KR101188544B1 - Data Transmission Method for Single Carrier-Frequency Division Multiple Access System and Pilot Allocation Method - Google Patents

Abstract

In the data transmission method of the SC-FDMA system, a subcarrier is allocated to a long block including data and a short block including a pilot, and the long block and the short block are converted into a time domain signal. The time interval of the short block is smaller than the time interval of the long block, and the short blocks are alternately assigned subcarriers having frequency domain orthogonality and subcarriers having code domain orthogonality. The channel estimation for data demodulation and the quality measurement of the channel for the entire frequency band can be simultaneously performed, and the performance deterioration does not occur significantly even if the moving speed of the terminal increases.

Single Carrier Frequency Division Multiple Access, SC-FDMA, Pilot, Channel Estimation, Channel Quality

Description

Data Transmission Method and Single Carrier-Frequency Division Multiple Access System and Pilot Allocation Method in Single Carrier Frequency Division Multiple Access System

1 is an exemplary diagram illustrating a mobile communication system.

2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

3 is an exemplary diagram illustrating a subframe transmitted by a transmitter.

4 shows various examples of subframes.

5 is an exemplary diagram showing a signal structure of the FDM-L method.

6 is an exemplary diagram illustrating a signal structure of an FDM-D scheme.

7 is an exemplary diagram illustrating a signal structure of a CDM method.

8 is a block diagram illustrating a receiver of an FDM-L scheme.

9 is a block diagram showing a receiver of the FDM-D scheme.

10 is a block diagram showing a CDM receiver.

11 is an exemplary view showing a data transmission method according to an embodiment of the present invention.

12 is a block diagram illustrating a receiver according to an embodiment of the present invention.

13 is a graph comparing channel estimation performance.

14 is a graph comparing channel quality performance for all frequency bands.

15 is an exemplary view showing a data transmission method according to another embodiment of the present invention.

16 is an exemplary view showing a data transmission method according to another embodiment of the present invention.

17 is an exemplary view showing a data transmission method according to another embodiment of the present invention.

18 is an exemplary view showing a pilot allocation method according to an embodiment of the present invention.

** Explanation of symbols in main part of drawing **

110: DFT unit

120: subcarrier mapper

130: IFFT unit

The present invention relates to a single carrier frequency division multiple access system, and more particularly, to a data transmission method and a pilot allocation method of a single carrier frequency division multiple access system.

3rd Generation Partnership Project (3GPP) mobile communication systems based on Wideband Code Division Multiple Access (WCDMA) radio access technology are widely deployed around the world. High Speed Downlink Packet Access (HSDPA), which can be defined as the first evolutionary step of WCDMA, provides 3GPP with highly competitive radio access technologies in the mid-term future. However, as the demands and expectations of users and operators continue to increase and the development of competing radio access technologies continues, new technological evolution in 3GPP is required to be competitive in the future.

One of the systems considered in 3rd generation and later systems is an Orthogonal Frequency Division Multiplexing (OFDM) system that can attenuate the effect of inter-symbol interfernce with low complexity. OFDM converts serially input data symbols into N parallel data symbols and transmits them on N subcarriers, respectively. The subcarriers maintain orthogonality in the frequency dimension. Each orthogonal channel experiences frequency selective fading that is independent of each other, and the interval between transmitted symbols is increased, 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 scheme.

One of the major problems with OFDM / OFDMA is that the peak amplitude of the transmitted signal can be significantly larger than the average amplitude. This Peak-to-Average Power Ratio (PAPR) problem is due to the fact that the OFDM signal is a superposition of N sinusoidal siganals on different subcarriers. In order to save transmission power, it is necessary to lower the PAPR.

One system proposed to lower PAPR is Single Carrier-Frequency Division Multiple Access (SC-FDMA). SC-FDMA is a form of combining Frequency Division Multiple Access (FDMA) with the existing Single Carrier-Frequency Division Equalization (SC-FDE) scheme. SC-FDMA has similar characteristics to OFDMA in that it modulates and demodulates a signal in a time domain and a frequency domain using a Discrete Fourier Transform (DFT), but the PAPR of a transmission signal is low, which is advantageous in reducing transmission power. In particular, it can be said that it is advantageous for uplink access to a base station from a terminal sensitive to transmission power in relation to battery usage.

In order to efficiently restore data at the receiver, channel estimation for data demodulation and channel quality estimation for frequency selective scheduling must be efficiently performed. In general, channel estimation and channel quality measurement are performed by pilots included in a signal transmitted from a transmitter. However, little is known about the efficient pilot architecture for SC-FDMA.

An object of the present invention is to provide a data transmission method and a pilot allocation method of a single carrier frequency division multiple access system capable of simultaneous channel estimation and channel quality measurement.

