In 3GPP (3-rd Generation Partnership Project) LTE (Long Term Evolution) system, the use of PRS (Positioning Reference Signal) for OTDOA (Observed Time Difference of Arrival) based positioning method has been agreed. However, PRSs can be overlapped at the receiver side in synchronous network because the frequency shift pattern of PRS is decided by cell ID (Identity). Moreover, in asynchronous network, the loss of orthogonality between received PRSs generates continuous interferences. Even though autonomous muting can be applied to solve the interference problems in synchronous and asynchronous networks, the muting scheme degrades the overall positioning efficiency and requires additional network complexity. Therefore, in this paper, we propose novel OTDOA based positioning methods at the receiver side to improve positioning efficiency: cancellation method of serving PRS for synchronous network, TDORS (Time Domain Orthogonal Reference Signal) generation and useful CIR (Channel Impulse Response) selection methods for asynchronous network. We verified that the proposed methods can achieve an accurate estimation and stable operation without PRS muting.

An inductorless low noise amplifier (LNA) with active balun for digital TV (DTV) applications is presented. The LNA exploits a noise cancellation technique which allows for simultaneous wide-band impedance matching and low noise design. The matching and amplifier stages in the LNA topology perform single-ended to differential signal conversion with balanced output. The second and third-order nonlinearity of the individual amplifiers as well as the distortion caused by the interaction between the stages are suppressed to achieve high IIP2 and IIP3. A method for intrinsic cancellation of the second-order interaction is employed to reduce the dependence of the IIP3 on the frequency spacing between the interfering signals in the two-tone test of DTV tuners. Fabricated in a 0.18 µm CMOS technology, the LNA core size is 0.21 mm2. Measurements show that the LNA IIP3 and IIP2 are +12 dBm and +21 dBm, respectively. The IIP3 variation is less than 5 dB in the 10 MHz to 200 MHz frequency spacing range. A voltage gain of 14.5 dB and a noise figure below 4 dB are achieved in a frequency range from 100 MHz to 1 GHz. The LNA consumes 11 mA from a 1.8 V supply voltage.

As the fundamental component of dynamic spectrum access, implementing spectrum sensing is one of the most important goals in cognitive radio networks due to its key functions of protecting licensed primary users from harmful interference and identifying spectrum holes for the improvement of spectrum utilization. However, its performance is generally compromised by the interference from adjacent primary channels. To cope with such interference and improve detection performance, this paper proposes a non-coherent power decomposition-based energy detection method for cooperative spectrum sensing. Due to its use of power decomposition, interference cancellation can be applied in energy detection. The proposed power decomposition does not require any prior knowledge of the primary signals. The power detection with its interference cancellation can be implemented indirectly by solving a non-homogeneous linear equation set with a coefficient matrix that involves only the distances between primary transmitters and cognitive secondary users (SUs). The optimal number of SUs for sensing a single channel and the number of channels that can be sensed simultaneously are also derived. The simulation results show that the proposed method is able to cope with the expected interference variation and achieve higher probability of detection and lower probability of false alarm than the conventional method in both hard combining and soft combining scenarios.

This paper proposes an adaptive algorithm for adaptive arrays that minimizes the bit error rate (BER) of the array output signals in radio communication systems with the use of multilevel modulation signals. In particular, amplitude phase shift keying (APSK) is used as one type of multilevel modulations in this paper. Simultaneous non-linear equations that are satisfied by the optimum weight vector of the proposed algorithm are derived and used for theoretical analyze of the performance of the adaptive array based on the proposed algorithm. As a result of the theoretical analysis, it can be shown that the proposed adaptive array improves the carrier to interference ratio of the array output signal without taking advantage of the nulls. Furthermore, it is confirmed that the result of the theoretical analysis agrees with that of computer simulation. When the number of the received antenna is less than that of the received signals, the adaptive array based on the proposed algorithm is verified to achieve much better performance then that based on the least mean square (LMS) algorithm.

In this paper, we propose an iterative minimum mean square error detection with interference cancellation (MMSED-IC) for frequency-domain filtered single carrier (SC)-frequency-division multiple-access (FDMA) uplink transmission. The use of a square-root Nyquist transmit filter reduces the peak-to-average power ratio (PAPR) while increases the frequency-diversity gain. However, if carrier-frequency separation among multiple-access users is kept the same as the one used for the case of roll-off factor α=0 (i.e., brick-wall filter), then the adjacent users' spectra will overlap and multi-user interference (MUI) occurs. The proposed MMSED-IC can sufficiently suppress the MUI from adjacent users while achieving the maximum frequency-diversity gain. We apply the proposed MMSED-IC to a packet access using filtered SC-FDMA, multi-input multi-output (MIMO) multiplexing, and hybrid automatic repeat request (HARQ). It is shown by computer simulation that filtered SC-FDMA with α=1 can achieve higher throughput than orthogonal frequency division multiple access (OFDMA).

