TIMING ACQUISITION. AND DISCOVERY

RELATED APPLICATIONS

[OOOi] This Application claims priority to US Provisional Application 61/937,195, filed February 7, 2014, entitled "Method and Apparatus for Small Ceil Timing Acquisition and Discovery", the contents of which are hereby expressly incorporated by reference as if set forth in their entirety.

TECHNICAL F!ELD

[0002] This present disclosure is related to cellular telecommunication systems, especially heterogeneous networks in which multiple low-power nodes are deployed in a macro base station's coverage area.

BACKGROUND

[0003] Today's cellular communication systems provide not only voice services, but aiso mobile broadband services ail over the world. As the number of applications for cell phones and other wireless devices continues to increase, consuming increasing amounts of data, an enormous demand for mobile broadband data services is generated. This requires telecom operators to improve data throughput and maximize the efficient utilization of limited resources.

[0004] As the spectrum efficiency for the point-to-point link already approaches its theoretical limit, one way to increase data throughput is to split, big cells into smaller and smaller cells. When such small cells become closer to each other, however, the adjacent cell interferences become more severe, and the cell splitting gain saturates. Furthermore, if is becoming more and more difficult and cosily to acquire new sites to install base stations for the operators. Therefore, cell- splitting alone cannot fulfill current systems' demands.

[0005] Recently, a new type of network deployment called HetNet (Heterogeneous Network) has been proposed and is attracting a lot of interest and effort by the industry, in HetNet. another tier consisting of multiple low-power nodes is added onto the existing macro base station coverage areas, if is desirable for the UE (User Equipment) to detect the presence of these low power nodes so that the UE can . adjust its behavior accordingly and communicate with the appropriate cell/node in order for the network to operate efficiently, Receniiy it has been found that such detection with the help of legacy signals and procedures, as they are standardized in 3GPP (the 3 ^rd Generation Partnership Project standard) up to release 11 , is not sufficient for efficient network communicaiion. Therefore, it may be useful in 3GPP and in other communication standards, to introduce a new discovery signal.

[0006] Several candidates for such a signal have been proposed and presented, but the proposed and presented signals all have various shortcomings and weaknesses.

SUMMARY

[0007] Embodiments of the present disclosure provide a new discovery signal that is designed so that each node is identified uniquely using a timing indicator and a geometry indicator, even when many low power nodes are to be distinguished.

[0008] Embodiments described herein are discussed in the context of an LIE (Long Term Evolution) system, however, the disclosure is not necessarily restricted to LTE systems and protocols and finds application in various other systems and protocols.

BRIEF DESCRIPTION OF THE DRAWING

[0009] The present invention is best understood from the following detailed description when read in conjunction with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not necessarily to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Like numerals denote like features throughout the specification and drawing.

[0010] FIG. 1 shows an embodiment of a deployment of a HetNet with one Macro node and multiple small cells;

[0011] FIG. 2 shows the location of REs (Resource Elements) for a Companion Discovery Signal (CDS) according to an embodiment of the disclosure;

[0012] FIG. 3 is a diagram showing a UE detecting discovery signals from cells other than the serving ceil, on otherwise unused REs; [0013] FIG, 4 shows two devices that are frame-synchronized and two devices that are SFN-synchronized;

[0014] FIG, 5 is a table showing timing indicator (Tl) and geometry indicator (G1) transmission according to an embodiment of the disclosure; and

[0015] FIG. 6 shows four Companion Discovery Signal (CDS) regions for one radio frame.

DETAILED DESCRIPTION

[0016] An example deployment of a HetNet with one Macro node and multiple small cells ("N cells") is shown in FIG. 1. Network 2 includes a number of small ceiis 4 that are deployed as a cluster 6. Various numbers of small cells 4 may be deployed as cluster 6. Network 2 also includes Macro node 8 with coverage area 10. A UE (not shown) may wish to communicate or exchange data, with one or more of the small ceils 4. In some embodiments, small cells 4 are divided into sub-sets of cells such as sub-sets 12A, 12B. Alternatively, the subsets 12A, 12B may each be considered a cell cluster. In some embodiments, the close proximity of small cells 4 creates significant interferences between adjacent and proximate cells, and the present disclosure provides for enabling a UE to distinguish small ceils 4 from one another and to identify the appropriate small cell 4.