According to an aspect of the present invention, there is provided a data transmission method of an SC-FDMA system. The data transmission method allocates a subcarrier to a short block including data and a short block including data, and converts the long block and the short block into a time domain signal. The time interval of the short block is smaller than the time interval of the long block, and the short blocks are alternately allocated subcarriers having frequency domain orthogonality and subcarriers having code domain orthogonality.

According to another aspect of the present invention, a pilot allocation method for a plurality of terminals is provided. The pilot allocation method allocates a DM pilot for data demodulation to a different frequency band for each terminal. In addition, the CQ pilot for channel quality measurement is allocated to frequency bands overlapping each other for each of the UEs.

According to another aspect of the invention there is provided a transmitter. The transmitter includes a DFT unit for converting an input signal into a frequency domain signal, a subcarrier mapper for allocating subcarriers to the frequency domain signal and a pilot, and an IFFT unit for converting the subcarrier allocated signal to a time domain signal. The subcarrier mapper allocates the pilot to the subcarriers having frequency domain orthogonality and code region orthogonality for each terminal.

According to another aspect of the invention there is provided a receiver. The receiver includes an FFT unit for converting a received signal into a frequency domain signal, a channel estimator for estimating a channel in a first pilot included in the frequency domain signal, and an equalization for equalizing data included in the frequency domain signal from the estimated channel. And a channel quality estimator for estimating channel quality in a second pilot included in the frequency domain signal and intersected with the first pilot.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals designate like elements throughout the specification.

1 is an exemplary diagram illustrating a mobile communication system.

Referring to FIG. 1, a mobile communication system includes a base station (BS) 10 and a plurality of UEs 20. This may be an SC-FDMA system. Mobile communication systems are widely deployed to provide various communication services such as voice and packet data.

The base station 10 generally refers to a fixed station that communicates with the terminal 20. Other terms such as node-B, base transceiver system (BTS), and access point (access point) terminology).

The terminal 20 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), and a wireless device.

Downlink (downlink) means communication from the base station 10 to the terminal 20, uplink (uplink) means communication from the terminal 20 to the base station 10. In the downlink, the transmitter may be part of the base station 10 and the receiver may be part of the terminal 20. In uplink, the transmitter may be part of the terminal 20 and the receiver may be part of the base station 10. The base station 10 may include a plurality of receivers and a plurality of transmitters, and the terminal 20 may include a plurality of receivers and a plurality of transmitters.

2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

Referring to FIG. 2, the transmitter 100 includes a Discrete Fourier Transform Unit 110, a Subcarrier Mapper 120, an Inverse Fast Fourier Transform Unit 130, and a CP Prefix Insert. Unit 140).

The DFT unit 110 converts the frequency domain signal X [k] by performing a DFT on the input signal x [n]. A DFT transform process having a size L may be represented by Equation 1 below.

The subcarrier mapper 120 allocates the frequency domain signal X [k] to each subcarrier by various signal structure schemes. A signal structure method allocated by the subcarrier mapper 120 will be described later.

The IFFT unit 130 performs an IFFT on the signal X '[k] allocated by the subcarrier mapper 120 and converts the time domain signal s [n]. The CP inserting unit 140 inserts a CP into the time domain signal s [n], and the signal is converted into an analog signal by the RF unit 150 and propagated to the wireless channel through the antenna 160.

3 is an exemplary diagram illustrating a sub frame transmitted from a transmitter. The length of the subframe may be equal to the minimum transmission time interval (TTI) for transmission.

Referring to FIG. 3, the subframe includes six long blocks (LBs) and two short blocks (SB1 and SB2). The short blocks SB1 and SB2 include a first short block SB1 and a second short block SB2. Here, the first short block SB1 is ahead of time compared to the second short block SB2. That is, the first short block SB1 is transmitted before the second short block SB2.

The long block LB is used for control and / or data transmission. The short blocks SB1 and SB2 may be used for control and / or data transmission and may be used for reference signal (pilot) transmission. When the pilots are included in the short blocks SB1 and SB2, they may be referred to as pilot blocks. Pilot is a priori known data between transmitter and receiver and is used for channel estimation and / or channel quality measurement. Cyclic prefix (CP) is inserted into the long block LB and the short blocks SB1 and SB2 to minimize intersymbol interference and interference by a multipath channel.

The time intervals of the short blocks SB1 and SB2 may be equal to or smaller than the time intervals of the long block LB. The time intervals of the short blocks SB1 and SB2 are not limited, but preferably, the time intervals of the short blocks SB1 and SB2 may be 0.5 times the time intervals of the long blocks LB. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB due to the duality of the time domain and the frequency domain, the frequency bands of the short blocks SB1 and SB2 are long blocks ( 2 times the frequency band of LB). For clarity, the case where the time intervals of the short blocks SB1 and SB2 are 0.5 times the time interval of the long block LB will be described.

