JP2002247007A - Interference removing part, radio terminal equipment and method for removing interference - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to build a circuit in a portable terminal by simplifying the circuit and to easily remove an interference signal from a signal of another channel. SOLUTION: A multiplier 3 multiplies a spread spectral signal received from an antenna 1 by the carrier of a required signal outputted from a synchronizing circuit 2. A multiplier 10 multiplies a receiving signal from a sampling circuit 9 by the diffusion code of the required signal outputted from the circuit 2. An adaptive filter part 7 obtains a synthetic signal concerned with a non- required signal by executing multiplication and synthesis on the basis of a tap coefficient applied from a tap coefficient control circuit 6 and a signal outputted from the circuit 9. A subtracter 8 subtracts an output of the filter part 7 from an output of the multiplier 10 to obtain a required receiving signal. A comparator 12 outputs an error signal having a difference between the input and output of a limiter 11. The control circuit 6 outputs the tap coefficient and controls the tap coefficient on the basis of the output from the comparator 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference canceller, a radio terminal, and an interference canceling method. The invention is particularly useful in code division multiple access (CDMA) or spread spectrum multiple access (SSMA) communication systems, for example, from received signals.
An interference canceller, a radio terminal device, an interference filter, which removes only an interference signal component by an adaptive filter (adaptive filter) without affecting the desired signal, and removes an interference signal component present together with the spread-demodulated desired signal by subtraction. It relates to the removal method.

[0002]

2. Description of the Related Art FIG. 6 shows a configuration diagram of a conventional spread spectrum communication system. This system includes a transmitter 100 and a receiver 200. The transmitter 100 includes a data transmission circuit 101, a primary modulation circuit 102, a secondary modulation circuit 103, a spreading code generation circuit 104, and an antenna 105. The receiver 200 includes a data receiving circuit 201, a primary demodulation circuit 202, a secondary demodulation circuit 203, a synchronization circuit 204, and an antenna 205.

Here, d ₁ (t) is the data transmitted by the own station, a
₁ (t) is a primary modulated signal, s ₁ (t) is a secondary modulated signal, a spread spectrum signal, and c ₁ (t) represents a code for spreading a spectrum. Spread spectrum signals from other stations are represented as s _i (t), i = 2,3,.

[0004] In a spread spectrum communication system, communication is performed in the same frequency band while a plurality of signals coexist.
Since each signal is modulated with a spreading code having a property orthogonal to each other, a signal containing a code that does not match the desired spreading code is excluded during demodulation. However, since they are not completely orthogonal, the cross-correlation values slightly exist, and the sum of the cross-correlation values becomes large as the number of signals of other stations increases, thereby limiting the number of simultaneous communication stations.

Next, the operation of the spread spectrum communication system will be described with reference to the drawings. In the transmitter 100, the data d ₁ (t) transmitted from the data transmission circuit 101 is +1
And -1 are taken as random data, and the primary modulation circuit 102
Is, for example, PSK (phase shift keying). The output a ₁ (t) of the primary modulation circuit 102 is described as follows. _{a 1 (t) = d 1} (t) cos (2πf c t + θ 1) , however, f _c is theta ₁ at the carrier frequency represents the phase of the carrier.

Here, c ₁ (t) is a spreading code that takes +1 and −1. The secondary modulation circuit 103 uses the spreading code c ₁ (t) and 1
The secondary modulation is performed by multiplication with the next modulated signal a ₁ (t) to generate a spread spectrum signal s ₁ (t). The spread spectrum signal s ₁ (t) is described as follows. s ₁ (t) = c ₁ (t) d ₁ (t) cos (2πf _c t + θ ₁ )

A spread spectrum signal from another station is expressed as follows. s _k (t) = c _k (t) d _k (t) cos (2πf _c t + θ _k ), k = 2,3,4,
, K On the other hand, the receiver 200 demodulates the spread spectrum signal s ₁ (t) as a desired signal. The received signal r (t) is described as follows.

