Digital Communication System PDF

INTRODUCTION TO DIGITAL COMMUNICATION SYSTEM Any communication system (DIGITAL, ANALOG, DATA) always has 3 components: Transmitter (TX) ANALOG CS – all info in tx, rx Receiver (RX) and medium a...

INTRODUCTION TO DIGITAL COMMUNICATION SYSTEM Any communication system (DIGITAL, ANALOG, DATA) always has 3 components: Transmitter (TX) ANALOG CS – all info in tx, rx Receiver (RX) and medium are all ANALOG signals Medium / Channel DIGITAL CS – all info transmitted are in DIGITAL format - Process digital information both at the transmitter DATA CS – info is DIGITAL but dadaan siya sa ANALOG and receiver medium - A DCS process digital information or discrete signals at uniform amplitude even though the time is ANALOG SIGNALS – continuously varying, or the voltage level is 1 or 0. change ang amplitude w/ respect to time Ex: voice / voltage signals, etc DIGITAL SIGNALS – discrete signals wherein there is a uniform height or level even w/ different time interval. Ex: computer system (1,0), electronic pulses So kung anong info type ang prinoprocess sa medium, malalaman kung anong cs yung gamit. INPUT TRANSDUCER - a device that can convert one form of energy to another. - Ex: voice signal -> electrical pulses usually microphone ENCODING - refers to the process of using various patterns of voltage or current levels to represent 1s and 0s of digital signals on the transmission link. - the process of turning thoughts into communication using various tools such as phone calls, email, or face-to-face meetings - Free series, free analysis DIGITAL MODULATOR - 3 types (ASK, FSK, PSK or combination of the 3 – QAM) CHANNEL - mediator between the transmitter and receiver - can be wired or wireless DEMODULATOR - amplify then process of detection, since we need to extract original information CHANNEL DECODING - to get original signal, decode in a series of 1 and 0 DECODING - identify the origin of the information MODEM – has the ADC and DAC component  - Digital Modulation - Digital Transmission DIGITAL MODULATION - also called as “DIGITAL RADIO” - the process of modulation which is similar to analog modulation NOTE: All information in digital should be in digital format modulating an analog carrier DIGITAL TRANSMISSION - defines as a transmission of information or intelligence in digital form. - transmit ang information into digital form NOTE: Analog intelligence must be converted into digital format prior to transmission Digital signals can’t be affected by noise due to the limiter value, so it can be cut and disregarded DISADVANTAGE bandwidth requirement (high needed) capacity must increase to transmit unlike analog SO WHAT IF MATAAS REQUIREMENT? - GIRLLLL, magkakaroon kasi channel scarcity ex: from 100 channels magiging 50 channels nalang to improve quality DIGITAL MODULATION The DIGITAL MODULATION process basically originated from analog modulation counterpart. The main difference is the modulating signal or information is in digital form. An analog information or intelligence must be converted to digital format to modulate an analog carrier. NOTE: The mathematics involve is SPECTRA in the conversion QUICK REVIEW: 3 ANALOG MODULATION: 1. Amplitude Shift Keying (ASK) - AM 2. Frequency Shift Keying (FSK) - FM 3. Phase Shift Keying (PSK) - PM 4. Quadrature Amplitude Modulation (QAM) In Amplitude Modulation, nababago amplitude ng AMPLITUDE SHIFT KEYING (ASK) – forms of modulation carrier depende sa which is the digital counterpart of Amplitude modulation amplitude ng information - process > pag tumaas carrier, tataas amplitude – hence, nagkakaroon ng AM ENVELOPE FREQUENCY SHIFT KEYING (FSK) – forms of modulation which is the digital counterpart of Frequency Modulation process PHASE SHIFT KEYING (PSK) - forms of modulation which is the digital counterpart of Phase Modulation process QUADRATURE AMPLITUDE MODULATION (QAM) - also called as “Quarternary Amplitude Modulation” - can be a combination of the 3 (PSK, ASK, FSK) - a hybrid form of modulation (analog and digital) - Derived from PSK and AM || ASK and PM - Efficient in terms of Amplitude & Value of information - most efficient form of modulation as it can interpret different types of signals even though they have the same phase - Truth Table - Phasor Diagram - Constellation Diagram QAM - 8 QAM - 16 QAM - 32 QAM - 64 QAM - 128 QAM  DIGITAL TRANSMISSION - defined as a transmission of information or intelligence in digital form. - Analog intelligence must be converted into digital format with the use of analog to digital converter (ADC). An analog carrier is needed in modulation process prior to transmission Transmission of information such as voice, video and data requires: - wider bandwidth - high speed transmission - reliable signal conversion Note: TDM – Time Division Multiplexing - One frequency pero iba iba ng timeslot - Ex: Cellular communication In this case, If DIGITAL SIGNAL mo, convert mo muna siya sa ANALOG with the use of MODEM (ADC and DAC), saka lang siya dadaan sa ANALOG TRANSMISSION medium DIGITAL SIGNAL -> MODEM -> ANALOG SIGNAL -> ANALOG MULTIPLEXING -> ANALOG TRANSMISSION -> ANALOG DEMULTIPLEXING -> MODEM -> DIGITAL SIGNAL Note: FDM –Frequency Division Multiplexing - Transmit sabay sabay pero ibat ibang frequency - Ex: broadcast stations like GMA, ABSCBN, TV5 CODEC - convert analog data to digital format - encoder decoder of data ANALOG SIGNAL (TELEPHONE: VOICE) -> CODEC -> DIGITAL SIGNAL -> DIGITAL TRANSMISSION (VSAT SATELLITE: CDMA) -> DIGITAL DEMULTIPLEXING -> CODEC -> ANALOG SIGNAL Digital transmission involves transmission of digital information over an analog carrier. All form of information prior to transmission will convert into digital format. A special type of converter such as ADC and DAC are required in the conversion process. DIGITAL TRANSMISSION requires a physical channel or medium like optical fiber and transmission line. At the receiver, the signal will pass to another conversion through digital to analog converter Advantages of digital signals over analog signals are synonymous to advantages of digital transmission over analog transmission. 1. Immunity to noise. Why? With fixed amplitude signal, it will limit the noise 2. Ease of signal processing. Why? Digital data is easier to process (1,0) unlike analog that is continuously changing 3. Ease of signal multiplexing. Why? Because digital signal can easily be multiplexed rather than analog. NOTE: MULTIPLEXING – process done at the transmitter to cater multiple input signal to be transmitted over a single transmission channel or medium 4. Much easier to measure, interpret and evaluate. Why? Logic 1 and logic 0 5. Using of signal re generator rather than signal amplifier to boost and extend signal NOTE: Amplifier and Regenerator functions the same - The amplifier is the common work we use to strengthen the signal when using analog. But in digital, amplifier is called re generator – purpose of signal boosting and extending signal coverage. Hence, - Analog (Amplifier) : Digital (Regenerator) Even though that digital transmission possess lots of advantages, among of the following are the disadvantages of it. 1. Large amount of bandwidth required. - Digital info require higher frequency with higher data gain - BANDWIDTH – capacity to allow signals or info to pass through. Hence, the wider the bandwidth, the faster the transmission of data is. 2. Requires additional devices for conversion process like ADC at the transmitter side and DAC at the receiver. 