Wireless Communications Principles and Practice

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21 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Lecture 8


M
ODERN

W
IRELESS

C
OMMUNICATION

S
YSTEMS



Second generation cellular
networks(
Contd
….)



Figure 2.1

Growth of cellular telephone subscribers throughout the world.



Figure 2.2

Worldwide subscriber base as a function of cellular technology in late 2001.





1
st

Generation cellular systems relied on FDMA / FDD and Analog FM.




2
nd

Generation standards use digital modulation formats and TDMA / FDD and
CDMA / FDD.




Global System Mobile (GSM)
supports 8 time slotted users for each 200 kHz
each, radio channel.




Interim Standard 136 (IS
-
136)
supports three time slotted users each of 30 kHz
each.
Pacific Digital Cellular (PDC)
is similar to IS
-
136.




Interim Standard 95 Code Division Multiple Access (IS
-
95),
also known as
cdmaOne supports up to 64 users that are orthogonally coded and simultaneously
transmitted on each 1.25 MHz channel.


Figure 2.3

Various upgrade paths for 2G technologies.

Upgrade paths for 2G&3G

EVOLUTION TO 2.5G MOBILE RADIO NETWORKS




2 G technologies use circuit
-
switched data modems that limit data users to a
single circuit
-
switched voice channel.




Data through put of an individual user is limited.




Data rates of the order of 10kbps supported which is slow for rapid e
-
mail and
internet browsing.




Data
-
centric 2.5 standards were introduced for increased throughput data rates
to support modern Internet applications.




2.5G technologies support a popular web browsing format language called
Wireless Applications Protocol (WAP)
that allows standard webpages to be
viewed in a compressed format designed for small, portable hand held devices.




EVOLUTION FOR 2.5G TDMA STANDARDS


HSCSD for 2.5G GSM




High Speed Circuit Switched Data is a circuit switched technique that allows a
single mobile subscriber to use consecutive time slots in the GSM standard.




Instead of limiting each user to a particular time slot, HSCSD allows individual
data users to use consecutive user time slots in the GSM standard to obtain high
speed data access.




Data rate increases to 14,400 bps as compared to 9,600 bps in GSM.




Using 4 consecutive time slots, HSCSD provides transmission rate of upto 57.6
kbps to individual users.



EVOLUTION FOR 2.5G TDMA STANDARDS


GPRS for 2.5G GSM and IS
-
136




General Packet Radio Service is a packet
-
based data network which is well
-
suited for non
-
real time internet usage, including retrieval of e
-
mail, faxes and
web browsing.




GPRS supports multi
-
user network sharing of individual radio channels and
time slots.




Can support many more users as compared to HSCSD but in a bursty manner !!




When all eight time slots of a GSM radio channel are dedicated to a GPRS, an
individual user is able to achieve as much as 171.2 kbps data throughput.

EVOLUTION FOR 2.5G TDMA STANDARDS


EDGE for 2.5G GSM and IS
-
136




Enhanced Data rates for GSM Evolution is an enhanced version of GSM
standard and requires addition of new hardware and software to existing BS.




EDGE introduces a new modulation format 8
-
PSK (Octal Phase Shift Keying)
which is used in addition to GMSK.




Provides practical data rate of about 384 kbps for a single dedicated user on a
single GSM channel.




By combining the capacity of different radio channels (Multiple Carrier
Transmission), EDGE can provide up to several megabits per second throughput.