Bandpass Modulation & Demodulation Detection CHAPTER 4 Bandpass Modulation & Demodulation Detection School of Computer and Communication Engineering, Amir Razif Arief b. Jamil Abdullah EKT 431: Digital Communications

Last time we talked about: Another source of error due to filtering effect of the system: Inter-symbol interference (ISI)‏ The techniques to reduce ISI Pulse shaping to achieve zero ISI at the sampling time Equalization to combat the filtering effect of the channel

Average   65.9 Max 97.0 Min 35.0 Stdev 13.9

Baseband Modulation and Demodulation Detection Digital Bandpass Modulation Techniques Detection of Signals in Gaussian Noise Coherent Detection Noncoherent Detection M-ary Signaling and Performance

Today, we are going to talk about: Some bandpass modulation schemes used in DCS for transmitting information over channel M-PAM, M-PSK, M-FSK, M-QAM How to detect the transmitted information at the receiver Coherent detection Non-coherent detection

Modulation Modulation~ is the process of digital symbols are transform into waveforms that are compatible with the characteristics of the channel. Bandpass Modulation~ the shape modulate the carrier wave. For radio transmission the carrier is converted to an electromagnetic (EM) field for propagation to the desired destination. Through carrier wave modulation the size of antenna can be reduced for high frequency transformation. FDMA Uses to minimize the effect of interference, to separate different signal transmitting using single channel.

Block Diagram of a DCS Digital Modulation ~ digital symbols transform into waveforms that are compatible with channel characteristics. Baseband modulation ~ shaped pulses modulate a sinusoid carrier wave (carrier) for radio transmission the carrier is converted to EM. Format Source encode decode Channel Pulse modulate Bandpass Demod. Sample Detect Digital modulation Digital demodulation

Digital Bandpass Modulation Techniques ~ The process of converting a data signal to a sinusoidal waveform where its amplitude, phase or frequency, or a combination of them, are varied in accordance with the transmitting data. Carrier wave; where wo~ radian frequency f(t)~ phase f & w~ frequency denotes average symbol energy given by Coherent detection~ The receiver exploits the knowledge of the carrier’s phase to detect the signals. noncoherent detection~ The receiver does not utilize the phase reference information.

Noncoherent demodulation~ Refers to systems employing demodulator that are designed to operate without knowledge of the absolute value of the incomming signal’s phase It reduce complexity compare to coherent demodulation and increase probability error (PE) Phasor representation of sinusoid ejwot consists of (1) inphase (real) component and (2) quadrature (imaginary) component that are orthogonal to each other.

Bandpass Modulation Bandpass signal: where is the baseband pulse shape with energy . We assume here (otherwise will be stated): is a rectangular pulse shape with unit energy. Gray coding is used for mapping bits to symbols. denotes average symbol energy given by

Contd… Bandpass Modulation

Bandpass Modulation Bandpass signal: where is the baseband pulse shape with energy. We assume here (otherwise will be stated): is a rectangular pulse shape with unit energy. Gray coding is used for mapping bits to symbols. denotes average symbol energy given by

Frequency Shift Keying (FSK) General analytic expression for FSK; where wi have M discrete values, s(t) is an arbitrary constant symbol transition depicts a gentle shift from one frequency tone to another. True for CPFSK only. In MFSK the change to a different tone is quite abrupt. Orthogonal signal, signal with mutually perpendicular vector.

Contd.. Frequency Shift Keying (FSK) FSK Bandwidth; Df ~ (fm-fs)/2 Df ~ frequency space and mark between different absolute (Hz) deviation frequency. fm-fs ~ absolute different between mark and space frequency. B= |(fs-fb) - (fm-fb)| = |fs-fm| + 2fb = 2Df + fb

Contd.. Frequency Shift Keying (FSK)

Amplitude Shift Keying (ASK) General analytic expression for ASK; where si(t) will have M discrete values where wi have M discrete values, s(t) is an arbitrary constant

Phase Shift Keying (PSK) General analytic expression for PSK; where si(t) will have M discrete values E ~ energy T~ duration For BPSK, M=2 Shift si(t) phase state zero and (p) 1800.

Contd… Phase Shift Keying (PSK) BPSK transmitter BPSK Receiver Bit value 0 –sine wave Bit value 1 –inverted sine wave Very simple PSK Low spectral efficiency Robust , used in satellite system

Two Dimensional Modulation, demodulation and detection (M-PSK)‏ M-ary Phase Shift Keying (M-PSK)‏

Two Dimensional Mod.,… (MPSK)‏ BPSK (M=2)‏ “0” “1” 8PSK (M=8)‏ “110” “000” “001” “011” “010” “101” “111” “100” QPSK (M=4)‏ “00” “11” “10” “01”

Two Dimensional Mod.,…(MPSK)‏ Coherent detection of MPSK Compute Choose smallest

Two Dimensional Mod., (M-QAM)‏ M-ary Quadrature Amplitude Mod. (M-QAM)‏

Two dimensional mod (M-QAM)‏ “0000” “0001” “0011” “0010” 1 3 -1 -3 “1000” “1001” “1011” “1010” “1100” “1101” “1111” “1110” “0100” “0101” “0111” “0110” 16-QAM

Two dimensional mod., (M-QAM)‏ Coherent detection of M-QAM ML detector Parallel-to-serial converter ML detector

Multi-Dimensional Modulation, Demodulation & Detection M-ary Frequency Shift keying (M-FSK)‏

Multi-dimensional mod.,…(M-FSK)‏ ML detector: Choose the largest element in the observed vector

Non-Coherent Detection No need for a reference in phase with the received carrier Less complexity compared to coherent detection at the price of higher error rate.

Non-Coherent Detection … Differential coherent detection Differential encoding of the message The symbol phase changes if the current bit is different from the previous bit. Symbol index: Data bits: Diff. encoded bits Symbol phase: 0 1 2 3 4 5 6 7 1 1 0 1 0 1 1 1 1 1 0 0 1 1 1 2006-02-13 Lecture 7

Non-Coherent Detection … Coherent detection for diff encoded mod. assumes slow variation in carrier-phase mismatch during two symbol intervals. correlates the received signal with basis functions uses the phase difference between the current received vector and previously estimated symbol

Non-Coherent Detect… Optimum differentially coherent detector Sub-optimum differentially coherent detector Performance degradation about 3 dB by using sub-optimal detector Decision Delay T Decision Delay T

Non-coherent detection … Non-coherent detection of BFSK Decision stage: + -