3. Requires accurate timing and synchronization. - If not synchronize, there will be an error in transmission (BER or Probability of Error (rubidium clock for accurate clock in network) DIGITAL MODULATION  Modulation performs a greater role in transmission of information. Modulation in any form analog or digital allows the signal to be transmitted over a greater distance. (without modulation, hindi mo maicoconvert or matratransmit ang information to greater distances) Voice, data and transmission must be modulated prior to its transmission The DIGITAL MODULATION PROCESS basically originated from analog modulation counterpart. The main difference is--- the modulating signal or information is in digital form. An analog information or intelligence must be converted to digital format to modulate an analog carrier. 1. Amplitude Shift Keying (ASK) 2. Frequency Shift Keying (FSK) 3. Phase Shift Keying (PSK) 4. Quadrature Amplitude Modulation (QAM) NOTES: PSK – has an inversion (HIGH FREQ) - Everytime there has a change in values, magkakaroon ng tinatawag na SHIFTING (FSK) 1. Binary Frequency Shift Keying (BFSK) – “2PSK” BPSK = FSK = 2PSK = BFSK 2. Minimum Shift Keying (MSK) 3. Gaussian Minimum Shift Keying (GMSK) (FSK) 1. Binary Phase Shift Keying (BPSK) – “2PSK” 1. 8 Quadrature Amplitude Modulation 2. Quarternary Phase Shift Keying (QPSK) (QAM) 3. 8 Phase Shift Keying (8PSK) 2. 16 Quadrature Amplitude Modulation 4. 16 Phase Shift Keying (16PSK) (QAM) 5. Differential Binary Shift Keying (DBPSK) 3. 32 Quadrature Amplitude Modulation (QAM) 4. 64 Quadrature Amplitude Modulation (QAM) (FSK)  a) Binary Frequency Shift Keying (BFSK) - a digital modulation technique causes the carrier to increase in frequency whenever a data 1 passes and lower the frequency for data 0. - the carrier signal is modified by altering its phase by 180 degrees - employed in comSmunication systems to transmit information via a communication channel b) Minimum Shift Keying (MSK) - a digital modulation technique that minimizes effect of phase shift whenever data changes from 1 to 0 or vice versa - biglaan daw shift from 1 to 0 kaya ginagamit msk - in cellsite, msk is used particularly GMSK and GFSK para maiwasan yung abrupt change, nadevelop yung msk c) Gaussian Minimum Shift Keying (GMSK) - form of MSK basically applied in cellular communication modulation technique Yung data na itratransmit ay nakadepende sa phase angle depending on modulation technique (PSK) 1. BINARY SHIFT KEYING (BPSK) - it changes the phase of the modulated signal whenever data changes from 1 to 0 or vice versa. - 2 possible combinations either 1 or 0 - NOTE: 1 = 0° 0 = 180° 2. QUARTERNARY SHIFT KEYING (QPSK) - “4PSK” - characterize with four (4) possible outcomes in different phase angle - also call dibit (2) : yung info group of 2 - NOTE: 00 2n ; n = 2 01 therefore, 10 22 = 4 (4 possible combinations) 11 3. 8 PHASE SHIFT KEYING (8PSK) - Has 8 phase possible outcome to interpret a digital tri-bit (3 bits) data. 2n ; n = 3 000 - phase angle therefore, 001 3 2 = 8 (8 possible 010 combinations) 011 100 101 110 111 4. 16 PHASE SHIFT KEYING (16 PSK) - with 16 phase possible outcome to interpret a digital quadbit (4) data - Quadbit = nibble 0000 - phase angle 2n ; n=4 0001 0010 therefore, 0011 0100 24 = 16 (8 possible 0101 combinations) 0110 0111 1000 1001 1011 1100 1101 1110 1111 5. DIFFERENTIAL BINARY SHIFT KEYING (DBPSK) - uses quadbits (4) data - Transmission will be 4 groups Habang dumadami yung bits, dumadami possible combinations. Formula: 2n Mas madaming possible combinations, mas mabilis transmission 16 PSK More possible combination, more complexity of 32 PSK circuit, costly, and dapat accurate timing 64 PSK 128PSK In terms of speed and capacity, mas Maganda 256 PSK - 28 siya