WO2016203312A2

WO2016203312A2 - Methods and apparatuses for cell searching in an mmc network

Info

Publication number: WO2016203312A2
Application number: PCT/IB2016/000957
Authority: WO
Inventors: Huan Sun
Original assignee: Alcatel Lucent
Priority date: 2015-06-15
Filing date: 2016-06-09
Publication date: 2016-12-22
Also published as: WO2016203312A3; CN106332226A; CN106332226B

Abstract

The present disclosure provides methods and apparatuses for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises a base station having a massive antenna array. One method comprises, at the base station: generating a plurality of transmit beams simultaneously using all antenna elements of the massive antenna array; and transmitting a plurality of PSSs and SSSs simultaneously to UEs in an MMC cell through the plurality of transmit beams, wherein each of the PSSs or SSSs includes a beam index of a corresponding transmit beam.

Description

METHODS AND APPARATUSES FOR CELL SEARCHING

IN AN MMC NETWORK

FIELD OF THE INVENTION

[0001] The present disclosure generally relates to the field of wireless communications, and specifically relates to methods and apparatuses for cell searching in an MMC network.

BACKGROUND OF THE INVENTION

[0002] A Millimeter- Wave refers to an electromagnetic wave which has a frequency between 30 GHz and 300 GHz and a wave length between 1 mm and 10 mm for which it is referred to as a millimeter wave. The millimeter wave has advantages such as a short wavelength, a wide frequency band, a strong anti-interference, a good privacy, and a small device volume, such that it can effectively solve many problems for high-speed wideband wireless access, thereby attaching wide attention. However, on the other hand, during the propagation process, the millimeter-wave will be absorbed by rain, air and the like, which may cause serious propagation depletion.

[0003] Millimeter wave communication (MMC) is concerned as one of key technologies in future 5G (fifth generation) wireless communication field. It is expected to support Gigabit level data communication. In a 5G network, many traditional solutions for supporting data transmission should be reconsidered to be suitable for a new transmission scenario.

[0004] For example, cell searching is an essential condition for implementing data transmission, and it is used for achieving synchronization between the user and the network and transmitting some basic system information to the user. However, severe propagation loss of millimeter wave causes a big challenge to a traditional cell searching solution, and it also affects data transmission.

SUMMARY OF THE INVENTION

[0005] In view of the problems above, the present disclosure provides methods and apparatuses for cell searching in an MMC network.

[0006] According to a first aspect of the present disclosure, there is provided a method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises a base station having a massive antenna array, the method including, at the base station: generating a plurality of transmit beams simultaneously using all antenna elements of the massive antenna array; and transmitting a plurality of PSSs and SSSs simultaneously to UEs in an MMC cell through the plurality of transmit beams, wherein each of the PSSs or SSSs includes a beam index of a corresponding transmit beam.

[0007] According to a second aspect of the present disclosure, there is provided a method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises a base station having a massive antenna array, the method comprising, at the base station: dividing a plurality of antenna elements of the massive antenna array into multiple antenna groups; at each timeslot, generating a transmit beam using one antenna group of the multiple antenna groups; and transmitting a PSS and an SSS to UEs in an MMC cell through the transmit beam, wherein the PSS or SSS includes a beam index of the transmit beam and time information indicating a beam scan period of the transmit beam.

[0008] According to a third aspect of the present disclosure, there is provided a method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises a base station having a massive antenna array, the method comprising, at the base station: dividing a plurality of antenna elements of the massive antenna array into multiple antenna groups, every two or more antenna groups in the multiple antenna groups form an antenna group combination; at each timeslot, generating a transmit beam combination including two or more transmit beams using two or more antenna groups in the antenna group combination; and transmitting a PSS and an SSS to UEs in an MMC cell through the antenna group combination, wherein the PSS or SSS includes a beam combination index corresponding to the transmit beam combination and time information indicating a beam scan period of the transmit beam combination.

