WO2015111957A1 - Transmitting device for lte device-to-device communication - Google Patents

Abstract

The present invention relates to technology for carrying out device-to-device communication according to an efficient way of transmitting used in device-to-device communication. The present invention relates to a transmitting device for LTE device-to-device communication, which conducts high-speed device-to-device communication using a bandwidth and transmitting technology that minimizes interference, wherein the transmitting device for LTE deice-to-device communication comprises a terminal for conducting device-to-device communication by transmitting, to a different terminal, a device-to-device synchronization signal and a discovery signal, and receiving a response to same from the different terminal.

Description

Device for direct communication between LTE terminals

The present invention relates to a device for transmitting direct communication between LTE terminals, and more particularly, to perform direct communication between terminals in an efficient transmission method used in direct communication between terminals. That is, the present invention relates to a transmission device for direct communication between LTE terminals which performs direct communication between terminals at high speed in a bandwidth and a transmission scheme where interference can be minimized.

Wireless communication technologies use various standards and protocols for transmitting data between base stations and terminals. Modulation technology for wireless communication uses orthogonal frequency-division multiplexing (OFDM) for high speed transmission.

Standards and protocols using OFDM are used in the third generation partnership project (3GPP) long term evolution (LTE), the 802.16 and IEEE 802.11 standards of the Institute of Electrical and Electronics Engineers (IEEE).

In a 3GPP LTE system, a base station is a combination of Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Node Bs (also commonly referred to as Evolved Node Bs, Enhanced Node Bs, eNodeBs, or eNBs) and Radio Network Controller (RNC). It may be in communication with a terminal known as a user equipment (UE). In IEEE 802.16, a base station may be called a base station (BS). In IEEE 802.11, a base station may be referred to as a WiFi wireless access point (WAP).

Currently, communication between terminals generally uses a base station. The reason is that the scheduling of radio resources at the base station is efficient while reducing the load on the terminal. However, if the distance between terminals is close or if the direct communication between terminals is performed through the base station due to multiplexing of radio resources, etc., the efficiency of the communication system can be increased more effectively. Has been going on.

As an example, Korean Patent Laid-Open No. 10-2013-0070661 mentions a control method for direct communication between terminals. Such a method discloses that a base station receives location information of each terminal and allocates resources for direct communication between terminals according to a selected resource allocation method so that resources for direct communication between terminals can be efficiently allocated.

Meanwhile, in addition to the above-described resource allocation, communication data must be demodulated smoothly for efficient inter-device direct communication, and should not be subjected to interference due to other communication entities. However, since there are a plurality of base stations and terminals on a typical wireless communication system, there is a high possibility that the communication between terminals is interfered by other base stations and other terminals. In addition, there is a possibility that an error occurs in demodulation of communication data between terminals due to fading in a frequency domain and / or a time domain existing in a wireless environment.

Accordingly, there is a need to develop a scheme capable of effectively and efficiently demodulating communication data for direct communication between terminals as well as a scheme for preventing interference by other communication entities.

An object of the present invention is to provide a transmission device for direct communication between LTE terminals to perform direct communication between terminals in an efficient transmission method used in direct communication between terminals.

Another object of the present invention is to provide an apparatus for transmitting direct communication between LTE terminals, which efficiently uses a radio channel by performing direct communication between terminals at a high speed in a bandwidth and transmission scheme where interference can be minimized.

An apparatus for performing direct communication between terminals according to an embodiment of the present invention, the RF unit for transmitting and receiving a radio signal; And a processor connected to the RF unit, wherein the processor may be configured to transmit a synchronization signal and a discovery signal between terminals to another terminal and receive a response from the other terminal to perform direct communication between the terminals.

The processor uses less than a specific value among codes less than 1/2 as a turbo code, uses 1/2 as an initial value, uses a bandwidth within 80 MHz, uses 20 MHz as an initial value, and uses FDD and TDD in duplex mode. Use any one, use TDD as initial value, use any modulation method below 64QAM as modulation method, use 64QAM as initial value, use normal and extended as cyclic prefix (CP), use normal as initial value Can be configured to use at least one of the parameters as a parameter.

The inter-terminal synchronization signal may include a primary D2D synchronization signal (PD2DSS) and a secondary D2D synchronization signal (SD2DSS). When the extended CP symbol is used, PD2DSS may be located at 0 and 1 of the first slot of the subframe and SD2DSS may be located at 3 and 4 of the second slot of the subframe.

An apparatus for performing direct communication between terminals according to an embodiment of the present invention, the RF unit for transmitting and receiving a radio signal; And a processor connected to the RF unit, wherein the processor performs direct communication between another terminal and the terminal and is configured not to receive at least one of a time and a frequency that do not need to be received among the signals of the other terminal. Can be.

The processor may be further configured to reduce processing time by using a DFT instead of FFT signal processing when there are frequencies that do not require reception, if the subcarrier that needs to be received is five or less of 1024 subcarriers. Processing time using at least one of performing carrier demodulation to reduce processing time, and reducing processing time by performing FFT signal processing using a look up table (LUT) for subcarriers requiring reception. It can be configured to reduce.

An apparatus for performing direct communication between terminals according to an embodiment of the present invention, the RF unit for transmitting and receiving a radio signal; And a processor connected to the RF unit, wherein the processor may be configured to perform direct communication between another terminal and a terminal and perform interleaving on a physical channel used for direct communication between terminals.

The processor may be configured to perform at least one of interleaving in the frequency domain and interleaving in the time domain.

Further, the processor may not interleave the interleaving reference symbol when interleaving in the frequency domain, do not interleave the interleaving reference subcarrier when interleaving in the time domain, and in the frequency domain and the time domain. When interleaving is performed at the same time, the interleaving may be configured not to perform interleaving in at least one of not interleaving with respect to an interleaving reference subcarrier located in an interleaving reference symbol.

The processor designates one or more symbols per subframe as the interleaving reference symbols, designates one or more subcarriers per subframe as the interleaving reference subcarriers, and differs in the interleaving reference subcarriers per symbol. It may be configured to perform at least one of the designation.