gamitin …… a. 8 Quadrature Amplitude Modulation (8QAM) ; quadrature means 4 - a combination of ASK and phase modulation with 8 possible outcomes to interpret a tri-bit data. - Data can have the same phase angle but differs in amplitude. - pinakamababang possibility na to - di-bit ang employed dito sa QAM 2n ; n = 3 therefore, 23 = 8 (8 possible combinations) b. 16 Quadrature Amplitude Modulation (16QAM) - a combination of ASK and phase modulation with 16 possible outcomes to interpret a quadbit data. - Data can have the same phase angle but differs in amplitude. 2n ; n = 4 therefore, 24 = 16 (16 possible combinations) 2n ; n = 5 c. 32 Quadrature Amplitude Modulation (32 QAM) - a combination of ASK and phase modulation with 32 possible therefore, outcomes to interpret a penta-bit data. - Data can have the same phase angle but differs in amplitude. 25 = 35 (35 possible - “EMARY CODING” combinations) d. 64 Quadrature Amplitude Modulation (QAM) 2n ; n = 6 - a combination of ASK and phase modulation with 64 possible therefore, outcomes to interpret a 6 bits data. - Data can have the same phase angle but differs in amplitude. 26 = 64 (64 possible combinations)  Frequency Shift Keying (FSK) - also called as “Binary Phase Shift Keying” (BPSK) or 2PSK - FSK = BPSK = 2PSK Binary Input Output Phase Logic 0 180° Truth table Logic 1 0° Note: Quadrant 1 – maximum data level Quadrant 3 – minimum data level Phasor Diagram Constellation Diagram Quaternary Phase Shift Keying (FSK) - “Quadrature PSK” ; dibit (2) data w/ 4 possible combinations - an M-ary encoding scheme where n = 2, m =4 ; inverted z Phasor Diagram Constellation Diagram Note: Note: in trigo, Majority of modulation technique follows inverted z positive angle – counter-clockwise direction analysis except sa 16 psk (roulette; counterclockwise) negative angle – clockwise direction  8 Phase Shift Keying (8PSK) - m-ary coding technique ; inverted z - tribit (n = 3), w/ m = 8 possible combinations / output phases Phasor Diagram Constellation Diagram 16 Phase Shift Keying (16PSK) - m-ary coding technique - quadbit (n = 4) data w/ 16 different combinations or output phases (m = 16) Phasor Diagram Constellation Diagram QUADRATURE-AMPLITUDE MODULATION (QAM) - is a form of digital modulation similar to PSK except the digital information is contained in both the amplitude and the phase of the transmitted carrier 8-QAM - an M-ary encoding technique where n = 3 → 2n ; m = 3 - inverted z analysis from least to most; follows truth table - Note: Unlike 8-PSK, the output signal from an 8-QAM modulator is not a constant- amplitude signal Phasor Diagram Constellation Diagram EX: In 8 QAM digital modulation technique, what is the amplitude voltage of data 011? Ans: 16-QAM - M-ary system where m = 16 (number of possible combinations); n = 4 → 24 = 16 EX: In 8 QAM digital modulation technique, what is the amplitude voltage of data 011? Ans: Phasor Diagram Constellation Diagram  4PSK INPUT OUTPUT PHASE 00 -135 01 -45 10 135 11 45 8PSK INPUT OUTPUT PHASE 000 -112.5 001 -157.5 010 -67.5 011 -22.5 100 112.5 101 157.5 110 67.5 111 22.5 16PSK INPUT OUTPUT PHASE 0000 11.25 0001 33.75 0010 56.25 0011 78.75 0100 101.25 0101 123.75 0110 146.25 0111 168.75 1000 191.25 1001 213.75 1010 236.25 1011 258.75 1100 281.25 1101 303.75 1110 326.25 1111 348.75  8QAM INPUT OUTPUT PHASE 000 0.765 V -135 001 1.848 V -135 010 0.765 V -45 011 1.848 V -45 100 0.765 V 135 101 1.848 V 135 110 0.765 V 45 111 1.848 V 45 16QAM INPUT OUTPUT PHASE 0000 0.311 V -135 0001 0.850 V -165 0010 0.311 V -45 0011 0.850 V -15 0100 0.850 V -105 0101 1.161 V -135 0110 0.850 V -75 0111 1.161 V -45 1000 0.311 V 135 1001 0.850 V 165 1010 0.311 V 45 1011 0.850 V 15 1100 0.850 V 105 1101 1.161 V 135 1110 0.850 V 75 1111 1.161 V 45