S Mobile Communications Services and Systems

Transcription

1 S-7.60 Mobile ommuniation Serie and Sytem Tutorial, Noember 9, 004. One a pyiit obert Wood did not top i ar beind te red trai ligt. He exue imel by uing oppler eet. Beaue o oppler it te red ligt ad turned to te green one. How quikly e ad to moe in order i laim to be true.. Solution Te teory a own te oppler it between te tranmitted and reeied waelengt a: l, l ' were l i waelengt emitted rom te oure, l' i waelengt reognized by a moing oberer, i peed o te uer, i peed o ligt km/. Te ortet wae orreponding to te red ligt a waelengt 630 nm, te longet waelengt orreponding to te green ligt a waelengt 560 nm. Inerting tee alue to te equation we get: From tere we ound te peed o te ar km 8 km = =.. alulate te oppler bandwidt in te GSM900 and in te UMTS-ytem operating at 960 and 50 MHz wen te mobile tation peed i 3, 50, 0, and 500 km/ and: a) Only reletion rom tationary truture are onidered, b) Alo reletion rom ar moing wit te ame peed are onidered.

2 . Solution a) Te oppler bandwidt i Wen B 3 km ν =, =960 MHz, ten = ν d km km = = B Hz Hz Te oppler bandwidt or te oter parameter ombination are obtained in te ame way (proportional to te peed and requeny) 3 km/ 50 km/ 0 km/ 500 km/ =960 MHz 5.33 Hz Hz 3.33 Hz Hz =50 MHz.94 Hz Hz Hz Hz b) Te igure ow te diret and releted ield obtained by te image priniple From te igure an be een tat λ = λ = = 0 wi gie / moing reletor, peed λ 0 BS moing image oure /

3 + = = = = Adding te oppler it rom MS moement te maximum oppler-it i +, wi in ti ae will triple te oppler-bandwidt obtained wit max ixed reletor. 3. Inetigate te UMTS ytem were te uer i moing wit peed 50 km WMA a) etermine te number o poitie going zero roing about te rm alue tat our oer 0 interal. b) etermine te aerage duration o te ade below te rm leel. ) etermine te aerage duration o te ade below te -0 db leel. 3. eerene. appaport T.S. Wirele ommuniation. Prentie Hall 996. a) Te leel roing rate i deined a te expeted rate at wi te ayleig ading enelop, normalized to te loal rm ignal leel, roe a peiied leel in a poitie -going diretion. = ( ) = 0 N r p, r dr π m ρe ρ were m i maximum oppler requeny and rm ρ = i te alue o te peiied leel, normalized to te loal rm amplitude o te ading enelop. For our ae te = Hz Te number o leel roing per eond i gien by N = π e = b) Te aerage ade duration i deined a te aerage period o time or wi te reeied ignal i below a peiied leel. For te ayleig ading ignal ti i Pr [ r ] N Pr r τ = were [ ] i probability tat r i le tan. Te probability tat te reeied ignal r i le tan te treold i ound rom te ayleig ditribution Pr [ r ] p( r) dr e ρ = = 0 were p( r ) i pd o a ayleig ditribution. Te aerage ade duration a untion o m an be expreed a

4 ρ e τ = ρ π For te rm leel ρ = e For te 0dB leel ρ = 0. e annel araterization Power [ ] db elay [ µ ] etermine te rm delay and mean exe time or te annel etermine te maximum exe delay 0 db. Etimate te oerene bandwidt o te annel. (oerene time). Aume tat mobile uing UMTS ytem traeling wit 50 km reeie te ignal troug ti annel determine te time oer wi te annel appear tationary (or at leat igly orrelated). 4. eerene. appaport T.S. Wirele ommuniation. Prentie Hall 996. a) Mean exe delay i te irt moment o te power delay proile and i deined a, P ( τ ) τ k k k τ = = 0.67 [ µ ] P ( τ ) k k For our annel it beome Te rm delay i te quare root o te eond entral moment o te power delay proile and i deined to be σ ( τ ) ( τ) τ = + P ( τ ) τ k k k Were ( τ ) i deined a ( τ ) = =.586 [ µ ] P ( τ ) k k σ = ( τ ) + ( τ) =.066. τ b) Maximum exe delay i deined to be delay during wi multipat energy all X db below te maximum. In our ae it would be 0dB. For te gien annel tat i delay till te lat multipat omponent omponent. 5 µ. ) Te oerene bandwidt an be aumed to be te requeny eparation at wi te annel i igly orrelated. For example it an be etimated to be at te leel were te normalized alue o te orrelation oeiient attain a alue 0.7. Te oerene bandwidt an be alulated a = were T i maximum πt exe delay. For te gien annel it i 3.8 khz.

5 d) Te oppler peed and oerene time are inerely proportional to ea oter T were m i te maximum oppler it., I te oerene time i deined a te time oer wi te time orrelation untion i 9 aboe 0.5, ten te oerene time i approximately T., 6π Te oerene time an be alulated a geometri mean o equation o tee two deinition o T T = = 6 π 0.00[ ] 5. o we need an equalizer or te GSM ignal in te annel gien in preiou exerie. 5. I te tranmitted ignal bandwidt i narrow ompared to te annel oerene bandwidt, all tranmitted requeny omponent enounter early idential propagation delay. Te annel an be araterized a a narrowband annel were all requeny omponent ae te ame ading. We ompare GSM bandwidt to te oerene bandwidt o te annel. For te GSM ignal i alloated 00 khz bandwidt ti i mu iger tan te orrelation bandwidt and te equalizer i ueul. m