Signal transmission pattern

An access point transmits signals (e.g., a cell reselection beacon) on a carrier frequency according to a multi-power level transmission pattern. Signals are transmitted at a high power level for a first defined period of time (e.g., between 4-7 milliseconds) and at a low power level for a second defined period of time (e.g., between 58-65 milliseconds).

BACKGROUND

This application relates generally to wireless communication and more specifically, but not exclusively, to transmission of signals at different power levels.

A wireless communication network may be deployed over a defined geographical area to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within that geographical area. In a typical implementation, access points (e.g., corresponding to different macro cells) are distributed throughout a network to provide wireless connectivity for access terminals (e.g., cell phones) that are operating within the geographical area served by the network.

As the demand for high-rate and multimedia data services rapidly grows, there lies a challenge to implement efficient and robust communication systems with enhanced performance. To supplement conventional network access points (e.g., macro access points), small-coverage access points may be deployed (e.g., installed in a user's home) to provide more robust indoor wireless coverage or other coverage to mobile units. Such small-coverage access points may be referred to as, for example, femto cells, femto access points, access point base stations, home NodeBs, or home eNodeBs. Typically, such small-coverage base stations are connected to the Internet and the mobile operator's network via DSL or cable.

In general, at a given point in time, an access terminal will be served by a given one of the access points in a network. As the access terminal roams throughout the network, the access terminal may move closer to another access point. Under certain circumstances, the access terminal may then reselect to the other access point (e.g., perform a cell reselection in idle mode from its current serving access point to the other access point). For example, to enable an access terminal to access the services provided by an associated femto cell (e.g., a home femto cell), it may be desirable for the access terminal to reselect from a current serving macro cell to the femto cell as soon as the access terminal enters the coverage area of the femto cell.

Accordingly, there is a need for techniques to ensure that an access terminal is able to discover a femto cell when the access terminal is in the vicinity the femto cell. Moreover, it is desirable to achieve discovery relatively quickly and reliably and without significantly interfering with the service provided by other access points operating in the area.

SUMMARY

A summary of several sample aspects of the disclosure follows. This summary is provided for the convenience of the reader and does not wholly define the breadth of the disclosure. For convenience, the term some aspects may be used herein to refer to a single aspect or multiple aspects of the disclosure.

The disclosure relates in some aspects to providing a transmission pattern for an access point. Techniques are described for defining a transmission pattern in a manner that facilitates discovery of an access point by a nearby access terminal, while mitigating the negative impact that transmissions by the access point may have on service provided by a neighboring access point. For example, transmit power may be defined for a femto cell in a manner that facilitates reselection to that femto cell by access terminals authorized to access the femto cell, while mitigating outages (e.g., call drops) at access terminals accessing a nearby macro cell that may otherwise occur as a result of the transmissions by the femto cell.

The disclosure relates in some aspects to a multi-level power transmission scheme. For example, an access point may usually transmit at a certain power level, but then occasionally (e.g., periodically) transmit at a burst power level (i.e., a higher power level) for short periods of time. In some aspects, this multi-level power scheme is used for transmissions on a non-service channel. As a specific example, a femto cell may transmit signals (e.g., a cell reselection beacon) on a macro cell frequency according to a transmission pattern where signals are transmitted at a high power level for a first defined period of time (e.g., between 4-7 milliseconds) and at a low power level for a second defined period of time (e.g., between 58-65 milliseconds).

In accordance with common practice the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus (e.g., device) or method. Finally, like reference numerals may be used to denote like features throughout the specification and figures.

DETAILED DESCRIPTION

FIG. 1illustrates several nodes of a sample communication system100(e.g., a portion of a communication network). For illustration purposes, various aspects of the disclosure will be described in the context of one or more access terminals, access points, and network entities that communicate with one another. It should be appreciated, however, that the teachings herein may be applicable to other types of apparatuses or other similar apparatuses that are referenced using other terminology. For example, in various implementations access points may be referred to or implemented as base stations, NodeBs, eNodeBs, and so on, while access terminals may be referred to or implemented as user equipment (UEs), mobile stations, and so on.

