KR20100093498A - Method and appratus for transmitting data in multiple antenna system - Google Patents

Abstract

PURPOSE: A method and an apparatus for transmitting data in a multiple antenna system are provided to transmit multiple codeword maintaining a single transmitting-wave characteristic. CONSTITUTION: A modulation mapper modulates codeword into modulation symbols which indicates the location of a signal constellation. A layer permutator maps the modulation symbols on different layers, respectively. A converting pre-coder discrete-Fourier-transform(DFT)s the mapped modulation symbols in order to generate the DFT symbol in a frequency region. A resource mapper maps the DFT symbol on a resource. A signal generator generates a single carrier-frequency division multiple access in a time region using the mapped DFT symbol. The modulation order of the modulation symbols is determined according to the mapped layer by the layer permutator.

Description

METHOOD AND APPRATUS FOR TRANSMITTING DATA IN MULTIPLE ANTENNA SYSTEM}

The present invention relates to wireless communications, and more particularly, to a data transmission apparatus and method in a multi-antenna system.

The next generation multimedia wireless communication system, which is being actively researched recently, requires a system capable of processing and transmitting various information such as video, wireless data, etc., out of an initial voice-oriented service. The purpose of a wireless communication system is to enable a large number of users to communicate reliably regardless of location and mobility. By the way, the wireless channel may include path loss, shadowing, fading, noise, limited bandwidth, power limitation of the terminal, and interference between different users. There are various problems. Other challenges in the design of wireless communication systems include resource allocation, mobility issues related to rapidly changing physical channels, portability, and the provision of security and privacy. Include design.

When a transport channel undergoes deep fading, the receiver is difficult to determine the transmitted signal unless another version or replica of the transmitted signal is transmitted separately. The resources corresponding to these separate versions or copies are called diversity and are one of the most important factors contributing to reliable transmission over the radio channel. By using such diversity, data transmission capacity or data transmission reliability can be maximized. A system that implements diversity using multiple transmission antennas and multiple reception antennas is called a multiple input multiple output (MIMO) system.

Techniques for implementing diversity in MIMO systems include Space Frequency Block Code (SFBC), Space Time Block Code (STBC), Cyclic Delay Diversity (CDD), frequency switched transmit diversity (FSTD), time switched transmit diversity (TSTD), Precoding Vector Switching (PVS) and Spatial Multiplexing (SM).

On the other hand, one of the systems considered in the 3rd generation and later systems is an Orthogonal Frequency Division Multiplexing (OFDM) system that can attenuate the effect of inter-symbol interference with low complexity. OFDM converts serially input data into N parallel data and transmits the data on N orthogonal subcarriers. Subcarriers maintain orthogonality in the frequency dimension. 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 scheme.

However, one of the main problems of the OFDM / OFDMA system is that the Peak-to-Average Power Ratio (PAPR) can be very large. The PAPR problem is caused by the fact that the peak amplitude of the transmitted signal is much larger than the average amplitude, due to the fact that the OFDM symbol is a superposition of N sinusoidal signals on different subcarriers. PAPR is a problem especially in terminals that are sensitive to power consumption in relation to battery capacity. To reduce power consumption, it is necessary to lower the PAPR.

One system proposed to lower PAPR is Single Carrier-Frequency Division Multiple Access (SC-FDMA). SC-FDMA combines Frequency Division Multiple Access (FDMA) with Single Carrier-Frequency Division Equalization (SC-FDE). SC-FDMA has similar characteristics to OFDMA in that it modulates and demodulates data in time and frequency domain using Discrete Fourier Transform (DFT). . In particular, it can be said that it is advantageous for the uplink to communicate with the base station from the terminal sensitive to the transmission power in relation to the use of the battery. When the terminal transmits data to the base station, an important point is that the bandwidth of the data to be transmitted is not large, but wide coverage that can concentrate power. SC-FDMA systems allow for small amounts of signal variation, resulting in greater coverage than other systems when using the same power amplifier.

In order to apply the MIMO transmission technique used for multi-codeword transmission to an SC-FDMA system, it is important to maintain a single carrier characteristic to ensure low PAPR or low cubic metric (CM).

In a multi-antenna based SC-FDMA (Single Carrier-Frequency Division Multiple Access) system, a method of transmitting multiple codewords maintaining a low peak to average power ratio (PAPR) or CM is provided.

In the multiple antenna system according to an aspect of the present invention, a data transmission apparatus

A modulation mapper for modulating codewords into modulation symbols representing positions on a signal constellation, a layer permutator for mapping the modulation symbols to different layers, and a Discrete Fourier Transform on the modulation symbols mapped to the layers A transform precoder for generating a DFT symbol in a frequency domain by performing a step C), and a resource element mapper for mapping the DFT symbol to a physical resource element; And an SC-FDMA signal generator for generating a DFT symbol mapped to the resource element as an SC-FDMA signal in a time domain, wherein the modulation symbols are determined to be modulated according to a layer mapped by the layer permutator. It features.

