JPH07250107A - Line quality estimation circuit - Google Patents
Line quality estimation circuitInfo
- Publication number
- JPH07250107A JPH07250107A JP6038015A JP3801594A JPH07250107A JP H07250107 A JPH07250107 A JP H07250107A JP 6038015 A JP6038015 A JP 6038015A JP 3801594 A JP3801594 A JP 3801594A JP H07250107 A JPH07250107 A JP H07250107A
- Authority
- JP
- Japan
- Prior art keywords
- signal
- frame
- adpcm
- quality
- line
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Landscapes
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
- Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
- Monitoring And Testing Of Transmission In General (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、ディジタル回線（伝送
路）の品質を推定する回路に関し、特に、フェージング
や、他チャネルの干渉により瞬時に回線品質が変動する
ような無線区間において、回線品質の改善処理をするた
めに必要な回線品質情報を迅速に得ることのできる回線
品質推定回路に係る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for estimating the quality of a digital line (transmission path), and particularly in a wireless section in which the line quality is instantaneously changed due to fading or interference of other channels. The present invention relates to a line quality estimation circuit that can quickly obtain the line quality information necessary for the improvement processing of.
【０００２】[0002]
【従来の技術】信号の伝送を行なう場合、伝送路の状態
の良否によって受信側での信号の信頼度が影響を受け
る。甚だしい場合には、信号が雑音に隠蔽されたり、情
報の欠落を生じたりする。2. Description of the Related Art When a signal is transmitted, the reliability of the signal on the receiving side is affected by the quality of the transmission path. In extreme cases, the signal is hidden by noise or information is lost.
【０００３】伝送路が有線である場合には、通常伝送路
で伝送中の信号が受ける影響として伝送系内部あるいは
外部からの振幅性雑音や、隣接回線からの漏話などがあ
る。伝送路が無線である場合には、その性格上、有線伝
送路に比して、諸外部条件の影響をより受け易い。殊に
それが移動通信の無線伝送路である場合には、移動局の
移動に伴ってフェージングや、他チャネル周波数の干渉
によって、伝送路の伝送品質が時時刻刻変化する。When the transmission line is wired, the influence of the signal being transmitted on the normal transmission line is amplitude noise from inside or outside the transmission system, crosstalk from an adjacent line, and the like. When the transmission line is wireless, by nature, it is more susceptible to external conditions than the wired transmission line. In particular, when it is a wireless transmission line for mobile communication, the transmission quality of the transmission line changes with time due to fading due to movement of the mobile station and interference with other channel frequencies.
【０００４】従って、良好な通信を保つためには、回線
の品質を常時監視していて、当該回線の品質が著しく劣
化した場合には、これを早期に検出し、良好な状態の伝
送路への切り替えを行なうなどの措置を講ずることが必
要となる。Therefore, in order to maintain good communication, the quality of the line is constantly monitored, and when the quality of the line significantly deteriorates, this is detected early and a transmission line in a good state is established. It is necessary to take measures such as switching between.
【０００５】従来、伝送路の品質の良否を推定する方法
として例えば受信レベルによる方式があった。このよう
な受信レベルによる伝送品質の判定には、一定時間内の
受信レベルの平均値が用いられる。Conventionally, as a method for estimating the quality of a transmission line, there is a method based on a reception level, for example. To determine the transmission quality based on such a reception level, an average value of the reception levels within a fixed time is used.
【０００６】受信側でのバースト状信号の受信レベルの
平均値は受信波の包絡線出力を対数圧縮した後で平均値
検出する方法などにより測定することができる。一方、
バースト信号のフレーム中の誤りの有無を検出してこれ
によりフレーム誤り率を算出することにより伝送路の品
質の良否を推定する方式もある。The average value of the reception level of the burst signal on the receiving side can be measured by a method of detecting the average value after logarithmically compressing the envelope output of the received wave. on the other hand,
There is also a method of estimating the quality of the transmission path by detecting the presence or absence of an error in the frame of the burst signal and calculating the frame error rate accordingly.
