Patent Publication Number: US-8976662-B2

Title: Apparatus and method for opportunistic relay association

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/597,059, entitled “Apparatus and Method for Opportunistic Relay Association” and filed on Feb. 9, 2012, which is expressly incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates generally to communication systems, and more particularly, to apparatuses, methods and products for opportunistic relay association. 
     2. Background 
     Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems. 
     Generally, a wireless multiple-access communication system can simultaneously support communication for multiple user equipment devices (UE). Each UE communicates with one or more base stations, such as an evolved Node B (eNB) via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the eNBs to the UEs, and the reverse link (or uplink) refers to the communication link from the UEs to the eNBs. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system. 
     Wireless communication systems can also employ one or more relays to extend coverage of one or more eNBs and/or support communications with a number of UEs. For example, the relays can facilitate communication between the eNBs and the UEs by relaying packets there between. In one example, the relays can communicate with one or more eNBs over a wireless backhaul link, and with one or more UEs over provided wireless access links. Current association algorithms for selecting eNBs for UEs may be insufficient for associating UEs with relays as the current algorithms utilize a received signal power or path loss to associate UEs with the eNBs. 
     SUMMARY 
     In an aspect of the disclosure, a method, a computer program product, and an apparatus for associating a user equipment (UE) with a relay in a wireless network are provided. The apparatus determines a relay backhaul link quality of a relay, determines a path loss from a UE to the relay, and compares the relay backhaul link quality to a direct link quality between the UE and a base station, and the path loss to a path loss threshold to determine whether to associate the UE with the relay. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed aspects will hereinafter be described in conjunction with the appended drawings, provided to illustrate and not to limit the disclosed aspects, wherein like designations denote like elements. 
         FIG. 1  illustrates a wireless communication system for associating an user equipment (UE) with a relay. 
         FIG. 2  illustrates a wireless communication system with access interference. 
         FIG. 3  illustrates an apparatus, e.g., an eNB, that associates UEs with relays based on link quality metrics and path loss measurements. 
         FIG. 4  illustrates a methodology for determining whether to associate a UE with a relay. 
         FIG. 5  illustrates a methodology for selecting a relay from a set of relays with which to associate a UE. 
         FIG. 6  illustrates a methodology for selecting a relay from an ordered list of relays with which to associate a UE. 
         FIG. 7  illustrates an apparatus that determines whether to associate a UE with a relay. 
         FIG. 8  illustrates an apparatus employing a processing system to determine whether to associate a UE with a relay. 
         FIG. 9  illustrates a multiple access wireless communication system according to one embodiment. 
         FIG. 10  illustrates a block diagram of a wireless communication system. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects are now described with reference to the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such aspect(s) may be practiced without these specific details. 
     Described herein are various aspects related to associating user equipment (UE) in a wireless network with a relay for providing wireless network access thereto. In one example, various metrics of the relay may be measured or otherwise approximated for determining whether a UE should be associated with a relay. Relay metrics may include, for example, a backhaul link quality of the relay, an access link path loss to the relay, a relay state and loading, etc., and/or additional metrics, such as a direct link quality between the UE and a base station, e.g., a serving evolved Node B (eNB). In one example, one or more relays may be determined to have a backhaul geometry, e.g., a link quality with a serving eNB of the relay, that is at least a threshold greater than a direct geometry of a UE, e.g., a link quality with a serving eNB of the UE. Of these relays, the ones with an access link path loss less than a threshold may be considered for association with the UE. In one example, of those relays considered for association, the relay with the best backhaul geometry may be chosen for association to the UE. In another example, the relay, of those considered for association, with a backhaul geometry within a threshold difference of the relay with the best backhaul geometry may be selected for association to the UE. In another example, relays may be sorted in a list based on the above metrics, and a relay from the list may be selected for association to the UE based on one or more threshold comparisons. In any case, the additional considerations of the association algorithm may lead to improved association results over current schemes that consider only received signal power or path loss. For example, the described association functions may avoid selecting relays that potentially cause interference to non-served UEs, while attempting to select relays that still provide reasonably good backhaul link quality. 
     As used in this application, the terms “component,” “module,” “system” and the like are intended to include a computer-related entity, such as but not limited to hardware, firmware, a combination of hardware and software/firmware, software/firmware, or software/firmware in execution. For example, a component may be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of illustration, both an application running on a computing device and the computing device may be a component. One or more components may reside within a process and/or thread of execution and a component can be localized on one computer and/or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures stored thereon. The components can communicate by way of local and/or remote processes such as in accordance with a signal having one or more data packets, such as data from one component interacting with another component in a local system, distributed system, and/or across a network such as the Internet with other systems by way of the signal. 
