JP3256646B2 - Adaptive interference cancellation receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an interference wave removing function for compensating for deterioration of transmission characteristics due to interference signals such as co-channel interference and intersymbol interference from adjacent zones in digital mobile communication. Suitable for receivers that have

[0002]

2. Description of the Related Art In radio communication such as digital mobile communication, the same frequency is repeatedly used at geographically distant places in order to avoid co-channel interference and to effectively use the frequency. . In today's automobiles and mobile phones, a cellular system having a small cell configuration composed of a plurality of cells (zones) is employed. In the cellular system, the same frequency is used for different communications between cells in a service area that are spaced apart from each other by interference, and the frequency is effectively used by devising a cell configuration method. However, as cells become smaller and three-dimensional,
It is becoming difficult to avoid co-channel interference only by devising the cell configuration.

[0003] "Equalization method and adaptive equalizer in variable transmission path in mobile radio" [Japanese Patent Application No. 4-85765].
Discloses a compensation technique using a maximum likelihood sequence estimator having an adaptive equalization function to compensate for multipath distortion in a signal transmitted by multipath fading in mobile communication. I have. In this document,
A channel parameter estimation method suitable for maximum likelihood sequence estimation that quickly and accurately follows a wireless channel that fluctuates at high speed has been proposed.Equalizers remove intersymbol interference, but co-channel interference is eliminated. Therefore, there is a drawback that the system does not operate under the co-channel interference condition with a high signal level. First, a receiver using the maximum likelihood sequence estimation having the above adaptive equalization function will be described as a conventional technique. FIG. 11 shows an example of the configuration of a conventional receiver using maximum likelihood sequence estimation having an adaptive equalization function. This receiver subtracts the desired received wave estimation signal from the desired signal estimating means 1 for estimating and outputting the received desired signal from the sampled received signal input to the terminal 100 to estimate the error signal. The likelihood of the estimated error signal output by the means 3 and obtained by subtracting the desired received wave estimation signal from the received signal is obtained by performing the maximum likelihood sequence estimation by the state estimating means 4. The conversion parameters of the desired signal estimation means 1 are controlled by the conversion parameter control means 5 based on the error signal.

As shown in FIG. 11, the state estimating means 4 includes a likelihood calculating circuit 401 to which an estimation error signal is supplied, and a maximum likelihood sequence for estimating a maximum likelihood sequence of a received signal from an output of the likelihood calculating circuit 401. An estimator 413 and a signal sequence generation circuit 415 for generating a desired signal sequence to be estimated by the maximum likelihood sequence estimation are provided. The desired signal estimating means 1 is composed of a transversal filter 101. The conversion parameter control means 5 for controlling the conversion parameters is constituted by a tap coefficient control section 51, and sets the tap coefficients of the transversal filter 101 based on the estimated error signal and the estimated desired signal sequence. The configuration of the tap coefficient control unit 51 will be described later. The operation of the receiver shown in FIG. 11 will be described focusing on the signal flow.

A state where a signal transitions is generated inside the maximum likelihood sequence estimator 413. Based on this transition state, a transmission signal sequence modulated by the signal sequence generation circuit 415 is generated and output to the terminal 4 a of the state estimation means 4. This transmission signal sequence is transmitted to the desired signal estimation unit 1 and the tap coefficient control unit 5.
Used in 1. The desired signal estimating means 1 is composed of the transversal filter 101 as described above, and the tap coefficient of the transversal filter 101 is adaptively adjusted by the tap coefficient control section 51 in accordance with the impulse response of the fluctuating transmission path. Can be changed.
The transversal filter 101 receives the transmission signal sequence generated by the state estimation unit 4 and outputs a reception estimation signal.

The error estimating means 3 comprises an adding circuit 31, which subtracts the desired received wave estimation signal output from the desired signal estimating means 1 from the received signal from the input terminal 100 and outputs an estimated error signal. . If the received signal does not include an interference wave component, the estimation error signal is only a noise component. The estimation error signal is input to a likelihood calculation circuit 401 of the state estimation means 4 and is converted into a likelihood signal.

As the likelihood calculation circuit 401, a squaring circuit for squaring the estimation error can be used. The likelihood signal is input to maximum likelihood sequence estimator 413. Here, likelihood calculation circuit 401
If a squaring circuit is used, the likelihood signal, that is, the output of the squaring circuit becomes the minimum and the likelihood becomes the maximum. As a result, the likelihood signal is input to the maximum likelihood sequence estimator 413, and the transmission signal sequence is estimated.

