JP3686839B2 - Interference cancellation apparatus, radio terminal apparatus, and interference cancellation method - Google Patents

Description

ただし、n(t)は受信機雑音である。
【０００９】
以後の説明では便宜上、雑音を省略して説明する。
同期回路２０４では、受信信号r(t)に含まれる拡散符号c₁(t)の同期を確立し、その符号を同期回路２０４から２次復調回路２０３に供給する。2次復調回路２０３では、受信信号r(t)と符号ｃ₁(t)との乗算を行い、次の計算によりa₁(t)を得る。
【００１０】
【数２】

【００１１】
ただし、γ_k(t) = c₁(t)×c_k(t), a_k(t) = d_k(t) cos(2πf_ct +θ_k), k = 2,3,〜,Kで、
c₁(t)×c₁(t) = 1の関係を使用している。
【００１２】
第１項が希望信号の変調信号で、第２項が、他局信号による雑音成分として寄与する項である。γ_k(t)は希望信号を拡散する符号c₁(t)と、他局信号を拡散する符号c_k(t)との積で、直交していない為、１周期積分してもゼロにならならず広帯域信号のままである。
１次復調器２０２では、a₁(t)を復調してデータd₁(t)を出力する。
【００１３】
【発明が解決しようとする課題】
従来においては、スペクトルを拡散する符号の直交性を利用して干渉除去を行うのが、本来、このシステムが備えている干渉除去能力である。しかしながら、新たに提案されてきたこれらの干渉除去方式では、受信信号すべてを個々に扱って処理するため、構成が複雑になり携帯端末等への適用はむずかしかった。
【００１４】
本発明は、以上の点に鑑み、回路を簡素化し、全体構成をできるだけ簡易にすることで、携帯端末などの小型装置や処理の負担をあまりかけたくないシステムへの適用を実現することを目的とする。また、本発明は、他局信号からの干渉成分を除去することで、同時通信局数を増やし、通信の品質を向上させることを目的とする。
【００１５】
【課題を解決するための手段】
本発明の第１の解決手段によると、
サンプルされた受信信号と希望信号の拡散符号とを乗算する乗算回路と、
タップ係数を出力するタップ係数制御回路と、
前記タップ係数制御回路により与えられたタップ係数と、サンプルされた受信信号との内積に基づき、希望信号及び非希望信号に関する合成信号を求めるアダプティブフィルタ部と、
前記乗算回路の出力から、前記アダプティブフィルタ部により求められた合成信号を減算し、希望受信信号を得る減算回路と
を備えた干渉除去装置を提供する。
【００１６】
本発明の第２の解決手段によると、
スペクトル拡散信号を受信するアンテナと、
前記アンテナで受信した信号を入力する上述に記載の干渉除去装置と、
前記干渉除去装置の出力から受信データを判定する判定回路と、
を備えた無線端末装置を提供する。
【００１７】
本発明の第３の解決手段によると、
サンプルされた受信信号と希望信号の拡散符号とを乗算し、
サンプルされた受信信号をタップ係数で重み付けすることにより、希望信号及び非希望信号に関する合成信号を求め、
前記乗算した出力から、前記合成信号を減算し、希望受信信号を得るようにした干渉除去方法を提供する。
【００１８】
本発明の第４の解決手段によると、
サンプルされた受信信号と希望信号の拡散符号とを乗算する乗算手順と、
タップ係数を出力するタップ係数制御手順と、
前記タップ係数制御手順により与えられたタップ係数と、サンプルされた受信信号との内積に基づき、希望信号及び複数の非希望信号について、各々Ｎチップから構成されるベクトルで表わされるあるビット目の受信信号を、Ｎ個の要素で構成されるタップ係数で重み付けすることにより、希望信号及び非希望信号に関する合成信号を求めるアダプティブフィルタ手順と、
前記乗算手順の出力から、前記アダプティブフィルタ手順により求められた合成信号を減算し、希望受信信号を得る減算手順と
をコンピュータに実行させるための干渉除去プログラムを含む無線端末装置を提供する。
【００１９】
【発明の実施の形態】
図１に、本発明に係る干渉波除去装置を備えた無線端末装置の構成図を示す。ここで、同時通信局数は K 局とし、また、希望信号に対しては、同期がとれているものとする。
この無線端末装置（受信機）は、アンテナ１、同期回路２、乗算回路３、低域フィルタ（ＬＰＦ）４、タップ係数制御部６、アダプティブフィルタ部７、減算回路８、標本化回路９、乗算回路１０、リミタ１１、比較器１２を備える。
【００２０】
同期回路２は、アンテナ１から受信されたスペクトル拡散信号の同期を検出する。乗算回路３は、アンテナ１から受信されたスペクトル拡散信号と、同期回路２から出力された希望信号の搬送波とを乗算する。低域フィルタ４は、乗算回路３の出力から、ベースバンド信号を取り出す。標本化回路９は、低域フィルタ４からのベースバンド信号をサンプルする。乗算回路１０は、標本化回路９からの受信信号と、同期回路２により出力された希望信号の拡散符号とを乗算する。アダプティブフィルタ部７は、タップ係数制御部６により与えられたタップ係数と、標本化回路９からの信号とに基づいて、乗算及び合成することにより、非希望信号に関する合成信号を求める。減算回路８は、乗算回路１０の出力から、アダプティブフィルタ部７の出力を減算し、希望受信信号を得る。リミタ１１は、減算回路８により求められた受信信号を制限する。比較器１２は、リミタ１１の入力と出力との差分をとった誤差信号を出力する。タップ係数制御部６は、タップ係数を出力し、また、比較器１２の出力に基づき、タップ係数を制御する。
【００２１】
つぎに、動作を詳細に説明する。
まず、アンテナ１から入力された受信信号r(t)を次のように記述する。
【００２２】
【数３】