[0017] In some embodiments, time-multiplexing between the small ceiis 4 is used to distinguish the ceiis.

[0018] The present disclosure also provides for the accomplishment of efficient small ceil discov/ery by enhancing the transmission and/or reception of existing SS/RS (Synchronization Signals/Reference Signals), including that of PSS/SSS/CRS (Primary Synchronization Signal/Secondary Synchronization Signal/Ceil Specific Reference Signal), CSI-RS (Channel State Information - Reference Signal), and PR ^' S (Positioning Reference Signal), Within one transmission occasion, e.g. one LTE radio frame or sub-frame in LTE (Long Term Evolution) embodiments, there are only a limited number of resources available that can be used to carry the discovery signal. Other embodiments also suffer from a limited number of available resources, in LTE these resources can be different resource elements (REs) and/or the use of different codes in various embodiments. These codes could be orthogonal but the disclosure is not limited to orthogonal codes. [0019] In the present disclosure, the existing PSS/SSS is extended without any impact on the legacy UEs operations by defining a zero-overhead discovery signal design based on the unused REs next to the existing PSS/SSS Resource Elements. Performance evaluation results are obtained by including the link level signal generation and detection in the system simulations. In various embodiments, the discovery signal is carried by the REs next to both the PSS and SSS by REs that were previously, i.e. otherwise, unused. Thus the discovery signal can be labelled a CDS (Companion Discovery Signal) and regarded as one extension to the existing PSS/SSS signals. This is illustrated graphically in FIG, 2 which shows the location of the REs for the CDS in the operating bandwidth

[0020] In FIG. 2, an embodiment for FDD (frequency division duplex) is shown. FIG. 2 illustrates sub-frame 0 of a radio frame according to an embodiment of the disclosure. The radio frame is 10 ms long and consists of 10 sub-frames 30. Hence, each sub-frame 30 is 1 ms long. A sub-frame 30 consists of two slots 32, slot 0 and slot 1 . Each slot 32 has a duration of 0.5 ms. In the embodiment of FIG. 2, the frame structure is configured such that there are 7 symbols in each slot 32 (symbol number 0 to 6). The SSS is transmitted on symbol number 5 and PSS is transmitted on symbol number 6. In the frequency domain, the PSS/SSS are transmitted over the central 62 sub-carriers of the transmission bandwidth. They span over the 6 center PRBs (physical resource blocks). Each PRB consists of 12 sub-carriers. Thus, in total there are 72 sub-carriers available for PSS/SSS. However, only 82 are used for PSS/SSS in the legacy standard. In the legacy standard, the remaining 10 subcarriers are undefined for transmission, with 5 of the remaining sub-carriers located above PSS/SSS and the other 5 be!ow the PSS/SSS. These fields are marked with grey in FIG. 2. They are not used for anything in conventional systems. According to aspects of the disclosure, the discovery signals are transmitted on these otherwise unused resource elements.

[0021] A modified PSS/SSS is provided with a companion discovery signal (CDS) on previously unused REs accompanying the legacy PSS/SSS. The CDS is transmitted on the previously unused REs next to the legacy PSS/SSS, i.e. as a companion to the PSS/SSS in various embodiments, in this embodiment, the cells on the carrier whereby the CDS is transmitted, are advantageously synchronized. The discovery signal (DS) does not interfere noticeably with any other legacy signals, in one PSS/SSS sub-frame, at least 4 different cells (one group) can transmit and be reliably detected and identified, as described in US Provisional Application Serial No. 61/870,583 titled "Using a Geometry Indicator in HetNei Deployments", filed on August 27, 2013, the contents of which are hereby incorporated by reference as if set forth in their entirety.