According to another aspect of the present invention, there is provided a method of performing a DFT for transmitting a SC-FDMA signal, modulating an input codeword into modulation symbols representing positions on a signal constellation, and assigning the modulation symbols to different layers. Mapping; And DFT the modulation symbols mapped to the different layers, wherein the modulation symbols are determined according to the mapping layer.

In SC-FDMA system, multiple codewords can be transmitted with low PAPR or CM while maintaining a single carrier characteristic.

1 shows a wireless communication system.
2 illustrates a structure of a radio frame in a 3rd generation partnership project (3GPP) long term evolution (LTE).
3 shows an example of a resource grid for one uplink slot in 3GPP LTE.
4 shows an example of a structure of an uplink subframe in 3GPP LTE.
5 is a flowchart illustrating an example of a data transmission method.
6 illustrates an example of a radio resource in which data is transmitted in the case of a normal cyclic prefix (CP).
7 illustrates an example of a radio resource for transmitting data in the case of an extended CP.
8 is a block diagram illustrating an example of a transmitter structure.
9 is a block diagram illustrating an example of a structure of a data processor.
10 illustrates an example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.
11 shows another example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.
12 is a block diagram illustrating another example of a data processing unit structure.
13 is a block diagram illustrating still another example of a data processing unit structure.
14 is a block diagram illustrating another example of a data processing unit structure.
15 is a block diagram showing a structure of a transmitter according to an embodiment of the present invention.
16 shows a relationship between modulation mapping described in Table 8 and subsequent layer permutation.
17 is a block diagram showing a structure of a transmitter according to another embodiment of the present invention.

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 for various multiple access schemes. 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 by a wireless technology such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of 3GPP LTE.

For clarity, the following description focuses on 3GPP LTE / LTE-A, but the technical spirit of the present invention is not limited thereto.

1 illustrates a wireless communication system.

Referring to FIG. 1, the wireless communication system 10 includes at least one base station 11 (BS). 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 user equipment (UE) 12 may be fixed or mobile, and may include a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), It may be called other terms such as a wireless modem and a handheld device. The base station 11 generally refers to a fixed station communicating with the terminal 12, and may be referred to as other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like. have.

Hereinafter, downlink (DL) means communication from the base station to the terminal, and uplink (UL) means communication from the terminal to the base station. In downlink, a transmitter may be part of a base station, and a receiver may be part of a terminal. In uplink, a transmitter may be part of a terminal, and a receiver may be part of a base station.

The wireless communication system may be any one of a multiple input multiple output (MIMO) system, a multiple input single output (MIS) system, a single input single output (SISO) system, and a single input multiple output (SIMO) system. The MIMO system uses a plurality of transmit antennas and a plurality of receive antennas. The MISO system uses multiple transmit antennas and one receive antenna. The SISO system uses one transmit antenna and one receive antenna. The SIMO system uses one transmit antenna and multiple receive antennas.

Hereinafter, the transmit antenna means a physical or logical antenna used to transmit one signal or stream, and the receive antenna means a physical or logical antenna used to receive one signal or stream.

2 shows a structure of a radio frame in 3GPP LTE.

Referring to FIG. 2, a radio frame consists of 10 subframes, and one subframe consists of two slots. Slots in a radio frame are numbered from 0 to 19 slots. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). TTI may be referred to as a scheduling unit for data transmission. For example, one radio frame may have a length of 10 ms, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

The structure of the radio frame is merely an example, and the number of subframes included in the radio frame or the number of slots included in the subframe may be variously changed.

3 is an exemplary diagram illustrating a resource grid for one uplink slot in 3GPP LTE.

Referring to FIG. 3, an uplink slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain and includes N ^UL resource blocks (RBs) in a frequency domain. do. The OFDM symbol is for representing one symbol period, and may be referred to as an SC-FDMA symbol, an OFDMA symbol, or a symbol period according to a system. The RB includes a plurality of subcarriers in the frequency domain in resource allocation units. The number N ^UL of resource blocks included in an uplink slot depends on an uplink transmission bandwidth set in a cell. Each element on the resource grid is called a resource element.

Here, an exemplary resource block includes 7 × 12 resource elements including 7 OFDM symbols in the time domain and 12 subcarriers in the frequency domain, but the number of subcarriers and the OFDM symbols in the resource block is equal to this. It is not limited. The number of OFDM symbols or the number of subcarriers included in the resource block may be variously changed. The number of OFDM symbols may change depending on the length of a cyclic prefix (CP). For example, the number of OFDM symbols is 7 for a normal CP and the number of OFDM symbols is 6 for an extended CP.

