WO2014059584A1

WO2014059584A1 - Cell discovery in enhanced local or macro area

Info

Publication number: WO2014059584A1
Application number: PCT/CN2012/082980
Authority: WO
Inventors: Yuantao Zhang; Haipeng Lei; Jianchi Zhu; Zhi Zhang; Kodo Shu
Original assignee: Nokia Corporation
Priority date: 2012-10-15
Filing date: 2012-10-15
Publication date: 2014-04-24

Abstract

The specification and drawings present a new method, apparatus and software related product (e.g., a computer readable memory) for a cell discovery in enhanced local or macro area (e.g., in LTE/LTE-A systems) using one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of the discovery signal relative to the each common sequence. When the UE receives from a network element (e.g., eLA eNB or MeNB) the one or more common sequences each comprising the time gap information, the UE can detect the discovery signal (e.g., comprising eLA cell ID, cluster ID, MeNB cell ID, etc.) using a value of the time gap for corresponding any (or at least one) detected common sequence of the one or more common sequences. The detected DL discovery signal can be used by the UE to determine, e.g., the eLA cell ID.

Description

CELL DISCOVERY IN ENHANCED LOCAL OR MACRO AREA Technical Field

The exemplary and non-limiting embodiments of this invention relate generally to wireless communications and more specifically to cell discovery in an enhanced local area or in a macro area, e.g., in LTE/LTE-A systems.

Background Art

This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.

The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

3 GPP 3 generation partnership proj ect

CA carrier aggregation

CDM code division multiplexing

CSI channel state information\

DCI downlink control indicator

DL downlink

DSP digital signal processor

eLA enhanced local area

eNB, eNodeB evolved node B /base station in an E-UTRAN system

E-UTRAN evolved UTRAN (LTE)

ID identification, identifier, identity

LTE long term evolution

LTE-A long term evolution advanced

MeNB macro eNB

OFDM orthogonal frequency division multiplexing

PRB physical resource block

PSS primary synchronization signal RAN radio access network

SSS Secondary synchronization signal

TA timing advance

UE user equipment

UL uplink

UTRAN universal terrestrial radio access network

X2 interface between eNBs

ZC Zadoff Chu An enhanced local area (eLA) concept will be an important topic in LTE 3 GPP Release

12. The enhanced local area cells may be deployed using a macro assisted eLA scenario and a standalone eLA scenario, with sparse and dense deployment, respectively. Figures la-Id show examples of different deployment scenarios. Typically the eLA cells utilizing a same frequency band are assumed to be time and frequency synchronized. In macro assisted eLA case (Figures la and lb), the eLA cells 13 are within the coverage of the Macro cell, e.g., MeNB 10, and the backhaul link between the MeNB 10 and eLA eNB 13 may be through an optical fiber, a cable, or through wireless means, which may correspond to different latency assumptions. In the standalone eLA case (Figures lc and Id), the eLA cells 13 are outside of the coverage of Macro cell 10. Figures la and lc demonstrate sparse deployment scenarios and Figures lb and Id demonstrate dense deployment scenarios.

Summary

According to a first aspect of the invention, a method, comprising: generating by a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the each common sequence; and sending downlink by the network element one or more common sequences enabling at least one user equipment to receive the discovery signal using the time gap comprised in at least one detected common sequence of the one or more common sequences.

According to a second aspect of the invention, a method, comprising: receiving by a user equipment from a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the common sequence; and detecting by the user equipment the discovery signal using a value of the time gap comprised in at least one detected common sequence of the one or more common sequences.

According to a third aspect of the invention, an apparatus comprising: at least one processor and a memory storing a set of computer instructions, in which the processor and the memory storing the computer instructions are configured to cause the apparatus to: generate one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the each common sequence; and send downlink one or more common sequences enabling at least one user equipment to receive the discovery signal using the time gap comprised in at least one detected common sequence of the one or more common sequences.

According to a fourth aspect of the invention, an apparatus comprising: at least one processor and a memory storing a set of computer instructions, in which the processor and the memory storing the computer instructions are configured to cause the apparatus to:

receive from a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the common sequence; and detect the discovery signal using a value of the time gap comprised in at least one detected common sequence of the one or more common sequences.