【０００７】[0007]
【発明が解決しようとする課題】上述したような従来の
回線品質推定方法の内、受信信号レベルによる方式は検
出した受信レベルの平均値が所望のレベルに達している
か否かによって回線品質の良否を推定するものである
が、干渉波が存在する場合には、希望波の受信レベルが
低い場合でも、干渉波が混入して見かけ上の受信レベル
の平均値が基準レベルを超えている場合が生じるため、
正しい回線品質推定が出来ない。と言う問題があった。Among the conventional channel quality estimation methods described above, the method based on the received signal level determines whether the channel quality is good or not depending on whether or not the average value of the detected received levels has reached a desired level. However, if there is an interference wave, even if the reception level of the desired wave is low, the interference wave may mix and the average value of the apparent reception levels may exceed the reference level. To occur,
I cannot estimate the line quality correctly. There was a problem to say.
【０００８】一方、フレーム中の誤りの有無を検出して
フレーム誤り率を検出する方式では、フレーム誤り率を
高精度に推定するためには、比較的長い推定時間（例え
ば、フレーム長５ｍｓｅｃ、最小単位５×１０-3の精度
の場合１秒）を要するため、音声回線のように回線品質
が劣化したとき、即座にこれに対応して回線品質改善処
理を行う必要のある目的のためには適用できない。本発
明は上述のような従来の伝送品質推定方式では実現が困
難であった。本発明は、このような従来の課題に鑑み、
干渉波が存在する場合の伝送路の品質の推定が、可能で
あって、更に、これを短時間で高い精度で推定すること
ができ、回線品質改善の為に必要な情報（例えば、移動
通信方式におけるチャネル切り替えの契機となるべき情
報）を迅速に得ることのできる手段を提供することを目
的としている。On the other hand, in the method of detecting the frame error rate by detecting the presence or absence of an error in the frame, in order to estimate the frame error rate with high accuracy, a relatively long estimation time (for example, frame length 5 msec, minimum Since it takes 1 second in the case of the accuracy of 5 × 10 -3 ), when the line quality deteriorates like a voice line, it is necessary for the purpose that the line quality improvement processing must be immediately performed in response to this. Not applicable. The present invention is difficult to realize with the conventional transmission quality estimation method as described above. The present invention, in view of such conventional problems,
It is possible to estimate the quality of the transmission line in the presence of an interference wave, and further, this can be estimated with high accuracy in a short time, and information necessary for improving the line quality (for example, mobile communication The purpose of the present invention is to provide a means capable of promptly obtaining (information that should trigger channel switching in the method).
【０００９】[0009]
【課題を解決するための手段】本発明によれば、上述の
目的は、前記特許請求の範囲に記載した手段により達成
される。According to the invention, the above mentioned objects are achieved by means of the patent claims.
【００１０】すなわち、請求項１の発明は、適応差分Ｐ
ＣＭ（ＡＤＰＣＭ）音声符号化方式を採るディジタル信
号の伝送系において、ＡＤＰＣＭ復号器の入力側の信号
を受信して、特定の差分を示す符号列からなるサンプル
を検出する手段と、該サンプルをフレームエラー検出信
号が入力されている場合だけ計数する手段と、上記サン
プルの計数値を出力する手段とを設けたことを特徴とす
る回線品質推定回路である。That is, according to the invention of claim 1, the adaptive difference P
In a digital signal transmission system adopting a CM (ADPCM) speech coding system, means for receiving a signal on the input side of an ADPCM decoder and detecting a sample consisting of a code string showing a specific difference, and a frame for the sample It is a circuit quality estimation circuit characterized in that means for counting only when an error detection signal is input and means for outputting the count value of the sample are provided.
【００１１】請求項２の発明は、適応差分ＰＣＭ（ＡＤ
ＰＣＭ）音声符号化方式を採るディジタル信号の伝送系
において、ＡＤＰＣＭ復号器の入力側の信号を受信し
て、一定の差分値以上を示す符号列からなるサンプルを
検出する手段と、該サンプルをフレームエラー検出信号
が入力されている場合だけ計数する手段と、上記サンプ
ルの計数値を出力する手段とを設けたことを特徴とする
回線品質推定回路である。According to a second aspect of the present invention, an adaptive difference PCM (AD
In a digital signal transmission system adopting the PCM) audio encoding system, a means for receiving a signal on the input side of an ADPCM decoder and detecting a sample consisting of a code string showing a certain difference value or more, and a frame for sampling the sample. It is a circuit quality estimation circuit characterized in that means for counting only when an error detection signal is input and means for outputting the count value of the sample are provided.
