JP2001160789A - Phasing simulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phasing simulator delaying short time which is not more than the sampling period of a digital signal. SOLUTION: A phasing simulator is provided with a local oscillator 3 generating a local frequency signal, a first mixer multiplying a transmitted RF signal by the local frequency signal and obtaining an IF signal, an A/D converter 5 digitizing the IF signal, the signal processing means 6 (6-1 to 6-n) of plural systems, which give phasing paths to the digitized signals in a simulating way and a second mixer 8 multiplying the IF signal obtained by adding the signals passing through the respective signal processing means 6 by the local frequency signal are disposed. The respective signal processing means have delay memory 11 giving delay quantity in a time unit corresponding to the sampling period and delay units 12 giving delay quantity in short time which is not more than time corresponding to the sampling period. Thus, the minute setting of delay quantity is possible and more truthful phasing phenomenon can be simulated in the respective signal processing means 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a fading simulator that simulates multipath fading between a transmitting unit and a receiving unit.

[0002]

2. Description of the Related Art Generally, in mobile communication, a mobile communication station communicates while moving in an environment surrounded by obstacles such as a building on which radio waves propagate, so that there are a plurality of propagation paths from a signal transmitting unit to a receiving unit. Then, the multiplexed wave arrives at the receiving unit via each propagation path. For this reason, each multiplex wave causes interference, which causes deterioration of reception characteristics. This is called multipath fading.

Therefore, it is necessary to evaluate how much a mobile communication device is affected by multipath fading, and a fading simulator has been conventionally used. The fading simulator is a device that is interposed between the transmission unit and the reception unit and generates pseudo multipath fading. As a conventional example, for example, Japanese Patent Application Laid-Open No. 4-3511024 (hereinafter, referred to as a conventional example) ) Are known.

The fading simulator described in the conventional example has a plurality of channels constituted by digital circuits, and multipath fading is performed by giving different delay amounts to an input signal for each channel. Is generated in a pseudo manner.

FIG. 3 shows a DSP for each channel mounted on a fading simulator described in the conventional example.
FIG. 2 is a circuit diagram showing the configuration of a (digital signal processor) 101. As shown in FIG.
Two RAMs 102 and 103, multiplier 104, ALU1
05, an accumulator 106 is provided. And
By shifting the data stored in the RAMs 102 and 103, the amount of delay can be changed, so that an arbitrary amount of delay can be set for each channel, fading simulation with a high degree of freedom is possible. Become.

However, in the above-described conventional fading simulator, although an arbitrary delay amount can be obtained by the DSP 101, the delay amount is determined in units of a digital signal sampling period. There is a disadvantage that a delay amount equal to or shorter than the sampling period cannot be obtained, and a more precise fading phenomenon cannot be simulated.

[0007]

As described above, in the conventional fading simulator, the DSP
By using 101, it is possible to easily set the delay amount for each channel, but it is not possible to delay a time shorter than the sampling period of the digital signal, and it is not possible to reproduce a fine fading phenomenon. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and an object thereof is to provide a fading simulator capable of delaying a short time shorter than a sampling period of a digital signal. It is in.

[0009]

In order to achieve the above object, the invention described in claim 1 of the present application discloses a method in which "a transmission unit and a reception unit are interposed and a pseudo unit is provided between the transmission unit and the reception unit. A fading simulator that generates a multipath fading, a local oscillator that generates a local frequency signal, a first mixer that obtains an intermediate frequency signal by multiplying an RF signal transmitted from the transmitting unit by the local frequency signal, A / D conversion means for digitizing the intermediate frequency signal at a predetermined sampling period, signal processing means for a plurality of series for pseudo-setting an arbitrary fading path for the digitized signal, Adding means for adding the output signal of the processing means, and multiplying the added signal by a local frequency from the local oscillator to RF
A second mixer that converts the signal into a signal, wherein each of the signal processing units delays a time that is an integral multiple of a time corresponding to the sampling period, A second delay means for delaying a time shorter than the sampling period, a phase shifter for giving an arbitrary phase to a signal output from the second delay means, and a signal output from the phase shifter being converted into an analog signal And D / A conversion means.

[0010] The invention described in claim 2 is the second invention.
Is constituted by a delay unit that performs a delay process by operating a tap coefficient of an FIR filter, and the phase unit performs a process of correcting a phase shift in the delay unit.

According to a third aspect of the present invention, a digital attenuator is provided before the D / A conversion means, and
An analog attenuator is provided at a stage subsequent to the A conversion means.

According to the present invention configured as described above, the RF signal supplied from the transmitter is multiplied by the local frequency signal to convert the RF signal into an intermediate frequency signal, and the intermediate frequency signal is digitized at a predetermined sampling period. . The digitized signal is provided to a plurality of series of signal processing means.

