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Teknik Modulasi Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu: • Menjelaskan teknik modulasi 3 Outline Materi • Teknik Modulasi • Modulasi analog • Modulasi digital 4 Encoding Techniques • Analog data, carrier analog signal • Digital data, carrier analog signal Analog Modulation • Analog data, carrier digital signal Digital Modulation • Digital data, carrier digital signal Encoding 5 Analog Data, Analog Signals • Why modulate analog signals? – Higher frequency can give more efficient transmission – Permits frequency division multiplexing • Types of modulation – Amplitude – Frequency – Phase 6 Analog Modulation 7 MODULASI TUJUAN: • MENGUBAH SINYAL DARI KOMPUTER YANG DIGITAL MENJADI SINYAL ANALOG YANG DIPERLUKAN OLEH SALURAN KOMUNIKASI • MEMPERPANJANG JARAK JANGKAU SINYAL INFORMASI • MODEM MERUPAKAN HARDWARE UNTUK KEDUA PROSES INI 8 LST/FASKD/CINQ Type Modulasi Digital /Analog 9 Modulation Techniques 10 Frequency Shift Keying • Most common form is binary FSK (BFSK) • Two binary values represented by two different frequencies (near carrier) • Less susceptible to error than ASK • Up to 1200bps on voice grade lines • High frequency radio • Even higher frequency on LANs using co-ax 11 Phase Shift Keying • Phase of carrier signal is shifted to represent data • Binary PSK – Two phases represent two binary digits • Differential PSK – Phase shifted relative to previous transmission rather than some reference signal 12 PSK Constellation 13 Quadrature PSK • More efficient use by each signal element representing more than one bit – e.g. shifts of /2 (90o) – Each element represents two bits – Can use 8 phase angles and have more than one amplitude – 9600bps modem use 12 angles , four of which have two amplitudes 14 4-PSK Constellation 15 4-QAM and 8-QAM 16 Quadrature Amplitude Modulation • QAM used on asymmetric digital subscriber line (ADSL) and some wireless • Combination of ASK and PSK • Logical extension of QPSK • Send two different signals simultaneously on same carrier frequency – Use two copies of carrier, one shifted 90° – Each carrier is ASK modulated – Two independent signals over same medium – Demodulate and combine for original binary output 17 BIT dan BAUD 18 Perbandingan Bit dan Baud rate Modulation Units Bits/Baud Baud rate Bit Rate Bit 1 N N 4-PSK, 4-QAM Dibit 2 N 2N 8-PSK, 8-QAM Tribit 3 N 3N 16-QAM Quadbit 4 N 4N 32-QAM Pentabit 5 N 5N 64-QAM Hexabit 6 N 6N 128-QAM Septabit 7 N 7N 256-QAM Octabit 8 N 8N ASK, FSK, 2-PSK 19 Teknik Encoding 20 Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : • Menjelaskan teknik encoding 21 Outline Materi • Polar • Bipolar • Unipolar 22 Digital to Digital Encoding 23 Terminologi • Unipolar – All signal elements have same sign • Polar – One logic state represented by positive voltage the other by negative voltage • Data rate – Rate of data transmission in bits per second • Duration or length of a bit – Time taken for transmitter to emit the bit 24 Terminologi • Modulation rate – Rate at which the signal level changes – Measured in baud = signal elements per second • Mark and Space – Binary 1 and Binary 0 respectively 25 Digital to Digital Encoding 26 Polar Encoding 27 Bipolar Encoding 28 Modulation Rate 29 Unipolar Encoding - NRZL 30 Nonreturn to Zero Inverted • • • • Polar, Non Return To Zero Inverted Non return to zero, inverted on ones Constant voltage pulse for duration of bit Data encoded as presence or absence of signal transition at beginning of bit time • Transition (low to high or high to low) denotes a binary 1 • No transition denotes binary 0 • An example of differential encoding 31 NRZ-L and NRZ-I 32 RZ Encoding 33 Biphase • Manchester – Transition in middle of each bit period – Transition serves as clock and data – Low to high represents one – High to low represents zero – Used by IEEE 802.3 • Differential Manchester – Mid bit transition is clocking only – Transition at start of a bit period represents zero – No transition at start of a bit period represents one – Used by IEEE 802.5 34 Manchester and Diff. Manchester 35 Multilevel Binary • Use more than two levels • Bipolar-AMI – zero represented by no line signal – one represented by positive or negative pulse – one pulses alternate in polarity – No loss of sync if a long string of ones (zeros still a problem) – No net dc component – Lower bandwidth – Easy error detection 36 Bipolar AMI Encoding 37 Perbandingan skema enkoding • Error detection – Can be built in to signal encoding • Signal interference and noise immunity – Some codes are better than others • Cost and complexity – Higher signal rate (& thus data rate) lead to higher costs – Some codes require signal rate greater than data rate 38