Patent Application
20090312044
The present invention relates, in general, to wireless communications systems and, more particularly, to channel estimation, scheduling, and resource allocation using pilot channel measurements.
Many modern wireless communications systems allocate system resources based, at least in part, on pilot channel measurements. For example, scheduling decisions are often based on pilot channel measurements in current third generation (“3G”) networks such as high speed data packet access (“HSDPA”) networks, and networks based on the Institute of Electrical and Electronics Engineers (“IEEE”) 802.16e specification, which is incorporated herein by reference. In such systems, base stations or other network nodes (sometimes referred to herein generically as “transmitters”) transmit a pilot channel. User equipment or another node in the network (sometimes referred to herein generically as “receivers” or “access terminals (“AT”)”) scan the various signals in its given area attempting to detect or decode each signal into a recognizable pilot channel. Once a pilot channel is found, the receiver, among other things, evaluates the strength or the quality of the pilot channel(s), or derives a channel quality indicator (“CQI”) using one or more pilot channels, and reports some result of that test or derivation back to the transmitter.
Using the pilot channel measurement made available to the transmitter, the transmitter may then allocate resources for communicating with the receiver. Thus, in such systems, resource allocation is based on some kind of feedback or closed-loop control provided by the receiver. Explicit feedback is typically used in frequency division duplex (“FDD”) systems, wherein channel reciprocity does not hold. However, in time division duplex (“TDD”) systems, or in systems wherein channel reciprocity holds, the pilot channel measurements made on one duplex direction may be used at least partially in allocating transmission resources in another duplex direction. In such systems, closed-loop control, or feedback, and subsequent resource allocation is made within the same transceiver unit, although it is also possible to obtain feedback from another spatially separate receiver. In TDD systems, such feedback could include information related to interference measurements at the receiver, or to information on available resources.
Problems arise in these systems because making such resource allocations or optimizations in pseudo-randomly time-varying channels is extremely complicated and threatens to increase the complexity at the receiver level. The goal in developing wireless system advances is typically to assure that simplicity is maintained at the AT and at the system level. For example, the measurements at the AT should be scalable in the sense that when more resources are added to a transmitter, the operations in the AT remain essentially unaffected.
Pseudo-random channels typically occur, for example, in connection with random transmit beam forming from a transmitter to a receiver or AT. Random transmit beam forming is generally used as an effective technique for increasing channel selectivity either in the frequency or time domains. In the time domain, it can be used, for example, in converting a static channel into a time varying channel, which is generally better for delay differentiated scheduling, or for services that require strict delay requirements, as the number of consecutive poor channel conditions is reduced. Thus, problems arise in determining suitable transmission channels or resources in a wireless multi-antenna system in order to maintain improved performance while keeping comparable simplicity at the AT and system level.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of the present invention, which include a transmitter for selecting or estimating a channel, beams, power information, modulation information, coding information, or transport format (including bit allocation and the like), for example, and methods for feeding back information or measurements for such purposes.
The representative methods may also include methods for a wireless communication system that includes forming one or more beam patterns at a first time by a transmitter, where the beam patterns are made up of at least a first set of beam patterns used to transmit data during the first time or channel resource, and a second set of at least partly different beam patterns (compared to the first set) provisioned to transmit data during a subsequent time or channel resource. The methods also include transmitting a pilot signal on a plurality of the beam patterns. An indicator is received from one or more receivers, wherein the indicator relates at least partly to one of the beam patterns or transmission resources of the second set. The transmitter will then determine transmission scheduling and/or resource allocation based, at least in part, on the indicator.
In accordance with another embodiment of the present invention, a transmitter includes a beam forming module configured to direct formation of one or more radio frequency (“RF”) beam patterns, a pilot module configured to generate pilot signals transmittable using the RF beam patterns, a decoder configured to decode feedback signals from one or more receivers, wherein the feedback signals relate to channel characteristics of some of the RF beam patterns, a scheduling module configured to schedule data transmission to the one or more receivers based at least in part on the decoded feedback signal, and a resource allocation module configured to allocate ones of the one or more RF beam patterns for the data transmission. The transmitter also includes a processor configured to run each of the beam forming module, the pilot module, the scheduling module, and the resource allocation module.
