Bandpass Sampling Technique Research Articles

Optimized digital radio over fiber system for medium range communication

In recent years, the demand of efficient and broadband wireless access has escalated, for which Radio over Fiber (RoF) is considered as an appropriate solution. In this paper, we present a Digitized Transmission of 20 MHz LTE signal having 64 quadrature amplitude modulation over 70 Km of Standard Single Mode Fiber (SSMF) for broadband wireless signal transportation and distribution applications. The performance analysis has been evaluated for conventional Analog Radio over Fiber (A-RoF) and proposed Digital Radio over Fiber (D-RoF). The bandpass sampling technique is discussed and employed for digitizing the RF signal. As a figure of merit, the performance evaluation of two architectures is reported by analyzing the Error Vector Magnitude (EVM), Signal to Noise Ratio and Eye-Opening Penalty. It is shown that digital optical links can mitigate the impairments present in A-RoF links and can support the transmission up to 70 Km. Moreover, it is shown that efficient D-RoF links can be obtained with a relatively low amount of analog to digital converter (ADC) resolution bits. An experimental validation of the proposed analytical D-RoF model is done for 30 Km of SSMF, whose experimental results are in line with the analytical ones. The evaluated parameters are within the LTE specifications, proving this is a cost and power effective solution for next generation wireless networks.

Low cost, faster detection of cognitive radio through filter banks with bandpass sampling

In cognitive radio communication systems, fast and reliable detection of the idle channels which are not occupied by the primary users is the most fundamental requirement. In this paper, we first review some of the classical designs of cognitive radio receiver architectures and then propose a new solution using filter banks with the bandpass sampling technique. In conventional heterodyne receiver, a low rate analog to digital convertor (ADC) is used, which contains an analog bandpass filter. This results in a barrier in lowering detection time as significant time is used in the scanning operation. While the homodyne receiver has the capability of fast detection due to the use of high rate ADC, this is an unfeasible or very costly approach. Compressive sensing based receiver architectures are proposed in recent years, however those receivers do not work efficiently under the condition when the spectrum is congested and the number of channels are increased. In this work, we propose a filter banks based receiver with bandpass sampling architecture capable of fast detection and using a low rate ADC as well. In addition, comparative analysis of classical designs and the proposed architecture is carried out by considering performance parameters of detection time, signal to noise ratio and complexity of the receivers.

Band-Pass Sampling in High-Order BOC Signal Acquisition

The binary offset carrier (BOC) modulation, which has been adopted in modern global navigation satellite systems (GNSS), provides a higher spectral compatibility with BPSK signals, and better tracking performance. However, the autocorrelation function (ACF) of BOC signals has multiple peaks. This feature complicates the acquisition process, since a smaller time searching step is required, which results in longer searching time or greater amounts of hardware resources. Another problem is the high Nyquist frequency, which leads to high computational complexity and power consumption. In this paper, to overcome these drawbacks, the band-pass sampling technique for multiple signals is introduced to BOC signals. The sampling frequency can be reduced significantly. Furthermore, the ACF of the sampled signal has only two secondary peaks, so that the code phase can be searched with a larger searching step. An acquisition structure base on dual-loop is proposed, to completely eliminate the ambiguity and compensate the subcarrier Doppler. The acquisition performance and the computational complexity are also analysed.

Broadband and High-Resolution Static Fourier Transform Spectrometer with Bandpass Sampling.

In this study, experimental demonstration of a static Fourier transform spectrometer (static-FTS), based on division of the spectrum into multiple narrowband signals, is presented. The bandpass sampling technique used in this novel spectrometer solves the Nyquist sampling rate limitations and enables recording of wideband spectrum in high resolution. The proposed spectrometer not only has the potential of operating in a wide spectral range, but also has a resolution potential better than 2 cm-1.

