JP2010074252A - Ofdm transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cost by greatly reducing the circuit scale of a filter in an OFDM (Orthogonal Frequency Division Multiplexing) transmitter which includes a rate conversion processing part that switches a plurality of rate conversion rates and converts a sampling rate of a digital signal at a switched rate conversion rate to perform transmission by an OFDM system. <P>SOLUTION: In a rate conversion processing part, a polyphase filter 1 filters a digital signal and converts a sampling rate of the digital signal, and a control means 2 stores a filter coefficient to be set in the polyphase filter for each combination of each phase of the polyphase filter with each tap, also stores a pattern of control performed over the polyphase filter about each of a plurality of rate conversion rates, and uses the stored filter coefficient to control the polyphase filter with the pattern of control corresponding to a rate conversion rate to be used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transmitter (OFDM transmitter) of an OFDM (Orthogonal Frequency Division Multiplexing) type mobile communication system, and in particular, a rate for converting a sampling rate of a digital signal to a desired sampling rate. The present invention relates to an OFDM transmitter that realizes a rate conversion function that can support a plurality of rate conversion rates by using a polyphase filter.

FIG. 6 shows a configuration example of a rate conversion processing unit according to the prior art.
As an example, there are three types of input signals: a 5 MHz band signal with a sampling rate of 5.6 MHz, a 10 MHz band signal with a sampling rate of 11.2 MHz, and a 20 MHz band signal with a sampling rate of 22.4 MHz. A rate conversion processing unit that performs rate conversion up to a sampling rate of 112 MHz will be described.

  The first rate converter 101 performs 20 times rate conversion, the second rate converter 102 performs 10 times rate conversion, and the third rate converter 103 performs 5 times rate conversion. The switch unit 104 switches the switch circuit based on the signal band information or the input sampling rate information, and selects one appropriate output signal from the three rate conversion units 101 to 103. Output.

FIG. 7 shows a configuration example of the internal structure of the rate conversion unit 111 (rate conversion units 101 to 103 shown in FIG. 6) according to the prior art.
The rate conversion unit 111 of this example includes an interpolation unit for 0 data (0 interpolation unit) 121 and a low pass filter (LPF) 122 for removing aliasing images generated by the 0 data interpolation. ing.

The 0 interpolation unit 121 converts the data rate by inserting the number of 0 data corresponding to the conversion magnification into the input data every other input sample. For example, when the sampling rate is converted to 5 times, four 0 data are inserted every other input sample, and when the sampling rate is converted to 10 times, nine 0 data are input every other sample. When the sampling rate is converted to 20 times, 19 zero data are inserted every other input sample.
The LPF 122 removes the aliasing image generated by inserting 0 data. The filter coefficient of the LPF 122 for removing the aliasing image differs depending on the signal band. The filter circuit constituting the LPF 122 may be prepared for each signal band, but it is also possible to share one filter circuit by switching the filter coefficient according to the signal band.

Japanese Patent Laid-Open No. 11-251969

  However, the OFDM communication apparatus may support a plurality of band signals, and the sampling rate of the baseband signal differs depending on the signal band. For example, in Mobile WiMAX which is an OFDM signal, as described above, the sampling rate of the 5 MHz band signal is 5.6 MHz, the sampling rate of the 10 MHz band signal is 11.2 MHz, and the sampling rate of the 20 MHz band signal is 22 .4 MHz is specified.

When a transmission signal is amplified by a power amplifier and transmitted, signal processing such as digital predistortion and peak power suppression is performed to improve power efficiency. For this purpose, the sampling rate of a digital IQ signal is used. Need to lift.
Here, in the rate conversion processing unit according to the conventional technique, rate conversion units (rate conversion units 101 to 103 in FIG. 6) are individually prepared for signals having different rate conversion rates, and the circuit scale is reduced. The cost increase due to the increase has been a problem.

  The present invention has been made in view of such a conventional situation. By using a polyphase filter, it is possible to cope with a plurality of rate conversion rates including fractional multiples. An object of the present invention is to provide an OFDM transmitter capable of realizing a rate conversion function by greatly reducing the scale, thereby reducing the cost of a communication device (transmission amplifier).