[0009] According to a fourth aspect of the present disclosure, there is provided a method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, the MMC network comprises a base station having a massive antenna array, and the plurality of antenna elements of the massive antenna arrays are divided into multiple antenna groups or multiple antenna group combinations, the method comprising, at the base station: receiving a common RS from a UE; obtaining direction information of the UE based on the common RS; associating, based on the direction information of the UE, the UE with a transmit beam corresponding to one antenna group in the multiple antenna groups or a transmit beam combination corresponding to one antenna group combination in the multiple antenna group combinations; and transmitting a PSS and an SSS to the UE using the transmit beam or the transmit beam combination.

[0010] According to a fifth aspect of the present disclosure, there is provided a method for cell searching in an MMC network, wherein the MMC network is coexistent with a low frequency network, the method comprising, at a UE of the MMC network: establishing a connection with a base station of the low frequency network; obtaining system information of the MMC network from the base station of the low frequency network; and establishing a connecting with a base station of the MMC network using the system information of the MMC network.

[0011] In order to support MMC in the 5G network, a cell searching solution should be designed so as to not only support a stand-alone millimeter wave network, but also support a heterogeneous network where the MMC cell is coexistent with an LTE cell.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0012] Through depiction of the preferred embodiments of the present disclosure with reference to the accompanying drawings, the present disclosure will be better understood, and other objectives, details, features and advantages of the present disclosure will become more apparent. In the accompanying drawings:

[0013] Fig. 1 illustrates a schematic diagram of a method for cell searching in an MMC network according to a first embodiment of the present disclosure;

[0014] Fig. 2 illustrates a schematic diagram of a method for cell searching in an MMC network according to a second embodiment of the present disclosure;

[0015] Fig. 3 illustrates a schematic diagram of a method for cell searching in an MMC network according to a third embodiment of the present disclosure;

[0016] Fig. 4 illustrates a schematic diagram of a method for cell searching in an MMC network according to a fourth embodiment of the present disclosure;

[0017] Fig. 5 illustrates a schematic diagram of a method for cell searching in an MMC network according to a fifth embodiment of the present disclosure; and

[0018] Fig. 6 illustrates a flow diagram of the method for cell searching of the embodiment of Fig. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Although the preferred embodiments of the present disclosure are illustrated in the accompanying drawings, it should be understood that the present disclosure may be implemented in various manners and should not be limited by the embodiments illustrated herein. Instead, these embodiments are provided to make the present disclosure more thorough and complete so as to convey the scope of the present disclosure completely to those skilled in the art.

[0020] First, a cell searching procedure will be simply explained with an LTE network as an example.

[0021] Cell searching refers to a procedure of implementing time and frequency synchronization between a user equipment (UE) and a network and detecting a cell ID, which generally comprises the following steps.

[0022] 1. A base station broadcasts a PSS (Primary Synchronization Signal) and an SSS (Secondary Synchronization Signal) to UEs within a cell. A UE, after receiving the PSS and the SSS, obtains a physical layer cell ID and a timeslot synchronization through the PSS and obtains a CP (Cyclic Prefix) length, a physical layer cell group ID, and a frame synchronization through the SSS, thereby establishing a downlink synchronization with the base station.

[0023] 2. The UE further implements time and frequency synchronization and channel estimation through a downlink RS (reference signal) from the base station.

[0024] 3. The UE obtains an MIB (Master Information Block) by receiving and decoding a PBCH (Physical Broadcasting Channel) from the base station, and obtains an SIB (System Information Block) by receiving and decoding a PDSCH (Physical Downlink Shared Channel) from the base station, thereby obtaining configuration information and system information required for random access to the base station.

[0025] For cell searching in an MMC network, there may exist two application scenarios. One is a scenario where only a millimeter wave cell exists, and the other is a scenario where a millimeter wave cell and a low-frequency cell (e.g., a LTE cell, a LTE-A cell, etc.) coexist. Hereinafter, proposed schemes of the present disclosure are presented with regard to the two scenarios, respectively.

[0026] Scenario 1: only an MMW cell exists.

[0027] In this scenario, because only a stand-alone millimeter wave network exists, propagation loss is big. Recent studies show that in a cell edge of an MMC cell with a radius of 200m, the propagation loss can reach 140dB (see bibliography [1]). Compared with the microwave in 2.6GHz for LTE, there is an additional 20dB path loss. In this situation, compared with the LTE cells, a user can hardly implement cell searching and synchronize to a searched cell in this MMC network at the same distance between the user and the base station (eNB).

