ECE 6640 Digital Communications

Transcription

1 ECE 6640 Digital Communications D. Badley J. Bazuin Assistant ofesso Depatment of Electical and Compute Engineeing College of Engineeing and Applied Sciences

2 Chapte 5 5. Communications Link Analysis. 1. What the System Link Budget Tells the System Enginee.. The Channel. 3. Received Signal owe and oise owe. 4. Link Budget Analysis. 5. oise Figue, oise Tempeatue, and System Tempeatue. 6. Sample Link Analysis. 7. Satellite Repeates. 8. System Tade-Offs. ECE 6640

3 Skla s Communications System otes and figues ae based on o taken fom mateials in the couse textbook: ECE 6640 Benad Skla, Digital Communications, Fundamentals and Applications, 3 entice Hall TR, Second Edition, 001.

4 What is a Link Budget An analysis of the entie communications path signal, noise, intefeence, ISI contibutions, etc. Include gains and losses Link Budget An estimate of the input to output system pefomance Will the message get communicated? What tade-offs can be made and what effect will they have? ECE

5 The Channel The popagation medium of the communicated signal Between the tansmitting device and the eceiving device (e.g. RF antennas, cable modems, fibe optic tansceives) Fo RF we think of Fee Space An ideal appoximation fo nea-gound, atmospheic RF tansmissions. on ideal atmospheic impaiments include: absoption, eflection, diffaction, scatteing. ECE

6 Eo-efomance Degadation Established in Chapte 3 Loss of SR Intesymbol intefeence Fo Digital Communications Eb S W 0 R The elationship between SR and Eb/o SR elates the aveage signal powe and aveage noise powe Eb/0 elates the enegy pe bit to the noise enegy Loss: efes to a loss in signal enegy oise: efes to an incease in noise o intefeence enegy ECE

7 Souces of Signal Loss and oise 1. Bandlimiting Loss. Intesymbol Intefeence (ISI) 3. Local Oscillato hase oise 4. AM/M Convesion (Amplitude vaiations) 5. Limite Loss o Enhancement 6. Multiple-caie Intemodulation oducts (non-linea devices) 7. Modulation Loss (message content powe) 8. Antenna Efficiency 9. Radome Loss and oise 10. ointing Loss 11. olaization Loss 1. Atmospheic Loss and oise 13. Space Loss 14. Adjacent Channel Intefeence 15. Co-channel Intefeence 16. Intemodulation oise 17. alactic o Cosmic, Sta and Teestial oise 18. Feede Line Loss 19. Receive oise 0. Implementation Loss 1. Impefect Synchonization Refeence See Figue 5.1, p. 46. ECE

8 Figue 5.1 ECE

9 ains and Losses to be Discussed Antenna Efficiency ointing Atmospheic oise Space Loss Receive ECE

10 Range Equations The powe density in a sphee fom a point souce antenna (suface aea of a sphee) p 4 t Receiving powe collected by an antenna (using the effective aea of the eceiving antenna so that p(d) can be collected) p A 4 t Ae e Effective Aea total powe extacted A e incident powe flux density ECE

11 Antenna Efficiency and ain The atio of the effective aea to the actual aea A A e p Antenna ain aveage maximum powe intensity powe intensity ove 4 steadians Fom wikipedia: Steadians the SI unit of solid angle. It is used to descibe twodimensional angula spans in thee-dimensional space, analogous to the way in which the adian descibes angles in a plane. ote: a sphee has 4 steadians ECE

12 Effective Radiated owe The effective adiated powe is the poduct of the tansmitted powe and the antenna gain EIR t t The same EIR can be achieved in many ways In tems of eceived powe using effective adiated powe EIR Ae 4 t t Ae 4 ECE

13 Antenna ain in tems of Aea Fo antennas with a lage aea as compaed to a signal wavelength ote: 4 Ae 4 Ae f c A e 4 Antenna Recipocity Fo given antenna and caie wavelength, the tansmitting and eceiving antenna gains ae identical. The effective aea of an isotopic antenna (equal tansmission in all diections) 4 A e 1 A e ECE f 13 c

14 Antenna Beamwidth Since an isotopic antenna is defined as having a gain of 1, the aea atio of the antenna beam patten fom maximum to -3dB to the aea of the sphee is often an estimate of the antenna gain. Fo an antenna with a half powe beamwidths in two planes the diectivity, D, (and gain) ae Fo a /4 beam D D ECE x 3 4 y 0.37

15 Received owe in EIR Fo an isotopic eceiving antenna, the eceived powe is iso A EIR 4 eisotopic iso EIR EIR EIR L 4 4 s Whee Ls is called the fee-space o path loss ote: It is defined based on an isotopic antenna with =1! L s 4 4 f c ECE