According to a fifth aspect of the invention, a computer program product comprising a computer readable medium bearing computer program code embodied herein for use with a computer, the computer program code comprising: code for generating by a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the each common sequence; and code for sending downlink by the network element one or more common sequences enabling at least one user equipment to receive the discovery signal using the time gap comprised in at least one detected common sequence of the one or more common sequences.

According to a sixth aspect of the invention, a computer program product comprising a computer readable medium bearing computer program code embodied herein for use with a computer, the computer program code comprising: code for receiving by a user equipment from a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the common sequence; and code for detecting by the user equipment the discovery signal using a value of the time gap comprised in at least one detected common sequence of the one or more common sequences. Brief Description of the Drawings:

For a better understanding of the nature and objects of the present invention, reference is made to the following detailed description taken in conjunction with the following drawings, in which:

Figures la through Id are diagrams of deployments of macro assisted eLA eNBs (Figures lc and Id) and standalone eLA eNBs (Figures la and lb) in LTE systems;

Figures 2a and 2b are timing diagrams for a slow discovery mode of operation for a standalone case, according to exemplary embodiments of the invention;

Figure 3 is a timing diagram for a slow discovery mode of operation for a macro assisted eLA case, according to an exemplary embodiment of the invention;

Figure 4 is a timing diagram for a fast discovery mode of operation, according to an exempl ary emb odiment o f the invention ;

Figure 5 is flow charts demonstrating implementation of exemplary embodiments of the invention by an eLA eNB in a slow discovery mode;

Figure 6 is flow charts demonstrating implementation of exemplary embodiments of the invention by an eLA eNB in a fast discovery mode;

Figure 7 is flow charts demonstrating implementation of exemplary embodiments of the invention by a UE; and

Figure 8 is a block diagram of wireless devices for practicing exemplary embodiments of the invention. Detailed Description

In the macro assisted eLA case, as stated in co-owned PCT application

PCT/CN2012/080929 filed on Septemebr 3, 2012, the MeNB may aperiodically indicate to the eLA cells to transmit a cell common or a cell cluster common sequence. UEs are triggered to detect the sequence and report the results to the MeNB. Then the MeNB could know whether the UEs are near or under the eLA coverage.

To save energy from both a MeNB and UE points of view, an eLA eNB may transmit a discovery signal with a long time period. The discovery signals from different eLA cells may be transmitted simultaneously and multiplexed using, e.g., a CDM technique. The UE trying to access to the eLA cell should be able to detect the discovery signal to make cell identification.

The mentioned discovery signal could be based on PSS/SSS, with possible longer periodicity and/or modified sequence, or could be a new wideband signal transmitted periodically (e.g., every few seconds). For both cases, there may be the following problems:

1) If the discovery signal is transmitted with a rather long period (e.g., every several seconds), the UE has to do detection (typically a correlation operation) in a long time window before detecting the sub frame/frame with a discovery signal. This can cause a significant UE power consumption which may be a significant problem especially for a standalone case (see Figure lc and Id).

2) If the discovery signal is transmitted with a rather long period (e.g., every several seconds), this may have an impact on handover, e.g., not able to fulfill the timing requirements for handover interruption time, because the UE needs to get fast synchronization to the target cell in the handover process.

The above issues may be resolved using embodiments of the invention described herein.

A new method, apparatus, and software related product (e.g., a computer readable memory) are presented for a cell discovery in enhanced local or macro area (e.g., in

LTE/LTE-A systems) using one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of the discovery signal relative to the common sequence. According to an embodiment of the invention, when the UE receives from a network element (e.g., eLA eNB or MeNB) the one or more common sequences each comprising the time gap information, the UE can detect the discovery signal (e.g., comprising eLA cell ID, cluster ID, MeNB cell ID, etc.) using a value of the time gap for corresponding any (or at least one) detected common sequence of the one or more common sequences. In other words, the UE does not need to detect the discovery signal in each frame (as in a conventional approach), because it can get the timing of the discovery signal from the detected common sequence (or cell common sequence), which can comprise the timing information of the discovery signal. In this case the UE can wake up based on the value of the time gap and detect only the frame comprising the discovery signal. The detected DL discovery signal can be used by the UE to determine, e.g., the eLA cell ID. The embodiments of the invention may be applied not only to a local network element such as eLA eNB but to a macro network element such as MeNB as well.The embodiments presented herein are related to 3GPP LTE/LTE-Advanced, especially for the LTE-based enhanced local area network with 3GPP LTE systems being deployed in the local area, but the broader teaching can be applied to other radio access technologies.

