WO2012028904A1 - Method and apparatus for carrier allocation for femto base stations - Google Patents

Abstract

A method, apparatus and computer program product are provided in order to facilitate carrier allocation to a femto base station. In this regard, a method, apparatus and computer program product may allocate a carrier to a femto base station that is operating autonomously in a manner that does not require allocation of the carrier by the network. In order to allocate the carrier, the method, apparatus and computer program product are configured to evaluate, for each of a plurality of uplink carriers, at least one of power level variations or arrival time variations of each of a plurality of transmissions supported by a respective uplink carrier and then select a respective one of the uplink carriers to support communication with a femto base station based upon evaluation of the power level variations and/or arrival time variations.

Description

METHOD AND APPARATUS FOR CARRIER ALLOCATION FOR FEMTO BASE

STATIONS

TECHNOLOGICAL FIELD

An example embodiment of the present invention relates generally to carrier allocation within a heterogeneous network and, more particularly, to carrier allocation for a femto base station within a heterogeneous network.

BACKGROUND

Heterogeneous networks are being increasingly deployed which have various network topologies integrated into a cellular network topology. For example, in accordance with Long Term Evolution (LTE)/LTE- Advanced (LTE-A) 3 ^rd Generation Partnership Project (3 GPP), a heterogeneous network may include a combination of microcells, pico cells, femto cells and relay cells operating in the same spectrum. Within a heterogeneous network, it may be desirable in some instances for various devices and machines to directly communicate in a local domain either with or without supervision of the network. Within a local domain, a heterogeneous network may therefore provide for network control or autonomous device-to-device (D2D) communication including communications in various clusters devices. Operation in the local domain of a heterogeneous network may also include a grid or group of local machines communicating and performing certain tasks in a cooperative manner. A heterogeneous network may also allow a device having advanced capabilities to serve as a gateway to the heterogeneous network for a number of devices or machines having relatively lesser capabilities.

A heterogeneous network may also provide for the autonomous operation of femto base stations. Femto base stations are local or sub-communication stations and may provide an access point, such as a user installed access point, that provides coverage to a corresponding femto cell that is located within a larger cell, e.g., a macro cell, defined by the coverage area of a network installed base station. As such, a femto base station may provide for in-home (or business) mobility with improved data rates and quality of service (QoS) as comparted to a network installed base station, which may be loaded heavily from communications with other mobile terminals or subscribers and/or may be shielded somewhat by buildings or other obstructions. As used herein, femto base station is used generally to reference femto base stations, home node Bs (HNBs), local nodes or the like.

Some femto base stations, known as cognitive femto base stations, are configured for autonomous operation. A femto base station configured to operate autonomously may be movable and/or may be configured to adapt into the prevailing radio environment at any location and at any time. As a result of its autonomous operation, a cognitive femto base station may identify a suitable carrier to support communications with the network without burdening the network with the task of allocating the carrier to the femto base station.

The integration of local heterogeneous communication, such as between devices in the local domain or by a femto base station, may require the devices to identify and use radio resources of the network in such a manner that a relatively limited amount of network assistance is required and interference is not created with the other users of the network. As such, it may be desirable to provide for the allocation of a carrier to a cognitive femto base station in a manner that reduces or eliminates network involvement while correspondingly taking into account an interference issues created for other users of the network.

BRIEF SUMMARY

A method, apparatus and computer program product are therefore provided in order to facilitate carrier allocation to a femto base station. In this regard, a method, apparatus and computer program product of one example embodiment may allocate a carrier to a femto base station that is operating autonomously in a manner that does not require allocation of the carrier by the network. Further, the method, apparatus and computer program product of one example embodiment may select an uplink carrier to support communications with a femto base station in a manner that takes into account interference issues, such as by selecting a respective uplink carrier in a manner that does not create interference problems for other network users. In accordance with one embodiment, a method is provided that includes, for each of a plurality of uplink carriers, evaluating at least one of power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier and then selecting a respective one of the uplink carriers to support communication with a femto base station based upon evaluation of the at least one of the power level variations or the arrival time variations.

In accordance with another embodiment, an apparatus is provided that includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to evaluate, for each of a plurality of uplink carriers, at least one of power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier and to then select a respective one of the uplink carriers to support communication with a femto base station based upon evaluation of the at least one of the power level variations or the arrival time variations.

In accordance with one embodiment, a computer program product is provided that includes at least one computer-readable storage medium having computer-executable code portions stored therein. The computer-executable code portions include program code instructions for evaluating, for each of a plurality of uplink carriers, at least one of power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier and program code instructions for selecting a respective one of the uplink carriers to support communication with a femto base station based upon evaluation of the at least one of the power level variations or the arrival time variations.

In accordance with a further embodiment, an apparatus is provided that includes means for evaluating, for each of a plurality of uplink carriers, at least one of power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier. The apparatus of this embodiment may also include means for selecting a respective one of the uplink carriers to support communication with a femto base station based upon evaluation of the at least one of the power level variations or the arrival time variations.

