JP3976313B2 - OFDM test signal generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a test signal generator, and more particularly to an OFDM test signal generator that easily generates an OFDM wave for testing digital terrestrial broadcasting.
[0002]
[Prior art]
As an OFDM test signal generator for measuring OFDM (Orthogonal Frequency Division Multiplexing) signals used in terrestrial digital broadcasting, it generates multi-carriers modulated by PN (Pseudo-random Noise) signals and video / audio signal data. There is something to make. Also, in order to make each multicarrier unmodulated, dedicated signal data is generated and input from an external device to the OFDM test signal generator.
[0003]
Incidentally, in Patent Document 1, in order to perform a good test of a transmission apparatus, a reception apparatus, and the like using an OFDM modulation signal, predetermined input data is converted from a time axis to a frequency axis for each predetermined unit by inverse Fourier transform. The signal is converted into an OFDM signal by a plurality of subcarriers, and the output of an arbitrary subcarrier among the plurality of subcarriers constituting the OFDM signal is stopped by a predetermined command.
[0004]
[Patent Document 1]
Patent Publication 2000-41018 (paragraphs 0007, 0008, FIG. 1)
[0005]
[Problems to be solved by the invention]
By the way, when transmitting the above-described OFDM signal to a receiving system, transmission characteristics may be deteriorated due to nonlinear distortion caused by an amplifier used in the receiving system, and it is important to accurately grasp the nonlinear distortion. However, in Patent Document 1 described above, no consideration is given to accurately grasping the nonlinear distortion.
[0006]
Incidentally, at present, when measuring nonlinear distortion of an amplifier in the UHF band, two continuous waves (hereinafter referred to as CW signals) are input to the amplifier, and third-order intermodulation distortion appearing on the output side is measured. . When a large number of input signals are assumed, the performance is estimated by converting the wave number from the measurement result of two waves.
[0007]
However, in terrestrial digital television broadcasting, since signals of two or more waves are transmitted, not only the nonlinear distortion measurement method is not matched, but also the distortion appearance itself is different from CW signals and analog TV signals. Therefore, the construction of an appropriate test method is desired.
[0008]
The present invention has been made in view of such a situation, and is intended to provide an OFDM test signal generator capable of easily and accurately grasping nonlinear distortion generated in an amplifier.
[0009]
[Means for Solving the Problems]
An OFDM test signal generator according to the present invention includes a data generation means for generating unmodulated data necessary for generating an OFDM signal, and an OFDM signal in which individual multicarriers are unmodulated by orthogonal modulation using the unmodulated data. It is characterized by comprising signal generating means for generating, and control means for controlling the signal generating means and the data generating means in a carrier mode in which individual multicarriers in one channel are not modulated .
The signal generating means has a modulation function and a frequency conversion function, and each includes a plurality of OFDM signal generating sections that generate OFDM signals in arbitrary channels, and the data generating means corresponds to the OFDM signal generating section. A plurality of modulation data generation units may be provided which provide unmodulated data necessary for generating an OFDM signal for one channel to the OFDM signal generation unit.
In the OFDM test signal generating apparatus according to the present invention, when the carrier mode is controlled by the control means and the non-modulated data necessary for generating the OFDM signal is generated from the data generating means, the non-modulated data is generated by the signal generating means. By the orthogonal modulation according to, an OFDM signal in which individual multicarriers are not modulated is generated.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0011]
FIG. 1 is a block diagram showing an embodiment of an OFDM test signal generator according to the present invention.
[0012]
The OFDM test signal generator shown in FIG. 1 generates a mode (hereinafter referred to as a normal mode) that generates an OFDM signal equivalent to a broadcast wave in which each multicarrier in one channel is modulated, and each multichannel in one channel. The carrier has a mode (hereinafter referred to as a carrier mode) that operates as if there is no modulation on the generated signal output. The OFDM test signal generator includes modulation data generators a1 to a5, a controller b, OFDM signal generators c1 to c5, a combined output unit d, and an input unit e, and can output an OFDM signal.
[0013]
The modulation data generation units a1 to a5 as data generation means are provided corresponding to the OFDM signal generation units c1 to c5 and operate independently of each other. The modulation data generators a1 to a5 have a function of generating data necessary for generating an OFDM signal, and are necessary for generating OFDM signals for one channel in the OFDM signal generators c1 to c5. I-axis and Q-axis modulated data or non-modulated data is read from the modulated data storage units a11 and a12, and is supplied to the OFDM signal generators c1 to c5.