In order to achieve the above object, in the present invention, a plurality of rate conversion rates can be switched, and a rate conversion processing unit that converts a sampling rate of a digital signal at the switched rate conversion rate is provided, and is transmitted by OFDM. An OFDM transmitter that performs the following configuration is used.
That is, in the rate conversion processing unit, the polyphase filter performs a filtering process on the digital signal to convert the sampling rate of the digital signal. In this case, the control means stores a filter coefficient to be set in the polyphase filter for each combination of each phase and each tap of the polyphase filter, and also sets the poly coefficient for each of the plurality of rate conversion rates. A pattern of control performed on the phase filter is stored, and the polyphase filter is controlled with a control pattern corresponding to a rate conversion rate to be used, using the stored filter coefficient.

  Therefore, by using a polyphase filter, it is possible to cope with multiple rate conversion rates including fractional multiples, and furthermore, the rate conversion function is realized by greatly reducing the circuit scale of the filter. An OFDM transmitter capable of reducing the cost of the communication device (transmission amplifier) can be realized.

Here, various aspects may be used as the number of rate conversion ratios and the respective rate conversion ratios.
Various configurations such as the number of taps of the polyphase filter may be used.
Various control patterns may be used for the polyphase filter. For example, a process for shifting input data to the polyphase filter or a filter coefficient of a predetermined phase may be changed to a polyphase filter. A control pattern relating to processing for setting each tap of the phase filter and processing for obtaining an output of one sample from the polyphase filter is used.

  As described above, according to the OFDM transmitter of the present invention, by using a polyphase filter, it is possible to cope with a plurality of rate conversion rates including fractional multiples, and further, the circuit scale of the filter is reduced. The rate conversion function can be realized by greatly reducing the cost, thereby reducing the cost of the communication device (transmission amplifier).

Embodiments according to the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration example of a rate conversion processing unit according to an embodiment of the present invention.
The rate conversion processing unit of this example includes a polyphase filter 1 and a phase control unit (processing unit having a function of a control unit) 2.
The polyphase filter 1 converts the sampling rate of the input signal to a desired sampling rate and outputs it.
The phase control unit 2 controls the phase switching process of the polyphase filter 1 according to the given band information.

Here, the internal structure and phase control of the polyphase filter 1 will be described.
The polyphase filter 1 has a form in which the multiplication process of 0 data and a filter coefficient, which is a wasteful process in the LPF circuit, is omitted from the rate conversion unit of the 0 interpolation method according to the prior art. The filter coefficient set in the polyphase filter 1 is obtained by decomposing the filter coefficient of the LPF according to the prior art into a plurality of phases.

As an example, the case of 5 times rate conversion will be described.
FIG. 8 shows an example of the impulse response (filter coefficient) of the LPF.
FIG. 3 shows an example of the impulse response (filter coefficient) of the polyphase filter.
FIG. 2 shows a configuration example of the polyphase filter 1 and the phase control unit 2.

When the LPF according to the prior art is configured with a 35-tap filter coefficient having an impulse response curve as shown in FIG. 8, the polyphase filter 1 of the present example has this 35 as shown in FIG. 3. What is necessary is just to use the filter coefficient of 7 tap x5 sets (phase) which extracted the filter coefficient of the tap every 5 taps.
Therefore, as shown in FIG. 2, as the polyphase filter 1, a 7-tap filter circuit may be assembled on the circuit, and the circuit scale is significantly larger than that of the prior art that requires a 35-tap filter circuit. It has been reduced.

Here, in the polyphase filter 1 shown in FIG. 2, seven registers A1 to A7 connected in series and seven multipliers B1 to B7 respectively corresponding to the seven registers A1 to A7. And one adder 11.
After the input signal (input data) is input to the first register A1, it sequentially moves from the second register A2 to the seventh register A7. Further, signals (data) are output from the seven registers A1 to A7 to the corresponding multipliers B1 to B7. The data from the registers A1 to A7 and the phase control unit 2 are output from the multipliers B1 to B7. Are multiplied by the filter coefficients. Then, the multiplication results from the seven multipliers B1 to B7 are added (summed) by the adder 11, and a signal of the addition result is output.