NAND multilevel cell flash memory devices are gaining popularity because they can increase the memory capacity by storing two or more bits to a single cell. However, when the number of levels of a cell increases, the inter-cell interference which shifts threshold voltage becomes more critical. There are two approaches to alleviate the errors caused by the voltage shift. One is the error correcting codes, and the other is the signal processing methods. In this paper, we focus on signal processing methods to reduce the inter-cell interference which causes the voltage shift, and propose two algorithms which reduce the voltage shift effects by adjusting read voltages. The simulation results show that the proposed algorithms are effective for interference mitigation.

We propose two types of active directional couplers to assure high TX cancellation: an asymmetric type and a symmetric type. For attaining low receiving through loss, coupling capacitors used in conventional couplers are replaced by amplifiers in the proposed active directional couplers. The asymmetric active directional coupler is composed of a small number of components and simple structure. The symmetric active directional coupler has wide-bandwidth TX cancellation. Measurement results show that receiving through loss of -5.3 dB and the TX cancellation of -67.6 dB are obtained in the asymmetric active directional coupler, and receiving through loss of -6.7 dB and the TX cancellation of -66.4 dB are obtained in the symmetric active directional coupler. Compared to the asymmetric active directional coupler, the symmetric active directional coupler has advantage of wider bandwidth of 1.25 MHz to reduce TX leakage of less than -55 dB. Both the proposed active directional couplers achieve high TX cancellation, and the symmetric active directional coupler can be applied in a UHF RFID system with 10-m communication range.

Broadband single-carrier frequency division multiple access (SC-FDMA) uplink using frequency-domain square-root Nyquist filtering is considered. The peak-to-average power ratio (PAPR) of filtered SC signals can be reduced by increasing the filter roll-off factor α. Furthermore, an additional frequency diversity gain can be obtained by making use of the excess bandwidth introduced by the transmit root Nyquist filtering. However, if the carrier-frequency separation is kept the same as in the case of α=0, the adjacent users' signal spectra overlap with the desired users' spectrum and the multiuser interference (MUI) is produced. In this paper, we propose two frequency-domain iterative MUI cancellation schemes which can achieve the frequency diversity gain through spectrum combining. The achievable bit error rate (BER) and throughput performances are evaluated by computer simulation.

Regularization plays a fundamental role in adaptive filtering. There are, very likely, many different ways to regularize an adaptive filter. In this letter, we propose one possible way to do it based on a condition that makes intuitively sense. From this condition, we show how to regularize the recursive least-squares (RLS) algorithm.

Distance to target is fundamental and very important information in numerous engineering fields. Many distance measurement methods using sound use the time delay of a reflected wave, which is measured in reference to the transmitted wave. This method, however, cannot measure short distances because the transmitted wave, which has not attenuated sufficiently by the time the reflected waves are received, suppresses the reflected waves for short distances. Therefore, we proposed an acoustic distance measurement method based on the interference between the transmitted wave and the reflected waves, which can measure distance in a short range. The proposed method requires a cancellation processing for background components due to the spectrum of the transmitted wave and the transfer function of the measurement system in real environments. We refer to this processing as background components cancellation processing (BGCCP). We proposed BGCCP based on subtraction or whitening. However, the proposed method had a limitation with respect to the transmitted wave or additive noise in real environments. In the present paper, we propose an acoustic distance measurement method based on the new BGCCP. In the new BGCCP, we use the calibration of a real measurement system and the whitening processing of the transmitted wave and introduce the concept of the cepstrum to the proposed method in order to achieve robustness. Although the conventional BGCCP requires the recording of the transmitted wave under the condition without targets, the new BGCCP does not have this requirement. Finally, we confirmed the effectiveness of the proposed method through experiments in real environments. As a result, the proposed method was confirmed to be valid and effective, even in noisy environments.

In this paper, a novel channel estimation method for time domain synchrotrons orthogonal frequency domain multiplexing (TDS-OFDM) based on training sequence cyclic reconstruction is proposed to eliminate residual inter-block interference (IBI); it estimates the channel impulse response (CIR) in an iterative manner. A simulation and analysis show that the proposed method can effectively perform the channel estimation over long-delay multipath channels with low complexity.

A 10-Gbit/s-class ac-coupled average-detection-type burst-mode receiver (B-Rx) with an ultra fast response and a high tolerance to the long consecutive identical digits has been developed. Key features of the circuit design are the baseline-wander common-mode rejection technique and the inverted distortion technique adopted in the limiting amplifier to cope with both the fast response and the high tolerance. Our B-Rx with newly developed limiting amplifier IC achieved a settling time of less than 150 ns, a sensitivity of -29.8 dBm, and a dynamic range of 23.8 dB with a 231-1 pseudo random bit sequences. Moreover, we also describe several potential B-Rx applications. We achieved better performance by applying the proposed systems to our B-Rx.

This paper presents the design of a wideband low noise amplifier (LNA) for the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard. The proposed LNA uses a common gate topology with a noise cancellation technique for wideband (0.7 to 2.7 GHz) and low noise operation. The capacitive cross coupling technique is adopted for the common gate amplifier. Consequently input matching is achieved with lower transconductance, thereby reducing the power consumption and noise contribution. The LNA is designed in a 0.18 µm process and the simulations show lower than -10 dB input return loss (S11), and 2.42.6 dB noise figure (NF) over the entire operating band (0.72.7 GHz) while drawing 9 mA from a 1.8 V supply.