     Furthermore, various aspects are described herein in connection with a terminal, which can be a wired terminal or a wireless terminal. A terminal can also be called a system, device, subscriber unit, subscriber station, mobile station, mobile, mobile device, remote station, remote terminal, access terminal, user terminal, terminal, communication device, user agent, user device, user equipment, or user equipment device. A wireless terminal can be a cellular telephone, a satellite phone, a cordless telephone, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a smart phone, a netbook, a smartbook, an ultrabook, a handheld device having wireless connection capability, a laptop, a tablet, a computing device, or other processing devices connected to a wireless modem. Moreover, various aspects are described herein in connection with a base station. A base station can be utilized for communicating with wireless terminal(s) and can also be referred to as an access point, access node, a Node B, evolved Node B (eNB), or some other terminology. 
     Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form. 
     The techniques described herein may be used for various wireless communication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other systems. The terms “system” and “network” are often used interchangeably. A CDMA system may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and other variants of CDMA. Further, cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA system may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA system may implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) (including LTE-Advanced, or LTE-A) is a release of UMTS that uses E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). Additionally, cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). Further, such wireless communication systems may additionally include peer-to-peer (e.g., mobile-to-mobile) ad hoc network systems often using unpaired unlicensed spectrums, 802.xx wireless LAN, BLUETOOTH and any other short- or long-range, wireless communication techniques. 
     Various aspects or features will be presented in terms of systems that can include a number of devices, components, modules, and the like. It is to be understood and appreciated that the various systems can include additional devices, components, modules, etc. and/or may not include all of the devices, components, modules etc. discussed in connection with the figures. A combination of these approaches can also be used. 
     Referring to  FIG. 1 , a wireless communication system  100  is illustrated that facilitates associating a UE with a relay to receive wireless network access. System  100  includes a relay  102  that is served by a relay backhaul serving eNB  104  over a relay backhaul link  106 . For example, the relay  102  receives signals from the relay backhaul serving eNB  104  over the relay backhaul link  106  and accordingly relays, e.g., retransmits, the signals for improved hearability at one or more UEs associated with relay  102 . The relay backhaul serving eNB  104  may be a macrocell, picocell, femtocell, or similar eNB, and/or substantially any component for which the relay  102  can retransmit communications. In addition, the relay backhaul link  106  can be a wired or wireless, e.g., over-the-air, link between relay backhaul serving eNB  104  and relay  102 . 
     System  100  also includes a UE  108  that may be served by an eNB  110  over a direct link  112  thereto. Similar to the relay backhaul serving eNB  104 , eNB  110  may be a macrocell, picocell, femtocell, or similar eNB, a device communicating in peer-to-peer or ad-hoc mode with UE  108 , and/or the like, that can provide access to a wireless network. UE  108  may be a wireless terminal, a modem (or other tethered device), or substantially any device that can receive wireless network access from eNB  110 . The direct link may be a wired or wireless link that facilitates communication between eNB  110  and UE  108 . The eNB  110  may associate UE  108  with a relay based on one or more parameters, as described herein. Where eNB  110  elects to associate UE  108  with relay  102 , for example, relay  102  can communicate with UE  108  over an access link  114 , which can similarly be a wired or wireless link that facilitates communication between relay  102  and UE  108 . 
     The association algorithms described herein use link qualities of the aforementioned direct, backhaul and access links. For the direct and backhaul links, link geometries serve as the metric and for the access link path loss (PL) serves as the metric. Other suitable link metrics may be used. The association algorithms may also benefit from knowledge of the active/inactive state of the relays and the loading of the eNBs and relays. In summary, the association algorithms work with the following metrics: direct link quality, backhaul link quality, access link, relay state and loading, e.g., the ON or OFF state of the relays and the loading metrics, which may be as detailed as resource utilization or as coarse as the number of UEs camped onto the relay. These metrics help the association algorithm to select a suitable relay or eNB for a given UE. The absence of one or more metrics (due to lack of procedures to obtain such metrics) can result in use of suitable approximate metrics, for example, instead of geometric difference in PL to serving cell, a strongest interfering cell could be used. In some cases, the backhaul geometry might not be signaled. In such cases, implicit values of backhaul geometrics can be inferred. The association algorithm can be implemented in any entity that has access to the aforementioned metrics. It association algorithm can be implemented in the UE, eNB network, relay network, or distributed among these nodes. 