[0028] In the MMC, a compact antenna array can be flexibly implemented due to the smaller wavelength of millimeter wave. Therefore, a massive antenna array having a large number of antenna elements may be used in a base station of the MMC network. The antenna array at the transmit side may be used to form a transmit beam to compensate signal propagation loss within a certain coverage. For example, in the MMC, a massive antenna array including 128 antenna elements may provide up to 21dB gain than an omnidirectional transmit antenna.

[0029] As mentioned above, the transmit beam may enhance the propagation quality within a certain coverage. This indicates that at a given transmit beam, only part of users can successfully perform cell searching. In order to achieve full coverage of the MMC cell, the following scheme is proposed.

[0030] Fig. 1 illustrates a schematic diagram of a method for cell searching in an MMC network according to a first embodiment of the present disclosure. As illustrated in Fig. 1, the MMC network is a standalone MMC network, which does not coexist with any low-frequency network (e.g., LTE or LTE-A network). In the MMC network, the MMC base station 10 includes a massive antenna array having a large number of antenna elements. Besides, it is supposed that the base station 10 performs cell searching in the cell A.

[0031] In this embodiment, all the antenna elements of the massive antenna array of the base station 10 transmit simultaneously to generate a plurality of transmit beams such as beam 1, beam 2 and beam 3 as shown in Fig. 1.

[0032] Next, the base station 10 simultaneously transmit PSSs and SSSs to UEs (not shown) in the MMC cell through the plurality of transmit beams, wherein each of the PSSs and SSSs includes beam indexes of respective transmit beams.

[0033] Here, the beam indexes may be configured at a reserved position in the known PSS or SSS format or may be designed into a new PSS or SSS format.

[0034] In this way, the transmit beams of the base station 10 may cover the entire MMC cell at the same time. A UE that receives and successfully decodes the PSS or SSS carried in a transmit beam may obtain the beam index of the corresponding transmit beam and other conventional information (e.g., cell ID, etc., as mentioned above) carried in the PSS or SSS, so as to implement a downlink synchronization similar to that in a network (e.g., 3G or 4G cell) having a lower frequency band than the MMC network. Furthermore, the UE will also perform uplink transmission using the beam index to implement uplink synchronization and other functions.

[0035] In the first embodiment, the base station transmits beams by using all antennas of the antenna array simultaneously, such that each transmit beam as generated is very wide (as shown in Fig. 1), while the cell coverage (i.e., the maximum distance for the UE to successfully access the MMC base station) is limited. In order to enhance the cell coverage, a beam scanning scheme is proposed, as provided below.

[0036] Fig. 2 illustrates a schematic diagram of a method for cell searching in an MMC network according to a second embodiment of the present disclosure. As illustrated in Fig. 2, the MMC network is a standalone MMC network, which does not coexist with any low-frequency network (e.g., LTE or LTE-A network). In the MMC network, the MMC base station 10 includes a massive antenna array having a large number of antenna elements. Besides, it is supposed that the base station 10 performs cell searching in the cell A.

[0037] In this embodiment, all the antenna elements of the massive antenna array of the base station 10 are divided into multiple antenna groups. Each antenna group may generate one transmit beam such as beam 1, beam 2, beam N as illustrated in Fig. 2.

[0038] Next, at each timeslot, the base station 10 generates a transmit beam through an antenna group, and transmits the PSS and the SSS to UEs in the MMC cell through the transmit beam, wherein the PSS or SSS includes a beam index of the corresponding transmit beam and a beam scan period of the transmit beam.

[0039] Here, the beam index may be configured at a reserved position in the known PSS or SSS format or may be designed into a new PSS or SSS format.

[0040] In this way, the base station 10 achieves a full coverage of the cell by performing beam scanning. Since only one transmit beam is used for PSS and SSS transmission in one timeslot, the transmit beam may provide a large link budget and expand the cell coverage.

[0041] The UE that receives and successfully decodes the PSS and SSS carried in the transmit beam can obtain the beam index of the corresponding transmit beam, the beam scan period and other conventional information, so as to implement downlink and uplink synchronization.

