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High Speed Cellular Technologies over the Internet
Guide : Prof. A. Sahoo
Outline Introduction to 1G and 2G Technologies.
GSM & CDMA. 2.5G Technologies.
GPRS & EDGE . 3G Technologies.
W-CDMA (UMTS), HSDPA & MBMS. 4G Technologies.
LTE, UMB & WIMAX .
1G Technologies Analog cellphone standard introduced in 1980. Radio signal used were analog.
voice during a call is modulated to high frequency 150 MHz.
AMPS (Advanced mobile phone systems) Based on FDMA. Developed by Bell Labs and deployed in US in 1983. No longer exists in the market.
2G Technologies GSM.
Global System for Mobile communications. Digital cellphone standard. Operate in the 900 MHz or 1800 MHz bands. Based on TDMA. Generally offer data rates of 9.6 kbps. Splits the frequency band into multiple channels and
increases each channel bandwidth by dividing it into multiple time slots.
Modulation based on GMSK a variant of FSK.
GSM Architecture
Source : www.gsmworld.com
GMSK In FSK the digital information is
transmitted through discrete frequency changes of a carrier wave.
MSK is spectrally efficient form of FSK.
In MSK the difference between the higher and lower frequency is identical to half the bit rate. As a result, the waveforms used to represent a 0 and a 1 bit differ by exactly half a carrier period.
In GMSK the digital data stream is first shaped with a Gaussian filter.
Source: Wikipedia.org
2G Technologies CDMA.
Code Division Multiple Access. Data rates are 14.4Kbps to 115K bps. Assign codes to seperate transmission which can then
run at the same time on a single channel spread across a wide range of radio frequencies.
Each receiver decodes only the transmission it is supposed to work with.
CDMA permits several radios to share the same frequencies.
2.5G Technologies Motivation
2G Technologies are Circuit Switched in which bandwidth remains idle ample amount of time during communication.
Why not use this idle time to transfer packets. Transfering Packets is Cheaper.
Use Existing infrastructure while adding some additional node which provide packet functionality to the network
Evolved During the transition of TDMA based 2G systems to 3G systems.
2.5G Technologies
Advantages Provides data rate comparable to 3G. Work on the same spectrum allocated to 2G. provide an opporunity to players to compete who do
not want to invest heavily in 3G. GPRS & EDGE are the main drivers.
General Packet Radio Service. GSM Infrastructure Enhancement. Packet-oriented Data Service. Allows IP packets to be sent and received across mobile
networks. Theoretical maximum speed: 171.2 kbps using all 8 time slots. Developed for optimum usage of radio resource which is
scrace. Small step compared to building a totally new 3G IMT-2000
network.
GPRS
GPRS continued Users will pay for actual data transmitted not for the
connection time. No change in air interface & modulation scheme this is
also a limitation for even higher data rate. Base Station Subsystem consist of Base Station Controller
(BSC) & Packet Control Unit (PCU). PCU support all GPRS protocols for communication over
the air interface. Introduced two new nodes SGSN & GGSN and HLR is
enhanced with GPRS subscriber data and routing information.
Source : WS 03/04, TKN TU Berlin, Cornelia Kappler
EDGE Enhanced data rates for GSM evolution. GSM/GPRS-Network Enhancementr Datarate compareable to UMTS Network (384 kBit/s and
more). Changing GSM Modulation from GMSK to 8PSK. 16-QAM was also proposed for EDGE. EDGE provide both PS & CS services. QoS profile is defined for each sevice with QoS parameters
include priority, reliability & delay.
EDGE continued... Link adaptation scheme is EDGE regularly estimate the link
quality and select the appropriate modulation and coding scheme to maximize the user bit rate.
Incremental redundancy is also used. RLC/MAC layer of GPRS need to be modified to accomodate
features for multiplexing & link adaptation.
PSK Phase shift keying is a digital modulation scheme that conveys
data by modulating the phase of the carrier wave. PSK uses a finite number of phases, each assigned a unique
pattern of binary bits (symbol). The demodulator determines the phase of the received signal
and maps it back to the symbol. BPSK uses 2 phases to transmit data (0's and 1's).
Able to transmit 1 bit per symbol. QPSK (4-PSK) uses 4 phases to transmit data thus forming 4
symbols (00,01,10,11). 8-PSK uses eight phases forming 8 symbols and is the highest
order PSK constellation Able to transmit 3 bit per symbol.
8-PSK
Source : www.gsmworld.com
Why 2.5G Provides Higher Data Rate
Packet data capabilities are added in GPRS. Some additional nodes are added in architecture to facilitate
IP functionality. In EDGE the modulation scheme is changed to 8-PSK while
GSM uses GMSK. GSM uses GMSK modulation that can send 1 bit per symbol
while EDGE uses 8-PSK which transmits 3 bits per symbol.
