JP3163817B2 - Code division multiple access receiver and frequency error detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver using a code division multiple access system and a frequency error detector for controlling the frequency of a local oscillator.

[0002]

2. Description of the Related Art In recent years, the bandwidth of information has been increased from several hundreds.
A so-called spread spectrum communication method (hereinafter referred to as S) in which communication is performed by spreading a modulated wave over a spectrum band that is several thousand times wider.
S: Spread Spectrum method).
In the SS system, the transmitter spreads a frequency spectrum by modulating a carrier with a pseudo-noise code sequence (hereinafter referred to as a PN code). In the receiver, data is reproduced by performing despreading (correlation) processing using a PN code generated by a code generator having the same structure as the transmitter and demodulating the baseband. .

[0003] In the case of the SS system, in order to demodulate data at the receiver, it is necessary to match not only the pattern of the PN code sequence but also the time. In other words, a communication line can be established only when the phases are the same and the phases match. By utilizing such a property, it is possible to use a large number of channels by using the same frequency band and by using different PN code sequences. A method of performing channel identification by PN code and performing multiple access is referred to as code division multiple access (CDMA: Code Division).
Multiple Access) method.

[0004] When performing CDMA communication using the SS system, there is a system for simultaneously transmitting a channel containing fixed-value data of which all bits are 0, in addition to a data channel containing communication data. Here, this channel is called a pilot channel.

[0005]

By the way, while the data transmitted from the transmitter arrives at the CDMA receiver, an error always occurs in the carrier frequency due to the influence of reflection or the like in the normal transmission path. Hereinafter, this is called a frequency error. In particular, when the CDMA receiver is mounted on a mobile object, a frequency error occurs due to the Doppler effect proportional to the speed of the mobile object, and this frequency error is inevitable.
Therefore, in order to demodulate data with a CDAM receiver, it is necessary to detect and correct this frequency error. CDs for systems using pilot channels
Although the MA receiver can easily detect the frequency error using this pilot channel, this method always uses a so-called signal-to-noise ratio (S / N: Signal to No.).
ise ratio) is reduced by half. Therefore, in order to prevent deterioration of S / N, conventionally, an input pilot channel is passed through a low-pass filter (hereinafter, referred to as LPF) to remove high-frequency noise components. However, when the frequency error increases and exceeds the pass band (cutoff frequency), there is a problem that the frequency error cannot be detected. On the other hand, if the pass band of the LPF is widened, the S / N ratio deteriorates, and the accuracy of frequency error detection deteriorates significantly.

When data is demodulated by a data demodulator of a CDMA receiver, it is common to convert the data to an IF (intermediate frequency) as low as possible before performing the processing. Oscillators (so-called local oscillators) cannot be used with high accuracy from the viewpoint of price, etc.
Instead, a so-called phase-locked loop (hereinafter PLL: Phase)
Locked Loop) is formed to maintain the frequency accuracy. In this case, P
Since the LL does not operate normally, there is a high possibility that the frequency error becomes extremely large, and there has been a problem that this frequency error cannot be detected by the above-described method. The present invention has been made in view of such a situation. For example, even when the frequency error is likely to become large after power-on or the like, the frequency error can be detected and the frequency error is small. An object of the present invention is to provide a CDMA receiver and a frequency error detector that can sometimes detect a frequency error with high accuracy and can improve the performance of a data demodulator.

[0007]

In order to solve the above problems, the present invention provides a code division multiple access receiver for receiving a data channel containing communication data and a pilot channel containing fixed value data. The frequency error detector of the apparatus has a first pass band, a first filter means for removing high-frequency noise components from received data, and a second pass band narrower than the first pass band. A second filter for removing a high-frequency noise component from the received data; a signal obtained by delaying a signal from the first or second filter for a predetermined time; and a signal from the first or second filter. Multiplying means for multiplying the current signal by a predetermined number of times and controlling the first filter means for a predetermined time after power-on, and selecting the second filter means after the predetermined time. And a Control means.