The time intervals of the first short block SB1 and the second short block SB2 are the same, but this is not a limitation and may have different time intervals. In addition, the time intervals of the short blocks SB1 and SB2 may be dynamically changed according to the time interval of the long block LB or the situation of the system.

The subframe includes six long blocks LB and two short blocks SB1 and SB2, but the number of long blocks and the number of short blocks included in the subframe are not limited. The subframe may include at least one long block and at least one short block.

 Four long blocks LB are disposed between the two short blocks SB1 and SB2 in the subframe, but the arrangement of the short blocks SB1 and SB2 and the long blocks LB is not limited and may vary depending on the system. You can change it. For example, three long blocks LB may be disposed between the short blocks SB1 and SB2, or five long blocks LB may be disposed. In addition, the arrangement of the short blocks SB1 and SB2 in the subframe may be dynamically changed according to the performance or environment of the system.

4 shows various examples of subframes. This is merely an example and the arrangement of the short block and the long block is not limited to the examples shown in FIG. 4 and may be arranged in various other ways.

Meanwhile, a plurality of terminals 20 may be connected to one base station 10. Hereinafter, the number of terminals 20 is referred to as M. The base station 10 allocates time / frequency resources for each terminal 20. In order for each terminal 20 to distinguish signals transmitted and received, frequency resources (or subcarriers) allocated to each terminal 20 should have orthogonality. Orthogonality is time domain orthogonality, frequency domain orthogonality, or code domain orthogonality. The time domain orthogonality has a problem in that accurate transmission timing control is required. Thus, SC-FDMA systems have better characteristics of frequency domain orthogonality and code domain orthogonality.

Frequency domain orthogonality may be achieved by transmitting signals through different subcarriers for each terminal. Frequency bands allocated to subcarriers do not overlap each other. Frequency domain orthogonality may be applied to localized signal structures or distributed signal structures. Local signals occupy a continuous spectrum, while distributed signals occupy a comb-shaped spectrum. Hereinafter, a signal structure using a local signal is referred to as frequency division multiplexing-localized (FDM-L), and a signal structure using a distributed signal is referred to as frequency division multiplexing-distributed (FDM-D).

Code region orthogonality is achieved by transmitting a signal through a common subcarrier for each terminal. Some or all of the frequency bands allocated to the subcarriers overlap with each terminal (overlap). Hereinafter, a signal structure using a signal orthogonal in the code region is called CDM (Code Division Multiplexing).

5 is an exemplary diagram showing a signal structure of the FDM-L method.

Referring to FIG. 5, subcarriers are locally concentrated for M users (terminals). Different terminals are allocated to different frequency bands so that frequency division multiplexing is used.

Two carriers SB1 and SB2 and a long block LB are allocated with a subcarrier locally densely located in each terminal. A pilot (reference signal) may be carried on the subcarriers of the short blocks SB1 and SB2, and the same subcarrier may be allocated to the first short block SB1 and the second short block SB2. Therefore, in the FDM-L scheme, the pilot and the data have the same frequency band.

When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, the subcarriers of the short blocks SB1 and SB2 occupy a band twice larger than the subcarriers of the long block LB. Therefore, two adjacent subcarriers of the long block LB are paired with one subcarrier of the short blocks SB1 and SB2.

In the FDM-L scheme, the pilot signals carried on the short blocks SB1 and SB2 may be used for a DM (data de-modulation) pilot that demodulates a data signal transmitted on a subcarrier of a long block (LB) of the same band. . This is because the subcarriers of the short blocks SB1 and SB2 overlap the frequency bands of the subcarriers of the long block LB. However, since the pilot signal is densely localized in the frequency domain with respect to the corresponding UE, it is difficult to use the CQ (Channel Quality) pilot for measuring the channel quality of the entire frequency band. That is, since the subcarriers are locally concentrated for each terminal, it is difficult to estimate the channel quality experienced by the subcarriers of other terminals.

6 is an exemplary diagram illustrating a signal structure of an FDM-D scheme.

Referring to FIG. 6, subcarriers are distributed to M users (terminals) and are non-contiguous.

The subcarriers of the long block LB and the short blocks SB1 and SB2 are distributed and allocated at regular intervals so that the same terminals are not adjacent to each other. That is, the subcarriers are distributed at predetermined intervals for each terminal.

