JPH08167860A - Propagation path estimator and mobile receiver using the same - Google Patents

Abstract

PURPOSE: To improve the accuracy of a propagation path estimation value by suppressing a noise without using a time average at the time of finding out the estimation value. CONSTITUTION: This propagation path estimator is constituted of a 1st correlator 13a for outputting a complex correlation signal (β.exp (jϕ)+N2) defined by the correlation values of a 2nd diffusion code sequency with the in-phase component and orthogonal component of a received base band respectively as a real number part and an imarginary number part and a low pass filter 13b to which the complex correlation signal is inputted. Since the frequency characteristics of amplitude β and a phase in a propagartion path estimation value (β.exp(jϕ)) are suppressed by maximum Doppler frequency and the frequency band of a noise (N2) is higher than the estimation value, the complex correlation signal is inputted to the low pass filter 13b having the frequency characteristic of fixed delay at the fixed amplitude up to the maximum Doppler frequency to remove or suppress the noie (N2) without exerting influence upon the characteristics of the propagation path. Consequently an accurate propagation path estimation value can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel estimator for calculating a channel estimated value of a channel characteristic, and more specifically, it suppresses noise without using an averaging process to obtain an accurate channel estimated value. The present invention relates to an obtainable propagation path estimator and a mobile receiver using the same.

[0002]

2. Description of the Related Art Generally, when a mobile communication device moves or the like, a medium of a propagation path through which a radio wave propagates changes, which causes a phenomenon (fading) in which the electric field strength of the radio wave changes slowly. This fading has a characteristic that it is more remarkable as the moving speed is higher, and causes fading of reception such as attenuation of radio waves and interference.

In order to solve such a problem, for example, the following document discloses a receiving device equipped with a propagation path estimator. The receiving device in the document, the transmission information is differentially encoded, and after being spread directly by the spreading code sequence,
A radio wave radiated by being modulated by PSK modulation (Phase Shift Keying: PSK) is received to be a reception signal, and the reception signal is arithmetically processed to estimate a propagation path characteristic.

Reference: Veli-Pekka Kaasila and Aarne Mam
mela `` The Adaptive RAKE Matched Filter in a Time-v
ariant Two-path Channel "IEEE PIMRC '92 pp.441-44
5, October 1992 That is, by despreading the received signal, a complex correlation signal including propagation path characteristics such as fading and noise can be obtained. Therefore, the propagation path estimation value is calculated from the complex correlation signal, and the data is demodulated based on the result.

At this time, since there is a problem that the reliability of the demodulated data deteriorates when the propagation path characteristics are estimated in the state of including noise, noise is suppressed by the method described later.

The propagation path characteristics have their amplitude and phase changing slowly due to fading. On the other hand, noise is generated almost independently of fading and vibrates around the true signal to be superimposed. Therefore, noise is suppressed by performing time averaging (moving averaging) for the time when the amplitude and phase of the propagation path characteristics can be regarded as substantially constant.

That is, the temporal change between the amplitude and the phase of the propagation path characteristics accompanied by fading is slow, and when the short time is considered, it is assumed that the amplitude and the phase are constant, so that the averaging process is enabled and the noise It is suppressing.

Then, the noise is suppressed by the above procedure to improve the accuracy of the propagation path estimation value, and the data is demodulated based on the result.

[0009]

However, the application limit of the above method is that the amplitude and the phase of the propagation path characteristic accompanied by fading change slowly with time, and the amplitude and the phase are kept constant when a short time is considered. It is when the assumptions hold.

Generally, in the noise suppression method based on time averaging, it is necessary to lengthen the averaging time in order to improve the suppression efficiency. However, due to the above assumption, it is not possible to arbitrarily lengthen the time average, and if this assumption is ignored and the time average is performed for a time longer than the time when the amplitude and phase of the propagation path characteristics are considered to be substantially constant, noise suppression is suppressed. While the effect is improved, there is a problem that the propagation path information is also averaged and the demodulation of the received signal is not accurate.

[0011]

In order to achieve the above object, a propagation path estimator according to a first invention is a propagation path estimator for outputting a propagation path estimation value in a propagation path characteristic of a received signal, wherein: A correlation calculation between the received signal and the first code sequence is performed, and a complex correlation signal represented by the sum of the propagation path estimation value reflecting the propagation path characteristics and a signal having a frequency component higher than the propagation path estimation value is obtained. It is characterized by comprising a first correlator that outputs and a low-pass filter that receives the complex correlation signal and removes or suppresses a harmonic component of the signal.

For example, the low-pass filter has a frequency characteristic that causes a signal delay of a fixed amplitude and a fixed time up to a predetermined frequency.

