KR101471409B1

KR101471409B1 - Orthogonal Frequency Division Multiplexing Transmitter

Info

Publication number: KR101471409B1
Application number: KR20130065176A
Authority: KR
Inventors: 김동규; 이동민; 안승혁; 장한용
Original assignee: (주)아이앤씨테크놀로지
Priority date: 2013-06-07
Filing date: 2013-06-07
Publication date: 2014-12-10

Abstract

The present invention introduces an OFDM transmitter that allows suitable peak attenuation to be achieved according to each communication mode comprising various modulation / coding levels and various bandwidths. The OFDM transmitter includes an error correction coding unit, a conversion unit, a LPF unit, a CFR unit, and a DAC unit, or includes an error correction coding unit, a conversion unit, a path selection unit, a LPF unit, a CFR unit, and a DAC unit.

Description

[0001] The present invention relates to an Orthogonal Frequency Division Multiplexing Transmitter (OFDM)

The present invention relates to an OFDM transmitter, and more particularly to an OFDM transmitter that allows suitable peak attenuation to be achieved according to each communication mode consisting of various modulation / coding levels and various bandwidths.

Peak-to-Average Power Ratio (PAPR) used as a criterion for indicating the influence of a baseband transmission signal on a transmitter is a ratio of a maximum power P _{avg to} an average power P _avg of a target signal _peak ) is defined as Equation (1).

Generally, the power of a transmitter means average power. However, since the peak power is present in the actually transmitted power, when the transmitter is designed without considering the peak power, the quality of the transmission signal is lowered due to mutual modulation.

Next Generation Orthogonal Frequency Division Multiplexing (OFDM) is characterized in that the output of the transmitter is large because the ratio of the maximum power to the average power is larger than other schemes. When trying to create a device that can transmit two signals with the same average power but different PAPRs without distortion, the device that transmits a signal with a large PAPR has a larger dynamic response than the signal processing component used with a device that transmits a signal with a smaller PAPR PAPR affects the complexity of the device and the manufacturing cost of the product because it requires the use of parts with a dynamic range.

To solve this problem, various techniques for lowering PAPR have been proposed. This technique is called Crest Factor Reduction (CFR). The most common technique of CFR is to find the peak of the transmitted signal and reduce its size (or power) to less than a certain size.

Figure 1 shows the concept of CFR.

1 (a) shows the relationship between the input signal of the CFR, the output signal of the CFR, and the peak attenuation signal used to attenuate the peak included in the input signal of the CFR. FIG. 1 (b) And the output signals of the first and second input /

A CFR input signal s (t) on the left side, a CFR output signal c (t) on the right side, and a peak attenuation signal k (t) on the lower side are shown around the adder 110 shown in the middle of FIG. ) And a peak reduction signal, respectively.

The relationship between the respective signals can be expressed by Equation (2).

The peak attenuation signal k (t) can be expressed by Equation (3).

here,

to be.

The horizontal solid line shown at the upper part of the CFR input signal s (t) is a target peak threshold. The CFR input signal s (t) includes the amplitude exceeding the peak threshold, It can be seen that the amplitude exceeding the peak threshold is decreased to the peak threshold in the CFR output signal shown on the right side.

This is because the peak attenuation signal k (t), which can detect the portion exceeding the peak threshold in the CFR input signal s (t) and can reduce the size of the excess portion using the detected signal, (Amplitude) of the portion exceeding the peak threshold in the CRF output signal c (t) by adding the generated peak attenuation signal k (t) to the CFR input signal s (t) Is reduced below the peak threshold value. Referring to FIG. 1 (b), the difference between the CFR input signal s (t) shown by the dotted line and the CFR output signal c (t) shown by the solid line can be known.

As described above, it is the CFR that detects a portion exceeding the set peak threshold in the input signal and generates a signal obtained by attenuating the portion of the input signal below the peak threshold (Peak Threshold).

2 is a block diagram of a conventional OFDM transmitter.

2, the OFDM transmitter 200 includes error correction encoding units 210 and 220, a transform unit 230, an LPF unit 240, a CFR unit 250, and a DAC unit 260.

The error correction coding units 210 and 220 perform an error correction coding process on the transmission data and the conversion unit 230 performs inverse fast Fourier transform (IFFT) on the signals passed through the error correction coding units 210 and 220, Inverse Fast Fourier Transform) to modulate the OFDM signal suitable for communication. The signal passed through the conversion unit 230 is subjected to up sampling and low pass filtering so as to conform to the channel characteristics required in the communication standard while passing through the LPF unit 240. The CFR unit 250 reduces a signal of a portion exceeding the peak threshold included in the signal passed through the LPF unit 340 and then transmits the signal to the DAC unit 260. The DAC unit 260 receives the CFR (250) to an analog RF (Radio Frequency) signal.

Lowering the size of the peak performed by the CFR unit 250 gives a distortion to the transmission signal. The noise component generated due to the distortion of the signal is distributed throughout the signal spectrum.

In the case of in-band, noise components are distributed in OFDM subcarriers, resulting in EVM (Error Vector Measurement) degradation. In the case of out-of-band noise components, As the spectral power of the out-of-band signal is distributed, the margin for the Tx spectrum mask required by the communication standard is reduced.

