JP2005192000A - Multicarrier communication system, and transmitter, receiver, transmission method, and reception method used for same system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multicarrier communication system which reduces an interference between sub-carriers. <P>SOLUTION: In a transmitter, code spreading is performed by copying modulation symbols for a number of times corresponding to a spreading factor and multiplying the copied symbols by random patterns. Inverse Fourier transform is performed to the signal after the code spreading, its phase is shifted by an amount of phase in proportion to the spreading factor by every OFDM symbol constituting the modulation symbol, and the resultant signal is transmitted to a receiver. The influence of the interference by the adjacent sub-carrier is reduced by rotating the phase of the sub-carrier by an amount corresponding to the amount of phase shifted on the transmitting side, multiplying every sub-carrier by the random patterns and adding a plurality of OFDM symbols constituting the modulation signal on the receiving side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a multicarrier communication system that combines orthogonal frequency code division multiplexing (OFDM) and code spreading, and a transmission apparatus, reception apparatus, transmission method, and reception method used in this system.

OFDM is known as a high-speed transmission technique in a frequency selective fading environment. (For example, refer nonpatent literature 1.)
In OFDM, the frequency interval between subcarriers can be narrowed by making each subcarrier orthogonal in a frequency space. For this reason, it is difficult to be affected by the frequency characteristics of the communication path, and high-speed transmission is easily realized. The schematic diagram of the subcarrier adjacent to FIG. 6 is shown. Since the two subcarriers are orthogonal to each other, the frequency components of the adjacent subcarriers are zero at the center frequency of a certain subcarrier as shown in FIG.
Matsue Hideaki, Morikura Masahiro, “802.11 High-Speed Wireless LAN Textbook” IDG Japan, March 29, 2003, p. 127-130, 183-18686

  By the way, the transmitter included in the transmitter and the receiver each have a frequency error with respect to a specific nominal oscillation frequency. When there is an offset between the oscillation frequencies of the transmitter and the receiver, as shown in FIG. 6B, the frequency component of the received signal in the receiver is offset to either on the frequency axis. At this time, the frequency component of the adjacent subcarrier is not 0, and this influence is called “intersubcarrier interference”.

  As can be seen from FIG. 6, the signal component of each subcarrier is attenuated as the center frequency is further away, so that the influence of adjacent subcarriers is particularly great. If there is inter-subcarrier interference, the signal components of other subcarriers are mixed in the signal components of each subcarrier after the fast Fourier transform (FFT), which causes deterioration in reception characteristics.

  The present invention has been made in view of this problem, and provides a multicarrier communication system capable of reducing inter-subcarrier interference, and a transmission device, a reception device, a transmission method, and a reception method used in this system. To do.

According to a first aspect of the present invention, in a multicarrier communication system including a transmission device and a reception device that communicate with each other using an Orthogonal Frequency Division Multiplexing (OFDM) scheme, the transmission device transmits one modulation symbol. A spreading factor indicating how many OFDM symbols are to be transmitted is set, a modulation symbol modulated for each subcarrier is copied a number of times corresponding to the spreading factor, and a random pattern is applied to each to perform code spreading. A second means for performing an inverse Fourier transform on the signal after spreading, and a phase shift of the signal after the inverse Fourier transform by a phase amount corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol. 3 for receiving a signal transmitted from the transmitter. The receiving apparatus for demodulating the modulation symbol rotates the phase of the subcarrier by a fourth means for performing Fourier transform and separating the subcarrier by subcarrier, and an amount corresponding to the phase amount shifted on the transmission side. Multicarrier communication comprising: fifth means; and sixth means for multiplying a random pattern used on the transmission side for each subcarrier and adding a plurality of OFDM symbols constituting the modulation symbol. A system is provided.

  According to the second aspect of the present invention, in a transmission device used in a multicarrier communication system that performs communication using an orthogonal frequency division division scheme, a spreading factor indicating how many OFDM symbols are used to transmit one modulation symbol is set. First means for copying the modulation symbol modulated for each subcarrier a number of times corresponding to the spreading factor, applying a random pattern to each, and performing code spreading, and second applying inverse Fourier transform to the spread signal And a third means for transmitting the signal after inverse Fourier transform with a phase shift corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol. A transmitting device is provided.