     According to an example, an eNB  110  can determine whether to associate a UE  108  with a relay  102  and/or one or more other relays based at least on geometries or other quality measurements of the various links or potential links (e.g., relay backhaul link  106 , direct link  112 , and/or access link  114 ). Though generally referred to herein as link quality, it is to be appreciated that concepts described herein can utilize substantially any measure of link geometry, such as received signal power, rise-over-thermal (RoT), path loss, signal-to-noise ratio (SNR), and/or the like. In addition, the link qualities may be measured, received from a related component, approximated based on other considerations, and/or the like. 
     In an example, in determining whether to associate the UE  108  with a relay, the eNB  110  may obtain relay backhaul link qualities of one or more relays, such as relay backhaul link  106  quality at relay  102 . This may include receiving the backhaul link quality over a backhaul link with the corresponding relay, e.g., relay  102 , with the relay backhaul serving eNB, e.g., eNB  104 , and/or the like. In one example, eNB  110  may serve one or more relays considered for association to UE  108 , and would thus know the relay backhaul link quality associated with the one or more relays. 
     In another example, in cases where the backhaul geometry information cannot be signaled to the eNB, the eNB  110  can infer the relay backhaul link quality based on whether the associated relay is operating in the wireless network, e.g., is the relay in an ON or OFF state. For example, the relay  102  can advertise services where its relay backhaul link  106  quality is at least a threshold quality. In this example, the eNB  110  can infer at least a worst case relay backhaul link  106  quality for the relay  102  based on determining that the relay  102  is communicating in the wireless network. For example, in one example, the UE  108  can report the relay  102  to the eNB  110  as a possible candidate for association, e.g., in a measurement report. Based on this indication, the eNB  110  can determine that the relay  102  is communicating in the network, and assume a worst case relay backhaul link  106  quality for the relay. In another example, the relay  102  can advertise its backhaul link  106  quality, and the UE  108  can determine the backhaul link  106  quality and notify the eNB  110 . 
     The eNB  110  can determine the direct link  112  quality based on control information received from the UE  108  communicating with the eNB  110 . Similarly, the UE  108  can report an access link  114  quality, e.g., as a path loss from the UE to the relay  102 , to the eNB  110 . This quality report may be part of a measurement report or other indication provided by the UE. 
     In one example, eNB  110  can determine a set of relays that are feasible for UE  108  association. The eNB  110  may define and generate this set of feasible relays based in part on determining relays having corresponding relay backhaul link qualities that are different from the direct link quality  112  by at least a threshold (e.g., where the relay backhaul link quality is greater than the direct link  112  quality). Thus, the eNB  110 , in this example, may determine whether relay backhaul link  106  quality is different from the direct link  112  quality by at least the threshold, and if so, can include the relay  102  in the set of feasible relays for associating to the UE  108 . The eNB  110  may also consider whether a path loss over the potential access link to the relay (e.g., the path loss of access link  114  for relay  102 ) achieves a threshold path loss to determine whether the relay should be in the set of feasible relays. 
     If there are no feasible relays, in an example, eNB  110  can continue serving UE  108  without relay association. In one example, given a set of feasible relays, eNB  110  can select a relay with the best backhaul link quality to associate to UE  108 . In one example, this can include relay  102 , and associating the relay to UE  108  can include communicating with the relay  102  to request or instruct relay  102  to serve UE  108 . 
     Where there is a plurality of relays with similarly strong backhaul link qualities, however, the chosen relay may interfere with one or more of the plurality of relays. This interference is referred to as access interference and is illustrated in  FIG. 2 , which shows a wireless communications system  200  having two relays, Relay  1  and  2 , and two UEs, UE  1  and UE  2 . Assume that UE 1  is served by Relay  1  and UE 2  is served by a macro (or micro) eNodeB. Then the eNodeB decides to off-load UE 2  to the relay network. Using the association schemes based on only backhaul geometry metric and access path loss, the eNB could potentially offload the UE 2  to Relay  2  (shown by dashed line in  FIG. 2 ). However, this could cause access interference (an X-channel), where Relay  1  interferes with Relay  2 , and vice-versa. The methods described above, which are based on only backhaul geometry and access PL to the serving relay, may be insufficient to handle the access interference issue. 
     Thus, to address the access interference issue, in another example, given the set of feasible relays, eNB  110  can determine the relay with the best backhaul link quality, but can associate UE  108  with a relay having a reasonable backhaul link quality as compared to the relay with the best backhaul link quality. For example, this can include selecting the relay with a backhaul quality that differs from the best backhaul link quality by no more than a threshold quality. Thus, the UE  108  avoids selecting the relay with the best backhaul quality, selection of which could cause interference to other relays, as described. 