Access points in the system100provide access to one or more services (e.g., network connectivity) for one or more wireless terminals (e.g., an access terminal102) that may be installed within or that may roam throughout a coverage area of the system100. For example, at various points in time the access terminal102may connect to an access point104, an access point106, or some access point in the system100(not shown). Each of these access points may communicate with one or more network entities (represented, for convenience, by a network entity108) to facilitate wide area network connectivity.

These network entities may take various forms such as, for example, one or more radio and/or core network entities. Thus, in various implementations the network entities may represent functionality such as at least one of: network management (e.g., via an operation, administration, management, and provisioning entity), call control, session management, mobility management, gateway functions, interworking functions, or some other suitable network functionality. In some aspects, mobility management relates to: keeping track of the current location of access terminals through the use of tracking areas, location areas, routing areas, or some other suitable technique; controlling paging for access terminals; and providing access control for access terminals. Also, two of more of these network entities may be co-located and/or two or more of these network entities may be distributed throughout a network.

For purposes of illustration, various aspects ofFIG. 1are not drawn to scale. For example, the low power coverage and high power coverage are not drawn to scale and are represented as simple ovals inFIG. 1. It should be appreciated that in practice such coverage would be more complex in shape and that the high power coverage may be significantly wider than the low power coverage. In addition, the distances between the entities ofFIG. 1are not drawn to scale.

The terms “carrier frequency” and “carrier” as used herein refer to a particular frequency band (e.g., corresponding to a designated nominal carrier frequency) allocated for wireless communication in a network (e.g., a cellular network). Conventionally, a carrier frequency or channel is simply referred to as a frequency. For example, a carrier frequency dedicated for femto cells is referred to as the femto frequency, while the carrier frequencies dedicated for macro cells are referred to as macro frequencies.

Upon deployment, the access point106(e.g., a femto cell) is configured to operate on a particular carrier frequency which is referred to herein, for convenience, as the service channel. Two typical deployment scenarios for femto cells are a co-channel deployment and a dedicated deployment. In a co-channel deployment, macro cells and femto cells operate on the same carrier frequency (e.g., carrier frequency f1). In a dedicated channel deployment, a femto cells operate on a carrier frequency (e.g., carrier frequency f2) that is not allocated for macro cells. In either case, other access points (e.g., macro cells) will operate on one or more other carrier frequencies (e.g., carrier frequencies f3-f6).

The access point106employs a multi-level power scheme to cause cell reselection at nearby access terminals, while mitigating interference to other access points operating in the vicinity. Such a scheme is advantageously employed to address discovery issues that otherwise arise for the access point106under certain conditions. For example, assume the access terminal102is camped on the access point104(e.g., a macro cell) operating on a first carrier frequency. The access point106is operating on a second carrier frequency. If the signal quality of the access point104is good, the access terminal102may not search any other frequencies (including the second carrier frequency) to discover nearby access points. Under these circumstances, the access terminal102may not be able to find and camp on the access point106.

Consequently, the access point106transmits signals on each carrier frequency other than its service channel (the second carrier frequency in the above example) to increase the likelihood that a nearby access terminal operating on another carrier frequency will discover the access point106. To provide a tradeoff between good discovery performance and mitigating interference on the other carrier frequencies, the access point106transmits on the other carrier frequencies at different power levels at different times according to a defined transmission pattern110. The access point106transmits at one power level to provide low power coverage as represented in a simplified manner by the corresponding dashed line inFIG. 1. In addition, the access point106transmits at a higher power level to provide high power coverage as represented in a simplified manner by the corresponding dashed line inFIG. 1.

FIG. 2illustrates an example of a transmission pattern. Time is represented along the horizontal axis and transmit power is represented along the vertical axis. The transmitted signal is modulated into two power levels Phighand Plowwhich are invoked on an alternate basis for different periods of time. Each high power signal202spans a short time period Thigh204(e.g., on the order of a few milliseconds). Each low power signal206spans a longer time period Tlow208. The high power signals are meant to cover a larger area around the access point106while the low power signals are for guaranteed access point discovery in the vicinity of the access point106.

The presence of the high power signal impacts the channel quality (e.g., CPICH Ec/Io) seen by the access terminal102on its serving macro frequency. As a result of this degradation of the macro frequency, an inter-frequency will be triggered at the access terminal102. Upon conducting this search, the access terminal102will discover the access point106on the corresponding service frequency and, if authorized, camp on the access point106.