According to a third aspect of the present invention, a spreading factor indicating how many OFDM symbols are used to transmit one modulation symbol is set in a multicarrier communication system that performs communication using an orthogonal frequency division division scheme, and subcarriers are set. A first means for copying the modulation symbol modulated every time a number of times corresponding to the spreading factor, applying a random pattern to each of the symbols, and a second means for performing an inverse Fourier transform on the spread signal; Receiving a signal transmitted from a transmission apparatus comprising: a third means for phase-shifting the signal after inverse Fourier transform by a phase amount corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol; A receiving device that demodulates the modulation symbol; a fourth means that performs Fourier transform and separates each subcarrier;
A fifth means for respectively rotating the phase of the subcarriers by an amount corresponding to the phase amount shifted on the transmission side, and a plurality of random symbols used on the transmission side are multiplied for each subcarrier to constitute the modulation symbol And a sixth means for adding the OFDM symbols. A receiving apparatus is provided.

  According to a fourth aspect of the present invention, in a transmission method used in a multi-carrier communication system that performs communication using an orthogonal frequency division division scheme, a spreading factor indicating how many OFDM symbols are used to transmit one modulation symbol is set. A first step of copying the modulation symbol modulated for each subcarrier a number of times corresponding to the spreading factor, applying a random pattern to each, and code spreading, and a second step of performing inverse Fourier transform on the spread signal And a third step of transmitting the signal after inverse Fourier transform with a phase shift corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol. A transmission method is provided.

According to a fifth aspect of the present invention, it is used in a multi-carrier communication system that performs communication by an orthogonal frequency division division method, sets a spreading factor indicating how many OFDM symbols are transmitted with one modulation symbol, and sets subcarriers. A first step of copying the modulation symbol modulated every time a number of times corresponding to the spreading factor, applying a random pattern to each, and performing code spreading; and a second step of performing inverse Fourier transform on the spread signal Receiving the signal transmitted through the third step of phase-shifting the signal after the inverse Fourier transform by a phase amount corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol, and demodulating the modulation symbol In the receiving method, a fourth step of performing Fourier transform and separating each subcarrier;
A fifth step of respectively rotating the phase of the subcarrier by an amount corresponding to the phase amount shifted on the transmission side and a random pattern used on the transmission side are multiplied for each subcarrier to form a plurality of modulation symbols And a sixth step of adding a plurality of OFDM symbols. A receiving method is provided.

According to a sixth aspect of the present invention, in a multicarrier communication system comprising a transmission device and a reception device that communicate with each other by an orthogonal frequency division division scheme, the transmission device performs serial-parallel conversion on a transmission information sequence that is input in series-parallel. Conversion means, modulation means for modulating a transmission information sequence after serial-parallel conversion to generate modulation symbols, and a spreading factor indicating how many OFDM symbols are used to transmit one modulation symbol, and setting the modulation symbols Modulation symbol holding means for holding a time obtained by multiplying one OFDM symbol length by the spreading factor; first random pattern generating means for generating a random pattern in which a pattern is updated every one OFDM symbol time length; and the modulation symbol holding Multiplication means for multiplying the modulation symbols held by the means by the random pattern, and random pattern multiplication Inverse Fourier transform means for inverse Fourier transforming the subsequent modulation symbol to convert it to a time waveform, phase shift means for phase-shifting the signal after inverse Fourier transform for each OFDM symbol, and the OFDM to the time waveform after phase shift Guard interval adding means for adding a guard interval for each symbol, and transmission means for converting the signal with the guard interval added to a high frequency band and transmitting the signal to the outside, wherein the receiving device is transmitted from the transmitting means. Receiving means for receiving the received signal, guard interval removing means for extracting the effective symbol by removing the guard interval from the signal received by the receiving means, and Fourier transforming the effective symbol by Fourier transform and separating it into subcarrier components Shift by the phase shift means for each subcarrier component with the conversion means Phase rotation means for rotating the phase of the subcarrier component according to the phase amount, and second random pattern generation means for generating a random pattern of the same series as the random pattern generated by the first random pattern generation means And integration means for integrating the modulation symbols for a time obtained by multiplying the subcarrier component whose phase is rotated by the phase rotation means by the random pattern in units of modulation symbols, and multiplying the 1 OFDM symbol length by the spreading factor, Multi-carrier comprising: demodulating means for demodulating the output of the integrating means to obtain received information; and parallel-serial converting means for converting the received information obtained by the demodulating means into a serial received information string A communication system is provided.

  According to a seventh aspect of the present invention, when one modulation symbol is transmitted as K (K is a natural number) OFDM symbols, the phase shift means performs time waveform length after inverse Fourier transform for each OFDM symbol. A multi-carrier communication system is provided that increases the phase shift amount by 1 / K of.