[0042] In the second embodiment, the cell coverage is improved, but the cell search period is prolonged. Therefore, the following embodiments are proposed to consider a compromise between the cell search period and the cell coverage.

[0043] Fig. 3 illustrates a schematic diagram of a method for cell searching in an MMC network according to a third embodiment of the present disclosure. As illustrated in Fig. 3, the MMC network is a standalone MMC network, which does not coexist with any low-frequency network (e.g., LTE or LTE-A network). In the MMC network, the MMC base station 10 includes a massive antenna array having a large number of antenna elements. Besides, it is supposed that the base station 10 performs cell searching in the cell A.

[0044] In this embodiment, similar to the second embodiment, a plurality of antenna elements of the massive antenna array of the base station 10 are divided into multiple antenna groups. Each antenna group may generate one transmit beam such as beam 1, beam 2, ..., beam N as illustrated in Fig. 3.

[0045] Different from the second embodiment, two or more antenna groups of the multiple antenna groups may form an antenna group combination.

[0046] Next, at each timeslot, the base station 10 generates a transmit beam combination through an antenna group combination, and transmits the PSS and the SSS to UEs in the MMC cell through the transmit beam combination, wherein the PSS or SSS includes a beam combination index of the corresponding transmit beam combination and a beam scan period of the transmit beam combination.

[0047] Here, the beam combination index may be configured at a reserved position in the known PSS or SSS format or may be designed into a new PSS or SSS format.

[0048] It may be seen that, different from Figs. 1 and 2, in the embodiment of Fig. 3, the base station transmits a combination of two or more beams each time rather than transmitting through all antenna elements simultaneously or only transmitting one beam each time. For example, it is supposed that a combination of two beams is transmitted each time, then the base station may transmit beam 1 and beam 2 (which may be referred to as beam combination I) in the first timeslot, transmit beam 3 and beam 4 (which may be referred to as beam combination II) in the second time slot, and so on and so forth. Of course, the present disclosure is not limited to this; instead, a combination of any beams may be transmitted each time.

[0049] In this implementation, since in each timeslot, the base stations selects a combination of several beam groups for transmitting PSS and SSS, a balance between fast cell searching and good cell coverage is achieved.

[0050] The UE that receives and successfully decodes the PSS and the SSS carried in the transmit beam can obtain a beam combination index of the corresponding transmit beam combination, the beam scan period and other conventional information, so as to implement downlink and uplink synchronization.

[0051] Fig. 4 illustrates a schematic diagram of a method for cell searching in an MMC network according to a fourth embodiment of the present disclosure. As illustrated in Fig. 4, the MMC network is a standalone MMC network, which does not coexist with any low-frequency network (e.g., LTE or LTE-A network). In the MMC network, the MMC base station 10 includes a massive antenna array having a large number of antenna elements. Besides, it is supposed that the base station 10 performs cell searching in the cell A.

[0052] Different from the embodiments illustrated in Figs. 1-3, the cell searching is initiated by a UE.

[0053] The UE first transmits a common reference signal (RS).

[0054] The base station 10 obtains directional information of the UE based on the common RS of the UE.

[0055] Here, similar to the second and third embodiments, the antenna elements of the massive antenna array of the base station 10 are divided into multiple antenna groups or antenna group combinations.

[0056] The base station may associate, based on the obtained directional information of the UE, the UE with a transmit beam corresponding to one antenna group thereof or a transmit beam combination corresponding to one antenna group combination, and transmit the PSS and the SSS through the transmit beam or the transmit beam combination, so as to perform downlink and uplink synchronization.

[0057] In this implementation, the UE may periodically or non-periodically, as desired, transmit the common reference signal such that the base station can quickly capture the UE direction and quickly associate the transmit beam or transmit beam combination, thereby shortening the beam tracking time and satisfying the low-delay service needs.

[0058] Here, for the MMC network that supports the UE to transmit a specific common RS, the solution of the fourth embodiment is preferred since cell searching can be implemented more quickly. However, if UE does not support transmission of such specific common RS, any one of the embodiments of Figs. 1-3 may be selected. In other words, the fourth embodiment can be back-compatible with the first to third embodiments.

[0059] Scenario 2: an MMC cell and a low-frequency cell coexist in a heterogamous network.