Therefore, since the influence of the noise component due to the distortion is to be handled in all the areas in and out of the band, the position of the CFR part 350 which gives a distortion to the signal is the position of the BBP (Baseband Processor) It is preferable to be located between the LPF unit 340 and the DAC unit 360. [ If the DPP unit (Digital Pre-Distortion) (not shown) is used in the BBP, the position of the CFR unit 250 will be between the LPF unit 240 and DPD (not shown).

This CFR function is disclosed in various parts such as a method of detecting a peak, a method of generating a peak attenuation signal, and a method of reflecting a peak attenuation signal in a CFR input signal. However, recent communication standards include various communication modes from low-speed communication mode to high-speed communication mode using various modulation / coding levels and various bandwidths, so that the CFR of the defined specification is universal in all communication modes It is not suitable to be applied.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an OFDM transmitter in which appropriate peak attenuation is achieved according to each communication mode composed of various modulation / coding levels and various bandwidths.

According to one aspect of the present invention, there is provided an OFDM transmitter including an error correction coding unit, a conversion unit, a LPF unit, a CFR unit, and a DAC unit. The error correction coding unit performs an error correction coding process on the input transmission data. The transform unit modulates the signal passed through the error correction coding unit into an OFDM signal by performing inverse fast Fourier transform. The LPF unit performs an up-sampling and a low-pass filter function so that the signal passed through the converting unit conforms to a channel characteristic required in a communication standard. The CFR unit generates a CFR output signal by attenuating a portion exceeding a peak threshold included in the signal passed through the LPF unit using some or all of MCS, operating bandwidth, channel bandwidth, and frequency offset information. The DAC unit converts the CFR output signal into an analog signal.

According to another aspect of the present invention, there is provided an OFDM transmitter including an error correction encoding unit, a conversion unit, a path selection unit, a LPF unit, a CFR unit, and a DAC unit. The error correction coding unit performs error correction coding on the transmission data. The transform unit performs inverse fast Fourier transform on the signal passed through the error correction coding unit and modulates the signal into an OFDM signal. The path selection unit selects a path through which the signal passed through the conversion unit is processed in response to the operating bandwidth and the channel bandwidth. The LPF unit performs an upsampling and a low-pass filter function so that the signal output from the path selector matches the channel characteristics required by the communication standard according to the processing path selected by the path selector, and then feeds back the signal to the path selector . Wherein the CFR unit attenuates a signal exceeding a peak threshold included in a signal output from the path selection unit according to a processing path selected by the path selection unit using an MCS, the operating bandwidth, the channel bandwidth, and a frequency offset value And feeds back the generated CFR output signal to the path selector. The DAC unit converts the output signal of the LPF unit or the output signal of the CFR unit output from the path selector into an analog signal.

The OFDM transmitter according to the present invention uses a variety of modulation / coding levels and various bandwidths, which is a recent communication standard, to transmit a signal exceeding a predetermined peak threshold included in a transmission signal in various communication modes from a low speed communication mode to a high speed communication mode It is possible to effectively attenuate the portion.

Figure 1 shows the concept of CFR.
2 is a block diagram of a conventional OFDM transmitter.
3 is a table showing the IEEE 802.11ac standard supporting 10 modulation / coding modes.
4 shows a spectrum of a transmission signal when operating bandwidth and channel bandwidth are both 20 MHz.
5 shows a spectrum of a transmission signal according to a combination with three usable channel bandwidths when the operating bandwidth is 40 MHz.
6 shows a spectrum of a transmission signal when the operating band width is 80 MHz and the channel bandwidth is 80 MHz, 40 MHz, and 20 MHz.
FIG. 7 is a table summarizing required values for various modulation levels and coding rates in IEEE 802.11ac.
8 is an embodiment of an OFDM transmitter according to the present invention.
Figure 9 shows the peak threshold for each MCS stored in the form of a look-up table.
10 is a table showing a bandwidth combination according to operating bandwidth and channel bandwidth.
11 shows the magnitude and the number of taps of the peak attenuation signal according to the oversampling ratio when the channel bandwidth is 20 MHz.
12 shows the coefficients of the peak attenuation signal in the form of a look-up table.
13 is another embodiment of an OFDM transmitter according to the present invention.
14 shows a frequency spectrum depending on whether two frequency shifters located before and after the CFR unit are used.
15 is another embodiment of an OFDM transmitter according to the present invention.
Fig. 16 shows a change in spectrum by the frequency shifter provided at the rear end of the CFR unit.
17 shows an example of a transmission signal having a width of various peaks.
Fig. 18 shows a peak attenuation signal in which the decimation is performed at 2: 1 in the peak attenuation signal shown in Fig. 11 (a).
19 is another embodiment of an OFDM transmitter according to the present invention.

In order to fully understand the present invention and the operational advantages of the present invention and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings, which are provided for explaining exemplary embodiments of the present invention, and the contents of the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

First, the background and rationale for the present invention will be described.

The present invention is based on the IEEE 802.11ac standard.

3 is a table showing the IEEE 802.11ac standard supporting 10 modulation / coding modes.

In FIG. 3, an MCS (Modulation Coding Scheme) value is used as a value for designating a modulation / coding mode to be used. Bi-Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), and Quadrature Amplitude Modulation (QAM) all represent modulation schemes.