Pilot signals allocated to the first short block SB1 and the second short block SB2 are staggered for each terminal in the frequency domain. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, the subcarriers of the short blocks SB1 and SB2 occupy a band twice larger than the subcarriers of the long block LB. Since the frequency bands of two long blocks LB are arranged in the frequency bands of one short block SB1 and SB2, in the FDM-D scheme, two short blocks with respect to a subcarrier position of a terminal corresponding to the long block LB are used. The pilot signals of (SB1, SB2) are allocated alternately for each terminal. For example, the pilot signal for the first terminal 302 of the long block LB is carried on the subcarrier 301 of the first short block SB1. The subcarrier 304 of the second short block SB2 carries a pilot signal for the second terminal 303 of the long block LB in the same band. Subsequently, the subcarriers of the short blocks SB1 and SB2 are loaded in a form in which pilot signals are continuously staggered for each terminal of the long block LB.

In the FDM-D scheme, the pilot signals carried on the short blocks SB1 and SB2 may be used as a DM pilot for demodulating data signals transmitted on subcarriers of a long block LB of the same band. This is because the subcarriers of the short blocks SB1 and SB2 overlap the frequency bands of the subcarriers of the long block LB. In addition, since the pilot signal is transmitted over the entire frequency band, it can be used as a CQ pilot for measuring the quality of the channel.

However, in the FDM-D scheme, the pilots of the first short block SB1 and the pilots of the second short block SB2 are alternately arranged so that a channel estimation error can be increased in a time-selective channel environment with a large moving speed of the terminal. In addition, as the number of terminals to be connected increases, the pilot interval may widen, which may cause deterioration of channel estimation.

7 is an exemplary diagram illustrating a signal structure of a CDM method.

Referring to FIG. 7, subcarriers of the pilot signal are transmitted to each other for M users (terminals).

The subcarriers of the long block LB are distributed and allocated at regular intervals without being adjacent to each other. That is, the subcarriers of the long block LB are allocated such that the subcarriers are distributed at regular intervals without being dense for each UE in the same manner as in the FDM-D scheme.

The pilot may be carried on the subcarriers of the short blocks SB1 and SB2, and the same subcarrier may be allocated to the first short block SB1 and the second short block SB2. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, the subcarriers of the short blocks SB1 and SB2 occupy a band twice larger than the subcarriers of the long block LB.

Subcarriers of the short blocks SB1 and SB2 may be allocated over the entire band. The subcarriers of the short blocks SB1 and SB2 are in a form in which frequency bands of terminals overlap each other. The subcarriers of the short blocks SB1 and SB2 maintain orthogonality in the code region for each terminal. Through this, each terminal extracts a pilot corresponding to itself from the short blocks SB1 and SB2.

In one embodiment, the pilot signal may be orthogonal in the code domain using a constant amplitude zero auto-correlation (CAZAC) sequence in the form of a cyclic shift. When L is a positive integer and k is relatively prime, L-th entry of the k-th CAZAC sequence can be expressed as Equation 2 below.

In another embodiment, the pilot signal may be orthogonal in the code region using a block sequence. Examples of block sequences are described in S. Zhou, et al., "Chip-Interleaved Block Spread Code Division Multiple Access", IEEE Trans. on Commun., vol. 50, no. 2, pp. 235-248, Feb. See 2002.

In the CDM scheme, the pilot signals carried on the short blocks SB1 and SB2 may be used as a DM pilot for demodulating data signals transmitted on subcarriers of the long block LB of the same band. In addition, since the pilot signal is transmitted over the entire frequency band, it can be used as a CQ pilot for measuring the quality of the channel.

8 is a block diagram illustrating a receiver of an FDM-L scheme.

Referring to FIG. 8, the receiver 400 includes an FFT unit 440, a subcarrier demapper 450, a channel estimator 460, and an IDFT unit 480.

The signal received by the antenna 410 becomes a digitized signal via the RF unit 420. In the digitized signal, the CP is removed by the CP remover 430. The time domain signal r _i [n] from which the CP is removed is converted into a frequency domain signal Y _i '[k] by performing an FFT by the FFT unit 440. Here, the size of the FFT is referred to as N _SB for the short blocks SB1 and SB2 and N _{LB for the} long block LB. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, N _LB = 2N _SB . The converted signals Y _i '[k] is a signal Y _i [k] through the reverse process of the sub-carrier allocation method by the subcarrier de-mapper (450).

The channel estimator 460 estimates the channel H _i [k] from the pilot signals of the short blocks SB1 and SB2. The pilot at this time is the use of the DM pilot to demodulate the data signal. Channel estimation may be performed as in Equations 3 and 4 below.

The equalizer 470 compensates the data signal included in the long block LB using the estimated channel H _i [k] as shown in Equation 5 below.

() * Is the conjugate, and SNR is the signal-to-noise ratio obtained through the channel.

The IDFT unit 480 performs an IDFT on the compensated signal X _i [k] and converts it to a time domain signal x _i [n]. The size of the IDFT is referred to as L _SB for the short blocks SB1 and SB2 and L _{LB for the} long block LB. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, L _LB = 2L _SB . In this case, the IDFT transform may be expressed as in Equation 6 below.