[0060] In the initial stage of the 5G network, it is very likely to deploy a heterogeneous network where 5G cells and 4G cells coexist, as illustrated in Fig. 5. In this scenario, due to existence of a low frequency cell with a high channel quality, it is possible to employ a multi-connection with the MMC cell and the low-frequency cell to overcome the large propagation loss of the MMC network, thereby achieving quick cell searching.

[0061] Fig. 5 illustrates a schematic diagram of a method for cell searching in an MMC network according to a fifth embodiment of the present disclosure, and Fig. 6 illustrates a flow diagram of the method for cell searching of the embodiment of Fig. 5. Different from the embodiments shown in Figs. 1-4, the MMC network coexists with a low-frequency network (e.g., LTE or LTE-A network) rather than being a stand-alone MMC network. The MMC network includes an MMC base station 10, the low-frequency network includes a low-frequency base station 20, and a UE 30 is located within coverage of both the MMC network and the low-frequency network and has a capability of communicating with both the MMC network and the low-frequency network.

[0062] As illustrated in Fig. 6, in this embodiment, the MMC base station 10 establishes an association with the low frequency base station 20 in advance so as to share information with each other. More specifically, the low-frequency base station 20 obtains system information of the MMC network from the MMC base station 10 and stores into the low-frequency base station 20.

[0063] Here, the system information of the MMC network may include, for example, at least one of system bandwidth of the MMC network, beam pattern of the UE in frequency domain and/or time domain, and low-frequency network cell recommendation information for the UE.

[0064] First, the UE 30 performs random access to the low-frequency base station 20 so as to establish a connection. The procedure for the UE 30 to establish a connection with the low-frequency base station 20 is similar to that in the prior art, which will not be detailed here.

[0065] The difference lies in that after the UE 30 establishes a connection with the low-frequency base station 20, it obtains system information of the MMC network from the low-frequency base station 20. The system information may be transmitted to the UE 30 from the low-frequency base station 20 through a physical downlink shared channel (PDSCH), for example.

[0066] Next, the UE 30 performs an initial access with the MMC base station 10 using the obtained system information of the MMC network so as to establish a connection.

[0067] Because the UE 30 can quickly obtain the system information of the MMC network, it can quickly perform beam association with the MMC base station, thereby implementing cell searching.

[0068] Here, after the system information of the MMC network has been obtained, the access process of the UE30 to the MMC base station 10 is similar to that in the low-frequency network (e.g., 4G or 3G network), which will not be detailed here.

[0069] In the solution of scenario 1, the UE and the MMC network can only perform beam association in the time domain. Different from scenario 1, in the scheme of scenario 2, the UE knows in advance the system information of the MMC network, therefore, the beam association may be performed in both the frequency domain and the time domain, thereby further reducing access latency.

[0070] In one implementation, after the connection is established between the UE 30 and the MMC base station 10, the UE 30 still maintains the connection with the low-frequency base station 20. In this case, control of the UE 30 may be implemented by the low-frequency base station 20, while only data interchange is performed between the UE 30 and the MMC base station 10.

[0071] In another implementation, after the UE has established the connection with the MMC base station 10, its connection with the low-frequency base station 20 will not be maintained. For example, the UE may maintain the connection with the low-frequency base station only when powered on or just roaming into an MMC network; while after obtaining the system information of the MMC network, it establishes the connection with the MMC base station 10 and is disconnected with the low-frequency base station 20. In this case, after the UE 30 establishes the connection with the MMC base station 10, the UE 30 is fully controlled by the MMC base station 10. Since this manner does not require always maintaining a multi-connection, it can save the resources of the low-frequency network and reduces the power consumption of the UE.

[0072] The present disclosure provides some solutions for 5G MMC access and data transmission so as to support all typical transmission scenarios, including the scenario with co-existence of 4G and MMC cells and the scenario with standalone deployment of the MMC cell.

