射频工程基础 Fundamentals of RF Engineering

1. 射频工程基础Fundamentals of RF Engineering 学时:60/20 学分: 3.5 孙利国 中国科技大学信息学院电子工程与信息科学系

2. 教材：理论教学 教材：以课堂讲义为主。 主要参考书： [1]“Microwave and RF Design: A System Approach”, Michael Steer, SciTech Publishing, 2010 其它参考书： [2] “射频电路设计-理论与应用”，Reinhold Ludwig等著，王子宇等译，电子工业出版社，2002 [3] “射频微电子学”，拉扎维著，余志平等译，清华大学出版社，2006 [4] RF and Microwave Circuit Design for Wireless Communications, Lawrence Larson, Artech House, 1997 [5]”无线网络RF工程：硬件、天线和传播“， Daniel M.Dobkin 著 ，科学出版社 ，2007

3. 第三讲 射频发射机和接收机 Session 3 RF Transmitter and Receiver 教材：以课堂讲义为主。 主要参考书： [1]“Microwave and RF Design: A System Approach”, Michael Steer, SciTech Publishing, 2010 其它参考书： [2] “射频电路设计-理论与应用”，Reinhold Ludwig等著，王子宇等译，电子工业出版社，2002 [3] “射频微电子学”，拉扎维著，余志平等译，清华大学出版社，2006 [4] RF and Microwave Circuit Design for Wireless Communications, Lawrence Larson, Artech House, 1997 [5]”无线网络RF工程：硬件、天线和传播“， Daniel M.Dobkin 著 ，科学出版社 ，2007

4. Reference “Microwave and RF Design: A System Approach”, Chapter 1 Modulation Techniques Chapter 1, §1.5–§1.8

5. Receiver and TransmitterNoise, Interference and DistortionTransmitterFundamental of demodulatorEarly ReceiverModern Receiver

6. Receiver and Transmitter 发射天线 接收天线 发射系统 接收系统 话筒 扬声器 电波传播 发射天线 接收天线 电波传播 低噪声放大器 混频器 混频器 功率放大器 话筒 PA LNA 扬声器 噪声与干扰 低通滤波器 带通滤波器 带通滤波器 振荡器 振荡器

7. Receiver and Transmitter Transmitter Receiver 选自“Microwave and RF Design: A System Approach”

8. Noise, Interference and Distortion C: the channel capacity in bits per second (bits/sec) B: the bandwidth of channel in hertz (Hz=1/sec) S: average received signal power over the bandwidth in watts (Joule/sec.) N: average noise or interference power over bandwidth in watts(Joule/sec) S/N: the signal to noise ratio (SNR) or signal to interference ratio (SIR) • Noise, interference and distortion are major concerns for RF Design (e.g. Receivers, Transmitters) • Power signal and energy signal • Power signal: finite power and infinite energy • Energy signal: zero average power and finite energy. • Signal to noise ratio is an important parameter in RF design. It determines the maximum rate at which information can be transmitted over a specified bandwidth in the presence of noise according to Shannon theorem:

9. Noise, Interference and Distortion • Analog Radio • Usually analog signal is power signal. Power is more meaningful than energy . • The signal to noise ratio (SNR) is a very useful parameter in analog radio. • SNR is defined as: • SNR = S/N=Signal power(Watt) /Total noise power(Watt). • The noise is due to background noise sources, including thermal noise, etc.

10. Noise, Interference and Distortion • When expressed in decibels, the noise figure (NF) is used: • In receiver chain, the input SNR (SNRi) to output SNR (SNRo) ratio is called the noise factor , F:

11. Noise, Interference and Distortion • Thermal Noise

12. Noise, Interference and Distortion • As NF increases, the sensitivity gets worse. • As B increases, the sensitivity gets worse • As SNRo increases, the sensitivity gets worse.

13. Noise, Interference and Distortion • Digital Radio • Usually digital signal is energy signal. Symbol energy or bit energy is more suitable than power. • In digital radio Eb/N0 is useful parameter instead of SNR. The Eb is the energy per bit (Joule/bit) and N0 is the noise power per hertz (Watt/Hz=Joule) . The is called SNR per bit , bit SNR, or normalized SNR.

14. Noise, Interference and Distortion • The spectral efficiency is defined as : • The relationship between Eb/N0 and SNR is given by:

15. Noise, Interference and Distortion • The spectral efficiency is defined as : • Spectral efficiency • the information rate that can be transmitted over a given bandwidth in a specific communication system. • It is a measure of how efficiently a limited frequency spectrum is utilized by the physical layer protocol。 • It is measured in bit/s/Hz or in (bit/s)/Hz. • It is the net bit rate in bit/s divided by the bandwidth in hertz of a communication channel.