9 is a block diagram showing a receiver of the FDM-D scheme.

9, the receiver 500 includes an FFT unit 540, a subcarrier demapper 550, a channel estimator 560, an IDFT unit 580, and a channel quality estimator 590.

The signal received by the antenna 510 becomes a digitized signal via the RF unit 520. In the digitized signal, the CP is removed by the CP removing unit 530. The time domain signal r _i [n] from which the CP is removed is converted into the frequency domain signal Y _i '[k] by performing an FFT by the FFT unit 540. Here, the size of the FFT is referred to as N _SB for the short blocks SB1 and SB2 and N _{LB for the} long block LB. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, N _LB = 2N _SB . The converted signals Y _i '[k] is a signal Y _i [k] through the reverse process of the sub-carrier allocation method by the subcarrier de-mapper (550).

The channel estimator 560 estimates the channel H _i [k] from the pilot signals of the short blocks SB1 and SB2. The pilot at this time is the use of the DM pilot to demodulate the data signal. Channel estimation may be performed as in Equations 7 and 8.

The equalizer 570 compensates the data signal included in the long block by using the estimated channel _Hi [k] as shown in Equation 9 below.

() * Is the conjugate and SNR is the received Signal-to-Noise Ratio obtained over the channel.

The IDFT unit 580 performs an IDFT on the compensated signal X _i [k] and converts it to a time domain signal x _i [n]. The size of the IDFT is referred to as L _SB for the short blocks SB1 and SB2 and L _{LB for the} long block LB. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, L _LB = 2L _SB .

The channel quality estimator 590 estimates the channel quality from the pilot signals of the short blocks SB1 and SB2. Preferably, the channel quality estimator may estimate the channel quality using the channel H ₆ [k] estimated from the pilot signal of the second short block SB2. The channel quality estimator 590 performs linear interpolation on the channel H ₆ [k] estimated at each subcarrier position as shown in Equation 10 below.

The interpolation method by a method other than the linear interpolation method is also applicable. As a result, the channel quality of the subcarriers of the entire frequency band is estimated.

10 is a block diagram showing a CDM receiver.

Referring to FIG. 10, the receiver 600 includes an FFT unit 640, a subcarrier demapper 650, an IDFT unit 670, a CIR estimator 680, and a channel quality estimator 695.

The signal received by the antenna 610 becomes a digitized signal via the RF unit 620. In the digitized signal, the CP is removed by the CP remover 630. The time domain signal r _i [n] from which the CP is removed is converted into the frequency domain signal Y _i '[k] by performing an FFT by the FFT unit 640. Here, the size of the FFT is referred to as N _SB for the short blocks SB1 and SB2 and N _{LB for the} long block LB. The converted signals Y _i '[k] is a signal Y _i [k] through the reverse process of the sub-carrier allocation method by the subcarrier de-mapper (650).

The CDM scheme estimates channel quality using a channel impulse response (CIR) in the time domain. CIR estimator 680 estimates CIR h _i [τ] from the time domain pilot signal. The CIR is obtained by using a cyclic correlation operation as shown in Equation 11 below.

mod represents a modulo operation. s _i is a time-domain pilot signal at the transmitter 100 and is a value previously known to the receiver 600.

The window portion 685 performs windowing as shown in Equation 12 with respect to the CIR.

That is, the window portion 685 replaces the portion excluding the predetermined region in CIR h _i [τ] with zero.

로 변환한다. The FFT unit 690 performs an FFT on the windowed CIR to perform frequency domain channel

.

Channel estimation for the data signal of the long block LB may be performed as in Equation 13.

을 이용하여 장블록(LB)에 포함된 데이터 신호를 다음 수학식 14와 같이 보상한다.Equalizer 660 is estimated channel

The data signal included in the long block LB is compensated by using Equation 14 below.

The IDFT unit 670 performs an IDFT on the compensated signal X _i [k] and converts it to a time domain signal x _i [n]. The size of the IDFT is referred to as L _SB for the short blocks SB1 and SB2 and L _{LB for the} long block LB.

을 구함으로써 결국 전체 주파수 대역에 대한 채널 품질을 구할 수 있다.The channel quality estimator 695 estimates the channel quality from the pilot signal of the second short block SB2. Estimated Channels at Each Subcarrier Location

Finally, the channel quality for the entire frequency band can be obtained.

In the case of the FDM-L method, since subcarriers are locally concentrated for each terminal, it is difficult to estimate the channel quality of the entire band for frequency selective scheduling. In the case of the FDM-D scheme, pilots are alternately arranged for each UE in the first short block SB1 and the second short block SB2, so that the channel estimation error increases in a time-selective channel environment in which the mobile speed is large. As the number of terminals increases, the pilot interval may widen, which may cause deterioration of channel quality estimation. In the case of the CDM scheme, as the number of terminals increases, the windowing interval decreases, and thus, when the windowing interval is smaller than the delay spread due to the multipath, accurate CIR estimation may be difficult, resulting in degradation of channel estimation and channel quality estimation. .