[0014]
The modulated data storage unit a11 stores the above-described I-axis modulated data and non-modulated data. The modulated data storage unit a12 stores the above-described Q-axis modulated data and non-modulated data. The modulation data stored in the modulation data storage units a11 and a12 are, for example, digital signals of 10 symbols. The unmodulated data in the modulation data storage units a11 and a12 is arbitrary data for one symbol. As the modulation data storage units a11 and a12, any storage medium such as a ROM, a RAM, or a memory card can be used.
[0015]
The control part b as a control means is a part which controls operation | movement of each part, and can be comprised with CPU, memory, etc. The control unit b controls the modulation data generation units a1 to a5 and the OFDM signal generation units c1 to c5 to either the normal mode or the carrier mode described above, details of which will be described later. The OFDM signal generators c1 to c5 as signal generating means can generate OFDM signals having contents independent of each channel based on the data generated from the modulated data generators a1 to a5. Further, the modulation data generators a1 to a5 have a function of repeatedly allocating the unmodulated data even if the symbols are different, and each multicarrier generates an unmodulated OFDM signal. The OFDM signal generators c1 to c5 have a modulation function and a frequency conversion function, and generate high-frequency OFDM signals on arbitrary channels, respectively.
[0016]
The synthesis output unit d is a part that synthesizes high-frequency signals output from the OFDM signal generation units c1 to c5. The input unit e is a part to which a command necessary for operating the apparatus is input, and a touch panel, a button, or the like can be used.
[0017]
Here, further referring to the multicarrier of the OFDM wave, the real part and the imaginary part of the input data of n samples IFFT (n is 8192, for example) corresponding to the position of each multicarrier can be arbitrarily set to 0. By setting, it is possible to control without generating a carrier.
[0018]
In addition, the data of the OFDM signal generators c1 to c5 is m (when the guard interval is added from the 0th data and the last (n-1) th data after the n-sample IFFT calculation by the set data. m <(n−1)) The data output is in order from the (n−1) th to the (n−1) th and from the (n−1) th to the 0th. If there is no guard interval, the data is output from the 0th to the (n−1) th. In this data output, the real part is the I axis and the imaginary part is the Q axis.
[0019]
The data generation in the OFDM signal generators c1 to c5 is generated by storing the calculation results in a computer or the like and reading them from the memory, or configuring the data setting, IFFT, and IFFT output processing by hardware. There are ways to occur.
[0020]
Also, assuming that the modulation data is a signal that has no guard interval and does not change for each symbol, the data in the OFDM signal generators c1 to c5 in which each multicarrier has no phase change due to symbol switching and each multicarrier is not modulated. Become.
[0021]
Next, the operation of the OFDM test signal generator will be described.
[0022]
In the following, since the operations of the modulation data generation units a1 to a5 and the OFDM signal generation units c1 to c5 are common, only the modulation data generation unit a1 and the OFDM signal generation unit c1 will be described for convenience of explanation.
[0023]
First, a case where the modulation data generation unit a1 and the OFDM signal generation unit c1 generate an OFDM signal in the normal mode will be described. When the channel of the OFDM signal generated by the OFDM signal generation unit c1 and the generation in the normal mode are specified in the input unit e, the control unit b causes the modulation data storage unit a11 to output the first symbol, the second symbol,. Data is called up in the order of the 10th symbol, and further repeated in that order, and controlled to be sent to the I-axis data input terminal of the OFDM signal generator c1. Similarly, the data is called from the modulation data storage unit a12 in the order of the first symbol, the second symbol,... The tenth symbol, and is repeated in that order and sent to the Q-axis data input terminal of the OFDM signal generation unit c1. Be controlled.
[0024]
Here, the modulation data in the modulation data storage units a11 and a12 is not particularly defined, but for example, a PN signal can be used. In this case, the orthogonal modulation data in the OFDM signal generation unit c1 may be stored separately in the modulation data storage units a11 and a12 for the I axis and the Q axis. Further, the length of the signal to be generated is not limited to 10 symbols, and may be any length.
[0025]
Next, an OFDM signal is generated by orthogonal modulation in the OFDM signal generation unit c1 based on the modulation data from the modulation data storage units a11 and a12, and further a frequency-converted high-frequency OFDM signal is generated. Since the operation of the OFDM signal generator c1 is known, its specific description is omitted. Usually, in order to reduce the amount of noise outside the band of the generated OFDM signal (in order to satisfy a predetermined spectrum mask), the modulation data is band-limited by the LPF.