2 includes a RAM (Random Access Memory) 21 for storing filter coefficients.
In the filter coefficient storage RAM 21, in this example, filter coefficients t (1,...) Corresponding to combinations (140 combinations) of each of the 20 phases (Phase) and each of the 7 taps (tap). 1) to t (20, 7) are stored. Then, the phase control unit 2 reads out the filter coefficients corresponding to the number of phases and the number of taps (in this example, taps 1 to 7 in the order of seven multipliers B1 to B7) from the filter coefficient storage RAM 21 and performs each multiplication. To the devices B1 to B7.

Next, phase control will be described.
When the input signal of the polyphase filter 1 is shifted by one sample, the phase control unit 2 sets the filter coefficients of each phase in a predetermined order for each clock at the converted rate and switches them. . As a result, the output from the polyphase filter 1 is equivalent to the output from the LPF according to the prior art.

A specific procedure of phase control will be described for the following rate conversion. The corresponding rate conversion is the following three patterns.
(Pattern 1-1) 5 MHz band signal: 5.6 MHz to 112 MHz (× 20)
(Pattern 1-2) 10 MHz band signal: 11.2 MHz to 112 MHz (× 10)
(Pattern 1-3) 20 MHz band signal: 22.4 MHz to 112 MHz (× 5)

  The filter coefficient of each phase set in the polyphase filter 1 is the same for the 10 MHz band signal and the 20 MHz band signal when the sampling rate of the 5 MHz band signal is converted from 5.6 MHz to 112 MHz. Can be used. This is because the filter coefficient for the 5 MHz band signal is a filter when the sampling rate of the 10 MHz band signal is converted from 11.2 MHz to 224 MHz and the sampling rate of the 20 MHz band signal is converted from 22.4 MHz to 448 MHz. This is because the same frequency characteristic as the coefficient can be obtained. That is, if the sampling factor, which is the ratio between the signal band and the sampling rate, has the same value, the filter coefficient can be shared.

  The polyphase filter 1 uses a set of filter coefficients of 20 phases in total from phase 1 to phase 20, and the phase control unit 2 sets the filter coefficient of each phase in the polyphase filter 1. The order of phase switching differs for each signal band, and phase switching is performed in the following order.

(Control 1-1) Phase control for 5 MHz band signal In the case of a 5 MHz band signal, the phase control unit 2 performs phase control as follows.
First, the input data of the polyphase filter 1 is shifted by one sample.
Next, a phase 1 coefficient (filter coefficient) is set, and an output of one sample is obtained.
Next, the phase 2 coefficient is set to obtain an output of one sample.
(Hereafter, the same processing is performed from phase 3 to phase 18.)
Next, the phase 19 coefficient is set to obtain an output of one sample.
Next, the coefficient of phase 20 is set, and an output of one sample is obtained.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 1 coefficient is set to obtain one sample output.
Next, the phase 2 coefficient is set to obtain an output of one sample.
(Hereafter, the same processing is performed from phase 3 to phase 18.)
Next, the phase 19 coefficient is set to obtain an output of one sample.
Next, the coefficient of phase 20 is set, and an output of one sample is obtained.
Thereafter, the same processing is repeated.

(Control 1-2) Phase control for 10 MHz band signal In the case of a 10 MHz band signal, the phase control unit 2 performs phase control as follows.
First, the input data of the polyphase filter 1 is shifted by one sample.
Next, a phase 1 coefficient (filter coefficient) is set, and an output of one sample is obtained.
Next, the phase 3 coefficient is set to obtain an output of one sample.
(Hereafter, the same processing is performed from phase 5 to phase 15.)
Next, the phase 17 coefficient is set to obtain an output of one sample.
Next, the phase 19 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 1 coefficient is set to obtain one sample output.
Next, the phase 3 coefficient is set to obtain an output of one sample.
(Hereafter, the same processing is performed from phase 5 to phase 15.)
Next, the phase 17 coefficient is set to obtain an output of one sample.
Next, the phase 19 coefficient is set to obtain an output of one sample.
Thereafter, the same processing is repeated.
In this way, by setting the filter coefficients prepared for 20-times rate conversion every two phases, 10-times rate conversion can be realized.