For example in one embodiment, each of the one or more common sequences may be sent by the local network element (e.g., a standalone eLA eNB or the eLA eNB assisted by a macro eNB, MeNB) or by the macro network element MeNB using a separate frame, so that the time gap may indicate a time interval between a frame comprising a corresponding common sequence of the one or more common sequences and a further frame comprising the discovery signal. The common sequence(s) and the discovery signal may be sent by the eLA eNB periodically or in aperiodic fashion as further discussed herein.

In the aperiodic case, the local network element (eLA eNB) may receive an indication signal from a macro network element such as MeNB to transmit a common sequence, where the one or more common sequences may be sent DL by the local network element in a predetermined time interval (e.g., 4 frames) after receiving the indication signal. The aperiodic case may be also applied to the MeNB as further discussed in reference to Figure 3.

According to a further embodiment at least one common sequence of the one or more common sequences may comprise bandwidth infomiation for the discovery signal which will further facilitate the detection of the discovery signal by the UE(s).

According to embodiments described herein, the discovery signal design should fulfill different requirements and may have the following two cell discovery modes:

1) A slow discovery mode, for example for the UE to initially access the eLA cell. There are periodically reserved time-frequency resources for the discovery signal. Before a frame/sub frame with the discovery signal, there is a DL common sequence transmitted, which may be a same for all the eLA cells or eLA cells in the same clusters. Besides, the DL common sequence may carry timing gap information between the common sequence and the discovery signal. The UE could get the timing of the discovery signal after detecting the DL common sequence, as described herein. Examples are demonstrated in Figures 2, 3, 5, 7 and 8 as further discussed herein.

2) A fast discovery mode, for example for the UE to do inter-eLA handover. The target eLA cell can transmit the discovery signal aperiodically right after it receives an appropriate indication from the serving eLA cell. Before the discovery signal is transmitted, the serving eLA cell may trigger a group of UEs or an individual UE to detect a DL common sequence. The triggering could be through physical layer signaling or higher layer signaling. The DL common sequence from the serving eLA sent after the triggering signal from the serving eLA eNB can carry the information of the timing gap between the common sequence and the target eLA's discovery signal. Examples are demonstrated in Figures 4, 6, 7 and 8 as further discussed herein.

Figure 2a demonstrates a slow discovery process for the UE(s) in standalone eLA case (demonstrated in Figures lc and Id). As stated herein, this scenario may be also applied to the discovery process involving eNB(s). For this case, between each two discovery signals, there may be predefined DL common sequences that are periodically transmitted. The predefined DL common sequences may be the same for all eLA cells in the same cluster.

According to one embodiment related to a slow discovery mode and a standalone eLA case defined herein, there is a one-to-one mapping between each common sequence and the timing gap between the common sequence and the discovery signal as shown in Figure 2a where the common sequence is transmitted once in each 10 ms radio frame. A sequence 1 1 in a frame 16 carries timing gap information of Δί=4, which means the time gap between this common sequence 11 and the discovery signal is 4 radio frames. Similarly, a sequence 12 in a frame 17 carries timing gap information of At=3, which means the time gap between this common sequence 12 and the discovery signal is 3 radio frames. The same may be applied to frames 18, 20 and 22 with corresponding sequences 13, 14, 15 and timing gap information of Δΐ=2, At=l and Δΐ=0.

The UE for initial access could get the timing of the discovery signal after detecting the DL common sequence. For example, if the UE first detected the sequence 1 1 in the frame 16, it can do nothing, e.g., get into sleeping mode after frame 16, and then wake up in 4 frames (Δΐ=4) to detect the discovery signal in a frame 22 where the discovery signal is transmitted. Similarly, if the UE first detected the sequence 12 in the frame 17, it can do nothing, e.g., get into sleeping mode after frame 17, and then wake up in 3 frames (Δΐ=3) to detect the discovery signal in the frame 22 where the discovery signal is transmitted, etc.