The duration and duty cycle of the high power burst are defined to provide quick access point discovery, while minimizing the interference to users on the other frequencies (e.g., macro cell users). If this interference is not mitigated, macro service in the coverage area of the high power burst may be subject to voice call drop, an increase in macro cell downlink transmit power, degradation in high speed downlink packet access (HSDPA) throughput, and battery life impact due to unnecessary searches.

In accordance with the teachings herein, a specific beacon pattern (e.g., Thighand Tlow) is provided to strike a good balance between quick access point discovery and reduced interference to the users on that carrier frequency. In terms of access point discovery, given that different access points have different idle mode implementations in terms of duration of wake up time, measurement frequency during wake up time and measurement filtering, the high power burst duration and duty cycle are designed to enable quick discovery for different access terminal implementations.

A Thighin the range of [4, 7] milliseconds and a Thigh+Tlowin the range of [62, 72] milliseconds gives the best results in terms femto cell discovery for the femto users and interference to macro users (e.g., call drop, HSDPA throughput degradation, battery life) for a wide range of access points. If Thighis less than 4 milliseconds, the discovery time is increased by at least 100% in some cases. On the other hand, a Thighvalue greater than 7 milliseconds causes significant degradation in voice quality and data throughput of nearby users (e.g., access terminals communicating with a macro cell). Thigh+Tlowabove 72 milliseconds increases the discovery time by at least 100% in some cases and the discovery does not work in some cases. Thigh+Tlowvalues below 62 milliseconds also increase the discovery time significantly unless Thigh+Tlowis reduced considerably. However, if Thigh+Tlowis significantly below 62 milliseconds, the impact on HSDPA throughput and voice call is severe. In some implementations, a Thighof 5 milliseconds and a Thigh+Tlowof 68 milliseconds results in the best performance out of the recommended range of Thighand Thigh+Tlow.

Sample operations of the system100will now be described in more detail in conjunction with the flowchart ofFIG. 3. For convenience, the operations ofFIG. 3(or any other operations discussed or taught herein) may be described as being performed by specific components (e.g., the components ofFIG. 1,FIG. 7, orFIG. 11). It should be appreciated, however, that these operations may be performed by other types of components and may be performed using a different number of components. It also should be appreciated that one or more of the operations described herein may not be employed in a given implementation.

As represented by block302ofFIG. 3, an access point maintains transmission pattern parameters that are used to control the transmission of signals for initiating cell reselection at nearby access terminals. In a sample embodiment, a femto cell stores parameters that define a high power level Phigh, a low power level Plow, a duration Thighfor the high power level, and a duration T10for the low power level. As mentioned above, in some embodiments the Thighparameter is constrained to be within a range of 4-7 milliseconds and the Tlowparameter is constrained to be within a range of 58-65 milliseconds. For example, in some implementations, Thighis set to 5 milliseconds and/or Thigh+Tlowis set to 68 milliseconds.

Parameters that define other characteristics of the transmitted signals also are maintained in some cases. For example, in an implementation where the transmitted signals comprise wideband code division multiple access (WCDMA) beacon signals, the signals may be defined to include a primary scrambling code (PSC) and one or more overhead channels.

As represented by block304, the access point normally transmits on a first carrier frequency. For example, a femto cell may be configured to provide service on a designated service channel.

As represented by block306, to attract nearby access terminals operating on at least one other carrier frequency, the access point uses the transmission pattern to transmit signals on each of the other carrier frequencies. Accordingly, the access point alternates between transmitting signals on at least one other carrier frequency at a first power level for a first defined period of time and a second power level for a second defined period of time. The first power level corresponds to Phighand the second power level corresponds to Plow. The first defined period of time corresponds to Thigh(i.e., is between 4 milliseconds and 7 milliseconds) and the second defined period of time corresponds to Tlow(i.e., is between 58 milliseconds and 65 milliseconds). In some aspects, the alternating transmissions for the first defined period of time and the second defined period of time provide a tradeoff between: 1) a nominal amount of time it takes for an inter-frequency search to discover the access point; and 2) a nominal amount of interference the transmission of signals on the at least one other carrier frequency causes on that frequency (or on those frequencies).