16 ECE The Fiis Tansmission Equation The eceived signal powe can be defined as Thee is a family of elationships (pick you use) t t s 4 L EIR e t t 4 A e et t e et t f c A A A A et t 4 A

17 ath Loss Consideations ath Loss is defined using an isotopic eceiving antenna L s 4 4 f c The eceived flux density is stictly a function of distance EIR 4 d Fo lage effective aea eceiving antennas p EIR A 4 e ECE

18 ath Loss Consideations () The effective aea fo =1 eceiving antennas change with fequency A e 4 c f 4 Fequency Aea ath Loss 1km 3 khz 7.96E+08 mete^ db 3 MHz 7.96E+0 mete^ db 3 Hz 7.96E-04 mete^ db ECE

19 Radio Receive Consideation Receives collect signals, intefeence, and noise Signals-of-Inteest (SOI) will equie gain and filteing pio to o as pat of the signal pocessing The noise collected by the eceive will be pocessed along with the signal but will be limited by filteing The electical components will add thei own noise to the pocessed signals. Theefoe, we need to discuss: Cascade gain stages Cascaded noise effects and component noise figues Bandwidth effects on themal noise powe ECE

20 RFID Receive Downconvesion ISM Band Downconvesion (90-98 MHz) Only mixing and filtes shown High-side Los Synthesize povides cente fequency selection IF filte sets bandwidth LF fo ADC anti-aliasing Convet to fs/4 fo post- ADC complex pocessing Fs > 4 x fmax ECE

21 Cascaded ain Multiple the gain (loss) of each stage togethe If gain in db, add the gains (in db) and subtact the losses (in db) db db db db db db pedemod RF 1stMixe IF1 ndmixe IF If the mixes have loss instead of gain (passive mixes) db db L db db L db db pedemod RF 1stMixe IF1 ndmixe IF Linea gain is multiplicative ain in db is additive ECE

22 oise Figue The noise figue is a measue of the additional noise that is added by any cicuit element. Effective additional input noise xt yt F SR SR in out Sin Sin in in amp Caution, oise Figue is often efeed to in db instead as a linea tem F SR SR in in amp 1 out in amp in ECE 6640

23 Cascaded oise Figue The noise figue is a measue of the additional noise that is added by any cicuit element. Effective additional input noise xt yt F SR SR in out 1 Sin amp1 1 amp 1 F 1 F 1 1 F1 1 F 1 F1 ECE 6640 in 1 in Sin 1 in in amp1 amp SR in amp in in amp amp 1 F SR out 1 in amp in

24 Basic Receive x c t Bandpass Filte Amplifie Bandpass Filte Lowpass Filte x ed t Demod x M t ed Tuning cos f LO1 t cos f LO t RF Filte emoves images Low oise Amplifie Mixe to IF IF BF sets the system BW Mixe to baseband Baseband LF to emove mixing poducts db db db db db db db RF BF LA 1stMixe BF ndmixe F ed F RF BF F F RF BF ndmixe 1stMixe 1 1 Amp F 1stMixe RF BF RF BF ECE RF BF Amp 1stMixe BF RF BF Amp 1stMixe BF ndmixe 1 Amp F LF F 1 BF 1 Amp 1stMixe LF

25 Themal oise owe Modeled as additive white aussian noise (AW) T B Whee is the noise powe κ is Boltzmann s constant T is absolute tempeatue in degees Kelvin B is the bandwidth in Hetz dbw / K Hz T 0 90K IEEE ef 0 T 1.38e e dbw / Hz 174 dbm / Hz ECE

26 Receive Opeating Chaacteistics Sensitivity minimum input value Dynamic Range usable signal ange Selectivity filte out adjacent noise and intefeence Adjacent Channel Intefeence (ACI) Rejection and Image Rejection oise Figue Building a pefomance diagam fo a softwae adio Input to ADC input ECE

27 FM Radio Design Diagam FM eceive 00 khz BW 1-bit ADC with 10-bit pefomance Multiple signal envionment SOI detection theshold ROC Sensitivity -103 dbm Dynamic Range 41 db ain 63 db F 10 db Selectivity: based on IF filte ACI: filte attenuation at n channels away (n x 00 khz) ECE

28 FM Radio Design Diagam FM eceive 00 khz BW 1-bit ADC with 10-bit pefomance Multiple signal envionment SOI detection theshold ECE

29 utting It All Togethe Fo dedicated communication systems, link budgets ae defined System Enginee s esponsibility to guaantee that successful communication will occu. Examples: WiFi access point locations, satellite communications, FM adio station coveage aeas (and tansmitting antenna siting), Cellula Telephone System Base Station Siting, etc. If you build it, will it be useful? Reliability, design magin, upgades, component eplacement ECE

30 Table 5. Eath Teminal to Satellite Link Budget ECE

31 Table 5.3 Link Budget Example ECE