Traditional wavelet-based speech enhancement algorithms are ineffective in the presence of highly non-stationary noise because of the difficulties in the accurate estimation of the local noise spectrum. In this paper, a simple method of noise estimation employing the use of a voice activity detector is proposed. We can improve the output of a wavelet-based speech enhancement algorithm in the presence of random noise bursts according to the results of VAD decision. The noisy speech is first preprocessed using bark-scale wavelet packet decomposition ( BSWPD ) to convert a noisy signal into wavelet coefficients (WCs). It is found that the VAD using bark-scale spectral entropy, called as BS-Entropy, parameter is superior to other energy-based approach especially in variable noise-level. The wavelet coefficient threshold (WCT) of each subband is then temporally adjusted according to the result of VAD approach. In a speech-dominated frame, the speech is categorized into either a voiced frame or an unvoiced frame. A voiced frame possesses a strong tone-like spectrum in lower subbands, so that the WCs of lower-band must be reserved. On the contrary, the WCT tends to increase in lower-band if the speech is categorized as unvoiced. In a noise-dominated frame, the background noise can be almost completely removed by increasing the WCT. The objective and subjective experimental results are then used to evaluate the proposed system. The experiments show that this algorithm is valid on various noise conditions, especially for color noise and non-stationary noise conditions.

In this paper, multiple-symbol differential detection (MSDD) is applied to the differential unitary space-time-frequency coding (DUSTFC) scheme over frequency selective fading multiple-input multiple-output (MIMO) channels. The motivation of applying MSDD is to compensate for the performance loss of conventional (two-symbol observation) differential detection comparing with coherent detection, by extending the observation interval and considering the fading autocorrelations. Since the differential coding of DUSTFC can be performed in time or frequency domain, both the time-domain and frequency-domain MSDD are investigated. After calculating the frequency-domain fading autocorrelation, the decision metrics of MSDD considering appropriate fading autocorrelations are derived in time and frequency domain respectively. Bit error rate (BER) performances of the two kinds of MSDD are analyzed by computer simulations. Simulation results demonstrate that a considerable performance gain can be got by applying MSDD in both cases, and the transmit diversity gain can also be enhanced by applying MSDD. So that it is proved that full advantage of transmit diversity with DUSTFC can be taken by applying MSDD.

This paper proposes a wide-locking range divide-by-3 injection-locked frequency divider (ILFD) fabricated in the 90 nm 1P9M CMOS technology. The divider consists of an nMOS cross-coupled LC oscillator and two injection MOSFETs in series with the cross-coupled nMOSFETs. The ILFD is formed with two linear mixers which share the same dc current so that a low power ILFD can be designed. At the supply voltage of 0.7 V, the free-running frequency is from 10.18 to 11.56 GHz, the current and power consumption of the divider without buffers are 2.8 mA and 1.96 mW, respectively. At the incident power of 0 dBm, the total operational locking range is 4.94 GHz, from the incident frequency 29.96 to 34.9 GHz.

A differential inter-symbol interference (ISI) cancellation method for time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) systems is proposed. The differential output of an OFDM system can greatly reduce the impact of ISI in the frequency domain and it constructs a convolutional structure, thus the Viterbi decoding algorithm can be used to recover the transmitted information from the output signal. Simulation results show the effectiveness of the proposed method.

This paper proposes a low complexity noise suppressor with hybrid filterbanks and adaptive time-frequency tiling. An analysis hybrid filterbank provides efficient transformation by further decomposing low-frequency bins after a coarse transformation with a short frame size. A synthesis hybrid filterbank also reduces computational complexity in a similar fashion to the analysis hybrid filterbank. Adaptive time-frequency tiling reduces the number of spectral gain calculations. It adaptively generates tiling information in the time-frequency plane based on the signal characteristics. The average number of instructions on a typical DSP chip has been reduced by 30% to 7.5 MIPS in case of mono signals sampled at 44.1 kHz. A Subjective test result shows that the sound quality of the proposed method is comparable to that of the conventional one.