The embodiment illustrated in Figure 2a may be also applied to a case of the macro network element such as MeNB in the slow discovery mode providing common sequence and discovery signals by the MeNB.

The common sequence may be generated at the eLA eNB or at the MeNB using a ZC or other constant-amplitude sequence with a one to one mapping between the sequence root and the timing gap between the DL common sequence and the discovery signal. Furthermore the common sequence could also carry the bandwidth information by properly defining the sequence for the case that the discovery signal is a wide-band signal and/or not to be positioned in central PRBs of the full bandwidth.

Figure 2b shows a further modification of the slow discovery process demonstrated in

Figure 2a in order to further save energy and resources. In this embodiment, after receiving by the UE(s) from the network element (e.g., eLA eNB or MeNB) the one or more common sequences each comprising the time gap information, the UE may send just before a discover signal scheduled time (known by the UE(s) based on the time gap comprised in the one or more common sequences) a UL common sequence to request the DL discovery signal transmission. In other words, the discovery signal is only transmitted by the eLA or MeNB cell(s) if the UL common sequence sent by the UE is received by the eLA eNB or MeNB, otherwise no discovery signal is transmitted. This approach may further reduce energy consumption at the eLA eNB or MeNB, so that the discovery signal is sent by the eLA eNB/MeNB only when/ifrequested by the UE in response to the common sequence(s). The UL common sequence may be the same for the UEs in the same cell, so that if more than one UE tries to access to the cell, these UEs may transmit the same UL sequence simultaneously just before the subframe carrying the discovery signal. The UL common sequence may be transmitted with a predefined fixed gap after the DL common sequence, for example if the DL common sequence is transmitted in a subframe/frame n, the UL common sequence will be transmitted then in subframe/frame n+4. In this way, the UEs could coordinate simultaneous transmission of the DL common sequence.

According to another embodiment related to the slow discovery mode and a macro assisted eLA case defined herein (e.g., shown in Figures lc and Id), the discovery process for the UE may be referred to as macro assisted eLA case as demonstrated in Figure 3. In this case, the common sequence may be aperiodically transmitted from eLA cell in response to an indication signal received from the MeNB. The common sequence could carry information of the timing gap between the discovery signal and the common sequence, by defining a mapping between the common sequence and the timing gap as described herein. For example as shown in Figure 3, a sequence 1 in a frame 24 carries timing gap information of At=k (k is a finite integer), which means the time gap between this common sequence 1 and the discovery signal is k radio frames. As shown in Figure 3, after k frames (or kxlO ms), in a frame 26, the eLA eNB transmits the discovery signal. Similarly to Figure 2a the common sequence 1 can also carry the bandwidth information of the discovery signal. Also Figure 3 shows only one frame 24 where the common sequence is sent, but in general it may be more than one frame with common sequences to be sent before the frame with the discovery signal, e.g., as shown in Figure 2a. The UE may know where to look for the common sequences based on a triggering signaling transmitted from the MeNB to the UE to detect the common sequence from the eLA eNBs.

It is further noted that the embodiment illustrated in Figure 3 may be also applied to a case of the macro network element such as MeNB in the aperiodic mode. In this case a single MeNB may simply send signals in frames 24 and 26 shown in Figure 3 using internal triggering. The embodiments of the invention may be also applied to a cluster of MeNBs, e.g., assisted by a cluster head in a similar way as the cluster of the eLA eNBs are assisted by the MeNB. According to a further embodiment related to a fast discovery mode, for example for providing signaling for the UE to do the inter-eLA handover, is demonstrated in Figure 4. A serving eLA cell (eLA eNB) may first send an indication to a target eLA cell to transmit the discovery signal at a scheduled time (frame/subframe).

Then, before the scheduled time for the discovery signal, the serving eLA cell can send in a frame 30 (see Figure 4) to the UE(s) a DL signaling using the DL common sequence, as described herein, to trigger the detection of the DL common sequence by the UE(s). The DL signaling could trigger groups of UEs to detect the common sequence, or trigger an individual UE to do the detection, either by the physical layer DCI signaling or higher layer signaling. Then the UE may detect the DL common sequence in a predefined time offset relative to a triggering signal in frame 30 by a fixed value. For example if the signaling is transmitted in subframe/frame n, the common sequence may be transmitted in the subframe/frame n+4, as shown in Figure 4.

