9/12/2004 4. Digital Transmisison - Lin 1 CPET/ECET 355 4. Digital Transmission Data Communications and Networking Fall 2004 Professor Paul I-Hai Lin Electrical

9/12/20044. Digital Transmisison - Lin1

CPET/ECET 355CPET/ECET 3554. Digital Transmission

Data Communications and NetworkingFall 2004

Professor Paul I-Hai LinElectrical and Computer Engineering TechnologyIndiana University-Purdue University Fort Wayne

www.ecet.ipfw.edu/~lin


4.1 Line Encoding4.1 Line Encoding A process converting binary data, a

sequence of bits, to a digital signal Binary data: data, text, numbers, graphical

images, audio, and video Some characteristics: Signal levels, bit rate,

dc components, self-synchronization

From p. 85, Figure 4.1 of Data Communications and Networking, Forouzan, McGrawHill


4.1 Line Encoding 4.1 Line Encoding (cont.)(cont.)

Signal Level vs. Data Level


Three signal levels, 2 data levels



Pulse Rate vs. Bit Rate Pulse Rate

– Number of pulses per second– A pulse is the min amount of time required to send a

symbol Bit Rate

– Number of bits per second BitRate = PulseRate x Log2L

– Level of signal = 2, BitRate = PulseRate– Level of signal = 4, BitRate = 2 x PulseRate

Example 1 & 2: Find Bit rate If - Pulse rate 1000 pulses/sec, L = 2, 1000 bps If - Pulse rate 1000 pulses/sec, L = 4, 2000 bps



DC Components (undesirable)– Cannot passing through a transformer– Unnecessary energy on the line




Self-Synchronization (desirable)– For correctly interpret signal– Sending 10110001; receiving 110111000011

Figure 4.4 Lack of Synchronization,

From p. 88, Data Communications and Networking, Forouzan, McGrawHill



Line Coding Schemes– Unipolar

Simple and primitive One voltage level Two problems: DC component & Lack of

synchronization

– Polar Two signal levels: positive & negative Eliminate DC component

– Biploar Three signal levels: positive, zero, and

negative



Unipolar Encoding

Figure 4.6 Unipolar Encoding,



4.1 Line Encoding 4.1 Line Encoding (cont.)(cont.) Polar Encoding

– NRZ: Non Return to Zero– RZ: Return to Zero– Manchester– Differential Manchester


4.1 Line Encoding 4.1 Line Encoding (cont.)(cont.) NRZ: Non Return

to Zero– NRZ-L

0 positive; 1 negative

Sync. Problem if long string of 0s or 1s is encountered

– NRZ-I the signal is

inverted if a 1 is encountered

A long string of 0s still cause sync. problem

Figure 4.8 NRZ-L and NRZ-I Encoding,



4.1 Line Encoding 4.1 Line Encoding (cont.)(cont.) RZ: Return to

Zero– Uses three

values: positive, zero, negative

– Ensure Sync: a signal change for each bit

– Main disadvantage: use more bandwidth

Figure 4.9 RZ Encoding,



4.1 Line Encoding 4.1 Line Encoding (cont.)(cont.) Manchester Encoding

– Uses two level signal values: positive, negative– Sync: Inversion at the middle of each bit– Zero: High -> Low; One: Low -> High

Figure 4.10 Manchester Encoding,



4.1 Line Encoding 4.1 Line Encoding (cont.)(cont.) Differential Manchester Encoding

– Uses two level signal values: positive, negative– Sync: Inversion at the middle of each bit– Zero: A transition; One: No transition

Figure 4.10 Differential Manchester Encoding,



4.1 Line Encoding 4.1 Line Encoding (cont.)(cont.) Biploar Encoding

– Uses three level signal values: positive, zero, negative– 0: Zero level; 1: Alternating positive and negative voltages– AMI: Alternate Mark Inversion– BnZS: Bipolar n-zero Substitution

