KR20100136401A - Method and apparatus of transmitting midamble in wireless communication system - Google Patents

Abstract

PURPOSE: A midamble transmission method in the wireless communication system and a device thereof are provided to apply the transmission power of each frequency partition to a midamble thereby exactly measuring interference level of a serving cell or a neighbor cell. CONSTITUTION: A base station generates midamble sequence about each of plurality of antennas(S100). The base station maps the generated midamble sequence in a plurality of sub carriers in a resource area(S110). The plurality of sub carriers is included in one among frequency partitions. Each different transmission power is applied to the each frequency partition. The base station transmits the mapped midamble sequence to a terminal by the antenna(S120).

Description

METHOD AND APPARATUS OF TRANSMITTING MIDAMBLE IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting a midamble in a wireless communication system.

The Institute of Electrical and Electronics Engineers (IEEE) 802.16e standard is the sixth standard for the International Mobile Telecommunications (IMT-2000) in the ITU-Radiocommunication Sector (ITU-R) under the International Telecommunication Union (ITU) in 2007. It was adopted under the name OFDMA TDD '. ITU-R is preparing the IMT-Advanced system as the next generation 4G mobile communication standard after IMT-2000. The IEEE 802.16 Working Group (WG) decided to implement the IEEE 802.16m project in late 2006 with the aim of creating an amendment specification for the existing IEEE 802.16e as a standard for IMT-Advanced systems. As can be seen from the above objectives, the IEEE 802.16m standard implies two aspects: the past continuity of modification of the IEEE 802.16e standard and the future continuity of the specification for next generation IMT-Advanced systems. Therefore, the IEEE 802.16m standard is required to satisfy all the advanced requirements for the IMT-Advanced system while maintaining compatibility with the Mobile WiMAX system based on the IEEE 802.16e standard.

In the case of broadband wireless communication systems, effective transmission and reception techniques and utilization methods have been proposed to maximize the efficiency of limited radio resources. One of the systems considered in the next generation wireless communication system is an Orthogonal Frequency Division Multiplexing (OFDM) system that can attenuate inter-symbol interference (ISI) effects with low complexity. OFDM converts serially input data symbols into N parallel data symbols and carries them on N subcarriers, respectively. The subcarriers maintain orthogonality in the frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, thereby reducing complexity at the receiving end and lengthening the interval of transmitted symbols, thereby minimizing inter-symbol interference.

Orthogonal Frequency Division Multiple Access (OFDMA) refers to a multiple access method for realizing multiple access by independently providing each user with a portion of available subcarriers in a system using OFDM as a modulation method. OFDMA provides each user with a frequency resource called a subcarrier, and each frequency resource is provided to a plurality of users independently so that they do not overlap each other. Eventually, frequency resources are allocated mutually exclusively for each user. In an OFDMA system, frequency diversity scheduling can be obtained through frequency selective scheduling, and subcarriers can be allocated in various forms according to permutation schemes for subcarriers. In addition, the spatial multiplexing technique using multiple antennas can increase the efficiency of the spatial domain.

Multiple input multiple output (MIMO) may be considered as a technology for supporting reliable high speed data service. MIMO technology uses multiple transmit antennas and multiple receive antennas to improve data transmission and reception efficiency. MIMO techniques include spatial multiplexing, transmit diversity, beamforming, and the like. The MIMO channel matrix according to the number of receive antennas and the number of transmit antennas may be decomposed into a plurality of independent channels. Each independent channel is called a layer or stream. The number of layers is called rank.

A pilot may be transmitted from the base station to the terminal through downlink. The pilot may be called a reference signal or the like according to a wireless communication system. Channel estimation may be performed using the pilot, or the channel quality indicator (CQI) may be measured. The CQI may include SINR, frequency offset estimation, and the like. In order to optimize the performance of the system in different transmission environments, the 802.16m system provides a common pilot structure and a dedicated pilot structure. The common pilot structure and the dedicated pilot structure may be distinguished according to resources used. The public pilot can be used by all terminals. The dedicated pilot may be used by a terminal to which specific resources are allocated. Therefore, the dedicated pilot may be precoded or beamformed in the same manner as a data subcarrier. The pilot structure may be defined up to eight transport streams, and may have a unified pilot structure according to the public pilot and the dedicated pilot.

The midamble is a signal transmitted by the base station in order for the terminal to directly measure the channel state. When the base station transmits a signal using a MIMO technology through a plurality of antennas, the antenna transmits a different signal for each antenna or a different position in a resource region, and the terminal receives the midamble to determine the channel state of each antenna of the base station. By measuring, a channel state of a serving cell or an interference level of a neighbor cell may be estimated. The base station may adaptively schedule resources by receiving the channel state estimated by the terminal.