FIG. 4illustrates an example of how such multi-level transmissions provide desired coverage areas in and near a building. An access point402is deployed in a room in a building404(shown in plan view). The boundary of the low power coverage is represented by the dashed line406. Thus, the low power coverage is limited to one area of the building (e.g., one room). The boundary of the high power coverage is represented by the dashed line408. Thus, the high power coverage covers a much larger area in and around the building. Consequently, the use of the high power beacon makes it much more likely that a user within the building will discover the access point. However, the interference caused by the access point402will be limited to a much smaller area (the low power coverage) most of the time.

For illustration purposes, sample operations that may be employed to provide WCDMA beacon signals in accordance with the teachings herein are described with reference toFIGS. 5 and 6.FIG. 5illustrates sample femto cell operations for transmitting a cell-reselection beacon.

As represented by block502ofFIG. 5, a beacon signal is repeatedly modulated at a first power level and a second power level. The modulation operation involves modulating a high power beacon burst that spans a first duration at the first power level and modulating a low power beacon that spans a second duration at the second power level. As discussed above, the first duration is between 4 and 7 milliseconds and the second duration is between 58 and 65 milliseconds.

As represented by block504, a WCDMA signal comprising the beacon signal modulated at block502is transmitted on a macro frequency. Thus, the beacon signal is transmitted at the first power level for the first duration, then at the second power level for the second duration, then at the first power level for the first duration, and so. In some implementations the transmitted beacon signal comprises a primary synchronization code and/or one or more overhead channels.

FIG. 6illustrates sample UE operations relating to performing an inter-frequency search. As represented by block602, at some point in time the UE receives the beacon signal transmitted by the femto cell at block504.

As represented by block604, the interference of the beacon signal at the UE causes the Common Pilot Channel Ec/Io for the UE's serving macro cell as measured at the UE to drop. Consequently, an inter-frequency search is triggered at the UE.

As represented by block606, as a result of the search, the UE discovers the femto cell on the femto cell's service frequency. Consequently, the UE commences camping on the femto cell.

FIG. 7illustrates several sample components (represented by corresponding blocks) that may be incorporated into nodes such as an access point702(e.g., corresponding to the access point106ofFIG. 1) to perform transmission-related operations as taught herein. The described components also may be incorporated into other nodes in a communication system. For example, other nodes in a system may include components similar to those described for the access point702to provide similar functionality. Also, a given node may contain one or more of the described components. For example, an access point may contain multiple transceiver components that enable the access point to operate on multiple carriers and/or communicate via different technologies.

As shown inFIG. 7, the access point702includes one or more transceivers (as represented by a transceiver704) for communicating with other nodes. Each transceiver704includes a transmitter706for sending signals (e.g., message, indications, pilot signals, beacons) and a receiver708for receiving signals (e.g., messages, indications).

The access point702also includes a network interface710for communicating with other nodes (e.g., network entities). For example, the network interface710may be configured to communicate with one or more network entities via a wire-based or wireless backhaul. In some aspects, the network interface710may be implemented as a transceiver (e.g., including transmitter and receiver components) configured to support wire-based or wireless communication.

The access point702also includes other components that are used in conjunction with transmission-related operations as taught herein. For example, the access point702includes a transmit controller712for managing transmissions on one or more carrier frequencies (e.g., causing signals to transmitted in an alternating manner at a first power level for a first defined period of time and a second power level for a second defined period of time) and for providing other related functionality as taught herein. In some implementations, operations of the transmit controller712may be implemented in the transmitter(s)706. The access point702also includes a memory component714(e.g., including a memory device) for maintaining information (e.g., transmission pattern parameters).

The components ofFIG. 7may be implemented in various ways. In some implementations the components ofFIG. 7may be implemented in one or more circuits such as, for example, one or more processors and/or one or more ASICs (which may include one or more processors). Here, each circuit (e.g., processor) may use and/or incorporate data memory for storing information or executable code used by the circuit to provide this functionality. For example, some of the functionality represented by block704and some or all of the functionality represented by blocks710-714may be implemented by a processor or processors of an access point and data memory of the access point (e.g., by execution of appropriate code and/or by appropriate configuration of processor components).

