Synchronization

Communication

In electrical engineering terms, for digital logic and data transfer, a synchronous circuit requires a clock signal. A clock signal simply signals the start or end of some time period, often measured in microseconds or nanoseconds, that has an arbitrary relationship to any other system of measurement of the passage of minutes, hours, and days.

In a different sense, electronic systems are sometimes synchronized to make events at points far apart appear simultaneous or near-simultaneous from a certain perspective. Timekeeping technologies such as the GPS satellites and Network Time Protocol (NTP) provide real-time access to a close approximation to the UTC timescale and are used for many terrestrial synchronization applications of this kind.

In computer science (especially parallel computing), synchronization is the coordination of simultaneous threads or processes to complete a task with correct runtime order and no unexpected race conditions; see synchronization (computer science) for details.

Synchronization is also an important concept in the following fields:

• Cryptography
• Lip sync
• Multimedia
• Network Physiology
• Neuroscience
• Photography
• Physics (The idea of simultaneity has many difficulties, both in practice and theory.)
• Rhythm
• Synthesizers
• Telecommunication
  • Frame synchronization
  • Synchronization (video)

Dynamical systems

Synchronization of multiple interacting dynamical systems can occur when the systems are autonomous oscillators. Poincaré phase oscillators are model systems that can interact and partially synchronize within random or regular networks. In the case of global synchronization of phase oscillators, an abrupt transition from unsynchronized to full synchronization takes place when the coupling strength exceeds a critical threshold. This is known as the Kuramoto model phase transition. Synchronization is an emergent property that occurs in a broad range of dynamical systems, including neural signaling, the beating of the heart and the synchronization of fire-fly light waves. A unified approach that quantifies synchronization in chaotic systems can be derived from the statistical analysis of measured data.

Applications

Network Physiology

Synchronization and global synchronization phenomena play essential roles in the multidisciplinary field of Network Physiology which focuses on understanding how the dynamic interactions among human physiological systems and organs across spatiotemporal scales give rise to emerging states at the organism level and influence human health. Amplitude, frequency, and phase synchronization, as forms of coupling and interaction, underlie biological and physiological network mechanisms through which global states, functions and behaviors emerge at the system and organism level. Synchronization has been reported across physiological systems and levels of integration, including cardio-respiratory coupling; maternal-fetal cardiac phase-synchronization; brain blood flow velocity vs. peripheral blood pressure in stroke; synchronization in neuron synaptic function; organ networks; EEG-synchronization and EEG-desynchronization in NREM and REM sleep; brain waves synchronization and anti-synchronization during rest, exercise, cognitive tasks, sleep and wake; cortico-muscular synchronization; synchronization in pancreatic cells and metabolism; inter-muscular muscle fibers synchronization in exercise and fatigue; neuromodulation and Parkinson's, dystonia and epilepsy; circadian synchrony of sleep, nutrition and physical activity.

Neuroscience

In cognitive neuroscience, (stimulus-dependent) (phase-)synchronous oscillations of neuron populations serve to solve the general binding problem. According to the so-called Binding-By-Synchrony (BBS) Hypothesis a precise temporal correlation between the impulses of neurons ("cross-correlation analysis") and thus a stimulus-dependent temporal synchronization of the coherent activity of subpopulations of neurons emerges. Moreover, this synchronization mechanism circumvents the superposition problem by more effectively identifying the signature of synchronous neuronal signals as belonging together for subsequent (sub-)cortical information processing areas.

Cognitive science

In cognitive science, integrative (phase) synchronization mechanisms in cognitive neuroarchitectures of modern connectionism that include coupled oscillators (e.g., "Oscillatory Networks") are used to solve the binding problem of cognitive neuroscience in perceptual cognition ("feature binding") and in language cognition ("variable binding").

Biological networks

There is a concept that the synchronization of biochemical reactions determines biological homeostasis. According to this theory, all reactions occurring in a living cell are synchronized in terms of quantities and timescales to maintain biological network functional.

Human movement

Synchronization of movement is defined as similar movements between two or more people who are temporally aligned. This is different from mimicry, which occurs after a short delay. Line dance and military step are examples.

Muscular bonding is the idea that moving in time evokes particular emotions. This sparked some of the first research into movement synchronization and its effects on human emotion. In groups, synchronization of movement has been shown to increase conformity, cooperation and trust.

In dyads, groups of two people, synchronization has been demonstrated to increase affiliation, self-esteem, compassion and altruistic behaviour and increase rapport. During arguments, synchrony between the arguing pair has been noted to decrease; however, it is not clear whether this is due to the change in emotion or other factors. There is evidence to show that movement synchronization requires other people to cause its beneficial effects, as the effect on affiliation does not occur when one of the dyad is synchronizing their movements to something outside the dyad. This is known as interpersonal synchrony.

The true effect of synchrony in these studies has been disputed. Research in this area detailing the positive effects of synchrony has attributed this to synchrony alone; however, many of the experiments incorporate a shared intention to achieve synchrony. Indeed, the Reinforcement of Cooperation Model suggests that perception of synchrony leads to reinforcement that cooperation is occurring, which leads to the pro-social effects of synchrony. More research is required to separate the effect of intentionality from the beneficial effect of synchrony.

Uses

Synchronization is important in digital telephony, video and digital audio where streams of sampled data are manipulated. Synchronization of image and sound was an important technical problem in sound film. More sophisticated film, video, and audio applications use time code to synchronize audio and video. In movie and television production, it is necessary to synchronize video frames from multiple cameras. In addition to enabling basic editing, synchronization can also be used for 3D reconstruction.

In electric power systems, alternator synchronization is required when multiple generators are connected to an electrical grid.

Arbiters are needed in digital electronic systems such as microprocessors to deal with asynchronous inputs. There are also electronic digital circuits called synchronizers that attempt to perform arbitration in one clock cycle. Synchronizers, unlike arbiters, are prone to failure. (See metastability in electronics).

Encryption systems usually require some synchronization mechanism to ensure that the receiving cipher is decoding the right bits at the right time.

Automotive transmissions contain synchronizers that bring the toothed rotating parts (gears and splined shaft) to the same rotational velocity before engaging the teeth.

Flash synchronization synchronizes the flash with the shutter.

Some systems may be only approximately synchronized, or plesiochronous. Some applications require that relative offsets between events be determined. For others, only the order of the event is important.