The Journal of Supercomputing

, Volume 71, Issue 6, pp 2153–2176 | Cite as

Using physical layer clock recovery to augment application layer time synchronization

  • S. M. Usman Hashmi
  • Imran Shafi
  • Jamil Ahmad
  • Anand Paul
  • Sang Oh Park


Achieving same notion of time remains an important task for most distributed systems. Time synchronization requires a unique combination of high accuracy (\(\upmu \)s level) and energy efficiency. Several application layer protocols have been developed to meet these requirements. This article proposes that the physical layer clock recovery process can provide application layer clock drift estimate, and the application layer clock can be corrected with the help of this estimate. This eliminates the need of application layer time synchronization protocol i.e. the cross-layer approach reduces the number of message exchanges required by application layer for time synchronization that leads to energy conservation. It argues that such a cross-layer approach can provide a more accurate frequency offset estimation, or can achieve greater energy savings, for a given accuracy, by reducing the message exchanges. Analysis of the proposed method provides concrete bounds on achieved improvement. Experimental evaluation showed that physical layer clock drift can be used to correct application layer clock drift as they are identical.


Time synchronization Clock recovery Wireless sensor network Cross-layer time synchronization Energy-efficient time synchronization Frequency offset estimation Distributed systems 

List of symbols

\({\mu }(k)\)

Fractional interval

\({\omega }(t)\)

Angular frequency of the oscillator

\(\tau \)

Timing frequency error

\(\xi \)

Loop parameter


Binary PAM \(k\)th symbol


Timing error signal

\(E_{P }\)

Energy required to transmit one packet

\(E_{S }\)

Energy required to transmit one sample

\({E_\mathrm{APP} }\)

Energy at application layer

\({E_\mathrm{eff} }\)

Energy efficiency

\({E_\mathrm{PHY} }\)

Energy at physical layer

\({E_\mathrm{sym} }\)

Energy required to transmit one symbol

\(f_{d }\)

Symbol rate

\(f_{e }\)

Frequency error

\(f_{s }\)

Sampling rate

\(m \)

Slope of the fractional change


Basepoint index

\(N_{b }\)

Bits per packet

\(N_{m }\)

Bits per sample

\(N_{P }\)

Number of packets

\(N_\mathrm{bsym }\)

bits per symbol


Symbols used for timing frequency synchronization

\(N_\mathrm{sym }\)

Total symbols

\(P_\mathrm{SYM }\)

Symbols used for timing phase synchronization

\(R \)

Symbol rate

\(T \)

Symbol time


Total transmission time

\(T_\mathrm{SYM }\)

Number of symbols per cross-layer packet

\(x_{i }\)

\(i\)th time stamp of receiver

\(y_{i }\)

\(i\)th time stamp of transmitter



Thanks to Almighty ALLAH, The Merciful, The Beneficent, whose bountiful blessings and exaltation flourished our thoughts and thrived our ambitions to have the cherished fruit of my modest efforts in the form of this research. We offer our humblest thanks from the core of my heart to the holy Prophet (Peace be upon Him) who is forever a model of guidance and knowledge for humanity. We feel great depth of obligation for our loving parents and wife whose prayers have enabled us to reach this stage. I (Usman Hashmi) owe a special debt of gratitude to my reverend supervisor Dr. Qasim Mahmood Chaudhari for the invaluable guidance, expert advices, cooperation, encouraging attitude, positive criticism and healthy suggestions. I also wish to record my sincere appreciations to Dr. Imran Shafi, Dr. Affan Ahmed, Dr. Ismail Shah, Dr. Jamil Ahmed and Engr. Ammar Ajmal for their support and guidance.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • S. M. Usman Hashmi
    • 1
  • Imran Shafi
    • 2
  • Jamil Ahmad
    • 2
  • Anand Paul
    • 3
  • Sang Oh Park
    • 4
  1. 1.Iqra UniversityIslamabadPakistan
  2. 2.Abasyn UniversityPeshawarPakistan
  3. 3.The School of Computer Science and EngineeringKyungpook National UniversityDaeguSouth Korea
  4. 4.Global Science Experimental Data Hub CenterKorea Institute of Science and Technology InformationSeoulSouth Korea

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