The processor may be configured to perform at least one of puncturing in the frequency domain and puncturing in the time domain before at least one of the interleaving and the interleaving.

The processor may be configured to perform puncturing more than the number of puncturing used when the wireless channel environment is bad when the wireless channel environment between the device and the other terminal is good. In addition, the processor may be configured to perform puncturing more than the number of puncturing used when a high level modulation method is used when a low level modulation method is used.

The processor may be configured to perform automatic gain adjustment based on an automatic gain adjustment reference symbol among symbols of direct communication between terminals transmitted from another terminal. In addition, the processor may be configured to demodulate the symbol on which the automatic gain adjustment is performed based on the automatic gain value during the automatic gain adjustment.

The processor may be configured to perform the automatic gain adjustment using reference symbols equal to or greater than the number of automatic gain adjustment reference symbols used when the wireless channel environment is good when the wireless channel environment between the device and the other terminal is bad. . In addition, the processor may be configured to perform the automatic gain adjustment using reference symbols equal to or greater than the number of automatic gain adjustment reference symbols used when using a low level modulation scheme when using a high level modulation scheme.

An apparatus for performing direct communication between terminals according to an embodiment of the present invention, the RF unit for transmitting and receiving a radio signal; And a processor connected to the RF unit, and the processor may be configured to receive information of a neighbor base station from at least one of a base station and another terminal and perform direct communication between the other terminal and the terminal.

The processor may store information of up to 16 neighboring base stations and then perform direct communication between the terminals by minimizing interference with neighboring base stations, or store information of up to 3 neighboring base stations or up to 16 if insufficient. It may be configured to perform direct communication between the terminals by minimizing interference with neighboring base stations after storing the information of the neighboring base stations.

The processor expands information of the neighboring base station when a communication failure occurs above the communication failure criterion value in the direct communication between the other terminals with the other terminal, and the communication failure is a communication failure reference in the direct communication between the terminals with the other terminal. If it is less than the value it can be configured to delete the information of the neighboring base station farthest away from the device.

The processor may be configured to store the location of the neighboring base station as a relative distance of at least one of one, two, and three dimensions with respect to the device. In addition, the processor may be configured to further receive at least any one of a usage frequency, a frequency band, transmission power, and coverage information of the neighboring base station together with the location of the neighboring base station.

The apparatus for transmitting LTE terminal-to-terminal direct communication according to the present invention has an advantage of performing direct terminal-to-terminal communication in an efficient transmission method used in direct terminal-to-terminal communication.

In addition, the apparatus for transmitting LTE direct communication according to the present invention has an advantage that the wireless channel can be efficiently used by performing the direct communication between the terminals at a high speed with a bandwidth and a transmission method that can minimize interference.

1 is a block diagram of an LTE network according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of dual connectivity for a case where the first base station of FIG. 1 operates as a primary base station and the second base station independently operates as a secondary base station.

FIG. 3 is a diagram illustrating a dual connection for a case where a first base station of FIG. 1 operates as a primary base station, a second base station operates as a secondary base station, and data is separated and combined through the primary base station.

4 is a detailed block diagram illustrating a case in which the secondary base station of FIGS. 2 and 3 is disconnected from the terminal.

FIG. 5 is a diagram illustrating in detail a case in which transmission power of a terminal is allocated to a primary base station or a secondary base station of FIGS. 2 and 3.

FIG. 6 is a detailed diagram illustrating a case where a terminal randomly accesses a primary base station or a secondary base station of FIGS. 2 and 3.

7 is a diagram illustrating a communication system for direct communication between LTE terminals according to another embodiment of the present invention.

8 is a diagram illustrating a configuration in which another terminal of FIG. 7 demodulates a subcarrier.

9 is a diagram illustrating that the terminal of FIG. 7 performs interleaving.

FIG. 10 is a block diagram illustrating that the terminal of FIG. 7 stores neighbor base station information.

11 is a block diagram illustrating a wireless communication system in which an embodiment of the present invention may be implemented.

Specific embodiments of the present invention will be described with reference to the accompanying drawings.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. It is not intended to limit the invention to the specific embodiments, it can be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the LTE terminal direct communication transmission apparatus according to the present invention.

Direct communication between terminals is a communication without passing through a base station, and it is a terminal-to-device synchronization method that synchronizes time and frequency synchronization between terminals, a method for discovering a terminal for discovering a terminal to be communicated after synchronizing between terminals, and a direct communication between terminals after the discovery of the terminal. There is a need for a communication method between terminals for performing communication.

First, a method of synchronizing between terminals is performed by a Device to Device Synchronization Signal (D2DSS) and a Physical D2D Synchronization Channel (PD2DSCH).

The D2DSS is transmitted by a terminal and received by another terminal so that the other terminal synchronizes time and frequency with the terminal. Meanwhile, PD2DSCH means a physical channel through which the D2DSS is transmitted.

If the cellular network to which the base station belongs is not available, the D2DSS provides the same function as the conventional synchronization signal transmitted from the base station. That is, it enables synchronization acquisition for D2D communication of UEs and delivers ID related information of a subject providing a common time reference.

When the cellular network operates normally, the D2D UEs may obtain a common time reference from the base station to which they belong. For example, in the LTE system, when the terminal accesses a base station, the terminal detects a primary synchronization signal (PSS) and a secondary synchronization signal (SSS), which are base station transmission synchronization signals, to obtain a time synchronization and a cell ID for the cell to which the terminal belongs. The acquired time synchronization can be used as a common time reference.

Meanwhile, the discovery method of the terminal should transmit discovery information to the surroundings in order to inform the other terminal of its existence in D2D communication. In addition, the other terminal may receive the discovery information to confirm the existence of the terminal.

When another terminal that recognizes such discovery information wants to perform data transmission to the terminal, the other terminal transmits the information related to the D2D own terminal to the terminal, and control information necessary for receiving the information may also be transmitted. .

The terminal receiving the information related to the other terminal communicates by transmitting the ACK / NACK and / or close loop control information to the other terminal based on the received signal.

