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INTRODUCTION TO WIRELESS MOBILE

COMMUNICATIONS

y History and evolutio n of mobil e r adio systems

y Types of mobil e wir eless ser vices/syst ems

C ellular WLL Paging Satellite syst ems

y Standar d

y Futur e tr ends in personal wir eless syst ems.

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INDEX

UNIT IINTRODUCTION TO WIRELESS MOBILE COMMUNICATIONS

Questionnumber Question Page no

1 Wh at is th e footpri nt ar eaof th e satellite? 52 Wh at ar e geostationary satellites? 53 Wh at is sider eal time? 54 Wh at is sider eal day? 55 Wh at is dir ect orbit ? 56 Wh at is r etrogr adeorbit ? 57 Wh at is equatorial orbit ? 58 Wh at is polar orbit ? 59 Wh at ar e classific ation orbit dependon attitu de? 610 Wh at ar e th e benefits of Paging? 611 W rite in sh ort about th e W orlds first C ellular System. 612 Wh at ar e th e principles of C ellular Arch itectur e? 613 Wh at ar e th e advantages of Digital tech niques in cellular Systems? 614 Wh at ar e th e ch ar acteristics of PC S? 615 Wh at is th e Tech nology usedby PC S? 716 Wh at ar e th e advantages of cellular syst ems with small cells? 717 Wh at ar e th e limitations of conventional mobil e teleph onesyst em? 718 Wh at ar e th e disadvantages of cellular systems with small cells? 719 Define BC A. 720 Wh at is br eath e? 721 Wh y 800 MHz fr equency is selected for mobil es? 722 Wh at is th e Mark eting nameof narrowband IS-95 C DMA network ? 823 Wh at ar e th e th r ee segments of paging? 824 W rite in sh ort about ERMES 825 Wh at ar e th e advantages of APO C standar d? 826 Wh at is C PP? 827 Wh at ar e th e advantages of Data Paging Signage System ? 8

28Wh

at ar e th

e diff er ent types of Handover ? 829 Wh at is th e necessity of Standar ds? 830 Wh at ar e th e applic ations of a satellite syst em? 931 Give th e benefits of pagingsyst ems? 932 Wh at is a page ? 933 Wh at ar e th e ch annels used in mobil e communication syst ems? 934 Wh at ar e th e basic units of a C ellular syst em? 935 Wh at ar e th e classific ations of W ir eless tech nologies andsyst ems? 9

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Questionnumber DESCRIPTIVE ANSWERS

Pagenumber

1 Explain th e development h istory of mobile r adio syst ems. 102 Describ e in detail about th e h istory of development of Paging and

th e futur e tr ends of pagingsystems. 11

3 Explain in detail about the Standar ds adopted for PagingSystems. 134 Discuss in detail about th e Recent Developments in PagingSystems. 15

5 Explain in detail about th e Mobile r adio standar ds around th e world. 166 Discuss in detail about th e Futur e tr ends of Personal W ir eless

Systems. 187 Describ e in detail about th e W ir eless L ocal loop andL MDS. 208 Explain about th e basic cellular system. 229 Discuss in detail about th e satellite mobil e systems. 2410 Discuss in detail about th e gener al satellite systems. 25

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UNIT I

INTRODUCTION TO WIRELESS MOBILE

COMMUNICATIONSSHORT ANSWERS

1. What is the footprint area of the satellite?

Th e satellite antenna tr ansmit signal towar ds th e earth in a particular Patten called its foot print . Th e signal is stro nger at th e center and decr ease to f ath er level towar ds out er edgeof th e footpri nt.

2. What are geostationary satellites?

The satellites t

hat rotate t

he samespeedof t

he eart

har e calledgeostationary sat ell it es.

3. What is sidereal time?

Th e sid er eal tim e is measur ed r elative to th e fixed stars. One complete rotation of th e eart h r elative to th e fixedstars is not a complete rotation r elative to th e sun th e r eason for th is is because th eearth moves in its orbit around th e sun.

4. What is sidereal day?

Th e sid er eal day can be defined as one complete rotation of th e earth r elative to th e fixed stars. One sider eal day h as 23 h ours, 4.1 sec, 56 min.

At an attitude of 35,786 th e orbit al period becomes 23 h ours, 4.1 sec, 56 min, wh ich th e time th eearth to rotate 360 arou nd th e axis th is period is called asider eal day.

5. What is direct orbit?

Anorbit in wh ich a satellite moves in same dir ectio n as th e earth is calleddir ect orbit .

6. What is retrograde orbit?

Anorbit in wh ich a satellite moves in opposit e dir ection as th e earth is calledr etro g rad e orbit .

7. What is equatorial orbit?

Anorbit with an inclination is 0 th e satellite is said to be equ atoria l orbit.

8. What is polar orbit?

Anorbit with an inclination is 90 th e satellite is said to be pol ar orbit .

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9. What are classification orbit depend on attitude?

1. L ow Eart h Orbit 2. Medium Earth Orbit 3. Inter mediate C ircul ar Orbit 4. Geostationary Orbit

10. What are the benefits of Paging?1. L ow cost message delivery 2. Extendedbattery lif e3. Strong in-buil dingpenetr ation4. Reliable and expandedcover age5. Effici ent messaging6. C ontroll ed accessibility 7. Broadcastingcapability

11. Write in short about the Worlds first Cellular System.

Th e worlds first cellul ar syst em was implemented by th e Nippo n Teleph one and Telegr aph C ompany (NTT)in Japan. Th e syst em deploy ed in 1979, uses 6 FM Duplex ch annels (25 K Hz for each one way link ) in th e 800 MHz band.

12. What are the principles of Cellular Architecture?

y L ow power Tr ansmitters andC over age Zones. y Fr equency Reuse. y C ell splitti ngto incr ease C apacity. y Handoff andC entr al C ontrol.

13. What are the advantages of Digital techniques in cellular Systems?y ImprovedSpectr al Utilization. y L ower Bit r ate Voice C odingy Reductio n of Over h eadfor Signaling. y R obust Sourc e andCh annel C oding Tech niques. y Mor e R obust Interf er ence. y Flexible Bandwidth . y Inclusio n of Newser vices y Improved Effici ency.

14. What are the characteristics of PCS?y Mass mark et applic ations y C an be custo mized by individual users y C over age:in-buil ding, outdoor stationary andoutdoor on-th e-movey Additional ser vices include:universal access ID, less in weigh t, longer battery lif e, etc

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15. What is the Technology used by PCS?

PC S is not based on any single tech nology but uses a number of standar ds including:

y GSM900/1800/1900 (Europ ean and Nort h Americ an GSM standar ds)y DEC T (Digital Enh anced C or dless Teleph ony)y PHS (Perso nal Handyph oneSystem)y IS-95C DMA (C ode Division Multipl e Access)y IS-136 TDMA (Time Division Multipl e Access)

16. What are the advantages of cellular systems with small cells?

y High er capacity y L ess tr ansmissio n power y L ocal interf er ence only y R obust ness

17. What are the limitations of conventional mobile telephone system?

y L imited ser vice capability y Poor ser vice perfor mancey Ineffici ent fr equency spectru m utiliz ation

18. What are the disadvantages of cellular systems with small cells?

y Requir es complex infr astructur ey Requir es fr equent hand-over y Involves complicated fr equency planning

19. Define BCA.

Borro wing C h annel Allocation is a meth od by wh ich mor e fr equencies ar e allott ed dynamically for h igh tr affic cells.

20. What is breathe?

Th e cells in wh ich th e fr equency allocation is based on C DMAtech nique ar e called as breathe.

21. Why 800 MHz frequency is selected for mobiles?

FixedStation Ser vices - 30 MHz to 100 MHz

Televisio n Broadcasting - 41 MHz to 960 MHz FM Broadcasting - 100 MHz Air to Grou ndsyst em - 118 MHz to 136 MHz Maritime mobil e ser vices - 160 MHz Military Aircr aft use - 225 MHz to 400 MHz

Fr equency bands between 30 MHz to 400 MHz is crowded with lar ge number of ser vices andabove 10 GHz is not used due to prop agation path loss, multip ath f ading andimprop er medium due to r ain activity. So 800 MHz is ch osen for mobil e communication.

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22. What is the Marketing name of narrowband IS- 95 CDMA network?

Th e Mark eting nameof narrowband IS-95C DMA networks is cdmaOne .

23. What are the three segments of paging?

y One-way paging

y Two-way pagingy Telemetry paging ser vices.

24. Write in short about ERMES.

ERMES (E n h an ced Radio M essa g in g Syst em) was develop ed in th e late 1980's by a group of paging manuf actur ers and Europ ean Paging Oper ators. It was designed to provide a h igh speed Pan-Europ ean syst em for standar d tone, numeric and alph anumeric messages in a multi-network environment, enablingusers to roam th rou gh out any r egion in wh ich an ERMES oper ates.

25. What are the advantages of APOC standard?

y Gr eater subscrib er capacity andlonger messages per r adio ch annel y Minimum ser vice costs per subscrib er y Minimum upgr ading and network investment costs y Improvedcompleted-call perfor mancey C ompetitivepager design with smaller and longer lif e batteries y Mor e user f aciliti es y C ompatibility with PO C SAGpagers and networks

26. What is CPP?

In C alle r Pays Pa g in g ( C PP) syst ems th er e ar e no ongoing f ees or contr actual obli gations for subscrib ers. Th e owner only pays for th e initial purc h ase of a paging device.

27. What are the advantages of D ata Pa g in g Si g na ge Syst em ?

Th e flexibility of th is paging f acility enables r emote management of a wide-r angeof syst ems, suc h as th ose usedby tr avel agents, water irrigation andpower controll ers, etc.

28 . What are the different types of Hand over?

y Intr a-satellite h andover y Inter -satellite h andover y Gateway h andover y Inter -syst emh andover

29. What is the necessity of Standards?

Standar ds h elp to ensur e or pro mote th e follo wing;

y W ide variety of products andser vices to custo mers y Interop er ability betweenproducts andser vices madeby diff er ent vendors.

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y Easier introductio n of PC S products into th e national mark et. y Health y competitiveness among vendors, wh ich in tur n may lead to r educed cost and improved

product quality. y Develop ment andinnovation accor ding to common guidelines. y Mor e accessibl e ser vices to custo mers

30. What are the applications of a satellite system?

y W eath er for ecasting. y Radio and TVbro adcast satellites. y Military ser vices. y Navigation.