     In yet another example, eNB  110  can consider possible relay access link interference in selecting a relay for associating to UE  108 , which can include consideration of additional parameters or comparisons thereof. For example, eNB  110  can additionally obtain information regarding whether a given relay is serving UEs and/or a number of UEs served, which can be received over a backhaul link with the relays or corresponding serving eNB, etc. In this example, eNB  110  can determine a set of relays visible to UE  108 . Visible relays include relays having an access link path loss from the UE  108  that is less than a threshold. The set of visible relays can be sorted based on one or more considerations, such as relay backhaul link quality. If relays have identical backhaul link quality (e.g., especially in the case where the backhaul link quality is assumed to be a worst case quality), ordering can be determined based on considerations such as the number of UEs served by the relays, access link path loss to the relays, a random determination algorithm, and/or the like. 
     Based on the ordered set of visible relays, the eNB  110  can select a first relay that meets certain comparisons as the relay for associating to UE  108 . For example, the comparisons can include a first metric to a first threshold, wherein the first metric is based on the path loss from the UE to a first relay and a second path loss from the UE to a second relay; a second metric to a second threshold, wherein the second parameter is based on the path loss from the UE to a first relay and a third path loss from the relay to another UE served by another relay; a third metric to a third threshold, wherein the third metric is based on a relay path loss from the relay to another relay; and a fourth metric to the direct link quality, wherein the fourth metric is based on the relay backhaul link quality and a fourth threshold. Based on the comparisons and various threshold values, the eNB  110  can select a relay for associating with UE  108  that does not cause undue interference to other relays, UEs served by other relays, and/or the like. 
     Though described above and herein as occurring in the eNB  110 , it is to be appreciated that the association algorithms described can be performed at substantially any node in a wireless network, e.g., UE, relay, core network components, such as a gateway, etc., and/or distributed across a plurality of such nodes. 
     Turning now to  FIG. 3 , system  300  illustrates an example of the eNB  110  in accordance with aspects described herein. The eNB  110  includes a direct link quality component  302  for obtaining one or more quality metrics or other measures of geometry of the direct link from the eNB  110  to one or more UEs, such as UE  108 . The eNB also includes a relay backhaul link quality component  304  for measuring, receiving, or otherwise approximating one or more quality metrics or other measures of geometry of a backhaul link from one or more relays to associated serving eNBs. The eNB  110  also includes a path loss component  306  for receiving or otherwise measuring path loss between a UE and one or more relays, and a relay associating component  308  for determining whether to associate a UE to a relay based in part on one or more of the quality or path loss metrics. 
     According to an example, the direct link quality component  302  can obtain a direct link quality  310  of a direct link between the eNB  110  and a related UE based on control information from the UE, a determined throughput of data to/from the UE, and/or the like. 
     The relay backhaul link quality component  304  can determine relay backhaul link quality  312  for one or more relays in part by receiving an indication of the backhaul link quality from the relay, e.g., over a backhaul link to the serving eNB thereof, approximating the backhaul link quality of the relay based on one or more parameters, and/or the like, as described. In one example, the relay backhaul link quality component  304  can approximate a relay backhaul link quality  312  of one or more relays as a worst case relay backhaul link quality where the relay backhaul link quality component  304  determines the relay is in an on state. In this example, the worst case relay backhaul link quality can be a threshold quality required for the relay to operate in the on state. The relay backhaul link quality component  304  can infer the relay is in the on state based on receiving an indication from the UE that the relay is operating in the network, e.g., in a measurement report, as described above. In one example, the relay backhaul link quality component  304  can determine the relay backhaul link quality  312  as the worst case backhaul link quality where no other backhaul link quality is received, e.g., from the relay or its associated serving eNB, or otherwise measured. In another example, the eNB  110  can serve the relay, and the relay backhaul link quality component  304  thus determines the relay backhaul link quality  312  of the relay based on one or more measurements of the backhaul link, control information received from the relay and/or the like. 
     The path loss component  306  can determine a path loss  314  between the UE and one or more of the relays. In one example, the path loss component  306  can determine the path loss based on a report from the UE, e.g., a measurement report, as previously described. In one example, the path loss component  306  can determine the path loss only for relays that have at least a threshold relay backhaul link quality  312 , e.g., as compared to the direct link quality  310  or otherwise independent thereof. 
     The relay associating component  308  can determine whether to associate a relay with a UE based on one or more of the direct link quality  310 , the relay backhaul link quality  312 , or the path loss  314 , as previously described. In one example, the relay associating component  308  can determine a set of feasible relays for associating to a UE. As previously described, the relay associating component  308  can determine the set of relays as those having a relay backhaul link quality  312  at least a threshold difference from the direct link quality  310 , e.g., relay backhaul link quality  312  greater than direct link quality  310 . In addition, the relay associating component  308  can further determine the set of feasible relays based on whether a path loss  314  from the UE to a given relay is less than a threshold. If there are no feasible relays, eNB  110  can continue serving the UE. 
