Title of Invention

METHOD AND APPARATUS FOR TRANSMITTING MESSAGES IN A WIRELESS COMMUNICATION SYSTEM

Abstract

The present invention relates to techniques to reduce transmit power required for transmission of messages from an access terminal to reduce interference to transmissions from other access terminals. In one aspect, messages to be transmitted are d~fmed and/or coded such that they may be detected at different received signal qualities. The codewords may be defined having different distances to their nearest codewords. In another aspect, messages to be transmitted are assigned to different points in a signal constellation, with the points being located such that they may be received at different signal qualities. Codewords that may be received at a lower signal quality ,may be assigned to messages more likely to be transmitted at higher transmit power levels (e.g., when the access terminal is located further away) or to more frequently transmitted messages.

Full Text

METHOD AND APPARATUS FOR TRANSMITTING MESSAGES IN A WIRELESS COMMUNICATION SYSTEM BACKGROUND In a wireless communication system, the transmit power required tor a transmi5sion is dependent on the propagation (or path) loss between a transmitting entity (e.g., an access terminal) and a receiving entity (e.g., an access point). As an access terminal moves further away from the access point, the path loss typically increases. Consequently, more transmit power is required so that the transmission can be received at the required signal quality for the desired level of performance (e.g., ore percent frame error rate). However, the higher transmit power for this transmission causes more interference to the transmissions from other access terminals. The higher transmit power also causes faster depletion of battery power on mobile wireless devices. There is therefore a need ix\ the art for a way to provide HDR services that mirimizes interference and depletion of battery power. SUMMARY The disclosed embodiments provide techniques to reduce the amount of transmit. power required for transmission of selected messages from an access terminal. In a first aspect, the reduction in transmit power is based on the expected path loss associated with the reverse link, thus tending to extend the operatir g range of an HDR access terminal, and at the same time decreasing reverse link interference in adjacent cells. In another aspect, the reduction in transmit; power is based on the relative frequency with which an HDR access terminal is expected to send each type of message thus tending to minimize reverse link interference in a serving cell- Both of these aspects also have the benefit of tending to extend battery life of a mobile wireless device such as a mobile HDR access terminal. The techniques described herein can also be applied to forward link transmissions from an access point. Various other aspects of the invention are also presented. The invention provides methods and system elements that implement various aspects, embodiments, and features of the invention, as described in further detail below. BRIEF DESCRIFIION OF THE DRAWINGS The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: FIG. 1 is a diagram of a wireless communication system that supports a number of users, and which can implement various aspects of the invention; FIG. 2 is a diagram of a packet trammission scheme used in the HDR system; FIG. 3 is a block diagram of a reverse link architecture employed in the HDR system and capable of transmitting Data Rate Control (DRC) messages and other information; PIGS. 4A and 4B are diagrams graphically illustrating an alphabet of codewords having equal distance and unequal distances, respectively, to the nearest codewords; HGS. 5A and 5B are diagrams of two signal constellations having points salected from different modulation formats; FlG. 6A is a block diagram of an embodiment of an access terminal, in accordance with various aspects of the invention; and FIG. 6B is a block diagram of an embodiment of a portion of a transmit (TX) data processor, which may be used to process DRC messages for various schemes described herein, DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS MG- 1 is a diagram of a wireless communication system 100 that supper a number of users, and which can implement various aspects of the invention- System 100 may be designed to support one or more CDMA standards and/or designs (e.g., the cdma2000 standard, the HDR specification). For simplicity, system 100 is shown to include three access points 104 (which may also be referred to as base stations) in communication with two access terminals 106 {which may also be referred to as remote terminals or mobile stations). The access point and its coverage area are often collectiveiy referred to as a "cell". Depending on the CDMA system being implemented, each access tenninal 106 may communicate with one (or possibly more) access points 104 on the forward link at any given moment and may communicate with one or more access points on the reverse link depending on whether or not the access terminal is in soft handoff. The forward link (i.e., downlink) refers to transmission from the access point to the access terminal, and the reverse link (i.e., uplink) refers to transmission from the access terminal to the access point. In a CDlvlA system, the cells may be operated on the same frequency band (i.e., with a frequency reuse of one, or K=l) to achieve better utilization of the available system resources. In this case, the transmission from each transmitting entity (e.g., access terminal) acts as interference to the transmissioas from other transmitting-entities. To minimize interference and increase system capacity on their verse link, the transmit power of each transmitting access terminal is controlled such that a desired level of performance (e.g., one percent frame error rate, or 1% FER) is achieved while minimiing the amount of interference to other transmitting access terminals. This transmit power adjustment is achieved by a power control loop maintained for each transmitting access terminaK The power control loop adjusts the