"WCNC 2005"

WCNC 2005

New Orleans, LA, USA

Outline

Problem definition and context

Problem: Achieve the synchronization of a set of geographically separated clocks located in every node of a wireless Ad Hoc network (single-hop or multi-hop) in a distributed manner.

The IEEE 802.11 TSF (IBSS)

CSMNS- (Clock-Sampling Mutual Network Synchronization)

Slide 7

CSMNS- (Clock-Sampling Mutual Network Synchronization)

Results

Results (simulations)

Numerical Results (Single-hop)

Numerical Results (Multi-hop)

Conclusion and remaining work

Slide 14

"EXTRA SLIDES FOLLOW"

EXTRA SLIDES FOLLOW

The extended TSF (1)

One arguable improvement to the IEEE 802.11 TSF performance is as follows:

Suspend the back-off timer of any pending non-beacon transmission.

Calculate a random delay uniformly distributed in the range between zero and .

Wait for the random delay before transmitting the beacon.

Cancel the remaining random delay and the pending beacon transmission if a beacon arrives before the random delay timer has expired and that the received beacon shows a larger time-stamp than its own.

Send a beacon if the random delay has expired and no beacon have arrived during the delay period with a larger time-stamp.

Upon reception of a beacon, a node will adjust the received timestamp to take into account its PHY layer delay. The receiving node will set its clock to the value of the adjusted timestamp if it is later than its own. Therefore, all nodes will try to gradually synchronize to the fastest clock.

The extended TSF (2)

Our numerical and analytical results show that the extended TSF improvement is marginal relative to CSMNS, additional to the extra cost of more overhead.

A simple numerical example


	Problem: Achieve the synchronization of a set of geographically separated clocks located in every node of a wireless Ad Hoc network (single-hop or multi-hop) in a distributed manner.


	One arguable improvement to the IEEE 802.11 TSF performance is as follows:

	Suspend the back-off timer of any pending non-beacon transmission.
	Calculate a random delay uniformly distributed in the range between zero and .
	Wait for the random delay before transmitting the beacon.
	Cancel the remaining random delay and the pending beacon transmission if a beacon arrives before the random delay timer has expired and that the received beacon shows a larger time-stamp than its own.
	Send a beacon if the random delay has expired and no beacon have arrived during the delay period with a larger time-stamp.
	Upon reception of a beacon, a node will adjust the received timestamp to take into account its PHY layer delay. The receiving node will set its clock to the value of the adjusted timestamp if it is later than its own. Therefore, all nodes will try to gradually synchronize to the fastest clock.


	Our numerical and analytical results show that the extended TSF improvement is marginal relative to CSMNS, additional to the extra cost of more overhead.