Further, the present invention provides a code division multiple access receiver for receiving a data channel containing communication data and a pilot channel containing fixed value data, wherein the received data is the same as the transmission side. Despreading means for performing a despreading process using a pseudo-noise code, and frequency error detecting means for detecting a frequency error of an output of the despreading processing means, wherein the frequency error detecting means has a first pass band. A first filter for removing a high-frequency noise component from an output of the despreading processing means; a second passband narrower than the first passband; A second filter for removing a high-frequency noise component; a signal obtained by delaying a signal from the first or second filter for a predetermined time; and a current signal from the first or second filter. And a control means for controlling to select the first filter means for a predetermined time after power-on, and to select the second filter means after the predetermined time. Prepare.

Further, the present invention provides a code division multiple access receiver for receiving a data channel containing communication data and a pilot channel containing fixed value data, wherein the received data is the same as the transmitting side. A plurality of despreading processing means for performing despreading processing with a pseudo-noise code;
A plurality of frequency error detecting means for respectively detecting a frequency error by each output of the plurality of despreading processing means, wherein the plurality of frequency error detecting means are configured to output a high-frequency noise component from the output of the despreading processing means. Filter means, and multiplication means for complexly multiplying a signal obtained by delaying a signal from the filter means for a predetermined time and a current signal from the filter means, respectively, At least one is provided with control means for controlling so as to widen the pass band of the filter means for a predetermined time after turning on the power, and for narrowing the pass band of the filter means after the predetermined time.

[0010]

In the frequency error detector according to the present invention, the first filter means is selected for a predetermined time after the power is turned on, and after the predetermined time, the second filter means is selected to detect the frequency error. Do.

In the code division multiple access receiver according to the present invention, in the second code division multiple access receiver, the pass band of the filter means is expanded for a predetermined time after the power is turned on, and after the predetermined time, the filter band of the filter means is expanded. The pass band is narrowed to detect a frequency error.

Further, in the code division multiple access receiver according to the present invention, in at least one of the plurality of frequency error detecting means, when there is a high possibility that the frequency error becomes large, the pass band of the filter means is expanded. When the frequency error is small, the pass band of the filter is narrowed to detect the frequency error.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a code division multiple access receiver and a frequency error detector according to the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to a code division multiple access (CDMA).
FIG. 1 is a block diagram showing a specific circuit configuration of a main part of the CDMA receiver.

In FIG. 1, spectrum is spread to an input terminal 10 and a so-called IF frequency (intermediate frequency) has already been obtained.
Is supplied. Here, this IF frequency is defined as fin. This signal Sin is divided into two and supplied to multipliers 11 and 12.

On the other hand, a voltage controlled oscillator (VCO: Volt
The output of 13) is 1
One is multiplied by the signal Sin in the multiplier 11 and the other is shifted in phase by π / 2 by the phase shifter 14 and is multiplied by the signal Sin in the multiplier 12. Is converted to
Here, the output of the multiplier 11 is called an I channel as an in-phase component, and the output of the multiplier 12 is called a Q channel as a quadrature component.

These signals are input to a despreader 15,
Each is despread by the same pseudo-noise code (hereinafter referred to as PN code) on the transmitting side. At this time, a data channel containing communication data and a pilot channel containing fixed value data are separated. There are various methods for this separation. For example, a sequence of orthogonal functions is applied to each channel on the transmission side, and P
In addition to the despreading process using the N code, the orthogonal function can be used to perform despreading process to separate each channel.

The signal despread by the despreader 15 and separated into a data channel and a pilot channel are respectively sent to a data demodulator 16 and a frequency error detector 20.
(Hereinafter referred to as an I channel signal and a Q channel signal, respectively). The data demodulator 16 demodulates the input data channel to reproduce data, and outputs the reproduced data via an output terminal 18. On the other hand, the frequency error detector 20 detects a frequency error Δf using the input pilot channel, and detects the detected frequency error Δf
, The oscillation frequency fvco of the VCO 13 (so-called local oscillator) is controlled. That is, a so-called phase locked loop (hereinafter, referred to as PLL: Phase Locked Loop) is formed, and the output of the multiplier 11 and the output of the multiplier 12 are controlled to be 0 Hz. With this series of controls, the frequency error Δf
Is minimized, and the performance of the data demodulator 16 is improved.

Here, the frequency error detector 20 will be described. FIG. 2 is a block diagram showing a specific circuit configuration of the frequency error detector 20.

