CN100483967C - Transmitter and receiver capable of controlling peak power - Google Patents

Abstract

The transmitter and receiver for controlling the peak power of the present invention are characterized in that the signals that have been transformed into the time domain by the inverse Fourier transform are passed through different all-pass filters to perform different perturbations on the signals in the frequency domain, thereby forming different peak distributions. characteristic filtering results; then select a group of filtering results with the minimum peak power to output; by filtering in the time domain, complex inverse Fourier transform operations can be avoided, and the characteristics of the all-pass filter will not affect the amplitude of the frequency domain signal. Unnecessary attenuation; through the channel estimation method that the transmitter interpolates pilot symbols in the frequency domain, and the receiver interpolates the channel impulse response of the carrier where these pilot symbols are located, the all-pass filter of the transmitter can be eliminated at the receiving end. impact without requiring additional signaling exchanges. It can not only reduce the amount of calculation required to control the peak power, but also fully restore the original data from the received signal without transmitting additional information.

Description

A transmitter and receiver for peak power control

Technical field:

The invention belongs to the technical field of Orthogonal Frequency Multiplexing Modulation (OFDM) communication, in particular to a transmitter and a receiver in the OFDM system.

Background technique:

Orthogonal Frequency Multiplex Modulation (OFDM) is a multiple access method that has developed rapidly in recent years, and has been applied in wireless local area network, digital audio broadcasting and digital video broadcasting systems.

The ratio of the peak power of a signal to the average power of a signal is generally defined as the peak-to-average power ratio (PAPR).

"Electronics Letters" (Electronics Letters, vol.32, No.21, pp.1963-1964, Oct.1996) introduced a method of controlling the peak-to-average power ratio (PAPR). The method is to multiply the transmitted signal with a set of coefficients before the inverse Fourier transform (IFFT) of the transmitter, and each set of coefficients performs different types of phase shifts on the data in the frequency domain; the results of each set of phase shifts are passed through the IFFT Transform to the time domain, and then extract the group with the smallest peak value from these different time domain signals as the final transmission signal; at the same time, the information of a set of coefficients that generate the final transmission signal is transmitted to the receiver through the signaling channel, and the receiver After knowing the set of coefficients used by the transmitter from the signaling channel, the received signal is multiplied by the conjugate of this set of coefficients to restore the original data.

The disadvantage of this method is that since the transmitter needs to compare the peak value after the IFFT of the result of multiplying the signal with multiple sets of coefficients, it needs to do multiple IFFTs to get the final result, which requires multiple additional IFFTs, and IFFT itself requires a lot of calculations, which greatly increases the computational complexity of the transmitter; in addition, which set of coefficients the transmitter selects needs to be notified to the receiver through a signaling channel, and such signaling transmission occupies both the channel , and is easily affected by channel interference, so that the receiver cannot recover the original data correctly.

"International Institute of Electronics and Electrical Engineers Broadcasting Journal" (IEEE Trans.Broadcasting, vol.48, No.3, pp.223-229, Sept.2002) introduces channel estimation and coherence of multipath channels in OFDM systems The demodulation method is to insert pilot symbols at a certain interval in the frequency domain. At the receiving end, by interpolating the channel conditions detected on these pilot carriers, the fading of the channel formed on each carrier can be obtained. factor, and then the influence of multipath channel on the transmitted signal can be removed in coherent demodulation. This method has not been used to control the peak power of the transmitted signal in the OFDM system before. In the present invention, it will be used to control the additional impact of the peak power of the transmitted signal in the receiver.

Technical content:

The invention provides a transmitter and a receiver for controlling the peak power, which can not only reduce the calculation amount required for controlling the peak power, but also fully restore the original data from the received signal without transmitting additional information.

