Self-adaptive transmit power control for wireless network

The present invention relates generally to wireless data communications. More particularly, the present invention relates to a self-adaptive method for transmit power control in a wireless network.

Many wireless network devices such as laptop computers are battery-powered to provide the mobility permitted by wireless networks such as those specified by IEEE 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16 and 802.20. For this reason, such portable wireless network devices must use power efficiently to permit long operation times. With respect to the wireless link, this involves controlling the transmit power of the wireless network device to maintain throughput levels with distance, maintain the quality and integrity of the signal, mitigate interference effects to other users, and maximize the signal-to-noise ratio of the signal.

In general, in one aspect, the invention features a wireless network apparatus and corresponding method and computer program. It comprises a receive circuit to receive a first signal over a wireless link, the first signal representing packets of first data; a transmit circuit to transmit a second signal over the wireless link at a power level indicated by a transmit power control signal, the second signal representing packets of second data; and a processor to determine a link quality of the wireless link based on the first signal, and to generate the transmit power control signal based on the link quality.

Particular implementations can include one or more of the following features. The processor determines the link quality of the wireless link based on at least one of the group consisting of a signal strength of the first signal; a signal quality of the first signal; a packet error rate of the packets of first data; and a current transmit power level of the second signal. The transmit circuit transmits the second signal over the wireless link at a data rate indicated by a transmit data rate control signal; and wherein the processor generates the transmit data rate control signal based on the link quality. The processor determines the link quality of the wireless link based on at least one of the group consisting of a signal strength of the first signal; a signal quality of the first signal; a packet error rate of the packets of first data; a current transmit power level of the second signal; and a current transmit data rate of the second signal. The wireless network apparatus further comprises an antenna in communication with the receive circuit and the transmit circuit. The processor asserts a decrease power state of the transmit power control signal when the link quality of the wireless link exceeds a predetermined link quality, and a current transmit power level of the second signal is greater than a maximum transmit power level for a next higher transmit data rate of the first data; and the transmit circuit decreases a power of the second signal in response to the decrease power state of the transmit power control signal. The processor increases a rate of transmission of the first data when the link quality of the wireless link exceeds a predetermined link quality, and a current transmit power level of the second signal is not greater than a maximum transmit power level for a next higher transmit data rate of the first data. The processor asserts an increase power state of the transmit power control signal when the link quality of the wireless link does not exceed a predetermined link quality, and a current transmit power level of the second signal is less than a maximum transmit power level for the current transmit data rate of the first data; and the transmit circuit increases the power of the second signal in response to the increase power state of the transmit power control signal. The processor decreases a rate of transmission of the first data when the link quality of the wireless link does not exceed a predetermined link quality, and a current transmit power level of the second signal is not less than a maximum transmit power level for the current transmit data rate of the first data. The processor asserts a decrease power state of the transmit power control signal when a packet error rate of the first packets of data does not exceed a predetermined packet error rate threshold, the signal strength of the first signal exceeds a predetermined signal strength threshold, and a current transmit power level of the second signal is greater than a maximum transmit power level for a next higher transmit data rate of the first data; and the transmit circuit decreases a power of the second signal in response to the decrease power state of the transmit power control signal. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. The processor increases a rate of transmission of the first data when a packet error rate of the first packets of data does not exceed a predetermined packet error rate threshold, a signal strength of the first signal exceeds a predetermined signal strength threshold, and a current transmit power level of the second signal is not greater than a maximum transmit power level for a next higher transmit data rate of the first data. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. The processor asserts an increase power state of the transmit power control signal when a packet error rate of the first packets of data exceeds a predetermined packet error rate threshold, the signal strength of the first signal does not exceed a predetermined signal strength threshold, and a current transmit power level of the second signal is less than a maximum transmit power level for the current transmit data rate of the first data; and the transmit circuit increases the power of the second signal in response to the increase power state of the transmit power control signal. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. The processor decreases a rate of transmission of the first data when a packet error rate of the first packets of data exceeds a predetermined packet error rate threshold, a signal strength of the first signal does not exceed a predetermined signal strength threshold, and a current transmit power level of the second signal is not less than a maximum transmit power level for the current transmit data rate of the first data. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. An integrated circuit comprises the wireless network apparatus. A wireless network device comprises the wireless network apparatus. A wireless client comprises the wireless network device. A wireless access point comprises the wireless network device. The wireless network device is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16, and 802.20. The receive circuit comprises a media access controller receive circuit; and a physical-layer device receive circuit. The transmit circuit comprises a media access controller transmit circuit; and a physical-layer device transmit circuit.

