Antenna Parameters. G=4pηA w /l 2. G=Gain η= loss-coefficient (efficiency) A w = electrical aperture l= wavelength. A w (G=1)=l 2 /4pη 180 0

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1 Anenna Parameers Half-Power Beamwidh Firs Null-o-Null G=4pηA w /l 2 G=Gain η= loss-coefficien (efficiency) A w = elecrical aperure l= wavelengh A w (G=1)=l 2 /4pη The loss-coefficien η is normally assumed o be close o 1 The effecive area for G=1 is he reference area and relaed o he square of wavelengh Chaper 2 Page 89

2 Shannon Theorem Shannon posulaed ha here is an upper value for he ransmission of informaion Over a channel. This value is called channel capaciy. c=b log 2 (1+S/N) c= Channel capaciy (b/s) B= Bandwidh S= Signal Energy (Power) N= Noise Energy (Power) Noise can be cause by eiher physical e.g. hermal energy or inerference Chaper 2 Page 90

3 Signal propagaion ranges Transmission range communicaion possible low error rae Deecion range deecion of he signal possible no communicaion possible Inerference range signal may no be deeced signal adds o he background noise sender ransmission deecion inerference disance Chaper 2 Page 91

4 Signal propagaion Propagaion in free space always like ligh (sraigh line) Receiving power proporional o 1/d² (d = disance beween sender and receiver) Receiving power addiionally influenced by fading (frequency dependen; H 2 O resonance a 2.5 GHz; O 2 Resonance a 60 GHz) shadowing reflecion a large obsacles refracion depending on he densiy of a medium scaering a small obsacles diffracion a edges shadowing reflecion refracion scaering diffracion Chaper 2 Page 92

5 Real world example Chaper 2 Page 93

6 Range Equaion according o Friis P r P a P x TX Anenna RX Anenna P rx Free Space, vacuum+ far-field d Lossless anenna (loss-coefficien η=1): P x = P r (r for radiaed) P a = P rx (a for absorbed) Disance beween anennas is d Chaper 2 Page 94

7 Explanaion d 2 Dependancy Isoropic anennas radiae ino each spacial angle seamlessly Raumwinkel isorop Ω i =4π [sr] (Seradian) Isorope Sendeanenne um den Sender sind konzenrische Kugeln mi dem Radius r vorsellbar (siehe Abbildung unen) Kein Verlus von Energie, also: Leisung vereil sich mi zunehmendem Radius r auf größere Kugeloberfläche (4πr² ) Leisungsdiche pro Fläche (S in [W/m²]) wird immer geringer wegen Kugeloberfläche nimm Leisungsdiche quadraisch mi r ab [1] S = P x /(4πd²) (I) [1] hp://de.wikipedia.org/w/index.php?ile=daei:angle_solide_coordonnees.svg [2] hp://de.wikipedia.org/w/index.php?ile=daei:leisungsdiche.png (Mi A 1, A 2 sind Flächen gleicher Energie) [2] Chaper 2 Page 95

8 Range Equaion according o Friis II Die am Ausgang des Empfängers verfügbare Leisung P rx ensprich dem Produk aus Leisungsdiche im Absand d & effekiver Aperur von RX A W Für die am Empfänger verfügbare Leisung P rx ergib sich mi (I) und (II) P rx = S * A W P rx = P x /4pd 2 * l 2 /4p P rx = P x * (λ/4 πd)² (III) Chaper 2 Page 98

9 Range Equaion according o Friis III Reale Anennen sind nich isorop in die Haupabsrahlrichung wird mehr Energie abgesrahl, in andere Richungen dafür weniger (Inegral konsan!) Richwirkung D (direciviy): Verhälnis zweier Raumwinkel isorope Anenne im Vergleich zu der beracheen Anenne bisher wurden verluslose Anennen angenommen reale Anennen srahlen die eingespeise Leisung P x nich komple ab (P r < P x ) bzw. können die aufgenommene Leisung am Empfänger nich komple am Ausgang der Anenne zur Verfügung sellen (P rx < P a ) Wirkungsgrad η der Anennen beschreib das jeweilige Verhälnis (siehe Abbildung nächse Folie) Chaper 2 Page 99