In transmitting the midamble for each antenna, a frequency partition or a reuse factor should be taken into consideration. In this case, the midamble transmitted from each antenna may be multiplexed in various ways. There is a need for a method of multiplexing the midamble considering the frequency partition or the reuse factor.

The present invention provides a method and apparatus for transmitting a midamble in a wireless communication system.

In one aspect, a method of transmitting a midamble in a wireless communication system is provided. The method generates a midamble sequence for each of a plurality of antennas, maps the generated midamble sequence to a plurality of subcarriers included in a resource region, and maps the mapped midamble sequence to each antenna. Including transmission to the terminal, wherein the plurality of subcarriers are included in any one of a plurality of frequency partitions, each frequency partition is applied with a different transmission power (transmission power), each of the midamble sequence Is multiplexed in the resource domain. Each of the midamble sequences may be multiplexed based on at least one multiplexing scheme of frequency division multiplexing (FDM) / code division multiplexig (CDM) / time division multiplexing (TDM). The number of the plurality of antennas may be any one of two, four, and eight. Each midamble sequence may be generated in units of one subband including 72 adjacent subcarriers in the resource region. When the reuse factor of the resource region is 3, each midamble sequence may be mapped at 12 subcarrier intervals. Each midamble sequence may be transmitted in a second downlink subframe in a radio frame including a plurality of subframes in a time domain. Each midamble sequence may be mapped to a first Orthogonal Frequency Division Multiplexing (OFDM) symbol of the second downlink subframe.

In another aspect, a midamble transmission apparatus in a wireless communication system is provided. The apparatus includes a transmission circuit for transmitting a midamble sequence for each of a plurality of antennas to a terminal through the plurality of antennas, a midamble sequence generator for generating the midamble sequence, and the midamble sequence in a resource region. And a subcarrier mapper for mapping to a plurality of subcarriers, wherein the plurality of subcarriers are included in any one of a plurality of frequency partitions, and each of the frequency partitions has a different transmit power, and each of the midambles The sequence is characterized in that it is multiplexed in the resource domain. Each of the midamble sequences may be multiplexed based on at least one multiplexing scheme of FDM / CDM / TDM. The number of the plurality of antennas may be any one of two, four, and eight. Each midamble sequence may be generated based on one subband including 72 adjacent subcarriers in the resource region. When the reuse factor of the resource region is 3, each midamble sequence may be mapped at 12 subcarrier intervals.

In another aspect, a midamble receiving apparatus in a wireless communication system is provided. The apparatus includes a plurality of midamble sequences transmitted from a base station and a reception circuit for receiving a radio signal, a channel estimator for measuring channel states for each antenna based on the plurality of midamble sequences, and the measured channel states. And a processor for processing the radio signal, wherein the plurality of midamble sequences are mapped to a plurality of subcarriers in a resource region, wherein the plurality of subcarriers are included in any one of a plurality of frequency partitions, and each frequency partition Different transmit powers are applied, and each of the plurality of midamble sequences is multiplexed in a resource domain. The plurality of midamble sequences may be multiplexed based on a multiplexing scheme of at least one of FDM / CDM / TDM, respectively. Each of the plurality of midamble sequences may be generated based on one subband including 72 adjacent subcarriers in the resource region.

By applying the transmission power of each frequency partition to the midamble and transmitting, the interference level of a serving cell or a neighbor cell can be measured more accurately.

(Created later)

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various wireless communication systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA), or the like. IEEE 802.16m is an evolution of IEEE 802.16e and provides backward compatibility with systems based on IEEE 802.16e. UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is part of Evolved UMTS (E-UMTS) using Evolved-UMTS Terrestrial Radio Access (E-UTRA), which employs OFDMA in downlink and SC in uplink -FDMA is adopted. LTE-A (Advanced) is the evolution of 3GPP LTE.

For clarity, the following description focuses on IEEE 802.16m, but the technical spirit of the present invention is not limited thereto.

1 illustrates a wireless communication system.

The wireless communication system 10 includes at least one base station (BS) 11. Each base station 11 provides a communication service for a particular geographic area (generally called a cell) 15a, 15b, 15c. The cell may again be divided into multiple regions (referred to as sectors). The UE 12 may be fixed or mobile, and may have a mobile station (MS), a mobile terminal (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a PDA ( Other terms may be referred to as a personal digital assistant, a wireless modem, a handheld device, etc. The base station 11 generally refers to a fixed station that communicates with the terminal 12. It may be called other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), and an access point.