Thereafter, the terminal-to-terminal communication method communicates using a physical channel, and the physical channel includes a plurality of traffic slots. In addition, independent link scheduling and data transmission are performed for each traffic slot, and are divided into functions of link scheduling, rate scheduling, data transmission, and acknowledgment transmission.

In link scheduling, a single-tone detection signal using an OFDM signal structure is transmitted for each end-to-end link for each unidirectional communication to measure a signal interference relationship between links between terminals and to transmit data in a corresponding traffic slot. You can decide whether to approach or give way.

In the rate scheduling, the detailed transmission rate is coordinated for the links for which the medium access is determined in the corresponding traffic slot. In the data transmission, the transmitting terminals of the links for the medium access are transmitted to the corresponding receiving terminal. In the acknowledgment transmission, An acknowledgment message for the data transmission may be sent.

1 is a configuration diagram of an LTE network according to an embodiment of the present invention, and FIGS. 2 to 6 are configuration diagrams for describing FIG. 1 in detail.

Hereinafter, an apparatus for transmitting direct communication between LTE terminals according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6.

First, referring to FIG. 1, an LTE network structure according to an embodiment of the present invention includes a base station and a terminal. In particular, the communication between terminals can be used by allocating a new frequency when the macro cell and the D2D channel are separately allocated.

Meanwhile, when allocating a macro cell and a D2D channel at the same time, the terminal-to-terminal communication may use at least one of adding a subchannel and utilizing a physical channel used in the macro cell. At least one of a channel management technique and a duplexing method may be used.

In addition, synchronization between terminals may use at least one of provision in the uplink, provision in the downlink, and simultaneous provision of uplink and downlink.

Looking at the LTE network structure in detail, the first terminal 110 and the third terminal 130 is located in the cellular link radius of the first base station 310 and the fourth terminal 240 and the fifth terminal 250 is the second base station Located at the cellular link radius of 320.

In addition, the third terminal 130 is located at a distance capable of D2D communication with the first terminal 110, the second terminal 120, and the fourth terminal 240. The D2D links of the third terminal 130 and the first terminal 110 are located in the same first base station 310, and the D2D links of the third terminal 130 and the fourth terminal 240 are located at different cellular radii. The D2D link of the third terminal 130 and the second terminal 120 includes a second terminal 120 not located at any cellular radius and a third terminal 130 located at a cellular radius of the first base station 310. have.

Here, the cellular link channel used between the first base station 310 and the third terminal 130 and the D2D link channel used by the third terminal 130 and the fourth terminal 240 may be allocated separately or simultaneously. .

For example, when the cellular link channel used between the first base station 310 and the third terminal 130 and the D2D link channel used by the third terminal 130 and the fourth terminal 240 use the same frequency, the PDSCH is used. OFDM symbols of, PDCCH, PUSCH, and PUCCH may be separately allocated.

In particular, the first base station 310 may perform an allocation schedule of a synchronization signal, a discovery signal, and a time slot for transmission of HARQ, used for the third terminal 130 and the fourth terminal 240. have.

Here, the synchronization signal transmitted by the first base station 310 may be used simultaneously with the information of the cellular link of the first base station 310, but the synchronization signal used by the third terminal 130 and the fourth terminal 240, The discovery signal and the time slot for transmitting the HARQ may be scheduled so that the cellular link channel and the time slot used between the first base station 310 and the third terminal 130 do not overlap.

Meanwhile, when the cellular link channel used between the first base station 310 and the third terminal 130 and the D2D link channel used by the third terminal 130 and the fourth terminal 240 use different frequencies, the third terminal is used. The 130 and the fourth terminal 240 may use the OFDM symbols of the PDSCH, the PDCCH, the PUSCH, and the PUCCH exclusively, and may be scheduled by the third terminal 130 or the fourth terminal 240.

In addition, when performing the D2D communication between the third terminal 130 and the fourth terminal 240, the interference affected by the first base station 310 and the first terminal 110 is avoided and used. In particular, when the third terminal 130 performs the D2D communication between the third terminal 130 and the fourth terminal 240, the first base station 310 uses the synchronization signal received by the first base station 310 from the first base station 310. Transmit to fourth terminal 240 via link channel, transmit to fourth terminal 240 via downlink channel used by first base station 310, or uplink downlink used by first base station 310 The channel is simultaneously provided using any one of methods for transmitting to the fourth terminal 240.

The following describes elements required for D2D data communication as another embodiment.

First, it may be divided into discovery for finding a D2D terminal for D2D data communication and D2D communication for actual communication thereafter.

Discovery consists of signals and messages necessary to find a D2D UE, and includes discovery information and channel prediction information in the signals and messages.

Frames used for discovery messages and sequences can be used similarly to the physical uplink shared channel (PUSCH) of LTE uplink, and discovery at short distances uses a normal cyclic prefix and can be used in an extended range. Discovery of uses an extended cyclic prefix.

QPSK, turbocode, interleaver, and CRC-24 are used for transmission of messages and sequences of discovery.

Discovery messages and sequences are sent at the same frequency and at the same time.

On the other hand, D2D communication is used for communication between terminals, and includes the use of physical channels for synchronization and communication between terminals.

Synchronization of D2D communication is for synchronizing between terminals by transmitting a D2D synchronization signal, and uses the same frequency and time between terminals.

The synchronization sequence of the D2D communication includes at least one of a ZC sequence or an M sequence.

The synchronization content of the D2D communication includes at least one of an ID of a synchronization source for transmitting a synchronization signal, a type of synchronization source, resource allocation of a control signal, and data.

Physical channels for D2D communication include D2D Synchronization Signal (D2DSS), which sends D2D synchronization signals, Physical D2D Synchronization Channel (PD2DSCH), a physical D2D synchronization channel, Cluster head control channel (CH-CCH), and cluster head control channel And at least one of a cluster head data channel (CH-DCH), a D2D data channel, and a REQ channel for requesting a resource.

Here, the D2DSS is transmitted from a cluster head which is a synchronization source of a cluster composed of D2D terminals and provides a synchronization reference.

The PD2DSCH also includes synchronization information indicating SFN, synchronization status, and the like, and configuration information indicating channel bandwidth, resource configuration information, and the like in the cluster head.

