WO2013141603A1

WO2013141603A1 - Apparatus and method for configuring control channels for narrowband user equipment

Info

Publication number: WO2013141603A1
Application number: PCT/KR2013/002298
Authority: WO
Inventors: Jianjun Li; Kyoung Min Park
Original assignee: Pantech Co Ltd
Current assignee: Pantech Co Ltd
Priority date: 2012-03-23
Filing date: 2013-03-20
Publication date: 2013-09-26
Anticipated expiration: 2014-09-23
Also published as: KR20130107855A

Description

APPARATUS AND METHOD FOR CONFIGURING CONTROL CHANNELS FOR NARROWBAND USER EQUIPMENT

The present invention relates to wireless communication and, more particularly, to an apparatus and method for configuring control channels for narrowband user equipment.

A Base Station (BS) classifies basic parameters for the operations of User Equipment (UE) in idle mode and UE in connected mode into several information blocks and broadcasts the information blocks. The information block can include, for example, a Master Information Block (MIB), a System Information Block1 (SIB1), a System Information Block2 (SIB2), and other System Information Blockn (SIBn). The MIB includes the most basic parameters necessary for UE to access a cell. An MIB message is broadcasted in a cycle of 40 ms, and MIB broadcasting is repeated in all radio frames within the 40 ms cycle. Furthermore, the MIB is broadcasted in a narrowband of 1.08 MHz irrespective of the operating bands of communication systems.

UE can be divided into high-end UE capable of receiving and decoding all the operating bands of communication systems and low-end UE capable of receiving and decoding only some of intermediate frequency bands, from among the operating bands of communication systems. Low-end UE can also be called low-cost UE or narrowband UE.

Communication between devices that is performed without the intervention of people is called Machine Type Communication (MTC). For example, MTC can include communication between a slot machine and a server and between a water supply read meter and a server. MTC supports communication between MTC devices or communication between an MTC device and an MTC server. In MTC, narrowband UE capable of receiving and decoding only some of intermediate frequency bands can be used in order to reduce costs because a small amount of data is periodically frequently transmitted from a viewpoint of a communication characteristic.

High-end UE performs a cell search in a narrow band and receives an MIB transmitted in a narrow band. Since a system operating band can be known from an MIB transmitted in a narrow band, high-end UE can receive control channels transmitted over all system operating bands and related data channels and obtain an SIB including random access parameters. This enables communication including the transmission and reception of actual data.

Even narrowband UE can receive a minimum control signal for communication. That is, narrowband UE can perform a cell search in a narrow band and receive an MIB transmitted in a narrow band, but cannot receive control channels transmitted in all system operating bands. For example, narrowband UE that supports a carrier band of 1.4 MHz cannot normally perform communication over a network in which a variety of control channels are transmitted in a carrier band of 1.4 MHz or more.

An object of the present invention is to provide an apparatus and method for configuring control channels for narrowband UE that supports narrowband carriers so that the narrowband UE can operate in a wireless communication system that supports a broadband.

Another object of the present invention is to provide an apparatus and method for transmitting control information unique to narrowband UE that supports narrowband carriers.

Yet another object of the present invention is to provide an apparatus and method for transmitting control information used to receive an Enhanced-PDCCH (E-PDCCH) through a data channel region.

Yet further another object of the present invention is to provide an apparatus and method for configuring control channels for narrowband UE that supports narrowband carriers.

Yet further another object of the present invention is to provide an apparatus and method for configuring an exclusive control channel region allocated to narrowband UE that supports narrowband carriers.

In accordance with an aspect of the present invention, there is provided a base station for sending a control channel in a wireless communication system. The base station includes a control information generation unit configured to generate a first Control Format Indicator (CFI) to be mapped to a first Physical Control Format Indicator CHannnel (PCFICH) and a second CFI to be mapped to a second PCFICH, a channel mapper configured to map the first CFI to the first PCFICH and map the second CFI to the second PCFICH, and a transmission unit configured to map the first PCFICH and the second PCFICH to one or more predefined Physical Resource Blocks (PRBs) on one or more predefined Orthogonal Frequency Division Multiplexing (OFDM) symbols in a central band on a system operating frequency and transmit the one or more PRBs to user equipment, wherein the first CFI indicates first 4 or smaller OFDM symbols within a subframe and the second CFI indicate the indices of the one or more predefined PRBs.

In accordance with another aspect of the present invention, there is provided user equipment for receiving a control channel in a wireless communication system. The user equipment includes a reception unit configured to receive a first PCFICH to which a first CFI indicative of first 4 or smaller OFDM symbols within a subframe has been mapped and a second PCFICH to which a second CFI indicative of one or more predefined PRBs in a central band on a system operating frequency has been mapped, from a base station in one or more predefined PRBs on one or more predefined OFDM symbols, and a control channel region detection unit configured to detect a control channel region in which a control channel regarding the user equipment is transmitted, wherein the control channel region is defined by the one or more predefined PRBs indicated by the second CFI on remaining OFDM symbols other than an OFDM symbol indicated by the first CFI, from among all OFDM symbols forming the subframe.

In accordance with yet another aspect of the present invention, there is provided a method of a base station sending a control channel to user equipment in a wireless communication system. The method includes generating a first CFI to be mapped to a first PCFICH and a second CFI to be mapped to a second PCFICH; mapping the first CFI to the first PCFICH and mapping the second CFI to the second PCFICH, and mapping the first PCFICH and the second PCFICH to one or more predefined PRBs on one or more predefined OFDM symbols in a central band on a system operating frequency and transmitting the one or more PRBs to the user equipment, wherein the first CFI indicates first 4 or smaller OFDM symbols within a subframe and the second CFI indicate the indices of the one or more predefined PRBs.

In accordance with yet further another aspect of the present invention, there is provided a method of user equipment receiving a control channel from a base station in a wireless communication system. The method includes receiving a first PCFICH to which a first CFI indicative of first 4 or smaller OFDM symbols within a subframe has been mapped and a second PCFICH to which a second CFI indicative of one or more predefined PRBs in a central band on a system operating frequency has been mapped, from the base station in one or more predefined PRBs on one or more predefined OFDM symbols, and detecting a control channel region in which a control channel regarding the user equipment is transmitted; generating an uplink signal, wherein the control channel region is defined by the one or more predefined PRBs indicated by the second CFI on remaining OFDM symbols other than an OFDM symbol indicated by the first CFI, from among all OFDM symbols forming the subframe.

A control channel region for narrowband UE which can minimize an influence on normal UE and reduce a waste of resource elements and efficiently supports narrowband UE can be provided. Furthermore, if it is necessary to transmit control channels to a plurality of pieces of UE in a hot spot or a crowded area, an efficiently extended control channel region can be provided.

FIG. 1 shows a wireless communication system to which the present invention is applied.

FIG. 2 shows the structure of a subframe to which the present invention is applied.

FIG. 3 shows the structure of a slot to which the present invention is applied.

FIG. 4 shows an example of a control channel region for narrowband UE which supports a narrowband carrier to which the present invention is applied.

FIG. 5 shows a first embodiment regarding the mapping of a first PCFICH and a second PCFICH for narrowband UE according to the present invention.

FIG. 6 is a detailed diagram showing, in an RE level, regions to which a first PCFICH and a second PCFICH are mapped in accordance with a first embodiment of the present invention.

FIG. 7 shows REs to which a first PCFICH is mapped in accordance with the first embodiment of the present invention.

FIG. 8 shows a second embodiment regarding the mapping of a first PCFICH and a second PCFICH for narrowband UE according to the present invention.

FIG. 9 is a detailed diagram showing, in an RE level, regions to which a first PCFICH and a second PCFICH are mapped in accordance with a second embodiment of the present invention.

FIG. 10 shows REs to which a first PCFICH is mapped in accordance with the second embodiment of the present invention.

FIG. 11 is a diagram showing that a control channel region for narrowband UE according to the present invention is divided into two regions.

FIG. 12 is a flowchart illustrating an operation in which a BS transmits a signal to narrowband UE in accordance with an embodiment of the present invention.

FIG. 13 is a flowchart illustrating an operation in which narrowband UE receives a signal in accordance with an embodiment of the present invention.

FIG. 14 is a flowchart illustrating an operation in which narrowband UE receives a signal in accordance with an embodiment of the present invention.

FIG. 15 shows wireless communication between a BS and narrowband UE in accordance with an embodiment of the present invention.

FIG. 16 shows a first embodiment of an E-PCFICH according to the present invention.

FIG. 17 shows mapping of an RE unit in accordance with a first embodiment of an E-PCFICH according to the present invention.

FIG. 18 shows a second embodiment of an E-PCFICH according to the present invention.

FIG. 19 shows mapping of an RE unit in accordance with a second embodiment of an E-PCFICH according to the present invention.