The UE belongs to one cell, and the cell to which the UE belongs is called a serving cell. A base station that provides a communication service for a serving cell is called a serving BS. Since the wireless communication system is a cellular system, there are other cells adjacent to the serving cell. Another cell adjacent to the serving cell is called a neighbor cell. A base station that provides communication service for a neighbor cell is called a neighbor BS. The serving cell and the neighbor cell are relatively determined based on the terminal.

This technique can be used for downlink or uplink. In general, downlink means communication from the base station 11 to the terminal 12, and uplink means communication from the terminal 12 to the base station 11. In downlink, the transmitter may be part of the base station 11 and the receiver may be part of the terminal 12. In uplink, the transmitter may be part of the terminal 12 and the receiver may be part of the base station 11.

2 shows an example of a frame structure.

Referring to FIG. 2, a superframe (SF) includes a superframe header (SFH) and four frames (frames, F0, F1, F2, and F3). Each frame in the superframe may have the same length. The size of each superframe is 20ms and the size of each frame is illustrated as 5ms, but is not limited thereto. The length of the superframe, the number of frames included in the superframe, the number of subframes included in the frame, and the like may be variously changed. The number of subframes included in the frame may be variously changed according to a channel bandwidth and a length of a cyclic prefix (CP).

The superframe header may carry essential system parameters and system configuration information. The superframe header may be located in the first subframe in the superframe. The superframe header may be classified into primary SFH (P-SFH) and secondary SFH (S-SFH; secondary-SFH). P-SFH and S-SFH may be transmitted every superframe.

One frame includes a plurality of subframes (subframe, SF0, SF1, SF2, SF3, SF4, SF5, SF6, SF7). Each subframe may be used for uplink or downlink transmission. One subframe includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain and a plurality of subcarriers in the frequency domain. An OFDM symbol is used to represent one symbol period, and may be called another name such as an OFDMA symbol, an SC-FDMA symbol, and the like according to a multiple access scheme. The subframe may be composed of 5, 6, 7, or 9 OFDM symbols, but this is only an example and the number of OFDM symbols included in the subframe is not limited. The number of OFDM symbols included in the subframe may be variously changed according to the channel bandwidth and the length of the CP. A type of a subframe may be defined according to the number of OFDM symbols included in the subframe. For example, the type-1 subframe may be defined to include 6 OFDM symbols, the type-2 subframe includes 7 OFDM symbols, the type-3 subframe includes 5 OFDM symbols, and the type-4 subframe includes 9 OFDM symbols. have. One frame may include subframes of the same type. Alternatively, one frame may include different types of subframes. That is, the number of OFDM symbols included in each subframe in one frame may be all the same or different. Alternatively, the number of OFDM symbols of at least one subframe in one frame may be different from the number of OFDM symbols of the remaining subframes in the frame.

A time division duplexing (TDD) scheme or a frequency division duplexing (FDD) scheme may be applied to the frame. In the TDD scheme, each subframe is used for uplink transmission or downlink transmission at different times at the same frequency. That is, subframes in a frame of the TDD scheme are classified into an uplink subframe and a downlink subframe in the time domain. In the FDD scheme, each subframe is used for uplink transmission or downlink transmission at different frequencies at the same time. That is, subframes in the frame of the FDD scheme are divided into an uplink subframe and a downlink subframe in the frequency domain. Uplink transmission and downlink transmission occupy different frequency bands and may be simultaneously performed.

The subframe includes a plurality of physical resource units (PRUs) in the frequency domain. The PRU is a basic physical unit for resource allocation and is composed of a plurality of OFDM symbols consecutive in the time domain and a plurality of subcarriers consecutive in the frequency domain. The number of OFDM symbols included in the PRU may be equal to the number of OFDM symbols included in one subframe. Thus, the number of OFDM symbols in the PRU may be determined according to the type of subframe. For example, when one subframe consists of 6 OFDM symbols, the PRU may be defined with 18 subcarriers and 6 OFDM symbols.

 Logical Resource Units (LRUs) are basic logical units for distributed resource allocation and contiguous resource allocation. The LRU is defined by a plurality of OFDM symbols and a plurality of subcarriers and includes pilots used in a PRU. Thus, the appropriate number of subcarriers in one LRU depends on the number of pilots assigned.

Distributed Logical Resource Units (DLRUs) may be used to obtain frequency diversity gains. The DRU includes subcarrier groups distributed in one frequency partition. The size of the DRU is equal to the size of the PRU. The smallest unit that forms a DRU is one subcarrier.

