Acquisition Of Ultra-wideband Signals Research Articles

QTT Ultra-wideband Signal Acquisition and Baseband Data Recording System Design Based on the RFSoC Platform

Abstract The 110 m QiTai radio Telescope (QTT) will be equipped with multiple Ultra-WideBand (UWB) receivers in the primary and Gregory focus to achieve continuous frequency coverage from 270 MHz to 115 GHz, which poses great challenges to signal acquisition, transmission, and real-time processing. Aiming at 10 GHz and above full-bandwidth acquisition and multi-scientific processing for the QTT UWB signals, an experimental system with high-speed signal acquisition, 100 Gb network multi-path distribution, and fast recording is designed by using advanced direct RF-sampling technology and heterogeneous architecture. The system employs a ZCU111 board to digitize dual-polarization signals with a sampling rate of 4.096 GigaSamples-Per-Second and 12-bit quantization. The collected wideband signals are channelized into 2048 chunks, which are then assembled into 16 sets of digital narrow basebands with 128 MHz bandwidth and transmitted to the processing servers through two 100 Gb ports. A HASPIPE pipeline, UWB_HASHPIPE is designed to receive and store multiple subbands in parallel. Data distribution links can be flexibly configured based on IP addresses and port numbers. The system is verified by pulsar observation experiments on the Nanshan 26 m telescope. 512 MHz bandwidth is selected from the collected L-band receiver signals and recorded in VDIF file format with 8 parallel instances. The test results show that the data integrity is excellent, and the signal-to-noise ratio of the band-merged pulsar profile is stronger than single subband data. This paper provides a high-performance and flexible solution for the design of versatile UWB backends. Meanwhile, the developed platform can be integrated into QTT backends for baseband data collection and Very Long Baseline Interferometry observation.

Ultra-wideband signal acquisition by use of channel-interleaved photonic analog-to-digital converter under the assistance of dilated fully convolutional network

We demonstrate a photonic architecture to enable the separation of ultra-wideband signals. The architecture consists of a channel-interleaved photonic analog-to-digital converter (PADC) and a dilated fully convolutional network (DFCN). The aim of the PADC is to perform ultra-wideband signal acquisition, which introduces the mixing of signals between different frequency bands. To alleviate the interference among wideband signals, the DFCN is applied to reconstruct the waveform of the target signal from the ultra-wideband mixed signals in the time domain. The channel-interleaved PADC provides a wide spectrum reception capability. Relying on the DFCN reconstruction algorithm, the ultra-wideband signals, which are originally mixed up, are effectively separated. Additionally, experimental results show that the DFCN reconstruction algorithm improves the average bit error rate by nearly three orders of magnitude compared with that without the algorithm.

Random projection method for ultra wideband signal acquisition

High-speed high-resolution analog-to-digital (A/D) conversion demanded by ultra wideband (UWB) signal processing is a very challenging problem. This paper proposes a parallel random projection method for UWB signal acquisition. The proposed method can achieve high sampling rate, high resolution and technical feasibility of hardware implementation. In the proposed method, an analog UWB signal is projected over a set of random sign functions. Then the low-rate high-resolution analog-to-digital convertors (ADCs) are used to sample the projection coefficients. The signal can be reconstructed by simple linear calculation with the sampling matrix, without complying with optimization algorithm and prior knowledge. In other aspects, unlike other approaches that need to utilize an accurate time-shift at extremely high frequency, or design a hybrid filter bank, or generate specific basis functions or work for signals with prior knowledge, the proposed method is a universal sampling approach and easy to apply. The simulation results of signal to noise ratio (SNR) and spurious-free dynamic range (SFDR) validate the efficiency of the proposed method for UWB signal acquisition.

Weighted Acquisition of UWB Signals Based on Energy Detection

Due to the low complexity and cost characteristics of ultra-wideband (UWB) systems, a weighted acquisition algorithm based on energy detection is proposed in this paper. This method is divided into two steps to acquire the direct path (DP) component. Firstly, weighted energy detection is applied to determine which energy block the DP lies in by generalized likelihood ratio test (GLRT). A sub-optimal weighted vector is obtained, by which the closed form of detection performance is proposed. In the second step, the precise position of DP within the detected energy block is obtained by the statistical characteristics of the channel energy distributions. Key parameters that affect acquisition performance are studied by analytical and numerical methods. Simulations and experiments are carried out for performance and complexity comparison with traditional ones. The results show that weighted acquisition achieves better performance under relative low complexity conditions.

A Rapid and Reliable Two-Step Search Scheme for UWB Signal Acquisition in Multipath Channels

We propose the “Two-Step Search scheme with Linear search based Second step (TSS-LS)” by improving the conventional “Two-Step Search scheme with Bit reversal search based Second step (TSS-BS)” for reliable as well as rapid acquisition of Ultra Wide Band (UWB) signals in multipath channels. The proposed TSS-LS utilizes two different thresholds and search windows to achieve fast acquisition. Furthermore, unlike the TSS-BS in which the bit reversal algorithm is applied in both steps, the linear search is adopted for the second step in the proposed TSS-LS to correctly find the starting point in the range of effective delay spread of the multipath channels, and to obtain reliable bit error rate performance of the UWB systems.

Ultra-wideband signal acquisition with hybrid DS-TH spreading

The usage of long spreading sequences and the fine timing resolution result in a large search space during acquisition in ultra-wideband (UWB) systems. This paper presents a two-stage signal acquisition scheme for UWB systems employing a hybrid signaling format involving direct sequence (DS) spreading and time hopping (TH), which significantly reduces the search space. The resulting acquisition system consists of two stages, one each for the acquisition of the TH and DS sequences. The dense multipath channel typical of UWB systems implies that there can exist more than one phase to which the receiver can lock on and achieve satisfactory demodulation performance subsequent to acquisition. We define the set of such phases as the hit set. The hybrid signaling format coupled with the multi-phase hit set help significantly improve the acquisition performance of the UWB system. The performance of the proposed acquisition system, measured in terms of the mean detection time, is evaluated analytically and supported by computer simulation

Timing Acquisition in Ultra-wideband Communication Systems

The goal of this paper is to highlight the significance of the timing acquisition problem in ultra-wideband (UWB) communication systems and discuss efficient solutions to the problem. We discuss how the distinguishing features of UWB communication systems, such as their wide bandwidth and low transmission power constraints, are responsible for making the acquisition of UWB signals a difficult task. A survey of the current approaches to UWB signal acquisition is also given. In addition, we discuss some of the issues and challenges in UWB signal acquisition which may not have received sufficient attention in existing literature.

A Generalized Signal Flow Graph Approach for Hybrid Acquisition of Ultra-Wideband Signals

This paper establishes a general framework for the study of various search procedures in which a group of observers is searching for a group of items in some arbitrary manner. A generalized signal flow graph approach yields a complete statistical description of the search time as well as the probability of correctly terminating the search. The motivation for this study comes from the acquisition of an ultra-wideband (UWB) signal in a dense multipath channel. In this particular problem many resolvable paths tend to cluster at a receiver containing multiple correlators allowing for a hybrid serial/parallel search. This hybrid search, as well as a bound on a sorted hybrid search, is analyzed using the generalized signal flow graph approach. Rapid code and frame acquisition at the receiver is desired and it is shown that a specific nonconsecutive search, the bit reversal search, yields an optimum hybrid search procedure under certain conditions. The acquisition of UWB signals also leads to the concept of a self-similar signal flow graph, in which a new search is initiated upon the completion of the previous one.