In 3GPP LTE of FIG. 3, a resource grid for one uplink slot may be applied to a resource grid for a downlink slot.

4 shows an example of a structure of an uplink subframe in 3GPP LTE.

Referring to FIG. 4, an uplink subframe may be divided into a control region to which a physical uplink control channel (PUCCH) carrying uplink control information is allocated and a data region to which a physical uplink shared channel (PUSCH) carrying uplink data is allocated. have. In order to maintain a single carrier property, resource blocks allocated to one UE are contiguous in the frequency domain. One UE cannot transmit a PUCCH and a PUSCH at the same time.

PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers in each of a first slot and a second slot. The frequency occupied by RBs belonging to the RB pair allocated to the PUCCH is changed based on a slot boundary. By transmitting uplink control information through different subcarriers over time, the UE may obtain a frequency diversity gain. m is a location index indicating a logical frequency domain location of a resource block pair allocated to a PUCCH in a subframe.

The uplink control information transmitted on the PUCCH includes a hybrid automatic repeat request (HARQ) acknowledgment (ACK) / negative acknowledgment (NACK), a channel quality indicator (CQI) indicating a downlink channel state, and an SR radio resource allocation request (SR). scheduling request).

PUSCH is mapped to an uplink shared channel (UL-SCH) which is a transport channel. The uplink data transmitted on the PUSCH may be a transport block which is a data block for the UL-SCH transmitted during the TTI. The transport block may be user information. Alternatively, the uplink data may be multiplexed data. The multiplexed data may be a multiplexed transport block and control information for the UL-SCH. For example, control information multiplexed with data may include a CQI, a precoding matrix indicator (PMI), an HARQ ACK / NACK, a rank indicator (RI), and the like. Or, the uplink data may consist of control information only.

Hereinafter, a data transmission method is explained in full detail. The following description will be described based on uplink data transmitted by the terminal to the base station, but can also be applied to downlink data transmitted by the base station to the terminal.

5 is a flowchart illustrating an example of a data transmission method.

Referring to FIG. 5, the base station BS transmits an uplink grant to the terminal UE (S110). The terminal transmits uplink data using the uplink grant to the base station (S120). The uplink grant may be transmitted on a physical downlink control channel (PDCCH), and the uplink data may be transmitted on a PUSCH. The relationship between the subframe in which the PDCCH is transmitted and the subframe in which the PUSCH is transmitted may be previously defined between the base station and the terminal. For example, in a frequency division duplex (FDD) system, if a PDCCH is transmitted through subframe n, a PUSCH may be transmitted through subframe n + 4.

The uplink grant is downlink control information for uplink data scheduling. The uplink grant includes a resource allocation field. The uplink grant includes a hopping flag indicating whether frequency hopping is performed, a flag distinguishing an uplink grant from other downlink control information, and a transmission format field indicating a transmission format for uplink data. A new data indicator (NDI) indicating whether the uplink grant is for new uplink data transmission or retransmission of uplink data, and a transmit power control (TPC) command for uplink power control The field may further include a CS field indicating a cyclic shift (CS) of a demodulation reference signal (DM RS), a CQI request indicator indicating a CQI request, and the like.

The resource allocation field indicates a radio resource for uplink data transmission. The radio resource may be a time-frequency resource. The radio resource allocated by the resource allocation field in 3GPP LTE is a resource block. The UE may know the location of the resource block, the number of resource blocks, etc. in the subframe allocated to uplink data transmission using the resource allocation field.

If the hopping flag does not indicate frequency hopping, the resource blocks allocated by the UE in each of the first and second slots in the subframe are the same in the frequency domain. When the hopping flag indicates frequency hopping, the resource blocks allocated by the UE in each of the first slot and the second slot in the subframe may be different in the frequency domain.

Radio resource scheduling methods include dynamic scheduling, persistent scheduling, and semi-persistent scheduling (SPS). If the radio resource scheduling scheme is a continuous scheduling scheme or a semi-persistent scheduling scheme, the terminal may transmit uplink data without receiving an uplink grant.

Hereinafter, it is assumed that a radio resource to which data is transmitted includes a plurality of OFDM symbols in a time domain and a plurality of subcarriers in a frequency domain.

6 illustrates an example of a radio resource for transmitting data in the case of a normal CP.