31. Give the benefits of paging systems?

y W idespr eadcover agey L ongbattery lif ey Small ligh t weigh t sets

y

Economical 32. What is a pa ge?

It is a brief message wh ich is bro adcast over th e entir e ser vice ar ea, usually in a simulcast f ash ionby many base stations at th e sametime.

33. What are the channels used in mobile communication systems?

1. For war d voice ch annels (FVC )2. Reverse voice ch annels (RVC )3. For war d control ch annels (FCC )4. Reverse C ontrol ch annels (R CC )

34. What are the basic units of a Cellular system?

y Mobil e stations y Base stations y Mobil e Switc h ingC enter (MSC ) or Mobil e Teleph oneSwitc h ing Offic e (MTSO).

35. What are the classifications of Wireless technologies and systems?

y C ellular mobil e r adio syst ems y C or dless teleph ones y W ide-ar ea wir eless data syst ems y High -speedWL ANs y Paging/messaging syst ems y Satellite-based mobil e syst ems

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DESCRIPTIVE ANSWERS

1. Explain the development history of mobile radio systems.

1921- Detroit Mich iganPolic e Dept. madeth e earliest signific ant use of Mobil e r adio in a veh iclein th e United States. Th e syst em oper ated at a fr equency clos e to 2 MHz. Th e ch annels soo nbecameovercro wded.

1940 - New fr equencies between 30 and 40 MHz wer e made available. Incr easing th e availablech annels encour aged asubst antial buil dup of polic e syst ems. Sh ortly th er eafter oth er users found aneed for th is for m of communication. Private individuals, companies, and public agencies purc h ased andoper ated th eir own mobil e units.

1945 - First public mobil e teleph one syst em in th e U.S. was inaugur ated in St. L ouis, Missouri with th r ee ch annels at 150 MHz. Six ch annels spaced 60kHz apart wer e allocated for th is ser viceby th e FCC , but th e mobil e equip ment was not sop h istic ated enough to pr event interf er ence.

1947 - A Public mobil e syst em using fr equencies in th e 35 to 44 MHz band began oper ations along th e h igh way between New York and Bosto n. Th ese fr equencies wer e th ough t to carry gr eater distances h owever a probl em with skip-distance prop agation carried interf eringconversations for long distances. Th ese early mobil e teleph one syst ems used pus h-to-talk oper ation.

1949 - FCC auth oriz ed separ ate r adio ch annels to common carrier entities k nown as "Radio C ommon C arriers" (R OC ). Th ese companies do not provide public teleph one ser vice, but interco nnect to th e public teleph one network to provide mobil e teleph one ser vices equivalent to th e wir e linecommon carriers.

1955 - Number of wir e line ch annels available at 150 MHz was expandedfrom 5 to 11 by th ecr eation of newch annels betweenth e old ones (ch annel spacingof 30 kHz ).

1956- 12 wir e line ch annels wer e added near 450 MHz. All syst ems oper ated in a manual mode, with each call to or from a mobil e unit beingh andled by a special mobil e teleph oneoper ator.

1964 - A newsyst em (150 MHz) was develop ed pro viding automatic ch annel selection for each call, eliminated th e needto pus h -to-talk oper ation, and allowedcusto mers to do th eir own dialing.

1969 - Automatic capability was extended to th e 450 MHz band andth e so called "Impro vedMobil e Teleph oneSystem" (IMTS) becameth e standar d for mobil e teleph oneser vice in th e U.S.

Advanced Systems (Cellular Concept)As early as 1947, it was r ealized th at small cells with fr equency r euse coul d incr ease tr affic capacity subst antially and th e basic cellular concept was develop ed. However, th e tech nology didnot exist.

1953 - AT&T propos ed to th e FCC a broadband mobil e teleph one syst em to oper ate in th e 800MHz r egion.

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1970 - FCC announced a tentative allocation of 75 MHz in th e 800 MHz r egion and invitedindustry to sub mit propos als for ach ievingcommunication objectives and demonstr ating f easibility.

1971 - AT&T r esponds with a tech nical r eport asserting f easibility by detailing h ow a "cellular syst em" migh t be compos ed. No oth er propos ed syst ems wer e submitted to th e FCC .

1974 - FCC mak es a fir m allocation of 40 MHz for mobil e teleph one ser vice and solicit edapplic ations for develop mental Systems to prove th e f easibility of so-called "C ellular Systems" but because of th e beginnings of Bell Systems divestitur e proc eedings, ruled th at W ester n Electric coul d not manuf actur e cellul ar ter minal equipment. Th is was because W ester n Electric mak es th enetwork equipment and th e r estrictio n from selling bot h ter minal and network products wer e to pr event furt h er monopoliz ation.

1975- AT&T appli ed for auth oriz ation to oper ate a develop mental cellular syst em in Ch icago.

1977 - L icense gr anted in March of 1977. Illinois Bell Teleph one constructs and oper ates adevelop mental cellul ar syst em.

1978 - Mid 1978th e Equipment Test ph ase commenced. Th e Ser vice Test-ph ase started in late1978. Twenty-one h undr ed mobil e sets wer e procur ed from th r ee suppli ers for th e test and th esyst emser vedover 2000trial custo mers.

1981 - FCC issu es standar d rules and due to th e dir ection alr eady tak en, In th e Bell Systemdivestitur e proc eedings, now rules th at W ester n Electric is per mitted to manuf actur e cellular ter minals as well as th e network equipment.

In th e years between 1974 and 1981, AT&T Bell L abs work ed with all oth er cellular ter minal vendors to develop th eir cellular ph ones so th at consumers would h ave quality products available to use on th ecellular network.

2. Describe in detail about the history of development of Paging and the future

trends of paging systems.

Historical Information

Paging is consider ed an import ant component of th e growing wir eless mark et. It was th e first mobil e communication ser vice for many as citywide paging syst ems wer e oper ating as early as 1963in th e USA and Europ e. Subscrib er growth r ate was around 15-20%per annum until 1997, r each ing appro ximately 144 million subscrib ers worldwide. However, th er e was a dr amatic slowdown in 1998 attribut ed to th e financial crisis in th e Asia-Pacific r egion wh er e most newsubscrib ers h ad been coming from. Despit e th e h uge succ ess of SMS (Sh ort Messaging Ser vices), th e paging mark et continues to be profit able in some ar eas due to th e introductio n of advancedmessaging tech nologies and sh eer number in developi ng countries lik e Ch ina. However, evenCh ina andoth er similar nations h ave suff er ed from lar ge loss es in subscrib er numbers due to th eadvent of cellul ar mobil e ph ones.

In th e early 70's, growth was r elatively slow due to th e limited applic ations of tone pagers off er edat th e time. For example, custo mers coul d not identify a caller 's number wh en th ey r eceived amessage. To r etrieve a message, th e custo mer h ad to call an answering ser vice. C onsumers wer eoff er ed much-improved tone and voice pagers wh en th e private sector was given access to telecommunication mark ets. Voice pagers spar ed custo mers th e inconvenience of searc h ing for teleph ones since messages wer e audible on small speak ers. However, problems included

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difficulti es in noisy environments and lack of privacy. Th ese voice syst ems ar e now limited to h ospit als andh omes.

In th e early 1980s, furt h er improvements to paging tech nology led to incr ease demand. Digital displays, introduced in 1982, allowedcallers to tr ansmit numeric messages andr ecall any messagethat had been stor ed. Th e new tech nology soon madepagers popul ar with work ers in ser viceindustri es r equiri ng constant contact with th eir or ganizations, suc h as r eal estate agents, sales people, h otel employ ees andpublic ser vants.

N ew C h allenges

Th e introductio n of cellular mobil e networks in th e mid 1980s also pr esented newopportu nities for companies in th e paging industry. Initially many outsi de obser vers f elt cellular mobil e ph ones would mak e pagers obsol ete. However, pagers have continued to sur vive particul arly in countries wh er e telecommunications infr astructur e is still developi ng, but mark ets worldwide ar e h aving to battle against th e steady drop in subscrib er numbers. Accor ding to Yank ee Group, th e number of worldwide subscrib ers is expected to r each 260 million by 2003.Perso nalized answering ser vice is a k ey growth ar ea. For example, a busi nessmanutiliz es a unique after -h ours teleph one number th at

dir ect calls to an answeringser vice center. Wh

en acusto mer calls the number, an oper ator answers th e ph one in th e busi nessman's name, tak es th e message andr elays it to th e busi nessman's pager.

Today, th e world tr ends indicate demandfor smaller and mor e flexible communication units. C r edit car d size devices and wrist watch-pagers ar e no longer science fictio n. Applic ations infinance, news and sports announcements have also begun in r ecent times. Most paging licenses give oper ators th e righ t to cover a wh ole nation. Th er efor e nation-wide offic e suppli ers and/or computer super -stor es ar e oftenused to distribut e pagers, making th emr eadily accessibl e to all.

F u t u r e T r ends

C ommunication ser vices ar e conver ging. Paging h as been incorpor ated into cellular andcor dless teleph ony as a cost eff ective way to r eceive messages, possibly limiting th e futur e of pager -only devices.

Th e paging ser vices mark et is divided into th r ee segments. One-way paging, two-way paging andtelemetry paging ser vices. Tr aditionally, one-way paging dominated th e mark et; h owever, it is being r eplaced by bot h two-way and telemetry ser vices, particul arly in develop ed nations. Accor ding to study undertak en in 1999by Frost & Sullivan, th e US h as experienced anincr ease inth e over all mark et growth r ate due to two-way paging andtelemetry ser vices. Th ese ser vices ar equickly advancing and will accou nt for clos e to h alf of mark et r evenues with in five years. One-way paging h as diminish ed r apidly as profits have been eroded by th e impact of newer tech nologies. Telemetry ser vice is an ar ea th at may experience some growth . Many see potential for th e ser vice in a variety of busi ness applic ations r anging from vending mach ines to utility meters.

