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. 第二讲 射频调制与解调 Session 2 RF Modulation and Demodulation 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. Reference “Microwave and RF Design: A System Approach”, Chapter 1 Modulation Techniques Chapter 1, §1.1–§1.4

4. Modulation Schemes • The process of converting baseband information to RF is called modulation • There are two types of modulations • Analog modulation • Digital modulation

5. Modulation Schemes Analog modulation • AM Amplitude modulation • FM Frequency modulation (used in 1G AMPS) • PM Phase modulation

6. Modulation Schemes Basic digital modulation ASK Amplitude shift keying FSK Frequency shift keying PSK Phase shift keying

7. Modulation Schemes Digital modulation MSK Minimum shift keying (a form of FSK) GMSK Minimum shift keying using Gaussian filtered data BFSK Binary frequency shift keying BPSK Binary phase shift keying QPSK Quadrature PSK (QPSK is also referred to as quarternary PSK, quadraphase PSK, and quadra PSK) π/4-DQPSK π/4 Differential encoded QPSK OQPSK Offset QPSK SOQPSK Shaped Offset QPSK SBPSK Shaped BPSK FOQPSK Feher Offset QPSK 8PSK 8-state phase shift keying 3π/8-8PSK 3 π/8, 8-state phase shift keying 16PSK 16-state phase shift keying QAM Quadrature amplitude modulation

8. Analog modulation FM* AM PM AM Amplitude modulation FM Frequency modulation (used in 1G AMPS) PM Phase modulation

9. Analog Modulation • Modulation is the process of varying some characteristic of a radio signal in order toconvey information Voltage Time Note that frequency and phasemodulation look very similar with this kind of input. • This analog waveform modulates a sine-wave. • The basic, unchanging, steady radio signal without modulation is called a “carrier”. Characteristics that can be modulated: Amplitude e.g. AM radio broadcasting Frequency e.g.FM broadcasting, Voice transmission in AMPS cellular Phase

10. Amplitude Modulation (AM) Analog Modulation The First Radio System to Transmit Voice were based on amplitude modulation.

11. Amplitude Modulation (AM) Analog Modulation The First Radio System to Transmit Voice were based on amplitude modulation.

12. PAR Peak-to-Average Ratio of AM Analog Modulation PAR is an important metric for modulation formats Determines how amplifier must be designed for specified distortion.

13. PAR Peak-to-Average Ratio of AM Analog Modulation

14. Analog Modulation PAR Peak-to-Average Ratio of AM

15. Analog Modulation PAR Peak-to-Average Ratio of AM

16. Analog Modulation PAR Peak-to-Average Ratio of AM

17. Analog Modulation PAR Peak-to-Average Ratio CW Envelope AM (100%) vpeak ENVELOPE PAR = 4.26 dB vaverage= ½ vpeak RF Power With FM amplitude distortion does not matter as there is no information in the amplitude of the signal. FM PAR = 0 dB

18. TIME AMPLITUDE FDMA FREQUENCY Bandwidth: Narrow Band Communication Analog Modulation AM The majority of modulation formats result in narrow band communication systems These were the easiest modulation schemes for most of the 20th century and dictated the assignment of radio into narrow band channels. 1912: Regulation began with the sinking of the Titanic.

19. Analog Modulation Bandwidth • The two other analog modulation schemes commonly used are Phase Modulation (PM) and Frequency Modulation (FM) . Both FM and PM are called angle modulation. FM is more used than PM in analog modulation. • The signals produced by the two schemes are identical. • The difference is how the signals are generated • In PM, the phase of the carrier depends on the instantaneous level of the baseband signal. • In FM, the amplitude of the baseband signal determines the frequency of the carrier. • The result in both cases is that the bandwidth of the time-varying signal is spread. • A receiver must compress the spread-out information to re-create the original narrowband signal, and this can be thought of as processing gain, as the compression of correlated signals significantly increases the tolerance to noise. fc

