Lab 4

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1 EE4650 通訊實驗 Lab 4 PSK, FSK, and ASK Digital Modulations 1

2 Lab 4:PSK, FSK, ASK Digital Modulations Baseband Tx RF Frontend M- Seq 0101 Error Correction coding Digital Modulation D/A BPF PA cos(2πf c t) AWGN Baseband Rx RF Frontend Error Correction decoding Digital Demodulation A/D BPF LNA cos(2πf c t) 2

3 實驗目的瞭解數位調變器 (Digital Modulator) 的原理及其相關應用學習如何用 LabVIEW 來模擬 PSK FSK ASK 觀察調變訊號的波形, 了解雜訊干擾下的解調狀況實驗器材 LabVIEW 軟體 Modulation Toolkit 3

4 Given a carrier signal, Digital Modulation ( π f t) s( t) = Acos 2, 0 t T c the binary sequence I i = {±1} is keyed into the carrier signal. ( π θ ) s ( t ) = A co s 2 f t +, 0 t T i i i i The carrier signal can be modulated with Phase (θ i ): Phase Shift Keying Frequency (f i ): Frequency Shift Keying Amplitude (A i ): Amplitude Shift Keying 4

5 Phase Shift Keying (PSK) Conveys data by modulating the phase of a reference carrier signal Usually represent on a constellation diagram Common examples: BPSK, QPSK Higher order: M-PSK 1 0 BPSK Symbol to signal mapping example 5

6 The simplest form of PSK General form: Binary PSK (BPSK) 2 E s i ( t ) = ± g ( t ) co s ( 2π f ct ) T 1, 0 t T w h ere g ( t ) = is called th e p u lse sh ap in g fu n ctio n. 0, o th erw ise T 2T 3T 4T 5T Timing diagram for BPSK 6

7 Pulse Shaping with Limited Bandwidth Ideal Infinite Bandwidth Channel H(f) h(t) t y(t) =h(t)*x(t)+w(t) Pulse shaping for limited bandwidth Careful pulse shaping needed to avoid inter-symbol interference (ISI) f 7

8 BPSK Modulation with sinc() Pulse Shaping Function 如果信號的取樣點取在整數 T b (=1/2W) 的位置, ISI 的效應會剛好消失具有這樣特性的 pulseshaping 函數稱作 Nyquist pulse 常用 pulse shaping function - Raised Cosine - Gaussian A series of sinc pulses corresponding to the sequence

9 常用的 Pulse Shaping Function Raised Cosine function Freq response Gaussian function Freq response Time response 9

10 General form of M-PSK QPSK and M-PSK 2 E π s i ( t ) = ± g ( t ) co s 2 π f ct + (2i 1), i = 1,..., M T M 1, 0 t T w h ere g ( t ) = is th e p u lse sh ap in g fu n ctio n. 0, o th erw ise I Q signal 0 T 2T 3T 4T 5T Timing diagram for QPSK 10

11 Frequency Shift Keying (FSK) Conveys data by modulating the frequency of a reference carrier signal The simplest FSK is binary FSK (BFSK): use a pair of frequencies to transmit binary bits General form of BFSK: Limitation: bandwidth T 2T 3T 4T 5T Timing diagram for BFSK 11

12 Amplitude Shift Keying (ASK) Conveys data by modulating the amplitude of a reference carrier signal Limitation: noise symbol carrier signal 0 T 2T 3T 4T 5T Timing diagram for BASK 12

13 實驗步驟一 : M-PSK transmitter channel receiver Information bits PSK/FSK/ASK modulator PSK/FSK/ASK demodulator Output sequence noise 運用 LabVIEW 完成 M-PSK modulation/demodulation 觀察星座圖並記錄波形 4-PSK, SNR= 25dB 32-PSK, SNR = 25dB 32-PSK, SNR = 35dB 13

14 實驗步驟二 : M-FSK 運用 LabVIEW 完成 M-FSK modulation/demodulation 14

實驗步驟二 : M-FSK 運用 LabVIEW 完成 M-FSK modulation/demodulation 設定

.., 6MHz, 進行以下頻譜觀察並記錄波形 4-FSK, total bits = 128, symbol rate

total bits = 128, symbol rate = 200KHz 8-FSK, total bits =

15 實驗步驟二 : M-FSK 運用 LabVIEW 完成 M-FSK modulation/demodulation 設定 carrier frequency = 5MHz,FSK deviation = 1MHz, i.e. f i = 4MHz, (4+2/(M-1))MHz, (4+4/(M-1))MHz,..., 6MHz, 進行以下頻譜觀察並記錄波形 4-FSK, total bits = 128, symbol rate = 200KHz 4-FSK, total bits = 128, symbol rate = 100KHz 8-FSK, total bits = 128, symbol rate = 200KHz 8-FSK, total bits = 512, symbol rate = 200KHz 15

16 實驗步驟三 : M-ASK 運用 LabVIEW 完成 M-ASK modulation/demodulation 操作控制面板 M =4/8, carrier freq. = 1MHz,symbol rate = 200k,pulse shaping filter = Raised Cosine, 並記錄星座圖及波形 16

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