On the other hand, CH-CCH is transmitted from the cluster head to the transmitting terminal and the receiving terminal in the cluster and includes transmission information for transmission and does not include a control part for decoding.

In addition, the CH-DCH is also transmitted from the cluster head to the transmitting terminal and the receiving terminal in the cluster and transmits data to be transmitted by scheduling the CH-CCH.

The D2D data channel is a channel for transmitting data through a channel transmitted by a transmitting terminal in a cluster to a receiving terminal and monitors CH-CCH information and transmits it through allocated resources.

The REQ channel is used when the transmitting terminal requests resource allocation from the cluster head. It requests the D2D buffer status, interference information measured by the transmitting terminal, available transmission power, and the like. The REQ channels of the various transmitting terminals are separated into frequencies and transmitted to the cluster head.

Therefore, the D2DSS, PD2DSCH, CH-CCH, and CH-SCH used for transmission from the cluster to the UE, the REQ channel used for transmission from the UE to the cluster head, and the D2D data channel used between the UE are LTE PBCH (physical broadcast). channel), PSS / SSS (primary synchronization signal / secondary synchronization signal), PDCCH (physical downlink control channel), PUCCH (physical uplink control channel) is used.

FIG. 2 is a configuration diagram of dual connectivity for the case where the first base station 310 of FIG. 1 operates as the primary base station 101 and the second base station 320 independently operates as the secondary base station 201.

The primary base station 101 (master eNB) and secondary base station 201 (secondary eNB) used for dual connectivity are configured to be individually connected to the core network.

Therefore, all protocols are independent of the primary base station 101 and the secondary base station 201, and in particular, the separation and combining of data communicating with the two base stations is characterized in that the base station does not perform.

Here, PDCP (Packet Data Convergence Protocol) is one of the radio traffic protocol stack in LTE that performs IP header compression and compression, transmission of user data, maintaining the sequence number for the radio bearer.

In addition, RLC (Radio Link Control) is a protocol stack that controls the radio connection between PDCP and MAC.

Media Access Control (MAC) is a protocol stack that supports multiple access of a wireless channel.

3 illustrates a case in which a first base station 310 of FIG. 1 operates as a primary base station 101, a second base station 320 operates as a secondary base station 201, and data is separated and combined through the primary base station 101. This is a schematic diagram of dual connectivity for.

That is, in the primary base station 101 and the secondary base station 201 used for dual connectivity are connected to the core network, only the primary base station 101 is connected to the core network and the secondary base station 201 connects to the primary base station 101. Connected with Core network.

Therefore, the primary base station 101 performs separation and combining for data communicating in the core network. That is, the data separated from the primary base station 101 is transmitted to the secondary base station 201 or the data received from the secondary base station 201 is combined to communicate with the core network.

4 is a diagram illustrating in detail the case in which the secondary base station 201 of FIG. 2 and FIG. 3 is disconnected from the terminal 301.

That is, the apparatus for transmitting direct communication between LTE terminals allocates a radio resource to the terminal 301 to perform data communication with the terminal 301 and simultaneously with the terminal 301 and the data with the main base station 101. A secondary base station 201 that performs communication, and a terminal 301 that communicates data simultaneously with the primary base station 101 and the secondary base station 201 and resets radio resource control when the link with the secondary base station 201 is lost. .

Here, when the terminal 301 is not normally connected with the secondary base station 201, the terminal base station notifies the primary base station 101 of the connection state information (connection state information), and the primary base station 101 is also connected to the secondary base station 201. It is characterized in that the link state information (link state information) between the base station 201 and the terminal 301.

Similarly, if there is an error in connection with the primary base station 101, the terminal 301 resets the radio resource control and reports that the secondary base station 201 is connected to the primary base station 101 by the secondary base station 201. Report.

In this case, the communication between the primary base station 101 and the secondary base station 201 may add information to a frame in the X2 interface or use a broadband network, or may use a wireless backhaul when not connected by wire. The information in the frame may use a signaling system including a link state header, a link state, a base station ID, and a terminal ID indicating a link state between the primary base station 101 and the secondary base station 201.

Therefore, when there is an error in the connection of any one of the primary base station 101 and the secondary base station 201, the terminal 301 reports to either of the primary base station 101 and the secondary base station 201 where there is no connection error. The base station received by the report informs the base station that the connection is abnormal to check the connection state with the terminal 301.

On the other hand, even if both the primary base station 101 and the secondary base station 201 is abnormal in connection, the terminal 301 resets radio resource control so that the communication through the base station.

FIG. 5 is a diagram illustrating in detail the case in which the transmission power of the terminal 301 is allocated to the primary base station 101 or the secondary base station 201 of FIGS. 2 and 3.

That is, the apparatus for transmitting direct communication between LTE terminals allocates a radio resource to the terminal 301 to perform data communication with the terminal 301 and simultaneously with the terminal 301 and the data with the main base station 101. The upper limit of the transmission power upper limit value of the primary base station 101 and the secondary base station 201 is set based on the statistical analysis of the power transmitted to the secondary base station 201 and the primary base station 101 and the secondary base station 201 that perform communication. The terminal 301 is included.

Here, the statistical analysis analyzes the transmission power ratio based on the average power transmitted by the terminal 301 to the primary base station 101 and the secondary base station 201, the terminal 301 is the primary base station 101 and the secondary base station 201 Report the upper limit of transmit power.

That is, the terminal 301 is based on the average power of the maximum power that can be transmitted from the terminal 301 and the transmission value that is transmitted to the primary base station 101 and the secondary base station 201 (primary base station 101 and secondary base station ( 201) sets the power ratio to be sent.

For example, the power ratios transmitted to the primary base station 101 and the secondary base station 201 are used by setting ratios such as 3: 1, 2: 2, and 1: 3.

As another example, in the distribution of the power to be transmitted, first, to maintain the connection with the main base station 101 or to transmit the control signal is very important, in order to transmit such a signal, power to the main base station 101 first, The remaining power may be allocated for data transmission and reception with the secondary base station 201.

As another example, the power available when transmitting data to secondary base station 201 may change dynamically. That is, even if the radio channel does not change, the MCS value to be used may vary according to the available power.

