JP2010124416A - Ofdm transmitter and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM transmitter and method capable of obtaining best performance in different situations. <P>SOLUTION: The OFDM transmitter includes: a storage means 101 for storing a plurality of pulse waveforms with different waveforms; a first selection means 101 for selecting a pulse waveform corresponding to band information relating to a transmission signal from among the plurality of pulse waveforms as a first selection pulse waveform; a calculation means 102 for calculating a cancel symbol such that leakage power becomes minimum in response to the first selection pulse waveform; a mapping means 103 for mapping a data symbol and the cancel symbol onto a subcarrier; a first obtaining means 103 for inverse-Fourier-transforming the data symbol and cancel symbol mapped onto the subcarrier to obtain an OFDM symbol; a second obtaining means 105 for wave-shaping the OFDM symbol based on the first selection pulse waveform to obtain a transmission OFDM symbol; and a transmission means 107 for transmitting the transmission OFDM symbol. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an OFDM transmitter and method applying a spurious power reduction technique.

In an OFDM transmitter, there is a technique for suppressing spurious power (interference power) outside a specific frequency band or out of band using subcarriers not used for data transmission (see, for example, Non-Patent Document 1 and Non-Patent Document 2). .
“Active interference cancellation technique for MB-OFDM cognitive radio” Proc of IEEE European Microwave Conference, vol.2, Oct. 2004, pp.1105-1108. “Reduction of Out-of-Band Radiation in OFDM Systems by Insertion of Cancellation Carriers”, IEEE Commun. Letter, vol.10, No6, June 2006.

  The conventional method does not operate to reduce the interference power by simultaneously controlling the pulse waveform and the interference canceling subcarrier. In the conventional method, transmission is performed with the same pulse waveform for all subcarriers, and an interference cancellation configuration using a plurality of pulse waveforms simultaneously is not studied. For this reason, in the conventional method, the effect of reducing the interference power varies depending on the width and position of the band in which interference is to be suppressed, so that it is difficult to obtain desired performance according to the situation.

  The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide an OFDM transmitter and method for obtaining the best performance corresponding to the situation.

  In order to solve the above-described problem, the OFDM transmitter of the present invention is a data carrier that transmits a data symbol, which is a part of a plurality of subcarriers, and a subcarrier that is a part of the data carrier. Storage means for storing a plurality of pulse waveforms having different waveforms, applied to a cancel carrier for transmitting a cancel symbol for reducing leakage power to the target band, and a band related to a transmission signal from the plurality of pulse waveforms First selection means for selecting a pulse waveform corresponding to information as a first selection pulse waveform; calculation means for calculating the cancel symbol so that the leakage power is minimized according to the first selection pulse waveform; Mapping means for mapping data symbols and the cancellation symbols to the subcarriers; First acquisition means for performing inverse Fourier transform on the mapped data symbol and cancellation symbol to acquire an OFDM (orthogonal frequency division multiplexing) symbol, and shaping the OFDM symbol according to the first selected pulse waveform, and transmitting the OFDM symbol Second acquisition means for acquiring the transmission OFDM symbol, and transmission means for transmitting the transmission OFDM symbol.

  The OFDM transmitter of the present invention also includes a data carrier that transmits a data symbol, which is a part of a plurality of subcarriers, and a leakage power to a target band that is a subcarrier different from the data carrier. Storage means for storing a plurality of pulse waveforms having different waveforms, applied to a cancel carrier for transmitting a cancel symbol for reducing the frequency, a first subcarrier group in a fixed frequency range from the target band, and A division means for dividing the plurality of subcarriers into a second subcarrier group other than the first subcarrier group, and the first subcarrier group corresponding to band information relating to a transmission signal from the plurality of pulse waveforms. First selection means for selecting a first pulse waveform to be selected as a first selection pulse waveform, and the leakage current according to the first selection pulse waveform Calculating means for calculating the cancellation symbol so as to minimize, mapping means for mapping the data symbol and the cancellation symbol to the subcarrier, and a part of the data symbol mapped to the first subcarrier group Third acquisition means for performing inverse Fourier transform on a first data symbol that is a part of the cancellation symbol and a first cancellation symbol that is a part of the cancellation symbol to obtain a first OFDM (orthogonal frequency division multiplexing) symbol; and the first selection pulse Fourth acquisition means for acquiring a first transmission OFDM symbol by shaping the first OFDM symbol according to a waveform, the remaining second data symbol of the data symbol mapped to the second subcarrier group, and the cancellation The second cancel symbol of the remaining symbol And fifth acquisition means for acquiring a second OFDM symbol, and sixth acquisition for acquiring a second transmission OFDM symbol by shaping the second OFDM symbol according to a preset second pulse waveform Means for adding the first transmission OFDM symbol and the second transmission OFDM symbol to obtain a combined OFDM symbol, and transmission means for transmitting the combined OFDM symbol. And

  Furthermore, the OFDM transmitter of the present invention includes a data carrier that transmits a data symbol, which is a part of a plurality of subcarriers, and a leakage power to a target band that is a subcarrier different from the data carrier. Storage means for storing a plurality of pulse waveforms having different waveforms, applied to a cancel carrier for transmitting a cancel symbol for reducing the frequency, a first subcarrier group in a fixed frequency range from the target band, and A division means for dividing the plurality of subcarriers into a second subcarrier group other than the first subcarrier group, and the first subcarrier group corresponding to band information relating to a transmission signal from the plurality of pulse waveforms. The first pulse waveform to be selected is selected as the first selection pulse waveform, and the second pulse waveform to be applied to the second subcarrier group is selected as the second selection waveform. Second selection means for selecting as a pulse waveform; calculation means for calculating the cancellation symbol so that the leakage power is minimized according to the first selection pulse waveform; and the data symbol and the cancellation symbol as the subcarrier. Mapping means for mapping to the first carrier, first acquisition means for obtaining a first OFDM (orthogonal frequency division multiplexing) symbol by inverse Fourier transforming the data symbol and the cancellation symbol mapped to the subcarrier, and the first selection pulse waveform Accordingly, fourth acquisition means for waveform-shaping the first OFDM symbol to acquire a first transmission OFDM symbol, a first data symbol that is a part of the data symbol mapped to the second subcarrier group, and the cancellation The first carrier that is part of the symbol 8th acquisition means for performing inverse Fourier transform on a cell symbol to acquire a second OFDM symbol, and waveform-shaping the second OFDM symbol according to a difference between the second pulse waveform and the first pulse waveform, and a second transmission OFDM Ninth acquisition means for acquiring a symbol, seventh acquisition means for adding the first transmission OFDM symbol and the second transmission OFDM symbol to acquire a composite OFDM symbol, and transmission means for transmitting the composite OFDM symbol It is characterized by comprising.

