Patent Publication Number: US-2015063253-A1

Title: Methods for neighbor csi-rs detection

Description:
CROSS REFERENCES 
     The present Application for Patent claims priority to U.S. Provisional Patent Application No. 61/874,187 by Barbieri et al., entitled “Methods for Neighbor CSI-RS Detection,” filed Sep. 5, 2013, assigned to the assignee hereof, and expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. 
     A wireless communication network may include a number of base stations or Node-Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station. 
     Multiple base stations may have overlapping coverage areas, and a UE may receive signals from a serving cell, as well as one or more potentially interfering signals from one or more non-serving cells. Various techniques exist for mitigation of interference from non-serving cells. For example, if a UE has a channel estimation of a signal from a non-serving cell, this information may be used to derive equalizer coefficients for the UE receiver and reduce the effects of the interfering signal on a signal from the UE&#39;s serving cell. Interference mitigation techniques may also include, for example, interference suppression (IS), minimum mean square error (MMSE) interference rejection, multi-user detection (MUD), joint maximum likelihood (ML) detection, symbol-level interference cancellation (SLIC), and/or codeword-level interference cancellation (CWIC). Such interference mitigation techniques may be enhanced if a UE has information related to the potentially interfering signals. 
     SUMMARY 
     Methods and apparatuses are described for identifying one or more channel state information reference signal (CSI-RS) from a non-serving cell in a wireless communications network. In some examples, a subset of virtual cell identity (VCID) candidates may be identified, and one or more CSI-RS locations for one or more CSI-RS in a received signal from a non-serving cell may be determined The CSI-RS locations may be determined, for example, based on periodicity properties of CSI-RS transmissions of the subset of VCID candidates. The one or more determined locations in the received signal may be used to identify the one or more CSI-RS in the received signal through searching the locations for all available VCIDs in a set of VCIDs. 
     A method for identifying one or more channel state information reference signal (CSI-RS) from a non-serving cell in a wireless communications network is described. The method may include identifying a subset of virtual cell identity (VCID) candidates, determining one or more CSI-RS locations for one or more CSI-RS in a received signal from a non-serving cell based on the subset of VCID candidates, and identifying one or more CSI-RS in the received signal based on the one or more CSI-RS locations. Identifying the one or more CSI-RS may include, for example, determining one or more of a subframe configuration, a resource configuration, a VCID, or an antenna port configuration for a CSI-RS contained in the received signal. 
     In some examples, identifying the one or more CSI-RS may include, for each CSI-RS location from the one or more CSI-RS locations, searching for a VCID, in a set of available VCIDs, corresponding to a CSI-RS sequence generated according to the VCID at the CSI-RS location, and determining the one or more CSI-RS responsive to the searching. The searching may include, for example, estimating one or more of a delay spread or power delay profile (PDP) of the received signal, averaging frequency domain samples of the received signal according to the estimated delay or PDP, and testing the averaged frequency domain samples with the VCID to determine whether the averaged frequency domain samples contain a CSI-RS based on the VCID. The estimating may be based on one or more antenna ports associated with a common reference signal (CRS), for example. The CRS antenna port(s) to be used for the estimation may be signaled by a network entity of the wireless communications network, or selected autonomously based on at least one of a physical cell identity (PCI), the CSI-RS location, or the VCID. 
     In some examples, the identifying the subset of VCID candidates may include selecting the subset of VCID candidates from a number of subsets of VCID candidates. The method may also include, in some examples, identifying one or more particular CSI-RS locations, and the selecting may include selecting the subset of VCID candidates from the number of subsets of VCID candidates responsive to the identifying. The identifying one or more particular CSI-RS locations may be based on, for example, information received from a network entity of the wireless communications network that restricts allowed locations for a CSI-RS. The VCID subsets may be provided in radio resource control (RRC) signaling, in some examples. 
     In some examples, the one or more CSI-RS locations may include time-domain locations, which may include, for example, a subframe configuration and/or a resource configuration for a CSI-RS contained in the received signal. In some examples, determining the one or more CSI-RS locations may include identifying a subset of subframes, measuring a time-domain correlation of received frequency domain samples across the subset of subframes for each VCID from the subset of VCID candidates, and determining the one or more CSI-RS locations based on the measured time-domain correlation. 
     In some examples, selecting the subset of VCID candidates may be based on, one or more of a physical cell identifier (PCI) of one or more non-serving cells, a random selection from a set of available VCID candidates, an indication of available VCID candidates provided by a network entity of the wireless communications network, cross-correlation measurements between VCID pairs from a set of available VCID candidates, information provided by a network entity of the wireless communications network, or a combination thereof. In some examples, the one or more CSI-RS locations may be determined irrespective of whether a CSI-RS contained in the received signal has a VCID in the identified subset of VCID candidates. 
     An apparatus for identifying one or more CSI-RS from a non-serving cell in a wireless communications network is described. The apparatus may include means for identifying a subset of VCID candidates, means for determining one or more CSI-RS locations for one or more CSI-RS in a received signal from a non-serving cell based on the subset of VCID candidates, and means for identifying one or more CSI-RS in the received signal based on the one or more CSI-RS locations. The means for identifying may determine, for example, one or more of a subframe configuration, a resource configuration, a VCID, or an antenna port configuration for a CSI-RS contained in the received signal. In some examples, the means for identifying the one or more CSI-RS, for each CSI-RS location from the one or more CSI-RS locations, may search for a VCID, in a set of available VCIDs, corresponding to a CSI-RS sequence generated according to the VCID at the CSI-RS location, and determine the one or more CSI-RS responsive to the search. 
     In some examples, the means for identifying the subset of VCID candidates may select the subset of VCID candidates from a number of subsets of VCID candidates. The CSI-RS locations may include, for example, a subframe configuration and/or a resource configuration for a CSI-RS contained in the received signal. The means for selecting the subset of VCID candidates may select the subset of VCID candidates based on, for example, one or more of a physical cell identifier (PCI) of one or more non-serving cells, a random selection from a set of available VCID candidates, a set of available VCID candidates provided by a network entity of the wireless communications network, cross-correlation measurements between VCID pairs from a set of available VCID candidates, information provided by a network entity of the wireless communications network, or a combination thereof. In some examples, the one or more CSI-RS locations may be determined irrespective of whether a CSI-RS contained in the received signal has a VCID in the identified subset of VCID candidates. 
     A device for identifying one or more CSI-RS from a non-serving cell in a wireless communications network including a processor and a memory in electronic communication with the processor is described. The memory may embody instructions being executable by the processor to identify a subset of VCID candidates, determine one or more CSI-RS locations for one or more CSI-RS in a received signal from a non-serving cell based on the subset of VCID candidates, and identify one or more CSI-RS in the received signal based on the one or more CSI-RS locations. The instructions may be executable by the processor to determine, for example, one or more of a subframe configuration, a resource configuration, a VCID, or an antenna port configuration for a CSI-RS contained in the received signal. The memory may also embody instructions being executable by the processor to, for each CSI-RS location from the one or more CSI-RS locations, search for a VCID, in a set of available VCIDs, corresponding to a CSI-RS sequence generated according to the VCID at the CSI-RS location, and determine the one or more CSI-RS responsive to the searching. 
     In some examples, the memory may further embody instructions being executable by the processor to estimate one or more of a delay spread or power delay profile (PDP) of the received signal, average frequency domain samples of the received signal according to the estimated delay or PDP, and test the averaged frequency domain samples with the VCID to determine whether the averaged frequency domain samples contain a CSI-RS based on the VCID. The estimate may be based on one or more antenna ports associated with a CRS. 