Contiguous Logical Resource Units (CLRUs) may be used to obtain frequency selective scheduling gains. The CRU includes a local subcarrier group. The size of the CRU is equal to the size of the PRU.

Meanwhile, in a cellular system in which multi-cells exist, a fractional frequency reuse (FFR) technique may be used. The FFR technique divides an entire frequency band into a plurality of frequency partitions (FPs) and allocates a frequency partition to each cell. Different frequency partitions may be allocated between adjacent cells through the FFR scheme, and the same frequency partition may be allocated between distant cells. Accordingly, inter-cell interference (ICI) may be reduced, and performance of a cell edge terminal may be improved.

3 shows an example of a method of dividing an entire frequency band into a plurality of frequency partitions.

Referring to FIG. 3, the entire frequency band is divided into a first frequency partition FP0, a second frequency partition FP1, a third frequency partition FP2, and a fourth frequency partition FP3. Each frequency partition may be divided logically and / or physically from the entire frequency band.

4 shows an example of a cellular system in which the FFR technique is used.

Referring to FIG. 4, each cell is divided into an inner cell and a cell edge. In addition, each cell is divided into three sectors. The entire frequency band is divided into four frequency partitions FP0, FP1, FP2, and FP3.

The first frequency partition FP0 is allocated inside the cell. Each sector of the cell edge is allocated any one of the second frequency partition FP1 to the fourth frequency partition FP3. In this case, different frequency partitions are allocated between adjacent cells. Hereinafter, the assigned frequency partition is referred to as an active frequency partition, and the unassigned frequency partition is referred to as an inactive frequency partition. For example, when the second frequency partition FP1 is allocated, the second frequency partition is an active frequency partition, and the third frequency partition FP2 and the fourth frequency partition FP3 become inactive frequency partitions.

The frequency reuse factor (FRF) may be defined as how many cells (or sectors) the entire frequency band can be divided into. In this case, the frequency reuse coefficient inside the cell may be 1, and the frequency reuse coefficient of each sector at the cell edge may be 3.

5 shows an example of a downlink resource structure.

Referring to FIG. 5, the downlink subframe may be divided into at least one frequency partition. Here, the subframe is divided into two frequency partitions (FP1, FP2) by way of example, but the number of frequency partitions in the subframe is not limited thereto. The downlink subframe may be divided into up to four frequency partitions. Each frequency partition may be used for other purposes, such as FFR or multicast broadcast service (MBS).

Each frequency partition consists of at least one PRU. Each frequency partition may include distributed resource allocation and / or contiguous resource allocation. The distributed resource allocation may be a DLRU, and the contiguous resource allocation may be a CLRU. Here, the second frequency partition FP2 includes distributed resource allocation and continuous resource allocation. 'Sc' means a subcarrier.

When a plurality of cells are present, the downlink resource may be mapped through a process such as subband partitioning, miniband permutation, frequency partitioning, or the like.

First, the subband partitioning process will be described.

6 shows an example of a subband partitioning process. 6 shows a subband partitioning process when the bandwidth is 10Mhz.

The plurality of PRUs are divided into subbands (SBs) and minibands (MBs). In FIG. 6- (a), a plurality of PRUs are allocated to subbands, and in FIG. 6- (b), a plurality of PRUs are allocated to minibands. The subband contains N1 contiguous PRUs, and the miniband contains N2 contiguous PRUs. N1 = 4 and N2 = 1. Subbands are suitable for frequency selective resource allocation because contiguous PRUs are allocated in the frequency domain. Minibands are suitable for frequency-distributed resource allocation and can be permuted in the frequency domain.

The number of subbands may be represented by K _SB . The number of PRUs allocated to a subband may be represented by L _SB , and L _SB = N1 * K _SB . K _SB can vary in bandwidth. K _SB may be determined by a downlink subband allocation count (DSAC). The length of the DSAC may be 3 to 5 bits, and may be broadcasted through SFH. The remaining PRUs allocated to the subbands are allocated to the minibands. The number of minibands can be represented by K _MB . The number of PRUs allocated to the miniband may be represented by L _MB , where L _MB = N2 * K _MB . The total number of PRUs is N _PRU = L _SB + L _MB .

The plurality of PRUs are divided into subbands and minibands and rearranged in subband PRUs (PRU _SBs ) and miniband PRUs (PRU _MBs ). The PRUs in the PRU _SB are each indexed to any of 0-(L _SB -1), and the PRUs in the PRU _MB are each indexed to either 0-(L _MB -1).