     A described above, given the set of feasible relays, the relay associating component  308  can select a relay with the best relay backhaul link quality  312  and/or a relay with a relay backhaul link quality  312  that is at most a threshold quality poorer than the relay with the best relay backhaul link quality for association to the UE. This can mitigate interference that may be caused by selecting the relay with the best relay backhaul link quality  312 , as previously described. In another example, the relay associating component  308  can generate a set of visible relays that have path loss  314  with the UE that is less than a threshold. The relay associating component  308  can determine whether a relay is active based in part on receiving an indication of such and/or a number of UEs supported by the relay over a backhaul link to a serving eNB of the relay or another component, receiving an indication of communicating with the relay from a UE, a recent handover of a UE from eNB  110  to the relay, and/or the like. 
     Upon determining the set of visible relays, relay associating component  308  can order the set based on the following criteria, in one example, where a relay with a greater backhaul quality is considered higher in the order. If two relays have identical or substantially similar backhaul link quality, then the relay that is active, e.g., serving at least one UE, is considered higher in the order. If both the relays are active then the relay with lesser number of UEs associated to it is deemed higher in order. If the relays are still tied or are inactive, the relay with a lower access link path loss  314  is deemed higher in order. If the relays are still tied, e.g., same or similar backhaul quality, same activity status, same or similar number of UEs associated to them, same or similar path loss, etc., one of the relays can be deemed higher in the order according to a random function. 
     Based on the generated ordered list of relays, relay associating component  308  can select a relay for associating the UE based on one or more additional determinations. For example, the relay associating component  308  can associate the UE to the top-most candidate relay in the ordered list that satisfies the following comparisons: 
     
       
         
           
             
               
                 
                   
                     
                       
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     If no such candidate visible relay exists, then the relay associating component  308  can retain association of the UE to eNB  110 . In one example, the thresholds above can be tuned to reduce access link interference. For example, to avoid range expansion, relay associating component  308  can set threshold 1 =0 and threshold 2 =0. Moreover, for example, relay associating component  308  can choose threshold 3  to ensure that nearby relays are not active, which might potentially cause interference with UE mobility. Relay associating component  308  can set threshold 4  as an offloading parameter to offload the UE to a relay, e.g., whose backhaul is not as good as the direct link of the UE. For example, this can be used to obtain cell-splitting gains. 
     Referring to  FIGS. 4-6 , example methodologies for associating relays to UEs are illustrated. While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more embodiments, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, it is to be appreciated that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with one or more embodiments. 
     Referring to  FIG. 4 , an example methodology  400  that facilitates associating a UE to a relay based on a relay backhaul link quality, direct link quality, and path loss to the relay is illustrated. At step  402 , a relay backhaul link quality of a relay can be determined. This can include receiving the relay backhaul link quality from the relay and/or from an eNB serving the relay, receiving the relay backhaul link quality from a device communicating with the relay, approximating the relay backhaul link quality based on one or more parameters of the relay, etc. In one example, determining the relay backhaul link quality at step  402  may be based on a worst case relay backhaul link quality required for the relay to operate in the wireless network. In this example, an indication that the relay is operating in the wireless network can be received, and the worst case relay backhaul link quality can be determined for the relay at step  402 . 
     At step  404 , a path loss from a UE to the relay can be determined. For example, this can include receiving the path loss in a measurement report or other indication from the UE, receiving the path loss in an indication from the relay, e.g., via a backhaul link to its serving eNB, and/or the like. 
     At step  406 , the relay backhaul link quality can be compared to a direct link quality between the UE and an eNB and the path loss can be compared to a path loss threshold to determine whether to associate the UE with the relay. As described above, this can include determining whether the difference between the relay backhaul link quality and the direct link quality is at least a quality threshold and determining whether the path loss is less than a path loss threshold. 
     If so, at step  408 , the UE can optionally be associated to the relay where the relay backhaul link quality is at least a quality threshold difference from the direct link quality and where the path loss is less than the path loss threshold. For example, associating the UE to the relay at step  408  can also be based on determining that the relay backhaul link quality of the relay is the best relay backhaul link quality out of a set of relays, no more than a threshold quality worse than the best relay backhaul link quality, etc., as described above. 
     In other examples, a list of relays can be created based on respective path losses, and the list can be ordered based on one or more criteria. In this example, a relay for associating with the UE at step  408  can be selected from the list based on one or more comparisons, as described above. 