Pagingcarriers will haveto focus on mark eting issu es andconcentr ate on particul ar segments suc h as yout h , especially as competition incr eases from Perso nal Digital Assist ants (PDAs). Pagingcarriers must use advanced two-way paging ser vices capable of sending andr eceiving subst antial amounts of data if th ey ar e to r emain competitive. At th e sametime, th ey must also r etain th eir lowcost advantageover cellular mobil e ph ones if th ey ar e to sur vive.

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Th e industry 's growth r ate h as f allen during last 2-3 years. However, manuf actur ers and pagingoper ators will not simply disr egar d th e massive investment th ey h ave madein paging tech nology and infr astructur e over th e years. Th e gloomy view of a cellular dominated world is not sh ar ed by all analysts. Accor ding to Global W ir eless, th er e ar e still many developi ng countries th at will driveth e paging mark et. Thailand, for example, had 1.4 million paging users in 1999 andr ank ed 11th ina list of th e top 20 inter national paging mark ets. At th e end of September 2000, Thailand h admoved to number nine on th e list with 1.64 million subscrib ers. Mexico is anoth er positi ve pagingmark et growing from 585,000subscrib ers in 1999to 825,000in 2000.

Develop ed countries ar e now concentr ating on particul ar mark et segments. For example, Japanesepaging carriers ar e tar geting corpor ate users. Some US carriers ar e tar geting users between ages 18-24 by mer ging Inter net applic ations with messaging, suc h as wir eless ch at sessio ns. Accor dingto Yank ee Group, sever al companies, including Apple and Hewlett -Pack ar d, ar e planning to aggr essively promote two-way pagers to th e mass mark et.

Pa g in g and SMS S ervi ces

Th e major advantageof paging over SMS is wh en sending a messageto multipl e r ecipi ents. Wh ile

it is capable with bot

h, it is muc

h c

heaper to use paging tec

hnology and t

he messages can be sent much mor e r apidly. Paging oper ators have off er ed applic ations to exploit th is advantage. One

example is for companies to use it as dir ect mark eting tool. That is, sh ops, cinemas andr estaur ants coul d use a multipl e messaging ser vice to broadcast detail of special sales, scr eenings or menus to r egular or potential custo mers. Th is allows th emto tar get infor mation to a specific audience.

SMS will dominate th e messaging mark et; h owever some users will pr ef er a device th at allows th em to prioritiz e th eir messages. Th er e ar e also network capacity issu es with SMS not r elevant to paging networks. Wh ile SMS messages can tak e sever al minutes to arrive, paging messages ar edeliver ed in seconds. Due to r apid growth in SMS, th er e is clear evidence th at consumers want messaging ser vices. Paging oper ators ar e often advised to dir ect th eir efforts to penetr ate various nich e mark ets suc h as yout h , doctors and engineers.

Mobil e communication is r apidly growing worldwide and users ar e coming from a broader prof essio nal and soci al spectru m. As consumers become mor e k nowledgeable about th e mark et, th ey often r ealize th e advantages and f aciliti es available with paging, be it on-site or wide-ar eapaging. Profit able growth will be possibl e if paging equipment manuf actur ers and oper ators continue to fost er tech nological develop ment and tr ansf er k nowledge into new pro ducts andser vices.

3. Explain in detail about the Standards adopted for Paging Systems.

POC

SAG

Oneof th e early develop ments in th e paging industry was th e cr eation of PO C SAG, a h igh-speedpagingprotocol for its time. It was named after th e Post Offic e Standar dization Advisory Group wh o first publis h ed th e code in th e UK in1978. Initially PO C SAGsupport ed asimple beep -only pager but later incorpor ated numeric and alph a text messaging. Th e original PO C SAGprotocol oper ated at 512b/s, but was later upgr adedto 1.2kb/s andth en again to 2.4kb/s. At 2.4kb/s, th edur ation of a numeric pagetr ansmission was r educed to 13-millis econds; incr easing th e th rou gh put of data by appro ximately 150times compar ed to th at of PO C SAG 512. Alth ough 80%of existing

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pagers r eceive numeric messages of less th an 10-digits, th e growth in longer paging messages is incr easing.

Today, PO C SAGis on th e ver ge of becoming obsol ete as much improvedcodes tak e over. In f act, th r ee diff er ent codes ar e now vying for th e leadersh ip: Europ ean Enh anced Radio MessagingSer vice (ERMES), Advanced Paging Oper ators C ode (APO C ) andFlexible (FL EX). Each codeach ieves gr eater capacity andlonger battery lif e th anPO C SAG.

E RM E S

ERMES (Enh anced Radio Messaging System) was develop ed in th e late 1980's by a group of paging manuf actur ers and Europ ean Paging Oper ators. It was designed to provide a h igh speedPan-Europ ean syst em for standar d tone, numeric and alph anumeric messages in a multi -network environment, enablingusers to roam th rou gh out any r egion in wh ich an ERMES oper ates.

ETSI appro ved ERMES standar d, ETS 300-1331, in 1992 andth e first commercial ser vice was launch ed in Fr ance in September 1994. ETSI h ad th e follo wingser vice r elatedobjectives in mind:

y Giveusers all th e basic ser vices th at existingpaging syst ems off er coupl ed with tr anspar ent

data ser vice. y Support a wide r ange of suppl ementary ser vices and f aciliti es, wh ich may be off er ed by various oper ators.

y Enable subscrib ers to use r eceivers for inter national roaming.

Th e committee also h ad th e follo wing perfor mance r elatedobjectives in mind:

y Per mit h igh level of spectru m effici ency at a r easonable cost. y Flexibility in alloc ating spectru m. y Optimize th e size andpower consumptio n of r eceivers. y C ompatibility with ISDN andfutur e standar dized messaging devices.

ERMES oper ates with sixteen fr equencies in one fr equency band, 169.4125- 169.8125MHz. L ongmessages can be up to 9000ch ar acters and tr anspar ent data (up to 64 K b/s) can be accepted andh andled in a very effici ent way. Th e ERMES MoU Group h as mer ged with th e Europ ean Public Paging Associ ation compris es 45 members across 26countries as of July 2000.

ETSI is curr ently developi ng a two-way versio n of ERMES intendedto improve usage of pagingnetworks. It has stated th at two-way paging sh ould be ach ieved with out incr easing paginginfr astructur e costs andpric es for pagers by mor e th an 25%.

APO C APO C was develop ed in 1993to "ser ve th e common r equir ements of paging oper ators in every country". It has been designedto off er :y gr eater subscrib er capacity and longer messages per r adio ch annel y minimum ser vice costs per subscrib er y minimum upgr ading and network investment costs y improvedcompleted-call perfor mancey competitivepager design with smaller and longer lif e batteries y mor e user f aciliti es y compatibility with PO C SAGpagers and networks

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Th e Radio Access Mail Protocol (RAMP) is a r ecent upgr ade to APO C off ering dir ect two-way access to th e Inter net. RAMP pro vides a h igh capacity message ser vice th rou gh downlinks from afixed network anduser gener ated upli nk messages from apock et ter minal.

FL EX

Anoth er protocol called FL EX was introduced in 1993. Th e standar d led to a r angeof pro ducts k nown as FL EXsuit e including:

y FL EX- 16~64kb/s one way pagingprotocol y ReFL EX - enables th rou gh put of 44~192kb/s with ack nowledgment paging andinter active

messagingy InFL EXion Voice - digitally compr essed voice for voice messaging applic ations y InFL EXion Data - intended for h igh -speed data applic ations supporti ng speeds of

28~112kb/s

Th is protocol h as become th e def acto standar d for h igh-speedpaging. It h as been adopted by 18 of th e top 20 US ser vice providers as well as by oth er mark et leaders in C anada, L atin America, Asia,

Afric a, th e Middle East and Europ e. Th e FL EXprotocol h as evenbecome th e national standar d for h igh -speed paging in Japan, K or ea, Ch ina, India and R ussi a. Motorol a also claims th er e ar eover 160FL EXtech nology-based syst ems in commercial oper ation in mor e th an 30countries.

4. Discuss in detail about the Recent Developments in Paging Systems.

New Developments in Paging

Paging migh t soon gain a boost in demandby capitalizing on pot ential Inter net applic ations, becoming a platfor m for a variety of wir eless infor mation ser vices. E-mail is possibly th e 'kill er 'applic ation. W ir eless e-mail utiliz es automatic scr eening andcan h andle an arr ay of incoming calls and messages.

Intelligent pagers can also automatically r etrieve infor mation for callers from databases, enter ch anges to sch edules in a calendar anduse dial-up f aciliti es for delayed two-way communications. One example of a new applic ation is th e delivery of news to subscrib ers wh er e topics of inter est ar e pr e-selected. A r angeof suc h public ations can be bro adcast to many diff er ent users at one time.

T wo-Way Pa g in g

A number of PC S-based two-way paging devices have begun commercial oper ation in th e U.S.

Th is tech nology h as enabled users to notify someone wh o h as sent a message th at it h as beenr eceived. L ik ewise it also enables subscrib ers to tr ansmit certain pr e-set messages. Similar tech niques h ave been mer ged with mobil e data tech nologies suc h as Sh ort Messaging Ser vice(SMS).

Th is sort of paging ser vices ar e r eport ed to be competitive with r eal-time cellul ar and PC S voic eser vices due to advantages in pric e, power, enh anced capabiliti es and mark et penetr ation. In th eUSA, th e aver agecellul ar teleph onebill costs much mor e th an today's paging ser vice.

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One of th e obst acles aff ecting th e paging industry h as been th e lack of two-way messagingnetworks. Accor ding to one r esearch er, th er e ar e still only two companies curr ently off ering two-way paging infr astructur e equipment.

Th e absence of mor e equipment pro viders h as giventh ese two companies significant power over paging infr astructur e equipment pric e and distributio n. Anoth er tech nology develop edby INC C ommunications, stor es codes in modified pagers. Th is will enable pagers to be used in tr ackingveh icles via GPS and in r emote meter r eadings.

C alle r Pays Pa g in g

In C aller Pays Paging (C PP ) syst ems th er e ar e no ongoing f ees or contr actual obli gations for subscrib ers. Th e owner only pays for th e initial purc h ase of a paging device. C PP was first introduced in Swedenin 1994 andis now used in many oth er countries. Much of th e succ ess h as been attribut ed to th e numeric message for mat and th e low cost of owners h ip. Many users develop th eir ownunique number codes to r elay messages to friends or f amily.

