KR101225182B1 - method for transmitting common feedback channel and tranceiver therefor - Google Patents

Abstract

Provided are a method and a transceiver for generating a feedback signal pattern of a common feedback channel using a cyclic shift in a multiple access system. A method of generating a feedback signal pattern includes generating a first transmission symbol by adding a cyclic prefix to a transmission symbol of a feedback signal, and performing a second and subsequent transmission by adding a cyclic prefix after cyclically shifting the first transmission symbol. Generating a symbol.

OFDM, OFDMA, feedback pattern, cyclic shift

Description

Method for transmitting common feedback channel and transceiver for same {method for transmitting common feedback channel and tranceiver therefor}

An embodiment of the present invention relates to a method for generating a feedback signal pattern of a common feedback channel and transmitting it to a counterpart using a cyclic shift in a multiple access system, and a transceiver for the same.

Recent mobile communication systems adopt link adaptation techniques such as Hybrid Automatic Retransmit request (HARQ) and adaptive modulation, which change the transmission scheme according to the channel state, thereby providing additional performance. Gaining benefits.

In order to use the link adaptation technique, it is necessary to feed back a successful decoding of the received data, channel state information, etc. from the receiver to the transmitter. In unicast communication, in which a transmission packet is transmitted to only one receiver, a dedicated feedback channel is allocated to each receiver. Therefore, since the transmitter and the receiver are kept in synchronization with each other, even if the response signal of the feedback signal is out of the cyclic prefix (CP) interval in a multiple access system using a plurality of subcarriers, the intersymbol interference or the intercarrier interference is performed. This is unlikely to occur.

In the case of multicast communication in which one packet is simultaneously transmitted to a plurality of receivers, only the worst channel state of the entire group of receiving the same packet needs to be obtained. Therefore, the same physical resource is used instead of individual feedback allocation that requires excessive feedback burden. A common feedback scheme in which multiple terminals transmit feedback signals at the same time by sharing the same has been considered.

As an example, a hybrid automatic retransmission request (HARQ) ACK / NACK common feedback scheme for multicast data is as follows. Here, the base station as a transmitter and the terminal as a receiver will be described.

The terminal receiving the data transmits an ACK (success reception) or NACK (reception failure) signal on a common feedback channel shared for the multicast group to inform the base station whether the reception was successful. In this case, when the ACK or NACK signal is transmitted in a general signal pattern, when all terminals sharing feedback resources are synchronized and all the transmitted signals are received inside the cyclic prefix, inter-symbol interference or inter-carrier interference does not occur. However, if there are some terminals out of sync, the occurrence of the interferences cannot be excluded.

1 illustrates an example of a configuration of a transmission signal in a common feedback channel according to a conventional scheme.

As an example of a synchronization mismatch between the base station and the terminal, it may be assumed that the terminal is in an idle mode. That is, when the terminal in the sleep mode receives a multicast service, the terminal does not maintain uplink synchronization with the base station. Therefore, when the terminal transmits a feedback signal on the common feedback channel, the reception time at the base station may be shifted from the original reception time. As shown in FIG. 1, when the time difference deviates from the cyclic prefix, inter-symbol interference and inter-carrier interference occur, which causes a problem in that reception performance is deteriorated.

In order to solve such a problem, an embodiment of the present invention proposes a signal configuration method having excellent reception performance even when there is a time delay of more than a cyclic prefix in a feedback channel commonly used for terminals belonging to the same multicast service.

One aspect of the present invention relates to a method for transmitting a feedback signal by a transmitter of a multiple access system, the method comprising: generating a first transmission symbol by adding a cyclic prefix to a transmission symbol of the feedback signal, and transmitting the first transmission symbol; Generating a second and subsequent transmission symbols by adding a cyclic prefix after cyclically shifting a symbol, and transmitting the generated transmission symbols to an uplink common feedback channel. It is about.