  Still further, the OFDM transmitter of the present invention is a data carrier that transmits a data symbol, which is a part of a plurality of subcarriers, and N (N is a subcarrier different from the data carrier). A storage means for storing a plurality of pulse waveforms having different waveforms, applied to a cancel carrier for transmitting a cancel symbol for reducing leakage power to a target band of an integer of 1 or more, All integers from 1 to N) N subcarrier groups of the nth subcarrier group within a certain frequency range from the target band, and not included in any nth subcarrier group from 1 to N Division means for dividing the plurality of subcarriers into N + 1 subcarrier groups which are subcarriers, and band information related to transmission signals from the plurality of pulse waveforms. Selection means for selecting the m-th pulse waveform to be applied to the m-th (m is an integer of 1 to N + 1) subcarrier group, and the cancel symbol so that the leakage power is minimized according to the m-th pulse waveform. Calculating means for calculating the data symbol, the mapping means for mapping the data symbol and the cancel symbol to the subcarrier, the mth data symbol that is a part of the data symbol mapped to the mth subcarrier group, and Eighth acquisition means for performing inverse Fourier transform on the first cancellation symbol that is a part of the cancellation symbol to acquire an mth OFDM (orthogonal frequency division multiplexing) symbol; and waveform shaping the mth OFDM symbol according to the mth pulse waveform And ninth acquisition means for acquiring the mth transmission OFDM symbol, and whether m is 1 And adding all of the m transmit OFDM symbols to N + 1, and the 10 acquisition means for acquiring the composite OFDM symbols, characterized by comprising a transmitting means for transmitting the composite OFDM symbol.

  According to the OFDM transmitter and method of the present invention, an appropriate pulse waveform can be selected according to the situation.

Hereinafter, an orthogonal frequency division multiplexing (OFDM) transmitter and method according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that, in the following embodiments, the same numbered portions are assumed to perform the same operation, and repeated description is omitted.
(First embodiment)
The OFDM transmitter of this embodiment will be described with reference to FIG.
The OFDM transmitter of this embodiment includes a cancellation method selection unit 101, a cancellation symbol calculation unit 102, an IFFT (inverse fast Fourier transform) unit 103, a CP (cyclic prefix cyclic prefix) addition unit 104, a window shaping unit 105, D A / A (digital-to-analog) converter 106 and an RF (radio frequency) transmitter 107 are included.
The OFDM transmitter according to the present embodiment uses a part of a plurality of subcarriers as a data carrier for data symbol transmission, and uses a part of subcarriers other than the data carrier to reduce leakage power to a target band. Used as a cancel carrier for cancel symbol transmission. The target band indicates a band where power is to be reduced. In the present embodiment, the target band may be a band where it is desired to reduce spurious power outside the band of the transmission signal, or a band where a notch is to be generated in the spectrum of the transmission signal. The data carrier is a subcarrier that maps a data symbol sequence, and the cancel carrier is a subcarrier that maps a cancel symbol sequence. An OFDM signal that leaks into the target band is simply called interference.

  The cancellation method selection unit 101 refers to band information and selects a pulse waveform to be applied to a plurality of subcarriers from a plurality of candidates. Band information relates to a transmission signal, and includes information on a band used by an OFDM transmitter and information on whether a target band position is in the middle of the band or a target band position is at the end of the band. is there. Band information is input from, for example, a modulation unit (not shown). An example of the band information includes the bandwidth of the target band (number of subcarriers) and the position of the target band as shown in FIG. The cancel method selection unit 101 stores band information and a plurality of pulse waveforms in association with each other, and selects a pulse waveform corresponding to the acquired band information from the plurality of pulse waveforms. Since the pulse waveform is defined by a convolution operation between a rectangular function and a roll-off function (or a root roll-off function), the cancel method selection unit 101 uses a rectangular function and a roll-off function as pulse information about the selected pulse waveform. Print information about and. The details of the cancellation method selection unit 101 will be described below from the description part described later with reference to Expression (11).

  The cancellation symbol calculation unit 102 receives pulse information from the cancellation method selection unit 101, and uses this pulse information and a data symbol sequence to be transmitted to calculate a cancellation symbol so that the leakage power to the target band is minimized. The cancellation symbol calculation unit 102 calculates a cancellation symbol using the Lagrange's undetermined multiplier method so that the interference power to the target band is minimized. The cancel symbol calculation unit 102 calculates a cancel symbol sequence using the frequency response of the pulse waveform. The details of the cancel symbol calculation unit will be described later in the description portion described with reference to FIG.

  IFFT section 103 performs an inverse Fourier transform on a plurality of subcarriers on which data symbols and cancellation symbols are mapped, to generate OFDM symbols. In the embodiment, a data symbol and a cancellation symbol are mapped to a data carrier and a cancellation carrier, respectively, before IFFT in the IFFT unit.

  CP adding section 104 adds only this length from the end of this OFDM symbol as a CP to the beginning of the OFDM symbol so that the OFDM symbol obtained from IFFT section 103 is cyclically lengthened by a certain length.

  Window shaping section 105 shapes the OFDM symbol received from CP adding section 104 according to the pulse waveform selected by cancellation method selection section 101 to obtain a transmission OFDM symbol. The transmission OFDM symbol is, for example, as shown in FIG.

The D / A conversion unit 106 converts the transmission OFDM symbol received from the window shaping unit 105 from a digital signal to an analog signal.
The RF transmitter 107 performs signal processing on the transmission signal received from the D / A converter 106 to generate a radio signal, and transmits this radio signal from the antenna.

