KR20070098063A - Transceiving method and apparatus in orthogonal frequency division multiple access system - Google Patents

Abstract

A method and an apparatus for transceiving in an OFDMA(Orthogonal Frequency Division Multiple Access) system are provided to perform a low power operation by using a control signal as an IDFT(Inverse Discrete Fourier Transform). An apparatus for transceiving in an OFDMA system includes an FFT unit(423), conjugation operating units(425,427), a control channel modulator, an up-link coupler(431), and switching units(421,433,435). The FFT unit(423) processes data according to up and down transceiving by receiving data transmitted from the outside and conjugation operated up transmission data to perform Fourier transform. At least one conjugation operating unit(425,427) transmits data to be transmitted into the FFT unit by performing conjugation operation when up-transmitting and operates the output data of the FFT unit. The control channel modulator generates the control information of up data when transmitting the up data. The up-link coupler(431) selectively transmits one of the up data and the control information according to the predetermined timing. At least one switching unit(421,433,435) controls the path control of up and down transceiving data.

Description

Transmission and reception method and apparatus in orthogonal frequency division multiple access system {TRANSCEIVING METHOD AND APPARATUS IN ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM}

1 is a block diagram showing the configuration of a terminal in a general OFDM system

2 is a diagram showing a frame structure and a processing time of an FFT / IFFT in a conventional OFDMA system.

3 illustrates a frame structure of a TDD-based OFDMA system according to the present invention.

4 is a block diagram illustrating a terminal in a TDD-based OFDMA system according to the present invention.

5 is a block diagram illustrating in detail a control channel modulator of FIG. 4.

6 is a timing diagram for a control signal in a terminal of the present invention.

7 illustrates signal processing timing in the control channel modulator of FIG.

The present invention relates to a transmission and reception apparatus and method in Orthogonal Frequency Division Multiple Access (OFDMA), and more particularly, to a transmission and reception apparatus in an OFDMA system based on a Time Division Duplexing (TDD) scheme. It is about a method.

Recently, in the mobile communication system, the OFDM transmission scheme has been actively studied as a method useful for high-speed data transmission in a wireless channel. The OFDM scheme is a method of transmitting data using a multi-carrier, and converts a series of symbol strings serially inputted in parallel so that each of them has a plurality of sub-carriers having mutual orthogonality. That is, it is a type of Multi Carrier Modulation (MCM) that modulates and transmits a plurality of sub-carrier channels. In addition, in the OFDM transmission method, an InterSymbol interference (ISI) from a previous symbol can be eliminated by adding a cyclic prefix (CP) copied from the second half of the OFDM symbol before the OFDM symbol. The strong characteristics of the multipath fading channel make the OFDM transmission scheme suitable for broadband high speed communication.

1 is a block diagram showing the configuration of a terminal 100 in a general OFDM system.

Referring to FIG. 1, the terminal 100 is divided into a transmission block and a reception block. Looking at the operation of the transmission block, the source data (FEC encoded) encoded by the frame encoder (111) is passed through the symbol mapper (113) to the QPSK / 16QAM Modulated with a signal such as / 64QAM. The modulated signal is allocated to a subcarrier according to a predetermined rule in subcarrier ordering 115. The subcarriers are multiplied by a scrambling sequence having a unique value by a scrambler 117, and a transmit output signal is generated through an Inverse Fast Fourier Transform (IFFT) 119. Lose. The output signal is transmitted via the antenna 123.

The operation of the reception block performs a reverse operation in contrast to the transmission block. The signal received from the outside through the antenna 123 performs a Fourier transform on the received signal via a Fast Fourier Transform (FFT) 109. The output signal of the FFT 109 is then descrambled via a descrambler 107. The descrambled signal performs channel compensation using a channel estimated from a channel estimator 105. The channel compensated signal is reallocated again through subcarrier reordering 103. The reordered signal then generates data via a symbol demapper and frame decoder 401.

As can be seen from FIG. 1, the terminal of the OFDMA system requires the FFT 109 for downlink reception and the IFFT 119 for uplink transmission. The FFT 109 and the IFFT 119 are represented by Equations 1 and 2, respectively.

