Method for increasing lifetime of network devices in a multi-hop structured wireless communication system

1. A method for increasing lifetime of network devices of a cluster-tree structured multi-hop wireless communication system which comprises a main network control device, referred to access point (AP) acting as a parent device, managing network operation and a plurality of network devices operating in a battery-powered mode, wherein a part of the plurality of network devices operate as a router having one or more child devices, the others of the plurality of network devices operate as an end device not having a child device, and the AP, the routers and the end devices are connected in a parent-child device relationship, the method comprising:

equalizing, by the AP, the average power consumption of the plurality of network devices by exchanging the role of the router and the end device, which each require different power consumption, without interrupting normal network operation including data transmission and reception operation while keeping network connectivity,

wherein the exchanging the role of the router and the end device comprises:

receiving, by the router and the end device, a role-change message transmitted from the parent device;

replacing, by the router, in response to the role-change message transmitted from the parent device, the role of the end device seamlessly by using an address and resources previously allocated to the end device; and

replacing, by the end device, in response to the role-change message transmitted from the parent device, the role of the router seamlessly by using an address and resources previously allocated to the router.

2. The method of claim 1 , wherein the equalizing average power consumption of the plurality of network devices by exchanging the role of the router and the end device requiring different power consumption without interrupting the normal network operation comprises:

(A) by the parent device, selecting one of child routers in a sequential manner and selects one of child end devices that can take the role of the selected child router in consideration of network connectivity and battery condition of child end devices; and

(B) by the parent device, making the selected child router operate as an end device, and making the selected child end device operate as a router to take the role of the selected child router, without interrupting the normal network operation.

3. The method of claim 2 , wherein step (A) comprises:

(A-1) by the parent device, sequentially selecting its child router in an one by one manner, and transmitting a role-change start message to the selected child router and all of its child end devices having the same network depth as the selected child router without interrupting normal network operation;

(A-2) by the selected child router that has received the role-change start message, repeatedly transmitting a role-change router information message including information on the selected child router itself a predetermined number of times;

(A-3) by the child end devices that have received the role-change start message, attempting to receive the role-change router information message transmitted by the selected child router;

(A-4) by the child end devices that have received the role-change router information message, transmitting to the parent device a role-change candidate message that includes signal strength of the received role-change router information message signal, battery condition and previous operation record as a router; and

(A-5) by the parent device, selecting a child end device having a best condition among child end devices that have transmitted the role-change candidate message, as the device that can take the role of the selected child router.

4. The method of claim 3 , further comprising, by the parent device, repeating step (A-1) when the selected child router fails to receive the role-change router information message transmitted by the selected child router in step (A-2).

5. The method of claim 3 , wherein (A-5) comprises:

by the parent device, selecting an end device that has experienced the highest received signal strength and has remaining battery power larger than a reference value among child end devices that did not operate as a router previously, as the device that can take the role of the selected child router; and

by the parent device, in the presence of no end device satisfying the above condition, selecting an end device that has experienced the highest received signal strength among child end devices that have remaining battery power larger than that of the selected child router, as the device that can take the role of the selected child router.

6. The method of claim 2 , wherein step (B) comprises:

(B-1) by the parent device, transmitting respectively a first and second role-change message to the child router and the child end device selected through step (A) during a regular communication interval, and making the selected child router as a child end device and then the selected child end device as a child router;

(B-2) by the selected child router, operating as an end device by using the address of the child end device included in the first role-change message after receiving the first role-change message; and

(B-3) by the selected child end device, operating as a router by using the address of the selected child router included in the second role-change message after receiving the second role-change message.

7. The method of claim 6 , wherein step (B-3) comprises:

by the selected child end device, operating as the router by using the address of the selected child router included in the role-change message after receiving the second role-change message, and confirming network operation with child devices;

by the device operating as a router, transmitting a role-change-enable message to a parent device after confirming normality of network operation; and

by the device operating as a router, transmitting a role-change-unable message to the parent device and starting to operate as the end device as being before, after confirming abnormality of network operation.

8. The method of claim 7 , further comprising, when the parent device has received the role-change-unable message:

by the parent device, selecting an end device as the device that can take the role of the selected child router among child end devices except the end device that has transmitted the role-change-unable message, in consideration of network connectivity and remaining battery power condition; and

by the parent device, transmitting the second role-change message to the end device to make the end device operate as a router through step (B-3).

9. The method of claim 6 , further comprising:

by the selected child end device operating as a router, making child devices of the selected child end device itself change roles through step (A) and step (B) as another parent device.

10. A multi-hop cluster-tree structured wireless communication system comprising:

child routers and child end devices which are connected to a parent device in parallel,

wherein a child router selected among the child routers in a sequential manner and the child end devices transmit information for a role-change in response to a role-change start message transmitted from the parent device;

the parent device selects a child end device among the child end devices in consideration of the information for the role-change transmitted from child end devices and transmits a role-change message to make the selected child end device and the selected child router exchange roles with each other;

the parent device makes the selected child end device operate as a child router by using the address of the selected child router by sending a first role-change message to the selected child end device; and

the parent device makes the selected child router operate as a child end device using the address of the selected child end device by sending a second role-change message to the selected child router,

wherein the multi-hop cluster-tree structured wireless communication system is for equalizing, by an access point acting as a parent device, average power consumption of the plurality of network devices by exchanging the role of the router and the end device, which each require different power consumption, without interrupting normal network operation including data transmission and reception operation while keeping network connectivity, and

wherein the exchanging the role of the router and the end device comprises:

receiving, by the router and the end device, the role-change message transmitted from the parent device;

replacing, by the router, in response to the role-change message transmitted from the parent device, the role of the end device seamlessly by using an address and resources previously allocated to the end device; and

replacing, by the end device, in response to the role-change message transmitted from the parent device, the role of the router seamlessly by using an address and resources previously allocated to the router.

11. A non-transitory computer readable storage medium storing one or more programs configured to be executed by one or more processors at a computer comprising:

a function of, by a parent device, receiving each of information for a role-change transmitted from a selected child router and child end devices;

a function of, by the parent device, selecting a child end device among child end devices in consideration of the received information from the child end devices;

a function of, by the parent device, transmitting a message to make the selected child end device and the selected child router exchange roles with each other;

a function of, by the parent device, transmitting a first role-change message to the selected child end device to make the selected child end device operate as a child router using the address of the selected child router included in the first role-change message; and

a function of, by the parent device, transmitting a second role-change message to the selected child router to make the selected child router operate as a child end device using the address of the selected child end device included in the second role-change message,

wherein the non-transitory storage medium is for operation management of a multi-hop cluster-tree structure wireless communication system in which the child routers and the child end devices are connected to the parent device in parallel,

wherein the non-transitory storage medium is for equalizing, by an access point acting as a parent device, average power consumption of the plurality of network devices by exchanging the role of the router and the end device, which each require different power consumption, without interrupting normal network operation including data transmission and reception operation while keeping network connectivity,

wherein the exchanging the role of the router and the end device comprises:

receiving, by the router and the end device, a role-change message transmitted from a parent device;

replacing, by the router, in response to the role-change message transmitted from the parent device, the role of the end device seamlessly by using an address and resources previously allocated to the end device; and

replacing, by the end device, in response to the role-change message transmitted from the parent device, the role of the router seamlessly by using an address and resources previously allocated to the router.