WO2019027495A1

WO2019027495A1 - Enhanced multi-user uplink power control during txop

Info

Publication number: WO2019027495A1
Application number: PCT/US2017/068924
Authority: WO
Inventors: Ziv AVITAL; Avi MANSOUR; Alexander W. Min; Juan FANG; Laurent Cariou; Ravikumar Balakrishnan
Original assignee: Intel Corp
Current assignee: Intel Corp
Priority date: 2017-08-04
Filing date: 2017-12-29
Publication date: 2019-02-07
Anticipated expiration: 2020-02-04

Abstract

In a multi-user wireless network (for example, a network conforming to wireless standard IEEE 802.11ax), an uplink power control module in an access point may determine Target RSSI and MCS parameters for each STA, transmit those values in a trigger frame, and wait for the solicited responses from the indicated STAs. Based on the RSSI measured in those responses from each STA, the AP may then place values into each Target RSSI, directing the STA to adjust its preceding transmit power up or down by a specified delta amount in the next uplink transmission. After a few passes, the transmitted power may settle down to a steady state value.

Description

ENHANCED MULTI-USER UPLINK POWER CONTROL

DURING TXOP

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to US provisional application serial number

62/541,478, filed August 4, 2017, and claims priority to that filing date for all applicable subject matter. Subject matter in that provisional is hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

[0002] Various embodiments of the invention pertain to controlling transmit power from uplink (UL) wireless communication devices (STAs) to an access point (AP).

BACKGROUND

[0003] In networks that involve simultaneous uplink transmissions from multiple

STAs to a single AP using either Orthogonal Frequency-Division Multiple Access (OFDMA) or Multi-User-MFMO (MU-MFMO) techniques, it is important that the relative transmission power from the various STAs be controlled so that the received signal strengths at the AP are relatively equal and therefore don't overwhelm each other. Since the STAs may be at different distances from the AP or have different obstacles in the transmission path, with correspondingly different path losses, each STA may use a different transmission power to achieve this equality of received signal strength at the AP. This transmission power for each STA may be determined by sending a series of 'trigger frames' from the AP (so-called because each trigger frame is intended to trigger a response from the STAs), and receiving a response to each trigger frame from each STA.

[0004] The TF may include a Target RSSI value that the AP expects to see for responses from the STA, as well as an AP TX power field indicating the transmit power at the AP (common for all STAs). Each STA could then calculate the path loss by determining its measured Received Signal Strength Indication (RSSI) for the received TF. By comparing the Target RSSI; and the estimated path loss, the STA may calculate a transmission strength it should use in its response that would achieve the desired Target RSSI at the AP. Each TF/response exchange would repeat this process without regard to previous values.

However, estimating the path loss involves inaccurate power measurement errors and normalization instability. So in previous implementations, for a particular STA there may be a variance of several decibels (dBs) from one uplink transmission to the next, even though no actual conditions changed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Some embodiments of the invention may be better understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:

[0006] Fig. 1 shows a diagram of a wireless communications network, according to an embodiment of the invention.

[0007] Fig. 2 shows a diagram of a wireless communications device, according to an embodiment of the invention.

[0008] Fig. 3 shows a timing chart of a communications exchange between an AP and multiple STAs, according to an embodiment of the invention.

[0009] Figs. 4A, 4B, 4C show a format for a trigger frame, according to an embodiment of the invention.

[0010] Fig. 5 shows a table of mapping for the Target RSSI field, according to an embodiment of the invention.

[0011] Fig. 6 shows a flow diagram of a method of controlling UL transmit power from a STA to an AP, according to an embodiment of the invention.

DETAILED DESCRIPTION

[0012] In the following description, numerous specific details are set forth. However, it is understood 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 an understanding of this description.

[0013] References to "one embodiment", "an embodiment", "example embodiment",

"various embodiments", etc., indicate that the embodiment s) of the invention so described may include particular features, structures, or characteristics, but not every embodiment necessarily includes the particular features, structures, or characteristics. Further, some embodiments may have some, all, or none of the features described for other embodiments.