20. Upper Sideband Lower Sideband Analog Modulation Bandwidth Time-Domain (as viewed on an Oscilloscope) Frequency-Domain (as viewed on a Spectrum Analyzer) Voltage Voltage 0 Frequency Time fc fc fc The bandwidth occupied by a signal depends on: • input information bandwidth • modulation method • Information to be transmitted, called “input” or “baseband” • bandwidth usually is small, much lower than frequency of carrier • Unmodulated carrier • the carrier itself has Zero bandwidth!! • AM-modulated carrier • Notice the upper & lower sidebands • total bandwidth = 2 x baseband • FM-modulated carrier • Many sidebands! bandwidth is a complex mathematical function • PM-modulated carrier • Many sidebands! bandwidth is a complex mathematical function fc

21. fc fc Analog Modulation Frequency Modulation & Bandwidth Time-Domain (as viewed on an Oscilloscope) Frequency-Domain (as viewed on a Spectrum Analyzer) Voltage Voltage 0 Frequency Time The bandwidth requirement for a frequency modulated signal is difficult to determine for arbitrary modulating signals as the frequency spectrum of this signal extends indefinitely but the amplitude of the spectrum falls off rapidly. The bandwidth occupied by a signal depends on: • input information bandwidth • modulation method • Information to be transmitted, called “input” or “baseband” • bandwidth usually is small, much lower than frequency of carrier • FM-modulated carrier • Many sidebands! bandwidth is a complex mathematical function

22. Analog Modulation Analog FM：How Much Bandwidth is Required? Input Signal Voltage fi= input signal frequency Time Voltage frequency deviation Carrier fc Frequency fc-fi fc+fi Sidebands Voltage fc+2fi fc-2fi fc+3fi fc-3fi Frequency c Carson’s Rule Bandwidth Required = 2 x (highest input frequency + frequency deviation)=2(fi+∆f) As time passes, the carrier moves back and forth in frequency in exact step with the input signal • frequency deviation is proportional to the input signal voltage • a group of many sidebands is created, spaced from carrier by amounts N xfi • relative strength of each sidebandN depends on Bessel functionNof (input signal freq./freq. deviation)

23. Analog Modulation Analog FM：How Much Bandwidth is Required? Theoretical Analysis: The βf is frequency modulation index The ∆f is the peak frequency deviation The fm is the modulating frequency

24. Analog Modulation Analog FM：How Much Bandwidth is Required? Theoretical Analysis: The βf is frequency modulation index

25. Analog FMHow Much Bandwidth is Required?

26. Analog FMHow Much Bandwidth is Required? The βf is frequency modulation index The ∆f is the peak frequency deviation The fm is the modulating frequency a group of many sidebands is created, spaced from carrier by amounts N xωm relative strength of each side band N depends on Bessel function Nof (freq. deviation/ input signal freq.)

27. Analog FMHow Much Bandwidth is Required? The βf is frequency modulation index The ∆f is the peak frequency deviation The fm is the modulating frequency It is called Carson’s rule. The bandwidth BT depends on βf and fm. 98% of total power is contained in the Bf given by:

28. Narrowband and Wideband FM The difference between Narrowband FM and Wideband FM. The best rule of thumb formula is Carson’s Rule: Bandwidth Required = BT = 2 x (highest input frequency + frequency deviation) Let's replace this by BT = Bandwidth Required f = frequency deviation fm = highest input frequency (bandwidth of modulating signal) So BT=2 * (f+ fm) Narrowband FM is when f << fm and then it can be shown that the bandwidth required is 2 * fm but only for Frequency Shift Keying (FSK) which is a two state form of FM. Wideband FM is when f>> fm and then it can be shown that the bandwidth required is 2 * f.

29. Analog Modulation PAR Peak-to-Average Ratio CW Envelope AM (100%) PAR = 4.26 dB FM PAR = 0 dB With FM amplitude distortion does not matter as there is no information in the amplitude of the signal.