Next, the function of each of the constituent blocks shown in FIG. 11 will be described. First, the state estimation means 4 will be described. The maximum likelihood sequence estimator 413 sequentially generates and outputs state sequence candidates corresponding to the transition state of the received signal. Next, a signal sequence generation circuit 415 generates a transmission signal sequence modulated by the candidates, and outputs it to the desired signal estimating means 1. The estimated error signal corresponding to this candidate is sent to the state estimating means 4
And input from the input terminal 4 b, converted into a likelihood signal in the likelihood calculation circuit 401. A sequence with a high likelihood is selected using the likelihood signal obtained here, and the signal is determined as a received signal sequence (that is, a desired signal sequence). The function of sequentially outputting received signal sequence candidates can be easily realized by an integrated circuit having a counter function. The maximum likelihood sequence estimator 413 searches for a sequence with a higher likelihood for all the received signal sequence candidates while the received signal sample value input from the input terminal 100 is held. However, the number of potential signal sequence candidates increases exponentially as the signal sequence becomes longer. Therefore, in practice, the number of signal sequence candidates searched using the Viterbi algorithm is appropriately reduced to reduce the amount of calculation.

In the example of FIG. 11, a transversal filter 101 is used as the desired signal estimating means 1. The output of the state estimating means 4 is
1 and becomes an estimated signal of the received wave. The tap coefficients of the transversal filter 101 are controlled by the tap coefficient control unit 51. The tap coefficient control unit 51 is configured as shown in FIG. 12, and includes a tap coefficient storage circuit 511, a tap coefficient changeover switch 512, and a tap coefficient update circuit 513.

[0010] The tap coefficient storage circuit 511 is a circuit for storing a set of tap coefficients (tap coefficient vector) corresponding to each state. The tap coefficient switch 512 is
A tap coefficient vector corresponding to each state is selected from the tap coefficient storage circuit 511, and the transversal filter 10 is selected.
Output to 1. When the maximum likelihood sequence estimation for each state by the maximum likelihood sequence estimator 413 is completed, the tap coefficient update circuit 513 sets a plurality of sets of tap coefficients corresponding to each state stored in the tap coefficient storage circuit 511. Update each vector. The updating of the tap coefficient is performed by the state estimating means 4.
And the estimated error signal output from the error estimating means 3. This update is performed for each tap coefficient vector corresponding to each state using an adaptive algorithm such as an RLS algorithm or an LMS (Least Mean Square Method) algorithm so that the estimated error signal is reduced. Therefore, the updated tap coefficient vector is
Since it reflects the current channel impulse response at the present time, when the transmission line fluctuates at high speed due to fading as in mobile radio communication, the followability to the transmission line is improved, so good reception characteristics are obtained. Can be obtained.

[0011] In the above literature, a transversal filter (34-4 ₁ used in desired signal estimation means, as shown in FIG. 13 as a technique for overcoming the reception characteristics degradation due to timing offset of the sampling clock of the received signal 34-4 ₂₎ maximum likelihood sequence estimation type adaptive equalizer using fractionally spaced transversal filter is also proposed.

That is, in FIG.
The input is a sampled signal that is sampled every symbol period T.
In FIG. 13, two digital signals were used.
Diversity reception of lunch and sampling
Circuit 34-2₁, 34-2 _TwoAt each symbol period
The digital signal is sampled at a period of 1 / T
No. Correlator 34-3₁, 34-3_TwoAt
Of the transmission path for each branch by the known signal contained in the signal
Estimate the impulse response and respond accordingly.
Subversal filter 34-4₁, 34-4_TwoEach fill
Set the data coefficient. This sampling circuit 34-2₁,
34-2_TwoOutput from the transversal filter 34-
4₁, 34-4_TwoDifference from the estimated received signal
Squared the estimated error signal of
Metric circuit 34-7₁, 34-7_TwoIn each
Calculation, add each metric value, and
The signal is supplied to the algorithm circuit 34-12. Viterbi algorithms
A code sequence is transmitted to the possible state transition from the system circuit 34-12.
Signal generation circuit 34-14, and the signal sequence
A modulated wave corresponding to the received signal is modulated by a modulated wave reproducing circuit 34-15.
Regenerate and transversal filter 34-4₁, 34-
4_TwoSupply to So-called oversampler
Timing offset of sampling clock
Degradation of receiving characteristics due to the

A replica is generated from transmission symbol candidates of a desired wave and an interference wave and transmission path parameters corresponding to these two signals, and a product of −1 is multiplied by the square of an error signal obtained by subtracting these replicas from the received signal. The logarithmic likelihood (Log
Some receivers have been proposed that use a maximum likelihood sequence estimator to determine a signal of a desired wave and an inter-channel interference wave under conditions where intersymbol interference occurs.

