HK1097965B - Adaptive transmit power control in wireless devices - Google Patents

Description

Adaptive transmit power control in a wireless device

Background

In a Wireless Local Area Network (WLAN), the transmit power of devices in the network may be reduced below a maximum level to maintain the battery power of the devices. But changing the transmit power level may affect other aspects of the communication process. Reducing the transmit power below a certain level may result in the receiver not receiving correctly because the signal is too weak. Conversely, excessive power increases can lead to interference problems between devices and/or between neighboring systems. These problems can reduce the efficiency of the overall communication process by causing a decrease in data rate and/or an increase in retransmissions.

Conventional approaches to transmit power control are too simple for highly variable network environments where station mobility or other variable conditions may cause frequent changes throughout the network environment.

Drawings

The invention may be understood by reference to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:

fig. 1 shows a flow diagram of a method of adjusting transmit power in response to a network parameter, according to an embodiment of the invention.

Fig. 2 shows a flow diagram of a method of adjusting transmit power based on throughput, according to an embodiment of the invention.

Fig. 3 shows a flow diagram of a method of adjusting transmit power based on network load, according to an embodiment of the invention.

Fig. 4 shows a schematic diagram of a portion of a network using a wireless device, according to an embodiment of the invention.

Detailed Description

Numerous specific details are set forth in the following description. It is understood, however, that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

References to "one embodiment," "an embodiment," "example embodiment," "embodiments," etc., indicate that the embodiment of the invention so described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Furthermore, repeated usage of the phrase "in one embodiment" may, but does not necessarily, refer to the same embodiment.

In the following description and claims, the terms "coupled" and "connected," along with their variants, are used. It should be understood that these terms are not intended as synonyms for each other. Rather, in some embodiments, "connected" is used to indicate that two or more elements are in direct physical or electrical contact with each other. And "coupled" means that two or more elements are directly connected, physically or electrically. Two or more elements that are not directly connected to each other, but yet still co-operate or interact with each other, are also referred to as "coupled".

In the context of this document, the term "wireless" and its variants are used to describe circuits, devices, systems, methods, techniques, communication channels, etc. that may communicate data via a non-solid medium using modulated electromagnetic radiation. The term does not imply that the associated device does not contain any wires, although in some embodiments it does.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing," "computing," "calculating," "determining," or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.

In a similar manner, the term "processor" may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. A "computing platform" may include one or more processors.

Unless specifically stated otherwise, the ordinal adjectives "first", "second", "third", etc., used herein to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects are necessarily described in a given temporal, spatial, sequential, or any other manner.

Embodiments of the invention may be implemented in one or a combination of hardware, firmware and software. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by a computing platform to perform the operations described herein. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium may include: read Only Memory (ROM), Random Access Memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, interfaces that transmit and/or receive such signals, etc.), and others.

Embodiments of the invention may include dynamically adjusting transmit power to affect a particular network parameter based on observations of the network parameter. In one embodiment, the network parameter may be the throughput of a particular device, i.e., the amount of data that the device transmits in a particular time interval. In another embodiment, the network parameter may be the network load, i.e. the fraction of time the medium in the network is busy on the relevant channel.

Fig. 1 shows a flow diagram of a method of adjusting transmit power in response to a network traffic parameter, according to one embodiment of the invention. The network traffic parameter may be any of a variety of parameters based on observed traffic capacity, such as: 1) data throughput of one or more devices, or 2) network load affected by multiple devices, although embodiments of the invention are not limited to these two examples. In flow chart 10, the process may be initialized by determining a value of a network traffic parameter for the current transmit power setting at 110. This value may be determined by observing, measuring, calculating, or otherwise determining a particular parameter value via any available means and information. In some embodiments, the initial value of the transmit power may be set to a default value (not shown) prior to 110, but in other embodiments a derived current value of the transmit power may be used.

The transmit power level is changed by increasing or decreasing the power level at 120. The choice of whether to increase or decrease, the manner in which such a choice is made, and how much to change is based on many factors not mentioned in the example of fig. 1. A new network traffic parameter value may then be determined at 130 based on the transmission at this new power level. If the network traffic parameter value improves, as determined at 140, the transmit power will again change in the same direction as the previous change at 150 (i.e., increase if the previous change was an increase and decrease if the previous change was a decrease). If the network traffic parameter value does not improve, as determined at 140, then it is determined that the transmit power will change in the opposite direction as the previous change at 160. In either case, a new value of the network traffic parameter may be determined for this new transmit power setting at 130 and the cycle repeated. Thus, the transmit power can be repeatedly adjusted to dynamically maintain the network traffic parameter within a specified range by using changes in the network traffic parameter value as feedback. The cycle may be repeated continuously, periodically, aperiodically, or in any feasible manner. The definition of "improvement" as used in this specification may vary depending on the type of network traffic parameter, the desired result, and/or other factors.