transmit pov/er level of the access terminal such that a transmission is receiv ed by the access point at a target signal quality (i.e., a particular signal-to-noise-plus-interference, C/I) needed for the desired level of performance. In the example shown in FIG. 1. access terminal 106a is located near access point l04a, and access terminal 106b is located near the cell boundaries of Access points 104a, 104b, and 104c, For this example, botl\ access terminals are vising the same coding and modulation to transmit. Since access terminal 106a is located (relatively) close to access point 104a. its transmit power rnay be adjusted to a (relatively) low level to achieve the desired level of performance at access point lC4a* This low* transmit power is possible since the path loss is approximately proportional to the 4th law of the distance between the transmitting and receiving entities (i.e. path loss (distance)"^). Because of the low transnut power level and further becaxise of the greater distances between access terminal lD6a and access points 104b and 104c, the transmL«ision from access terminal 206a causes little interference to other rrat\sm:ssiori$ received at access points 104b and lC4c- In contrast, access terminal 106b is located further awav from access points 104a, l04b, and lC4c- Due to the longer distances to these access points, the transmit power of access terminal 106b is likely to be adjusted to a high level to achieve the same level of performance. Because of the high transnut power level and the shorter distances between access terminal lG6b and access pomts l04b and 104c, the transmission from access terminal 106b is likely to cause more interference to other transmissions received at access points l04b and l04c. As seeh by the above example, when an access terminai is located near an access point, less transnut power is required for a transmission, and the transmis*-xon causes litde interference at other access points. In contrast, when ail access terminal is located further av/a)' from an access pointy more transmit points in a signal constellation. In such an aspect, duin refers to the distance Control (DRC) channel defined for the reverse link in a High Data Rate (HDR) example packet shown in FIG. 2. For each slot, the access terminal receives and The 8-bit DRC codeword is then repeated twice in block 334 to generate 16 transmitted at higher transmit power levels, and codewords from access As shown by the above relationships, at least some (and not necessanly all) of shown by the above relationships, at least some (and not necessarily all) of In the above-described HDK system, the 8-bit DRC code word is I QAM is employed and four different messages are assigned to points 514a, 2, the next most likely DRC value of 1 is assigned with a codeword having the receiver unit 622 conditions (e.g., filters, amplifies, and downconverts) and signal constelation, signal point mapping element 666 maps the received CDMA standards and/or designs. WHAT IS CLAIMED IS; CLAIMS 1. In a wireless communication systum, a method for transmitting a control message from a first entity to a second entity, comprising: at the first entity, measuring at least one characteristic of a channel through which a signal is received from the second entity to produce channel state information; forming the control message indicative of the channel state information; and transmitting the control message from the first entity to the second entity at a particular power level determined based at least in part on the control message. 2. The method of claim 1, wherein the control message comprises a particular codeword selected from among a plurality of possible codewords. 3. The method of claim '2, wherein the power level is determined based on a minimum; distance of the selected codeword. 4. The method of claim 2, wherein the power level is determined based on an expected frequency of the selected codeword being transmitted, 5. The method of claim 2, wherein the power level is determined based on a particular number of times the selected codeword is repeated for a trarsmission- 6. The method of claim 1, wherein the control message is a data rate control message indicative of a rate for a data transmission requested from the second entity. 7. The method of claim 1, wherein the at least one characteristic comprises a carrier-to-noise-plus interference ratio (C/I). 8. The method of claim 1, wherein the control message is selected from among a plurality of data rate control messages. 9. The method of claim 2, wherein the selected codeword has a minimum distance based on quality- of the channel. 10. The method of claim % wherein the selected codeword has a mininum distance based on frequency in which the control message is transmitted. 11. In a wireless communication system, a method for transmitting a message from a first entity to a second entity, comprising; identifying a codeword associated with the message, wherein the identified codeword is one of a plurality of codewords defined for an alphabet, and wherein at least two codewords in the alphabet have unequal distances to their nearest codewords; and transmitting the identified codeword from the first entity to the second entity. 2. The method of claim 11, further compusing: deternuning a transmit power level for the identified codeword, and wherein the identified codeword is transmitted at the determined transmit power level. 13- The method of claim 12, wherein the transmit power level for the ic entified codeword :s based at least in part on the distance of the identified codeword to its nearest codeword 14. The method of claim 12, wherein the transmit power level for the identified codeword is determined to achieve a particular level of performance. 15. The method of claim 14, wherein the particular level of performance is approximately one percent frame error rate or better. 16. The method of claim 11, wherein the message to be transmitted is one of a plurality of possible messages, and wherein the plurality of codewords m the alphabet are assigned to the plurality of possible messages in accordance with a particular assignment scheme. 