Due to the reuse factor reduction, the attendant increase in co-channel interference (CCI) becomes the limiting factor in the performance of the orthogonal frequency division multiplexing (OFDM) based cellular systems. In the previous work, we proposed the least mean square-blind joint maximum likelihood sequence estimation (LMS-BJMLSE) algorithm, which is effective for CCI cancellation in OFDM systems with only one receive antenna. However, LMS-BJMLSE requires a long training sequence (TS) for channel estimation, which reduces the transmission efficiency. In this paper, we propose a subcarrier identification and interpolation algorithm, in which the subcarriers are divided into groups based on the coherence bandwidth, and the slowest converging subcarrier in each group is identified by exploiting the correlation between the mean-square error (MSE) produced by LMS and the mean-square deviation (MSD) of the desired channel estimate. The identified poor channel estimate is replaced by the interpolation result using the adjacent subcarriers' channel estimates. Simulation results demonstrate that the proposed algorithm can reduce the required training sequence dramatically for both the cases of single interference and dual interference. We also generalize LMS-BJMLSE from single antenna to receiver diversity, which is shown to provide a huge improvement.

In this paper, we propose a novel iterative transmit/receive equalization technique for single-carrier (SC) block transmission in a severe frequency-selective fading channel. Iterative frequency-domain inter-symbol interference (ISI) cancellation (FDIC) is introduced to the previously proposed joint iterative transmit/receive frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion. 1-tap FDE is employed at the transmitter. At the receiver, a 1-tap FDE and FDIC are jointly used and they are updated in an iterative manner. The transmit FDE weight is derived based on the MMSE criterion by taking into account the reduction of residual ISI in the receiver. To derive the weight, the transmitter assumes that the receiver can partially reduce the residual ISI after the FDIC. We conduct a computer simulation to investigate the achievable bit error rate (BER) performance to confirm the effectiveness of our proposed technique.

One of the major drawbacks of orthogonal frequency division multiplexing (OFDM) systems is their vulnerability to synchronization errors. To remedy the inter-carrier interference (ICI) effect caused by carrier frequency offset (CFO) estimation errors, this paper proposes a weighted linear parallel ICI cancellation (WLPICIC) equalizer. The optimal weights in the WLPICIC scheme are derived in closed-form expressions by maximizing the average signal-to-interference ratio (SIR) at the WLPICIC output of each sub-carrier. The simulation results show that the WLPICIC equalizer significantly improves the performance of OFDM systems with frequency estimation errors in both AWGN channels and frequency selective fading channels.

For multiple-input multiple-output (MIMO) spatial multiplexing, signal separation/detection is one of the most important signal processing parts, so that signal separation/detection schemes are being vigorously researched. As a promising signal separation/detection scheme, frequency-domain iterative soft interference cancellation (FD-SIC) has been proposed. Although iterative FD-SIC can provide the transmission performance close to lower bound for QPSK, the accuracy of signal separation/detection significantly degrades in case of high level data modulation. Therefore, in this paper, we propose layered soft interference cancellation (LSIC). We consider single-carrier (SC)-MIMO spatial multiplexing with frequency domain equalization (FDE). The achievable frame error rate (FER) performances with LSIC are evaluated by computer simulation to show that LSIC can provide better FER performance than iterative FD-SIC.

This paper presents a new approach for the Capon beamformer to provide robustness against array pointing errors. This robustness is achieved by incorporating an uncertainty constraint with diagonal loading and injected pseudo-interference. A simple performance analysis of this new beamformer is also investigated. Simulation results demonstrate that the power estimator has excellent performance.

Previously reported wideband CMOS low-noise amplifiers (LNAs) have difficulty in achieving both wideband input impedance matching and low noise performance at low power consumption and low supply voltage. We present a transformer noise-canceling wideband CMOS LNA based on a common-gate topology. The transformer, composed of the input and shunt-peaking inductors, partly cancels the noise originating from the common-gate transistor and load resistor. The combination of the transformer with an output series inductor provides wideband input impedance matching. The LNA designed for ultra-wideband (UWB) applications is implemented in a 90 nm digital CMOS process. It occupies 0.12 mm2 and achieves |S11|<-10 dB, NF<4.4 dB, and |S21|>9.3 dB across 3.1-10.6 GHz with a power consumption of 2.5 mW from a 1.0 V supply. These results show that the proposed topology is the most suitable for low-power and low-voltage UWB CMOS LNAs.

In this Letter, a residual acoustic echo suppression method is proposed to enhance the speech quality of hands-free communication in an automobile environment. The echo signal is normally a human voice with harmonic characteristics in a hands-free communication environment. The proposed algorithm estimates the residual echo signal by emphasizing its harmonic components. The estimated residual echo is used to obtain the signal-to-interference ratio (SIR) information at the acoustic echo canceller output. Then, the SIR based Wiener post-filter is constructed to reduce both the residual echo and noise. The experimental results confirm that the proposed algorithm is superior to the conventional residual echo suppression algorithm in terms of the echo return loss enhancement (ERLE) and the segmental signal-to-noise ratio (SEGSNR).