     Turning to  FIG. 5 , an example methodology  500  is shown for selecting a relay from a set of relays for associating to a UE. At step  502 , a set of relays having a respective relay backhaul link quality that is different from a direct link quality of a UE by at least a threshold, and a respective path loss to the UE that is less than a path loss threshold can be determined. For example, the set can be determined based in part on comparing the link qualities and path losses as received from the relays, UEs, etc., or otherwise approximated based on other parameters, as previously described. 
     At step  504 , one relay out of the set of relays can be selected for associating to the UE based on its respective relay backhaul link quality. As described, this can include comparing the relay backhaul link quality to those of other relays and determining the relay backhaul link quality of the selected relay is the best. In another example, this can include selecting a relay with a relay backhaul link quality that is no more than a threshold worse than the best relay backhaul link quality to mitigate potential interference caused by selecting the relay with the best relay backhaul link quality. 
     In  FIG. 6 , an example methodology  600  is shown for selecting a relay from an ordered list of relays for associating to a UE. At step  602 , a list of relays is determined, where each relay has a respective path loss from the UE that is less than a path loss threshold to the UE. A step  604 , the list of determined relays is ordered based on one or more criteria regarding a relay backhaul link quality thereof. The one or more criteria, as described above, can include comparing the relay backhaul link quality with that of other relays in the list. The list can also be ordered based on a number of UEs served by the relays, the access link path loss from the relays to the UE, and/or the like. 
     At step  606 , one relay in the ordered list is selected for associating to the UE based on one or more comparisons of the relay backhaul link quality and/or a path loss from the relay. As described above, the comparisons can include comparing metrics or parameters to a plurality of thresholds that can be defined for different purposes, e.g., to avoid range expansion, to mitigate interference with UE mobility, to offload the UE, etc. 
     It will be appreciated that, in accordance with one or more aspects described herein, inferences can be made regarding determining a relay backhaul link quality, determining thresholds for selecting a relay from an ordered list of relays for association to a UE, and/or the like, as described. As used herein, the term to “infer” or “inference” refers generally to the process of reasoning about or inferring states of the system, environment, and/or user from a set of observations as captured via events and/or data. Inference can be employed to identify a specific context or action, or can generate a probability distribution over states, for example. The inference can be probabilistic—that is, the computation of a probability distribution over states of interest based on a consideration of data and events. Inference can also refer to techniques employed for composing higher-level events from a set of events and/or data. Such inference results in the construction of new events or actions from a set of observed events and/or stored event data, whether or not the events are correlated in close temporal proximity, and whether the events and data come from one or several event and data sources. 
     Turning now to  FIG. 7 , an apparatus  700  for determining whether to associate a UE to a relay is illustrated. The apparatus  700  is configured to implement one or more of the methods of the flow charts of  FIGS. 4-6 , and may reside entirely or at least partially within an eNB or other device for determining association. It is to be appreciated that apparatus  700  is represented as including functional blocks, which can be functional blocks that represent functions implemented by a processor, software/firmware, or combination thereof. The apparatus  700  includes a logical grouping  702  of components (e.g., electrical components) that can act in conjunction. For instance, logical grouping  702  can include an electrical component for determining a relay backhaul link quality of a relay ( 704 ). As described, this can include measuring, receiving, or otherwise approximating the backhaul link quality for the relay. 
     Moreover, logical grouping  702  can include an electrical component for determining a path loss from a UE to the relay ( 706 ). Logical grouping  702  can also include an electrical component for comparing the relay backhaul link quality to a direct link quality between the UE and an eNB and the path loss to a path loss threshold to determine whether to associate the UE with the relay ( 708 ). In one example, electrical component  708  can compare such to determine a set of relays and select a relay from the set based on the relay backhaul link quality or one or more other comparisons or determinations based on such. 
     The electrical component  704  may comprise a relay backhaul link quality component  304 , the electrical component  706  may comprise a path loss component  306 , the electrical component  708  may comprise a relay associating component  308 , etc., in one example. Additionally, apparatus  700  can include a memory  710  that retains instructions for executing functions associated with the electrical components  704 ,  706 , and  708 , stores data used or obtained by the electrical components  704 ,  706 ,  708 , etc. While shown as being external to memory  710 , it is to be understood that one or more of the electrical components  704 ,  706 , and  708  can exist within memory  710 . In one example, electrical components  704 ,  706 , and  708  can comprise at least one processor, or each electrical component  704 ,  706 , and  708  can be a corresponding module of at least one processor. Moreover, in an additional or alternative example, components  704 ,  706 , and  708  can be a computer program product including a computer readable medium, where each component  704 ,  706 , and  708  can be corresponding code. 