17. The method of claim 16, wherein the plurality of codewords in the alphabet are assigned to the plurality of possible messages such that messages more likely to be transmitted at higher transmit power levels are assigned with codewords having larger distances to their nearest codewords. 18. The method of claim 16, wherein the plurality of codewords in the alphabet are assigned to the plurity of possible messages such that messages more likely to be transmitter are assigned with codewords having larger distances to their nearest codewords- 19. The method of claim 11, wherein the 5dphabet includes N codewords having minimum distances of d1 through d2, and wherein the minimum distanctes conform to the following: d1 > d22:... > dj,3.j >d,, and iy > d_v. 20. The method of claim 11/wherein the message identifies a particular data rate for a data transmission requested by the first entity from the second entity, 11. The method of claim 11, wherein the first entity is an access terminal in the wireless communication system. 22. The method of claim 11, wherein the wireless communication system is a CDMA system. 23. In a wireless comimicatioa system, a method for transmitting a aiessage from a first entity to a second entity, comprising: identifying a codeword associated with the message wherein the "dentified codeword is one of a plurality of codewords defined for an alphabet, and wherein at least two codewords in the alphabet may be transmitted with dil'ferenl amounts of energy for a particular level of performance under similar link condition; determining a transmit power level for the identified codeword; and transmitting the identified codeword at the determined transmit power level. 24. The method of claim 23, wherein at least two codewords in the alphabet have unequal distances to their nearest codewords. 25. The method of claim 23, wherein the plurality of codewords in the alphabet are associate with a plurality of points in a signal constellation, and wherein at least two points in the signal constellation have unequal distances to iheir nearest codewords. 26. The method of claim 25, wherein the plurality of points in the signal constellation are selected from points in signal constellatioris for quadrature phase shift keying (QPSK), M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM), or a combination thereof- 27. The method of claim 23, wherein at least two codewords in the alphabet have unequal lengths. 28. The method of claim 27, further comprising: encoding the identified codeword in accordance with a particular coding scheme. 29. The method of claim 23, wherein the message to be transmitted is cne of a plurality of possible messages, and wherein the plurality of codewords in the alphabet are assigned to the pluralit of possible messages such that messages more likely to be transmitted at higher transmit power level are assigned with codewords requiring lower transmit power to achieve the particular level of performance. 30. The method of claim 23, wherein the message to be transmitted is one of a plurality of possible messages, and wherein the plurality of codewords in the alphabet are assigned to the plurality of possible messages such that messages more likely to be transmitted are assigned with codewords requiring less transmin power to achieve the particular level of performance. 31. An access terminal in a wireless communication system, comprising: a receiver for receiving a signal from an access network and determining at least one characteristic of a forward link channel through which the signal is received; a data processor configured to form a control message indicative of a state of the forward link channel; and a transmitter unit configured to transmit the control message at a particular transmit power determined based at least in part on the control message. 32, An access terminal in a wireless communication system, comprising: a data processor configured to receive and process a codeword for a message wherein the codeword is one of a plurality of codewords defined for an alphabet, and wherein at least two codewords in the alphabet may be transmitted with different amounts of energy for a particular level of performance under similar link condition; and a transmitter unit operatively coupled to the data processor and configured to transmit the processed codeword. 33. The access point of claim 32, further comprising: a controller operatively coupled to the data processor and configured to provide a signal indicative of transmit power level to be used for the processed codeword, 34. The access point of claim 32, further comprising: a signal quality measurement unit configured to receive samples for a received signal and to deternrune a received signal quality of signals transmitted from one or more transmitting sources, and wherein the processed codeword is transmitted at a power level based in part on the received signal quality of a transmitting source to which the processed codeword is transmitted. 35. A communication unit in a wireless communication system, comprising: a receiver configured to receive a signal from a transmitting source and determire at least one characteristic of a communication link through which the signal is received; a data processor configured to form a message indicative of a state of the communication link; and a transmitter unit configured to transmit the message at a particular transmit power determined based at least in part on the message. 36 An access point in a CDMA system comprising the communication unit of chaim 35. A wireless communication system, substantially as hereinabove described and illustrated with reference to the accompanying drawings.

Documents:

1232-chenp-2003 claims-duplicate.pdf

1232-chenp-2003 description (complete) granted.pdf

1232-chenp-2003 description (complete)-duplicate.pdf

1232-chenp-2003 drawings-duplicate.pdf

1232-chenp-2003-assignement.pdf

1232-chenp-2003-claims.pdf

1232-chenp-2003-correspondnece-others.pdf

1232-chenp-2003-correspondnece-po.pdf

1232-chenp-2003-description(complete).pdf

1232-chenp-2003-drawings.pdf

1232-chenp-2003-form 13.pdf

1232-chenp-2003-pct.pdf