16. Noise, Interference and Distortion • Another similar parameter is Es/N0. Es is signal energy per symbol (e.g. symbol energy).

17. Noise, Interference and Distortion • Alternatively, the spectral efficiency may be measured in bit/symbol, which is equivalent to bits per channel use (bpcu), implying that the net bit rate is divided by the symbol rate (modulation rate).

18. Noise, Interference and Distortion • The SNR can be expressed by :

19. Noise, Interference and Distortion

20. Noise, Interference and Distortion

21. Noise, Interference and Distortion • As NF increases, the sensitivity gets worse. • As Rs or Rb increases, the sensitivity gets worse • As Es/N0 or Eb/N0 increases ,the sensitivity gets worse. • Es/N0 or Eb/N0 is related to the BER (Bit Error Rate)

22. Noise, Interference and Distortion • In digital transmission, the probability of bit error (Pe) or bit error rate (BER) is usually used to measure deterioration. • the number of bit errors is the number of received bits that have been altered due to noise, interference, distortion or bit synchronization errors. • The bit error rate or bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER is often expressed as a percentage. • In a noisy channel, the BER is often expressed as a function of the Eb/N0, (energy per bit to noise power spectral density ratio), or Es/N0 (energy per modulation symbol to noise spectral density).

23. Noise, Interference and Distortion • The bit error probabilitype (BER) in an additive white Gaussian noise (AWGN) environment with respect to the Eb/N0 is given by: BER decreases (gets better) with the Eb/N0

24. Noise, Interference and Distortion • The bit error probabilitype (BER) in an additive white Gaussian noise (AWGN) environment with respect to the Eb/N0 is given by:

25. 0 -10 -20 -30 -40 -50 fc fc+1fbit fc+2fb fc+4fb fc+3fb Noise, Interference and Distortion Comparison of QPSK and FSK Power Spectral Density QPSK vs. FSK FSK QPSK Frequency Treat GMSK (as in GSM) as FSK; Treat pi/4 DQPSK (as in DAMPS) as QPSK. Power Spectral Density • QPSKmain lobe narrower than FSK • QPSKbetter for high capacity applications such as voice channels of TDMA cellular • FSKside lobes roll of faster than QPSK • FSK better for control channel use • Other Observations: • FSKmodulation simpler to implement. • With filtering, both methods have attenuation >26 db on adj. ch.

26. BER Performance Comparison QPSK vs FSK 1 0.01 FSK 0.0001 1E-6 1E-8 QPSK BER 1E-10 1E-12 1E-14 1E-16 1E-18 1E-20 0 2 4 6 8 10 12 14 16 18 20 Eb/No (db) Noise, Interference and Distortion Comparison of QPSK and FSK Treat GMSK (as in GSM) as FSK; Treat pi/4 DQPSK (as in DAMPS) as QPSK. For same BER, for example 1E-8, Eb/N0 for QPSK (around 12dB) is 3 dB less than that for FSK (around 15dB). It results that the sensitivity for QPSK will be 3dB better than that for FSK. BER Performance • QPSK approx. 3dB better than FSK Eb/No = (S/N)(BN/R) Eb = Energy per bit No = Noise per bit N = Total noise power S = Signal power BN = Noise bandwidth R = Bit Rate BN is the bandwidth over which the signal is spread using the modulation technique or perhaps coding. It just so happens to also be the noise bandwidth and any noise outside this bandwidth can be eliminated through digital signal processing. If the signal is spread over bandwidth BN then the noise in this bandwidth cannot be avoided. The Processing gain that derives from the redundancy in the transmitted information is (BN/R).

27. Noise, Interference and Distortion Example for sensitivity calculation

28. Noise, Interference and Distortion • Example for WLAN • Sensitivity is -94dBm for 1Mbps • Sensitivity is around -91dBm for 2Mbps (10log102=3dB） • Sensitivity is around -87dBm for 5.5 Mbps (10log105.5=7.4dB） • Sensitivity is around -84 dBm for 11 Mbps (10log1011=10.4dB）

29. Noise, Interference and Distortion • In cellular wireless system, the minimum signal detectable is determined by the signal to interference ratio (SIR). The dominate interference is due to other transmitter. • The interference produced in the signal band from other transmitter at the same frequency is called the co-channel interference. • Adjacent-channel interference (ACI) is interference caused by extraneous power from a signal in an adjacent channel. ACI is the result of several factors • Different digital modulation scheme has different spectrum. • The ideal filtering cannot be achieved, there is inherent overlap of neighboring channels. • The nonlinear behavior of transmitters also contributes to adjacent channel interference. Thus characterization of nonlinear phenomena is important in RF design. • Adjacent channel interference occurs with both digitally-modulated and analog modulated RF signals.