[0014] The term "wireless" may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that communicate data by using modulated electromagnetic radiation through a non-solid medium. A wireless device may comprise at least one antenna, at least one radio, at least one memory, and at least one processor, where the radio(s) transmits signals through the antenna that represent data and receives signals through the antenna that represent data, while the processor(s) may process the data to be transmitted and the data that has been received. The processor(s) may also process other data which is neither transmitted nor received.

[0015] As used within this document, the term access point, or AP, is intended to cover devices that schedule and control, at least partially, wireless communications by other devices in the network. An AP may also be known as a network controller (NC), base station (BS), central point (CP), PBSS Control Point (PCP) or any other term that may arise to describe the functionality of a network controller.

[0016] As used within this document, the term "STA" is intended to cover those devices whose wireless communications are at least partially scheduled and controlled by an AP. A STA may also be known as a mobile station (MS), subscriber station (SS), user equipment (UE), or any other term that may arise to describe the functionality of a STA. In some embodiments, STAs may move during such communications, but movement is not required.

[0017] As used within this document, the term "communicate" is intended to include transmitting and/or receiving. This may be particularly useful in claims when describing the organization of data that is being transmitted by one device and received by another, but the claim can be interpreted to cover the functionality of either one of those devices. Similarly, the bidirectional exchange of data between two devices (both devices transmit and receive during the exchange) may be described as 'communicating', even if only the functionality of one of those devices is being claimed.

[0018] Various embodiments of the invention may be implemented fully or partially in software and/or firmware. This software and/or firmware may take the form of instructions contained in or on a non-transitory computer-readable storage medium. The instructions may be read and executed by the one or more processors to enable performance of the operations described herein. The instructions may be in any suitable form, such as but not limited to source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. Such a computer-readable medium may include any tangible non-transitory medium for storing information in a form readable by one or more computers, such as but not limited to read only memory (ROM); random access memory (RAM);

magnetic disk storage media; optical storage media; a flash memory, etc. The medium may also be external to the device that is to execute the instructions, with the intention that the instructions will eventually be loaded into, and executed by, that device.

[0019] Fig. 1 shows a diagram of a wireless communications network 100, according to an embodiment of the invention. In network 100, AP 110 may act as a network controller by coordinating and scheduling communications of the STAs 120, 130, 140, 150, and 160. Five STAs are shown in this network as an example, but other numbers of STAs may also be in the network. Each of devices 110, 120, 130, 140, 150, and 160 may have additional functionality beyond what is described in this document.

[0020] Fig. 2 shows a wireless communications device, according to an embodiment of the invention. In some embodiments, wireless communications device 200 may be an example of any of devices 110, 120, 130, 140, 150, or 160 in Fig. 1. Device 200 may include modules such as, but not limited to, processor 202, memories 204 and 206, sensors 228, network interface 220, antenna(s) 230, graphics display device 210, alphanumeric input device 212 (such as a keyboard), user interface navigation device 214, storage device 216 containing a machine readable medium, power management device 232, and output controller 234. Instructions 224 may be executed to perform the various functions described in this document. They are shown in multiple memories, though this is not a requirement.

Communications network 226 may be a wireless network external to the device, through which the device 200 may communicate with other devices.

[0021] Fig. 3 shows a timing chart of a communications exchange between an AP and multiple STAs, according to an embodiment of the invention. In Fig. 3, the downlink line indicates transmissions from the AP to the STAs, while the uplink line indicates

transmissions from the STAs to the AP. The sequence may begin with a trigger frame (TF), in which the AP may direct the STAs to respond. This TF may contain some common information for all the STAs, as well as some STA-specific information intended for each specific STA. A format for the TF will be shown in Figs. 4A, 4B, 4C.

[0022] Once the trigger frame has been received by the STAs, they may each respond simultaneously, using directional transmissions. Each transmission is labeled in Fig. 3 with the STA that it represents (STA 120, STA 130, STA 140, STA 150, STA 160 from Fig. 1). Five transmissions from five STAs are shown, but other embodiments may use other quantities of STAs. After completion of these transmissions from the STAs, a Block

Acknowledgement (BA) may be transmitted by the AP to indicate successful reception of all transmissions from the STAs.