As discussed above, in some aspects the teachings herein may be employed in a network that includes macro scale coverage (e.g., a large area cellular network such as a 3G network, typically referred to as a macro cell network or a WAN) and smaller scale coverage (e.g., a residence-based or building-based network environment, typically referred to as a LAN). As an access terminal (AT) moves through such a network, the access terminal may be served in certain locations by access points that provide macro coverage while the access terminal may be served at other locations by access points that provide smaller scale coverage. In some aspects, the smaller coverage nodes may be used to provide incremental capacity growth, in-building coverage, and different services (e.g., for a more robust user experience).

In the description herein, a node (e.g., an access point) that provides coverage over a relatively large area may be referred to as a macro access point while a node that provides coverage over a relatively small area (e.g., a residence) may be referred to as a femto access point. It should be appreciated that the teachings herein may be applicable to nodes associated with other types of coverage areas. For example, a pico access point may provide coverage (e.g., coverage within a commercial building) over an area that is smaller than a macro area and larger than a femto area. In various applications, other terminology may be used to reference a macro access point, a femto access point, or other access point-type nodes. For example, a macro access point may be configured or referred to as an access node, base station, access point, eNodeB, macro cell, and so on. Also, a femto access point may be configured or referred to as a Home NodeB, Home eNodeB, access point base station, femto cell, and so on. In some implementations, a node may be associated with (e.g., referred to as or divided into) one or more cells or sectors. A cell or sector associated with a macro access point, a femto access point, or a pico access point may be referred to as a macro cell, a femto cell, or a pico cell, respectively.

FIG. 8illustrates a wireless communication system800, configured to support a number of users, in which the teachings herein may be implemented. The system800provides communication for multiple cells802, such as, for example, macro cells802A-802G, with each cell being serviced by a corresponding access point804(e.g., access points804A-804G). As shown inFIG. 8, access terminals806(e.g., access terminals806A-806L) may be dispersed at various locations throughout the system over time. Each access terminal806may communicate with one or more access points804on a forward link (FL) and/or a reverse link (RL) at a given moment, depending upon whether the access terminal806is active and whether it is in soft handoff, for example. The wireless communication system800may provide service over a large geographic region. For example, macro cells802A-802G may cover a few blocks in a neighborhood or several miles in a rural environment.

FIG. 9illustrates an exemplary communication system900where one or more femto access points are deployed within a network environment. Specifically, the system900includes multiple femto access points910(e.g., femto access points910A and910B) installed in a relatively small scale network environment (e.g., in one or more user residences930). Each femto access point910may be coupled to a wide area network940(e.g., the Internet) and a mobile operator core network950via a DSL router, a cable modem, a wireless link, or other connectivity means (not shown). As will be discussed below, each femto access point910may be configured to serve associated access terminals920(e.g., access terminal920A) and, optionally, other (e.g., hybrid or alien) access terminals920(e.g., access terminal920B). In other words, access to femto access points910may be restricted whereby a given access terminal920may be served by a set of designated (e.g., home) femto access point(s)910but may not be served by any non-designated femto access points910(e.g., a neighbor's femto access point910).

FIG. 10illustrates an example of a coverage map1000where several tracking areas1002(or routing areas or location areas) are defined, each of which includes several macro coverage areas1004. Here, areas of coverage associated with tracking areas1002A,1002B, and1002C are delineated by the wide lines and the macro coverage areas1004are represented by the larger hexagons. The tracking areas1002also include femto coverage areas1006. In this example, each of the femto coverage areas1006(e.g., femto coverage areas1006B and1006C) is depicted within one or more macro coverage areas1004(e.g., macro coverage areas1004A and1004B). It should be appreciated, however, that some or all of a femto coverage area1006may not lie within a macro coverage area1004. In practice, a large number of femto coverage areas1006(e.g., femto coverage areas1006A and1006D) may be defined within a given tracking area1002or macro coverage area1004. Also, one or more pico coverage areas (not shown) may be defined within a given tracking area1002or macro coverage area1004.