The transmitter for controlling the peak power of the present invention passes the input data signal 1 through the IFFT transformation module 2 to obtain the time domain signal 3; in the cyclic prefix adding module 12, the last section of the time domain signal 11 is added to the time domain signal 11 as it is. Form the output signal 13 of band cyclic prefix in front; It is characterized in that:

In the cyclic prefix addition module 4, the last section of the signal 3 is added to the front of the signal 3 as it is, to form a signal 5 with a cyclic prefix; the signal 5 is passed through each all-pass filter in a group of all-pass filters 6 respectively, A group of different time-domain output signals 7 are respectively obtained; in the cyclic prefix removal module 8, a section equal to the length of the cyclic prefix at the beginning of the filtering result 7 is removed, and then a section equal to the number of samples of the signal 3 is extracted as a filter output The result signal 9; Select the sending module 10 to count the peak power of the result signal 9 output by each filter respectively, and use a signal with the smallest peak power as the selected result signal 11;

Each all-pass filter is formed by cascading a series of filter subunits 14; the input signal 15 of each filter subunit is added to the feedback signal 16 to obtain a signal 17, and the signal 17 is delayed by one clock cycle Time module 18 obtains delay signal 19, and delay signal 19 is multiplied with filter subunit coefficient 20 to obtain feedback signal 16; Addition, obtain the output signal 23 of filter subunit; Said filter subunit coefficient 20 and filter subunit coefficient 21 constitute the coefficient of all-pass filter, satisfy the relation that is conjugate each other;

The transmitter sends the information of the time-domain all-pass filter through which the final transmitted signal passes to the receiver through signaling 23 .

The last section of the time-domain signal 11 is added to the front of the time-domain signal 11 as it is to form an output signal 13 with a cyclic prefix, which means: intercepting a section of the time-domain impulse response of the time-domain all-pass filter 6 to approximate the real For the time-domain impulse response, the length of the cyclic prefix added here is selected to be greater than the length of the intercepted time-domain all-pass filter 6 impulse response.

Said adding the last section of signal 3 to the front of signal 3 as it is to form signal 5 with cyclic prefix refers to: the length of the cyclic prefix added here is greater than the maximum time delay of multipath time delay and the intercepted time domain full length The sum of the lengths of the pass filter 6 impulse responses.

Transmitter of the present invention can also insert known pilot symbols evenly with a certain interval in input data signal 1, and this refers to: get the maximum time delay of multipath time delay and intercepted time domain all-pass filter 6 impulses The ratio of the sum of the lengths of the excitation responses to the length of the OFDM symbol, uniformly insert known pilot symbols on the input data signal 1, so that the ratio of the number of carriers occupied by the pilot symbols to the total number of carriers is greater than the aforementioned two lengths The ratio of the sum to the length of the OFDM symbol.

With the receiver corresponding to the transmitter of the above-mentioned peak power control of the present invention, the input signal 24 is transformed into a frequency domain signal 26 by the FFT module 25, and it is characterized in that: in the all-pass filter phase shift recovery module 27, from the signaling 23 Restore the conjugate signal 28 that the all-pass filter of the transmitter causes phase shift to the frequency domain signal 26. In the multiplication module 29, the frequency domain signal 26 is multiplied correspondingly by the conjugate signal 28 of the phase shift to obtain the signal 30, and then perform Subsequent processing such as demodulation and decoding.

When corresponding to the described transmitter, the known pilot symbols are evenly inserted at certain intervals in the input data signal 1, then in the receiver, the received signal 31 is first transformed into a frequency domain signal 32 in the FFT module 25, In module 33, the channel impulse response on the carrier where the pilot symbol in the signal 32 is located is detected, and then interpolated to obtain the conjugate signal 34 of the channel impulse response on each carrier; in module 35, the signal 32 is multiplied by the signal 34 correspondingly to obtain the signal 36, which is then subjected to subsequent processing such as demodulation and decoding.