[0073] In one or more exemplary designs, functions of the present application may be implemented by hardware, software, firmware, or any combination thereof. In case of being implemented by software, the functions may be stored on a computer-readable medium as one or more instructions or codes, or transmitted as one or more instructions or odes on the computer-readable medium. The computer-readable medium includes a computer storage medium and a communication medium, wherein the communication medium includes any medium facilitating the computer program to be delivered from one place to another place. The storage medium may be any available medium that is accessible to a general or dedicated computer. Such computer-readable medium may comprise, for example, but not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disk storage device, magnetic disk storage device, or other magnetic storage device, or any other medium available for carrying or storing desired program code modules in a form of instructions or data structure that is accessible by a general or dedicated computer or by a general or dedicated processor. Moreover, any connection may also be referred to as a computer readable medium. For example, if software is transmitted from a website, a server or other remote sources using a co-axial cable, an optical fiber cable, a twisted pair cable, a digital subscriber line (DSL) or radio technologies such as infrared, radio, microwave and the like, then the co-axial cable, optical fiber cable, twisted pair cable, DSL or radio technologies such as infrared, radio, microwave and the like are also included in the definition of the medium.

[0074] Various kinds of exemplary logical blocks, modules and circuits as described in conjunction with the present disclosure may be implemented or executed using a general processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a discrete gate, or a transistor logic, discrete hardware components, or any combinations thereof for performing the functions of the present disclosure. The general-purpose processor may be a microprocessor; or, the processor may also be any common processor, controller, micro-controller or state machine. The processor may also be implemented as a combination of computing devices, e.g., a combination of DSP and microprocessor, a combination of microprocessors, or a combination of one or more microprocessors and DSP kernel, or any other kind of such structure.

[0075] A person of normal skill in the art should understand that various kinds of exemplary logic blocks, modules, circuits and algorithm steps described in conjunction with the embodiments of the present application may also be implemented as electronic hardware, computer software or a combination thereof. In order to clearly illustrate such exchangeability between hardware and software, various exemplary components, blocks, modules, circuits, and steps have been described above in general around their functions. As to whether these functions are implemented into hardware or software, it depends on a specific application and a design constraint condition applied onto the entire system. Those skilled in the art may implement the described functions in a flexible manner for each specific application. However, such implementation decision should not be construed as departing from the protection scope of the present disclosure.

[0076] The description above of the present disclosure is to enable any person of normal skill in the art to implement or use the present disclosure. For a person of normal skill in the art, various modifications of the present disclosure are obvious; moreover, a general principle of the definition herein may also be applied to other variations without departing from the spirit and protection scope of the present disclosure. Therefore, the present disclosure is not limited to the instances and design as described here; instead, it is consistent with the broadest scope of the principle and novelty features of the present disclosure.

Bibliography:

[1]. Mustafa Riza Akdeniz, Yuanpeng Liu: Millimeter Wave Channel Modeling and Cellular Capacity Evaluation. IEEE Journal on Selected Areas in Communications 32(6): 1164-1179 (2014).

Claims

1. A method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises a base station having a massive antenna array, the method comprising, at the base station:

generating a plurality of transmit beams simultaneously using all antenna elements of the massive antenna array; and

transmitting a plurality of PSSs and SSSs simultaneously to UEs in an MMC cell through the plurality of transmit beams, wherein each of the PSSs or SSSs includes a beam index of a corresponding transmit beam.

2. A method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises a base station having a massive antenna array, the method comprising, at the base station:

dividing a plurality of antenna elements of the massive antenna array into multiple antenna groups;

at each timeslot, generating a transmit beam using one antenna group of the multiple antenna groups; and

transmitting a PSS and an SSS to UEs in an MMC cell through the transmit beam, wherein the PSS or SSS includes a beam index of the transmit beam and time information indicating a beam scan period of the transmit beam.

3. A method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises a base station having a massive antenna array, the method comprising, at the base station:

dividing a plurality of antenna elements of the massive antenna array into multiple antenna groups, every two or more antenna groups in the multiple antenna groups form an antenna group combination;

at each timeslot, generating a transmit beam combination including two or more transmit beams using two or more antenna groups in the antenna group combination; and

transmitting a PSS and an SSS to UEs in an MMC cell through the antenna group combination, wherein the PSS or SSS includes a beam combination index corresponding to the transmit beam combination and time information indicating a beam scan period of the transmit beam combination.