Referring to FIG. 6, a subframe includes a first slot and a second slot. Each of the first slot and the second slot includes 7 OFDM symbols. 14 OFDM symbols in a subframe are symbol indexed from 0 to 13. The demodulation reference signal (DM RS) may be transmitted through OFDM symbols having symbol indices of 3 and 10. Data may be transmitted through the remaining OFDM symbols except for the OFDM symbol through which the demodulation reference signal is transmitted. The demodulation reference signal is a signal known to both the transmitter and the receiver used for channel estimation for demodulating the data.

7 illustrates an example of a radio resource for transmitting data in the case of an extended CP.

Referring to FIG. 7, a subframe includes a first slot and a second slot. Each of the first slot and the second slot includes 6 OFDM symbols. 12 OFDM symbols in a subframe are indexed from 0 to 11 symbols. The demodulation reference signal is transmitted through OFDM symbols having symbol indices of 2 and 8. Data is transmitted through the remaining OFDM symbols except for the OFDM symbol to which the demodulation reference signal is transmitted.

Although not shown in FIGS. 6 and 7, a sounding reference signal (SRS) may be transmitted through an OFDM symbol in a subframe. The sounding reference signal is a reference signal transmitted by the terminal to the base station for uplink scheduling. The base station estimates an uplink channel based on the received sounding reference signal and uses the estimated uplink channel for uplink scheduling. The reference signal means a demodulation reference signal and / or a sounding reference signal.

Hereinafter, an OFDM symbol for data transmission is referred to as a data symbol, an OFDM symbol for demodulation reference signal transmission is referred to as a demodulation reference signal symbol, and an OFDM symbol for sounding reference signal transmission is called a sounding reference signal symbol. The reference signal symbol means a demodulation reference signal symbol and / or a sounding reference signal symbol. In FIG. 6, there are 12 data symbols and two demodulation reference signal symbols in one subframe. In FIG. 7, there are 10 data symbols and 2 demodulation reference signal symbols in one subframe.

8 is a block diagram illustrating an example of a transmitter structure. Here, the transmitter may be part of the terminal or the base station.

Referring to FIG. 8, the transmitter 100 includes a data processor 110, a reference signal processor 120, and a radio frequency (RF) unit 130. The RF unit 130 is connected to the data processor 110 and the reference signal processor 120. The data processor 110 processes the data to generate a baseband signal for the data. The reference signal processor 120 generates and processes a reference signal to generate a baseband signal for the reference signal. The RF unit 130 converts a baseband signal (a baseband signal for data and / or a baseband signal for a reference signal) into a radio signal and transmits the radio signal. In this case, the baseband signal may be upconverted to a carrier frequency, which is a center frequency of the cell, and then converted to a wireless signal.

9 is a block diagram illustrating an example of a data processor. Here, the data processor may be included in the transmitter.

Referring to FIG. 9, the data processor 110 includes a discrete fourier transform (DFT) unit 111, a subcarrier mapper 112, an inverse fast fourier transform (IFFT) unit 113, and a CP insertion unit 114. . The data processor 110 may further include a scrambled unit (not shown), a modulation mapper (not shown), a layer mapper (not shown), and a layer permutator (not shown) at the front end of the DFT unit 111. Not shown blocks will be described later.

The DFT unit 111 outputs complex-valued symbols by performing a DFT on the input symbols. For example, when Ntx symbols are input, the DFT size is Ntx (Ntx is a natural number). Hereinafter, the DFT unit 111 may also be referred to as a transform precoder.

The subcarrier mapper 112 maps the complex symbols to each subcarrier in the frequency domain. Complex symbols may be mapped to resource elements corresponding to resource blocks allocated for data transmission. The subcarrier mapper 112 may be referred to as a resource element mapper hereinafter. The IFFT unit 113 performs an IFFT on the input symbol and outputs a baseband signal for data which is a time domain signal. When an IFFT size N _FFT d, N _FFT may be determined by the channel bandwidth (channel bandwidth) (N _FFT is a natural number). The CP inserter 114 copies a part of the rear part of the baseband signal for data and inserts it in front of the baseband signal for data. By interpolating CP, Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) are prevented, so that orthogonality can be maintained even in a multipath channel.

As such, a transmission scheme in which IFFT is performed after DFT spreading is called SC-FDMA. SC-FDMA may also be referred to as DFT-s OFDM. In SC-FDMA, a peak-to-average power ratio (PAPR) or a cubic metric (CM) may be lowered. In the case of using the SC-FDMA transmission scheme, transmission power efficiency may be increased in a terminal with limited power consumption. Accordingly, user throughpupt may be high.

10 illustrates an example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.

Referring to FIG. 10, the subcarrier mapper maps complex symbols output from the DFT unit to consecutive subcarriers in the frequency domain. '0' is inserted into a subcarrier to which complex symbols are not mapped. This is called localized mapping. In 3GPP LTE, a centralized mapping scheme is used.