  According to an eighth aspect of the present invention, in a transmission device used in a multicarrier communication system that performs communication by an orthogonal frequency division division method, the transmission device performs serial-parallel conversion means for performing serial-parallel conversion on an input transmission information sequence. And modulation means for modulating the transmission information sequence after serial-parallel conversion to generate modulation symbols, and a spreading factor indicating how many OFDM symbols are used to transmit one modulation symbol. Modulation symbol holding means for holding a time obtained by multiplying the symbol length by the spreading factor, random pattern generation means for generating a random pattern in which a pattern is updated every 1 OFDM symbol time length, and held by the modulation symbol holding means Multiplication means for multiplying the modulation symbol by the random pattern, and a modulation pattern after the random pattern multiplication. Inverse Fourier transform means for transforming Bol into a time waveform by inverse Fourier transform, phase shift means for phase-shifting the signal after inverse Fourier transform for each OFDM symbol, and time waveform after phase shift for each OFDM symbol There is provided a transmission apparatus comprising guard interval addition means for adding a guard interval, and transmission means for converting a signal to which the guard interval is added into a high frequency band and transmitting the signal to the outside.

According to a ninth aspect of the present invention, a serial-parallel conversion means for serial-parallel conversion of an input transmission information sequence and transmission after serial-parallel conversion is used for a multi-carrier communication system that performs communication by orthogonal frequency division division. Modulation means that modulates an information sequence to generate modulation symbols, and a spreading factor indicating how many OFDM symbols are transmitted in one modulation symbol are set, and the modulation symbol is multiplied by the spreading factor by one OFDM symbol length. A modulation symbol holding means for holding the time, a first random pattern generating means for generating a random pattern whose pattern is updated every 1 OFDM symbol time length, and a modulation symbol held by the modulation symbol holding means The multiplication means for multiplying the random pattern and the inverse Fourier transform of the modulation symbol after the random pattern multiplication Inverse Fourier transform means for converting to a waveform, phase shift means for phase-shifting the signal after inverse Fourier transform for each OFDM symbol, and guard interval addition for adding a guard interval for each OFDM symbol to the time waveform after the phase shift And a transmission device comprising: a transmission device comprising: a transmission device that converts a signal to which a guard interval is added into a high-frequency band and transmits the signal to the outside, wherein the reception device is transmitted from the transmission device. Receiving means for receiving a signal; guard interval removing means for extracting a valid symbol by removing a guard interval from the signal received by the receiving means; and Fourier transform means for Fourier-transforming the effective symbol and separating it into subcarrier components And the position shifted by the phase shift means for each subcarrier component. Phase rotation means for rotating the phase of the subcarrier component according to the amount; second random pattern generation means for generating a random pattern of the same series as the random pattern generated by the first random pattern generation means; Integrating means for multiplying a subcarrier component whose phase has been rotated by the phase rotation means by the random pattern in units of modulation symbols, and integrating modulation symbols for a time obtained by multiplying one OFDM symbol length by the spreading factor; and the integration A receiving device is provided, comprising: demodulating means for demodulating the output of the means to obtain received information; and parallel-serial converting means for converting the received information obtained by the demodulating means into a serial received information string Is done.

  According to the present invention, inter-subcarrier interference can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1 and 2 are block diagrams showing a first embodiment according to the present invention, and FIG. 1 shows a configuration example of a transmitter. FIG. 2 shows a configuration example of a receiver corresponding to this transmitter.

  The transmitter and receiver of the present invention employ a scheme that combines OFDM and a code spreading scheme. The code spreading method includes a time spreading method, a frequency spreading method, and a method in which both methods are combined. In the present invention, the time spreading method is used.

  In OFDM, one modulation symbol modulated for each subcarrier is transmitted in one OFDM symbol time. On the other hand, the method employed in the present invention copies a plurality of modulation symbols, applies a random pattern to each of them, performs code spreading, performs IFFT (Inverse Fast Fourier Transform) on the spread signal, A waveform is generated.

  On the other hand, the receiver performs reception processing in the same way as normal OFDM until the FFT processing, but for each subcarrier after FFT, the reverse is performed by multiplication based on the random pattern used on the transmission side and the combination of a plurality of OFDM symbols. Spreading processing is performed, and then modulation symbols are demodulated by subsequent detection.

  1 includes a serial-to-parallel converter 101, a modulator 102, a copy unit 103, a random pattern generator 104, a multiplier 105, an inverse Fourier transformer 106, a phase shift unit 107, a guard interval adder 108, and a transmitter. 109.

2 includes a receiving unit 200, a guard interval removing unit 201, a Fourier transform unit 202, a rotation amount control unit 203, a phase rotation unit 204, a random pattern generation unit 205, a multiplication unit 206, a synthesis unit 207, and a detection unit 208. The parallel-serial conversion unit 209 is configured. Note that the error correction encoding / decoding unit and the interleaving unit of both the transmitter and the receiver are not directly related to the present invention, and are not described.

