JP2004320088A - Spread spectrum modulated signal generating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spread spectrum modulated signal generating method and an apparatus thereof for generating a signal for spreading having less amplitude variation. <P>SOLUTION: In the apparatus for generating a signal for spreading used for a spread spectrum communication system, a spread code which is excellent in correlative property and has less amplitude variation as a spread code is sampled with one chip and one sample, and this is subjected to discrete Fourier transform to obtain spectrum. Band limitation processing is performed in a frequency band on the basis of this spectrum, the spectrum subjected to the band limitation processing is subjected to inverse Fourier transform to generate a signal for spreading, and spread modulation is performed by using the signal for spreading. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２２】
で表される。ここで、Ｒｓ（τ）のメインローブ（振幅１）から一つ目のサイドローブ（振幅ａ）までの時間をτ_ｄとおいて次のようなＸ（ｔ）を考える。
【００２３】
【数２】

【００２４】
このＸ（ｔ）の自己相関関数Ｒｘ（τ）を求めると、
【００２５】
【数３】

【００２６】
となる。数３の第１項はもとの拡散符号の時間波形ｓ（ｔ）の自己相関関数Ｒｓ（τ）そのものである。第２項はＲｓ（τ）をτｄだけ左にずらして振幅をａ倍したものであり、これによりもとの自己相関関数Ｒｓ（τ）の左側のサイドローブが抑えられる。同じように第３項はＲｓ（τ）をτ_ｄだけ右にずらして振幅をａ倍したものであり、これによりもとの自己相関関数Ｒｓ（τ）の右側のサイドローブが抑えられる。したがって、Ｘ（ｔ）を求めることで、ある程度帯域が制限され、かつ自己相関関数のサイドローブが抑えられた新たな拡散用信号を得ることができる。
【００２７】
図４に遅延加算処理前後での自己相関及び電力スペクトルを矩形の拡散符号の特性とともに示す。ここで、遅延加算処理前の帯域制限をロールオフファクタ０．３、また遅延加算処理前後でサイドローブを半分に抑えるように設定している。遅延加算処理を行うことで、電力スペクトルの中央付近が平坦でなくなるが、帯域外スペクトルは広がることなく、自己相関関数のサイドローブも抑えられている。さらにサイドローブを抑えるように設定すると、電力スペクトルの振幅変動は大きくなるので、サイドローブの抑圧の設定は、それらの兼ね合いによる。
【００２８】
以上により，遅延加算処理を行うことで帯域外スペクトル特性と自己相関特性に優れた拡散用信号を得られることがわかる。
【００２９】
次に、相互相関特性を改善するための変形Ｍ系列に加えるＤＣバイアス付加部２の作用について述べる。
【００３０】
Ｍ系列にＤＣバイアスを加えて変形Ｍ系列を作る際のバイアス値αは以下の式で求めることができる。
【００３１】
【数４】

【００３２】
数４より、ＤＣバイアス値αは２種類考えられる。そこで、元のＭ系列をｂ_１（ｔ），ｂ_２（ｔ）， ＤＣバイアス値をα_１，α_２とすると、２種類のバイアス付Ｍ系列は
【００３３】
【数５】

【００３４】
【数６】

【００３５】
と表される。ｃ_１（ｔ）とｃ_２（ｔ）の相互相関関数Ｒ_{ｃ １２}（τ）は、ｂ_１（ｔ）とｂ_２（ｔ）の相互相関関数をＲ_{ｂ １２}（τ）とすると
【００３６】
【数７】

【００３７】
となる。ここでα_１＝α_２、つまりバイアス値が１種類の場合、数７は、
【００３８】
【数８】

【００３９】
となり、バイアスを付加することにより自己相関の部分相関はなくなるものの、相互相関値が増加する。一方、α_１≠α_２、つまりバイアス値が２種類の場合、同じように数７は、
【００４０】
【数９】