The existing technique is to multiply the transmitted signal with a set of coefficients before the inverse Fourier transform (IFFT) at the transmitter, and each set of coefficients performs a different type of phase shift on the data in the frequency domain. The results of each group of phase shifts are transformed to the time domain by IFFT, and then the group with the smallest peak value is extracted from these different time domain signals as the final transmitted signal. In the present invention, different phase perturbations are performed on different frequency components of the signal by directly filtering the signal 3 that has been transformed into the time domain, so as to obtain signals 9 with different peak characteristics for selective transmission. This eliminates the need to use multiple IFFT transformation modules 2 . On the other hand, through the selection of the zero and pole points of each filter in the filter bank 6, the phase-frequency characteristics of each filter 6 are different, which is pseudo-randomized, so that it is still possible to achieve the different frequency components of the input signal. The purpose of performing different phase perturbations is to obtain a group of candidate signals 9 with different peak power distributions. Therefore, the present invention converts the original computational complexity required by multiple IFFT transformation modules 2 into the computational complexity required by filters in the time domain. By designing the pole-zero position of the filter unit 14, the coefficients of multiplication in each filter subunit are in the form of 1/2, 3/4, 5/8, etc., and the corresponding multiplication can be converted into 1-2 additions to accomplish. Therefore, in the case of a reasonable design, complex multipliers may not be needed in the present invention, and only complex adders can be implemented. In addition, since the coefficient 20 and the coefficient 21 are conjugate numbers to each other, the operation of multiplying the coefficient 20 can be repeatedly used in the calculation of multiplying the coefficient 21. These factors work together to make the amount of calculation required by the present invention much smaller than that of the prior art.

A general all-pass filter has an infinitely long time-domain impulse response, but the present invention uses a finite-length filter for approximation, so the final transmitted signal 9 can be regarded as the transmitted signal 3 passing through a finite impulse The result of the filter for the response. In the case that the number of poles and zeros of the all-pass filter used is not too much, for the receiver, the filter with a finite impulse response can be regarded as a component of the multipath channel, so in the receiver The aforementioned method of channel estimation and coherent demodulation for multipath channels can be used to eliminate the influence of the all-pass filter in the transmitter. Therefore, the present invention can allow the receiver to correctly restore the correct data that has not been processed by the all-pass filter without any additional information sent to the receiver.

The present invention uses a time-domain all-pass filter bank to perform different phase perturbations on the signals on different carriers of the OFDM signal that has been transformed into the time domain, to obtain a group of time domain signals with different peak values, and select the one with the smallest peak power The characteristics of the all-pass filter keep the amplitude of the signal on each carrier constant, so that the signal will not be attenuated. This method converts the complexity of multiple IFFT transformations into the complexity of an all-pass filter in the time domain. The all-pass filter in the time domain can be simply implemented in a cascaded manner. When the coefficient is selected to be an integer number of 2 The implementation is especially simple when combining powers, so all-pass filter banks can be easily implemented. Since the impulse response of the time-domain all-pass filter can be approximated by a finite-length response filter, the phase disturbance caused by the time-domain filter of the transmitter to the transmitted signal can be regarded as a component of the multipath channel. Therefore, a certain number of pilot symbols can be inserted into the frequency domain signal of the transmitter, and the receiver can use these pilot symbols to estimate the channel impulse response on the corresponding carrier, and then perform interpolation to restore the channel on all carriers Impulse response, so that the phase disturbance caused by the transmitter to the transmitted signal can be eliminated and the original signal can be restored. In this way, the present invention does not need special signaling to send the information of peak power control from the transmitter to the receiver.

Description of drawings:

Accompanying drawing 1 is the structural principle schematic diagram of the transmitter of peak power control of the present invention;

Accompanying drawing 2 is the structural representation of the subunit of a time-domain all-pass filter;

Accompanying drawing 3 is corresponding to the structural schematic diagram of the receiver of peak power control when the information of the time-domain all-pass filter through which the final transmission signal is passed by the transmitter to the receiver through signaling 23;

Accompanying drawing 4 is the schematic diagram of the structural principle of the receiver corresponding to the control peak power when the transmitter inserts known pilot symbols evenly at a certain interval in the input data signal 1;

Fig. 5 is a probability distribution diagram of transmitting signal power exceeding the threshold under different thresholds.

Detailed ways:

Embodiments of the present invention are described below in conjunction with the accompanying drawings.

Example 1:

Assume a peak power controlled transmitter and receiver with 256 carriers.

