The Abdus Salam International Centre for Theoretical Physics ICTP-ITU/BDT School on Sustainable Wireless ICT Solutions for Environmental Monitoring 6 – 22 February 2012, ICTP, Miramare-Trieste, Italy RF Channel & Modulation Fundamentals Prof. Ryszard Struzak National Institute of Telecommunications, Poland r.struzakATieee.org Objective • Review of basic physical processes involved in modern communication systems that may be needed to understand better the further training/ teaching activities at ICTP (CC) R Struzak <[email protected]> 2 Topics for discussion • Radio transmission • Modulation schemes • Constellation diagrams • Modulation spectra (CC) R Struzak <[email protected]> 3 http://ursi.org/files/RSBissues/ RSB_339_2011_12.pdf (CC) R Struzak <[email protected]> 4 (CC) R Struzak <[email protected]> 5 Source: URSI RSB No 339 Dec. 2011 (CC) R Struzak <[email protected]> 6 Source: URSI RSB No 339 Dec. 2011 (CC) R Struzak <[email protected]> 7 Radio Transmission System • A message, from a source of messages, is delivered to a distant destination via radio communication channel using energy of radio waves » Message in its most general meaning is the object of communication. Depending on the context, the term may apply to both the information contents and its actual presentation, or signal. » The baseband signal usually consist of a finite set of symbols. E.g. text message is composed of words that belong to a finite vocabulary of the language used. Each word in turn is composed by letters of a (finite) alphabet. (Analog-to-digital conversion) » The channel consists of a transmitter node, radio propagation path and receiver node. • The radio propagation process distorts the signal » Predictable vs unpredictable distortions • The transmitter & receiver pair process the signal to repair the signal distortions following common communication protocol and communication policy (CC) R Struzak <[email protected]> 8 Volume of information transmitted by isolated communication channel C = B*log2{1 + [S/(No*B)]} Noise power density, W/Hz Received signal power, W Bandwidth, Hz Capacity (maximum throughput), bit-per-second • The capacity to transfer error-free information is enhanced with increased bandwidth B, even though the signal-to-noise ratio is decreased because of the increased bandwidth. • C/B (bps/Hz) → bandwidth efficiency (CC) R Struzak <[email protected]> 9 • The actual throughput can only approach the channel capacity using an extremely complicated encoder. – The statistical properties of the signal approach those of Gaussian noise and the coding time increases indefinitely. – Rice (1950) has shown that in order to achieve a data rate which is 96 percent of the channel capacity with S/NoB = 10 and an error probability of 10-5 the number of block encoded channel signals required is 210,000. This is just as impractical as theinfinite coding delay required. • Source: R. F. Linfield: Radio Channel Capacity Limitations; ITS NTIA (CC) R Struzak <[email protected]> 10 Frequency V division FrequencyslotB Time slot T V = B*T*log2{1 + [S/(No*B)]} Time division headers; interactive & real-time applications that require acknowledgment! (CC) R Struzak <[email protected]> 11 FDD radio links • Two stations can talk and listen to each other at the same time (time-sharing). • This requires separate synchronized frequency channels – a technique known as Frequency Division Duplex (FDD) Frequency Channel 2 TX RX Station 1 Station 2 RX TX Frequency Channel 1 (CC) R Struzak <[email protected]> 12 TDD radio links • Two stations can talk and listen to each other using the same frequency channel (frequency-sharing), one after another. • This requires time synchronization/ handshaking – a technique known as Time Division Duplex (TDD) Single Frequency Channel TX TX Station 1 Station 2 RX RX (CC) R Struzak <[email protected]> 13 Broadband (INTEL: 100+ Mbps) INTEL opinion: 100 Mbps necessary! Ch. Legutko (Intel Corp. Wireless Standards & Regulations Mngr): „Regulatory & Spectrum”; presentation, Broadband Forum, Warsaw, July 2006 (CC) R Struzak <[email protected]> 14 !"#$%&'()*+)+#,-*.()&/$/-/01),*$$20/,#-/*0),3#00'&),#%#,/-4)) 534(/,#&)) 6',30*&*1/,#&) 7'12&#-*.4) !,*0*$/,)))))) ,*0(-.#/0-() ,*0(-.#/0-() ,*0(-.#/0-() ,*0(-.#/0-() 8#09:/9-3) =%2./*2() A.'B2'0,4) C*(-)) '$/((/*0)) #((/10$'0-() ;*/(') >).','%-/*0) 5*:'.) !0</.*0$'0-#&) ,3#00'&() &/$/-#-/*0() (/10#&() ?#.9:#.') =/--/01) 0*0&/0'#./-/'() .'(-./,-/*0() ?