Software Defined Radio Receiver Research Articles

Integrated Water Vapor Estimation Through Microwave Propagation Measurements: First Experiment on a Ground-to-Ground Radio Link

Measurement of water vapor (WV) in the lower troposphere on a continuous temporal basis would improve our knowledge of the atmospheric dynamics and the performance of numerical weather prediction models. In recent studies, a new measurement concept, the normalized differential spectral attenuation (NDSA) approach, was proposed. It is based on measurements of differential attenuation at 18.8 and 19.2 GHz performed along a tropospheric radio link. While NDSA measurement at a fixed elevation angle provides information on integrated WV (IWV), measurements at different elevation angles allow to retrieve the vertical WV content profile. A prototype NDSA demonstrator, which consists of two units, a synthesized transmitter and a software-defined radio receiver, has been designed and implemented. The system was accurately characterized through several laboratory tests, and then a first experimental campaign was conducted at fixed elevation angle along a ground-to-ground radio link. Obtained results confirm the sensitivity of the NDSA measurements to the IWV along such link with a good agreement with the existing ground-based and satellite data products.

Through-Wall Human Sensing With WiFi Passive Radar

Through-wall human sensing is of high interest for both military and nonmilitary applications, including counter-terrorism and law enforcement purposes, particularly in the modern, highly urbanized environment. Conventional active radar sensors possess good performance, however, at the expense of high cost and complexity of the transmitter/receiver design. This article demonstrates the effectiveness of a passive through-wall human sensing technique using opportunistic WiFi signals. With a simple software-defined radio receiver and advanced signal processing techniques, the position of indoor WiFi access point can be accurately localized, and its signal can be exploited to clearly detect the Doppler/micro-Doppler of human motions inside the room. Compared to the results in the current literature, this article demonstrates better detection sensitivity and capability to sense not only major motions such as walking and waving hand, but also very small human motions such as keyboard typing and breathing. In addition, an iterative adaptive approach is applied to effectively improve the Doppler resolution of WiFi passive radar. These enhanced sensitivities greatly expand the potential of WiFi passive radar for through-wall sensing applications.

A Novel Highly Linear Voltage-To-Time Converter (VTC) Circuit for Time-Based Analog-To-Digital Converters (ADC) Using Body Biasing

Time-based analog-to-digital converter is considered a crucial part in the design of software-defined radio receivers for its higher performance than other analog-to-digital converters in terms of operation speed, input dynamic range and power consumption. In this paper, two novel voltage-to-time converters are proposed at which the input voltage signal is connected to the body terminal of the starving transistor rather than its gate terminal. These novel converters exhibit better linearity, which is analytically proven in this paper. The maximum linearity error is reduced to 0.4%. In addition, the input dynamic range of these converters is increased to 800 mV for a supply voltage of 1.2 V by using industrial hardware-calibrated TSMC 65 nm CMOS technology. These novel designs consist of only a single inverter stage, which results in reducing the layout area and the power consumption. The overall power consumption is 18 μW for the first proposed circuit and 15 μW for the second proposed circuit. The novel converter circuits have a resolution of 5 bits and operate at a maximum clock frequency of 500 MHz.

Software-defined Radio GNSS Receiver Signal Tracking Methods

Software-defined radio (SDR) - based GNSS receivers are flexible. SDR technology allows changing processing algorithms and adding new signals without any hardware modifications. The main drawback of such a receiver is high computation load. Signal tracking module takes most part of CPU time. This paper considers distributed receiver architectures where most of the processing is performed in a remote PC or a server.The amount of raw data in the SDR receiver is too large for complete transfer. Two methods of reduction are discussed: truncating epochs and disabling tracking for a certain period. The limitations of each method are estimated using simulations. Epochs can be truncated by 50-75% depending on signal-to-noise ratio. The maximum disabling time is about 0.5s for a stationary receiver and 0.1s for a car receiver. Using both methods in combination reduce data volume by 95.4% for a stationary receiver and 83.3% for a car receiver.