Hereinafter, in this specification, some exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be noted that in assigning reference numerals to elements in the drawings, the same reference numerals denote the same elements throughout the drawings even in cases where the elements are shown in different drawings. Furthermore, in describing the embodiments of the present invention, a detailed description of the known functions and constitutions will be omitted if it is deemed to make the gist of the present invention unnecessarily vague.

Hereinafter, in this specification, narrowband UE includes UE that supports narrowband carriers and UE that supports both broadband carriers and narrowband carriers. Furthermore, in some embodiments of the present invention, a method and apparatus for allocating a data channel region to a control channel region for narrowband UE can be likewise applied to a method and apparatus for allocating a data channel region to an enhanced-control channel region without departing from the intrinsic characteristic of the present invention.

Referring to FIG. 1, the wireless communication systems 10 are widely deployed in order to provide a variety of communication services, such as voice and packet data. The wireless communication system 10 includes one or more Base Stations (BSs) 11. The BSs 11 provide communication services to respective

geographical areas

15a, 15b, and 15c.

User Equipment (UE) 12 can be fixed or mobile and can also be called another terminology, such as a Mobile Station (MS), a Mobile Terminal (MT), a User Terminal (UT), a Subscriber Station (SS), a wireless device, a Personal Digital Assistant (PDA), a wireless modem, or a handheld device.

The BS 11 refers to a fixed station which communicates with the UE 12, and the BS 11 can also be called another terminology, such as an evolved-NodeB (eNodeB or eNB), a Base Transceiver System (BTS), an access point, a femto eNB, a Home eNodeB (HeNB), or a relay. A cell should be interpreted as a comprehensive meaning that indicates some area covered by the BS 11. The cell has a meaning to cover various coverage areas, such as a mega cell, a macro cell, a micro cell, a pico cell, and a femto cell.

Hereinafter, downlink refers to communication or a communication path from the BS 11 to the UE 12, and uplink refers to communication or a communication path from the UE 12 to the BS 11. In downlink, a transmitter can be part of the BS 11, and a receiver can be part of the UE 12. In uplink, a transmitter can be part of the UE 12, and a receiver can be part of the BS 11. Multiple access schemes applied to the wireless communication system are not limited. A variety of multiple access schemes, such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA, can be used. In uplink transmission and downlink transmission, a Time Division Duplex (TDD) scheme using different times or a Frequency Division Duplex (FDD) scheme using different frequencies can be used.

Referring to FIG. 2, one radio frame includes 10 subframes, and one subframe includes 2 consecutive slots. The former one, two, three, or four OFDM symbols in the first slot of a subframe correspond to a control channel region to which PDCCHs are mapped, and the remaining OFDM symbols correspond to a data channel region to which Physical Downlink Shared CHannels (PDSCHs) are mapped. The control channel region can be called a control region, and the data channel region can be called a data region. Control channels, such as PCFICHs and PHICHs, in addition to the PDCCHs can be allocated to the control channel region. UE can read data transmitted through a PDSCH by decoding a PDCCH. The number of OFDM symbol that forms the control channel region within the subframe can be known through a PCFICH. For example, if a system bandwidth is N^DL _RB>10, a PCFICH indicates the first one, two, or three OFDM symbols as a control channel region. If a system bandwidth is N^DL _RB=10, a PCFICH indicates the first two, three, or four OFDM symbols as a control channel region.

Control information mapped to a PDCCH is called Downlink Control Information (DCI). DCI can include a Modulation and Coding Scheme (MCS) field indicative of the modulation scheme of a PDSCH, an uplink or downlink resource allocation field, an uplink power control command field, a control field for paging, a control field for indicating a Random Access (RA) response).

DCI has a different use according to its format and has a different field defined therein. Table 1 shows pieces of DCI according to various types of formats.

Table 1

DCI format	description
0	Used for the scheduling of a PUSCH (uplink grant)
1	Used for the scheduling of one PDSCH codeword in one cell
1A	Used for the compact scheduling of one PDSCH codeword in one cell and used in a random access procedure reset by a PDCCH command
1B	Used for the compact scheduling of one PDSCH codeword in one cell using precoding information
1C	Used for the compact scheduling of one PDSCH codeword and used to notify a change of an MCCH
1D	Used for precoding and the compact scheduling of one PDSCH codeword in one cell including power offset information
2	Used for the PDSCH scheduling of UE configured in spatial multiplexing mode
2A	Used for the PDSCH scheduling of UE configured in CDD mode of large delay
2B	Used in transfer mode 8 (dual layer transfer, etc.)
2C	Used in transfer mode 9 (multi-layer transfer, etc.)
3	Used to send a TPC command for a PUCCH and PUSCH including 2-bit power coordination
3A	Used to send a TPC command for a PUCCH and PUSCH including single-bit power coordination
4	Used for the scheduling of a PUSCH (uplink grant) with SU MIMO

Referring to Table 1, DCI Format 0 is uplink scheduling information. There are illustrated DCI Format 1 for the scheduling of one PDSCH codeword, DCI Format 1A for the compact scheduling of one PDSCH codeword, DCI Format 1C for the very compact scheduling of a DL-SCH, DCI Format 2 for PDSCH scheduling in closed-loop spatial multiplexing mode, DCI Format 2A for PDSCH scheduling in open-loop spatial multiplexing mode, and DCI Formats 3 and 3A for Transmission Power Control (TPC) command for an uplink channel.

The fields of the DCI are sequentially mapped to n information bits a₀ to a_n-1, respectively. For example, assuming that DCI is mapped to information bits having a total of 44 bits in length, the fields of the DCI are sequentially mapped to a₀ to a₄₃, respectively. DCI Formats 0, 1A, 3, and 3A can have the same payload size.

DCI format

0 and 4 may also be called an uplink grant.

FIG. 3 shows the structure of a slot to which the present invention is applied.

Referring to FIG. 3, as described above, one subframe includes two slots. One slot can include a plurality of symbols in a time domain. For example, in the case of a wireless system which uses Orthogonal Frequency Division Multiple Access (OFDMA) in downlink (DL), a symbol can be an Orthogonal Frequency Division Multiplexing (OFDM) symbol. Meanwhile, an expression of a symbol period in the time domain is not restricted by a multiple access scheme or name. For example, in the time domain, a plurality of symbols may include a Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbol and a symbol period in addition to the OFDM symbol.

The number of OFDM symbols included in one slot may vary depending on the length of a Cyclic Prefix (CP). For example, in the case of a normal CP, 1 slot may include 7 OFDM symbols. In the case of an extended CP, 1 slot may include 6 OFDM symbols.

One slot includes a plurality of subcarriers in the frequency domain and includes 7 OFDM symbols in the time domain. A Resource Block (RB) is a resource allocation unit. If an RB includes 12 subcarriers in the frequency domain, one RB can include 7×12 Resource Elements (REs). The RB may be called a Physical Resource Block (PRB).

An RE indicates the smallest frequency-time unit to which the modulation symbol of a data channel or the modulation symbol of a control channel is mapped. If M subcarriers are present on one OFDM symbol and one slot includes N OFDM symbols, one slot includes M×N REs.

Referring to FIG. 4, a PDCCH (hereinafter referred to as a 0^th PDCCH) for normal UE in a wireless communication system is mapped to all communication bandwidths. For example, in an LTE communication system using a 20 MHz frequency bandwidth, a 0^th PDCCH is spread over the entire 20 MHz frequency bandwidth. However, narrowband UE that supports narrowband carriers can use only some intermediate bandwidths (e.g., 6 central PRBs) from the 20 MHz frequency bandwidth. Accordingly, the narrowband UE is unable to detect the 0^th PDCCH. The same principle applies to a PHICH (hereinafter referred to as a 0^th PHICH) and a PCFICH (hereinafter referred to as a 0^th PCFICH) for normal UE.

Accordingly, an additional control channel region that can be detected by the narrowband UE may be defined. For example, a control channel region for narrowband UE can be located within a data channel region to which PDSCHs are mapped and can be allocated or mapped to at least one of the PRBs of a central band when being seen from the frequency domain. That is, the control channel region for the narrowband UE is allocated to at least one of the PRBs of the central band when being seen from the frequency domain, from among the remaining regions other than the control channel region to which the 0^th PDCCH is mapped. The central band may mean a band that can be received by the narrowband UE. PRBs that remain after the PRBs of the central band are allocated to the control channel region for the narrowband UE can be allocated as a data channel region for the narrowband UE or can be allocated as a data channel region for normal UE. Here, the number of PRBs of the central band may be 6. This number is only illustrative, and the number of PRBs of the central band may be 4, 5, 7, etc., according to a variety of embodiments.

