Mobile phone systems (Re: Di ddo^.ng from Ddo^~ Hu`ng)

[Phan Anh Son <Phan@PGSM.HU>]

Cha`o ba'c Ddo^~ Hu`ng va` ca'c ba'c quan ta^m dde^'n Mobile phone,

Ba'c Hu`ng ho?i ca'ch dda^y dda~ la^u, nay ra?nh ro^~i to^i xin tra?
lo+`i:
>
>Na(m ngoa'i, va`o khoa?ng cuo^'i tha'ng 10, to^i co' tham quan trie^?n
>la~m Telecom ta.i TP HCM, tha^'y ca'c ha~ng nu+o+'c ngoa`i tie^'p thi.
>kha' ghe^ ve^` PHS va` CDMA. Kho^ng bie^'t ca'c co^ng nghe^. na`y co'
>thi'ch ho+.p vo+'i VN kho^ng. Ba'c na`o co' tho^ng tin xin "chi? gia'o".
>
>

To^i xin ddi tu+` xa ho+n mo^.t chu't:
Ca'c he^. mobile phone co' hai loa.i chi'nh: Digital (GSM, CDMA,
D-AMPS...)
va` Analog (AMPS, NMT,..) 

Ti'nh theo Access Technology thi` co' 3 loa.i:
   FDMA (Frequency-Division Multiple Access) -  Mo^~i ng` no'i tre^n 1
ke^nh
   TDMA (Time- ===#===) - Mo^~i ng` no'i tre^n 1 Time Slot
   CDMA (Code-Division Multiple Access) -ta^'t ca? du`ng chung 1 freq.
mo^~i ng` chi? kha'c nhau ve^` ma~ so^'.

CDMA
^^^^^^^^
la` he^. cu?a My~ do ha~ng Qualcom dde^` xu+o+'ng va` chu? ye^'u
du`ng o+? My~ va ` mo^.t so^' n'c cha^u A'. He^. na`y cu`ng vo+'i GSM 
ddu+o+.c coi la` tie^n tie^'n nha^'t hie^.n nay. Hie^.n CDMA co' khoa?ng
1 trie^.u subs. (GSM: ~35 trie^.u). 
U+u ddie^?m:
   +Capacity lo+'n (8-10 la^`n so vo'+i AMPS, 1,5 - 3 la^`n so vo"i GSM)
   +De^~ thie^'t ke^' ma.ng: ta^'t ca? dde^`u du`ng chung 1 freq.
   +Wide-ban=>Kho' ga^y nhie^~u
Nhu+o+.c die^?m: mo^.t mobile co' su+. co^' co' the^? ga^y ro^'i loa.n
cho ca? da`i pha't.

PHS (Personal Handyphone System) 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(theo anh Le Thanh Nam va` mo^.t so^' nguo^`n tin kha'c)

la` he^. cu?a Nha^.t tu+` giu+~a na(m '95. Dda^y kho^ng ha(?n la`
mobile phone, ma` gio^'ng cordless phone ho+n, da`nh cho ng` ddi bo^.
U+u die^?m: 
   +low power (10-20 mW vs. 1-5W in other systems)  
   +Gia' tha`nh re?
   +high-speed digital connection: du`ng cho laptop ddu+o+.c
Nhu+o+.c ddie^?m:
   +Chi? du`ng ddu+o+.c cho ng` di bo^ (<10km/h)
   +Die^.n phu? so'ng nho? (ba'n ki'nk 100-500m/tra.m pha't)

Theo to^i thi` GSM hay CDMA dde^`u thi'ch ho+.p cho VN ca?.
Hie^.n ta.i thi` dda~ co' 2 he^. GSM va` 1(?) he^. D-AMPS, nhu+
va^.y thi` kha? na(ng CDMA va`o VN la` nho? vi` 1 nu+o+'c chi?
ne^n co' 3,4,5 operator la` cu`ng. PHS co' nhie^`u kha? na(ng va`o
VN ho+n. Theo to^i ddu+o+.c bie^'t thi` cuo^'i na(m '96 NEC co'
giu'p VN la`m 1 he^. PHS pilot vo"i khoa?ng 40 tra.m pha't va`
100 handset.
NEC vu+`a la^.p join venture vo+'i VNPT ve^` mobile communiction

Tha^n,
Son,

P.S: Ba'c na`o quan ta^m sa^u ho+n dde^'n dde^` ta`i na`y mail
rie^ng cho to^i, to^i se~ gu+?i cho.