【００２３】
ここで、k＝１を希望局の信号（希望信号）と定める。その他k＝2,3,〜Kは非希望局の信号（非希望信号）とする。乗算回路３では、同期回路２で同期の確立した希望信号の搬送波 cos(2πf_ct+θ₁)を受信信号と乗算する。つぎに、差成分を低域フィルタ４で取り出すと次のようになる。
【００２４】
【数４】

【００２５】
低域フィルタ４により、希望信号成分も非希望信号成分もベースバンド信号として変換される。次の標本化回路９ではチップ速度のm (m=1, 2, - - -) 倍で標本化する。以下の説明では、便宜上 m=1 とする。
標本化回路９の出力信号r_b(i)は、T_bを１ビット時間、そして、T_cを１チップ時間とすると、N=T_b/T_cチップから構成されるベクトルで次のように表される。ここに、引き数のiは、iビット目の信号を意味する。
【００２６】
【数５】

タップ係数w(i)は次のようにＮ個の要素で構成される。
【００２７】
【数６】

タップ係数w(i)で重み付けされた信号r_b(i)は、次の演算によりy(i)として出力される。
【００２８】
【数７】

一方、乗算回路１０により、標本化回路９の出力信号r_b(i)は、同期回路２から出力される希望信号の拡散符号c₁(i)と乗算され、拡散復調が行われる。ただし、c₁(i)=[c_1.i(0),c_1.i(1),…,c_1.i(N-1)]^Tである。乗算回路１０の出力信号r_d(i)は、次のように表される。
【００２９】
【数８】

【００３０】
この信号r_d(i)は、他局からの干渉成分（r_d.i ⁽²⁾, r_d.i ⁽³⁾,・・,r_d.i ^(K)）を含んでいる。もし、アダプティブ・フィルタ部７から出力された信号y(i)がこの干渉成分を表すことができれば、希望信号のデータだけを求めることができる。それが実現されるものとして、減算回路８により、信号r_d(i)より信号y(i)を引き算して信号z(i)を得る。この信号z(i)は、もし干渉成分が除去されて希望信号のデータだけなら、＋１か−１の一定値になるが、干渉成分を含むと、変動する。そこで、信号z(i)をリミタ１１で制限し、データの予測値d^₁(i)を得ると同時に、誤差信号e(i)= d^₁(i)- z(i) を計算する。タップ係数制御部６では、この誤差信号が小さくなるようにタップ係数w(i)を制御する。
具体的には、y_i(1)=0,y_i(m)= r_d.i ^(m),m=2,3,--,Kとなるようにタップ係数を制御する。なお、「^」は、式及び図で示されるように文字・記号の真上に付されるものであるが、便宜上文字・記号の横に記載する。
【００３１】
図２に、信号r_b(i)を構成する信号の説明図を示す。この図では、一例として、信号r_b(i)は、希望信号Ｄと４つの干渉信号U₁,U₂,U₃,U₄で構成されるものとする。
信号r_b(i)を行列で表わすと次のようになる。
【００３２】
【数９】