In general, in one aspect, the invention features a wireless network apparatus and corresponding method and computer program. It comprises a receive circuit to receive a first signal over a wireless link, the first signal representing packets of first data; a processor to determine a link quality of the wireless link based on the first signal; and a transmit circuit to transmit a second signal over the wireless link at a data rate based on the link quality of the wireless link, the second signal representing packets of second data.

Particular implementations can include one or more of the following features. The processor determines the link quality of the wireless link based on at least one of the group consisting of a signal strength of the first signal; a signal quality of the first signal; a packet error rate of the packets of first data; and a current transmit power level of the second signal. The wireless network apparatus further comprises an antenna in communication with the receive circuit and the transmit circuit. An integrated circuit comprises the wireless network apparatus. A wireless network device comprises the wireless network apparatus. A wireless client comprises the wireless network device. A wireless access point comprises the wireless network device. The wireless network device is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16, and 802.20.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

FIG. 1 shows a wireless network device in communication with another wireless network device according to a preferred embodiment of the present invention.

FIG. 2 shows a transmit power control process for the wireless network device of FIG. 1 according to a preferred embodiment.

FIG. 3 shows a process for determining a link quality according to a preferred embodiment.

FIG. 4 shows a table of the power levels for each data rate according to a preferred embodiment.

FIG. 5 shows a flow diagram for embodiments in which the only the power level of the transmitted signal is adjusted.

FIG. 6 shows a process for decreasing the power level of a transmitted signal for a wireless network device having three transmit power levels P 0 , P 1 , and P 2 where P 0 <P 1 <P 2 according to a preferred embodiment.

FIG. 7 shows a process for increasing the power level of a transmitted signal for a wireless network device having three transmit power levels P 0 , P 1 , and P 2 where P 0 <P 1 <P 2 according to a preferred embodiment.

The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears.

Conventional wireless devices, on detecting a wireless link of insufficient quality, for example by detecting a failed transmission of a packet, simply repeat the transmission of the packet until the packet is successfully transmitted. This method wastes considerable power and time. In contrast, embodiments of the present invention, on detecting a wireless link of insufficient quality, adjust the power level and/or data rate of the transmitted signal to obtain successful transmissions. The techniques employed, described in detail below, can result in a reduction of power consumption of 30%-40% compared to conventional methods. In addition, these techniques provide reduced interference and enhanced security.

Embodiments of the present invention provide power and/or data rate control for a transmitted signal in a wireless network such as an IEEE 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16 or 802.20 wireless local-area network, a personal-area network such as a Bluetooth network, and other sorts of wireless networks and communication links. In particular, the power level and/or data rate of the transmitted signal are controlled based on a link quality of the wireless link. In a preferred embodiment, the link quality is determined based on the packet error rate of packets in the transmitted signal and the signal strength of received signals, as described in detail below. In some embodiments the power level of the transmitted signal is controlled based on the packet error rate of packets in the transmitted signal, the signal strength of received signals, and a current transmit power level of the transmitted signal, also as described in detail below.

FIG. 1 shows a wireless network device 100 in communication with another wireless network device 108 according to a preferred embodiment of the present invention. Wireless network devices 100 and 108 can be wireless clients, wireless access points, or other sorts of wireless network devices. Wireless network device 100 is preferably otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16, and 802.20.

Wireless network device 100 comprises a host 102 such as a laptop computer, personal digital assistant, and the like, a media access controller (MAC) 104 , a physical-layer device (PHY) 106 , and an antenna 122 . MAC 104 comprises a processor 110 , a memory 112 , a MAC receive circuit 114 , and a MAC transmit circuit 116 . PHY 106 comprises a PHY receive circuit 118 and a PHY transmit circuit 120 . MAC receive circuit 114 and PHY receive circuit 118 together define a receive circuit 134 . MAC transmit circuit 116 and PHY transmit circuit 120 together define a transmit circuit 136 .