4. A method for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, the MMC network comprises a base station having a massive antenna array, and a plurality of antenna elements of the massive antenna array are divided into multiple antenna groups or multiple antenna group combinations, the method comprising, at the base station:

receiving a common RS from a UE;

obtaining direction information of the UE based on the common RS;

associating, based on the direction information of the UE, the UE with a transmit beam corresponding to one antenna group in the multiple antenna groups or a transmit beam combination corresponding to one antenna group combination in the multiple antenna group combinations; and

transmitting a PSS and an SSS to the UE using the transmit beam or the transmit beam combination.

5. A method for cell searching in an MMC network, wherein the MMC network is coexistent with a low frequency network, the method comprising, at a UE of the MMC network:

establishing a connection with a base station of the low frequency network;

obtaining system information of the MMC network from the base station of the low frequency network; and

establishing a connecting with a base station of the MMC network using the system information of the MMC network.

6. The method according to claim 5, wherein the low-frequency network is an LTE network or LTE-A network.

7. The method according to claim 5, wherein the system information of the MMC network comprises at least one of system bandwidth of the MMC network, beam pattern of the UE in frequency domain and/or time domain, and low-frequency network cell recommendation information for the UE.

8. A base station for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network and the MMC network comprises the base station having a massive antenna array, the base station comprising:

a beam generating unit configured to generate a plurality of transmit beams simultaneously using all antenna elements of the massive antenna array; and

a transmitting unit configured to transmit a plurality of PSSs and SSSs simultaneously to UEs in an MMC cell through the plurality of transmit beams, wherein each of the PSSs or SSSs includes a beam index of a corresponding transmit beam.

9. A base station for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises the base station having a massive antenna array, the base station comprising:

an antenna dividing unit configured to divide a plurality of antenna elements of the massive antenna array into multiple antenna groups;

a beam generating unit configured to, at each timeslot, generate a transmit beam using one antenna group in the multiple antenna groups; and

a transmitting unit configured to transmit a PSS and an SSS to a UE in an MMC cell through the transmit beam, wherein the PSS or SSS includes a beam index of the transmit beam and time information indicating a beam scan period of the transmit beam.

10. A base station for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, and the MMC network comprises the base station having a massive antenna array, the base station comprising:

an antenna group dividing unit configured to divide a plurality of antenna elements of the massive antenna array into multiple antenna groups, every two or more antenna groups in the multiple antenna groups form an antenna group combination;

a beam generating unit configured to, at each timeslot, generate a transmit beam combination including two or more transmit beams using two or more antenna groups in the antenna group combination; and

a transmitting unit configured to transmit a PSS and an SSS to UEs in an MMC cell through the antenna group combination, wherein the PSS or SSS includes a beam combination index corresponding to the transmit beam combination and time information indicating a beam scan period of the transmit beam combination.

11. A base station for cell searching in an MMC network, wherein the MMC network is a stand-alone MMC network, the MMC network comprises the base station having a massive antenna array, and the plurality of antenna elements of the massive antenna arrays are divided into multiple antenna groups or multiple antenna group combinations, the base station comprising:

a receiving unit configured to receive a common RS from a UE;

a direction information obtaining unit configured to obtain direction information of the UE based on the common RS;

an associating unit configured to associate, based on the direction information of the UE, the UE with a transmit beam corresponding to one antenna group in the multiple antenna groups or a transmit beam combination corresponding to one antenna group combination in the multiple antenna group combinations; and

a transmitting unit configured to transmit a PSS and an SSS to the UE using the transmit beam or the transmit beam combination.

12. A UE for cell searching in an MMC network, wherein the MMC network is coexistent with a low frequency network, the UE comprising:

a connection establishing unit configured to establish a connection with a base station of the low frequency network; and

a receiving unit configured to obtain system information of the MMC network from the base station of the low frequency network,

wherein the connection establishing unit is further configured to establish a connecting with a base station of the MMC network using the system information of the MMC network.

13. The UE according to claim 12, wherein the low-frequency network is an LTE network or LTE-A network.

14. The UE according to claim 12, wherein the system information of the MMC network comprises at least one of system bandwidth of the MMC network, beam pattern of the UE in frequency domain and/or time domain, and low-frequency network cell recommendation information for the UE.