Kalman filtering with noncoherent integrations for Galileo E6‐B tracking

The former Galileo Commercial Service (CS) will provide a High Accuracy Service (HAS) and a Commercial Authentication Service (CAS). The first will disseminate free Precise Point Positioning (PPP) corrections through the E6-B signal whereas the second will provide authentication capabilities through the E6-C pilot component that will be encrypted. For this reason, improved processing strategies for data-only processing need to be investigated. The combined use of Kalman filtering and noncoherent integrations is analyzed in this work. A Software Defined Radio (SDR) receiver has been developed and used for the analysis. Different scenarios were considered including simulated data with decreasing Carrier-to-Noise Power Spectral Density Ratio (C/N0) levels and live static and dynamic data collected under harsh environments. It emerges that the use of Kalman filtering with extended noncoherent integrations is an effective approach to improve the performance of data-only processing.

Erratum to "A Software-Defined Radio Receiver for Wireless Recording From Freely Behaving Animals".

Erratum to "A Software-Defined Radio Receiver for Wireless Recording From Freely Behaving Animals".

GnuRadar: An Open-Source Software-Defined Radio Receiver Platform for Radar Applications

In this article, we present the development and integration of an existing cost-effective, open-source software-defined radio (SDR) receiver into a complete, pulsed-radar system used to study meteor reflections that ablate in the Earth's atmosphere. The use of SDR technology in radar applications is not, in itself, a new concept, but details regarding construction of back-end processing, formatting, and storage have not been widely discussed. More specifically, SDR systems, in general, are used to provide a communication link, meaning that precise time of arrival and signal levels are not of primary importance, but these parameters are critical in a radar system. This article addresses in detail methods used to redesign an existing, open-source receiver into a pulse-synchronized radar system for use by anyone interested in cost-effective radar data acquisition solutions. Additionally, we provide test data from an experimental observation to validate operation and performance of the resulting system.

A Doppler Correcting Software Defined Radio Receiver Design for Satellite Communications

We present a flexible software defined radio (SDR) receiver design for the reception and demodulation of satellite signals. The proposed SDR performs an online Doppler search, as well as a code-rate and code-phase search online. The use of graphics processing units (GPUs) allows the radio to compensate Doppler offsets and achieve symbol synchronization in real time. This eliminates the need for a priori information on the satellites position and velocity to perform Doppler compensation on the downlink. To successfully utilize the enhanced computational power of graphics processing units (GPUs) and achieve real-time performance, we utilize acausal batch based signal processing, which allows for the use of fast convolution algorithms. These can efficiently be parallalized and run on GPUs. The Doppler search and demodulation is done by using matched filters. This allows one to adapt the demodulator to work for many modulation schemes by merely changing the set of filters. The demodulator itself essentially works as a batched correlation receiver. Additionally, the proposed SDR can decode signals from multiple antennas that are located at geographically spread ground stations simultaneously. The decoded bits are compared using soft decisions. This can greatly increase the rejection of local burst interference as well as polarized interference and tracking signals that rotate in polarization.

Batch Compressive Sensing for Passive Radar Range-Doppler Map Generation

By exploiting the sparsity of the scene containing only a few moving targets, a high-resolution and real-time range-Doppler map generation algorithm for passive bistatic radar is proposed. The proposed algorithm divides the long integration time into multiple short batches, from which a few batches are randomly selected on the basis of compressive sensing theory. A one-dimensional cross correlation is performed for each selected batch to obtain the range-compressed profile. Mean-value subtraction is then performed to suppress the direct path interference and stationary target reflections. Finally, an extended orthogonal matching pursuit algorithm is proposed for the effective estimation of target Doppler frequency. Practical application of this novel algorithm is examined by the detection of airplanes and ships via two synchronized general-purpose software-defined radio receivers. The results show that the proposed algorithm can achieve an improved resolution and a reduced sidelobe level compared to the conventional algorithms.

A Software-Defined Radio Receiver for Wireless Recording From Freely Behaving Animals.