  First, the operation of the transmitter will be described. In FIG. 1, a transmission information sequence that has been subjected to error correction coding or the like is divided into subcarriers by a serial-to-parallel conversion unit 101 and subjected to modulation processing by a modulation unit 102 for each subcarrier. If the number of subcarriers is 100 and the modulation scheme is QPSK (Quadrature Phase Shift Keying), 200 are extracted from the transmission information sequence, and 2 bits are assigned to each subcarrier to generate modulation symbols.

  The copy section 103 of each subcarrier copies one modulation symbol by the spreading factor. Here, the spreading factor means how many OFDM symbols transmit one modulation symbol. In terms of mounting, it can be realized by performing serial-parallel conversion and modulation processing for each OFDM signal generation processing for the spreading factor, and holding modulation symbols for the time corresponding to the spreading factor. For example, when the spreading factor is 4, the same modulation symbol value may be held while four OFDM symbols are generated.

  The random pattern generation unit 104 generates a pseudo-random pattern of a series having sufficiently low correlation when one or more patterns are out of phase. For example, an M-sequence pseudo-random pattern having a long code length can be used. Also, in order to perform spreading processing for the purpose of reducing interference between other stations, the sequence or phase of the random pattern used for each transmitting station is different.

  Multiplier 105 multiplies the random pattern generated by random pattern generator 104 and the modulation symbol held by copy unit 103. When the modulation signal is considered as a complex signal and the random pattern is a complex random sequence having different real and imaginary components, the multiplication unit 105 performs complex multiplication. Assuming that the complex amplitude of the random pattern is 1, the modulated symbol after multiplication is a phase symbol rotated at an angle of, for example, ± 45 degrees or ± 135 degrees with respect to the modulation symbol.

  The inverse Fourier transform unit 106 performs IFFT processing on the outputs of the multiplication unit 105 of each subcarrier at once to generate a time waveform.

  The generated time waveform is subjected to a phase shift of a different shift amount for each OFDM symbol in the phase shift unit 107. This phase shift will be described later.

  In the guard interval adding unit 108, the specified length of the end portion is added to the start end portion for each OFDM symbol.

  The signal to which the guard interval is added is frequency-converted to an RF band in the transmission unit 109, amplified, and transmitted from the antenna.

  The above is the outline of the operation of the transmitter. The operation of the phase shift unit 107, which is a characteristic part of the transmitter according to the present invention, will be described in detail below with reference to the drawings.

FIG. 3 is a diagram for explaining the relationship between the time spreading process and the phase shift. FIG. 3 shows an example where the spreading factor = 4. 1, the transmission information sequence is divided into N subcarriers, and the portion surrounded by the one-dot chain line in the upper part of the figure is a modulation symbol of subcarrier # 1, and four OFDM symbols. It is transmitted in time (S1 to S4 in FIG. 3). Four consecutive random patterns (r1, r2, r3, r4) generated by the random pattern generation unit 104 are applied to S1 to S4. The same random pattern is applied to all subcarriers in one OFDM symbol. That is, random pattern r1 is applied to all subcarriers in the OFDM symbol at time S1, and random pattern r2 is applied to all subcarriers in the OFDM symbol at time S2, and all subcarriers in the OFDM symbol at time S3. Is multiplied by the random pattern r3, and all subcarriers in the OFDM symbol at time S4 are multiplied by the random pattern r4.

  The lower part of FIG. 3 shows the relationship between phase shift and guard interval addition. In the phase shift in the phase shift unit 107, the time waveform after IFFT is divided into four according to the spreading factor = 4, and the phase shift is performed in units thereof. In the figure, the time waveform for each quarter is shown by four, a, b, c, and d. In order to make it easy to see, the waveform of the first ¼ portion (indicated as a) is underlined.

  The OFDM symbol S1 corresponding to the head of one modulation symbol has a phase shift amount of 0, S2 is 1/4, S3 is 2/4, and S4 is 3/4. Since the end portion of the waveform after the phase shift is copied as a guard interval signal, S1 is d, S2 is c, S3 is b, and S4 is a guard interval waveform.

  The state of phase rotation for each subcarrier after IFFT by this phase shift will be described with reference to FIG.

  The time waveform after IFFT is a waveform obtained by adding the time waveforms of all subcarrier components. For simplicity, the lowest frequency component (denoted as subcarrier # 1) of the time waveform after IFFT and the next High frequency components (denoted as subcarrier # 2) are shown individually. In accordance with FIG. 3, four divisions a, b, c and d are also shown.

