Acquisition and Tracking Performance of Satellite Navigation System Signal using Tiered Differential Polyphase Code

의사위성은 우주상공의 GPS 위성과는 달리 지상이나 비행체에 설치되어 GPS 위성과 같이 거리를 측정할 수 있는 ranging 신호를 전송하는 전송기이다. 의사위성은 정확성, 가용성, 무결성을 향상시킬 수 있으나 GPS 위성 신호에 대해 신호의 포화 또는 간섭을 일으킨다. 의사위성의 근원거리 문제를 해결하기 위해 의사위성의 신호를 펄싱이 있을 때만 내보내는 기법을 주로 사용한다. 본 논문에서는 의사위성의 정적 펄싱, 이동 펄싱, 랜덤 펄싱 기법과 의사위성의 개수가 GPS 소프트웨어 수신기의 L1 및 L2C 신호획득에 미치는 영향을 분석하였다. GPS L1신호의 경우 의사위성이 1개일때는 정적펄싱에 대한 GPS 소프트웨어 수신기의 신호 획득 및 추적 성능이 가장 좋았고 2개 이상일 때는 랜덤펄싱에 대한 성능이 가장 좋았다. L2C 신호는 세가지 펄싱에 대한 성능이 비슷하게 안정적으로 나왔는데 정적펄싱에 대한 성능이 약간 좋게 나왔다. L1, L2C 모두 위사위성 3개까지는 모든 펄싱에 대해서 측위가 가능한 것으로 나왔다. Pseudolites are ground-based transmitters that can be configured to emit GPS-like signals for enhancing the GPS by providing increased accuracy, integrity, and availability. However, a pseudolite (PL) can interfere with GPS satellite signals while it is transmitting or cause saturation to automatic gain control circuit. To solve these problems pulsing scheme is used, which transmits PL signal during a short period of time. In this paper the effect of the number of PL and pulsing scheme on the software GPS L1 and L2C signal acquisition performance is studied for the three pulsing schemes such as static pulsing, sweep pulsing, and pseudo random pulsing. For GPS L1 signal, static pulsing shows the best signal acquisition and tracking performance with one PL, and random pulsing shows the best performance with more than or equal to two PLs. For GPS L2C signal, all three pulsing schemes show the similar signal acquisition and tracking performance, but static pulsing shows a little better performance. For GPS L1 and L2C signals, software GPS receivers can do positioning with up to three PLs.

This paper presents a systematic discussion on GPS C/A code cross correlation and its impact on signal acquisition, tracking and Ground-Based Augmentation System (GBAS) performance. Three types of cross correlation effects are investigated: 1) between two satellites that have approximately the same Doppler frequency; 2) between two satellites that have an offset at an integer number of kHz in Doppler frequency; 3) between a C/A code signal and a signal that consists of alternating zeros and ones. The first type of cross correlation has been well studied in the past decade, and its impact is often found similar to that of multipath. There exist some subtle, but important, differences between cross correlation and multipath, which will be discussed in this paper. Cross correlation cannot be treated as a random interference source, since it is inherently constrained by the Doppler frequency difference between the two satellites. Based on this constraint, the cross correlation functions will be analytically modeled in the time domain and in the frequency domain for each of the three types. All three types of cross correlation are potential threats to weak signal acquisition, PseudoRange tracking and carrier phase tracking. There are impacts on both mobile users and ground reference stations. More specifically, the PseudoRange tracking error will likely not be common between a ground reference and a mobile user, which becomes a concern for differential systems like GBAS. The PseudoRange error is not only a function of the Doppler offset and signal strength, but is also dependent on the tracking loop configuration. For example, the relative motion between the satellites and the antenna, the tracking loop bandwidth, coherent integration time and the carrier smoothing time constant all play key roles in the PseudoRange error model. It has been discovered in previous studies that a sufficiently large time constant in carrier smoothing provides effective mitigation for cross correlation errors. Most GPS users are protected against cross correlation in signal acquisition and tracking. In some worst-case scenarios, however, meter-level PseudoRange errors in GBAS may occur. As a result, cross correlation must be carefully monitored for high-accuracy safety of life applications. It can also falsely trigger other GBAS monitors, which may include the low power monitor and the signal deformation monitor. An overview of the implications of cross correlation on GBAS is provided in this paper.