7 shows an example of a miniband permutation process. In the miniband permutation process, the PRU _MB is mapped to a permutation PRU (PPRU _MB ). This is to ensure frequency diversity in each frequency partition. FIG. 7 may be performed following the subband partitioning process of FIG. 6 when the bandwidth is 10 MHz. PRUs in the PRU _MB are permuted and mapped to the PPRU _MB .

8 shows an example of a frequency partitioning process. 8 may be performed after the subband partitioning process of FIG. 6 and the miniband permutation process of FIG. 7 when the bandwidth is 5 MHz. PRUs of PRU _SB and PPRU _MB are allocated to at least one frequency partition. The number of frequency partitions may be up to four. The frequency partition configuration information may be determined by downlink frequency partition configuration (DFPC). The configuration of the DFPC may vary depending on the bandwidth, and may be broadcasted through S-SFH. The DFPC may indicate the size of the frequency partition, the number of frequency partitions, and the like. Frequency Partition Count (FPCT) indicates the number of frequency partitions. FPSi represents the number of PRUs allocated to the i-th frequency partition FPi. In addition, the downlink frequency partition subband count (DFPSC) defines the number of subbands allocated to FPi (i> 0). The DFPSC may have a length of 1 bit to 3 bits.

9 shows a structure of downlink MIMO in a transmitter. In order to perform downlink MIMO, the transmitter may include a MIMO encoder 51, a precoder 52, and a subcarrier mapper 53. The MIMO encoder 51 maps L (L ≧ 1) MIMO layers into Mt (Mt ≧ L) MIMO streams. In the case of spatial multiplexing in single-user MIMO (SU-MIMO), a rank is defined as the number of streams to be used by a user assigned to a resource unit. In SU-MIMO, one resource unit is allocated to only one user, and only one Forward Error Correction (FEC) block exists as an input of the MIMO encoder 51. In the case of multi-user MIMO, a plurality of users may be allocated to one resource unit. Therefore, a plurality of FEC blocks may exist as an input of the MIMO encoder 51. The Mt MIMO streams are input to the precoder 52. The precoder 52 generates a plurality of antenna-specific data symbols according to the selected MIMO mode and maps Mt MIMO streams to each antenna. The subcarrier mapper 53 maps each antenna specific data symbol to an OFDM symbol.

The channel state can be measured for each antenna through the MIMO midamble (hereinafter, referred to as a midamble). The terminal may receive the midamble from each antenna and measure the channel state and the degree of interference from adjacent cells. The base station may adaptively schedule the resource by receiving the channel state measured by the terminal. In the case of a closed-loop MIMO, the midamble may be used to select a precoding matrix indicator (PMI). In the case of open-loo MIMO, the midamble can be used to measure the channel quality indicator (CQI). In addition, the midamble may be transmitted in the second downlink subframe of each frame. The midamble may occupy one OFDM symbol in the second downlink subframe. When the subframe consists of six OFDM symbols (type 1 subframe), the subframe may consist of the remaining five OFDM symbols (type 3 subframe). In addition, when the subframe consists of 7 OFDM symbols (type 2 subframe), the subframe may be composed of the remaining 6 OFDM symbols (type 1 subframe).

The midamble is transmitted in the form of a sequence. Various kinds of sequences may be used as the midamble sequence, and in particular, the Golay sequence may be used as the midamble sequence. Table 1 shows an example of a Golay sequence having a length of 2048 bits.

0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0x121D 0x12E2 0x121D 0xED1D 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0x121D 0x12E2 0xEDE2 0x12E2 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D

The midamble signal s (t) transmitted by each antenna may be determined by Equation 1.

k is the subcarrier index, N _used is the number of subcarriers to which the midamble sequence is mapped, f _c is the frequency of the carrier, Δf is the subcarrier spacing, and Tg is the guard time. b _k is a complex coefficient that modulates subcarriers within an OFDM symbol to which a midamble is mapped.

Meanwhile, when transmitting the midamble, it is necessary to consider the frequency partition. The configuration of frequency partitions may be different for each cell, and each frequency partition may set different transmission powers differently. Data transmitted in each frequency partition is transmitted according to the transmission power of each frequency partition, and the midamble used to measure the channel state is also transmitted by applying the transmission power of each frequency partition. Therefore, if the transmission power of each frequency partition is not taken into account, the channel state of the serving cell or the degree of interference of neighboring cells cannot be accurately measured. Therefore, a method of constructing a midamble considering the transmission power of each frequency partition needs to be proposed.

10 is an embodiment of a proposed midamble transmission method.