  As shown in the upper part of FIG. 4, the IFFT output time waveform includes one wavelength for subcarrier # 1 and two wavelengths for subcarrier # 2. The phase of each subcarrier in this state is set to 0 degree. Similarly, the waveform when the phase shift amount is 1/4 (the lower part of FIG. 4) includes waveforms of one wavelength and two wavelengths, respectively. A phase rotation of −90 degrees occurs in # 1 and −180 degrees occurs in subcarrier # 2. That is, even with the same phase shift amount (1/4 of the total length in FIG. 4), the phase rotation amount differs for each subcarrier.

  As described above, the transmitter of FIG. 1 copies a plurality of modulation symbols by the number corresponding to the spreading factor, performs code spreading by applying a random pattern to each, and performs IFFT using the modulation symbols of all subcarriers. After the conversion to the time waveform, the phase shift unit 107 performs a phase shift of a different shift amount for each OFDM symbol, so that each subcarrier component of the time waveform transmitted after IFFT is rotated by an amount different in phase. It has been made.

  Next, the operation of the receiver will be described with reference to FIG.

  A signal transmitted from the transmitter is received by the antenna, and frequency-converted by the receiving unit 200. A received signal that has passed through the receiving unit 200 is input to the guard interval removing unit 201.

  The guard interval removing unit 201 extracts a received signal having an effective symbol length obtained by subtracting the guard interval length from the OFDM symbol length from a portion not affected by the preceding and following OFDM symbols from the received signal, and passes the received signal to the Fourier transform unit 202.

  The Fourier transform unit 202 performs fast Fourier transform on the waveform of the input effective symbol and separates it into subcarrier components.

  Each separated subcarrier component is input to the phase rotation unit 204, and the phase of the subcarrier component is rotated according to the rotation amount instructed from the rotation amount control unit 203.

  The rotation amount control unit 203 determines the rotation amount of each subcarrier based on the phase shift amount on the transmission side. The phase shift amount on the transmission side is sent from the transmitter side when the receiver negotiates with the transmitter. Alternatively, the phase shift amount or spreading factor may be fixed between the transmitter and the receiver in advance. In this case, it is not necessary for the transmitter to send a phase shift amount to the receiver for each communication negotiation.

  When the phase is shifted by 1 / M of the effective symbol length on the transmitter side, the phase of the lowest frequency subcarrier in which one wavelength is equal to the effective symbol length is rotated by −360 / M degrees (M is a natural number). For subcarriers having a frequency that includes N wavelengths in the effective symbol length, the phase rotates by −360 / M × N degrees. The rotation amount control unit 203 generates control information for reversely rotating the phase by + 360 / M × N according to the subcarrier in order to cancel the influence of the phase shift, and sends the control information to the phase rotation unit 204.

  The signal after the influence of the phase shift is removed is multiplied by the pattern generated by the random pattern generation unit 205 that generates the same pattern as that used by the transmitter, by the multiplication unit 206. However, the phase rotation is reversed from the processing on the transmission side.

  Thereafter, the signal after the pattern multiplication is added by the combining unit 207 for the spreading factor, the demodulation unit 208 performs detection processing, and the parallel / serial conversion unit 209 converts the signal into a serial signal to obtain a reception information sequence. In order to perform synchronous detection in the demodulator 208, propagation path distortion for each subcarrier is obtained, and amplitude / phase compensation is performed using the value.

  The relationship between phase rotation and intersubcarrier interference in the receiver will be described with reference to FIG. FIG. 5 shows an example in which one modulation symbol is spread over four OFDM symbols. FIG. 5 shows only one subcarrier. However, in order to simplify the explanation, it is assumed that phase rotation by a random pattern is not performed and that there is no influence of noise.

  The four spread vectors obtained by spreading the modulation symbols are Sa, Sb, Sc, and Sd. Since they are the same symbol, they are all equal vectors S. Also, let Ia, Ib, Ic, and Id be interference components due to adjacent subcarriers on the higher frequency side when there is a frequency offset. If fluctuations in frequency offset in four OFDM symbol times can be ignored, the interference components are all equal (I). Therefore, when the phase shift is not performed, the received signal is as shown in FIG. Since the receiver vector-combines 4 symbols and returns them to one modulation symbol,

となっている。

It has become.

Next, consider a case where phase shift is performed. Assume that when a certain amount of phase shift is performed, a phase rotation of 45 degrees occurs in the subcarrier currently focused on. As shown in FIG. 6 (b), the phase shift is not performed in the first OFDM symbol and is the same as in FIG. 6 (a). However, the second and subsequent symbols are rotated by 45 degrees, and Sd is 180 degrees. . In adjacent subcarriers, a phase rotation twice 45 degrees occurs, so the components leaking into the subcarriers also have the same amount of rotation. Therefore, phase rotation of Ib is 45 × 1 × 2 = 90 degrees, Ic is 45 degrees × 2 × 2 = 135 degrees, and Id is 45 degrees × 3 × 2 = 270 degrees.

