LTE Basics

Introduction to 3GPP UMTS/LTE389.168 Advanced Wireless Communications 1

[email protected]

Contents

1 Historical Development

2 Description of the LTE Downlink PHY

3 Enhancements of Legacy LTE – LTE-Advanced

4 Summary

Slide 2 / 48 Contents

Contents




4 Summary

Slide 3 / 48 Historical Development

History of UMTS/LTE

1G (analog)

A, B, C Netz

GSM

GPRS

EDGE

1991 1997 1998

Creation of the 3GPP

UMTS

HSPA

HSPA+

2G 3G

1999

LTE

LTE advanced

2009 20102004 2007

4G

5G

(ETSI)

First generation (1G) cellular networks: analog telephony

Second generation (2G) era: digital networks

Global system for mobile communications (GSM): circuit-switched, timedivision multiple access (TDMA), frequency division duplex (FDD)

General packet radio service (GPRS): packet-switched data traffic

Enhanced data rates for GSM evolution (EDGE): max. 472 kbit/s throughhigher order modulation (8 PSK instead of GMSK)

200 kHz bandwidth

Standardized by the European telecommunications standard institute (ETSI)


History of UMTS/LTE (2)

1G (analog)

A, B, C Netz

GSM

GPRS

EDGE

1991 1997 1998


UMTS

HSPA

HSPA+

2G 3G

1999

LTE

LTE advanced

2009 20102004 2007

4G

5G

(ETSI)

Worldwide standardization: third generation partnership project (3GPP)

Universal mobile telecommunications system (UMTS): release 99

Wideband code division multiple access (WCDMA)

First release: 384 kbit/s

5 MHz bandwidth

High speed packet access (HSPA) and HSPA+ (release 5 and 7)

Up to 4× 4 multiple-input multiple-output (MIMO)

Up to 20 MHz (carrier aggregation)

Adaptive modulation and coding (AMC)

⇒ 330 Mbit/s (release 11)


History of UMTS/LTE (3)

1G (analog)

A, B, C Netz

GSM

GPRS

EDGE

1991 1997 1998


UMTS

HSPA

HSPA+

2G 3G

1999

LTE

LTE advanced

2009 20102004 2007

4G

5G

(ETSI)

UMTS long term evolution (LTE) release 8 (3.75G)

Orthogonal frequency division multiple access (OFDMA)

Up to 4× 4 MIMO

Up to 20 MHz

First release: 300 Mbit/s

LTE advanced release 10 (4G)

Up to 8× 8 MIMO

Up to 100 MHz⇒ > 1 Gbit/s


Technology Utilization

201820172016201520142013201220112010

10

9

8

7

6

5

4

3

2

1

0

Year

Bill

ion

subc

ribe

rs

Worldwide subcriptions (Source: Ericsson, June 2013)

LTEWCDMA/HSPAGSM/EDGECDMAothers

GSM still dominates the market

HSPA will become dominant around 2017

LTE still has to gain momentum


Contents




4 Summary

Slide 8 / 48 Description of the LTE Downlink PHY

LTE PHY Overview

Modulation and multiple-accessDownlink: orthogonal frequency division multiple access (OFDMA)

Orthogonal frequency division multiplexing (OFDM) modulation

Sharing of subcarriers between users

Advantages: flexibility, efficiency, complexity

Disadvantages: overhead, peak-to-average power ratio (PAPR)

Uplink: single-carrier frequency division multiple access (SCFDMA)

Discrete Fourier transform (DFT)-precoded OFDM

Sharing of consecutive subcarriers between users

Advantage: lower PAPR

Disadvantage: reduced efficiency (multi-user diversity)

7.5 kHz and 15 kHz subcarrier spacing (impact of Doppler spread)

Two cyclic prefix (CP) length (normal/extended 4.7µs/16.7µs @ 15 kHz)

Time division duplex (TDD) and frequency division duplex (FDD) support


LTE PHY Overview (2)

Channel coding and modulation-alphabetsMother channel code: rate 1/3 Turbo code

Puncturing and repetition to obtain code rates between 0.08 and 0.93

Strong interleaving for robustness against error bursts

24 bit cyclic redundancy check (CRC) for error detection

Hybrid automatic repeat request (HARQ) with soft-combining

Quadratur amplitude modulation (QAM) symbol alphabets

4/16/64 QAM (256 is considered)

Bit-interleaved coded-modulation (BICM) architecture

channelcoding

modulationmapping

coded bits

bitinterleaving

modulated symbolsdata bits interleaved bits


LTE PHY Overview (3)spatial multiplexing

diversity

error probability

beamforming

receive power

MIMO key dataSupported MIMO schemes

Transmit diversity

Beamforming

Spatial multiplexing

Antenna configurations

Up to eight base station antennas (LTE-A Rel. 10, before up to four)