  Next, two examples showing subcarrier configurations in the OFDM transmitter of FIG. 1 will be described with reference to FIG. 2 and FIG. In the example of FIG. 2, the target band is in the OFDM signal band, and a notch is generated at the position of the target band using a cancel carrier. Similarly, in the example of FIG. 3, the target band is the end of the OFDM signal, and the configuration is for reducing out-of-band power using a cancel carrier. In FIG. 2 and FIG. 3, the arrows mean subcarriers.

  The guard band is a frequency band between the data carrier and the target band, and a part or all of the subcarriers in the guard band and the target band are used as the cancel carrier. The data symbol sequence and the cancellation symbol sequence output from the cancellation symbol calculation unit 102 are mapped to each subcarrier whose subcarrier interval is Δfs, as shown in FIGS.

Next, the CP adding unit 104 and the window shaping unit 105 in FIG. 1 will be described with reference to FIG.
The plurality of subcarriers mapped as shown in FIG. 2 or FIG. 3 are subjected to inverse Fourier transform in IFFT section 103 to generate OFDM symbols. The length Ts of the OFDM symbol is Ts = 1 / Δfs.

CP adding section 104 adds only the length Tc from the end of the OFDM symbol to the beginning of the OFDM symbol as a cyclic prefix (CP) so that the OFDM symbol cyclically becomes longer by the length Tc.
In accordance with the pulse waveform specified by the pulse information from the cancellation method selection unit 101, the window shaping unit 105 further cyclically converts the OFDM symbol with the length Tw before and after the OFDM symbol to which the CP is added. Append windows shaped to expand (first window and last window). The final OFDM symbol length T including the CP and window portion output from the window shaping unit 105 is T = Ts + Tc + 2Tw.

Next, the pulse waveform selected by the cancellation method selection unit 101 in FIG. 1 will be described with reference to FIG.
FIG. 5 is a diagram illustrating an example of a pulse waveform of a subcarrier. FIG. 4 illustrates the operation for the entire OFDM symbol, that is, the entire subcarrier, which means that a pulse waveform as shown in FIG. 5 is applied to each subcarrier. The pulse waveform of FIG. 5 is shaped into a shape having a leading window portion and a trailing window portion of length Tw, and the portions corresponding to the remaining CP and OFDM symbols of length Tc + Ts are flat at a height of 1. It is a shape like this.

Next, the relationship between the time waveform of the pulse waveform shown in FIG. 5 and the frequency response will be described.
FIG. 6 is a diagram for explaining the relationship among a pulse waveform, a rectangular function, and a window function. The pulse waveform p (t) in FIG. 5 is a convolution of the rectangular function rect (t) having the length Ts + Tc + Tw shown in FIG. 6 and the window function win (t) having the integration area 1 and the length Tw as follows: It can be expressed as (1).

At this time, the relationship between the shape of the head window and the shape of the tail window of the pulse waveform in FIG. 5 can be expressed as the following equations (2) and (3), respectively.

However, Expressions (2) and (3) extract only the Tw portion of the first window and the last window from the pulse waveform, and are defined in the range of time 0 to Tw.

  From the above relationship, the frequency response of the pulse waveform in FIG. 5 is calculated as the product of the frequency response of rect (t) and the frequency Fourier transform of win (t) from the nature of the Fourier transform and convolution operation.

Next, an example of the frequency response of the pulse waveform shown in FIG. 5 will be described with reference to FIG.
The frequency response RECT (f) of the rectangular function rect (t) is the SINC function Sinc (f / Δf). However, Δf = 1 / (Ts + Tc + Tw). Therefore, since the frequency response P (f) of the pulse waveform has a shape obtained by multiplying the SINC function by the frequency response WIN (f) of the window function win (t), it is expressed by the following equation (4). Can do.

For example, when win (t) is a roll-off function having a roll-off rate α, WIN (f) can be expressed by the following formula (5).

However, Δfw = (1 + α) / Tw, and since Tw is usually smaller than T, Δfw is often several to several tens of times larger than Δf. As the window waveform, there can be various shapes such as a root roll-off function, a Blackman window function, and a Hanning window function. The cancel symbol calculation unit 102 calculates a cancel symbol using the frequency response of the pulse waveform.

Next, a cancellation symbol string calculation method in the cancellation symbol calculation unit 102 of FIG. 1 will be described.
The cancellation symbol calculation unit 102 calculates a cancellation symbol string mapped to the cancellation carrier, using the frequency response P (f) of the pulse waveform shown in Expression (4). The set of subcarrier numbers of the data carrier is M, the data symbol mapped to the mth (mεM) subcarrier is d (m), the set of cancel carrier numbers is N, and the nth (nεN) If the cancel symbol mapped to the subcarriers is x (n), the frequency spectrum of the transmission signal can be expressed by the following equation (6).

The purpose of the cancellation symbol calculation unit 102 is to calculate a cancellation symbol sequence {x (n) | n∈N} under the energy constraint condition such that the power in the target band is minimized in Equation (6). It is. That is, a cancel symbol string that satisfies the following conditions is calculated.

Here, E _max is a value indicating the upper limit of the total power of the cancel symbol.

Since Expression (7) is a continuous function and difficult to handle, by discretizing P (f) at a certain frequency interval, {x (n) | n∈N} satisfying Expression (7) is changed to Lagrange's undetermined multiplier. It can be calculated using the method. For example, if the frequency sampling interval is F _S , and the IFFT size of the IFFT unit 103 is K, P (f) can be defined as a discretized vector as shown in the following equation (8).

In order to make the explanation easy to understand, Δf _S is an integral multiple of F _S , and Δf _S = rF _S. At this time, if a vector that is cyclically shifted downward by the vector r × n is defined as q (r), Expression (6) can be expressed by Expression (6-2) discretized as follows.

Where m ₁ , m ₂ , m ₃ ,... Are data carrier numbers, and n ₁ , n ₂ , n ₃ ,. Similarly, Expression (7) can be discretely described as Expression (7-2) below.

However, vector

Is a vector obtained by extracting only the target band portion from the vector S. Matrix

Is defined as a matrix in which only rows corresponding to the target band portion are extracted from A.