[0022] To illustrate aspects of the disclosure, in one embodiment, 4 small cells per group are present, but further discovery signal design optimizations may yield a larger number of cells/group. More cells can be detected by time-multiplexing different groups of ceils, as will be described with reference to Table 1 below, in this embodiment of Table 1 , 10 PSS/SSS subframes, i.e. 50 ms, are used for a UE to detect 40 small cells. The CDS can also be used for signal quality measurements as will be described below, and these measurements can be used for instance to rank the signal quality of the different discovered small cells or for other purposes.

[0023] Timely discover of many surrounding small cells is important to expand the possibilities for efficient operations in the dense smail eel! layer such as cell association, CoMP (Cooperative Multipoint) /iCIC (Inter-Cell interference Coordination), and to enhance mobility robustness in the small cell layer.

[0024] The infra-frequency UE procedure to detect small cells using the CDS according to one embodiment, is summarized and now briefly described. First, the UE synchronizes to the serving cell using PSS/SSS/CRS (Ceil Specific Reference Signal). Then, the UE detects the CDS from other cells on the previousl and otherwise unused REs next to the PSS/SSS of the serving cell. Then, the UE reports the detected CDS and corresponding measurement results to the serving cell. The serving cell then translates the reported CDS into a small cell identity.

[0025] This is illustrated in FIG. 3 which illustrates the UE detecting the CDS from other cells on the unused REs next to the PSS/SSS of the serving ceil and the detected CDS and corresponding measurements being reported to the serving ceil. In FIG. 3, UE 14 communicates with serving cell 16. Serving ceil 16 transmits the PSS/SSS/CRS/CDS signals to UE 14. In some embodiments, serving ceil 16 transmits PSS/SSS/CRS. UE 14 synchronizes to serving eel! 16 using the PSS/SSS/CRS (Ceil Specific Reference Signal). UE 14 aiso detects CDS (companion discovery signals) from other cells 18, i.e. from cells other than serving cell 16. After reading the discovery signals, UE 14 reports the discovery signal and measurements, described below, in discovery report 20 sent to serving cell 16. Serving eel! 16 then translates the discovery report 20 into a small cell identity, i.e. one of the small cells 4 of cluster 6 shown in FIG. 1 .

[0026] In some embodiments, more ceils are needed to be distinguished than there are resources (e.g. REs) available during one transmission occasion. In such embodiments, time-multiplexing betwee the small cells may be employed.

[0027] An embodiment of time-multiplexing for discovery signals is presented in Table 1 and discussed below. In time-multiplexing, different cells use the same transmission resources, but send at different occasions, in LTE embodiments, this may be on different radio frames or sub-frames, depending on the specific design of the discovery signal.

[0028] Table 1 below illustrates one embodiment of time-multiplexing. In this embodiment, a certain number of cells can be distinguished, e.g. by using different REs and/or codes within one transmission occasion. These cells can be combined into one "Set" of cells. A "Set" is the number of cells that can transmit their discovery signal within the same occasion, e.g., within the same sub-frame or radio frame at the same time. If more cells are needed to be detected than can be expressed within one Set at one time, i.e. on the same occasion, then several Sets are used and their transmission is time-multiplexed.

[0029] For brevity of description, the discovery signal design is explained for the case of periodic signal transmission, but the time-multiplexing aspects of the disclosure apply in both periodic and non-periodic patterns. Non-periodic patterns with shorter time scales and periodic patterns with longer time scales are common.

[0030] For a periodic transmission, the period is defined by the time that elapses until the same Set is transmitted again. In the example shown in Table 1 , different transmission configurations for 1 to 5 Sets are given. In this embodiment, the previously described "companion discovery signal" (CDS) is used. The CDS is transmitted concurrently on unused REs next to primary synchronization signals and/or secondary synchronization signals (PSS/SSS). As such, in this embodiment, the discovery reference signals (DRS) (e.g., a CDS represents one embodiment of a DRS) can be and are transmitted on the otherwise unused REs which occur next to PSS/SSS signals on the 0th and 5th sub-frame in every radio frame, but other arrangements are used in other embodiments.