Referring again toFIG. 9, the owner of a femto access point910may subscribe to mobile service, such as, for example, 3G mobile service, offered through the mobile operator core network950. In addition, an access terminal920may be capable of operating both in macro environments and in smaller scale (e.g., residential) network environments. In other words, depending on the current location of the access terminal920, the access terminal920may be served by a macro cell access point960associated with the mobile operator core network950or by any one of a set of femto access points910(e.g., the femto access points910A and910B that reside within a corresponding user residence930). For example, when a subscriber is outside his home, he is served by a standard macro access point (e.g., access point960) and when the subscriber is at home, he is served by a femto access point (e.g., access point910A). Here, a femto access point910may be backward compatible with legacy access terminals920.

A femto access point910may be deployed on a single frequency or, in the alternative, on multiple frequencies. Depending on the particular configuration, the single frequency or one or more of the multiple frequencies may overlap with one or more frequencies used by a macro access point (e.g., access point960).

In some aspects, an access terminal920may be configured to connect to a preferred femto access point (e.g., the home femto access point of the access terminal920) whenever such connectivity is possible. For example, whenever the access terminal920A is within the user's residence930, it may be desired that the access terminal920A communicate only with the home femto access point910A or910B.

In some aspects, if the access terminal920operates within the macro cellular network950but is not residing on its most preferred network (e.g., as defined in a preferred roaming list), the access terminal920may continue to search for the most preferred network (e.g., the preferred femto access point910) using a better system reselection (BSR) procedure, which may involve a periodic scanning of available systems to determine whether better systems are currently available and subsequently acquire such preferred systems. The access terminal920may limit the search for specific band and channel. For example, one or more femto channels may be defined whereby all femto access points (or all restricted femto access points) in a region operate on the femto channel(s). The search for the most preferred system may be repeated periodically. Upon discovery of a preferred femto access point910, the access terminal920selects the femto access point910and registers on it for use when within its coverage area.

Access to a femto access point may be restricted in some aspects. For example, a given femto access point may only provide certain services to certain access terminals. In deployments with so-called restricted (or closed) access, a given access terminal may only be served by the macro cell mobile network and a defined set of femto access points (e.g., the femto access points910that reside within the corresponding user residence930). In some implementations, an access point may be restricted to not provide, for at least one node (e.g., access terminal), at least one of: signaling, data access, registration, paging, or service.

In some aspects, a restricted femto access point (which may also be referred to as a Closed Subscriber Group Home NodeB) is one that provides service to a restricted provisioned set of access terminals. This set may be temporarily or permanently extended as necessary. In some aspects, a Closed Subscriber Group (CSG) may be defined as the set of access points (e.g., femto access points) that share a common access control list of access terminals.

Various relationships may thus exist between a given femto access point and a given access terminal. For example, from the perspective of an access terminal, an open femto access point may refer to a femto access point with unrestricted access (e.g., the femto access point allows access to any access terminal). A restricted femto access point may refer to a femto access point that is restricted in some manner (e.g., restricted for access and/or registration). A home femto access point may refer to a femto access point on which the access terminal is authorized to access and operate on (e.g., permanent access is provided for a defined set of one or more access terminals). A hybrid (or guest) femto access point may refer to a femto access point on which different access terminals are provided different levels of service (e.g., some access terminals may be allowed partial and/or temporary access while other access terminals may be allowed full access). An alien femto access point may refer to a femto access point on which the access terminal is not authorized to access or operate on, except for perhaps emergency situations (e.g., 911 calls).

From a restricted femto access point perspective, a home access terminal may refer to an access terminal that is authorized to access the restricted femto access point installed in the residence of that access terminal's owner (usually the home access terminal has permanent access to that femto access point). A guest access terminal may refer to an access terminal with temporary access to the restricted femto access point (e.g., limited based on deadline, time of use, bytes, connection count, or some other criterion or criteria). An alien access terminal may refer to an access terminal that does not have permission to access the restricted femto access point, except for perhaps emergency situations, for example, such as 911 calls (e.g., an access terminal that does not have the credentials or permission to register with the restricted femto access point).