     In some examples, the memory may further embody instructions being executable by the processor to select the subset of VCID candidates from a number of subsets of VCID candidates, identify one or more particular CSI-RS locations, and select the subset of VCID candidates from the number of subsets of VCID candidates responsive to the identification. The CSI-RS locations may include, for example, a subframe configuration and/or a resource configuration for a CSI-RS contained in the received signal. In some examples, the memory may further embody instructions being executable by the processor to identify a subset of subframes, measure a time-domain correlation of received frequency domain samples across the subset of subframes for each VCID from the subset of VCID candidates, and determine the one or more CSI-RS locations based on the measured time-domain correlation. 
     A non-transitory computer-readable medium for identifying one or more CSI-RS from a non-serving cell in a wireless communications network is described. The computer readable medium may include code for identifying a subset of VCID candidates, determining one or more CSI-RS locations for one or more CSI-RS in a received signal from a non-serving cell based on the subset of VCID candidates, and identifying one or more CSI-RS in the received signal based on the one or more CSI-RS locations. The computer-readable medium may include code for determining one or more of a subframe configuration, a resource configuration, a VCID, or an antenna port configuration for a CSI-RS contained in the received signal, for example. The computer-readable medium may also include code for, for each CSI-RS location from the one or more CSI-RS locations, searching for a VCID, in a set of available VCIDs, corresponding to a CSI-RS sequence generated according to the VCID at the CSI-RS location, and determining the one or more CSI-RS responsive to the searching. 
     In some examples, the computer-readable medium may also include code for estimating one or more of a delay spread or PDP of the received signal, averaging frequency domain samples of the received signal according to the estimated delay or PDP, and testing the averaged frequency domain samples with the VCID to determine whether the averaged frequency domain samples contain a CSI-RS based on the VCID. The computer-readable medium may also include code for selecting the subset of VCID candidates from a number of subsets of VCID candidates, identifying one or more particular CSI-RS locations, and selecting the subset of VCID candidates from the number of subsets of VCID candidates responsive to the identification. The CSI-RS locations may include, for example, a subframe configuration and/or a resource configuration for a CSI-RS contained in the received signal. In some examples, the computer-readable medium may include code for identifying a subset of subframes, measuring a time-domain correlation of received frequency domain samples across the subset of subframes for each VCID from the subset of VCID candidates, and determining the one or more CSI-RS locations based on the measured time-domain correlation. 
     The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the spirit and scope of the appended claims. Features which are believed to be characteristic of the concepts disclosed herein, both as to their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purpose of illustration and description only, and not as a definition of the limits of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the nature and advantages of the present invention may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
         FIG. 1  shows a diagram that illustrates an example of a wireless communications system according to various aspects of the disclosure; 
         FIG. 2  shows a diagram that illustrates an example of interfering cells in a wireless communications system according to various aspects of the disclosure; 
         FIG. 3  shows an example of CSI-RS locations within an LTE signal transmission according to various aspects of the disclosure; 
         FIG. 4  shows a flow diagram of an example method for identifying a CSI-RS from a non-serving cell according to various aspects of the disclosure; 
         FIG. 5  shows a flow diagram of an example method for determining CSI-RS locations based on a subset of VCID candidates according to various aspects of the disclosure; 
         FIG. 6  shows a flow diagram of an example method for identifying a CSI-RS based on CSI-RS location information according to various aspects of the disclosure; 
         FIGS. 7A and 7B  show block diagrams of examples of devices, such as eNBs or UEs, for use in wireless communications according to various aspects of the disclosure; 
         FIG. 8  shows a block diagram of a CSI-RS identification module according to various aspects of the disclosure; 
         FIG. 9  shows a block diagram that illustrates an example of an eNB architecture according to various aspects of the disclosure; 
         FIG. 10  shows a block diagram that illustrates an example of a UE architecture according to various aspects of the disclosure; and 
         FIG. 11  shows a block diagram of a MIMO communication system including a base station and a mobile device according to various aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Described embodiments are directed to systems and methods for wireless communications in which one, or more, channel state information reference signal (CSI-RS) from a non-serving cell in a wireless communications network may be identified. In embodiments, a subset of virtual cell identity (VCID) candidates may be identified. The subset of VCID candidates may be identified, for example, through random selection, use of physical cell identifiers (PCIs) for neighboring cells, and/or selection of a subset from a number of available subsets. Information related to the identification of the VCID subset may be signaled through radio resource control (RRC) signaling. The subset of VCIDs may be used to determine CSI-RS locations for the CSI-RS(s) in a received signal from a non-serving cell. The CSI-RS locations may be determined, for example, based on periodicity properties of CSI-RS transmissions of the subset of VCID candidates. The determined CSI-RS locations in the received signal may be used to identify the one or more CSI-RS in the received signal through searching each location for a VCID corresponding to a CSI-RS sequence generated according to the VCID at the CSI-RS location, for example. 
     Techniques described herein may be used for various wireless communications systems such as cellular wireless systems, Peer-to-Peer wireless communications, wireless local access networks (WLANs), ad hoc networks, satellite communications systems, and other systems. The terms “system” and “network” are often used interchangeably. These wireless communications systems may employ a variety of radio communication technologies such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal FDMA (OFDMA), Single-Carrier FDMA (SC-FDMA), and/or other radio technologies. Generally, wireless communications are conducted according to a standardized implementation of one or more radio communication technologies called a Radio Access Technology (RAT). A wireless communications system or network that implements a Radio Access Technology may be called a Radio Access Network (RAN). 
     Examples of Radio Access Technologies employing CDMA techniques include CDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releases 0 and A are commonly referred to as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 1×EV-DO, High Rate Packet Data (HRPD), etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. Examples of TDMA systems include various implementations of Global System for Mobile Communications (GSM). Examples of Radio Access Technologies employing OFDM and/or OFDMA include Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), 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) and LTE-Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from an organization named “3rd Generation Partnership Project” ( 3 GPP). CDMA2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the systems and radio technologies mentioned above as well as other systems and radio technologies. 
     Thus, the following description provides examples, and is not limiting of the scope, applicability, or configuration set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the spirit and scope of the disclosure. Various embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, features described with respect to certain embodiments may be combined in other embodiments. 
     Referring first to  FIG. 1 , a diagram illustrates an example of a wireless communications system  100 . The wireless communications system  100  includes base stations (or cells)  105 , communication devices  115 , and a core network  130 . The base stations  105  may communicate with the communication devices  115  under the control of a base station controller (not shown), which may be part of the core network  130  or the base stations  105  in various embodiments. Base stations  105  may communicate control information and/or user data with the core network  130  through backhaul links  132 . In embodiments, the base stations  105  may communicate, either directly or indirectly, with each other over backhaul links  134 , which may be wired or wireless communication links. The wireless communications system  100  may support operation on multiple carriers (waveform signals of different frequencies). Multi-carrier transmitters can transmit modulated signals simultaneously on the multiple carriers. For example, each communication link  125  may be a multi-carrier signal modulated according to the various radio technologies described above. Each modulated signal may be sent on a different carrier and may carry control information (e.g., reference signals, control channels, etc.), overhead information, data, etc. 