As the MCS increases, the amount of data bits that can be transmitted per unit time increases and the required signal accuracy increases. Conversely, as the MCS decreases, the required signal accuracy decreases. In the conventional method, the same peak threshold is applied regardless of the MCS of the transmission signal. However, when the MCS is lower, the output power can be increased by further lowering the peak threshold.

The IEEE 802.11ac standard defines two kinds of bandwidth, so that various combinations of bandwidths can actually be used. These bandwidths are operating bandwidth (Op-BW) and channel bandwidth (Ch-BW), and operating bandwidth (Op-BW) is the maximum bandwidth Which is the maximum bandwidth that can be used by all communication devices connected to the AP. The channel bandwidth (Ch-BW) is equal to or smaller than the operating band-width (Op-BW) by the bandwidth of the signal when each communication apparatus transmits a signal.

4 shows a spectrum of a transmission signal when operating bandwidth and channel bandwidth are both 20 MHz.

The spectrum shown in FIG. 4 has a constant frequency width around 0 Hz and corresponds to the WLAN initial standard IEEE 802.11a / g.

5 shows a spectrum of a transmission signal according to a combination with three usable channel bandwidths when the operating bandwidth is 40 MHz.

5 (a) shows a case where only a low 20 MHz of the channel bandwidth (Ch-BW) of 40 MHz is used and FIG. 5 (c) shows a case where only a channel of 40 MHz Respectively, when using only the high 20 MHz of the bandwidth (Ch-BW), and corresponds to the WLAN latest standard IEEE 802.11n. Here, the criterion of low and high is based on the middle of the channel bandwidth, and the spectrum on the left is centered at the middle, that is, 0 Hz, and the spectrum on the right is set high.

Particularly, the OFDM transceiver uses only 20 MHz or 20 MHz which is low in frequency among the 40 MHz bandwidth as shown in FIG. 5 (b) and FIG. 5 (c) To be able to transmit and receive a signal having a channel bandwidth of 20 MHz.

6 shows a spectrum of a transmission signal when the operating band width is 80 MHz and the channel bandwidth is 80 MHz, 40 MHz, and 20 MHz.

6 (a) shows a case where only the lower 40 MHz of the channel bandwidth (Ch-BW) of 80 MHz is used and FIG. 6 (c) 6 (d) shows the case where only the lowest 20 MHz among the channel bandwidths Ch-BW of 80 MHz is used, and FIG. 6 (e) shows the channel bandwidths of 80 MHz 6 (f) shows a case where only the second lowest 20 MHz of the channel bandwidth (Ch-BW) of 80 MHz is used and FIG. 6 (g) shows a case where only the second lowest channel And the spectrum of the transmitted signal when only the lowest 20 MHz of the bandwidth (Ch-BW) is used, and corresponds to the IEEE 802.11ac standard scheduled to be completed in 2013.

As described above, the communication apparatus supporting the IEEE 802.11ac standard is required to provide backward compatibility, so that the transceiver for transmitting and receiving signals having the spectrum shown in FIG. 6 can transmit and receive signals having the spectrum shown in FIG. 6 It is also possible to transmit and receive signals having the spectra of FIG. 4 and FIG.

Since the conventional technique is implemented to process a signal centered at zero (Hz) of the transmission signal spectrum as shown in FIG. 4, FIG. 5A and FIG. 6A, The process of FIG. 5 (b), FIG. 5 (c), and FIG. 6 (b) to FIG. 6 (g) Also, the conventional technique implemented in accordance with FIG. 6 (a) requires an additional function to process a signal having a smaller channel bandwidth as shown in FIGS. 4 (a) and 5 (a).

FIG. 7 is a table summarizing required values for various modulation levels and coding rates in IEEE 802.11ac.

Referring to FIG. 7, an MCS value is assigned to a combination of a modulation level and a coding rate to define MCS 0 (zero) to MCS 9 (nine), and an EVM That is, RCE (Relative Constellation Error) is defined differently. The lower the EVM value, the lower the error and the higher the accuracy. The higher the modulation level or the lower the coding rate, the smaller the error.

One of the implementations of the present invention is to be able to apply a suitable peak threshold according to MCS.

8 is an embodiment of an OFDM transmitter according to the present invention.

8, an OFDM transmitter 800 according to the present invention includes error correction coding units 810 and 820, a transform unit 830, an LPF unit 840, a CFR unit 850, and a DAC unit 860 .

The error correction coding units 810 and 820 perform an error correction coding process on the transmission data and the conversion unit 830 performs inverse fast Fourier transform (IFFT) on the signals passed through the error correction coding units 810 and 820 IFFT (Inverse Fast Fourier Transform) to modulate the OFDM signal suitable for communication. The LPF unit 840 performs Upsampling and a low pass filtering function so that the signal passed through the converting unit 830 conforms to the channel characteristics required in the communication standard.

The CFR unit 850 uses the values of the Modulation Coding Scheme (MCS), the operating band width Op-BW, and the channel bandwidth (Ch-BW) to exceed the peak threshold included in the signal passed through the LPF unit 840 Thereby generating a CFR output signal CFR _{o obtained} by attenuating the signal. The DAC unit 860 converts the CFR output signal CFR _o output from the CFR unit 850 into an RF (Radio Frequency) analog signal.

