Precision Time and Frequency Joint Synchronization Protocol for Wireless Ad Hoc Networks

White-box switches have emerged as a pivotal component in modern networking architectures due to their flexibility, cost-effectiveness, and programmability. Within a data center network, achieving precise time synchronization within these switches is imperative for various critical functions such as packet scheduling, network security, and compliance with regulatory requirements. Conventional time synchronization protocols, like the Network Time Protocol (NTP), fail to meet the stringent time synchronization demands of the white-box switches because they are software-based. In contrast, the Precision Time Protocol (PTP), a hardware-based solution, offers sub-microsecond accuracy and low-latency time synchronization. However, despite the advantages of PTP, integrating it into white-box switches may pose challenges due to additional hardware requirements. This paper elaborates on a study conducted to understand the role of white-box switches and their precise time synchronization in data center networking, as well as a comparative measurement between NTP and PTP. Ultimately, this research contributes to a nuanced understanding of the role of PTP in modern white-box switches and lays down decision making processes regarding time synchronization protocols in networking deployments.

The Precision Time synchronization Protocol (PTP), defined by IEEE-1588[1], is a time synchronization protocol which is capable of synchronizing clocks in a local area network within the precision of sub-microsecond. In this paper, we propose and test a new type of frequency counter using programmed Raspberry Pi 3[2] to be the slave clocks in PTP network for syncing the time base of our frequency counter with PTP grand master, and as input channels to receive the frequency under measuring. The test results showed the frequency stability of our PTP frequency counter is about 5.25E-9 at average time 1000 second with respect to the PTP grand master in the test network when measure the 2K Hz test signal. That means our PTP frequency counter is very potential to be used for massive low frequency and low resolution measurement.

The Precision Time Protocol (PTP) plays a pivotal role in achieving precise frequency and time synchronization in computer networks. However, network delays and jitter in real systems introduce uncertainties that can compromise synchronization accuracy. Three clock skew estimators designed for the PTP scenario were obtained in our earlier work, complemented by closed-form approximations for the Mean Squared Error (MSE) under the generalized fractional Gaussian noise (gfGn) model, incorporating the Hurst exponent parameter (H) and the a parameter. These expressions offer crucial insights for network designers, aiding in the strategic selection and implementation of clock skew estimators. However, substantial computational resources are required to fit each expression to the gfGn model parameters (H and a) from the MSE perspective requirement. This paper introduces new closed-form estimates that approximate the MSE tailored to match gfGn scenarios that have a lower computational burden compared to the literature-known expressions and that are easily adaptable from the computational burden point of view to different pairs of H and a parameters. Thus, the system requires less substantial computational resources and might be more cost-effective.

The IEEE 1588 Precision Time Protocol (PTP) has emerged as a critical standard for achieving highly accurate time synchronization across distributed systems, particularly where precision and low latency are essential. Widely applied in domains such as industrial automation, telecommunications, power grid management, nuclear fusion, and scientific facilities. PTP facilitates synchronized operations and enhances control reliability across networked devices. Utilizing the versatility, real-time processing capabilities, and hardware timestamping of field-programmable gate arrays (FPGAs), recent implementations of PTP on FPGA platforms have brought forth advancements in time synchronization precision, flexibility, and integration with complex systems. FPGAs offer significant advantages in implementing PTP, including customizable hardware acceleration, low latency, and compatibility with high-performance interfaces, which enable precise, scalable, and cost-effective solutions for time-critical applications. This paper presents a comprehensive review of FPGA-based PTP implementations, examining the selection of FPGA platforms, design of Intellectual Property (IP) cores, and evaluation of application-specific performance metrics. By synthesizing recent research, we outline the advancements, challenges, and future directions for FPGA-based PTP solutions, with an emphasis on addressing the needs of modern distributed control and data acquisition systems.

Wide-area monitoring (WAM) applications for power distribution rely on accurate global time synchronization. Furthermore, there is interest in replacing current time synchronization methods such as Inter Range Instrumentation Group (IRIG), with distributed time synchronization protocols that utilize the data communication lines eliminating the need for dedicated timing signals within the substation. By understanding the factors impacting synchronization performance, the testbed facilitates the characterization of metrics needed to meet industry requirements. The testbed provides an experimental venue to explore IEEE 1588 Precision Time Protocol (PTP) technologies and determine how new features and requirements for time synchronization can impact the performance of next-generation power distribution applications. Initial results indicate PTP has the capabilities to support an accurate and scalable time synchronization solution given the components are interoperable.