     The base stations  105  may wirelessly communicate with the devices  115  via one or more base station antennas. Each of the base station  105  sites may provide communication coverage for a respective geographic area  110 . In some embodiments, base stations  105  may be referred to as a base transceiver station, a radio base station, an access point, a radio transceiver, a basic service set (BSS), an extended service set (ESS), a NodeB, eNodeB (eNB), Home NodeB, a Home eNodeB, or some other suitable terminology. The coverage area  110  for a base station may be divided into sectors making up only a portion of the coverage area (not shown). The wireless communications system  100  may include base stations  105  of different types (e.g., macro, micro, and/or pico base stations). There may be overlapping coverage areas for different technologies. 
     In embodiments, the wireless communications system  100  is an LTE/LTE-A network. In LTE/LTE-A networks, the terms evolved Node B (eNB) and user equipment (UE) may be generally used to describe the base stations  105  and devices  115 , respectively. The wireless communications system  100  may be a Heterogeneous LTE/LTE-A network in which different types of eNBs provide coverage for various geographical regions. For example, each eNB  105  may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). 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. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. Femto cells and pico cells may be referred to generally as small cells. An eNB may support one or multiple (e.g., two, three, four, and the like) cells. 
     The core network  130  may communicate with the eNBs  105  via a backhaul  132  (e.g., S1, etc.). The eNBs  105  may also communicate with one another, e.g., directly or indirectly via backhaul links  134  (e.g., X2, etc.) and/or via backhaul links  132  (e.g., through core network  130 ). The wireless communications system  100  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 either synchronous or asynchronous operations. 
     The UEs  115  are dispersed throughout the wireless communications system  100 , and each UE may be stationary or mobile. A UE  115  may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. A UE  115  may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a wearable device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. 
     The communication networks that may accommodate some of the various disclosed embodiments may be packet-based networks that operate according to a layered protocol stack. For example, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use Hybrid ARQ (HARQ) to provide retransmission at the MAC layer to improve link efficiency. At the Physical layer, the transport channels may be mapped to Physical channels. 
     The communication links  125  shown in the wireless communications system  100  may include uplink (UL) transmissions from a UE  115  to a base station  105 , and/or downlink (DL) transmissions, from a base station  105  to a UE  115 . The downlink transmissions may also be called forward link transmissions while the uplink transmissions may also be called reverse link transmissions. In some embodiments of the wireless communications system  100 , base stations  105  and/or UEs  115  may include multiple antennas for employing antenna diversity schemes to improve communication quality and reliability between base stations  105  and UEs  115 . 
     The UEs  115  may be configured to collaboratively communicate with multiple base stations  105  through, for example, Multiple Input Multiple Output (MIMO), Coordinated Multi-Point (CoMP), or other schemes. MIMO techniques use multiple antennas on the base stations  105  and/or multiple antennas on the UEs  115  to transmit multiple data streams. CoMP includes techniques for dynamic coordination of transmission and reception by a number of base stations  105  to improve overall transmission quality for UEs  115  as well as increasing network and spectrum utilization. Such MIMO and/or CoMP techniques may provide for enhanced user experiences by providing enhanced overall bandwidth for data transmission in the system  100 . 
     As is well understood, data may be transmitted to a UE using a shared channel, such as a physical downlink shared channel (PDSCH), which may be associated with the physical cell ID (PCI) of the transmitting base station  105 . For example, the scrambling sequence for the PDSCH may be initialized with a seed based on the PCI of the transmitting base station  105 . For various CoMP scenarios, however, the PDSCH may be transmitted using a virtual cell ID (VCID). For example, the scrambling sequence for the shared channel and the control channel in a cell can be initialized with a seed based on a VCID. The VCID may or may not be the same as the PCI, and may be specified for CoMP and MIMO operation, such as dynamic cell selection, decoupled control and data, multi-user MIMO (MU-MIMO) in a cell. 
     As indicated above, different base stations  105  may have overlapping coverage areas  110 , and a UE  115  within a coverage area  110  may receive potentially interfering signals from one or more non-serving base stations  105 . UEs  115  may employ one or more interference mitigation techniques to compensate for such interfering signals. In some interference mitigation techniques, knowledge of various characteristics of an interfering signal may significantly enhance interference mitigation. According to various embodiments described herein, various techniques may be used to detect a channel state information reference signal (CSI-RS) from a non-serving base station  105 . The detection of a CSI-RS may allow a receiver, such as a UE  115 , to enhance performance of interference cancelation techniques in order to mitigate the effect of interference that may be present. Additional details regarding the detection of CSI-RSs in a system, such as the wireless communications system  100 , as well as other features and functions, are provided below with reference to  FIGS. 2-11 . 
     With reference now to  FIG. 2 , a diagram illustrating an example of a wireless communications system  200  in which interference may occur is described. The wireless communications system  200  may be an example of portions of the wireless communications system  100  described with reference to  FIG. 1 . The wireless communications system  200  includes a number of base stations or eNBs  205 , which may be examples of base stations or eNBs  105  described with reference to  FIG. 1 . The eNBs  205  may communicate with a UE  215 , which may be an example a UE  115  described with reference to  FIG. 1 . In the example of  FIG. 2 , a serving eNB  205 - a  may communicate with the UE  215  using bidirectional link  220 , and two non-serving eNBs  205 - b  and  205 - c  may transmit interfering signals  225  that may be received at UE  215 . Each eNB  205  may have a corresponding coverage area  210 . 
     Various techniques exist for mitigation of interfering signals  225  at the UE  215 . For example, if the UE  215  has a channel estimation of one or more of interfering signals  225 , this information may be used to derive equalizer coefficients for the UE  215  receiver and reduce the effects of the interfering signal  225 . Interference mitigation techniques may also include, for example, interference suppression (IS), minimum mean square error (MMSE) interference rejection, multi-user detection (MUD), joint maximum likelihood (ML) detection, symbol-level interference cancellation (SLIC), and/or codeword-level interference cancellation (CWIC). According to various embodiments, the UE  215  may identify one or more CSI-RS transmissions from interfering eNBs  205 - b  and  205 - c.  Detection of CSI-RS transmissions from eNBs  205 - b  and  205 - c  may allow the UE  215  to estimate the channel from the non-serving eNBs  205 - b  and  205 - c,  and cancel interfering CSI-RS transmissions. Detection of CSI-RS transmissions may also allow the UE  215  to determine VCIDs of the non-serving eNBs  205 - b  and  205 - c.  Additionally or alternatively, detection of CSI-RS transmissions may allow UE  215  to determine resource element (RE) locations of interfering signals  225  where rate matching is carried out, and/or may allow UE  215  to determine tone matching at non-serving eNBs  205 - b  and  205 - c.  Furthermore, in some embodiments, the UE  215  may also identify one or more CSI-RS transmissions from the serving cell  205 - a  in cases where the UE  215  may not be aware of all CSI-RS transmissions from the serving cell  205 - a.    