8, the CFR unit 850 includes a delay 851, a peak detector 852, a CFR controller 853, an attenuation signal storage 854, an attenuation signal generator 855, and an adder 856 .

The delay unit 851 generates a delay signal D _S delayed by a predetermined time period through the LPF unit 840. The peak detector 852 detects a peak value D _{P that} is larger than the received peak threshold value P _th among the peak values of the signal through the LPF unit 840. The attenuation signal storage 854 stores coefficients (C _f ) of the peak reduction signal.

The CFR controller 853 outputs a peak threshold value P _th according to the MCS value among the received parameters required for the CFR, i.e., the MCS, the operating band width Op-BW and the channel bandwidth (Ch-BW) 852 and delivers the bandwidth combination value C _BW determined in accordance with the operating bandwidth Op-BW and the channel bandwidth (Ch- _BW ) to the attenuation signal generator 855. The CFR controller 853 includes a storage device in which a peak threshold value P _th corresponding to the MCS value is stored in a lookup table format.

The attenuation signal generator 855 outputs the peak decrease signal D _P stored in the attenuation signal storage 854 according to the peak value D _P output from the peak detector 852 and the bandwidth combination value C _BW output from the CFR controller 853, receiving a factor (C _f) to generate a peak decay signal (P _R).

The adder 856 adds the delay signal D _S and the peak attenuation signal P _R and generates a CFR output signal CFR _{O obtained} by attenuating a peak larger than the peak threshold included in the delay signal D _S.

Figure 9 shows the peak threshold for each MCS stored in the form of a look-up table.

9, a peak threshold [dB] stored in the form of a look-up table may be stored in the CFR controller 853, but may be stored in the MAC layer of the communication apparatus (not shown) . When the peak threshold value is stored in the MAC layer or the PHY layer, the peak threshold value to be applied to the transmission signal is transmitted to the CFR controller 853, thereby performing the same operation as described above.

Hereinafter, the operation of the CFR unit 850 according to the present invention shown in FIG. 8 will be described in detail.

10 is a table showing a bandwidth combination according to operating bandwidth and channel bandwidth.

10, it is assumed that there are three operating bandwidths (Op-BW) and three channel bandwidths (Ch-BW) in total for convenience of description. In this case, a total of six bandwidth combinations are generated .

The sample rates listed in the table shown in FIG. 10 are examples of sample rates when the signal for each bandwidth is applied to the CFR, and are sample rates oversampled by a multiple of four. Generally, an effective CFR is achieved at a sample rate of 2 to 8 times the bandwidth of the signal. The oversampling is performed in the LPF unit 840 located at the front end of the CFR unit 850.

As described above, the channel bandwidth (Ch-BW) is equal to or smaller than the operating bandwidth (Op-BW). Therefore, when the operating band-lock (Op-BW) is 20 MHz in the table shown in Fig. 10, it is possible to combine the case where the channel bandwidth (Ch-BW) is 20 MHz. BW) is not available for 40 MHz and 80 MHz (N / A). Similarly, when the operating band-lock (Op-BW) is 40 MHz, the combination can be performed when the channel bandwidth (Ch-BW) is 20 MHz and 40 MHz. The case is not possible (N / A).

In the table shown in FIG. 10, when the operating bandwidth (Op-BW) is 80 MHz, the channel bandwidth (Ch-BW) can have three bandwidths of 20 MHz, 40 MHz and 80 MHz. When the channel bandwidth (Ch-BW) is 80 MHz, the spectrum is applied to the CFR at 320 × 10 ⁶ samples / second (320 Msps) with the spectrum shown in FIG. 6 (a) x4). < / RTI > In the table shown in FIG. 10, x4 means a sample rate of 4 times oversampling, and x8 and x16 mean a sample rate of 8 times and 16 times oversampling, respectively.

(B) or 5 (c) and can be applied to the CFR portion 850 at a sample rate of 160 Msps or 320 Msps in case of a channel bandwidth of 40 MHz (Ch-BW) The sampling rate is 4 times oversampling. If the sample rate is 320Msps, the sampling rate is 8 times the oversampling rate.

10, the bandwidth combination value C _BW output from the CFR controller 853 is a combination determined according to an externally input operating bandwidth Op-BW and a channel bandwidth Ch-BW And information about the value.

11 shows the magnitude and the number of taps of the peak attenuation signal according to the oversampling ratio when the channel bandwidth is 20 MHz.

11A shows a case where the sample rate is 80Msps and the number of taps of the peak attenuation signal is 15, FIG. 11B shows a case where the sample rate is 160Msps and the number of taps of the peak attenuation signal is 31, (c) shows a case where the sample rate is 320 Msps and the number of taps of the peak attenuation signal is 63, respectively.

The number of coefficients of the peak attenuation signal (the number of taps) also increases and the channel bandwidth (Ch-BW) increases when the operating bandwidth (Op-BW) And the operating band width (Op-BW) of the peak attenuation signal. Therefore, it is desirable to adjust the number of coefficient taps suitable for various combinations of bandwidths.

12 shows the coefficients of the peak attenuation signal in the form of a look-up table.

12, it is assumed that each D (D is a natural number) coefficients C _f stored in a table form in the attenuation signal storage unit 854 has a size of L (L is a natural number) bit.