In this case, when the power distribution and the MCS value are changed at the same time, a data transmission error may be caused, so that the change of the power distribution and the change of the MCS value may not be performed at the same time.

Alternatively, if the power distribution and the MCS value are changed at the same time, the reporting period of the channel quality indicator (CQI) for the MCS change, which is a feedback signal system, may be set so as not to occur at the same time as the power distribution change so as not to cause a data transmission error.

On the other hand, at least one of the maximum value of the terminal, the power ratio used, the maximum transmission power for each base station according to the power ratio, and the margin with the maximum power that can be transmitted per base station to the power currently transmitted by the terminal to the main base station 101 ) And the secondary base station 201.

FIG. 6 is a detailed diagram illustrating a case where the terminal 301 randomly accesses the primary base station 101 or the secondary base station 201 of FIGS. 2 and 3.

That is, the apparatus for transmitting direct communication between LTE terminals allocates a radio resource to the terminal 301 to perform data communication with the terminal 301 and simultaneously with the terminal 301 and the data with the main base station 101. Among the primary base station 101 and the secondary base station 201, one of the primary base station 201 and the secondary base station 201, and the random access by triggering to the primary base station 101 and the secondary base station 201, its own random access without triggering, It includes a terminal 301 that transmits to at least one.

Here, triggering is performed by a triggering command of any one of PDCCH, MAC, and RRC, and the secondary base station 201 includes a base station to which the base station which can operate as the secondary base station 201 is connected first.

In this case, the random access is transmitted in the form of one of a preamble having no content, an initial access, a radio resource control message, and a terminal ID.

That is, the random access is performed by the terminal 301 to the primary base station 101 or the secondary base station 201 such as initial access, establishment and re-establish of radio resource control, handover, and the like. As used in this case, random access may be sent to either the primary base station 101 or the secondary base station 201, and the random access may be simultaneously transmitted to the primary base station 101 or the secondary base station 201.

In this case, random access may be transmitted by PDCCH, MAC, RRC (radio resource control) triggering from the primary base station 101 or the secondary base station 201, but may also be transmitted by the terminal itself triggering.

In addition, the random access may be transmitted by using the remaining power other than the power distributed in the uplink for the random access.

Meanwhile, when the primary base station 101 or the secondary base station 201 is newly turned on, neighboring terminals including the terminal 301 may perform random access at the same time, thereby causing an error in data communication due to the random access.

Accordingly, in order to reduce such an effect, when the primary base station 101 or the secondary base station 201 is newly turned on, the terminal 301 may perform random access by additionally using a random time of about 10 seconds. Here, 10 seconds is a maximum random access time that can vary depending on the number of terminals and the number of base stations. The maximum random access time may use any value within 1 second to 60 seconds depending on the environment.

Meanwhile, since the terminal 301 may use multiple antennas, the terminal 301 may identify a location transmitted from the primary base station 101 or the secondary base station 201 and perform random access toward the primary base station 101 or the secondary base station 201. The influence of interference can be minimized.

Alternatively, when the positions of the primary base station 101 and the secondary base station 201 are not correct, the terminal 301 may perform random access by sweeping 360 degrees.

7 is a diagram illustrating a communication system for direct communication between LTE terminals according to another embodiment of the present invention. The system may include a base station 100, a terminal 200, and another terminal 300. Here, the terminal 200 may transmit a synchronization signal and a discovery signal between terminals to another terminal 300 and receive a response from the other terminal 300 to perform direct communication between the terminals.

In this case, the terminal 200 uses less than a specific value among codes less than 1/2 as a turbo code, uses 1/2 as an initial value, uses a bandwidth within 80 MHz, uses 20 MHz as an initial value, and uses the FDD in duplex mode. Use any one of TDD and TDD as the initial value, use any modulation method below 64QAM as the modulation method, use 64QAM as the initial value, use normal and extended as the cyclic prefix (CP), and initialize normal At least one of the values can be used as a parameter.

In addition, the inter-device synchronization signal may include a primary D2D synchronization signal (PD2DSS) and a secondary D2D synchronization signal (SD2DSS). When the extended CP symbol is used, PD2DSS may be located at 0 and 1 of the first slot of the subframe and SD2DSS may be located at 3 and 4 of the second slot of the subframe.

That is, when the terminal 200 performs the inter-terminal communication to the other terminal 300, the other terminal 300 may be close to or far from the terminal 200. Therefore, turbocode, bandwidth, duplex, modulation scheme, and cyclic prefix are used as appropriate in some cases.

First of all, the turbo code for recovering an error caused by the quality of a wireless channel uses a specific value below a maximum value of 1/2 or less codes, which is the maximum value of the turbo code, in case a channel condition between terminals is not good. In case of no use, 1/2 is used as initial value.

In addition, the frequency bandwidth to be used is to use the minimum bandwidth of 20MHz or more and the maximum bandwidth of 80MHz or less, and considering the interference problem, the lowest bandwidth 20MHz is used as an initial value.

As a transmission and reception separation method, both a frequency division duplex (FDD) and a time division duplex (TDD) can be used. In this case, when the FDD is used as the terminal-to-terminal communication, the transmission / reception frequency for communicating with the base station 100 may be changed, so that the terminal 200 or the other terminal 300 may include transmission / reception hardware for two frequencies.

However, when using TDD, only the transmission / reception hardware for one frequency may be provided. Therefore, when the terminal 200 communicates with another terminal 300, the duplex mode uses both FDD and TDD, and the transmission / reception hardware may use a simple TDD as an initial value.

The modulation method uses a maximum of 64QAM assuming a good radio channel, and can be set to 64QAM, which can transmit 3 times faster than QPSK.

Meanwhile, the cyclic prefix, which is a guard time for recovering a signal of fading according to a wireless environment, may use normal and extended in consideration of the distance between terminals, and the terminal 200 and another terminal 300 may be in a close distance. It is assumed that normal can be used as the initial value.

Meanwhile, the D2D synchronization signal (D2DSS), which is a synchronization signal between terminals, may transmit a PD2DSS (primary D2DSS) and an SD2DSS (secondary D2DSS) for accurate synchronization acquisition.