Downlink: up to eight (four) spatial streams (layers)

Uplink: up to four (one) spatial streams

See [Dahlman et al., 2011, Rupp, 2012] for details on the PHY


OFDM Processing

IDFT + CP

OFDM-TX

-CP + DFT

OFDM-RX x[n,k] y[n,k]

h[n,k]

subcarriers n

x[1,k] x[N,k]

subcarriers n

h[1,k] h[N,k]

subcarriers n

y[1,k] y[N,k]

(I)DFT... (inverse) discrete Fourier transform

CP... cyclic pre!x

Transmit symbol on OFDM subcarrier n at OFDM symbol k : x [n, k ] ∈ C

Channel gain on subcarrier n at symbol k : h[n, k ] ∈ C

Noisy input-output relationship

y [n, k ] = h[n, k ]x [n, k ] + z[n, k ] (1)

Receiver noise z[n, k ] ∈ C


OFDM Processing (2)

Implicit assumptions:Perfect timing and frequency synchronization⇒ synchronization signals: 0.2%− 3% overhead in LTE

Sufficient CP length⇒ normal/extended CP: 7%− 25% overhead in LTE

Negligible temporal channel variation during OFDM symbols (≈ 72µs)

If one of these is violated:Inter-carrier interference

Inter-symbol interference

(Can be considered in the noise)

For details, please visit 389.133 Wireless OFDM Systems


MIMO-OFDM

IDFT + CP

OFDM-TX

-CP + DFT

OFDM-RX

y[n,k]

H[n,k]

IDFT + CP -CP + DFT

x[n,k]

Nt Nr

Transmit symbol vector on subcarrier n at symbol k

x[n, k ] =[x (1)[n, k ], . . . , x (Nt )[n, k ]

]T(2)

Channel matrix: H[n, k ] ∈ CNr×Nt

H[n, k ] =

h(1,1)[n, k ] h(1,2)[n, k ] . . . h(1,Nt )[n, k ]h(2,1)[n, k ] h(2,2)[n, k ] . . . h(2,Nt )[n, k ]

.... . .

...h(Nr ,1)[n, k ] h(Nr ,2)[n, k ] . . . h(Nr ,Nt )[n, k ]

(3)

Noisy input-output relationship

y[n, k ] = H[n, k ]x[n, k ] + z[n, k ] ∈ CNr×1 (4)


LTE Frame Structure (FDD)

1 frame: 10 ms

1 subframe: 1ms

1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 1 2 3 4 5 6 7

14 OFDM symbols

slot 1 slot 2

The subframe duration (1 ms) is the basic transmission time interval (TTI)

Each subframe is processed individually

e.g., the user-data within each subframe is jointly channel coded

The frame is used to organize the allocation of subframes to traffic channels

Physical downlink shared channel (PDSCH)

Physical broadcast channel (PBCH)

Physical multicast channel (PMCH)

. . .


LTE Time-Frequency Grid

......

12 subcarriers

180 kHz (15 kHz subcarrier spacing)

freq

time one resource

element

slot (0.5ms)

subframe: 1ms

14 OFDM symbols

......

......

one resource block

Resource element (RE): one subcarrier during one OFDM symbol

Resource block (RB): 7 OFDM symbols in time, 12 subcarriers in frequency

Slot: 7 OFDM symbols over the full bandwidth

Subframe: two slots in time over the full bandwidth


Resource Allocation

spa

ce

freq

uency

time

} spatial streamsor layers

UE 1 UE 2 UE 3

resource block

Based on (multiples of) RBs

Handled by the scheduler

Exploit multi-user diversity: double-logarithmic rate-growth with the numberof users for independent fading [Viswanath, 2006]

Fulfill quality of service (QoS) requirements (max. delay, min. rate)

Potentially varying over space, time and frequency


LTE Downlink Transmit Signal Processing Chain

Adaptive modulation and coding

precoded signal

Nt dimensional

channel

coding

interleaving

scrambling

modulation

mapping

MIMO processing

layer

mapping

(+pilot insertion)precoding

user data bits coded bits

up to 2 codewords

modulated symbols

Transmit signal

composition

resource element

mappingIDFT/CP

+ RF

precoded signal user transmit signal

multi-user

multiplexing

+ pilot insertion

other users’ signals

transmit signal

Nt dimensional

wireless

channel

spatial streams

up to 8 layers

AMC: 15 combinations of code rates and modulation alphabets are supported(0.15 bit/symbol – 5.55 bit/symbol)