[0031] One transmission occasion embodiment includes one PSS/SSS sub- frame, represented by the column "SF" (sub-frame) in Table 1 . If only few cells are to be distinguished, the same set can be repeated every 5ms, i.e. no time- mulfipiexing is required. If more cells are to be detected, e.g. 5 Sets, then the transmission period is longer, !n one embodiment with 5 sets, the transmission period is 25ms and different Sets are time-multiplexed. The rightmost column shows a configuration for 5 Sets and a period of 25 ms. At system frame number (SFN) = 0 and sub-frame number (SF) = 0, Set "0" is transmitted. At SFN=0, SF=5, Set "1 " is transmitted. This goes on until the Set "4" has been transmitted at (SFN=2,SF=0). At the next occasion (SFN-2.SF-5) the transmission starts again and Set "0" is transmitted again at SFN=2,SF=5.

[0032] The shaded rows (SFN=0,SF=5 / SFN=4,SF=5 / SFN-=8,SF=5 / SFN-12,SF=5. ./ SFN=16,SF=5 / etc. etc.) in Table 1 indicate a UE performing a measurement in a configured measurement gap. In various LTE embodiments, when a UE is required to perform measurements on another frequency, it can be configured with 6ms long gaps that have a periodicity of 40ms or 80ms. The shaded gaps in that example are always 40ms apart. In the first measurement at (SFN=0,SF=5) the UE would detect Set "1 ", at the second gap at (SFN=4.SF=5> the UE detects set "4", and so on.

[0033] In one time-multiplexing embodiment, the UE can separate the cells within one transmission occasion and also has knowledge about the transmission time of the cell, so that the UE knows which set is received In a transmission occasion. The ceils within one set may use the same resources as the ceils of a different set in time-multiplexing. One way for the UE to tell the Sets apart is to have knowledge about the transmission timing and such transmission timing is as provided in this disclosure and as discussed below. With such timing information, the UE can extract the sets and the UE identifies which results are coming from the same cell and may be averaged before reporting. In various embodiments, it is advantageous for the UE to have this liming information regardless of the nature of the transmission pattern, i.e. regardless whether the transmission is periodic or non- periodic.

[0034] In Table 1 below, the discovery signal transmission timing of the small ceils is shown and expressed relative to the small cell's own SFN counter. [0035]

Table 1 - Discover Signal Transmission

[0036] UEs or other devices may he synchronized in various manners. Two different synchronization states of two devices (e.g UEs or an evolved node B, "eNodeB" or "eNB) are described as follows. One embodiment of a synchronization state is frame synchronization between two devices and frame synchronization means that the transmission is aligned according to the radio frame border, which in various LTE embodiments, is 10ms. Another embodiment of a synchronization state is SFN-synchronization (System Frame Number synchronization) between two devices and SFN-synchronization means that the two devices operate at any given time on identical system frame numbers. This is illustrated in FIG. 4. When two devices are SFN-synchronized, then they are also frame synchronized, but not necessarily vice versa.

[0037] In the following embodiment, all small cells (or other transmitters) within the same cluster are SFN-synchronized. There are no synchronization requirements on cells not belonging to the same cluster.

[0038] The UE detects new cells based on their discovery signal according to the disclosure, in some embodiments as described above, the cells of a set of ceils are distinguished from one another using time-multiplexing. In this and other embodiments, the UE also performs radio resource management (RRM) measurements based on the discovery signal. In various embodiments, the UE also reports the detected ce!l(s) to the serving cell, i.e. the ceil with which the UE is communicating, together with signal quality information such as RSRP/RSRQ (Reference Signal Received Power/ Reference Signal Received Quality) but other parameters are reported in other embodiments.