The control channel region for the narrowband UE for which some of the PRBs of the central band are used can be predefined so that it can be detected by the narrowband UE. In this case, the predefined control channel region for the narrowband UE can be indicated by a PCFICH for narrowband UE. For example, the PCFICH for narrowband UE can indicate the number of PRBs that are used as the control channel region for the narrowband UE, from among the PRBs of the central band. Regions other than the control channel region for the narrowband UE, from among the PRBs of the central band, can be used as data channel regions for the narrowband UE. The narrowband UE can detect a PCFICH, an FHICH, and a PDCCH dedicated to the narrowband UE based on a Cell-specific Reference Signal (CRS).

The PCFICH can be classified into a 0^th PCFICH, a first PCFICH, and a second PCFICH. Both the 0^th PCFICH and the first PCFICH indicate a control channel region for normal UE. That is, the 0^th PCFICH and the first PCFICH indicate how many OFDM symbols of the first slot within a corresponding subframe are allocated to the original control channel region. Here, the 0^th PCFICH differs from the first PCFICH in that the 0^th PCFICH is detected by normal UE and the first PCFICH is detected by narrowband UE. Furthermore, the 0^th PCFICH differs from the first PCFICH in that the 0^th PCFICH is mapped to a control channel region for normal UE, whereas the first PCFICH is mapped to a control channel region for narrowband UE.

The second PCFICH indicates that a control channel region for narrowband UE is allocated to what PRBs, from among the PRBs of a central band. The first PCFICH and the second PCFICH for narrowband UE, but also a PHICH for narrowband UE (hereinafter referred to as a 'first PHICH' and a PDCCH (hereinafter referred to as a 'first PDCCH' for narrowband UE can be mapped to the control channel region for narrowband UE.

A Control Format Indicator (CFI) of 2 bits is coded in the form of a 32-bit block code and mapped to the 0^th PCFICH, the first PCFICH, and the second PCFICH. Table 2 shows the CFI codewords of the PCFICH.

Table 2

CFI	CFI codewords<b_0,b_{1, …,}b₃₁>
1(00)	<0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1>
2(01)	<1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0>
3(10)	<1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1>
4(11)	<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0>

Referring to Table 2, a CFI indicates the format of a control channel region and indicates four types of pieces of information of 2 bits by using 32-bit codewords. A PCFICH to which a corresponding CFI is mapped can be different depending on each CFI value.

For example, assuming that a CFI is a 0^th CFI when the CFI is mapped to the 0^th PCFICH, a control channel region for normal UE indicated by the 0^th CFI is indicated by one, two, or three OFDM symbols when N^DL _RB>10 and is indicated by two, three, or four OFDM symbols when N^DL _RB=10. Table 3 shows the formats of a control channel region for normal UE according to the 0^th CFIs (when N^DL _RB>10).

Table 3

0^th CFI	TYPE OF CONTROL CHANNEL REGION FOR NORMAL UE
1(00)	One OFDM symbol
2(01)	Two OFDM symbols
3(10)	Three OFDM symbols
4(11)	reserved

Referring to Table 3, when the 0^th CFI is 00, it indicates that the number of OFDM symbols forming the 0^th PDCCH is 1. When the 0^th CFI is 01, it indicates that the number of OFDM symbols forming the 0^th PDCCH is 2. When the 0^th CFI is 10, it indicates that the number of OFDM symbols forming the 0^th PDCCH is 3. When the 0^th CFI is 11, it does not indicate anything and indicates a reserved code point. Meanwhile, assuming that a CFI is a first CFI when the CFI is mapped to the first PCFICH, the first CFI indicates the same thing as indicated by the 0^th CFI.

In contrast, assuming that a CFI is a second CFI when the CFI is mapped to the second PCFICH, the object indicated by the second CFI is determined based on Table 4 below. This is described later.

Assuming that a CFI codeword of 32 bits is modulated in accordance with Quadrature Phase Shift Keying (QPSK), 16 Resource Elements (REs) are necessary for each PCFICH.

The first PCFICH and the second PCFICH can be mapped to one or more predefined OFDM symbols and one or more predefined PRBs. In this case, each pair of the one or more predefined OFDM symbols can be located at each of two slots that form a corresponding subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of a central band. In some embodiments, the one or more predefined OFDM symbols can be located at respective two slots forming a corresponding subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of a central band.

FIG. 5 shows a first embodiment regarding the mapping of the first PCFICH and the second PCFICH for narrowband UE according to the present invention.

Referring to FIG. 5, a first CFI indicates Resource Element Groups (REGs) to which the first PCFICH is mapped. A second CFI indicates REGs to which the second PCFICH is mapped. When seen from the frequency domain, 6 PRBs at the center are assigned respective indices No. 0 to No. 5 from the top.

The first PCFICH is mapped to the No. 0 PRB and the No. 5 PRB on the last OFDM symbol of a first slot within one subframe. Furthermore, the first PCFICH is mapped to the No. 0 PRB and the No. 5 PRB on the last OFDM symbol of a second slot within the same subframe.

The second PCFICH is mapped to the No. 0 PRB and the No. 5 PRB on the second last OFDM symbol of the first slot within the same subframe. Furthermore, the second PCFICH is mapped to the No. 0 PRB and the No. 5 PRB on the second last OFDM symbol of the second slot within the same subframe.

A Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) can be allocated to the last symbol of each slot and the last second symbol of each slot and transmitted. However, in a wireless communication system, a PSS and an SSS occupy 62 subcarriers at the center. Accordingly, it can be seen that, assuming that one PRB includes 12 subcarriers, 5 subcarriers over the No. 0 PRB and 5 subcarriers under the No. 5 PRB are regions not occupied by the PSS and the SSS because a total of 72 subcarriers are present in 6 PRBs. Accordingly, 16 REs for the codewords of the first CFI and 16 REs for the second CFI can be divided and allocated to subcarriers remaining after the PSS and the SSS are allocated to the subcarriers. Furthermore, the last symbol of each slot and the second last symbol of each slot are regions to which a Demodulation Reference Signal (DMRS) used in channel estimation is allocated. If the first PCFICH and the second PCFICH are mapped to the regions, channel estimation performance can be improved.

FIG. 6 is a detailed diagram showing, in an RE level, regions to which the first PCFICH and the second PCFICH are mapped in accordance with a first embodiment of the present invention. FIG. 6 shows the No. 0 PRB and the No. 5 PRB on the last two OFDM symbols of each slot within the corresponding subframe.

Referring to FIG. 6, the regions of REs to which the first PCFICH is mapped include 4 subcarriers over the No. 0 PRB and 4 subcarriers under the No. 5 PRB on the last OFDM symbol of the first slot and 4 subcarriers over the No. 0 PRB and 4 subcarriers under the No. 5 PRB on the last OFDM symbol of the second slot.

The regions of REs to which the second PCFICH is mapped include 4 subcarriers over the No. 0 PRB and 4 subcarriers under the No. 5 PRB on the second last OFDM symbol of the first slot and 4 subcarriers over the No. 0 PRB and 4 subcarriers under the No. 5 PRB on the second last OFDM symbol of the second slot.

FIG. 7 shows REs to which the first PCFICH is mapped in accordance with the first embodiment of the present invention.

The REs to which the first PCFICH is mapped in the first embodiment can be gathered as in FIG. 7. Here, l is the index of an OFDM symbol, and l=0,1,...,6 (in the case of a normal CP). It can be seen that the number of REs to which the first PCFICH is mapped is a total of 16 and the REs can represent 32-bit codewords in accordance with QPSK modulation. The same principle applies to the second PCFICH.

Referring to FIG. 8, a first CFI indicates the regions of REGs to which the first PCFICH is mapped. A second CFI indicates the regions of REGs to which the second PCFICH is mapped. When viewed from the frequency domain, the PRBs of a central band are assigned respective indices No. 0 to No. 5 from the top. Here, l is the index of an OFDM symbol, and l=0,1,...,6 (in the case of a normal CP).

The first and the second PCFICHs for narrowband UE can be mapped to symmetric PRBs in each slot within one subframe. For example, the first PCFICH can be mapped to the No. 0 PRB on an OFDM symbol having l=4, of the second slot, and the No. 5 PRB on an OFDM symbol having l=4, of the first slot. The second PCFICH can be mapped to the No. 0 PRB on an OFDM symbol having l=4, of the first slot, and the No. 5 PRB on an OFDM symbol having l=4, of the second slot.

A time and frequency diversity can be obtained by the above-described mapping of the first and the second PCFICHs. Furthermore, an OFDM symbol having l=4 is a region to which a CRS is allocated in a wireless communication system, and a waste of REs can be avoided by the mapping of the first and the second PCFICHs for narrowband UE within the regions.