11 is an exemplary view showing a data transmission method according to an embodiment of the present invention.

Referring to FIG. 11, subcarriers are locally allocated to each UE in the long block LB. That is, the long block LB is allocated a continuous frequency band for each terminal.

The pilot is carried on the subcarriers of the short blocks SB1 and SB2. The first short block SB1 may be allocated subcarriers of the same long block LB and the same band. That is, subcarriers are allocated to the long block LB and the first short block SB1 in the same manner as the FDM-L scheme.

The FDM-L scheme and the CDM scheme are alternately allocated to the second short block SB2. That is, the second short block SB2 is alternately allocated a subcarrier having frequency domain orthogonality and a subcarrier having code domain orthogonality. Orthogonality in the code domain may be achieved using a CAZAC sequence or a block sequence in the form of a cyclic transform. In the second short block SB2, subcarriers having the same band as the band allocated to the subcarrier of the long block LB of the corresponding UE and subcarriers allocated overlapping with each other are alternately allocated.

The second short block SB2 is alternately allocated a DM pilot (first pilot) for channel estimation and a CQ pilot (second pilot) for measuring a full band channel quality. The DM pilot is used for channel estimation and the CQ pilot is used for channel quality measurement. The DM pilot is allocated to different frequency bands for each terminal and has orthogonality in the frequency domain. The CQ pilots are allocated to frequency bands overlapping each other for each UE and have orthogonality in the code domain. Channel estimation through the DM pilot is made after passing the FFT to obtain the frequency domain channel value. The channel quality measurement through the CQ pilot is made after passing the FFT to obtain the frequency domain channel value after the CIR estimation is performed in the time domain.

According to the present invention, a subcarrier, such as a band of the long block LB, is allocated to a pilot included in the first short block SB1, but a subcarrier having orthogonality in the frequency domain is assigned to a pilot included in the second short block SB2. Subcarriers with orthogonality are alternately allocated in the code domain. Therefore, channel estimation and channel quality measurement can be performed at the same time, which is advantageous for scheduling in a high speed environment.

In the structure of the subframe, the first short block SB1 is transmitted in time ahead of the second short block SB2. Data is loaded in the long block LB, and control signals of the data are generally loaded in the long block LB. That is, the control signal is carried in the long block LB closer to the first short block SB1 than the second short block SB2. Since only the pilot for channel estimation is transmitted to the first short block SB1, the pilot of the first short block SB1 can be used to demodulate and decode the control signal, thereby achieving nearly FDM-L performance. . Therefore, by arranging the CQ pilot for channel quality measurement later in time, the degradation of the channel estimation due to the addition of the CQ pilot can be effectively reduced.

12 is a block diagram illustrating a receiver according to an embodiment of the present invention.

Referring to FIG. 12, the receiver 700 includes an FFT unit 740, a subcarrier demapper 750, a channel estimator 755, an IDFT unit 765, and a channel quality estimator 790.

The signal received by the antenna 710 becomes a digitized signal via the RF unit 720. In the digitized signal, the CP is removed by the CP removing unit 730. The time domain signal r _i [n] from which the CP is removed is converted into the frequency domain signal Y _i '[k] by performing an FFT by the FFT unit 740. Here, the size of the FFT is referred to as N _SB for the short blocks SB1 and SB2 and N _{LB for the} long block LB. When the time intervals of the short blocks SB1 and SB2 are 0.5 times the time intervals of the long block LB, N _LB = 2N _SB . The converted signals Y _i '[k] is a signal Y _i [k] through the reverse process of the sub-carrier allocation method by the subcarrier de-mapper (750).

The channel estimator 755 estimates the channel H _i [k] from the pilot of the first short block SB1 and the DM pilot signal of the second short block SB2 as shown in Equations 15 to 17 below.

The equalizer 760 compensates for the data signal included in the long block LB using the estimated channel _Hi [k] as shown in Equation 18 below.

() * Is the conjugate and SNR is the received signal-to-noise ratio that passed through the channel. The IDFT unit 765 performs an IDFT on the compensated signal X _i [k] and converts it to a time domain signal x _i [n].

On the other hand, when the second short block (SB2) signal is received, the IDFT unit 770 passes through the CQ pilot Y ₆ [k] separated in the frequency domain, and converts the time domain signal y ₆ [n]. The CIR estimator 775 estimates the CIR through a cyclic correlation operation with respect to the time domain signal y ₆ [n] as shown in Equation 19 below.

Here, s [n] is a value previously known to the receiver 700 as a time domain CQ pilot signal of the transmitter 100. mod represents a modulo operation.

