Direct Radio Frequency Sampling Research Articles

Concurrent Multiband Direct RF Sampling Receivers

Direct radio frequency (RF) sampling receivers are investigated for use in concurrent multiband reception for mobile broadband (MBB) applications. The recent proliferation of different frequency bands and standards in wireless communications has allowed large increases in mobility and throughput, but the number of receivers in a device is limited by physical space and power consumption. Software Defined Radio (SDR) is increasingly being explored to reduce the number of analog RF components required. This paper examines the use of direct RF digitization, allowing tunable and concurrent reception of multiple bands with a single RF front-end. Full mathematical models of both Nyquist and subband sampling receivers are presented and used to investigate a quadband LTE receiver, which is modeled in Simulink and implemented in a hardware-in-the-loop (HWIL) testbed. Individual bands are simulated to have at worst -95dBm sensitivity for 16-QAM with Nyquist sampling and -83dBm with subband sampling. Desensitization of the receivers due to multiband processing is evaluated theoretically and experimentally, showing a maximum of 3dB degradation, which is within the LTE standard for adjacent band interference.

Theoretical Analysis and Design Optimization for Multi-GNSS Direct Radio Frequency Sampling Receiver

Abstract: Recently, a considerable amount of research has been conducted on multiple GNSS receivers using the Direct RF sampling concept. This approach greatly reduces the hardware requirements of the traditional receiver by placing the analog-todigital converter as close as possible to the antenna, eliminating the mixer stages. Furthermore, directly sampling the RF signal using the ADC allows for a more efficient design. In this paper, a Multi-GNSS Direct Radio Frequency Sampling Method is designed, optimized, and its performance is presented for several GNSS signals, including GPS L1, GPS L2, and GPS L5. The implemented method is used to find the ranges of valid sampling frequencies in single and multiple band RF signal cases. The algorithm presented results in an easier way to find valid sampling frequencies and a straightforward implementation without the need for complicated mathematical calculations. We consider aliasing issues and computational problems, providing a full theoretical and practical analysis compared to previously presented algorithms in the literature. This paper also examines the relationship between the sampling frequency, noise folding, and its effect on the signal-to-noise ratio (SNR), thus allowing for the selection of the optimal sampling frequency.

다중대역 GNSS 신호 동시 수신을 위한 직접 RF 표본화 수신기 설계 및 성능

이 논문에서는 GNSS(global navigation satellite system) 신호를 RF(radio frequency) 대역에서 표본화하여 디지털 영역에서 복조하는 직접 RF 표본화 수신기를 설계하고 그 성능을 살펴보고자 한다. 직접 RF 표본화 방식은 IF(intermediate frequency) 대역에서 AD(analog to digital) 변환을 하고 복조하는 기존의 IF 변환 방식과 다르게, 아날로그 믹서(mixer)를 전혀 사용하지 않고 안테나 출력인 통과대역 신호를 직접 AD 변환하여 이후의 수신기의 모든 과정을 디지털 영역에서 처리하는 기술이다. IF 변환 방식과 비교하면 하드웨어 구조가 덜 복잡하고 전송환경 변화에 따른 재구성이 가능하며 하나의 AD 변환기를 사용하여 여러 대역의 신호를 동시에 변환할 수 있다는 장점이 있다. 이와 같은 재구성 기능과 동시 수신 기능은 특정 대역의 신호가 적으로부터 전파방해를 받았을 때 후속시스템으로의 빠른 전환이 필요한 군용 시스템에서 매우 중요한 역할을 한다. 한편 여러 대역의 신호를 한 번에 AD 변환하려면 수신하고자 하는 신호의 반송파 주파수, 대역폭, 표본화 후의 중간주파수 그리고 보호 대역 등을 고려하여 표본화 주파수를 정하는 것이 중요하다. 이 논문에서는 GPS L1, GLONASS G1 및 G2 등의 GNSS 신호를 동시에 수신할 수 있는 표본화 주파수를 선택하고 이를 적용한 직접 RF 표본화 수신기를 설계한다. 또한 설계한 수신기를 상용 AD 변환기와 소프트웨어를 사용하여 구현한 후 실제 신호의 수신시험을 통해 수신 성능을 살펴본다. In this paper, we design a direct radio frequency (RF) sampling receiver for multiband GNSS signals and demonstrate its performance. The direct RF sampling is a technique that does not use an analog mixer, but samples the passband signal directly, and all receiver processes are done in digital domain, whereas the conventional intermediate frequency (IF) receiver samples the IF band signals. In contrast to the IF sampling receiver, the RF sampling receiver is less complex in hardware, reconfigurable, and simultaneously converts multiband signals to digital signals with an analog-to-digital (AD) converter. The reconfigurability and simultaneous reception are very important in military applications where rapid change to other system is needed when a system is jammed by an enemy. For simultaneous reception of multiband signals, the sampling frequency should be selected with caution by considering the carrier frequencies, bandwidths, desired intermediate frequencies, and guard bands. In this paper, we select a sampling frequency and design a direct RF sampling receiver to receive multiband global navigation satellite system (GNSS) signals such as GPS L1, GLONASS G1 and G2 signals. The receiver is implemented with a commercial AD converter and software. The receiver performance is demonstrated by receiving the real signals.

Direct radio frequency sampling methodology for multiple signals in an energy-sparse spectrum

Direct radio frequency sampling methodology for multiple signals in an energy-sparse spectrum

Direct Radio Frequency Sampling System on Software-defined Radio

Direct Radio Frequency Sampling System on Software-defined Radio

Direct Radio Frequency Sampling System on Software-defined Radio

A traditional assumption underlying most data converters is that the signal should be sampled at a rate exceeding twice the highest frequency. In this paper, we employ a method for low-rate sampling of multi- band signals via applying periodic nonuniform sampling in shift-invariant spaces generated by m kernels with period T. So, the sampling and reconstruction of signals were transformed into matrix and vector operations, the generalized inverse can be use to find the answer and an interpolator is used to insure that complete reconstruction will be achieved. Finally, we validate the method in MATLAB; the conclusion of simulation shows the frame-work presented here is feasible.

A Comparison of Direct Radio Frequency Sampling and Conventional GNSS Receiver Architectures

The novel concept of a direct radio frequency (RF) sampling receiver front end was analyzed, experimentally tested, and compared with a traditional superheterodyne front end that uses mixing to downconvert the signal before sampling. This study's goal was to demonstrate that signal power and phase are not adversely influenced by the use of direct RF sampling. The direct RF sampling strategy examined in this work uses sampling rates that are much lower than the carrier frequency but more than twice the signal bandwidth. Such a system employs a bandpass filter in front of the analog-to-digital converter (ADC) to avoid sensitivity loss via aliasing of out-of band noise and interfering signals. This design approach was evaluated analytically to determine the effects of sample clock jitter, and experimental results using GPS signals were used to confirm the analytical results. The results indicate that direct RF sampling yields performance equivalent to that of superheterodyne mixing.