10 Range Equaion according o Friis IV P r P a P x TX Anenne RX Anenne P rx d η x P r /P x = η x und P rx /P a = η rx η rx Anennengewinn G fass Absrahlcharakerisik & Wirkungsgrad zusammen: G (gain): G = η * D für die am Ausgang der RX-Anenne verfügbare Leisung P rx ergib sich: P rx = P x * (λ/4πd)² * G rx * G x Umrechnung in logarihmische Form: P dbm = 10 * log(p/1 mw) L pah db = 20 * log(4πd/ λ) P rx dbm = P x dbm + G x dbi + G rx dbi L pah db Chaper 2 Page 100

11 Examples Compare wo radio ransmission sysems of he following characerisics: 1. IEEE wih 868 MHz, Transmi Power 10 dbm Anenna on ransmier wih 6 dbi gain; receiver sensiiviy -100 dbm; minimum Signal over noise 10 db, receive anenna wih 3 dbi gain, 2. IEEE g wih 2.4 GHz, Transmi Power 20 dbm, Anenna on ransmier wih 10 dbi gain; receiver sensiiviy -85 dbm, minimum signal over noise 16 db, receive anenna gain wih 3 dbi Quesions: Wha maximal disance can be achieved? Wha are he anenna sizes if you assume l/4 anennas? Chaper 2 Page 101

12 Mulipah propagaion Signal can ake many differen pahs beween sender and receiver due o reflecion, scaering, diffracion A LOS pulses A mulipah pulses signal a sender signal a receiver Time dispersion: signal is dispersed over ime (delay spread) inerference wih neighbor symbols, Iner Symbol Inerference (ISI) The signal reaches a receiver direcly and phase shifed disored signal depending on he phases of he differen pars Chaper 2 Page 102

13 RMS Delay Spread The roo mean square delay spread is a mean o describe he dispersion of he signal due o muli-pah fading. I akes ino accoun he delay of all received signals wih respec o he delay of he firs received signal. Each pah is weighed wih he received power d rms n i1 n i1 ( ip n P i1 i i) ( n i1 2 i P P i i Example: Take his room, go up o 3 reflecions, assume (wors case): no aenuaion a he reflecion poin, ake longes pahs Guessing: Wha is your firs guess of he delay spread of his lecure room? 2 d Chaper 2 Page 103

14 Effecs of mobiliy Channel characerisics change over ime and locaion signal pahs change differen delay variaions of differen signal pars differen phases of signal pars quick changes in he power received (shor erm fading) Addiional changes in disance o sender obsacles furher away slow changes in he average power received (long erm fading) Doppler Effecs: power shor erm fading long erm fading Doppler Shif: The change of frequency due o sum of own speed o he speed of propagaion Doppler spread: The change of he frequency mix due o he summaion of all doppler reflecions o he received signal Chaper 2 Page 104

15 Muliplexing Muliplexing in 4 dimensions space (s i ) ime () frequency (f) code (c) Goal muliple use of a shared medium Increase capaciy Imporan: guard spaces needed in space, ime, frequency and code! Chaper 2 Page 105

16 Space Muliplexing Separaion of space ino differen spaial regions The differen channels can use any frequency a any ime if he spaial separaion is good Spaial guards have o be provided o allow inerference free operaion Advanage: Works wih any echnology Simple o use Disadvanage: No very flexible Expensive due o several anennas Use in segmened cells for cellular radio sysems channels k i k 1 c s 1 s 3 k 2 k 3 k 4 k 5 k 6 c SM f s 2 c f f Chaper 2 Page 106

17 Frequency muliplex Separaion of he whole specrum ino smaller frequency bands A channel ges a cerain band of he specrum for he whole ime Advanages: no dynamic coordinaion necessary works also for analog signals c k 1 k 2 k 3 k 4 k 5 k 6 f Disadvanages: wase of bandwidh if he raffic is disribued unevenly inflexible guard spaces Chaper 2 Page 107