For example, W.S. Van Etten proposes and considers a receiver using the Viterbi algorithm as a maximum likelihood sequence estimator (W. Van Etten, “Ma
xium Likelihood Receiver
for MultipleChannel Trans
mission Systems ”IEEE Tran
saction on Communication
s, February 1976). However, in this receiver, the value of the transmission path impulse response is known. Howard proposes a receiver that estimates a channel parameter and uses a maximum likelihood sequence estimator.
E. FIG. Nichols, Arithur A. Giord
nano and Jhon G .; Proakis. In their proposal, in the transmission path parameter estimation, a transmission path parameter is estimated by an adaptive algorithm using a symbol decision estimation value of a maximum likelihood sequence estimator output with the same time delay as a received signal sample fixedly delayed for a fixed time. Is estimated and updated. This works well when the time variation of the transmission path is relatively moderate. However, in a mobile communication channel, the amplitude and phase of the desired wave and the interference wave fluctuate at a high speed.
E. FIG. Since the estimated value of the received signal sample delayed by a certain time proposed by Nichols et al. Is not the current estimated value, the transmission characteristics are significantly deteriorated.

A. P. Clark, J .; D. Harve
y, J. et al. P. Driscoll uses Near-M as a method for overcoming the degradation of transmission path parameter estimation caused by fixed delay, which is a problem in an adaptive maximum likelihood receiver using maximum likelihood sequence estimation.
Maximum-Likelihood detective
on is proposed to improve the characteristics of the adaptive equalizer based on maximum likelihood sequence estimation (AP Clark, JD Harr
Vey and J.M. P. Driscoll, "Nea
r-maximum-likelihooddetec
Tion processes for distor
ted digital signals ”, Radi
o & Electronics Engineer vo
l. 48, no. 6, pp. 301-309). Also,
Further, A. P. Clark is Near-maximu
FD that transmits two signals using the same frequency channel using m-likelihood detection
M (Frequency Division Multi)
ixing) method (US Pa.
tent 4, 862, 483). However, A. P. C
Near-maximum-li proposed by Lark et al.
Kelihooddetection has a large number of transmission signal sequence candidates (First Vector) stored in the memory and sets (vectors) of transmission path parameters corresponding to the transmission signal sequence candidates, and an extended reception signal sequence candidate (Se).
cond Vector) are sequentially selected in the order of likelihood, and a new transmission signal sequence candidate (First Vector) is selected.
or). Therefore, if the likelihood of the transmission signal sequence candidate (First Vector) having the highest likelihood is significantly larger than the likelihood of the other transmission signal sequence candidates (First Vector), the extended reception signal sequence candidate (First Vector) is considered. SecondVector) likelihood rank is:
Since it is determined by the likelihood of the first vector, there is almost no possibility that another first vector will be selected, and it will not be the maximum likelihood detection.

On the other hand, "Method of removing interference wave and receiver and communication system using the same" [PCT / JP94 / 000]
59], the above-mentioned "Equalization method and adaptive equalizer in a transmission path that fluctuates in mobile radio [Japanese Patent Application No. Hei 4-8576].
5] is applied to an interference canceller using a maximum likelihood sequence estimator, and the amplitude and phase of the desired wave and the interference wave independently and rapidly fluctuate. Technology that efficiently separates the desired wave and the interference wave by utilizing the fading nature of the moving mobile channel, and enables accurate estimation of the transmission path parameters of the rapidly changing desired wave and the interference wave. Have been. This will be briefly described with reference to FIG. The state estimating means 6 generates a desired signal sequence candidate corresponding to a state transition of a desired signal estimated to be received and an interference signal sequence candidate corresponding to a state transition of an interference signal from another station. Then, the estimated received desired signal by desired signal estimation means 8 from the desired signal sequence candidates, generating respective estimated received interference signal by the interference signal estimation means 7 ₁ to _7-k from interference signal sequence candidate. The estimated desired reception signal and the estimated received interference signal obtained in this manner are converted into error
Subtracts from the received signal to calculate an estimated error signal.
The state estimating means 6 estimates a desired signal sequence and an interference signal sequence based on the estimated error signal obtained for each candidate. The conversion parameter control means 9 controls the transmission path parameters of the desired signal estimating means 8 and the interference signal estimating means 7 _{1 to} 7 _k by an adaptive algorithm based on the estimated desired signal sequence and interference signal sequence and the estimation error signal. .

For the same set of signal sequence candidates as the transmitted set of the desired signal sequence and the interference signal sequence, the estimated error signal has only the noise component since the interference signal component has been removed. Using the estimated error signal obtained in this way, the state estimating means 6 calculates likelihood and estimates the desired signal and the interference signal. Therefore, the influence of the interference signal is eliminated in the maximum likelihood estimation of the received signal, so that even if the received signal includes the interference signal, it is possible to prevent the reception performance from being degraded due to the interference signal, and to achieve a good reception. Performance can be obtained.