【００４１】
となり、逆に相互相関値が減少する。これより、マルチコード多重時では、α_１とα_２を半々で使い分けることによって、バイアス付加による相互相関関数の劣化を防ぐことができ、自己相関関数と合わせて、相関特性の良好な拡散符号が得られる。図５にバイアス付加による相互相関値の変化の様子を示す。相互相関値の大きさはバイアスが１種類の場合、なしの場合、２種類の場合の順に小さくなっており、式で示したとおりであることが分かる。
【００４２】
なお、上記実施の形態では、スペクトル情報抽出部５で生成されたスペクトルに対して、さらに帯域制限処理などを行うようにしたが、このような帯域制限処理を施すことなく、図２に示すように、そのスペクトルに関する情報をメモリ１７に蓄積し、これをＯＦＤＭのパイロット信号として用いても良い。図２において、図１と同じ符号を付したものは、図１の説明で説明したものと同じ構成を有する。このようにすれば、このＯＦＤＭのパイロット信号は、ほぼ定包絡線状でありながら相関特性に優れたものとなる。このため、非線形ひずみの影響をうけにくくなり、また、パイロット信号を用いて同期をとる場合に、相関特性が優れたものとなる。
【００４３】
【実施例】
図６にシミュレーションシステムの構成を示す。送信側でランダムな４値のシンボルデータにパイロットシンボルを付加し、ＱＰＳＫ（Ｑｕａｔｅｒｎａｒｙ Ｐｈａｓｅ Ｓｈｉｆｔ Ｋｅｙｉｎｇ）により一次変調した後、拡散用信号を用いて二次変調を行い、受信側で逆拡散及びデータ復調を行う。ユーザ１の系統を希望局とし、他のユーザは干渉局とする。
【００４４】
表１に拡散用信号の諸元を示す。
【００４５】
【表１】