Inter-satellite time transfer is implemented through inter-satellite links (ISLs) with the system of bidirectional ranging. With the influence of the transmission delay of ranging signals and the relative movements of satellites, the bidirectional ranging measurements are not simultaneous. The time-tags are required to be corrected to a reference epoch with the estimated orbits and clocks to get the inter-satellite clock deviations. The algorithm of BeiDou inter-satellite time synchronization is introduced. And the synchronization performance of BeiDou-3 satellites has been analyzed with real ISL measurements and post-processed precise orbit and clock deviation products. The precision of time synchronization is superior to 0.2 ns. Besides time transfer between BeiDou satellites, the ISLs are available for precise time transfer from BeiDou satellites to extended users whose positions and clock deviations can be solved with GNSS receivers with larger errors compared to BeiDou satellites. The influence of positioning and timing precisions used in the time-tag correction on the synchronization precision has been analyzed in theory and with simulations. The results have demonstrated the precision of two-way time synchronization is free of continuous orbit and clock deviation errors which are varying slowly. And it is feasible that precise time transfer with two-way links between Beidou satellites and extended users in space.

Precise time synchronization amongst network devices is a basic requirement for time critical applications. Despite that time synchronization is a well-established functionality in the wired network domain, its wireless counterpart is very basic or even non-existing. This is because commercial off-the-shelf (COTS) wireless chipsets still focus on basic network connectivity for consumer applications, hence no dedicated software/hardware features are required for time-bounded services in professional wireless environments. This work leverages on openwifi - an opensource Wi-Fi chip design based on Software-Defined Radio (SDR), by adding the support of hardware timestamping in openwifi to support precise time protocol (PTP) application. In addition, openwifi Access Point (AP) is connected to nodes in wired network through a TSN capable switch, and synchronization offset between devices in wired and wireless network is measured. Next, the measurement is done with the same setup in wired network but replacing openwifi by COTS Wi-Fi devices. We observe the synchronization offset with COTS is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> fold larger than the offset achieved with openwifi. The experiment setup is in w-iLab.t, an open testbed infrastructure freely accessible for the academic wireless research community.

To support system-wide synchronization accuracy and precision in the sub-microsecond range without using GPS technique, the Precise Time Protocol (PTP) standard IEEE-1588V2 is introduced. Various factors affect the clock synchronization precision, such as the location of timestamp point, frequency difference between Master and Slave, delay asymmetry and error accumulation. In this paper, we analyze these factors and propose an implementation of 1588v2 over UDP in Ethernet. This implement method efficiently reduces the effect of the above factors and guarantees the time and frequency synchronization precision supported by PTP.

To solve the problems of time delay and different frequency offset between different transmit antennas and the same receive antennas for distributed multiple input multiple output orthogonal frequency division multiplexing systems. In this paper, a new timing and frequency synchronization algorithm is proposed. The search range of the fine timing synchronization is set with coarse time synchronization position and cyclic prefix, and the precise timing synchronization is obtained by utilizing the correlation between data information and training sequence. In the integer frequency offset estimation algorithm, the real component of the training sequence is taken as the real sequence, and then the differential relationship between the first and last samples is estimated accordingly. Theoretical analysis and simulation show that: (1) under multipath fading channel, the timing offset and frequency offset between different transmit and receive antennas can be effectively estimated with the synchronization algorithm proposed in this paper; (2) with signal noise ratio $$-$$-5Â dB, the probability of the correct synchronization is 95Â % and the precision of the frequency offset estimation can be as high as $$10^{-2}$$10-2, which is over the similar synchronization algorithm.

With the development of cooperative autonomous vehicles, devices may operate in a limited environment such as war field where the devices are necessary to communicate with each other for automatic operation by themselves. Particularly, time critical data processing is difficult because each device has a different local time. This is why the time synchronization is an essential requirement for communicating between devices. As the scale of the network is larger, the number of exchange messages is also increased and it may cause raise the network congestion. The increased network congestion results in poor time synchronization. Therefore, the new time synchronization mechanism for reducing the network latency is required. In this paper, we propose a novel ad-hoc routing protocol for low latency ad-hoc network. In order to reduce the network latency, the protocol decreases the number of exchange messages compared with legacy ad-hoc routing protocol and time synchronize protocol during routing discovery and time synchronization process. We verify the performance of the proposed protocol by comparing precise time protocol. As a result, the proposed protocol reduces the network latency and the time synchronization complete 273% faster compared with the precise time protocol.