The singular value decomposition and the singular value are represented by the following equations (9) and (10), respectively.

At this time, x satisfying the equation (7-2) can be calculated as the following equation (7-3) by using Lagrange's undetermined multiplier method.

However, the following equation (11) holds.

Ζ is a constant such that よ う な x‖ ² = E _max in the above equation. If the above-described method gives a form such as equation (6-2), the calculation can be performed in exactly the same way under other conditions described later.

Next, the operation of the cancel method selection unit 101 will be described.
As described above, the cancellation method selection unit 101 determines a pulse waveform to be applied to the subcarrier, and transmits this waveform to the cancellation symbol calculation unit 102 and the window shaping unit 105 as pulse information. As is clear from the equations (6) and (7), the interference with the target band is a function of the pulse waveform P (f).

In the embodiment, not only the cancel symbol but also the pulse waveform P (f) is simultaneously optimized to minimize interference with the target band. However, since the pulse waveform P (f) has a very high degree of freedom as shown in Expression (4), P (f) is optimized with respect to Expression (7) for each data symbol sequence to be transmitted. Is not a realistic method.
Therefore, in the embodiment, by performing the evaluation of Expression (7) using a random data symbol sequence for several pulse waveforms in advance according to an assumed target band pattern, the target band is obtained in advance. A method of determining a pulse waveform to be used for each pattern is used. In the embodiment, the items to be classified in the target band pattern are first notches (there is a data carrier within a certain frequency range on both sides of the target band) or outside the band (constant on one side of the target band). Second, the bandwidth of the target band is used. As will be described later, since the optimum pulse waveform has a correlation with the bandwidth of the target band, it is not necessary to calculate all the bandwidths, and intermediate values and outer values can be handled by interpolation or extrapolation. .

  The cancel method selection unit 101 stores information on a pulse waveform that is determined in advance and used for each pattern of the target band. An example of this information is the content shown in FIG. FIG. 8 is a table in which optimum pulse waveforms for each pattern of the target band are associated. However, in this example, pulse waveform candidates are limited to those in which the roll-off rate α is changed from 0 to 1 in increments of 0.1 using Equations (4) and (5). Other conditions are Tc = Ts / 8, Tw = Ts / 16, Emax = total number of cancel carriers / 2, number of guard band subcarriers = 4, and number of cancel carriers on one side of the target band = 8. However, since these results are based on the above-described conditions, a table corresponding to FIG. 8 may be prepared in advance using the same method under other conditions. In FIG. 8, the window function is limited to the roll-off function for the purpose of easy understanding, but it is obvious that the same method can be applied even if a window function other than the loaf-off function is included in the pulse waveform candidates.

  Further, here, when the cumulative probability distribution of the interference level is 0.9, an optimum pulse waveform has a minimum interference level. From the results of FIG. 8, it can be seen that the optimum pulse waveform differs depending on the target band. As a trend, it can be seen that the roll-off rate of the roll-off function increases as the target bandwidth increases. However, in the case of the notch, when the number of subcarriers is 28, it is 0.5, and after that it is 0.4, so it cannot be said that the increase is monotonous, but the actual interference level is that the roll-off rate is 0 .4 is almost the same. In addition, when the target band is out of the band, the number of subcarriers is 12 or more and the roll-off rate is the same as 0.4, which indicates that the tendency is different from the case of the notch.

  According to the first embodiment described above, it is noted that there is a difference in the spurious power reduction effect by the subcarrier for interference cancellation depending on the pulse waveform of the subcarrier, and an appropriate pulse waveform can be selected according to the situation. And the best performance corresponding to the situation can be obtained.

(Second Embodiment)
The second embodiment is different from the first embodiment in that two types of subcarrier pulse waveforms are used simultaneously.

An OFDM transmitter according to the second embodiment will be described with reference to FIG.
Compared with the OFDM transmitter of the first embodiment, the OFDM transmitter of this embodiment includes a data dividing unit 901, a second IFFT unit 902, a second CP adding unit 104, a second window shaping unit 105, and an adder 903. Newly included.

  The data division unit 901 divides the data symbol sequence into a first data symbol sequence and a second data symbol sequence according to the pulse information acquired from the cancellation method selection unit 904. The first data symbol sequence corresponds to a first subcarrier group that is in a certain frequency range from the target band. The second data symbol string is a data symbol string other than the first data symbol string.

  Second IFFT section 902 performs inverse Fourier transform on the remaining second data symbols of the data symbols mapped to the second subcarrier group to generate second OFDM symbols.

  The adder 903 adds the first OFDM symbol that has been waveform-shaped by adding the CP from the first window shaping unit 105 and the second OFDM symbol that has been waveform-shaped by being added the CP from the second window shaping unit 105.

  The cancellation method selection unit 904 selects a pulse waveform to be applied to a plurality of subcarriers from a plurality of candidates with reference to the subband information. The subband information is information on the band corresponding to the first data symbol sequence, information on the band corresponding to the second data symbol sequence, and the position of the target band corresponding to the first data symbol sequence is in the middle of the band. Or information indicating whether the position of the target band is the end of the band. That is, information corresponding to the first data symbol sequence in the subband information is band information.

Next, two examples showing the subcarrier configuration and pulse waveform assignment in the OFDM transmitter of FIG. 9 will be described with reference to FIGS. 10 and 11. FIG.
FIGS. 10 and 11 show examples in which different pulse waveforms are applied to the subcarriers around the target band and the other portions in FIGS. 2 and 3, respectively. For example, the second pulse waveform that is the default pulse waveform is fixed, and the first pulse waveform that is the pulse waveform around the target band is selected by the cancel method selection unit 904 as described above. It is determined. Here, a data carrier to which the first pulse waveform is applied is a first data carrier, and a data carrier to which the second pulse waveform is applied is a second data carrier.

  Based on the pulse information, the data division unit 901 divides the data symbol sequence into a first data symbol sequence that is transmitted with the first pulse waveform and a second data symbol sequence that is transmitted with the second pulse waveform. The data is sent to the 1 IFFT unit 103 and the second IFFT unit 902 in the lower stage. In other words, the data subcarrier is divided into a first data carrier using the first pulse waveform and a second data carrier using the second pulse waveform. The criteria for division will be described later.