       FIG. 8  is a diagram  800  illustrating an example of a hardware implementation for an apparatus  700 ′ employing a processing system  814 . The processing system  814  may be implemented with a bus architecture, represented generally by the bus  824 . The bus  824  may include any number of interconnecting buses and bridges depending on the specific application of the processing system  814  and the overall design constraints. The bus  824  links together various circuits including one or more processors and/or hardware modules, represented by the processor  804 , the relay backhaul link quality module  704 ′, the path loss module  706 ′, the comparison module  708 ′, and the computer-readable medium  806 . The bus  824  may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. 
     The processing system  814  may be coupled to a transceiver  810 . The transceiver  810  is coupled to one or more antennas  820 . The transceiver  810  provides a means for communicating with various other apparatus over a transmission medium. The transceiver  810  receives a signal from the one or more antennas  820 , extracts information from the received signal, and provides the extracted information to the processing system  814 . In addition, the transceiver  810  receives information from the processing system  814 , and based on the received information, generates a signal to be applied to the one or more antennas  820 . The processing system  814  includes a processor  804  coupled to a computer-readable medium  806 . The processor  804  is responsible for general processing, including the execution of software/firmware stored on the computer-readable medium  806 . The software/firmware, when executed by the processor  804 , causes the processing system  814  to perform the various functions described supra for any particular apparatus. The computer-readable medium  806  may also be used for storing data that is manipulated by the processor  804  when executing software/firmware. The processing system further includes at least one of the modules  704 ′,  706 ′, and  708 ′. The modules may be software modules running in the processor  804 , resident/stored in the computer readable medium  806 , one or more hardware modules coupled to the processor  804 , or some combination thereof. 
     In one configuration, the apparatus  700 / 700 ′ for wireless communication includes means for determining a relay backhaul link quality of a relay, means for determining a path loss from a UE to the relay, and means for comparing the relay backhaul link quality to a direct link quality between the UE and a base station, and the path loss to a path loss threshold to determine whether to associate the UE with the relay. The apparatus  700 / 700 ′ may further include means for associating the UE with the relay when the relay backhaul link quality is different from the direct link quality by at least a quality threshold and the path loss is less than the path loss threshold. The aforementioned means may be one or more of the aforementioned components/modules of the apparatus  700  and/or the processing system  814  of the apparatus  700 ′ configured to perform the functions recited by the aforementioned means. 
       FIG. 9  shows a wireless communication network  900 , which may be an LTE network. The wireless network  900  may include a number of evolved Node Bs (eNBs)  910  and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a Node B, an access point, etc. Each eNB  910  may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of an eNB and/or an eNB subsystem serving this coverage area, depending on the context in which the term is used. 
     An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cells. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG), UEs for users in the home, etc.). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. An eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown in  FIG. 9 , the eNBs  910   a ,  910   b  and  910   c  may be macro eNBs for the macro cells  902   a ,  902   b  and  902   c , respectively. The eNB  910   x  may be a pico eNB for a pico cell  902   x . The eNBs  910   y  and  910   z  may be femto eNBs for the femto cells  902   y  and  902   z , respectively. An eNB may support one or multiple (e.g., three) cells. 
     The wireless network  900  may also include relay stations. A relay station can receive a transmission of data and/or other information from an upstream station (e.g., an eNB or a UE) and send a transmission of the data and/or other information to a downstream station (e.g., a UE or an eNB). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in  FIG. 9 , a relay station  910   r  may communicate with the eNB  910   a  and a UE  920   r  in order to facilitate communication between the eNB  910   a  and the UE  920   r . A relay station may also be referred to as a relay eNB, a relay, etc. 
     The wireless network  900  may be a heterogeneous network that includes eNBs of different types, e.g., macro eNBs, pico eNBs, femto eNBs, relays, etc. These different types of eNBs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless network  900 . For example, macro eNBs may have a high transmit power level (e.g., 20 Watts) whereas pico eNBs, femto eNBs and relays may have a lower transmit power level (e.g., 1 Watt). 
     The wireless network  900  may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time. The techniques described herein may be used for both synchronous and asynchronous operation. 
     A network controller  930  may couple to a set of eNBs and provide coordination and control for these eNBs. The network controller  930  may communicate with the eNBs  910  via a backhaul. The eNBs  910  may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul. 
     The UEs  920  (e.g.,  920   x ,  920   y ) may be dispersed throughout the wireless network  900 , and each UE may be stationary or mobile. A UE may also be referred to as a device, a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem (or other tethered device), a wireless communication device, a handheld device, a laptop computer, a tablet, a smart phone, a netbook, a smartbook, an ultrabook, a cordless phone, a wireless local loop (WLL) station, etc. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, etc. In  FIG. 9 , a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates potentially interfering transmissions between a UE and an eNB. Moreover, eNBs  910  can provide functionality to attempt to associate UE  920   r  with a relay  910   r , as described above. 