FIG. 9 is a detailed diagram showing, in an RE level, regions to which the first PCFICH and the second PCFICH are mapped in accordance with a second embodiment of the present invention. Here, l is the index of an OFDM symbol, and l=0, 1, , 6 (in the case of a normal CP). FIG. 9 shows a No. 0 PRB and a No. 5 PRB on OFDM symbols having l=4, of each slot within one subframe.

Referring to FIG. 9, each PRB is assumed to include 12 subcarrier and the subcarriers forming each PRB are assigned respective indices No. 0 to No. 11 from the top. The first PCFICH can be mapped to the Nos. 0, 1, 3, 4, 6, 7, 9, and 10 subcarriers (a total of 8) of the No. 0 PRB on an OFDM symbol having l=4, of a second slot within one subframe. Furthermore, the first PCFICH can be mapped to the Nos. 0, 1, 3, 4, 6, 7, 9, and 10 subcarriers (a total of 8) of the No. 5 PRRB on an OFDM symbol having l=4, of a first slot within the same subframe. In this case, REs for the total of 16 first PCFICHs can be secured. The second PCFICH can be mapped to the No. 0 PRB on the OFDM symbol having l=4, of the first slot and the No. 5 PRB on the OFDM symbol having l=4, of the second slot within the same subframe in the same manner as the first PCFICH. In this case, in a wireless communication system, since the Nos. 2, 5, 8, and 11 subcarriers of an OFDM symbol having l=4, of each slot are regions to which a CRS can be mapped, the remaining REs can be reduced and overlapping can be prevented.

FIG. 10 shows REs to which the first PCFICH is mapped in accordance with the second embodiment of the present invention.

Referring to FIG. 10, the REs to which the first PCFICH is mapped in the second embodiment can be gathered as in FIG. 10. The remaining REs are regions to which a CRS is mapped. Here, l is the index of an OFDM symbol, and l=0, 1, , 6 (in the case of a normal CP). It can be seen that the number of REs to which the first PCFICH is mapped is a total of 16 and the REs can represent 32-bit codewords in accordance with QPSK modulation. The same principle applies to the second PCFICH.

The first PCFICH can indicate a control channel region for normal UE and the second PCFICH can indicate a control channel region for narrowband UE through the above-described mapping of the first and the second PCFICHs for narrowband UE. Table 4 shows control channel regions for narrowband UE according to the second CFI values of the second PCFICH.

Table 4

SECOND CFI	CONTROL CHANNEL REGION FOR NARROWBAND UE
1(00)	2 PRB (0, 5)
2(01)	3 PRB (0, 2, 5)
3(10)	3 PRB (0, 3, 5)
4(11)	4 PRB (0, 2, 3, 5)
5	4 PRB (0, 1, 4, 5)

Referring to Table 4, if the second CFI of the second PCFICH indicates 1, a control channel region for narrowband UE is allocated to Nos. 0 and 5 PRBs, from among the PRBs of the central band. If the second CFI indicates 2, a control channel region for narrowband UE is allocated to Nos. 0, 2, and 5 PRBs, from among the PRBs of the central band. If the second CFI indicates 3, a control channel region for narrowband UE is allocated to Nos. 0, 3, and 5 PRBs, from among the PRBs of the central band. If the second CFI indicates 4, a control channel region for narrowband UE is allocated to Nos. 0, 2, 3, and 5 PRBs, from among the PRBs of the central band. Furthermore, if the second CFI indicates 5 (it can be indicated by a joint of the first PCFICH and the second PCFICH), a control channel region for narrowband UE is allocated to Nos. 0, 1, 4, and 5 PRBs, from among the PRBs of the central band.

In this case, if joint coding for jointing 2 bits indicative of the second CFI of the second PCFICH and 2 bits indicative of the first CFI of the first PCFICH is used in order for the second CFI of the second PCFICH to indicate 5, a control channel region for normal UE and a control channel region for narrowband UE can be represented by 4 bits. Table 5 shows the number of possible cases when the first and the second CFIs are jointed.

Table 5

Joint Coded CFI bits	CFI values
0000	CFI1=1, CFI2=1
0001	CFI1=1, CFI2=2
0010	CFI1=1, CFI2=3
0011	CFI1=1, CFI2=4
0100	CFI1=1, CFI2=5
0101	CFI1=2, CFI2=1
0110	CFI1=2, CFI2=2
0111	CFI1=2, CFI2=3
1000	CFI1=2, CFI2=4
1001	CFI1=2, CFI2=5
1010	CFI1=3, CFI2=1
1011	CFI1=3, CFI2=2
1100	CFI1=3, CFI2=3
1101	CFI1=3, CFI2=4
1110	CFI1=3, CFI2=5
1111	reserved

Referring to Table 5, the first CFI of the first PCFICH is indicated by CFI1 and the second CFI of the second PCFICH is indicated by CFI2. 4 bits are allocated to CFI bits. The number of possible cases sequentially includes CFI1=1, CFI2=1 when the CFI bits are 0000 to CFI1=3, CFI2=5 when the CFI bits are 1110 and RESERVED when the CFI bits are 1111. Accordingly, the total number of 16 cases can be represented. Table 4 is illustrative, and a variety of combinations are possible based on the number of 16 cases.

The mapping of the first PCFICH and the second PCFICH for narrowband UE and the allocation of the control channel region for the narrowband UE by way of the first PCIFCH and the second PCFICH for the narrowband UE have been described above. A first PHICH and a first PDCCH mapped to the control channel region for the narrowband UE are described below.

The first PDCCH for the narrowband UE is allocated to the control channel region for the narrowband UE. The first PHICH for the narrowband UE is also allocated to the control channel region for the narrowband UE. Accordingly, the first PDCCH for the narrowband UE can be detected by the narrowband UE in regions other than a region to which the first PHICH for the narrowband UE has been allocated.

In general, PHICHs, that is, the 0^th PHICH and the first PHICH, are control channels on which ACK/NACK signals for the uplink data transmission of UE are carried. A plurality of PHICHs can be mapped to the same REG that forms a PHICH group. The PHICHs within the same PHICH group are distinguished from each other by different orthogonal sequences. Resources through which a PHICH is transmitted are called PHICH resources, and the PHICH resources are identified by an index pair, such as (n^group _PHICH, n^seq _PHICH). n^group _PHICH indicates the index of a PHICH group, and n^seq _PHICH indicates the index of an orthogonal sequence within the PHICH group.

The following math figure indicates an index pair indicative of PHICH resources.

MathFigure 1

In Math Figure 1, I_{PRB_RA} becomes I^lowest_index _{PRB_RA} or I^lowest_index _{PRB_RA}+1, if necessary. I^lowest_index _{PRB_RA} is the index of a minimum Physical Resource Block (PRB) of the first slot of a corresponding PUSCH, and n_DMRS is a value indicative of the cyclic shift of a DeModulation Reference Signal (DMRS) in the corresponding PUSCH. The DMRS refers to a reference signal used to demodulate data transmitted on a PUSCH. Furthermore, N^group _PHICH is the number of PHICH groups, N^PHICH _SF is a spreading factor for PHICH modulation, and I_PHICH is a value of 1 or 0. If a PUSCH is transmitted in a subframe n=4 or 9 (n is any one of 0 to 9, wherein n is 4 or 9) and Time Division Duplex (TDD) uplink-downlink (UL-DL) configuration is 0, I_PHICH is 1. In other cases, I_PHICH is 0.

In a radio frame used in Frequency Division Duplex (FDD), the number of PHICH groups N^group _PHICH is a constant for all subframes. In the case of the 0^th PHICH for normal UE, the number of PHICH groups N^group _PHICH is given as follows.

MathFigure 2

In Math Figure 2, N_g∈{1/6, 1/2, 1, 2} and is given by a higher layer signal. The index n^group _PHICH of Math Figure 1 has a range from 0 to N^group _PHICH -1.

Meanwhile, in the case of the first PHICH for the narrowband UE that is allocated to the control channel region for the narrowband UE, N^group _PHICH is given as follows.

MathFigure 3

In Math Figure 3, N_g∈{1/6, 1/2, 1, 2} and is given by a higher layer signal. N^DL _symb indicates the number of OFDM symbols per slot. l_DataStart indicates the number of an OFDM symbol at which the original data region other than the original control channel region indicated by the first PCFICH within a corresponding subframe is started. For example, if the first PCFICH indicates that the original control channel region is up to the third OFDM symbol of the first slot of a corresponding subframe, the l_DataStart=3 because the original data channel region is started from a fourth OFDM symbol and the number of the fourth OFDM symbol is l=3 (the number of the first OFDM symbol is l=0).