In FIG. 2, input terminals 19 _I , 1
9 _Q receives an I channel signal and a Q channel signal of a pilot channel, respectively, which correspond to the output of the despreader 15 shown in FIG.
These signals are respectively provided by changeover switches 21 _I and 21 _Q
, And the signal of the I channel is selected to pass through, for example, either the LPF 23 _I having the first pass band or the LPF 22 _I having the second pass band narrower than the first pass band. . The signal of the Q channel is, for example, an LPF 23 _Q having a first pass band.
And a L having a second passband narrower than the first passband.
PF22 _Q is selected to pass either. Here, these LPFs 22 _I , 23 _I , 22 _Q
, 23 _Q after signal I _LPF ,
Q _LPF . Signal _{I LPF} is divided into two, one is directly to the multiplier 25 _I, one after passing through the delay device 24 _I (referred to hereinafter delayed signal _{I D),} is input to the multiplier 25 _Q. Signal _{Q LPF} is also divided into two, one is directly to the multiplier 25 _Q, one delay unit 2
After passing through the 4 _Q (referred to hereinafter delayed signal _{Q D),}
It is input to the multiplier 25 _I.

The multiplier 25 _I multiplies the signal I _LPF by the signal Q _D (I _LPF × Q _D ), and the multiplier 25 _Q outputs the signal Q LP
Performs multiplication of the _LPF and the signal _{I D} to _{(Q LPF} × _{I D),} the adder 26 subtracts the output of multiplier 25 _I from the output of the multiplier 25 _Q. The adder 26 calculates the addition result (Q
Via the _{LPF × I D -I LPF × Q} D) output terminal 29 as a frequency error Delta] f, shown in FIG. 1 above VCO13
To supply.

The above processing is described theoretically as follows.

For example, assuming that the signal Sin is phase-modulated and the pilot channel data is all 0, the signals (I-channel signal and Q-channel signal) input to the frequency error detector 20 are expressed by the following equation (1). Can be.

A exp (jθ) (1) where A is an amplitude and θ is a phase component due to a frequency error component.

The signals (I _D , Q _D ) delayed by a predetermined time t in the delay units 24 _I , 24 _Q can be expressed by the following equation (2).

Aexp (j (θ-Δθ)) (2) That is, since the phase is rotated by Δθ during the fixed time t, the frequency error Δf is detected by calculating Δθ. Can be. Therefore, as shown in the following equation 3, after multiplying the complex conjugate of the signal input to the frequency error detector 20 by the signal before the time t, the signal is expanded by Euler's formula to take the imaginary part. , −sin (Δθ).

Aexp (−jθ) × Aexp (j (θ−Δθ)) = A ² exp (−Δθ) Expression 3 When Δθ is a small value, an approximate expression (−sin (Δθ))
= −Δθ) to determine the frequency error Δf. That is, when this is actually realized by hardware, the output of the above-described adder 26 (Q _LPF × I _D −I _LPF × Q
_D ).

However, when the above calculation is performed, the signal-to-noise ratio (hereinafter, S / N: Si) is calculated as described in the background art.
gnal to Noise ratio) is reduced by half. Specifically, for example, assuming that the signal component of the pilot channel is s and the noise component is n, detection of the frequency error Δf requires the multiplication of the pilot channel as described above. Calculation will be performed.

(S + n) × (s + n) = s ² + 2sn + n ² Equation 4 As a result, the signal component is s ² and the noise component is 2sn
+ A ^{n 2.} Here, since the second term (n ² ) of the noise component can be ignored, the noise component is 2sn. Therefore, the S / N becomes s / 2n (= s ² / 2sn), and 1
/ 2.

Therefore, in the present invention, in order to prevent the deterioration of S / N, a noise component is removed as much as possible through the LPF. That is, noise components are removed by the LPFs 22 _I , 23 _I , 22 _Q , and 23 _Q shown in FIG.

Specifically, for example, if the frequency of the carrier is 8
When the CDMA receiver is mounted on an automobile and the maximum speed of the automobile is, for example, 300 km / h, the frequency error Δf due to the Doppler effect is about 300 Hz.
It is as follows. Therefore, it is sufficient for the LPF for removing the above-mentioned noise component to pass a component of 300 Hz or less. By the way, the VCO 13 shown in FIG. 1 cannot make the accuracy of the oscillation frequency fvco too high from the viewpoint of price or the like.
If the frequency fin is 80M, the oscillation frequency is about 3kHz
The frequency is shifted more than the frequency error Δf due to the above-mentioned Doppler effect. Normally, the PLL composed of the VCO 13 and the like is naturally designed in consideration of this. However, since the PLL cannot operate normally for a predetermined time after the power is turned on, the accuracy of the VCO 13 comes out as it is. become. Therefore, if the LPF having a pass band (cutoff frequency) of 300 Hz as described above is used in the frequency error detector 20, the signal of 3 kHz is considerably attenuated, and the frequency error cannot be detected in practice. On the other hand, if an LPF having a pass band of 3 kHz is used, S
/ N is severely degraded, and the accuracy of frequency error detection is reduced.