11 shows another example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.

Referring to FIG. 11, the subcarrier mapper inserts L-1 '0's between two consecutive complex symbols output from the DFT unit (L is a natural number). That is, the complex symbols output from the DFT unit are mapped to subcarriers distributed at equal intervals in the frequency domain. This is called distributed mapping.

When the subcarrier mapper uses a centralized mapping scheme as shown in FIG. 10 or a distributed mapping scheme as shown in FIG. 11, a single carrier characteristic is maintained.

12 is a block diagram illustrating another example of a data processing unit structure. Here, the data processor may be included in the transmitter.

Referring to FIG. 12, the data processor 210 includes a DFT unit 211, a subcarrier mapper 212, an IFFT unit 213, and a CP inserter 214. The data processor 210 may further include a scrambled unit (not shown), a modulation mapper (not shown), a layer mapper (not shown), and a layer permutator (not shown) at the front end of the DFT unit 211. Not shown blocks will be described later.

The complex symbols output from the DFT unit 211 are divided into N subblocks (N is a natural number). Herein, N subblocks may be represented by subblock # 1, subblock # 2, ..., subblock #N. The subcarrier mapper 212 distributes N subblocks in the frequency domain and maps the subcarriers to subcarriers. NULL may be inserted between every two consecutive subblocks. Complex symbols in one subblock may be mapped to consecutive subcarriers in the frequency domain. That is, the centralized mapping scheme may be used in one subblock.

The data processor of FIG. 12 may be used for both a single carrier transmitter or a multi-carrier transmitter. A single carrier transmitter is a transmitter with one carrier, and a multicarrier transmitter is a transmitter with multiple carriers. When used in a single carrier transmitter, all N subblocks correspond to one carrier. When used in a multi-carrier transmitter, one subcarrier may correspond to each subblock among N subblocks. Alternatively, even when used in a multi-carrier transmitter, a plurality of subblocks among N subblocks may correspond to one carrier.

In the data processor of FIG. 12, a time domain signal is generated through one IFFT unit. Accordingly, in order for the data processor of FIG. 12 to be used in a multicarrier transmitter, subcarrier spacing between adjacent carriers must be aligned in a continuous carrier allocation situation.

13 is a block diagram illustrating still another example of a data processing unit structure. Here, the data processor may be included in the multi-carrier transmitter.

Referring to FIG. 13, the data processor 310 may include a DFT unit 311, a subcarrier mapper 312, a plurality of IFFT units 313-1, 313-2,..., 313 -N and a CP insertion unit ( 214), where N is a natural number. The data processor 310 may further include a scrambled unit (not shown), a modulation mapper (not shown), a layer mapper (not shown), and a layer permutator (not shown) at the front end of the DFT unit 311. Not shown blocks will be described later. IFFT is performed separately for each subblock among the N subblocks. The nth IFFT unit 313-n performs an IFFT on subblock #n and outputs an nth baseband signal (n = 1, 2,..., N). The nth baseband signal is multiplied by an nth carrier signal fn to generate an nth radio signal. After the N radio signals generated from the N subblocks are added, a CP is inserted by the CP inserting unit 314.

The data processor of FIG. 13 may be used in a non-contiguous carrier allocation situation in which carriers allocated by the transmitter are not adjacent to each other.

12 and 13, a method in which symbols output from the DFT unit are divided into a plurality of subblocks and processed is referred to as a clustered SC-FDMA.

14 is a block diagram illustrating another example of a data processing unit structure. Here, the data processor may be included in the multi-carrier transmitter.

Referring to FIG. 14, the data processor 410 includes a code block divider 411, a chunk divider 412, a plurality of channel coding units 413-1,. Modulators 414-1, ..., 414-N, a plurality of DFT units 415-1, ..., 415-N, a plurality of subcarrier mappers 416-1, ..., 416-N ), A plurality of IFFT units 417-1,..., 417 -N and a CP insertion unit 418 (N is a natural number). Here, N may be the number of multicarriers used by the multicarrier transmitter. Each of the channel coding units 413-1,..., 413 -N may include a scrambled unit (not shown). The modulators 414-1,..., 414 -N may also be referred to as modulation mappers. A layer mapper (not shown) and a layer permutator ( Not shown). Not shown blocks will be described later.

The code block dividing unit 411 divides the transport block into a plurality of code blocks. The chunk divider 412 divides the code block into a plurality of chunks. Here, the code block may be referred to as data transmitted from the multicarrier transmitter, and the chunk may be referred to as a piece of data transmitted through one carrier of the multicarrier. The data processor 410 performs a DFT in chunk units. The data processor 410 may be used both in a discontinuous carrier allocation situation or in a continuous carrier allocation situation. A transmission scheme in which DFT is performed in chunks as shown in FIG. 14 is referred to as chunk specific DFTS-OFDM or N × SC-FDMA.