A mobile receiver according to a second aspect of the present invention is a propagation path estimator according to the first invention, and is connected in parallel with the propagation path estimator to receive a received signal and a first code sequence. A correlation device that performs a correlation operation with a second code sequence that is orthogonal or pseudo-orthogonal to obtain a complex correlation signal, and outputs the complex correlation signal at the same time as the time of the channel estimation value and the channel estimation. And the output from the correlator is input, and the phase compensator for compensating the phase of the complex correlation signal from the correlator based on the propagation path estimated value, and the positive and negative of the signal from the phase compensator are judged and received. And a determiner for demodulating a signal.

[0014]

The propagation path estimator according to the first aspect of the invention focuses on the difference in the frequency band between the noise and the amplitude and phase of the propagation path characteristics without using the averaging process to remove noise (harmonic components). Then, the noise is filtered to suppress the noise and the propagation path characteristics are accurately estimated.

For this reason, the received signal is subjected to correlation calculation by the first correlator, and the propagation path estimation value "β (t) · exp (jφ"
(t)) ”and the noise“ N2 ”are output as a complex correlation signal R2. Β and φ respectively indicate the amplitude and phase of the propagation path characteristic, and the influence of fading appears as the time change of the parameter, and the frequency characteristic is suppressed by the maximum Doppler frequency, so the propagation path estimated value also has the maximum Doppler frequency. It will have a frequency characteristic with an upper limit.

On the other hand, the noise frequency has a higher value (that is, higher harmonic) than the propagation path estimated value. Therefore, by inputting the complex correlation signal to the low-pass filter and filtering the noise of the harmonic, it is possible to obtain a highly accurate propagation path estimation value in which the noise is suppressed or removed.

A mobile receiving device according to a second aspect of the present invention uses a channel estimation value output from the channel estimator according to the first aspect of the present invention, and correlates a received signal by a correlating device, A complex correlation signal represented by R1 = β (t ′) · d · exp (jφ (t ′)) + N1 is obtained. d is transmission data that takes +1 or -1, and N1 is noise. Therefore, R
By multiplying 1 by the complex conjugate of the channel estimation value obtained by the channel estimator, the first term “β (t ′) · d · exp (jφ (t ′))”
Can be compensated for by the phase compensator.

By the way, the complex correlation signal R2 has noise removed or suppressed by a low-pass filter and is output as a channel estimation value. At this time, a signal delay occurs due to the filtering.

Generally, even if the same signal is input to different circuits, the time of the output signal will be different because of the delay of the signal peculiar to the circuit. Therefore, the channel estimation value “β (t) · exp (jφ (t))” output from the channel estimator
And the complex correlation signal R1 "β (t ') ・ d ・ exp (jφ (t'))
+ N1 ”are not equal in time. That is, t ≠ t '. Therefore, even if the complex conjugate of the propagation path estimated value is multiplied by the complex correlation signal R2, the phase compensation cannot be performed.

Therefore, the correlator is provided with a delay device for delaying the complex correlation signal R1 so that the time of the complex correlation signal R1 is the same as the time of the complex correlation signal R2.

In this way, the phase compensation is performed by the phase compensator, and the signal represented by "ββd + N1βexp (-jφ)" is output from the phase compensator. If the second term is smaller than the first term of this signal, its output can be approximated by "β-β-d". Since the approximate value takes a positive or negative value depending on the value of the transmission data d, it is possible to demodulate the transmission data by determining whether the value is positive or negative.

[0022]

Embodiment A mobile communication apparatus according to this embodiment has a transmitter and a receiver. Hereinafter, these will be divided into items and described with reference to the drawings.

(A) Transmitting Device FIG. 2 shows a schematic block diagram of the transmitting device. The transmitter 4 comprises a first spreading code sequence signal device 20, a second spreading code sequence signal device 24, multipliers 21 and 26, an adder 23, baseband filters 22 and 25, a carrier generator 27 and an antenna 28. There is.

The transmission information and the first spreading code sequence signal from the first spreading code sequence signal device 20 are input to the multiplier 21, and the transmission information is directly spread by the first spreading code sequence to form transmission data. Become. Then, the transmission data is input to the baseband filter 22, limited to a predetermined frequency band, and input to the adder 23.

On the other hand, the spread code sequence signal orthogonal or pseudo-orthogonal to the first spread code sequence is transmitted to the second spread code sequence signal device 2.
4 is output to the baseband filter 25, is limited to a predetermined frequency band by the baseband filter 25, and is input to the adder 23. As a result, the two signals (each in the orthogonal or pseudo orthogonal state) are input to the adder 23 and added. Further, the added signal is subjected to PSK modulation (two-phase PSK modulation) in the adder 23 and output to the multiplier 26. In the multiplier 26, the signal output from the adder 23 is added to the carrier output from the carrier generator 27, and the radio wave is radiated from the antenna. The adder 23 may be provided between the antenna 28 and the multiplier 26.