Scrambling: inter-cell interference whitening

Pilot insertion for channel sounding and channel estimation

Channel state information (CSI) calculation for AMC and MIMO

Channel equalization and data detection


LTE Downlink Receive Signal Processing Chain

wireless

channelRF +

DFT/CP

receive signal

Nr dimensional

user signal

and pilot

extraction

channel

estimation

+ feedback

calculation

equalization

spatial streams

up to 8 layers

data detection

+ symbol

demapping

descrambling

deinterleaving

decoding

HARQ combining

coded bits

up to 2 codewords

estimated user

data bits

CRC check

ACK/NACK

Channel estimation: estimate the channel matrices using pilot signals

Equalization: invert the distortions of the channel (per subcarrier)

Data detection: soft/hard symbol detection (log-likelihood ratios)

HARQ combining in case of retransmission


LTE Downlink Performance

2520151050-5-10SNR [dB]

Blo

ck e

rror

ratio

SISO_1.4MHz_AWGN_TU

MCS1 MCS15

100

10-1

10-2

10-3

242220181614121086420-2-4-6

8

7

6

5

4

3

2

1

0

SNR [dB]

Spec

tral

eff

icie

ncy

[bit/

s/H

z]

SISO_AWGN

Shannon capacity

BICM 64 capacity

BICM 16 capacity

BICM 4 capacity LTE efficiency

Transmission over single-input single-output (SISO) additive white Gaussiannoise (AWGN) channel

Performance of LTE’s 15 modulation and coding schemes (MCSs)

No imperfections considered (channel estimation, synchronization)

Shannon capacity: log2(1 + SNR)

BICM capacity [Caire et al., 1996]


LTE Downlink Reference Signals

time

freq

uenc

y

time

freq

uenc

y

time

freq

uenc

y

antenna port 0antenna port 3antenna port 2

antenna port 1

one antenna two antennas

four antennas

Two types of reference signals:

Non-precoded reference signals (cell-specific, sounding)

Precoded reference signals (UE-specific, demodulation)

Employed for channel sounding and estimation

Pilot-symbols are known to users

Pilots are non-overlapping in time/frequency

Channel distortions can be estimated


LTE Downlink Channel Estimation [Simko, 2013]

0

5

10

0

5

100

0.5

1

OFDM symbol indexsubcarrier index

cha

nn

el

pilot 2

pilot 1

pilot 3 data symbol

Least squares channel estimation plus linear interpolation (triangulation)

hLS[np, kp] =y [np, kp]

r [np, kp](5)

r [np, kp] reference symbol at pilot position [np, kp]

Linear minimum squared error channel estimation

min E(∥∥∥h− hLMMSE

∥∥∥2

2

), subject to hLMMSE = ALMMSEhLS (6)

Requires second-order channel and noise statistics


Performance of Channel Estimation employing LTE’s ReferenceSignals [Simko, 2013]

Doppler frequency

0 Hz

200 Hz

400 Hz

600 Hz

800 Hz

1000 Hz

1200 Hz

0 5 10 15 20 25 3010-4

10-3

10-2

10-1

100

SNR [dB]

MSE

0 5 10 15 20 25 3010-4

10-3

10-2

10-1

100

SNR [dB]

MSE

Doppler frequency

0 Hz

200 Hz

400 Hz

600 Hz

800 Hz

1000 Hz

1200 Hz

Least squares channel estimator Linear minimum mean-squared error channel estimator

Channel estimation for a noisy SISO channel

Performance degradation with increasing channel Doppler frequency fd due togrowing channel variation in time

Corresponding speed v at center frequency fc

v =cfc

fd , e.g. fc = 2 GHz, fd = 500 Hz⇒ v = 270 km/h (7)


LTE’s HARQ Protocol

} equal retransmissions

reconstructed code block (chase combining)punctured bitscombined bits

} differentversions

reconstructed code block (incremental redundancy)combined bits

original code block

original code block

Fast PHY/MAC retransmission using ACK/NACK feedback

Higher layers not involved (transparent, reduced delay/latency)

Two possible types:

Chase combining (repetition gain)

Incremental redundancy (coding gain and repetition gain)

LTE employs incremental redundancy with soft combining


LTE’s HARQ Protocol Performance [Colom-Ikuno, 2013]

−10 −5 0 5 10 1510 −3

10 −2

10 −1

10 0

BL

ER

SNR [dB]

m=0m=1m=2m=3

. . . . 5.7 dB

HARQgain

2.5 dB

1.4 dB

10% BLER

Improvement of block error ratio (BLER) with retransmissions due to bitrepetitions and code rate reduction

Up to three retransmissions are supported in LTE


Simplified System Model

precoding

Hu

equalization

Fu Gu

x yusu su^

precoding

F1

s1

precoding

FU

sU

+

+

Assume perfect operation of OFDM and consider a specific RE [n, k ]

Omit channel coding and modulation mapping

Neglect channel estimation errors, synchronization errors, etc.