In accordance with a further embodiment of the present invention, a receiver is made up from an antenna configured to receive one or more beam patterns transmitted by a transmitter, wherein the one or more beam patterns include at least a first set of beam patterns used to transmit data during a first time, and a second set of beam patterns potentially used to transmit data during a subsequent time. It also includes a processor, a decoder configured to decode one or more pilot signals transmitted on the beam patterns, a decision module run on the processor and configured to determine the quality of the beam patterns using pilot measurements and possibly also resource information, a quality indicator module run on the processor and configured to generate at least one quality indicator based on results output from the decision module, wherein the quality indicator relates to one of the one or more beam patterns, and a signaling unit configured to signal the quality indicator before transmission to the transmitter.
In accordance with a further embodiment of the present invention, a computer program product has a computer readable medium with computer program logic recorded thereon. The computer program product includes code for forming one or more beam patterns by a transmitter at a first time, wherein the beam patterns are made up of at least a first set of beam patterns used to transmit data during the first time, and a second set of beam patterns used to transmit data during a subsequent time. It also includes code for transmitting a pilot signal on each of the beam patterns, code for receiving an indicator from one or more receivers, wherein the indicator relates to one of the beam patterns having a high channel quality, and code for determining transmission scheduling and/or resource allocation based, at least in part, on the indicator.
One advantage of the various embodiments of the present invention is that each AT or user equipment already knows the channel quality or channel performance (e.g., throughput and the like) of a future time slot during signal reception. Another advantage of the present invention is that the transmitter can select whichever time slot and/or beam pattern shows a better performance characteristic, whether that is the current data transmission beam or a future data transmission beam. Thus, transmission resources need not be wasted on a poor-quality current channel of a given user, if the future channel quality is estimated to be better. The same channel (time slot) may then be allocated to another user. Moreover, if several users transmit feedback in a similar way, the transmission resources (e.g., time slots, frequency slots) may be determined jointly for all users, so as to improve performance or fairness accordingly.
A further advantage of the present invention is that, with beam-specific pilot signals in at least the second set, the receivers do not need to know how the beams are formed at the transmitters. The number of beam patterns or the formation of beam patterns (beam shapes or beam forming coefficients) may increase or decrease when transmission resources are upgraded or changed. Therefore, the solution is scalable to any number of beams/array elements without changing the receiver operations.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
Each of the beam patterns may include a single beam pattern or a set of two or more beam patterns formed (e.g., via digital or analog beam forming). In any of the beam patterns, during a first time, the beam pattern is used to transmit data and pilot symbols to a given user. Similarly, during the first time at least one of the different beam patterns is used to transmit only pilot/probing symbols. For example, at time, t, some of the beam patterns are used to transmit data and pilot signals, while at least one different one of is used to transmit only pilot/probing symbols. At a later time, t+1, those same beam patterns may be used for the other purpose. It should be noted that probing beams may be sent during a given time slot using a beam pattern or set of beam patterns for any of the future time slots.
As Rx 102 operates within the coverage area of the Txs 100, 101, the first determination is made as to which of the Txs Rx 102 should select for operation. For purposes of this example, Rx 102 is operating further into the coverage area of Tx 100. The Rx 102 receives and decodes pilot signals P11, P12, P13 and evaluates or tests beam patterns BP11, BP12, BP13 to determine which beam pattern or set of beam patterns therein has the highest quality or utility at that time with the available transmission resources (such as power, modulation, coding resources, and the like). After analyzing and comparing the signal quality of beam patterns BP11, BP12, BP13, the Rx 102 transmits feedback to Tx 100. The Tx 100 uses this feedback information from Rx 102 to make resource allocation decisions and scheduling decisions.
For example, the Rx 102 measures the channel power at time t1 using beams BP11, BP12, BP13 to determine both the current channel power and the assumed future channel power at a time t2. For the sake of this example, the Rx 102 measures one of the beams, BP11, for example, which is not currently used for transmitting data, to determine which has the highest channel power. Having made the measurements, the Rx 102 instructs the Tx 100 to schedule any data transmissions for the time slot t2, thus, prompting the Tx 100 to allocate a beam pattern, such as BP11, as the resource for that data transmission. Therefore, at least one resource control decision affecting a future transmission is affected by this pilot structure. Naturally, the transmission may occur also on other beams or during other time slots or channel uses. The same user may transmit on other beams with a different data rate or a different power, or the beams may be allocated to another user. Moreover, the receiver may signal the relative or absolute channel quality related to a number of “future” or “current” beams, and let the transmitter decide how to make best use of the available feedback.