3G Technologies Based on ITU standard IMT-2000 3G capabilities mainly means supporting higher bit rates. 3G capabilities implies the addition of
Packet Switched Services. internet Access & IP Connectivity.
Provide service at 2 Mbps for stationary users and 384 Kbps for mobile users.
3G standards are W-CDMA (UMTS) and CDMA-2000.
IMT - 2000 International Mobile Telecommunications. Operates at the frequency of 2000 Mhz. Bandwidth upto 2000 Mbps. Basic services of IMT-2000 network
High-quality voice transmission. Messaging (e-mail, fax, sms, chat). Multimedia (playing music, videos). Internet access (surfing).
UMTS Universal Mobile Telecommunications System. UTRAN - UMTS Terrestrial Radio Access Network. UMTS system uses the same core network as the GPRS and
uses entirely new radio interface UTRAN. UMTS Multiplexing
Wideband CDMA for air interface. Up/Downlink Frequency
Uplink: 1920 – 1980MHz. Downlink: 2110 - 2170MHz.
The UE is connected to Node-B over high speed Uu (up to 2 Mbps) Interface.
UMTS Architecture
Source : www.iec.org
UMTS Interfaces The Core Network of UMTS is same as that of GPRS. The
air interface is totally different. Uu: UE to Node B (UTRA, the UMTS W-CDMA air interface. Iu: RNC to GSM Phase 2+ CN interface (MSC/VLR or
SGSN) Iu-CS for circuit-switched data. Iu-PS for packet-switched data.
Iub: RNC to Node B interface. Iur: RNC to RNC interface, not comparable to any interface
in GSM.
UTRAN The UTRAN is the new Radio interface of UMTS. Its constituting
element are RNC, Node-B and UE. RNC
The RNCs enables autonomous radio resource management (RRM) by UTRAN.
RNCs also assist in Soft Handover of the UEs. Node B
The Node-B is physical unit of radio transmission /reception with cells.
It connects to UE via Uu W-CDMA radio interface and RNC via Iub ATM interface.
The main task of Node B is forward error correction (FEC), rate adaptation, W-CDMA spreading /despreading, and quadrature phase shift keying (QPSK) modulation on the air interface.
W-CDMA W-CDMA is the air interface of UMTS. W-CDMA is coming from GSM side Is a part of 3GPP and used in UMTS systems. Utilizes the direct sequence Code Division Multiple Access
signalling method to achieve higher speeds and support more users
Radio channels are 5MHz wide.. Release 5 came out in 2002 introduced improved support for
downlink packet data (HSPDA). Release 6 in 05 impoved packet capabilities in Uplink MBMS.
Why 3G Provides Higher Data Rate than 2.5G
New radio interface UTRAN is added which connects to the CN via lu interface.
Introduction of IP based multimedia service in the core network.
4G Technologies ITU-R will release the requirements of 4G in 2008. Could go beyond the cell phone and provide mobile data
services to consumer electronics & other devices. Example are sending of photos from camera to printer. All 4G technologies will be IP-based & packet-switched. Spectrally efficient modulation schemes have been developed
but they wont work with existing 3G as it requires recievers to work with more complex technology Example 64 QAM.
The 4G Technology would enable IP-based voice, data and streaming multimedia theoretically at the speed of 288 Mbps.
4G continued.... Motivation
The continuing growth of wireless usage. Rise of household broadband internet subscription. Users want wireless technolgy that approximate the
experience they have at home. Demand for better quality faster video viewing and
quicker downloading even for mobile users with handheld devices.
4G continued.... According to ITU recomendations 4G should provide data rates
of at least 100 Mbps and use OFDMA a multiuser version of OFDM.
OFDM increases bandwidth by splitting data-bearing radio signal into smaller signal sets and modulating each onto a different subcarrier, transmitting them simultaneously at different frequencies.
The subcarriers are spaced orthogonally. 64 QAM is higher order modulation scheme in which each
transmitted unit conveys 6 data bits compared to 16 QAM 4 and 8-PSK 3 bits.
4G and ITU LTE, UBM and IEEE 802.16m are the principle 4G
candidates. They work with various antenna approaches including
MIMO which uses multiple antennas at transmitter & receiver to improve performance.
ITU-R will select candidate technology in 2008 or 09 and develope detailed specifications in 2009-10.
Vendors begin implementation between 2010-12 with wide deployment occuring by 2015.