【００１２】[0012]
【実施例】以下本発明の作用等に関し、一実施例に基づ
いて説明する。図１は本発明の一実施例を示す図であっ
て、数字符号１０は回線品質推定回路、１１はサンプル
検出回路、１２は検出カウンタ、１３は、受信信号とサ
ンプル検出回路の出力との関係、１４はカウンタ値と回
線品質推定信号との関係、１５は回線品質改善回路を表
わしている。The operation and the like of the present invention will be described below based on an embodiment. FIG. 1 is a diagram showing an embodiment of the present invention, in which numeral 10 is a line quality estimation circuit, 11 is a sample detection circuit, 12 is a detection counter, and 13 is a relationship between a received signal and an output of the sample detection circuit. , 14 represents the relationship between the counter value and the line quality estimation signal, and 15 represents the line quality improving circuit.
【００１３】図２は実施例の制御を示す流れ図である。
以下、これらの図に基づいて実施例を説明する。図１に
示すように、本実施例は特定の差分を示す符号列からな
るサンプルを検出するサンプル検出回路１１、及び、そ
のサンプル数をカウントする検出カウンタ１２とから構
成されている。サンプル検出回路１１にはＡＤＰＣＭ４
ビットの受信信号、及び、フレームエラー検出信号が入
力され、フレームエラー検出信号がエラー有りを示した
時のみ、ＡＤＰＣＭ４ビットの受信信号を検出する。FIG. 2 is a flow chart showing the control of the embodiment.
An embodiment will be described below with reference to these drawings. As shown in FIG. 1, this embodiment comprises a sample detection circuit 11 for detecting a sample consisting of a code string indicating a specific difference, and a detection counter 12 for counting the number of samples. ADPCM4 for the sample detection circuit 11
Only when the bit reception signal and the frame error detection signal are input and the frame error detection signal indicates that there is an error, the ADPCM 4-bit reception signal is detected.
【００１４】被検出信号が特定の差分（ここでは例とし
て最大差分とする）を示す場合のみ、検出出力として
“１”を出力し、検出カウンタ１２ではサンプル検出回
路出力が“１”となった場合のみカウンタ値を１インク
リメントする。"1" is output as the detection output only when the detected signal shows a specific difference (here, the maximum difference is taken as an example), and the output of the sample detection circuit in the detection counter 12 becomes "1". Only in this case, the counter value is incremented by 1.
【００１５】１フレーム分のサンプル出力が終了した
ら、カウンタ値の値に応じて回線品質を推定し、推定信
号を回線品質改善回路１５に入力した後、検出カウンタ
１２をリセットする。以下、この動作を繰り返すことに
より、無線区間での回線品質の推定がフレーム単位で可
能となる。When the sample output for one frame is completed, the line quality is estimated according to the value of the counter value, the estimated signal is input to the line quality improvement circuit 15, and then the detection counter 12 is reset. After that, by repeating this operation, it becomes possible to estimate the channel quality in the wireless section on a frame-by-frame basis.
【００１６】次に、本発明の作用効果を確認するために
構成した模擬伝送系について説明する。図３は、本発明
を適用した模擬伝送系の例を示す図であって、３１は音
源、３２はＡ／Ｄ変換器、３３はＡＤＰＣＭ符号器、３
４は誤りを含んだ受信信号、３５はＡＤＰＣＭ復号器、
３６はＤ／Ａ変換器、３７はスピーカ、３８はフレーム
エラー検出信号、３９は品質通知信号１０は回線品質推
定回路を表わしている。同図において、音源１としては
コンパクトディスクに納められた人の声をＣＤプレーヤ
でアナログ信号として再生したものが用いられる。Next, a simulated transmission system constructed to confirm the effects of the present invention will be described. FIG. 3 is a diagram showing an example of a simulated transmission system to which the present invention is applied, where 31 is a sound source, 32 is an A / D converter, 33 is an ADPCM encoder, 3
4 is a received signal containing an error, 35 is an ADPCM decoder,
36 is a D / A converter, 37 is a speaker, 38 is a frame error detection signal, 39 is a quality notification signal 10 is a line quality estimation circuit. In the figure, as the sound source 1, a person's voice stored in a compact disc is reproduced as an analog signal by a CD player.