Here, the cyclic shift includes the steps of dividing the remaining portions of the transmission symbols before the cyclic shift except for the cyclic transposition into a plurality of blocks, transitioning the transmission symbols one block by one direction, and the transition Moving the last block of a transmission symbol to the front of the transmission symbol.

The length of the block may be set to be equal to the length of the cyclic prefix, and the cyclic prefix may be added by copying the last block of the transmission symbol to the front part of the transmission symbol.

Another aspect of the present invention relates to a transmitter for transmitting a feedback signal in a multiple access system, comprising: a feedback pattern generator for cyclically shifting a transmission symbol of the feedback signal to generate a feedback pattern, and a cyclic prefix to the generated feedback pattern A cyclic prefix adder to be added and a transmitting circuit for transmitting the cyclic prefix added feedback pattern to a common feedback channel, and determining whether to perform feedback on a signal received from a counterpart, and if the feedback is needed, the feedback. The pattern generator may further include a feedback controller for requesting generation of a feedback pattern.

Herein, the feedback pattern generator generates a first transmission symbol by adding a cyclic prefix to a transmission symbol of the feedback signal, generates a first transmission symbol by cyclically shifting the first transmission symbol, and then adds a cyclic prefix to the second and subsequent transmission symbols. Create

The feedback pattern generator divides the remaining portions excluding the cyclic prefix from the transmission symbols before the cyclic shift into a plurality of blocks of a predetermined length, transitions the transmission symbols by one block in one direction, and then transmits the transition. Cyclic transition is performed by moving the last block of symbols to the front of the transmission symbol.

The feedback pattern generator may generate a feedback signal pattern for each cell by generating the same feedback signal pattern for each cell and scrambled the feedback signal pattern with a different scramble code for each cell. An algorithm may be used to generate a feedback signal pattern for each cell at once.

According to the present invention, when multiple terminals simultaneously transmit feedback information by sharing the same physical resource in the same OFDMA-based communication system, mutual interference between sub-symbols and inter-carrier interference, which may occur due to different reception timings of signals fed back from each terminal, may be minimized. Can be.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. In order to clearly illustrate the present invention, parts not related to the description are omitted, and like parts are denoted by similar reference numerals throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

In general, a communication system includes a transmitter and a receiver. Here, the transmitter and the receiver may be referred to as a transceiver that performs both a transmission function and a reception function. However, in order to clarify the description of feedback, one side of transmitting feedback data is called a transmitter, and the other side in charge of transmitting general data to the transmitter is defined as a receiver.

Throughout the specification, the feedback signal collectively refers to a signal that the terminal or the base station reports to the other party about a signal received from the other party, and includes channel quality information (CQI) and channel state information (eg, SINR (Signal). to Interference and Noise Ratio (SNR), Signal to Noise Ratio (SNR), Precoding Matrix Index (PMI), and ACK / NACK response message according to HARQ retransmission.

Embodiments of the present invention can be used in various multi-carrier communication systems. As an example of multi-carrier communication, orthogonal frequency division multiplexing (OFDM) is used by dividing the entire system bandwidth into a plurality of subcarriers with orthogonality. In terms of frequency, a certain number of subcarriers are gathered to form one symbol. constructs a symbol.

Embodiments of the present invention relate to a method and apparatus for transmitting a common feedback channel such that interference between symbols and adjacent subcarriers do not occur even when there is a time offset from the cyclic prefix in the reception of the feedback signal.

Transmission Patterns for Public Feedback Channels

2 is a diagram illustrating a transmission pattern of a common feedback channel according to an embodiment of the present invention.

In the multicast environment, even if there is no synchronization between the transmitter and the receiver, and there is a delay out of the cyclic prefix at the receiver, the receiver maintains orthogonality between subcarriers after the Fast Fourier Transform and no interference between adjacent symbols. To do this, the feedback signal viewed in the time domain must have a continuous repetitive characteristic.