15 is a block diagram showing a structure of a transmitter according to an embodiment of the present invention. The transmitter may be used for uplink transmission using the SC-FDMA scheme.

Referring to FIG. 15, the transmitter 1500 includes a modulation mapper 1510-1,..., 1510 -K, a layer mapper 1520, a layer permutator 1530, and a transform. Transform percoder (DFT unit), 1540-1, ..., 1540-N, MIMO precoder (1550), resource element mapper (1560-1, ..., 1560-) N), a signal generator (signal generator) 1570-1,..., 1570-N.

The modulation mapper 1510-1,..., 1510 -K receives a codeword and maps it to a modulation symbol representing a position on a signal costellation. Codeword means data encoded by encoding according to a predetermined coding scheme. Although not shown in the drawings, the codeword may be input to the modulation mapper 1510-1,..., 1510 -K after being scrambling. The codeword q may be expressed as in the following equation.

Where q is the index of the codeword and N ^(q) _bit is the number of _bits of the codeword q. k has a value from 0 to N ^(q) _bit −1.

The modulation scheme is not limited and may be m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM). For example, m-PSK may be BPSK, QPSK or 8-PSK. m-QAM may be 16-QAM, 64-QAM or 256-QAM. That is, the modulation symbol modulated by the modulation mapper has a complex value. Codeword q mapped to a symbol on the signal constellation may be represented by a modulation symbol sequence as shown in Equation 2.

In Equation 2, q is the index of the codeword, and M ^(q) _symb is the number of symbols of the codeword q.

The mapping relationship between b ^(q) (k) and d ^(q) (i) performed in the modulation mapper 1510-1, ..., 1510-K according to the embodiment of the present invention is compared with the conventional method. Will be described later.

The layer mapper 1520 receives a modulation symbol string (that is, d ^(q) (i)) from the modulation mapper 1510-1,..., 1510 -K, and codeword to layer mapping. Do this. The modulation symbol x (i) on which codeword-to-layer mapping is performed may be represented by Equation 3 below.

In Equation 3, v means the number of layers, i = 0, 1, ..., M ^layer _symb -1.

M ^layer _symb Denotes the number of modulation symbols per layer.

When the number of codewords is 1 or 2, codeword-to-layer mapping for spatial multiplexing may be performed as defined in Table 1 below.

The layer permutator 1530 may perform permutation or interleaving at the modulation symbol level on the modulation symbol x (i) on which the codeword-to-layer mapping is performed. The unit of permutation may be performed in units of bits, modulation order, modulation order x DFT size, modulation order x DFT size x (SC-FDMA symbol number of slot or subframe). When performing modulation symbol level permutation, x (i) outputs modulation symbol y (i) sent to each antenna port p.

The modulation symbol on which the modulation symbol level permutation is performed is denoted by y (i). Then, modulation symbols x (i) = [x ⁽⁰⁾ (i), ..., x ^(v-1) (i)] ^T , i = 0, 1,... If M ^layer _symb -1 is given as the input vector of the layer permutator 1530, the output vector y (i) = [y ⁽⁰⁾ (i), ..., y ^(p-1) (i)] ^T , i = 0, 1, ..., M ^layer _symb -1 may be given by Equation 4 below. In Equation 4, it is assumed that v and p are 2.

In Equation 4, it can be seen that permutation of the modulation symbol level is performed on x ⁽¹⁾ (2i + 1) and x ⁽⁰⁾ (2i + 1). Equation 4 is merely an example, and the modulation symbol level permutation may be performed in various ways.

The transform precoder 1540-1,..., 1540 -N receives a modulation symbol y (i) subjected to modulation symbol level permutation and performs a Discrete Fourier Transform (DFT) operation. The DFT operation and permutation may be performed after (1) permutation is performed, and (2) after performing DFT operation, permutation may be performed. For example, when the unit of permutation is performed in bit unit or modulation order unit, the method of (1) may be performed, and the unit of permutation may be modulation order x DFT size unit, modulation order x DFT size x When performed in units of (number of SC-FDMA symbols in a slot or subframe), the method may be any one of the methods (1) and (2).

The MIMO precoder 1550 processes the input symbols in a MIMO scheme according to multiple transmit antennas. That is, the MIMO precoder 1550 may perform layer to antenna mapping. The MIMO precoder 1550 distributes antenna specific symbols to resource mappers 1560-1,..., 1560 -N in the path of the corresponding antenna. Each information path sent by the MIMO precoder 1550 through one resource mapper to one antenna is called a stream. This may be referred to as a physical antenna.

