KR20140129982A - Inter-cell Interference Management Using Terminal-Triggered Control Information - Google Patents

Abstract

The present invention relates to a wireless communications, and more specifically, to a method for transmitting a control signal in a wireless communications system. For this purpose, a new structure in which control and data channels can coexist in one time-frequency resource is proposed, thereby increasing an efficiency of a wireless resource. The control and data channels mutually coexist in time division manner and the coexistent control channel newly assigns regions of a control signal and a reference signal, thereby maintaining a reliability of the control signal. In addition, a method for controlling an interference of a base station/terminal is proposed, by measuring an interference between adjacent cells or newly suggesting a sub-control signal. Furthermore, proposed is a method for transmitting/receiving relevant information between the base station and the terminal by designing a new control channel structure so as to transmit the suggested sub-control signal. Therefore, it is possible to coexist with an existing legacy terminal, thereby preventing a malfunction of the legacy terminal.

Description

(Inter-cell Interference Management Using Terminal-Triggered Control Information)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly to a method for transmitting a control signal in a wireless communication system.

A 3rd Generation Partnership Project (3GPP) wireless communication system based on Wideband Code Division Multiple Access (WCDMA) radio access technology is widely deployed all over the world. HSDPA (High Speed Downlink Packet Access), which can be defined as the first evolutionary phase of WCDMA, provides 3GPP with highly competitive wireless access technology in the mid-term future.

There is E-UMTS to provide high competitiveness in the long term future. E-UMTS is a system that evolved from existing WCDMA UMTS and is being standardized in 3GPP. E-UMTS is also called Long Term Evolution (LTE) system. Details of the technical specifications of UMTS and E-UMTS can be referred to Release 8 or later of "3rd Generation Partnership Project (Technical Specification Group Radio Access Network) ", respectively.

The E-UMTS is largely composed of an Access Gateway (AG) located at the end of a User Equipment (UE), a base station and a network (E-UTRAN) and connected to an external network. Typically, a base station may simultaneously transmit multiple data streams for broadcast services, multicast services, and / or unicast services. In the LTE system, Orthogonal Frequency Divisional Multiplexing (OFDM) and Multi-input Multi-out (MIMO) are used to downlink various services.

OFDM represents a high-speed data downlink access system. The advantage of OFDM is the high spectral efficiency that the entire spectrum allocated can be used by all base stations. In OFDM modulation, a transmission band is divided into a plurality of orthogonal subcarriers in the frequency domain and a plurality of symbols in the time domain. Since OFDM divides the transmission band into a plurality of subcarriers, the bandwidth per subcarrier decreases and the modulation time per carrier increases. Since the plurality of subcarriers are transmitted in parallel, the digital data or symbol transmission rate of a specific subcarrier is lower than that of a single carrier.

A multiple input multiple output (MIMO) system is a communication system using a plurality of transmit and receive antennas. The MIMO system can linearly increase the channel capacity without increasing the additional frequency bandwidth as the number of transmit and receive antennas increases. The MIMO technique uses a spatial diversity scheme that can increase transmission reliability using symbols that have passed through various channel paths and a scheme in which each antenna simultaneously transmits a separate data stream using a plurality of transmit antennas, And a spatial multiplexing scheme for increasing the size of the network.

MIMO technology can be roughly divided into open-loop MIMO technology and closed-loop MIMO technology depending on whether channel information is known at a transmitter. In the open-loop MIMO technique, the transmitter does not know the channel information. Examples of the open-loop MIMO technique include per antenna rate control (PARC), per common basis rate control (PCBRC), BLAST, STTC, and random beamforming. On the other hand, in the closed-loop MIMO technique, the transmitter knows the channel information. The performance of the closed-loop MIMO system depends on how accurately the channel information is known. Examples of the closed-loop MIMO technique include per-stream rate control (PSRC), TxAA, and the like.

Channel information means radio channel information (e.g., attenuation, phase shift, or time delay) between a plurality of transmission antennas and a plurality of reception antennas. In the MIMO system, there are various stream paths by a plurality of transmission / reception antenna combinations, and the channel state has a fading characteristic that varies irregularly in the time / frequency domain due to multipath time delay. Therefore, the transmitting end calculates channel information through channel estimation. The channel estimation is to estimate channel information necessary for restoring a distorted transmission signal. For example, channel estimation refers to estimating the size and reference phase of a carrier wave. That is, the channel estimation is to estimate the frequency response of the radio section or the radio channel.

In order to implement various transmission or reception techniques for high-speed packet transmission, it is indispensable to transmit control signals for time, space and frequency domain. The channel through which the control signal is transmitted is called a control channel. The uplink control signal includes an Acknowledgment (ACK) / Negative-Acknowledgment (ACK) signal, a CQI (Channel Quality Indicator) indicating a downlink channel quality, a Precoding Matrix Index (PMI) Indicator), and the like.

In general, the control channel uses more limited time-frequency resources than the data channel. In order to increase the spectral efficiency and multi-user diversity gain of the system, state information feedback of the radio channel is required. Therefore, efficient control channel design for high capacity feedback is inevitable. In addition, a control channel must be designed to have good Peak-to-Average Power Ratio (PAPR) / CM (Cubic Metric) characteristics in order to lower the power consumption of the UE.

3GPP TS 36.211 V8.4.0 (2008-09) "Evolved Universal Terrestrial Radio (3GPP) Technical Specification Release 8 and later based on LTE (Long Term Evolution) (Physical Downlink Shared Channel), PDSCH (Physical Uplink Shared Channel), and PDSCH (Physical Uplink Shared Channel), which are data channels, in the LTE, as shown in " Access (E-UTRA) Physical Downlink Control Channel (PUCCH) and Physical Uplink Control Channel (PUCCH).