【００４６】
従来方式は符号長３１のＭ系列（１，−１の矩形波）にフィルタリングを行うもので、これを基準とする。それぞれの方式における評価の対象は、比較方式１では周波数領域でのフィルタリングの処理の効果、比較方式２、３ではＤＣバイアス付加の効果、提案方式では遅延加算処理の効果である。そして最後に従来方式と提案方式の間で特性評価を行う。ロールオフファクタについては、フィルタリングによる劣化が少ない値（０．５）に設定したが、提案方式では遅延加算処理により自己相関のサイドローブは抑えられることからより厳しい値（０．３）に設定した。
【００４７】
シミュレーションの実施法としては、今回は伝送路をガウス伝送路とする。受信側では受信信号のレベルは等レベルとし、また同期捕捉、位相補償ともに理想的であるとする。このときのビット当りのＳＮ比対ビット誤り率（ＢＥＲ）特性を算出する。
【００４８】
図７に拡散用信号としてＭ系列を用い、ロールオフフィルタ０．５を用いた場合のＥ_ｂ／Ｎ_０対ＢＥＲ特性を示す。ユーザ数１の特性はＱＰＳＫの理論値に一致している。
【００４９】
図８に比較方式１として拡散用信号にＭ系列を用い、周波数領域でのフィルタリングを行った場合の特性を示す。図７の特性に比べて若干特性が良くなっている。この原因は従来方式のように帯域制限による電力損失がないためかと思われる。
【００５０】
図９、図１０に比較方式２、３の特性を示す。これらは、提案方式から遅延加算処理による自己相関の改善が適用されていない場合の特性である。図９は図８と比較して、劣化しており、ユーザ数が増えるに従ってその大きさは顕著になっている。一方、図１０は図９と比較して大幅に改善されており、さらに図８よりも良くなっている。これは図５に示したＤＣバイアス付加による、希望信号と干渉信号との相互相関の特性と一致しており、相互相関は図９、図８、図１０の順に良くなっている。
【００５１】
図１１に提案方式の拡散用信号を用いた場合の特性を示す．このとき図１０との違いは遅延加算処理による自己相関改善があるかないかということである．図１０と比較して、特性に劣化はみられず、従来方式（図７）よりも改善している。自己相関改善処理でのＢＥＲ特性の劣化はないということが分かった。以上より、提案方式ではＢＥＲ特性を劣化させることなく自己相関を改善することができる。
【００５２】
【発明の効果】
本発明は、スペクトル拡散通信方式に用いられる拡散用信号を生成するものにおいて、拡散符号を１チップ１サンプルで標本化し、これを離散フーリエ変換してスペクトルを求める。そして、このスペクトルに基づいて周波数領域にて帯域制限処理を行い、この帯域制限処理されたスペクトルを逆フーリエ変換することで拡散用信号を生成し、この拡散用信号を用いて拡散変調を行うようにしたものである。これにより、拡散符号として相関特性に優れ、かつ、振幅変動の少ないものを使用した場合、得られた拡散用信号は帯域制限が良好であって相関特性に優れ、また、振幅変動の少ないものになる。
【図面の簡単な説明】
【図１】本実施形態における信号発生用の波形、スペクトルデータの算出を示す機能ブロック図
【図２】本実施形態におけるＯＦＤＭのパイロット信号を生成する機能ブロック図
【図３】同形態における周波数領域処理による拡散用信号生成過程図
【図４】同形態における遅延加算による自己相関特性と電力スペクトル図
【図５】同形態における変形Ｍ系列においてＤＣバイアス印加方法と相関特性図
【図６】実施例におけるシミュレーションシステム図
【図７】実施例におけるビット誤り率特性（従来方式の場合）図
【図８】実施例におけるビット誤り率特性（比較方式１の場合）図
【図９】実施例におけるビット誤り率特性（比較方式２の場合）図
【図１０】実施例におけるビット誤り率特性（比較方式３の場合）図
【図１１】実施例におけるビット誤り率特性（提案方式の場合）図
【符号の説明】
１・・・拡散符号発生部
２・・・バイアス付加部
３・・・標本化部
４・・・離散フーリエ（ＤＦＴ）変換部
５・・・スペクトル情報抽出部
６・・・帯域制限処理部
７・・・逆高速フーリエ変換（ＩＦＦＴ）部
８・・・電力スペクトル算出部
９・・・逆フーリエ（ＩＦＦＴ）部
１０・・・算出部
１１・・・振幅調整・遅延加算処理部
１２・・・加算部
１６・・・メモリ
２０・・・変調部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to wireless communication, and more particularly, to a wireless communication technique suitably used in, for example, a spread spectrum communication system.
[0002]
[Prior art]
In the direct spread spectrum method, a binary rectangular wave is often used as a spread code, and the spectrum of the modulated signal spreads out of the band. Therefore, there are problems in adjacent channel interference and frequency use efficiency. Out-of-band spectra have been suppressed using filters to make the spectral distribution of the modulated signal flat within the transmission band.
[0003]
However, there is a problem that the correlation characteristic is degraded when a strong band restriction is applied, and a method of restricting the band without deteriorating the correlation characteristic has been studied. Patent Literature 1 and the like exist regarding a method of limiting the bandwidth without deteriorating the correlation characteristic.
[0004]
[Patent Document 1]
JP-A-5-327656
According to Patent Document 1, in order to obtain a spreading signal having a high band utilization rate by synthesizing sine waves of a plurality of frequencies, a phase of each frequency is determined by a component dependent on a random sequence An and a period of 0 to T of one cycle. Is set as the sum of the specific values Bn, and the degradation of the correlation characteristic is suppressed even when the band is limited.
[0006]
[Problems to be solved by the invention]
However, this method has a problem that the amplitude of the spreading signal is not constant. For this reason, if the amplitude fluctuation is large, there arises a problem that a linear amplifier that does not cause nonlinear distortion must be used.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a spread spectrum modulation signal generating method and an apparatus for generating a spread signal having small amplitude fluctuations by focusing on such a problem.
[0008]
[Means for Solving the Problems]
That is, in order to solve the above-mentioned problems, the present invention is to generate a spread signal used in a spread spectrum communication system. In this method, a spread code is sampled by one sample per chip, and a discrete Fourier transform is performed to obtain a spectrum. . Then, a band limiting process is performed in the frequency domain based on the spectrum, a signal for spreading is generated by performing an inverse Fourier transform on the spectrum subjected to the band limiting process, and spread modulation is performed using the signal for spreading. It was made.
[0009]
With this configuration, when a spreading code having excellent correlation characteristics and a small amplitude fluctuation is used, the obtained spreading signal has a good band limitation and excellent correlation characteristics, and has a small amplitude fluctuation. Become something. This eliminates the need to use a linear amplifier that does not cause nonlinear distortion.
[0010]