For convenience, the disclosure herein describes various functionality in the context of a femto access point. It should be appreciated, however, that a pico access point may provide the same or similar functionality for a larger coverage area. For example, a pico access point may be restricted, a home pico access point may be defined for a given access terminal, and so on.

The teachings herein may be employed in a wireless multiple-access communication system that simultaneously supports communication for multiple wireless access terminals. Here, each terminal may communicate with one or more access points via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the access points to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the access points. This communication link may be established via a single-in-single-out system, a multiple-in-multiple-out (MIMO) system, or some other type of system.

A MIMO system may support time division duplex (TDD) and frequency division duplex (FDD). In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beam-forming gain on the forward link when multiple antennas are available at the access point.

FIG. 11illustrates a wireless device1110(e.g., an access point) and a wireless device1150(e.g., an access terminal) of a sample MIMO system1100. At the device1110, traffic data for a number of data streams is provided from a data source1112to a transmit (TX) data processor1114. Each data stream may then be transmitted over a respective transmit antenna.

The modulation symbols for all data streams are then provided to a TX MIMO processor1120, which may further process the modulation symbols (e.g., for OFDM). The TX MIMO processor1120then provides NTmodulation symbol streams to NTtransceivers (XCVR)1122A through1122T. In some aspects, the TX MIMO processor1120applies beam-forming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

Each transceiver1122receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. NTmodulated signals from transceivers1122A through1122T are then transmitted from NTantennas1124A through1124T, respectively.

At the device1150, the transmitted modulated signals are received by NRantennas1152A through1152R and the received signal from each antenna1152is provided to a respective transceiver (XCVR)1154A through1154R. Each transceiver1154conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.

A receive (RX) data processor1160then receives and processes the NRreceived symbol streams from NRtransceivers1154based on a particular receiver processing technique to provide NT“detected” symbol streams. The RX data processor1160then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor1160is complementary to that performed by the TX MIMO processor1120and the TX data processor1114at the device1110.

A processor1170periodically determines which pre-coding matrix to use (discussed below). The processor1170formulates a reverse link message comprising a matrix index portion and a rank value portion. A data memory1172may store program code, data, and other information used by the processor1170or other components of the device1150.

The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor1138, which also receives traffic data for a number of data streams from a data source1136, modulated by a modulator1180, conditioned by the transceivers1154A through1154R, and transmitted back to the device1110.

At the device1110, the modulated signals from the device1150are received by the antennas1124, conditioned by the transceivers1122, demodulated by a demodulator (DEMOD)1140, and processed by a RX data processor1142to extract the reverse link message transmitted by the device1150. The processor1130then determines which pre-coding matrix to use for determining the beam-forming weights then processes the extracted message.

FIG. 11also illustrates that the communication components may include one or more components that perform transmit control operations as taught herein. For example, a transmit control component1190may cooperate with the processor1130and/or other components of the device1110to send signals to another device (e.g., device1150) as taught herein. It should be appreciated that for each device1110and1150the functionality of two or more of the described components may be provided by a single component. For example, a single processing component may provide the functionality of the transmit control component1190and the processor1130.

The teachings herein may be incorporated into various types of communication systems and/or system components. In some aspects, the teachings herein may be employed in a multiple-access system capable of supporting communication with multiple users by sharing the available system resources (e.g., by specifying one or more of bandwidth, transmit power, coding, interleaving, and so on). For example, the teachings herein may be applied to any one or combinations of the following technologies: Code Division Multiple Access (CDMA) systems, Multiple-Carrier CDMA (MCCDMA), Wideband CDMA (W-CDMA), High-Speed Packet Access (HSPA, HSPA+) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Single-Carrier FDMA (SC-FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, or other multiple access techniques. A wireless communication system employing the teachings herein may be designed to implement one or more standards, such as IS-95, cdma2000, IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, or some other technology. UTRA includes W-CDMA and Low Chip Rate (LCR). The cdma2000 technology covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). The teachings herein may be implemented in a 3GPP Long Term Evolution (LTE) system, an Ultra-Mobile Broadband (UMB) system, and other types of systems. LTE is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP), while cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). Although certain aspects of the disclosure may be described using 3GPP terminology, it is to be understood that the teachings herein may be applied to 3GPP (e.g., Rel99, Rel5, Rel6, Rel7) technology, as well as 3GPP2 (e.g., 1xRTT, 1xEV-DO Rel0, RevA, RevB) technology and other technologies.