The resource mapper 1560-1,..., 1560 -N allocates an antenna specific symbol to an appropriate resource element and multiplexes according to a user. The signal generators 1570-1, ..., 1570-N perform an Inverse Fast Fourier Transform (IFFT) operation or an Inverse Fourier Transform (IFT) operation, and then perform digital to analog conversion (DAC). The signal generators 1570-1,..., 1570 -N may include an IFFT unit and a CP insertion unit. The analog signal output from the signal generators 1570-1,..., 1570 -N is transmitted through a physical antenna port.

Now, the mapping relationship between b ^(q) (k) and d ^(q) (i) performed in the modulation mapper 1510-1, ..., 1510-K will be described in detail in comparison with the conventional method.

<Conventional method>

According to the prior art, the modulation mapper maps b ^(q) (k) to d ^(q) (i) according to the modulation order allocated to each codeword as shown in the following table.

In Table 2, M ^(q) means the modulation order of the codeword q (M ^(q) has values such as BPSK: 1, QPSK: 2, 16QAM: 4, 64QAM: 6, etc.). k: k + M ^(q) −1 indicates that the variable k ranges from k to k + M ^(q) −1. 3GPP TS. 36.211. According to V8.4.0, f () in Table 2 is defined as follows.

The modulation mapper receives binary values 0 or 1 and outputs complex values such as x = I + jQ. In case of BPSK modulation, one bit b (i) is mapped as shown in the following table.

In the case of QPSK modulation, two bits b (i) and b (i + 1) are mapped as shown in the following table.

For 16QAM modulation, four bits b (i), b (i + 1), b (i + 2) and b (i + 3) are mapped as shown in the following table.

For 64QAM modulation, six bits b (i), b (i + 1), b (i + 2), b (i + 3), b (i + 4), b (i + 5) It is mapped as shown in the table.

If the modulation order of x ⁽⁰⁾ (2m), x ⁽⁰⁾ (2m + 1) ({2m, 2m + 1} ∈ i} for layer 0 is 2 (that is, QPSK), x ⁽¹⁾ (2m), x ⁽¹⁾ (2m + 1) ({2m, 2m + 1} ∈ i} if the modulation order is 4 (ie 16QAM), then y ⁽⁰⁾ (2m) and y ⁽⁰⁾ (2m +1) (same as y ⁽¹⁾ (2m) and y ⁽¹⁾ (2m + 1)) have different modulation orders according to Table 1 and Equation 4. That is, modulation orders for a plurality of codewords If is different from each other, y (i) subjected to modulation symbol level permutation includes modulation symbols having different modulation orders, thereby increasing CM or PAPR Table 7 below shows examples of CM values.

QPSK only 16 QAM only QPSK + 16 QAM CM (dB) 1.22 2.14 1.72`

In order to solve this problem, according to an embodiment of the present invention, the modulation mapper is composed of symbols having the same modulation order for the same antenna port after y (i) of the modulation symbol level permutation performed in the layer permutator. Map b ^(q) (k) to d ^(q) (i).

For clarity, it is assumed that layer permutation is performed in units of modulation symbols only when i has an odd number of two codewords, that is, codeword 0 and codeword 1. FIG. In this case, the modulation mapper may perform modulation mapping as shown in Table 8 below.

16 shows a relationship between modulation mapping described in Table 8 and subsequent layer permutation.

Referring to Table 8 and FIG. 16, modulation symbols d ⁽⁰⁾ (i) after modulation mapping for codeword 0 are divided into two bits according to modulation order M ⁽⁰⁾ of codeword 0 when i is a multiple of 2. For example, QPSK modulates b ⁽⁰⁾ (0), b ⁽⁰⁾ (1), and if i is not a multiple of two, four bits (e.g., according to modulation order M ⁽¹⁾ of codeword 1 16QAM modulation of b ⁽⁰⁾ (2), b ⁽⁰⁾ (3), b ⁽⁰⁾ (4), b ⁽⁰⁾ (5)). That is, QPSK, 16QAM, QPSK, 16QAM ... are repeated in the order of 2 bits, 4 bits, 2 bits, 4 bits.

Modulation symbol d ⁽¹⁾ (i) after modulation mapping for codeword 1 is 16QAM modulated 4 bits according to modulation order M ⁽¹⁾ of codeword 1 when i is a multiple of 2, and i is a multiple of 2. Otherwise, two bits are QPSK-modulated according to the modulation order M ^(o) of codeword 0. That is, 16QAM, QPSK, 16QAM, QPSK ... are repeated in the order of 4 bits, 2 bits, 4 bits, 2 bits ...

