Gugl?elmo ?nto the follow?ng c?tegor?es: • p?g?ng systems, •

        Gugl?elmo M?rcon? ?nvented the w?relesstelegr?ph ?n 1896. ?n 1901, he sent telegr?ph?cs?gn?ls ?cross the ?tl?nt?c Oce?n from Cornw?ll to St.

John’s Newfoundl?nd; ? d?st?nceof ?bout 3200 km. H?s ?nvent?on ?llowed two p?rt?es to commun?c?te by send?ng e?chother ?lph?numer?c ch?r?cters encoded ?n ?n ?n?log s?gn?l. Over the l?stcentury, ?dv?nces ?n w?reless technolog?es h?ve led to the r?d?o, the telev?s?on,the mob?le telephone, ?nd commun?c?t?ons s?tell?tes. ?ll types of ?nform?t?on c?nnow be sent to ?lmost every corner of the world. Recently, ? gre?t de?l of ?ttent?onh?s been focused on s?tell?te commun?c?t?ons, w?reless network?ng, ?nd cellul?rtechnology.The cellul?r or mob?le telephone ?s the modern equ?v?lent of M?rcon?’s w?relesstelegr?ph,offer?ng two-p?rty, two-w?y commun?c?t?on. The f?rst-gener?t?on w?reless phonesused ?n?log technology. These dev?ces were he?vy ?nd cover?ge w?s p?tchy, butthey successfully demonstr?ted the ?nherent conven?ence of mob?le commun?c?t?ons.

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The current gener?t?on of w?reless dev?ces ?s bu?lt us?ng d?g?t?l technology. D?g?t?lnetworks c?rry much more tr?ff?c ?nd prov?de better recept?on ?nd secur?ty th?n?n?log networks. ?n ?dd?t?on, d?g?t?l technology h?s m?de poss?ble v?lue-?ddedserv?ces such ?s c?ller ?dent?f?c?t?on. Newer w?relessdev?cesconnect to the ?nternet us?ng frequency r?nges th?t support h?gher ?nform?t?onr?tes. (STALLINGS, 2005)           1.1  W?relessCommun?c?t?on Systems         W?reless commun?c?t?onsystems ?re ch?r?cter?zed by ? v?r?ous of propert?es.

They ?re d?fferent from e?chother ?n terms of how complex they ?re, Wh?t serv?ces they c?n prov?de ?nd howmuch they cost to run. The most ?mport?nt property of ?ll mob?le commun?c?t?onsystems ?s th?t one user most be mov?ng ?nd ?lso th?s commun?c?t?on does notuse ?ny w?res ?s ? med?um of commun?c?t?on. One of the t?xonomy cr?ter?? of themob?le systems ?s how complex they ?re ?nd the r?nge of the offered serv?ces. ?ccord?nglythe mob?le commun?c?t?on systems c?n be cl?ss?f?ed ?nto the follow?ng c?tegor?es:• p?g?ng systems,• w?reless telephony,• trunk?ng systems,• cellul?r telephony,1.1.1                   P?G?NG SYSTEMS: P?g?ngsystems ?re ?n ex?mple of br??dc?st?ng systems. ?n ? cl????c?l p?g?ng systemthe commun?c?t?on ?s un?d?rect?on?l. The s?gn?l ?s tr?n?m?tted from the b?se st?t?onconnected w?th the c?ll center to ? selected rece?ver (p?ger).

?ll rece?versl?sten to the bro?dc?st s?gn?ls, detect?ng th?t p?rt?cul?r one wh?ch ?s ?ddressedd?rectly to ?t. ?n ? cl?ss?c?l system the p?ger ?s ?ble only to rece?ve s?gn?ls.?n the e?rly ph?se of development the p?g?ng s?gn?l w?s very s?mple. ?t tr?ggered? beeper gener?t?ng ?n ?coust?c tone.

?t present the p?g?ng s?gn?l typ?c?lly h?sthe form of ? sequence of ?lph?numer?c?l symbols or ?s ? short vo?ce mess?ge.The p?ger ?s selected by send?ng the mess?ge w?th ?ts un?que ?ddress. Typ?c?lly,mess?ges ?re tr?nsm?tted us?ng ? frequency modul?t?on. Due to the f?ct th?t ? p?ger?s very s?mple ?nd not ?ble to tr?nsm?t s?gn?ls, ?ts power consumpt?on ?s verylow ?nd ?ts s?ze ?s sm?ll. 1.1.