After the UE detected the DL common sequence in a frame/subframe 32, it can get the timing gap information between the detected common sequence 1 in the frame/subframe 32 and the discovery signal. As illustrated in Figure 4, the UE can learn from the received sequence 1 that the time gap between the sequence 1 and the frame/subframe carrying the discovery signal is kms (k is a finite integer). The UE may do nothing (e.g., go to sleep) until the frame/subframe 34 where the target eLA eNB transmits the discovery signal and then wake up to detect the discovery signal at the right time from the target eLA eNB. As stated herein, the common sequence 1 can also carry the bandwidth information of the discovery signal. Also Figure 4 shows only one frame 32 where the common sequence is sent, but in general it may be more than one frame with common sequences to be sent before the frame with the discovery signal, e.g., as shown in Figure 2a.

It is noted that the backhaul latency between the serving eLA eNB and target eLA eNB is not known by the UE. Here the timing gap actually may be indicative of the latency between the two eLA eNBs.

It is further noted that the embodiment illustrated in Figure 4 may be also applied to a case of the macro network elements such as serving MeNB and target MeNB using the same signaling as shown in frames 30, 32 and 34 in Figure 4.Examples shown in Figures 5-6 below are illustrated for the local network element such as eLA eNB, but may be also applied at least in part to the macro network element such as MeNB.

Figure 5 shows an exemplary flow chart demonstrating implementation of

embodiments of the invention by a local network element (eLA eNB) in a slow discovery mode (see Figures 2 and 3). It is noted that the order of steps shown in Figure 5 is not absolutely required, so in principle, the various steps may be performed out of the illustrated order. Also certain steps may be skipped, different steps may be added or substituted, or selected steps or groups of steps may be performed in a separate application.

In a method according to the exemplary embodiment shown in Figure 5, in a first step 40, the local network element (eLA eNB) generates (configures) one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the each common sequence. In a next step 42, the local network element (eLA eNB) receives an indication signal from a macro network element, MeNB (this step is optional for macro assisted eLA case). In a next step 44, the local network element (eLA eNB) sends DL one or more common sequences. This step may be performed periodically, or aperiodically in response to the indication signal if received from the MeNB.

In a next step 46, before a discovery signal scheduled time identified based on the time gap comprised in at least one of the one or more common sequences, the local network element (eLA eNB) receives from the at least one UE a request for sending the discovery signal (this step is optional). In a next step 48, the local network element (eLA eNB) sends the discovery signal at the scheduled time so that at least one UE receives the discovery signal.

Figure 6 shows an exemplary flow chart demonstrating implementation of embodiments of the invention by a local network element (eLA eNB) in a fast discovery mode (demonstrated in Figure 4). It is noted that the order of steps shown in Figure 6 is not absolutely required, so in principle, the various steps may be performed out of the illustrated order. Also certain steps may be skipped, different steps may be added or substituted, or selected steps or groups of steps may be performed in a separate application.

In a method according to the exemplary embodiment shown in Figure 6, in a first step 50, the serving local network element (eLA eNB) configures/generates one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of the discovery signal relative to the each common sequence. In a next step 52, the serving eLA eNB sends to a target eLA eNB an indication signal for sending a discovery signal at a predefined time. In a next step 54, the serving eLA eNB sends DL a triggering signal to the at least one user equipment. In a next step 54, the serving eLA eNB sends at least one common sequence to enable at least one UE to receive the discovery signal from the target eLA eNB using the time gap information comprised in the at least one common sequence, wherein the at least one common sequence is sent by the serving eLA eNB in a predefined time offset relative to the triggering signal.

Figure 7 shows an exemplary flow chart demonstrating implementation of

embodiments of the invention by a UE. It is noted that the order of steps shown in Figure 7 is not absolutely required, so in principle, the various steps may be performed out of the illustrated order. Also certain steps may be skipped, different steps may be added or substituted, or selected steps or groups of steps may be performed in a separate application.

