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

        Gugl?elmo M?rcon? ?nvented the w?reless
telegr?ph ?n 1896. ?n 1901, he sent telegr?ph?c
s?gn?ls ?cross the ?tl?nt?c Oce?n from Cornw?ll to St. John’s Newfoundl?nd; ? d?st?nce
of ?bout 3200 km. H?s ?nvent?on ?llowed two p?rt?es to commun?c?te by send?ng e?ch
other ?lph?numer?c ch?r?cters encoded ?n ?n ?n?log s?gn?l. Over the l?st
century, ?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?n
now be sent to ?lmost every corner of the world. Recently, ? gre?t de?l of ?ttent?on
h?s been focused on s?tell?te commun?c?t?ons, w?reless network?ng, ?nd cellul?r

technology.
The cellul?r or mob?le telephone ?s the modern equ?v?lent of M?rcon?’s w?reless

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telegr?ph,
offer?ng two-p?rty, two-w?y commun?c?t?on. The f?rst-gener?t?on w?reless phones
used ?n?log technology. These dev?ces were he?vy ?nd cover?ge w?s p?tchy, but
they successfully demonstr?ted the ?nherent conven?ence of mob?le commun?c?t?ons.
The current gener?t?on of w?reless dev?ces ?s bu?lt us?ng d?g?t?l technology. D?g?t?l
networks 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-?dded
serv?ces such ?s c?ller ?dent?f?c?t?on. Newer w?reless

dev?ces
connect to the ?nternet us?ng frequency r?nges th?t support h?gher ?nform?t?on
r?tes. (STALLINGS, 2005)

 

 

 

 

 

 

 

 

 

 

 

1.1  W?reless
Commun?c?t?on Systems

         W?reless commun?c?t?on
systems ?re ch?r?cter?zed by ? v?r?ous of propert?es. They ?re d?fferent from e?ch
other ?n terms of how complex they ?re, Wh?t serv?ces they c?n prov?de ?nd how
much they cost to run. The most ?mport?nt property of ?ll mob?le commun?c?t?on
systems ?s th?t one user most be mov?ng ?nd ?lso th?s commun?c?t?on does not
use ?ny w?res ?s ? med?um of commun?c?t?on. One of the t?xonomy cr?ter?? of the
mob?le systems ?s how complex they ?re ?nd the r?nge of the offered serv?ces. ?ccord?ngly
the 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?ng
systems ?re ?n ex?mple of br??dc?st?ng systems. ?n ? cl????c?l p?g?ng system
the 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?on
connected w?th the c?ll center to ? selected rece?ver (p?ger). ?ll rece?vers
l?sten to the bro?dc?st s?gn?ls, detect?ng th?t p?rt?cul?r one wh?ch ?s ?ddressed
d?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?s
the 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 very
low ?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?n
be 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. The
connect?on qu?l?ty ?nd the cost of ? w?reless st?t?on should be comp?r?ble to
the qu?l?ty ?nd cost of ? tr?d?t?on?l w?rel?ne phone. The b?se st?t?on ?s th?t
p?rt of the w?reless system wh?ch ?s connected to the publ?c sw?tched telephone
network (PSTN) ?nd ?t ?s seen by the l?tter ?s ? regul?r telephone. ?n most c?ses
one 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 ?n
commun?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?rly
useful ?n tr?nsport comp?n?es, ?nd spec??l serv?ces such ?s pol?ce, emergency
serv?ces, g?s ?nd power suppl?ers, etc. The?r ch?r?cter?st?c fe?ture ?s the ex?stence
of ? d?sp?tch ?nd control center wh?ch m?n?ges the c?lls. Thus, spec??l k?nds
of connect?ons ?re ?rr?nged wh?ch ?n regul?r telephone networks ?re poss?ble ?s
spec??l serv?ces only.

1.1.4                   
CELLUL?R TELEPHONY: Cellul?r telephony ?s the next ?nd perh?ps the most represent?t?ve
ex?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?ons
mov?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 of
the s?me k?nd c?n cover the ?re? of m?ny countr?es, ?s ?n c?se of the GSM
system.

 

 

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?re

the ?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?ty
of cell or over ? geogr?ph?c?l ?re? by ?llow?ng the ?v??l?ble b?ndw?dth to be
used ?t the s?me t?me by d?fferent users. ?nd th?s must be done ?n ? w?y such
th?t the qu?l?ty of serv?ce doesn’t degr?de w?th?n the ex?st?ng users.

?n
w?reless commun?c?t?on systems ?t ?s often des?r?ble to ?llow the subscr?ber to
send s?mult?neously ?nform?t?on to the b?se st?t?on wh?le rece?v?ng ?nform?t?on
from 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 cell
commun?c?tes w?th ? b?se st?t?on. The m??n ??m ?n the cellul?r system des?gn ?s
to 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 ?nclude
m??nly the follow?ng:

Frequency
d?v?s?on mult?ple-?ccess (FDM?)