[0039] When a UE Is connected to a ceil, e.g. Macro cell 8 In Figure 1 , then the UE is SFN-synchronized to this eel! which is a serving cell, i.e. the UE has knowledge of. the SFN timing being transmitted by the serving cell. Other cells that the UE is not connected to, but are discovered by the UE, in general, need not be assumed to be synchronized to the serving cell. Only cells from the same cluster such as cluster 6 of Figure 1 , are assumed to be synchronized. In general, the UE needs to acquire timing information about a cell of a cell cluster before it. can identify and/or measure a cell from that cluster and the disclosure provides such timing information. [0040] In some discovery signal embodiments, the UE acquires this timing by relying upon information other than that coming from the discovery signal itself. It can for instance read the SFN of the cell to be measured or the least significant bits of the SFN to derive the timing of the discovery signal. Then, the UE can tell the Sets apart and keep track of the transmissions also for the case of time-multiplexing. With the legacy mechanism to obtain the SFN of the cell to be measured, the UE first needs to find frame-synchronization with a PSS/SSS eel! search followed by decoding the Master Information Block (MSB) to read the SFI according to some embodiments. This may take a long time in some embodiments and can be avoided by using the timing information provided by the disclosure as described below.

[0041] in one embodiment of the disclosure, a simpler and more efficient mechanism to indicate the transmission time of the discovery signal is presented. A timing indicator (Ti) is disclosed. The Tl is transmitted to indicate the ceil timing and to enable the UE to read the geometry indicators (Gl) of the cell. The Ti and G! can be transmitted as two separate signals or they can also be part of the same signal in various embodiments, where some of the network resources, i.e. codes and/or REs, are used for the TI and others for the Gl.

[0042] In various embodiments, the Tl and Gl are transmitted by the ceils that also transmit the discovery signal as will be shown in FIG, 5. In one embodiment, the Ti is transmitted synchronously from all ceils in the cluster or from a sub-set of cells and the Gl is used for cell detection and RRM measurements and is only transmitted by the cells of one set at a time. Referring again to FIG. 1 , the Tl is transmitted synchronously from all cells 4 of cluster 6 in one embodiment and, in another embodiment the Tl is transmitted synchronously from a sub-set of cells such as sub-sets 2A, 12B of cluster 6.

[0043] In the embodiments discussed below, all ceils within the cluster transmit synchronized to each other, but other arrangements are used in other embodiments.

[0044] In some discovery signal embodiments, two parameters are used for discovery. One parameter is the timing indicator (Tl). The timing indicator provides information that contains, in some embodiments, the least significant bits of the SFN and/or the sub-frame number of the ceils. This information is transmitted simultaneously by all cells or a sub-set in the cluster. Another parameter is the Geometry indicator (Gl). The Gl information is transmitted only by cells of the scheduled Set and used for discovery and RR measurements. The Ti and Gi are sent along with the discovery signal and by the cells of the cluster, in some embodiments.

[0045] The table of FIG. S shows how TI and Gi are transmitted in accordance with one embodiment of the disclosure. In this embodiment, there are two transmission occasions during one radio frame, i.e. during one SFN (System Frame Number), at sub-frame 0 and at sub-frame 5. The embodiment of FIG. 5 includes four cells combined into 1 set and 16 ceils in total. These cells are to be distinguished. In this embodiment, 4 Sets are needed for time-multip!exed transmission. The ceils of the same set transmit at every 4th occasion. Onl enough timing information to distinguish the transmission time instants is required. In this embodiment, it is enough to transmit two bits for timing information at every occasion. For 4 sets, for instance, only 4 different occasions need to be separated. According to the embodiment in which transmission occurs on every 0th and 5th SF, there are two occasions within one SFN and in total, 2 different SFNs are needed. According to this embodiment, the timing information includes one bit for the least significant bit of SFN ("SFN mod 2") and another bit thai indicates the sub-frame number of the cell, 0 or 5. In various LTE embodiments, the sub-frame number may be derived directly from the PSS/SSS and in this embodiment, only the SFN (one bit) would be signaled in the TI. In this embodiment, the sub-frame may also be signaled to illustrate the concept of transmission time signaling.