     Detection of CSI-RS transmissions, according to various embodiments, may be performed by the UE  215  without network assistance provided by the eNB  205 - a.  In other embodiments, detection of CSI-RS transmissions may be performed by the UE  215  with some amount of network assistance, such as an indication of one or more restrictions on allowed CSI-RS transmissions. In any event, detection of CSI-RS transmissions with little or no network assistance requires that the UE  215  determine locations of CSI-RS transmissions, identities of the transmitting cell, and number of antenna ports used by the transmitting cell. The locations of CSI-RS transmissions may include a subframe configuration and/or a resource configuration for the CSI-RS transmission. Identities of the transmitting cell may include a PCI or VCID. The number of potential permutations for CSI-RS transmissions can therefore be quite large, as numerous options for each of these items may exist. In some deployments, for example, the possible number of CSI-RS configurations, without any network restrictions, is over 1.5 million. Even with one or more network restrictions, such as restrictions on allowed CSI-RS transmissions, the possible number of CSI-RS configurations may be very large. According to various embodiments, the UE  215  may first determine CSI-RS locations through analysis of a subset of VCID candidates, and may then detect one or more CSI-RS in received interfering signals  225  through an exhaustive search over all VCID candidates only for the determined CSI-RS locations. Such CSI-RS detection will be described in more detail below. 
     With reference now to  FIG. 3 , a diagram illustrates an example of a subframe structure  300  that may be used in a wireless communications system, including the wireless communications systems  100  and/or  200  described above with reference to  FIGS. 1  and/or  2 . In this example, the subframe structure  300  may be transmitted during a frame (10 ms) that may be divided into 10 equally sized subframes  305 . Each subframe  305  may include two consecutive time slots, namely slot  0  and slot  1 . An OFDMA component carrier may be illustrated as a resource grid representing two time slots. The resource grid may be divided into multiple resource elements  310 . 
     In LTE/LTE-A, a resource block may contain 12 consecutive subcarriers (numbered  0 - 11  in  FIG. 3 ) in the frequency domain and, for a normal cyclic prefix in each OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84 resource elements  310  per slot. Some of the resource elements, shaded and denoted  330 , may include a CSI RS transmission. Note additional resource blocks other than illustrated in  FIG. 3  may include such CSI-RS transmissions. Furthermore, other resource elements  310  may include one or more reference signals other than a CSI-RS such as, for example, one or more UE-specific RS (UE-RS), shaded and denoted  325 . Various other reference signals may be transmitted by an eNB according to various LTE/LTE-A transmission protocols. 
     A CSI-RS may be provided to improve link adaptation by providing a reference signal that occupies resource elements  310  usually allocated to PDSCH, which may provide more meaningful measures of channel quality. As noted above, characteristics of a CSI-RS, including locations of resource elements that contain a CSI-RS include a number of different available options that depend upon a variety of factors. In some implementations, for example, a CSI-RS configuration may be based on a configuration value between 0 and 31, that points to a look-up table that specifies a reference resource element  310  to be used for a CSI-RS. The actual resource elements  310  used by the CSI-RS may then be derived from this reference resource element using antenna specific offsets. Furthermore, different VCIDs may generate different CSI-RS sequences. Furthermore, a CSI-RS period may be defined in which the CSI-RS occupies a single subframe  305  per CSI-RS period. For example, the CSI-RS may occupy one subframe  305  per 5, 10, 20, 40, or 80 subframes. 
       FIG. 4  illustrates a flow diagram of an example method  400  for identifying one or more CSI-RS from a non-serving cell according to various embodiments. The method  400  may be performed by, for example, the UEs  115  of  FIG. 1  and/or UEs  215  of  FIG. 2 . While aspects of  FIG. 4  are described with respect to a UE, in some embodiments the method  400  may be performed by, for example, an eNB  105  of  FIG. 1  and/or an eNB  205  of  FIG. 2 , and resulting information may be provided to a UE that is served by the eNB. 
     At block  405 , the UE identifies a VCID subset. The VCID subset may be identified according to one or more of a number of different techniques. For example, the subset of VCID candidates may be identified through random selection, or based on detected PCIs of non-serving cells. In other examples, an indication of available VCID candidates may be provided by a network entity through, for example, radio resource control (RRC) signaling. In further examples, the subset of VCID candidates may be identified based on cross-correlation measurements between VCID pairs from a set of available VCID candidates. According to some examples, the selected VCID subset may not necessarily include an actual VCID associated with a received signal from a non-serving cell. 
     Additionally or alternatively, a number of VCID subsets may be preset or preprogrammed on the UE, or may be provided to the UE through network signaling such as RRC signaling. In further examples, a number of VCID subsets may be established according to a communications standard. The particular VCID subset in such cases may be selected from the number of subsets based on, for example a CSI-RS location of a CSI-RS of the serving cell, and/or based on one or more detected PCI of a neighboring cell. In some examples, the particular VCID subset from the plurality of VCID subsets may be selected based on information received from a network entity of the wireless communications network that restricts allowed locations for a CSI-RS. 
     At block  410 , the UE determines CSI-RS locations in a received signal for VCIDs in the VCID subset. The CSI-RS locations may include time-domain locations for one or more CSI-RS in the signal of the non-serving cell. Such CSI-RS time-domain locations may include, for example, a subframe configuration and a resource configuration for a CSI-RS contained in the received signal from the non-serving cell. The subframe configuration may provide information on a CSI-RS period and subframes within the CSI-RS period that include a CSI-RS, for example. The resource configuration may provide information on resources, such as slots and/or OFDM symbols within a subframe that include a CSI-RS. 
     At block  415 , a first CSI-RS location is selected from the determined CSI-RS locations. The first CSI-RS location may be the first CSI-RS location in time associated with the received signal, for example. As noted above, the first CSI-RS location may include time domain locations associated with one or more CSI-RS received in one or more signals from a non-serving cell. 
     The UE, at block  420 , then searches the received signal at the CSI-RS location from block  415  for a VCID from all available VCIDs. Thus, for the specific location, a complete search over all available VCID candidates is performed. Such a search may include frequency domain correlation to determine whether particular resource elements at the identified location include a CSI-RS. For example, the search may include searching for a CSI-RS sequence generated according to the VCID candidate at the CSI-RS location. In the event that a CSI-RS sequence corresponding to the VCID candidate is found, it may be determined that the particular CSI-RS location includes a CSI-RS. 
     At block  425 , it is determined if the location is the last CSI-RS location that was identified at block  410 . Such a determination may be made, for example, by determining if all of the CSI-RS locations determined at block  410  have been searched according to block  420 . A UE may, for example, store a list of determined CSI-RS locations and also an indication of whether the CSI-RS location has been searched. Following the completion of a search according to block  420 , the indication may be updated to indicate that associated CSI-RS locations have been searched. 
     If it is determined at block  425  that further CSI-RS locations remain to be searched, the next CSI-RS location is selected according to block  430 . The next CSI-RS location may be selected based on a next location in a stored list that has not yet been searched according to block  420 . Following the selection of the next CSI-RS location at block  430 , the operations at blocks  420  and  425  are performed. 
     If it is determined at block  425  that the last CSI-RS location of the CSI-RS locations determined at block  410  has been searched, the UE determines one or more CSI-RS for the received signal at block  435 . The determination of the one or more CSI-RS may include, for example, determining the subframe configuration, resource configuration, VCID, and/or an antenna port configuration for a CSI-RS contained in the received signal. Such a determination may be based on, for example, each of the particular resource elements searched at each of the determined CSI-RS locations. 
       FIG. 5  illustrates a flow diagram of an example method  500  for identifying one or more CSI-RS locations in a signal received from a non-serving cell according to various embodiments. The method  500  may be performed byu, for example, the UEs  115  of  FIG. 1  and/or UEs  215  of  FIG. 2 . While aspects of  FIG. 5  are described with respect to a UE, in some embodiments the method  500  may be performed by, for example, an eNB  105  of  FIG. 1  and/or eNB  205  of  FIG. 2 , and resulting information may be provided to a UE that is served by the eNB. 