In a method according to the exemplary embodiment shown in Figure 7, in a first step 60, the UE receives from a local network element (eLA eNB) or from a macro network element (MeNB) one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of the discovery signal relative to the each common sequence. In a next step 62, before a discovery signal scheduled time identified based on the time gap information, the UE sends to the local network element eLA eNB or the macro network element MeNB a request (a UL common sequence as shown in Figure 2a) for sending the discovery signal (this step is optional). In a next step 62, the UE detects the discovery signal using a value of the time gap comprised in the at least one detected common sequence of the one or more common sequences. Figure 8 shows an example of a block diagram demonstrating LTE devices including a local network elements (e.g., eLA eNB or MeNB) 80 and 81, a UE 82 and a MeNB 84 comprised in a network 100, according to an embodiment of the invention. Figure 8 is a simplified block diagram of various electronic devices that are suitable for practicing the exemplary embodiments of this invention, and a specific manner in which components of an electronic device are configured to cause that electronic device to operate. The eLA eNBs (or the MeNBs) 80 and 81 may be identical and each of them may function as a serving or a target eLA eNB. The UE 82 may be a mobile phone, a camera mobile phone, a wireless video phone, a portable device or a wireless computer, etc.

The device 80 (the same is applied to the device 81) may comprise, e.g., at least one transmitter 80a at least one receiver 80b, at least one processor 80c at least one memory 80d and a common sequence and discovery application module 80e. The transmitter 80a and the receiver 80b may be configured to provide a wireless communication with the UE 82 (and others not shown in Figure 8), e.g., through corresponding links 83a and 83b, according to the embodiments of the invention. The transmitter 80a and the receiver 80b may be generally means for transmitting receiving and may be implemented as a transceiver, or a structural equivalence thereof. It is further noted that the same requirements and considerations are applied to transmitter and receiver of the UE 82. It is noted that devices 80 and 81 may also communicate with MeNB 84 through corresponding links 85a and 85b (wired or wireless), according to the embodiments of the invention.

Various embodiments of the at least one memory 80d (e.g., computer readable memory) may include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the processor 80c include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors. Similar embodiments are applicable to memories and processors in other devices such as the UE 82 and the MeNB 84 shown in Figure 8.

The common sequence and discovery application module 80e may provide various instructions for performing steps 40-48 shown in Figure 4 and/or steps 50-56 shown in Figure 6, according to different embodiments described herein. The module 80e may be implemented as an application computer program stored in the memory 80d, but in general it may be implemented as software, firmware and/or hardware module or a combination thereof. In particular, in the case of software or firmware, one embodiment may be implemented using a software related product such as a computer readable memory (e.g., non-transitory computer readable memory), computer readable medium or a computer readable storage structure comprising computer readable instructions (e.g., program instructions) using a computer program code (i.e., the software or firmware) thereon to be executed by a computer processor. Furthermore, the module 80e may be implemented as a separate block or may be combined with any other module/block of the device 80 or 81, or it may be split into several blocks according to their functionality.

The UE 82 and the MeNB 84 may have similar components as the devices 80 or 81, as shown in Figure 8, so that the above discussion about components of the eLA eNB 80 is fully applicable to the components of the UE 82 and the MeNB 84.

A discovery application module 82e in the UE 82 may perform steps 60-64 shown in Figure 7. The module 82e may be implemented as an application computer program stored in the memory 82d of the UE, but in general it may be implemented as software, firmware and/or hardware module or a combination thereof. In particular, in the case of software or firmware, one embodiment may be implemented using a software related product such as a computer readable memory (e.g., non-transitory computer readable memory), computer

readable medium or a computer readable storage structure comprising computer readable instructions (e.g., program instructions) using a computer program code (i.e., the software or firmware) thereon to be executed by a computer processor. Furthermore, the module 82e may be implemented as a separate block or may be combined with any other module/block of the device 82, or it may be split into several blocks according to their functionality.