To eliminate tethering effects on the small animals' behavior during electrophysiology experiments, such as neural interfacing, a robust and wideband wireless data link is needed for communicating with the implanted sensing elements without blind spots. We present a software-defined radio (SDR) based scalable data acquisition system, which can be programmed to provide coverage over standard-sized or customized experimental arenas. The incoming RF signal with the highest power among SDRs is selected in real-time to prevent data loss in the presence of spatial and angular misalignments between the transmitter (Tx) and receiver (Rx) antennas. A 32-channel wireless neural recording system-on-a-chip (SoC), known as WINeRS-8, is embedded in a headstage and transmits digitalized raw neural signals, which are sampled at 25 kHz/ch, at 9 Mbps via on-off keying (OOK) of a 434 MHz RF carrier. Measurement results show that the dual-SDR Rx system reduces the packet loss down to 0.12%, on average, by eliminating the blind spots caused by the moving Tx directionality. The system operation is verified in vivo on a freely behaving rat and compared with a commercial hardwired system.

Determination of LO frequency for reception of maximum number of GNSS signals in presence of interference

A method for the frequency determination of a local oscillator (LO) is presented to facilitate reception of the maximum number of satellite signals via the use of a multi-global navigation satellite system (GNSS) receiver under interference. The authors have herein suggested a model for estimating the number of GNSS satellites with changing LO frequency. This estimation model was derived based on GNSS and interference spectra, used to determine the LO-frequency value to avoid interference and facilitate reception of maximum GNSS signals. The proposed method was verified by means of an experiment involving the use of software-defined radio receiver and actual GNSS signals. The authors expect the proposed method to be the basis of anti-interference processes in reconfigurable GNSS receivers.

Design and implementation of an open-source BDS-3 B1C/B2a SDR receiver

GNSS software-defined radio (SDR) receiver has been and will continue to be a tremendous research enabler given its flexibility and GNSS modernization as well as improvements to complimentary technologies. An open-source suite of GNSS SDRs capable of post-processing all open-service GNSS signals has been developed by the GNSS Lab at the University of Colorado, Boulder. As the latest expansion, processing capabilities for the B1C/B2a signals of the third-generation BeiDou navigation satellite system (BDS-3) are incorporated into this SDR package. To provide a basic implementation framework for GNSS community, separate or joint processing of the data and pilot channels are realized in the B1C/B2a SDR; and both narrowband and wideband tracking modes are implemented specifically for B1C pilot channel. Soon after the launch of the first two BDS-3 satellites, the B1C/B2a signals have been captured and the initial tracking results have been obtained. We describe the design strategy and implementation of the BDS-3 B1C/B2a SDR and report the processing results. The emphasis is placed on the B1C processing due to the novelty and complexity of the quadrature multiplexed binary offset carrier modulation employed by B1C.

Optimal Design of Multiplier-Less Non-uniform Channel Filters with Successive Approximation of Vectors

Applications such as software-defined radio (SDR) receivers utilize channel filters to isolate the individual frequency bands of different communication standards present in a wideband input signal. Low complexity and sharp transition width are the two important design constraints of channel filters in SDR receivers. Frequency response masking (FRM) with the multiplier-less design is an effective approach for designing sharp filters with low complexity. This paper presents an optimal design for multiplier-less implementation of FRM-based non-uniform channel filters. In the proposed design, multiplier-less channel filters are realized basing upon decomposing their impulse response values in generalized bit planes. This decomposition is based on a vector successive approximation technique in which impulse responses are successively approximated using a dictionary of vectors. The resulting coefficients of channel filters belong to signed sums of powers of two form. The proposed channel filter designs are simulated using MATLAB R2017b, and the results have been compared with the existing ones in order to signify the effectiveness of the proposed design. The simulations show that the proposed channel filter design has low complexity (number of adders) and the design time is considerably low.

A varactor based tunable RF filter for multistandard wireless communication receivers

This paper presents the design of a tunable RF filter dedicated for multistandard operation in Software Defined Radio (SDR) receivers. This filter is based on the Dual-Behaviour Resonators (DBR) topology realized in microstrip technology with PTFE substrate and using SMV1405 varactors as tuning elements. It provides the independent control of its center frequency and bandwidth relative to the radio standards UMTS, Wi-Fi and LTE (Band N°7). The center frequency ranges from 2.142 to 2.65 GHz and the required bandwidth varies from 86 to 108 MHz. S-parameters simulations and measurements with non-linearity study are provided to evaluate the performance of the designed filter. A very good agreement between simulations and measurements is obtained and the designed filter shows acceptable performances in terms of insertion and return losses which are less than 6 dB and more than 14 dB, respectively for all bands. Moreover, linear properties regarding receiver requirements with a minimum 1-dB compression point (P1dB) of 11.4 dBm and a minimum third order intercept point (IP3) of 21.2 dBm are satisfying.