[0031] Therefore, the LPF 22 _I, 22 _Q, for example, as shown in FIG. 3, the LPF cutoff frequency has a frequency characteristic of 300 Hz, LPF 23 _I, 23
_{Let Q be} an LPF having a frequency characteristic of a cut-off frequency of 3 kHz, for example, as shown in FIG.

When the possibility that the frequency error Δf is large is high, the controller 28 sets the changeover switches 21 _I and 21 _Q to the LPFs 23 _I and 23 _Q , respectively, for example, until power is turned on and the PLL starts operating normally.
_Q is selected, the PLL operates and the VCO
When the accuracy of 13 exceeds a certain standard, the changeover switch 2
Control is performed so that 1 _I and 21 _Q select the LPFs 22 _I and 22 _Q , respectively.

Specifically, as shown in the flowchart of FIG. 5, when power is supplied in step ST1, the controller 28 detects the power supply and detects the power supply in step ST1.
Proceed to 2.

In step ST2, the controller 2
8 indicates that the changeover switches 21 _I and 21 _Q have LPFs respectively.
Control to select 23 _I and 23 _Q , and step S
Proceed to T3.

In step ST3, the controller 2
8 judges whether or not a predetermined time has elapsed, and if so, proceeds to step ST4; otherwise, returns to step ST2.

In step ST4, the controller 2
8 indicates that the changeover switches 21 _I and 21 _Q have LPFs respectively.
Control is performed to select 22 _I and 22 _Q , and the process ends.

Thus, for a predetermined time after power-on, the LPF
23 _I and 23 _Q are selected.
_I and 22 _Q are selected. That is, the frequency error Δf
The predetermined time after power-on is large, the frequency error detector 2
By switching the LPF of 0 to LPFs 23 _I and 23 _Q having a wide pass band, the frequency error Δf can be detected, and the LPF having a narrow pass band after a predetermined time can be detected.
By switching to 22 _I and 22 _Q , when the frequency error Δf is small, the frequency error Δf can be detected with high accuracy. As a result, the performance of the data demodulator 16 can be improved.

It should be noted that the present invention is not limited to only when the power is turned on. For example, when the frequency error due to the Doppler effect changes, for example, when the moving object changes from an automobile to an airplane, the LPF corresponding to the change is used. You may make it select.

As shown in FIG. 2, the speed detector 27 constantly detects the moving speed, and the controller 28 controls the LPF in real time based on the moving speed.
May be controlled. Furthermore, the switching of the pass band may be performed by controlling the constant of the LPF instead of the switching by the changeover switches 21 _I and 21 _Q.

Next, a CDMA receiver in a multi-RAKE system will be described. FIG. 6 is a block diagram showing a specific circuit configuration of a main part of a CDMA receiver in a multi-RAKE system to which the present invention is applied. The same circuits as those constituting the CDMA receiver shown in FIG. 1 described above are denoted by the same reference numerals, and description thereof will be omitted.

CDMA in Multi-RAKE System
Receiver, as shown in FIG. 6, and M despreaders 15 ₁ to 15 _M to despreading processing by the same pseudo-noise code and the transmission side to the reception data, these M despreaders 1
5 _1-15 a data demodulator ₁₆ 1 ~ 16 _M for reproducing data by demodulating the outputs of the _M, M-number of despreaders 15 ₁
The respective outputs of to 15 _M, and controls the M frequency error detector ₂₀ 1 to 20 _M for detecting a frequency error, respectively, the VCO13 and synthesizing the frequency error from frequency error detector ₂₀ 1 to 20 _M A synthesizer 17 is provided to simultaneously and independently demodulate so-called multipaths and the like. Also, the oscillation frequency fvco of the VCO 13 is controlled by detecting a plurality of frequency errors, synthesizing them, and applying feedback. in this case,
Any one frequency error detector 20 _k (k = 1 to M)
There by detecting the large frequency error, since the feedback is applied accordingly, may be performed in at least any one of the frequency error detector 20 _k is to switch a pass band of the LPF described above. In other words, multi-RA
In a CDMA receiver in a KE system, if at least one frequency error detector controls the VCO 13,
Since the same effect as described above is obtained, the conventional multi-R
The circuit scale can be simplified as compared with a CDMA receiver in an AKE system.

