ECE 4371, Fall, 2013 Introduction to Telecommunication Engineering/Telecommunication Laboratory

1. ECE 4371, Fall, 2013Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 15 Oct. 16th, 2013

2. Outline • BER and Decision • Digital Carrier System • Carrier band vs. baseband • Baud rate, bit rate, bandwidth efficiency • Spectrum • Coherent, noncoherent receiver • BER • Comparison • Homework 4 • 7.2.6, 7.3.4, 7.4.2, 7.5.1, 7.7.4, 7.8.1 • Due 11/18/13

3. Bit Error Probability Noisena(t) gTx(t) gRx(t) d(i) We assume: • binary transmission with • transmission system fulfills 1st Nyquist criterion • noise , independent of data source Probability density function (pdf) of Mean and variance

4. if • if Conditional pdfs The transmission system induces two conditional pdfs depending on

5. Example of samples of matched filter output for some bandpass modulation schemes

6. Figure 5.8 Illustrating the partitioning of the observation space into decision regions for the case when N 2 and M 4; it is assumed that the M transmitted symbols are equally likely.

7. Placing a threshold Probability of wrong decisions Probability of wrong decision When we define and as equal a-priori probabilities of and we will get the bit error probability s

8. Conditions for illustrative solution and  With  equivalently with  substituting for

9. Special Case: Gaussian distributed noise • many independent interferers • central limit theorem • Gaussian distribution Motivation: é ù 2 - 1 2 ê ú ò 2 s = - 2  P 1 e d N ê ú b p s 2 2 0 N ê ú 0 ë û no closed solution Definition of Error Function and Error Function Complement

10. 2.5 2 1.5 1 0.5 0 -0.5 -1 -1.5 -3 -2 -1 0 1 2 3 Error function and its complement • function y = Q(x) y = 0.5*erfc(x/sqrt(2)); erf(x) erfc(x) erf(x), erfc(x) x

11. Expressions with and Bit error rate with error function complement  antipodal: unipolar Q function

12. Bit error rate for unipolar and antipodal transmission • BER vs. SNR theoretical -1 simulation 10 unipolar -2 10 BER antipodal -3 10 -4 10 -2 0 2 4 6 8 10

13. Digital Carrier System Baseband analysis Signal in baseband: mean symbol energy: signal in carrier band: mean symbol energy: Conclusion: analysis of carrier band = base band. Fc=0 in project

14. Baud Rate, Bit Rate, Bandwidth Efficiency • Remember channel capacity C=Wlog2 (1+ SNR)> fb

15. Power Spectrum, ASK • Baseband • Sy(W)=Sx(W) P(W) • ASK: Sy(t)=b Acoswct, Square wave convolute with sinusoid.

16. FSK Spectrum • FSK: two sinc added together

17. BPSK Spectrum • BPSK: Sx(W): NRZ. P(t): raised cosine function. Sy(W)= P(W) • Rb baud rate

18. QPSK Spectrum • Same Rb Narrow BW

19. Pulse Shaped M-PSK • Different 

20. Bandwidth vs. Power Efficiency • Bandwidth efficiency high, required SNR is high and low power efficiency

21. QAM efficiencies • For l =1  PSD for BPSK • For l =2  PSD for QPSK, OQPSK … • PSD for complex envelope of the bandpass multilevel signal is same as the PSD of baseband multilevel signals • Same baud rate, higher bit rate. • Same bit rate, less bandwidth. But higher power

22. Minimum Shift Keying spectra • Continuous phase and constant envelop. So narrow spectrum

23. GMSK spectral shaping

24. Coherent Reception • An estimate of the channel phase and attenuation is recovered. It is then possible to reproduce the transmitted signal, and demodulate. It is necessary to have an accurate version of the carrier, otherwise errors are introduced. Carrier recovery methods include:

25. Coherent BER • PSK • BPSK QPSK • MPSK

26. Coherent BER performance • ASK • FSK • MSK: less bandwidth but the same BER • MQAM

27. Non-coherent detection • Non-coherent detection • does not require carrier phase recovery (uses differentially encoded mod. or energy detectors) and hence, has less complexity at the price of higher error rate. • No need in a reference in phase with the received carrier • Differentially coherent detection • Differential PSK (DPSK) • The information bits and previous symbol, determine the phase of the current symbol. • Energy detection • Non-coherent detection for orthogonal signals (e.g. M-FSK) • Carrier-phase offset causes partial correlation between I and Q braches for each candidate signal. • The received energy corresponding to each candidate signal is used for detection.

28. Differential Reception

29. Differential Coherent • DBPSK • 3dB loss

30. Non-coherent detection of BFSK Decision stage: + -

31. Rician pdf Non-coherent detection BER • Non-coherent detection of BFSK • Similarly, non-coherent detection of DBPSK Rayleigh pdf

32. BER Example

33. Example of samples of matched filter output for some bandpass modulation schemes

34. Comparison of Digital Modulation

35. Comparison of Digital Modulation

36. Spectral Efficiencies in practical radios • GSM- Digital Cellular • Data Rate = 270kb/s, bandwidth = 200kHz • Bandwidth Efficiency = 270/200 =1.35bits/sec/Hz • Modulation: Gaussian Minimum Shift Keying (FSK with orthogonal frequencies). • “Gaussian” refers to filter response. • IS-54 North American Digital Cellular • Data Rate = 48kb/s, bandwidth = 30kHz • Bandwidth Efficiency = 48/30 =1.6bits/sec/Hz • Modulation: pi/4 DPSK

37. Modulation Summary • Phase Shift Keying is often used, as it provides a highly bandwidth efficient modulation scheme. • QPSK, modulation is very robust, but requires some form of linear amplification. OQPSK and p/4-QPSK can be implemented, and reduce the envelope variations of the signal. • High level M-ary schemes (such as 64-QAM) are very bandwidth efficient, but more susceptible to noise and require linear amplification. • Constant envelope schemes (such as GMSK) can be employed since an efficient, non-linear amplifier can be used. • Coherent reception provides better performance than differential, but requires a more complex receiver.