[0023] The AP may then transmit another trigger frame to initiate another group of uplink transmissions from the STAs. Upon reception of the uplink responses, the AP may transmit another BA to signify successful reception of those responses. A Transmit

Opportunity (TXOP) may contain several of these TF/response/BA sequences, before another TXOP occurs.

[0024] In various embodiments of the invention, rather than have the STA recalculate transmit power for every UL transmission from the beginning, the first TF in a TXOP may have the STA calculate its uplink power in this way, but subsequent UL transmissions in the same TXOP may have their UL power calculated as a specified variance from the previous UL transmission. By starting with a single path loss measurement, and then using subsequent TF/response exchanges to incrementally approach a steady state value for the STA's transmit power, the error-prone technique of recalculating path loss for each TF/response exchange may be avoided.

[0025] Figs. 4A, 4B, 4C show a format for a trigger frame, according to an embodiment of the invention. Numerous fields are shown, but only those directly involved in this process are described. Fig. 4A shows the overall format for the trigger frame. Of particular note here is the Common Info field, which is shown in more detail in Fig. 4B and includes information of interest to all the STAs. The User Info field (one for each STA) is shown in more detail in Fig. 4C. The Common Info field includes an AP TX Power field, which shows the transmit power from the AP. This value should be the same for all the STAs. On the other hand, the User Info field shows a Target RSSI field, which is intended only for the STA associated with that User and contains an indication of a targeted value for a received signal strength of a response from the STA to the AP. These two fields (AP TX Power and Target RSSI) may be significant in the implementation of embodiments of the invention.

[0026] Fig. 5 shows a table of mapping for the Target RSSI field, according to an embodiment of the invention. In various embodiments of the invention, the Target RSSI field has been redefined. With 7 bits, the Target RSSI field may have 127 different values (0 - 127 decimal). In the particular mapping shown, a value in this field of 0-90 may equate to a transmission power of -110 dBm to -20 dBm, with a difference of 1 in this field being the equivalent of 1 dBm. Similarly, a value of 127 in this field may equate to the maximum transmit power for the assigned MCS.

[0027] By contrast, a value of 106-126 in this field may equate to a difference of -10 dB to +10 dB from the power of the previous transmission by this same STA. In the particular mapping shown, 106 may indicate a change of -10 dB, 116 may indicate no change, 126 may indicated a change of +10 dB, with a one-to-one distribution of mapping between those points. In this table, values 91-105 are not used and are reserved for possible future use. This technique may avoid a calculation of transmit power for any uplink transmission except the first in a TXOP.

[0028] Fig. 6 shows a flow diagram of a method of adjusting transmit power by a

STA in uplink transmissions, according to an embodiment of the invention. In some embodiments, multiple STAs may transmit simultaneously, but for simplicity only one STA is shown. The other STAs may follow the same procedure.

[0029] In flow diagram 600, at 605 the AP may create a TF. This TF may include a value for the AP's transmit power, a value for the MCS to be used, and an initial value in a Target RSSI field. This TF may then be transmitted at 610. Typically, this transmission may be to multiple STAs, with a separate MCS field and separate Target RSSI field for each STA. When a STA receives the TF, it may measure the received signal strength of the TF at 615, and subtract that from the AP TX transmit power value to determine path loss at 620. This path loss may then be used to determine the transmit power at 625 that will be used to transmit a response to the TF at 630, with the goal of having the RSSI of that signal, as measured at the AP, be equal to the Target RSSI value indicated in the TF.

[0030] At 635, the AP may measure the actual RSSI of the response received from the STA. At 640, this value may be used to determine a new desired RSSI value to send to the STA in the next TF. This desired RSSI may be affected by the actual measured RSSI received from other STAs at the same time as block 635.