The latest adaptation of the Frontier Radio, an X/Ka-band deep space implementation, has been transitioned into a finished product for Solar Probe Plus (SPP) and future missions. Leveraging the technology readiness level (TRL) 9 software-defined radio (SDR) platform successfully flown on the Van Allen Probes (VAP) mission, the Frontier Radio now brings a low-power, low-mass, yet highly radiation-tolerant and robust SDR to deep space applications. This implementation brings with it a suite of enhanced capabilities and improvements to the Frontier Radio platform. The core deep space software implementation is designed to match or improve upon the signal acquisition and tracking performance, as well as improve the receive and transmit implementation losses of its predecessors (JHU/APL and industry). The deep space radio operates using less than 6W at 30V in receive mode, and approximately 10W with either the X- or Ka-band exciter enabled and operating in two-way coherent duplex mode. The power consumption in these modes can be further reduced to as low as 3W and 9W respectively, depending on the spacecraft bus and mission requirements. In addition to providing standard deep space navigation features such as two-way Doppler, two-way ranging, and differential one-way ranging (DOR), firmware and software enhancements were made to improve the receiver acquisition and tracking robustness. A software enhancement was also essential in 1) reducing the effects of turnaround noise on the Ka-band link and 2) reducing the impact on downlink frame error rates while operating in a coherent turnaround mode. These improvements enable simultaneous science return and navigation over the Ka-band link with minimal implementation loss. A number of enhancements to the hardware and test platforms have been made to improve manufacturability, reduce manufacturing and test cost and turnaround time, improve portability across multiple frequency bands and applications, and increase processing capacity. The parts selection provides for a total ionizing dose (TID) tolerance of at least 100krads, subject to the parts purchased at time of manufacturing, without spot or bulk shielding. The Frontier Radio provides a robust selection of single event mitigation and fault protection techniques. Future deep space missions such as Europa Clipper plan to utilize the Frontier Radio. A single board version of the Frontier Radio is also under development for CubeSat and other small form factor spacecraft, with a current best estimate (CBE) of 1W receive mode and less than 5W duplex mode with a 1W power amplifier; this implementation leverages the same robust parts selection as the parent product, with a streamlined hardware implementation that leverages advancements in high speed signal conversion and processing. This paper describes the current capabilities of the Frontier Radio for deep space and provides a short discussion of future efforts related to the platform.

GPS signal is very weak and easily influenced by interference or jamming. An antenna array with adaptive algorithm combing with temporal anti-jamming processing can be used to mitigate interference and improve GPS signal acquisition and tracking performance. This paper addresses an all digital temporal and spatial anti-jamming implementation scheme based on adaptive antenna array. Temporal adaptive Altering techniques can effectively suppress narrowband interference, which is less ability to code with broadband interference. However, the presence of an antenna array allows the receiver to operate in spatial domain in addition to time or frequency domain, which can improve the performance of GPS receiver with broadband interference. Simulation results show the scheme can greatly enhance the robustness of GPS receiver in a large number of interference signals.

In recent years, with the increasing living standards, LBS (location-based service) has been gradually integrated into all aspects of daily life. However, compared to the outdoor environment, indoor environment is very complex. In this paper, we discuss the problem of TC-OFDM (time divided CDMA-OFDM superimposed signal system) multipath interference in the design of indoor positioning receiver based on the terrestrial broadcasting network. In the TC-OFDM system, because of the complexity of the indoor environment, the problem of multipath, especially the short-delay multipath, is particularly severe, which causes a serious impact on the receiver signal acquisition and tracking performance. Through theoretical analysis and mathematical simulation, we specify the characteristics of the fading channel in the indoor location and influence of the multipath signal. We also build the models of signals through the MATLAB software. Through the analysis in this paper, we can understand the propagation characteristics and the main error sources of the indoor signal better, furthermore, we provide theoretical basis for the system optimization in the future.

GPS signal is very weak and easily influenced by interference or jamming. An antenna array with beamforming algorithm can be used to mitigate interference and improve GPS signal acquisition and tracking performance. This paper addresses interference mitigation and signal enhancement performance analysis by an adaptive antenna array. Adaptive filtering techniques can effectively suppress narrowband interference, which is less ability to code with broadband interference. However, the presence of an antenna array allows the receiver to operate in spatial domain in addition to time or frequency domain, which can improve the performance of GPS receiver with broadband interference. In the paper, a design scheme for antenna array based on software radio is proposed for improving the whole performance of the receiver. The single and multiple MVDR beamformers are used for interference cancellation and the performance of GPS receivers. Simulation results show the scheme using multiple MVDR beamformer can greatly enhance the robustness of GPS receiver in a large number of interference signals.