[0008]

(Equation 1) Here, n (t) is the receiver noise.

In the following description, noise is omitted for convenience. The synchronization circuit 204 establishes synchronization of the spread code c ₁ (t) included in the received signal r (t), and
04 to the secondary demodulation circuit 203. The secondary demodulation circuit 203 multiplies the received signal r (t) by the code c ₁ (t), and obtains a ₁ (t) by the following calculation.

[0010]

(Equation 2)

Where γ _k (t) = c ₁ (t) × c _k (t), a _k (t)
= d _k (t) cos (2πf _c t + θ _k ), k = 2,3, 〜, K, c ₁ (t) × c
₁ (t) = 1 relationship is used.

The first term is a modulated signal of a desired signal, and the second term is a term which contributes as a noise component due to a signal from another station.
γ _k (t) is the product of the code c ₁ (t) that spreads the desired signal and the code c _k (t) that spreads the signals of other stations. It remains a wideband signal. The primary demodulator 202 demodulates a ₁ (t) to obtain data d
₁ (t) is output.

[0013]

Conventionally, it is the interference elimination capability inherent in this system that performs the interference elimination using the orthogonality of the code for spreading the spectrum. However, these newly proposed interference cancellation schemes treat all received signals individually and process them, so that the configuration becomes complicated and application to portable terminals and the like is difficult.

In view of the above, the present invention simplifies the circuit and makes the overall configuration as simple as possible, thereby realizing application to a small device such as a portable terminal or a system in which the processing load is not to be excessively reduced. The purpose is to: Another object of the present invention is to increase the number of simultaneous communication stations and improve communication quality by removing interference components from signals of other stations.

[0015]

According to a first aspect of the present invention, there is provided a multiplication circuit for multiplying a sampled received signal by a spread code of a desired signal, a tap coefficient control circuit for outputting a tap coefficient, An adaptive filter unit for obtaining a composite signal relating to a desired signal and a non-desired signal based on an inner product of a tap coefficient provided by the tap coefficient control circuit and a sampled received signal; and And a subtraction circuit for subtracting the combined signal obtained by the section to obtain a desired received signal.

According to a second aspect of the present invention, there is provided an antenna for receiving a spread spectrum signal, the above-described interference canceller for inputting a signal received by the antenna, and receiving data from an output of the interference canceller. And a determination circuit for determining the wireless terminal.

According to a third solution of the present invention, a desired signal and a non-desired signal are multiplied by a spread code of a desired signal and a sampled received signal are weighted by tap coefficients. The present invention provides an interference removal method for obtaining a desired combined signal by obtaining a combined signal of the multiplied signals and subtracting the combined signal from the multiplied output.

According to a fourth aspect of the present invention, a multiplication procedure for multiplying a sampled received signal by a spread code of a desired signal, a tap coefficient control procedure for outputting a tap coefficient, and the tap coefficient control procedure are provided. Based on the inner product of a given tap coefficient and a sampled received signal, a desired signal and a plurality of non-desired signals are converted into N bits of the received signal represented by a vector composed of N chips. By weighting with the tap coefficients composed of the elements, an adaptive filter procedure for obtaining a composite signal regarding the desired signal and the non-desired signal, and from the output of the multiplication procedure, subtracting the composite signal obtained by the adaptive filter procedure, Wireless terminal device including an interference cancellation program for causing a computer to execute a subtraction procedure for obtaining a desired reception signal To provide.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration diagram of a wireless terminal device provided with an interference wave removing device according to the present invention. Here, the number of simultaneous communication stations is assumed to be K stations, and for a desired signal,
It is assumed that synchronization is established. The wireless terminal device (receiver) includes an antenna 1, a synchronization circuit 2, a multiplication circuit 3, a low-pass filter (LPF) 4, a tap coefficient control unit 6, an adaptive filter unit 7, a subtraction circuit 8, a sampling circuit 9, The circuit includes a circuit 10, a limiter 11, and a comparator 12.

