Transcript 4-G Cellular Systems

4-G Cellular Systems
What is 4-G?
 High data speed: 100 Mbps to 1Gbps anywhere,
anytime
 Enable voice, data and streamed multimedia
(enough speed for streaming HDTV, digital
video broadcasting, video chat, …) with low
latency
 Based on TCP/IP (Internet protocol) only (3-G
systems use both circuit switched and packet
switched networks)
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Technologies used in 4-G
 It uses OFDMA and other new technologies
(Single Carrier FDMA, Interleaved FDMA, Multicarrier CDMA, …) instead of CDMA, which is
used by all 3-G systems. The problem with
CDMA is it cannot adjust spectrum allocated to
users (all users get the same amount of
spectrum). Also, the highest data rate is limited.
 MIMO (Multiple-Input Multiple-Output) antennas
 New modulation techniques (64QAM:
Quadrature amplitude modulation)
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MIMO
Multiple antennas used by the transmitter
and the receiver
Parallel streams are transmitted
simultaneously by those antennas
Data rate is increased (if 4 pairs of
antennas are used, the data rate can be
increased by 4 times)
Can also increase reliability
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64QAM
The amplitude of two waves, 90 degrees
out-of-phase (in quadrature) are changed
(modulated) to represent the data signal.
Phase modulation is a special case of
QAM.
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4-G Systems
WiMax
UMB (Ultra Mobile Broadband)
LTE (Long Term Evolution)
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UMB
 To bring CDMA2000 (US standard) to 4-G
 Based on Internet (TCP/IP) networking
 Peak rates of up to 280 Mbps
 Support handoffs with CDMA2000 and 1xEV-DO
 Use OFDMA
 In Novemver 2008, Qualcomm, UMB’s lead
sponsor, announced it was ending development
of the technolgy, favoring LTE instead.
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LTE (Long Term Evolution)
 To bring UMTS (Europe 3G) to 4-G
 Uses OFDMA for downlink with a maximum of 2048 subchannels
 Download rate: 326 Mbps for 4x4 antennas for every 20 MHz of
bandwidth
 Uses Single Carrier Frequency Division Multiple Access (SC-FDMA)
for uplink. A problem with OFDMA is the high peak-to-average
power ratio. SC-FDMA can provide higher power efficiency which is
crucial for mobile stations.
 Uses 64QAM modulation
 Uses MIMO and beam forming with up to 4 antennas
 All IP Network
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LTE (cont.)
Downlink peak data rates 300Mbps per
20MHz of spectrum and uplink data rates,
75 Mbps per 20 MHz
Supports at least 200 active users per cell
in 5MHz
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Comparison of LTE and WiMax
 Similar technologies
 WiMax is already in the market in Pakistan and Sprint
Nextel and Clearwire has deployed it in the US (first in
Baltimore this year). LTE is still under standardization.
 LTE is the upgrade for GSM network that accounts for
over 85% of all mobile subscribers in the world. The
existing GSM/GPRS/EDGE operators can use their
current infrastructure (base station towers) with new
equipment to upgrade to LTE. A WiMax operator has to
start from scratch.
 AT&T and Verizon will roll out LTE in 2011/2012.
Qualcomm supports LTE.
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