Fig. 2 shows a flow diagram of a method of adjusting transmit power based on throughput, according to an embodiment of the invention. Throughput may be determined using various methods, such as but not limited to: 1) an amount of data transmitted in a given period of time, 2) an amount of data passed through a transmit queue in a given period of time, 3) an amount of data that is effectively received in a given period of time. In some embodiments, a single network device may control its own transmit power and be able to determine its own data throughput without regard to those of other devices, although other embodiments are not limited in this respect. In some embodiments, a single network device may measure the throughput of one or more devices in the network and control the transmit power of the one or more devices through packet transmissions indicating transmit power adjustments or indicating new transmit power levels to be used by the devices.

In flow diagram 20, the current value of transmit power may be initialized at 210 to a predetermined value, which in a particular embodiment may be the maximum value supported by the device, although other embodiments of the invention are not limited in this respect. At 215, the process waits until there are enough packets to make a determination that a statistically valid transmission throughput has been buffered. In some embodiments, looping at 215 may also include waiting a minimum period of time even when enough packets have accumulated. Other processes may also be performed during the waiting period indicated at 215 and may include sending packets that are not used for the throughput evaluation of flowchart 20. Once enough packets have accumulated, the packets are transmitted at the current transmit power value and the current value of throughput is determined for the transmissions at 220. Once the value of the throughput is determined, the current transmit power level is compared to the minimum and maximum values of the power level at 225 and 245, respectively. These minimum and maximum power levels may be set based on various criteria, such as, but not limited to: 1) a range of power levels supported by the device, 2) a range of power levels for which the communication error is below a certain threshold, and 3) battery reserves in the transmitting device.

If the current transmit power level setting is not above the minimum value, then the evaluation process for the system at a lower power level (230) is skipped along with 235 and 240, as determined at 225, to avoid the power level falling below the minimum value. If, however, the current transmit power level is set above the minimum value, then the power is reduced, more data is transmitted and a new throughput is determined at 230 based on the newly transmitted data, as determined at 225. At 235, if the new throughput value does not vary sufficiently from the throughput determined at 220 (where "sufficient" refers to more than a predetermined amount), the new power level is maintained and considered the current power level for the next cycle of flowchart 20. If this new throughput value changes sufficiently, the power level is restored at 240 to the value associated with the throughput determined at 220 and compared to the predetermined maximum power level at 245, as determined at 235.

If the power level is not below the maximum, as determined at 245, then the evaluation process for the system at the higher power level is skipped (250-. If, however, the current transmit power level setting is less than the maximum, as determined at 245, the power is increased, new data is transmitted, and a new throughput is determined at 250. At 255, if the throughput value at this new power level has increased sufficiently compared to the throughput determined at 220, then the new power level is maintained and considered the current power level as the next cycle of flowchart 20. If this new throughput value has not increased sufficiently, as determined at 255, the power level is restored again at 260 to the value associated with the throughput determined at 220 and a new cycle begins through flowchart 20. The process of flow chart 20 may be repeated periodically or aperiodically to continuously adjust the transmit power level based on feedback on the resulting impact on throughput.

Fig. 3 shows a flow diagram of a method of adjusting transmit power based on network load, according to an embodiment of the invention. Network load is a fraction of time indicating that the medium is busy on the channel, where "busy" includes observed device transmissions as well as transmissions of other devices detected by the observed device. Furthermore, instead of monitoring the actual transmission, the "busy" may also be estimated by checking the amount of data buffered for transmission in the transmit queue. In some embodiments, busy may be determined by a combination of monitoring and checking of the transmit queue. The transmission includes, but is not limited to, transmitting data and/or transmitting a carrier and/or detecting energy on the channel above some threshold. There are many ways to determine a value indicative of network load, including but not limited to: 1) busy time divided by the total elapsed time for observation, 2) the amount of time the medium is now busy divided by the amount of time the medium will be busy when all stations have buffered traffic, and 3) the amount of time the medium is busy multiplied or divided by a predetermined number. The observation of the medium may be made at a single point in the network or at multiple points in the network along with the collectively merged values. The network load may be expressed as a fraction, percentage, value, or any other feasible manner. The network may include various components, for example the network in one embodiment may include all devices capable of receiving detectable transmissions on the same channel at one or more detection points. The network load may be determined by direct measurement, calculation, other techniques, or a combination thereof. The calculation to determine the network load value may be performed in a single device or distributed to multiple devices.

In the flow diagram 30, data is transmitted at 310 and a current value of the network load is determined based on the transmissions. The network load may be determined by any feasible technique, including the foregoing and other techniques not described. The current value of the network load may be compared to a predetermined minimum target value at 320. The target value range may comprise a range of values for which it is desired to maintain the actual network load, with minimum and maximum values at the lower and upper limits of the range, respectively. In a particular embodiment, the width of the range may be close to zero, i.e., the minimum and maximum values are approximately equal.