The window unit 780 performs windowing as shown in Equation 20 with respect to the CIR.

로 변환한다. That is, the window unit 780 replaces the portion excluding the predetermined region in CIR h ₆ [τ] with 0. The DFT unit 785 performs an FFT on the windowed CIR to perform frequency domain channel

.

The channel quality estimator 790 can obtain a channel value for the entire frequency band as shown in Equation 21 below.

를 얻음으로써 결국 전체 주파수 대역에 대한 채널 품질을 얻게 되는 것이다. Channel value estimated at each subcarrier location

By finally we obtain the channel quality for the entire frequency band.

The receiver 700 can be applied to the CDM scheme as well as the proposed scheme. In a typical SC-FDMA system, a guard band is set in the frequency bands at both ends of all the frequency bands that can be transmitted. Due to the setting of the guard band, the length L _SB of the CAZAC sequence forming the subcarrier signals of the short blocks SB1 and SB2 in the CDM scheme is set to a value smaller than the total available N _SB sizes. Therefore, the proposed receiver 700 can be applied to the CDM method, and the process is as follows. The IDFT unit 770 performs an IDFT having an L _SB size on the pilot signal passing through the FFT unit 740 and the subcarrier demapper 750. Subsequently, the CIR estimator 775 and the window unit 780 pass, and the DFT unit 785 performs a DFT having an L _SB size. In the CDM method, the channel estimation value of the frequency domain passing through the DFT can be used for both quality measurement and equalization of the channel.

13 is a graph comparing channel estimation performance. This indicates a BER (bit error rate) according to the moving speed of the terminal. The simulation was performed by recording statistical performance figures through a sufficient number of iterations in randomly changing wireless channels and AWGN (Additive White Gaussian Noise) environments. The radio channel model is based on the COST 207 TU (Typical Urban), which is a mathematical representation of the radio channel situation in a real urban environment. Since each performance evaluation is only for channel estimation performance and quality measurement performance of the channel, the synchronization of the receiver is assumed to be perfect.

Referring to FIG. 13, the signal structure according to the present invention is basically based on the FDM-L scheme, and since a part of the channel estimation pilot is used for measuring the quality of the channel, as shown in the result, the existing FDM-L It can be seen that the BER performance is slightly degraded compared to the method. However, the proposed scheme shows lower bit error performance than the FDM-D and CDM schemes, and as a whole, it can be seen that the performance degradation due to the moving speed is relatively large.

14 is a graph comparing channel quality performance for all frequency bands. Mean square error (MSE) performance according to Eb / No is shown to compare the channel quality measurement performance of each signal structure. As mentioned above, the FDM-L method is excluded from this experiment because it is impossible to measure the channel quality over the entire frequency band.

Referring to FIG. 14, the signal structure according to the present invention exhibits lower MSE performance, that is, the smallest error rate, compared to FDM-D or CDM. Therefore, it can be seen that the quality measurement performance of the channel is improved.

Unlike the FDM-L method, the proposed signal structure is capable of simultaneously performing channel estimation for data demodulation and channel quality measurement for the entire frequency band, and is superior to the FDM-D and CDM methods. Demonstrate performance of estimation performance and quality measurement of channels.

15 is an exemplary view showing a data transmission method according to another embodiment of the present invention.

Referring to FIG. 15, subcarriers are locally allocated to each terminal in the long block LB. The long block LB is allocated with a continuous frequency band for each terminal.

The pilot is carried on the subcarriers of the short blocks SB1 and SB2. Subcarriers of the first short block SB1 are allocated with the same terminals distributed at regular intervals without being adjacent to each other. The subcarriers are distributed to each terminal at regular intervals without being crowded. That is, subcarriers are allocated to the first short block SB1 in the same manner as in the FDM-D scheme.

The FDM-L scheme and the CDM scheme are alternately allocated to the second short block SB2. That is, the second short block SB2 is alternately allocated a subcarrier having frequency domain orthogonality and a subcarrier having code domain orthogonality. That is, the subcarriers having the same band as the band allocated to the subcarrier of the long block LB of the corresponding UE and the subcarriers overlapped with the other terminals are alternately allocated to the pilot signal of the second short block SB2.

Channel estimation and channel quality measurement may use both the pilot of the first short block (SB1) and the pilot of the second short block (SB2). This is because both are transmitted over the entire frequency band.

16 is an exemplary view showing a data transmission method according to another embodiment of the present invention.

Referring to FIG. 16, subcarriers are allocated to the long block LB in each terminal locally.

