4g and beyond
TRANSCRIPT
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Sara Bavarian
September 2009
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Fast moving industry Growth despite economic downturn!
Increase available bandwidth
Improve spectral efficiency
Diverse applications Wireless sensor networks, RFID
Ubiquitous data connection
Goals Broadband wireless
Trends Last decade was all about CDMA, now we hear MIMO, OFDM,...
Challenges New technologies, new bottlenecks! No free lunch!
Standards
Facts and politics!
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Where are we going?
Source [6].
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Outline Technologies
OFDM: Orthogonal-Frequency Division Multiplexing
OFDMA: OFDM with multiple access
SC-FDMA: Single Carrier Frequency Division Multiple Access MIMO: Multiple-input, multiple-output
Iterative decoding
Adaptive schemes
Standards
Cellular 4G standards
Long Term Evolution (LTE)
Mobile WiMAX
Wi-Fi 802.11n
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Why OFDM?
Solutions
Equalization Time Frequency
OFDM: bandwidth efficient multi-carrier modulation
High Data Rate
Wide Bandwidth
Inter-Symbol Interference (ISI) Time Domain: Multiple copies of signalFrequency Domain: Frequency selectivity
Single Carrier
Transmission
Time or Frequency
Domain Equalizer
Time
Dispersive
Channel
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OFDM Structure Discrete implementation of multicarrier
modulation.
Decomposing the wideband channel into
orthogonal sub-channels, using digitalsignal processing.
ISI can be eliminated by using cyclicprefix.
Great for high data rate communications
in moderate to large delay spreads.
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Drawbacks of OFDM Peak-to-Average Power Ratio (PAPR)
IFFT operation is a weighted sum of a large number of input values,certain input combinations can cause a spike.
Large PAPR causes difficulties because of the need for power amplifierswith large dynamic range.
Frequency offset
Slowly varying frequency offset between the transmit and receivecrystals.
Phase noise at the receiver
Doppler spread
Causing inter-carrier interference, and irreducible error floor.
Length of delay spread
If the length of delay spread is more than cyclic prefix, it causes ISI.
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OFDMA OFDMA is a multiple access technique based on OFDM.
Subcarriers are divided into sub-channels.
Could be used in downlink or uplink.
Source [2].
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SC-FDMA
Source [2].
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SC-FDMA New hybrid transmission scheme combining low PAPR of
single carrier schemes with frequency allocation flexibility
and multipath protection of OFDMA.
SC-FDMA spreads the signal over all sub-carriers, and it is
sometimes called DFT-spread FDMA.
Lower sensitivity to carrier frequency offset.
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SC-FDMA vs. OFDMA
Source [2].
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MIMO Basics Multiple antennas offer multiplexing gain as well as array
and diversity gain.
Increase capacity
Increase the reliability by combating fading.
Increase transmission range
MIMO system performance is best in scenarios with high
multipath scenarios. Channel matrix full rank in single user case.
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Types of MIMO Closed Loop
Feedback from receiver totransmitter
Beamforming
Preferable in closely spacedantennas, aiming the beam of thearray antenna towards the receiver.
Pre-coded spatial divisionmultiplexing
Using the singular valuedecomposition of the channelmatrix. Linear pre-coding intransmitter and linear combining inthe receiver.
=
H
H U V
Source [1].
Source [3].
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Types of MIMO (Contd) Open Loop
Transmit diversity
Single data stream
Space-time block codes e.g. Alamouti code or space-time trellis
codes, etc.
Spatial division multiplexing (SDM)
Single user (SU-MIMO)
Multi-user (MU-MIMO)
Hybrid schemes
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Iterative Codes Very close to the information-theoretic bounds.
Turbo codes
Repeat accumulate (RA) codes
Low-density parity check (LDPC) codes
Iterative detection and decoding schemes.
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Adaptive Schemes Adaptive modulation
More complex modulation
scheme when the channel
is good.
Increased capacity.
More reliability.
Channel dependentscheduling (CDS)
Source [4].
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3GPP LTE The 3rd Generation Partnership Project (3GPP) is a
collaboration between groups of telecommunications
associations, to make a globally applicable third
generation standard.
The working group continued the work towards 4G.
Work on LTE started in 2004 , expected to be
implemented in 2010. More releases are expected LTE-advanced.
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3GPP Evolution
Source [4].
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LTE Goals All IP network
Reduced latency
Higher user data rates Improved system capacity and coverage
Spectral efficiency 2-4 times better than release 6
Support for scalable bandwidth
Cost-reduction
Cost effective migration from legacy networks
Reduced capital operational expenditure including backhaul
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LTE Major Features Packet only no circuit switched voice or data
Access modes: FDD and TDD
Common 10ms frame timing but different frame structure
Variable channel bandwidth 1.4,3,5,10,15, and 20MHz
User data rates
Downlink: 172.8 Mbps(2x2 single user MIMO, 64 QAM)
Uplink: 86.4 Mbps (single link 64 QAM)
Guard period between symbols
Sub-carriers modulated with QPSK, 16 QAM, or 64 QAM
Transmission time interval 1ms
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LTE Major Features (Contd) Downlink: OFDMA
Robust against multipath
Uplink: SC-FDMA
Simplify handset design
Reduce PAPR
Spatial Diversity:
DL: Open loop Tx diversity, single user MIMO up to 4x4
UL
Optional open look Tx diversity
2x2 multi-user MIMO
Optional 2x2 single user MIMO
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LTE Acronyms
Source [1].
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IEEE 802.16 Addresses the first mile/last mile connection in wireless
metropolitan area networks (MAN)
Standards
802.16: LOS, 10-66 GHz (70 Mbps up to 30 miles) 802.16a: NLOS, 2-11GHz
802.16b, c: Extensions for QoS, testing and interoperability
802.16d: Fixed extension
802.16e: 2-6GHz, mobility 802.16m: Higher data rate
WiMAX forum
http://www.wimaxforum.org/
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Mobile WiMAX (IEEE802.16e) LTEs main competitors
Very Similar
Main difference OFDMA in uplink instead of SC-FDMA
Lower battery drain in LTE
Higher user latency in Mobile WiMAX
The differences are not substantial
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Comparison of LTE and Mobile WiMAX (in 10MHz TDD)
Source [3].
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Next Generation Wi-Fi : IEEE 802.11n Draft approved in 2007, a new version expected to be
published Oct 2009.
Baseline configuration
Up to 4 Tx and 4 Rx antennas
40 MHz operation with 64-point IFFT
Mixed mode preamble recognizable by legacy networks
Open loop SDM with cyclic delay Max PHY data rate up to 600Mbps
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Various Modulation and Coding Schemes
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Comparison
Source [1] published in 2007.
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What next? Cooperation
Cross-Layer design
Cognitive radio
Cooperative MIMO Reduce radiation levels
Base Station Cooperation
Practical issues
Interference cancellation
Cost reduction
Modelling and propagation
Extremely high frequency (EHF)
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References[1] J. Winters, and S.A. Mujtaba, Standardization of MIMO-
OFDM, a tutorial in IEEE GLOBECOM 2007.
[2] M. Rumnay, SC-FDMA the new LTE uplink explained, a
tutorial sponsored by Agilent Technologies, March 2008.[3] D.H. Morais, UMTSs LTE Webcast, Adroit Wireless
Technologies, 2009.
[4] H.G. Myung, Single Carrier FDMA, May 2008.
[5] C. Gessner and A. Roessler, LTE technology and LTE test: adeskside chat, Rohde and Schwarz, May 2009.
[6] M.D. Katz, and F.H. Fitzek, Cooperation in Wireless Networks:Principles and Applications, Springer, 2006.