[0031] Rather than send this desired RSSI in the Target RSSI field of the next TF, at

645 the AP may calculate a delta based on the difference between the actual measured RSSI at 635 and the Target RSSI of the previous TF as determined at 605. This delta value may then be put into the next TF in the field previously used for Target RSSI, and the TF transmitted to the STA at 650.

[0032] At 655, when the new TF is received by the STA, the STA may adjust its transmit power for the next uplink response by this delta amount. By not using a path loss estimation to determine its transmit power at 655, the STA may avoid the inaccuracies that are inherent in determining path loss. The response may then be transmitted to the AP at 630. The loop of 630-635-640-645-650-655 may be followed for each TF/response exchange (after the first) that take place in the same TXOP. In a typical scenario, the STA's transmit power may become closer and closer to its optimal value until the delta value equals zero for subsequent TFs in that TXOP. [0033] In some embodiments, a TXOP only lasts for 5 milliseconds (msec), so external conditions such as movement of the STA, or obstacles moving between the AP and a STA, are not likely to affect the stability of the communications link during a single TXOP.

[0034] EXAMPLES

The following examples pertain to particular embodiments:

[0035] Example 1 includes a wireless communications device having a processor, a memory, and a network interface, wherein: the network interface is to transmit a trigger frame (TF) in a wireless network, the TF to solicit a response from a STA, the TF containing a field to indicate a target value for a received signal strength indication (RSSI) of the response to be measured at the AP; the network interface is to receive the response from the STA and measure an actual RSSI value for the response; the processor and memory are to determine a difference between the target value for the RSSI and the actual RSSI value and place a value indicating the difference in the field; and the network interface is to transmit a second TF to the STA, the second TF containing the value indicating the difference.

[0036] Example 2 includes the device of example 1, wherein the device is configured to operate as either an OFDMA or MU MEVIO uplink device.

[0037] Example 3 includes the device of example 1, wherein: the network interface is to receive a second response to the second TF repeat the operation of measuring; the processor and memory are to repeat the operations of determining a difference and placing the difference in the field; and the network interface is to transmit a third TF.

[0038] Example 4 includes the device of example 1, wherein the TF has a Target

RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field is to contain the difference value in subsequent TFs in the TXOP. [0039] Example 5 includes a method of communicating in a wireless network, comprising: transmitting a trigger frame (TF) in a wireless network, wherein the TF is to solicit a response from a STA and the TF contains a field to indicate a target value for a received signal strength indication (RSSI) of the response to be measured at the AP; receiving the response from the STA; measuring an actual RSSI value for the response; determining a difference between the target value for the RSSI and the actual RSSI value; placing a value in the field indicating the difference; and transmitting a second TF to the STA, the second TF containing the value indicating the difference.

[0040] Example 6 includes the method of example 5, wherein the device is configured to operate as either an OFDMA or MU MEVIO uplink device.

[0041] Example 7 includes the method of example 5, further comprising: receiving a second response to the second TF; repeating the operations of measuring and determining for the second response; repeating the operation of placing in a third TF; and transmitting the third TF.

[0042] Example 8 includes the method of example 5, wherein the TF has a Target

RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field is to contain the difference value in subsequent TFs in the TXOP.

[0043] Example 9 includes a computer-readable non-transitory storage medium that contains instructions, which when executed by one or more processors result in performing operations comprising: transmitting a trigger frame (TF) in a wireless network, wherein the TF is to solicit a response from a STA and the TF contains a field to indicate a target value for a received signal strength indication (RSSI) of the response to be measured at the AP; receiving the response from the STA; measuring an actual RSSI value for the response; determining a difference between the target value for the RSSI and the actual RSSI value; placing a value in the field indicating the difference; and transmitting a second TF to the STA, the second TF containing the value indicating the difference.

[0044] Example 10 includes the medium of example 9, wherein the operations further comprise: receiving a second response to the second TF; repeating the operations of measuring and determining for the second response; repeating the operation of placing in a third TF; and transmitting the third TF.

[0045] Example 11 includes the medium of example 9, wherein the TF has a Target

[0046] Example 12 includes a wireless communications device having means to perform the operations of examples 5-8.