FIG. 2 shows a transmit power control process 200 for wireless network device 100 according to a preferred embodiment. Processor 110 initializes wireless network device 100 by setting the power level of the signal transmitted by wireless network device 100 to its minimum power level, and by setting the data rate of the data transmitted by wireless network device 100 to its maximum rate (step 202 ). Processor 110 preferably sets the power level of the transmitted signal by asserting a predetermined state of a transmit power control (TPC) signal 124 , although other methods can be used. PHY transmit circuit 120 sets the power level according to TPC signal 124 . Processor 110 preferably sets the data rate of the transmitted signal by asserting a predetermined state of a data rate control (DRC) signal 134 , although other methods can be used. PHY transmit circuit 120 sets the data rate according to DRC signal 134 .

Processor 110 then determines the link quality of the link 128 between wireless network device 100 and wireless network device 108 (step 204 ). In preferred embodiments the determination of link quality is based on a packet error rate (PER) of the signal 130 transmitted by wireless network device 100 to wireless network device 108 and a received signal strength indication (RSSI) 126 of the signal 132 received by wireless network device 100 from wireless network device 108 .

Processor 110 compares the link quality to one or more predetermined link qualities. In a preferred embodiment the link quality threshold comprises a packet error rate threshold and a signal strength threshold. In some embodiments multiple such thresholds can be used to provide hysteresis. Preferably the thresholds are selected based on the current power level of the transmitted signal 130 .

FIG. 3 shows a process 300 for determining a link quality according to a preferred embodiment. Of course, other processes can be used. For example, assume that physical-layer transmit circuit 120 is capable of transmitting at three different power levels P 0 , P 1 , and P 2 , where P 0 <P 1 <P 2 and otherwise complies with at least one of IEEE 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16 and 802.20. FIG. 4 shows a table of the power levels for each data rate according to a preferred embodiment. Note that some of the data rates have only one or two possible power levels. Thus there is only one possible path through the table, as shown by the arrows in FIG. 4 . This path reflects the fact that, when increasing the data rate, it is necessary to first decrease the transmitted power to avoid distortion in the transmitted waveform.

Process 300 first determines the transmit power level P of the transmitted signal 130 and the link quality LQ of wireless link 128 (step 302 ). The link quality LQ can be determined based on a signal strength of received signal 132 , a signal quality of received signal 132 , a packet error rate of the packets of data in received signal 132 , a current transmit power level of transmitted signal 130 , a current transmit data rate of transmitted signal 130 , other such criteria, or any combination thereof. If P=P 0 , then the link quality LQ is compared to a predetermined link quality LQ 01 (step 304 ). The link quality LQ is determined to be below threshold when LQ<LQ 01 (step 306 ) and above threshold otherwise (step 308 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 01 and a PER threshold PER 01 . In particular, the link quality is determined to be below threshold when RSSI≦RSSI 01 or PER≧PER 01 , and above threshold otherwise.

But if at step 302 P=P 1 , then the link quality LQ is compared to a predetermined link quality LQ 12 (step 310 ). The link quality LQ is determined to be below threshold when LQ<LQ 12 (step 306 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 12 and a PER threshold PER 12 . In particular, the link quality is determined to be below threshold when RSSI<RSSI 12 or PER≧PER 12 . But if at step 306 LQ≧LQ 12 , then the link quality LQ is compared to a predetermined link quality LQ 10 (step 312 ). The link quality LQ is determined to be below threshold when LQ>LQ 10 (step 314 ) and neither above nor below threshold otherwise (step 316 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 10 and a PER threshold PER 10 . In particular, the link quality is determined to be above threshold when RSSI≧RSSI 10 and PER≦PER 10 , and neither above nor below threshold otherwise.