Improving two-way satellite time and frequency transfer with redundant links for UTC generation

Two-way satellite time and frequency transfer (TWSTFT) is a primary technique for the generation of coordinated universal time (UTC). At present, more than 12 timing laboratories around the world use SAtellite Time and Ranging Equipment (SATRE) modems in TWSTFT operations and contribute data for the realization of UTC. The advantages of TWSTFT are its small calibration uncertainty (⩽1.0 ns if the link is calibrated with a TWSTFT mobile station) and its long-term link stability. However, the precision of SATRE TWSTFT in the operational networks is degraded by a daily variation pattern (diurnal) in the TWSTFT results. The diurnal with varying amplitude appears virtually in all SATRE TWSTFT links. The observed peak-to-peak variation of the diurnals can reach 2.0 ns in some cases. So far, studies on the sources of the diurnal have not provided conclusive understanding of the diurnal’s dominant origin.Therefore, efforts have been made to reduce the impact of the diurnal variation in TWSTFT for UTC computation. The BIPM has been using the combination of SATRE TWSTFT results and GPS carrier-phase precise point positioning solutions (GPSPPP) for UTC computation since 2010. The combination adjusts the GPSPPP results to long-term averages of TWSTFT and is effectively free from the diurnal variations because the GPSPPP results contain almost no diurnal. Lately, the use of software-defined radio receivers (SDR) in TWSTFT has shown one way of how to reduce the diurnal variations by a factor of two to three in most of the inner-continental SATRE TWSTFT links, and furthermore, how the short-term stability for all UTC SDR TWSTFT links can be improved. In addition, there has been research on the full use of the redundancy in the TWSTFT network to improve the TWSTFT link stability. Recent studies on evaluating indirect links revealed that it is possible to apply a simplified procedure to use the redundancy, in a most effective way, to reduce the diurnal variations in the Europe-to-Europe SATRE TWSTFT links by a factor of two to three. Based on these findings, we gained new insights about the diurnals and its dominant origin(s) which are discussed in this paper. The methods of the combination of SATRE TWSTFT and GPSPPP as well as the indirect SATRE TWSTFT links utilize the redundancy in the UTC time transfer network. SDR TWSTFT can largely reduce the diurnal in SATRE TWSTFT, but noticeable residual diurnal remains. In this paper, we provide the analyses of using the combination of SDR TWSTFT and GPSPPP results, as well as using the indirect SDR TWSTFT links. This paper concludes that the use of SDR TWSTFT redundant links can further improve the stabilities of UTC TWSTFT links. In addition, the use of SDR TWSTFT indirect links is a pure TWSTFT solution. The independence of the TWSTFT results to GPS results can improve the robustness of UTC computation.

SDR-Fi: Deep-Learning-Based Indoor Positioning via Software-Defined Radio

Wi-Fi fingerprinting-based indoor localization has received increased attention due to its proven accuracy and global availability. The common received-signal-strength-based (RSS) fingerprinting presents performance degradation due to well-known signal fluctuations, but more recently, the more stable channel state information (CSI) has gained popularity. In this paper, we present SDR-Fi, the first reported Wi-Fi software-defined radio (SDR) receiver for indoor positioning using CSI measurements as features for deep learning (DL) classification. The CSI measurements are obtained from a fast-prototyping LabVIEW-based 802.11n SDR receiver platform. SDR-Fi measures CSI data passively from pilot beacon frames from a single access point (AP) at almost 10 Hz rate. A feed-forward neural network and a 1D convolutional neural network are examined to estimate location accuracy in representative testing scenarios for an indoor cluttered laboratory area, and an adjacent, covered outdoor area. The proposed DL classification methods leverage CSI-based fingerprinting for low AP scenarios, as opposed to traditional RSS-based systems, which require many APs for reliable positioning. Demonstration results are threefold: (a) A fast-prototyping SDR platform that passively extracts CSI measurements from Wi-Fi beacon frames, providing a genuine possibility for vendor network cards to provide such measurements, (b) two state-of-the-art DL classification methods outperforming traditional RSS-based methods for low AP scenarios, (c) a testing methodology for performance evaluation of the proposed indoor positioning system.