Embodiments of the present invention impart repetitive characteristics to the feedback signal through cyclic shift and cyclic transposition. This will be described in detail as follows.

As shown in FIG. 2, an embodiment of the present invention divides a feedback signal pattern of an original symbol into a plurality of blocks corresponding to the size of a cyclic prefix CP.

The first symbol transmitted in the common feedback channel is the same as the configuration of the normal OFDM symbol, the latter signal sample (block 1 in the original symbol of Figure 2) corresponding to the size of the cyclic prefix (CP) to the front of the OFDM symbol Is created by copying to.

The second symbol is the trailing signal sample corresponding to the magnitude of the cyclic prefix (CP) in the original signal pattern except for the cyclic prefix (CP) portion of the first symbol (the first block in the first symbol of FIG. 2). (The first block after the first symbol in FIG. 2) is moved to the front part. This is called a cyclic shift. In the cyclically shifted signal pattern, a signal part of the rear part corresponding to the magnitude of the cyclic prefix (CP) (block 2 after the second symbol in FIG. 2) is copied to the front part.

From the third symbol, the process of generating the second symbol is repeated. In other words, the magnitude of the cyclic prefix (CP) in the original signal pattern, except for the cyclic prefix (CP) portion (the second block in the second symbol of FIG. 2) in the second symbol for cyclic shift. The signal signal of the latter part corresponding to (the second block after the second symbol in FIG. 2) is moved to the front part. In the cyclically shifted signal pattern, the signal part of the rear part corresponding to the size of the cyclic prefix (CP) (block 3 after the third symbol in FIG. 2) is copied to the front part.

Configuration of the Public Feedback Channel

FIG. 3A illustrates a case in which a feedback signal of a common feedback channel includes two symbols, and FIG. 3B illustrates a case in which a feedback signal of a common feedback channel includes three symbols. In the feedback channel of FIG. 3A, the pattern in which the first symbol and the second symbol are sequentially transmitted is repeated, and in the feedback channel of FIG. 3B, the pattern in which the first symbol, the second symbol, and the third symbol are sequentially transmitted is repeated. Similarly, even when the common feedback channel is composed of N-1 symbols (N is a natural number of 2 or more), the feedback signal is repeated to repeat the pattern in which the first symbol, ..., and the N-1 th symbol are sequentially transmitted. Can be configured.

When the symbols configured as shown in FIGS. 3A and 3B are transmitted through a feedback channel, even if a signal is received with a time difference greater than the length of the cyclic prefix, the symbols have a continuous pattern, so that orthogonality between subcarriers is maintained and interference occurs between adjacent symbols. I never do that.

4 illustrates an example of configuration of physical resources of a common feedback channel for transmission of a feedback signal pattern according to an embodiment of the present invention.

The common feedback channel resource is composed of N_block basic blocks, and each basic block is composed of N_time symbols arranged on the time axis and N_freq subcarriers arranged on the frequency axis. FIG. 4 illustrates a case in which 15 basic blocks (N_block = 15) including three symbols (N_time = 3) and two subcarriers (N_freq = 2) are arranged. Therefore, the common feedback channel occupies N_freq x N_block subcarriers in an OFDM symbol, and transmits a predetermined pattern by occupying the same subcarrier for N_time symbols.

When the common feedback signal pattern according to the embodiment of the present invention is expressed by the equation (1).

Where i is the index of subcarriers occupied by the physical resources of the feedback channel, k _i is the frequency index of the actual physical subcarriers occupied by the physical resources of the feedback channel, N _cp is the number of samples of the cyclic prefix, and N _FFT is the FFT Is the size. Scr _m (i) is a basic sequence value (or scrambling sequence value) to be transmitted from the m th cell to the i th feedback subcarrier, and satisfies a relationship of N _time <N _FFT / N _CP . P _l (i) means a value of a signal transmitted through the i th feedback subcarrier of the l th symbol.