(Control 1-3) Phase Control for 20 MHz Band Signal In the case of a 20 MHz band signal, the phase control unit 2 performs phase control as follows.
First, the input data of the polyphase filter 1 is shifted by one sample.
Next, a phase 1 coefficient (filter coefficient) is set, and an output of one sample is obtained.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Next, the phase 9 coefficient is set to obtain an output of one sample.
Next, the phase 13 coefficient is set to obtain an output of one sample.
Next, the phase 17 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 1 coefficient is set to obtain one sample output.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Next, the phase 9 coefficient is set to obtain an output of one sample.
Next, the phase 13 coefficient is set to obtain an output of one sample.
Next, the phase 17 coefficient is set to obtain an output of one sample.
Thereafter, the same processing is repeated.
In this way, by setting the filter coefficients prepared for 20-times rate conversion every 4 phases, 5-times rate conversion can be realized.

  Here, FIG. 4 shows an example of the time waveform of the input / output signal of the rate conversion processing unit when the sampling rate is converted from 11.2 MHz to 112 MHz. It can be seen that the input data samples are interpolated to generate a signal having a sampling rate of 10 times.

Next, another example of phase control is shown.
In this example, the phase control procedure will be described for the case where the rate conversion rate is a fractional multiple. The corresponding rate conversion is the following three patterns.
(Pattern 2-1) 5 MHz band signal: 5.6 MHz to 28 MHz (× 5)
(Pattern 2-2) 10 MHz band signal: 11.2 MHz to 28 MHz (× 5/2)
(Pattern 2-3) 20 MHz band signal: 22.4 MHz to 28 MHz (× 5/4)

  In the case of this example, the polyphase filter 1 uses a set of filter coefficients of 5 phases in total from phase 1 to phase 5, and the phase control unit 2 sets the filter coefficients of each phase in the polyphase filter 1. The order of phase switching differs for each signal band, and phase switching is performed in the following order.

(Control 2-1) Phase control for 5 MHz band signal In the case of a 5 MHz band signal, the phase control unit 2 performs phase control as follows.
First, the input data of the polyphase filter 1 is shifted by one sample.
Next, a phase 1 coefficient (filter coefficient) is set, and an output of one sample is obtained.
Next, the phase 2 coefficient is set to obtain an output of one sample.
Next, the phase 3 coefficient is set to obtain an output of one sample.
Next, the phase 4 coefficient is set to obtain an output of one sample.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter is shifted by one sample.
Next, the phase 1 coefficient is set to obtain one sample output.
Next, the phase 2 coefficient is set to obtain an output of one sample.
Next, the phase 3 coefficient is set to obtain an output of one sample.
Next, the phase 4 coefficient is set to obtain an output of one sample.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Thereafter, the same processing is repeated.

(Control 2-2) Phase control for 10 MHz band signal In the case of a 10 MHz band signal, the phase control unit 2 performs phase control as follows.
First, the input data of the polyphase filter 1 is shifted by one sample.
Next, a phase 1 coefficient (filter coefficient) is set, and an output of one sample is obtained.
Next, the phase 3 coefficient is set to obtain an output of one sample.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 2 coefficient is set to obtain an output of one sample.
Next, the phase 4 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter is shifted by one sample.
Next, the phase 1 coefficient is set to obtain one sample output.
Next, the phase 3 coefficient is set to obtain an output of one sample.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 2 coefficient is set to obtain an output of one sample.
Next, the phase 4 coefficient is set to obtain an output of one sample.
Thereafter, the same processing is repeated.

(Control 2-3) Phase Control for 20 MHz Band Signal In the case of a 20 MHz band signal, the phase control unit 2 performs phase control as follows.
First, the input data of the polyphase filter 1 is shifted by one sample.
Next, a phase 1 coefficient (filter coefficient) is set, and an output of one sample is obtained.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 4 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 3 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 2 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 1 coefficient is set to obtain one sample output.
Next, the phase 5 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 4 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 3 coefficient is set to obtain an output of one sample.
Next, the input data of the polyphase filter 1 is shifted by one sample.
Next, the phase 2 coefficient is set to obtain an output of one sample.
Thereafter, the same processing is repeated.

  FIG. 5 shows an example of the time waveform of the input / output signal of the rate conversion processing unit when the sampling rate is converted from 11.2 MHz to 28 MHz. It can be seen that the input data samples are interpolated to generate a signal having a sampling rate of 5/2 times.