Stores the coefficient C _f of the peak attenuation signal P _R for the maximum sample rate corresponding to the combination of various bandwidths, that is, the bandwidth combination value C _BW , in the attenuation signal storage device 854 in a look-up table format. 10, when the operating bandwidth (Op-BW) is 80 MHz and the channel bandwidth (Ch-BW) is 20 MHz, the maximum sample rate is 16 times (x16), so that the peak attenuation signal P a factor (C _f) of _R) is applied to generate a peak decay signal (P _R).

C _f = c ₀ , c ₁ , c ₂ , c ₃ , c ₄ , ... c _D-4 , c _D-3 , c _D-2 , c _D-1

When the operating band width (Op-BW) is 80 MHz and the channel bandwidth (Ch-BW) is 40 MHz, and the peak is reduced in the signal with 8 times (x8) sample rate, 2: 1 decimation is performed in one of the coefficient (C _f) of the peak attenuation signal (P _R) and reads from the look-up table is applied to generate a peak decay signal (P _R). The following example is an example when the number of coefficients is an even number.

C _f = c ₀ , c ₂ , c ₄ , ... c _D-4 , c _D-2

C _f = c ₁ , c ₃ , ... c _D-3 , c _D-1

If the peak is to be reduced in a signal with a quadruple (x4) sample rate where the operating bandwidth (Op-BW) is 80 MHz and the channel bandwidth (Ch-BW) is equal to 80 MHz, 4: 1 decimation is performed to either and reads the coefficient (C _f) of the peak attenuation signal (P _R) from the look-up table is applied to a peak decay signal (P _R). The following example is an example when the number of coefficients is a multiple of four.

C _f = c ₀ , c ₄ , c ₈ , ... c _D-8 , c _D-4

C _f = c ₁ , c ₅ , c ₉ , ... c _D-7 , c _D-3

C _f = c ₂ , c ₆ , c ₁₀ , ... c _D-6 , c _D-2

C _f = c ₃ , c ₇ , c ₁₁ , ... c _D-5 , c _D-1

13 is another embodiment of an OFDM transmitter according to the present invention.

13, an OFDM transmitter 1300 according to the present invention includes error correction coding units 1310 and 1320, a transform unit 1330, a LPF unit 1340, a CFR unit 1350, and a DAC unit 1360 .

The error correction coding units 1310 and 1320 perform an error correction coding process on the transmission data and the conversion unit 1330 performs inverse fast Fourier transform on the signals passed through the error correction coding units 1310 and 1320 IFFT) to modulate the OFDM signal suitable for communication. The LPF unit 1340 performs an upsampling and a low-pass filter function so that the signal passed through the converting unit 1330 conforms to the channel characteristics required in the communication standard.

CFR Part 1350 is the signal passed through the LPF unit 1340 by using the MCS (Modulation Coding Scheme), the operating bandwidth (Op-BW), the channel bandwidth (Ch-BW), and frequency offset (f _off) value And generates a CFR output signal (CFR _OS ) obtained by attenuating a signal exceeding the included peak threshold value. The DAC unit 1360 converts the CFR output signal CFR _OS output from the CFR unit 1350 into an RF analog signal.

The CFR unit 1350 includes a first frequency shifter 1351, a CFR unit 1352, and a second frequency shifter 1353. The first frequency shifter 1351 and the second frequency shifter 1353 operate in response to the frequency offset f _off and the CFR unit 1352 operates in accordance with the MCS, the operating band width Op-BW and the channel band width Ch-BW). Although not shown in FIG. 13, the CFR unit 1352 performs the same configuration and functions as the CFR unit 850 shown in FIG. 8, and therefore will not be described in detail here. Hereinafter, the operation of the two frequency shifters 1351 and 1353 Will be described.

13, two frequency shifters 1351 and 1353 that perform a frequency shift function are disposed before and after the stage of the CFR unit 1352, respectively, So that the frequency band can be changed.

This is because when a signal using only a part of the operating band width Op-BW is generated as shown in FIGS. 5 (b), 5 (c) and 6 (b) This is to apply CFR to the frequency band.

14 shows a frequency spectrum depending on whether two frequency shifters located before and after the CFR unit are used.

14A shows a spectrum of a transmission signal having a bandwidth of 20 MHz centered at a center frequency of 0 Hz and a channel bandwidth of Ch-BW output from the LPF unit 1340, and FIG. 14 (b) The shifter 1351 shifts the center frequency of the spectrum of the transmission signal shown in Fig. 14A by -10 MHz and shows that the center frequency of the transmission signal output from the LPF unit 1340 is 0 Hz. The peak included in the transmission signal shifted by -10 MHz from the center frequency shown in FIG. 14 (b) is removed from the CFR unit 1352 and then applied to the second frequency shifter 1351. The second frequency shifter 1351 moves the center frequency of the output signal of the CFR unit 1352 by +10 MHz, and Fig. 14 (c) shows this.

The two frequency shifters 1351 and 1353 located before and after the CFR unit 1352 function to shift the center frequency of the signal spectrum, but the directions of movement are opposite to each other.

The output signal s' (n) of the frequency shifters 1351 and 1353 in which the center frequency of the input signal s (n) is shifted by? F [Hz] can be expressed by Equation (4).