A number of inter-cell interference coordination schemes have been proposed to mitigate the inter-cell interference problem for orthogonal frequency division multiple access (OFDMA) systems and among them, partial frequency reuse is considered one of the most promising approaches. In this paper, we propose an inter-cell interference mitigation scheme for an OFDMA downlink system, which makes use of both partial frequency reuse and soft handover. The basic idea of this hybrid scheme is to dynamically select between a partial frequency reuse scheme and a soft handover scheme to provide better signal quality for cell edge users. Compared with the standard partial frequency reuse scheme, simulation results show that approximately one quarter of cell edge users can get improvements in signal quality as well as link spectral efficiency from using the proposed hybrid scheme. We also observe that by using our approach, there is a significant cell edge throughput gain over the standard partial frequency reuse scheme. Furthermore, based on a well defined data rate fairness criterion, we show that our method achieves higher overall system capacity as compared with the standard partial frequency reuse scheme.

A circuit technique to correct Vdd/PM distortion and improve efficiency as supply modulation of cascode class-E PAs has been proposed. The experimental result shows that the phase distortion can be improved from 20 degrees to 5 degrees. Moreover, a system co-simulation result demonstrated that the EVM can be improved from -17 dB to -19 dB.

A generalized formulation of the instantaneous frequency based on the symmetric higher order differential energy operator is proposed. The motivation for the formulation is that there is some frequency misalignment in time when the ordinary higher order differential energy operator is used for the instantaneous frequency estimator. The special cases of the generalized formulation are also presented. The proposed instantaneous frequency estimators are compared with existing methods in terms of error performance measured in the mean absolute error. In terms of the estimation error performance, the third order instantaneous frequency estimator with the symmetrical structure shows the best result under noise free condition. Under noisy situation, the fourth order instantaneous frequency estimator with the symmetrical structure produces the best results. Application examples are provided to show the usefulness of the estimator.

Due to the importance of maintaining the orthogonality among subcarriers, the estimation of carrier frequency offset (CFO) is a crucial issue in orthogonal frequency division multiplexing (OFDM) systems. The CFO estimation becomes complicated in OFDM direct-conversion receivers (DCRs), where additional analog impairments such as I/Q imbalance and time-varying DC offset (TV-DCO) exist. In this paper, we propose a novel joint estimation method for CFO and I/Q imbalance in the presence of TV-DCO. By using the linear property of the TV-DCO and employing a periodic pilot sequence, the desired estimates can be obtained in closed-form. Simulation results confirm the validity of the proposed method.

There is a trend towards flexible radios which are able to cope with a range of wireless communication standards. For the integrated processing of widely different signals -- including single-carrier, multi-carrier, and spread-spectrum signals -- monolithic baseband receivers need universal formats for the signal representation and channel description. We consider a reconfigurable receiver architecture building on concepts from time-frequency (TF) signal analysis. The core elements are TF signal representations in form of a Gabor expansion along with a compatible parameterization of time-variant channels. While applicable to arbitrary signal types, the TF channel parameterization offers similar advantages as the frequency domain channel description employed by orthogonal frequency-division multiplexing receivers. The freedom in the choice of the underlying analysis window function and the scalability in time and frequency facilitate the handling of diverse signal types as well as the adaptation to radio channels with different delay and Doppler spreads. Optimized window shapes limit the inherent model error, as demonstrated using the example of direct-sequence spread-spectrum signaling.

A novel structure for a composite right/left-handed (CRLH) corrugated waveguide in the millimeter-wave band is proposed. The CRLH waveguide is composed of a rectangular waveguide with tilted corrugations on its bottom broad wall. By operating above and below the cutoff frequency of the dominant mode of the rectangular waveguide, the CRLH waveguide provides, respectively, an inherent series inductance and shunt capacitance, and an inherent shunt inductance. Moreover, the tilted corrugations provide a series inductance and a series capacitance, which can support CRLH propagation. A frequency-scanning antenna using this CRLH waveguide is also studied numerically and experimentally. The results demonstrate that the antenna can provide backward-to-forward beam scanning, including the broadside direction. A scanning angle from -9.9 to +2.2 is achieved within a 1.8-GHz frequency range in the 60-GHz band.

This letter proposes a nonlinear DCT discriminant feature extraction approach for face recognition. The proposed approach first selects appropriate DCT frequency bands according to their levels of nonlinear discrimination. Then, this approach extracts nonlinear discriminant features from the selected DCT bands by presenting a new kernel discriminant method, i.e. the improved kernel discriminative common vector (KDCV) method. Experiments on the public FERET database show that this new approach is more effective than several related methods.