つぎに、図３に、信号r_b(i)と信号c₁(i)の内積r_d(i)の説明図を示す。また、数式で表わすと次のようになる。
【００３３】
【数１０】

【００３４】
上記の非希望信号U₁〜U₄の各成分が、干渉雑音となって、希望信号Dを妨害する。また、タップ係数制御部６では、誤差信号 e(i) を入力して、１ステップ前のタップ係数 w(i-1) に修正の演算結果を補正し、w(i) として出力する。このタップ係数w(i) を使用して y(i) を計算し、再び誤差 e(i+1) を求める。この誤差が小さくなるように、再び、w(i) に補正を行い w(i+1) を求め、アダプティブフィルタ部７に供給する。タップ係数更新のアルゴリズムは、ＬＭＳ (least mean square algorithm)等の各種のアルゴリズムを適用することができる。タップ係数w(i)は、次のように得られた。
【００３５】
【数１１】

よって、信号r_b(i)とタップ係数w(i)との内積をとると、y(i)は次のようになる。
【００３６】
【数１２】

この演算で、希望信号成分に相当する部分は結果の第１項で、ほぼ零である。この値を信号r_d(i)の第１項から引き算しても、影響はない。すなわち、希望信号成分は影響を受けない。一方、y(i)の第２項から第５項の値は、r_d(i)の第２項から第５項の値とほとんど同じである。数式で表わすと、次のようになり、雑音成分として、存在する非希望信号の干渉成分が、ほぼ除去されていることが分かる。
【００３７】
【数１３】

【００３８】
図４に、アダプティブフィルタ部の構成図を示す。このアダプティブフィルタ部７は、遅延回路７１−０〜７１−（Ｎ−２）、乗算回路７２−０〜７２−（Ｎ−２）及び和回路７３を有する。標本化回路９から出力された信号r_b(i)は、このアダプティブフィルタ部７に入力される。信号r_ｂ(i)は、遅延回路７１−０〜７１−（Ｎ−２）により、1チップずつ遅延されて、各成分r_b.i(N-1)〜r_b.i(0)が出力される。
【００３９】
【数１４】