The synchronization circuit 2 detects synchronization of the spread spectrum signal received from the antenna 1. The multiplication circuit 3
The spread spectrum signal received from the antenna 1 is multiplied by the carrier of the desired signal output from the synchronization circuit 2.
The low-pass filter 4 extracts a baseband signal from the output of the multiplication circuit 3. The sampling circuit 9 samples the baseband signal from the low-pass filter 4. Multiplication circuit 10
Multiplies the received signal from the sampling circuit 9 by the spread code of the desired signal output by the synchronization circuit 2. The adaptive filter section 7 multiplies and combines the tap coefficient provided by the tap coefficient control section 6 and the signal from the sampling circuit 9 to obtain a combined signal related to the undesired signal. The subtraction circuit 8 subtracts the output of the adaptive filter unit 7 from the output of the multiplication circuit 10 to obtain a desired reception signal. The limiter 11 limits the reception signal obtained by the subtraction circuit 8. The comparator 12 includes a limiter 11
And outputs an error signal obtained by calculating the difference between the input and the output. The tap coefficient control unit 6 outputs the tap coefficient, and controls the tap coefficient based on the output of the comparator 12.

Next, the operation will be described in detail. First, the received signal r (t) input from the antenna 1 is described as follows.

[0022]

(Equation 3)

Here, k = 1 is determined as a signal of a desired station (desired signal). In addition, k = 2, 3, to K are signals of undesired stations (undesired signals). The multiplier circuit 3 multiplies the carrier wave cos Synchronization established desired signal in the synchronous circuit 2 (2πf _c t + θ ₁₎ and the received signal. Next, the difference component is extracted by the low-pass filter 4 as follows.

[0024]

(Equation 4)

The low-pass filter 4 converts both a desired signal component and a non-desired signal component as a baseband signal. In the next sampling circuit 9, sampling is performed at m times the chip speed (m = 1, 2,---). In the following description, m = 1 for convenience.
The output signal r _b (i) of the sampling circuit 9 is represented by T _b for one bit time,
If _Tc is one chip time, it is expressed as follows by a vector composed of N = _Tb / _Tc chips. here,
The argument i means a signal of the i-th bit.

[0026]

(Equation 5) The tap coefficient w (i) is composed of N elements as follows.

[0027]

(Equation 6) Signals weighted by the tap coefficient _{w (i) r b (i} ) is output as y (i) by the following calculation.

[0028]

(Equation 7)On the other hand, the output signal r of the sampling circuit 9 is output by the multiplication circuit 10._b
(i) is the spread code c of the desired signal output from the synchronization circuit 2
₁(i), and spread demodulation is performed. Where c₁(i) =
[c_1.i(0), c_1.i(1),…, c_1.i(N-1)]^TIt is. Multiplication circuit 1
Output signal r of 0 _d(i) is expressed as follows.

[0029]

(Equation 8)

This signal r _d (i) has an interference component (r
_di ⁽²⁾ , r _di ⁽³⁾ , ..., r _di ^(K) ). if,
If the signal y (i) output from the adaptive filter unit 7 can represent this interference component, only the data of the desired signal can be obtained. To realize this, the signal y (i) is subtracted from the signal r _d (i) by the subtraction circuit 8 to obtain the signal z (i). This signal z (i) has a constant value of +1 or -1 if the interference component is removed and only the data of the desired signal is obtained, but fluctuates if the interference component is included. Therefore, the signal z (i) is limited by the limiter 11, and the data prediction value d ^
At the same time as obtaining ₁ (i), the error signal e (i) = d ^ ₁ (i) -z (i) is calculated. The tap coefficient control unit 6 controls the tap coefficient w (i) so as to reduce the error signal. Specifically, the tap coefficients are controlled such that y _i (1) = 0, y _i (m) = r _di ^(m) , and m = 2, 3,-, K. Note that "^" is added immediately above the character / symbol as shown in the formulas and figures, but is written next to the character / symbol for convenience.