Each signal processing means comprises a first delay means, a second delay means,
The first delay means can delay an input signal by a time that is an integral multiple of the time corresponding to the sampling period. Also, the second
The delay means can delay by a time shorter than the sampling period. Therefore, it is possible to set a fine delay amount.

Further, by providing the digital attenuator and the analog attenuator, it is possible to prevent the dynamic range from being reduced to less than the sampling bit when performing the process of attenuating the input signal.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of a fading simulator 1 to which the present invention is applied. As shown in FIG. 1, the fading simulator 1 includes a first BPF (bandpass filter) 2 for extracting a signal in a desired frequency band from an RF signal transmitted from a transmitter, and a local unit for outputting a local frequency signal. An oscillator 3 and a first mixer 4 for multiplying the RF signal extracted by the first BPF 2 by a local frequency signal output from the local oscillator 3 to obtain an IF signal (intermediate frequency signal)
And an A / D converter 5 for digitizing the IF signal obtained via the first mixer 4 at a desired sampling frequency.
And a plurality of series of signal processing means 6-1 to 6-n (n is the number of multipath fading paths, for example, n = 12) installed on the output side of the A / D converter 5. are doing.

Further, an adder (addition means) 7 for adding signals (analog signals) output from the respective signal processing means 6-1 to 6-n, and a local signal added to an output signal (IF signal) of the adder 7 A second mixer 8 that outputs an RF signal by multiplying the local frequency signal output from the oscillator 3, a second BPF 9 that extracts a desired frequency signal from the RF signal output from the second mixer 8, Is provided.

Each of the signal processing means 6 (6-1 to 6-n) has the same configuration and has a delay memory (first delay means) connected to the output side of the A / D converter 5. ) 11, a delay unit (second delay unit) 12, a phase shifter 13, a digital attenuator 14, a D / A converter 15, an analog attenuator 16, and an interpolation filter 17. I have.

The delay memory 11 stores data obtained in each sampling period in a memory and delays and outputs the stored data.
The output signal can be delayed with respect to the input signal by a time that is an integral multiple of the sampling period of the A / D converter 5.

The delay unit 12 is composed of, for example, an FIR type filter as shown in FIG. 2. By appropriately changing the counts of the coefficient units C0 to Cm mounted on the FIR filter, the delay unit 12 Thus, an output signal delayed by a time shorter than the sampling period can be obtained. The phase shifter 13 is for giving an arbitrary phase to the signal output from the delay unit 12 and correcting a phase shift generated in the delay unit 12.

The digital attenuator 14 includes the delay memory 1
1, for attenuating a signal (digital signal) delayed by the delay unit 12 and the phase shifter 13 to a desired level. The analog attenuator 16 attenuates the signal analogized by the D / A converter 15 to a desired level.

The delay memory 11, the delay unit 12, the phase shifter 13, the digital attenuator 14, and the analog attenuator 16 are connected to a state input unit 19 via a rate converter 18, respectively. By performing a setting input operation at 19, each parameter is set under the control of the rate converter 18.

Next, the operation of the present embodiment configured as described above will be described. The fading simulator 1 shown in FIG. 1 is installed and used between a transmitter and a mobile receiver. First, when an RF signal is output from the transmitter, a desired frequency band component is extracted from the RF signal by the first BPF 2 and supplied to the first mixer 4.

Since the local frequency signal output from the local oscillator 3 is applied to the first mixer 4, the RF signal is multiplied by the local frequency signal, and the IF signal (intermediate frequency signal) is output from the first mixer 4. ) Is output. IF
After the signal is digitized by the A / D converter 5,
The signal is supplied to the delay memory 11 of the signal processing means 6 (6-1 to 6-n) of a plurality of systems.

In the delay memory 11, the rate converter 1
Since the delay amount is set in advance under the control of 8, the output signal is delayed and output by this delay amount. That is, the delay memory 11 stores and stores the signal input at the sampling cycle of the A / D converter 5 and delays the output timing so that the output signal can be converted to the input signal by an integral multiple of the sampling cycle. Can be delayed by the following time.

Next, in the delay unit 12, the FI shown in FIG.
By appropriately setting the count of the coefficient units C0 to Cm of the R filter, the delay is delayed by a time shorter than the sampling period. The output signal of the delay unit 12 is given an arbitrary phase by the phase shifter 13 and performs a process of correcting a phase shift generated in the process of the delay unit 12.