In this case, when using a normal CP and when using an extended CP, the number of OFDM symbols transmitted in a timeslot in a subframe in which PD2DSS and SD2DSS can be transmitted is defined differently according to the length of the CP. That is, when normal CP is used, 14 (0 ~ 13 times) OFDM symbols are used per one timeslot, and when extended CP is used, 12 (0 ~ 11 times) OFDM symbols are used per one timeslot.

To maintain accurate synchronization, the PD2DSS and the SD2DSS may use two OFDM symbols in succession, respectively. In this case, when using the normal CP, the PD2DSS can be positioned at 1 and 2 of the first timeslot and the SD2DSS can be positioned at 4 and 5 consecutively using two time slots consisting of 14 OFDM symbols per timeslot. .

However, when extended CP is used, since 12 OFDM symbols are configured per time slot, the positions of PD2DSS and SD2DSS can be changed.

For example, without changing the OFDM symbol, PD2DSS is located at 1 and 2 of the first timeslot and SD2DSS is located at 4 and 5 consecutively of the second timeslot, or if an OFDM symbol is sent one earlier. PD2DSS is located at 0 and 1 of the first timeslot and SD2DSS is located at 3 and 4 of the second timeslot continuously, or when delayed by one OFDM symbol, PD2DSS is 2 of the first timeslot. SD2DSS of times 2 and 3 can be placed consecutively at 5 and 6 times.

By arranging the synchronization signals between terminals, the present invention can achieve accurate synchronization maintenance and easy demodulation of the synchronization signals.

8 is a diagram illustrating a configuration in which another terminal of FIG. 7 demodulates a subcarrier.

 Here, the device for direct communication between LTE terminals performs direct communication between other terminals 300 and terminals, and does not receive intervals such as time and frequency that do not require reception among signals of other terminals 300. It includes.

In this case, when there are frequencies that do not require reception, when the subcarrier requiring reception is 5 or less of 1024 subcarriers, the terminal 200 reduces processing time by using a DFT instead of FFT signal processing. At least one of performing a demodulation of only necessary subcarriers to reduce processing time, and reducing processing time by performing FFT signal processing using a look up table (LUT) for subcarriers requiring reception. To reduce processing time.

That is, a frame that does not need to receive a frame can be saved by not receiving a battery, but a battery can be saved in a region that is not necessary even in a frequency domain. In case that FFT (Fast Fourier Transform) must be performed at one time according to frequency band, all frequency bandwidth must be demodulated, so if only some subcarriers need to be demodulated, processing time is wasted.

Therefore, only necessary subcarriers can be performed on the DFT to lower the processing speed. The FFT and the Discrete Fourier Transform (DFT) differ remarkably according to the algorithm, but when the memory is not used, the number of subcarriers is N and the number of subcarriers to be demodulated is M. Is defined as N / 2 * log2 (N).

That is, in the case of 1,024 subcarriers, the DFT is calculated by 1,048,576 clocks and the FFT by 5,120 clocks. However, the FFT has a disadvantage in that all the subcarriers must be calculated, but the DFT has the advantage that it can be calculated for each subcarrier.

Therefore, when there are few subcarriers to be demodulated, DFT is used to reduce the amount of computation, thereby saving battery usage.

For example, when only 5 subcarriers of 1,024 subcarriers are demodulated, 5,120 clocks are required when the DFT is used. Therefore, the amount of calculation of the DFT is reduced when demodulating less than 5 subcarriers.

Another way of demodulating only some subcarriers is to compute only the parts of the FFT that are needed. That is, the FFT demodulates the received data in the time domain through several steps. In this case, the FFT can reduce the amount of computation if the necessary subcarrier is to be demodulated. For example, if the adjacent subcarriers are not demodulated, the operation amount of one clock per at least two subcarriers can be reduced.

On the other hand, the subcarrier of the repeating form each time allows a quick calculation through the look up table (LUT). When using LUT, it takes up a lot of memory, but it is very efficient when the position of subcarriers to be demodulated is determined and the number of subcarriers to be demodulated is small. That is, it can be used as a calculation amount of one clock per subcarrier.

9 is a diagram illustrating that the terminal of FIG. 7 performs interleaving.

Here, the apparatus for transmitting direct communication between LTE terminals includes a terminal 200 for performing data communication with another terminal 300 and interleaving a physical channel used for inter-terminal communication.

Here, the terminal 200 may perform at least one of interleaving in the frequency domain and interleaving in the time domain.

In addition, the terminal 200 does not perform interleaving on the interleaving reference symbol when interleaving in the frequency domain, does not perform interleaving on the interleaving reference subcarrier when interleaving in the time domain, and the frequency domain and the time domain. When interleaving is performed at the same time, the interleaving is not performed by interleaving with respect to the interleaving reference subcarrier located in the interleaving reference symbol.

Herein, the terminal 200 designates one or more symbols per subframe as an interleaving reference symbol, designates one or more subcarriers per one subframe as an interleaving reference subcarrier, and sets the interleaving reference subcarrier for each symbol. At least one of these can be used.

In addition, the terminal 200 may perform at least one of puncturing in the frequency domain and puncturing in the time domain before at least one of interleaving and interleaving.

Here, the terminal 200 may perform puncturing more than the number of puncturing used when the wireless channel environment is bad when the wireless channel environment between the terminal 200 and the other terminal 300 is good.

In addition, when the low level modulation method is used, the terminal 200 may perform puncturing more than the number of puncturing used when the high level modulation method is used.

Here, the terminal 200 may perform automatic gain adjustment based on the automatic gain adjustment reference symbol among the symbols of the terminal-to-terminal communication transmitted from another terminal 300.

In addition, the terminal 200 may demodulate the symbol on which the automatic gain adjustment is performed based on the automatic gain value during the automatic gain adjustment.

Here, the terminal 200 may perform automatic gain adjustment using more than the number of automatic gain adjustment reference symbols used when the wireless channel environment is good when the wireless channel environment between the terminal 200 and the other terminal is bad. have.