       FIG. 10  is a block diagram of an embodiment of a transmitter system  1010  (also known as, e.g., access point) and a receiver system  1050  (also known as, e.g., access terminal) in a MIMO system  1000 . At the transmitter system  1010 , traffic data for a number of data streams is provided from a data source  1012  to a transmit (TX) data processor  1014 . In addition, it is to be appreciated that transmitter system  1010  and/or receiver system  1050  can employ the systems (e.g.,  FIGS. 1 ,  2 ,  3 ,  7 ,  8 ,  9 ) and/or methods (e.g.,  FIGS. 4 ,  5 ,  6 ) described herein to facilitate wireless communication there between. For example, components/modules or functions of the systems and/or methods described herein can be part of a memory  1032  and/or  1072  or processors  1030  and/or  1070  described below, and/or can be executed by processors  1030  and/or  1070  to perform the disclosed functions. 
     In an embodiment, each data stream is transmitted over a respective transmit antenna. TX data processor  1014  formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data. 
     The coded data for each data stream can be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and can be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (e.g., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream can be determined by instructions performed by processor  1030 . 
     The modulation symbols for all data streams are then provided to a TX MIMO processor  1020 , which can further process the modulation symbols (e.g., for OFDM). TX MIMO processor  1020  then provides N T  modulation symbol streams to N T  transmitters (TMTR)  1022   a  through  1022   t . In certain embodiments, TX MIMO processor  1020  applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted. 
     Each transmitter  1022  receives 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. N T  modulated signals from transmitters  1022   a  through  1022   t  are then transmitted from N T  antennas  1024   a  through  1024   t , respectively. 
     At receiver system  1050 , the transmitted modulated signals are received by N R  antennas  1052   a  through  1052   r  and the received signal from each antenna  1052  is provided to a respective receiver (RCVR)  1054   a  through  1054   r . Each receiver  1054  conditions (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. 
     An RX data processor  1060  then receives and processes the N R  received symbol streams from N R  receivers  1054  based on a particular receiver processing technique to provide N T  “detected” symbol streams. The RX data processor  1060  then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor  1060  is complementary to that performed by TX MIMO processor  1020  and TX data processor  1014  at transmitter system  1010 . 
     A processor  1070  periodically determines which pre-coding matrix to use. Processor  1070  formulates a reverse link message comprising a matrix index portion and a rank value portion. 
     The reverse link message can 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 processor  1038 , which also receives traffic data for a number of data streams from a data source  1036 , modulated by a modulator  1080 , conditioned by transmitters  1054   a  through  1054   r , and transmitted back to transmitter system  1010 . 
     At transmitter system  1010 , the modulated signals from receiver system  1050  are received by antennas  1024 , conditioned by receivers  1022 , demodulated by a demodulator  1040 , and processed by a RX data processor  1042  to extract the reserve link message transmitted by the receiver system  1050 . Processor  1030  determines which pre-coding matrix to use for determining the beamforming weights then processes the extracted message. 
     Processors  1030  and  1070  can direct (e.g., control, coordinate, manage, etc.) operation at transmitter system  1010  and receiver system  1050 , respectively. Respective processors  1030  and  1070  can be associated with memory  1032  and  1072  that store program codes and data. For example, processors  1030  and  1070  can perform functions described herein with respect to associating UEs with relays, and/or can operate one or more of the corresponding components/modules. Similarly, memory  1032  and  1072  can store instructions for executing the functionality or components/modules, and/or related data. 
     The various illustrative logics, logical blocks, modules, components, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Additionally, at least one processor may comprise one or more modules operable to perform one or more of the steps and/or actions described above. An exemplary storage medium may be coupled to the processor, such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. Further, in some aspects, the processor and the storage medium may reside in an ASIC. Additionally, the ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
     In one or more aspects, the functions, methods, or algorithms described may be implemented in hardware, software/firmware, or combinations thereof. If implemented in software/firmware, the functions may be stored or transmitted as one or more instructions or code on a computer-readable medium, which may be incorporated into a computer program product. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage medium may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, substantially any connection may be termed a computer-readable medium. For example, if software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs usually reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     While the foregoing disclosure discusses illustrative aspects and/or embodiments, it should be noted that various changes and modifications could be made herein without departing from the scope of the described aspects and/or embodiments as defined by the appended claims. Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and/or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise. 
     It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the widest scope consistent with the principles and novel features disclosed herein. Reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.”