The cancel symbol calculation unit 102 calculates a cancel symbol string by the same method as in the example of FIG. However, since two types of pulse waveforms are used in this example, the frequency spectrum of the transmission signal can be expressed by the following equation (12) instead of equation (6).

However, M1 is a set of subcarrier numbers of the data carrier (first data carrier) to which the first pulse waveform is applied, and M2 is a subcarrier number of the data carrier (second data carrier) to which the second pulse waveform is applied. Is a set of Formula (12) can be expressed in a similar manner by discretizing Formula (6-2) by redefining Formula (6-2) as in Formula (8-2) below.

  Accordingly, the cancel symbol sequence {x (n) | nεN} can be calculated in the same manner as described above. At this time, when the second data carrier and the target band are sufficiently separated from each other, it is possible to approximate by ignoring the first term of Expression (12).

  In FIG. 9, the first data symbol sequence and the cancel symbol sequence are subjected to inverse Fourier transform processing in the upper first IFFT unit 103, and the second data symbol sequence is subjected to inverse Fourier transform processing in the lower second IFFT unit 902. The first and second CP adding units 104 add CPs. The OFDM symbols to which CPs are added are subjected to window shaping in the first and second window shaping sections 105 according to the first pulse waveform and the second pulse waveform, respectively, and then added by an adder 903. The added signal is transmitted from the antenna through the same processing as in FIG.

Next, a data carrier dividing method in the data dividing unit 901, that is, a method for determining a boundary of a pulse waveform applied to the data carrier will be described.
The first determination method uses an intermediate point between the first target band and the end of the second target band or signal band adjacent to the target band as a boundary.
In the second determination method, a boundary between the first data carrier and the second data carrier is determined such that interference power from the signal of the second data carrier adjacent to the first data carrier to the target band is equal to or less than a threshold value. . The interference power hardly needs to be actually measured, and is determined only from the pulse information selected by the cancel method selection unit 904. The interference power is almost determined by the pulse waveform.
The third determination method determines that the power level leaking from the signal of the first data carrier into the second target band is equal to the power level leaking from the signal of the second data carrier into the first target band.
In the fourth determination method, a pulse waveform in which a certain number of subcarriers are determined is assigned to the higher priority in the first target band and the second target band.

  Note that the cancellation method selection unit 904 in FIG. 9 has information on two types of pulse waveforms (first pulse 1 waveform and second pulse waveform) as described above, and which subcarrier uses which pulse waveform (first waveform). Pulse information including information such as a subcarrier boundary between the 1 pulse waveform and the second pulse waveform is generated and output.

  According to the second embodiment described above, when two types of pulse waveforms of subcarriers are used, the pulse waveform of a subcarrier around the target band whose interference is to be reduced is changed, or there are a plurality of target bands. In addition, an appropriate pulse waveform can be set for each target band, and the best performance corresponding to the situation can be obtained. In addition, a transmission signal composed of a plurality of pulse waveforms can be generated simultaneously by a simple method.

(Third embodiment)
In the third embodiment, unlike the second embodiment, the cancel symbol calculation unit 102 generates a first cancel symbol string mapped to the first cancel carrier and a second cancel symbol string in the second cancel carrier. These are respectively sent to the upper first IFFT unit 103 and the lower second IFFT unit 1201. The rest is the same as in the second embodiment.

  As shown in FIG. 12, the OFDM transmitter of this embodiment includes a second IFFT unit 1201 instead of the second IFFT unit 902 of the second embodiment.

  The second IFFT unit 1201 generates an OFDM symbol by performing inverse Fourier transform on the plurality of subcarriers on which the second data symbol and the second cancellation symbol are mapped.

The OFDM transmitter of the third embodiment is used in a situation where there are cancel carriers (first cancel carrier and second cancel carrier) for two locations in the target band, respectively. That is, a subcarrier configuration as shown in FIG. 13 is assumed. Therefore, the second embodiment can be regarded as a special example of the third embodiment. FIG. 13 is a diagram illustrating an example of assignment of subcarriers and pulse waveforms in the OFDM transmitter according to the third embodiment. In this case, the frequency spectrum of the transmission signal can be expressed by the following equation (13) instead of equation (6).

However, N1 is a set of subcarrier numbers of the first cancel carrier, and N2 is a set of subcarrier numbers of the second cancel carrier. Similarly to the above, it can be expressed by the equation (9-2) discretized as follows.

  Therefore, the cancellation symbol sequence {x (n) | nεN1, N2} can be calculated by the same method as before. At this time, the first cancel symbol sequence that is x (n) included in the third term and the second cancel symbol sequence that is x (k) included in the fourth term are approximately the first and third terms. It is also possible to calculate using the terms or only the second and fourth terms.

A case where the above discussion is generalized will be briefly described.
N (N is an integer greater than or equal to 1), where cancellation method selection section 904 is a data carrier that transmits a data symbol, which is a part of a plurality of subcarriers, and a subcarrier that is a part of the data carrier. A plurality of pulse waveforms having different waveforms, which are applied to a cancel carrier for transmitting a cancel symbol for reducing the leakage power to the target band, are stored. A dividing unit that generalizes the data dividing unit 901 includes N subcarrier groups of an nth subcarrier group in a certain frequency range from the nth (n is an integer from 1 to N) target band, and n is The plurality of subcarriers are divided into N + 1 subcarrier groups that are subcarriers not included in any nth subcarrier group from 1 to N. The cancellation method selection unit 904 selects the m-th pulse waveform to be applied to the m-th (m is an integer of 1 to N + 1) subcarrier group corresponding to the band information related to the transmission signal from the plurality of pulse waveforms. A calculation unit that generalizes the cancel symbol calculation unit 102 calculates a cancel symbol according to the mth pulse waveform so that the leakage power is minimized. An IFFT unit obtained by mapping the data symbol and the cancel symbol to the subcarrier, and generalizing the IFFT unit 103, includes the mth data symbol that is a part of the data symbol mapped to the mth subcarrier group, and one of the cancel symbols. An inverse Fourier transform is performed on the first cancellation symbol, which is a part, to obtain an mth OFDM (orthogonal frequency division multiplexing) symbol. A shaping unit that generalizes the window shaping unit 105 shapes the m-th OFDM symbol according to the m-th pulse waveform, and acquires the m-th transmission OFDM symbol. An adder that generalizes the adder 903 adds all m-th transmission OFDM symbols from m to 1 + 1, obtains a combined OFDM symbol, and the RF transmitter 107 transmits the combined OFDM symbol.