各成分は、対応するタップ係数w(i)と乗算回路７２−０〜７２−（Ｎ−１）で乗算される。各成分はその後、和回路７３により合成されて、y(i)が出力される。
【００４０】
図５は、本発明による干渉除去のシミュレーション結果を示す図である。横軸が同時通信局数、縦軸が平均ＢＥＲ（Bit Error Rate，ビット誤り率）である。この例では、信号雑音比Eb/No を20 dB とし、符号はGold 符号を使用した。処理利得は 31 である。従来による誤り率を、黒丸実線で示し、本発明を採用した場合の平均誤り率を白丸実線として示した。本発明の採用により、同時通信局数を増加させることができる。
【００４１】
本発明はＢＰＳＫの他、適宜の変調方式に適用することができる。例えば、ＱＰＳＫへ適用する場合、同相成分と直交成分に本発明の回路を設けるようにすれば良い。
本発明は、マイクロプロセッサ又はＣＰＵを備え、干渉除去のための各回路による構成をマイクロプロセッサ・ＣＰＵによるソフトウェア処理として実現するようにしてもよい。そして、本発明はこのような各手順をコンピュータに実行させるための干渉除去プログラムを含む無線端末装置として提供されるようにしてもよい。さらに、本発明は、干渉除去プログラムを記録したコンピュータ読み取り可能な記録媒体、干渉除去プログラムを含みコンピュータの内部メモリにロード可能なプログラム製品、そのプログラムを含むマイクロプロセッサ、等により提供されることができる。
【００４２】
【発明の効果】
本発明によると、以上のように、回路を簡素化し、全体構成をできるだけ簡易にすることで、携帯端末などの小型装置や処理の負担をあまりかけたくないシステムへの適用を実現することができる。また、本発明によると、他局信号からの干渉成分を除去することで、同時通信局数を増やし、通信の品質を向上させることができる。
【図面の簡単な説明】
【図１】本発明に係る干渉波除去装置を備えた無線端末装置の構成図。
【図２】信号r_b(i)を構成する信号の説明図。
【図３】信号r_b(i)と信号c₁(i)の内積r_d(i)の説明図。
【図４】１ビットごとの処理によるアダプティブフィルタ部の構成図。
【図５】本発明による干渉除去のシミュレーション結果を示す図。
【図６】従来のスペクトル拡散通信システムの構成図。
【符号の説明】
１ アンテナ
２ 同期回路
３ 乗算回路
４ 低域フィルタ（ＬＰＦ）
５ 非希望信号発生回路
６ タップ係数制御回路
７ アダプティブフィルタ部
８ 減算回路
９ 標本化回路
１０ 乗算回路
１１ リミタ
１２ 比較器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an interference cancellation apparatus, a radio terminal apparatus, and an interference cancellation method. In particular, in the code division multiple access (CDMA) or spread spectrum multiple access (SSMA) communication system or the like, the present invention does not affect a desired signal from an received signal, and only an interference signal component is applied to an adaptive filter (adaptive filter). ), And an interference cancellation apparatus, a radio terminal apparatus, and an interference cancellation method that removes interference signal components present together with the desired signal subjected to spread demodulation by subtraction.
[0002]
[Prior 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 spread code generation circuit 104, and an antenna 105. The receiver 200 includes a data reception circuit 201, a primary demodulation circuit 202, a secondary demodulation circuit 203, a synchronization circuit 204, and an antenna 205.
[0003]
Where d ₁ (t) is the data transmitted by the local station, a ₁ (t) is the first-order modulated signal, s ₁ (t) is the second-order modulated signal, the spread spectrum signal, and c ₁ ( t) represents a code for spreading the 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 a state where a plurality of signals coexist in the same frequency band. Since each signal is modulated with a spreading code having orthogonal characteristics, a signal including a code that does not match the desired spreading code is excluded during demodulation. However, since they are not completely orthogonal, there are a small number of cross-correlation values, and the sum thereof increases as the number of other station signals increases, limiting the number of simultaneous communication stations.
[0005]
Next, the operation of the spread spectrum communication system will be described with reference to the drawings. In the transmitter 100, data d ₁ (t) transmitted from the data transmission circuit 101 is data that randomly takes +1 and −1, and the primary modulation by 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 )
Where f _c is the carrier frequency and θ ₁ represents the phase of the carrier wave.
[0006]
Here, c ₁ (t) is a spreading code that takes +1 and −1. Secondary modulation circuit 103, the multiplication of this spread code c ₁ (t) and the primary modulation signal a ₁ (t) subjected to secondary modulation, 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 )
[0007]
The spread spectrum signal from the other 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]
[Expression 1]

Here, n (t) is receiver noise.
[0009]
In the following description, noise will be omitted for convenience.
The synchronization circuit 204 establishes synchronization of the spread code c ₁ (t) included in the received signal r (t), and supplies the code from the synchronization circuit 204 to the secondary demodulation circuit 203. The secondary demodulation circuit 203 multiplies the received signal r (t) and the code c ₁ (t), and obtains a ₁ (t) by the following calculation.
[0010]
[Expression 2]