In step S100, the base station generates a midamble sequence for each of the plurality of antennas. In step S110, the base station maps the generated midamble sequence to a plurality of subcarriers included in a resource region. The plurality of subcarriers are included in any one of a plurality of frequency partitions, and different transmission powers are applied to each frequency partition. In step S120, the mapped midamble sequence is transmitted to the terminal for each antenna.

11 is an example of a midamble configuration in a resource region according to the proposed midamble transmission method. The entire resource region is divided into a plurality of subbands. The midamble is mapped to one OFDM symbol in subband units. However, the proposed invention is not limited thereto, and the midamble may be mapped to two or more OFDM symbols. The frequency partition consists of a plurality of distributed subbands and transmits data at respective transmission powers. The first frequency partition FP0 transmits data at a first transmit power Tx power 0 and the second frequency partition FP1 transmits at a second transmit power Tx power 1. Accordingly, the midamble transmitted in the first frequency partition is transmitted at the first transmission power, and the midamble transmitted in the second frequency partition is transmitted at the second transmission power.

In addition, when the midamble is transmitted, not all of the resource regions may be used, but only some of them may be used. For example, the subcarrier may be divided for each cell in consideration of the reuse factor, and thus the midamble may be mapped and transmitted. For example, if the reuse factor is 3, each cell uses only one-third of the distributed or adjacent subcarriers of the subcarriers assigned to the midambles and reserves the remaining subcarriers for the midambles of other cells. In this case, the subcarriers allocated to the midamble of each cell may be configured in various ways. For example, the first cell is the 3kth subcarrier of all subcarriers, the second cell is the (3k + 1) th subcarrier of all subcarriers, and the third cell is the (3k + 2) th of all subcarriers (where k = 0,1). , ...) subcarriers can be assigned to the midamble.

In addition, when the number of antennas transmitting the midamble of each cell is N, each cell may allocate N adjacent subcarriers to the midamble. For example, if the reuse factor is 3 and the number of antennas transmitting the midamble is N, the first cell allocates N adjacent subcarriers to the midamble and 2N numbers for the midambles of the second and third cells. Reserve subcarriers. Subcarriers are allocated to the midambles of the second and third cells, and N adjacent subcarriers are allocated to the midambles. In the following embodiment, it is assumed that the FFR technique is not applied, but the present invention is not limited thereto, and it can be considered that the configuration of the midamble in each cell after the reuse factor is applied.

The midamble may be transmitted in the form of a sequence, and the midamble sequence may be mapped to a subcarrier by applying various multiplexing schemes.

12 shows another example of a midamble configuration according to the proposed midamble transmission method.

The midamble sequence is constructed over the entire bandwidth. All subcarriers constituting the midamble are multiplexed by frequency division multiplexing (FDM) and allocated to each antenna, and a midamble sequence is mapped to subcarriers of each antenna. That is, the subcarriers constituting the resource region are sequentially assigned to a plurality of antennas, and the midamble sequence is multiplexed and mapped to the subcarriers assigned to each antenna by the FDM scheme. In this example, it is assumed that the FDM scheme is multiplexed, but various types of multiplexing schemes may be applied, and multiplexing schemes such as CDM (Code Division Multiplexing) or CDM / FDM hybrid may be applied. In the case of transmitting the midamble over the entire band, the length of the midamble sequence is increased, and thus the midamble detection performance of the UE can be improved. On the other hand, since the subcarriers constituting one midamble sequence vary the transmit power according to each frequency partition, detection performance may decrease accordingly.

13 shows another example of a midamble configuration according to the proposed midamble transmission method.

The midamble sequence is composed of subband units rather than the entire resource region. Since one subband includes four adjacent PRUs and one PRU may include 18 subcarriers, the length of the midamble sequence may be 72. The midamble sequence of length 72 is mapped to 72 adjacent subcarriers, and each antenna is multiplexed using the CDM scheme. That is, if the number of midamble sequences is N and the number of antennas for transmitting the midamble by the UE is A, each antenna may use N / A midamble sequences and transmit a predetermined midamble sequence for each cell. Can be. The terminal receives the multiplexed midamble sequence by the CDM method at each antenna.

14 shows another example of a midamble configuration according to the proposed midamble transmission method.

The midamble sequence is composed of subband units rather than the entire resource region. The midamble sequence of length 72 is mapped to 72 adjacent subcarriers, and each antenna is multiplexed by FDM. If the number of antennas transmitting the midamble is A, the midamble sequence of each antenna has a length of 72 / A. For example, if the number of antennas is eight, the midamble sequence of each antenna is mapped to nine subcarriers. That is, as the number of antennas increases, the length of the midamble sequence becomes shorter, so that the midamble detection performance of the terminal may decrease.