#.9:#.') /0(-#@/&/-/'() ) ) (CC) R Struzak <[email protected]> 15 • The fundamental physical limitations are bandwidth and noise. • The bandwidth limits the number of signaling elements or symbols which can be transmitted per unit time. • The noise limits the number of distinguishable features on each symbol. • The combined effects limit the capacity of a communication system. (CC) R Struzak <[email protected]> 16 Radio Channel Model Original message/ data Coding/ Transmitter Processing Time series T-antenna EM waves: time- Propagation medium distance- direction- polarization Environment R-antenna Noise, Fading, Time series Receiver Processing/ De-coding Reconstructed message/ data (CC) R Struzak <[email protected]> 17 SISO, SIMO, MISO, MIMO 1 SISO Tx Rx MISO Tx Rx m 1 1 1 SIMO Tx Rx MIMO Tx Rx n m n Oestges C, Clerckx B, "MIMO Wireless Communications : From Real-world Propagation to Space-time Code Design," Academic, 2007 http://en.wikipedia.org/wiki/MIMO (CC) R Struzak <[email protected]> 18 Radio transmitter 1. Generates a RF carrier 2. Combines it with the baseband signal into a RF signal through modulation • Performs additional operations E.g. analog-to-digital conversion, formatting, coding, spreading, adding additional messages/ characteristics such as error-control, authentication, or location information 3. Radiates the resultant signal in the form of modulated radio wave - it maps the original message into the radio-wave signal launched at the transmitting antenna (CC) R Struzak <[email protected]> 19 Propagation process • Transforms (maps) the radio-wave launched by the transmitter into the incident radio wave at the receiver antenna • Depends on extra variables (e.g. distance), additional radio waves (e.g. reflected wave, environmental waves), random uncertainty additive (noise), multiplicative (fading), etc. • A separate talk (CC) R Struzak <[email protected]> 20 Radio receiver: 1. Extracts the wanted signal from the Wanted signal incident radio waves (a solid “window” in the signal hyperspace) Noise 2. Recovers the original message through • reversing the transmitter operations (demodulation, decoding, de-spreading, etc.), + Receiver • compensating propagation transformations, and • correcting transmission distortions • Maps the incident signals into the Unwanted signals recovered message • Coexistence - Separate talk! Unwanted signals and nonlinearities are often ignored! (CC) R Struzak <[email protected]> 21 Modulation & Demodulation • Modulation - translation the baseband message signal to radio frequencies • Demodulation -- the reverse process) – Single carrier: • continuous (sinusoidal), • Walsh functions (http://mathworld.wolfram.com/WalshFunction.html) • Random carriers (http://en.wikipedia.org/wiki/Category:Radio_modulation_modes) – Multiple carriers (e.g. OFDM) (CC) R Struzak <[email protected]> 22 Modulation Process ffaaaat= ( 123, , ,...n ,) (= carrier) aaa123, , ,... an (= modulation parameters) t (= time) • Moves information from baseband to RF • Implies varying one or more characteristics (modulation parameters a1, a2, … an) of a carrier f in accordance with the information-bearing (modulating) baseband signal. (CC) R Struzak <[email protected]> 23 Frequency translation Signal's baseband bandwidth is its bandwidth before modulation and multiplexing, or after demultiplexing and demodulation • Signal "at baseband" comprises all frequency components carrying information. Modulation shifts the signal up to RF frequencies to allow for radio transmission. Usually, the process increases the signal bandwidth. Steps are often taken to reduce this effect, such as filtering the RF signal prior to transmission. (CC) R Struzak <[email protected]> 24 0 802.11g -10 -20 dB -30 -40 -50 -50 -40 -30 -20 -10 0 10 20 30 40 50 Frequency from centre, MHz (CC) R Struzak <[email protected]> 25 802.11b/g channels (Center frequencies in GHz) 1. 2,412 8. 2,447 • Different subsets of these channels are 2. 2,417 9. 2,452 made available in 3. 2,422 10. 2,457 various countries 4. 2,427 11. 2,462 • Spacing: ~5 (12) MHz 5. 2,432 12. 2,467 • Occupied bandwidth: 6. 2,437 13. 2,472 ~22 MHz (802.11b), ~16.6 MHz (802.11g) 7. 2,442 14. 2,484 Source:(CC) R Morrow: R Struzak Wireless <[email protected]> network coexistence, p. 198 26 Why translation? • Effective radiation of EM energy requires antenna dimensions to be comparable with the wavelength: – 3 kHz: wavelength 100 km – 3 GHz: wavelength 10 cm • Allows shared use of the radio transmission medium (CC) R Struzak <[email protected]> 27 Continuous sinusoidal carrier A sin[ωt +ϕ]; A, ω, or/and ϕ = var. • Amplitude • Frequency Phase modulation modulation modulation (AM) (FM) (PM) – A = A(t) – A = const – A = const – ω = const – ω = ω(t) – ω = const – ϕ = const – ϕ = const – ϕ = ϕ(t) (CC) R Struzak <[email protected]> 28 AM, FM, PM The modulating signal superimposed on the carrier wave & the resulting modulated signal. [wikipedia] Java simulation: http://www.home.agilent.com/upload/cmc_upload/All/ Amplitude_Modulation.htm?cmpid=zzfindnw_amplitudemod (CC) R Struzak <[email protected]>