  The receiver performs phase rotation for each subcarrier. In this case, phase rotation of 0 degrees, −45 degrees, −90 degrees, and −135 degrees is performed every OFDM symbol time. At this time, since the interference component from the adjacent subcarrier is also subjected to the same phase rotation as the subcarrier component of interest, as shown in FIG. 6C, Sa to Sd return to the same vector, Ia to Id do not return to the same vector as the original. Therefore, the result of vector synthesis of 4 symbols is

となり、変調シンボル成分と干渉成分の電力比は、

The power ratio between the modulation symbol component and the interference component is

となり、本願発明の処理により変調シンボル成分と干渉成分の電力比を改善、すなわち隣接サブキャリアによる干渉の影響を低減することができる。

Thus, the power ratio between the modulation symbol component and the interference component can be improved by the processing of the present invention, that is, the influence of interference caused by adjacent subcarriers can be reduced.

  The above describes the case where the phase is shifted by 45 degrees. However, when the phase shift is set to 90 degrees, the interference components for each OFDM time after the reverse rotation in the receiver are each 90 degrees out of phase. Interfering components cancel each other out to zero by the vector synthesis. Therefore, the interference component due to the adjacent subcarrier can be reduced to 0 by appropriately selecting the phase shift amount.

  The phase shift amount for setting the interference component due to the adjacent subcarrier to 0 can be obtained as follows. When each OFDM symbol is phase-shifted by 1 / M of the effective symbol length, it is rotated by −360 / M × N degrees in a certain subcarrier, and adjacent subcarriers are only −360 / M × (N + 1) degrees. Rotates (M is a natural number). Therefore, the difference is -360 / M degrees. When the phase rotation for each subcarrier is performed in the receiver, the phase rotation generated here is canceled, but the interference component remains by a rotation amount of −360 / M degrees. When one modulation symbol is transmitted in K OFDM symbol times, the residual of 0 degrees, −360 / M degrees,..., −360 / M × (K−1) degrees from the first OFDM symbol. Become. The component after vector synthesis becomes 0 when K = M.

  Therefore, when one modulation symbol is spread over K OFDM symbols, the phase shift amount is increased by 1 / K of the effective symbol length for each OFDM symbol.

  As described above, in the present invention, the modulation symbol is copied a number of times corresponding to the spreading factor by the transmission device, and each is multiplied by a random pattern to perform code spreading. The code-spread signal is subjected to inverse Fourier transform, and is phase-shifted by a phase amount corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol and transmitted to the receiving apparatus. On the receiving side, the phase of the subcarrier is rotated by an amount corresponding to the phase amount shifted on the transmitting side, the random pattern is multiplied for each subcarrier, and a plurality of OFDM symbols constituting the modulation symbol are added. Reduce the influence of interference by adjacent subcarriers.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows the structure of the transmitter which concerns on embodiment of this invention. The block diagram which shows the structure of the receiver which concerns on embodiment of this invention. The figure explaining the relationship between a spreading | diffusion process and a phase shift. The figure which shows the mode of the phase rotation for every subcarrier by a phase shift. The figure explaining the relationship between the phase rotation in a receiver, and intersubcarrier interference. The figure for demonstrating the frequency offset and subcarrier interference in OFDM communication.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Serial / parallel conversion part, 102 ... Modulation part, 103 ... Copy part, 104,205 ... Random pattern generation part, 105 ... Multiplication part, 106 ... Inverse Fourier transform part, 107: phase shift unit, 108: guard interval adding unit, 109 ... transmitting unit, 200 ... receiving unit, 201 ... guard interval removing unit, 202 ... Fourier transform unit, 203 ..Rotation amount control unit, 204 ... phase rotation unit, 206 ... multiplication unit, 207 ... synthesis unit, 208 ... detection unit, 209 ... parallel to serial conversion unit

Claims (9)