In addition, the spread signal generated in this manner is configured to be subjected to delay addition processing.
[0011]
With this configuration, it is possible to obtain a spreading signal having better autocorrelation.
[0012]
Further, in another invention, a spread code is sampled by one sample per chip, and a discrete Fourier transform is performed on the sample to obtain a spectrum, and this spectrum information is stored in a memory. Then, the spread spectrum signal is generated by using the stored spectrum information as an OFDM modulation input.
[0013]
With this configuration, when a spread spectrum modulation signal is used as an OFDM pilot signal, the OFDM pilot signal has a substantially constant envelope shape but excellent correlation characteristics. For this reason, it is less susceptible to nonlinear distortion. Also, when synchronization is achieved using a pilot signal, the correlation characteristics are improved.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described. FIG. 1 shows an overall functional block diagram of the spreading signal generation system in the present embodiment.
[0015]
The spectrum information extracting unit 5 includes a spreading code generating unit 1 that generates a spreading code (for example, an M-sequence) having excellent correlation characteristics and small amplitude fluctuation, a sampling unit 3, and a discrete Fourier transform (DFT) unit 4. . Then, a DC bias is applied from a DC bias applying unit 2 to the spreading code generating unit 1, and the signal converted into the modified M-sequence is replaced by a sampling unit 3 with a discrete impulse train of one sample per chip. To extract spectrum information for generating a signal for spreading by performing a discrete Fourier transform.
[0016]
Further, the band limitation processing unit 6 has a function of limiting the band in the frequency domain. Specifically, as shown in FIG. 3B, a component of “0” is inserted into the spectrum extracted earlier to generate a band-limited spectrum as shown in FIG. 3C. The inverse fast Fourier transform (IFFT) unit 7 performs an inverse Fourier transform on the band-limited spectrum to generate a spreading signal. The power spectrum calculation unit 8 obtains a power spectrum from the frequency spectrum subjected to the band limitation processing. The IFFT unit 9 performs an inverse Fourier transform on the power spectrum to obtain an autocorrelation characteristic. The calculation unit 10 calculates a delay time τd and an amplitude magnification a, which are parameters for performing the delay addition. The amplitude adjustment / delay addition processing section 11 performs delay addition processing on the spreading signal generated by performing the inverse Fourier transform in the IFFT section 7. The addition unit 12 adds the original time axis signal and the output from the amplitude adjustment / delay addition processing unit 11.
[0017]
On the other hand, the modulator 20 spreads information to be transmitted based on the spreading signal thus obtained. The spreading signal may be stored in the memory 13 and output from the memory 13 each time modulation is performed. Further, the spreading signal may be Fourier-transformed once by the FFT unit 14 and stored in the memory 15, and may be inversely Fourier-transformed by the IFFT unit 16 before being output to the modulation unit 20.
[0018]
FIG. 3 shows processing results of the spectrum information extracting unit 5, the band limiting unit 6, and the IFFT unit 7 in the block diagram of FIG. FIG. 3A shows a signal in which a binary spreading code (M sequence) is replaced with an impulse train by one sample per chip. FIG. 3A shows an example of 31 generally used as a code length. FIG. 3B shows a discrete Fourier transform of this signal. Since the autocorrelation is an impulse function, the frequency spectrum is a line spectrum having the same amplitude. In this case, the code length is 31 and it is difficult to use the FFT method. However, if one 0 is inserted at the 17th line spectrum, the number of line spectra becomes 32, and IFFT can be applied. Further, to perform band limitation by the rectangular filter, 0 is further inserted, the number of sampling points is increased, and the spectrum after band limitation is shown in FIG. FIG. 3D shows a signal obtained by IFFT of the signal, and a smooth waveform obtained by filtering is obtained. As can be seen from this figure, it is possible to obtain a spreading signal having relatively small amplitude fluctuation.
[0019]
Next, processing contents of the amplitude adjustment / delay addition processing unit 11, the calculation unit 10, and the addition unit 12 for improving the autocorrelation characteristic will be described.
[0020]
First, assuming that the time waveform (period T 2) of the band-limited spread code is s (t 2), the autocorrelation function Rs (τ) is given by the following equation (1).
[0021]
(Equation 1)