In accordance with any of the foregoing embodiments, the evaluation of the power level variations may include determining a ratio of the highest power level to the lowest power level across the plurality of transmissions supported by the uplink carrier and then selecting the uplink carrier having the greatest ratio to thereafter support communications with the femto base station. In an alternative embodiment, the evaluation of the power level variations may include determining a difference between a highest power level and a lowest power level across the plurality of transmissions supported by respective uplink carriers and then normalizing the difference based upon an average power level across the plurality of transmissions supported by the respective uplink carrier. In this alternative embodiment, the uplink carrier having the greatest normalized difference may then be selected to thereafter support communications with the femto base station.

In one embodiment, the evaluation of the arrival time variations may include the determination of a difference in arrival times across the plurality of transmissions supported by the respective uplink carrier. In this embodiment, the selection of a respective one of the uplink carriers may include the selection of the uplink carrier having the greatest difference in arrival times to support communications with the femto base station.

The evaluation of at least one of the power level variations or the arrival time variations and the selection of a respective uplink carrier may be repeated in order to re-select an uplink carrier. For example, a control signal may be received indicating that the uplink carrier should be re-selected and an evaluation of at least one of the power level variations or the arrival time variations and the selection of a respective uplink carrier may be performed in response to the control signal.

BRIEF DESCRIPTION OF THE SEVERAL OF THE DRAWINGS

Having thus described certain example embodiments of the present invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

Figure 1 is an illustration of an heterogeneous network in accordance with an example embodiment of the present invention in which a femto cell is relatively far away from the base station;

Figure 2 is a block diagram of an apparatus in accordance with an example embodiment of the present invention that may be embodied, for example, by a femto base station; Figure 3 is a flow chart illustrating the operations performed in accordance with an example embodiment of the present invention;

Figure 4 is a graphical representation of the power levels associated with a plurality of resource blocks for each of a number of different uplink carriers;

Figure 5 is a flow chart illustrating the operations performed in accordance with an example embodiment of Figure 3;

Figure 6 is a graphical representation of various parameters, such as power levels and arrival times, of the transmissions supported by a respective uplink carrier in an instance in which a femto node is relatively far away from the base station;

Figure 7 is an illustration of an heterogeneous network in which a femto cell is relatively near to the base station;

Figure 8 is a graphical representation of various parameters, such as power levels and arrival times, of the transmissions supported by a respective uplink carrier in an instance in which a femto node is relatively near to the base station; and

Figure 9 is a flow chart illustrating the operations performed in accordance with another example embodiment of Figure 3.

DETAILED DESCRIPTION

Some embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, various embodiments of the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout. As used herein, the terms "data," "content," "information" and similar terms may be used interchangeably to refer to data capable of being transmitted, received and/or stored in accordance with embodiments of the present invention. Thus, use of any such terms should not be taken to limit the spirit and scope of embodiments of the present invention.

Additionally, as used herein, the term 'circuitry' refers to (a) hardware- only circuit implementations (e.g., implementations in analog circuitry and/or digital circuitry); (b) combinations of circuits and computer program product(s) comprising software and/or firmware instructions stored on one or more computer readable memories that work together to cause an apparatus to perform one or more functions described herein; and (c) circuits, such as, for example, a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term herein, including in any claims. As a further example, as used herein, the term 'circuitry' also includes an implementation comprising one or more processors and/or portion(s) thereof and accompanying software and/or firmware. As another example, the term 'circuitry' as used herein also includes, for example, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, other network device, and/or other computing device.

As defined herein a "computer-readable storage medium," which refers to a non-transitory, physical storage medium (e.g., volatile or non-volatile memory device), can be differentiated from a "computer-readable transmission medium," which refers to an electromagnetic signal.

With the increasing utilization of heterogeneous networks having a number of different access networks with varying spectrum allocations, a cognitive pilot channel (CPC) has been proposed to facilitate utilization of a heterogeneous network by mobile terminal. The CPC is designed to carry information regarding the different network operators, the ratio access technology employed within the heterogeneous network, the frequencies allocated to a particular region and the like. Based upon the information provided via the CPC, a mobile terminal may identify an appropriate system within the heterogeneous network without having to scan the entire spectrum.

Techniques have also been developed to allow femto base stations having flexible spectrum usage to utilize opportunistically overlaying cellular system uplink resources. In order to avoid causing interference for a base station, femto base stations must generally be deployed sufficiently far away from the base station. As such, a femto base station must be able to determine if the femto base station is sufficiently far away from the base station, and, if so, to select the most suitable carrier. In order to determine if the femto base stations are sufficiently far enough away from the base station, the femto base station may rely on measurement assistance from the users of the femto base station to estimate the downlink path loss from the base station. As such, these techniques have required the femto base station and/or the users of the femto base station to listen to the downlink transmissions from the base station.