[0011]
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 so,
The relationship c ₁ (t) × c ₁ (t) = 1 is used.
[0012]
The first term is a modulation signal of the desired signal, and the second term is a term that contributes as a noise component due to the other station signal. 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 other station signal, and is not orthogonal, so it is zero even if it integrates for one period It must remain a broadband signal.
In primary demodulator 202, and outputs the data d ₁ (t) demodulates a ₁ a (t).
[0013]
[Problems to be solved by the invention]
Conventionally, the interference removal capability inherently provided in this system is to perform interference removal by utilizing the orthogonality of the code that spreads the spectrum. However, in these newly proposed interference cancellation methods, all received signals are handled and processed individually, so that the configuration is complicated and it is difficult to apply to mobile terminals and the like.
[0014]
SUMMARY OF THE INVENTION In view of the above points, the present invention aims to realize application to a small device such as a portable terminal or a system that does not require much processing load by simplifying the circuit and simplifying the overall configuration as much as possible. And Another object of the present invention is to increase the number of simultaneous communication stations and improve communication quality by removing interference components from other station signals.
[0015]
[Means for Solving the Problems]
According to the first solution of the present invention,
A multiplication circuit that multiplies the sampled received signal by the spreading code of the desired signal;
A tap coefficient control circuit for outputting tap coefficients;
An adaptive filter unit for obtaining a combined signal related to the desired signal and the undesired signal based on the inner product of the tap coefficient given by the tap coefficient control circuit and the sampled received signal;
Provided is an interference canceller comprising: a subtractor circuit that subtracts a combined signal obtained by the adaptive filter unit from an output of the multiplier circuit to obtain a desired received signal.
[0016]
According to the second solution of the present invention,
An antenna for receiving a spread spectrum signal;
The interference cancellation apparatus described above that inputs a signal received by the antenna;
A determination circuit for determining received data from the output of the interference canceller;
A wireless terminal device comprising:
[0017]
According to the third solution of the present invention,
Multiply the sampled received signal by the spreading code of the desired signal,
By weighting the sampled received signal with a tap coefficient, a composite signal for the desired signal and the undesired signal is obtained,
An interference cancellation method is provided in which a desired received signal is obtained by subtracting the combined signal from the multiplied output.
[0018]
According to the fourth solution of the present invention,
A multiplication procedure for multiplying the sampled received signal by the spreading code of the desired signal;
Tap coefficient control procedure for outputting tap coefficients;
Based on the inner product of the tap coefficient given by the tap coefficient control procedure and the sampled received signal, the reception of a certain bit represented by a vector composed of N chips for each of the desired signal and the plurality of undesired signals. An adaptive filter procedure for obtaining a combined signal for the desired signal and the undesired signal by weighting the signal with a tap coefficient composed of N elements;
There is provided a radio terminal apparatus including an interference cancellation program for causing a computer to execute a subtraction procedure for subtracting a synthesized signal obtained by the adaptive filter procedure from an output of the multiplication procedure to obtain a desired received signal.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration diagram of a wireless terminal apparatus provided with an interference wave removing apparatus according to the present invention. Here, it is assumed that the number of simultaneous communication stations is K and that the desired signal is synchronized.
This 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, and multiplication. A circuit 10, a limiter 11, and a comparator 12 are provided.
[0020]
The synchronization circuit 2 detects the synchronization of the spread spectrum signal received from the antenna 1. The multiplier circuit 3 multiplies the spread spectrum signal received from the antenna 1 and the carrier wave 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. The multiplication circuit 10 multiplies the reception signal from the sampling circuit 9 and the spread code of the desired signal output from the synchronization circuit 2. The adaptive filter unit 7 obtains a synthesized signal related to the undesired signal by multiplying and synthesizing based on the tap coefficient given by the tap coefficient control unit 6 and the signal from the sampling circuit 9. 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 received signal. The limiter 11 limits the reception signal obtained by the subtraction circuit 8. The comparator 12 outputs an error signal obtained by taking the difference between the input and output of the limiter 11. The tap coefficient control unit 6 outputs the tap coefficient, and controls the tap coefficient based on the output of the comparator 12.
[0021]
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]

[0023]
Here, k = 1 is determined as a desired station signal (desired signal). In addition, k = 2, 3, and -K are undesired station signals (unwanted signals). The multiplier circuit 3 multiplies the received signal by the carrier wave cos (2πf _c t + θ ₁ ) of the desired signal that has been synchronized by the synchronization circuit 2. Next, the difference component is extracted by the low-pass filter 4 as follows.
[0024]
[Expression 4]

[0025]
The low pass filter 4 converts the desired signal component and the undesired signal component as baseband signals. The next sampling circuit 9 samples at a chip speed m (m = 1, 2, − − −) times. In the following description, m = 1 is set for convenience.
The output signal r _b (i) of the sampling circuit 9 is a vector composed of N = T _b / T _c chips, where T _b is 1 bit time and T _c is 1 chip time, as follows: expressed. Here, the argument i means the i-th bit signal.
[0026]
[Equation 5]

The tap coefficient w (i) is composed of N elements as follows.
[0027]
[Formula 6]

The signal r _b (i) weighted with the tap coefficient w (i) is output as y (i) by the following calculation.
[0028]
[Expression 7]

On the other hand, the output signal r _b (i) of the sampling circuit 9 is multiplied by the spreading code c ₁ (i) of the desired signal output from the synchronization circuit 2 by the multiplication circuit 10, and spread demodulation is performed. However, c ₁ (i) = [c _1.i (0), c _1.i (1),..., C _1.i (N−1)] ^T. The output signal r _d (i) of the multiplier circuit 10 is expressed as follows.
[0029]
[Equation 8]