The PDCCH, which is a downlink control channel, carries a downlink grant for PDSCH reception of the UE and an uplink grant for PUSCH transmission of the UE. The PUCCH, which is an uplink control channel, includes a positive acknowledgment (ACK) / negative acknowledgment (NACK) signal for a hybrid automatic repeat request (HARQ), a CQI an SR (scheduling request) requesting radio resource allocation for uplink transmission, and the like. It can be said that the transmission reliability is more important than the transmission capacity of the control channel. If an error occurs in the transmission of the control channel, the data channel can not be received at all, or it may seriously affect scheduling or HARQ performance. Therefore, the payload of the control channel is generally limited within a few bits to several tens bits. In addition, the uplink control channel has a peak-to-average power ratio (PAPR) / cubic metric (CM) characteristic for power management of the UE. For long latency and low battery consumption, the uplink control channel needs to have low PAPR / CM characteristics.

An object of the present invention is to provide a method for transmitting a reference signal suitable for a small cell using a common reference signal.

Another object of the present invention is to provide an apparatus for allocating a common reference signal, a demodulation reference signal, and a data addition resource suitable for a channel environment of a small cell.

As the communication system develops, it adopts a method of achieving the target with minimum cost by improving the performance of the existing system, rather than defining a new system for each communication technique. In particular, in the case of the communication system, since it can affect not only the RF interface of the terminal or the base station but also all the infrastructure, a method of minimizing the change thereof becomes commercially meaningful. In this environment, It is necessary to maintain the characteristics of the image. In particular, the key requirement is to provide the functionality of the new system without compromising the performance of the existing system, and this situation is occurring in relation to the current LTE / LTE-A release 8/9/10 / and later. This situation also occurs when IEEE 802.16m or other communication systems are required to guarantee the operation of the legacy system. Fundamentals of performance improvement require techniques such as increasing the modulation order, increasing the number of antennas, reducing interference effects, etc. In this case, more feedback information is needed. In other words, transmission of control signals for the time, space and frequency domain is indispensable in order to implement various transmission or reception techniques for high-speed packet transmission. The channel through which the control signal is transmitted is called a control channel. A method for maximizing the efficiency of limited radio resources by performing effective retransmission in a transmitter based on feedback information at the receiver is actively discussed.

Since the reliability of the control signal is related to the reliability of the system, it is necessary to increase the reliability according to the detection of the control signal in the control channel. A control channel structure robust to a changing channel environment is needed while increasing terminal capacity and transmission capacity. Further, in a variety of cell topologies having a cell coverage of 100 m or less such as a pico-cell or a femtocell like a small cell, the delay characteristic of a radio channel experienced in each cell differs from that of a large-sized cell. It is necessary to design the control channel structure.

1) Frequency selectivity of a wireless channel: A wireless channel defined as a delay spread receives signals with various delay times through multiple paths. For this reason, the radio channel is not defined as an impulse function, but has a delay profile defined by a plurality of delays. This does not provide a constant channel gain in the frequency domain and causes a channel change in frequency, which is called frequency selective characteristic. In the case of a small cell, the coverage is small, and the delay characteristic differs from the poor environment of the mobile communication due to the channel characteristics of the room, and the delay spreading time may be reduced to several ns or less. As a result, since the frequency selective characteristic is not serious, the coherent bandwidth is large, and the channel characteristics between adjacent subcarriers are similar.

2) Time selectivity of wireless channel: In order to reduce frequent handover due to a small cell, it is preferable that the small cell is used by a pedestrian or a stationary user, Stop. In this case, the Doppler effect, which affects the change of the radio channel, is reduced, and the time selectivity of the channel is reduced in the amount of channel change between adjacent symbols unlike the high-speed mobile. This results in a longer coherent time and less channel variation between adjacent subcarriers in time.

In addition to the strength of the time-frequency channel change of the small cell as described above, the terminal is smaller than the macrocell in the small cell, and the multiplexing characteristic of the control channel is also required to be re-considered. In other words, a scheme to reduce the overhead of control channel resources for efficient utilization of resources in the current legacy control channel structure and to support a small number of terminals compared to macro with a minimum resource in a control channel structure that can be supported in the coverage of a small cell need. In addition, it is preferable that new resources are secured in order to transmit new control channel information of a terminal for supporting only a small cell.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for efficiently allocating resources of an uplink control channel in consideration of a small cell environment in a wireless communication system for transmitting an uplink control signal, And to provide a method of transmitting control information and signaling the same.

Another object of the present invention is to provide a new uplink control channel transmission method by extending dedicated control information for a small cell supporting terminal.

It is still another object of the present invention to provide a method of transmitting / receiving a reference signal with backward compatibility when an uplink control channel is extended and a signaling method thereof.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

In order to solve the above problems, in a cellular communication system using uplink control signals according to an embodiment of the present invention, a control signal transmission channel and a data transmission channel coexist within one time-frequency resource allocation area To provide a cellular communication system. The one time-frequency resource allocation region is characterized by one physical resource block, and the control signal transmission channel is characterized by a PUCCH as an uplink control channel. The coexistence of the control signal transmission channel and the data transmission channel does not use the slot-based frequency hopping of the control channel. The coexistence of the control signal transmission channel and the data transmission channel is controlled by Time Division Multiplexing Lt; / RTI >

In one aspect, the present invention provides a method of transmitting a control signal in a wireless communication system, the method comprising: allocating an OFDM symbol in a slot for transmission of the control signal; Allocating an OFDM symbol in a slot for data transmission; And assigning a common reference signal for control and data transmission. Wherein the number of OFDM symbols allocated in the slots allocated for the control signal and data transmission is 4 or less. The number of OFDM symbols in the slots allocated for the reference signal transmission is 3 or less. Characterized in that the control and data channels are allocated to the same user in the same time-frequency resource and the time-domain spreading code of length 4 or less is used for control signal transmission, , And 1 or 2 bit information control information transmission as SR.