Moreover, a discovery indication application module 84e in the MeNB 84 may assist for performing step 42 shown in Figure 5 in case the devices 80 and 81 are eLA eNBs. The module 84e may be implemented as an application computer program stored in the memory 84d of the MeNB, but in general it may be implemented as software, firmware and/or hardware module or a combination thereof. In particular, in the case of software or firmware, one embodiment may be implemented using a software related product such as a computer readable memory (e.g., non-transitory computer readable memory), computer readable medium or a computer readable storage structure comprising computer readable instructions (e.g., program instructions) using a computer program code (i.e., the software or firmware) thereon to be executed by a computer processor. Furthermore, the module 84e may be implemented as a separate block or may be combined with any other module/block of the device 84, or it may be split into several blocks according to their functionality.

It is noted that various non-limiting embodiments described herein may be used separately, combined or selectively combined for specific applications.

Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope of the invention, and the appended claims are intended to cover such modifications and

arrangements.

Claims

WHAT IS CLAIMED IS:

1. A method, comprising:

generating by a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the each common sequence; and

sending downlink by the network element one or more common sequences enabling at least one user equipment to receive the discovery signal using the time gap comprised in at least one detected common sequence of the one or more common sequences.

2. The method of claim 1 , wherein each of the one or more common sequences is sent by the network element using a different frame, so that the time gap indicates a time interval between a frame comprising a corresponding common sequence of the one or more common sequences and a further frame comprising the discovery signal.

3. The method of claim 1 , wherein the network element is an eNB.

4. The method of claim 1 , wherein the network element is a local network element assisted by a macro network element.

5. The method of claim 4, wherein before sending the one or more common sequences, the method comprising:

receiving by the local network element an indication signal from a macro network element for sending at least one common sequence aperiodically so as to enable at least one user equipment to receive the discovery signal using the time gap of at least one detected common sequence.

6. The method of claim 4, wherein the local network element is a standalone network element.

7. The method of claim 1 , wherein the one or more common sequences and the discovery signal are sent by the network element periodically. 7. The method of claim 1 , wherein the one or more common sequences and the discovery signal are sent by the network element periodically.

8. The method of claim 1 , wherein the one or more common sequences and the discovery signal are sent by the network element aperiodically.

9. The method of claim 1 , wherein at least one common sequence of the one or more common sequences comprises bandwidth information of the discovery signal.

10. The method of claim 1 , wherein the network element is a serving eLA eNB, and before sending the one or more common sequences, the method comprising:

sending by the serving eLA eNB an indication signal to a target eLA eNB to send a discovery signal at a predefined time; and

sending downlink by the serving eLA eNB a triggering signal to the at least one user equipment, so that at least one common sequence of the one or more common sequences sent by the serving eLA eNB to the at least one user equipment enables the at least one user equipment to receive the discovery signal from the target eLA eNB using the time gap information comprised in the at least one common sequence, wherein the at least one common sequence is sent by the serving eLA eNB in a predefined time offset relative to the triggering signal.

11. The method of claim 1 , further comprising

receiving by the network element from the at least one user, before a discovery signal scheduled time identified based on the time gap comprised in the at least one of the one or more common sequences, a request for sending the discovery signal; and

sending, only in response to the request, by the network element the discovery signal at the scheduled time.

12. A method, comprising:

receiving by a user equipment from a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the common sequence; and detecting by the user equipment the discovery signal using a value of the time gap comprised in at least one detected common sequence of the one or more common sequences.

13. The method of claim 12, wherein each of the one or more common sequences is received by the user equipment in a different frame, so that the time gap indicates a time interval between a frame comprising a corresponding common sequence of the one or more common sequences and a further frame comprising the discovery signal.

14. The method of claim 12, wherein the user equipment is mobile phone, a camera mobile phone, a wireless video phone, a portable device or a wireless computer.

15. The method of claim 12, wherein the one or more common sequences are received by the user equipment periodically.

16. The method of claim 12, wherein the one or more common sequences are received by the user equipment aperiodically.

17. The method of claim 12, wherein at least one common sequence of the one or more common sequences comprises bandwidth information of the discovery signal.

18. The method of claim 12, wherein before a discovery signal scheduled time identified based on the time gap comprised in the at least one of the one or more common sequences, the method comprising:

sending by the user equipment based on the time gap infomiation an uplink request for sending the discovery signal.