If the first PHICH for the narrowband UE is distributed over and allocated to a No. 0 PRB (i.e., a first PRB from the top) and a No. 5 PRB (i.e., a sixth PRB from the top) within the control channel region for the narrowband UE, a scheme for the allocation can be likewise performed by changing only order in the frequency domain and the time domain from the 0^th PHICH allocation scheme. In this case, the first PDCCH for the narrowband UE can be mapped within the control channel region for the narrowband UE other than the region to which the first PHICH for the narrowband UE is mapped.

Meanwhile, in order to reduce complexity, the control channel region for the narrowband UE can be previously divided into two regions.

FIG. 11 is a diagram showing that a control channel region for narrowband UE according to the present invention is divided into two regions. One of the two regions indicates first PCFICH, second PCFICH, and first PHICH regions for narrowband UE, and the other of the two regions indicates first PDCCH regions for the narrowband UE. FIG. 11 shows an example in which Nos. 0, 2, 3, and 5 PRBs are allocated as the control channel region for the narrowband UE. In this case, the remaining Nos. 1 and 4 PRB regions can be allocated as data channel regions for the narrowband UE.

Referring to FIG. 11, the No. 0 PRB and the No. 5 PRB of two slots that form a corresponding subframe are allocated as the first PCFICH, the second PCFICH, and the first PHICH regions for narrowband UE. Furthermore, the No. 2 PRB and the No. 3 PRB of the two slots are allocated as the first PDCCH regions for the narrowband UE. In this case, the narrowband UE can detect the first PCFICH, the second PCFICH, and the first PHICH for the narrowband UE in the No. 0 PRB and the No. 5 PRB and can detect the first PDCCH for the narrowband UE in the No. 2 PRB and the No. 3 PRB. In this case, one, two, or three OFDM symbols indicated by the original control channel region in a 0^th PCFICH or a first PCFICH, for example, in the front of the first slot of a corresponding subframe will be excluded from the control channel region for the narrowband UE.

An operation of a BS which sends a signal in downlink is described below.

Referring to FIG. 12, the BS generates PSS and SSS signals at step S1200. The PSS is transmitted in a cycle of a 1/2 radio frame and the PSS has three types of pieces of cell ID information. The PSS is used for symbol timing and frequency synchronization and is used to track a cell ID group. The PSS can be generated using a Zadoff-Chu sequence, such as Math Figure 4.

MathFigure 4

In Math Figure 4, a u value has a value of 25, 29, or 34. In the case of an FDD method, the u value is transmitted in a first slot and the last symbol of an eleventh slot.

The SSS is transmitted in a cycle of a radio frame. In the case of an FDD method, the SSS is transmitted right before the PSS of the first slot and the eleventh slot and is used to estimate the starting timing of a radio frame. Furthermore, since the SSS has 168 cell group IDs, it can detect a cell group ID by using a cell ID obtained using a PSS. The SSS can be generated by combining two binary sequences having a length of 31 as in Math Figure 5.

MathFigure 5

In Math Figure 5,

,

, and

are distinguished from each other by the cyclic shifts of different M sequences, and and are defined by the cyclic shift of an M sequence and a PSS.

The BS generates a PBCH signal at step S1210.

The BS generates the PBCH signal including basic system information for communication to which a PBCH will be mapped. The PBCH signal includes a Master Information Block (MIB).

The BS generates pieces of control information to be mapped to a 0^th PCFICH, a 0^th PHICH, and a 0^th PDCCH for normal UE, respectively, and pieces of control information to be mapped to a first PCFICH, a second PCFICH, a first PHICH, and a first PDCCH for the narrowband UE, respectively, at step S1220.

The control information mapped to the 0^th PCFICH is a 0^th CFI indicative of the OFDM symbol length of a control channel region for the normal UE, and the control information mapped to the 0^th PHICH is an ACK/NACK signal for uplink data received by the BS from the normal UE. Furthermore, the control information mapped to the 0^th PDCCH is DCI regarding the normal UE. Meanwhile, the pieces of control information mapped to the first PCFICH and the second PCFICH are a first CFI and a second CFI, respectively, and the control information mapped to the first PHICH is an ACK/NACK signal for uplink data received by the BS from the narrowband UE. The control information mapped to the first PDCCH is DCI regarding the narrowband UE.

The BS encodes the 0^th CFI to second CFI based on Table 2. The BS maps the 0^th CFI, the first CFI, and the second CFI to the 0^th PCFICH, the first PCFICH, and the second PCFICH, respectively, at step S1230. Furthermore, the BS maps an ACK/NACK signal for uplink data, received from the normal UE, to the 0^th PHICH and maps an ACK/NACK signal for uplink data, received from the narrowband UE, to the first PHICH at step S1240. Furthermore, the BS maps DCI about the normal UE to the 0^th PDCCH and DCI about the narrowband UE to the first PDCCH at step S1250. A process of mapping the DCI to the PDCCH includes adding Cyclic Redundancy Check (CRC) bits to the DCI, scrambling a Cell-Radio Network Temporary Identifier (C-RNTI), that is, a unique identifier for the normal UE, to the DCI to which the CRC bits have been added, and mapping the scrambled C-RNTI to the PDCCH.

The BS transmits the PSS, the SSS, and the PBCH signal to the UE at step S1260.

The PSS is located at the last OFDM symbols of the first and eleventh slots of each radio frame in the case of FDD. The SSS is located at a symbol right before the OFDM symbol where the PSS is located. When viewed from the frequency domain, the PSS and SSS are mapped to 62 subcarriers at the center irrespective of a bandwidth of a wireless communication system. A PBCH is allocated to only the second slot of the first subframe of each radio frame. The PBCH includes four OFDM symbols, and the PBCH is allocated to 74 subcarriers at the center irrespective of a bandwidth of a wireless communication system.

The BS transmits the 0^th PCFICH, the 0^th PHICH, and the 0^th PDCCH to the normal UE on a control channel region for the normal UE at step S1270. Here, the 0^th PCFICH is modulated in accordance with a QPSK scheme. Furthermore, the 0^th PHICH is mapped to REs, determined by an index pair (n^group _PHICH, n^seq _PHICH) determined based on Math Figures 1 and 2 below, in the form of a PHICH group. The 0^th PHICH can be modulated in accordance with a BPSK scheme, and the 0^th PDCCH can be modulated in accordance with a QPSK scheme.

The BS transmits the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH to the narrowband UE on a control channel region for the narrowband UE at step S1280. The control channel region for the narrowband UE can be previously determined. Here, the first PCFICH and the second PCFICH are modulated in accordance with a QPSK scheme. Furthermore, the first PHICH is mapped to REs, determined by an index pair (n^group _PHICH, n^seq _PHICH) determined based on Math Figures 1 and 3, in the form of a PHICH group. Here, the first PHICH can be modulated in accordance with a BPSK scheme, and the first PDCCH can be modulated in accordance with a QPSK scheme.

Referring to FIG. 13, the narrowband UE detects a PSS and an SSS for synchronization at step S1300.

When viewed from the frequency domain, the PSS and the SSS are mapped to 62 subcarriers irrespective of a bandwidth of a wireless communication system. Accordingly, the narrowband UE that supports a narrowband can detect the PSS and the SSS.

The narrowband UE detects a PBCH for an MIB at step S1310.

When viewed from the frequency domain, the PBCH is allocated to 72 subcarriers at the center irrespective of a bandwidth of a wireless communication system. Accordingly, the narrowband UE which supports a narrowband can detect a PBCH signal transmitted on the PBCH.

For example, the narrowband UE can detect a first PCFICH at predefined locations, such as those shown in FIGS. 5 to 10, and recognize a format of a control channel region for normal UE based on the first CFI of the first PCFICH and Table 3 at step S1320. Thus, the narrowband UE can obtain the starting point of a data channel region for the normal UE.

For example, the narrowband UE can detect a second PCFICH at predefined locations, such as those shown in FIGS. 5 to 10, and recognize a format of a control channel region for the narrowband UE based on the second CFI of the second PCFICH and Table 4 at step S1330.

When seeing from the time domain, the narrowband UE can know that what PRBs of a corresponding subframe have been allocated as the control channel region for the narrowband UE based on the second PCFICH. The narrowband UE may also know a data channel region for the narrowband UE.

The narrowband UE detects a first PHICH for the narrowband UE at step S1340.

The narrowband UE detects a first PDCCH for the narrowband UE at step S1350.

The narrowband UE performs uplink transmission or downlink reception based on DCI mapped to the first PDCCH at step S1360. For example, the uplink transmission can include a case where the narrowband UE transmits a new uplink signal to a BS when an ACK/NACK signal mapped to the first PHICH is an ACK signal. In some embodiments, the uplink transmission can include a case where the narrowband UE retransmits a previously transmitted uplink signal to a BS when an ACK/NACK signal mapped to the first PHICH is a NACK signal.