In addition, the terminal 200 may perform automatic gain adjustment using more than the number of automatic gain adjustment reference symbols used when the low level modulation method is used when the high level modulation method is used.

In addition, in order to perform inter-terminal communication between the terminal 200 and another terminal 300, the present invention may perform interleaving to compensate for fading phenomenon in which attenuation temporarily occurs in a frequency domain and a time domain occurring in a wireless environment. Can be.

In this case, interleaving may be performed in the time domain or the frequency domain, and may be simultaneously performed in the time domain and the frequency domain. In addition, interleaving may not be performed to determine interleaving reference symbols as interleaving criteria.

In addition, interleaving may not be performed to determine an interleaving criterion for the interleaving reference subcarrier. In this case, the interleaving reference subcarrier may be different for each symbol.

On the other hand, when interleaving is performed simultaneously in the time domain and the frequency domain, interleaving may not be performed for the interleaving reference subcarrier in the interleaving reference symbol as an interleaving reference.

Punching may be used to reduce data transmission, and may be performed at least either before or after interleaving. In this case, when the wireless environment is good, the number of puncturing data can be reduced since the accuracy of the data to be transmitted is high and the error probability is small.

In addition, since the transmission accuracy of data is higher than when using a lower modulation than a high modulation, the number of puncturing data can be reduced.

Similarly, automatic gain adjustment may be performed based on data received from the terminal 200 or the other terminal 300. In this case, when the wireless environment is good, the accuracy of the data to be transmitted is high and the error probability is small. Therefore, the number of automatic gain adjustment symbols may be smaller than when the wireless environment is bad.

In addition, when the high modulation is used, the number of puncturing data can be reduced since the data transmission accuracy is higher than when the low modulation is used.

In this case, the number of symbols may be used depending on the case. However, since the reliability of data demodulation is excellent when automatic gain adjustment is performed at the front of the subframe, the symbol located at the front of the subframe may be used first.

The present invention can adaptively reduce the amount of computation of communication data between terminals according to a channel environment or a modulation scheme by using such a puncturing or automatic gain adjustment scheme.

FIG. 10 is a block diagram illustrating that the terminal of FIG. 7 stores neighbor base station information.

Here, the communication system of FIG. 10 for direct communication between LTE terminals may include a base station 100, a terminal 200, and another terminal 300. The terminal 200 may receive information of a neighbor base station from at least one of the base station 100 and the other terminal 300 and communicate with another terminal 300.

In addition, the terminal 200 stores information of up to 16 neighboring base stations and then performs communication between terminals by minimizing interference with neighboring base stations, or when storing information of up to three neighboring base stations or less, up to 16 The terminal may store the information of the neighboring base station to expand the information to the neighboring base station and then perform the inter-terminal communication by minimizing the interference with the neighboring base station.

In addition, the terminal 200 expands information of neighboring base stations when a communication failure occurs above the communication failure criterion value in the terminal-to-device communication with another terminal 300, and the communication failure is based on the communication failure in the communication between the terminals with the other terminal 300. If the value is less than or equal to, the terminal 200 may delete information from the neighboring base station farthest away.

Here, the terminal 200 may store the location of the neighbor base station information as relative distances such as one-dimensional, two-dimensional, and three-dimensional based on the terminal 200.

In addition, the terminal 200 may further receive information such as a use frequency, frequency band, transmission power, and coverage information of the neighboring base station together with the location of the neighboring base station information.

That is, when the terminal 200 communicates between the terminals, the terminal 200 detects the characteristics of the neighboring base station and performs communication between the other terminals 300 and the terminal with reliability. At this time, 16 base stations or less may be distinguished using 4 bits to distinguish enough neighbor base station information.

On the other hand, when managing the neighbor base station information takes a lot of resources in the management of the neighbor base station can manage only at least four neighbor base station information, and can be extended to 16 if necessary.

In this case, the number of management of the neighbor base station information is that the terminal 200 measures the quality of the radio channel between the terminal 200 and the other terminal 300, and if the radio quality is good, the neighbor base station management number is less because the influence of the neighbor base station is less. The minimum number is used, and if the quality of the radio channel is bad, the neighbor base station may have a large influence, and thus the management number of the neighbor base station may be extended.

The neighbor base station information may include one of distance information in one dimension, vector information in two dimensions, and three-dimensional position information in three dimensions. When the management of the neighbor base station is reduced, the neighbor base station located farthest from the terminal 200 may be reduced.

The information of the neighbor base station may include not only the location but also the frequency, frequency band, transmission power, and coverage information used by the neighbor base station.

The present invention can reduce the amount of unnecessary data computation by adjusting the number of neighbor base station information adaptively used for interference cancellation according to the communication environment and the like in the above-described manner.

11 is a block diagram illustrating a wireless communication system in which an embodiment of the present invention may be implemented. The wireless communication system according to FIG. 8 may include at least one base station 800 and at least one terminal 900.

The base station 800 may include a memory 810, a processor 820, and an RF unit 830. The memory 810 may be connected to the processor 820 to store instructions and various information for executing the processor 820. The RF unit 830 may be connected to the processor 820 to transmit / receive a radio signal with an external entity. The processor 820 may execute the operations of the base station in the embodiments described above. Specifically, the operation of the base station 100, 101, 201, etc. in the above-described embodiments may be implemented by the processor 820.

The terminal 900 may include a memory 910, a processor 920, and an RF unit 930. The memory 910 may be connected to the processor 920 to store instructions and various information for executing the processor 920. The RF unit 930 may be connected to the processor 920 to transmit / receive a radio signal with an external entity. The processor 920 may execute the operations of the terminal in the above-described embodiments. Specifically, the operation of the terminal 200, 300, 301, 400, etc. in the above-described embodiments may be implemented by the processor 920.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is referred to as being connected or connected to another component, it will be understood that there may be a direct connection or connection to that other component, but there may be other components in between. On the other hand, when a component is mentioned as being directly connected to or directly connected to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, the term including or having is intended to indicate that there is a feature, number, step, operation, component, part, or a combination thereof described in the specification, but one or more other features or numbers, step It is to be understood that the present invention does not exclude in advance the possibility of the presence or the addition of an operation, a component, a part, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. In the following description of the present invention, the same reference numerals are used for the same elements in the drawings and redundant descriptions of the same elements will be omitted.

