CN1400830A - Method for reducing multicarrier signal peak level ratio - Google Patents

Abstract

A method to reduce the peak-to-average ratio of multi-carrier signals: set a pulse signal generator in the baseband or intermediate frequency modulation process of the downlink; set the threshold for reducing the peak-to-average ratio in the time domain, and perform a Detection: If the amplitude peak value of the multi-carrier signal exceeds the threshold, record the characteristic parameters of the peak value and pass these parameters to a pulse signal generator; then, according to the above parameters and the different single-carrier signals that constitute the multi-carrier signal, generate corresponding The pulse is superimposed on the signal, and the peak value is cancelled, so that the peak value of the multi-carrier signal drops to the threshold after the combination, thereby reducing the peak-to-average ratio of the multi-carrier signal; if the peak value of the multi-carrier signal amplitude does not exceed the threshold, no processing is performed . The invention is used in a multi-carrier communication system to reduce the peak-to-average ratio of the downlink modulation signal of the base station, thereby reducing the requirement on the linear range of the power amplifier caused by the signal peak-to-average ratio being too high, improving the efficiency of the power amplifier, and reducing equipment investment costs.

Description

A Method for Reducing the Peak-to-Average Ratio of Multi-carrier Signals

(1) Technical field

The invention relates to a method for reducing the signal peak-to-average ratio in the downlink modulation link of a multi-carrier broadband system.

(2) Background technology

Since the size of the base station can be effectively reduced and the cost of the base station can be reduced, the multi-carrier technology has received widespread attention and research at present. Moreover, people also hope to use multi-carrier technology to achieve high bit rate transmission in multi-path fading channels.

However, one of the disadvantages of the multi-carrier communication system is that when the number of sub-carriers increases, the peak-to-average ratio of the transmitted signal will also increase. Because if each single-carrier signal is regarded as a cosine signal with random phase, the multi-carrier signal synthesized after the superposition of several single-carrier signals must have an amplitude envelope fluctuation that is not constant, and many higher peaks will inevitably appear. As a result, the peak-to-average ratio of the multi-carrier signal is higher than the peak-to-average ratio of the original carrier signal.

In a multi-carrier signal, if the peak-to-average ratio is relatively large, the signal amplitude will exceed the linear range of the power amplifier at the RF end, resulting in intermodulation interference and out-of-band regeneration of the signal, causing high interference to adjacent channels and deteriorating system transmission quality. Bad, the system capacity is reduced. If the signal to be transmitted has a high peak-to-average ratio, in order to avoid out-of-band signal regeneration, the power amplifier needs to have a larger linear range, so that the power amplifier has a larger backoff, which will result in lower efficiency of the power amplifier. It can be seen that excessive peak-to-average ratio has always been one of the important reasons affecting the application of multi-carrier base stations, and reducing the peak-to-average ratio can effectively increase the power of the power amplifier, improve the efficiency of the power amplifier, and reduce the cost of power amplifier equipment.

At present, there are usually several methods to reduce the peak-to-average ratio of multi-carrier signals: direct clipping, designing spreading codes, changing the initial phase of subcarriers, superimposing out-of-band artificial signals, etc. Direct clipping can effectively reduce the signal peak-to-average ratio, but it is easy to cause in-band noise interference and out-of-band spectrum regeneration of the modulated signal, affecting adjacent channels and system capacity; for existing systems, redesign The spread spectrum code will bring a series of problems; changing the initial phase of the subcarrier signal is not operable, and it is difficult to implement; superimposing out-of-band artificial signals, such as artificial amplitude modulation signals modulated outside the band, can reduce multi-carrier The signal peak-to-average ratio, but in the actual system, it needs to spend a relatively high cost to design a filter at the radio frequency end to filter out the out-of-band signal.

(3) Contents of the invention

The purpose of the present invention is to provide a method for reducing the peak-to-average ratio of a multi-carrier signal, which is used in a multi-carrier communication system to reduce the peak-to-average ratio of a downlink modulation signal of a base station, thereby reducing the impact caused by an excessively high signal peak-to-average ratio. The requirements of the linear range of the power amplifier improve the efficiency of the power amplifier and reduce the cost spent on the power amplifier equipment.

