Method and apparatus to maintain specification absorption rate at a wireless node
A system and method for medium access control (MAC) protocol which controls transmissions in wireless devices to at least substantially comply with specific absorption rate (SAR) limits. The system and method of MAC protocol uses “source-based” time averaging measurements of transmitter “on-times” and an integral of transmission power to direct transmitter duty-cycle such that SAR limits are met. The system and method monitors and controls topology-dependent functions of a node transceiver, including transceiver duty cycle, transceiver transmit power levels and transceiver power-time products, using a automatic transmission control protocol (ATP) to vary functions to maintain specific absorption rate (SAR) limits for handheld and portable devices which are used close to human bodies. In cases in which SAR limits are approached, the ATP can direct the transceiver at the device to adjust each function, or combination of functions, to maintain an acceptable SAR limit.
1. A method for operation of a wireless node to maintain a specific absorption rate (SAR) level when communicating within a communications network, the method comprising:
comparing a current specific absorption rate with a maximum specific absorption rate level;
when the current specific absorption rate is greater than the maximum specific absorption rate level, adjusting at least one topology-dependent function to modify the current specific absorption rate to meet the maximum specific absorption rate level; and
wherein the topology-dependent function comprises a power-time product, the method further comprising:
prioritizing data traffic between the node and one or more other nodes of said network based on said power-time product of the node.
2. A method as claimed in claim 1 , wherein the topology-dependent function comprises a duty cycle of a transceiver of the node, wherein the duty cycle comprises a percentage of time the transceiver is transmitting during a time interval and further wherein the adjusting comprises reducing the duty cycle.
3. A method as claimed in claim 2 , wherein the adjusting step further comprises:
using source-based time averaging to adjust the duty cycle.
4. A method as claimed in claim 1 , wherein the topology-dependent function comprises an average transmit power level of a transceiver of the node during a time interval, and further wherein the adjusting comprises adjusting the transmit power level.
5. A method as claimed in claim 4 , further comprising:
measuring a transmit power over an “on time” of the transceiver of the node; and
wherein the adjusting further comprises adjusting the transmit power “on time”.
6. A method as claimed in claim 4 , further comprising:
calculating an acceptable power level for each of a unicast and a broadcast transmission; and
wherein the adjusting step includes adjusting the transmit power level within the acceptable power levels while meeting the maximum specific absorption rate.
7. A method as claimed in claim 1 , wherein the adjusting comprises adjusting the power-time product to adjust a total transmit power per a time interval of a transceiver of the node.
8. A method as claimed in claim 7 , further comprising:
comparing the power-time product over the time period to a maximum power-time product limit; and adjusting at least one of a modem data rate and spreading factor at the node when the power-time product exceeds the maximum power-time product limit.
9. A method as claimed in claim 8 , further comprising:
adjusting at least one of a spreading factor and a radio frequency power to meet the maximum specific absorption rate.
10. A method as claimed in claim 1 , wherein the adjusting comprises adjusting the at least one topology-dependent functions via an adaptive transmission protocol of a media access control.
11. A wireless node operating within a communications network, the node comprising:
a controller for:
comparing a current specific absorption rate with a maximum specific absorption rate level,
when the current specific absorption rate is greater than the maximum specific absorption rate, adjusting at least one topology-dependent to modify the current specific absorption rate to meet the maximum specific absorption rate level, and
wherein the topology-dependent function comprises a power-time product, prioritizing data traffic between the node and one or more other nodes of said network based on said power-time product of the node.
12. A node as claimed in claim 11 , further comprising:
a transceiver coupled to the controller, wherein the transceiver operates using a duty cycle comprising a percentage of time the transceiver is transmitting during a time interval,
wherein the topology-dependent function comprises the duty cycle of the transceiver.
13. A node as claimed in claim 12 , wherein:
the controller uses source-based time averaging to adjust the duty cycle.
14. A node as claimed in claim 11 , further comprising:
a transceiver coupled to the controller, wherein the transceiver operates using an average transmit power level during a time interval,
wherein the topology-dependent function comprises a current transmit power level.
15. A node as claimed in claim 14 , wherein:
the controller measures a transmit power-over an “on time” of the transceiver and wherein the topology-dependent function comprises the transmit power “on time”.
16. A node as claimed in claim 14 , wherein:
the controller further:
calculates an acceptable power level for each of a unicast and a broadcast transmission, and
wherein the controller adjusts the transmit power level within the acceptable power levels while meeting the maximum specific absorption rate.
17. A node as claimed in claim 11 , wherein:
the controller further:
compares the power-time product over the time period to a maximum power-time product limit, and
adjusts at least one of a modem data rate and spreading factor of the node when the power-time product exceeds the maximum power-time product limit.
18. A node as claimed in claim 17 , wherein:
the controller adjusts at least one of a modem data rate and spreading factor at said at least one node by increasing said spreading factor and lowering said transmission power at a transceiver at said at least one node.
19. A node as claimed in claim 11 , wherein said controller adjusts said at least one topology-dependent function via an adaptive transmission protocol of a media access control.