Filter Receiver Research Articles

Exact Signal Model and New Carrier Frequency Offset Compensation Scheme for OFDM

Carrier frequency offset (CFO) causes spectrum misalignment of transmitter and receiver filters. This misalignment leads to energy loss and distortion of received signal, resulting in performance degradation of the whole system. However, these issues are often overlooked by existing works. This paper presents an exact signal model for OFDM that takes into account the CFO-induced spectral misalignment and related aliasing effects. Incorporating these practical issues, we also propose a new preamble structure and a new CFO compensation approach to mitigate their negative effects. Theoretical analysis and simulation results substantiate the importance of the exact signal model and the advantage of the proposed CFO compensation scheme.

Detailed theoretical investigation on relative intensity noise reduction enhancement based on reflective SOAs

The enhanced performance for relative intensity noise (RIN) reduction based on reflective semiconductor optical amplifiers (R-SOA) has been investigated theoretically by comparison with conventional transmission SOA. The results show that, by selecting appropriate input optical power, as large as >20dB RIN suppression improvement can be achieved for R-SOA, without sacrificing the noise rejection bandwidth. With increased injection current, the optimized input signal power is decreased and the operation region is extended for the best RIN reduction. For RIN suppression in WDM spectrum slicing, the bandwidth optimization of receiver filter should be performed to avoid the spectral broadening induced by self-phase modulation (SPM) and four wave mixing (FWM). Our derived result is helpful for designing and optimizing the R-SOA in application of noise suppression enhancement.

Inter-Stage Tunable Notch Filter for a Multi-Band WCDMA Receiver

This paper presents a multi-band WCDMA receiver consisting of a multi-band low noise amplifier (LNA), a multi-band mixer and an inter-stage tunable notch filter. The notch filter is used to suppress Tx leakage, and 0.8-1.5GHz (66%) of tuning range is achieved. The receiver achieves 33 and 30dB conversion gain, 6.4 and 8dB NF, 50 and 35.5dBm IIP2, and -6 and -4.7dBm IIP3 at 0.8 and 1.5GHz, respectively. The power consumption is 121mW from a 1.8-V power supply. The receiver is implemented in a 0.18-µm CMOS process.

Ultracompact UHF Tunable Filter Embedded Into Multilayered Organic Packaging Substrate

In this paper, we developed a new ultracompact ultrahigh frequency tunable band-pass filter embedded into multilayered organic packaging substrate with high dielectric composite film. For embedding the tunable filter circuit into the packaging substrate, it was modified by using a scalable lumped circuit model instead of using magnetically coupled resonant circuit. Since most of the conventional TV receiver tuners utilize magnetically coupled circuit, which is formed of several passive components and air core inductors assembled and controlled manually, there are several problems such as large size, difficulty in tuning, and high cost. The embedded tunable filter was optimally designed to obtain high performances by using high Q spiral stacked inductors, high dielectric SrTiO3 composite metal-insulator-metal capacitors, and surface mounted varactor diodes. It exhibited low insertion loss of approximately -2 dB, return less than -10 dB, large tuning range of 56.3% and tunable frequency ranged from 500 to 900 MHz. It had extremely compact size and volume of 3.4 × 4.4 × 0.6 mm3, which was the smallest one in the reported tunable filters for TV tuner receivers.

Correction of frequency characteristics of seismic sensors and noise of corresponding measuring channels

The paper has assessed the noise of the measuring channel, which includes a seismic receiver, preliminary amplifier, and correction filter (this filter broadens the frequency characteristics of the seismic receiver into the low frequencies range). The correction, mainly from the preliminary amplifier, contributes an additional noise into the measuring channel, therefore application of corrected seismometers and geophones is restricted by the class of signals that provide a signal-to-noise ratio of no less than 3–5. Such signals are seismic waves from regional earthquakes and industrial blasting.