As described above, when converting the sampling rate of the digital signal, the rate conversion processing unit of this example has a filter inside and can cope with a plurality of rate conversion rates by switching the filter coefficient.
In addition, when converting the sampling rate of the digital signal, the rate conversion processing unit of the present example has a filter inside, and by switching the filter coefficient, signals of a plurality of sampling rates are determined in advance by a fixed sampling rate. Can be converted to a rate signal.

Further, in the rate conversion processing unit of this example, the above-described filter is realized by the polyphase filter 1, and the phase control unit 2 performs phase control of the polyphase filter 1 in accordance with the rate conversion rate.
Also, in this example, an OFDM transmitter and an OFDM transmitter amplifier having the rate conversion processing unit as described above can be realized, and multirate conversion can be supported.
Note that the configuration and operation of the rate conversion processing unit as in this example may be applied to an apparatus that uses a communication method other than the OFDM method, for example.

  Therefore, by mounting the rate conversion processing unit as in this example, the circuit scale is reduced when there are input signals of a plurality of sampling rates or when rate conversion is performed at a plurality of rate conversion rates. One filter circuit can realize rate conversion, and the circuit scale of the rate conversion unit can be greatly reduced. In particular, an OFDM transmission amplifier may process signals in a plurality of bands with different sampling rates. By using the rate conversion processing unit of this example, it is possible to realize a transmission amplifier with reduced apparatus cost. it can.

Here, the configuration of the system and apparatus according to the present invention is not necessarily limited to the configuration described above, and various configurations may be used. The present invention can also be provided as, for example, a method or method for executing the processing according to the present invention, a program for realizing such a method or method, or a recording medium for recording the program. It is also possible to provide various systems and devices.
The application field of the present invention is not necessarily limited to the above-described fields, and the present invention can be applied to various fields.
In addition, as various processes performed in the system and apparatus according to the present invention, for example, the processor executes a control program stored in a ROM (Read Only Memory) in hardware resources including a processor and a memory. A controlled configuration may be used, and for example, each functional unit for executing the processing may be configured as an independent hardware circuit.
The present invention can also be understood as a computer-readable recording medium such as a floppy (registered trademark) disk or a CD (Compact Disc) -ROM storing the control program, and the program (itself). The processing according to the present invention can be performed by inputting the program from the recording medium to the computer and causing the processor to execute the program.

It is a figure which shows the structural example of the rate conversion process part which concerns on one Example of this invention. It is a figure which shows an example of the internal structure of a polyphase filter, and a phase control part. It is a figure which shows an example of the impulse response (filter coefficient) of a polyphase filter. It is a figure which shows an example of the time waveform of the input-output signal of a rate conversion part when the sampling rate is rate-converted from 11.2 MHz to 112 MHz. It is a figure which shows an example of the time waveform of the input-output signal of a rate conversion part when the sampling rate is rate-converted from 11.2 MHz to 28 MHz. It is a figure which shows the structural example of the rate conversion process part which concerns on a prior art. It is a figure which shows an example of the internal structure of the rate conversion part which concerns on a prior art. It is a figure which shows an example of the impulse response (filter coefficient) of LPF.

Explanation of symbols

  1... Polyphase filter 2... Phase control unit A1 to A7 register B1 to B7 Multiplier 11 Adder 21 21 Filter coefficient storage RAM 101 to 103 111・ Rate conversion part, 104 ・ ・ Switch part, 121 ・ ・ 0 interpolation part, 122 ・ ・ LPF,

Claims (1)

In an OFDM transmitter that can switch between a plurality of rate conversion rates and has a rate conversion processing unit that converts a sampling rate of a digital signal at the switched rate conversion rate, and performs transmission by the OFDM method,
The rate conversion processing unit
A polyphase filter that filters the digital signal to convert a sampling rate of the digital signal;
Stores filter coefficients to be set in the polyphase filter for each combination of each phase and each tap of the polyphase filter, and controls the polyphase filter for each of the plurality of rate conversion rates Control means for controlling the polyphase filter with a control pattern corresponding to a rate conversion rate to be used, using the stored filter coefficients.
An OFDM transmitter characterized by that.

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