  According to the third embodiment described above, it is possible to generate a transmission signal composed of a plurality of pulse waveforms at the same time by a more general method than in the second embodiment.

(Fourth embodiment)
Differences of the fourth embodiment from the third embodiment will be described below. In the fourth embodiment, data input to the first IFFT unit 103 is different from that in the third embodiment. Another difference is that, in the fourth embodiment, as shown in FIG. 14, the second CP adding unit 104 is not provided.

  In the present embodiment, the first IFFT unit 103 inputs the entire data symbol sequence and the cancellation symbol sequence, that is, the first data symbol sequence, the first data symbol sequence, the first cancellation symbol sequence, and the second cancellation symbol sequence. On the other hand, the second IFFT unit 1201 receives the second data symbol sequence and the second cancel symbol sequence as in the third embodiment. At this time, if the second data symbol sequence and the second cancel symbol sequence are defined so that the number of symbols input to the second IFFT unit 1201 is reduced, the overall calculation amount is reduced. That is, the first and second may be defined such that the sum of the second data symbol sequence and the second cancel symbol sequence is smaller than the sum of the first data symbol sequence and the first cancel symbol sequence.

Next, OFDM symbols generated by the OFDM transmitter of this embodiment will be described with reference to FIG.
In the upper stage, a window portion to which the first pulse waveform (p1 (t)) is applied is added by the first window shaping unit 105 to the first OFDM symbol to which the CP is added by the CP adding unit 104 (FIG. 15 (a)). )). On the other hand, in the lower stage, the second IFFT unit 1201 does not have to calculate the entire second OFDM symbol, and only calculates the portion that becomes the first window and the last window as shown in FIG. The second window shaping unit 105 calculates a window portion to which the second pulse waveform minus the first pulse waveform (p2 (t) −p1 (t)) is applied. Thereafter, the adder 903 adds only the OFDM symbol including the window portion calculated by the first CP adding unit 104 and the first window shaping unit 105 and the window portion calculated by the second window shaping unit 105, and D Is sent to the / A converter 106 and transmitted in the same manner as before.

  According to the fourth embodiment described above, the same transmission signal is generated and used for the same purpose as in the third embodiment. However, since the transmission signal generation method differs, two types of pulse waveforms are used. In this case, the transmission signal can be generated with a small amount of calculation.

  As described above, the present invention pays attention to the difference in spurious power reduction effect due to the subcarrier for interference cancellation depending on the pulse waveform of the subcarrier, and can select an appropriate pulse waveform according to the situation. The OFDM transmitter that can obtain the best performance corresponding to the situation was clarified. In addition, an OFDM transmitter that generates a transmission signal composed of a plurality of pulse waveforms simultaneously using a simple method has been clarified.

  In the above-described embodiment, the pulse waveform of the subcarrier of the OFDM signal is controlled and transmitted according to the situation, or transmitted using a plurality of pulse waveforms simultaneously. However, since the difference in the pulse waveform affects only the window portion, there is no problem even if a normal OFDM receiver is used for reception. That is, it is not necessary for the receiver to know the pulse waveform, and there is no problem even if demodulation is performed with the same configuration regardless of the pulse waveform or the type of pulse waveform.

  Note that the present invention is not limited to the above-described embodiment as it is, 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 of the OFDM transmitter of 1st Embodiment. The figure which shows the 1st example which shows the structure of the subcarrier in the OFDM transmitter of FIG. The figure which shows the 2nd example which shows the structure of the subcarrier in the OFDM transmitter of FIG. The figure for demonstrating the CP addition part and window shaping part of FIG. The figure which shows an example of the pulse waveform which the cancellation method selection part of FIG. 1 selects. The figure for demonstrating the relationship between a pulse waveform, a rectangular function, and a window function. The figure which shows an example of the frequency response of the pulse waveform shown in FIG. The figure which shows the content which the cancellation method selection part of FIG. 1 has memorize | stored. The block diagram of the OFDM transmitter of 2nd Embodiment. The figure which shows the 1st example which shows the structure of the subcarrier in the OFDM transmitter of FIG. The figure which shows the 2nd example which shows the structure of the subcarrier in the OFDM transmitter of FIG. The block diagram of the OFDM transmitter of 3rd Embodiment. 12 is a diagram showing an example of subcarrier configuration and pulse waveform assignment in the OFDM transmitter. The block diagram of the OFDM transmitter of 4th Embodiment. The figure for demonstrating the OFDM symbol which the OFDM transmitter of FIG. 14 produces | generates.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Cancel method selection part, 102 ... Cancel symbol calculation part, 103 ... IFFT part, 104 ... CP addition part, 105 ... Window shaping part, 106 ... D / A conversion part 107, RF transmitting unit, 901 ... data dividing unit, 902, 1201 ... second IFFT unit, 903 ... adder.