Effect of channel estimation error on performance of time reversal-UWB communication system and its compensation by pre-filter

Time reversal (TR) technique is an effective and simple method for data transmission in extremely multipath indoor ultra-wideband (UWB) channels. Temporal focusing property supported by TR, mitigates the complexity of receiver by reducing the effective channel taps. In spite of its good performance in perfect channel state information (CSI), TR method is very sensitive to the channel estimation error. The effect of channel imperfection on TR technique is considered the study. At first, the bit error rate (BER) of the TR-UWB communication system under the assumptions of the simple matched filter (MF) receiver under the channel estimation errors is derived in closed-form. Then, based on optimal minimum mean square error (MMSE) estimator receiver, a pre-filter is calculated in closed-form to improve the performance of the TR-UWB system in an imperfect CSI scenario. Furthermore, in order to compare the results, similar calculation for pre-filter is carried out based on a simple MF receiver. Unfortunately, it was not possible for us to drive a closed-form solution for pre-filter in this case. To overcome this shortcoming, a two stage iteration-based algorithm is developed at transmitter to calculate a pre-filter in MF receiver. This improved algorithm causes the channel estimation error tends to zero in some steps for the TR-UWB system with MF. The initial value for this iteration-based improved algorithm is considered to be closed-form pre-filter where is calculated based on TR-UWB system with an optimal MMSE estimator. Finally, exhaustive simulations are done to demonstrate the performance advantage attained by the proposed algorithms.

Dynamic Pilot Channel Transmission with Adaptive Receive Filter Configuration for Cognitive Radio System

When a cognitive radio system dynamically utilizes a frequency band, channel control information must be communicated over the network in order for the currently available carrier frequencies to be shared. In order to keep efficient spectrum utilization, this control information should also be dynamically transmitted through channels such as cognitive pilot channels based on the channel conditions. If transmitters dynamically select carrier frequencies, receivers must receive the control signal without knowledge of its carrier frequencies. A novel scheme called differential code parallel transmission (DCPT) enables receivers to receive low-rate information without any knowledge of the carrier frequency. The transmitter simultaneously transmits two signals whose carrier frequencies are separated by a predefined value. The absolute values of the carrier frequencies can be varied. When the receiver receives the DCPT signal, it multiplies the signal by a frequency-shifted version of itself; this yields a DC component that represents the data signal, which is then demodulated. However, the multiplication process results in the noise power being squared, necessitating high received signal power. In this paper, to realize a bandpass filter that passes only DCPT signals of unknown frequency and that suppresses noise and interference at other frequencies, a DCPT-adaptive bandpass filter (ABF) that employs an adaptive equalizer is proposed. In the training phase, the received signal is the filter input and the frequency-shifted signal is the training input. Then, the filter is trained to pass the higher-frequency signal of the two DCPT signals. The performance of DCPT-ABF is evaluated through computer simulations. We find that DCPT-ABF operates successfully even under strong interference.

On Optimal Front-End Filter for Single-User Detection in IR-UWB Systems

We consider a K user Gaussian multiple access system with impulse radio ultra-wideband signaling. The receiver is assumed to treat the Multi-Access Interference (MAI) as additive noise and does not enjoy multiuser detection. It is well known that for such a system the MAI is neither Gaussian nor white. Although, the non-Gaussianity of the MAI has been extensively studied, little attention has been directed to the non-whiteness of it. In this paper, we show that by employing a new front-end filter at the receiver, the non-whiteness of the MAI can be exploited to improve the performance of the single-user detector. We use the signal-to-interference-plus-noise ratio (SINR) as a merit to evaluate the performance improvement brought to the system. The SINR improvement depends on the interference level as well as pulse waveform. The bit error rate of the system is also simulated and compared with that of conventional matched filter receiver.

Performance of constrained blind adaptive DS-CDMA UWB multiuser detector in multipath channel with IEEE 802.11a interference

Ultra wideband wireless systems are supposed to coexist with other spectrally overlapping narrowband wireless systems especially IEEE 802.11a wireless LAN. Presence of narrowband interference degrades the performance of UWB. In this paper we study bit error probability performance of the constrained blind DS-CDMA UWB multi-user detection algorithms in the presence of IEEE 802.11a OFDM narrowband interference. The constrained blind adaptive algorithm is implemented using both least mean square and recursive least square algorithm and the bit error probability performance is compared with Rake matched filter receiver. The constrained blind receiver does not require spreading code knowledge of all users other than that of the user of interest. Simulation results show that the constrained blind detector cancels IEEE 802.11a interference significantly in comparison with that of the Rake matched filter in the UWB multipath channel.