18 Time muliplex A channel ges he whole specrum for a cerain amoun of ime Advanages: only one carrier in he medium a any ime hroughpu high even for many users c k 1 k 2 k 3 k 4 k 5 k 6 Disadvanages: precise synchronizaion necessary f Chaper 2 Page 108

19 Time and frequency muliplex Combinaion of boh mehods A channel ges a cerain frequency band for a cerain amoun of ime Example: GSM Advanages: beer proecion agains apping proecion agains frequency selecive inerference higher daa raes as compared o code muliplex bu: precise coordinaion required c k 1 k 2 k 3 k 4 k 5 k 6 f Chaper 2 Page 109

20 Code muliplex Each channel has a unique code k 1 k 2 k 3 k 4 k 5 k 6 All channels use he same specrum a he same ime Advanages: bandwidh efficien no coordinaion and synchronizaion necessary good proecion agains inerference and apping Disadvanages: lower user daa raes more complex signal regeneraion Implemened using spread specrum echnology c f Chaper 2 Page 110

21 Muliplexing: ineresing Exension Space Muliplexing: Roaing anennas, Elecronic beam seering Frequency Muliplexing: Muliple frequencies can be allocaed o a channel a he same ime e.g. for muli carrier modulaion Cogniive sysems: The specrum is dynamically allocaed due o use and no due o saic reservaion Chaper 2 Page 111

22 Modulaion Digial modulaion digial daa is ranslaed ino an analog signal (baseband: wihou a specific carrier) ASK, FSK, PSK - main focus in his chaper differences in specral efficiency, power efficiency, robusness Analog modulaion shifs cener frequency of baseband signal up o he radio carrier Moivaion smaller anennas (e.g., l/4, in case of car-2-car communicaion a 5,9 GHz : l=5cm, l/4= 1,25 cm) Frequency Muliplexing (wih consan bandwidh we can have more bands a higher frequencies) medium characerisics (radio propagaion is massively impaced by aenuaion e.g. by O 2 absorpion) Basic schemes Ampliude Modulaion (AM) Frequency Modulaion (FM) Phase Modulaion (PM) Chaper 2 Page 112

23 Modulaion and demodulaion analog baseband digial signal daa digial analog modulaion modulaion radio ransmier radio carrier analog demodulaion analog baseband signal Synchronizaion/digial Demodulaion/decision digial daa radio receiver radio carrier Chaper 2 Page 113

24 Digial modulaion Modulaion of digial signals known as Shif Keying Ampliude Shif Keying (ASK): very simple low bandwidh requiremens very suscepible o inerference (Picure shows as example a special case he so called On/Off keying OOK) Frequency Shif Keying (FSK): needs larger bandwidh More robus agains fading of signals (can also be used wih several frequencies) Phase Shif Keying (PSK): more complex More robus agains inerference (Here a special form he BPSK is shown) Chaper 2 Page 114

25 Advanced Phase Shif Keying BPSK (Binary Phase Shif Keying): bi value 0: sine wave bi value 1: invered sine wave very simple PSK low specral efficiency robus, used e.g. in saellie sysems QPSK (Quadraure Phase Shif Keying): 2 bis coded as one symbol symbol deermines shif of sine wave needs less bandwidh compared o BPSK more complex Ofen also ransmission of relaive, no absolue phase shif: DQPSK - Differenial QPSK (IS-136, PHS) A Chaper 2 Page Q Q 0 I 11 I 01

26 Advanced PSK 8-PSK (used in EDGE) 3 bis/symbol Needs beer SNR han QPSK Please keep in mind ha he disance beween symbols express An energy value. If we add o he sigmnal a noise or inerference energy wih he same value of he disance beween 2 symbols we can no longer differeniae beween hese wo symbols Chaper 2 Page 116