D ata Pa g in g Si g na ge Syst em

In Austr alia, data-paging signage was develop ed as an advanced syst em to pro vide multipl e andimmediate data updatingon signs. Th e tech nology uses r adio tr ansmitted paging signals to providean immediate update capability from onesourc e to a network of infor mation signs.

It was initially develop ed for financial mark ets signage as an easy to use andcost/l abor effici ent nation-wide ser vice. Infor mation is updated by placing just one call to th e paging center. All signs attach ed to th e network ar e th en automatically updated wh en r eceiving th e infor mation r equested. Alter natively, any individual sign (with in a group of signs) can be updated with a special message.

Th e flexibility of th is paging f acility enables r emote management of a wide-r angeof syst ems, suc h as th ose used by tr avel agents, water irrigation andpower controll ers, etc. Th e applic ations of th epaging signagesyst em ar e numerous.

5. Explain in detail about the Mobile radio standards around the world.

Many mobil e r adio standar ds h ave been developed for W ir eless syst ems th rou gh out th eworld, and mor e standar ds ar e lik ely to emer ge. Some of th e standar ds pr evalent th rou gh out th eworld ar e listedbelow.

Th e worlds first cellul ar syst em was implemented by th e Nippo n Teleph one and Telegr aph C ompany (NTT)in Japan. Th e syst em deploy ed in 1979, uses 6 FM Duplex ch annels (25 K Hz for each one way link ) in th e 800 MHz band.

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MOBIL E RADIO STANDARDS IN NORTH AMERIC A

Standard Type Year of Introduction

MultipleAccess

Frequencyband

Modulation ChannelBandwidth

AMPS cellular 1983 FDMA 824-894 MHz FM 30 K Hz NAMPS cellular 1992 FDMA 824-894 MHz FM 10 K Hz

USDC cellular 1991 TDMA 824-894 MHz /4- DQPSK 30K Hz

C DPD cellular 1993FH/

pack et 824-894 MHz GMSK 30 K Hz

IS-95C ellular/

PC S 1993 C DMA

824-894MHz/

1.8-2.0 GHz

QPSK / BPSK

1.25 MHz

GSC paging 1970S Simplex sever al FSK 1.25 K Hz

POC SAG Paging 1970S Simplex sever al FSK 1.25 K Hz FL EX Paging 1993 Simplex sever al 4-FSK 15 K Hz

DC S-900(GSM)

PC S 1994 TDMA1.85-1.99

GHz GMSK 200 K Hz

PAC S C or dless/

PC S 1994

FDMA/ TDMA

1.85-1.99GHz

/4- DQPSK

300 K Hz

MIR S SMR /PC S 1994 TDMA sever al 16-QAM 25 K Hz iDen SMR /PC S 1995 TDMA sever al 16-QAM 25 K Hz

MOBIL E RADIO STANDARDS IN EUR OPEStandard Type Year of Introduction

MultipleAccess

Frequencyband Modulation

ChannelBandwidth

ETAC S C ellular 1985 FDMA 900MHz FM 25 K Hz NMT-450 C ellular 1981 FDMA

450-470MHz FM 25 K Hz

NMT-900 C ellular 1986 FDMA

890-960MHz FM 12.5 K Hz

GSMC ellular/

PC S 1990 TDMA 890-960

MHz GMSK 200 K Hz

C -450 C ellular 1985 FDMA 450-465MHz FM 20 K Hz/ 10 K Hz ERMES Paging 1993 FDMA Sever al 4-FSK 25 K Hz

C T2 C or dless 1989 FDMA 864-868MHz GFSK 100 K Hz

DEC T C or dless 1993 TDMA 1880-1900MHz GFSK 1.728 MHz DC S-1800

C or dless/ PC S 1993 TDMA

1710-1880MHz GFSK 200 K Hz

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Th e first gener ation Europ eancellular syst ems ar e gener ally incompatible with one anoth er because of th ediff er ent fr equencies andcommunication protocols used.

MOBIL E RADIO STANDARDS IN JAPAN

Standard Type Year of IntroductionMultipleAccess

Frequencyband Modulation

ChannelBandwidth

JTAC S C ellular 1988 FDMA 860-925 MHz FM 25 K Hz PDC C ellular 1993 TDMA 810-1501 MHz

/4- DQPSK

25 K Hz

NTT C ellular 1979 FDMA 400/800 MHz FM 25 K Hz NTAC S C ellular 1993 FDMA 843-925 MHz FM 12.5 K Hz

NTT Paging 1979 FDMA 280 MHz FSK 12.5 K Hz NEC Paging 1979 FDMA Sever al FSK 10 K Hz

PHS C or dless 1993 TDMA 1895-1907MHZ/4-

DQPSK 300 K Hz

6. Discuss in detail about the Future trends of Personal Wireless Systems.

Trends in Personal wireless system

Personal C ommunications Networks (PC Ns), also calledPersonal C ommunication Ser vices (PC S), ar e defined as off ering perso nal communications at a cost level th at is suffici ently low as to attr act a mass subscrib er audience. Th ese ar e pois ed for a mass mark et br eakth rou gh towar ds th e endof th e decade andth ey may ch allengeth e role of th e fixed network. PC N was originally envisaged as a public ser vice off ering a r angeof functions, at a r angeof tariffs covering h ome zone or limitedmobility oper ation, pedestrian speed mobility, andlow speed veh icle mobility.

Th e ter m perso nal communications is gener ally consider ed to h ave come into being as a r esult of an initiative launch ed in 1989by th e UK DTI (Department of Tr ade and Industry ), wh ich is th egover nment body r esponsibl e for licensingpublic telecommunications ser vices networks in Britain. Public ation by th e DTIof Ph ones on th e Move was intendedto stimulate discussio n about wh at types of mobil e ser vices coul d be off er ed if suffici ent fr equency spectru m coul d be fou nd, th eviability of tar geting th e pock et r adioteleph one andh ow th e mark et for mobil e communications migh t develop.

Subsequently, anoth er very import ant category of usage, th e corpor ate PC N, spr ead over wider ar eas and integr ating th e fixed network with th e mobil e th rou gh a common numberingsch eme.

PC S is not based on any single tech nology but uses a number of standar ds including:

y GSM900/1800/1900 (Europ ean and Nort h Americ an GSM standar ds)y DEC T (Digital Enh anced C or dless Teleph ony)y PHS (Perso nal Handyph oneSystem)y IS-95C DMA (C ode Division Multipl e Access)y IS-136 TDMA (Time Division Multipl e Access)

In th at sense PC S is less a newtech nology enabler but r ath er a busi ness focus ed on capturi ng th emass consumer mark et.

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DEC T was develop ed as a cor dless adjunct to a PABX especially for h igh density busi ness environments typic al of multistory offic e buil dings. However r ecent enh ancements to th e GSMstandar d h as seen many vendors swing arou nd to th e idea th at DEC T may be unnecessary with many functio ns suppl anted by GSM 1800. Th e latter standar d h as th e advantage of seamless integr ation with GSM 900 networks andr eady availability of dual bandh andsets.

PC S networks in th e United States h avebeenbased on anup-banded versio n of GSM oper ating inth e Nort h American-specific 1.9 GHz band as well as 1.9 GHz variants of cdmaOne (th emark eting namefor narrowband IS-95 C DMA networks ) and th e IS-136 standar d. Dual modeGSM/DEC T ph ones h ave been extensively trialed in th e mark et since th e first prototyp e ph onewas exh ibited by Ericsso n at th e Telecom 95 in Geneva. Britis h Telecom became th e first or ganization to actually announce th e launch of a commercial ser vice most existing cellular oper ators h ave concluded th at a dual mode ser vice is not viable considering probl ems lik enumberingplans and lack of h andoff between GSM 900 and DEC T.

DEC T continues to do well as a standalone cor dless product for th e h ome and offic e. Th eequivalent DEC T tech nology in Japan is PHS h owever it was develop ed at th e outs et as a public access product not as a h ome andbusi ness cor dless syst em. Th e PHS mark et in Japan expandedr apidly at first but now appears to have plateaued at around 7 million users due to pr essur e fromcellul ar competitors. Th e initial r apid expansion h ad a lot to do with th e unique r egulatory andprici ng environment of mobil e communications in Japan.

Inter nationally, th e PC S mark et has become one of th e big growth mark ets of th is decade. In th eUnitedStates h undr eds of newcarriers h avebeen licensed as a r esult of spectru m auctio ns causingtariffs to drop by as much as 30 per cent in th e last year. In Hong K ong, newPC S oper ators h avecaptur ed almost twenty per cent of th e mobil e ph one mark et with th eir shar e doubli ng in th e last year. In K or ea newPC S oper ators have been r esponsible for a sh arp lift in th e number of mobil ecusto mers despit e th e economic r ecessio n.

As th e mark et expands, it will dr aw in a growing number of low-end r esidential users, drivingbasic voice ser vices up from h alf th e PC S mark et. PC Ns will use bot h existing andfutur e wir eline

and wir eless networks andf eatur e th r ee k ey elements: an easy-to-use, h igh -functionality h andset; asingle personal number th at can r each th e subscrib er anywh er e; and anindividualized f eatur eprofil e maintained in r eal time to custo mize th e end-user 's ser vice. By 2005 wir eless ph ones will accou nt for 20 per cent of worldwide teleph one tr affic up from 4 per cent in 1997say telecomr esearc h ers at Th e Yank ee Group.

PC Ns will not be a single all-encompassing wir eless solutio n but a combination of standar ds, networks and pro ducts th at meet a r ange of user r equir ements at a r easonable pric e with a high level of support, filling gaps left by oth er modes of wir eless and wir eline teleph ony. In th e longrun, microc ellul ar and macro cellul ar ser vices ar e lik ely to mer ge, allowing seamless h and-off androamingbetween network types.

Major data-based players lik e IBM, Apple, HP and DEC may enter th e mark et with th eir lar geleading-edge R&D departments, strong economic bases, name r ecognition and skill at cr eatingalliances, integr ating th eir data products with voice products and suddenly posi ng stro ng newcompetition to telecommunications manuf actur ers and carriers. In th e past year th er e h ave been anumber of announcements from major industry players on collabor ative initiatives suc h as Bluetoot h (a new wir eless standar d interco nnecting mobil e ph ones with oth er devices suc h as laptops ), Symbian (a newoper ating syst em for wir eless perso nal digital assist ants) and th eW ir eless Applic ation Foru m (developi ng th e standar d by wh ich mobil e ph ones will connect with th e Inter net).

