4G and Beyond

8/3/2019 4G and Beyond

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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.

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4G and Beyond