[0030]
This signal r _d (i) includes interference components (r _di ⁽²⁾ , r _di ⁽³⁾ ,..., R _di ^(K) ) from other stations. If the signal y (i) output from the adaptive filter unit 7 can represent this interference component, only desired signal data can be obtained. As a result, the subtracting circuit 8 subtracts the signal y (i) from the signal r _d (i) to obtain the signal z (i). The 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, but changes if the interference component is included. Therefore, the signal z (i) is limited by the limiter 11 to obtain the predicted value d ^ ₁ (i) of the data, and at the same time, 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 that this error signal becomes small.
Specifically, the tap coefficients are controlled so that y _i (1) = 0, y _i (m) = r _di ^(m) , m = 2, 3, −−, K. Note that “^” is added immediately above the characters / symbols as shown in the formulas and figures, but is written next to the characters / symbols for convenience.
[0031]
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 , U ₄ .
The signal r _b (i) is expressed as 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). Moreover, it is as follows when expressed in mathematical formulas.
[0033]
[Expression 10]

[0034]
Each component of the undesired signals U _{1 to} U ₄ becomes interference noise and interferes with the desired signal D. Further, the tap coefficient control unit 6 inputs the error signal e (i), corrects the correction calculation result to the tap coefficient w (i-1) one step before, and outputs it as w (i). Using this tap coefficient w (i), y (i) is calculated, and the error e (i + 1) is obtained again. In order to reduce this error, w (i) is corrected again to obtain w (i + 1) and supplied to the adaptive filter unit 7. Various algorithms such as LMS (least mean square algorithm) can be applied as an algorithm for updating the tap coefficient. The tap coefficient w (i) was obtained as follows.
[0035]
[Expression 11]

Therefore, taking the inner product of the signal r _b (i) and the tap coefficient w (i), y (i) is as follows.
[0036]
[Expression 12]

In this calculation, the portion corresponding to the desired signal component is the first term of the result and is substantially 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). This can be expressed by the following formula, and it can be seen that the interference component of the existing undesired signal is almost removed as a noise component.
[0037]
[Formula 13]

[0038]
FIG. 4 shows a configuration diagram of the adaptive filter unit. The adaptive filter unit 7 includes delay circuits 71-0 to 71- (N-2), multiplication circuits 72-0 to 72- (N-2), and a sum circuit 73. The signal r _b (i) output from the sampling circuit 9 is input to the adaptive filter unit 7. The signal r _b (i) is delayed one chip at a time by the delay circuits 71-0 to 71- (N-2), and the components r _bi (N−1) to r _bi (0) are output.
[0039]
[Expression 14]

Each component is multiplied by a corresponding tap coefficient w (i) by multiplication circuits 72-0 to 72- (N-1). The components are then synthesized by the sum circuit 73 and y (i) is output.
[0040]
FIG. 5 is a diagram showing a simulation result of interference removal according to the present invention. The horizontal axis is the number of simultaneous communication stations, and the vertical axis is the average BER (Bit Error Rate). In this example, the signal-to-noise ratio Eb / No is set to 20 dB, and the Gold code is used as the code. The processing gain is 31. The error rate according to the prior art is indicated by a solid black solid line, and the average error rate when the present invention is adopted is indicated by a solid white solid line. By employing the present invention, the number of simultaneous communication stations can be increased.
[0041]
The present invention can be applied to an appropriate modulation method in addition to BPSK. For example, when applied to QPSK, the circuit of the present invention may be provided for the in-phase component and the quadrature component.
The present invention may include a microprocessor or a CPU, and the configuration of each circuit for removing interference may be realized as software processing by the microprocessor / CPU. The present invention may also be provided as a wireless terminal device including an interference removal program for causing a computer to execute each of these procedures. Furthermore, the present invention can be provided by a computer-readable recording medium in which an interference cancellation program is recorded, a program product that includes the interference cancellation program and can be loaded into an internal memory of a computer, a microprocessor including the program, and the like. .
[0042]
【The invention's effect】
According to the present invention, as described above, by simplifying the circuit and simplifying the overall configuration as much as possible, it is possible to realize application to a small device such as a portable terminal or a system that does not require much processing burden. . Further, according to the present invention, the number of simultaneous communication stations can be increased and communication quality can be improved by removing interference components from other station signals.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a wireless terminal device including an interference wave canceling device according to the present invention.
FIG. 2 is an explanatory diagram of signals constituting the signal r _b (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 by 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]
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 unit 8 Subtraction circuit 9 Sampling circuit 10 Multiplication circuit 11 Limiter 12 Comparator

