Sync Error Research Articles

Islanding Scheme for Microcontroller Based Load Frequency Controller

This paper is for detecting power sync errors. The actual power grid consists of power sources that are synchronously connected to power the system. These power supplies must be powered according to grid rules. These rules include voltage and frequency fluctuations within certain limits. Deviations from these limits require that this data source be immediately disconnected from the network and affected. This is known as solo operation. It is used to avoid large voltage drops or power outages from the grid. Our system is designed to warn the network of a power failure, so the network can use other backup data sources as needed to avoid a complete power failure. Our system demonstrates this with the ATmega328P microcontroller. MC is used to detect voltage and frequency from a set of comparators. Since the frequency cannot be changed, use the frequency generator (555 timer). Standard variacs are also used to vary the input voltage of the system. Normal loads are used to indicate the expected power outage or power outage if the voltage / frequency deviation exceeds the limit.

Signal Detection in Distributed MIMO Radar With Non-Orthogonal Waveforms and Sync Errors

Although routinely utilized in literature, orthogonal waveforms may lose orthogonality in distributed multi-input multi-output (MIMO) radar with spatially separated transmit (TX) and receive (RX) antennas, as the waveforms may experience distinct delays and Doppler frequency offsets unique to different TX-RX propagation paths. In such cases, the output of each waveform-specific matched filter (MF), employed to unravel the waveforms at the RXs, contains both an \auto term and multiple cross terms, i.e., the filtered response of the desired and, respectively, undesired waveforms. We consider the impact of non-orthogonal waveforms and their cross terms on target detection with or without timing, frequency, and phase errors. To this end, we present a general signal model for distributed MIMO radar, examine target detection using existing coherent/non-coherent detectors and two new detectors, including a hybrid detector that requires phase coherence locally but not across distributed antennas, and provide a statistical analysis leading to closed-form expressions of false alarm and detection probabilities for all detectors. Our results show that cross terms can behave like foes or allies, respectively, if they and the auto term add destructively or constructively, depending on the propagation delay, frequency, and phase offsets. Regarding sync errors, we show that phase errors affect only coherent detectors, frequency errors degrade all but the non-coherent detector, while all are impacted by timing errors, which result in a loss in the signal-to-noise ratio (SNR).

High-Reliability Sub-Nanosecond Network Time Synchronization Method Enabled by Double-Frequency Distributed Time Synchronization

Time synchronization is a long-standing challenge in distributed systems like indoor/outdoor positioning, coordinated multi-point in 4G/5G mobile communication, etc., which require nanosecond-level high-reliable time sync networks. At present, a widely adopted solution for time sync networks is the precision time protocol specified in IEEE 1588v2, which can provide sub-microsecond sync accuracy. In addition, a novel network time sync method called distributed time synchronization has also been proposed recently, which can achieve 50-ns-level accuracy and stronger survivability in metro, regional, and backbone networks. However, both of the above methods encounter difficulties in achieving nanosecond sync accuracy and network reliability simultaneously. In this paper, by analyzing the main factors influencing the degradation of time sync accuracy, we reveal that the finite clock resolution is a major barrier to achieving nanosecond-level time synchronization. In order to establish a low-cost, high-reliability, and sub-nanosecond-level time sync network, we propose a novel network time sync method called double-frequency distributed time synchronization (DF- DTS). By selecting two specific and distinct frequencies for the sending and receiving clocks of the nodes/devices being synchronized, the time sync errors induced by the finite clock resolution can be reduced by a statistical approach. We set up a theoretical model for the DF-DTS and analyze the time sync accuracy through both mathematical derivations and network simulations. Furthermore, we propose a failure-restoration mechanism to enhance the reliability of DF-DTS networks by improving the time sync accuracy under failures and reducing the failure recovery time. Finally, we conduct both point- to-point and network time sync experiments to validate the proposed DF-DTS method. The results demonstrate that DF-DTS can achieve sub-nanosecond-level sync accuracy that is 1-2 orders of magnitude higher than the clock resolution in a prototype four-node DF-DTS network. Moreover, a network simulation under failure cases is conducted, and the results show that our method has significant advantages in both time sync accuracy and recovery time in the failure-restoration process compared to IEEE 1588v2.