Thereafter, a process of attenuating the signal output from the phase shifter 13 is performed by the digital attenuator 14 and the analog attenuator 16. That is, in normal multipath fading, a signal obtained by reflecting off an obstacle or the like is attenuated with respect to a signal obtained through a normal path. Therefore, in order to simulate this, the signal is attenuated. Perform processing. If all the attenuation processing is performed by the digital attenuator 14, the dynamic range of the signal system is reduced to less than the sampling bit. Are analogized by the D / A converter 15 and then attenuated by the analog attenuator 16. Then, the signal subjected to the attenuation processing is subjected to interpolation processing by an interpolation filter 17, and then supplied to an adder 7 to be processed by each signal processing unit 6.
The signals output from (6-1 to 6-n) are added.

Next, the signal (I
The F signal) is multiplied by a local frequency signal in the second mixer 8 and converted into an RF signal (carrier). This RF
The signal is output via the second BPF 9 and provided to a receiver (not shown). Accordingly, on the receiver side, a signal as if the signal output from the transmitter arrived via a plurality of paths (n-sequence paths), that is, a signal as if multipath fading had occurred, was generated. You can get it.

Thus, in the fading simulator according to the present embodiment, a plurality of signal processing means 6
(6-1 to 6-n), and it is possible to set different amounts of delay and attenuation for each of the signal processing means 6.
Simulation based on the actual fading reduction becomes possible.

Each signal processing means 6 includes a delay memory 1
1 and a delay unit 12, of which the delay memory 11 can set the amount of delay with the sampling period of the A / D converter 5 as one unit. Since a very short time (that is, a time shorter than the sampling period) can be delayed, it is possible to set the delay amount with extremely high flexibility and versatility.

Further, a digital attenuator 14 is provided at a stage preceding the D / A converter 15, and an analog attenuator 16 is provided at a stage subsequent thereto.
Are installed, and the signal is attenuated using these, so that the signal can be attenuated without reducing the dynamic range below the sampling bit.

A signal for providing a reference signal (a signal corresponding to a path of a signal directly transmitted from the transmitter to the receiver) among the signal processing means 6 (6-1 to 6-n). By delaying the delay memory 11 of the processing means by a plurality of steps in advance and setting some of the other signal processing means to a smaller delay amount, the time is faster than the reference signal. It is possible to simulate the multipath fading signal that arrives.

[0032]

As described above, in the fading simulator according to the present invention, since each signal processing means provided with a plurality of streams has the first delay means and the second delay means, the input signal , A fine delay amount can be given, and a more realistic fading phenomenon can be simulated.

In each of the signal processing means, a digital attenuator is provided at a stage before the D / A conversion means and an analog attenuator is provided at a stage after the D / A conversion means. No. Smooth attenuation processing becomes possible.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a fading simulator according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an FIR filter used as a delay unit.

FIG. 3 is an explanatory diagram showing a configuration of a DSP mounted on a conventional fading simulator.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fading simulator 2 first BPF (band-pass filter) 3 local oscillator 4 first mixer 5 A / D converter (A / D conversion means) 6 (6-1 to 6-n) signal processing means 7 adder (Addition unit) 8 Second mixer 9 Second BPF 11 Delay memory (First delay unit) 12 Delay unit (Second delay unit) 13 Phase shifter 14 Digital attenuator 15 D / A converter 16 Analog attenuation Unit 17 interpolation filter 18 rate converter 19 state input unit 101 DSP 102, 103 RAM 104 multiplier 105 ALU 106 accumulator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G036 AA28 BA13 BA14 BA15 CA12 5K042 BA08 BA11 CA02 CA11 CA12 CA23 DA01 EA02 EA13 FA06 FA08 FA15 FA24 GA06 GA11 GA14 GA15

Claims (3)

[Claims] 1. A fading simulator interposed between a transmission unit and a reception unit for generating pseudo multipath fading between the transmission unit and the reception unit, comprising: a local oscillator for generating a local frequency signal; A first mixer that obtains an intermediate frequency signal by multiplying an RF signal transmitted from the transmission unit by the local frequency signal; A / D conversion means that digitizes the intermediate frequency signal at a predetermined sampling cycle; A plurality of series of signal processing means for artificially setting an arbitrary fading path with respect to a digitized signal; an adding means for adding output signals of the respective signal processing means; and the local oscillator to the added signal And a second mixer that multiplies the signal by a local frequency to convert the signal into an RF signal. A first delay means for delaying the time is an integral multiple of the time corresponding to the sampling period, the delay time equal to or less than the sampling period 2
Delay means, a phase shifter for giving an arbitrary phase to the signal output from the second delay means, and a D / A for converting the signal output from the phase shifter into an analog signal
A fading simulator, comprising: conversion means. 2. The delay device according to claim 1, wherein the second delay unit includes a delay unit that performs a delay process by operating a tap coefficient of an FIR filter, and the phase unit performs a process of correcting a phase shift in the delay unit. The fading simulator according to claim 1, wherein: 3. A digital attenuator is provided before the D / A conversion means, and an analog attenuator is provided after the D / A conversion means. The fading simulator according to any one of the above.