WIRELESS SENSOR NETWORKS

• US 20100008256A1
• Filed: 06/10/2009
• Published: 01/14/2010
• Est. Priority Date: 06/10/2008
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Abedi, Saled, CHEBBO, Hind
• Granted Patent: US 9,526,062 B2
• Time in Patent Office: Days
• US Class Current: 370/254
• CPC Class Codes: H04W 40/04 based on wireless node resources
• CPC Class Codes: H04W 40/32 for defining a routing cluster membership
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

In a wireless sensor network having a plurality of mobile sensor nodes (62, 63, 64, 65), a sink (70) is provided and re-positioned as required by assigning the role of sink to one of the mobile sensors at a time. Re-positioning involves finding candidate sinks in the vicinity of a current sink, a temporary sink or a central candidate in the network; judging the suitability of each candidate, for example by estimating the data throughput likely to be achieved if each candidate is selected as the new sink; and transferring the role of sink to the best candidate found. The temporary sink or central candidate may be selected with the aid of a positioning system (80) of the network. Suitability of a candidate sink may take into account a desired transmission rate of each sensor node in the vicinity of a candidate, this desired rate being found from a 3-D look-up table of each sensor.

Claims

1. A method of locating a sink in a wireless sensor network, the wireless sensor network comprising sensors at least some of which are capable of acting as the sink and one of which is currently acting as the sink, the method comprising:

selecting two or more of said sensors as candidate sinks;

finding the suitability of each candidate sink to act as the sink using a calculation producing a result indicating the suitability of the candidate sink for communication with a plurality of the sensors;

comparing the result for each candidate sink to determine the most suitable candidate sink; and

transferring the role of the current sink to the most suitable candidate sink thus found.

2. The method according to claim 1, wherein possible states for said sensors in addition to acting as the sink include active and relay states, and said selecting step comprises selecting active or relay sensors among said sensors.

3. The method according to claim 2 further comprising providing a positioning entity with knowledge of the locations of the active and relay sensors, the method further comprising, prior to said selecting step, the positioning entity choosing a lead sensor for carrying out the method.

4. The method according to claim 3 wherein the lead sensor is made a temporary sink prior to the selecting step.

5. The method according to claim 3 wherein the lead sensor is made a central candidate but the current sink remains as the sink until the transferring step.

6. The method according to claim 3 wherein each sensor has a communication range with other sensors and the finding step comprises:

the lead sensor requesting data from candidate sinks comprising each of the active and relay sensors within its range;

each candidate sink requesting at least the active and relay sensors within its communication range to provide at least its location and state, and/or transmit a reference signal, to the candidate sink; and

each candidate sink calculating a transmission rate possible with each of the active and relay sensors within its communication range and notifying a result to the lead sensor.

7. The method according to claim 6 wherein the comparing step comprises the lead sensor comparing the results received from the candidate sinks to determine which candidate sink can provide the maximum throughput.

8. The method according to claim 2 wherein each sensor has a communication range with other sensors and knowledge of its own location, and the selecting step comprises the current sink signalling its own location to at least active and relay sensors within its communication range, whereupon each of the active and relay sensors receiving said signalling from the current sink becomes a candidate sink and likewise signals its location to the active and relay sensors within its range.

9. The method according to claim 8 wherein each sensor has knowledge of its current energy level, buffer occupancy and upon receiving location information from a candidate sink, uses these parameters to derive and transmit a desired transmission rate.

10. The method according to claim 9 wherein each sensor, upon receiving a signal from a candidate sink, transmits a reference signal used by the candidate sink to estimate the channel between the sensor and the candidate sink, and each candidate sink derives and transmits a measure of the probability of fulfilling the desired transmission rate for each of the sensors over each channel so estimated, to provide said result indicating the suitability of the candidate sink for communication with a plurality of the sensors.

11. The method according to claim 10 wherein the comparing step comprises the current sink comparing the results received from the candidate sinks to determine which candidate sink can provide the maximum throughput.

12. A wireless sensor network operating in accordance with the method of claim 1.

13. A sensor for use in a wireless sensor network comprising:

a wireless transceiver arranged to transmit sensor data and to receive data including a location of a candidate sink;

a sensor for generating sensor data;

a memory for storing sensor data and the sensor'"'"'s location in the network;

an energy source; and

desired rate finding means for finding, based on an energy capacity of the energy source, the amount of the sensor data, and the distance between the sensor location and a candidate sink location, a desired transmission rate to transmit sensor data to the candidate sink.

14. A device capable of acting as both a sensor and a sink in a wireless sensor network having a plurality of such devices, the device comprising:

wireless transceiver means for receiving and transmitting data within a communication range;

selecting means operable, when the device assumes the role of a central device, to select as candidate sinks two or more other said devices within the communication range;

calculating means operable to provide a measure of the suitability of the device for communication with a plurality of the sensors, the transceiver means being arranged to transmit said measure to the central device; and

decision means operable, when the device is the central device, to determine the most suitable candidate sink based on said measure.

15. The device according to claim 14 wherein the device assumes the role of said central device by being made the current sink or a temporary sink.