Claims (15)

A data carrier that transmits a data symbol, which is a part of a plurality of subcarriers, and a subcarrier that is a part of a subcarrier different from the data carrier and transmits a cancellation symbol for reducing leakage power to the target band Storage means for storing a plurality of pulse waveforms having different waveforms to be applied to the cancel carrier;
First selection means for selecting, as a first selection pulse waveform, a pulse waveform corresponding to band information relating to a transmission signal from the plurality of pulse waveforms;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the first selection pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
First acquisition means for acquiring an orthogonal frequency division multiplexing (OFDM) symbol by performing inverse Fourier transform on the data symbol and the cancellation symbol mapped to the subcarrier;
Second acquisition means for acquiring a transmission OFDM symbol by shaping the OFDM symbol according to the first selected pulse waveform;
An OFDM transmitter comprising: transmission means for transmitting the transmission OFDM symbol. A data carrier that transmits a data symbol that is a part of a plurality of subcarriers, and a cancellation symbol that is a part of a subcarrier that is different from the data carrier and that reduces leakage power to the target band Storage means for storing a plurality of pulse waveforms having different waveforms to be applied to the cancel carrier;
Dividing means for dividing the plurality of subcarriers into a first subcarrier group in a certain frequency range from the target band and a second subcarrier group other than the first subcarrier group;
First selection means for selecting, as a first selection pulse waveform, a first pulse waveform to be applied to the first subcarrier group corresponding to band information related to a transmission signal from the plurality of pulse waveforms;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the first selection pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
A first data symbol that is part of the data symbol mapped to the first subcarrier group and a first cancel symbol that is part of the cancellation symbol are inverse Fourier transformed to obtain a first OFDM (orthogonal frequency division multiplexing). ) Third acquisition means for acquiring a symbol;
Fourth obtaining means for obtaining a first transmission OFDM symbol by shaping the first OFDM symbol according to the first selected pulse waveform;
Fifth acquisition means for acquiring a second OFDM symbol by performing inverse Fourier transform on the remaining second data symbol of the data symbol mapped to the second subcarrier group and the remaining second cancellation symbol of the cancellation symbol; ,
Sixth acquisition means for acquiring a second transmission OFDM symbol by shaping the second OFDM symbol according to a preset second pulse waveform;
Seventh acquisition means for adding the first transmission OFDM symbol and the second transmission OFDM symbol to acquire a combined OFDM symbol;
An OFDM transmitter comprising: transmission means for transmitting the combined OFDM symbol. A data carrier that transmits a data symbol that is a part of a plurality of subcarriers, and a cancellation symbol that is a part of a subcarrier that is different from the data carrier and that reduces leakage power to the target band Storage means for storing a plurality of pulse waveforms having different waveforms to be applied to the cancel carrier;
Dividing means for dividing the plurality of subcarriers into a first subcarrier group in a certain frequency range from the target band and a second subcarrier group other than the first subcarrier group;
A second pulse applied to the second subcarrier group is selected from the plurality of pulse waveforms as a first selected pulse waveform corresponding to band information related to a transmission signal and applied to the first subcarrier group. Second selection means for selecting a pulse waveform as a second selection pulse waveform;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the first selection pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
First acquisition means for acquiring a first OFDM (orthogonal frequency division multiplexing) symbol by performing inverse Fourier transform on the data symbol and the cancellation symbol mapped to the subcarrier;
Fourth obtaining means for obtaining a first transmission OFDM symbol by shaping the first OFDM symbol according to the first selected pulse waveform;
The first data symbol that is part of the data symbol mapped to the second subcarrier group and the first cancellation symbol that is part of the cancellation symbol are inverse Fourier transformed to obtain a second OFDM symbol. 8 acquisition means;
Ninth acquisition means for acquiring a second transmission OFDM symbol by shaping the second OFDM symbol according to a difference between the second pulse waveform and the first pulse waveform;
Seventh acquisition means for adding the first transmission OFDM symbol and the second transmission OFDM symbol to acquire a combined OFDM symbol;
An OFDM transmitter comprising: transmission means for transmitting the combined OFDM symbol.   4. The OFDM transmitter according to claim 2, wherein the dividing unit is configured such that the number of subcarriers in the first subcarrier group is equal to the number of subcarriers in the first subcarrier group.   4. The OFDM transmitter according to claim 2, wherein the dividing unit divides the power so that power leaked from the second subcarrier group to the target band is equal to or less than a threshold value. 5. Leakage to a data carrier that transmits a data symbol that is a part of a plurality of subcarriers and to N target bands (N is an integer of 1 or more) that is a subcarrier that is a part of the data carrier. Storage means for storing a plurality of pulse waveforms having different waveforms applied to a cancel carrier for transmitting a cancel symbol for reducing power;
N subcarriers in an nth subcarrier group in a certain frequency range from the nth (n is an integer from 1 to N) target band, and any nth subcarrier group in which n is from 1 to N Dividing means for dividing the plurality of subcarriers into an (N + 1) th subcarrier group that is a subcarrier not included in the subcarrier,
Selecting means for selecting the m-th pulse waveform to be applied to the m-th (m is an integer of 1 to N + 1) subcarrier group corresponding to the band information related to the transmission signal from the plurality of pulse waveforms;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the m-th pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
An m-th OFDM (orthogonal frequency division multiplexing) is performed by performing an inverse Fourier transform on the m-th data symbol that is part of the data symbol mapped to the m-th subcarrier group and the first cancellation symbol that is part of the cancellation symbol. ) Eighth acquisition means for acquiring a symbol;
Ninth acquisition means for acquiring a m-th transmission OFDM symbol by shaping the m-th OFDM symbol according to the m-th pulse waveform;
a tenth acquisition means for adding all mth transmission OFDM symbols from m 1 to N + 1 to obtain a combined OFDM symbol;
