI keep operating continuously even during the voltage transition of the target module by introducing the newly developed dynamic de-skewing system (DDS) which watches and control the clock edge of the target module.

In deep sub-micrometer CMOS process, owing to the thin gate oxide and small subthreshold voltage, the leakage current becomes more and more serious. The leakage current has made the impact on phase-locked loops (PLLs). In this paper, the compensation circuits are presented to reduce the leakage current on the charge pump circuit and the MOS capacitor as the loop filter. The proposed circuit has been fabricated in 0.13-µm CMOS process. The power consumption is 3 mW and the die area is 0.270.3 mm2.

This paper presents a fast switching CMOS frequency synthesizer with a new coarse tuning method for PHS applications. To achieve the fast lock-time and the low phase noise performance, an efficient bandwidth control scheme is proposed. To change the bandwidth, the charge pump current and the loop filter zero resistor should be changed. Charge pump up/down current mismatches are compensated with the current mismatch compensation block. The proposed coarse tuning method selects the optimal tuning capacitances of the LC-VCO to optimize the phase noise and the lock-time. The measured lock-time is about 20 µs and the phase noise is -121 dBc/ at 600 kHz offset. This chip is fabricated with 0.25 µm CMOS technology, and the die area is 0.7 mm2.1mm. The power consumption is 54 mW at 2.7 V supply voltage.

In this letter, we propose a partial minimum mean-squared error (MMSE) with successive interference cancellation (PMMSESIC) method in frequency domain to mitigate ICI caused by channel variation. Each detection, the proposed method detects the symbol with the largest received signal-to-interference-plus-noise ratio (SINR) among all the undetected symbols, using an MMSE detector that considers only the interference of several neithborhood subcarriers. Analysis and simulations show that it outperforms the MMSE method at relatively high Eb/N0 and its performance is close to the MMSE with successive detection (MMSESD) method in relatively low Doppler frequency region.

This paper presents a simple method to determine weights of single carrier multiple input multiple output (MIMO) broadband communication systems adopting tapped delay line (TDL) structure in receiver side for the effective communication under frequency selective fading (FSF) environment. First, assuming the perfect knowledge of the channel matrix in both arrays, an iterative design method of transmitter and receiver weights is proposed. In this approach, both weights are determined alternately to maximize signal to noise plus interference ratio (SINR) by fixing the weight of one side while optimizing the other, and this operation is repeated until SINR converges. Next, considering the case of uninformed transmitter, maximum SINR design method of MIMO system is extended for space time block coding (STBC) scheme working under FSF. Through computer simulations, it is demonstrated that the proposed schemes achieves higher SINR than conventional method with delay-less structure, particularly for the fading with long duration.

For alleviating the high peak-to-average power ratio (PAPR) problem of orthogonal frequency division multiplexing (OFDM), the OFDM combined with time division multiplexing (TDM) using frequency-domain equalization (FDE) was proposed. In this paper, the theoretical bit error rate (BER) analysis of the OFDM/TDM in a frequency-selective fading channel is presented. The conditional BER expression is derived, based on a Gaussian approximation of the inter-symbol interference (ISI) arising from channel frequency-selectivity, for the given set of channel gains. Various FDE techniques as in multi-carrier code division multiple access (MC-CDMA), i.e., zero forcing (ZF), maximum ratio combining (MRC) and minimum mean square error (MMSE) criteria are considered. The average BER performance is evaluated by Monte-Carlo numerical computation method using the derived conditional BER expression.