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7. Describe in detail about the Wireless Local loop and LMDS.

Th e r apid growth of Inter net has cr eated a concurr ent demand for Broadband Inter net andcomputer access from busi ness andh omes th rou gh out th e world. Particul arly in developi ng nations wh er e th er e is inadequate telecommunication backbo ne infr astructur e, th er e is a tr emendous needfor inexpensive, r eliable, r apidly deploy able broadbandconnectivity th at can bring individuals andenterpris es into th e infor mation age. Inf act, as voice over Inter net protocols (VoIP) becomepr evalent, it is quite conceivable th at a single bro adband Inter net connection coul d someday provide all of th e neededtelecommunication ser vices, including teleph one ser vice, television, r adio, f ax, and inter net, for a h ome or Business custo mer. Fixed wir eless equipment is extr emely well suit ed for r apidly deployi ng a broadband connection in many instances, and th is appro ach is steadily becoming mor e popul ar for providing last mile bro adband local loop access, as well as for emer gency or r edundant point-to-point or Point-to-Multipoi nt private networks.

Unlik e Mobil e C ellular teleph one syst ems, fixed wir eless communication syst ems ar e able to tak eadvantage of th e very well defined, time-invariant natur e of th e prop agation ch annel betweenth efixed tr ansmitter and fixed r eceiver. Furt h er mor e, moder n fixed wir eless syst ems ar e usually assigned microwave or millimeter r adio fr equencies in th e 28 GHz band andh igh er, wh ich is gr eater than ten times th e carrier fr equency of 3G terr estrial cellular teleph one networks. At th eseh

igher fr equencies, t

he wavelengt

hs ar e extr emely small, w

hic

h in tur n allows very

hig

hgaindir ectional antennas to be f abricated in small ph ysic al for m f actors. At High er fr equencies, too,

mor e bandwidth can be easily used. High gain antennas havespatial filter prop erties that can r eject multip ath signals th at arrive from dir ections oth er th an th e desir ed line of sigh t, and th is in tur nsupport th e tr ansmissio n of very wide bandwidth signals with out distortio n. Also, since th e carrier fr equencies of th ese fixed wir eless access ter minals ar e so h igh , th e r adio ch annel beh aves muc h lik e optic al ch annels. Th us, fixed wir eless network at very h igh microwavefr equencies ar e only viable wh er e th er e ar e no obstructio ns, suc h as in a r elatively flat sub-urban or rur al setting. Micro wave wir eless links can be used to cr eate a wir eless local loop (WLL ) suc h as th e one sh ownin th e figur e below.

BackboneNetwork

LargeBusiness in

high densityareas

Small business

Mid marketbusiness outsidethe urban core

Residences

CentralOffice

Wireless

Fiber

Copper/xDSL

CentralOffice

DAX

ISP Cable

Example of the emerging applications and markets for broadband services

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Th e local loop can be th ough t of as th e last mile of th e telecommunication network th at r esides betweenth e centr al offic e (C O) andth e individual h omes and busi nesses in clos e pro ximity to th eC O. In develop ed countries, copp er or fiber optic cable h as been installed to r esidences andbusi nesses. However in many developi ng nations, cable is too expensive or can tak e month s or years to install. W ir eless equipment, on th e oth er h and, can easily be deploy ed in just in coupl e of h ours.

An additional benefit of WLL tech nology is that once th e wir eless equipment is paid for, th er e ar eno additional costs for tr ansport between th e C O and th e custo mer pr emises Equipment (C PE), wh er eas buri ed cables often must be leased from a ser vice provider or utility company on amonth ly basis. It s possibl e th at WLL syst ems coul d compete copp er wir e based Digital Subscrib er loops (DSL ) tech nologies th at ar e r apidly prolif er ating.

Th e concept of L MDS (L ocal Multipoi nt Distributio n Ser vice) is used for th e WLL applic ations wh ich pro videbro adbandtelecommunications access in th e local exch ange.

Most L MDS allocations sh ar e fr equencies with th e teledesic band wh ich was appro vedby th e ITUW orld Radio C onf er ence for Broadband Satellite Systems. Th e Teledesic band was originally establis h ed by th e Motorol a Iridium System, wh ose spectru m was later mer ged into th e Teledesic syst em. Th e figur e below gives th e alloc ation of fr equency for Broadband wir eless ser vices th rou gh out th e world.

Th e US L MDS band is 27.5-28.35 GHz, 29.1-29.5 GHz and 31.075-31.225 GHz. Th e IEEE802.16 Standar ds committee is developi ng interop er ability standar ds for fixedbro adband wir eless access. In Europ e, a similar standar d, HIPERACC ESS, is being develop ed by a standar dizationcommittee for Broadband Radio Access Networks (BRAN)for oper ation in th e 40.5-43.5 GHz band. Also, HIPER L INK is a very h igh speed sh ort r ange interco nnection for HIPER L ANs andHIPERACC ESS, up to 155 Mbps with in150 meters, and is plannedto oper ate in th e 17GHz bandin Europ e.

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In th e given figur e, each r ectangle h as an ar ea proportio nal to th e amount of r adio spectru mallocated to th e specifi ed ser vice. Th e US cellul ar ser vice was first issu ed spectrum in 1983 andcurr ently occupi es 50 MHz of total Bandwidth . Th e PC S ser vice occupi es 150 MHz of Bandwidth . L

MDS was allocated 1300 MHz of bandwidth

to provide over 200 bro adcast quality televisionch annels or 65000full duplex voic e ch annels.

One of th e pro mising applic ations of L MDS is in a local exch ange carrier (L EC ) network. Th efigur e given above sh ows a typic al network configur ation wh er e th e L EC owns a wide bandwidth asynch ronous tr ansf er mode (ATM)or Synch ronous Optical Network (SO NET)backbo ne switc h , capable of connecting h undr eds of Mbps of tr affic with th e Inter net, th e PSTN, or its own privatenetwork. As long as th e L OS path exists, L MDS will allow L EC s to install wir eless equipment onth e pr emises of custo mers for r apid bro adband connectivity with out h aving to lease or install its owncables to th e custo mers.

8. Explain about the basic cellular system.

A basic cellul ar syst emconsists of th r ee parts :A Mobil e Unit (MU)A C ell Site (C S)A Mobil e Teleph oneSwitc h ingOffic e (MTSO )

Andh as a connection to link th e th r ee subsyst ems.

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Mobile Unit (MU): It contains A C ontrol Unit A Tr ansceiver An AntennaSystem

Cell Site (CS): It provides th e interf ace betweenth e MTSO andth e mobil e units. It has

A C ontrol Unit Radio cabinets Antennas A Power Plant &Data ter minals

MTSO:It contains

C ellular proc essor C ellular switc h

It functions as Switch ingoffic e centr al coor dinating element for all cell sites Interf aces with teleph one company zoneoffic es C ontrols call proc essi ngHandles billing activities

Connections:Th e r adio and h igh-speed data links connect th e th r ee subsyst ems. Each mobil e unit can

only use one ch annel at a time for its communication link. But th e ch annel is not fixed; it can beany one in th e entir e band assigned by th e ser ving ar ea, with each site h aving multic h annel capabiliti es th at can connect simultaneously to many mobil e units.

Switches andprocessor

Voicecircuits

Mobile telephone switchingoffice

Dedicatedvoice graded

Land telephone network

Cell #1 Cell #2

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Th e MTSO is th e h eart of th e cellular mobil e syst em. Its proc essor provides th e centr al coor dination andcellular administr ation.

Th e cellular switch , wh ich can be eith er analog or digital, switch es calls to connect mobil esubscrib ers to oth er mobil e subscrib ers and to th e nationwide teleph one network. It uses voic etrunks similar to teleph one company interoffic e voice trunks. It also contains data links pro vidingsuper vision links betweenth e proc essor andth e switc h andbetweenth e cell sites andth e proc essor. Th e r adio link carries voice andsignalingbetweenth e mobil e unit andth e cell site. Th e h igh -speeddata links cannot be tr ansmitted over th e standar d teleph one trunks and th er efor e must use eith er microwave links or T-carriers (wir e lines). Micro waver adio links or T-carriers carry bot h voiceand data betweenth e cell site andth e MTSO.

9. Discuss in detail about the satellite mobile systems.

Mobil e satellite communications ar e particul arly significant to long-distance tr avelers over parts of th e world th at cannot be cover ed by conventional land-based communications syst ems. For aircr aft and sh ips, mobil e satellite links gr eatly improve air tr affic control, navigation and r escu er equir ements for tr ansoc eanic crossi ngs th at wer e ser ved by unr eliable h igh-fr equency (HF)

communications. Experiments in mobil e satellite communications wer e conducted in th e 1960s and th e early 1970s, but not until 1979 was th e Inter national Maritime Satellite Or ganization (INMAR SAT) for medto provide th e first mobil e satellite ser vice. Tech nical f easibility of mobil e satellite communications for aeronautical syst ems was proved during th e early 1970s using th e National Aeronautics andSpace Administr ation (NASA) ATS-6 satellite. In 1983th e Inter national C ivil AviationOr ganization (IC AO) set up a committee to study potential air navigation and communications syst ems. By th e early 1990s standar ds for land mobil e satellite communications wer e f ar less develop ed th an th ose for eith er aeronautical or maritimesyst ems.

Ser vices in aeronautic al mobil e satellite communications include data ser vices for th e aircr aft cr ew, cockpit voice communications, and passenger teleph ony. INMAR SAT is a leader in th edevelop ment of a worldwide aeronautical satellite communications syst em.

Th e INMAR SAT maritime communications syst em, Standar d-A, pro vides teleph one and telexser vices. Standar d-A is primarily an analog FM syst em, alth ough a 56-kb/s data ser vice is also available. Th e size andcost of Standar d-A ter minal equipment is lar ge, andth e cost is h igh , so it is installed only on lar ge sh ips. A low-r ate data ser vice th at pro vides telex andbro adcast f aciliti es, k nown as Standar d-C , will be introduced in th e futur e; its smaller size andr educed cost enable it to be installed on smaller sh ips. A fully digital syst em, Standar d-B, was developed during th e early 1990s to allow for additional ser vices andconnection into th e ISDN.