30. Noise, Interference and Distortion

31. Noise, Interference and Distortion The signal between frequencies F1 and F2 is due to the digital modulation scheme and filtering. Most of the signal outside this region is due to nonlinear effects which result in what is called spectral regrowth, a process similar to third and fifth-order intermodulation in two-tone systems. The lower channel ACPR is defined as:

32. Noise, Interference and Distortion ACPR (Adjacent Channel Power Ratio) for WLAN （IEEE 802.11） In accordance with IEEE802.11b/g, if the transmitting modulation operates at the modes of 1Mbps of DPSK, 2 Mbps of QPSK, and 5.5 and 11 Mbps of CKK, the transmitted spectral products shall be less than –30 dBr (dB relative to the Sin(x)/x peak) for fc – 22 MHz < f < fc –11 MHz; and fc + 11 MHz < f < fc + 22 MHz; and shall be less than –50 dBr for f < fc – 22 MHz; and f > fc + 22 MHz. where fc is the channel center frequency.

33. Noise, Interference and Distortion ACPR for WLAN （IEEE 802.11） Transmit spectrum mask.

34. Noise, Interference and Distortion ACPR for WLAN （IEEE 802.11） On the other hand, if the transmitting modulation operates using the OFDM modes, the transmit power spectrum mask is defined as Transmit Spectrum Mask for OFDM Modes.

35. Digitally-Modulated Signal: Frequency Domain Noise, Interference and Distortion WCDMA, BW = 5 MHZ GSM, BW = 200 kHZ CDMA = 1.23 MHz MAIN CHANNEL 80 dB 80 dB LOBES WCDMA

36. Noise, Interference and Distortion Digitally-Modulated Signal: Time Domain 80 dB 1 part 104 in voltage 80 dB Modeling Nonlinear RF Systems Corollaries: Using time-domain data to model nonlinear RF effects will not work. BER Adjacent Channel Interference

37. 5 MHz 1 Part in 400 FREQUENCY Noise, Interference and Distortion Perspectives: WCDMA in the Frequency Domain FREQUENCY (GHz) 2 GHz

38. Noise, Interference and Distortion • Distortion • In-Band: • Intermodulation • Noise • Bit Errors • Out-of-Band: • Spectral Regrowth • Affect on other radios

39. Distortion Noise, Interference and Distortion x(t) y(t) Ideally an amplifier is assumed as a linear system: y(t) x(t) Practically it is a nonlinear system: Simply it limited to three terms

40. Noise, Interference and Distortion Distortion Input: x(t) y(t) Output: y(t) x(t) DCShift Linear Term Gain Compression (a3<0) Second Harmonic Third Harmonic

41. Noise, Interference and Distortion Distortion Gain Compression (a3<0) x(t) y(t) y(t) x(t) This effect is quantified by the “1-dB compression point” defined as the input signal level that cause gain to drop by 1 dB. A measure of the maximum input of the circuit.

42. Noise, Interference and Distortion Distortion y(t) Input( two tones): x(t) y(t) x(t) Output:

43. Noise, Interference and Distortion Distortion y(t) x(t) y(t) Input: x(t) Output:

44. Noise, Interference and Distortion Distortion y(t) x(t) y(t) Input: x(t) Output:

45. Noise, Interference and Distortion Distortion y(t) Input: x(t) y(t) x(t) Assume signal1 is fundamental and signal2 is interference. • If a3<0, the gain is a decreasing function of A2. For significantly large A2, the gain drops to zero, which is said that the signal is blocked. • The “blocking signal” refers to interference that desensitize a circuit even if the gain does not fall to zero. • In addition, the variation in A2 affects the amplitude of the output of signal1, which is called “cross modulation”

46. Noise, Interference and Distortion Distortion • In addition, the variation in A2 affects the amplitude of the output of signal1, which is called “cross modulation” For example, if the amplitude of the interferer is modulated by a sinusoid: The desired signal at the output contains amplitude modulation. Nonlinearities in the amplifier corrupt each signal with the amplitude variations in other channels.

47. Distortion Noise, Interference and Distortion y(t) Input （A1=A2=A）: x(t) y(t) x(t) Output:

48. Noise, Interference and Distortion Distortion y(t) Input: x(t) y(t) x(t) Output (especially):

49. Noise, Interference and Distortion Distortion TWO-TONE INPUT SIGNAL(f1 and f2) CLIPPED OUTPUT SIGNAL Clipping results in third-order intermodulation products (f3 and f4) Intermodulation distortion is the worst kind of distortion.

50. Noise, Interference and Distortion Distortion y(t) x(t) y(t) x(t) Output (especially): Intermodulation Corruption of a signal due to intermodulation between two interferers