【００１７】この人声のアナログ信号出力はＡＤ変換器
３２に入力され、１４ビットのリニアのディジタル信号
として出力される。更に、Ａ／Ｄ変換器３２のディジタ
ル信号出力はＡＤＰＣＭ符号器３３に入力され、４ビッ
トのＡＤＰＣＭ符号（差分信号）に符号化した後、無線
回線を経由して、誤りを含んだ受信信号（ＡＤＰＣＭ符
号）に変換される。尚、この時の無線区間の条件は、 １ビット当りの信号電力対１Ｈｚ当りの雑音電力比＝１
５ｄＢ 最大ドップラー周波数＝１５Ｈｚ 遅延分散＝２５０ｎｓｅｃ の２波レイリーフェージング回線とした。The analog signal output of this human voice is input to the AD converter 32 and is output as a 14-bit linear digital signal. Furthermore, the digital signal output of the A / D converter 32 is input to the ADPCM encoder 33, encoded into a 4-bit ADPCM code (difference signal), and then received via the wireless line. ADPCM code). The condition of the wireless section at this time is that the ratio of signal power per bit to noise power per 1 Hz = 1
5 dB Maximum Doppler frequency = 15 Hz Delay dispersion = 250 nsec Two-wave Rayleigh fading line.
【００１８】また、本実施例では、検出すべき特定の差
分として、最大差分を示す“０１１１”と“１０００”
を検出する。誤りを含んだ４ビットのＡＤＰＣＭ符号
は、ＡＤＰＣＭ復号器３５の入力側で４ビット毎に識別
され、最大差分（０１１１又は１０００）を示し、かつ
フレームエラー検出信号３８が入力されている場合だけ
検出カウンタ１２によってカウントされる。更にＡＤＰ
ＣＭ復号器３５から出力された１４ビットのリニアのデ
ィジタル信号は、ＤＡ変換器３６でアナログ信号に変換
され、スピーカ３７から出力される。Further, in the present embodiment, as the specific difference to be detected, "0111" and "1000" showing the maximum difference.
To detect. The 4-bit ADPCM code containing an error is identified every 4 bits at the input side of the ADPCM decoder 35, shows the maximum difference (0111 or 1000), and is detected only when the frame error detection signal 38 is input. It is counted by the counter 12. Further ADP
The 14-bit linear digital signal output from the CM decoder 35 is converted into an analog signal by the DA converter 36 and output from the speaker 37.
【００１９】フレームごとの検出カウンタ１２の値は品
質通知信号３９として出力され、チャネル切り替えその
他の伝送路の良好な品質を確保するための基となる情報
として使用される。図４は音声信号を伝送した場合の４
ビットＡＤＰＣＭ符号の確率分布を示す図である。The value of the detection counter 12 for each frame is output as a quality notification signal 39, and is used as information that serves as a basis for ensuring a good quality of the transmission path such as channel switching. Figure 4 shows 4 when transmitting audio signals
It is a figure which shows the probability distribution of a bit ADPCM code.
【００２０】通常、誤りがない場合に音声をＡ／Ｄ変換
し、４ビットのＡＤＰＣＭ符号器に入力した場合の出力
分布は図４のようになり、このとき、最大差分０１１１
及び１０００となる確率をそれぞれＰ0111及びＰ1000と
すると、“数１”で表わされるようになり、一定時間内
にＳ（サンプル）伝送された場合、最大差分をとる期待
値は“数２”のようになる。Normally, when there is no error, speech is A / D converted and input to a 4-bit ADPCM encoder, the output distribution is as shown in FIG.
If the probabilities of 1 and 1000 are P 0111 and P 1000 , respectively, the result is represented by “Equation 1”, and when S (sample) is transmitted within a fixed time, the expected value that takes the maximum difference is “Equation 2” become that way.