Referring to FIG. 14, a BS generates a PSS and an SSS at step S1400.

The BS generates a PBCH signal at step S1410.

The BS generates pieces of control information to be mapped to a first PCFICH, a second PCFICH, a first PHICH, and a first PDCCH and maps the pieces of control information to the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH at step S1420. Control information to be mapped to the first PCFICH is a first CFI, and control information to be mapped to the second PCFICH is a second CFI. The control information mapped to the first PHICH is an ACK/NACK signal for uplink data that is received by the BS from the narrowband UE, and the control information mapped to the first PDCCH is DCI about the narrowband UE. The first CFI can indicate the first 4 or smaller OFDM symbols within a subframe, and the second CFI can indicate the indices of one or more predefined PRBs. In some embodiments, a combination of the first CFI and the second CFI can indicate the first 4 or smaller OFDM symbols within the subframe and the indices of the one or more predefined PRBs.

The BS transmits the PSS, the SSS, and the PBCH signal to the narrowband UE and transmits the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH to the narrowband UE on a control channel region for the narrowband UE at step S1430. Here, the BS maps the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH to the one or more predefined PRBs on a central band. The PRB to which a control channel for the narrowband UE is mapped can be indicated by the second CFI or a combination of the first CFI and the second CFI. The BS can map the first PCFICH and the second PCFICH to the one or more predefined PRBs on an OFDM symbol predefined in a central band on a system operating frequency and transmit the one or more predefined PRBs to the narrowband UE. In this case, each pair of the one or more predefined OFDM symbols can be located at each of two slots that form a corresponding subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of a central band. In some embodiments, the one or more predefined OFDM symbols can be located at each of two slots that forms a subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of a central band. For example, the one or more predefined OFDM symbols and the one or more predefined PRBs can be located as shown in FIGS. 5 to 10.

The narrowband UE detects the PSS and the SSS for synchronization at step S1440.

The narrowband UE detects a PBCH for an MIB at step S1450.

The narrowband UE detects the first PCFICH and the second PCFICH and recognizes a format of a control channel region for the narrowband UE at step S1460. The narrowband UE can detect the first PCFICH and the second PCFICH by receiving the first PCFICH and the second PCFICH through the one or more predefined PRBs on the one or more predefined OFDM symbols. Since the first CFI mapped to the first PCFICH can indicate the number of OFDM symbols for a control channel region for normal UE, the narrowband UE can know the starting point of a data channel region for the normal UE based on the first CFI. The narrowband UE can know that what PRBs of the one or more predefined PRBs in the central band, from the remaining regions other than the control channel region for the normal UE, have been predefined as the control channel region for the narrowband UE based on the second CFI mapped to the second PCFICH. In some embodiments, the narrowband UE can know the number of OFDM symbols for the control channel region for the normal UE and the predefined the PRB based on a combination of the first CFI and the second CFI.

The narrowband UE recognizes and detects a format of the control channel region for the narrowband UE based on the first CFI and the second CFI.

The narrowband UE detects the first PHICH at step S1470. The narrowband UE detects ACK/NACK information mapped to the first PHICH.

The narrowband UE detects the first PDCCH at step S1480. The narrowband UE detects DCI mapped to the first PDCCH.

The narrowband UE can perform uplink transmission or downlink reception based on the ACK/NACK information and the DCI.

The BS 1500 includes a reception unit 1510, a control information generation unit 1520, a channel mapper 1530, and a transmission unit 1540.

The reception unit 1510 receives an uplink signal from narrowband UE 1550. The uplink signal can include a PUSCH and a PUCCH.

The control information generation unit 1520 generates pieces of control information to be mapped to a first PCFICH, a second PCFICH, a first PHICH, and a first PDCCH. For example, the pieces of control information mapped to the first PCFICH and the second PCFICH are a first CFI and a second CFI, respectively, the control information mapped to the first PHICH is an ACK/NACK signal for uplink data that is received by the BS 1500 from the narrowband UE 1550, and the control information mapped to the first PDCCH is DCI about the narrowband UE 1550. The first CFI can indicate first 4 or smaller OFDM symbols within a subframe, and the second CFI can indicate the indices of one or more predefined PRBs. In some embodiments, a combination of the first CFI and the second CFI can indicate the first 4 or smaller OFDM symbols within the subframe and the indices of the one or more predefined PRBs.

The channel mapper 1530 maps the pieces of generated control information to the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH, respectively, according to their types.

The transmission unit 1540 transmits a PSS, an SSS, and a PBCH signal on a central band and the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH on a control channel region for the narrowband UE to the narrowband UE 1550. Here, the transmission unit 1540 maps the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH to the one or more predefined PRBs on the central band. The PRB to which the control channel for the narrowband UE is mapped can be indicated by the second CFI or a combination of the first CFI and the second CFI. The transmission unit 1540 can map the first PCFICH and the second PCFICH to the one or more predefined PRBs on the one or more predefined OFDM symbols in the central band on a system operating frequency and transmit the one or more predefined PRBs to the narrowband UE. In this case, each pair of the one or more predefined OFDM symbols can be located at each of two slots that form a corresponding subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of the central band. In some embodiments, the one or more predefined OFDM symbols can be located at respective two slots that forms a subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of the central band. For example, the one or more predefined OFDM symbols and the one or more predefined PRBs can be located as shown in FIGS. 5 to 10.

The narrowband UE 1550 includes a reception unit 1560, a control channel region detection unit 1570, a signal generation unit 1580, and a transmission unit 1590.

The reception unit 1560 receives the PSS/SSS, the PBCH signal, the first PCFICH, the second PCFICH, the first PHICH, and the first PDCCH transmitted by the BS 1500. In this case, the reception unit 1560 can receive the first PCFICH and the second PCFICH through the one or more predefined PRBs on the one or more predefined OFDM symbols.

The control channel region detection unit 1570 detects the received first PCFICH and second PCFICH. Since the first CFI mapped to the first PCFICH can indicate the number of OFDM symbols of a control channel region for normal UE, the control channel region detection unit 1570 can know the starting point of a data channel region for the normal UE. Furthermore, the control channel region detection unit 1570 can know that what PRBs of the one or more predefined PRBs in the central band, from the remaining regions other than the control channel region for the normal UE, have been predefined as a control channel region for the narrowband UE 1550 based on the second CFI mapped to the second PCFICH. In some embodiments, the control channel region detection unit 1570 can know the number of OFDM symbols of the control channel region for the normal UE and the one or more predefined PRBs based on a combination of the first CFI and the second CFI. The control channel region detection unit 1570 detects a control channel region for the narrowband UE based on the first CFI and the second CFI.

The signal generation unit 1580 detects the first PHICH and the first PDCCH within the control channel region for the narrowband UE and generates an uplink signal. For example, if an ACK/NACK signal mapped to the first PHICH is a NACK signal, the signal generation unit 1580 can generate a previously transmitted uplink signal. If an ACK/NACK signal mapped to the first PHICH is an ACK signal, the signal generation unit 1580 can generate a new uplink signal based on DCI about the narrowband UE mapped to the first PDCCH. The uplink signal can include a Physical Uplink Shared CHannel (PUSCH) and a Physical Uplink Control CHannel (PUCCH). The PUCCH carries pieces of control information, such as HARQ ACK/NAK for downlink transmission, a scheduling request, a Sounding Reference Signal (SRS), and a CQI. An Uplink Shared Channel (UL-SCH), that is, a transport channel, is mapped to the PUSCH.

The transmission unit 1590 transmits the generated uplink signal to the BS 1500.

A method of allocating specific PRBs of the central band of a system operating frequency band to a control channel region for narrowband UE can also be applied to an Extended PDCCH (E-PDCCH) provided for normal UE.

If it is necessary to send a control channel to a plurality of pieces of UE in a hot spot or a crowded area, the capacity of the control channel is increased. However, since radio resources for the control channel is limited, an E-PDCCH is being discussed as a method for efficiently supporting the increasing capacity of the control channel. A normal PDCCH is mapped to the existing control channel region, whereas the E-PDCCH can be mapped to the existing PDSCH region (i.e., a data channel region). Here, the E-PDCCH may have a meaning of a control channel that is newly defined in order to guarantee extended and enhanced performance. Furthermore, a PDCCH transmitted in a PDSCH region is not limited to denote an E-PDCCH in terms of a term, and can be used as another term having the same function or meaning (e.g.., the PDCCH can also be called a New-PDCCH (N-PDCCH) or an X-PDCCH). More radio resources are allocated to the data channel region than to the control channel region, and thus the capacity of the PDCCH can be overcome by the E-PDCCH. That is, the E-PDCCH can support a great PDCCH transmission capacity while not reducing the reception reliability of the PDCCH.