One example of a communications system 10, such as a wireless communications system, having a heterogeneous network 12 which, in turn, includes a femto base station 14 is depicted in Figure 1. The system may include a plurality of devices comprising the heterogenous network 12 and enabling a mobile terminal 16 to communicate with other terminals or devices of the network. In this regard, the mobile terminal 16 may interface with the network 12 via one or more access points, base sites or base stations (BS). The mobile terminal 16 may be embodied in various manners and may include, for example, a portable digital assistant (PDA), pager, mobile computer, mobile television, gaming device, laptop computer, camera, video recorder, global positioning system (GPS) device, mobile telephone, cellular telephone and other types of voice and text communications systems. The access points may be a part of one or more cellular networks (e.g., first-generation (1G), second-generation (2G), 2.5G, third-generation (3G), 3.5G, 3.9G, fourth-generation (4G) mobile communication protocols, LTE, and/or the like ) or data networks (e.g., local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), such as the Internet, and/or the like).

The network 12 may include a collection of various different nodes, devices or functions that may be in communication with each other via corresponding wired and/or wireless interfaces. As such, the illustration of Figure 1 should be understood to be an example of a broad view of certain elements of the system and not an all inclusive or detailed view of the system 10 or the network 12. One or more communication terminals such as the mobile terminal 16 may be in communication with each other or network devices via the network 12 and each may include an antenna or antennas for transmitting signals to and for receiving signals from a base station. In turn, other devices such as processing elements (e.g., personal computers, server computers or the like) may be coupled to the mobile terminal 16 via the network 12. By directly or indirectly connecting the mobile terminal 16 and other devices to the network 12, the mobile terminal may be enabled to communicate with the other devices, for example, according to numerous communication protocols including Hypertext Transfer Protocol (HTTP) and/or the like, to thereby carry out various communication or other functions of the mobile terminal. Furthermore, the mobile terminal 16 may communicate in accordance with, for example, radio frequency (RF), Bluetooth (BT), Infrared (IR) or any of a number of different wireline or wireless communication techniques, including LAN, wireless LAN (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), WiFi, ultra-wide band (UWB), Wibree techniques and/or the like. As such, the mobile terminal 10 may be enabled to communicate with the network 12 and other devices by any of numerous different access mechanisms. For example, mobile access mechanisms such as wideband code division multiple access (W-CDMA), CDMA2000, global system for mobile communications (GSM), general packet radio service (GPRS) and/or the like may be supported as well as wireless access mechanisms such as WLAN, WiMAX, and/or the like and fixed access mechanisms such as digital subscriber line (DSL), cable modems, Ethernet and/or the like. As shown in Figure 1, the mobile terminal 16 may be in communication with the network 12 via an access point having a coverage area in which the mobile terminal is located. Examples of such access points may include one or more base stations 18 and one or more femto base stations 14 having corresponding femto cells 20 at least partially overlapping with the coverage area of a base station.

Figure 2 shows an example of an apparatus 22 that may facilitate carrier allocation for a femto base station 14 according to an example embodiment. The apparatus 22 may therefore be embodied or otherwise associated with the femto base station 16. The apparatus 22 may include or otherwise be in communication with a processor 24, a communication interface 26 and a memory device 28. The memory device 28 is a computer-readable storage medium and, as such, may be non-transitory. The memory device 28 may include, for example, volatile and/or non- volatile memory. The memory device 28 may be configured to store information, data, applications, instructions or the like for enabling the apparatus 22 to carry out various functions in accordance with an example embodiment of the present invention. For example, the memory device 28 could be configured to buffer input data for processing by the processor 24. Additionally or alternatively, the memory device 28 could be configured to store instructions for execution by the processor 24. As yet another alternative, the memory device 28 may be one of a plurality of databases that store information and/or media content.

The processor 24 may be embodied in a number of different ways. For example, the processor 24 may be embodied as one or more of various processing means such as a coprocessor, a microprocessor, a controller, a digital signal processor (DSP), a processing element with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), a microcontroller unit (MCU), a hardware accelerator, a special-purpose computer chip, processing circuitry, or the like. In an example embodiment, the processor 24 may be configured to execute instructions stored in the memory device 28 or otherwise accessible to the processor. Alternatively or additionally, the processor 24 may be configured to execute hard coded functionality. As such, whether configured by hardware or software methods, or by a combination thereof, the processor 24 may represent an entity (e.g., physically embodied in circuitry) capable of performing operations according to embodiments of the present invention while configured accordingly. Thus, for example, when the processor 24 is embodied as an ASIC, FPGA or the like, the processor may be specifically configured hardware for conducting the operations described herein. Alternatively, as another example, when the processor 24 is embodied as an executor of software instructions, the instructions may specifically configure the processor to perform the algorithms and/or operations described herein when the instructions are executed. However, in some cases, the processor 24 may be a processor of a specific device (e.g., a mobile terminal or network device) adapted for employing embodiments of the present invention by further configuration of the processor by instructions for performing the algorithms and/or operations described herein. The processor 24 may include, among other things, a clock, an arithmetic logic unit (ALU) and logic gates configured to support operation of the processor 70.

