Power and data rate control in a multi-rate wireless system

Transmit parameters are adjusted for a wireless device based on link margin. In at least one embodiment, link margin is calculated as a difference between a received power level and receiver sensitivity.

FIELD OF THE INVENTION

The invention relates generally to wireless communication and, more particularly, to methods and structures for controlling transmit parameters within a wireless system.

DETAILED DESCRIPTION

FIG. 1is a block diagram illustrating an example wireless network arrangement10in which embodiments of the present invention may be practiced. As illustrated, the wireless network arrangement10may include a wireless access point12and a number of wireless client devices14,16,18. The wireless access point12provides wireless access to the corresponding network for the wireless client devices14,16,18. Although illustrated with three wireless client devices, it should be appreciated that any number of client devices may access a network through an access point at a particular time. Each of the wireless client devices14,16,18may transmit data to the access point12and receive data from the access point12through a corresponding wireless channel. As illustrated, each of the client devices14,16,18being serviced by the access point12may be located at a different distance from the access point12than the other client devices. Also, one or more of the client devices14,16,18may be in motion while it is communicating with the access point12. As a client device gets farther away from the access point12, the quality of the corresponding wireless link may decrease. For example, the signal-to-noise ratio (SNR) of a received signal will typically decrease as the signal strength of the signal grows smaller due to the increased distance. Also, other events may occur that can adversely affect the quality of a wireless link. For example, a client device may move to a location that is partially blocked from the access point12(e.g., behind a wall, etc.) or an object or individual may move to a location that is between the client device and the access point.

In many wireless networking standards, the transmit power level of the client devices remains fixed during network operation. Thus, client devices that are relatively close to an access point may transmit at the same power level as client devices that are relatively far from the access point. The client devices that are close may therefore transmit at a power level that is much greater than necessary for accurate communication. Likewise, the client devices that are far away from the access point (and/or client devices that are blocked in some manner) may not generate a strong enough signal to reach the access point. To overcome such problems, power control methods have been proposed to allow the transmit power level of client devices to adapt to the present condition of the channel. Most of the wireless LAN devices now available, however, do not have transmit power control capabilities. The present invention relates to techniques and structures that allow open loop control methods to be used within a wireless network or other wireless communication system to control transmit parameters therein. In an open loop approach, the transmit parameters of a wireless device can adapt to present channel conditions without knowing related information about the other side of the communication.

In at least one embodiment of the present invention, the transmit parameters of a wireless device are adapted based upon a link margin determined for the device. That is, a link margin may be calculated for a wireless device and used to select, for example, a transmit power level, a transmit data rate, and/or other transmit parameter values for the device. As used herein, the phrase “wireless device” is intended to encompass any type of device that has wireless communication capability and may include, for example, a wireless client device for use in a wireless network, a laptop, desktop, palmtop, or tablet computer having wireless networking capability, a personal digital assistant (PDA) having wireless networking capability, a pager, a cellular telephone or other handheld wireless communicator, a wireless network interface card (NIC) or other wireless network interface structure, and/or others.

FIG. 2is a block diagram illustrating an example wireless device20in accordance with an embodiment of the present invention. As illustrated, the wireless device20may include one or more of: a wireless transceiver22, a controller24, a user interface26, a link margin determination unit28, a transmit data rate determination unit30, a transmit power determination unit32, a memory34, and an antenna36. The wireless transceiver22is operative for supporting wireless communication with a remote wireless entity (e.g., a wireless access point or other wireless device) via antenna36. The transceiver22may be configured to operate in accordance with one or more wireless standards which may include, for example, the IEEE 802.11 wireless networking standard (ANSI/IEEE Std 802.11-1999 Edition) and its related standards (e.g., the IEEE 802.11a standard (IEEE Std 802.11a-1999), etc.), other wireless networking standards, cellular standards, and/or others. The antenna36may be any type of antenna including, for example, a dipole, a patch, a helical antenna, an antenna array, and/or others. In at least one embodiment, multiple antennas are provided in an antenna diversity arrangement. The controller24is operative for controlling the operation of the wireless device20. The user interface26provides an interface between a user of the wireless device20and the controller24.