In another aspect, the present invention provides a method of transmitting a control signal in a wireless communication system, comprising: allocating an OFDM symbol in a slot for transmission of the control signal; Allocating an OFDM symbol in a slot for data transmission; And assigning common reference signals to different symbols for control and data transmission. The number of OFDM symbols allocated in the slots allocated for transmission of the control signal and the data signal is 4 or less and the number of OFDM symbols in the slots allocated for the reference signal transmission is 3 or less. And does not allow assignment of control and data channels to the same user within the same time-frequency resource, and uses time domain spreading codes of length 4 or less for control signal transmission. And the control signal includes ACK / NACK, SR, and CQI.

According to another aspect of the present invention, there is provided a method of transmitting a plurality of control signals and data in a wireless communication system in one subframe, the method comprising the steps of: configuring a transmission resource of a first control signal transmission resource and a transmission resource of a second control signal; Assigning a reference signal in a first control signal transmission resource and a reference signal in a second control signal transmission resource to the same symbol; Allocating a cyclic shift of a specific sequence differently to distinguish the first control signal from the second transmission signal; And transmitting the sub-frame. The first control signal and the second control signal are characterized by PUCCH format 1, 2, or 3, and the specific sequence has a specific root index of a Zad-off Chu sequence. In addition, the control signal transmission resource does not overlap data transmission resources in one subframe.

According to another aspect of the present invention, there is provided a cellular communication system including a plurality of base stations including a macro cell, the method comprising: acquiring interference information of a neighboring cell from a signal received from a plurality of base stations; Transmitting the interference information of the neighboring cell to the serving base station; Determining a neighboring cell interference control request based on interference information received from one or more terminals; And transmits the interference control information to the neighbor base stations. The interference information of the neighbor cell includes a pico cell, a micro cell, and a femtocell as a small cell, and the time-frequency resource used by the terminal to transmit neighbor cell information to the base station is used as a common resource among terminals, The interference information of the plurality of terminals acquiring the information through the detection of the power or energy level.

According to another aspect of the present invention, there is provided a cellular communication system including a plurality of base stations including macrocells, the base station including: allocating radio resources for signal detection of a mobile station to a mobile station; Transmitting additional control information of the terminal through the allocated resources; And generating and transmitting a control signal based on the control information of the received mobile station. Wherein the resource allocated by the base station branches the PUCCH region, and the additional control information detects a signal strength of the terminal or provides interference information of neighboring cells to the base station. Wherein the control signal generated by the base station is terminal request information for confirming a connection state of the terminal, and the control signal generated by the base station includes information for interference control of the neighbor base station, The new control information of the base station selectively operates based on the additional control information transmitted by the terminal. In addition, the new control information of the base station is transmitted after the maximum number of HARQ retransmissions is achieved.

In another aspect, the present invention provides a method of transmitting a control signal in a wireless communication system, the method comprising: allocating four OFDM symbols in a slot for transmission of the control signal; And a time domain using a [1, +1, -1, -1, -1] sequence of length 4 to transmit a control signal. The control signal is characterized by cell coverage control information having a small coverage, and the control signal includes a signal for detecting a user signal strength, and information indicating interference of neighboring cells. The control signal is characterized in that it is transmitted through M-QAM modulation or modulated with a change in energy level or power level, and is coexistent with PUCCH Format 1 or 2.

According to the embodiments of the present invention, the following effects are obtained.

According to the embodiment of the present invention, the overhead of the uplink control signal can be minimized and the efficiency of data and control signal resources can be improved.

Also, according to an embodiment of the present invention, a structure and operation principle of a control signal channel for measuring and effectively managing interference between adjacent cells are provided.

The effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
1 shows a structure of a radio frame used in 3GPP LTE.
2 shows a resource grid for a downlink slot.
3 shows a structure of a downlink radio frame.
4 shows a time-frequency resource structure for uplink control signal transmission in 3GPP LTE.
5 shows a control channel structure in a slot for transmission of a scheduling request (SR) signal and ACK / NACK as a PUCCH format 1 / 1a / 1b.
6 shows a conceptual diagram of ACK / NACK transmission supporting downlink carrier combination.
FIG. 7 shows a control channel structure in one slot for transmission of channel quality information (CQI) as PUCCH format 2.
FIG. 8 shows a control channel structure for ACK / NACK information transmission for a multicarrier combination in the PUCCH format 3.
9 shows a method in which frequency hopping is removed with a new PUCCH structure suitable for a small cell.
10 shows a method of allocating a PUSCH after removing frequency hopping with a new PUCCH structure suitable for a small cell.
11 shows a method of considering frequency hopping with a new PUCCH structure suitable for a small cell and further allocating a PUSCH.
12 shows a new per-slot PUCCH format 1 structure suitable for a small cell to which reference signal sharing is applied.
13 shows a new PUCCH format 1 structure per slot suitable for a small cell to which a PUSCH dedicated reference signal is allocated.
Figure 14 shows a new PUCCH Format 2 structure per slot suitable for small cells.
15 shows an example in which different PUCCH formats and PUSCH coexist in the same PRB using the cyclic shift of the ZC sequence.
16 shows an interference scenario considering adjacent macrocells in a small cell environment.
FIG. 17 shows an example of feedback-based inter-base station cooperation of a UE in a method of controlling interference between macro cells and small cells.
FIG. 18 shows a process of controlling interference by a base station detecting interference conditions of a mobile station by a method of controlling interference between macro cells and small cells.
FIG. 19 shows a specific operation process of the base station for detecting a user signal.
20 proposes a small-cell dedicated control information transmission channel structure such as a user signal detection.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to be illustrative of the present invention and not to limit the scope of the invention. Should be interpreted to include modifications or variations that do not depart from the spirit of the invention.