Meanwhile, the communication interface 26 may be any means such as a device or circuitry embodied in either hardware, software, or a combination of hardware and software that is configured to receive and/or transmit data from/to a network and/or any other device or module in communication with the apparatus 22. In this regard, the communication interface 26 may include, for example, an antenna (or multiple antennas) and supporting hardware and/or software for enabling communications with a wireless communication network. In some environments, the communication interface 26 may alternatively or also support wired communication. As such, for example, the communication interface 26 may include a communication modem and/or other hardware/software for supporting communication via cable, digital subscriber line (DSL), universal serial bus (USB) or other mechanisms.

In some example embodiments, one or more of the processor 24, communication interface 26 and/or memory device 28 illustrated in Figure 2 may be embodied as a chip or chip set. In other words, the apparatus 22 may comprise one or more physical packages (e.g., chips) including materials, components and/or wires on a structural assembly (e.g., a baseboard). The structural assembly may provide physical strength, conservation of size, and/or limitation of electrical interaction for component circuitry included thereon. In this regard, the processor 24, memory 28 and/or communication interface 16 may be embodied as a chip or chip set. The apparatus 22 may therefore, in some cases, be configured to or may comprise component(s) configured to implement embodiments of the present invention on a single chip or as a single "system on a chip." As such, in some cases, a chip or chipset may constitute means for performing one or more operations for providing the functionalities described herein and/or for enabling user interface navigation with respect to the functionalities and/or services described herein.

As an increasing number of femto base stations 14 are being deployed, it would be desirable to provide an improved technique for channel allocation for a femto base station within a heterogeneous network 12. In one example embodiment, a method, apparatus and computer program product are provided for selecting an uplink carrier to support communications with a femto base station 14 based upon an evaluation of one or more parameters of other transmissions supported by the respective uplink carrier. In this regard, the apparatus 22, such as the processor 24, may initially determine if an uplink carrier is unused on a local basis, that is, within the local domain. If a locally unused carrier is identified, the apparatus 22, such as the processor 24, may select the locally unused carrier to support communications with the femto base station 24. However, if all uplink carriers are used in the local domain to some degree, the method, apparatus and computer program product may evaluate the channel candidates and then select a candidate in accordance with an example embodiment of the present invention as shown in Figure 3 and described below.

Referring now to operation 30 of Figure 3, the apparatus 22 may include means, such as the processor 24 or the like, for evaluating one or more parameters of each of a plurality of transmissions supported by the respective uplink carrier. In this regard, a base station 18 may support a plurality of uplink carriers, such as uplink carriers that operate at different frequencies. Each uplink carrier may be capable of supporting a plurality of transmissions, such as transmissions with each of a plurality of mobile terminals 16. In one example embodiment, the transmissions may be in the form of resource blocks that are transmitted from the mobile terminals 16 to the base station 18 via a respective uplink carrier. In this example embodiment, the means, such as the processor 24, for evaluating one or more parameters of each of a plurality of transmissions supported by a respective uplink carrier may be configured to evaluate one or more parameters of each of a plurality of resource blocks transmitted via the respective uplink carrier.

Various parameters may be evaluated in accordance with various example embodiments in order to select an appropriate uplink carrier. In one embodiment, for example, the power level variations between the respective transmissions are evaluated, while in another embodiment, the arrival time variations between the respective transmissions are considered. In other embodiments, however, both the power level variations and the arrival time variations may be evaluated, while in still further embodiments, still other parameters may be evaluated in addition to or instead of the power level variations and/or the arrival time variations. The method, apparatus and computer program product of one example embodiment may make a plurality of measurements of the various parameters prior to the evaluation of the carrier candidates and the selection of an uplink carrier since the measurements of the various parameters is generally a small time scale operation (such as on the order of tens of milliseconds in one embodiment) while the evaluation and selection is a larger time scale operation (such as hundreds of milliseconds to tens of seconds in one embodiment).

For purposes of explanation, reference is now made to Figure 4 in which the power levels associated with each of a plurality of resource blocks transmitted via each of a plurality of different uplink carriers (designated Carrier 1, Carrier 2 and Carrier 3) is graphically illustrated. In the illustration of Figure 4, each set of bar graphs represents the power levels for the resource blocks (RBs) transmitted via a respective uplink carrier. For each uplink carrier, the power levels for a plurality of different resource blocks, identified as RB#1, RB#2 ... RB#n, are illustrated.