2                   W?RELESS TELEPHONY: W?reless telephone systems ?ppe?red ?n the l?te sevent?es. They c?nbe ch?r?cter?zed ?s ? low power w?reless commun?c?t?on me?ns ?ntended for ?user mov?ng slowly ?nd loc?ted ? short d?st?nce from the b?se st?t?on. The b?s?c??m of ?ntroduc?ng ? w?reless telephone ?s to repl?ce ? w?rel?ne one.

Theconnect?on qu?l?ty ?nd the cost of ? w?reless st?t?on should be comp?r?ble tothe qu?l?ty ?nd cost of ? tr?d?t?on?l w?rel?ne phone. The b?se st?t?on ?s th?tp?rt of the w?reless system wh?ch ?s connected to the publ?c sw?tched telephonenetwork (PSTN) ?nd ?t ?s seen by the l?tter ?s ? regul?r telephone. ?n most c?sesone b?se st?t?on co-works w?th ? s?ngle mob?le st?t?on. 1.1.3                   TRUNK?NG SYSTEMS: Trunk?ng systems ?re mob?le commun?c?t?on systems spec??l?z?ng ?ncommun?c?t?ons w?th?n l?rge enterpr?ses wh?ch m?n?ge resources d?spersed ?n sp?ce,such ?s ? fleet of trucks or serv?ce veh?cles. Trunk?ng systems ?re p?rt?cul?rlyuseful ?n tr?nsport comp?n?es, ?nd spec??l serv?ces such ?s pol?ce, emergencyserv?ces, g?s ?nd power suppl?ers, etc. The?r ch?r?cter?st?c fe?ture ?s the ex?stenceof ? d?sp?tch ?nd control center wh?ch m?n?ges the c?lls.

Thus, spec??l k?ndsof connect?ons ?re ?rr?nged wh?ch ?n regul?r telephone networks ?re poss?ble ?sspec??l serv?ces only. 1.1.4                   CELLUL?R TELEPHONY: Cellul?r telephony ?s the next ?nd perh?ps the most represent?t?veex?mple of mob?le commun?c?t?on systems. The cellul?r phone system ?s ch?r?cter?zed?s ? system ensur?ng b?d?rect?on?l w?reless commun?c?t?on w?th mob?le st?t?onsmov?ng even ?t h?gh speed ?n ? l?rge ?re? covered by ? system of b?se st?t?ons.The cellul?r system c?n cover ? whole country.

Moreover, ? f?m?ly of systems ofthe s?me k?nd c?n cover the ?re? of m?ny countr?es, ?s ?n c?se of the GSMsystem.   1.2  Mult?ple?ccess Techn?ques for W?reless Commun?c?t?ons:        Mult?ple?ccess techn?ques ?re used to ?llow ? l?rge number of mob?le users to sh?rethe ?lloc?ted spectrum ?n the most eff?c?ent m?nner.?s the spectrum ?s l?m?ted, so the sh?r?ng ?s requ?red to ?ncre?se the c?p?c?tyof cell or over ? geogr?ph?c?l ?re? by ?llow?ng the ?v??l?ble b?ndw?dth to beused ?t the s?me t?me by d?fferent users.

?nd th?s must be done ?n ? w?y suchth?t the qu?l?ty of serv?ce doesn’t degr?de w?th?n the ex?st?ng users.?nw?reless commun?c?t?on systems ?t ?s often des?r?ble to ?llow the subscr?ber tosend s?mult?neously ?nform?t?on to the b?se st?t?on wh?le rece?v?ng ?nform?t?onfrom the b?se st?t?on.?cellul?r system d?v?des ?ny g?ven ?re? ?nto cells where ? mob?le un?t ?n e?ch cellcommun?c?tes w?th ? b?se st?t?on. The m??n ??m ?n the cellul?r system des?gn ?sto be ?ble to ?ncre?se the c?p?c?ty of the ch?nnel ?.e.

to h?ndle ?s m?ny c?lls?s poss?ble ?n ? g?ven b?ndw?dth w?th ? suff?c?ent level of qu?l?ty of serv?ce.There ?re sever?l d?fferent w?ys to ?llow ?ccess to the ch?nnel. These ?ncludem??nly the follow?ng:Frequencyd?v?s?on mult?ple-?ccess (FDM?)