Modulation Used in 4G. QAM (Quadrature amplitude modulation)
QAM is a modulation scheme which conveys data by modulating the amplitude of two carrier waves.
These two waves are out of phase to each other. Example of 4-QAM. 64 QAM can send 6 bits at a time.
OFDM (Orthogonal frequency divison multiplexing) OFDM is a is a digital multi-carrier modulation scheme, which
uses a large number of closely-spaced orthogonal sub-carriers to carry data.
These sub-carriers typically overlap in frequency. Each sub-carrier is modulated with a conventional
modulation scheme as 64-QAM.
OFDMA Orthogonal Frequency Division Multiple Access (OFDMA). In OFDMA frequency-division multiple access is achieved
by assigning different OFDM sub-channels to different users.
OFDMA supports differentiated quality-of-service by assigning different number of sub-carriers to different users in a similar fashion as in CDMA.
Long Term Evolution (LTE) 3GPP is developing LTE. LTE builds on GSM technology thereby easing migration
for the many providers – but uses OFDM based air-interface.
Provides Spectrum flexibility i.e can be deployed in frequency band between 1.25 & 20 Mhz wide
Maximum data rate is expected to be 250 Mbps in a channel 20-Mhz wide.
Ultra Mobile Broadband (UMB) 3GPP2 is developing UMB Could be deployed in frequency band between 1.25 & 20
Mhz wide. UMB offers data rates for mobile users 288 Mbps
downstream & 75 Mbps upstream using 20 Mhz channels. The technology would provide a transition path for CDMA
based carriers.
IEEE 802.16m (WIMAX II) Based of IEEE 802.16e (Mobile WIMAX) Built on existing OFDMA technology. Operates in frequencies between 10 and 66 Ghz. Offer data rates upto 100 Mbps for mobile application and 1
Gbps for stationary users
4G 's Future Barriers
Cost will hinder adoption To achieve this higher speed the carriers would have to
transmit over wide frequency slices which would be difficult because of limited spectrum availability.
Carriers are still recovering their cost they have invested in 3G.
Advantages Transmission cost are lower for wireless technologies which
are spectrally efficient as 4G promises to be.
WiMax 802.16d Worldwide interoperability for microwave access. MAN technology based on standards in IEEE 802.16
specification. Used for fixed wireless access with substantially higher
bandwidth than most cellular networks. Uses orthogonal frequency division multiplexing. 802.16 will offer a mobile & quickly deployable alternative
(Mobile Wimax) to cabled access networks. 802.16 will provide mobilty upto 70/80 mi/hr.
Physical Layer Operates in the frequency band of 2-11 Ghz. 256-carrier OFDM scheme is used OFDM is a digital multi-carrier modulation scheme, which uses
a large number of closely-spaced orthogonal sub-carriers to carry data
These sub-carriers typically overlap in frequency, but are designed not to interfere with each other
Each sub-carrier is modulated with a conventional modulation scheme (such as QAM).
Adaptive modulation and coding is used.
Modulation Vs Bit Rate
Source : References [1]
Future Enhancements to 802.16 Spatial multiplexing
Also known as MIMO. Increases the data rate in proportion to number of
transmit antennas. Hybrid ARQ
Uses an error control code in conjunction with the retransmission to ensure realiability.
Subsequent retransmissions are combined with the previous transmissions to improve reliability.
HARQ greatly increases the data rate.
Conclusion WiMax(802.16d/e) becomes a competitor against 3GPP
3.5G(HSDPA, High Speed Downlink Packet Access) for 4G wireless technology WiMAXwill take over the 3G networks and become the 4G
wireless technology –AT&T. The high cost of adoption may cause hinderance initially but the
4G networks will capture the market by 2015. To further increase the data rates above 4G we need to
improve the modulation techniques as the spectrum is already congested and limited.
Backward compatability and Interoperability among different technologies & networks will be the important factor after the Introduction of 4G.
References A. Ghosh and D. R.Wolter SBC labs & J.G.Andrews and Runhua
chen University of Texas, “ Broadband Wireless Access with WiMax/802.16,” IEEE Communication Magazine, Feb 2005.
Sixto Ortiz Jr , “4G Wireless Begins to Take Shape,” IEEE Computer Society Nov 2007.
S.Parkvall, E. Englund, Lundevall, and J. Torsner Ericsson Research, “Evolving 3G Mobile Systems WCDMA,” IEEE Communication Magazine Feb 2006.
TE Kolding, KI Pedersen, J. Wigard, F. Frederiksen & PE Mogensen Nokias Networks, “High Speed Downlink Packet Access: WCDMA Evolution, ” IEEE Vehicular Technology Society News FEB 2003.
GSM World : www.gsmworld.com.