【００２１】[0021]
【数１】 [Equation 1]
【００２２】[0022]
【数２】 [Equation 2]
【００２３】一定長のフレーム内に誤りがある場合に
も、ほとんど音声に影響を与えない程度の誤りであれば
図２の分布と差異は無いため、この場合の最大差分検出
回数の期待値は“数２”と同等になる。Even if there is an error in a frame of a certain length, there is no difference from the distribution of FIG. 2 if the error has almost no effect on speech, so the expected value of the maximum difference detection count in this case is It is equivalent to "Equation 2".
【００２４】一方、回線品質が極度に劣化した場合、瞬
時の符号誤り率は約１／２とみなせ、ＡＤＰＣＭ出力は
０，１のランダムパターン（確率１／２）となるため、
ＡＤＰＣＭ４ｂｉｔが最大差分（０１１１ｏｒ１００
０）をとる確率Ｐ′0111及びＰ′1000は“数３”のよう
になり、一定時間内にＳ（サンプル）伝送された場合の
最大差分検出回数の期待値は“数４”のようになる。On the other hand, when the line quality is extremely deteriorated, the instantaneous code error rate can be regarded as about 1/2, and the ADPCM output becomes a random pattern of 0 and 1 (probability 1/2).
ADPCM 4bit is the maximum difference (0111or100
The probabilities P ′ 0111 and P ′ 1000 that take 0) are as in “Equation 3”, and the expected value of the maximum difference detection number when S (sample) is transmitted within a fixed time is as in “Equation 4”. Become.
【００２５】[0025]
【数３】 [Equation 3]
【００２６】[0026]
【数４】 [Equation 4]
【００２７】これを、先の“数２”と比較した場合約１
２．５倍の最大差分検出が行なわれることになる。図５
は最大差分検出回数とＡＤＰＣＭサンプル誤り数との関
係を示す図であって、上記実施例による実験結果を示す
ものでもある。ここでは、１フレームに４ビットＡＤＰ
ＣＭを４０サンプル含む構成としている。同図におい
て、ＡＤＰＣＭサンプル誤りが増加する程、最大差分検
出回数も増加する事が分かる。When this is compared with the above "Equation 2", it is about 1
The maximum difference detection of 2.5 times will be performed. Figure 5
FIG. 6 is a diagram showing the relationship between the maximum number of times of difference detection and the number of ADPCM sample errors, and also shows the experimental results according to the above-mentioned embodiment. Here, 4-bit ADP per frame
It is configured to include 40 samples of CM. In the figure, it can be seen that as the number of ADPCM sample errors increases, the maximum number of times of difference detection also increases.
【００２８】フレーム中の誤りの有無を検出する回路の
みを用いた場合には、図中のフレームは全て同等（誤り
あり）に扱われるが、最大差分検出回路をカウトンする
事により誤りを含んだフレームの分離が可能になる。更
に、フレーム単位での推定を可能にしたため、回線品質
改善処理に不可欠な情報を瞬時に取得する事ができる。When only the circuit for detecting the presence / absence of an error in the frame is used, all the frames in the figure are treated equally (with an error), but the error is included by couting the maximum difference detection circuit. Frames can be separated. Furthermore, since it is possible to estimate in frame units, it is possible to instantly acquire information that is indispensable for the line quality improvement processing.
【００２９】[0029]
【発明の効果】以上説明したように本発明によれば、Ａ
ＤＰＣＭ音声符号化方式を採るディジタル信号の伝送系
において、干渉波が存在する場合であっても、伝送路の
品質の推定が可能であり、しかも、これを非常に高速に
高い精度で行なうことができる利点がある。As described above, according to the present invention, A
In a digital signal transmission system adopting the DPCM voice coding system, the quality of the transmission line can be estimated even when there is an interference wave, and this can be performed at extremely high speed and with high accuracy. There are advantages.
【図１】本発明の一実施例を示す図である。FIG. 1 is a diagram showing an embodiment of the present invention.
【図２】実施例の制御を示す流れ図である。FIG. 2 is a flow chart showing control of the embodiment.