Where n is the sample number of the signal and t is the sampling period. 14, if the frequency of -Δf [Hz] is shifted by the first frequency shifter 1351 provided at the front end of the CFR unit 1352, the second frequency shifter 1353 provided at the rear end of the CFR unit 1352 By performing the frequency shift of? F [Hz], the frequency shifts cancel each other out.

15 is another embodiment of an OFDM transmitter according to the present invention.

15, an OFDM transmitter 1500 according to the present invention includes error correction coding units 1510 and 1520, a transform unit 1530, an LPF unit 1540, a CFR unit 1550, and a DAC unit 1560 .

The error correction coding units 1510 and 1520 perform an error correction coding process on the transmission data and the conversion unit 1530 performs inverse fast Fourier transform on the signals passed through the error correction coding units 1510 and 1520 And modulates it into an OFDM signal suitable for communication. The LPF unit 1540 performs an upsampling and a low-pass filter function so that the signal passed through the converting unit 1530 conforms to the channel characteristics required in the communication standard.

The CFR unit 1550 uses the MCS, the operating band width Op-BW, the channel band width Ch-BW and the frequency offset f _off to calculate a peak threshold included in the signal passed through the LPF unit 1540 And generates a CFR output signal (CFR _OS ) in which the exceeding signal is attenuated. The DAC unit 1560 converts the CFR output signal CFR _OS output from the CFR unit 1550 into an analog signal and outputs an RF analog signal.

CFR Part 1550 includes a frequency shifter, which operates in response to the MCS, value of the operating bandwidth (Op-BW), and channel bandwidth CFR unit operative in response to the (Ch-BW) (1551) and frequency offset (f _off) (1552). Although not shown in FIG. 15, the CFR unit 1351 performs the same configuration and functions as the CFR unit 850 shown in FIG. 8, and thus will not be described in detail here.

Fig. 16 shows a change in spectrum by the frequency shifter provided at the rear end of the CFR unit.

16A shows a spectrum of a transmission signal with a channel bandwidth of Ch-BW of 20 MHz output from the CFR unit 1551 and FIG. 16B shows a spectrum of a transmission signal with a channel bandwidth of Ch- And a spectrum obtained by shifting the center frequency of the spectrum of the illustrated transmission signal by +10 MHz.

The OFDM transmitter 1300 shown in FIG. 13 is different from the OFDM transmitter 1500 shown in FIG. 15 in that two frequency shifters 1351 and 1353 are provided, while one frequency shifter 1552 is included in the OFDM transmitter 1500 shown in FIG. 15 . The reason why only one frequency shifter can be used without using two frequency shifters is that since the characteristic of OFDM can generate a signal having a center frequency of 0 Hz through the inverse fast Fourier transform (IFFT) Because.

17 shows an example of a transmission signal having a width of various peaks.

17 (a) shows a peak value having a width of 3 samples with three samples 10, 11 and 12 exceeding a peak threshold (blue horizontal line), and Fig. 17 (b) And a peak value having a width of 7 samples exceeding the peak threshold (blue horizontal line).

The peak attenuation signal shown in FIG. 11 (a) is effective for processing a case where the width of the sample exceeding the peak threshold is at maximum 7. Therefore, it is difficult to handle the case where the peak attenuation signal has a width of 8 or more samples. The peak attenuation signal shown in Fig. 11 (a) is wide to be used in the case of a peak having one or two sample widths narrower than that of Fig. 17 (a). Therefore, it is desirable to use a peak attenuation signal having an appropriate width for each peak width (sample width).

Fig. 18 shows a peak attenuation signal in which the decimation is performed at 2: 1 in the peak attenuation signal shown in Fig. 11 (a).

When the detected peak width (sample width) is 3 to 7 samples, the peak attenuation signal shown in FIG. 11A is directly used to remove the peak, and when the detected peak width (sample width) is less than 3 The peak is removed using the peak attenuation signal shown in FIG. 18, and when the detected peak width (sample width) is 7 or more, the peak attenuation signal having a sampling rate twice as high as that shown in FIG. 11 (b) It is possible to appropriately cope with various peaks having different widths.

When the positions of the CFR units 850, 1350 and 1550 are located between the LPF units 840, 1340 and 1540 and the DAC units 860, 1360 and 1560 as shown in Figs. 8, 13 and 15, various operating bandwidths And a peak attenuation signal having different sample rates according to the channel bandwidth (Ch-BW) and the channel bandwidth (Ch-BW) are used as a lookup table. This is because the combination of various bandwidths, that is, the bandwidth combination value C _BW , is changed, but the positions of the CFR units 850, 1350, and 1550 are fixed.

19 is another embodiment of an OFDM transmitter according to the present invention.

FIG. 19A is a block diagram of an OFDM transmitter 1900 according to the present invention, and FIGS. 19B and 19C show a processing path of a transmission signal selected according to an operation of a switch.

19A, an OFDM transmitter 1900 according to the present invention includes error correction encoding units 1910 and 1920, a conversion unit 1930, an LPF unit 1940, a CFR unit 1950, a DAC unit 1960 and a path selection unit 1970. [

The error correction coding units 1910 and 1920 perform an error correction coding process on the transmission data and the conversion unit 1930 performs inverse fast Fourier transform on the signals passed through the error correction coding units 1910 and 1920 And modulates it into an OFDM signal suitable for communication.