Looking at <Equation 1> and <Equation 2>, it can be seen that the relationship as shown in <Equation 3>.

Where K is the scaling factor and depends on how 1 / N is distributed between the FFT and IFFT.

Referring to Equation 3, it can be seen that if the input signal X (k) is conjugated (Conjugate) and then FFT processed and the result is conjugated (Conjugate), the result is the same as the IFFT result. That is, the FFT and the IFFT are actually the same block, and since the uplink / downlink signals exist in time division in the TDD type OFDMA system, they are shared and used as one.

2 illustrates a frame structure and a processing time of an FFT / IFFT in a TDD-based OFDMA system. The parts (a), (b), and (c) indicate the frame structure, the processing time of the FFT, and the processing time of the IFFT, respectively.

Referring to FIG. 2, the frame structure of the OFDMA system shown in (a) is composed of a downlink section T1 and an uplink section T3, for switching time between downlink and uplink transmission. Interval T2 exists. The T2 section is typically about the same time as one symbol time. It is assumed that the FFT processing for the symbol takes one symbol time.

In order to implement the frame structure, FFT processing is performed after all symbols are received in downlink reception as in (b) in the FFT, and in case of uplink transmission, as in (c), IFFT must be completed beforehand. Accordingly, a portion in which the operations overlap, such as the time point 213 at which the operation of the FFT is completed, is generated from the time point 211 at which the operation in the IFFT is performed. Accordingly, the conventional FFT and IFFT are implemented separately.

In order to reduce the complexity of the UE, a time division processing method has been used in which one symbol processing time of the FFT is 1/2 symbol time or less in an overlapping section by sharing FFT and IFFT. When sharing FFTs and IFFTs through time division, problems related to the operating frequency of the FFT block become important. The actual FFT and IFFT are shared. A section in which one symbol FFT processing time is to be operated at 1/2 symbol time or less is only an overlapping section corresponding to 3 symbols, as shown in FIG. However, since the 1/2 symbol time operation is the basis for determining the basic operating frequency of the FFT block design, there is a problem in that the terminal complexity increases compared to the 1 symbol time FFT. In addition, since the up / down data flows overlap in the section where the FFT / IFFT operations overlap, such control is complicated. Recently, reducing the complexity of a terminal in a mobile communication system has become an important factor of product competitiveness. Accordingly, there is a need to propose a new structure so that the FFT / IFFT can be shared.

Accordingly, an object of the present invention is to provide a transmission and reception apparatus and method for reducing complexity in a TDD-based OFDMA system.

Another object of the present invention is to provide a transmission and reception apparatus and method using a new frame structure that can reduce the complexity in a TDD-based OFDMA system.

The present invention for achieving the above-described device is a terminal of an Orthogonal Frequency Division Multiple Access (OFDMA) system based on Time Division Duplexing (TDD), the data transmitted from the outside, and conjugated Fast Fourier Transform (FFT) that receives the calculated uplink data and performs Fourier Transform to process data according to up and down transmission and reception, and performs a conjugate operation on the data to be transmitted during uplink transmission and transmits it to the FFT At least one conjugation operation unit for reconjugating the output data of the FFT, a control channel modulator for generating control information of the next upstream data when the current upstream data is transmitted, and the upstream data and the control information according to a predetermined timing. An uplink combiner transmitting to an antenna, and data flow in the up / down transmission / reception data Switch referred to is characterized in that it includes at least one of the switching.

According to an aspect of the present invention, a method of transmitting data in a terminal of an Orthogonal Frequency Division Multiple Access (OFDMA) system based on time division duplexing (TDD) is provided. Performing a Fourier transform after performing a conjugate operation, performing a conjugate operation on the Fourier transformed data, generating control information of the next upstream data based on previously received control allocation information, and And selecting and transmitting control information of current upstream data and next upstream data of the current context data according to timing.

