Recursive time synchronization protocol method for wireless sensor networks
First Claim
1. A computer-implemented recursive time synchronization protocol method for a clustered wireless sensor network (WSN), comprising the steps of:
- electing a single reference node i for offset and drift compensation, the electing being limited to nodes that are clusterheads;
calculating a time read by a logical clock of the ith node of the clustered WSN, the calculation utilizing the relation;
Ci(t)=α
i+β
it, where α
i is the clock offset deviation from ideal time at the reference time t=0 and β
i is the frequency of the clock;
re-synchronizing the clock within a time T≦
δ
/2ρ
, where δ
is an offset and ρ
is a skew rate;
estimating the offset and a drift of the clock, thereby re-synchronizing the clock;
initiating a time synchronization request, the time synchronization request being initiated by any initiating node in the clustered WSN, wherein the step of initiating the time synchronization request comprises the steps of;
initiating the time synchronization request from the initiating node at the initiating node'"'"'s local time T1 and transmitting the time synchronization request to a first intermediate node;
receiving the time synchronization request at the first intermediate node at the first intermediate node'"'"'s local time T2;
storing identification data and local times T1 and T2 in computer readable memory, the local times T1 and T2 being respectively stored as variables T1 old and T2old; and
forwarding the time synchronization request from the first intermediate node to a second intermediate node at the first intermediate nodes local time T1;
recursively forwarding the time synchronization request from the second intermediate node to the reference node, thereby establishing a request-path, the reference node receiving the forwarded time synchronization request at the reference node'"'"'s local time T2;
using a REP (reply to time synchronization) message to forward the time T back to the initiating node via the request-path; and
compensating the time T with a propagation delay time at each hop in the request-path, thereby time synchronizing all clustered WSN nodes in the request-path, wherein the step of compensating the time T comprises the steps of;
transmitting the REP message from the reference node to the second intermediate node at the reference node'"'"'s local time T3;
receiving the REP message at the second intermediate node at the second intermediate node'"'"'s local time T4;
calculating a first propagation delay, d1, as
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Abstract
The recursive time synchronization protocol method for wireless sensor networks provides a modified and extended RTSP method to make it work with clustered networks. In case of non-clustered or flat network, each node is assumed to be a clusterhead in order to run the RTSP method correctly. The RTSP method involves the election of a reference node, and compensation for offset and drift. Simulation results show that the extended RTSP method further improves the accuracy and energy consumption, i.e., it can provide an average accuracy of 0.23 μs in a large multi-hop clustered network while using only 1/7th of the energy consumed by FTSP in the long run.
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Citations
9 Claims
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1. A computer-implemented recursive time synchronization protocol method for a clustered wireless sensor network (WSN), comprising the steps of:
-
electing a single reference node i for offset and drift compensation, the electing being limited to nodes that are clusterheads; calculating a time read by a logical clock of the ith node of the clustered WSN, the calculation utilizing the relation;
Ci(t)=α
i+β
it,where α
i is the clock offset deviation from ideal time at the reference time t=0 and β
i is the frequency of the clock;re-synchronizing the clock within a time T≦
δ
/2ρ
, where δ
is an offset and ρ
is a skew rate;estimating the offset and a drift of the clock, thereby re-synchronizing the clock; initiating a time synchronization request, the time synchronization request being initiated by any initiating node in the clustered WSN, wherein the step of initiating the time synchronization request comprises the steps of; initiating the time synchronization request from the initiating node at the initiating node'"'"'s local time T1 and transmitting the time synchronization request to a first intermediate node; receiving the time synchronization request at the first intermediate node at the first intermediate node'"'"'s local time T2; storing identification data and local times T1 and T2 in computer readable memory, the local times T1 and T2 being respectively stored as variables T1 old and T2old; and forwarding the time synchronization request from the first intermediate node to a second intermediate node at the first intermediate nodes local time T1; recursively forwarding the time synchronization request from the second intermediate node to the reference node, thereby establishing a request-path, the reference node receiving the forwarded time synchronization request at the reference node'"'"'s local time T2; using a REP (reply to time synchronization) message to forward the time T back to the initiating node via the request-path; and compensating the time T with a propagation delay time at each hop in the request-path, thereby time synchronizing all clustered WSN nodes in the request-path, wherein the step of compensating the time T comprises the steps of; transmitting the REP message from the reference node to the second intermediate node at the reference node'"'"'s local time T3; receiving the REP message at the second intermediate node at the second intermediate node'"'"'s local time T4; calculating a first propagation delay, d1, as - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification