System and Method for Multiple Access Sensor Networks

• US 20130077565A1
• Filed: 09/28/2011
• Published: 03/28/2013
• Est. Priority Date: 09/28/2011
• Status: Active Grant

• Current Assignee: Fiskars Oyj Abp
• Original Assignee: Gilmour, Inc., Robert Bosch GmbH
• Inventors: Watkins, Roger Dwight, Travis, Dexter Grant, Jacobs, Scott William, Kleimenhagen, Karl William
• Granted Patent: US 8,885,558 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04W 40/08 based on transmission power
• CPC Class Codes: H04W 74/0825 with collision detection
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method enables a radio receiver to distinguish sensor probes supplying data to the receiver over a long period of time. The method includes each probe generating a random number sent to the receiver to identify the probe. Each probe and the receiver also uses a pseudo-random process to identify a time of transmission for each probe. The pseudo-random process helps keep the transmission times for the probes separate in the presence of oscillator drift. If a transmission collision occurs, the receiver ignores all probes in the collision and waits until the pseudo-random process separates the probe transmissions.

Claims

1. A method for multiple access comprising:

generating a first random number in a first radio transmitter;

transmitting the first random number from the first radio transmitter to a radio receiver;

generating a second random number in a second radio transmitter;

transmitting the second random number from the second radio transmitter to the radio receiver;

identifying a first time for transmission of a first data message from the first radio transmitter with reference to a current time measurement identified by the first transmitter and a predetermined time period that is adjusted by a first time offset, the first time offset being identified with reference to the first random number and a predetermined pseudo-random process;

transmitting the first data message from the first radio transmitter at the first identified time;

identifying a first time for transmission of a first data message from the second radio transmitter with reference to a current time measurement identified by the second transmitter and the predetermined time period that is adjusted by a second time offset, the second time offset being identified with reference to the second random number and the predetermined pseudo-random process; and

transmitting the second data message from the second radio transmitter at the second identified time.

2. The method of claim 1, the identification of the first time offset and the second time offset further comprising:

initiating the predetermined pseudo-random process with the first random number in the first transmitter;

generating with the pseudo-random process operating in the first transmitter a first pseudo-random number;

identifying the first time offset with reference to the first pseudo-random number;

initiating the predetermined pseudo-random process with the second random number in the second transmitter;

generating with the predetermined pseudo-random process operating in the second transmitter a second pseudo-random number; and

identifying the second time offset with reference to the second pseudo-random number.

3. The method of claim 2 further comprising:

continuing to generate pseudo-random numbers with the pseudo-random process operating in the first transmitter and to identify a time offset with reference to each generated pseudo-random number;

identifying successive transmission times for successive data messages to be transmitted by the first transmitter, the identified successive transmission times being generated with reference to a prior identified transmission time, the predetermined time period, and a currently identified time offset; and

transmitting the data messages with the first transmitter at the identified successive transmission times for the first transmitter.

4. The method of claim 2, the identification of the time measurement with the first transmitter and the identification of the time measurement with the second transmitter further comprising:

identifying the time measurement in the first transmitter with reference to a signal generated by a first oscillator, the first oscillator having a first frequency drift, the time measurement in the first transmitter having a first time drift corresponding to the first frequency drift; and

identifying the time measurement in the second transmitter with reference to a second signal generated by a second oscillator, the second oscillator having a second frequency drift that is different than the first frequency drift, the time measurement in the second transmitter having a second time drift corresponding to the second frequency drift.

5. The method of claim 1, the transmission of the first random number and the first data message with the first transmitter further comprising:

transmitting the first random number at a first electrical power level; and

transmitting the first data message at a second electrical power level, the second electrical power level being greater than the first electrical power level.

6. The method of claim 1 further comprising:

identifying with a receiver a first reception time with reference to a current time measurement identified by the receiver, the predetermined time period, the first random number received from the first transmitter, and the predetermined pseudo-random process operating in the receiver;

operating the receiver at a first electrical power level for a first time period between the current time measurement identified by the receiver and the first reception time; and

operating the receiver at a second electrical power level for a second time period after the first reception time to enable the receiver to receive the first data message transmitted by the first transmitter, the second electrical power level being greater than the first electrical power level.