The terms and accompanying drawings used herein are for the purpose of facilitating the present invention and the shapes shown in the drawings are exaggerated for clarity of the present invention as necessary so that the present invention is not limited thereto And are not intended to be limited by the terms and drawings.

In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

The structure, operation and other features of the present invention can be easily understood by the preferred embodiments of the present invention described with reference to the accompanying drawings. The embodiments described below are examples in which technical features of the present invention are applied to a wireless communication system. Preferably, the wireless communication system may support at least one of an SC-FDMA scheme, an MC-FDMA scheme, and an OFDMA scheme. Hereinafter, a method of allocating an additional reference signal through various channels will be exemplified. Although the present specification describes the 3GPP LTE channel as an example, the present example can be applied to a control channel of IEEE 802.16 (or a revision version thereof) or a reference signal resource allocation method using a control channel of another system.

Abbreviations used herein are as follows.

RE: Resource element

REG: Resource element group

CCE: Control channel element

CDD: Cyclic delay diversity

RS: Reference signal

CRS: a cell specific reference signal or a cell common reference signal,

CSI-RS: Channel state information reference signal

DM-RS: Demodulation reference signal for data channel demodulation

MIMO: Multi-input multi-output

PBCH: Physical broadcast channel

PCFICH: Physical control format indicator channel.

PDCCH: Physical downlink control channel

PDSCH: Physical downlink shared channel

PHICH: Physical H-ARQ indicator channel

PMCH: Physical multicast channel

PRACH: Physical random access channel

PUCCH: Physical uplink control channel

PUSCH: Physical uplink shared channel

1 shows a structure of a radio frame used in 3GPP LTE.

Referring to FIG. 1, a radio frame has a length of 10 ms (327200 × Ts) and is composed of 10 equal-sized subframes. Each subframe is 1 ms long and consists of two slots. Each slot has a length of 0.5 ms (15360 x Ts). Here, Ts represents the sampling time, and is represented by Ts = 1 / (15 kHz x 2048) = 3.2552 x 10-8 (about 33 ns). A slot includes a plurality of OFDM symbols in a time domain and a plurality of resource blocks in a frequency domain. A TTI (Transmission Time Interval), which is a unit time at which data is transmitted, may be defined in units of one or more subframes. The structure of the radio frame is merely an example, and the number of subframes included in a radio frame, the number of slots included in a subframe, and the number of OFDM symbols included in a slot can be variously changed.

2 shows a resource grid for a downlink slot. Referring to FIG. 2, a downlink slot includes an NDLsymb OFDM symbol in a time domain and an NDLRB resource block in a frequency domain. Since each resource block includes NRBsc subcarriers, the downlink slot includes NDLRB x NRBsc subcarriers in the frequency domain. 2 illustrates that the downlink slot includes 7 OFDM symbols and the resource block includes 12 subcarriers, but the present invention is not limited thereto. For example, the number of OFDM symbols included in the downlink slot may be modified according to the length of a cyclic prefix (CP). Each element on the resource grid is referred to as a resource element, indicated by one OFDM symbol index and one subcarrier index. One resource block is composed of NDLsymb NRBsc resource elements. The number of resource blocks (NDLRB) included in the downlink slot depends on the downlink transmission bandwidth set in the cell.

3 shows a structure of a downlink radio frame.

Referring to FIG. 3, a downlink radio frame includes 10 subframes having an equal length. Each subframe includes an L1 / L2 control region (Layer 1 / Layer 2 control region) and a data region (data region). Unless specifically stated otherwise in the following description, the L1 / L2 control region is referred to simply as a control region. The control region starts from the first OFDM symbol of the subframe and includes one or more OFDM symbols. The size of the control area can be set independently for each subframe. The control area is used to transmit the L1 / L2 control signal. To this end, control channels such as PCFICH, PHICH, PDCCH, etc. are allocated to the control area. Meanwhile, the data area is used to transmit downlink traffic. A PDSCH is assigned to the data area.

4 shows a time-frequency resource structure for uplink control signal transmission in 3GPP LTE.

Referring to FIG. 4, a channel structure is designed by allocating a part of both end bands of the entire system band, and diversity gain through slot-based frequency hopping is considered. In order to maximize the frequency efficiency and the multi-user diversity gain of the OFDM (A) with respect to the time-frequency resources for the limited control channel, it is necessary to provide state information feedback of the radio channel, and an efficient channel structure Design is inevitable.

5 shows a control channel structure in a slot for transmission of a scheduling request (SR) signal and ACK / NACK as a PUCCH format 1 / 1a / 1b.

Referring to FIG. 5, a frequency diversity gain of 3 dB level is obtained by repeatedly transmitting the same signal through slot-based frequency hopping in one subframe as shown in FIG. The pre-allocated control channel region for transmission of the time-frequency spread ACK / NACK signal is transmitted in the same structure even when the UE transmits SR for uplink data transmission.

The ACK / NACK channel is a control channel through which ACK (Acknowledgment) / NACK (Negative-Acknowledgment) signals for performing HARQ (Hybrid Automatic Repeat Request) of downlink data are transmitted. The ACK / NACK signal is a transmission and / or acknowledgment signal for downlink data. Referring to FIG. 5, a reference signal (RS) is put on three consecutive OFDM symbols in the middle part of seven OFDM symbols included in one slot, and an ACK / NACK signal is put on the remaining four OFDM symbols. The reference signal is carried in three contiguous OFDM symbols in the middle of the slot.

When a control signal is transmitted in a pre-allocated band, frequency domain spreading and time domain spreading are simultaneously applied to increase the number of multiplexable terminals or control channels. A frequency-domain spreading sequence is used as a base sequence to spread the ACK / NACK signal in the frequency domain. The Zadoff-Chu (ZC) sequence, which is one of the CAZAC (Constant Amplitude Zero Auto-Correlation) sequences, can be used as the frequency domain sequence.