[0042]

As described above, according to the present invention, there is a high possibility that the frequency error becomes large, for example, when the power is turned on or when the speed of the moving object equipped with the CDMA receiver changes greatly. By widening the pass band of the signal containing the frequency component accordingly, the frequency error can be detected even when the frequency error is large, and the frequency error is detected with high accuracy when the frequency error is small. Therefore, the performance of the data demodulator can be improved.

Also, C in the multi-rake system
In the DMA receiver, if at least one of the plurality of frequency error detectors controls the local oscillator, the same effect as described above can be obtained. Therefore, the CDMA receiver in the conventional multi-RAKE system can be obtained. Thus, the circuit scale can be simplified as compared with the first embodiment.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a specific circuit configuration of a main part of a CDMA receiver to which the present invention is applied.

FIG. 2 is a block diagram showing a specific circuit configuration of a frequency error detector included in the CDMA receiver.

FIG. 3 is a diagram showing specific frequency characteristics of an LPF constituting the frequency error detector.

FIG. 4 is a diagram showing specific frequency characteristics of an LPF constituting the frequency error detector.

FIG. 5 is a flowchart illustrating an operation of a controller constituting the frequency error detector.

FIG. 6 is a block diagram showing a specific circuit configuration of a main part of a CDMA receiver in a multi-RAKE system to which the present invention has been applied.

[Explanation of symbols]

15: despreader 20: frequency error detector 21 _I , 21 _Q: changeover switch 22 _I , 22 _Q: LPF 23 _I , 23 _Q: LPF 24 _I , 24 _Q · delay device _{25 I,} 25 Q ··· multiplier _{26 I,} 26 Q ··· adder

Claims (3)

(57) [Claims] 1. A frequency error detector for a code division multiple access receiver for receiving a data channel containing communication data and a pilot channel containing fixed value data, wherein the frequency error detector has a first pass band. First filter means for removing high-frequency noise components from received data, and second filter means having a second pass band narrower than the first pass band and removing high-frequency noise components from the received data. Filter means; multiplication means for complexly multiplying a signal obtained by delaying a signal from the first or second filter means for a predetermined time by a current signal from the first or second filter means; Control means for controlling the selection of the first filter means during the predetermined time and selecting the second filter means after the predetermined time. The difference detector. 2. A code division multiple access receiver for receiving a data channel containing communication data and a pilot channel containing fixed value data, wherein the same pseudo noise code as the transmitting side is used for the received data. A despreading means for performing a despreading process; and a frequency error detecting means for detecting a frequency error of an output of the despreading processing means, wherein the frequency error detecting means has a first pass band, A first filter for removing a high-frequency noise component from an output of the diffusion processing means, a second passband narrower than the first passband, and a high-frequency noise from the output of the despreading processing means. A second filter for removing a component; a signal obtained by delaying a signal from the first or second filter for a predetermined time and a current signal from the first or second filter; Multiplying means for multiplying, and control means for controlling to select the first filter means for a predetermined time after power-on and to select the second filter means after the predetermined time. And a code division multiple access receiver. 3. A code division multiple access receiver for receiving a data channel containing communication data and a pilot channel containing fixed value data, wherein the same pseudo noise code as on the transmitting side is used for the received data. A plurality of despreading processing means for performing despreading processing, and a plurality of frequency error detection means for detecting a frequency error by each output of the plurality of despreading processing means, the plurality of frequency error detection means, Filter means for removing high-frequency noise components from the output of the despreading processing means, and multiplication means for complexly multiplying a signal obtained by delaying a signal from the filter means for a predetermined time and a current signal from the filter means. At least one of the plurality of frequency error detecting means has a wide pass band of the filter means for a predetermined time after power-on. A code division multiple access receiver comprising control means for controlling the filter so as to narrow the pass band of the filter means after the predetermined time.