A method for reducing the peak-to-average ratio of multi-carrier signals provided by the present invention includes the following steps: setting a pulse signal generator in the baseband or intermediate frequency modulation process of the downlink; setting the threshold for reducing the peak-to-average ratio in the time domain , and detect the peak amplitude of the multi-carrier signal: if the peak amplitude of the multi-carrier signal exceeds the threshold, record the characteristic parameters of the peak, and pass these parameters to a pulse signal generator; then, according to the above parameters and form a multi-carrier signal The different single-carrier signals of each channel generate corresponding pulses, superimpose on the signal, and cancel the peak value, so that the peak value of the multi-carrier signal drops to the threshold after the combination, thereby reducing the peak-to-average ratio of the multi-carrier signal; if the multi-carrier signal If the amplitude peak value does not exceed the threshold, it will not be processed.

In the above method for reducing the peak-to-average ratio of a multi-carrier signal, the pulse is a band-limited pulse.

In the above-mentioned method for reducing the peak-to-average ratio of a multi-carrier signal, the characteristic parameters of the recorded peak may be occurrence time, peak height, and peak phase.

In the above method for reducing the peak-to-average ratio of a multi-carrier signal, the band-limited pulse may be a band-limited Gaussian pulse.

In the above method for reducing the peak-to-average ratio of multi-carrier signals, the superposition operation can be performed at baseband, or after single-carrier signal combination, or after multi-carrier signal combination.

In the above-mentioned method for reducing the peak-to-average ratio of multi-carrier signals, the manner of superimposing pulses can not only superimpose band-limited signals of the same amplitude, but also superimpose band-limited signals of different amplitudes.

In the above method for reducing the peak-to-average ratio of a multi-carrier signal, the pulse is a pulse that has a relatively small impact on the frequency spectrum of the signal within the bandwidth and a relatively large attenuation outside the signal bandwidth, thereby reducing the impact on the adjacent channel signal. Impact.

Due to the adoption of the above-mentioned technical solutions, in the existing system, pulse signals can be directly superimposed on signals with higher amplitudes, thereby reducing the peak-to-average ratio of multi-carrier signals. In particular, the superposition of band-limited pulses can make the spectrum impact on the signal relatively small within the bandwidth, and the attenuation is relatively large outside the signal bandwidth range, which will not cause out-of-band spectrum regeneration of the modulated signal, thereby greatly reducing the impact on adjacent channel signals. This kind of band-limited pulse occurs in a short time in the time domain, does not cause new high-amplitude peaks to appear in the signal after the band-limited pulse signal is superimposed, and is easy to operate, and the cost of implementation is relatively small.

(4) Description of drawings

Fig. 1 (a), Fig. 1 (b) is the signal processing flow chart after adding pulse signal generator in the base station;

Fig. 2 is a flow chart of signal processing in the first embodiment of the present invention;

Fig. 3 is a flow chart of signal processing in the second embodiment of the present invention;

Fig. 4 is a flow chart of signal processing in the third embodiment of the present invention.

(5) specific implementation

As shown in Figure 1(a), on each single-carrier downlink, the complex-valued chip sequence generated by spread spectrum passes through the serial-to-parallel converter 11 and is separated into two signals of the real part and the imaginary part. The signals are pulse-shaped through root-raised cosine filters 12 to reduce inter-symbol interference.

The 2-way signal after pulse shaping is multiplied by the 2-way carrier frequency signal generated by the digitally controlled oscillator 13 in the multiplier 14 to carry out intermediate frequency modulation. These two channels of signals modulated to the intermediate frequency are combined by the adder 15 . It should be noted that the carrier frequency of each single-carrier downlink is different from each other, that is, in each single-carrier downlink, the frequency of the carrier frequency signal generated by the digitally controlled oscillator 13 is different.

The signals generated by each single-carrier downlink are added in the adder 16 to become a multi-carrier combined signal.

The multi-carrier combined signal is sent to the band-limited pulse generator 17 for detection, and the band-limited pulse generator 17 generates a corresponding band-limited pulse signal for processing to reduce the peak-to-average ratio.

As shown in Figure 1(b), on each single-carrier downlink, the complex-valued chip sequence generated by spread spectrum passes through the serial-to-parallel converter 11 and is separated into two signals of the real part and the imaginary part. The signals are pulse-shaped through root-raised cosine filters 12 to reduce inter-symbol interference.