The pilot is carried on the subcarriers of the short blocks SB1 and SB2. The FDM-L scheme and the CDM scheme are alternately allocated to the first short block SB1. That is, subcarriers having frequency domain orthogonality and subcarriers having code domain orthogonality are alternately allocated to the first short block SB1. The subcarriers having the same band as the band allocated to the subcarrier of the long block LB of the corresponding terminal and the subcarriers allocated overlapping with each other are alternately allocated. The first short block SB1 is alternately allocated a DM pilot (first pilot) for channel estimation and a CQ pilot (second pilot) for measuring the full band channel quality.

The second short block SB2 may be allocated subcarriers of the same long block LB and the same band. That is, subcarriers are allocated to the long block LB and the second short block SB2 in the same manner as the FDM-L scheme.

Channel estimation and channel quality measurement may use the pilot of the first short block (SB1), the pilot of the second short block (SB2) can be used for channel estimation.

17 is an exemplary view showing a data transmission method according to another embodiment of the present invention.

Referring to FIG. 17, subcarriers are locally allocated to each UE in the long block LB.

The pilot is carried on the subcarriers of the short blocks SB1 and SB2. The short blocks SB1 and SB2 are alternately allocated subcarriers with frequency domain orthogonality and subcarriers with code domain orthogonality. The subcarriers having the same band as the band allocated to the subcarrier of the long block LB of the corresponding terminal and the subcarriers allocated overlapping with each other are alternately allocated. The short blocks SB1 and SB2 are alternately allocated a DM pilot (first pilot) for channel estimation and a CQ pilot (second pilot) for measuring the full band channel quality.

Channel estimation and channel quality measurement may use both the pilot of the first short block (SB1) and the pilot of the second short block (SB2). This is because both are transmitted over the entire frequency band.

18 is an exemplary view showing a pilot allocation method according to an embodiment of the present invention.

Referring to FIG. 18, pilots are alternately allocated to subcarriers having frequency domain orthogonality and subcarriers having code domain orthogonality. Therefore, orthogonality between terminals is guaranteed and channel estimation and channel quality measurement are possible at the same time.

The first pilot is carried on subcarriers that do not overlap each other for each terminal, and the second pilot is carried on subcarriers that overlap each other for each terminal. The first pilot becomes a DM pilot for channel estimation and the second pilot becomes a CQ pilot for full band channel quality measurement.

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.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can 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.

As described above, according to the present invention, channel estimation for data demodulation and channel quality measurement for the entire frequency band can be simultaneously performed, and performance deterioration does not occur significantly even when the moving speed of the terminal increases. Therefore, scheduling is advantageous in a high speed environment.

Claims (13)

Allocating subcarriers to a long block including data and a short block including pilots; Converting the long block and the short block into a time domain signal, The time interval of the short block is smaller than the time interval of the long block, and the short block is assigned to the sub-carrier having frequency domain orthogonality and the sub-carrier having code region orthogonality for each terminal alternately. The method of claim 1, The frequency domain orthogonality is the data transmission method of the SC-FDMA system by assigning the sub-carriers do not overlap each other for each terminal. The method of claim 1 The code region orthogonality allocates subcarriers overlapping each other for each terminal, and the terminals are classified through a constant amplitude zero auto-correlation (CAZAC) sequence that is cyclically transformed. The method of claim 1 The code region orthogonality allocates subcarriers overlapping each other for each terminal, and the terminals are classified through a block sequence. The method of claim 1, The short block includes a first short block and a second short block transmitted in time later than the first short block, And a subcarrier having frequency domain orthogonality and a subcarrier having code domain orthogonality, which are alternately allocated to the second short block. 6. The method of claim 5, And a subcarrier having frequency domain orthogonality to the first short block. 6. The method of claim 5, And a subcarrier having frequency domain orthogonality and a subcarrier having code domain orthogonality are alternately allocated to the first short block. In the pilot allocation method for a plurality of terminals, Allocating a DM pilot for data demodulation in a different frequency band for each terminal; And allocating a CQ pilot for channel quality measurement to a frequency band overlapping each other for each of the UEs. 9. The method of claim 8, And the CQ pilot has orthogonality in code region. The method of claim 9, wherein The UEs are distinguished through a CAZAC sequence that is cyclically transformed. A DFT unit converting an input signal into a frequency domain signal; A subcarrier mapper for allocating subcarriers to the frequency domain signal and a pilot; And Including an IFFT unit for converting the sub-carrier assigned signal to a time domain signal, And the subcarrier mapper allocates the pilot to the subcarriers alternately having frequency domain orthogonality and code region orthogonality for each terminal. An FFT unit converting the received signal into a frequency domain signal; A channel estimator estimating a channel in a first pilot included in the frequency domain signal; An equalizer for equalizing data included in the frequency domain signal from the estimated channel; And And a channel quality estimator included in the frequency domain signal and estimating channel quality in a second pilot intersected with the first pilot. In claim 12, The channel quality converts the second pilot into the time domain and obtains and measures a channel impulse response.

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