[0026]
As the bandwidth limitation by the LPF, software processing can be employed. In this case, using the fact that the modulation data to be used is known, the data obtained when the original modulation data (data before passing through the LPF) is passed through the LPF constituted by the digital filter is obtained by calculation. The data is stored in the modulation data storage units a11 and a12. As a result, a filter with a hardware configuration can be omitted, and a measurement signal with a high CN ratio can be generated.
[0027]
Next, generation of an OFDM signal in the carrier mode will be described.
[0028]
When the OFDM signal channel generated by the OFDM signal generation unit c1 and the generation in the carrier mode are specified in the input unit e, the control unit b calls unmodulated data from the modulation data storage unit a11. The call is repeated and controlled to be sent to the I-axis data input terminal of the OFDM signal generator c1. Similarly, non-modulated data is called from the modulation data storage unit a12, and the call is repeated and controlled to be sent to the Q-axis data input terminal of the OFDM signal generation unit c1. Here, the non-modulated data in the modulation data storage units a11 and a12 is data of one symbol having an arbitrary content, and here it is generated without providing a guard interval.
[0029]
For each of the I-axis and Q-axis, the OFDM signal generation unit c1 to which unmodulated data is input generates an OFDM signal by orthogonal modulation and generates a high-frequency OFDM signal by frequency conversion, as in the normal mode.
[0030]
As described above, in the carrier mode according to the present embodiment, when non-modulated data necessary for generating an OFDM signal is generated from the modulated data generators a1 to a5 by an instruction from the controller b, an OFDM signal is generated. Since the OFDM signals in which individual multicarriers are not modulated are generated by orthogonal modulation using unmodulated data by the sections c1 to c5, nonlinear distortion generated in an amplifier used in the receiving system can be easily and accurately performed. Can grasp.
[0031]
That is, since the above-described modulation data supplied to the OFDM signal generator c1 is exactly the same data between symbols, when individual multicarriers are observed on the time axis, a sine wave whose phase between symbols is continuous It becomes. Therefore, although modulated by the OFDM signal generation unit c1, each multicarrier generated from the OFDM signal generation unit c1 has no energy spread on the frequency axis, that is, it is transmitted as if there is no modulation. Signal.
[0032]
In addition, the OFDM signal generators c2 to c5 generate OFDM signals in the normal mode, so that a channel for measuring the composite third-order distortion component and the composite second-order distortion component generated at the output of an amplifier or the like in multiwave transmission is obtained. Can be accurately grasped by a spectrum analyzer or the like without turning off the signal.
[0033]
In the present embodiment, the modulation data storage units a11 and a12 of the modulation data generation units a1 to a5 store data necessary for generating OFDM signals for one channel by the OFDM signal generation units c1 to c5. Therefore, as in the prior art, it is not necessary to input dedicated signal data for making each multicarrier unmodulated from an external device to the OFDM test signal generator.
[0034]
【The invention's effect】
As described above, according to the OFDM test signal generating apparatus of the present invention, an OFDM signal can be generated, and the carrier mode is controlled by the control means, and unmodulated data necessary for generating the OFDM signal from the data generating means is generated. Then, an OFDM signal in which each multicarrier is unmodulated is generated by orthogonal modulation using unmodulated data by the signal generating means, so that non-linear distortion generated in a receiving device such as an amplifier can be easily and accurately performed. I can grasp it.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an OFDM test signal generator of the present invention.
[Explanation of symbols]
a1 to a5 Modulation data generation unit a11, a12 Modulation data storage unit b Control unit c1 to c5 OFDM signal generation unit d Composite output unit e Input unit

Claims (2)

Data generating means for generating unmodulated data necessary for generating an OFDM signal;
Signal generating means for generating an OFDM signal in which each multicarrier is unmodulated by orthogonal modulation using the unmodulated data;
An OFDM test signal generation apparatus comprising: control means for controlling the signal generation means and the data generation means in a carrier mode in which the individual multicarriers in one channel are not modulated . The signal generating means has a modulation function and a frequency conversion function, each including a plurality of OFDM signal generation units for generating the OFDM signal in an arbitrary channel,
The data generation means is provided corresponding to the OFDM signal generation unit, and includes a plurality of modulation data generation units for providing the OFDM signal generation unit with unmodulated data necessary for generating the OFDM signal for one channel. The OFDM test signal generator according to claim 1, comprising: an OFDM test signal generator according to claim 1.

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