The means for evaluating one or more parameters of each of the plurality of transmissions supported by a respective uplink carrier as discussed above in conjunction with operation 30 of Figure 3 may include means, such as the processor 24 or the like, for evaluating the power level variations of the plurality of transmissions supported by a respective uplink carrier. See the operations collectively designated as 40 of Figure 5. In this regard, the means for evaluating the power level variations may include means, such as the processor 24 or the like, for determining a ratio of the highest power level to the lowest power level across the plurality of transmissions supported by a respective uplink carrier. See operation 42 of Figure 5. In regards to the example of Figure 4 and assuming that the power levels for the RBs between RB#3 and RB#n have intermediate power levels between those of RB#1 and RB#2, the power level associated with RB#1 is the highest power level on uplink carrier 1 and the power level for RB#2 is the lowest power level on uplink carrier 1. As such, the processor 24 may determine a ratio of the power level of RB#1 to the power level of RB#2 for uplink carrier 1. The processor 24 of this example embodiment may also determine the ratio of the highest power level to the lowest power level for each of the other uplink carriers such that a ratio is therefore determined for each respective uplink carrier.

In an alternative embodiment, a difference may be determined between the highest power level and the lowest power level across the plurality of transmissions supported by a respective uplink carrier. In this regard, the means for evaluating the power level variations may include means, such as the processor 24 or the like, for determining the difference between the highest power level and the lowest power level across the plurality of transmissions supported by a respective uplink carrier. See operation 44 of Figure 5. With reference again to Figure 4 by way of example, the processor 24 may determine a difference between the power level of RB#1 and the power level of RB#2 for uplink carrier 1. The resulting difference may then be normalized, as shown at operation 46 of Figure 5. As such, the means for evaluating the power level may also include means, such as the processor 24 or the like, for normalizing the difference between the highest and lowest power levels across the plurality of transmissions supported by a respective uplink carrier. In one example embodiment, the difference between the highest and lowest power levels is normalized based upon an average power level across the plurality of transmissions supported by the respective uplink carrier. As such, with respect to the example of Figure 4, the difference between the highest and lowest power levels, that is, the power levels of RB#1 and RB#2, respectively, acorss the resource blocks of uplink channel 1 may be normalized by being divided by the average power level of each of the resource blocks supported by uplink channel 1. The processor 24 of this example embodiment may also determine the normalized difference between the highest power level and the lowest power level for each of the other uplink carriers such that a normalized difference is therefore determined for each respective uplink carrier. By normalizing the difference between the highest and lowest power levels, additional weight may be given to the carrier on which data transmission would need less transmission power from the femto base station 14.

As shown in operation 32 of Figure 3, the apparatus 22 may also include means, such as the processor 24 or the like, for selecting a respective one of the uplink carriers to support communications with the femto base station 14 based upon the evaluation of the one or more parameters, such as the power level variations and/or arrival time variations of the plurality of transmissions supported by the respective uplink carrier. In the embodiment in which the power level variations of the plurality of transmissions supported by the respective uplink carrier are evaluated, such as by determining the ratio of the highest power level to the lowest power level or the normalized difference between the highest and lowest power levels across the plurality of transmissions supported by the respective uplink carrier, the apparatus 22 may include means, such as the processor 24 or the like, for selecting the uplink carrier that supports transmissions, such as the transmission of resource blocks, having the largest ratio or the largest normalized difference to support communications with the femto base station 14. See operation 48 of Figure 5. In this regard, the uplink carrier having the greatest variation in the power levels of the transmissions from the various mobile terminals 16 as represented by the largest ratio or the greatest difference may be representative of a femto base station 14 that is spaced a relatively far distance from the base station 18, such as shown in Figure 1. By selecting the uplink carrier that is associated with the femto base station 14 being spaced relatively far away from the base station 18, the use of the respective uplink carrier by the femto base station may be less likely to cause interference for the base station.

Figure 6 provides another example of the power levels of each of a plurality of transmissions supported by a respective uplink carrier. Each trace or line in the graph of Figure 6 represents the power level received by the femto base station 14 over time for a transmission from a different mobile terminal 16 over a common (the same) uplink carrier. As will be recognized from a comparison of Figure 6 to other graphical representations of the power levels of each of a plurality of transmissions supported by a respective uplink carrier, such as the graphical representation of Figure 8 discussed below, the power levels of the plurality of transmissions depicted in Figure 6 vary significantly and are therefore representative of a configuration in which the femto base station 14 is spaced from the base station 18 by a relatively far distance. As such, the interference created by use of the uplink carrier that supports the transmissions of Figure 6 to support communications with the femto base station 14 should be relatively small, thereby suggesting that the respective uplink carrier be selected.