The transmitter for controlling the peak power of the embodiment of the present invention passes the input data signal 1 through the IFFT transformation module 2 to obtain the time domain signal 3; in the cyclic prefix adding module 12, the last section of the time domain signal 11 is added to the time domain signal as it is The front of 11 forms the output signal 13 with cyclic prefix;

In the cyclic prefix addition module 4, the last section of the signal 3 is added to the front of the signal 3 as it is, to form a signal 5 with a cyclic prefix; the signal 5 is passed through each all-pass filter in a group of all-pass filters 6 respectively, A group of different time-domain output signals 7 are respectively obtained; in the cyclic prefix removal module 8, a section equal to the length of the cyclic prefix at the beginning of the filtering result 7 is removed, and then a section equal to the number of samples of the signal 3 is extracted as a filter output The result signal 9; Select the sending module 10 to count the peak power of the result signal 9 output by each filter respectively, and use a signal with the smallest peak power as the selected result signal 11;

Each all-pass filter is formed by cascading a series of filter subunits 14; the input signal 15 of each filter subunit is added to the feedback signal 16 to obtain a signal 17, and the signal 17 is delayed by one clock cycle Time module 18 obtains delay signal 19, and delay signal 19 is multiplied with filter subunit coefficient 20 to obtain feedback signal 16; Addition, obtain the output signal 23 of filter subunit; Said filter subunit coefficient 20 and filter subunit coefficient 21 constitute the coefficient of all-pass filter, satisfy the relation that is conjugate each other;

The transmitter sends the information of the time-domain all-pass filter through which the final transmitted signal passes to the receiver through signaling 23 .

The last section of the time-domain signal 11 is added to the front of the time-domain signal 11 as it is to form the output signal 13 with a cyclic prefix, which means: intercepting a section of the time-domain impulse response of the time-domain all-pass filter 6 to approximate the true The time-domain impulse response of , the length of the cyclic prefix added here is selected to be greater than the length of the intercepted time-domain all-pass filter 6 impulse response.

Adding the end of signal 3 to the front of signal 3 as it is to form signal 5 with cyclic prefix refers to: the length of the cyclic prefix added here is greater than the maximum delay of multipath delay and the intercepted time domain The sum of the lengths of the all-pass filter 6 impulse responses.

Transmitter of the present invention can also be adopted in input data signal 1 and evenly inserts known pilot symbol with certain interval: get the maximum time delay of multipath time delay and the time domain all-pass filter 6 impulse responses that are intercepted out The ratio of the sum of the lengths to the length of the OFDM symbol, uniformly insert known pilot symbols on the input data signal 1, so that the ratio of the number of carriers occupied by the pilot symbols to the total number of carriers is greater than the sum of the aforementioned two lengths The ratio of the length of the OFDM symbol.

This embodiment corresponds to the receiver for controlling the peak power of the above-mentioned transmitter controlling the peak power. The FFT module 25 converts the received signal 31 into a frequency domain signal 32. In the module 33, the pilot symbol in the signal 32 is located on the carrier The channel impulse response is detected, and then interpolated to obtain the conjugate signal 34 of the channel impulse response on each carrier; in module 35, the signal 32 is multiplied by the signal 34 to obtain the signal 36, and then the solution Tuning, decoding and other follow-up processing.

In this transmitter that controls the peak power, there is a known pilot symbol for every 4 data in the 256-point signal 1 in the frequency domain, and the module 2 is a 256-point IFFT transformation, transforming the signal 1 into 256 points In the time-domain signal 3, in the cyclic prefix adding module 4, the last 32 samples of the signal 3 are added to the front of the signal 3 to form a 288-point long sequence 5 with a cyclic prefix. Sequence 5 is sent to a group of all-pass filters 6 to obtain the corresponding output sequence 7. In the cyclic prefix removal module 8, starting from the 33rd sample in the output sequence 7, 256 consecutive samples are taken out as signal 8 . The selection module 9 counts the peak power of the output signal 8 of each filter branch, and then selects a signal 8 with the smallest peak power as the selected result signal 11 . In the cyclic prefix adding module 12, the first 64 samples of the signal 11 are copied to finally form a 320-point OFDM symbol and finally transmitted.