Figure 4.12 Bipolar AMI Encoding,



4.2 Block Encoding 4.2 Block Encoding Improve performance

Ensure synchronization through redundancy bits

Block Encoding Schemes– 4B/5B: 4-bit data encoded into 5-bit code– 8B/10B: 8-bit data encoded into 10-bit code– 8b/6T: 8-bit data encoded into 6-symbol code


4.2 Block Encoding 4.2 Block Encoding (cont.)(cont.) Block Encoding

Figure 4.15 Block Encoding,



4.2 Block Encoding 4.2 Block Encoding (cont.)(cont.)

4B/5B Block Substitution– Better Sync

& Error detection

– 16 groups -> 32 groups

– No more than 3 consecutive 0s

Figure 4.16 Substitution in Block Encoding,




4B/5B Encoding Table

Table 4.1 4B/5B Encoding,


Data Code Data Code

0000 1111011110 1000 10010100100001 0100101001 1001 10011100110010 1010010100 1010 1011010110

0011 1010110101 1011 1011110111

0100 0101001010 1100 1101011010

0101 0101101011 1101 1101111011

0110 0111001110 1110 1110011100

0111 0111101111 1111 1110111101



4B/5B Encoding Table

Table 4.1 4B/5B Encoding,


Data Code

Q (Quiet) 0000000000

I (Idle) 1111111111

H (Halt) 0010000100J (start delimiter) 1100011000

K (start delimiter) 1000110001

T (end delimiter) 0110101101

S (Set) 1100111001R (Reset) 0011100111



8B/6T Encoding– 28: 256 possibilities– 36: 729 six-symbol ternary signal

Figure 4.17 Example of 8B/6T Encoding,



4.3 Sampling 4.3 Sampling Pulse Amplitude Modulation

(PAM)– Sample & Hold circuit

Pulse Code Modulation (PCM)– Quantized PAM

Sampling Rate– Nyquist theorem– How many bit per sample


4.3 Sampling 4.3 Sampling (cont.)(cont.)

PAM

Figure 4.18 PAM,




Quantized PAM Signal

Figure 4.19 Quantized PAM Signal,




Quantization, sign & magnitude

Figure 4.20 Quantizing by using sign and magnitude,




PCM

Figure 4.21 PCM,




PCM

Figure 4.22 From analog signal to PCM digital code,




Nyquist Theorem– Sampling

rate must be at least 2 times the highest frequency

Figure 4.23 Nyquist Theorem,


= x Hz

= 2 x samples

= ½ x



Examples– Q1: What sampling rate is needed for

a signal with a bandwidth of 10 KHz (1KHz to 11KHz)

– A1: Sampling rate = 2 x 11 KHz = 22,000 samples per second



Examples– Q2: A signal is sampled. Each sample

requires at least 12 levels of precision (+0 to +5 and 0 to -5). How many bits should be sent for each sample?

– A2: 4-bit 1-bit for sign 3-bit for magnitude (8-levels)



Examples– Q3: We want to digitize the human voice. What

is the bit rate, assuming 8-bits per sample?

– A3: BW of Human voice 0-4000 Hz Sampling rate 4000 x 2 = 8000 samples/secBit rate

– 8000 sample/sec x 8 bit/sample = 64,000 bps


4.4 Transmission Mode4.4 Transmission Mode Parallel Serial

– Synchronous– Asynchronous

Figure 4.25 Parallel transmission,



4.4 Transmission Mode4.4 Transmission Mode Serial Transmission

Figure 4.26 Serial transmission,



4.4 Transmission Mode4.4 Transmission Mode Serial -

Asynchronous

Figure 4.27Asynchronlus transmission,



4.4 Transmission Mode4.4 Transmission Mode Serial -

Synchronous

Figure 4.28 Synchronlus transmission,



SummarySummary

Questions?

Documents

9/12/2004 4. Digital Transmisison - Lin 1 CPET/ECET 355 4. Digital Transmission Data Communications and Networking Fall 2004 Professor Paul I-Hai Lin Electrical