Geostar s Radio Deter mination Satellite System (RDDS) beganinitial oper ations in 1988 and was th e first domestic satellite syst em to provide r egular ser vice to mobil e users with in th e UnitedStates. Th is syst em integr ates r adio navigation, r adio location, and messaging with in a singlesatellite syst em. Dir ect-Sequence Spr ead-Spectru m Binary Ph ase Sh ift Keying (BPSK) signals over R F bandwidth of 16MHz ar e tr ansmitted via th is syst em.

Th e OmniTr acs syst em oper ated by Qualcomm, Inc., a two-way mobil e satellite communications and veh icle positio n r eporti ng syst em in th e United States and Europ e, beganoper ations in 1989. Dir ect-sequence spr ead-spectru m tech niques ar e used in th is syst em. Th e signal occupi es a 1-MHz bandwidth .

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Th e Austr alian MOBIL ESAT syst em provides circuit -switc h ed voice and data ser vices andpack et-switc h ed data ser vices for land, aeronautical, and maritime users. Th e syst em supports digital voice modulation at 4.8 kb/s in 5-kHz ch annels.

Telesat Mobil e, Inc. (TMI) andth e American Mobil e Satellite C orpor ation (AMSC ) ar e auth oriz edto provide mobil e satellites in C anada andth e United States. Oper ational syst ems using tr ellis-coded 16 quadr atur e amplitu de modulation (16-QAM) QAM, also for 4.8 kb/s voice modulation in5 kHz ch annels, ar e available.

10. Discuss in detail about the general satellite systems.

Satellite Technology

A satellite is madeup of two main elements, th e payload andth e bus. Th e payload includes all th eequipment th at h elps th e satellite perfor m its work, including antennas, camer as, r adar andelectronics. Th e bus is th e part of th e satellite th at carries th e payload into space. Th e bus also provides electrical power, comput ers and propulsio n for th e spacecr aft and h elps th e satellit ecommunicate with earth .

Th e US Department of Def ense h as been using satellites for quite some time. Th eir GPS (Global Positio ning System) is an example of one satellite installation. Th e GPS, wh ich was built for $12billio n, is a worldwide r adio-navigation syst embased on a constellation of 24 satellites, orbiti ng at 10,900 miles above th e earth (classifi ed as Medium-earth orbit or MEO satellites).

Grou nd stations, located in Hawaii, Ascension Island, Diego Garcia, Kwajalein and C olor ado Springs, monitor th e satellites. Receiver units use th e signals from th ese satellites to calculate th epositio n of objects or people anywh er e on Earth .

Th er e ar e sever al typ es of satellit es; geostationary, low-earth and medium-earth , ch ar acterized by th eir elevation above earth .

Geostationary satellites

Geostationary satellites ar e positio ned at about 22,300 miles above th e earth 's surf ace, dir ectly over th e equator. Th e satellites rotate at th e same speed as th e earth (24 h ours )- and th er efor eappear to r emain stationary with r espect to th e equator. Due to th is f actor, th ey ar e often used as communication satellit es and for r emote imaging, as th ey can scan th e same points on th e earth 's surf ace r epeatedly.

Applications

Geostationary satellites ar e often used for meteorolo gical purpos es as well. For example, a set of satellites called th e GOES (Geostationary Oper ational Environmental Satellites) produce imagery used to watc h sever e weath er conditions and to estimate r ainf all. DIREC TV is an example of anoth er succ essful geostationary satellite syst em. Dir ecTV uses five h igh-power satellites (orbit al locations ar e 101, 110 and 119 degr ees W est L ongitude) to broadcast content to 18-inch satellitedish es on th e consumer 's rooftop. A digital integr ated r eceiver/decoder separ ates each ch annel anddecompr esses/tr anslates th e digital signal so th e televisio n can sh ow it. Voice communications ar enot yet an optio n for geostationary satellites due to th e long round trip from earth to th e satellite, wh ich pro duces a h alf -second delay.

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LEO and MEO

L EOs (low-earth -orbit ) wh ich orbit from 400 to 1600 miles above earth . L EO satellit e syst ems h avebeen develop ed to pro vide global r eal-time voice communications, but due to th e complexity, cost of th e syst ems and widespr ead growth of cellul ar tech nology, th ey h ave not been very succ essful. Two examples ar e Iridium and Globalstar. Both syst ems ar e still in partial oper ation.

MEOs (medium-earth -orbit ) usually orbit at about 6,000 miles above th e earth (but orbits canr ange between 1,000 miles and 22,300 miles). MEOs ar e mainly used for GPS- styl e surf acenavigation syst ems but h ave also beenpropos ed for global communication syst ems.

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MODULATION AND SIGNAL PROCESSING

y Analog modulation techniques

y Digital modulation techniques

y Performance of various modulation techniques

Sp ectral efficiency Error rate Power Am p lification

y Equalization/Rake receiver conce p ts

y Diversity and Sp ace-time p rocessing

y Sp eech coding

y C hannel coding

UNIT IV

MODULATION AND SIGNAL PROCESSING

1. Define modulation.

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It is the p rocess of encoding information from a message source in a manner suitable for transmission.

2 . State the different analog modula tion schemes.Amp litude and frequency modulation.

3. State the different modulation schemes.Amp litude shift keying, frequency shift keying, p hase shift keying.

4. Define amplitude modulation.The am p litude of the high frequency carried is varied in a ccordance to the instantaneous am p litude of

the message signal.

5. State the techniques used for SSB generation.Filter method and balanced modulator method.

6. State the advantages of digital modulation schemes .Power efficiency and bandwidth efficien cy.

7. Define bandwidth efficiency.It describes the ability of the modulation scheme to accommodate data within a limited bandwidth.

8. Define Power efficiency.It describes the ability of the modulation scheme to p reserve the fidelity of the digital message at low

p ower levels.

9. State the different types of line coding.Return to zero, non-return to zero and Manchester.

10. State the types of modulation schemes used in mobile communication.GMSK, GFSK and DQPSK .

11. Give the equation used to represent a BPSK signal.

SBPSK (t) = m (t)

12 . What is coherent detector?If the receiver has p rior knowledge of the transmitted signal then the receiver is known as coherentdetector.

13. State the advantage of using GMSK rather than MSK.The bandwidth occu p ied by GM SK modulated signal is less in com p arison to MSK modulated signal.

14. What is CPFSK ?C ontinuous p hase frequency shift keying. It is another name for M SK.

15. What is QAM ?Q uadrature am p litude modulation.

16. State the difference between MSK and GMSK.GMSK uses a Gaussian p ulse sha p ing filter p rior to MSK.

17. What is a diversity receiver?Diversity receiver is the diversity scheme a pp lied at the receiver end of the antenna in all effective

technique for reducing interfer ence, where selective combiner is used to combine two -correlated signal.

18. Expand PCS, PLMR, NLOS and DECT.PC S - Personal C ommunication Systems.

PLMR Public Land Mobile RadioNLOS Non Line O f Sight

2 Eb cos (2 f ct + c)Tb

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DEC T Digital Equip ment C ordless Telep hone

19. Mention the three partially separable effects of radio propagation.The three p artially sep arable effects of radio p rop agation are,

Multip ath fading Shadowing Path loss

20. What is known as Quadrature Modulation?In digital modulations, instead of tran smitting one bit at a time, we transmit two or more bits simultaneously. Thisis known as M-ary transmission. This typ e of transmission results reduced channel BW. However sometimes theuse two quadrature carriers for modulation. This p rocess of transm itting 2 quadrature carrier for modulation isknown as quadrature modulation.

21. What are the design characteristics of digital modulation scheme?

Maximum data rate, Minimum transmitted p ower, Maximum channel BW, Maximum resistance to interfering signal s, Minimum circuit com p lexity.

22 . What are coherent digital modulation techniques?C oherent digital modulation techniques are those techniques which em p loy coherent detection. In coherentdetection, the local carrier generated at the receiver is p hase l ocked with the carrier at the transmitter. Thus,the detection is done by correlating received noisy signal and locally generated carrier. The coherentdetections a synchronous detection.

23. What are the non-coherent digital modulation techniques?Non-coherent digital modulation techniques are those techniques in which the detection p rocess does notneed receiver carrier to be p hase locked with transmitter carrier. The advantage of such ty p e of system is thatthe system becomes sim p le. But the drawbac k of such a system is that the error p robability increases.

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24. Give some advantage of QPSK:

For the same bit error rate, the BKJ required by QPSK is reduced to half as com p ared to BPSK. Because of reduced BW, the information transmission rate of QPSK i s higher C arrier p ower almost remains constant.

25. Drawbacks of MSK as compared to QPSK:1 . The BW requirement of M SK is 1 .5 fb, whereas it is fb in QPSK . Actually this cannot be said series drawback of MSK. Because p ower to BW ratio of MSK is m ore 99% of signal.2. Power can be transmitted within the BW of 1 .2 fb in MSK. While QPSK needs around 8fb to transmit the samep ower.

26. Bring out the difference between coherent and noncoherent binary modulation schemes

C oherent binary modulation Non-coherent binary modulation1 . Here the local carrier generated atthe receiver is p hase locked with the carrier at the transmitter. Thus detection is done bycorrelating received noisy signal and locallygenerated carrier.2. The coherent detection is asynchronous detection. Here the error p robability does not decreases

1 . Here the detection p rocessdoes not need receiver carrier to bep hase locked with transmitter carrier.2. Here error p robabilityincreases.

27. What is the error probability of MSK and D PSK?

The error p robability of MSK is given by

!

No

EberfcPe

21

The error p robability of DPSK is given by

!

No

EbPe exp

21

28. In minimum shift keying what is the relation between the signal frequencies and bit rate? The bit rate isgiven by

!

No

EberfcPe

21

WhereEb >>>>> Transmitted signal energy p er bit;No >>>>> Noise density

29. What is maximum likelihood decoder?

Set mk xf x / is always non-negative and since the logarithmic function is a monotonically inc reasingfunction of its argument we may restate the decision rule in terms of metric as follows

Set ,imm ! if ? Amk X f x /ln is maximum for k = iWhere ln denotes the a natural log. This decision rate is referred to as maximum likelihood rule and

device for its im p lementation is referred to as maximum likelihood decoder.