[0018]

By the way, in "Equalization method and adaptive equalizer in transmission path fluctuating in mobile radio" (Japanese Patent Application No. 4-85765), the state estimating means uses an interference signal sequence from another station. Since no candidate is considered, an estimated received interference signal (interference signal replica) corresponding to an interference signal from another station cannot be generated. For this reason, reception characteristics are significantly degraded with respect to interference from other stations. In “Interference wave removal method and receiver and communication system using the same” [PCT / JP94 / 00059],
In order to solve the drawback of "Equalization method and adaptive equalizer in transmission path fluctuating in mobile radio" [Japanese Patent Application No. 4-85765], the state estimating means is used even for expected interference signals from other stations. Considering the interference signal sequence candidates, an estimated reception interference signal (interference signal replica) corresponding to the interference signal from another station is generated. There is.
However, there is a disadvantage that it is difficult to generate an estimated reception interference signal for an interference signal that cannot be predicted in advance, and the reception characteristics deteriorate.

[0019]

In order to achieve the above object, the present invention comprises a desired signal estimating means and at least one interference signal estimating means, wherein the desired signal estimating means and the interference signal estimating means are provided. Received estimated signals (replicas) of the desired signal and one or more interference signals respectively generated by the estimating means
Is subtracted from the received signal by the error estimating means to calculate an error signal, and is received by the state estimating means taking into account the state transition of the desired signal and one or more interference signals by the likelihood signal calculated from the error signal. In the interference cancellation receiver that estimates the signal sequence of the desired signal and the interference signal, and decodes and outputs the transmitted signal based on the estimated signal sequence, a plurality of reception antennas and a plurality of receptions corresponding to these antennas are provided. A signal weighting means and a synthesizing means for synthesizing the outputs of the respective received signal weighting means; a received signal received by each receiving antenna being weighted by the received signal weighting means; Is used as the received signal input to the error estimating means. The error signal from the error estimator
Signal sequence of desired signal and interference signal from state estimation means
Desired signal estimation means and interference signal estimation using candidates
Weighting of the received signal along with the tap coefficients used in the means
Estimation of the tap coefficient of the
To renew.

Further, a desired signal is estimated from the synthesized received signal.
Constant value (replica) and estimated value of interference signal (replica)
Subtracting each estimated value in the error estimating means for subtracting
Error for sequentially selecting one by one the output error signal of the adder
A signal selection switch is provided, and the error signal selection switch is
Using the output error signal, the conversion parameter control means
Tap coefficient of received signal weighting means and desired signal estimation
Selection of error signal in tap coefficient of error means and error estimation means
State estimation means side than the adder selected by the switch
Signal except the interference signal estimation means corresponding to the adder in
The tap coefficient of the signal estimating means is estimated and updated.
Fixed tap coefficients of the new received signal weighting means
The desired signal estimator and all interference signal estimators
The tap coefficient of the stage is determined by the desired signal output by the state estimation means.
Signal sequence candidates for the
Of the desired signal to be
The estimated value of each output interference signal is calculated from the synthesized received signal.
Conversion parameter control is performed using the error signal obtained by subtraction.
It is characterized in that the estimation is updated by control means.

The invention of claim 2 is the invention according to claim 1.
Thus, each of the reception signal weighting means corresponds to
The input received signal is represented by T (where T is the symbol of the input received signal)
Multiple delays with different delay times
Delay means for outputting a delay signal, the reception input signal,
Each delayed signal is multiplied by the corresponding tap coefficient.
Multiplying means, and the reception input multiplied by a tap coefficient
Signal and a synthesizing means for synthesizing each delayed signal.
It is characterized by being performed.

The invention of claim 3 is the invention of claim 1
Each of the received signal weighting means has a corresponding input
T / n (where T is the symbol of the input received signal)
Time, n is an integer of 2 or more).
Delay means for outputting a plurality of delay signals having a delay time of
Corresponds to the received input signal and each delay signal
Multiplying means for multiplying tap coefficients by
Combining the received reception signal and each delay signal
It is characterized in that it is constituted by a synthesizing means.

The invention of claim 4 is the invention of claim 1
Each of the reception signal weighting means is provided with the reception input
Multiply the signal by the corresponding tap coefficient
And a calculating means.

According to a fifth aspect of the present invention, there is provided any one of the first to fourth aspects.
In this invention, the error estimating means is provided with an estimation signal switching means for switching the connection between the adder and the estimating means, and by switching the error estimating means, the order of subtraction of the estimated values in the adder is changed so that the error signal selecting switch is switched. Change the configuration of the interference signal component included in the output error signal,
The update value of the tap coefficient of the reception signal weighting means obtained as a result is changed, and the tap coefficient of the optimum reception signal weighting means is compared and selected. That is, in this case, the interference signal estimation value may be subtracted without first subtracting the desired signal estimation value, and then the desired signal estimation value may be subtracted. In this case, the desired signal level slightly decreases, but a level difference occurs with the interference signal, and the desired signal can be separated from the interference signal.