If the value of the network load is below the minimum value, the transmit power may be reduced at 330, as determined at 320, otherwise the value of the network load is compared to a predetermined maximum target value at 340. If the value of the network load is greater than the maximum value, the transmit power is increased at 350. The current power level (whether it be the reduced value setting at 330, the increased value setting at 350, or the unchanged value determined to be within the target range at 320 and 340) may then be used for transmission in the next estimation phase in which the network load may then be determined at 310 during the next cycle by flowchart 30. In some embodiments, successive loops throughout the flowchart 30 may be separated by a wait period at 360. In some embodiments, the target range of network loads may be intentionally set below the actual or theoretical maximum network load, so that increments outside this range can be observed and corrected for.

The cycles described in fig. 1-3 can be repeated periodically or aperiodically in a desired and/or feasible manner. By dynamically adjusting the transmit power based on observed operating conditions, repeated adjustments can be made to maintain the transmit power at a level that accommodates changes in operating conditions. In some embodiments, the difference between the observed value and the compared value must exceed a predetermined delta threshold before being considered valid, although other embodiments of the invention are not limited in this respect.

Fig. 4 shows a schematic diagram of a portion of a network using wireless devices, according to one embodiment of the invention. In some embodiments, the wireless device may be comprised of an Access Point (AP) or a mobile Station (STA), the wireless device may include an AP or STA, or the wireless device may be part of a larger apparatus. In other embodiments, devices other than APs and STAs may be used, although the invention is not limited in this respect. The AP 410 is shown with an antenna 420 for communicating with STAs 431-434 via their antennas 441-444, respectively, although the actual antenna may be different than the illustrated structure. In some embodiments, some or all of the devices may have multiple antennas, rather than the single antenna in the illustrated embodiment. In some embodiments, some or all of the antennas may be relatively omni-directional, while in other embodiments the antennas may be relatively directional. In the illustrated embodiment, AP 410 may have established communication with STAs 431-434. The communication may be performed using any feasible technique, such as, but not limited to; frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), Ultra Wideband (UWB), Spatial Division Multiple Access (SDMA), combinations thereof, and the like. In some embodiments, multiple groups of devices (e.g., multiple APs each communicating with a different group of STAs) may share and/or merge network parameter values to accommodate the effect of power variations on the more device groups shown in fig. 4.

The foregoing description is illustrative and not restrictive. Variations thereof may be made by those of ordinary skill in the art. Such variations are intended to be included in the various embodiments of the invention, which are limited only by the spirit and scope of the following claims.

Claims (27)

1. A method for communicating within a wireless network, comprising:

transmitting data at a first transmit power level;

determining a first value of a network traffic parameter at the first transmit power level;

determining a second transmit power level different from the first transmit power level;

transmitting data at the second transmit power level;

determining a second value of a network traffic parameter at the second transmit power level;

wherein the network traffic parameter is based on a communication capacity observed by a single network device.

2. The method of claim 1, wherein the determining the first value comprises determining a first throughput value and the determining the second value comprises determining a second throughput value.

3. The method of claim 2, further comprising subsequently transmitting data at the second transmit power level in response to one of two conditions:

the second transmit power level is less than the first transmit power level, and the second throughput value is approximately equal to the first throughput value; and

the second transmit power level is greater than the first transmit power level, and the second throughput value is greater than the first throughput value.

4. The method of claim 2, further comprising subsequently transmitting data at the first transmit power level in response to one of two conditions:

the second transmit power level is less than the first transmit power level and the second throughput value is not approximately equal to the first throughput value; and

the second transmit power level is greater than the first transmit power level, and the second throughput value is not greater than the first throughput value.

5. The method of claim 1, wherein the determining the first value comprises determining a first network load value and the determining the second value comprises determining a second network load value.

6. The method of claim 5, wherein the determining the second transmit power level comprises determining that the second transmit power level is less than the first transmit power level in response to the first network load value being less than a target value.

7. The method of claim 5, wherein the determining the second transmit power level comprises determining that the second transmit power level is greater than the first transmit power level in response to the first network load value being greater than a target value.

8. An apparatus for communicating within a wireless network, comprising:

means for transmitting data at a first transmit power level in a single network device;

means for determining, in a single network device, a first data throughput value based on transmissions at the first transmit power level;

means for transmitting data at a second transmit power level different from the first transmit power level;

means for determining a second data throughput value based on the transmission at the second transmit power level; and

means for setting, in a single network device, a subsequent transmit power level to one of the first transmit power level and the second transmit power level based on a comparison between the first and second data throughput values.

9. The apparatus of claim 8,

the second transmission power level is less than the first transmission power level, and

the setting comprises setting the subsequent transmit power level to the second transmit power level in response to determining that the second data throughput value is about equal to the first data throughput value.