The teachings herein may be incorporated into (e.g., implemented within or performed by) a variety of apparatuses (e.g., nodes). In some aspects, a node (e.g., a wireless node) implemented in accordance with the teachings herein may comprise an access point or an access terminal.

For example, an access terminal may comprise, be implemented as, or known as user equipment, a subscriber station, a subscriber unit, a mobile station, a mobile, a mobile node, a remote station, a remote terminal, a user terminal, a user agent, a user device, or some other terminology. In some implementations an access terminal may comprise a cellular telephone, a cordless telephone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music device, a video device, or a satellite radio), a global positioning system device, or any other suitable device that is configured to communicate via a wireless medium.

An access point may comprise, be implemented as, or known as a NodeB, an eNodeB, a radio network controller (RNC), a base station (BS), a radio base station (RBS), a base station controller (BSC), a base transceiver station (BTS), a transceiver function (TF), a radio transceiver, a radio router, a basic service set (BSS), an extended service set (ESS), a macro cell, a macro node, a Home eNB (HeNB), a femto cell, a femto node, a pico node, or some other similar terminology.

In some aspects a node (e.g., an access point) may comprise an access node for a communication system. Such an access node may provide, for example, connectivity for or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link to the network. Accordingly, an access node may enable another node (e.g., an access terminal) to access a network or some other functionality. In addition, it should be appreciated that one or both of the nodes may be portable or, in some cases, relatively non-portable.

Also, it should be appreciated that a wireless node may be capable of transmitting and/or receiving information in a non-wireless manner (e.g., via a wired connection). Thus, a receiver and a transmitter as discussed herein may include appropriate communication interface components (e.g., electrical or optical interface components) to communicate via a non-wireless medium.

A wireless node may communicate via one or more wireless communication links that are based on or otherwise support any suitable wireless communication technology. For example, in some aspects a wireless node may associate with a network. In some aspects the network may comprise a local area network or a wide area network. A wireless device may support or otherwise use one or more of a variety of wireless communication technologies, protocols, or standards such as those discussed herein (e.g., CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, and so on). Similarly, a wireless node may support or otherwise use one or more of a variety of corresponding modulation or multiplexing schemes. A wireless node may thus include appropriate components (e.g., air interfaces) to establish and communicate via one or more wireless communication links using the above or other wireless communication technologies. For example, a wireless node may comprise a wireless transceiver with associated transmitter and receiver components that may include various components (e.g., signal generators and signal processors) that facilitate communication over a wireless medium.

The functionality described herein (e.g., with regard to one or more of the accompanying figures) may correspond in some aspects to similarly designated “means for” functionality in the appended claims. Referring toFIG. 12, an apparatus1200is represented as a series of interrelated functional modules. Here, a module for transmitting signals on a first carrier frequency1202may correspond at least in some aspects to, for example, a transmitter as discussed herein. A module for maintaining transmission pattern parameters1204may correspond at least in some aspects to, for example, a memory component as discussed herein. A module for alternating between transmitting on at least one other carrier frequency at a first power level for a first defined period of time and a second power level for a second defined period of time1206may correspond at least in some aspects to, for example, a transmitter and/or a controller as discussed herein.

The functionality of the modules ofFIG. 12may be implemented in various ways consistent with the teachings herein. In some aspects the functionality of these modules may be implemented as one or more electrical components. In some aspects the functionality of these blocks may be implemented as a processing system including one or more processor components. In some aspects the functionality of these modules may be implemented using, for example, at least a portion of one or more integrated circuits (e.g., an ASIC). As discussed herein, an integrated circuit may include a processor, software, other related components, or some combination thereof. The functionality of these modules also may be implemented in some other manner as taught herein. In some aspects one or more of any dashed blocks inFIG. 12are optional.

It should be understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations may be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements may comprise one or more elements. In addition, terminology of the form “at least one of A, B, or C” or “one or more of A, B, or C” or “at least one of the group consisting of A, B, and C” used in the description or the claims means “A or B or C or any combination of these elements.”