[0047] Example 13 includes a wireless communications device having a processor, a memory, and a network interface, wherein: the network interface is to receive a first trigger frame (TF) from an AP in a wireless network and determine a received signal strength of the received first TF; the processor and memory are to read an AP TX Power field from the first TF, determine a path loss, and determine a first transmit power level for a response to the first TF, the first transmit power level based at least partly on the AP TX Power and the path loss; the network interface is to transmit the response to the AP at the first transmit power level; the network interface is to receive a second TF from the AP, the second TF containing a delta value in a Target RSSI field; the processor and memory are to determine a second transmit power level by combining the delta value with the first transmit power level; and the network interface is to transmit a second response to the AP at the second transmit power level.

[0048] Example 14 includes the device of example 13, wherein the device is configured to operate as either an OFDMA or MU MEVIO uplink device. [0049] Example 15 includes the device of example 13, wherein the TF has a Target

[0050] Example 16 includes a method of communicating in a wireless network, comprising: receiving a first trigger frame (TF) from an AP in a wireless network and determining a received signal strength of the received first TF; reading an AP TX Power field from the first TF, determining a path loss, and determining a first transmit power level for a response to the first TF, the first transmit power level based at least partly on the AP TX Power and the path loss; transmitting the response to the AP at the first transmit power level; receiving a second TF from the AP, the second TF containing a delta value in a Target RSSI field; determining a second transmit power level by combining the delta value with the first transmit power level; and transmitting a second response to the AP at the second transmit power level.

[0051] Example 17 includes the method of example 16, wherein said transmitting the response and said transmitting the second response comprise transmitting in a manner compatible with either OFDMA or MU MEVIO uplink.

[0052] Example 18 includes the method of example 16, wherein the TF has a Target

RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field contains the difference value in subsequent TFs in the TXOP.

[0053] Example 19 includes a computer-readable non -transitory storage medium that contains instructions, which when executed by one or more processors result in performing operations comprising: receiving a first trigger frame (TF) from an AP in a wireless network and determining a received signal strength of the received first TF; reading an AP TX Power field from the first TF, determining a path loss, and determining a first transmit power level for a response to the first TF, the first transmit power level based at least partly on the AP TX Power and the path loss; transmitting the response to the AP at the first transmit power level; receiving a second TF from the AP, the second TF containing a delta value in a Target RSSI field; determining a second transmit power level by combining the delta value with the first transmit power level; and transmitting a second response to the AP at the second transmit power level.

[0054] Example 20 includes the medium of example 19, wherein said transmitting the response and said transmitting the second response comprise transmitting in a manner compatible with either OFDMA or MU MEVIO uplink.

[0055] Example 21 includes the medium of example 19, wherein the TF has a Target

[0056] Example 22 includes a wireless communications device having means to perform the operations of examples 16-18.

[0057] The foregoing description is intended to be illustrative and not limiting.

Variations will occur to those of skill in the art. Those variations are intended to be included in the various embodiments of the invention, which are limited only by the scope of the following claims.

Claims

CLAIMS What is claimed is:

1. A wireless communications device having a processor, a memory, and a network interface, wherein:

the network interface is to transmit a trigger frame (TF) in a wireless network, the TF to solicit a response from a STA, the TF containing a field to indicate a target value for a received signal strength indication (RSSI) of the response to be measured at the AP;

the network interface is to receive the response from the STA and measure an actual RSSI value for the response;

the processor and memory are to determine a difference between the target value for the RSSI and the actual RSSI value and place a value indicating the difference in the field; and

the network interface is to transmit a second TF to the STA, the second TF containing the value indicating the difference.

2. The device of claim 1, wherein the device is configured to operate as either an OFDMA or MU MEVIO uplink device.

3. The device of claim 1, wherein:

the network interface is to receive a second response to the second TF and repeat the operation of measuring;

the processor and memory are to repeat the operations of determining a difference and placing the difference in the field; and

the network interface is to transmit a third TF.