An OFDM transmitter comprising: transmission means for transmitting the combined OFDM symbol.   The dividing means includes an m-th target band within a frequency range of the m-th subcarrier group, and is within a frequency range of the n-th (n excludes m) sub-carrier group adjacent to the m-th target band. When the nth target band is included, the boundary between the mth subcarrier group and the nth (n is excluded m) subcarrier group is a power leaking from the mth subcarrier group to the nth target band. 7. The OFDM transmitter according to claim 6, wherein a boundary is defined so that power leaking from the n-th (n is excluded m) subcarrier group to the m-th target band is equal.   The dividing means includes an m-th target band within a frequency range of the m-th subcarrier group, and is within a frequency range of the n-th (n excludes m) sub-carrier group adjacent to the m-th target band. When the nth target band is included, the nth (n is excluded from m) so that the power leaked from the nth (n is excluded from m) subcarrier group to the mth target band is equal to or less than a threshold value. 7. The OFDM transmitter according to claim 6, wherein a subcarrier group is defined.   9. The calculation unit according to claim 1, wherein the calculation unit calculates the cancellation symbol using a Lagrange's undetermined multiplier method so that interference power to a target band is minimized. The described OFDM transmitter.   The selection means selects a pulse waveform from the plurality of candidates according to a frequency position in the plurality of subcarriers of the targate band and a bandwidth of the target band. The OFDM transmitter according to any one of 9.   The plurality of pulse waveform candidates are waveforms defined by a convolution operation of a rectangular function and a roll-off function, and the roll-off rate of the roll-off function increases as the bandwidth of the target band increases. The OFDM transmitter according to claim 10. A data carrier that transmits a data symbol that is a part of a plurality of subcarriers, and a cancellation symbol that is a part of a subcarrier that is different from the data carrier and that reduces leakage power to the target band Storage means for storing a plurality of pulse waveforms having different waveforms to be applied to the cancel carrier;
First selection means for selecting, as a first selection pulse waveform, a pulse waveform corresponding to band information relating to a transmission signal from the plurality of pulse waveforms;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the first selection pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
First acquisition means for acquiring an orthogonal frequency division multiplexing (OFDM) symbol by performing inverse Fourier transform on the data symbol and the cancellation symbol mapped to the subcarrier;
Second acquisition means for acquiring a transmission OFDM symbol by shaping the OFDM symbol according to the first selected pulse waveform;
An OFDM transmitter comprising: transmission means for transmitting the transmission OFDM symbol. A data carrier that transmits a data symbol that is a part of a plurality of subcarriers, and a cancellation symbol that is a part of a subcarrier that is different from the data carrier and that reduces leakage power to the target band Storage means for storing a plurality of pulse waveforms having different waveforms to be applied to the cancel carrier;
Dividing means for dividing the plurality of subcarriers into a first subcarrier group in a certain frequency range from the target band and a second subcarrier group other than the first subcarrier group;
First selection means for selecting, as a first selection pulse waveform, a first pulse waveform to be applied to the first subcarrier group corresponding to band information related to a transmission signal from the plurality of pulse waveforms;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the first selection pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
A first data symbol that is part of the data symbol mapped to the first subcarrier group and a first cancel symbol that is part of the cancellation symbol are inverse Fourier transformed to obtain a first OFDM (orthogonal frequency division multiplexing). ) Third acquisition means for acquiring a symbol;
Fourth obtaining means for obtaining a first transmission OFDM symbol by shaping the first OFDM symbol according to the first selected pulse waveform;
Fifth acquisition means for acquiring a second OFDM symbol by performing inverse Fourier transform on the remaining second data symbol of the data symbol mapped to the second subcarrier group and the remaining second cancellation symbol of the cancellation symbol; ,
Sixth acquisition means for acquiring a second transmission OFDM symbol by shaping the second OFDM symbol according to a preset second pulse waveform;
Seventh acquisition means for adding the first transmission OFDM symbol and the second transmission OFDM symbol to acquire a combined OFDM symbol;
An OFDM transmitter comprising: transmission means for transmitting the combined OFDM symbol. A data carrier that transmits a data symbol that is a part of a plurality of subcarriers, and a cancellation symbol that is a part of a subcarrier that is different from the data carrier and that reduces leakage power to the target band Storage means for storing a plurality of pulse waveforms having different waveforms to be applied to the cancel carrier;
Dividing means for dividing the plurality of subcarriers into a first subcarrier group in a certain frequency range from the target band and a second subcarrier group other than the first subcarrier group;
A second pulse applied to the second subcarrier group is selected from the plurality of pulse waveforms as a first selected pulse waveform corresponding to band information related to a transmission signal and applied to the first subcarrier group. Second selection means for selecting a pulse waveform as a second selection pulse waveform;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the first selection pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
First acquisition means for acquiring a first OFDM (orthogonal frequency division multiplexing) symbol by performing inverse Fourier transform on the data symbol and the cancellation symbol mapped to the subcarrier;
Fourth obtaining means for obtaining a first transmission OFDM symbol by shaping the first OFDM symbol according to the first selected pulse waveform;
The first data symbol that is part of the data symbol mapped to the second subcarrier group and the first cancellation symbol that is part of the cancellation symbol are inverse Fourier transformed to obtain a second OFDM symbol. 8 acquisition means;
Ninth acquisition means for acquiring a second transmission OFDM symbol by shaping the second OFDM symbol according to a difference between the second pulse waveform and the first pulse waveform;
Seventh acquisition means for adding the first transmission OFDM symbol and the second transmission OFDM symbol to acquire a combined OFDM symbol;
An OFDM transmitter comprising: transmission means for transmitting the combined OFDM symbol. Leakage to a data carrier that transmits a data symbol that is a part of a plurality of subcarriers and to N target bands (N is an integer of 1 or more) that is a subcarrier that is a part of the data carrier. Storage means for storing a plurality of pulse waveforms having different waveforms applied to a cancel carrier for transmitting a cancel symbol for reducing power;
N subcarriers in an nth subcarrier group in a certain frequency range from the nth (n is an integer from 1 to N) target band, and any nth subcarrier group in which n is from 1 to N Dividing means for dividing the plurality of subcarriers into an (N + 1) th subcarrier group that is a subcarrier not included in the subcarrier,
Selecting means for selecting the m-th pulse waveform to be applied to the m-th (m is an integer of 1 to N + 1) subcarrier group corresponding to the band information related to the transmission signal from the plurality of pulse waveforms;
Calculating means for calculating the cancel symbol so that the leakage power is minimized according to the m-th pulse waveform;
Mapping means for mapping the data symbols and the cancellation symbols to the subcarriers;
An m-th OFDM (orthogonal frequency division multiplexing) is performed by performing an inverse Fourier transform on the m-th data symbol that is part of the data symbol mapped to the m-th subcarrier group and the first cancellation symbol that is part of the cancellation symbol. ) Eighth acquisition means for acquiring a symbol;
Ninth acquisition means for acquiring a m-th transmission OFDM symbol by shaping the m-th OFDM symbol according to the m-th pulse waveform;
a tenth acquisition means for adding all mth transmission OFDM symbols from m 1 to N + 1 to obtain a combined OFDM symbol;
An OFDM transmitter comprising: transmission means for transmitting the combined OFDM symbol.

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