The Parallel Loop Filter and NCO in the All-Digital Parallel Receiver

The Parallel Loop Filter and NCO in the All-Digital Parallel Receiver

2차원 확산을 사용하는 다중전송률 MC-DS/CDMA 시스템

직교 주파수분할 다중(OFDM)시스템과 직접확산 코드분할다중접속(DS/CDMA)시스템이 결합된 다중반송파(MC) DS/CDMA 시스템은 대역폭 효율, 고 전송률과 페이딩에 강한 특성으로 많은 주목을 받고 있다. 본 논문에서는 시간영역과 주파수영역에서 확산을 수행하는 다중전송률 MC-DS/CDMA 시스템에서 복잡성이 감소된 다중사용자 검출기를 살펴본다. 여기서 시간영역과 주파수영역의 확산부호로는 2차원 직교 가변확산부호(OVSF)로부터 만들어진 1차원 OVSF 코드를 사용한다. 제안된 시스템에서는 다중사용자간섭(MUI)을 감소시키기 위해 코드그룹 간섭제거(CGIC) 수신기를 사용하는데, 이 CGIC 수신기는 1차원 OVSF 코드들의 상관특성을 이용하여 코드 그룹이라는 개념을 사용하여 다른 사용자들의 정보 없이도 사용자 선호를 검출할 수 있는 수신기이다. CGIC를 갖는 다중사용자 검출기가 시간 및 주파수영역에 따로 또는 같이 적용될 것이다. AWGN 채널 환경 하에서 시스템의 성능을 분석하며, 단일(다중) 전송률, 다중사용자를 갖는 시간/주파수 영역에서 확산된 MC-DS/CDMA과 비교할 것이다. 이러한 결과로서 기존의 정합검출기에 비해 제안된 시스템의 성능이 향상됨을 알 수 있다. Multicarrier-Direct Sequence/Code Division Multiple Access(MC-DS/ CDMA) which is a combination of Orthogonal Frequency Division Multiplexing(OFDM) and DS/CDMA has been of significant interest as a means to take such advantages as bandwidth efficiency, high bit rate and robustness against multipath fading. In this paper we study a reduced-complexity multiuser detection aided multirate MC-DS/CDMA with time(T)-domain and frequency(F)-domain spreading. The one- dimensional orthogonal variable spreading factor(1D OVSF) code extracted from 2D OVSF code are used as a spreading code in T/F-domain. The proposed system will use code grouping interference cancellation(CGIC) receiver to reduce Multiuser Interference(MUI). The CGIC receiver uses code grouping by the correlation properties of 1D OVSF code and dose not requires the code information and activity of other user. The multiuser detector with CGIC receiver will be analyzed in Time- and Frequency-domain separately(jointly). The system performance is analytically derived in Additive White Gaussian Noise(AWGN) channel and we also compare the system performance between proposed system and T/F spreaded single(multi) rate multiuser MC-DS/CDMA system. In the computer simulation results, the proposed receiver of demonstrated huge performance improvement over conventional matched filter receiver.

Mutual interference signal processing for active sonar

Active sonar for anti-submarine warfare (ASW) can at times be hampered by interference from the transmissions of other vessels—either friend or foe. For practical reasons, there are typically only a limited number of center-frequencies, bandwidths, and useful waveform types available. We explore the cross-correlation of various frequency modulated waveforms with varying characteristics—particularly bandwidths, pulse lengths, and the degree of frequency overlap. The impact on the ambiguity function is also explored, along with the efficacy of several transmitter and receiver filters. Real world data containing interfering transmissions are presented including examples where basic theoretical effects are revealed. This work represents an early stage of research to ultimately explain subtle nuances in real data and to develop novel signal processing techniques to mitigate interference. [Work sponsored by ONR 321US.]

Application of CIC filter in digital receiver

Application of CIC filter in digital receiver

Radar Phase-Modulated Waveform Design for Extended Target Detection

Extended target detection performance can be enhanced by using phase-modulated waveform designs in band-limited radar systems. Unlike waveforms designed for the total energy constraint, phase-modulated waveforms can fully exploit the transmit power in the pulse duration, which is more suitable for practical radar systems. An alternating iterative algorithm was developed to optimize the phase-modulated baseband waveform by maximizing the signal-to-noise ratio (SNR) at the receiver filter output. The output SNR increases continuously with the number of iterations and the algorithm is guaranteed to converge. Simulations validate the effectiveness of this approach. The waveforms designed by this method outperform other commonly used waveforms for extended target detection.