[0025] From the receiver of the invention 請 Motomeko 1, considering only the state of a desired signal in the state estimation means eliminates an interference signal estimation means, a plurality of antennas, the received signal weighting means, by synthetic means, 1 than the number of antennas It is also possible to adopt a configuration in which the directivity characteristics in a smaller number of directions are set to zero (null) and only the intersymbol interference is removed . Converting parameter control means any one of the 請 Motomeko 1 to 5, the error signal output from the error estimating means, by using a signal sequence candidate of the desired signal and the interference signal output of the state estimator, the tap coefficients An updating RLS adaptation algorithm can also be used .

[0026] In any one of the 請 Motomeko 1 to 5, wherein the conversion parameter control means, the error signal output from the error estimating means, a signal sequence candidate of the desired signal and the interference signal output of the state estimator using To update the tap coefficient
An S-adaptive algorithm can also be used .

[0027]

As described above, according to the present invention, reception signals from a plurality of antennas are weighted by the reception signal weighting means and combined, so that interference signals which cannot be predicted in advance by the interference signal estimation means can be used for the interference. The arrival direction characteristics of the signal are improved. Further, even if the number of interference signal estimating means is small or absent in order to reduce the amount of calculation, it is possible to reduce interference signals from other stations and prevent deterioration of reception characteristics.

[0028]

EXAMPLES hereinafter be described with reference to details of the invention with reference to the accompanying drawings. Figure 1 is an input received signal weighting means 2 for weighting the received signal y ₁ from the receiving antennas 1-1 to 1-N _B of multiple _{(i) ~y NB (i)} , synthesized weighted received signal Means 3 for inputting and weighting means 2 for input received signal
In that it has a conversion parameter control means 9 for estimating and updating the weighted complex tap coefficients. N _B receive antennas 1-1 to 1-N received signal y ₁ received by _B (i) ~y
_NB (i) is weighted and combined by input received signal weighting means 2 respectively.

The input signal weighting means 2 receives the received signal y ₁
For (i) to y _NB (i), for example, each of the transversal filters FFF _{1 to} FFF _NB is configured. FIG. 2A shows a configuration example of the transversal filter. FIG. 1 shows the configuration of a transversal filter FFF _j connected to the j-th antenna (j = 1, 2,..., N _B ). FIG. 2A shows that the corresponding input received signal is T (where T is the symbol time of this input received signal).
Delay means 201-1 to 201-m for outputting a plurality of delay signals having different delay times by delaying in units, and complex tap coefficients hfj0 to hfjm corresponding to the input reception signal and each delay signal, respectively; Multiplying means 2 for multiplying
02-0 to 202-m, and combining means 203 for combining the received input signal multiplied by these complex tap coefficients and each delay signal. FIG. 2B shows a case where a corresponding input received signal is delayed in units of T / n (where T is the symbol time of the input received signal, n is an integer of 2 or more, for example, n = 2). Delay means 201-l to 201-m for outputting a plurality of delay signals having different delay times from each other
Multiplying means 202-0 to 202-m for multiplying the input reception signal and each delay signal by the corresponding complex tap coefficients hfj0 to hfjm, and the reception input signal multiplied by these complex tap coefficients and This is an example composed of a synthesizing unit 203 for synthesizing each delay signal.

Each of the transversal filters FFF ₁ to FFF
The output of the FF _NB is further combined by the combining means 3. The output of the combining means 3 is an error as a combined received signal y _c (i).
Is input to the estimated unit 4. Input synthesized reception signal y _c
(I) is the error estimating unit 4, the desired signal estimation means 8 and the interference signal estimation unit 7-1 to 7-N estimates of the desired signals output from the _I estimate of (desired signal replica) and the interference signal (Interference signal replica) is subtracted and output as an error signal. The state estimating means 6 generates a desired signal sequence candidate estimated to have been transmitted and outputs it to the desired signal estimating means 8 corresponding to a plurality of states to which the desired signal transits, and a plurality of states to which each interference signal transits. corresponds to the state for supplying to a plurality of interference signal sequence candidates each to generate an interference signal estimation unit 7-1 to 7-N _I.
From the estimated error signal ε obtained corresponding to these desired signal sequence candidates and interference signal sequence candidates, the likelihood calculating means 5 calculates likelihood, and the state estimating means 6 uses the obtained likelihoods to generate a combined reception signal. A desired signal sequence and an interference signal sequence included in y _c (i) are estimated, and a sequence determination result is output. The conversion parameter estimating unit 9 calculates the weighting coefficient of the received signal weighting unit 2, the desired signal estimating unit 8, and the interference signal estimating units 7-1 to 7- from the estimated error signal, the desired signal sequence candidate, and the interference signal sequence candidate by an adaptive algorithm. controlling the conversion parameters i.e. the impulse response coefficients of the transmission path N _I.