In the foregoing discussion, the femto base station 14 has been located relatively far away from the base station 18 as shown, for example, in Figure 1. As such, the variations in the power levels between the transmissions supported by a respective carrier are relatively large such that a selection of the respective uplink carrier could be made in order to support subsequent communications with the femto base station 14 without creating substantial interference for the other users of the base station 18. In contrast, Figure 7 illustrates a network 14 in which the femto base station 14 is much closer to the base station 18. In this embodiment, the power levels of the transmissions supported by the respective uplink carrier are much more similar with less difference in power levels than that shown in Figures 5 and 6. In this regard, Figure 8 is a graphical representation of the powers levels of each of a plurality of transmissions supported by a respective uplink carrier in which the femto base station 14 is closer to the base station 18, such as illustrated in Figure 7, in comparison to the configuration represented by Figure 1. As will be recognized from the comparison of Figure 8 to Figure 6, the power levels of the plurality of transmissions depicted in Figure 8 do not vary significantly and are therefore representative of a configuration in which the femto base station 14 is not spaced very far from the base station 18. As such, the interference that would be created by the use of the uplink carrier that supports the transmissions of Figure 8 to support communications with the femto base station 14 could be substantial or at least more than is desired. As such, the uplink carrier represented by Figure 8 would therefore generally not be selected to support communications with the femto base station 14 and, instead, a different uplink carrier having a greater variation in the power levels of the transmissions supported by the uplink carrier would more preferably be selected in order to reduce the likelihood of interference at the base station 18. As discussed above, the power level variations of the transmissions supported by a respective uplink carrier may be evaluated in order to determine if the respective uplink carrier is to be selected to support communications with the femto base station 14. However, the method, apparatus and computer program product of example embodiments of the present invention may evaluate any of a number of different parameters including, for example, the arrival time variations of the transmissions supported by the respective uplink carriers in order to determine the appropriate uplink carrier to be selected. As shown in operation 50 of Figure 9, for example, the apparatus 22 may include means, such as the processor 24 or the like, for determining, for each uplink carrier, a difference in arrival times for the transmissions supported by the respective uplink carrier. By way of comparison, Figure 6 illustrates a plurality of transmissions supported by an uplink carrier in which the difference in arrival times is relatively great in comparison to the difference in arrival times of a plurality of transmissions supported by the uplink carrier represented by Figure 8. In this regard, the arrival times may be identified as those times at which the initial, relatively constant signals change, such as by decreasing relatively rapidly as shown at about 1000 μ≤ in Figures 6 and 8. In this embodiment, a relatively large difference between the arrival times of the transmissions supported by respective uplink carriers is indicative of a femto base station 14 that is located further from the base station 18 than an instance in which the arrival times of the transmissions supported by respective uplink carrier are more similar and have less difference therebetween.

In order to reduce the interference for other uses at the base station 18, the apparatus 22 of one example embodiment may also include means, such as the processor 24 or the like, for selecting the uplink carrier having the greatest difference in arrival times to support communications with the femto base station 14. See operation 52 of Figure 9. As noted above, other embodiments of the method, apparatus and computer program product may evaluate multiple parameters, such as both the power level variations and the arrival time variations, and/or may evaluate different and/or other combinations of parameters associated with the transmissions supported by respective uplink carriers in order to intelligently select a respective uplink carrier to support communications with a femto base station 14.

Once selected, the femto base station 14 may utilize the respective uplink carrier for communication. In some embodiments, the uplink carrier utilized by the femto base station 14 may be re-selected after having been utilized for some period of time. In this regard, the femto base station 14 may be configured to periodically re- select the uplink carrier. Alternatively, the femto base station 14 may be configured to monitor the performance of the uplink carrier and to initiate a reselection process if the performance of the uplink carrier falls below a predefined threshold. The femto base station 14, such as the processor 24, may be configured to perform carrier evaluation or measurement and possible carrier selection based upon a system parameter which may be defined as a predefined function of, for example, the designated identity, such as a cell ID, of the femto base station, the System Frame Number (SFN) and/or the cell ID of the base station 18, or based upon a parameter k that defines the number of subframes or system frames that exists between two successive carrier reselection operations. The self-configurable parameter k may be determined based on, for example, a comparison of the monitored carrier interference or load state against predefined threshold levels.

Still further, the network 14, such as the base station 18, may cause control signals to be transmitted to the femto base station 14 indicating that the femto base station should reselect the uplink carrier utilized by the femto base station. For example, the network may transmit the control signals over various channels, such as a Physical Downlink Control Channel (PDCCH), a Broadcast Channel (BCH) or a Paging Channel (PCH), and may identify the femto base station 14 by a designated identity, such as the cell ID of the femto base station. The network may cause the control signals to be transmitted either on a periodic basis, in accordance with a timeframe defined by a parameter k as described above, or in response to a predefined event, such as in response to the interference created for the base station 18 by the use of the respective uplink carrier by the femto base station 14 exceeding a predefined threshold. In this embodiment, the apparatus 22 may include means, such as the processor 24, the communication interface 26 and/or the like, for receiving a control signal indicating that an uplink carrier reselection is merited and thereafter repeating the process, such as shown in Figures 3, 5 or 9, for selecting an uplink carrier. See operation 34 of Figure 3.