     At block  505 , the UE identifies a VCID subset. Block  505  may be performed as described above with reference to block  405  of  FIG. 4 . 
     At block  510 , the UE may identify possible CSI-RS subframes based on possible subframe configurations. Such possible subframe configurations may be based on, for example, different CSI-RS periods and one or more related offsets such as discussed above with respect to  FIG. 3 , for VCIDs of the VCID subset. The possible subframes may include subframes where it is expected that a CSI-RS may be transmitted. According to some embodiments, the number of VCIDs in the VCID subset may be identified based on likelihood of misdetection or false alarms versus a size, and associated complexity, of the subset. 
     At block  515 , the UE may obtain frequency domain samples across the identified subframes. For example, the UE may obtain samples from the entire frequency domain for each of the identified subframes. In some examples, frequency domain samples may be obtained for time periods that are likely to transmit a CSI-RS. 
     At block  520 , the UE may measure a time-domain correlation for each VCID of the VCID subset. Such a measurement may include measuring a time-domain correlation of each of the received frequency domain samples across the subset of subframes for each VCID from the subset of VCID candidates. 
     At block  525 , the UE may determine the locations of CSI-RS based on the time-domain correlation. As discussed above with respect to  FIG. 4 , the CSI-RS locations may include a subframe configuration and resource configuration. Following block  525 , in some examples, operations  415  through  435  of  FIG. 4  may be performed. 
       FIG. 6  illustrates a flow diagram of an example method  600  for identifying one or more CSI-RS from a non-serving cell according to various embodiments. The method  600  may be performed by, for example, the UEs  115  of  FIG. 1  and/or UEs  215  of  FIG. 2 . While aspects of  FIG. 6  are described with respect to a UE, in some embodiments the method  600  may be performed by, for example, an eNB  105  of  FIG. 1  and/or eNB  205  of  FIG. 2 , and resulting information may be provided to a UE that is served by the eNB. 
     At block  605 , the UE identifies one or more CSI-RS locations. CSI-RS locations may include time domain locations such as a subframe configuration and a resource configuration for one or more CSI-RS. The CSI-RS locations may be identified as described above with reference to blocks  405  and  410  of  FIG. 4  and/or blocks  505 - 525  of  FIG. 5 . 
     At block  610 , the UE may receive a non-serving cell signal. Such a signal may be received from one or more non-serving eNBs, for example, that may have an overlapping coverage area with a serving eNB. 
     The UE may then, at block  615 , estimate one or more of a delay spread or power delay profile (PDP) of the received signal. Such an estimation may be made according to, for example a statistical evaluation of the spread of delayed signal components about a mean value of overall channel power. In some examples, the estimation may be based on one or more antenna ports associated with a common reference signal (CRS). According to some examples, the one or more CRS antenna ports to be used for the estimation may be signaled by a network entity, or may be selected autonomously based on at least one of a PCI, the CSI-RS location, or a VCID. 
     At block  620 , the UE may acquire frequency domain samples of the received signal according to the estimated delay and/or PDP. The UE, in some examples, may obtain samples from the frequency domain for each CSI-RS location adjusted according to estimated delay spread and/or PDP. 
     At block  625 , the UE may average the frequency domain samples. Such an average may be determined by, for example, averaging the frequency domain samples of the received signal according to the estimated delay spread or PDP to obtain an averaged sample. Such an averaged sample according to block  625  may reduce the likelihood of errors that may be associated with the individual samples acquired at block  620 . 
     At block  630 , the UE may test the averaged samples with the VCID. The testing may include a comparison between an expected signal associated with the VCID and the averaged samples. The testing may indicate a difference between the expected and averaged values, for example, which may be used in other operations related to identifying a CSI-RS in a received signal. 
     At block  635 , the UE may determine whether the averaged frequency domain samples contain a CSI-RS based on the VCID. Such a determination may be made, for example, based on the difference between the expected and averaged values as discussed with respect to block  630 . If the difference between the expected and averaged values meets one or more criteria, for example, it may be determined that the averaged frequency domain samples include a CSI-RS. If the difference is outside of the criteria, it may be determined that the averaged frequency domain samples do not include a CSI-RS, and another VCID may be tested. 
     Referring now to  FIG. 7A , a block diagram  700  illustrates a device  705  for use in wireless communications in accordance with various embodiments. In some embodiments, the device  705  may be an example of one or more aspects of the eNBs  105  and/or  205  and/or UEs  115  and/or  215  described with reference to  FIGS. 1  and/or  2 . The device  705  may also be a processor. The device  705  may include a receiver module  710 , a CSI-RS identification module  720 , and/or a transmitter module  730 . Each of these components may be in communication with each other. 
     The components of the device  705  may, individually or collectively, be implemented with one or more application-specific integrated circuits (ASICs) adapted to perform some or all of the applicable functions in hardware. Alternatively, the functions may be performed by one or more other processing units (or cores), on one or more integrated circuits. In other embodiments, other types of integrated circuits may be used (e.g., Structured/Platform ASICs, Field Programmable Gate Arrays (FPGAs), and other Semi-Custom ICs), which may be programmed in any manner known in the art. The functions of each unit may also be implemented, in whole or in part, with instructions embodied in a memory, formatted to be executed by one or more general or application-specific processors. 
     The receiver module  710  may be used to receive various types of data and/or control signals (i.e., transmissions) over one or more communication links of a wireless communications system, such as one or more communication links of the wireless communications systems  100  and/or  200  described with reference to  FIG. 1  and/or  2 . In some embodiments, the receiver module  710  may be or include a radio frequency (RF) receiver, such as an RF receiver operable to receive transmissions  714 . The received transmissions  714  may include signals from a serving cell intended for a UE and also one or more interfering signals from non-serving cell(s). The receiver  710  may condition (e.g., filter, amplify, downconvert, and digitize) the received signal to obtain input samples  716  and pass the input samples  716  to the CSI-RS identification module  720 . 
     In some embodiments, the transmitter module  730  may be or include an RF transmitter. The transmitter module  730  may be used to transmit various types of data and/or control signals (i.e., transmissions) over one or more communication links of a wireless communications system, such as one or more communication links of the wireless communications systems  100  and/or  200  described with reference to  FIGS. 1  and/or  2 . 
     In some embodiments, the CSI-RS identification module  720  may process the input samples  716  and detect one or more CSI-RS that may be received in one or more signals from one or more non-serving cells. The CSI-RS detection may be performed according to any one or more of the techniques described above. According to some embodiments, CSI-RS detection may be performed by first determining CSI-RS locations based on evaluations of a subset of VCID candidates, and then determining whether one or more CSI-RS is present in the received signal(s) based on a search over all VCID candidates at the determined CSI-RS locations. The CSI-RS identification module  720  may determine CSI-RS information  722  related to the detected CSI-RS signals. CSI-RS information  722  may include a subframe configuration, a resource configuration, a VCID, and/or a number of antenna ports associated with a CSI-RS included in a received signal. The CSI-RS identification module  720  may pass the CSI-RS information  722  to other modules (e.g., receiver  710 , etc.) for use in additional processing of the received signals  714  (e.g., channel estimation, interference cancellation, etc.) or other functions. 