A pseudo differential Gm—C complex filter with frequency tuning for IEEE802.15.4 applications

This paper presents a CMOS Gm—C complex filter for a low-IF receiver of the IEEE 802.15.4 standard. A pseudo differential OTA with reconfigurable common mode feedback and common mode feed-forward is proposed as well as the frequency tuning method based on a relaxation oscillator. A detailed analysis of non-ideality of the OTA and the frequency tuning method is elaborated. The analysis and measurement results have shown that the center frequency of the complex filter could be tuned accurately. The chip was fabricated in a standard 0.35 μm CMOS process, with a single 3.3 V power supply. The filter consumes 2.1mA current, has a measured in-band group delay ripple of less than 0.16 μs and an IRR larger than 28 dB at 2 MHz apart, which could meet the requirements oftheIEEE802.15.4 standard.

SNR approach for performance evaluation of time-stretching photonic analogue to digital converter system

A semi-analytical simulation method (SASM) is proposed to evaluate the signal-to-noise ratio (SNR) of time stretched signals at the output of photonic analogue-to-digital converter (Ph-ADC) system. Analytical expressions of the signal at Ph-ADC output considering generic electrical signals applied to the electro-optic modulators of the Ph-ADC are derived. The contribution to the total variance of the received signal from the noise introduced by the electrical transmitter and receiver, and by the optical amplifier are derived analytically taking into account the pulsed nature of the optical signal. The proposed SASM shows excellent agreement of SNR estimates with the estimates provided by Monte Carlo simulation. This result is confirmed for variance dominantly imposed by the noise introduced by the electrical transmitter, by the optical amplifier and by the electrical receiver. A simplified approach is also proposed and compared with previous work. It is shown that mean power estimates obtained from this simplified approach are valid while the modulator is operating in the linear region and the signal is not affected by the frequency response of the electrical receiver filter. Additionally, it is concluded that the estimates of the noise variance due to the electrical transmitter are acceptable when a small signal analysis of noise along the Ph-ADC is valid.

A New Power-Consumption Optimization Technique for Two-Stage Operational Amplifiers

This paper proposes a technique for two-stage operational amplifiers (OPAMPs) to optimize power consumption according to various channel conditions of wireless communication systems. The proposed OPAMP has the ability of reducing the quiescent current of each stage independently by introducing additional common-mode feedback, therefore more optimization is possible according to the channel conditions than conventional two-stage OPAMPs. The simulations verify the benefits of the technique. As a proof-of-concept topology, the proposed OPAMPs were used in a channel-selection filter for a multi-standard mobile-TV receiver. The power consumption of the filter, 3.4-5.0mW, was adjustable according to the bandwidth, the noise, and the jammer level. The performance of the filter meets the requirements and verifies the effectiveness of the proposed approach. The filter was fabricated in 0.18-µm CMOS and occupied 0.64mm2.

Transformed lumped element integrated passive bandpass filters for gigahertz range spectrum monitor receivers

Two integrated bandpass filters have been designed and fabricated on standard 130 nm CMOS technology. The lumped element, third-order Butterworth bandpass filters at 9.45 and 1.75 GHz are designed for sub-band filtering in a spectrum monitoring receiver function in a future cognitive radio. A series coupled resonator topology is selected and a novel delta–star transformation technique is applied to obtain element values suitable for reliable fabrication on an integrated circuit. Occupying die areas of 780×200 µm and 1750×500 µm each, the filters achieve insertion losses of 15.6 and 8.6 dB, and bandwidths of 1 GHz and 210 MHz, respectively, which are suitable for the chosen spectrum monitor receiver architecture.

滤光片对三角位移传感器测量误差的影响

In order to improve receiving system signal to noise ratio of the laser displacement sensor,people often place receiver filter in front of CCD or PSD.But the filter for receiving light refraction will cause measurement error,the error is non-linear,and can not be ignored by high-precision displacement sensor.We design a compensation method for this non-linear measure error.The experiments show that the method is feasible.

Non-linear effects of intensity-modulated and directly detected optical links on receiving a linear frequency-modulated waveform

Limitations imposed by the non-linearity of optical links, in the front end of a receiving array antenna, on the performance of a pulse compression radar are studied. Particularly linear frequency-modulated waveforms backscattered from a pair of targets are inspected. Inter-modulation and gain compression by noise are presented as two remarkable phenomena. For an interconnection of two dual-drive Mach-Zehnder modulators, the sensitivity of the compressed echo at the output of a matched filter receiver to certain tunable parameters is studied numerically. Finally, certain values of DC bias and phase shift between the modulators- electrodes are recommended.