DETAILED DESCRIPTION Hereinafter, detailed descriptions of preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the same components in the figures represent the same numerals wherever possible. Specific details are set forth in the following description, which is provided to aid a more general understanding of the invention. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

According to the present invention, Fast Fourier Transform (FFT) and IFFT are used for down-modulation and up-modulation in a terminal modem of an Orthogonal Frequency Division Multiple Access (OFDMA) system based on Time Division Duplexing (TDD). We propose a new frame structure for efficiently sharing (Inverse Fast Fourier Transform), and a transmission and reception apparatus and method thereof.

3 is a diagram illustrating a frame structure according to the present invention, which is applied to a TDD-based OFDMA system.

In the OFDMA system, the control channel is allocated to a predetermined symbol in the uplink direction. In case of OFDMA defined in IEEE802.16, the control channel may be a channel quality indicator channel (CQICH) and a ranging channel with respect to an uplink signal. It can exist anywhere in the uplink symbol. In case of a symbol to which a control channel is assigned, only some of actual subcarriers are used.

In the present invention, as shown in FIG. 3, the symbol corresponding to the control channel 305 is allocated to the three symbols before the uplink symbol. When the symbol corresponding to the control channel 305 is forcibly allocated to three symbols overlapping the FFT / IFFT of FIG. 1, a low power design and an effective structure for FFT sharing are possible.

In detail, when both the CQICH and the ranging channel are allocated to the same symbol, one fifth of the maximum usable subcarrier is used. If the control channel is always assigned to the upstream three symbols as shown in FIG. 3, the N-point IDFT is used instead of the IFFT during this period, so that the section where the FFT / IFFT overlaps can be separated, thereby allowing the FFT to perform one symbol time. The design is optimized for low power to operate at

Since the control channel uses a low-order modulation technique such as QPSK, the control channel modulator (including N-point IDFT) is performed by operation of only the sign bit to the input terminal of the IDFT, thereby reducing the complexity. In addition, the control channel 305 assigned to these three symbols may have a separate signal processing flow separate from the normal data flow. Therefore, when the generation of the control channel signal is completed during the entire frame period, an optimal design is possible in terms of power consumption by lowering the operating frequency of the control channel signal generator or using a simple digital signal processor with low performance. That is, the uplink first three symbols are fixedly separated from the uplink symbol that is allocated only the control channel 305 and does not allocate data.

4 is a block diagram showing a terminal according to a preferred embodiment of the present invention.

Referring to FIG. 4, the terminal 400 of the present invention includes an FFT block 423, a control channel modulator 419 for generating a control channel, and a conjugate operation unit 425 and 427 for uplink transmission. And switching units 421, 433, and 435 for controlling transmission and reception, and an uplink combiner 431 for outputting a control signal and a data signal according to timing on a time axis. It is composed. The other functional blocks shown in FIG. 4 perform the same functions as those of FIG. 1, and thus are omitted here.

The conjugate operators 425 and 427 perform a conjugate operation to share the FFT block 423. Referring to the uplink transmission method according to the present invention, the data received from the scrambler 417 performs a conjugate operation by the first conjugate calculating unit 425, performs an FFT process, and then returns the result to the second conjugate calculating unit 427. ) To perform the same function as IFFT. The conjugate operators 425 and 427 are controlled by a transmit / receive FFT control signal (Rx / Tx FFT Control).

The control channel modulator 429 generates a control channel 305 such as a CQICH and a ranging channel, and transmits the generated control channel 305 to the uplink combiner 431.

The uplink combiner 431 transmits a control channel 305 in a three symbol period in which up / down FFT / IFFT overlaps on a time axis, and then transmits data in an uplink transmission period. That is, the uplink combiner 431 assigns only three symbols after the start of the control channel 305, and then the second conjugate calculator 427 until the interval 309 for converting the next uplink and the downlink. Allocate data sent from The control channel and data allocation are controlled by time adjust control information.

In the present invention, since the transmission / reception operation is performed using one FFT, a plurality of switching units 421, 433, and 435 are provided. The FFT input and output are controlled for uplink / downlink reception, and the FFT control is performed at the conjugate calculation units 425 and 427. That is, when the downlink reception is performed, the FFT is connected to the downlink receiving flow, and the uplink is connected.