15 shows another example of a midamble configuration according to the proposed midamble transmission method.

The midamble sequence is composed of subband units rather than the entire resource region. The midamble sequence of length 72 is mapped to 72 adjacent subcarriers, and each antenna is multiplexed in a CDM / FDM hybrid scheme. That is, some antennas are multiplexed by the FDM scheme and the other antennas are multiplexed by the CDM scheme. For example, odd-numbered antennas are multiplexed in the CDM scheme to odd-numbered subcarriers in a subband, even-numbered antennas are multiplexed in the CDM scheme to even-numbered subcarriers in a subband, and odd-numbered and even-numbered antennas are multiplexed in the FDM scheme. Can be.

When the midamble sequences are allocated in units of subbands as shown in FIGS. 13 to 15, each midamble sequence is transmitted at the same transmit power as that of the frequency partition of each cell. The UE may receive the midamble sequence to which the transmission power of the frequency partition is applied for each cell. If the reuse factor is 3, the midamble sequence is mapped to 72/3 = 24 subcarriers for each subband. In the case of assigning the midamble sequence in subband units, since the sequence length is shorter than in the case of allocating the midamble sequence to the entire band, the detection performance may be reduced, but the advantage of detecting the midamble sequence within the same transmission power is advantageous. have.

Alternatively, the midamble sequence may be configured in units of subbands constituting the same frequency partition, and transmission power according to the frequency partition may be applied. If the number of subbands constituting one frequency partition is n, the total number of subcarriers constituting one frequency partition is 72n. The midamble sequence is configured using 72n subcarriers, and the multiplexing method of FIGS. 13 to 15 may be used as a method of assigning the midamble sequence to each antenna. If the reuse factor is 3, the midamble sequence is mapped to 72n / 3 = 24n subcarriers for each subband. In the case of configuring the midamble sequence by subbands in one frequency partition, orthogonality may be broken because the channel state is different for each subband, but the length of the sequence may be increased, thereby improving the midamble detection performance of the UE. You can.

16 illustrates an example of a midamble structure according to the proposed midamble transmission method when the reuse factor 3 is applied. By using the reuse factor 3, signals in adjacent cells can be distinguished from each other, and inter-cell interference (ICI) can be reduced. The midamble structure of FIG. 16 shows a case in which a midamble sequence is configured in subband units as shown in FIG. 14 and each midamble sequence is multiplexed using the FDM scheme. Since the reuse factor is 3, each cell transmits the midamble sequence based on one of A, B, and C patterns. 16- (a) and 16- (b) show midamble sequences allocated to 1/2 subbands in the frequency domain, respectively. FIG. 16- (a) shows an example of the midamble structure when there are four antennas, and FIG. 16- (b) shows an example of the midamble structure when there are two antennas. Here, the position of the antenna may vary for each subband. That is, the position of the antenna within each pattern may be cyclically shifted according to the subband index. The midamble configuration of FIG. 16 may be represented by Equation 2. Equation 2 embodies the coefficient b _k of Equation 1, and the index k of the subcarrier to which the midamble sequence is mapped may be determined.

k is the index of the subcarrier (0≤k≤N _used -1), N _used is the number of subcarriers to which the midamble sequence is mapped, Nt is the number of transmit antennas, and G (x) is a Golay having a length of 2048 bits in Table 1. A sequence (0 ≦ x <2047), fft represents the size of the FFT, and BSID represents the cell ID. u may be determined by u = mod (BSID, 128) as a shift value (0 ≦ u ≦ 127).

offset _D (fft) is an offset value that depends on the FFT size. Table 2 shows the offset values according to the FFT size.

FFT size Offset 2048 30 1024 60 512 40

In addition, g is an index of the transmission antenna, s is a parameter that changes depending on k, where s = 0 when k≤ (N _used -1) / 2 and s = 1 when k> (N _used -1) / 2. .

17 is a block diagram of a base station and a terminal in which an embodiment of the present invention is implemented.

The transmitter 800 includes a midamble sequence generating unit 810, a subcarrier mapper 820, and a transmit circuitry 830. The midamble sequence generator 810 generates a midamble sequence. The subcarrier mapper 820 maps the midamble sequence to a plurality of subcarriers included in a resource region. The transmitting circuit 830 transmits a midamble sequence for each of the plurality of antennas to the terminal through the plurality of antennas 890-1,. The plurality of subcarriers are included in any one of a plurality of frequency partitions, different frequency powers are applied to each frequency partition, and each midamble sequence is multiplexed in a resource domain. Each of the midamble sequences may be multiplexed based on at least one of FDM / CDM / TDM multiplexing schemes, and each of the midamble sequences may be configured based on one subband including 72 adjacent subcarriers in the resource region. Can be generated. Accordingly, the midamble sequence of FIGS. 11 to 16 may be configured.