Feedback pattern transmitter

5 is a block diagram schematically illustrating a configuration of a feedback channel transmitter according to an embodiment of the present invention. The transmitter 100 of the present embodiment includes a receiving circuit 110, a feedback controller 120, a feedback pattern generator 130, a subcarrier mapper 140, and parallel-serial. A parallel-serial converter 150, an inverse fast fourier transformer (IFFT) 160, a cyclic prefix adder 170, and a transmit circuitry 180.

The receiving circuit 110 receives a signal received from the other party through an antenna, digitizes it and sends it to the feedback controller 120.

The feedback controller 120 determines whether to perform feedback on the signal received from the counterpart, and requests feedback generation to the feedback pattern generator 130 when feedback is required. For example, if it is determined that an error that cannot be recovered is included as a result of decoding the signal received from the counterpart, the feedback pattern generator 130 is requested to generate a feedback pattern of the NACK message. As another example, when it is determined that the channel state is degraded by a predetermined reference or more while receiving a signal from the other party or when the predetermined period is returned, the feedback pattern generator generates a feedback pattern for the channel state information of the corresponding reception channel. Ask 130.

The feedback pattern generator 130 generates a feedback signal pattern through the aforementioned cyclic shift. The feedback pattern generator 130 may generate a feedback signal pattern for each cell by generating the same feedback signal pattern for each cell and scrambling the feedback signal pattern with a different scramble code for each cell. 1 may be used to generate a feedback signal pattern for each cell at a time.

The subcarrier mapper 140 maps the feedback signal pattern to the subcarrier, and if there is data and / or control signal transmitted together with the feedback signal, maps the feedback signal pattern to the subcarrier together with the feedback signal.

Parallel-to-serial converter 150 serializes the feedback signal mapped to the subcarrier.

The inverse fast Fourier transformer 160 converts a signal in a frequency domain mapped to a frequency subcarrier into a signal in a time domain.

The cyclic prefix adder 170 copies the last predetermined length portion of the inverse Fourier transformed feedback signal to the front portion of the corresponding signal.

The transmitting circuit 180 performs IF (intermediate frequency) processing and RF (radio frequency) processing on the feedback signal to which the cyclic prefix is added, and transmits it through the antenna.

Feedback pattern transmitter

6 is a block diagram schematically illustrating a configuration of a feedback channel receiver according to an embodiment of the present invention. The receiver 200 of the present embodiment includes a receive circuitry 210, a cyclic prefix remover 220, a fast fourier transformer (FFT) 230, and a serial-parallel converter. 240, a subcarrier selector 250, a feedback pattern detector 260, and a data detector 270.

The reception circuit 210 receives a feedback signal received from the transmitter 100 through an antenna, processes the radio frequency (RF) and the intermediate frequency (IF), and digitizes the signal to the cyclic prefix remover 220.

The cyclic prefix remover 220 removes the cyclic prefix from the front of the received feedback signal and sends the cyclic prefix to the fast Fourier transformer 230.

The fast Fourier transformer 230 converts the feedback signal in the time domain from which the cyclic prefix has been removed to the signal in the frequency domain, and the serial-parallel converter 240 parallelizes the feedback signal converted into the frequency domain into a plurality of subcarriers.

The feedback pattern detector 260 extracts a feedback pattern from each subcarrier selected by the subcarrier selector 250, and the data detector 270 extracts data and / or control signals from the subcarrier.

Receiving Performance According to Patterning of Feedback Signal

7A and 7B are graphs illustrating an experimental result on a reception performance of a feedback pattern according to an embodiment of the present invention in comparison with a conventional feedback method.

FIG. 7A shows a comparison of the SNR loss ratio of a receiver for a feedback pattern transmission method using three symbols and two subcarriers as a basic block and a conventional feedback transmission method, and FIG. 7B shows two symbols and four subcarriers as a basic block. The SNR loss ratio of the receiver is compared with that of the feedback pattern transmission scheme and the conventional feedback transmission scheme.