[0022]
Is represented by Here, the following X (t) is considered, where τ _d is the time from the main lobe (amplitude 1) of Rs (τ) to the first side lobe (amplitude a).
[0023]
(Equation 2)

[0024]
When the autocorrelation function Rx (τ) of X (t) is obtained,
[0025]
[Equation 3]

[0026]
It becomes. The first term of Equation 3 is the autocorrelation function Rs (τ) of the original spread code time waveform s (t). The second term is obtained by shifting Rs (τ) to the left by τd and amplifying the amplitude by a, thereby suppressing the left side lobe of the original autocorrelation function Rs (τ). The third term in the same way are those the amplitude multiplied by a shifted Rs a (tau) to the right by tau _d, thereby suppressing the original right side lobes of the autocorrelation function Rs (tau). Therefore, by obtaining X (t), it is possible to obtain a new spreading signal in which the band is limited to some extent and the side lobe of the autocorrelation function is suppressed.
[0027]
FIG. 4 shows the autocorrelation and the power spectrum before and after the delay addition process together with the characteristics of the rectangular spreading code. Here, the band limitation before the delay addition processing is set so that the roll-off factor is 0.3, and the side lobe before and after the delay addition processing is reduced to half. By performing the delay addition process, the vicinity of the center of the power spectrum is not flat, but the out-of-band spectrum does not spread and the side lobe of the autocorrelation function is suppressed. If the setting is made so as to further suppress the side lobes, the amplitude fluctuation of the power spectrum becomes large. Therefore, the setting of the suppression of the side lobes depends on the balance between them.
[0028]
From the above, it can be seen that by performing the delay addition process, a spreading signal having excellent out-of-band spectral characteristics and autocorrelation characteristics can be obtained.
[0029]
Next, the operation of the DC bias adding unit 2 added to the modified M-sequence for improving the cross-correlation characteristic will be described.
[0030]
The bias value α for applying a DC bias to the M sequence to generate a modified M sequence can be obtained by the following equation.
[0031]
(Equation 4)

[0032]
From Equation 4, two types of DC bias values α can be considered. Therefore, assuming that the original M sequence is b ₁ (t), b ₂ (t) and the DC bias values are α ₁ and α ₂ , the two types of biased M sequences are as follows:
(Equation 5)

[0034]
(Equation 6)

[0035]
It is expressed as The cross-correlation function R _{c 12} (τ) between c ₁ (t) and c ₂ (t) is given by letting the cross-correlation function between b ₁ (t) and b ₂ (t) be R _{b 12} (τ).
(Equation 7)

[0037]
It becomes. Here, when α ₁ = α ₂ , that is, when there is one kind of bias value, Expression 7 becomes
[0038]
(Equation 8)

[0039]
By adding a bias, the partial correlation of the autocorrelation disappears, but the cross-correlation value increases. On the other hand, when α ₁ ≠ α ₂ , that is, when there are two kinds of bias values, similarly, Expression 7 is
[0040]
(Equation 9)