30. Analog Modulation AMPS (Advanced Mobile Phone System) • AMPS (Advanced Mobile Phone System): 1G • 800 MHz Cellular FM band • Up-link(TX): 824–849 MHz, 25MHz range • Downlink(RX): 869–894 MHz, 25MHz range • 21 control channels and 395 voice channels (416 channels, FDMA). • Control channels are dedicated to digital data transmissions, providing access and paging functions (FSK). • Voice channels carry the analog voice (FM). • Each AMPS channel has a one way bandwidth of 30 kHz, for a total of 60 kHz for each duplex channel. • Supervisory audio tones (SATs) • SAT is a high pitched, inaudible tone that helps the system distinguish between callers on the same channel but in different cells. One of three tones, at 5970 Hz, 6000 Hz, or 6030 Hz, is transmitted by the base station and repeated back by the mobile. • Blank and Burst • When a base station needs to communicate information to the mobile during a conversation, it will temporarily mute the audio path and send a burst of digital data. These periods, known as blank-and-burst, generally last less than half a second, and are rarely noticed by the user.

31. Voltage 30 KHz. Channel fc Analog FM is used on : Analog Cellular (1G) Voice Channels Analog Modulation Time-Domain (as viewed on an Oscilloscope) Frequency-Domain (as viewed on a Spectrum Analyzer) Voltage Voltage Voice 0 Frequency Time Voltage Voltage SAT 0 6KHz Frequency Time Voltage Two signals simultaneously modulate the AMPS cellular voice channel: • user’s voice waveform • fm: complex, many frequencies approx. 300Hz (0.3KHz) to 3500 Hz (3.5KHz). • ∆f: peak deviation limited to +/- 12 KHz • BT:2(fm + ∆f)=2(3.5+12)KHz=31KHz • Supervisory Audio Tone (“SAT”) • fm: tone frequency 5970, 6000, or 6030 Hz (5.97kHz, 6KHz, or 6.03KHz). • ∆f: peak deviation set as +/- 2.0 KHz. • BT:2(fm + ∆f)=2(6.03+2)KHz=16.06KHz • The resulting composite FM signal fits within the assigned 30 KHz.-wide channel • Signaling Tone at 10 KHz with +/- 8 kHz. deviation is also transmitted in occasional bursts for call control. BT=36KHz

32. Analog FM is used on : Analog Cellular (1G) Voice Channels Analog Modulation -15 15 LOWER UPPER Adjacent Channels Overlap but through frequency planning a basestation does not transmit on adjacent channels. The adjacent channel is used in another cell in the cluster. CHANNEL ADJACENT ADJACENT OVERLAP OVERLAP CHANNEL CHANNEL AMPLITUDE 0 -30 30 -17.5 -12.5 17.5 12.5

33. Digital Modulation Basic digital modulations ASK Amplitude shift keying FSK Frequency shift keying PSK Phase shift keying

34. Digital Modulation Digital modulation MSK Minimum shift keying (a form of FSK) GMSK Minimum shift keying using Gaussian filtered data(used in 2G: GSM, Bluetooth) BFSK Binary frequency shift keying BPSK Binary phase shift keying (Used in Wifi: 802.11b, Bluetooth) QPSK Quadrature PSK (QPSK is also referred to as quarternary PSK, quadraphase PSK, and quadra PSK)(used in 2G: IS-95(CDMA),3G:UMTS,LTE and Wifi:802.11b) π/4-DQPSK π/4 Differential encoded QPSK (Used in extended data rate of Bluetooth) OQPSK Offset QPSK (Used in 2G: NADC(CDMA)) SOQPSK Shaped Offset QPSK SBPSK Shaped BPSK FOQPSK Feher Offset QPSK 8PSK 8-state phase shift keying (Used in 2.5G: EDGE) 3π/8-8PSK 3 π/8, 8-state phase shift keying（Used in EDGE） 16PSK 16-state phase shift keying QAM Quadrature amplitude modulation (used in 3G:LTE, Wifi 802.11g)

35. Digital Modulation • In analog modulation, frequency modulation is more used than phase modulation. • In digital modulation , phase modulation is more used than frequency modulation. ASK Amplitude shift keying FSK Frequency shift keying PSK Phase shift keying

36. Digital Modulation Voltage 1 0 1 0 Time • For example, let this digital waveform modulate a signal. No more continuous analog variations, now we’re “shifting” between discrete levels. We call this “shift keying”. • The steady radio signal without modulation is called a “carrier”. Amplitude Shift Keying ASK example: digital microwave Frequency Shift Keying FSK example:control messages in AMPS cellular; TDMA cellular Phase Shift Keying PSK examples: TDMA cellular, GSM