[0046] In one embodiment, ail ceils or a sub-set of cells transmit the T! at all occasions to enable the UE the opportunit to read the cluster timing. Because the cluster Is synchronized In this embodiment, it is sufficient for the UE to receive the T! from one ceil. In one embodiment such as shown in FIG. 5, ail cells transmit the TI and in another embodiment a sub-set of ceils transmit the TI, where the sub-set is selected such that the TI can be received anywhere within the cluster. In various embodiments, GI is oniy transmitted by those cells belonging to the set that is scheduled for the current occasion.

[0047] According to the illustrated embodiment of FIG. 5 thai shows discovery signal transmission, at SFN mod 2 - 0 and SF 0, cells 0 to 3 transmit GI. This discovery signal, including the GI, may be a CDS as discussed above. At SFN mod 2 = 0 and SF 5, ceils 4 to 7 transmit GI. This discovery signal, including the GI, may also be an CDS. [0048] !n one embodiment, the UE eel! detection procedure with help of the newly defined discovery signal can be described by the following steps. In step 1 , the UE acquires frame synchronizes to the target cell (e.g. with legacy PSS/SSS cell search). This is a legacy procedure. In step 2, the UE reads the Tl to acquire necessary transmission timing synchronization on the discovery signal For instance, the least significant bits of SFN, so that the UE can judge from which Set the transmission has occurred. Step 3 involves defection and reporting the new cells whereby the UE reports the detected CDS and corresponding measurements to the serving cell which then translates the same to cell identity.

[0049] in various embodiments, the timing Information is transmitted on one occasion, in one embodiment, the timing information is repeated each occasion, in one embodiment, the timing information is transmitted over multiple occasions.

0050] in various embodiments, the Tl and Gl are transmitted during the same occasion.

[0051] In one embodiment, there are 40 total unused REs in one radio frame, but only 32 of them are used for the discovery signal. The REs closest to the PSS/SSS REs are excluded in order to be resistant to the initial frequency offset up up to ±7.5kHz for the PSS stage. In this embodiment, these 32 REs can be divided Into four regions (two in each PSS/SSS su.bframe) for one radio frame, according to their locations in the time and frequency domain: first upper, first lower, second upper and second lower regions, as shown in FIG. 6. The sequences are further described in previously incorporated US Provisional Application No. 61/870,583 titled "Using a Geometry Indicator in HetNet Deployments", filed August 27, 2013, and in the article "Small Cell Discovery Signal - Design and Simulation Results", R1 -134324 as provided in the 3GPP TSG-RAN WG1 meeting number 74bis in Guangzhou, China, on October 7-1 1 , 2013, the contents of which are incorporated by reference as if set forth in its entirety. The use of these orthogonal sequences enables not only the simultaneous multiple sequences transmission in one 8-RE region, but also reliable noise power estimation based on the rest of the orthogonal sequences, thus increases the detectability and the quality measurements of CDS. These sequences are used for the Tl and Gl and are mapped to the unused REs. Some sequences are used for Tl and the remaining for the GL in some embodiments, the sequences defined above are divided into two parts. One part is used to represent the timing information which is transmitted commonly by all ceils and the other sequences are used to transmit the cell specific discovery part, the Gl in various embodiments.

[0052] !n various embodiments, the sequences to represent the timing information and sequences to represent the cells are used and mapped to REs. in one embodiment, the sequences can be mapped to the same REs and are separated by different codes, in another embodiment, the sequences are mapped to different REs.

[0053] In various embodiments, the Tl is transmitted by all cells and the Gl is only transmitted by cells within one set. in one embodiment the Tl Is transmitted by a sub-set of cells and the G! is only transmitted by cells within one set.

[0054] In various embodiments, the timing information is built u from combinations of the timing sequences. For instance if 4 occasions shall be distinguished, two sequences are enough to be reserved for timing.

[0055] in various embodiments, the transmission or no transmission of a sequence indicates a bit in timing information.

[0056] In another embodiment, a Channel State Information Reference Signal (CS!-RS) resources are used to carry the Tl and Gl.

[0057] in other embodiments, variously modified reference signals are used to carry the Tl and Gl. In one embodiment, some of the REs reserved for CSi-RS are used to transmit timing information and other REs are used to carry cell specific information. In another embodiment, the timing information is transmitted on the same REs as the ceil specific information, but using different codes.