In one or more illustrative embodiments, the described functions may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, these functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another.

In a hardware implementation, the functions described herein may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), It may be implemented in a processor, controller, microcontroller, microprocessor, other electronic units designed to perform the functions described herein, or a combination thereof.

In a software implementation, the functions described herein may be implemented in software codes. Software codes may be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case the memory unit may be communicatively coupled to the processor by various means as is known in the art.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

The present invention can be used in a wireless communication system and a mobile communication system that transmits a synchronization signal and a discovery signal between terminals to another terminal and receives a response from the other terminal to perform direct communication between the terminals.

Claims (21)

An apparatus for performing direct communication between terminals, RF unit for transmitting and receiving a radio signal; And It includes a processor connected to the RF unit, And the processor is configured to transmit an inter-terminal synchronization signal and a discovery signal to another terminal and receive a response thereto from the other terminal to perform direct communication between terminals. The method of claim 1, The processor, Use less than a specific value among codes less than 1/2 as turbo code, use 1/2 as initial value, use within 80MHz as bandwidth, use 20MHz as initial value, use either FDD or TDD in duplex mode TDD is used as an initial value, any modulation method of 64QAM or less is used as a modulation method, 64QAM is used as an initial value, normal and extended are used as cyclic prefix (CP), and normal is used as an initial value. Apparatus for performing direct communication between terminals configured to use either as a parameter. The method of claim 2, The inter-terminal synchronization signal includes a primary D2D synchronization signal (PD2DSS) and a secondary D2D synchronization signal (SD2DSS), When the extended CP symbol is used, PD2DSS is located at 0 and 1 of the first slot of the subframe and SD2DSS is located at 3 and 4 of the second slot of the subframe. Device. An apparatus for performing direct communication between terminals, RF unit for transmitting and receiving a radio signal; And It includes a processor connected to the RF unit, The processor is configured to perform direct communication between another terminal and the terminal and not to receive at least one of a time and a frequency in which the signal of the other terminal does not need to be received. The method of claim 4, wherein The processor, If there are frequencies that do not require reception, if the subcarriers that need to be received are less than 5 out of 1024 subcarriers, use DFT instead of FFT signal processing to reduce processing time, and only demodulate the necessary subcarriers during FFT signal processing. Reduce processing time by performing at least one of the following steps to reduce the processing time by performing FFT signal processing using a look up table (LUT) for subcarriers requiring reception. The apparatus for performing direct communication between terminals. An apparatus for performing direct communication between terminals, RF unit for transmitting and receiving a radio signal; And It includes a processor connected to the RF unit, The processor is And performing direct communication between other terminals and performing interleaving on a physical channel used for direct communication between terminals, and transmitting data. The method of claim 6, And the processor is configured to perform at least one of interleaving in a frequency domain and interleaving in a time domain. The method of claim 7, wherein The processor does not perform the interleaving on an interleaving reference symbol in the interleaving in the frequency domain, does not perform the interleaving on an interleaving reference subcarrier in the interleaving in the time domain, and the frequency When the interleaving is performed simultaneously in the region and the time domain, the inter-terminal direct communication is configured not to perform the interleaving in at least one of the interleaving reference subcarriers located in the interleaving reference symbol. Device for performing the. The method of claim 8, The processor designates one or more symbols per subframe as the interleaving reference symbols, designates one or more subcarriers per subframe as the interleaving reference subcarriers, and differs in the interleaving reference subcarriers per symbol. Configured to perform at least any one of the above. The method of claim 6, And the processor is configured to perform at least one of puncturing in the frequency domain and puncturing in the time domain at least one of the interleaving before and after the interleaving. The method of claim 10, The processor is configured to perform puncturing more than the number of puncturing used when the wireless channel environment is bad when the wireless channel environment between the device and the other terminal is good. The method of claim 10, And the processor is configured to perform puncturing more than the number of puncturing used when using a high level modulation method when using a low level modulation method. The method of claim 6, And the processor is configured to perform automatic gain adjustment based on an automatic gain adjustment reference symbol among symbols of the terminal-to-terminal direct communication transmitted from the other terminal. The method of claim 13, And the processor is configured to demodulate the symbol on which the automatic gain adjustment is performed based on the automatic gain value during the automatic gain adjustment. The method of claim 14, The processor is configured to perform the automatic gain adjustment using reference symbols equal to or greater than the number of automatic gain adjustment reference symbols used when the wireless channel environment is good when the wireless channel environment between the device and the other terminal is bad. Device for performing direct communication between the two. The method of claim 14, The processor is configured to perform the automatic gain adjustment using reference symbols equal to or greater than the number of automatic gain adjustment reference symbols used when using a low level modulation scheme when using a high level modulation scheme. Device for An apparatus for performing direct communication between terminals, RF unit for transmitting and receiving a radio signal; And It includes a processor connected to the RF unit, And the processor is configured to receive information of a neighbor base station from at least one of a base station and another terminal and to perform direct communication between the other terminal and the terminal. The method of claim 17, The processor may store information of up to 16 neighboring base stations and then perform direct communication between the terminals by minimizing interference with neighboring base stations, or store information of up to 3 neighboring base stations or up to 16 if insufficient. And expand and store the information of the neighbor base station and perform direct communication between the terminals by minimizing interference with the neighbor base station. The method of claim 18, The processor expands information of the neighboring base station when a communication failure occurs above the communication failure criterion value in the direct communication between the other terminals with the other terminal, and the communication failure is a communication failure reference in the direct communication between the terminals with the other terminal. The apparatus for performing direct communication between terminals, when the value is less than the value, is configured to delete the information of the neighboring base station farthest from the apparatus. The method of claim 17, And the processor is configured to store a location of a neighbor base station as a relative distance of at least one of one, two, and three dimensions with respect to the device. The method of claim 17, And the processor is further configured to further receive at least one of a usage frequency, a frequency band, a transmission power, and coverage information of the neighboring base station together with the location of the neighboring base station.

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