The receiver 900 includes a processor 910, a channel estimator 920, and a receiver circuit 930. The receiving circuit 930 receives a plurality of midamble sequences and radio signals transmitted from a base station. The channel estimator 920 measures a channel state for each antenna based on the plurality of midamble sequences. The processor 910 processes the radio signal based on the measured channel state. The plurality of midamble sequences are mapped to a plurality of subcarriers in a resource region, the plurality of subcarriers are included in any one of a plurality of frequency partitions, and each of the plurality of frequency partitions has different transmit powers applied thereto. Each amble sequence may be multiplexed in the resource domain. At least one multiplexing scheme of FDM / CDM / TDM may be used as the multiplexing scheme, and each of the plurality of midamble sequences may be configured based on one subband including 72 adjacent subcarriers in the resource region. Can be generated.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In the software implementation, the module may be implemented as a module that performs the above-described function. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (15)

In the midamble transmission method in a wireless communication system,
Generate a midamble sequence for each of the plurality of antennas,
The generated midamble sequence is mapped to a plurality of subcarriers included in a resource region.
It includes transmitting the mapped midamble sequence to the terminal for each antenna,
The plurality of subcarriers are included in any one of a plurality of frequency partitions, each frequency partition is applied with a different transmission power (transmission power),
Wherein each midamble sequence is multiplexed in a resource domain. The method of claim 1,
Each of the midamble sequences is multiplexed based on a multiplexing scheme of at least one of frequency division multiplexing (FDM) / code division multiplexig (CDM) / time division multiplexing (TDM). The method of claim 1,
The number of the plurality of antennas, characterized in that any one of two, four and eight. The method of claim 1,
Wherein each midamble sequence is generated in units of one subband including 72 adjacent subcarriers in the resource region. The method of claim 4, wherein
If the reuse factor of the resource zone is 3,
Wherein each midamble sequence is mapped at intervals of 12 subcarriers. The method of claim 1,
Wherein each midamble sequence is transmitted in a second downlink subframe in a radio frame including a plurality of subframes in a time domain. The method according to claim 6,
Wherein each midamble sequence is mapped to a first Orthogonal Frequency Division Multiplexing (OFDM) symbol of the second downlink subframe. In the midamble transmission apparatus in a wireless communication system,
A transmission circuit for transmitting a midamble sequence for each of a plurality of antennas to the terminal through the plurality of antennas, respectively; And
A midamble sequence generator for generating the midamble sequence; And
A subcarrier mapper for mapping the midamble sequence to a plurality of subcarriers included in a resource region;
The plurality of subcarriers are included in any one of a plurality of frequency partitions, each frequency partition is applied with a different transmission power (transmission power),
Each of the midamble sequences is multiplexed in a resource region. The method of claim 8,
Each of the midamble sequences is multiplexed based on a multiplexing scheme of at least one of frequency division multiplexing (FDM) / code division multiplexing (CDM) / time division multiplexing (TDM). The method of claim 8,
The number of the plurality of antennas, the base station, characterized in that any one of two, four and eight. The method of claim 8,
Each of the midamble sequences is generated based on one subband including 72 adjacent subcarriers in the resource region. The method of claim 11,
If the reuse factor of the resource zone is 3,
Each of the midamble sequences is mapped to 12 subcarrier intervals. In the midamble receiving apparatus in a wireless communication system,
A receiving circuit for receiving a plurality of midamble sequences and radio signals transmitted from a base station;
A channel estimator for measuring a channel state for each antenna based on the plurality of midamble sequences; And
A processor for processing the wireless signal based on the measured channel state,
The plurality of midamble sequences are mapped to a plurality of subcarriers in a resource domain.
The plurality of subcarriers are included in any one of a plurality of frequency partitions, each frequency partition is applied with a different transmission power (transmission power),
Each of the plurality of midamble sequences is multiplexed in a resource domain. The method of claim 13,
And the plurality of midamble sequences are multiplexed based on at least one multiplexing scheme of frequency division multiplexing (FDM), code division multiplexing (CDM), and time division multiplexing (TDM). The method of claim 13,
Each of the plurality of midamble sequences is generated in units of one subband including 72 adjacent subcarriers in the resource region.

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