It should be noted that the different sets of beam patterns from different antenna, such as antennae 103, 104, may be intended for two different receivers of ATs (i.e., user-specific beam indexing). For example, with reference to
Turning now to
The transmitter also includes a scheduling module (“SM”) 420 configured to schedule data transmission to one or more receivers based at least in part on the decoded feedback signal. The transmitter also includes a resource allocation module (“RAM”) 425 configured to allocate one or more RF beam patterns for data transmission. An antennae interface (“AI”) 430 of the transmitter is configured to enable communication between the transmitter and one or more antennae 435, wherein one or more antennae 435 transmit RF signals to generate one or more RF beam patterns, and wherein the feedback signals are received at the one or more antennae 435. The transmitter also includes a processor 440 configured to control the modules and subsystems of the transmitter and a memory 445 that stores programs and data of a temporary or more permanent nature.
The receiver includes an antenna 450 configured to receive one or more beam patterns transmitted by a transmitter, wherein the one or more beam patterns have a first set of beam patterns used to transmit data during a first time, and a second set of beam patterns used to transmit data during a subsequent time. The receiver also includes a decoder 455 configured to decode one or more pilot signals transmitted on the one or more beam patterns. The receiver also includes a test module (“TM”) 460 configured to test a quality of the one or more beam patterns. The receiver also includes a quality indicator module (“QIM”) 465 configured to generate a quality indicator based on results output from the test module 460, wherein the quality indicator relates to one of the beam patterns having a high channel quality.
The receiver also includes a coder 470 configured to encode the quality indicator in the form of a feedback signal before transmission to the transmitter. The feedback signal includes one of a channel quality indicator (“CQI”), a signal identifying one of the beam patterns having the high channel quality, and/or a designation for receiving data transmission from the transmitter at one of a first time, when one or more beam patterns having the high channel quality is in the first set, or a subsequent time, when one or more beam patterns having the high channel quality is in the second set. An antennae interface (“AI”) 475 of the receiver is configured to enable communication between the receiver and the antenna 450. The receiver also includes a processor 480 configured to control the modules and subsystems of the receiver and a memory 485 that stores programs and data of a temporary or more permanent nature.
Turning now to
It should be noted that in the various embodiments of the present invention, the receiver does not need to know the beam coefficients of any of the transmitted beam patterns. The receiver does not even need to know how many elements the transmitter has, although this information may affect the optimal choice of proposed pilots at the first time, t1. Thus, various embodiments of the present invention may provide for the receiver to know the beam coefficients and/or the number of elements of the transmitter by some means.
It should be noted that while
The program or code segments making up the various embodiments of the present invention may be stored in a computer readable medium or transmitted by a computer data signal embodied in a carrier wave, or a signal modulated by a carrier, over a transmission medium. The “computer readable medium” may include any medium that can store or transfer information. Examples of the computer readable medium include an electronic circuit, a semiconductor memory device, a read-only memory (“ROM”), a flash memory, an erasable ROM (“EROM”), a floppy diskette, a compact disk (“CD-ROM”), an optical disk, a hard disk, a fiber optic medium, a radio frequency (“RF”) link, and the like. The computer data signal may include any signal that can propagate over a transmission medium such as electronic network channels, optical fibers, air, electromagnetic, RF links, and the like. The code segments may be downloaded via computer networks such as the Internet, Intranet, and the like.
The bus 802 is also coupled to input/output (“I/O”) adapter 805, communications adapter 811, user interface adapter 808, and display adapter 809. The I/O adapter 805 connects storage devices 806, such as one or more of a hard drive, a CD drive, a floppy disk drive, and a tape drive, to computer system 800. The I/O adapter 805 is also connected to a printer (not shown), which would allow the system to print paper copies of information such as documents, photographs, articles, and the like. Note that the printer may be a printer (e.g., dot matrix, laser, and the like), a fax machine, scanner, or a copier machine.
Obviously, numerous variations and modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the form of the present invention described above and shown in the figures of the accompanying drawing is illustrative only and is not intended to limit the scope of the present invention.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the processes discussed above can be implemented in different methodologies and replaced by other processes, or a combination thereof as described herein. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