In the present invention, the conventional interference signal estimating means 7
-1~7-N when the other interfering signals that can not be removed using the output (interference signal replica signal) of the _I is present, a plurality of antennas 1-1 to 1-N _B and the reception signal weighting means 2 By combining means 3, a null point is provided in the antenna directivity for the direction of arrival of the other interference signal, and the other interference signal can be suppressed and removed, thereby improving the reception characteristics. Further, the conventional interference signal estimating means 7-1 to 7-1
When removing the interference signal using the output (interference signal replica signal) of 7-N _I, it was necessary to estimate the signal sequence candidate of the interference signal, in the present invention, in the direction of arrival of the interfering signal On the other hand, null is directed to the directional characteristics of the antenna to suppress and remove interference, so that it is unnecessary to estimate signal sequence candidates. Therefore, even in the case where the interference signal has a modulation scheme different from that of the desired signal, it is possible to eliminate the interference without specially preparing an interference signal estimation unit corresponding to the interference signal. In addition, by using the complex taps delayed by T / n intervals in FIG. 2B for the input signal weighting means 2 in FIG. 1, deterioration of the reception characteristics due to the timing clock shift of the received signal can be suppressed.

FIG. 3 shows a configuration in the case where the number of receiving antennas NB is 2 and the number of interference signals from other stations to be considered by the interference signal estimating means 7 is one. In addition, redundant description will be omitted . FIG. 4 shows an example in which the configuration of the error estimating means is different from that of FIG. 1 and the method of controlling the weighting coefficient of the input signal weighting means 2 is different. It is. 4 the error signal selector switch 1 for selecting outputs take the output signal of the adder 4-1 to 4-N _I in error estimation means 4
Has 0. In the error estimating means 4 of FIG.
In addition to the error signal output from the likelihood calculation circuit 5 and output from the output terminal 402 of the selection switch 10, an error signal is generated. The error signal output from the output terminal 402 is applied to the conversion parameter estimating means 9. This error signal is a complex tap coefficient of each transversal filter of the input signal weighting means 2 and an estimated value of the interference signal (replica of the interference signal) which has already been subtracted and removed by the error estimating means 4 when generating the error signal at the output terminal 402. Is used to update the complex tap coefficient of the interference signal estimating means that generates

In each error signal input to the error selection switch 10, an interference signal component subtracted by an adder subsequent to the adder remains without being subtracted. The conversion parameter control means 9 corresponds to the complex tap coefficient of the input signal weighting means 2 and the complex tap coefficient of the desired signal estimation means 8 and the interference signal to be subtracted so that the error selected by the error selection switch 10 is minimized. Update the complex tap coefficient of the interference signal estimating means. Therefore, a null point is directed to the arrival direction of the interference signal component not removed by the error estimating means included in the composite received signal y _c (n) by the directional characteristics of the antenna, and these interference signal components are suppressed. You. Therefore, even when an equal-level interference signal arrives, the equal-level interference which is a drawback of the interference canceller disclosed in "Interference wave canceling method and receiver and communication system using the same" [PCT / JP94 / 00059]. Of the antenna signal can be avoided by the null point control of the antenna directivity by the input signal weighting means 2 and the combining means 3.

FIG. 5 shows an example in which the number of receiving antennas is two and the number of complex taps of each transversal filter of the input signal weighting means 2 is one in the embodiment of FIG.
In the figure, the number of interference signals considered by the interference signal estimation means 7-1 is set to one. Next, referring to FIG. 5, the complex tap coefficients of the input signal weighting means 2, the complex tap coefficients of the transversal filter TVFD of the desired signal estimating means 8, and the complex tap coefficients of the transversal filter TVFI1 of the interference signal estimating means 7-1. Will be described with a specific example. Here, the case where the reception signal levels of the desired signal and the interference signal are the same level will be described. Here, if the received signal levels of the desired signal and the interference signal are equal, a conventional interference cancellation receiver, for example, "Interference wave removal method and receiver and communication system using the same" [PCT / JP94 / 00059] It is known that the disclosed interference cancellation receiver causes significant characteristic degradation. First, the error signal selection switch 10 is switched to 10 ₁ to select the output of the adder 4-1 as an error signal for tap coefficient control. Since the estimated value (replica of the desired signal) of the desired received signal generated by the desired signal estimating means 8 has already been subtracted by the adder 4-1 , the desired signal component is removed from this error signal, The signal component as a main component includes a transmission path estimation error, a thermal noise component, and the like. Using the error signal and the desired signal sequence candidate output from the state estimating means 6, the complex tap coefficient of the input signal weighting means 2 and the complex tap coefficient of the transversal filter TVFD of the desired signal estimating means 8 are updated. At this time, the complex tap coefficient at a position corresponding to the current time of the transversal filter TVFD or any of the complex tap coefficients (for example, hf1 in FIG. 5) of the input signal weighting means 2 is set to 1.0 (only the real part). can do. Next, the error signal selection switch 10 is set to the 10 ₂ side while the updated complex tap coefficient of the input signal weighting means 2 is fixed, and the error signal output from the adder 4-2 and the output from the state estimation means 6 are desired. The complex tap coefficients of the transversal filters TVFI1 and TVFD are updated using the signal sequence candidates and the interference signal sequence candidates. At this time, since the null point is directed in the arrival direction of the interference signal component and the interference signal component is suppressed to some extent by the weighting by the tap coefficient of the input signal weighting unit 2 that has been updated, the desired signal in the state estimation unit 6 The interference signal can be separated and identified, and the interference signal can be removed.