The kth element c (k) of the ZC sequence with index M can be expressed as:

Where N is the length of the ZC sequence, index M is a natural number less than or equal to N, and M and N are relatively prime. It is possible to distinguish each control channel by applying a basic sequence having different cyclic shift values. The number of available cyclic shifts may vary depending on the delay spread of the channel. The frequency-domain spread ACK / NACK signal is spread in the time domain using a time domain sequence after performing IFFT. For example, the ACK / NACK signal is spread using four orthogonal sequences of length 4 (w0, w1, w2, w3) for four OFDM symbols. Also, the reference signal is spread through an orthogonal sequence of length 3. This is called orthogonal covering. Thus, three orthogonal covering bundles are generated in the time domain, and when a maximum of 12 circular switching shifts of ZC are used, a total of 36 users can be multiplexed in one PUCCH Format 1 structure.

6 shows a conceptual diagram of ACK / NACK transmission supporting downlink carrier combination.

Referring to FIG. 6, ACK / NACK information transmission is closely related to a downlink carrier. In case of a plurality of downlink carrier combinations, one PDSCH is allocated to one UE for each downlink component carrier, . Therefore, a plurality of acknowledgments (one acknowledgment for downlink component carrier or two acknowledgment for spatial multiplexing) must be transmitted in the uplink. PUCCH format 1 may be used to support more than two bits of acknowledgment on the uplink using resource selection. Assume that four bits should be transmitted in the uplink. Through the resource selection, 2 bits indicate which PUCCH resource to use and the remaining 2 bits are transmitted using the normal PUCCH structure on the resources indicated by the first 2 bits. 6, when a total of four PUCCH resources are needed, one resource is known through the first CCE using the same rules as in the case of no carrier combination (the scheduling assignment is transmitted on the primary component carrier and the primary component carrier), and the remaining resources are quasi-statically set via RRC signaling. For more than 4 bits, PUCCH format 3 added to LTE release 10 is used.

FIG. 7 shows a control channel structure in one slot for transmission of channel quality information (CQI) as PUCCH format 2.

Referring to FIG. 7, a frequency diversity gain of 3 dB level is obtained by repeatedly transmitting the same signal through slot-based frequency hopping in one subframe as shown in FIG. The control signal transmission method considering a plurality of users in the resource structure for a control signal may divide users by spreading codes in a time and frequency domain, assign spreading codes to neighboring cells in consideration of correlation characteristics, A method of distributing the influence of inter-cell interference can be applied. For example, as shown in FIG. 6, two OFDM symbols are used for a reference signal in one or a plurality of RBs (1RB = 12 subcarriers). Therefore, 6 UEs are classified using a cyclic shift of a ZC sequence in the frequency domain, The different CQI information modulated by QPSK is mapped for each OFDM symbol, and 10 bits are transmitted per slot. In other words, a channel code having a 1/2 code rate is applied in one subframe (1 TTI = 1 msec), and a maximum of 10 bits of information bits are transmitted using a QPSK modulation scheme.

FIG. 8 shows a control channel structure for ACK / NACK information transmission for a multicarrier combination in the PUCCH format 3.

Referring to FIG. 8, when a plurality of component carriers are simultaneously transmitted on a downlink carrier combination, a plurality of HARQ asknowledgements must be fed back. A UE capable of supporting more than two downlink component carriers, that is, a UE capable of transmitting more bits than 4 bits with HARQ acknowledgment, should support PUCCH format 3. The basic of PUCCH Format 3 is OFDM precoded by the same DFT as the transmission scheme used for PUSCH. The acknowledgment bit, which is one or two bits per downlink component carrier according to the transmission mode set for the corresponding component carrier, is concatenated with the scheduling request bit to form a bit string when the scheduling request bit is present. At this time, bits corresponding to unscheduled transport blocks are set to zero. After block coding is applied thereto, scrambling using a cell-specific scrambling sequence is performed to randomize inter-cell interference. The generated 48 bits are divided into two groups after QPSK modulation, and 12 QPSK symbols are transmitted per slot. Assuming a normal CP, there are 7 OFDM symbols per slot. Two OFDM symbols per slot (one for the extended CP) are used for reference signal transmission, and five symbols are used for data transmission, similar to PUCCH Format 2. In each slot, QPSK symbols precoded by twelve DFTs are transmitted in five available DFTS-OFDM symbols. In order to make the inter-cell interference more random, a cyclic shift which is different for each OFDM symbol in a different pattern for each cell is applied to 12 QPSK symbol blocks before DFT precoding.

In a variety of cell topologies having a cell coverage of 100 m or less such as a picocell or a femtocell like a small cell, the delay characteristic of a radio channel experienced in each cell differs from that of a large cell. Therefore, Control channel structure design is needed.

1) Frequency selectivity of a wireless channel: A wireless channel defined as a delay spread receives signals with various delay times through multiple paths. For this reason, the radio channel is not defined as an impulse function, but has a delay profile defined by a plurality of delays. This does not provide a constant channel gain in the frequency domain and causes a channel change in frequency, which is called frequency selective characteristic. In the case of a small cell, the coverage is small, and the delay characteristic differs from the poor environment of the mobile communication due to the channel characteristics of the room, and the delay spreading time may be reduced to several ns or less. As a result, since the frequency selective characteristic is not serious, the coherent bandwidth is large, and the channel characteristics between adjacent subcarriers are similar.

2) Time selectivity of wireless channel: In order to reduce frequent handover due to a small cell, it is preferable that the small cell is used by a pedestrian or a stationary user, Stop. In this case, the Doppler effect, which affects the change of the radio channel, is reduced, and the time selectivity of the channel is reduced in the amount of channel change between adjacent symbols unlike the high-speed mobile. This results in a longer coherent time and less channel variation between adjacent subcarriers in time.