(B) Receiving Device Next, a receiving device for demodulating the transmission information signal-processed as described above will be described.

(1) Data Demodulation Principle In mobile communication, fading occurs as the mobile system moves, as described above. Therefore, consider a complex correlation signal in which the correlation between the first spreading code sequence signal and the in-phase component and the quadrature component of the received baseband signal (carriers are removed) is the real part and the imaginary part, respectively. In this case, the complex correlation signal R1 is given as R1 = β · d · exp (jφ) + N1 (1). Where j is an imaginary unit and d is +1 or -1
And the transmission data that takes N1 is noise. Further, β and φ represent the amplitude and phase of the propagation path characteristic, respectively, which are functions of time due to the effect of fading. Note that exp (jφ) is cosφ + jsi as is well known.
It is an exponential expression of nφ.

Therefore, if d can be obtained,
The transmission data can be demodulated. However, this requires information on β and φ that are affected by fading. Since it is difficult to obtain these parameters independently, consider a complex correlation signal in which the correlation between the second spreading code sequence and the in-phase component and quadrature component of the received baseband signal is the real part and the imaginary part, respectively. The complex correlation signal R2 in this case is given by R2 = β · exp (jφ) + N2 (2) In the above equation, the first term represents the estimated value of the propagation path, and the second term represents the noise.

Therefore, if the noise can be suppressed by some method, it becomes possible to obtain a channel estimation value, that is, information about a component depending on fading.

In general, the upper limit of the frequency characteristics in β and φ that reflects the propagation path characteristics is given by the maximum Doppler frequency proportional to the product of the relative speed of the receiver and transmitter and the carrier frequency. Therefore, the upper limit of the propagation path estimated value is similarly regulated by the maximum Doppler frequency. Such maximum Doppler frequency is usually 100 to 2
The frequency is about 00 Hz, which is sufficiently lower than the frequency band of the noise N2.

The propagation path estimator according to the present embodiment utilizes the difference in the frequency band between the propagation path estimated value and the noise N2. The complex correlation signal R2 is passed through a low pass filter to remove harmonic noise N2. Or it suppresses.

When the noise N2 is removed by passing the complex correlation signal R2 through a low-pass filter, its output becomes a propagation path estimation value represented by β · exp (jφ) (3). Then, when the complex conjugate β · exp (−jφ) (4) of the equation (3) is multiplied by the equation (1), β · β · d + N1 · β · exp (−jφ) (5) is obtained. The first term in equation (5) represents the data component and the second term
The term indicates noise. If the power due to noise is
If it is smaller than the power of the data component, noise can be ignored, and equation (5) can be expressed as β · β · d (6). Equation (6) has a value that does not include the phase, which means that phase compensation is performed in this sense. formula
In (6), d is the transmission data that takes +1 or -1 as defined above, and β is the amplitude, so it is possible to demodulate the transmission data by judging the sign of Eq. (6). become.

(B) Configuration of Receiving Device Next, the configuration of the receiving device based on the above-mentioned transmission data demodulation principle will be described. FIG. 1 shows a block diagram of a receiving device.

The receiving device 2 includes a second correlator 11a which forms a complex correlation signal [R1] represented by the equation (1) by a correlation calculation with the received signal and a delay device which delays the complex correlation signal [R1] by a predetermined time. A correlator 11 having 11b, the received signal into a complex correlation signal [R2] represented by equation (2), and
Data determination is performed from the output signal from the phase compensator 14 and the phase compensator 14 that receive the signals from the propagation path estimator 13, the correlator 11, and the propagation path estimator 13 that suppress the noise N2 and perform phase compensation. It has a decision device 15 for performing demodulation of data.

The propagation path estimator 13 first receives the received signal and performs a correlation operation on the first correlator 13a, and a low pass filter 13b for removing noise of a harmonic component of the output signal from the first correlator 13a. And have.

The received signal input to the propagation path estimator 13 is
In the first correlator 13a, a baseband complex reception signal in which the in-phase component of the baseband signal is the real part and the quadrature component is the imaginary part is obtained, and the baseband complex reception signal and the second spreading code sequence synchronized with the reception signal The product of is integrated over a 1-bit interval, and the complex correlation signal [R
2] is calculated. Then, the complex correlation signal [R2] is input to the low-pass filter 13b.

The low-pass filter 13b has a frequency characteristic of delaying a signal for a constant time with a constant amplitude up to a predetermined frequency fd. Therefore, this frequency fd is set to the maximum Doppler frequency that is proportional to the product of the maximum allowable relative speed of the transceiver and the carrier frequency.