【図３】本発明を適用した模擬伝送系の例を示す図であ
る。FIG. 3 is a diagram showing an example of a simulated transmission system to which the present invention is applied.
【図４】音声信号を伝送した場合の４ビットＡＤＰＣＭ
符号の確率分布を示す図である。FIG. 4 is a 4-bit ADPCM when an audio signal is transmitted.
It is a figure which shows the probability distribution of a code.
【図５】最大差分検出回数とＡＤＰＣＭサンプル誤り数
との関係を示す図である。FIG. 5 is a diagram showing a relationship between the maximum number of times of difference detection and the number of ADPCM sample errors.
１０ 回線品質推定回路 １１ サンプル検出回路 １２ 検出カウンタ １３ 受信信号とサンプル検出回路の出力との関係 １４ カウンタ値と回線品質推定信号との関係 １５ 回線品質改善回路 ３１ 音源 ３２ Ａ／Ｄ変換器 ３３ ＡＤＰＣＭ符号器 ３４ 誤り付加回路 ３５ ＡＤＰＣＭ復号器 ３６ Ｄ／Ａ変換器 ３７ スピーカ ３８ フレームエラー検出信号 ３９ 品質通知信号 10 line quality estimation circuit 11 sample detection circuit 12 detection counter 13 relationship between received signal and output of sample detection circuit 14 relationship between counter value and line quality estimation signal 15 line quality improvement circuit 31 sound source 32 A / D converter 33 ADPCM Encoder 34 Error addition circuit 35 ADPCM decoder 36 D / A converter 37 Speaker 38 Frame error detection signal 39 Quality notification signal
Claims (2)
化方式を採るディジタル信号の伝送系において、 ＡＤＰＣＭ復号器の入力側の信号を受信して、特定の差
分を示す符号列からなるサンプルを検出する手段と、 該サンプルをフレームエラー検出信号が入力されている
場合だけ計数する手段と、 上記サンプルの計数値を出力する手段とを設けたことを
特徴とする回線品質推定回路。1. In a digital signal transmission system adopting an adaptive differential PCM (ADPCM) speech coding system, a signal on the input side of an ADPCM decoder is received and a sample consisting of a code string showing a specific difference is detected. A line quality estimating circuit comprising: means, a means for counting the samples only when a frame error detection signal is input, and a means for outputting the count value of the samples.
化方式を採るディジタル信号の伝送系において、 ＡＤＰＣＭ復号器の入力側の信号を受信して、一定の差
分値以上を示す符号列からなるサンプルを検出する手段
と、 該サンプルをフレームエラー検出信号が入力されている
場合だけ計数する手段と、 上記サンプルの計数値を出力する手段とを設けたことを
特徴とする回線品質推定回路。2. A digital signal transmission system adopting an adaptive differential PCM (ADPCM) speech coding system, wherein a signal on the input side of an ADPCM decoder is received and a sample consisting of a code string showing a certain difference value or more is sampled. A line quality estimation circuit comprising: a means for detecting, a means for counting the samples only when a frame error detection signal is input, and a means for outputting the count value of the samples.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03801594A JP3220321B2 (en) | 1994-03-09 | 1994-03-09 | Line quality estimation circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03801594A JP3220321B2 (en) | 1994-03-09 | 1994-03-09 | Line quality estimation circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07250107A true JPH07250107A (en) | 1995-09-26 |
| JP3220321B2 JP3220321B2 (en) | 2001-10-22 |
Family
ID=12513758
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP03801594A Expired - Lifetime JP3220321B2 (en) | 1994-03-09 | 1994-03-09 | Line quality estimation circuit |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3220321B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009022407A1 (en) | 2007-08-13 | 2009-02-19 | Fujitsu Limited | Inspection method |
-
1994
- 1994-03-09 JP JP03801594A patent/JP3220321B2/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009022407A1 (en) | 2007-08-13 | 2009-02-19 | Fujitsu Limited | Inspection method |
| US8488473B2 (en) | 2007-08-13 | 2013-07-16 | Fujitsu Limited | Voice communication quality assessing system |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3220321B2 (en) | 2001-10-22 |
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