An E-PDCCH is mapped to a data region. Thus, when a transmission terminal transmits an E-PDCCH to UE, pieces of UE have to receive an indication regarding whether the E-PDCCH is present or not and regarding a precise region of a resource block to which the E-PDCCH has been mapped in each cell. To this end, DCI has to include a new field related to the E-PDCCH, and DCI having a new format may be defined if necessary.

In order to receive an E-PDCCH, UE has to know resource blocks to which the E-PDCCH has been mapped. To this end, a location and region (e.g., the number of resource blocks) where the resource blocks regarding the E-PDCCH are allocated may be predefined between a BS and the UE, and the BS may know the UE of the region by using higher layer signaling different from DCI. Here, semi-static signaling, such as Radio Resource Control (RRC) signaling, may be an example of higher layer signaling.

For example, the resource blocks mapped to the E-PDCCH is mapped can be predefined in a cell-specific way or indicated by higher layer signaling (e.g.. Radio Resource Control (RRC) signaling) and can be represented by the starting point y0 of the allocated resource blocks and the number of resource block(s) y corresponding to the length of the allocated resource blocks. Basic DCI mapped to a PDCCH is allocated to UE-specific resources and transmitted, but extended DCI mapped to an E-PDCCH is allocated to cell-specific resources and transmitted.

An E-PDCCH region can be basically divided into two regions. One region is a common search space region and the other region is a UE-specific search space region. The common search space region and the UE-specific search space region can also be indicated by higher layer signaling, such as RRC signaling.

The common search space region is shared by all pieces of UE that support an E-PDCCH. Furthermore, an extended PCFICH (E-PCFICH) and an extended-PHICH (E-PHICH) can be allocated to the common search space region. The common search space region can be distributed based on a pair of PRBs in transfer mode. The common search space regions of the E-PCFICH, the E-PHICH, and the E-PDCCH can be detected based on a DMRS. The E-PCFICH can be mapped to the first PRB and last PRB of the common search space region of the E-PDCCH. In this case, four OFDM symbols can become a candidate group of the E-PCFICH. The four OFDM symbols can become the last OFDM symbols of two slots and l=4 OFDM symbols within a corresponding subframe when viewed from the time domain. For example, the E-PCFICH can be mapped to a first PRB and a last PRB on the last OFDM symbol of a first slot and a first PRB and a last PRB on the last OFDM symbol of a second slot within one subframe of the common search space region of an E-PDCCH. In some embodiments, the E-PCFICH can be mapped to a first PRB on an OFDM symbol having l=4, of a first slot within one subframe of the common search space region of the E-PDCCH, and a last PRB on an OFDM symbol having l=4, of a second slot within the corresponding subframe. In some embodiments, the E-PCFICH can be mapped to a first PRB on an OFDM symbol having l=4, of a second slot within one subframe of the common search space region of the E-PDCCH, and to a last PRB on an OFDM symbol having l=4, of a first slot within the corresponding subframe. That is, the E-PCFICH can be allocated by way of the first PRB, the last PRB, and the number of all possible cases according to a combination of the four OFDM symbol candidate group. The E-PHICH can be allocated to the first PRB pair and last PRB pair of the common search space region of the E-PDCCH. The E-PHICH is mapped to REs determined by an index pair (n^group _PHICH, n^seq _PHICH) determined based on Math Figures 1 and 3 in the form of a PHICH group.

A target of the UE-specific search space region is specific UE. The UE-specific search space region can be distributed or localized.

An extended control channel in accordance with an embodiment of the present invention is described below.

First, an E-PCFICH indicates a control channel region for normal UE. That is, the E-PCFICH indicates that how many former OFDM symbols in the first slot of a corresponding subframe are allocated as a 0^th PDCCH for the normal UE. Furthermore, the E-PCFICH indicates the starting point of a PDSCH region, that is, a data channel region for the normal UE. The E-PCFICH can be mapped to one or more predefined OFDM symbols and one or more predefined PRBs. In this case, each pair of the one or more predefined OFDM symbols can be located in each of two slots that form a corresponding subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of some band. In some embodiments, the one or more predefined OFDM symbols can be located at respective two slots that form a subframe, and the one or more predefined PRBs can be located at respective frequencies at both side ends of some band.

A CFI index mapped to the E-PCFICH can be based on Tables 2 and 3. In this case, 16 REs are necessary in accordance with QPSK modulation. The mapping of the 16 REs is as follows. The E-PCFICH is mapped to a first PRB and a last PRB from the top, from among a plurality of PRBs of a common search space region.

Referring to FIG. 16, the E-PCFICH can be mapped to the last OFDM symbol of a first slot and the last OFDM symbol of a second slot in a corresponding subframe of a first PRB and the last OFDM symbol of the first slot and the last OFDM symbol of the second slot in the corresponding subframe of a last PRB from the top within the common search space region of the E-PDCCH.

In this case, the last OFDM symbol of the first slot and the last OFDM symbol of the second slot in the corresponding subframe are locations where a DMRS is mapped. Accordingly, channel estimation performance can b e improved.

Mapping of an RE unit is described in detail below.

Referring to FIG. 17, (A) shows a first PRB on the last OFDM (l=6) symbol of a first slot and a first PRB on the last OFDM (l=6) symbol of a second slot in one subframe within the common search space region of the E-PDCCH, and (B) shows a last PRB on the last OFDM (l=6) symbol of a first slot and a last PRB on the last OFDM (l=6) symbol of a second slot in the same subframe within the common search space region of the E-PDCCH. In the time domain, one PRB is assumed to include 12 subcarriers, and the 12 subcarriers are assigned indices No. 0 to No. 11 from the top.

The E-PCFICH is mapped to the first to fourth subcarriers of the first PRBs on the last OFDM symbols of the first and the second slots of the subframe. Furthermore, the E-PCFICH is mapped to the seventh to ninth and eleventh subcarriers of the last PRBs of the last OFDM symbols of the first and the second slots of the subframe. In this case, the total number of REs to which the E-PCFICH is mapped is 16.

The 0^th, fifth, and tenth subcarriers of the first PRBs on the last OFDM symbols of the first and the second slots are REs to which a DMRS is mapped. Furthermore, the 0^th, fifth, and tenth subcarriers of the last PRBs on the last OFDM symbols of the first and the second slots are also REs to which a DMRS is mapped. The E-PCFICH is allocated to REs other than the REs to which the DMRS is mapped.

FIG. 18 shows mapping of an RE unit in accordance with a second embodiment of an E-PCFICH according to the present invention.

Referring to FIG. 18, the E-PCFICH can be mapped to each of PRBs at the locations of two slots that are symmetrical to each other. For example, the E-PCFICH can be mapped to a first PRB on an OFDM symbol having l=4, of the first slot of one subframe within the common search space region of the E-PDCCH, and the E-PCFICH can be mapped to a last PRB on an OFDM symbol having l=4, of the second slot of the same subframe within the common search space region of the E-PDCCH. In this case, time and frequency diversities can be obtained. Furthermore, the remaining REs can be reduced because an OFDM symbol having l=4, of each slot, is a region to which a CRS is allocated.

Mapping of an RE unit according to the second embodiment is described in detail below.

Referring to FIG. 19, (A) shows a first PRB on an OFDM symbol having l=4, of the first slot of one subframe within the common search space region of the E-PDCCH, and (B) shows a second PRB on an OFDM symbol having l=4, of the second slot of the same subframe.

It is assumed that one PRB includes 12 subcarriers in the time domain, and the 12 subcarriers are assigned indices No. 0 to No. 11 from the top.

The E-PCFICH can be mapped to the Nos. 0, 1, 3, 4, 6, 7, 9, and 10 subcarriers of the first PRB on the OFDM symbol having l=4, of the first slot. Furthermore, the E-PCFICH can be mapped to the Nos. 0, 1, 3, 4, 6, 7, 9, and 10 subcarriers of the last PRB of the OFDM symbol having l=4, of the second slot. In this case, the total number of REs to which the E-PCFICH is mapped becomes 16.

The Nos. 2, 5, 8, and 11 subcarriers of the first PRB on the OFDM symbol having l=4, of the first slot, are REs to which a CRS is mapped. Furthermore, the Nos. 2, 5, 8, and 11 subcarriers of the last PRB on the OFDM symbol having l=4, of the second slot, are also REs to which a CRS is mapped. The E-PCFICH is mapped to REs other than the REs to which the CRS is mapped.

Meanwhile, the E-PCFICH may not be mapped to the first PRB and the last PRB of the common search space region of the E-PDCCH. That is, the E-PCFICHs can be classified into four RE groups and can be equally allocated to specific PRBs in the common search space region of the E-PDCCH. For example, the E-PCFICHs can be equally allocated to specific OFDM symbols, from among the l=4 OFDM symbol and last OFDM symbol of a first slot and the l=4 OFDM symbol and last OFDM symbol of a second slot within a corresponding subframe in two specific PRBs.

