符号に関する概要は、「伝送符号とは」をご覧ください。
❑ C2. Multilevel code 多値符号 4値の形式
多値符号は3値以上の電圧とパルスの組み合わせで表現するものをここに分類しました。ここで解説するのは4値の形式です。
C2-1. 2B1Q
2B1Qは、DSL (IDSL, SDSL, HDSL) に使われた符号化方式です。いずれもDSLが普及し始めた初期の頃のものです。
- DSL
- Digital Subscriber Line
ADSLはDSLの一種。
ADSL＝Asymmetric Digital Subscriber Line - 参考記事
- ADSLについて詳細は、モデムとはをどうぞ。
符号化は、2ビットのデータと4種類の信号電圧レベルを組み合わせます。この方式の伝送容量（速度）の平均値はNRZ-Lに比べ2倍で、一つの符号あたり２つのデータを伝送できます。（NRZ-Lについて詳細は、伝送符号 [A2] Polar NRZ ポーラーNRZの記事をどうぞ。）
- 2B1Q (2 Binary 1 Quaternary)
- ・m ＝2 00, 01, 10, 11 データは4つのうちのどれか一つ
・B binary
・n ＝1 データを表現する符号の長さ
・L ＝4 信号レベルは4値（Quaternary「4つの要素」）
「多値符号」は「mBnL」の形式で名前が付いているものがあります。一般化するとそれぞれ文字の意味は次のとおりです。
- Multilevel code 多値符号
- ・m データのバイナリーパターンの長さ
・B バイナリー (binary)
・n 符号の長さ
・L 信号レベル（電圧振幅）の数
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> if I had not discovered such a point like this. I am able to now relish my future. Thanks for
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