[0041]
And conversely, the cross-correlation value decreases. Than this, in the multi-code multiplexing, by selectively using the alpha ₁ and alpha ₂ in half and half, it is possible to prevent deterioration of the cross-correlation function by the bias added, together with the autocorrelation function, good spreading code correlation characteristic can get. FIG. 5 shows how the cross-correlation value changes due to bias addition. It can be seen that the magnitude of the cross-correlation value is smaller in the case of one type of bias, in the case of no bias, and in the case of two types of bias, as shown by the equation.
[0042]
In the above-described embodiment, band limiting processing and the like are further performed on the spectrum generated by the spectrum information extracting unit 5. However, without performing such band limiting processing, as shown in FIG. Alternatively, information on the spectrum may be stored in the memory 17 and used as an OFDM pilot signal. In FIG. 2, components denoted by the same reference numerals as those in FIG. 1 have the same configurations as those described in the description of FIG. By doing so, the pilot signal of this OFDM has excellent correlation characteristics while having a substantially constant envelope shape. For this reason, it is less likely to be affected by nonlinear distortion, and when synchronization is achieved using a pilot signal, the correlation characteristics are excellent.
[0043]
【Example】
FIG. 6 shows the configuration of the simulation system. A pilot symbol is added to random four-valued symbol data on the transmission side, and primary modulation is performed by QPSK (Quaternary Phase Shift Keying), then secondary modulation is performed using a spreading signal, and despreading and data demodulation are performed on the reception side I do. The system of user 1 is a desired station, and the other users are interference stations.
[0044]
Table 1 shows the specifications of the spreading signal.
[0045]
[Table 1]

[0046]
In the conventional method, filtering is performed on an M sequence having a code length of 31 (a rectangular wave of 1, −1), and this is used as a reference. The targets of evaluation in each method are the effect of filtering processing in the frequency domain in the comparison method 1, the effect of DC bias addition in the comparison methods 2 and 3, and the effect of delay addition processing in the proposed method. Finally, characteristics are evaluated between the conventional method and the proposed method. The roll-off factor was set to a value (0.5) that causes little deterioration due to filtering, but the proposed method was set to a stricter value (0.3) because side-lobes of autocorrelation were suppressed by delay addition processing. .
[0047]
As a method of performing the simulation, the transmission path is a Gaussian transmission path this time. On the receiving side, the level of the received signal is assumed to be the same level, and both the synchronization acquisition and the phase compensation are ideal. At this time, the SNR per bit versus bit error rate (BER) characteristic is calculated.
[0048]
FIG. 7 shows the E _b / N ₀ vs. BER characteristics when an M sequence is used as the spreading signal and a roll-off filter 0.5 is used. The characteristic of the number of users 1 matches the theoretical value of QPSK.
[0049]
FIG. 8 shows characteristics in the case where filtering is performed in the frequency domain using an M-sequence as a spreading signal as a comparison method 1. The characteristics are slightly better than those of FIG. This is probably because there is no power loss due to band limitation unlike the conventional method.
[0050]
9 and 10 show the characteristics of the comparison methods 2 and 3. FIG. These are the characteristics when the improvement of the autocorrelation by the delay addition process is not applied from the proposed method. FIG. 9 is deteriorated as compared with FIG. 8, and its size becomes remarkable as the number of users increases. On the other hand, FIG. 10 is greatly improved as compared with FIG. 9, and is better than FIG. This coincides with the cross-correlation characteristic between the desired signal and the interference signal due to the addition of the DC bias shown in FIG. 5, and the cross-correlation is improved in the order of FIGS. 9, 8, and 10.
[0051]
Figure 11 shows the characteristics when the proposed signal for spreading is used. At this time, the difference from FIG. 10 is whether there is any autocorrelation improvement by the delay addition processing. As compared with FIG. 10, no deterioration is observed in the characteristics, which is an improvement over the conventional method (FIG. 7). It was found that the BER characteristics did not deteriorate in the autocorrelation improvement processing. As described above, in the proposed method, the autocorrelation can be improved without deteriorating the BER characteristics.
[0052]
【The invention's effect】
According to the present invention, in generating a spread signal used in a spread spectrum communication system, a spread code is sampled by one sample per chip, and this is subjected to discrete Fourier transform to obtain a spectrum. Then, a band limiting process is performed in the frequency domain based on the spectrum, a signal for spreading is generated by performing an inverse Fourier transform on the spectrum subjected to the band limiting process, and spread modulation is performed using the signal for spreading. It was made. With this, when a spread code having excellent correlation characteristics and a signal with small amplitude fluctuation is used, the obtained spreading signal has a good band limitation and excellent correlation characteristics, and has a small amplitude fluctuation. Become.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing calculation of a signal generation waveform and spectrum data in the present embodiment. FIG. 2 is a functional block diagram of generating an OFDM pilot signal in the present embodiment. FIG. 3 is a frequency domain in the same embodiment. FIG. 4 is a diagram illustrating a process of generating a signal for spreading by processing. FIG. 4 is a diagram illustrating an autocorrelation characteristic and a power spectrum diagram by delay addition in the same embodiment. FIG. FIG. 7 shows a bit error rate characteristic in the embodiment (in the case of the conventional method) FIG. 8 shows a bit error rate characteristic (in the case of the comparison method 1) in the embodiment FIG. 9 shows a bit error in the embodiment FIG. 10 shows the bit error rate characteristic (in the case of the comparison method 3) in the embodiment. FIG. 10 shows the bit error rate characteristic (in the case of the comparison method 3) in the embodiment. Takes bit error rate (in the case of proposed method) Figure EXPLANATION OF REFERENCE NUMERALS
DESCRIPTION OF SYMBOLS 1 ... Spread code generation part 2 ... Bias addition part 3 ... Sampling part 4 ... Discrete Fourier (DFT) transformation part 5 ... Spectrum information extraction part 6 ... Band limitation processing part 7 ··· Inverse fast Fourier transform (IFFT) unit 8 ··· Power spectrum calculation unit 9 ··· Inverse Fourier (IFFT) unit 10 ··· Calculation unit 11 ··· Amplitude adjustment / delay addition processing unit 12 ··· Adder 16—Memory 20—Modulator