FIG . 6 shows the configuration of FIG.
In that an estimated signal switching means 11 is further provided. By providing the estimated signal switching means 11, the estimated interference signals from the interference signal estimating means 7 _{1 to} 7 _N1 are added to the serially connected adders 4-1 to 4-N ₁ in the error estimating means 4.
Can be switched and supplied. Thereby, the component of the interference signal component included in the error signal obtained by switching the error signal selection switch 10 can be changed. The estimated signal switching means 11 can change the configuration of the interference signal component included in the error signal used for updating the tap coefficient in the conversion parameter control means 9 , and the input signal weighting means 2 , And the null point can be suppressed. That is, "Interference wave removal method and receiver and communication system using the same" [PCT / JP94 / 000
59] is effective in avoiding the characteristic degradation when there is an equal-level interference signal, which is a drawback of the interference canceller disclosed in [59].

FIG. 7 shows the configuration of FIG. 6 in which the number of receiving antennas is 2 and the number of interference signals considered by the interference signal estimating means is 2
This is a specific example in the case of a wave. The case where the level of the desired signal is equal to the level of the interference signal corresponding to the interference signal estimating means 7-1 in FIG. The connection state of the switch in the estimation signal switching means 11 is indicated by a terminal A-
a, Bb, Cc, the error switch 10
To 10 ₁ , it is necessary to lower the signal level of the interference signal by null point control of the antenna directivity to the desired interference signal corresponding to the interference signal estimating means 7-1 by the input signal weighting means 2 and the combining means 3. There is. At this time, since the output of the error signal also includes an interference signal component corresponding to the interference signal estimating means 7-2, an operation is performed to suppress the interference signal also for the interference signal. That is, a null point is formed even for an interference signal that does not require suppression of the interference signal by null point control, and the reception characteristics are degraded. Therefore, the connection state of the switch in the estimation signal switching means 11 is indicated by a terminal A- as shown by a solid line.
b, Ba, and Cc, and by switching the error signal selection switch 10 to 10 ₂ , the interference signal that can suppress and remove the interference signal using the input signal weighting means 2 and the combining means 3 of the present invention is arbitrary. Can be selected.

In FIG. 6, the estimation signal switching means 11 may be switchable including the desired signal estimation means 8.
That is, in the error estimating means 4, for example, a certain interference signal estimated value may be subtracted first, and then the desired signal estimated value may be subtracted. By doing so, the level of the desired signal is slightly reduced, but it is possible to avoid the characteristic deterioration in the case where the interference signal of the same level exists in the related art.
In FIGS. 6 and 7, the input signal weighting means 2 may be one tap as in FIG.

FIG . 8 shows a case where the number of complex taps of the transversal filter in the input signal weighting means 2 is one. In this case, the input signal weighting means 2 has no delay means. FIG. 9 shows a configuration having no interference signal estimating means. In this case, the elimination of the interference signal depends only on the effect of the null point control of the antenna directivity operated using the input signal weighting means 2 and the combining means 3 of the present invention. In FIG. 9, the input signal weighting means 2 may be constituted by a transversal filter as in FIG. In this case, the delay amount of the unit delay means is T or T /
Any of n may be used.

FIG. 10 shows a case where there is one receiving antenna. The input signal weighting means 2 has a configuration using a two-tap transversal filter using delay means for each T / n time (n is an integer of 2 or more; FIG. 10 shows an example of n = 2). Show. In this configuration, the interference signal suppression elimination effect by the null point control of the antenna directivity cannot be obtained. Deterioration can be improved.

[0040]

As described above, according to the present invention, it is possible to avoid the deterioration of reception characteristics due to the same level of interference signal from another station, which is a drawback of the conventional interference canceller. Also, the amount of signal processing is small, and low power consumption is achieved. Further, even when an unknown interference signal arrives on the interference canceller side, there is an interference suppression removal effect, and it is possible to obtain better reception characteristics than before.

[Brief description of the drawings]

1 is a block diagram illustrating a configuration example of the array antenna combining type interference canceling receiver associated with the first aspect of the present invention.

FIG. 2 is a diagram showing a configuration example of an input signal weighting means 2 used in FIG.