37. Amplitude Shift Keying (ASK) Digital Modulation

38. Digital Modulation FSK (Frequency Shift Keying) Input Signal Voltage 1 0 0 1 0 Time Output Signal Time Voltage fc Frequency E.G. AMPS Analog Radio (signaling) • Input signal is Manchester-encoded data (no DC component) • 10 KB rate • Output Signal is FSK-modulated • +/- 8 KHz deviation • Binary 0 = transition fc @ +8 to -8 KHz • Binary 1 = transition fc @ -8 to +8 KHz. • On voice channels, when system messages must be sent, the FM voice and SAT modulation is briefly muted and replaced by FSK (this is called “blank and burst” mode) • On control channels, FSK data is transmitted exclusively (no voice)

39. FSK Modulation Digital Modulation

40. 1 0 0 T 0 T/2 T 1 0 X Modified forms of FSK: MSK & GMSK Digital Modulation MSK Minimum Shift Keying NRZ Data FILTER FSK Modulated Output FSK Modulator 1 0 1 Carrier GMSK Gaussian Minimum Shift Keying Input: Binary Data Gaussian Filter MSK Modulator GMSK Output • MSK and GMSK are forms of FSK • input signal is pre-filtered to eliminate abrupt shifts • this reduces the spectrum occupied by the output signal • MSK • The frequency shift never produces a phase discontinuity; this reduces spectrum required • the output spectrum still contains sidelobes • GMSK: Used in GSM, Side lobes in output spectrum are prevented by the gaussian pre-filtering • Generates narrow power spectrum • Spectrally efficient modulation technique • BER is slightly worse than MSK. This is a worthwhile tradeoff since error control coding is available

41. Digital Modulation Constellation Diagram (IQ Modulation) In real world, a signal is represented as following: It can be expended as: If I(t) and Q(t) are defined: I(t) or Q(t）is called the in-phase or quadrature component repectivelly. I/Q representation for S(t) is :

42. Digital Modulation Constellation Diagram Q I(t) and Q(t）can be expressed in IQ diagram or constellation diagram in real signal space. It is called signal space diagram. (I,Q) I IQ Diagram

43. Digital Modulation Constellation Diagram S(t) can be represented in following way: . If SC(t) is defined as: So that SC(t) is representation of S(t) in complex plane

44. Digital Modulation Constellation Diagram SC(t) jQ I+jQ IQ diagram or constellation diagramcan be expressed in complex plane. I IQ or constellation diagram in complex plane

45. Digital Modulation Constellation Diagram Serial bit stream serial to parallel b0b1b2b3b4b5b6b7b8b9… bi is either binary 1 or binary 0

46. Q I ASK Modulation Digital Modulation Constellation Diagram Voltage 1 0 1 0 Time 0 1

47. Digital Modulation FSK Modulation Constellation Diagram Voltage 1 0 1 0 Time Q I 1 It is hard to represent FSK in I-Q diagram because frequency is changed ?

48. Q I Digital Modulation PSK Modulation Constellation Diagram Voltage 1 0 1 0 Time 1 -1

49. Digital Modulation BPSK(Binary Phase Shift Keying) (1) PSK(Phase Shift Keying) • A theoretical definition of a symbol is a waveform, a state, an event or a significant condition of the communication channel that persists for a fixed period of time. Simply, a symbol is an electrical waveform that can present one or more bits. • In IQ diagram a symbol is a point. • In BPSK (Binary Phase Shift Keying) a symbol carries a binary bit. States: 21=2 Voltage 1 0 1 0 Time b0b1b2b3b4b5b6b7b8 b9…→b0, b1, b2, b3, b4, b5, b6, b7, b8 , b9,…

50. BPSK(Binary Phase Shift Keying) (1) Digital Modulation PSK(Phase Shift Keying) b0, b1, b2, b3, b4, b5, b6, b7, b8 , b9,… serial to parallel b0, b1, b2, b3, b4, b5, b6, b7, b8 , b9,… 0