4. The device of claim 1, wherein the TF has a Target RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field is to contain the difference value in subsequent TFs in the TXOP.

5. A method of communicating in a wireless network, comprising:

transmitting a trigger frame (TF) in a wireless network, wherein the TF is to solicit a response from a STA and the TF contains a field to indicate a target value for a received signal strength indication (RSSI) of the response to be measured at the AP;

receiving the response from the STA;

measuring an actual RSSI value for the response;

determining a difference between the target value for the RSSI and the actual RSSI value;

placing a value in the field indicating the difference; and

transmitting a second TF to the STA, the second TF containing the value indicating the difference.

6. The method of claim 5, wherein the device is configured to operate as either an OFDMA or MU MEVIO uplink device.

7. The method of claim 5, further comprising:

receiving a second response to the second TF;

repeating the operations of measuring and determining for the second response; repeating the operation of placing in a third TF; and

transmitting the third TF.

8. The method of claim 5, wherein the TF has a Target RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field is to contain the difference value in subsequent TFs in the TXOP.

9. A computer-readable non-transitory storage medium that contains instructions, which when executed by one or more processors result in performing operations comprising:

receiving the response from the STA;

measuring an actual RSSI value for the response;

placing a value in the field indicating the difference; and

10. The medium of claim 9, wherein the operations further comprise:

receiving a second response to the second TF;

transmitting the third TF.

11. The medium of claim 9, wherein the TF has a Target RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field is to contain the difference value in subsequent TFs in the TXOP.

12. A wireless communications device having means to perform the operations of claims 5- 8.

13. A wireless communications device having a processor, a memory, and a network interface, wherein:

the network interface is to receive a first trigger frame (TF) from an AP in a wireless network and determine a received signal strength of the received first TF;

the processor and memory are to read an AP TX Power field from the first TF, determine a path loss, and determine a first transmit power level for a response to the first TF, the first transmit power level based at least partly on the AP TX Power and the path loss; the network interface is to transmit the response to the AP at the first transmit power level;

the network interface is to receive a second TF from the AP, the second TF containing a delta value in a Target RSSI field;

the processor and memory are to determine a second transmit power level by combining the delta value with the first transmit power level; and

the network interface is to transmit a second response to the AP at the second transmit power level.

14. The device of claim 13, wherein the device is configured to operate as either an OFDMA or MU MEVIO uplink device.

15. The device of claim 13, wherein the TF has a Target RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field is to contain the difference value in subsequent TFs in the TXOP.

16. A method of communicating in a wireless network, comprising:

receiving a first trigger frame (TF) from an AP in a wireless network and determining a received signal strength of the received first TF;

reading an AP TX Power field from the first TF, determining a path loss, and determining a first transmit power level for a response to the first TF, the first transmit power level based at least partly on the AP TX Power and the path loss;

transmitting the response to the AP at the first transmit power level;

receiving a second TF from the AP, the second TF containing a delta value in a Target RSSI field;

determining a second transmit power level by combining the delta value with the first transmit power level; and

transmitting a second response to the AP at the second transmit power level.

17. The method of claim 16, wherein said transmitting the response and said transmitting the second response comprise transmitting in a manner compatible with either OFDMA or MU MEVIO uplink.

18. The method of claim 16, wherein the TF has a Target RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field contains the difference value in subsequent TFs in the TXOP.

19. A computer-readable non-transitory storage medium that contains instructions, which when executed by one or more processors result in performing operations comprising:

transmitting the response to the AP at the first transmit power level;

transmitting a second response to the AP at the second transmit power level.

20. The medium of claim 19, wherein said transmitting the response and said transmitting the second response comprise transmitting in a manner compatible with either OFDMA or MU MEVIO uplink.

21. The medium of claim 19, wherein the TF has a Target RSSI field to contain the target value in an initial TF transmitted in a Transmit Opportunity (TXOP), and the Target RSSI field contains the difference value in subsequent TFs in the TXOP.

22. A wireless communications device having means to perform the operations of method claims 16-18.