Remote-sensing satellite ground station evaluation using QPSK emulator with test pattern and PRBS generation

In order to validate the performance of X-band (8000–8400 MHz) remote-sensing satellite receive chain, when the satellite is not in the vicinity of ground station, local loop end–end evaluation tests are mandatory to certify the RF downlink and base band receive chain performance. A customised test patterns compatible to IRS satellite series and PRBS sequence are generated, which are modulated using QPSK emulator to check and verify the satellite downlink chain performance. The design and implementation are done using novel digital techniques, and QPSK modulator is integrated with Test pattern and PRBS generator using state-of-art FPGAs. The QPSK emulator output is connected to high-speed fibre optic link which transfers the signal to near field bore-site antenna system. The test signal is thus up converted from 2557.5 MHz (S-band) frequency to required satellite carrier frequency of 8212.5 MHz; the emulated test signal is radiated from bore-site antenna, which simulates real-time satellite data transmission from space. Thus, the signal received by the parabolic dish antenna is down converted to 720 MHz, demodulated, bit synchronized, clock recovered, and frame synchronized. The evaluation of frame sync errors is done for good video data quality check. Also in the QPSK emulator, there is option of PRBS mode. Hence, using this option, the RF downlink and receive chain are evaluated for good Bit error rate (BER). The BER requirement is 1 error (tolerable) in 106 Million bits. The QPSK emulator has the provision to support different frequencies and data rates corresponding to all IRS satellite missions.

Lightweight Precision-Adaptive Time Synchronization in Wireless Sensor Networks

Time synchronization is an essential service for wireless sensor networks (WSNs). However, fixed-period time synchronization can not serve multiple users efficiently in terms of energy consumption. This paper proposes a lightweight precision-adaptive protocol for cluster-based multi-user networks. It consists of a basic average time synchronization algorithm and an adaptive control loop. The basic average time synchronization algorithm achieves 1µs instantaneous synchronization error performance. It also prolongs re-synchronization period by taking the average of two specified nodes' local time to be cluster global time. The adaptive control loop realizes diverse levels of synchronization precision based on the proportional relationship between sync error and re-synchronization period. Experimental results show that the proposed precision-adaptive protocol can respond to the sync error bound change within 2 steps. It is faster than the exponential convergence of the adaptive protocols based on multiplicative iterations.

Determining the Amount of Audio-Video Synchronization Errors Perceptible to the Average End-User

The media and acoustics perception lab (MAPL) designed a study to determine the minimum amount of audio-visual synchronization (a/v sync) errors that can be detected by end-users. Lip synchronization is the most noticeable a/v sync error, and was used as the testing stimuli to determine the perceptual threshold of audio leading errors. The results of the experiment determined that the average audio leading threshold for a/v sync detection was 185.19 ms, with a standard deviation of 42.32 ms. This threshold determination of lip sync error (with audio leading) will be widely used for validation and verification infrastructures across the industry. By implementing an objective pass/fail value into software, the system or network under test is held against criteria which were derived from a scientific subjective test.

Audio-Video Synchronization across DTV Transport Interfaces: The Impossible Dream?

The end-to-end DTV production, distribution, and broadcast system is a complex assemblage of many digital processing and storage devices. A number of interfaces are required to transport compressed and uncompressed DTV audio and video signals between devices in the system. Each component of the DTV system imposes its own latency on the audio and/or video signals flowing through it, and the delays imposed on audio and video signals respectively, are typically unequal, compromising audio-video synchronization. It is incumbent on those implementing DTV production, post-production, and broadcast systems to be aware of the latencies present at each interface and to take steps in correcting synchronization errors at each stage, thereby preventing the buildup of lip sync errors. This paper will discuss the potential trouble spots within the DTV system.