Generalized frequency division multiplexing (GFDM) is a waveform for the next-generation communication but requires a step dedicated to time and frequency synchronization. The current time and frequency synchronization methods of GFDM do not fully address the requirements on accuracy, robustness to a large frequency offset, and low complexity. This paper develops an accurate synchronization method tailored to large time and frequency offsets. The proposed method jointly synchronizes time and frequency and derives a decision variable from the real part of an inner product. The accuracy of time and frequency synchronization increases because an error in the frequency offset is corrected simultaneously during the process of time synchronization and because the decision variable does not depend on the imaginary part, which we show to be noise. The proposed method can correct a full range of frequency offsets. We compare synchronization accuracy of the proposed method to the state of the art analytically, numerically, and experimentally, in terms of the discriminant probability, the range of correctable frequency offsets, the probability of perfect time synchronization, the root mean square error (RMSE) between estimates and actual offsets, and the bit error ratio. The proposed method outperforms existing methods on all of these metrics. Moreover, it has practical utility and increases the transmission reliability for GFDM-based communication systems.

Precise frequency linking method based on phase group synchronization

New mobile 5G networks development is focused on guaranteeing reliable low-latency services to a large number of connected devices. To achieve these goals, 5G Radio Access Techniques (RAT) require unprecedentedly accurate time synchronization of network elements. Therefore, synchronization performance evaluation is essential in system design. We evaluated the performance of time synchronization networks for 5G Front/Mid-Haul Transport systems. In the time domain, we simulated clock systems as defined by ITU-T in the Full Timing Support architecture, where frequency and time synchronization are achieved via Synchronous Ethernet (SyncE) and IEEE 1588 / Precision Time Protocol (PTP), respectively. Clock models have been coded in Simulink modules, which can be combined to simulate various network topologies. In this paper, we present simulations of clocks and ring synchronization networks for 5G Front/Mid-Haul, considering generated noise and rearrangements after link failures. Experimental measurements on real equipment were carried out, to tune model parameters and for comparison with simulation results.

Precise time and frequency synchronization measurements are critical for many advanced applications, including mobile communications, the internet of things (IoT), and low earth orbit (LEO) satellite internet. Real-time precise point positioning (RT-PPP) technology has become one of the dominant methods for real-time high-precision time-frequency transfer and synchronization. This study proposes an enhanced BDS RT-PPP time transfer and synchronization method utilizing bias modeling and develops a high-precision RT-PPP time synchronization terminal. After correcting inconsistent pseudorange biases, the RT-PPP time transfer precision reaches 0.19 ns for GPS and 0.16 ns for BDS, while the frequency stability over an averaging time of 1.5×104 s reaches 4.01×10-15. Compared with the conventional RT-PPP solution, the proposed bias-corrected method improves the time and frequency transfer performance of both GPS and BDS by approximately 30%. Furthermore, after clock information processing based on BDS RT-PPP, real-time pulse-per-second (PPS) physical signal synchronization with an average precision of 0.20 ns is achieved, and average frequency stability reaches 2.56×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-15</sup> at 1 day averaging time in two time links. When combined with a low-cost oven-controlled crystal oscillator (OCXO), the proposed system demonstrates frequency stability comparable to that of commercial hydrogen masers at 1 day averaging time, providing a portable solution for modern time and frequency stability measurements.

Time synchronization has played an important role in modern measurement and control systems which require high time accuracy to maintain optimal performance in sample acquisition, signal control and safety protection. The Ethernet/IP based IEEE 1588 precise time protocol (PTP) provides us a prospective solution. By means of taking hardware timestamps, the time synchronization accuracy can be kept in the range of sub-microsecond with minimal network load and low demand on computing resources. Based on the OMNeT++ simulator, we build the PTP ordinary clock model and simulate the typical process of the PTP clock synchronization. The complete clock synchronization process and its performance are both analyzed and evaluated.