In response to the selection mode determined by the operating bandwidth (Op-BW) and the channel bandwidth (Ch-BW), the path selection unit 1970 selects the signal that has passed through the conversion unit 1930 from the LPF unit 1940 and The first processing path (Fig. 19 (b)) for outputting the signal generated while passing through the order of the CFR unit 1950 and the CFR unit 1950 and the LPF unit 1940, which have passed through the conversion unit 1930, (Fig. 19 (c)) for outputting the generated signal while passing through the second processing path (Fig. 19 (c)).

The LPF unit 1940 outputs a signal applied in accordance with the first processing path (FIG. 19 (b)) or the second processing path (FIG. 19 (c)) selected by the path selecting unit 1970, Sampling and a low-pass filter function so as to coincide with each other. The CFR unit 1950 uses the MCS, the operating bandwidth Op-BW, the channel bandwidth Ch-BW, and the frequency offset f _off to select the first processing path The CFR output signal CFR _{OS obtained} by attenuating the signal exceeding the peak threshold included in the signal applied according to the second processing path (FIG. 19 (b)) or the second processing path (FIG. 19 (c)) is generated.

The DAC unit 1960 converts the CFR output signal CFR _OS output from the path selecting unit 1970 into an RF analog signal.

19A, the path selector 1970 includes all five selection switches 1971 to 1975 whose switching operation is controlled according to the selection mode.

The first selection switch 1971 switches the signal output from the conversion unit 1930 applied to one input terminal to the LPF unit 1940. The second selection switch 1972 switches the signal output from the conversion unit 1930 applied to one input terminal to the CFR unit 1950. The fifth selection switch 1975 switches one of the signals applied to the two input terminals to the DAC unit 1960. The third selection switch 1973 switches the signal output from the LPF 1940 to one input terminal of the second selection switch 1972 or one input terminal of the fifth selection switch 1975. The fourth selection switch 1974 switches the signal output from the CFR unit 1950 to another input terminal of the first selection switch 1971 or another input terminal of the fifth selection switch 1975.

The five switches 1571 to 1575 constituting the path selector 1970 may be implemented by using a general switch, but may be implemented by using a multiplexer / demultiplexer.

19A, the first selection switch 1971, the second selection switch 1972, and the fifth selection switch 1975 are respectively connected to one of the signals applied to the two input terminals in response to the selection mode, And the third selection switch 1973 and the fourth selection switch 1974 are switches for selectively switching the signal applied to one input terminal to one of the two output terminals in response to the selection mode, Lt; / RTI >

In the present invention, the path selecting unit 1970 shown in FIG. 19 (a) is introduced because the order of execution of the CFR function can use the same peak attenuation signal regardless of the combination of various bandwidths, that is, the bandwidth combination value C _BW I will.

In the embodiment of the present invention, the multiplexer / demultiplexer (hereinafter, referred to as a switch) is controlled to perform CFR so that the position of the CFR unit 1950 is positioned at a position at which the sampling rate is quadrupled.

When the operating bandwidth (Op-BW) and the channel bandwidth (Ch-BW) are the same, the switch is determined to be the path of the first processing path (Fig. 19 1950 processes the output signal of the LPF unit 1940. When the channel bandwidth (Ch-BW) is smaller than the operating bandwidth (Op-BW), the switch is routed to the second processing path (FIG. 19 (b) ) Is performed before the LPF unit 1940. At this time, the conversion unit 1930 is controlled so that the output of the conversion unit 1930 becomes a 4-times sample rate with respect to the signal.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

110: adder
210 and 220, 810 and 820, 1310 and 1320, 1510 and 1520, and 1910 and 1920:
230, 830, 1330, 1530, and 1930:
240, 840, 1340, 1540, and 1940:
250, 850, 1350, 1550, 1950:
260, 860, 1360, 1560, 1960: DAC unit
Path selection part: 1970

Claims

An error correction coding unit for performing an error correction coding process on input transmission data;
A transform unit for performing an inverse fast Fourier transform on the signal passed through the error correction coding unit and modulating the signal into an OFDM signal;
An LPF unit performing an up-sampling and a low-pass filter function so that the signal passed through the converting unit conforms to a channel characteristic required by a communication standard;
A Crest Factor Reduction (CFR) output obtained by attenuating a portion exceeding a peak threshold included in a signal passed through the LPF unit using some or all of the modulation bandwidth, the MCS (Modulation Coding Scheme), the operating bandwidth, the channel bandwidth, A CFR unit for generating a signal and a frequency shifter for shifting a center frequency of a signal output from the CFR unit in response to a value of the frequency offset and outputting the shifted frequency; And
A DAC unit for converting the CFR output signal into an analog signal;
The OFDM transmitter comprising:

The apparatus of claim 1, wherein the CFR unit comprises:
A delay unit for generating a delay signal by delaying a signal passed through the LPF unit by a predetermined time;
A peak detector for detecting a peak value of a peak value of a signal passed through the LPF unit, the peak value being larger than a received peak value;
An attenuation signal storage for storing coefficients of the peak reduction signal;
A CFR controller for delivering the peak threshold value according to the MCS value to the peak detector and generating a bandwidth combination value determined according to the operating bandwidth and the channel bandwidth value;
An attenuation signal generator for receiving the coefficient of the peak reduction signal stored in the attenuation signal storage device according to the peak value output from the peak detector and the bandwidth combination value to generate a peak attenuation signal; And
An adder for summing the delay signal and the peak attenuation signal to generate the CFR output signal attenuated by a peak greater than a peak threshold included in the delay signal;
The OFDM transmitter comprising:

3. The apparatus of claim 2, wherein the CFR controller comprises:
Wherein the peak threshold value corresponding to the MCS value is stored in a lookup table format.