The link margin determination unit28calculates a link margin for the wireless device20to be used in determining appropriate transmit parameters for the device20. Link margin may be defined as a relationship between a current received power and a power that is required to achieve a predetermined performance level or communication quality within a communication link. In at least one embodiment of the present invention, link margin is determined by calculating a difference between a present received power level and a receiver sensitivity of the wireless device20. The link margin determination unit28may obtain an indication of a present received power level from, for example, the transceiver22. In an IEEE 802.11 compatible device, for example, the link margin determination unit28may obtain a received power level (RPL) parameter value from the transceiver22for use in determining link margin. The link margin determination unit28may estimate a receiver sensitivity value for the transceiver22, use a factory calibrated value, or pre-determine receiver sensitivity in some other fashion. In one possible approach, the link margin determination unit28obtains a data rate of a signal received by the transceiver22(e.g., a beacon signal received from an access point, etc.) and then selects a receiver sensitivity value for use in calculating link margin from a table based on the data rate. The table may be stored, for example, within the memory34. Table I below is an example of a table that may be used for this purpose.

Once values have been obtained for the received power level and the receiver sensitivity, the link margin determination unit28may calculate the link margin by determining the difference of the two values. Other techniques for calculating link margin (e.g., determining a ratio, etc.) may alternatively be used. The link margin value may then be delivered to the transmit data rate determination unit30which may use the link margin value to determine a transmit data rate for the wireless device20. In general, the higher the calculated link margin, the higher the data rate that will be selected by the transmit data rate determination unit30. In one possible approach, a number of link margin ranges are defined and each range is assigned a corresponding transmit data rate value. The transmit data rate determination unit30may then determine which range the calculated link margin value falls within and deliver the corresponding transmit data rate value to the transceiver22.

The transmit power determination unit32may also receive an indication of the link margin and use it to adjust a transmit power level for the wireless device20. In at least one embodiment, if the link margin is greater than a predetermined threshold value, the transmit power determination unit32may enter a power reduction loop that is designed to reduce the transmit power of the wireless device20to a level that is lower but still adequate to support wireless communication. The link margin determination unit28, the transmit data rate determination unit30, and the transmit power determination unit32may each operate in a continuous or repetitive fashion so that the transmit power level and/or transmit data rate may adapt to the changing channel conditions between the wireless device20and the remote wireless entity. In at least one embodiment of the present invention, only a single transmit parameter is adjusted based on link margin. Thus, the wireless device20may be modified to include only the transmit data rate determination unit30or only the transmit power determination unit32.

It should be appreciated that the individual blocks illustrated inFIG. 2(and in other block diagrams herein) may be functional in nature and do not necessarily correspond to discrete hardware elements. For example, in at least one embodiment, two or more of the blocks are implemented in software within a single (or multiple) digital processing device(s). The digital processing device(s) may include, for example, a general purpose microprocessor, a digital signal processor (DSP), a reduced instruction set computer (RISC), a complex instruction set computer (CISC), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and/or others, including combinations of the above. Hardware, software, firmware, and/or hybrid implementations may be used. With reference toFIG. 2, in at least one embodiment, the link margin determination unit28, the transmit data rate determination unit30, and/or the transmit power determination unit32are implemented within the controller24.

FIG. 3is a flowchart illustrating an example method40for use in controlling transmit parameters within a wireless device in accordance with an embodiment of the present invention. First, the data rate of a signal received by the wireless device is obtained (block42). This signal may include, for example, a beacon signal received from a wireless access point (when implemented within a wireless network) or some other form of control signal. A received power level indication is then obtained for the wireless device (block44). Any form of received power level indication may be used. In an IEEE 802.11 compatible device, for example, an RPL value may be obtained as the received power level indication. A receiver sensitivity may then be determined for the communication device based on the receive data rate previously obtained (block46). This may be performed using, for example, a look up table, an equation, or in some other manner. Other methods for determining receiver sensitivity may alternatively be used.