In an embodiment in which the network causes control signals to be transmitted to the femto base station 14 indicating that the femto base station should reselect its carrier, both the femto base station and the mobile terminals 16 that are communicating with the femto base station via the respective uplink carrier may be able to receive the control signals from the base station 18 via the corresponding downlink. In instances in which the femto base station 14 is identified by a designated identity, such as a cell ID, the mobile terminals 16 that are communicating with the femto base station may recognize the control signals to be directed to the femto base station since the mobile terminal will also recognize the designated identity of the femto base station. Upon receiving the control signals, the mobile terminals 16 of one example embodiment may then autonomously attempt to locate the femto base station 14 in another carrier. Alternatively, the femto base station, such as the processor 24, may be configured to operate a semi-static, self-configurable and ciphered common control channel via which the femto base station may notify the mobile terminals 16 with which the femto base station is in communication about the carrier reselection and the cell status so as to assist the mobile terminals in discovering the reselected carrier of the femto base station.

Figures 3, 5 and 9 are flowcharts of a method and program product according to example embodiments of the invention. It will be understood that each block of the flowcharts, and combinations of blocks in the flowcharts, may be implemented by various means, such as hardware, firmware, processor, circuitry and/or other devices associated with execution of software including one or more computer program instructions. For example, one or more of the procedures described above may be embodied by computer program instructions. In this regard, the computer program instructions which embody the procedures described above may be stored by a memory device 28 of the apparatus 22 and executed by a processor 24. As will be appreciated, any such computer program instructions may be loaded onto a computer or other programmable apparatus, e.g., hardware, to produce a machine, such that the instructions which execute on the computer or other programmable apparatus create means for implementing the functions specified in the flowcharts block(s).

These computer program instructions may also be stored in a computer-readable memory that may direct a computer or other programmable apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowcharts block(s). The computer program instructions may also be loaded onto a computer or other programmable apparatus to cause a series of operations to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus implement the functions specified in the flowcharts block(s).

Accordingly, blocks of the flowcharts support combinations of means for performing the specified functions, combinations of operations for performing the specified functions and program instructions for performing the specified functions. It will also be understood that one or more blocks of the flowcharts, and combinations of blocks in the flowcharts, can be implemented by special purpose hardware-based computer systems which perform the specified functions, or combinations of special purpose hardware and computer instructions.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions other than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation

Claims

That Which is Claimed:

1. A method comprising:

for each of a plurality of uplink carriers, evaluating at least one of power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier; and

selecting a respective one of the uplink carriers to support communications with a femto base station based upon evaluation of the at least one of the power level variations or the arrival time variations.

2. A method according to Claim 1 wherein evaluating the power level variations comprises determining a ratio of highest power level to lowest power level across the plurality of transmissions supported by a respective uplink carrier, and wherein selecting a respective one of the uplink carriers comprises selecting the uplink carrier having a greatest ratio to support communications with the femto base station.

3. A method according to Claim 1 wherein evaluating the power level variations comprises determining a difference between a highest power level and a lowest power level across the plurality of transmissions supported by a respective uplink carrier and normalizing the difference based upon an average power level across the plurality of transmissions supported by the respective uplink carrier, and wherein selecting a respective one of the uplink carriers comprises selecting the uplink carrier having a greatest normalized difference to support communications with the femto base station.

4. A method according to Claim 1 wherein evaluating the arrival time variations comprises determining a difference in arrival times across the plurality of transmissions supported by a respective uplink carrier, and wherein selecting a respective one of the uplink carriers comprises selecting the uplink carrier having a greatest difference in arrival times to support communications with the femto base station.

5. A method according to any one of Claims 1-4 further comprising repeating the evaluation of at least one of the power level variations or the arrival time variations and selection of a respective uplink carrier in order to reselect an uplink carrier.

6. A method according to Claim 5 further comprising receiving a control signal indicating that the uplink carrier should be reselected and wherein repeating the evaluation of at least one of the power level variations or the arrival time variations and the selection of a respective uplink carrier is performed in response to the control signal.

7. An apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to at least: for each of a plurality of uplink carriers, evaluate at least one of power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier; and

select a respective one of the uplink carriers to support communications with a femto base station based upon evaluation of at least one of the power level variations or the arrival time variations.

8. An apparatus according to Claim 7 wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to evaluate the power level variations by determining a ratio of highest power level to lowest power level across the plurality of transmissions supported by a respective uplink carrier, and wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to select a respective one of the uplink carriers by selecting the uplink carrier having a greatest ratio to support communications with the femto base station.

9. An apparatus according to Claim 7 wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to evaluate the power level variations by determining a difference between a highest power level and a lowest power level across the plurality of transmissions supported by a respective uplink carrier and normalizing the difference based upon an average power level across the plurality of transmissions supported by the respective uplink carrier, and wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to select a respective one of the uplink carriers by selecting the uplink carrier having a greatest normalized difference to support communications with the femto base station.