Fully digital BPSK demodulator for satellite supressed carrier telecommand system

SummaryIn this paper, we present the design of a fully digital binary phase shift keying demodulator for application in satellite high‐rate suppressed carrier telecommand system. The proposed system digitalizes the received signal in the intermediate frequency stage using bandpass sampling technique, and the resulting baseband signal is used to synchronization of symbol and phase and to bit detection. The design of all functional modules is presented in details. Another innovation presented in this work is the inclusion of a non‐linearity in the phase synchronizer module to permit its operation independent from the signal amplitude. Moreover, aiming the characterization and performance evaluation of the system, we do some original mathematical analyses. Finally, test results show that the demodulator complies all the project requirements, and the prototype implementation loss, in terms of bit energy to noise power density ratio, is less than 0.3 dB. Copyright © 2016 John Wiley & Sons, Ltd.

Generalized Bandpass Sampling Algorithm for Multiband Wireless Receivers Suitable for SDR Applications

The bandpass sampling technique is a promising solution for the architecture of software-defined radio receivers. It is possible to digitize signals directly from the radio frequency stage when properly selecting the sampling frequency. With multistandard or multiband radio receivers, system nonlinearities mainly due to low noise amplifiers and downconversion circuits can generate rich output spectra with variable amplitude component levels. Bandpass sampling of such a spectrum, without causing aliasing, is a challenging task. For a nonlinear system, the minimum sampling frequency has been derived only for single-band and dual-band input signals. In this paper, a generalized bandpass sampling algorithm is developed to determine a minimum valid bandpass sampling frequency for either linear or nonlinear systems by considering a multiband input spectrum. Our objective is reducing the complexity of the sampling frequency calculation. Implementation results demonstrate the efficiency and low complexity of the proposed algorithm.

Bandpass sampling based digital coherent receiver with free-running local oscillator laser for phase-modulated radio-over-fiber links.

A bandpass sampling based digital coherent receiver is presented for phase modulated radio-over-fiber links with coherent detection. In the scheme, the bandpass sampling technique is introduced in RoF systems to overcome the high sampling rate requirement and front-end hardware dependency of conventional digtal coherent receivers. In particular, the selection rule of bandpass sampling rate was defined by taking into account the frequency offset induced by free-running optical local oscillator. Analytical assessment and simulations are used to determine the ultimate performance in terms of tolerances to ADC bit resolution and laser linewidth. Thereafter, a 40Mbps QPSK modulated data signal at 2.4GHz RF carrier frequency is experimentally demonstrated over the proposed 50.6-km radio-over-fiber link employing bandpass sampling.

Down-Conversion Gain of an All-Optical SOA-MZI-Based Mixer Using Bandpass Sampling

The frequency conversion is one function of utmost importance in radio over fiber technologies. In this letter, we propose an optical implementation of a radio frequency down conversion based on a bandpass sampling technique realized by a semiconductor optical amplifier Mach-Zehnder interferometer used as an optical signal sampler. An optical pulse source generating 23-ps width pulses at a repetition rate of 7.8 GHz is employed to sample an intensity-modulated optical carrier carrying the signal to be frequency down converted. The frequency down conversion from a radio frequency signal at 37 GHz to an intermediate frequency at 2 GHz shows a positive conversion gain of 4 dB.

Duplex Digitized Transmission of 64-QAM Signals over a Single Fiber Using a Single Pulsed Laser Source

We demonstrate digitized duplex transmission of 64-QAM signals using pulsed optical communications. Bidirectional data transmission is achieved over a single 25 km optical fibre using a single optical pulsed source. The choice of suitable parameters for bandpass sampling technique used for the digitization of the 16 MSamples/s 64-QAM signal are discussed. It is demonstrated that using digitized transmission of RF signals, long distance transmission can be supported at a performance close to that of the back-to-back analogue benchmarker.