     Referring now to  FIG. 7B , a block diagram  750  illustrates a device  755  for use in wireless communications in accordance with various embodiments. In some embodiments, the device  755  may be an example of one or more aspects of the eNBs  105 ,  205  and/or UEs  115 ,  215  described with reference to  FIGS. 1  and/or  2 . The device  755  may also be a processor. The device  755  may include a receiver module  712 , a CSI-RS identification module  760 , and/or a transmitter module  732 . Each of these components may be in communication with each other. 
     The components of the device  755  may, individually or collectively, be implemented with one or more ASICs adapted to perform some or all of the applicable functions in hardware. Alternatively, the functions may be performed by one or more other processing units (or cores), on one or more integrated circuits. In other embodiments, other types of integrated circuits may be used (e.g., Structured/Platform ASICs, FPGAs, and other Semi-Custom ICs), which may be programmed in any manner known in the art. The functions of each unit may also be implemented, in whole or in part, with instructions embodied in a memory, formatted to be executed by one or more general or application-specific processors. 
     In some embodiments, the receiver module  712  may be an example of the receiver module  710  of  FIG. 7A . The receiver module  712  may be used to receive various types of data and/or control signals (i.e., transmissions) over one or more communication links of a wireless communications system, such as one or more communication links of the wireless communications systems  100  and/or  200  described with reference to  FIGS. 1  and/or  2 . In some embodiments, the receiver module  712  may be or include a radio frequency (RF) receiver, such as an RF receiver operable to receive transmissions  764 . The received transmissions  764  may include signals from a serving cell intended for a UE and also one or more interfering signals from non-serving cell(s). The receiver  712  may condition (e.g., filter, amplify, downconvert, and digitize) the received signal to obtain input samples  766  and pass the input samples  766  to the CSI-RS identification module  760 . 
     In some embodiments, the transmitter module  732  may be an example of the transmitter module  730  of  FIG. 7A . The transmitter module  732  may be or include an RF transmitter. The transmitter module  732  may be used to transmit various types of data and/or control signals (i.e., transmissions) over one or more communication links of a wireless communications system, such as one or more communication links of the wireless communications systems  100  and/or  200  described with reference to  FIGS. 1  and/or  2 . 
     In some embodiments, the CSI-RS identification module  760  may process the input samples  766  and detect one or more CSI-RS that may be received in one or more signals from one or more non-serving cells. The CSI-RS identification module  760  may be an example of the CSI-RS identification module  720  described with reference to  FIG. 7A  and may include a VCID subset module  765 , a CSI-RS location determination module  770 , and a CSI-RS determination module  775 . Each of these components may be in communication with each other. 
     In some embodiments, the VCID subset module  765  may identify a VCID subset as described above with respect to  FIG. 2 ,  FIG. 3 , block  405  of  FIG. 4 , and/or block  505  of  FIG. 5 . The VCID subset module  765  may provide VCID subset information  768  to the CSI-RS location determination module  770 . The CSI-RS location determination module  770  may receive the VCID subset information  768  and the input samples  766  obtained from signals received from the non-serving cell, and may determine CSI-RS locations  772  based on evaluations of a subset of VCID candidates, such as described above with reference to  FIG. 2 ,  FIG. 3 , block  410  of  FIG. 4 , blocks  510 - 525  of  FIG. 5 , and/or block  605  of  FIG. 6 . The CSI-RS determination module  775  may determine whether one or more CSI-RS is present in the received signal(s) based on a search over all VCID candidates at CSI-RS locations  772  determined by the CSI-RS location determination module  770 , such as described above with reference to  FIG. 2 ,  FIG. 3 , blocks  420 - 435  of  FIG. 4 , and/or blocks  610 - 635  of  FIG. 6 . The CSI-RS identification module  760  may determine CSI-RS information  782  related to the detected CSI-RS signals. CSI-RS information  782  may include a subframe configuration, a resource configuration, a VCID, and/or a number of antenna ports associated with a CSI-RS included in a received signal. The CSI-RS identification module  760  may pass the CSI-RS information  782  to other modules (e.g., receiver  712 , etc.) for use in additional processing of the received signals  764  (e.g., channel estimation, interference cancellation, etc.) or other functions. 
     Referring now to  FIG. 8 , a block diagram  800  illustrates a CSI-RS identification module  820  for use in wireless communications in accordance with various embodiments. In some embodiments, the CSI-RS identification module  820  may be an example of one or more aspects of the CSI-RS identification modules  720  and/or  760  described with reference to  FIGS. 7A  and/or  7 B. The CSI-RS identification module  820  may also illustrate aspects of eNBs  105 ,  205  and/or UEs  115 ,  215  described with reference to  FIG. 1  and/or  2 . The CSI-RS identification module  820  may also be a processor. The CSI-RS identification module  820  may include a CSI-RS location determination module  870 , and a CSI-RS determination module  875 . Each of these components may be in communication with each other. 
     The components of the CSI-RS identification module  820 , individually or collectively, be implemented with one or more ASICs adapted to perform some or all of the applicable functions in hardware. Alternatively, the functions may be performed by one or more other processing units (or cores), on one or more integrated circuits. In other embodiments, other types of integrated circuits may be used (e.g., Structured/Platform ASICs, FPGAs, and other Semi-Custom ICs), which may be programmed in any manner known in the art. The functions of each unit may also be implemented, in whole or in part, with instructions embodied in a memory, formatted to be executed by one or more general or application-specific processors. 
     In some embodiments, the CSI-RS location determination module  870  may determine CSI-RS locations  887 , and may be an example of CSI-RS location determination module  770  of  FIG. 7B , for example. The CSI-RS location determination module  870  may include a VCID subset module  880  and a CSI-RS location module  885 . The VCID subset module  880  may identify a VCID subset and provide VCID subset information  882  to the CSI-RS location module  885 , such as described above with respect to  FIG. 2 ,  FIG. 3 , block  405  of  FIG. 4 , and/or block  505  of  FIG. 5 . The CSI-RS location module  885  may receive the VCID subset information  882  and signals received from the non-serving cell  864 , and provide CSI-RS location information  887  based on evaluations of a subset of VCID candidates, such as described above, for example, with reference to  FIG. 2 ,  FIG. 3 , block  410  of  FIG. 4 , and/or blocks  510 - 525  of  FIG. 5 . 
     The CSI-RS determination module  875  may determine whether one or more CSI-RS is present in the received signal(s), and may be an example of CSI-RS determination module  775  of  FIG. 7B , for example. The CSI-RS determination module  875  may include a VCID set module  890  and a CSI-RS module  895 . The VCID set module  890  may provide each available VCID  892  from a set of available VCIDs to the CSI-RS module  895 , such as described above with respect to  FIG. 2 ,  FIG. 3 , and/or block  420  of  FIG. 4 . The CSI-RS module  895  may receive the CSI-RS location information  887  from CSI-RS location determination module  870 , the VCID information  892  from the VCID set module  890 , and the received signal  864 , and determine the presence of one or more CSI-RS in the received signal(s)  864 , such as described above, for example, with reference to  FIG. 2 ,  FIG. 3 , blocks  415 - 435  of  FIG. 4 , and/or blocks  610 - 635  of  FIG. 6 . The CSI-RS determination module  875  may determine CSI-RS information  897  related to the detected CSI-RS signals. CSI-RS information  897  may include a subframe configuration, a resource configuration, a VCID, and/or a number of antenna ports associated with a CSI-RS included in a received signal. Such a determination may be based on, for example, each of the particular resource elements searched at each of the determined CSI-RS locations  887 . The CSI-RS determination module  875  may pass the CSI-RS information  897  to other modules such as a receiver (not shown), interference cancellation module (not shown), and the like, for use in additional processing of the received signals (e.g., channel estimation, interference cancellation, etc.) or other functions. 