27 Quadraure Ampliude Modulaion Quadraure Ampliude Modulaion (QAM): combines ampliude and phase modulaion i is possible o code n bis using one symbol (bi-loading) 2 n discree levels, n = 2 idenical o QPSK bi error rae increases wih n, bu less errors compared o comparable PSK schemes (due o addiional use of differen ampliudes) Q I 1000 Example: 16-QAM (4 bis = 1 symbol) Symbols 0011 and 0001 have he same phase, bu differen ampliude and 1000 have differen phase, bu same ampliude. Used in several high speed sysems Chaper 2 Page 117

28 Hierarchical Modulaion DVB-T modulaes wo separae daa sreams ono a single DVB-T sream High Prioriy (HP) embedded wihin a Low Prioriy (LP) sream Muli carrier sysem, abou 2000 or 8000 carriers (OFDM) QPSK, 16 QAM, 64 QAM Example: 64 QAM good recepion: resolve he enire 64QAM consellaion poor recepion, mobile recepion: resolve only QPSK porion 6 bi per QAM symbol, 2 mos significan deermine QPSK HP service coded in QPSK (2 bi), LP uses remaining 4 bi Q I Chaper 2 Page 118

29 Muli Carrier Modulaion (MCM) Wih Muli Carrier Modulaion (MCM) he daa sream is spli ino several concurren communicaion sreams using differen frequencies Example of MCM are ADSL and OFDM where each frequency is furher modulaed using BPSK or QAM For IEEE802.11a/g and LTE OFDM is used OFDM uses orhogonal frequencies o avoid iner carrier inerference I uses long symbols o reduce ISI and o avoid complex equalizaion The iniial symbol rae n can be divided ono m carriers such ha he symbol rae/carrier is n/m. The disance beween symbols (in he ime domain) becomes larger and hus he ISI smaller. Chaper 2 Page 119

30 MCM model for ransmission T s = T = N(2 (k-1) /R b ) R b bi rae (bps) FFT Chaper 2 Page 120

31 Fourier ransform of a single puls F -T/2 +T/2 F*T rec(t) si(t) = sin(t)/t Chaper 2 Page 121

32 OFDM model for ransmission (con d) 1 2 N 2 N 2π 2π T 2 T ) ( n f n j n f j e a e s o 1 2 N 2 N T π T π sin T ) ( n n f n f f n f a f S Fourier Transform Modulaion facor Consan phase How do we selec an appropiae value for f? Chaper 2 Page 122

33 OFDM model for ransmission (con d) f = 0.8/T f T We find ICI (Iner-Carrier-Inerference) f = 1.2/T f T Chaper 2 Page 123

34 OFDM model for ransmission (con d) f = 1/T f T No ICI We have orhogonaliy beween he differen subcarriers Because of orhogonaliy we have minimum Iner carrier inerference Chaper 2 Page 124

35 Componens of a real OFDM sysem Transmier Channel Coding Modulaion Inerleaving FFT D/A RF- Transmission Receiver Channel Decoding Demodulaion Deinerleaving IFFT A/D RF- Recepion Channel Esimaor Synchronizer Chaper 2 Page 125

36 Required Signal/Noise a he Receiver During ransmission and recepion noise will be added o he signal Thermal noise (Bolzmann noise) Receiver Noise (Noise Figure) Transmier Noise caused by non lineariy ec. The effec for he received signal is ha in he consellaion diagram no a signal poin bu a cloud of poins around he expeced poin are received. Due o hese noise and disorion impacs he signal/noise (S/N) raio o receive a signal correcly is a leas around >6 db (in he case of BPSK). The S/N is dependen on he modulaion and he ransmission ype For 64 QAM he S/N is a leas 4 db higher han for 16 QAM ec. Explanaion: The densiy of he consellaion becomes higher wih higher modulaion. Higher S/N means ha he spread around he expeced consellaion poin becomes smaller Chaper 2 Page 126

37 Consellaion Diagram of 60 GHz OFDM Link - Bandwidh 2GHz - OFDM, 16 QAM, r= 3/4, 3,8 Gbi/s - TX-Power: 10 dbm - Disance: ca. 15 m - Vivaldi Anenna Use of commercial Signal Generaor wih precalculaed waveform and Vecor Signal Analyzer H/W in he loop approach wih sofware synchronizer & BB-receiver Chaper 2 Page 127