[0058] In another embodiment the Gl and Tl are mapped to PRS.

[0059] In some embodiments, a method for wireless communication is presented. The method comprises: transmitting a discovery signal to a UE (user equipment) to identify a new cell of a cluster of new cells in a system with a HetNet (Heterogeneous Network); transmitting a Tl (timing indicator) that provides timing information about the discovery signal and the new cell; transmitting a Gl (geometry indicator) describing the new cell; and the UE detecting the discovery signal and the new cell identified by the discovery signal.

[0060] In some embodiments, a method for wireless communication is presented, The method comprises a serving ceil transmitting at least PSS/SSS/CRS signals; a UE synchronizing to the serving ceil using the PSS/SSS/CRS signals; small cells of a cluster of small cells transmitting respective discovery signals; transmitting timing indicators (Tl) that indicate cell timing of the small cells and geometry indicators (Gi) of the smai! ceils; and the UE detecting the discovery signals. The method further comprises the UE measuring at least one the small cell based on ai least one of the discovery signals; the UE reporting the discovery signal and measurements of the measuring to the serving cell, in a discovery report, and the serving cell translating the discovery report to identif a small cell of the small cells.

[0061] In some embodiments, a wireless communication system is provided. The system comprises a heterogeneous network (HetMet), a ceil in a cluster of ceils and configured to transmit a discovery signal, a timing indicator (Tl) and a geometry indicator (GI), a user equipment (UE) configured to detect the discovery signal, the Tl and the Gi; and a serving ceil configured to identify the cell based on at least the discovery signal.

[0062] The word "exemplary ^' ' is used herein to mean "serving as an example or illustration," Any aspect or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs.

[0063] This description of the exemplary embodiments is intended to be read in connection with the figures of the accompanying drawing, which are to be considered part of the entire written description. In the description, relative terms such as "lower," "upper," "horizontal," "vertical," "above," "below," "up," "down," "top" and "bottom" as well as derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as "connected" and "interconnected," refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as wel! as both movable or rigid attachments or relationships, unless expressly described otherwise.

[0064] The preceding merely illustrates the principles of the disclosure. St will thus be appreciated that those of ordinary skill in the art will be able to devise various arrangements which, although not explicitiy described or shown herein, embody the principles of the disclosure and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogica! purposes and to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions,

[0065] While one or more embodiments of the invention have been described above, it should be understood that they have beer? presented by way of example only, and not by way of limitation. Likewise, the various figures or diagrams may depict an example architectural or other configuration for the disclosure, which Is done to aid in understanding the features and functionality that can be included in the disclosure. The disclosure is not restricted to the illustrated example architectures or configurations, but can be implemented using a variety of alternative architectures and configurations.

[0066] One or more of the functions described in this document may be performed by an appropriately configured module. The term "module" as used herein, can refer to hardware, firmware, software and any associated hardware that executes the software, and any combination of these elements for performing the associated functions described herein. Additionally, various modules can be discrete modules; however, as would be apparent to one of ordinary skill in the art, two or more modules may be combined to form a single module that performs the associated functions according to various embodiments of the invention.

[0067] Additionally, one or more of the functions described in this document may be performed by means of computer program code that is stored in a "computer program product", "non-transitory computer-readable medium", and the like, which is used herein to generally refer to media such as, memory storage devices, or storage unit. These, and other forms of computer-readable media, may be involved in storing one or more instructions for use by processor to cause the processor to perform specified operations. Such Instructions, generally referred to as "computer program code" (which may be grouped in the form of computer programs or other groupings), which when executed, enable the computing system to perform the desired operations.

[0068] ft will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to different functional units and processors. However, it wiii be apparent that any suitable distribution of functionality between different functional units, processors or domains may be used without detracting from the invention, For example, functionality illustrated to be performed by separate units, processors or controllers may be performed by the same unit, processor or controller. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization,

[0069] Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.