An Evaluation for Phase and Gain Imbalance Compensation in Direct-Conversion Receivers

In this paper, we present a modified compensation method for phase and gain in direct-conversion software-defined radio (SDR) receivers. In direct-conversion receivers, degradation owing to the phase and gain imbalances caused by analog devices. To solve this problem, we present a modified blind compensation techniques based on digital signal processing using a feedback control loop with a practical computation process. The modified method can reduce the complexity when a hardware logic circuit is used, like an FPGA. The simulation results verify that the modified method achieves better BER performance.

Switched Beam through Parasatic Antenna Array for Radio Direction Finding Using I/Q Samples

An electronically controlled parasitic antenna array consisting of one active element connected to a software defined radio (SDR) receiver and four passive parasitic elements used to design and construct affordable radio direction finding system. The directivity of the antenna array achieved by increasing/degreasing the electrical length of the parasitic elements. The design based on a central active monopole and an array of four parasitic monopoles equidistantly from the central element by 0.20 λ, placed on ground plane to provide the 360 degree azimuthal coverage without any moving parts, provides excellent directional resolution. The system is controlled by using Arduino to switch between regions (0-90),(90-180),(180-270) or (270-360) and analysed by using a newly developed method based on I/Q samples to extract the amplitude and phase of the desired signal to find the exact direction in that region. The antenna design, its application to determine the direction finding, the new algorithm are presented below.

Passive bistatic radar using digital video broadcasting-terrestrial receivers as general-purpose software-defined radio receivers.

We investigate the use of low-cost digital video broadcasting-terrestrial (DVB-T) receivers as general-purpose software-defined radio (SDR) receivers for passive bistatic radar (PBR) applications. Two DVB-T receivers are synchronized using a common clock to perform coherent measurements. By exploiting the direct-path signal in the surveillance channel, we use the cross-correlation process to estimate the time offset between the data streams of reference and surveillance channels caused by the universal serial bus communication. We demonstrate the detection of static and moving targets as well as short-range targets, including a landing airplane at 8 km, multiple ships with different velocities, and vehicles within 20 m from the receiver acquiring at a 2 MHz bandwidth, by using Japan's Integrated Services Digital Broadcasting Terrestrial digital TeleVision (TV) signal broadcast. We also propose to improve the range resolution of the designed PBR system by combining multiple SDR receivers tuned to different carrier frequencies. The designed system and proposed method can be used for various applications, such as airplane navigation, harbor protection, and traffic density monitoring.

A 0.8–4-GHz Software-Defined Radio Receiver With Improved Harmonic Rejection Through Non-Overlapped Clocking

The RF section of a software-defined-radio receiver front-end with harmonic rejection is presented. The proposed mixer-based receiver provides two programmable notches that can be located in any desired frequencies, e.g., the third and fifth harmonics of the sampling frequency in the proposed receiver. These rejections at the third and fifth harmonics are implemented using two RF-signal paths with a non-overlapped clocking strategy. The receiver also shows a good rejection at the seventh harmonic. The circuit is implemented in 130-nm CMOS and operates from a 1.5-V supply. Measurement results show that, for a 1-GHz RF input, the receiver has a harmonic rejection of 45 and 46 dB for the third and fifth harmonics, respectively. Moreover, the rejection of the seventh harmonic is as high as 44 dB for a 0.8-GHz RF input. Verifying the results on four different chips shows less than 2-dB variation in the rejection values. The receiver shows a noise figure of 3.8 dB at a baseband frequency of 5 MHz for a 1-GHz RF signal, with a power consumption of 33 mW.