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Traditional Time and Reference-Broadcast Synchronization

tts-illustration

November 3, 2016
Published By : Pratik Kataria
Categorised in:

Time synchronization is highly critical in sensor networks for purposes such as:

  • Data Diffusion (Merging individual sensor readings into a high level sensing result)
  • Coordinated Actuation (all surrounding nodes made active at the same time)
  • Object Tracking

To Synchronize all the nodes in the sensor network using a method that:

  • Eliminates error efficiently
  • Energy conservative
  • Provides tight synchronization

Applications of Time Synchronization

Secure cryptographic schemes
Coordination of future action
Ordering logged events during system debugging

Concept of TTS- Traditional Time Synchronization

The sender periodically sends a message with its current clock as a timestamp to the receiver
Receiver then synchronizes with the sender by changing its clock to the timestamp of the message it has received from the sender (if the latency is small compared to the desired accuracy)
Sender calculates the phase error by measuring the total round trip-time by sending and receiving the respective response from the receiver (if the latency is large compared to the desired accuracy)

Illustration of TTS

tts-illustration

Concept of RBS – Reference-Broadcast Synchronization

Reference broadcasts do not have an explicit timestamp
Receivers use reference broadcast’s arrival time as a point of reference for comparing nodes’ clocks
Receivers synchronizes with one another using the message’s timestamp (which is different from one receiver to another)

Illustration of RBS

rbs-illustration

RBS vs. TTS

RBS – Synchronizes a set of receivers with one another
Traditional – Senders synchronizes with receivers

RBS – Supports both single hop and multi hop networks
Traditional – mostly supports only single hop networks

rbs-vs-tts

Types of errors that TTS should detect and eliminate

Send Time Latency
–time spent at the sender to construct the message
Access Time Latency
–time spent at the sender to wait for access to transmit the message
Prorogation Time Latency
–time spent by the message in traveling from the sender to the receiver
Receive Time Latency
–time spent at the receiver to receive the message from the channel and to notify the host

Types of errors that RBS should detect and eliminate

Phase error
–due to nodes’ clock that contains different times
Clock skew
–due to nodes’ clock that run at different rate

Therefore, RBS is better than TTS.

Pratik Kataria is a budding programmer, web designer and developer.