Digital Communication Lecture 6 1 Frequency Shift Keying

Frequency Shift Keying (FSK) n In frequency shift keying Binary FSK (BFSK), 1 and

BW calculations: BW =2(∆f + 2 fm)=2(∆f+ r) Carson’s Rule Modulation Index (MI): 4

Example: For a binary FSK modulator with space, rest, and mark frequencies of 60,

Orthogonal FSK: If the difference between the carriers f 1 and f 2 is

BFSK Demodulator: Non-Coherent Method: 9

4 FSK (4 -carriers FSK): n need 4 carriers n the digital data is

4 FSK Transmitter: n In case of Orthogonality the bandwidth is reduced (BW=5 r/2)

FSK Summary Binary FSK has a poorer error performance than PSK or QAM n

Phase Shift Keying: n In BPSK, two phases are used to represent 1 and

Example 2: n For a BPSK modulator with a carrier frequency of 70 MHz

Quadrate PSK(QPSK) This type takes the bits in pairs and therefore it uses 4

Example 3: n For a QPSK modulator with an input data rate equal to

Example (4) n In a QPSK Process, if the signal is I=1, Q=0 determine

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Digital Communication Lecture 6 1

Frequency Shift Keying (FSK) n In frequency shift keying Binary FSK (BFSK), 1 and 0 are represented by two different frequencies of the carrier. 2

Serial binary Data 1 0 0 1 FSK signal 3

BW calculations: BW =2(∆f + 2 fm)=2(∆f+ r) Carson’s Rule Modulation Index (MI): 4

Example: For a binary FSK modulator with space, rest, and mark frequencies of 60, 70, and 80 MHz, respectively and an input bit rate of 20 Mbps, determine the output baud and the minimum required bandwidth. 5

Orthogonal FSK: If the difference between the carriers f 1 and f 2 is equal to the bit rate r, then we have orthogonal FSK in this case the bandwidth is equal to 3 r. 6

BFSK modulator: 7

BFSK Demodulator: Coherent Method: 8

BFSK Demodulator: Non-Coherent Method: 9

4 FSK (4 -carriers FSK): n need 4 carriers n the digital data is taken as pairs n The output bit rate is reduced by half the input bit rate 10

4 FSK Transmitter: n In case of Orthogonality the bandwidth is reduced (BW=5 r/2) 11

FSK Summary Binary FSK has a poorer error performance than PSK or QAM n seldom used for high-performance digital radio systems. n restricted to low-performance, low-cost, asynchronous data modems that are used for data communications over analog, voice band telephone lines. n 12

Phase Shift Keying: n In BPSK, two phases are used to represent 1 and 0. n PSK is more immune to noise than FSK 13

BPSK Modulator: 15

Example 2: n For a BPSK modulator with a carrier frequency of 70 MHz and an input bit rate on 10 Mbps, determine the maximum and minimum upper and lower side frequencies draw the output spectrum, determine the minimum Nyquist bandwidth, and calculate the baud. 16

BPSK Demodulator: 17

Quadrate PSK(QPSK) This type takes the bits in pairs and therefore it uses 4 output phase shift angles. n Bandwidth is half the bandwidth in BPSK n 18

QPSK Modulator 19

Example 3: n For a QPSK modulator with an input data rate equal to 10 Mbps and a carrier frequency of 70 MHz, determine the minimum Nyquist bandwidth and the baud. Compare the results with those achieved with the BPSK modulator in Example 2. Use the QPSK block diagram modulator model. 20

Example (4) n In a QPSK Process, if the signal is I=1, Q=0 determine the output phase waveform and the amplitude of the QPSK Signal 21