19. An apparatus comprising:

at least one processor and a memory storing a set of computer instructions, in which the processor and the memory storing the computer instructions are configured to cause the apparatus to:

generate one or more common sequences, each common sequence comprising infomiation on a time gap being indicative of a timing of a discovery signal relative to the each common sequence; and

send downlink one or more common sequences enabling at least one user equipment to receive the discovery signal using the time gap comprised in at least one detected common sequence of the one or more common sequences.

20. The apparatus of claim 19, wherein each of the one or more common sequences is sent by the apparatus using a different frame, so that the time gap indicates a time interval between a frame comprising a corresponding common sequence of the one or more common sequences and a further frame comprising the discovery signal.

21. The apparatus of claim 19, wherein the apparatus comprises an eNB.

22. The apparatus of claim 19, wherein the apparatus comprises a local network element assisted by a macro network element.

23. The apparatus of claim 22, wherein before sending the one or more common sequences, the computer instructions are configured to cause the apparatus to:

receive an indication signal from a macro network element for sending at least one common sequence aperiodically so as to enable at least one user equipment to receive the discovery signal using the time gap of at least one detected common sequence.

24. The apparatus of claim 22, wherein the local network element is a standalone network element.

25. The apparatus of claim 19, wherein the one or more common sequences and the discovery signal are sent by the apparatus periodically.

26. The apparatus of claim 19, wherein the one or more common sequences and the discovery signal are sent by the apparatus aperiodically.

27. The apparatus of claim 19, wherein at least one common sequence of the one or more common sequences comprises bandwidth information of the discovery signal.

28. The apparatus of claim 19, wherein the apparatus is a serving eLA eNB, and before sending the one or more common sequences, the computer instructions are configured to cause the apparatus to:

send an indication signal to a target eLA eNB to send a discovery signal at a predefined time; and

send downlink a triggering signal to the at least one user equipment, so that at least one common sequence of the one or more common sequences sent by the apparatus to the at least one user equipment enables the at least one user equipment to receive the discovery signal from the target eLA eNB using the time gap information comprised in the at least one common sequence, wherein the at least one common sequence is sent by the apapratus in a predefined time offset relative to the triggering signal.

29. The apparatus of claim 19, wherein the computer instructions are configured to cause the apparatus to:

receive from the at least one user, before a discovery signal scheduled time identified based on the time gap comprised in the at least one of the one or more common sequences, a request for sending the discovery signal; and

send, only in response to the request, the discovery signal at the scheduled time.

30. An apparatus comprising:

receive from a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the common sequence; and

detect the discovery signal using a value of the time gap comprised in at least one detected common sequence of the one or more common sequences.

31. The apparatus of claim 30, wherein each of the one or more common sequences is received by the apparatus in a different frame, so that the time gap indicates a time interval between a frame comprising a corresponding common sequence of the one or more common sequences and a further frame comprising the discovery signal.

32. The apparatus of claim 30, wherein the apparatus comprises mobile phone, a camera mobile phone, a wireless video phone, a portable device or a wireless computer.

33. The apparatus of claim 30, wherein the one or more common sequences are received by the apparatus periodically.

34. The apparatus of claim 30, wherein the one or more common sequences are received by the apapratus aperiodically.

35. The method of claim 30, wherein at least one common sequence of the one or more common sequences comprises bandwidth information of the discovery signal.

36. The apparatus of claim 30, wherein before a discovery signal scheduled time identified based on the time gap comprised in the at least one of the one or more common sequences, the computer instructions are configured to cause the apparatus to:

send based on the time gap information an uplink request for sending the discovery signal.

37. A computer program product comprising a computer readable medium bearing computer program code embodied herein for use with a computer, the computer program code comprising:

code for generating by a network element one or more common sequences, each common sequence comprising information on a time gap being indicative of a timing of a discovery signal relative to the each common sequence; and

code for sending downlink by the network element one or more common sequences enabling at least one user equipment to receive the discovery signal using the time gap comprised in at least one detected common sequence of the one or more common sequences.

38. A computer program product comprising a computer readable medium bearing computer program code embodied herein for use with a computer, the computer program code comprising:

code for receiving by a user equipment from a network element one or more common sequences, each common sequence comprising infomiation on a time gap being indicative of a timing of a discovery signal relative to the common sequence; and

code for detecting by the user equipment the discovery signal using a value of the time gap comprised in at least one detected common sequence of the one or more common sequences.