Leveraging Software-Defined Radio Techniques in Multichannel Digital Weather Radar Receiver Design

This paper describes the instrumentation, design, and implementation of an inexpensive nearly all-digital field-programmable gate-array (FPGA)-based radar receiver useful in a variety of applications including single-/dual-polarization weather radar, sidelobe cancellation, subarray modules for a digital beam-forming phased-array radar, and other applications where a compact, low-power, and low-cost receiver is needed. The design of the receiver includes a minimal analog radio-frequency front-end followed by an analog-to-digital converter utilizing a bandpass sampling technique which allows the FPGA to produce baseband in-phase (I) and quadrature (Q) signals without the use of multipliers or lookup tables.

SDR front-end를 위한 Complex Bandpass Sampling

Bandpass sampling(BPS) 기술은 나이퀴스트(Nyquist) 샘플링 주파수보다 낮은 주파수를 사용하여 RF 대역의 신호를 직접 하향변환 할 수 있다는 장점을 가지고 있지만, 나이퀴스트 영역에서 self-image의 중복을 피하기 위해서는 샘플링 주파수의 선택에 제약이 따른다. 2개의 ADC를 사용하는 2차(second-order) BPS는 self-image를 제거하기 위한 신호처리가 추가 된다는 조건으로 샘플링 주파수의 선택이 자유롭다. 하지만 RF 대역이 바뀌면 신호처리를 위한 파라미타를 재구성해야 한다. 본 논문에서는 2차 BPS의 한 형태인 quadrature BPS의 구조를 가지면서, 재구성이 필요 없는 간단한 보상 필터만을 사용하여 임의 RF 대역으로부터 나이퀴스트 영역으로 하향 변환하는 complex BPS 기반의 SDR front-end에 대하여 기술한다. Bandpass sampling technique has an advantage that it uses lower sampling frequency than Nyquist criterion. But special care is required in choosing sampling frequency to avoid self-image overlapping in the first Nyquist region. Recently, the second-order BPS techniques which can suppress possible self-image by using an additional ADC and by employing digital signal processing have been proposed. This paper addresses a complex BPS based SDR front-end. Unlike general second-order BPS, it needs simple FIR filter to compensate delay in the second ADC. We show a method to find proper sampling frequencies to down convert RF signals selected by tunable RF filter operating in arbitrary frequency range.

Bandpass sampling of high-frequency tissue motion

The characterization of tissue viscoelastic properties requires the measurement of tissue motion over a region of interest at frequencies that significantly exceed the frame rates of conventional ultrasound systems. In this paper, we propose that the bandpass sampling technique be applied to tissue motion sampling. With this approach, high-frequency signals limited to a frequency band can be sampled and reconstructed without aliasing at a sampling frequency that is lower than the Nyquist rate. We first review this approach and discuss the selection of the tissue excitation frequency band and of the feasible sampling frequencies that allow signal reconstruction without aliasing. We then demonstrate the approach using simulations based on the finite element method and ultrasound simulations. Finally, we perform experiments on tissue-mimicking materials and demonstrate accurate motion estimation using a lower sampling rate than that required by the conventional sampling theorem. The estimated displacements were used to measure the elasticity and viscosity in a phantom in which an inclusion has been correctly delineated. Thus, with bandpass sampling, it is feasible to use conventional beamforming on diagnostic ultrasound systems to perform high-frequency dynamic elastography. The method is simple to implement because it does not require beam interleaving, additional hardware, or synchronization.

Design and Analysis of Digitized RF-Over-Fiber Links

In this paper, we present a performance analysis of microwave signal transmission by deploying digitized RF transport over a standard optical fiber link. The bandpass sampling technique is used to digitize the RF signal. An analytical model, which is transparent to any modulation format, was developed to assess the transmission performance of a digitized RF signal in M-level quadrature amplitude modulation (M-QAM) format. Using this analytical model, key design parameters such as bit resolution, link bit rate, receiver sensitivity, and link signal-to-noise ratio (SNR) were analyzed for a digitized 2.475 GHz RF signal with 16-QAM data modulation format and 6 MSymbols/s baud rate over a 20-km optical link. The analytical results show that the link SNR is predominantly determined by the performance of the analog-to-digital converter (ADC). We experimentally demonstrated the digitized RF transmission over a 20-km optical link. The analytical model and experimental results show that the performance of the link SNR is governed by jitter noise beyond 7 bits of resolution of the ADC. Using an ADC with 8-bit resolution, a 2.475 GHz RF signal with 16-QAM 6 MSymbols/s data was successfully transmitted and recovered with very good error vector magnitude of 1.77.