10. An apparatus according to Claim 7 wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to evaluate the arrival time variations by determining a difference in arrival times across the plurality of transmissions supported by a respective uplink carrier, and wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to select a respective one of the uplink carriers by selecting the uplink carrier having a greatest difference in arrival times to support communications with the femto base station.

11. An apparatus according to any one of Claims 7-10 wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to repeat the evaluation of at least one of the power level variations or the arrival time variations and selection of a respective uplink carrier in order to reselect an uplink carrier.

12. An apparatus according to Claim 11 wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to receive a control signal indicating that the uplink carrier should be reselected and wherein the at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus to repeat the evaluation of at least one of the power level variations or the arrival time variations and the selection of a respective uplink carrier in response to the control signal.

13. An apparatus comprising :

means for evaluating, for each of a plurality of uplink carriers, at least one power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier; and means for selecting a respective one of the uplink carriers to support communications with a femto base station based upon evaluation of at least one power level variations or the arrival time variations.

14. An apparatus according to Claim 13 wherein the means for evaluating the power level variations comprises means for determining a ratio of highest power level to lowest power level across the plurality of transmissions supported by a respective uplink carrier, and wherein the means for selecting a respective one of the uplink carriers comprises means for selecting the uplink carrier having a greatest ratio to support communications with the femto base station.

15. An apparatus according to Claim 13 wherein the means for evaluating the power level variations comprises means for determining a difference between a highest power level and a lowest power level across the plurality of transmissions supported by a respective uplink carrier and means for normalizing the difference based upon an average power level across the plurality of transmissions supported by the respective uplink carrier, and wherein the means for selecting a respective one of the uplink carriers comprises means for selecting the uplink carrier having a greatest normalized difference to support communications with the femto base station.

16. An apparatus according to Claim 13 wherein the means for evaluating the arrival time variations comprises means for determining a difference in arrival times across the plurality of transmissions supported by a respective uplink carrier, and wherein the means for selecting a respective one of the uplink carriers comprises means for selecting the uplink carrier having a greatest difference in arrival times to support communications with the femto base station.

17. An apparatus according to any one of Claims 13-16 further comprising means for repeating the evaluation of at least one of the power level variations or the arrival time variations and selection of a respective uplink carrier in order to reselect an uplink carrier.

18. An apparatus according to Claim 17 further comprising means for receiving a control signal indicating that the uplink carrier should be reselected and wherein the means for repeating the evaluation of at least one of the power level variations or the arrival time variations and the selection of a respective uplink carrier is performed in response to the control signal.

19. A computer program product comprising at least one computer- readable storage memory having computer-executable code portions stored therein, the computer-executable code portions comprising:

program code instructions for evaluating, for each of a plurality of uplink carriers, at least one of power level variations or arrival time variations for a plurality of transmissions supported by a respective uplink carrier; and

program code instructions for selecting a respective one of the uplink carriers to support communications with a femto base station based upon evaluation of at least one of the power level variations or the arrival time variations.

20. A computer program product according to Claim 19 wherein the program code instructions for evaluating the power level variations comprise program code instructions for determining a ratio of highest power level to lowest power level across the plurality of transmissions supported by a respective uplink carrier, and wherein the program code instructions for selecting a respective one of the uplink carriers comprise program code instructions for selecting the uplink carrier having a greatest ratio to support communications with the femto base station.

21. A computer program product according to Claim 19 wherein the program code instructions for evaluating the power level variations comprise program code instructions for determining a difference between a highest power level and a lowest power level across the plurality of transmissions supported by a respective uplink carrier and program code instructions for normalizing the difference based upon an average power level across the plurality of transmissions supported by the respective uplink carrier, and wherein the program code instructions for selecting a respective one of the uplink carriers comprises program code instructions for selecting the uplink carrier having a greatest normalized difference to support communications with the femto base station.

22. A computer program product according to Claim 19 wherein the program code instructions for evaluating the arrival time variations comprise program code instructions for determining a difference in arrival times across the plurality of transmissions supported by a respective uplink carrier, and wherein the program code instructions for selecting a respective one of the uplink carriers comprise program code instructions for selecting the uplink carrier having a greatest difference in arrival times to support communications with the femto base station.

23. A computer program product according to any one of Claims 19-22 further comprising program code instructions for repeating the evaluation of at least one of the power level variations or the arrival time variations and selection of a respective uplink carrier in order to reselect an uplink carrier.

24. A computer program product according to Claim 23 further comprising program code instructions for receiving a control signal indicating that the uplink carrier should be reselected and wherein the program code instructions for repeating the evaluation of at least one of the power level variations or the arrival time variations and the selection of a respective uplink carrier is performed in response to the control signal.