     Turning to  FIG. 9 , a block diagram  900  is shown that illustrates an eNB  905  configured for CSI-RS detection. In some embodiments, the eNB  905  may be an example of one or more aspects of the eNBs  105 ,  204  or devices  705  and/or  755  described with reference to  FIGS. 1 ,  2 ,  7 A and/or  7 B. The eNB  905  may be configured to implement at least some of the CSI-RS determination features and functions described with respect to  FIGS. 1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 A,  7 B, and/or  8 . The eNB  905  may include a processor module  910 , a memory module  920 , one or more transceiver module(s)  955 , one or more antenna antenna(s)  960 , and an eNB CSI-RS module  965 . The eNB  905  may also include one or both of a base station communications module  935  and a network communications module  940 . Each of these components may be in communication with each other, directly or indirectly, over one or more buses  930 . 
     The memory module  920  may include random access memory (RAM) and/or read-only memory (ROM). The memory module  920  may store computer-readable, computer-executable software (SW) code  925  containing instructions that are configured to, when executed, cause the processor module  910  to perform various functions described herein for determining one or more aspects related to CSI-RS signals from non-serving cells of a UE, including providing one or more forms of network assistance, such as described above, and/or performing CSI-RS detection for the non-serving cells and providing this information to a UE in communication with an eNB  905 . Alternatively, the software code  925  may not be directly executable by the processor module  910  but be configured to cause the eNB  905 , e.g., when compiled and executed, to perform various of the functions described herein. 
     The processor module  910  may include an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an ASIC, etc. The processor module  910  may process information received through the transceiver module(s)  955 , the base station communications module  935 , and/or the network communications module  940 . The processor module  910  may also process information to be sent to the transceiver module(s)  955  for transmission through the antenna(s)  960 , to the base station communications module  935  for transmission to one or more other base stations or eNBs  905 - a  and  905 - b,  and/or to the network communications module  940  for transmission to a core network  945 , which may be an example of aspects of the core network  130  described with reference to  FIG. 1 . The processor module  910  may handle, alone or in connection with the eNB CSI-RS Module  965 , various aspects of CSI-RS detection in signals from non-serving cells. 
     The transceiver module(s)  955  may include a modem configured to modulate packets and provide the modulated packets to the antenna(s)  960  for transmission, and to demodulate packets received from the antenna(s)  960 . The transceiver module(s)  955  may be implemented as one or more transmitter modules and one or more separate receiver modules. The transceiver module(s)  955  may be configured to communicate bi-directionally, via the antenna(s)  960 , with one or more of the UEs  115 ,  215  and/or devices  705 ,  715  described with reference to  FIGS. 1 ,  2 ,  7 A and/or  7 B, for example. The eNB  905  may typically include multiple antennas  960  (e.g., an antenna array). The eNB  905  may communicate with the core network  945  through the network communications module  940 . The eNB  905  may communicate with other base stations or eNBs, such as the eNBs  905 - a  and  905 - b,  using the base station communications module  935 . 
     According to the architecture of  FIG. 9 , the eNB  905  may further include a communications management module  950 . The communications management module  950  may manage communications with other base stations, eNBs, and/or devices. The communications management module  950  may be in communication with some or all of the other components of the eNB  905  via the bus or buses  930 . Alternatively, functionality of the communications management module  950  may be implemented as a component of the transceiver module(s)  955 , as a computer program product, and/or as one or more controller elements of the processor module  910 . 
     The eNB CSI-RS module  965  may be configured to perform and/or control some or all of the CSI-RS determination functions or aspects described with reference to  FIGS. 1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 A,  7 B, and/or  8  related to CSI-RS detection and/or network assistance to a UE related to CSI-RS detection. The eNB CSI-RS module  965  may include a non-serving cell signal detection module  970  configured to detect signals from one or more neighboring eNBs, such as eNBs  905 - a  and  905 - b.  Non-serving cell signal detection module  970  may be an example of non-serving cell signal detection module  765  of  FIG. 7B , and/or non-serving cell signal detection module  865  of  FIG. 8 , for example. The eNB CSI-RS module  965  may include a CSI-RS location determination module  975  configured to detect locations of one or more CSI-RS in a received signal. The CSI-RS location determination module  975  may be an example of CSI-RS location determination module  770  of  FIG. 7B , and/or CSI-RS location determination module  870  of  FIG. 8 , for example. The CSI-RS determination module  980  may determine whether one or more CSI-RS is present in the received signal(s). The CSI-RS determination module  980  may be an example of CSI-RS determination module  775  of  FIG. 7B , and/or CSI-RS determination module  875  of  FIG. 8 , for example. The eNB CSI-RS module  965 , or portions of it, may include a processor and/or some or all of the functionality of the eNB CSI-RS module  965  may be performed by the processor module  910  and/or in connection with the processor module  910 . 
     Turning to  FIG. 10 , a block diagram  1000  is shown that illustrates a UE  1015  configured for CSI-RS detection in signals received from non-serving cells. The UE  1015  may have various other configurations and may be included or be part of a personal computer (e.g., laptop computer, netbook computer, tablet computer, etc.), a cellular telephone, a PDA, a digital video recorder (DVR), an internet appliance, a gaming console, an e-readers, etc. The UE  1015  may have an internal power supply (not shown), such as a small battery, to facilitate mobile operation. In some embodiments, the UE  1015  may be an example of one or more of the UEs  115 ,  215  and/or devices  705 ,  755  described with reference to  FIGS. 1 ,  2 ,  7 A and/or  7 B. The UE  1015  may be configured to communicate with one or more of the eNBs  105 ,  205  and/or devices  705 ,  755  described with reference to  FIGS. 1 ,  2 ,  7 A and/or  7 B. 
     The UE  1015  may include a processor module  1010 , a memory module  1020 , one or more transceiver module(s)  1060 , one or more antenna(s)  1080 , and/or a UE CSI-RS identification module  1040 . Each of these components may be in communication with each other, directly or indirectly, over one or more buses  1035 . 
     The memory module  1020  may include RAM and/or ROM. The memory module  1020  may store computer-readable, computer-executable software (SW) code  1025  containing instructions that are configured to, when executed, cause the processor module  1010  to perform various functions described herein for determining the presence of one or more CSI-RS in a signal from a non-serving cell. Alternatively, the software code  1025  may not be directly executable by the processor module  1010  but be configured to cause the UE  1015  (e.g., when compiled and executed) to perform various of the UE functions described herein. 
     The processor module  1010  may include an intelligent hardware device, e.g., a CPU, a microcontroller, an ASIC, etc. The processor module  1010  may process information received through the transceiver module(s)  1060  and/or information to be sent to the transceiver module(s)  1060  for transmission through the antenna(s)  1080 . The processor module  1010  may handle, alone or in connection with the UE CSI-RS identification module  1040 , various aspects of determining CSI-RS presence and properties in received signals from one or more non-serving cells. 
     The transceiver module(s)  1060  may be configured to communicate bi-directionally with eNBs. The transceiver module(s)  1060  may be implemented as one or more transmitter modules and one or more separate receiver modules. The transceiver module(s)  1060  may support LTE/LTE-A communications. The transceiver module(s)  1060  may include a modem configured to modulate packets and provide the modulated packets to the antenna(s)  1080  for transmission, and to demodulate packets received from the antenna(s)  1080 . While the UE  1015  may include a single antenna, there may be embodiments in which the UE  1015  may include multiple antennas  1080 . 