But if at step 302 P=P 2 , then the link quality LQ is compared to a predetermined link quality LQ 21 (step 318 ). The link quality LQ is determined to be above threshold when LQ>LQ 21 (step 320 ) and below threshold otherwise (step 322 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 2 , and a PER threshold PER 21 . In particular, the link quality is determined to be above threshold when RSSI≧RSSI 21 and PER≦PER 21 , and below threshold otherwise.

Example numbers for thresholds RSSI 01 , RSSI 12 , RSSI 21 , RSSI 10 , PER 01 , PER 12 , PER 21 and PER 10 are given below in Table 1 for an IEEE 802.11a link and a IEEE 802.11g link. Of course these numbers are given for example only, and should not be considered limiting.

Returning to FIG. 2 , if in step 204 the link quality is determined to be above threshold ( 206 ), process 200 determines whether the current transmit power level P is greater than the maximum power level Pmh for the next higher data rate (step 208 ). If the current transmit power level is greater than the maximum power level for the next higher data rate, process 200 decreases the power level of transmitted signal 130 (step 210 ), and resumes at step 204 .

In other embodiments, processor 110 adjusts only the data rate of transmitted signal 130 based on the link quality. In still other embodiments, processor 110 adjusts only the power level of transmitted signal 130 based on the link quality, for example as illustrated by the flow diagram of FIG. 5 .

FIG. 6 shows a process 600 for decreasing the power level of transmitted signal 130 for a wireless network device having three transmit power levels P 0 , P 1 , and P 2 where P 0 <P 1 <P 2 according to a preferred embodiment. Of course, other processes can be used. If the transmit power level P of the transmitted signal 130 is equal to P 0 (step 602 ), then process 600 ends because the power level is already at its minimum level. Otherwise if the transmit power level P of the transmitted signal 130 is greater than, or equal to, P 2 (step 604 ), then process 600 sets the transmit power level to P 1 and sets the data rate of the transmitted signal to its maximum rate (step 606 ). However if at step 604 the transmit power level P of the transmitted signal 130 is less than P 2 , process 600 sets the transmit power level to P 0 and sets the data rate of the transmitted signal to its maximum rate (step 610 ).

However, returning again to FIG. 2 , if at step 208 process 200 determines that the current transmit power level is not greater than the maximum power level for the next higher data rate then process 200 increases the data rate (step 212 ) and resumes at step 204 . Any process can be used to increase the data rate.

Process 200 can use multiple link quality thresholds at step 204 to provide hysteresis, for example as described above with respect to FIG. 5 . Therefore process 200 can determine that the link quality is neither above nor below the link quality thresholds ( 209 ). In that case, no action is taken, and process 200 repeats step 204 .

On the other hand, if at step 204 process 200 determines that the link quality is below the link quality threshold ( 207 ), process 200 compares the power level of transmitted signal 130 to respective predetermined values (step 214 ). In other embodiments, other criteria are used. If the current transmit power level P is less than the maximum power level Pmc for the current data rate then process 200 increases the power level of transmitted signal 130 (step 216 ), and returns to step 204 .

FIG. 7 shows a process 700 for increasing the power level of transmitted signal 130 for a wireless network device having three transmit power levels P 0 , P 1 , and P 2 where P 0 <P 1 <P 2 according to a preferred embodiment. Of course, other processes can be used. If the transmit power level P of the transmitted signal 130 is not less than P 2 (step 702 ), then process 700 ends because the power level is already at its maximum level. Otherwise if the transmit power level P of the transmitted signal 130 is less than P 1 (step 704 ), then process 700 sets the transmit power level to P 1 and sets the data rate of the transmitted signal to its maximum rate (step 706 ). However if at step 704 the transmit power level P of the transmitted signal 130 is greater than, or equal to, P 1 , process 700 sets the transmit power level to P 2 and sets the data rate of the transmitted signal to its maximum rate (step 710 ).

However, returning again to FIG. 2 , if at step 214 process 200 determines that the current transmit power level P is not less than the maximum power level Pmc for the current data rate, then process 200 decreases the data rate (step 218 ) and resumes at step 204 . Any process can be used to decrease the data rate.

The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Apparatus of the invention can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the invention can be performed by a programmable processor executing a program of instructions to perform functions of the invention by operating on input data and generating output. The invention can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).

A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.