FIG. 3 is a block diagram more specifically showing FIG. 1 ;

FIG. 4 is a block diagram showing a configuration of an embodiment of the invention according to claim 1 ;

FIG. 5 is a block diagram showing a more specific example of the invention of claim 1 ;

FIG. 6 is a block diagram showing one embodiment of the invention of claim 5 ;

FIG. 7 is a block diagram showing a more specific embodiment of the invention of claim 5 ;

FIG. 8 is a block diagram showing an example in which the input signal weighting means has no delay means .

FIG. 9 is a block diagram showing an example having no interference signal estimating means .

FIG. 10 is a block diagram showing another example having no interference signal estimating means .

FIG. 11 is a block diagram illustrating a configuration of a receiver using a conventional maximum likelihood sequence estimation circuit.

FIG. 12 is a diagram illustrating a specific configuration of a tap coefficient control unit 51 in FIG. 11;

FIG. 13 is a block diagram showing a conventional technique of diversity reception using a fractionally spaced transversal filter as a transversal filter.

FIG. 14 is a block diagram illustrating a configuration of a conventional nonlinear interference canceller.

──────────────────────────────────────────────────の Continuation of the front page (56) References JP-A-7-86972 (JP, A) Hitoshi Yoshino, et al., “Characteristics of Adaptive Interference Canceller Equalizer in B-258 Frequency Selective Fading”, 1993 IEICE Autumn Conference Volume 2, p. 2-258 (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 7/005 H04L 1/00 H04L 1/06

Claims (5)

(57) [Claims] 1. An apparatus comprising a desired signal estimating means and one or more interference signal estimating means, and a reception estimation signal (replica) of the desired signal and one or more interference signals generated by the desired signal and the interference signal estimating means. Is subtracted from the received signal by the error estimating means to calculate an error signal, and is received by the state estimating means taking into account the state transition of the desired signal and one or more interference signals by the likelihood signal calculated from the error signal. An adaptive interference cancellation receiver for estimating a signal sequence of a desired signal and an interference signal, decoding a signal transmitted based on the estimated signal sequence, and outputting the decoded signal. Receiving signal weighting means for weighting the received signal, and combining the outputs of the received signal weighting means to generate the error signal. Combining means for supplying a received signal to the difference estimating means, an error signal from the error estimating means, and a signal sequence candidate of the desired signal and the interference signal from the state estimating means, A conversion parameter control unit for estimating and updating the tap coefficient of the reception signal weighting unit together with the tap coefficient used by the interference signal estimation unit, and an output of an adder for subtracting the estimated value from the error estimation unit.
An error signal selection switch for selecting a force error signal.
The conversion parameter control means controls the error signal selection switch.
Switch output error signal and the output error signal
It corresponds to an adder located on the state estimating means side with respect to the adder.
Tap unit of the interference signal estimation means except for the interference signal estimation means
Number and tap coefficient of the reception signal weighting means and the
Tap section of the desired signal estimation means to which the selection switch is connected
And the estimated received signal is updated.
With the tap coefficient of the weighting means fixed,
Tap of the signal estimator and all interference signal estimators
Coefficients are calculated as desired signal and interference signal from the state estimation means.
Signal sequence candidate and the desired signal from the desired signal estimation means
Of each interference signal from all interference signal estimation means
Obtained by subtracting the signal estimate from the combined received signal
It is a means to estimate and update using the error signal.
The adaptive interference cancellation receiver to be featured. 2. The reception signal weighting means delays a corresponding input reception signal by T (where T is the symbol time of the input reception signal) and outputs a plurality of delay signals having different delay times. Delaying means, multiplying means for multiplying the received input signal, each delayed signal by a corresponding tap coefficient, and synthesizing the received input signal and each delayed signal multiplied by these tap coefficients and outputting the combined signal. 2. The adaptive interference cancellation receiver according to claim 1, comprising a combining unit. 3. Each of the received signal weighting means delays a corresponding input received signal by a unit of T / n (where T is a symbol time of the input received signal, and n is an integer value of 2 or more), and Delay means for outputting a plurality of delay signals having different delay times, the reception input signal, multiplication means for multiplying each delay signal by a corresponding tap coefficient, and the reception input signal multiplied by these tap coefficients 2. The adaptive interference canceling receiver according to claim 1, further comprising: synthesizing means for synthesizing and outputting each delayed signal. 4. The adaptive interference cancellation receiver according to claim 1, wherein each of said received signal weighting means is configured by multiplying said received input signal by a corresponding tap coefficient and outputting the result. 5. The error estimating means is provided with an estimated signal switching means capable of exchanging the connection between each adder of the error estimating means with the desired signal estimating means and the interference signal estimating means. Changing the configuration of the interference signal component included in the error signal output from the error signal selection switch, and changing the updated value of the tap coefficient of the reception signal weighting means obtained as a result to optimize the reception signal weighting means. The adaptive interference cancellation receiver according to any one of claims 1 to 4, wherein the tap coefficients are compared and selected.