Orthogonal Frequency Division (Orthogonal Frequency Division)
In a multicarrier communication system composed of a transmission device and a reception device that perform communication in a Multiplexing (OFDM) scheme,
The transmitter is
A spreading factor indicating how many OFDM symbols are transmitted with one modulation symbol is set, the modulation symbol modulated for each subcarrier is copied a number of times corresponding to the spreading factor, and a random pattern is applied to each to spread the code. A first means for performing
A second means for performing an inverse Fourier transform on the signal after spreading;
A third means for phase-shifting the signal after the inverse Fourier transform by a phase amount corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol;
A receiver that receives a signal transmitted from the transmitter and demodulates the modulation symbol,
A fourth means for performing Fourier transform and separating each subcarrier;
Fifth means for respectively rotating the phase of the subcarrier by an amount corresponding to the phase amount shifted on the transmission side;
A multicarrier communication system comprising: a sixth means for multiplying a random pattern used on the transmission side for each subcarrier and adding a plurality of OFDM symbols constituting the modulation symbol. Orthogonal Frequency Division (Orthogonal Frequency Division)
In a transmission device used in a multicarrier communication system that performs communication in a Multiplexing (OFDM) scheme,
A spreading factor indicating how many OFDM symbols are transmitted with one modulation symbol is set, the modulation symbol modulated for each subcarrier is copied a number of times corresponding to the spreading factor, and a random pattern is applied to each to spread the code. A first means for performing
A second means for performing an inverse Fourier transform on the signal after spreading;
And a third means for transmitting the signal after the inverse Fourier transform with a phase shift corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol. Orthogonal Frequency Division (Orthogonal Frequency Division)
It is used in a multi-carrier communication system that performs communication in a Multiplexing (OFDM) system, sets a spreading factor indicating how many OFDM symbols are transmitted with one modulation symbol, and spreads the modulation symbols modulated for each subcarrier. A number of times corresponding to the rate, a first means for performing code spreading by applying a random pattern to each, a second means for performing an inverse Fourier transform on the spread signal, and a signal after the inverse Fourier transform, In a receiving apparatus for receiving a signal transmitted from a transmitting apparatus comprising a third means for phase shifting by a phase amount corresponding to the spreading factor for each OFDM symbol constituting a modulation symbol, and demodulating the modulation symbol,
A fourth means for performing Fourier transform and separating each subcarrier;
Fifth means for respectively rotating the phase of the subcarrier by an amount corresponding to the phase amount shifted on the transmission side;
And a sixth means for multiplying a random pattern used on the transmission side for each subcarrier and adding a plurality of OFDM symbols constituting the modulation symbol. Orthogonal Frequency Division (Orthogonal Frequency Division)
In a transmission method used in a multi-carrier communication system that performs communication in a Multiplexing (OFDM) scheme,
A spreading factor indicating how many OFDM symbols are transmitted with one modulation symbol is set, the modulation symbol modulated for each subcarrier is copied a number of times corresponding to the spreading factor, and a random pattern is applied to each to spread the code. A first step of performing
A second step of applying an inverse Fourier transform to the spread signal;
And a third step of transmitting the signal after the inverse Fourier transform with a phase shift corresponding to the spreading factor for each OFDM symbol constituting the modulation symbol. Orthogonal Frequency Division (Orthogonal Frequency Division)
It is used in a multi-carrier communication system that performs communication in a Multiplexing (OFDM) system, sets a spreading factor indicating how many OFDM symbols are transmitted with one modulation symbol, and spreads the modulation symbols modulated for each subcarrier. A number of times corresponding to the rate, a first step of performing code spreading by applying a random pattern to each, a second step of performing an inverse Fourier transform on the signal after spreading, and a signal after the inverse Fourier transform, In a receiving method of receiving a signal transmitted through a third step of phase shifting by a phase amount corresponding to the spreading factor for each OFDM symbol constituting a modulation symbol, and demodulating the modulation symbol,
A fourth step of performing Fourier transform and separating each subcarrier;
A fifth step of rotating the phase of each of the subcarriers by an amount corresponding to the phase amount shifted on the transmission side;
And a sixth step of multiplying a random pattern used on the transmission side for each subcarrier and adding a plurality of OFDM symbols constituting the modulation symbol. Orthogonal Frequency Division (Orthogonal Frequency Division)
In a multicarrier communication system composed of a transmission device and a reception device that perform communication in a Multiplexing (OFDM) scheme,
The transmitter is
Serial-parallel conversion means for serial-parallel conversion of the input transmission information sequence;
Modulation means for modulating a transmission information sequence after serial-parallel conversion to generate a modulation symbol;
Modulation symbol holding means for setting a spreading factor indicating how many OFDM symbols are transmitted with one modulation symbol, and holding the modulation symbol for a time obtained by multiplying one OFDM symbol length by the spreading factor;
First random pattern generation means for generating a random pattern in which a pattern is updated every one OFDM symbol time length;
Multiplying means for multiplying the modulation symbols held by the modulation symbol holding means by the random pattern;