In addition to the strength of the time-frequency channel change of the small cell as described above, the number of terminals in the small cell is smaller than that of the macrocell, and the multiplexing capability of the control channel needs to be re-considered. In other words, a scheme to reduce the overhead of control channel resources for efficient utilization of resources in the current legacy control channel structure and to support a small number of terminals compared to macro with a minimum resource in a control channel structure that can be supported in the coverage of a small cell need. In addition, it is preferable that new resources are secured in order to transmit new control channel information of a terminal for supporting only a small cell.

As for the PUCCH structure as well as the small channel characteristics of the small cell as described above, in the case of the format 1, 36 UEs can be multiplexed when the cyclic shift of the ZC sequence is considered to be the maximum, and 12 UE multiplexing is possible in the case of the format 2 . In the case of the small cell scenario, in general, there are not many user UEs compared to the macro cell, and a large portion of PUCCH resources are wasted without being used. Therefore, it is required to maximize resource efficiency for a small cell and to design an optimized PUCCH considering channel characteristics. More specifically, it is necessary to increase the utilization of resources by further subdividing the basic unit of resource allocation, and to define PUCCH and PUSCH in the same PRB at the same time. A proposal for a new structure suitable for a small cell is required while maintaining the single carrier characteristic and reducing the burden on the RF amplifier.

9 shows a method in which frequency hopping is removed with a new PUCCH structure suitable for a small cell.

As shown in FIG. 4, the existing PUCCH acquires a frequency diversity gain of about 3 dB through frequency hopping. However, in the case of a small cell, it is desirable to improve the resource efficiency by minimizing the PUCCH resource and the time-frequency channel characteristic as compared with the macro cell as described above. Therefore, as shown in FIG. 9, it can be considered that the frequency hopping function is not used in the small cell in order to allocate the PUCCH resource twice in the same PRB. In this case, the structure per slot of the existing PUCCH format 1/2/3 can be reused as it is.

10 shows a method of allocating a PUSCH after removing frequency hopping with a new PUCCH structure suitable for a small cell.

As shown in FIG. 4, the existing PUCCH acquires a frequency diversity gain of about 3 dB through frequency hopping. However, in the case of a small cell, it is desirable to improve the resource efficiency by minimizing the PUCCH resource and the time-frequency channel characteristic as compared with the macro cell as described above. Therefore, it is possible to consider not using the frequency hopping function in the small cell in order to allocate the same PUCCH resource in the same PRB and secure additional PUSCH resources as in FIG. In this case, the structure per slot of the existing PUCCH format 1/2/3 can be reused as it is. Since frequency hopping is not used, a PUSCH resource of about one slot can be additionally generated.

11 shows a method of considering frequency hopping with a new PUCCH structure suitable for a small cell and further allocating a PUSCH.

In the case of a small cell, as mentioned above, it is preferable that the time-frequency channel characteristic is relatively superior to the macrocell and the resource efficiency is improved by minimizing the PUCCH resource. Therefore, as shown in FIG. 11, it is possible to newly design a per-slot PUCCH format suitable for a small cell in order to secure additional PUSCH resources while allocating the same PUCCH resource and maintaining frequency hopping in the same PRB. In this case, half of the existing PUCCH resources are utilized as new PUCCH resources, and the remaining PUCCH resources are further allocated as PUSCHs. In FIG. 11, a new PUCCH per slot may maintain frequency diversity through frequency hopping, but it may be additionally applied to remove frequency hopping to increase resource efficiency by twice the PUCCH resource.

12 shows a new per-slot PUCCH format 1 structure suitable for a small cell to which reference signal sharing is applied.

In the conventional PUCCH format 1, one or two bits of information are transmitted by applying an orthogonal code of length 4 in consideration of four OFDM symbols in the time domain. Considering three OFDM symbols, the reference signal secures three orthogonal resources in a time domain to form a PUCCH format. Referring to FIG. 12, in the PUCCH format 1 suitable for a small cell, the time domain spreading for transmission of the PUCCH information is reduced from 4 symbols to 2 symbols, and an interval of about 2 symbols generated in the slot is allocated as PUSCH data . Here, the reference signal sharing technique can be applied. In the case of the new PUCCH and PUSCH simultaneous transmission structures, when the PUCCH and PUSCH are simultaneously allocated to the same user (UE), the reference signal can be utilized both in PUCCH and PUSCH demodulation. Therefore, it is also possible to use the existing PUCCH reference signal without further identification. In this case, since there are more reference signal OFDM symbols in the time domain, it is also possible to divide the resources of the reference signal into dedicated PUSCH channels. In this new PUCCH format 1, as the orthogonal spreading length is changed from 3 to 2, the UE multiplexing tolerance is reduced from the existing 36 UE support to 24 UE support in consideration of the maximum cyclic shift 12. As mentioned in FIG. 11, if frequency hopping is further removed, it can be extended to 48 UE support. The added PUSCH channel can be transmitted by applying the DFT-S-OFDM technique applied in the conventional uplink as it is.

13 shows a new PUCCH format 1 structure per slot suitable for a small cell to which a PUSCH dedicated reference signal is allocated.

In the conventional PUCCH format 1, one or two bits of information are transmitted by applying an orthogonal code of length 4 in consideration of four OFDM symbols in the time domain. Considering three OFDM symbols, the reference signal secures three orthogonal resources in a time domain to form a PUCCH format. Referring to FIG. 12, in the PUCCH format 1 suitable for a small cell, the time domain spreading for transmission of the PUCCH information is reduced from 4 symbols to 2 symbols, and an interval of about 2 symbols generated in the slot is allocated as PUSCH data . Here, PUSCH dedicated reference signal allocation is possible. In the case of the new PUCCH and PUSCH concurrent transmission structures, when the PUCCH and PUSCH are not simultaneously allocated to the same user (UE) and different users use the PUCCH and PUSCH, the reference signal is utilized for both PUCCH and PUSCH demodulation. I can not. Therefore, it is desirable to allocate a dedicated reference signal for the new PUCCH format 1 and separately assign the added PUSCH dedicated reference signal. In this case, if the new PUCCH format 1 uses a spreading code of length 2, it is preferable to apply a time spread of the same length also in the case of the PUCCH dedicated reference signal to maintain a one-to-one mapping relationship for user multiplexing. In addition, it is possible to assign a reference signal of at least one symbol to the dedicated PUSCH and utilize it in PUSCH demodulation. In the present invention, the PUSCH includes transmission of data other than the information defined in the existing PUCCH format 1/2/3 including new control information transmission which has not been previously defined.