Each all-pass filter 6 is formed by cascading four first-order single-zero and single-pole all-pass filter units 14 . In each all-pass filter unit 14 , the input signal 15 is added to the feedback signal 16 to obtain a signal 17 , and the signal 17 is delayed by a delay unit 18 for one clock cycle to obtain a delayed signal 19 . The delayed signal 19 is multiplied by a factor 20 to obtain the feedback signal 16 . At the same time, the signal 17 is multiplied by the coefficient 21 to obtain the signal 22 , and the signal 22 is added to the delayed signal 19 to obtain the output signal 23 .

As the coefficient of the first-order single-zero single-pole all-pass filter unit 14, the coefficient 20 and the coefficient 21 are conjugate complex numbers, and the coefficient 20 is -r ^* , and the coefficient 21 is -r, where r is the corresponding all-pass filter unit The position of the zero point on the complex plane.

Here four different all-pass filters are taken, and their zero positions are 0, 0, 0, 0; 0.875, 0.75+0.5j, -0.25+0.875j, -0.75-0.5j; -0.375+0.75j, -0.75+0.375j, -0.125-0.875j, 0.75-0.375j; -0.375-0.75j, 0.125-0.875j, 0.375+0.75j, -0.625+0.625j. The first all-pass filter corresponds to the output of the signal as it is. The selection module 9 selects the output with the smallest peak power from the outputs of the four all-pass filters.

Calculating an IFFT with a length of 256 points and an accuracy of 8 bits requires 76*256=19456 complex number additions. On the other hand, the present invention only needs 22.67*256=5804 complex number additions, which is about 1/3 of the calculation amount of IFFT. If an IFFT with a precision of 10 bits is used, the present invention only needs about 1/4 of the calculation amount.

In order to obtain a value closer to the peak power of the continuous waveform after shaping and filtering when calculating the peak power in the selection module 10, an oversampling rate of twice is used, that is, the end of the original input data in the frequency domain is added The zero sequence of the same length forms the input signal 1, and then sends it to the IFFT module 2 for subsequent processing.

The receiver of the present invention first transforms the 256-point received signal 31 into a frequency domain signal 32 in the IFFT module 25 . In module 33, the signal on the carrier where the pilot symbol is located in the signal 32 is extracted and multiplied by the conjugate of the corresponding pilot symbol to obtain the frequency domain impulse response of the channel on these carriers, and then the frequency domain on these carriers The impulse response is interpolated to obtain the corresponding frequency-domain impulse response on each carrier, and these frequency-domain impulse responses are conjugated to obtain a signal 34. In module 35, the conjugate of the impulse response on each carrier It is multiplied with the signal on the corresponding carrier in the signal 32 to obtain the signal 36 that has eliminated the influence of the channel and the time-domain all-pass filter bank of the transmitter, and performs subsequent processing.

对平均功率

归一化后的dB值，纵坐标为输出结果波形序列中功率超出门限

的采样比例。图中曲线A为没有经过选择发送的原始序列的性能，曲线B为从两个滤波器的输出结果中选择输出的具有最小峰值功率的序列的性能，曲线C对应于从四个全通滤波器的输出结果中选择输出的具有最小峰值功率的序列的性能。从结果中可以看到，当超出门限的概率设定为10^-6的时候，如果从两个滤波器选择输出，可以把对应的门限从11.5dB降到10.5dB，如果从四个滤波器中选择输出，可以把门限降到9.5dB。这表明，本发明可以显著地降低输出序列中出现比较大的峰值功率的概率。The performance of this embodiment is shown in Figure 5. The abscissa in the figure is different thresholds

for average power

The normalized dB value, the ordinate is the power exceeding the threshold in the output result waveform sequence

The sampling ratio of . Curve A in the figure is the performance of the original sequence that has not been selected and sent, curve B is the performance of the sequence with the minimum peak power selected from the output results of the two filters, and curve C corresponds to the output from the four all-pass filters The performance of the output sequence with the smallest peak power is selected in the output results of . It can be seen from the results that when the probability of exceeding the threshold is set to 10 ^-6 , if the output is selected from two filters, the corresponding threshold can be reduced from 11.5dB to 10.5dB. Select the output, you can drop the threshold to 9.5dB. This shows that the present invention can significantly reduce the probability of relatively large peak power appearing in the output sequence.