This paper presents a wide tuning range VCO with an automatic frequency, gain, and two-step amplitude calibration loop for Digital TV (DTV) tuner applications. To cover the wide tuning range, the fully digital automatic frequency calibration (AFC) loop is used. In addition to the AFC loop, a two-step negative-Gm tuning loop is proposed to provide the optimum negative-Gm to the LC tank in a wide frequency range with a fine resolution. In the coarse negative-Gm tuning loop, the number of active negative-Gm cells is selected digitally based on the target frequency. In the fine negative-Gm tuning loop, the negative-Gm is tuned finely with the bias voltage of the VCO. Also, the digital VCO gain calibration scheme is proposed to compensate for the gain variation in a wide tuning range. The VCO tuning range is 2.6 GHz, from 1.7 GHz to 4.3 GHz, and the power consumption is 2 mA to 4 mA from a 1.8 V supply. The measured VCO phase noise is -120 dBc/Hz at 1 MHz offset.

In this paper, we use frequency-domain equalization (FDE) to create coherent optical single-carrier (CO-SC) transmission systems that are very tolerant of chromatic dispersion (CD) and polarization mode dispersion (PMD). The efficient transmission of a 25-Gb/s NRZ-QPSK signal by using the proposed FDE is demonstrated under severe CD and PMD conditions. We also discuss the principle of FDE and some techniques suitable for implementing CO-SC-FDE. The results show that a CO-SC-FDE system is very tolerant of CD and PMD and can achieve high transmission rates over single mode fiber without optical dispersion compensation.

In this paper, the issue of carrier frequency offset (CFO) compensation in interleaved orthogonal frequency division multiple access (OFDMA) uplink system is investigated. To mitigate the effect of multiple access interference (MAI) caused by CFOs of different users, a new parallel interference cancellation (PIC) compensation algorithm is proposed. This scheme uses minimum mean square error (MMSE) criterion to obtain the estimation of interference users, then circular convolutions are employed to restore MAI and compensate CFO. To tackle the complexity problem of circular convolutions, an efficient MAI restoration and cancellation method is developed. Simulations illustrate the good performance and low computational complexity of the proposed algorithm.

This paper proposes a frequency asynchronous cross-polarization interference canceller for Vertical/Horizontal (V/H) polarization multiplexing satellite communications. In satellite communications, V/H polarization signals are likely to experience different frequency fluctuations, and so the cross-polarization undergoes two different frequency fluctuations. To cancel this cross-polarization interference, a new frequency asynchronous cross-polarization interference canceller that removes interference and frequency offsets is proposed. Computer simulations are carried out to evaluate its fundamental performance. The results show that the proposed canceller can remove the cross-polarization interference created by the two different frequency offsets, simultaneously.

An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.

We present an attractive approach for OFDM transmission using an adaptive pre-FFT equalizer, which can select ICI reduction mode according to channel condition, and a degenerated-inverse-matrix-based channel estimator (DIME), which uses a cyclic sinc-function matrix uniquely determined by transmitted subcarriers. In addition to simulation results, the proposed system with an adaptive pre-FFT equalizer and DIME has been laboratory tested by using a software defined radio (SDR)-based test bed. The simulation and experimental results demonstrated that the system at a rate of more than 100 Mbps can provide a bit error rate of less than 10-3 for a fast multi-path fading channel that has a moving velocity of more than 200 km/h with a delay spread of 1.9 µs (a maximum delay path of 7.3 µs) in the 5-GHz band.

This paper presents a prototype group modem for a hyper-multipoint data gathering satellite communication system. It can handle arbitrarily and dynamically assigned FDMA signals by employing a novel FFT-type block demultiplexer/multiplexer. We clarify its configuration and operational principle. Experiments show that the developed modem offers excellent performance.

In this letter, we propose a simple adaptive switching scheme to enhance the performance of space-time/frequency block coded OFDM systems (STBC/SFBC-OFDM). Since STBC-OFDM and SFBC-OFDM undergo severe performance degradation in time- and frequency-selective fading channels, respectively, performance enhancement can be achieved by switching between STBC-OFDM and SFBC-OFDM over a continuously varying channel environments. Thus, a new switching scheme based on the characteristics of the actual channel is proposed. The effectiveness of the proposed scheme is demonstrated by computer simulations.