Encoding techniques
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Encoding is the process of converting data into a digital format for transmission. There are different encoding techniques for analog and digital data. Common digital to digital encoding techniques include NRZ, NRZI, Manchester, and 4B/5B encoding. NRZ assigns a voltage level to represent each bit but can cause issues with long strings of the same bit. NRZI and Manchester encoding add transitions to distinguish bits and allow synchronization. 4B/5B encoding groups bits into blocks and maps them to code words, preventing long runs of the same bit. These encoding techniques allow reliable transmission of digital data over networks.
Encoding techniques
- 1. ENCODING TECHNIQUES Group Members • Goriha Naveed • Maria Banaras • Naila Naz • Riffat Yaqoob
- 2. Encoding Encoding is the process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized digital format for efficient transmission or transfer. Decoding is the opposite process -- the conversion of a digital signal into a sequence of characters.
- 3. Types of Encoding Digital Data , Analog signals Basis for analog signaling is a continuous, constant-frequency signal known as the carrier frequency. By modulating(Amplitude , Frequency , Phase) Analog Data ,Digital signals Analog-to-digital conversion is an electronic process in which a continuously variable analog signal is changed, without altering its essential content, into a multi-level digital signal. Digital Data , Digital signals Digital signal –is a sequence of discrete, discontinuous voltage pulses. Bit duration :: the time it takes for the transmitter to emit the bit.
- 4. Digital To Digital Encoding Techniques In order to transport digital bits of data across carrier waves, encoding techniques have been developed. some of the more common techniques are given below Physical layer NRZ( non return to zero) NRZI(non return to zero inverted) MANCHESTER ENCODING 4B/5B ENCODING
- 5. Encoder Decoder 1 0 1 1 01 0 1 1 0 1 0 1 1 0 Digital message Digital Signal Digital to digital encoding Frame
- 6. NRZ encoding (Non Return to Zero) The most common, and easiest, way to transmit digital signals. Uses two different voltage levels (one positive and one negative) as the signal elements for the two binary digits. Voltage does not return to zero during the bit interval. The voltage is constant during the bit interval . 0 negative voltage 1 positive voltage
- 7. NRZ Encoding 0 0 1 0 1 1 1 0 0 + -
- 8. NRZ Encoding The problem with this is that it is difficult to distinguish a series of '1's or '0's. Leads to baseline wander Sender and Receiver clocks have to highly precise Reference: Data communication & networking By Behrouz A. Forouzan "In decoding a digital signal, the incoming signal power is evaluated against the baseline (a running average of the received signal power). A long string of 0s or 1s can cause baseline wandering (a drift in the baseline) and make it difficult for the receiver to decode correctly."
- 9. 0 0 1 0 1 1 1 0 0 1 0 1 1 1 NRZ BASE LINE WONDER
- 10. NRZI ENCODING NRZI stands for non return to zero inverted. NRZ inverted (NRZI) Solve the problem of consecutive 1’s. At zero, state of current signal remains same. Transition at beginning of bit time Transition (either low-to-high or high-to-low) denotes a binary 1 No transition denotes a binary 0.
- 11. 1 0 1 1 0 1 0 NRZI(Non return to zero inverted) + -
- 12. Manchester encoding There is a transition at the middle of each bit period. A transition in the middle of each bit makes it possible to synchronize the sender and receiver and also as data: low to high represents 0, high to low represents 1 Used by IEEE 802.3 Ethernet LAN 1 High-to-low transition 0 low-to-high transition
- 13. 0 0 1 0 1 1 1 0 Manchester encoding - +
- 14. Pros and Cons Pros Self-clocking: Because there is a predictable transition during each bit time, the receiver can synchronize on that transition. Error detection: the absence of an expected transition can be used to detect errors 50% efficient(1/2 bit per transition) Cons The maximum modulation rate is twice that for NRZ Requires more bandwidth
- 15. 4B/5B Encoding 4B/5B block encoding scheme designed to breakup long strings of 0’s and 1’s without increasing the frequency bandwidth. In this scheme bit sequence is broken up in to four bit blocks. Each block of four bit is replaced with a five bit block. The five bits codes were selected so that there is no more than one leading zero and no more than two trailing zeros. Only half of the five bits are used for encoding , the remaining cods can be used for other purposes. Thus, when the codes are strung together there can be no more than three consecutive zeros The string of bits after the replacement are transmitted using NRZI. 4B/5B encoding followed by NRZI is used in 10BaseTX (Fast Ethernet).
- 16. 4B/5B Encoding
- 17. 1 0 0 1 0 1 1 0 1 1 1 0 Bit Sequence 1 0 0 1 0 1 1 0 1 1 1 0 1 0 0 1 1 0 1 1 1 0 1 1 1 0 0 1 0 0 1 1 0 1 1 1 0 1 1 1 0 0 4B/5B Encoding Not more than 3 consecutive zeros 4B/5B Encoding
- 18. NRZI Encoder NRZI Decoder 1 0 1 01 0 1 0 1 0 1 1 0 Digital Signal 4B/5B Encoder 4B/5B Decoder 1 0 1 1 01 0 1 1 0 Digital data Digital data 4B/5B Encoding Frame
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