7. The method of claim 6 further comprising:

identifying with the receiver a second reception time with reference to a current time measurement identified by the receiver, the predetermined time period, the first random number received from the second transmitter, and the predetermined pseudo-random process operating in the receiver;

operating the receiver at a first electrical power level for a first time period between the current time measurement identified by the receiver and the second reception time; and

operating the receiver at a second electrical power level for a second time period after the second reception time to enable the receiver to receive the first data message transmitted by the second transmitter, the second electrical power level being greater than the first electrical power level.

8. The method of claim 6 wherein the first time period is greater than the second time period.

9. The method of claim 1, wherein the first data message includes moisture data generated by a moisture sensor that is communicatively coupled to the first transmitter, and the second data message includes moisture data generated by another moisture sensor that is communicatively coupled to the second transmitter.

10. A sensor probe for use in a sensor system comprising:

a sensor configured to generate sensor signals;

a radio transmitter module; and

a controller operatively connected to the sensor and the radio transmitter module the controller being configured to;

generate a random number;

operate the radio transmitter module to transmit the random number to a radio receiver;

identify a first time period with reference to a predetermined time period that is adjusted by a first time offset, the first time offset being identified with reference to the random number and a predetermined pseudo-random process;

wait for an expiration of the first time period; and

transmit a data message from the first radio transmitter at the expiration of the first time period.

11. The sensor probe of claim 10, the data message including the random number and data corresponding to the sensor signals.

12. The sensor probe of claim 10, the controller being further configured to:

initiate the predetermined pseudo-random process with the first random number;

generate a first pseudo-random number with the pseudo-random process; and

identify the first time offset with reference to the first pseudo-random number.

13. The sensor probe of claim 10, the controller being further configured to:

continue generation of pseudo-random numbers with the pseudo-random process and to identify a time offset with reference to each generated pseudo-random number;

identify successive time periods to separate transmission of successive data messages, the identified successive time periods being generated with reference to the predetermined time period, and a currently identified time offset; and

operate the radio transmitter module to transmit a data message at an expiration of each successive time period.

14. The sensor probe of claim 10, the transmitter module being further configured to:

transmit the first random number at a first electrical power level; and

transmit the first data message at a second electrical power level, the second electrical power level being greater than the first electrical power level.

15. The sensor probe of claim 10 further comprising:

an oscillator operatively connected to the controller; and

the controller being further configured to identify the expiration of the first time period with reference to a signal generated by the oscillator, the oscillator having a first frequency drift, the identified expiration of the first time period having a first time drift corresponding to the first frequency drift.

16. The sensor probe of claim 15, the sensor being a soil moisture sensor further comprising:

a capacitive element that is configured to be inserted in soil; and

a sensor oscillator operatively coupled to the capacitive element.

17. The sensor probe of claim 16, the controller being configured to generate the random number with reference to the signal generated by the oscillator and another signal generated by the sensor oscillator.

18. A receiver for use in a sensor system comprising:

a radio receiver module;

an output device; and

a controller operatively connected to the radio receiver module and the output device and configured to;

receive data corresponding to a random number from a signal transmitted by a first transmitter and received by the radio receiver module;

identify a first time period with reference to a predetermined time period that is adjusted by a first time offset, the first time offset being identified with reference to the random number and a predetermined pseudo-random process;

operate the radio receiver module at a first electrical power level for the first time period; and

operate the radio receiver module at a second electrical power level for a second time period after the first time period to enable the receiver to receive a first data message transmitted by the first transmitter, the second electrical power level being greater than the first electrical power level.

19. The receiver of claim 18, the controller being further configured to:

receive data corresponding to a second random number from a signal transmitted by a second transmitter and received by the radio receiver module;

identify a third time period with reference to the predetermined time period that is adjusted by a second time offset, the second time offset being identified with reference to the second random number and the predetermined pseudo-random process;

operate the radio receiver module at the first electrical power level for the third time period; and

operate the radio receiver module at the second electrical power level for a fourth time period after the third time period to enable the receiver to receive a second data message transmitted by the second transmitter.

20. The receiver of claim 18 wherein the first time period is greater than the second time period.