As described above, the present invention proposes a method of allocating some of a data channel region as a control channel region for low-cost type UE or an extended control channel region. In accordance with the method, influence on normal UE can be minimized, a waste of resource elements can be reduced, and low-cost type UE can be efficiently supported. Furthermore, if it is necessary to send a control channel to a plurality of pieces of UE in a hot spot or a crowded area, an extended control channel region can be efficiently provided.

While some exemplary embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may change and modify the present invention in various ways without departing from the essential characteristic of the present invention. Accordingly, the disclosed embodiments should not be construed as limiting the technical spirit of the present invention, but should be construed as illustrating the technical spirit of the present invention. The scope of the technical spirit of the present invention is not restricted by the embodiments, and the scope of the present invention should be interpreted based on the following appended claims. Accordingly, the present invention should be construed as covering all modifications or variations derived from the meaning and scope of the appended claims and their equivalents.

Claims

A base station for sending a control channel in a wireless communication system, the base station comprising:

a control information generation unit configured to generate a first Control Format Indicator (CFI) to be mapped to a first Physical Control Format Indicator CHannnel (PCFICH) and a second CFI to be mapped to a second PCFICH;

a channel mapper configured to map the first CFI to the first PCFICH and map the second CFI to the second PCFICH; and

a transmission unit configured to map the first PCFICH and the second PCFICH to one or more predefined Physical Resource Blocks (PRBs) on one or more predefined Orthogonal Frequency Division Multiplexing (OFDM) symbols in a central band on a system operating frequency and transmit the one or more PRBs to user equipment;

wherein the first CFI indicates first 4 or smaller OFDM symbols within a subframe and the second CFI indicate indices of the one or more predefined PRBs.
The base station of claim 1, wherein:

the control information generation unit further generates ACK/NACK information to be mapped to a first Physical HARQ Indicator Channel (PHICH) and Downlink Control Information (DCI) to be mapped to a first Physical Downlink Control CHannel (PDCCH),

the channel mapper maps the ACK/NACK information to the first PHICH and maps the DCI to the first PDCCH, and

the transmission unit maps the first PHICH and the first PDCCH to the one or more predefined PRBs and transmits the one or more predefined PRBs to which the first PHICH and the first PDCCH have been mapped to the user equipment.
The base station of claim 1, wherein:

each pair of the one or more predefined OFDM symbols are located at each of two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The base station of claim 1, wherein:

the one or more predefined OFDM symbols are located at respective two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The base station of claim 2, wherein when the transmission unit maps the ACK/NACK information to the first PHICH, N^group _PHICH indicative of a number of groups of the first PHICHs is

wherein, N_g∈{1/6, 1/2, 1, 2} and is given by a higher layer signal, N^DL _symb indicates the number of OFDM symbols per slot, l_DataStart indicates the number of an OFDM symbol at which the original data region other than the original control channel region indicated by the first PCFICH within a corresponding subframe is started.
User equipment for receiving a control channel in a wireless communication system, the user equipment comprising:

a reception unit configured to receive a first Physical Control Format Indicator CHannnel (PCFICH) to which a first Control Format Indicator (CFI) indicative of first 4 or smaller Orthogonal Frequency Division Multiplexing (OFDM) symbols within a subframe has been mapped and a second PCFICH to which a second CFI indicative of one or more predefined Physical Resource Blocks (PRBs) in a central band on a system operating frequency has been mapped, from a base station in one or more predefined PRBs on one or more predefined OFDM symbols; and

a control channel region detection unit configured to detect a control channel region in which a control channel regarding the user equipment is transmitted;

wherein the control channel region is defined by the one or more predefined PRBs indicated by the second CFI on remaining OFDM symbols other than an OFDM symbol indicated by the first CFI, from among all OFDM symbols forming the subframe.
The user equipment of claim 6, wherein:

the reception unit further receives a first Physical HARQ Indicator Channel (PHICH) to which ACK/NACK information has been mapped and a first Physical Downlink Control CHannel (PDCCH) to which Downlink Control Information (DCI) has been mapped from the base station, and

the signal generation unit detects the ACK/NACK information and the DCI and generates the uplink signal based on the ACK/NACK information and the DCI.
The user equipment of claim 6, wherein:

each pair of the one or more predefined OFDM symbols are located at each of two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The user equipment of claim 6, wherein:

the one or more predefined OFDM symbols are located at respective two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The user equipment of claim 7, wherein when the signal generation unit detects the ACK/NACK information mapped to the first PHICH, a number of groups of the first PHICHs N^group _PHICHis

wherein, N_g∈{1/6, 1/2, 1, 2} and is given by a higher layer signal, N^DL _symb indicates the number of OFDM symbols per slot, l_DataStart indicates the number of an OFDM symbol at which the original data region other than the original control channel region indicated by the first PCFICH within a corresponding subframe is started.
A method of a base station sending a control channel to user equipment in a wireless communication system, the method comprising:

generating a first Control Format Indicator (CFI) to be mapped to a first Physical Control Format Indicator CHannnel (PCFICH) and a second CFI to be mapped to a second PCFICH;

mapping the first CFI to the first PCFICH and mapping the second CFI to the second PCFICH; and

mapping the first PCFICH and the second PCFICH to one or more predefined Physical Resource Blocks (PRBs) on one or more predefined Orthogonal Frequency Division Multiplexing (OFDM) symbols in a central band on a system operating frequency and transmitting the one or more PRBs to the user equipment;

wherein the first CFI indicates first 4 or smaller OFDM symbols within a subframe and the second CFI indicate indices of the one or more predefined PRBs.
The method of claim 11, further comprising:

generating ACK/NACK information to be mapped to a first Physical HARQ Indicator Channel (PHICH) and Downlink Control Information (DCI) to be mapped to a first Physical Downlink Control CHannel (PDCCH),

mapping the ACK/NACK information to the first PHICH and mapping the DCI to the first PDCCH, and

mapping the first PHICH and the first PDCCH to the one or more predefined PRBs and transmitting the one or more predefined PRBs to which the first PHICH and the first PDCCH have been mapped to the user equipment.
The method of claim 11, wherein:

each pair of the one or more predefined OFDM symbols are located at each of two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The method of claim 11, wherein:

the one or more predefined OFDM symbols are located at respective two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The method of claim 12, wherein when mapping the ACK/NACK information to the first PHICH, N^group _PHICH indicative of a number of groups of the first PHICHs is

wherein, N_g∈{1/6, 1/2, 1, 2} and is given by a higher layer signal, N^DL _symb indicates the number of OFDM symbols per slot, l_DataStart indicates the number of an OFDM symbol at which the original data region other than the original control channel region indicated by the first PCFICH within a corresponding subframe is started.
A method of user equipment receiving a control channel from a base station in a wireless communication system, the method comprising:

receiving a first Physical Control Format Indicator CHannnel (PCFICH) to which a first Control Format Indicator (CFI) indicative of first 4 or smaller Orthogonal Frequency Division Multiplexing (OFDM) symbols within a subframe has been mapped and a second PCFICH to which a second CFI indicative of one or more predefined Physical Resource Blocks (PRBs) in a central band on a system operating frequency has been mapped, from the base station in one or more predefined PRBs on one or more predefined OFDM symbols; and

detecting a control channel region in which a control channel regarding the user equipment is transmitted;

wherein the control channel region is defined by the one or more predefined PRBs indicated by the second CFI on remaining OFDM symbols other than an OFDM symbol indicated by the first CFI, from among all OFDM symbols forming the subframe.
The method of claim 16, further comprising:

receiving a first Physical HARQ Indicator Channel (PHICH) to which ACK/NACK information has been mapped and a first Physical Downlink Control CHannel (PDCCH) to which Downlink Control Information (DCI) has been mapped from the base station, and

detecting the ACK/NACK information and the DCI and generates the uplink signal based on the ACK/NACK information and the DCI.
The method of claim 16, wherein:

each pair of the one or more predefined OFDM symbols are located at each of two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The method of claim 16, wherein:

the one or more predefined OFDM symbols are located at respective two slots forming the subframe, and

the one or more predefined PRBs are located at respective frequencies at both side ends of the central band.
The method of claim 17, wherein when detecting the ACK/NACK information mapped to the first PHICH, a number of groups of the first PHICHs N^group _PHICHis

wherein, N_g∈{1/6, 1/2, 1, 2} and is given by a higher layer signal, N^DL _symb indicates the number of OFDM symbols per slot, l_DataStart indicates the number of an OFDM symbol at which the original data region other than the original control channel region indicated by the first PCFICH within a corresponding subframe is started.