A simple nonlinear algorithm is examined which significantly enhances the signal acquisition and tracking performance of second-order phase-locked loops (PLLs). This algorithm is significant in that it reduces the signal acquisition time of an otherwise conventional loop by a factor of up to several thousand while enabling a narrowband PLL to remain locked onto very-high-dynamics signals without switching loop bandwidths or increasing the loop order. It is shown that the phase noise is improved as compared to a PLL having an equivalent wider bandwidth. These improvement factors in acquisition time and dynamic tracking, as well as the tradeoffs in phase noise performance, are examined through explicit analysis and computer modeling. >

Due to the low signal power, the Global Navigation Satellite System (GNSS) signal is vulnerable to interference and even cannot be captured or tracked in harsh environments. As an alternative, the Low Earth Orbit (LEO) satellite has been widely used in the navigation field due to the advantages of low cost and strong signals. It is becoming a significant component of the new combined navigation system with GNSS. The combination of an LEO Doppler signal and GNSS observables can improve the positioning accuracy and high-precision positioning convergence time of the GNSS receiver. However, the GNSS signal receiving capability cannot be improved from this data fusion level. We propose a novel assisted structure where GNSS signal acquisition and Doppler tracking are assisted by LEO Doppler positioning. The receiver uses the LEO signal to achieve Doppler positioning firstly. Then, the coarse position with the GNSS navigation messages received from LEO, as well as the estimated clock information, is used to assist in the acquisition and tracking of GNSS. In this way, the GNSS receiver’s sensitivity can get the benefit from this integrated system. The paper presents the structure of the assisted receiver and analyzes the assisted GNSS signal acquisition and carrier tracking performance in detail. Simulation experiments of this assisted structure are carried out to verify its superiority of acquisition and tracking sensitivity in comparison with standalone GNSS receivers. Theoretical analysis and experimental results show that the proposed acquisition method can achieve 90% detection probability at a carrier-to-noise ratio (C/N0) of 15 dB-Hz, which is about 8 dB higher than the conventional acquisition method without assistance; the proposed tracking method can track weak signals of 5 dB-Hz, which is about 4 dB higher than the conventional method. Therefore, this novel LEO-assisted receiver has significantly improved weak signal acquisition and tracking sensitivity.

SummaryWith the proliferation of Internet of Things (IoT), a large number of devices are expected to connect to the Internet over different networks due to various demands and characteristics of IoT devices (IoTDs). One of the networks that will connect IoTDs to the Internet is cellular networks. The 3rd Generation Partnership Project (3GPP) proposes a connectivity model for cellular networks in which IoTDs connect to the network via relay devices. In this model, discovering the relay devices is a challenging task due to energy budget constraints, mobility of devices, and collision of discovery messages. Since IoTDs are constrained devices, it is important that they perform discovery with the minimum energy consumption by intermittently sleeping and waking up. In this paper, we propose signature‐based and energy‐efficient relay discovery protocol (SERDP) using Zadoff–Chu sequences. Since Zadoff–Chu is a Constant Amplitude Zero Autocorrelation (CAZAC) sequence, we use the sequence for pointing the active slots of the devices within the proposed three‐stage original period structure. The probabilistic analysis and simulation results show that SERDP discovers more devices with less energy consumption as well as preventing collisions, as compared with the existing protocols.

In recent years, fifth-generation (5G) is receiving attention in wide research and progress efforts from the wireless communication society. 5G provides a new frequency bands alongside amid the wider spectral bandwidth per frequency channel. To solve the new challenges in 5G, different kind of new modulation techniques and multiple access (MA) schemes have to be adopted. To increase spectral efficiency new techniques called orthogonal multiple access (OMA) and nonorthogonal multiple access (NOMA) techniques are used in 5G wireless system. Here, we propose a class of polyphase sequences called Zadoff Chu sequences which have uniform amplitude, and these sequences bear good correlation properties. Since these sequences are also identified as constant amplitude zero autocorrelation (CAZAC) sequences, Zadoff Chu sequences are used to spread data in OMA and NOMA schemes for 5G networks. The simulation result shows that Zadoff Chu sequence has good correlation properties, and ZCT precoded-based OFDM system is capable of reducing the PAPR significantly.

1D convolutional neural network-based adaptive algorithm structure with system fault diagnosis and signal feature extraction for noise and vibration enhancement in mechanical systems

We have proposed a new visible light Orthogonal Frequency Division Multiplex (OFDM) system using the Constant Amplitude Zero Auto-Correlation (CAZAC) equalization. In visible light systems, LEDs or LDs in transmitters have small dynamic range of input signal magnitude for linear operation and the bias current must be carefully set to consider the maximum allowable forward current of LEDs or LDs, to reduce magnitude distortion and to control signal clipping. The OFDM enables the limited frequency bandwidth of LEDs or LDs to be fully-used and the CAZAC equalization drastically reduces magnitude fluctuation of OFDM time-domain signal. We found that one CAZAC sequence in cooperation with IFFT process converts the PAPR of the M-Quadrature Amplitude Modulation (QAM) OFDM signal into the PAPR of an M-QAM single-carrier signal. This fact is our new discovery. Moreover, since the CAZAC equalization has potential capacities of frequency diversity effect, the system has an advantage in improvement of the BER performance under frequency selective fading environments, which also includes the frequency-dependent attenuation due to the frequency response of LEDs and LDs. Furthermore, we verified for 16QAM-OFDM and 16PSK-OFDM, and confirmed that the communication distance is much extended by the CAZAC.