30. What is DPSK?Differential p hase shift keying is the non-coherent version of PSK. It is differentially coherent modulation

method. It does not need a synchronous carrier at the demodulator. The in p ut sequence of binary bits ismodified such that the next bit de p ends u p on the p revious bit. Therefore in the receiver bits are used ot detectthe p resent bit.

31. What are the advantages of DPSK?

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DPSK does not need carrier at its receiver. This means that the com p licated circuitry for generation oflocal carrier is avoided.

The bandwidth requirement of DPSK is reduced com p ared to that of BPSK

32 . What is capture effect?The ca p ture-effect is a direct result of the ra p id nonlinear im p rovement in received quality for an increase inthe received p ower. If two signals in the same frequency band are available at an FM receiver, the onea pp earing at the higher received signal level is acce p ted and demodulated, while the weaker one is rejected.This inherent ability to p ick-up the strongest signal and reject the rest makes FM systems very resistant to co -channel interference and p rovides excellent subjective received quality. This effect is called as ca p ture -effect .

Descriptive answers:

1. Describe in detail about the Analog Amplitude Modulation techniques used in mobile radio.

Modulation is the p rocess of encoding information from a message source in a manner suitable for transmission.Modulation may be done by varying the am p litude, p hase or frequency of a high carrier in accordance withthe am p litude of the message signal.

Types of Modulation1 . Analog modulation

- Amp litude modulation- Angle modulation ( PM, FM)

2. Digital modulation- Linear modulation- Non-linear modulation

Amplitude ModulationThe am p litude of a high frequency carrier signal is varied in accordance to the instantaneous

am p litude of the modulating message signal.If Accos(2 ct) is the carrier signal and m(t) is the modulating signal, the AM signal can be re p resented as

sAM(t) = Ac [1+ m(t)] cos(2 ct) ..( 1 )Where,

m(t) = (Am Ac ) cos(2 mt)

The modulation index k of an AM signal is defined as the ratio of th e p eak message signal am p litude tothe s p eak carrier am p litude.

Am k =

AcEquation ( 1 ) may be ex p ressed as

sAM(t) = Re{g(t)exp (j2 ct)}

where g(t) is the com p lex envelo p e of the AM signal is given by

g(t) = Ac [1+ m(t)]

The sp ectrum of an AM signal is

sAM(h) = Ac [H(h c ) + M(h c ) + H(h c ) + M(h c )]

where H( ) p unit imp ulse functionM(h) p message signal s p ectrum

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Sp ectrum of a message signal

Sp ectrum of the corres p onding AMsignal

The AM sp ectrum consists of an im p ulse at the carrier frequency, and two sidebands which re p licate themessage s p ectrum. The sidebands above and below the carrier frequency are called the u pp er and low er sidebands.

The RF bandwidth of an AM signal isBAM = 2 m

wherem p maximum frequency of modulating message signal

The total p ower in an AM signal is

P AM = Ac2 [1 + 2m(t)+ m2(t)] .(2) Where,

p average valueIf the modulating signal is m(t) = k cos(2 mt) eqn (2) is ex p ressed as

P AM = Ac2 [1 + Pm ] = Pc [1+ k2 2]Where Pc = Ac2/ 2 p carrier signal p ower

Pm = m2(t) p modulating signal p ower k p modulation index

Single Sideband AM

SSB-AM systems transmit only one of the sidebands (either u pp er or lower) about the carrier, and henceoccu p y only half the bandwidth of conventional AM systems.

An SSB signal can be ex p ressed as

..(3)Where

(-) p upp er sideband SSB (+ ) p lower sideband SSB

| M(h) |

- m m h

| sAM(h) |

upp er sideband

lower sideband

lower sideband

upp er sideband

- c- m - c - c+ m c- m c c+ m

S SSB (t) = Ac [m(t)cos (2T ct) s m(t) sin(2T ct) ]

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The two common techniques used for generating an SSB signal are the filter method and the balancedmodulator method.In the filter method , SSB signals are generated by p assing a double sideband AM signal through a band p as sfilter which removes one of the sidebands. Excellent sideband su pp ression can be obtained using crystal filtersat an Intermediate frequency ( IF).

In balanced modulator the modulating signal is s p lit into two identical signals, one which mod ulates the in-p hase carrier and the other which is p assed through a 90r p hase shifter before modulating a quadraturecarrier. The sign used for the quadrature com p onent determines whether U SSB or LSSBis transmitted.

m(t) p Hilb ert tr ansfor m of m(t)

m(t) = m(t) h HT(t) = m(t) 1T t

H HT( ) p Fouri er tr ansfor m of h HT(t), corresponds to a 90 r phase shiftnetwork

H ( ) = {

j " 0j 0

m(t) S SSB (t) Bandpass Filter (filt ers out oneof th e sidebands)

Accos (2T ct)

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Pilot Tone SSB

SSB systems have the advantage of being very bandwidth efficient, their p erformance in fading channels isvery p oor. In conventional SSB receivers, it is difficult to electronically tune the local oscillator frequency to the

identical frequenc y of the incoming carrier. Dopp ler sp reading and Rayleigh fading can shift the signalsp ectrum causing p itch and am p litude variations in the received signal. These p roblems may be overcome bytransmitting a low level p ilot tone along with the SSB signal. A p hase locked loo p at the receiver can detectthis p ilot tone and use it to lock the frequency and am p litude of the local oscillator. If the p ilot tone and theinformation bearing signal undergo correlated fading, it is p ossible at the receiver to count eract the effects offading through signal p rocessing based on tracking the p ilot tone. This p rocess is called feed forward signalregeneration (FFSR). By tracking the p ilot tone, the p hase and am p litude of the transmitted signal can bereestablished. Kee p ing the p hase and am p litude of the received p ilot tone as a reference, the p hase andam p litude distortions in the received sidebands caused by Rayleigh fading can be corrected.

Three different ty p es of p ilot tone SSB systems are [Gos 78], [ Lus 78] and [ Wel78]. Three systems transmit a lowlevel p ilot tone, -7.5 d B, to -1 5 dB below the p eak envelo p e p ower of the single sideband signal. Theyessentially differ in the sp ectral p ositioning of the low level p ilot tone. O ne system transmits a low level carrie r

along with the sideband signal (tone -in-band), while the other two p lace a p ilot tone above or within the SSB band.

In tone-in-band SSB system a small p ortion of the audio s p ectrum is removed from the central region of theaudio band using a notch filte r, and a low level p ilot tone is inserted in its p lace. This has the advantage ofmaintaining the low bandwidth p rop erty p f the SSB signal, and also p rovides good adjacent channelp rotection. For p rop er o p eration of tone -in-band SSB, the tone must be trans p arent to data and be s p acedacross the band to avoid s p ectral overla p with audio frequencies called Transparent Tone-in-band (TTIB).

Demodulation of AM SignalsDemodulation is the p rocess of extracting the baseband message signal from the carrier so th at it may bep rocessed and inter p reted by the intended receiver (sink).

Typ es of Demodulation- C oherent demodulation- non coherent demodulationC oherent demodulation requires knowledge of the transmitted carrier frequency and p hase at the receiver,whereas non coherent detection requires no p hase information. In p ractical AM receivers, the received signalis filtered and am p lified at the carrier frequency and then converted to an intermediate frequency ( IF) using asup er heterodyne receiver.

Product detector

m(t)

C arrier Oscill ator

c

Accos (2T ct)

90 r Phase Shift

90 r

S SSB (t)m t

m t

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A p roduct detector (or p hase detector) is a down converter circuit which converts the in p ut band p ass signal toa baseband signal. If the inp ut to the p roduct detector is an AM signal of the form R(t)cos (2 c t + Ur), themultip lier outp ut is

v1 (t) = R(t)cos (2 c t + Ur)A 0cos (2 c t + U0) . (4) where

c p oscillator carrier frequencyUr p receiver signal p haseU0 p oscillator signal p hase

Using trigonometric identities in eqn (4)

LPFremoves

the doublecarrier

frequency,the out p utis

Where

K p gain constantNon coherent envelo p e detectors which are easy and chea p to build. An ideal envelo p e detector is a circuitthat has an out p ut p rop ortional to the real envelo p e of the i n p ut signal.If the inp ut to the envelo p e detector is R(t)cos (2 c t + Ur), the out p ut is

vout (t) = K R(t) This is useful when the inp ut signal p ower is atleast 1 0 d B > noise p ower.

2. Describe in detail about the Angle Modulation techniques used in mobile radio.

Angle modulation varies a sinusoidal carrie r signal in such a way that the angle of the carrier is variedaccording to the am p litude of the modulating baseband signal.This is a form of angle modulation in which the instantaneous frequency of the carrier signal is varied linearlywith the baseband message signal m(t)

whereAc p carrier am p litude

c p carrier frequencyk p frequency deviation constant( H z/V)

If the modulating signal is a sinusoid of am p litude a A m and frequency m

2 R(t)cos( 2T ct + Ur)

A0cos( 2T ct + U0)

L PF v1(t)vout (t) = 1 A0R(t)cos( Ur U0)

2 2 v1(t) = 1 1A0R(t)cos( Ur U0) + A0R(t)cos( 2T ct + Ur U0)

vout (t) = 1 A0R(t)cos( Ur U0) = K R(t)

SFM (t) = A ccos[ 2T ct + U(t)] = A ccos?2T ct + 2T k m(L)dLA..(a) g

t

SFM (t) = A ccos ?2T ct + k Am sin( 2T m t) A . (b) m

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The frequency modulation index F defines the relationshi p between message am p litude and the bandwidthof the transmitted signal,

(c)

whereAm p modulating signal p eak value

p Transmitter p eak frequency deviationW p modulating signal maximum bandwidth

Phase Modulation

This is a form of angle modulation in which the angle U(t) of the carrier signal is varied linear ly with thebaseband message signal m(t)

SPM(t) = A c cos[ 2 c t + k Um (t)]where

k U p p hase deviation constant(rad/volt)

An FM signal can be generated by first integrating m(t) and then using the result as the in p ut to thep hase modulator . C onversely, a PM wave can be generated by first differentiating m(t) and using the resultas the in p ut to frequency modulator.

