Second-order Bandpass Sampling Research Articles

Second-order bandpass sampling with direct baseband signal reconstruction

Continuous-time lowpass signal can be perfectly reconstructed from its uniformly-spaced samples at the Nyquist rate. While sampling bandpass signal at the Nyquist rate usually needs higher rate than necessary, second-order sampling, which involves two uniform samplings of the signal at the same sampling rate with a time offset between the two sampling sets, can perfectly reconstruct a bandpass signal from sub-Nyquist rate samples. However, most findings in the literature focus on the theoretical analysis of second-order sampling without addressing its practical implementation. Moreover, bandpass signals are primarily restored at the original band positions. The frequency-translated version of signal is frequently required in typical applications. Conventional methods will recover the original signal first, then shift it to the band of interest. In this paper, a direct reconstruction of the second-order sampled arbitrary real-valued bandpass signal onto the baseband is discussed, and the uniformly-spaced samples at the baseband will be reconstructed. Reconstruction with frequency-shifting interpolants are designed. To enable second-order sampling in practice, the feasible time offsets are determined analytically. Also, the design of digital interpolants for reconstructing second-order sampled signals in baseband is included. Simulation results are included to confirm our theoretical calculations and show the superiority over several existing schemes.

Antialiasing method for image aliasing in bandpass-sampling-based receiver

It is well known that image aliasing limits the flexibility of bandpass sampling receivers. In this context, a method that utilizes a second-order bandpass sampling structure with a tunable delay to eliminate image aliasing via digital signals is proposed. The antialiasing filter in the proposed method incorporates a simplified gains model/algorithm in which image aliasing is suppressed by adjustment of the complex gain in accordance with the location/position of the RF signal in the frequency domain. The proposed algorithm is easier to implement and can realize unaliased reception regardless of the location of the RF signal. Simulation results demonstrate that bandpass signals at arbitrary positions around 0.5–6 GHz can be received through the same receiver, and image aliasing is suppressed by almost 30 dB. Thus, the proposed method improves the extensibility of the receiver.

Multistandard Receiver Design for Telemedicine Monitoring System

In short-distance wireless communications for telemedicine monitoring, different medical data measurement equipment has different wireless transmission modes. A multistandard receiver is designed that can adapt to different medical data measuring equipment. Using a second-order bandpass sampling for the design of antialiasing filters, two aliasing signals can be separated. Simultaneously, constraint conditions for sampling frequency are not as critical. The design is useful for a multistandard receiver in a telemedicine monitoring system and has the advantages such as saving spectrum resources and facilitating spectrum planning.

2차 BPS 시스템에서 표본화 최적 오프셋 시간의 탐색 방법

2차 BPS 시스템에서 표본화 최적 오프셋 시간의 탐색 방법

2차 BPS 시스템의 interpolant 필터에 대한 최적 위상 설계

2차 BPS 시스템의 interpolant 필터에 대한 최적 위상 설계

2차 BPS 시스템의 다중 대역 interpolant 필터

In a bandpass sampling (BPS), the frequency of the sampler is lower than that of the signal being sampled. In this method, the baseband spectrum directly appears by the sampling operation, so that it is not necessary to use any frequency down-converter, which makes the receiver`s hardware simpler. The second-order BPS uses two identical BPS samplers, of which sampling times are offset by each other. By exploiting the relationship between two sampled signals, it can be possible to cancel the aliased signal component or the interference due to the bandpass sampling. In order to cancel the interference, an interpolant filter is used to manipulate the phase characteristics of the BPS sampled signal. In this paper, it is introduced a multiband interpolant filter which can simultaneously cancel multiple interference signals that have been aliased from multiple frequency bands. In case of no need of interference cancellation, another method is suggested to enhance the signal quality by 3dB. A computer simulation has been performed, and the feasibility of the suggested methods has been verified.

Design and compensation of second-order sub-sampling digital frontend

The problem of designing a digital frontend (DFE) was considered which can dynamically access or sense dual bands in any radio frequency (RF) regions without requiring hardware changes. In particular, second-order bandpass sampling (BPS) as a technique that enables to realize the multiband reception function was discussed. In a second-order BPS system, digital reconstruction filters were utilized to eliminate the interferences generated while down converting arbitrarily positioned RF-band signals by using the direct digitization method. However, the inaccuracy in the phase shift or the amplitude mismatch between the two sample streams may cause insufficient rejection of interference. Practical problems were studied, such as performance degradation in signal-to-interference ratio (SIR) and compensation methods to overcome them. In order to demonstrate the second-order BPS as a flexible DFE suitable for software-defined radio (SDR) or cognitive radio (CR), a DFE testbed with a reconfigurable structure was implemented. Moreover, with a view to further demonstrate the proposed compensation algorithms, experimental results show that dual bands are received simultaneously.

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.

RF Band-Pass Sampling Frontend for Multiband Access CR/SDR Receiver

Radio frequency (RF) subsampling can be used by radio receivers to directly down-convert and digitize RF signals. A goal of a cognitive radio/software defined ratio (CR/SDR) receiver design is to place the analog-to-digital converter (ADC) as near the antenna as possible. Based on this, a band-pass sampling (BPS) frontend for CR/SDR is proposed and verified. We present a receiver architecture based second-order BPS and signal processing techniques for a digital RF frontend. This paper is focused on the benefits of the second-order BPS architecture in spectrum sensing over a wide frequency band range and in multiband receiving without modification of the RF hardware. Methods to manipulate the spectra are described, and reconstruction filter designs are provided. On the basis of this concept, second-order BPS frontends for CR/SDR systems are designed and verified using a hardware platform.

Signal combination using bandpass sampling

A signal combination technique, based on the spectral replication property of sampling, is presented. The technique uses second-order bandpass sampling to provide some phase control over the component signals. Although the phase control is not independent between the signals and is constrained by inherent amplitude scaling, quasi-independent control can be achieved. The performance of the combination technique is established for three applications. These applications are diversity antenna combination, interception of slow frequency hopping spread spectrum, and a switchable beam, linear antenna array.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency-shifting using bandpass sampling

A frequency-shifting technique is discussed that uses a digital filter to interpolate a bandpass-sampled signal at a low-pass position. The discussion focuses on the derivation of the required digital filter. It is shown that second-order bandpass sampling offers more flexibility than first-order bandpass sampling. It is also shown how well-known quadrature-sampling methods for frequency-shifting are special cases of the general second-order sampling technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>