3. The apparatus of claim 2, wherein the CFR controller comprises:
And receives the peak threshold value corresponding to the MCS value stored in the MAC layer or the PHY layer of the communication apparatus and transmits the peak threshold value to the peak detector.

3. The apparatus of claim 2, wherein the coefficient of the peak reduction signal stored in the attenuation signal storage device
And stored in a look-up table format for reference according to the bandwidth combination value.

The apparatus of claim 1, wherein the CFR unit comprises:
A first frequency shifter for shifting the center frequency of the signal output from the LPF unit in one direction according to the frequency offset;
A CFR unit for generating the CFR output signal in which a portion exceeding a peak threshold included in a signal output from the first frequency shifter in response to the MCS, the operating bandwidth, and the channel bandwidth is attenuated; And
A second frequency shifter for shifting the CFR output signal in a direction opposite to a direction in which the CFR output signal is shifted in the first frequency shifter according to the frequency offset and outputting the shifted signal to the DAC unit;
The OFDM transmitter comprising:

7. The apparatus of claim 6, wherein the CFR unit comprises:
A delay unit for generating a delay signal by delaying a signal passed through the LPF unit by a predetermined time;
A peak detector for detecting a peak value of a peak value of a signal passed through the LPF unit, the peak value being larger than a received peak value;
An attenuation signal storage for storing coefficients of the peak reduction signal;
A CFR controller for delivering the peak threshold value according to the MCS value to the peak detector and generating a bandwidth combination value determined according to the operating bandwidth and the channel bandwidth value;
An attenuation signal generator for receiving the coefficient of the peak reduction signal stored in the attenuation signal storage device according to the peak value output from the peak detector and the bandwidth combination value to generate a peak attenuation signal; And
An adder for summing the delay signal and the peak attenuation signal to generate the CFR output signal attenuated by a peak greater than a peak threshold included in the delay signal;
The OFDM transmitter comprising:

8. The method of claim 7,
Wherein a frequency of a frequency shifted by the first frequency shifter is equal to a frequency of a frequency shifted by the second frequency shifter.

delete

An error correction coding unit for performing an error correction coding process on the transmission data;
A transform unit for performing an inverse fast Fourier transform on the signal passed through the error correction coding unit and modulating the signal into an OFDM signal;
The first processing path is selected when the operating band width and the channel bandwidth are equal to each other, and when the operating band width is greater than the channel band width A path selecting unit that selects a second processing path when the second processing path is larger than the second processing path;
An LPF unit for performing an up-sampling and a low-pass filter function so as to match a signal output from the path selection unit according to a channel characteristic required in a communication standard, and feeding back the signal to the path selection unit according to a processing path selected by the path selection unit;
A MCS, a CFR output obtained by attenuating a signal exceeding a peak threshold included in a signal output from the path selection unit according to the processing path selected by the path selection unit using the operating bandwidth, the channel bandwidth, A CFR unit for generating a signal and feeding it back to the path selector; And
Wherein the first path is selected by the path selection unit and a signal output in the order of the LPF unit and the CFR unit or a signal output from the CFR unit and the LPF unit in the order of the second processing path is selected as an analog signal Converting the DAC part;
The OFDM transmitter comprising:

12. The apparatus as claimed in claim 11,
And a selection mode determined according to the operating bandwidth and the channel bandwidth.

13. The method according to claim 12,
When the operating band width and the channel bandwidth are the same, includes information corresponding to the first processing path,
And information corresponding to a second processing path when the channel bandwidth is smaller than the operating band width.

14. The method of claim 13,
Wherein the first processing path causes a signal output from the converting unit to pass through in the order of the LPF unit and the CFR unit,
And the second processing path causes a signal output from the conversion unit to pass through in the order of the CFR unit and the LPF unit.

15. The apparatus according to claim 14,
A first selection switch for switching, according to the selection mode, a signal output from the conversion unit applied to one input terminal to the LPF unit;
A second selection switch for switching a signal output from the conversion unit applied to one input terminal according to the selection mode to the CFR unit;
A fifth selection switch for switching one of signals applied to two input terminals according to the selection mode to the DAC unit;
A third selection switch for switching a signal output from the LPF unit to another input terminal of the second selection switch or one input terminal of the fifth selection switch in accordance with the selection mode; And
And a fourth selection switch for switching a signal output from the CFR unit according to the selection mode to another input terminal of the first selection switch or another input terminal of the fifth selection switch
The OFDM transmitter comprising:

16. The method of claim 15,
Each of the first selection switch, the second selection switch and the fifth selection switch being a multiplexer for switching one of the signals applied to the two input terminals to one output terminal in response to the selection mode,
And the third selection switch and the fourth selection switch are demultiplexers for selectively switching a signal applied to one input terminal to one of two output terminals in response to the selection mode.