The p hase modulation index Fp

Fp = k UAm = (U where

(U p Transmitter p eak p hase deviation

FM Modulation Methods

There are two methods:- Direct MethodThe carrier frequency is directly varied in accordance with the in p ut modulating signal.- Indirect MethodA narrow band FM signal is generated using a balance modulator, and frequency multi p lication is used toincrease both the frequency deviation and the carrier frequency to the required level.

Direct Method:

In this method voltage controlled oscillators (V C O s) are used to vary the frequency of the carrier signal inaccordance with the baseband signa l am p litude variations. These oscillators use variable reactance device,voltage variable ca p acitor called a Varactor. This Varactor is obtained by using a reverse biased p -n junctiondiode. The larger the reverse voltage a pp lied, the smaller will be the t ransition ca p acitance of the diode.Incor p orating this into a standard Hartley or C olp itts O scillator, FM signals can be generated. In wideband FMgeneration, the stability of the center frequency of V C O can be im p roved by using a PLL.

Indirect Method

Narrowband FM signal is obtained by the sum of a carrier signal and a SSB signal where the sideband is90r out of p hase with the carrier.

Using Taylor series for small values of U(t), eqn (a) becomes

SFM(t) $ Ac cos (2 c t) Ac U(t)sin (2 c t)

q carrier sideband

q

F = k Am = ( W

W

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A narrowband FM signal is generated using a balanced modulator. The maximum frequency deviation is ke p tconstant and small, to maintain the validity of above eqn, p roviding a narrowband FM out p ut signal.

A wideband FM signal is then p roduced using frequency multi p liers.Disadvantage: p hase noise in the system increases with the frequency multi p lying factor N.

3. Describe in detail about the demodulation techniques for FM waves used in mobile radio.FM Detection Techniques

A frequency-to-am p litude converted circuit is a frequency demodulator. Various techniques areslop e detection, zero-crossing detection, p hase locked discrimination, and quadrature detection is used todemodulate FM. Devices which p erform FM demodulation are often called frequency discriminators. Inp ractical receivers, the RF signal is received, am p lified, and filtered at the carrier, and then converted to anintermediate frequency ( IF) which contains the same s p ectrum as the original received si gnal.

Slope Detector

The FM signal isp assed through an am p litude limiter which removes in am p litude p erturbations which thesignal might have undergone due to fading in the channel, and p roduces a constant envelo p e signal.

Using eqn (a),the signal

at the out p ut of limiter is

.Eqn (A) can be

differentiated by p assing the signal through a filter with the transfer function that has gain that increases linearlywith frequency. Such a filer is called a slo p e filter. (Slop e detector).T he out p ut of differentiator is

And the envelo p e detector out p ut is

The outp ut of the envelo p e detector contains a dc term p rop ortional to the carrier frequency and a timevarying term p rop ortional to the origin al message signal m(t). The dc term can be filtered out using aca p acitor to obtain the desired demodulated signal.

Zero-crossing detector (pulse-averaging discriminator)

v1 (t) = V 1cos[ 2T ct + U(t)] = V 1 cos?2T ct + 2T k m( L)d LA..(A)

t

vin (t) L imiter

v1 (t) Diff er entiator v2 (t) Envelop eDetector vout (t)

v2 (t) = V1?2T ct + d UAsin[ 2T ct + U(t)]dt

vout (t) = V 1?2T ct + d A dt

= V 12T ct + V 12T k m(t)

U(t)

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When linearity is required over a broad range of frequencies, such as for data c ommunications, a zero-crossing detector is used to p erform frequency -to-am p litude conversion by directly counting the number ofzero crossings in the in p ut FM signal.The rationale behind this technique is to use the out p ut of the zero -crossing detector to generate a p ulse trainwith an average value that is p rop ortional to the frequency of the in p ut signal.

The inp ut FM signal is firstp assed through a limiter circuit which converts the in p ut signal to a frequencymodulated p ulse train. Thisp ulse train v 1 (t) is then p assed through a differentiator whose out p ut triggers amonostable multivibrator (one -shot). The one -shot out p ut consists of a p ulse train with average durationp rop ortional to the desired message signal. LPF is used to p erform the averaging o p eration by extracting theslowly varying dc com p onent of the out p ut signal of one shot. The out p ut of LPF is the desired demodulatedsignal.

PLL For FM Detection The PLL is a closed loo p control system that can track the variations in the received signal p hase andfrequency.

It consists of a V C O H(s) with an out p ut frequency varied in accordance with the demodulated out p ut voltagelevel. The outp ut of the V C O is com p ared with the in p ut signal using a p hase com p arator, which p roduces anout p ut voltage p rop ortion to the p hase difference. The p hase difference signal is then fed back to the V C O tocontrol the out p ut frequency. The feedback loo p functions in the locking of V C O frequency to the in p ut signal.O nce the V C O frequency is locked to the in p ut frequency, the V C O continues to track the variations in theinp ut frequency. O nce this tracking is achieved, the control voltage to the V C O is the demodulated FM signal.

Quadrature Detection

This technique can be easily im p lemented on an integrated circuit at a very low cost. The detector consists of a network which shifts the p hase of the incoming FM signal by an amount p rop ortional to itsinstantaneous frequency, and uses a p roduct ( p hase) detector to deduct the p hase difference between theoriginal FM signal and the out p ut signal of p hase -shift network. Since the p hase shift introduced by the p hase -shift network isp rop ortional to instantaneous frequency of FM signal, the out p ut volt age of p hase detector willalso be p rop ortional to the in p ut FM signal instantaneous frequency. Thus a frequency -to-am p litude conversionis achieved, and the FM signal is demodulated.

SFM (t)input FMsignal

PhaseDetector

L oop Amplifi er andL PF

VoltageC ontroll edOscillator (VC O)

m(t)demodulatedoutput signal

L imiter Diff er entiator MonostableMultivibr ator L PF vin (t)

v1 (t) v2 (t) v3 (t) vout (t)

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To achieve o p timum p erformance, a very s mall (< s 5r) p hase shift is to be introduced across the modulatedsignal bandwidth. The p hase -shift network should have a constant am p litude resp onse and a linear p haseresp onse over the occu p ied FM signal sp ectrum. Further, the network should have a nomi nal 90 r p hase shift atthe carrier frequency.

The p hase res p onse function of the p hase -shift network is

whereKp Prop ortionality constant

When an FM signal is p assed through the p hase -shift network, the out p ut is

(t) = Ac cos[2 f ct + 2 k f m( )d + (f i(t)) ]

The outp ut of the p roduct detector is p rop ortional to the cosine of the p hase difference between and (t)and Sfm(t).

0(t) = 2 Ac 2cos ( (f i(t)))0(t) = 2 Ac 2cos (- /2 + 2 K[fi(t) fc] )0(t) = 2 Ac 2 sin(2 K.k f. m(t))

If the p hase shift varies only over a small angle, the above ex p ression becomes as0(t) = 2 Ac 22 K.k f. m(t) = C m(t).

Hence the quadrature detector out p ut is the desired message signal multi p lied by a constant.

4. Describe in detail about the Digit al modulation schemes BPSK.

Modern mobile communication systems use digital modulation techniques.

ADVANTAGES

Greater noise immunity Robustness to channel im p airments Easier multip lexing of various forms of information Greater security

Factors That Influence the Choice of Digital Modulation

L PF

SFM (t)input FMsignal

Phase-sh ift network Z( )

with 90 r shift at f c

VJ(t)

vout (t)demodulatedoutput signal

J( ) = T + 2T K( - c)2

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Several factors influence the choice of a digital modulation scheme. A desirable modulation schemep rovides low bit error rates at low received signal -to-noise ratios.The p erformance of a modulation scheme is meas ured in terms of p ower efficiency and bandwidth efficiency .

Power (energy) efficiencyThis describes the ability of a modulation technique to p reserve the fidelity of the digital message at low

p ower levels. In digital communication system, to increase n oise immunity, it is necessary to increase the signalp ower.

It is defined as the ratio of the signal energy p er bit to noise p ower sp ectral density (Eb / N 0). It is denotedas Lp .

Bandwidth efficiencyThis describes the ability of a modulation scheme to accommodate data within a limited bandwidth.It is defined as the ratio of the through p ut data rate p er Hertz in a given bandwidth.If R is the data rate in bits p er second, and B is the bandwidth occu p ied by the modulated RF signal, then

bandwidth efficiency LB is exp ressed as

The systemca p acity of adigital mobilecommunicatio

n system is directly related to the bandwidth efficiency of the modulation scheme, for > LB transmit more datain a given s p ectrum allocation.

Shannons channel coding theorem states that for an arbitrarily small p robability of error, the maximump ossible bandwidth efficiency is limited by the noise in the channel and the channel ca p acity formula is

WhereC p channel

ca p acity (b p s)B p RFbandwidth

S/N p signal-to-noise ratio

Bandwidth and Power Spectral Density of Digital Signals

The definition of signal bandwidth is based on the p ower sp ectral density ( PSD) of the signal. The PSD of arandom signal w(t ) is defined as

Where the bar denotes ensemble av erageWT(h) p Fourier transform of WT(t) is the truncated version of the signal w(t )

WT(t) = {

The PSD of a modulated (band p ass) signal is related to the PSD of its basebandcom p lex envelo p e. If a band p ass signal s(t) is rep resented as

LB = R B .1.1 bps/Hz

LBmax = C = log 2?1 + S/N A B .1. 2

P w (h) = limT p g ..1. 3

W T (h) 2

T

w(t ) -T/2

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s(t) = Re { g(t)exp (j2 ct) .. 1 .4where

g(t) p com p lex baseband envelo p e

The PSD of the band p ass signal is

wherePg (h) p

PSD of g(t)

The absolutebandwidth of a

signal is defined as the range of frequencie s over which the signal has a non -zero p ower sp ectral density.

The null-to-null bandwidth is equal to the width of the main s p ectral lobe.The disp ersion of the s p ectrum is measured using the half- p ower bandwidth ( 3 d B bandwidth) . It is defined asthe interval between frequencies at which the PSD has dro pp ed to half p ower, or 3 d B below the p eak value.