Figure 14 shows a new PUCCH Format 2 structure per slot suitable for small cells.

In the conventional PUCCH format 2, five OFDM symbols per slot are used for QPSK information transmission. It is possible to increase the amount of information that can be transmitted through the channel code by increasing the coding rate in the case of the CQI to which the channelization coding is applied with the block code such as the RM code. Therefore, in the case of a small cell, it is possible to increase the coding rate and minimize the PUCCH occupation resource, thereby increasing the efficiency of the PUCCH resource. In the present invention, a method of allocating a part of a symbol of a conventional PUCCH format 2 as a PUSCH resource and simultaneously transmitting PUCCH and PUSCH in the same PRB is proposed. As shown in FIG. 14, three OFDM symbols and one reference signal are defined as a new PUCCH format 2, and two OFDM symbols and one reference signal symbol are allocated to a PUSCH. The number of symbols between the PUCCH and the PUSCH can be arbitrarily set. In the case of the reference signal, the PUCCH and the PUSCH are not distinguished from each other, and the user can utilize them to demodulate the PUCCH and PUSCH.

15 shows an example in which different PUCCH formats and PUSCH coexist in the same PRB using the cyclic shift of the ZC sequence.

In Fig. 12 through 14, a new structure for PUCCH formats 1 and 2 is proposed. In order to increase the efficiency of resources, new PUCCH formats 1 and 2 coexist in the same PRB. The distinction between the PUCCH formats can be distinguished by differently applying the cyclic shift of the ZC sequence. Therefore, it is preferable that the PUCCH area to which the ZC sequence is applied is kept the same between format 1 and 2. For example, in FIG. 13 and FIG. 14, it is possible to coexist in the same PRB if the preceding four symbol intervals are set as PUCCH regions and cyclic shifts of different ZC sequences are used. In the case of PUSCH, it is assigned to a specific UE, so that they can be distinguished from each other. Although the reference signal can be divided into the same ZC sequence cyclic shift, it may be preferable to adjust the position and number of the reference signal between the PUCCH formats in consideration of the importance of the reference signal. Furthermore, coexistence with the legacy PUCCH can also coexist with different cyclic shifts of the ZC sequence. In this case, in order to minimize the interference to the legacy PUCCH, it is preferable to consider the ZC sequence spreading scheme having the same PUSCH structure.

16 shows an interference scenario considering adjacent macrocells in a small cell environment.

Referring to FIG. 16, BS1 and BS2 are base stations of a macro cell, MS2 and MS5 are macro MSs connected to BS1, MS3 is a macro MS connected to BS2, MS1 is a femto MS connected to Femto1, and MS4 is MS connected to Femto2. Large and small circles represent coverage of Macro BS and Femto BS, respectively. That is, Macro BS transmits with a large power and Femto BS transmits with a small power. In such a network layout, the following problems may occur.

- Case 1. Femto Downlink on Macro Downlink: Downlink performance of MS2 is degraded due to downlink signal of BS of Femto1 (Femto near Femto1) when Macro BS performs downlink transmission to MS2.

- Case 2. Femto on Downlink of Macro Uplink: Downlink performance of MS2 is degraded by signal of MS1 (Femto MS near Femto1) of Femto1 when Macro BS is transmitting downlink to MS2.

- Case 3. Femto on Macro's Uplink When Downlink, Femto1 is close to BS1: macro When MS2 sends uplink to BS1, uplink performance of MS2 is degraded by downlink signal of Femto1 (Femto near BS1).

- Case4. Femto is also Uplink in Macro Uplink, Femto1 is close to BS1: macro When MS2 sends uplink to BS1, MS2 performance is degraded by uplink signal of MS1 of Femto1 (Femto MS near BS1).

In order to effectively mitigate the interference between various macro-small cells (here assumed as femtocells), it is necessary for the UE to transmit the information of the neighboring interference to the corresponding base station (macro or femtocell base station). For example, when it is difficult for a terminal accessing a femtocell to receive an upward signal of a corresponding terminal to a femtocell due to an uplink signal of a terminal or a connected terminal to access as a peripheral macro (case 4 in FIG. 16), the corresponding femtocell A user signal detection / indicator signal is required to distinguish whether the signal of the corresponding terminal is weak or is a temporary problem or strong interference of the surroundings. Such a signal is transmitted periodically or aperiodically (according to a terminal / base station request) through a resource allocated in advance from the small cell base station, and the small cell base station receiving the signal transmits the signal strength of the corresponding terminal as peripheral interference It can be used to determine whether a signal detection error has occurred or a temporary error.

In order to more effectively manage the interference between the small cells and the macro cells, an effective mechanism for acquiring the degree of interference directly sensed by the terminal connected to the small cell is also required. For example, when a terminal connected to a macro is difficult to receive a signal from a macro cell due to a strong signal of the surrounding small cell base station (case 1 in FIG. 16), the degree of peripheral interference is notified to the macro base station, It is possible to readjust the transmission power or resources of the cell, alleviate interference, and eliminate the interference. In order to achieve this, a new uplink information transmission channel, which can indicate the degree of interference at an early stage, is required for the UE, and even if various UEs simultaneously transmit such a channel, And the grouped UEs transmit the corresponding information through different new transmission channels, and the base station can measure the degree of interference for each group.