     According to the architecture of  FIG. 10 , the UE  1015  may further include a communications management module  1030 . The communications management module  1030  may manage communications with various base stations or eNBs. The communications management module  1030  may be a component of the UE  1015  in communication with some or all of the other components of the UE  1015  over the one or more buses  1035 . Alternatively, functionality of the communications management module  1030  may be implemented as a component of the transceiver module(s)  1060 , as a computer program product, and/or as one or more controller elements of the processor module  1010 . 
     The UE CSI-RS identification module  1040  may be configured to perform and/or control some or all of the UE CSI-RS identification functions or aspects described in  FIGS. 1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  and/or  9  related to determining one or more CSI-RS in signals received from one or more non-serving cells. The UE CSI-RS identification module  1040  may include a non-serving cell signal detection module  1065  configured to detect signals from one or more non-serving cells. The non-serving cell signal detection module  1065  may be an example of non-serving cell signal detection module  765  of  FIG. 7B , and/or non-serving cell signal detection module  865  of  FIG. 8 , for example. The UE CSI-RS identification module  965  may include a CSI-RS location determination module  1070  configured to detect locations of one or more CSI-RS in a received signal. The CSI-RS location determination module  1070  may be an example of CSI-RS location determination module  770  of  FIG. 7B , and/or CSI-RS location determination module  870  of  FIG. 8 , for example. The CSI-RS determination module  1075  may determine whether one or more CSI-RS is present in the received signal(s). The CSI-RS determination module  1075  may be an example of CSI-RS determination module  775  of  FIG. 7B , and/or CSI-RS determination module  875  of  FIG. 8 , for example. The UE CSI-RS identification module  1040 , or portions of it, may include a processor and/or some or all of the functionality of the UE CSI-RS identification module  1040  may be performed by the processor module  1010  and/or in connection with the processor module  1010 . 
     Turning next to  FIG. 11 , a block diagram of a multiple-input multiple-output (MIMO) communication system  1100  is shown including an eNB  1105  and a UE  1115 . The eNB  1105  and the UE  1115  may support LTE-based communications, for example. The eNB  1105  may be an example of one or more aspects of the eNBs  105 ,  205  and/or devices  705 ,  755 , and/or  905  described with reference to  FIGS. 1 ,  2 ,  7 A,  7 B, and/or  9 , while the UE  1115  may be an example of one or more aspects of the UEs  115 ,  215  and/or devices  705 ,  755 , and/or  1015  described with reference to  FIGS. 1 ,  2 ,  7 A,  7 B, and/or  10 . The system  1100  may illustrate aspects of the wireless communications systems  100 , and/or  200  described with reference to  FIGS. 1  and/or  2 , and may perform CSI-RS determination in received signals from non-serving cells according to one or more of various different techniques such as described with reference to  FIGS. 2 ,  3 ,  4 ,  5  and/or  6 . 
     The eNB  1105  may be equipped with antennas  1134 - a  through  1134 - x,  and the UE  1115  may be equipped with antennas  1152 - a  through  1152 - n.  In the system  1100 , the eNB  1105  may be able to send data over multiple communication streams at the same time. Each communication stream may be called a “layer” and the “rank” of a communication link may indicate the number of layers used for communication. For example, in a 2×2 MIMO system where eNB  1105  transmits two “layers,” the rank of the communication link between the eNB  1105  and the UE  1115  may be two. 
     At the eNB  1105 , a transmit (Tx) processor  1120  may receive data from a data source. The transmit processor  1120  may process the data. The transmit processor  1120  may also generate reference symbols and/or a cell-specific reference signal. A transmit (Tx) MIMO processor  1130  may perform spatial processing (e.g., precoding) on data symbols, control symbols, and/or reference symbols, if applicable, and may provide output symbol streams to the transmit (Tx) modulators  1132 - a  through  1132 - x.  Each modulator  1132  may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator  1132  may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink (DL) signal. In one example, DL signals from modulators  1132 - a  through  1132 - x  may be transmitted via the antennas  1134 - a  through  1134 - x,  respectively. 
     At the UE  1115 , the antennas  1152 - a  through  1152 - n  may receive the DL signals from the eNB  1105  and may provide the received signals to the receive (Rx) demodulators  1154 - a  through  1154 - n,  respectively. Each demodulator  1154  may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator  1154  may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector  1156  may obtain received symbols from all the demodulators  1154 - a  through  1154 - n,  perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive (Rx) processor  1158  may process (e.g., demodulate, deinterleave, and decode) the detected symbols, providing decoded data for the UE  1115  to a data output, and provide decoded control information to a processor  1180 , or memory  1182 . The processor  1180  may include a module or function  1181  that may perform various functions related to detection of CSI-RS in one or more signals received from a non-serving cell. For example, the module or function  1181  may perform some or all of the functions of the CSI-RS identification modules  720 ,  760 , and/or  820  described with reference to  FIGS. 7A ,  7 B, and/or  8 , and/or of the UE CSI-RS identification module  1040  described with reference to  FIG. 10 . 
     On the uplink (UL), at the UE  1115 , a transmit (Tx) processor  1164  may receive and process data from a data source. The transmit processor  1164  may also generate reference symbols for a reference signal. The symbols from the transmit processor  1164  may be precoded by a transmit (Tx) MIMO processor  1166  if applicable, further processed by the transmit (Tx) modulators  1154 - a  through  1154 - n  (e.g., for SC-FDMA, etc.), and be transmitted to the eNB  1105  in accordance with the transmission parameters received from the eNB  1105 . At the eNB  1105 , the UL signals from the UE  1115  may be received by the antennas  1134 , processed by the receiver (Rx) demodulators  1132 , detected by a MIMO detector  1136  if applicable, and further processed by a receive (Rx) processor  1138 . The receive processor  1138  may provide decoded data to a data output and to the processor  1140 . The processor  1140  may include a module or function  1141  that may perform various functions related to detection of CSI-RS in one or more signals received from a non-serving cell. For example, the module or function  1141  may perform some or all of the functions of the CSI-RS identification modules  720 ,  760 , and/or  820  described with reference to  FIG. 7A ,  7 B, and/or  8 , and/or of the eNB CSI-RS module  965  described with reference to  FIG. 9 . 
     The components of the eNB  1105  may, individually or collectively, be implemented with one or more ASICs adapted to perform some or all of the applicable functions in hardware. Each of the noted modules may be a means for performing one or more functions related to operation of the system  1100 . Similarly, the components of the UE  1115  may, individually or collectively, be implemented with one or more ASICs adapted to perform some or all of the applicable functions in hardware. Each of the noted components may be a means for performing one or more functions related to operation of the system  1100 . 
     The detailed description set forth above in connection with the appended drawings describes exemplary embodiments and does not represent the only embodiments that may be implemented or that are within the scope of the claims. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and not “preferred” or “advantageous over other embodiments.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described embodiments. 
     Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, instructions, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative blocks and modules described in connection with the disclosure 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, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). 
     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 medium that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, 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 means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the 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, include 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 reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media. 
     The previous description of the disclosure is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Throughout this disclosure the term “example” or “exemplary” indicates an example or instance and does not imply or require any preference for the noted example. Thus, the disclosure is not to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.