Inverse Fourier transform means for transforming the modulation symbol after the random pattern multiplication into a time waveform by inverse Fourier transform;
Phase shift means for phase-shifting the signal after inverse Fourier transform for each OFDM symbol;
Guard interval adding means for adding a guard interval for each OFDM symbol to the time waveform after the phase shift;
A transmission means for frequency-converting the signal with the guard interval added to a high frequency band and transmitting the signal to the outside;
The receiving device is:
Receiving means for receiving a signal transmitted from the transmitting means;
Guard interval removing means for removing the guard interval from the signal received by the receiving means and extracting an effective symbol;
Fourier transform means for Fourier transforming the effective symbol and separating it into subcarrier components;
Phase rotation means for rotating the phase of the subcarrier component according to the phase amount shifted by the phase shift means for each subcarrier component;
Second random pattern generation means for generating a random pattern of the same series as the random pattern generated by the first random pattern generation means;
Integrating means for integrating the modulation symbols for a time obtained by multiplying the subcarrier component whose phase has been rotated by the phase rotation means and the random pattern in units of modulation symbols, and multiplying the OFDM symbol length by the spreading factor;
Demodulation means for demodulating the output of the integration means to obtain received information;
A multi-carrier communication system comprising: parallel-serial conversion means for converting the reception information acquired by the demodulation means into a serial reception information sequence.   When transmitting one modulation symbol with K OFDM symbols (K is a natural number), the phase shift means increases the phase shift amount by 1 / K of the time waveform length after inverse Fourier transform for each OFDM symbol. The multi-carrier communication system according to claim 1 or 6, wherein Orthogonal Frequency Division (Orthogonal Frequency Division)
In a transmission device used in a multicarrier communication system that performs communication in a Multiplexing (OFDM) scheme,
The transmitter is
Serial-parallel conversion means for serial-parallel conversion of the input transmission information sequence;
Modulation means for modulating a transmission information sequence after serial-parallel conversion to generate a modulation symbol;
Set the spreading factor to indicate how many OFDM symbols to transmit one modulation symbol,
Modulation symbol holding means for holding the modulation symbol for a time obtained by multiplying one OFDM symbol length by the spreading factor;
Random pattern generating means for generating a random pattern in which a pattern is updated every one OFDM symbol time length;
Multiplying means for multiplying the modulation symbols held by the modulation symbol holding means by the random pattern;
Inverse Fourier transform means for transforming the modulation symbol after the random pattern multiplication into a time waveform by inverse Fourier transform;
Phase shift means for phase-shifting the signal after inverse Fourier transform for each OFDM symbol;
Guard interval adding means for adding a guard interval for each OFDM symbol to the time waveform after the phase shift;
A transmission apparatus comprising: a transmission unit that converts a signal to which a guard interval is added into a high frequency band and transmits the signal to the outside. Orthogonal Frequency Division (Orthogonal Frequency Division)
Used in a multi-carrier communication system that performs communication using a Multiplexing (OFDM) method, and generates a modulation symbol by serial-parallel conversion means for performing serial-parallel conversion on an input transmission information sequence, and modulating the transmission information sequence after serial-parallel conversion. Modulation means for setting, a spreading factor indicating how many OFDM symbols to transmit one modulation symbol, and a modulation symbol holding means for holding the modulation symbol for a time obtained by multiplying the OFDM symbol length by the spreading factor; First random pattern generation means for generating a random pattern whose pattern is updated every one OFDM symbol time length; and multiplication means for multiplying the modulation symbol held by the modulation symbol holding means by the random pattern; Inverse Fourier transform of modulation symbol after random pattern multiplication to time waveform Inverse Fourier transform means, phase shift means for phase-shifting the signal after inverse Fourier transform for each OFDM symbol, guard interval addition means for adding a guard interval for each OFDM symbol to the time waveform after the phase shift, In a receiving apparatus that communicates with a transmitting apparatus that includes a transmission unit that converts a signal with a guard interval to a high frequency band and transmits the signal to the outside,
The receiving device is:
Receiving means for receiving a signal transmitted from the transmitting means;
Guard interval removing means for removing the guard interval from the signal received by the receiving means and extracting an effective symbol;
Fourier transform means for Fourier transforming the effective symbol and separating it into subcarrier components;
Phase rotation means for rotating the phase of the subcarrier component according to the phase amount shifted by the phase shift means for each subcarrier component;
Second random pattern generation means for generating a random pattern of the same series as the random pattern generated by the first random pattern generation means;
Integrating means for integrating the modulation symbols for a time obtained by multiplying the subcarrier component whose phase has been rotated by the phase rotation means and the random pattern in units of modulation symbols, and multiplying the OFDM symbol length by the spreading factor;
Demodulation means for demodulating the output of the integration means to obtain received information;
A receiving apparatus comprising: parallel-serial conversion means for converting the reception information acquired by the demodulation means into a serial reception information sequence.

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