FIG. 2 is an explanatory diagram of signals constituting the signal r _b (i). In this figure, as an example, the signal r _b (i) is assumed to be composed of a desired signal D and four interference signals U ₁ , U ₂ , U ₃ , and U ₄ . The signal r _b (i) is represented by a matrix as follows.

[0032]

(Equation 9) Next, FIG. 3 shows an explanatory diagram of the inner product r _d (i) of the signal r _b (i) and the signal c ₁ (i). In addition, the expression is as follows.

[0033]

(Equation 10)

The components of the undesired signals U _{1 to} U ₄ become interference noise and interfere with the desired signal D. Further, the tap coefficient control unit 6 inputs the error signal e (i), corrects the calculation result of the correction to the tap coefficient w (i-1) one step before, and
Output as w (i). Using this tap coefficient w (i)
Calculate y (i) and find the error e (i + 1) again. In order to reduce this error, w (i) is corrected again and w (i + 1)
And supplies it to the adaptive filter unit 7. The algorithm for updating tap coefficients is LMS (least mean squ
various algorithms such as are algorithm) can be applied. The tap coefficient w (i) was obtained as follows.

[0035]

[Equation 11] Therefore, taking the inner product of the signal r _b (i) and the tap coefficient w (i), y (i ) is as follows.

[0036]

(Equation 12) In this operation, the part corresponding to the desired signal component is the first part of the result.
Term, which is almost zero. Subtracting this value from the first term of the signal r _d (i) has no effect. That is, the desired signal component is not affected. On the other hand, the values of the second to fifth terms of y (i) are almost the same as the values of the second to fifth terms of r _d (i). The expression is as follows, and it can be seen that the interference component of the existing undesired signal is almost removed as the noise component.

[0037]

(Equation 13)

FIG. 4 shows a configuration diagram of the adaptive filter section. The adaptive filter unit 7 includes a delay circuit 7
1-0 to 71- (N-2), multiplying circuits 72-0 to 72-
(N−2) and the sum circuit 73. Signal r _b output from the sampling circuit 9 (i) is input to the adaptive filter unit 7. Signal _{r b} (i), the delay circuit 71-0～7
Each component r _bi (N−1) to r _bi (0) is output after being delayed by 1 chip by 1- (N−2).

[0039]

[Equation 14] Each component is represented by a corresponding tap coefficient w (i) and a multiplication circuit 72-0.
Multiplied by ~ 72- (N-1). Thereafter, the components are combined by the sum circuit 73, and y (i) is output.

FIG. 5 is a diagram showing a simulation result of interference cancellation according to the present invention. The horizontal axis represents the number of simultaneous communication stations, and the vertical axis represents the average BER (Bit Error Rate). In this example, the signal-to-noise ratio Eb / No was set to 20 dB, and a Gold code was used as the code. The processing gain is 31. The conventional error rate is indicated by a solid black line, and the average error rate when the present invention is adopted is indicated by a solid white line. By employing the present invention, the number of simultaneous communication stations can be increased.

The present invention can be applied to an appropriate modulation method other than BPSK. For example, when applying to QPSK, the circuit of the present invention may be provided for the in-phase component and the quadrature component. The present invention relates to a microprocessor or CPU
And the configuration of each circuit for removing interference may be realized as software processing by a microprocessor / CPU. Then, the present invention may be provided as a wireless terminal device including an interference removal program for causing a computer to execute each of such procedures. Further, the present invention can be provided by a computer-readable recording medium on which an interference removal program is recorded, a program product including the interference removal program and loadable into an internal memory of a computer, a microprocessor including the program, and the like. .

[0042]

According to the present invention, as described above, by simplifying the circuit and simplifying the overall configuration as much as possible, the present invention can be applied to a small device such as a portable terminal or a system in which the processing load is not excessively reduced. Can be realized. Further, according to the present invention, by removing interference components from signals of other stations, the number of simultaneous communication stations can be increased, and the quality of communication can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a wireless terminal device including an interference wave removing device according to the present invention.