Layer mapping by the layer mapper may be performed by Table 1. Then, (x ⁽⁰⁾ (0) x ⁽⁰⁾ (1) ... x ⁽⁰⁾ (M ^layer _symb -1)] means [d ⁽⁰⁾ (0), d ⁽⁰⁾ (1), ... d ⁽⁰⁾ (M ^layer _symb -1)]. (x ⁽¹⁾ (0) x ⁽¹⁾ (1) ... x ⁽¹⁾ (M ^layer _symb -1)] means [d ⁽¹⁾ (0), d ⁽¹⁾ (1), ... d ⁽¹⁾ (M ^layer _symb -1)]. When layer permutation by Equation 4 is performed, [y ⁽⁰⁾ (0) y ⁽⁰⁾ (1). . . ] = [d ⁽⁰⁾ (0) d ⁽¹⁾ (1) ...], [y ⁽¹⁾ (0) y ⁽¹⁾ (1). . . ] = [d ⁽¹⁾ (0) d ⁽⁰⁾ (1) ...] Therefore, when the modulation symbol level permutation is performed by the layer permutator, y ⁽⁰⁾ (i) is equal to the modulation order of two, and y ⁽¹⁾ (i) is equal to the modulation order of four.

That is, the modulation mapper repeatedly performs different modulation schemes for one codeword in consideration of the modulation symbol level permutation performed by the layer permutator. As a result, modulation symbols of the same modulation order are generated for each antenna port. This may be expressed as a modulation symbol of a modulation order that matches the DFT size of the transform precoder. Accordingly, layer permutation may be performed while maintaining low CM and single carrier properties.

17 is a block diagram showing a structure of a transmitter according to another embodiment of the present invention.

There is a difference that the layer permutator is located in front of the layer mapper compared to FIG. 15. In other words, the present invention only needs to place the layer permutator at the front end of the transform precoder.

In addition, the layer mapper may be omitted. For example, in Table 1, when the number of layers is 1 and the number of codewords is 1, when the number of layers is 2 and the number of codewords is 2, modulation symbol d ^(q) (i) and layer-mapped symbol x ^{(q )} (i) are equivalent to each other (equivalent). Therefore, the layer mapping may not be performed, and the modulation symbol d ^(q) (i) modulated with a complex value may be directly applied to the layer permutator.

The present invention can be applied when performing the DFT for the transmission of the SC-FDMA signal. For example, when the terminal transmits an uplink signal to the base station, the apparatus and method according to the present invention can be applied.

All the above functions may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), or the like according to software or program code coded to perform the function. The design, development and implementation of the code will be apparent to those skilled in the art based on the description of the present invention.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

1500: transmitter

Claims (8)

In the data transmission apparatus in a multi-antenna system,
A modulation mapper for modulating codewords with modulation symbols representing positions on a signal constellation;
A layer permutator for mapping the modulation symbols to different layers;
A transform precoder for generating a DFT symbol in a frequency domain by performing a Discrete Fourier Transform (DFT) on a modulation symbol mapped to the layer;
A resource element mapper for mapping the DFT symbol to a physical resource element; And
And a signal generator for generating a DFT symbol mapped to the resource element as an SC-FDMA signal in a time domain, wherein the modulation symbols are determined to have a modulation order according to a layer mapped by the layer permutator. Transmission device. The data transmission apparatus of claim 1, further comprising a layer mapper for mapping the modulation symbol to any one of a plurality of layers according to a predetermined mapping rule. The apparatus of claim 1, wherein the layer permutator maps to different layers in modulation symbol units. The method of claim 1, wherein when the modulation symbols are mapped to the first layer or the second layer by the layer permutator, the modulation symbols mapped to the first layer have a first modulation order, The modulation symbols to be mapped have a second modulation order, wherein the first and second modulation orders are different. 5. The method of claim 4, wherein when there are two codewords, the modulation mapper modulates one codeword in order of a modulation symbol having a first modulation order and a modulation symbol having a second modulation order, and the other codeword is a first codeword. And a modulation symbol having two modulation orders and then a modulation symbol having a first modulation order. In the DFT method for transmitting the SC-FDMA signal,
Modulating the codeword with modulation symbols representing a position on the signal constellation;
Mapping the modulation symbols to different layers; And
DFTing modulation symbols mapped to the different layers, wherein the modulation symbols are determined to have a modulation order according to the mapped layer. 7. The method of claim 6, wherein when the modulation symbols are mapped to the first layer or the second layer, the modulation symbols mapped to the first layer have a first modulation order, and the modulation symbols mapped to the second layer are the first symbols. And having a second modulation order, wherein the first and second modulation orders are different from each other. The method as claimed in claim 6, wherein the mapping to the different layers comprises mapping to different layers in modulation symbol units.

Images