Claims (7)

A sampling unit that samples a baseband signal obtained from the received spread spectrum signal and outputs the sampled received signal;
A multiplier that multiplies the sampled received signal from the sampling unit by the spreading code of the desired signal;
A tap coefficient control unit that outputs a tap coefficient;
An adaptive filter unit for obtaining a combined signal including a desired signal component and an undesired signal component based on an inner product of a tap coefficient given by the tap coefficient control unit and a sampled received signal from the sampling unit;
A subtracting unit that subtracts the synthesized signal obtained by the adaptive filter unit from the output of the multiplying unit to obtain an output signal ;
A limiter for limiting the output signal obtained by the subtracting unit;
A comparator that outputs an error signal between the input and output of the limiter ;
The tap coefficient control unit inputs an error signal between the input and output of the limiter output from the comparator, and controls the tap coefficient to reduce the error signal so that the desired signal of the combined signal An interference canceling apparatus in which the component is made substantially zero and the undesired signal component becomes an interference component from another station so that the interference component is almost removed . The ADAPTIVE Boeuf filter unit, the desired signal and a plurality of non-desired signal, the reception signal of a certain bit, each represented by a vector composed of N chips, be weighted by tap coefficients consisting of N elements The interference cancellation apparatus according to claim 1, wherein a combined signal is output by the operation. A synchronizer for detecting synchronization of the received spread spectrum signal;
A multiplier that multiplies the received spread spectrum signal by the carrier of the desired signal output from the synchronization unit;
A low-pass filter that extracts a baseband signal from the output from the multiplier;
Further comprising a,
The interference cancellation apparatus according to claim 1 , wherein the sampling unit samples a baseband signal from the low-pass filter .   The sampling unit outputs a sampled received signal represented by a vector composed of N chips based on 1 bit time and 1 chip time,
  The tap coefficient control unit outputs tap coefficients of N elements,
  The adaptive filter unit includes:
  A plurality of delay circuits for delaying the sampled received signal by one chip and outputting each component of the sampled received signal;
  A plurality of multiplication circuits for multiplying each component by a corresponding tap coefficient;
  After multiplication, a sum circuit that combines the components and
The interference cancellation apparatus according to claim 1, comprising: An antenna for receiving a spread spectrum signal;
The interference cancellation apparatus according to any one of claims 1 to 4 , wherein a signal received by the antenna is input;
A determination unit for determining received data from the output of the interference canceller;
A wireless terminal device. The baseband signal obtained from a received spread spectrum signal by sampling, and outputs the received signal samples,
Multiply the sampled received signal by the spreading code of the desired signal,
Based on the inner product of the given tap coefficient and the sampled received signal, a composite signal including a desired signal component and an undesired signal component is obtained.
From the result of the multiplication, the obtained synthesized signal is subtracted to obtain an output signal,
Limit the desired output signal,
Output error signals before and after the limit,
The error signal before and after the restriction is input, the tap coefficient is controlled, and the desired signal component of the combined signal is made substantially zero and the undesired signal component is made an interference component from another station so that the error signal becomes small. An interference canceling method in which interference components are substantially removed . A sampling procedure for sampling a baseband signal obtained from a received spread spectrum signal and outputting a sampled received signal;
A multiplication procedure for multiplying the received signal sampled in the sampling procedure by the spreading code of the desired signal;
An adaptive filter procedure for obtaining a composite signal including a desired signal component and an undesired signal component based on an inner product of a given tap coefficient and the received signal sampled in the sampling procedure;
A subtraction procedure for obtaining an output signal by subtracting the synthesized signal obtained by the adaptive filter procedure from the output of the multiplication procedure;
A limit procedure for limiting the output signal determined by the subtraction procedure;
A comparison procedure for outputting an error signal between the input and output of the limit procedure;
An error signal between the input and output of the limit procedure output from the comparison procedure is input, the tap coefficient is controlled, and the desired signal component of the combined signal is made substantially zero so that the error signal becomes small, and In order to cause an undesired signal component to become an interference component from another station, to substantially eliminate the interference component, and to cause the computer to execute a tap coefficient control procedure for outputting the tap coefficient A wireless terminal device including an interference cancellation program.

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