5 is a block diagram illustrating the control channel modulator 429 of FIG. 4. Referring to FIG. 5, the control channel modulator 429 generates a control signal for allocating the first three symbols during uplink transmission. The control channel modulator 429 includes a control symbol mapper 501, a scrambler 503, and an IDFT 505. The control symbol mapper 501 and the scrambler 503 perform mapping and scrambling of the encoded control signals, respectively. The IDFT 505 obtains time-axis data by performing N-Point Discrete Fourier Transform on the mapped and scrambled control signals according to N subcarriers. It is then sent to the uplink coupler 431. At this time, the symbol mapping of the control channel is performed by a table lookup, etc., without additional signal processing, as a result of the signal processing of the upper layer implemented by software, and the number of actual subcarriers (N) is 1/5 or less. The control symbol is a code signal of QPSK, and much of the operation is represented in a simple form of sign operations and additions, thereby reducing the required signal throughput. At the same time, the usable signal processing time spans one frame, so it can be implemented in S / W in a general signal processor or a central processor (CPU).

Next, the control signal of each switching unit in the terminal of the present invention will be described with reference to FIG. 6.

6 is a timing diagram related to a control signal in a terminal of the present invention. Referring to FIG. 6, antenna control for controlling the switching unit 435 of the antenna 437 generates a downlink reception process in the T1 section and generates a control signal to control for uplink transmission processing in the T2 section. In addition, the up / down FFT control allows downlink reception processing in the T3 section and uplink transmission processing in the T4 section. In this case, there is antenna control and delay in the up / down FFT control according to the downlink reception FFT operation. In the uplink transmission process, IFFT is performed on data symbols.

The uplink combiner 431 performs the time adjustment control accordingly since the output of the control channel modulator 429 goes beyond the output of the control channel modulator 429 and the actual FFT output is used only for the subsequent symbols. That is, the uplink combiner 431 transmits the output signal of the control channel modulator 429 to the antenna in the section T5 of 3 symbol periods from the correct uplink transmission time. Then, the fourth symbol is connected to the antenna to transmit uplink transmission data during the T6 period.

7 is a diagram illustrating signal processing timing in the control channel modulator 429. After the control channel allocation information is acquired in the previous frame, the terminal 400 of the present invention ends at a time when signal processing is performed and an uplink signal should be emitted. In the case of OFDMA, since the operation-related contents of the entire frame must be lowered before the general data to decode the general data, the uplink control channel allocation information is loaded before the down period of the previous frame.

Referring to FIG. 7, the terminal 400 may know n + 1th control channel allocation information at a predetermined time point 709 while receiving an nth downlink. Then, the control channel allocation information can be obtained at the time of transmitting the nth uplink frame. At this point, the control channel modulator 429 starts the control channel signal processing and completes the transmission start point 715 of the next N + 1th uplink frame. That is, the control channel modulator 429 can secure the time of one frame until the completion time 715.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention can reduce the complexity of the UE by sharing one FFT through a frame structure in which the uplink three symbols are fixedly allocated to the control channel in the frame of the TDD-based OFDMA. Therefore, it is possible to operate at low power. In addition, there is an effect that can increase the utilization (actual operation time / total time) of each block.

Claims (2)

In a terminal of an Orthogonal Frequency Division Multiple Access (OFDMA) system based on Time Division Duplexing (TDD), A Fast Fourier Transform (FFT) for receiving data transmitted from the outside and conjugated uplink data and performing Fourier transform to process data according to up and down transmission and reception; At least one conjugate operation unit performing conjugation to data to be transmitted during uplink transmission to the FFT, and conjugating the output data of the FFT again; A control channel modulator for generating control information of the next uplink data during the current uplink data transmission; An uplink combiner for selectively transmitting the uplink data and the control information according to a predetermined timing; And at least one switching unit for controlling path control of the up / down transmission / reception data. A method of transmitting data in a terminal of an orthogonal frequency division multiple access (OFDMA) system based on time division duplexing (TDD), Performing a Fourier transform after the data is conjugated; Performing a conjugate operation on the Fourier transformed data again; Generating control information of the next upstream data based on the received control allocation information; Selectively transmitting control information of current upstream data and next upstream data of the current context data according to a predetermined timing.

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