Claims (6)

In a spread spectrum modulation signal generating method for generating a spread signal used in a spread spectrum communication system,
Sampling the spreading code with one sample per chip and performing a discrete Fourier transform to obtain a spectrum;
Performing a band limiting process in the frequency domain based on the spectrum;
Generating a signal for spreading by inverse Fourier transforming the band-limited spectrum; and
Performing spread modulation using the spread signal;
A method for generating a spread spectrum modulated signal, comprising: 2. The method according to claim 1, further comprising the step of performing a delay addition process on the spread signal generated in the step of generating the spread signal. In a spread spectrum modulation signal generating method for generating a spread signal used in a spread spectrum communication system,
Sampling the spreading code with one sample per chip and performing a discrete Fourier transform to obtain a spectrum;
Storing information about the spectrum in a memory;
Generating a spread modulation signal using the stored spectrum information as an OFDM modulation input;
A method for generating a spread spectrum modulated signal, comprising: In a spread spectrum modulation signal generator for generating a spread signal used in a spread spectrum communication system,
A spectrum information extractor for sampling the spread code in one sample per chip and performing a discrete Fourier transform on the sample to obtain a spectrum;
A band-limiting processing unit that performs band-limiting processing in the frequency domain based on the spectrum;
An inverse Fourier transform unit that generates a signal for spreading by performing an inverse Fourier transform on the band-limited spectrum;
A modulation unit that performs spread modulation using a signal for spreading,
A spread-spectrum modulated signal generator characterized by comprising: 5. The spread spectrum modulation signal generating apparatus according to claim 4, further comprising a delay addition processing unit that performs a delay addition process on the spread signal generated by the inverse Fourier transform unit that generates the spread signal. In a spread spectrum modulation signal generator for generating a spread signal used in a spread spectrum communication system,
A spectrum information extractor for sampling the spread code in one sample per chip and performing a discrete Fourier transform on the sample to obtain a spectrum;
A memory for storing information about the spectrum,
A modulator for generating a spread modulation signal using the stored spectrum information as an OFDM modulation input;
A spread-spectrum modulated signal generator characterized by comprising:

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