Link margin is next calculated using the received power level indication and the receiver sensitivity (block48). In at least one approach, the link margin is calculated as a difference between the received power level indication (e.g., RPL value) and the receiver sensitivity. Other techniques for calculating link margin (e.g., calculating a ratio, etc.) may alternatively be used. One or more transmit parameters may then be adjusted for the wireless device based on the calculated link margin (block50). For example, in at least one approach, the transmit data rate of the wireless device is adjusted based on link margin. In another approach, the transmit power level is adjusted. In yet another approach, both transmit data rate and transmit power level are adjusted. Other transmit parameters and/or combinations of transmit parameters may also be adjusted based on calculated link margin. The method40may be repeated at, for example, predetermined times or predetermined intervals (or in some other manner) during device operation so that the transmit parameters may adapt over time to a possibly changing channel.

FIG. 4is a flowchart illustrating an example method60for use in selecting a transmit data rate based on a link margin value (D) in accordance with an embodiment of the present invention. The method60may be used, for example, as part of the method40ofFIG. 3or within other transmit parameter control procedures. After the method60begins (block62), it is first determined whether the link margin (D) falls within a first range 0<D<3 (block64). If so, the transmit data rate is set to 9 Mega bits per second (Mbps) (block66). If not, it is next determined whether the link margin falls within a second range 3≦D<5 (block68). If so, the transmit data rate is set to 12 Mbps (block70). If not, it is next determined whether the link margin falls within a third range 5≦D<8 (block72). If so, the transmit data rate is set to 18 Mbps (block74). If not, it is next determined whether the link margin falls within a fourth range 8≦D<12 (block76). If so, the transmit data rate is set to 24 Mbps (block78). If not, it is next determined whether the link margin falls within a fifth range 12≦D<16 (block80). If so, the transmit data rate is set to 36 Mbps (block82). If not, it is next determined whether the link margin falls within a sixth range 16≦D<18 (block84). If so, the transmit data rate is selected as 48 Mbps (block86). If not, the transmit data rate is selected as 54 Mbps (block88) and it is then determined whether the link margin falls within a seventh range D>21 (block90). If so, a power reduction loop is initiated to reduce the transmit power level of the wireless device (block92). If not, the method60is terminated (block94).

In the method60described above, the individual transmit data rates (i.e., 6, 9, 12, 18, 24, 36, 48, and 54 Mbps) that are used are the data rates that are specified within the IEEE 802.11a wireless networking standard. It should be appreciated that a similar approach may be used in systems using other wireless standards and other data rates. In IEEE 802.11a, 54 Mbps is the maximum specified data rate. However, the method60does not have to use the maximum data rate specified in the corresponding standard. For example, it may be determined that a wireless device implementing IEEE 802.11a is not to exceed 24 Mbps (e.g., if link distances are known to be long). In such a case, the method60may be modified so that 24 Mbps (block78) is the maximum data rate. The method60may then go to the power reduction loop when, for example, D>15. In at least one embodiment of the invention, the maximum data rate may be a user specified value. As will be appreciated, the number of link margin ranges, the boundaries of the individual ranges, and the specific data rate values may vary from implementation to implementation.

FIG. 5is a flowchart illustrating an example method100for implementing a transmit power reduction loop in a wireless device in accordance with an embodiment of the present invention. The method100may be used, for example, as part of the method60ofFIG. 4or within other transmit parameter control procedures. After the method100has initiated (block102), the transmit power level of the subject communication device is reduced by 3 deciBels (dB) (block104). A signal is transmitted and it is determined whether an acknowledgement signal (ACK) has been received in response to the transmission (block106). If so, the transmit power level is again reduced by 3 dB (block104) and the ACK is again checked (block106). This is repeated until an ACK is no longer detected (block106). At this point, the transmit power level is increased by 6 dB (block108). A signal is again transmitted and it is determined whether an acknowledgement signal (ACK) is properly returned (block110). If so, the method100is terminated with the present transmit power level (block112). If an ACK is not returned, the transmit power level is increased by 3 dB (block114), another signal is transmitted, and the ACK is again checked (block110). This is repeated until an ACK signal is received by the wireless device, at which time the method100terminates (block112). It should be appreciated that the method100ofFIG. 5is merely an example of one type of power reduction loop that may be implemented in accordance with the present invention. Many alternative power reduction schemes may also be used.

The principles of the present invention may be implemented within any wireless system including, for example, wireless networks, wireless communication systems, and/or others. The inventive principles may also be used in wireless systems following any of a wide range of different wireless standards.

In the foregoing detailed description, various features of the invention are grouped together in one or more individual embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of each disclosed embodiment.