Dept. of EE, NDHU 1 Chapter Four Bandpass Modulation and Demodulation

Dept. of EE, NDHU 2 Bandpass Signaling

Dept. of EE, NDHU 3 Why Modulate? The transmission of EM fields through space is accomplished with the antenna The size of the antenna depends on the wavelength l –Telephone industry benchmark of l/4 as the antenna dimension –Example : 3kHz baseband signal needs about 15 miles for the antenna diameter –Example: 900MHz signal needs about 8cm for the antenna diameter Bandpass modulation is an essential step for all systems involving radio transmission Modulation can separate the different signals (Ex. FDMA) Modulation can also be used to place a signal in a frequency band where design requirement can be easily met

Dept. of EE, NDHU 4 Digital Bandpass Modulation Techniques Bandpass modulation is the process by which an information signal is converted to a sinusoidal waveform (carrier waveform) Three features can be used to distinguish the sinusoidal waveform –Amplitude, frequency, phase Coherent detection –The receiver exploits knowledge of the carrier’s phase to detect the signa –PSK, FSK, ASK, CPM, and Hybrid forms Non-coherent detection –The receiver does not utilize the carrier’s phase reference information –DPSK, FSK, ASK, CPM, and Hybrid forms

Dept. of EE, NDHU 5 Digital Modulations

Dept. of EE, NDHU 6 Detection of Signals in Gaussian Noise Bandpass model of the detection process is virtually identical to the baseband model Decision regions –Minimum error decision rule is to choose the signal class that the distance d(r,s i ) is minimized, where r is the received signal Correlation receiver –Transform the received waveform into a point in the decision space –Determine in which decision region the point is located Choose the s i (t) whose index corresponds to max z i (T)

Dept. of EE, NDHU 7 Decision Regions

Dept. of EE, NDHU 8 Correlator Receiver with Reference Signals

Dept. of EE, NDHU 9 Binary Correlator Receiver

Dept. of EE, NDHU 10 Coherent Detection of PSK BPSK signal Decision stage chooses the signal with largest output value of matched filter

Dept. of EE, NDHU 11 Sampled Matched Filter

Dept. of EE, NDHU 12 Coherent Detection of MPSK MPSK signal Signal space and decision regions for a QPSK (M=4) system –As shown in Fig.4.11 –Make a decision by the phase information

Dept. of EE, NDHU 13 Demodulator for MPSK Signals

Dept. of EE, NDHU 14 Coherent Detection of FSK FSK signal The distance between any two signal vectors is Choose the largest output of matched filter

Dept. of EE, NDHU 15 Signal Space for a 3-ary FSK Signal

Dept. of EE, NDHU 16 Signal Space for DPSK

Dept. of EE, NDHU 17 Detection of Differential PSK Differential encoding for the PSK signal Signaling characteristics Non-coherent detection Compare with PSK and DPSK –PSK detection is with only one noise signal –DPSK detection is with two noise signal (differentially decoding)

Dept. of EE, NDHU 18 Binary Differential PSK Example Suboptimum detection Optimum detection

Dept. of EE, NDHU 19 Non-coherent Detection of FSK Quadrature Receiver

Dept. of EE, NDHU 20 Non-coherent Detection of FSK Non-coherent detection of FSK with envelop detector

Dept. of EE, NDHU 21 Tone Spacing for Non-coherent Orthogonal FSK Signaling Two tones f 1 and f 2 are orthogonal –For a transmitted tone f 1, the sampled envelop of the receiver output filter tuned to f 2 is zero Minimum tone spacing for orthogonal FSK signaling –Non-coherently detected FSK –Coherent FSK signaling is 2/T

Dept. of EE, NDHU 22 Minimum Tone Spacing for Non- coherent Orthogonal FSK For binary FSK, bandwidth is two times the tone spacing For M-ary FSK, bandwidth is M/T

Dept. of EE, NDHU 23 D8PSK Modulator

Dept. of EE, NDHU 24 D8PSK Demodulator

Dept. of EE, NDHU 25 Error Performance for Binary Systems Bit error probability for BPSK signaling Probability of bit error for coherent detected, differential encoded binary PSK Probability of bit error for coherently detected binary orthogonal FSK Probability of bit error for non-coherently detected binary orthogonal FSK

Dept. of EE, NDHU 26 Binary DPSK DPSK signaling Pairs of DPSK signals, S 1 (t) and S 2 (t) are orthogonal DPSK detection can be implemented by matching signal envelopes Bit error probability is similar to the one for non-coherently detected binary FSK

Dept. of EE, NDHU 27 DPSK Detection

Dept. of EE, NDHU 28 Bit Error Probability of Binary Systems

Dept. of EE, NDHU 29 M-ary Signals and Performance

Dept. of EE, NDHU 30 Ideal Probability of Bit Error Performance

Dept. of EE, NDHU 31 Bit Error Performance for M-ary Orthogonal Signaling

Dept. of EE, NDHU 32 Bit Error Performance for Multiple Phase Signaling

Dept. of EE, NDHU 33 M-ary Signaling M-ary signaling instructs the modulator to produce one of M=2 k waveforms M-ary multiple phase signaling –The BER curve moves in the direction of degraded error performance as k increases –A larger bit rate can be transmitted within the same bandwidth as k increases M-ary orthogonal signaling –The BER curve moves in the direction of improved error performance as k increases –The required system bandwidth increases as k increases

Dept. of EE, NDHU 34 Vectorial View of MPSK Signaling

Dept. of EE, NDHU 35 Relation Between Eb/N0 and S/N General relationship between Eb/N0 and S/N For the QPSK signaling –QPSK bit stream is usually partitioned into an even and odd stream; each new stream is at half the bit rate of the original stream –Each of the quadrature BPSK signals has half of the average power of the original QPSK signal (as shown in Fig. 4.31)

Dept. of EE, NDHU 36 Vectorial View of MFSK Signaling

Dept. of EE, NDHU 37 Symbol Error Performance for Coherent FSK Signaling

Dept. of EE, NDHU 38 Eb/N0 and SNR in the MFSK

Dept. of EE, NDHU 39 Symbol Error Versus Bit Error for FSK Signaling

Dept. of EE, NDHU 40 Symbol Error Performance for M- ary Systems Symbol error performance for coherently detected M-ary PSK Symbol error performance for differentially coherent detection of MPSK signal Probability of symbol error for coherently detected MFSK signal Probability of symbol error for non-coherently detected MFSK signal

Dept. of EE, NDHU 41 Symbol Error Performance for Coherently Detected MPSK

Dept. of EE, NDHU 42 Symbol Error Performance for Coherently Detected MFSK

Dept. of EE, NDHU 43 Symbol Error Performance for Non-coherently Detected MFSK

Dept. of EE, NDHU 44 Bit Error Versus Symbol Error Probability Orthogonal signal

Dept. of EE, NDHU 45 Bit Error Versus Symbol Error Probability Multiple Phase signals with Gray coded For BPSK and QPSK signaling