Experimental Demonstration of the Transport of Digitized Multiple Wireless Systems Over Fiber

We experimentally demonstrate high-performance transmission of multiple distinct microwave signals via digitized radio-frequency (RF) transport over a 20-km standard optical fiber link. A bandpass sampling technique is used to digitize a 2.475-GHz wireless signal [worldwide interoperability for microwave access (WiMAX)] carrying 6-MSymbol/s data in 16 quadrature amplitude modulation format and a 1.95-GHz wireless signal [global system for mobile communication (GSM)] with 270.833-kb/s data in Gaussian minimum shift keying modulation format. Using an analog-to-digital converter with 8-bit resolution, the WiMAX and GSM RF signals are simultaneously transmitted and recovered successfully with very good error-vector magnitudes of ~3.44 and ~1.42, respectively.

A novel method for down-conversion of multiple bandpass signals

Simultaneous down-conversion of multiple band-pass signals is desirable for a number of wireless applications. Bandpass sampling technique can be used for this purpose, but it is difficult to implement and has several drawbacks. In this paper we propose a novel front-end technique to directly down-convert multiple frequency- division multiplexed (FDM) signals separated by certain minimum frequency. A special downconversion function is derived to achieve simultaneous downconversion of the received signals. The technique requires simpler bandpass filters and the ADC has a baseband input as compared to bandpass sampling, which imposes strict requirements on bandpass filters and requires an ADC which can handle RF inputs. The performance of the method has been evaluated by simulating a BPSK receiver employing this technique.

An Improved Transducer Configuration for Phase-Coded Surface Acoustic Wave Devices

The influence of second order effects on the performance of a 13 bit phase-coded surface acoustic wave (SAW) device, realized on Y-Z LiNbO3, is demonstrated. A bandpass sampling technique is used to reduce the acoustic regeneration phenomenon in highly dispersive delay lines. An improvement in the correlation peak of a 6.5 use long phase-coded delay line is obtained after reducing the member of sensors by this technique. The results are compared with the device fabricated using conventional design methodology. The degradation in the impulse response due to acoustic regeneration is compared for the devices fabricated on high and low coupling materials.

Development of a TDM/FDM Transmultiplexer

Recently, digital systems such as digital telephone switching systems and digital transmission paths are being introduced more and more into communications networks in which signals are handled with Time Division Multiplex (TDM). There still exists, on the other hand, a number of analog transmission paths in which signals are multiplexed with Frequency Division Multiplex (FDM). Therefore, it is important to develop a scheme to interconnect efficiently TDM and FDM systems. Transmultiplexer, which is an equipment directly converting PCM.TDM signals and SSB.FDM signals with each other, is expected to provide an efficient interconneetion between TDM and FDM systems. Authors have developed an experimental transmultiplexer which can provide mutual conversion between a 24-channel PCM primary group (1.544 Mbits/s) and two 12-channel FDM basic groups (60-108 kHz). The developed equipment is designed so as to achieve reduction of the computation rate and simplicity of the hardware by the following techniques: (1) The FFT (Fast Fourier Transform) technique is used to optimize the filtering and multiplexing processes. (2) The spectrum reversion of odd-numbered channel signals is achieved by inverting the sign bits of the PCM signals every other frame. (3) The bandpass sampling technique is applied to obtain SSB.FDM signals directly without frequency shifts at analog FDM stages. In order to evaluate the characteristics of the developed transmultiplexer, experiments have been conducted by connecting it with FDM terminal equipments. The experimental results showed that the transmultiplexer can offer better performance than the tandem connection of standard PCM multiplex equipments and standard FDM terminal equipments with reasonable hardware.