10. The apparatus of claim 8,

the second transmit power level is greater than the first transmit power level, and;

the setting comprises setting the subsequent transmit power level to the second transmit power level in response to determining that the second data throughput value is greater than the first data throughput value.

11. The apparatus of claim 8, wherein the first and second transmit power levels are both less than a predetermined maximum transmit power level and greater than a predetermined minimum transmit power level.

12. An apparatus for communicating within a wireless network, comprising:

means for setting a first transmit power level in a single network device;

means for transmitting data at a first transmit power level in a single network device;

means for determining, in a single network device, a first network load value based on data transmitted at the first transmit power level;

means for comparing, in a single network device, the network load value to a predetermined range of network load values; and

means for varying the transmit power level for subsequent data transmissions of data based on a result of the comparison in a single network device.

13. The apparatus of claim 12, wherein the means for varying comprises means for decreasing the transmit power level for a subsequent transmission in response to the network load value being less than a minimum value of the predetermined range.

14. The apparatus of claim 12, wherein the means for changing comprises means for increasing the transmit power level for subsequent transmissions in response to the network load value being greater than a maximum value of the predetermined range.

15. The apparatus of claim 12, wherein the means for changing comprises one of:

means for increasing the transmit power level for subsequent transmissions in response to the network load value being greater than the predetermined value; and

means for reducing the transmit power level for subsequent transmissions in response to the network load value being less than the predetermined value.

16. An apparatus for communicating within a wireless network, comprising:

a single network device to:

determining a first transmit power level;

transmitting data at the first transmit power level;

determining a first value of a network traffic parameter based at least in part on the transmission at the first transmit power level;

determining a second transmit power level different from the first transmit power level;

transmitting data at the second transmit power level; and

determining a second value of a network traffic parameter based at least in part on the transmission using the second transmit power level;

wherein the network traffic parameter is based on a traffic capacity observed by a mobile station;

wherein the operations of determining and transmitting are performed within the single network device.

17. The apparatus of claim 16,

the network traffic parameter is a data throughput parameter;

the single network device further subsequently transmitting data at the second transmit power level in response to the second transmit power level being less than the first transmit power level and the second value being approximately equal to the first value; and

the single network device further subsequently transmits data at the first transmit power level in response to the second transmit power level being less than the first transmit power level and the second value not being about equal to the first value.

18. The apparatus of claim 17,

the single network device further transmits data subsequently at the second transmit power level in response to the second transmit power level being greater than the first transmit power level and the second value being greater than the first value; and

the single network device further subsequently transmits data at the first transmit power level in response to the second transmit power level being greater than the first transmit power level and the second value not being greater than the first value.

19. The apparatus of claim 16,

the network traffic parameter is a network load parameter; and is

The single network device also sets the second transmit power level to be less than the first transmit power level in response to the first value being less than a first predetermined value.

20. The apparatus of claim 19, wherein the single network device further sets the second transmit power level to be greater than the first transmit power level in response to the first value being greater than a second predetermined value.

21. The apparatus of claim 20, wherein the first predetermined value is a minimum value within a predetermined range of values and the second predetermined value is a maximum value within the predetermined range of values.

22. A system for communicating within a wireless network, comprising:

a single network device comprising an omni-directional antenna, the single network device to:

determining a first transmit power level;

transmitting data at the first transmit power level;

determining a first value of a network traffic parameter based at least in part on the transmission at the first transmit power level;

determining a second transmit power level different from the first transmit power level;

transmitting data at the second transmit power level; and

determining a second value of a network traffic parameter based at least in part on the transmission using the second transmit power level;

wherein the network traffic parameter is based on the observed communication capacity.

23. The system of claim 22,

the network traffic parameter is a data throughput parameter;

the single network device further subsequently transmitting data at the second transmit power level in response to the second transmit power level being less than the first transmit power level and the second value being approximately equal to the first value; and

the single network device further subsequently transmits data at the first transmit power level in response to the second transmit power level being less than the first transmit power level and the second value not being about equal to the first value.

24. The system of claim 23,

the single network device further subsequently transmitting data at a second transmit power level in response to the second transmit power level being greater than the first transmit power level and the second value being greater than the first value; and

the single network device further subsequently transmits data at the first transmit power level in response to the second transmit power level being greater than the first transmit power level and the second value not being greater than the first value.

25. The system of claim 22,

the network traffic parameter is a network load parameter; and is

The single network device also sets the second transmit power level to be less than the first transmit power level in response to the first value being less than a first predetermined value.

26. The system of claim 25, wherein the single network device further sets the second transmit power level to be greater than the first transmit power level in response to the first value being greater than a second predetermined value.

27. The system of claim 26, wherein the first predetermined value is a minimum value within a predetermined range of values and the second predetermined value is a maximum value within the predetermined range of values.