In this paper, we propose a joint DoA and TDoA estimation algorithm for mmWave communications. The key idea of proposed scheme is to use the pilot signal generated from the Zadoff-Chu sequence. Zadoff-Chu sequence is a type of constant amplitude zero auto-correlation (CAZAC) sequence that has a circular auto-correlation property. Using this property, we can effectively determine the time delay of multi-path signals. Also, by applying the maximum likelihood (ML) estimation at the Zadoff-Chu pilot measurements, we can acquire high resolution DoAs and corresponding path gains.

대표적인 D2D (Device-to-Device) 통신 시스템 중 하나인 Qualcomm사의 FlashLinQ 시스템에서는 링크 스케줄링 과정을 낮은 복잡도로 실현할 수 있도록 하기 위해 단일-톤 (single-tone) 신호를 이용한 우선순위 및 SIR (Signal-to-Interference power Ratio) 기반의 링크 스케줄링 기법을 수행한다. 하지만 다중 경로 채널 환경에서는 주파수 선택적 페이딩의 영향으로 단일-톤 위치에서와 실제 데이터가 전송되는 전체 대역에서의 수신 전력 간 오차가 발생할 수 있으며, 이는 공평성 측면에서 문제가 될 뿐만 아니라 셀 전체 전송률 상의 손실을 일으킬 수 있다. 따라서, 본 논문에서는 이러한 문제를 해결하기 위해 CAZAC (Constant Amplitude Zero Auto-Correlation) 시퀀스의 상관 특성을 이용해 전체 대역에 대한 SIR 에 가까운 값을 획득할 수 있는 링크 스케줄링 기법을 제안한다. 제안 기법은 전체 대역을 다수의 sub-block 으로 구분하고 각 sub-block 마다 링크의 우선순위에 해당하는 순환 오프셋 (cyclic offset) 을 적용한 CAZAC 시퀀스를 전 대역에 걸쳐 전송하여, 수신 신호와 참조 신호간의 순환 상호 상관 연산 (cyclic cross-correlation)을 통해 전체 대역에 대한 SIR 에 근접한 값을 획득할 수 있다. FlashLinQ, one of the typical D2D communication systems developed by Qualcomm, considers a single-tone communication based distributed channel-aware link scheduling method to realize the link scheduling process with low control overheads. However, considering the frequency selective fading effect of practical multi-path channel, the single-tone based SIR estimation causes a critical scheduling error problem because the received single-tone signal has quite different channel gain at each sub-carrier location. In order to overcome this problem, we propose a novel link scheduling method based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence for D2D communication system. In the proposed method, each link has a unique offset value set for the generation of CAZAC sequences. CAZAC sequences with the cyclic offsets are transmitted using multiple sub-blocks in the entire bandwidth, and then each device can obtain nearly full-band SIR using a good cyclic cross-correlation property of CAZAC sequence.

This paper presents an adaptive modulation in a single-input-single-output (SISO)-OFDM-based cooperative system that employs a Constant Amplitude Zero Autocorrelation (CAZAC) preamble-based SNR estimator. A novel CAZAC preamble-based SNR estimator that does not incur a throughput penalty is derived by exploiting a modified CAZAC preamble structure for the OFDM system. The proposed CAZAC SNR estimator is used to estimate the channel quality by finding the instantaneous SNR of the received cooperative data, which is sent to the transmitter via feedback channel. The modulation scheme is then changed according to the estimated SNR. The performance of the CAZAC preamble-based SNR estimator exhibits less than 0.02 dB and less than 0.2 dB bias when communicating over AWGN and SUI-5 channels, respectively. The proposed adaptive modulation scheme with the CAZAC SNR estimator significantly improved the channel throughput in comparison with the corresponding benchmarker scheme dispensing with adaptive modulation that invokes <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -PSK and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -QAM. More explicitly, the proposed adaptive modulation system with the CAZAC SNR estimator that invokes <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -PSK exhibits significant improvement by about 5 dB at BER=10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in comparison to its corresponding benchmarker scheme dispensing with adaptive modulation when communicating over the SUI-5 channel. On the other hand, the relay-aided cooperative transmission exhibited an approximately 6 dB SNR gain in terms of channel throughput in comparison to the corresponding non-cooperative benchmarker scheme, and benefited from spatial diversity.