(5) Manchester(曼彻斯特码) 0—在间隔中间负向跳变; 1在间隔中间正向跳变; 优点: 同步好,每bit均有跳变,又称为自对称; 没有直流成分 有助于差错检测; 缺点:带宽是NRZ的2倍 (6)差分曼彻斯特码 ·0—在间隔的起始位置跳变,在中间有跳变; ·1—在间隔的起始位置不跳变,在中间有跳变
6 （5）Manchester（曼彻斯特码） • 0—在间隔中间负向跳变； • 1—在间隔中间正向跳变； • 优点： - 同步好，每bit均有跳变，又称为自对称； - 没有直流成分； - 有助于差错检测； • 缺点：带宽是NRZ的2倍 （6）差分曼彻斯特码 • 0—在间隔的起始位置跳变，在中间有跳变； • 1—在间隔的起始位置不跳变，在中间有跳变；
不同编码方式的频谱特性 a23d10 b1厂aca上5用2 yon n legend 21用O B8Zs HDB3 d: AMI i a Alternate mark inversion SP B8ZS Bipolar with 8 zeros substitution Freque HDB3 ligh-density bipolar--3 zeros NRZ-L NRZL-L= Nonreturn to zero level 1.0 F.NRZI 128 NRZI= Nonreturn to zero inverted R 0.8 aml pseudoternary o d s 1o sungod or 90.6 e wesTener Manchester Differential Mancheste 0.2 0.40.60.81.01.21.4161.8 2.0 Normalized frequency (/R) Figure 5.3 Spectral Density of Various Signal Encoding Schemes
7 不同编码方式的频谱特性
各种编码方法的错误率(理论值) 101 AMI, pseudoternary, 102 ASK FSK 10 NRZ, biphase PSK, QPSK 104 105 106 10 O1=2345678910112131445 (EyNo(dB) Figure 5.4 Theoretical Bit Error Rate for Various Encoding Schemes
8 各种编码方法的错误率（理论值）
不同数字信号编码速率的归一化信号跳变速率 Table 5.3 Normalized Signal Transition Rate of Various Digital Signal Encoding Rates Minimum 101010 Maximum NRZ-L 0(all Os or 1s) 1.0 1.0 NRZI 0(all 0.5 1.0(all 1s)L Bipolar-AMI 0(all Os) 1.0 1.0 Pseudoternary o(all 1s)L 1.0 1.0 Manchester 1.0(010-) 1.0 2.0(all Os or 1s) Differential Manchester 1.0 (all 1s 15 20(l0s)
9 不同数字信号编码速率的归一化信号跳变速率
2. Modulation rate(调制速率) Description: When signal encoding techniques are used, a distinction needs to be made between data rate(expressed in bits per second) and modulation rate (expressed in baud). The data rate, or bit rate, is R-1/Tb, where Tb is bit duration The modulation rate is the rate at which signal elements are generated Consider for example, Manchester encoding. The minimum size signal element is a pulse of one-half the duration of a bit interval. For a string of all binary zeros or all binary ones, a continuous stream of such pulses is generated. Hence the maximum modulation rate for manchester is d=2 /Tb. This situation is illustrated in Figure 5.5(E6), which shows the transmission of a stream of binary ls at a rate of MBps using nrzi and manchester. In general, D=R/b where D= modulation rate. baud R=data rate. bps b=number of bits per signal element
10 2. Modulation Rate（调制速率） Description: When signal encoding techniques are used, a distinction needs to be made between data rate (expressed in bits per second) and modulation rate (expressed in baud). The data rate, or bit rate, is R=1/Tb, where Tb is bit duration. The modulation rate is the rate at which signal elements are generated. Consider, for example, Manchester encoding. The minimum size signal element is a pulse of one-half the duration of a bit interval. For a string of all binary zeros or all binary ones, a continuous stream of such pulses is generated. Hence the maximum modulation rate for Manchester is D=2/Tb. This situation is illustrated in Figure 5.5（E6）, which shows the transmission of a stream of binary 1s at a rate of 1Mbps using NRZI and Manchester. In general, D=R/b. where D = modulation rate, baud R = data rate, bps b = number of bits per signal element