FIG. 17 shows an example of feedback-based inter-base station cooperation of a UE in a method of controlling interference between macro cells and small cells.

Referring to FIG. 17, a plurality of terminals receives a signal from a plurality of base stations and measures a degree of interference of neighboring base stations (eg, I _UE1 or I _UE2 ). Considering the degree of interference at each terminal, a terminal experiencing interference above a certain level transmits interference information to a serving base station through a newly defined interference information transmission channel. The base station determines whether it is necessary to control interference of neighboring cells based on the interference information received from one or more terminals. If necessary, the base station transmits the control information or interference information to the neighboring base station through the inter- send.

FIG. 18 shows a process of controlling interference by a base station detecting interference conditions of a mobile station by a method of controlling interference between macro cells and small cells.

Referring to FIG. 18, it is assumed that a UE allowed uplink resource allocation and scheduling from a base station transmits uplink data through a PUSCH, and the base station fails in the process of demodulating the uplink data. In the case of a base station, it is assumed that the UE transmits UL data through the PUSCH. However, a terminal that missed the UL Grant may not transmit the PUSCH and also transmits the PUSCH. However, The base station may not be able to demodulate the PUSCH. Therefore, it is important for the base station to determine whether or not the corresponding terminal is experiencing interference in order to receive the uplink data of the terminal. To this end, the base station requests the terminal to transmit a predetermined user detection signal (User Signal Detection Signal), and the terminal that receives the signal transmits the corresponding signal through the newly designed USD channel. The base station detecting the interference may determine whether the corresponding terminal is experiencing interference or a simple link failure, and may perform a reconnection or a connection state check such as a keep alive confirmation of the terminal, or may request interference control to a neighbor base station.

FIG. 19 shows a specific operation process of the base station for detecting a user signal.

Referring to FIG. 19, the USD signal may obtain specific modulated information or may be in the form of power / energy detection indicating the strength of the detected signal. The base station that has detected this determines whether or not there is a USD signal (DTX detection). In case of DTX detection, if the corresponding base station performs the maximum retransmission, the connection state of the UE is re-checked. In the USD signal detection, the interference information (or the link level information between the terminal and the base station) is obtained through the USD signal other than the DTX, and it is determined whether the interference control of the neighboring cell is based on the obtained information. If interference control is required, interference control is requested to the neighboring base stations through the x2 interface, or HARQ retransmission is performed based on the maximum retransmission, or the connection state of the UE is re-checked.

In order to control the small cell interference as described above, an information transmission channel capable of directly or indirectly measuring interference information is required. In order to obtain the function of transmitting differentiated additional information, it is preferable to recycle the existing legacy system as much as possible and to find a resource that can additionally allocate a channel, in order to coexist with 3GPP LTE Release 8 and later terminals and to transmit differentiated information. 3GPP TS 36.211 V11.1.0 (2012-12) " Evolved Universal Terrestrial Radio Access (E-UTRA); PUCCH format 1 applies time domain spreading to four orthogonal codes of ACK / NACK or SR for transmission of four orthogonal codes of length 4, and orthogonal code of length 3 is used for PUCCH format 1 according to " Physical Channels and Modulation Is used for time spreading of the reference signal region. The orthogonal codes used at this time are shown in Table 1 and Table 2. As can be seen from the table, in the case of the PUCCH format 1, the number of symbols of the reference signal and the information transmission interval is different, and one orthogonal code of length 4 is not used to maintain the one-to-one mapping between time domain spreading codes. In other words, as shown in Tables 1 and 2, the sequence indexes 0, 1 and 2 selectively maintain one-to-one mapping of three sequences of orthogonal code lengths 4 and 3. Therefore, [+1 +1 -1 -1], which is an orthogonal code of length 4, can be used for other purposes.

Sequence index Orthogonal sequences (length 4) 0 [+1 +1 +1 +1] One [+1 -1 +1 -1] 2 [+1 -1 -1 +1]

Sequence index Orthogonal sequences (length 2) 0 [+1 +1 +1] One

2

As described above, since the spreading code mapping of the reference signal of length 3 is difficult in the additional time domain spreading code of length 4, the above-mentioned interference level information is converted into the energy / power level by the modulation technique considering the demodulation scheme such as the noncoherent It is possible to modulate and transmit the interference information at a level of limited (e.g., 1 to 2 bit information).

 20 proposes a small-cell dedicated control information transmission channel structure such as a user signal detection.

Referring to FIG. 20, the existing PUCCH Format 1 is reused, and [+1 +1 -1 -1] that is not currently used is used as a time domain spreading code to transmit interference, control information and the like suitable for a small cell . As can be seen, the reference signal uses all three DFT codes in PUCCH Format 1, and a new channel of length 4 can be transmitted without a reference signal. In addition, the small cell dedicated control information may transmit the above-described user signal detection information, or may transmit the interference information of the power / energy level, which measures the degree of interference by a sum of power / energy levels transmitted by a plurality of terminals . Further, it is also possible to transmit information of several bits or less through arbitrary control information through a modulation technique such as M-QAM.

Claims (4)

In a cellular communication system in which a plurality of base stations including macro cells are present,
Obtaining interference information of a neighboring cell from a signal received from a plurality of base stations by a terminal;
Transmitting the interference information of the neighboring cell to the serving base station;
Determining a neighboring cell interference control request based on interference information received from one or more terminals;
And transmits the interference control information to the neighboring base stations. The method according to claim 1,
Wherein the interference information of the neighboring cell includes a pico cell, a micro cell, and a femtocell as a small cell. The method according to claim 1,
Wherein the time-frequency resource used by the terminal to transmit neighbor cell information to the base station is used as a common resource among the terminals. The method of claim 3,
Wherein the interference information of a plurality of terminals received by the common resource acquires information through detection of a power or an energy level.

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