The band-limited pulse generator 17 generates a corresponding band-limited pulse signal for processing to reduce the peak-to-average ratio.

The 2-way signal is multiplied by the 2-way carrier frequency signal generated by the digitally controlled oscillator 13 in the multiplier 14 to perform intermediate frequency modulation. These two channels of signals modulated to the intermediate frequency are combined by the adder 15 . The carrier frequency of each single-carrier downlink is different from each other, that is, in each single-carrier downlink, the frequency of the carrier frequency signal generated by the digitally controlled oscillator 13 is different.

The signals generated by each single-carrier downlink are added in the adder 16 to become a multi-carrier combined signal.

The first embodiment of the method of the present invention is described below.

As shown in FIG. 2 , the flow chart of signal processing in the band-limited Gaussian pulse generator in the first embodiment.

Referring to FIG. 1 , the process of superimposing band-limited Gaussian pulses on multi-carrier signals to reduce the peak-to-average ratio in the first embodiment can be implemented by software. Its process is shown in Figure 2.

The unit 21 inputs the amplitude of the multi-carrier signal, and the unit 22 compares the signal amplitude X with the peak-to-average ratio reduction threshold (Threshold). If X<Threshold, then do not do any processing, and directly send to unit 25 for output; if X>Threshold, then record the parameters of the signal amplitude in unit 23, such as the moment when the amplitude peak occurs, the height of the peak, etc. These parameters are input into the unit 24, and the band-limited Gaussian pulse generator generates corresponding band-limited Gaussian pulses according to these parameters, which are superimposed on the multi-carrier signal, so that the amplitude of the multi-carrier signal is reduced to the required threshold.

Every time when the multi-carrier signal has a peak value, a single-carrier signal is randomly selected to superimpose the corresponding modulated band-limited Gaussian pulse, and the remaining branch single-carrier signals are not processed, and finally the multi-carrier signal after reducing the peak-to-average ratio The amplitude drops to the set threshold.

Amplitude of the modulated band-limited Gaussian pulse used for superposition

=(The peak amplitude of the multi-carrier signal at the threshold of reducing the peak-to-average ratio-reducing the peak-to-average ratio threshold)

The signal processed for peak-to-average ratio reduction is sent to unit 25 for output.

The first embodiment of the method of the present invention has been described above. Introduce the second of the inventive method below

Example.

As shown in FIG. 3 , the flow chart of signal processing in the band-limited Gaussian pulse generator in the second embodiment.

Referring to Figure 1, the process of superimposing band-limited Gaussian pulses on multi-carrier signals to reduce the peak-to-average ratio can be implemented by software. Its process is shown in Figure 3.

The unit 31 inputs the amplitude of the multi-carrier signal, and the unit 32 compares the signal amplitude X with the peak-to-average ratio reduction threshold Threshold. If X<Threshold, then do not do any processing, directly send to the output in unit 35; These parameters are input into the unit 34, and the band-limited Gaussian pulse generator generates corresponding band-limited pulses according to these parameters, which are superimposed on the multi-carrier signal, so that the amplitude of the multi-carrier signal is reduced to the required threshold.

For each single-carrier signal that constitutes a multi-carrier signal plus a modulated band-limited Gaussian pulse, the amplitude of the modulated band-limited Gaussian pulse superimposed on each single-carrier signal is exactly the same, so that the multi-carrier signal after reducing the peak-to-average ratio The amplitude drops to the set threshold. Right now

The amplitude of each modulated band-limited Gaussian pulse

=(beyond the peak amplitude of the multi-carrier signal at the threshold for reducing the peak-to-average ratio-reduce the peak-to-average ratio threshold)/number of carriers

The signal processed for peak-to-average ratio reduction is sent to unit 35 for output.

The second embodiment of the method of the present invention has been described above. Introduce the 3rd of the inventive method below

Example.

As shown in FIG. 4 , the flow chart of signal processing in the band-limited Gaussian pulse generator in the third embodiment.

Referring to Figure 1, the process of superimposing band-limited Gaussian pulses on multi-carrier signals to reduce the peak-to-average ratio can be implemented by software. Its process is shown in Figure 4.