As can be seen from FIGS. 7A and 7B, in the case of transmission using a feedback pattern, even if the receiving time difference of the receiver increases according to a time delay, it can be seen that there is no significant change in the loss ratio of the SNR compared to the conventional feedback transmission method. Therefore, high QoS can be guaranteed even for signals fed back from the terminal in idle mode.

The above-described embodiments of the present invention are not implemented only through methods and apparatuses, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiments of the present invention or a recording medium on which the program is recorded. The implementation can be easily implemented from the description of the above-described embodiments.

In addition, although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of the invention.

1 illustrates an example of a configuration of a transmission signal in a common feedback channel according to a conventional scheme.

2 is a diagram illustrating a transmission pattern of a common feedback channel according to an embodiment of the present invention.

FIG. 3A illustrates a case in which a feedback signal of a common feedback channel includes two symbols, and FIG. 3B illustrates a case in which a feedback signal of a common feedback channel includes three symbols.

4 illustrates an example of configuration of physical resources of a common feedback channel for transmission of a feedback signal pattern according to an embodiment of the present invention.

5 is a block diagram schematically illustrating a configuration of a feedback channel transmitter according to an embodiment of the present invention.

6 is a block diagram schematically illustrating a configuration of a feedback channel receiver according to an embodiment of the present invention.

7A and 7B are graphs illustrating an experimental result on a reception performance of a feedback pattern according to an embodiment of the present invention in comparison with a conventional feedback method.

Claims (10)

In the method of the transmitter of the multiple access system transmits a feedback signal, Generating a first transmission symbol by adding a cyclic prefix to the transmission symbol of the feedback signal; Cyclically shifting the first transmitted symbol and adding a cyclic prefix to generate second and subsequent transmitted symbols; And Transmitting the generated transmission symbols on an uplink common feedback channel Method of transmitting a common feedback channel comprising a. The method of claim 1, wherein the cyclic shift Dividing the remaining portion except for the cyclic prefix from the transmission symbol before the cyclic shift into a plurality of blocks of the cyclic prefix length; Translating the transmission symbols by one block in one direction; And Moving the last block of the shifted transmission symbol to the front of the corresponding transmission symbol Method of transmitting a common feedback channel comprising a. delete The method of claim 2, wherein the cyclic transpose The method of transmitting a common feedback channel added by copying the last block of the transmission symbol to the front of the transmission symbol. In the transmitter for transmitting a feedback signal in a multiple access system, A feedback pattern generator for generating a feedback pattern by cyclically shifting a transmission symbol of the feedback signal; A cyclic prefix adder that adds a cyclic prefix to the generated feedback pattern; And Transmission circuit for transmitting the feedback pattern to which the cyclic prefix is added to a common feedback channel / RTI &gt; The feedback pattern generator, And generating a first transmission symbol by adding a cyclic prefix to the transmission symbol of the feedback signal, and generating a second and subsequent transmission symbols by adding a cyclic prefix after cyclically shifting the first transmission symbol. delete The method of claim 5, wherein the feedback pattern generator is The remaining portion of the transmission symbol before the cyclic shift except for the cyclic prefix is divided into a plurality of blocks of the cyclic prefix length, the transmission symbols are shifted one block by one direction, and the last block of the transition symbol is transmitted. A transmitter that performs a cyclic shift by moving to the front of the transmission symbol. The method of claim 5, And a feedback controller for determining whether to perform feedback on a signal received from a counterpart and requesting generation of a feedback pattern to the feedback pattern generator when feedback is required. The method of claim 5, wherein the feedback pattern generator is And generating a feedback signal pattern for each cell by generating the same feedback signal pattern for each cell and scrambling the feedback signal pattern with a different scramble code for each cell. The transmitter of claim 5, wherein the feedback pattern generator generates a feedback signal pattern for each cell at a time by using a prepared algorithm.

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