Claims (5)

1, a kind of transmitter of controlling peak power obtains importing time-domain signal (3) with input data signal (1) through inverse Fourier transform module (2); In the cyclic prefix adding module after filtering (12), one section front of being added to the consequential signal (11) of selection by former state, the end of the consequential signal of selection (11) forms the final output signal (13) of being with Cyclic Prefix; It is characterized in that:

In the cyclic prefix adding module before filtering (4), will import one section former state in end of time-domain signal (3) and add the front of importing time-domain signal (3) to, form the filter input signal (5) of band Cyclic Prefix; To be with the filter input signal (5) of Cyclic Prefix respectively by each all-pass filter in one group of all-pass filter (6), domain output signal (7) when obtaining a different set of filter respectively, remove in the module (8) at Cyclic Prefix, one section of equating with circulating prefix-length of domain output signal during with filter (7) beginning part removes, and extracts out then and imports one section consequential signal (9) of exporting as filter that time-domain signal (3) number of samples equates; Select sending module (10) to add up the peak power of the consequential signal (9) of each filter output respectively, with a signal of peak power minimum as the consequential signal of selecting (11);

Each all-pass filter is all formed by a series of filter sub-unit (14) cascade; The input signal of each filter sub-unit (15) obtains adding and signal (17) with feedback signal (16) addition, add and signal (17) obtains time delayed signal (19) through the time delay module (18) of a clock cycle, time delayed signal (19) multiplies each other with feedback filter subelement coefficient (20) and obtains feedback signal (16); On the other hand, add and signal (17) and forward-direction filter subelement coefficient (21) multiplied result (22) and delay time signal (19) addition, the output signal that draws filter sub-unit is as signaling (23); Described filter sub-unit coefficient (20) and filter sub-unit coefficient (21) constitute the coefficient of all-pass filter, satisfy the relation of conjugation each other;

To finally the transmit information of the time domain all-pass filter that passed through of transmitter is passed to receiver by signaling (23).

2, control the transmitter of peak power according to claim 1, it is characterized in that the described one section former state in end that will import time-domain signal (3) adds the front of input time-domain signal (3) to, the filter input signal (5) that forms the band Cyclic Prefix is meant: the length sum of time domain all-pass filter (6) impulse response that the length of getting the Cyclic Prefix that is added is come out greater than the maximum delay and the intercepting of multidiameter delay.

3, control the transmitter of peak power according to claim 1, it is characterized in that this transmitter evenly inserts known frequency pilot sign at certain intervals in input data signal (1), this is meant: the length sum of getting the maximum delay of multidiameter delay and time domain all-pass filter (6) impulse response that intercepting is come out accounts for the ratio of the length of orthogonal frequency division multiplexed modulation symbol, go up at input data signal (1) and evenly to insert known frequency pilot sign, make the ratio of carrier number that frequency pilot sign is shared and total carrier number account for the ratio of the length of orthogonal frequency division multiplexed modulation symbol greater than aforementioned two length sums.

4, a kind of receiver of controlling peak power, comprise by Fourier transform module (25) input signal (24) is transformed to frequency-region signal (26), it is characterized in that: recover in the module (27) frequency-region signal (26) to be caused the conjugated signal (28) of phase shift from the all-pass filter that signaling (23) recovers transmitter in the all-pass filter phase shift, in multiplier module (29), frequency-region signal (26) obtains demodulation front signal (30) with corresponding the multiplying each other of conjugated signal (28) of phase shift, carries out demodulation, decode successive processing then.

5, receiver as control peak power as described in the claim 4, it is characterized in that: when taking in input data signal (1), evenly to insert known frequency pilot sign at certain intervals corresponding to transmitter, then in receiver, receiving inputted signal (31) transforms in Fourier transform module (25) earlier and receives frequency-region signal (32), in Channel Detection and interpose module (33), the channel impulse response that receives on the frequency pilot sign place carrier wave in the frequency-region signal (32) is detected, and carries out the conjugated signal (34) that interpolation obtains the channel impulse response on each carrier wave then; In the module that multiplies each other (35), receive corresponding the multiplying each other of conjugated signal (34) of frequency-region signal (32) and channel impulse response, obtain receiving demodulation front signal (36), carry out demodulation, decode successive processing then.

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