The unit 41 inputs the amplitude of the multi-carrier signal, and the unit 42 compares the signal amplitude X with the peak-to-average ratio reduction threshold Threshold. If X<Threshold, then do not do any processing, directly sent to the unit 45 output; These parameters are input into the unit 44, and the band-limited Gaussian pulse generator generates corresponding band-limited Gaussian pulses according to these parameters, which are superimposed on the multi-carrier signal, so that the amplitude of the multi-carrier signal is reduced to the required threshold.

For the modulated band-limited Gaussian pulses added to each single-carrier signal constituting the multi-carrier signal, the amplitudes of the modulated band-limited Gaussian pulses superimposed on each single-carrier signal are not exactly the same. For the single-carrier branch with relatively higher amplitude, the amplitude of the superimposed modulated band-limited Gaussian pulse is higher; for the single-carrier branch with relatively lower amplitude, the amplitude of the superimposed modulated band-limited Gaussian pulse is lower. The amplitude information of each single-carrier branch can be extracted before being combined into multi-carrier signals, and passed as an input parameter to the pulse generator with Gaussian limit, as the amplitude of the band-limited Gaussian pulse selected to be superimposed on each single-carrier signal Finally, the amplitude of the multi-carrier signal after reducing the peak-to-average ratio is reduced to the set threshold. Right now

The amplitude of each modulated band-limited Gaussian pulse

=(the peak amplitude of the multi-carrier signal beyond the peak-to-average ratio threshold reduction-the peak-to-average ratio threshold reduction)*(the amplitude peak value of the single-carrier signal at this moment)/(the amplitude peak value of the multi-carrier signal at this moment)

The signal processed for peak-to-average ratio reduction is sent to unit 45 for output.

Superimposed on the multi-carrier signal in the above embodiments are band-limited Gaussian pulses. The impact of this kind of pulse on the frequency spectrum of the signal is relatively small within the bandwidth, and the attenuation is relatively large outside the signal bandwidth range, which will not cause the out-of-band spectrum regeneration of the modulated signal, thus greatly reducing the influence on adjacent channel signals. This band-limited pulse occurs for a short time in the time domain, and will not cause a new high-amplitude peak to appear in the signal after the band-limited pulse signal is superimposed. The pulse generation method is simple and easy to operate.

Claims (7)

1. A method for reducing the peak-to-average ratio of multi-carrier signals, comprising the following steps: Set a pulse signal generator in the baseband or intermediate frequency modulation process of the downlink; Set the peak-to-average ratio reduction threshold in the time domain, and detect the amplitude peak of the multi-carrier signal: If the peak value of the multi-carrier signal amplitude exceeds the threshold, record the characteristic parameters of the peak value, and pass these parameters to a pulse signal generator; Then, according to the above parameters and the different single-carrier signals that constitute the multi-carrier signal, corresponding pulses are generated, superimposed on the signal, and the peak value is cancelled, so that the peak value of the multi-carrier signal after the combination is reduced to the threshold, thereby reducing the multi-carrier signal. Carrier signal peak-to-average ratio; If the peak amplitude of the multi-carrier signal does not exceed the threshold, no processing is performed. 2. A method for reducing the peak-to-average ratio of a multi-carrier signal according to claim 1, wherein the pulse is a band-limited pulse. 3. A method for reducing the peak-to-average ratio of multi-carrier signals according to claim 1, characterized in that the characteristic parameters of the recorded peak can be time of occurrence, peak height and peak phase. 4. A method for reducing the peak-to-average ratio of a multi-carrier signal according to claim 2, characterized in that the band-limited pulse may be a band-limited Gaussian pulse. 5. A kind of method for reducing the peak-to-average ratio of multi-carrier signals according to claim 1, characterized in that, the operation of the superposition can be carried out at baseband, also can be carried out after single-carrier combination, also can be carried out at It is performed after multi-carrier signal combination. 6. A method for reducing the peak-to-average ratio of multi-carrier signals according to claim 1, wherein the mode of superimposing pulses can superimpose band-limited signals of the same amplitude or superimpose different amplitudes. band-limited signal. 7. A method for reducing the peak-to-average ratio of multi-carrier signals according to claim 1, wherein the pulse has a relatively small influence on the frequency spectrum of the signal within the bandwidth and a relatively large attenuation outside the bandwidth of the signal The characteristic pulse, thereby reducing the influence on the adjacent channel signal.

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