FIG. 2 is an explanatory diagram of signals constituting a signal _rb (i).

FIG. 3 is an explanatory diagram of an inner product r _d (i) of a signal r _b (i) and a signal c ₁ (i).

FIG. 4 is a configuration diagram of an adaptive filter unit that performs processing for each bit.

FIG. 5 is a diagram showing a simulation result of interference removal according to the present invention.

FIG. 6 is a configuration diagram of a conventional spread spectrum communication system.

[Explanation of symbols]

 Reference Signs List 1 antenna 2 synchronization circuit 3 multiplication circuit 4 low-pass filter (LPF) 5 undesired signal generation circuit 6 tap coefficient control circuit 7 adaptive filter section 8 subtraction circuit 9 sampling circuit 10 multiplication circuit 11 limiter 12 comparator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K022 EE01 EE31 EE35 5K052 AA01 AA12 BB02 CC06 DD04 EE02 EE30 FF05 FF32 GG19 GG20 GG46

Claims (8)

[Claims] A multiplication unit for multiplying a sampled received signal by a spreading code of a desired signal; a tap coefficient control unit for outputting a tap coefficient; a tap coefficient provided by the tap coefficient control unit;
An adaptive filter unit for obtaining a composite signal relating to a desired signal and a non-desired signal based on an inner product of the sampled received signal; and subtracting a composite signal obtained by the adaptive filter unit from an output of the multiplication unit. An interference canceller comprising a subtraction unit for obtaining a signal. 2. The adaptive filter section according to claim 1, wherein said adaptive filter section converts a received signal of a certain bit represented by a vector composed of N chips for a desired signal and a plurality of non-desired signals into taps composed of N elements. The interference removal apparatus according to claim 1, wherein the composite signal is output by weighting with a coefficient. A synchronizing unit for detecting synchronization of the received spread spectrum signal; a multiplying unit for multiplying the received spread spectrum signal by a carrier of a desired signal output from the synchronizing unit; 3. A low-pass filter for extracting a baseband signal from an output from the control unit, and a sampling unit that samples the baseband signal from the low-pass filter and outputs a sampled received signal. 3. The interference removal device according to item 1. 4. The apparatus according to claim 1, further comprising a limiter configured to limit a reception signal obtained by the subtractor, wherein the tap coefficient controller controls the tap coefficient based on an error signal between an input and an output of the limiter. The interference removal apparatus according to claim 1, wherein 5. An antenna for receiving a spread spectrum signal, and a signal received by said antenna is input.
A wireless terminal device, comprising: the interference removal device according to any one of claims 1 to 4; and a determination unit that determines received data from an output of the interference removal device. 6. A composite signal relating to a desired signal and a non-desired signal is obtained by multiplying a sampled received signal by a spreading code of a desired signal and weighting the sampled received signal by a tap coefficient. An interference cancellation method for subtracting the combined signal from an output to obtain a desired received signal. 7. A method according to claim 6, further comprising the step of performing feedback control on the value of the tap coefficient so that the error component of the demodulated signal is reduced. 8. A multiplication procedure for multiplying a sampled received signal by a spreading code of a desired signal, a tap coefficient control procedure for outputting a tap coefficient, a tap coefficient given by the tap coefficient control procedure, Weighting the received signal of a certain bit represented by a vector composed of N chips with a tap coefficient composed of N elements for the desired signal and a plurality of non-desired signals based on the inner product of the received signal By doing so, an adaptive filter procedure for obtaining a composite signal relating to a desired signal and a non-desired signal, and a subtraction procedure for subtracting the composite signal obtained by the adaptive filter procedure from the output of the multiplication procedure to obtain a desired reception signal A wireless terminal device including an interference removal program to be executed by a computer.