As a result, R2 = β · exp according to the equation (2).
The second term (N2: noise) of the harmonic component in the complex correlation signal [R2] represented by (jφ) + N2 is filtered to obtain the propagation path estimation value [A] of the first term (β · exp (jφ)). It will be output.

On the other hand, the received signal input to the input terminal 10 is
It is also input to the second correlator 11a. The second correlator 11a becomes a baseband complex reception signal in which the in-phase component of the received baseband signal is the real part and the quadrature component is the imaginary part, and the baseband complex reception signal and the first spreading code sequence synchronized with the reception signal. Integrate the product of
The complex correlation signal [R1] represented by (1) is calculated. Then, the complex correlation signal [R1] is input to the delay device 11b.

The delay device 11b is a low-pass filter 1
Since the propagation path estimation value [A] output to the phase compensator 14 via 3b is delayed for a predetermined time due to the filtering process, the complex correlation signal [R] output from the second correlator 11a.
1] also works by synchronizing the time of both signals by delaying by the same time.

For example, when the low-pass filter 13b is composed of a non-recursive filter with the number of taps N, the delay time in the low-pass filter 13b is (N-1) / 2.
Be a sample. Therefore, the complex correlation signal [R2] is (N-
1) It becomes a propagation path estimation value [A] delayed by 2 samples and is input to the phase compensator 14. Therefore, the delay device 11b performs phase adjustment by delaying the complex correlation signal [R1] by (N-1) / 2 samples, and outputs this signal [B] to the phase compensator 14.

The time-adjusted signal [A],
[B] is input to the phase compensator 14, and the phase compensator 1
4, the complex conjugate of the propagation path estimated value [A] is multiplied by the signal [B] and the phase-compensated signal [C] is output to the decision unit 15. This signal [C] corresponds to the equation (5).

Then, the decision unit 15 decides whether the real part of the signal [C] is positive or negative and demodulates the data. For example, if the real part of the signal [C] is "0" or "positive", then "0"
If "negative", "1" is output as demodulation data.

As described above, according to the present embodiment, the complex correlation signal [R2] is applied to the low-pass filter having a constant amplitude and a constant delay frequency characteristic up to the maximum Doppler frequency.
By inputting, the harmonic noise is removed or suppressed, so that a highly accurate propagation path estimation value can be obtained.

Further, since the received signal is demodulated using such a channel estimation value, accurate data demodulation can be performed.

[0046]

According to the first aspect of the present invention, by using a low-pass filter having a frequency characteristic of constant amplitude and constant delay up to the maximum Doppler frequency, it is possible to achieve an accuracy that cannot be achieved by the time averaging process, and , It is possible to remove or suppress the noise without affecting the data reflecting the channel characteristics, and thereby it is possible to obtain an accurate channel estimation value.

Further, according to the second invention, accurate data demodulation is possible by using the propagation path estimated value according to the first invention.

[Brief description of drawings]

FIG. 1 is a block diagram of a receiving device applied to a description of an embodiment.

FIG. 2 is a block diagram of a transmission device applied to the description of the embodiment.

[Explanation of symbols]

 2 Receiver 11 Correlator 11a Second Correlator 11b Delayer 13 Propagation Path Estimator 13a First Correlator 13b Low-pass Filter 14 Phase Compensator 15 Judger

Claims (3)

[Claims] 1. A channel estimator that outputs a channel estimation value in a channel characteristic of a received signal, performs a correlation operation between the received signal and a first code sequence, and reflects the channel characteristic. A first correlator that outputs a complex correlation signal represented by the sum of an estimated value and a signal having a frequency component higher than the propagation channel estimated value, and a complex correlation signal that is input to determine a harmonic component of the signal. A propagation path estimator, comprising: a low-pass filter that removes or suppresses. 2. The propagation path estimator according to claim 1, wherein the low-pass filter has a frequency characteristic that causes a signal delay of a constant amplitude and a constant time up to a predetermined frequency. 3. A propagation path estimator according to claim 1, and a reception signal and a second code sequence orthogonal or pseudo-orthogonal to the first code sequence connected in parallel with the propagation path estimator. And a complex correlation signal is obtained by performing the correlation calculation of, and a correlation device that outputs the time of the complex correlation signal at the same time as the time of the propagation path estimation value, and the output from the propagation path estimator and the correlation device is input. And a phase compensator for compensating the phase of the complex correlation signal from the correlator based on the propagation path estimation value, and a determiner for judging whether the signal from the phase compensator is positive or negative and demodulating the received signal. A mobile receiving device characterized by the following.