su = GuHuFusu + GuHu

U∑j=1,j 6=u

Fj sj + Guzu , (8)

Gu ∈ CLu×Nr , Hu ∈ CNr×Nt , Fu ∈ CNt×Lu (9)

The noise zu also contains interference from other base stations


LTE’s Transmission Modes

IDFT + CP

+ CPCDD

+

=

PDP frequency response

Single antenna transmission (Nt = 1), single user U = 1, single stream Lu = 1

su = gHu husu + zu , gu ,hu ∈ CNr×1 (10)

Transmit diversity (Nt > 1), U = 1, Lu = 1

Alamouti space-time (-frequency) coding [Alamouti, 1998]

Open-loop spatial multiplexing (Nt > 1), U = 1, Lu ≥ 1

Cyclic delay diversity (CDD) precoding⇒ transforms spatial diversity to frequency diversity


LTE’s Transmission Modes (2)

0 45 90 135 1800

2

4

6

8

Steering Angle [°]

An

ten

na

ga

in

UE1 UE2

Closed-loop spatial multiplexing (Nt > 1), U = 1, Lu ≥ 1

Adaptive precoding utilizing CSI feedback

Adaptive transmission rank (layers) – beamforming vs. multiplexing

Multi-user MIMO (Nt > 1), U = 2, Lu = 1

Based on predefined precoders (codebook)

Powerful receivers required to cancel residual inter-user interference

Details to come...


Performance Comparison of LTE’s Single-User Transmission Modes

403020100-10

10

8

6

4

2

0

SNR [dB]

aver

age

user

thro

ughp

ut [M

bit/s

]

4x2 CLSM 2x2 OLSM

1x1 SISO

2x2 TxD

4x2 CLSM 2x2 OLSM

1x1 SISO

2x2 TxD

Transmission over independent Rayleigh fading channels

Saturation at high signal to noise ratio (SNR) due to limitation to 64 QAM(6 bit/symbol)

Different saturation values because of growing reference symbol overhead withincreasing number of transmit antennas


Contents




4 Summary

Slide 30 / 48 Enhancements of Legacy LTE – LTE-Advanced

Reasons for Further Enhancements

201820172016201520142013201220112010

15

12

9

6

3

0

Year

Glo

bal t

raff

ic [E

xaby

tes/

mon

th]

Global traffic voice and data (Source: Ericsson, June 2013)

Data: mobile PCs, tablets, mobile routersData: smartphonesVoice

Estimated growth of mobile traffic (1 Exabyte = 1018 bytes); source: Ericsson traffic exploration tool, June 2013

Mobile data traffic in 2012 was twelve times the size of the Internet in 2000

Average smart phone usage grew 81 percent in 2012

Smart phones represented only 18 percent of total global handsets in use in2012, but represented 92 percent of total global handset traffic

[Cisco Systems Inc., 2013, Ericsson, 2013]


LTE-A Enhancements: Enhanced MIMO

Higher-order single-user MIMOImproved peak spectral efficiency: up to eight spatial streams

Gains in cell edge spectral efficiency: high signal to interference and noise ratio(SINR) through beamforming

Support of uplink single-user MIMO (up to four streams)

Reduced reference signal overhead (UE-specific vs. cell-specific)

Improved multi-user MIMONon-codebook based precoding

Up to eight users in parallel

Improved CSI feedback using nested codebooks

e.g., given a valid rank 2 precoder F = [f1, f2] ∈ CNt×2

⇒ f1, f2 ∈ CNt×1 are valid rank 1 precoders


LTE-A Enhancements: Carrier Aggregation

1.4 MHz 1.4 MHz 1.4 MHz

frequency band 1 (800 MHz)

5 MHz

frequency band 2 (2 GHz)

scenario A scenario B scenario C

Enables up to 100 MHz bandwidth

Better utilization of fragmented spectrum

Contiguous/non-contiguous aggregation

Inter-/Intra-band aggregation


LTE-A Enhancements: Carrier Aggregation Scenarios

F1

F2

F1

F2

F1

F2 Low-latency high-bandwidth connectionBase station Remote radio unit

Cover the same area – peak capacity enhancement

Potentially different coverage area depending on carrier frequency

Cover each others’ cell-edge – cell edge improvement

Hot-spot coverage using remote radio heads (RRHs)


LTE-A Enhancements: Relaying

coverage improvement

cell-edge improvement

Base station Relay node User

Provide coverage in dead zones and improve cell-edge performance

In-band versus out-band relays

Layer 1 relays: amplify and forward

Layer 2 relays: decode and forward

Layer 3 relays: appear to users as ordinary cells


LTE-A Enhancements: Coordinated Multipoint Transmission/Reception

Coordinated scheduling:Time/frequency sharingDynamic point selectionInter-cell interference coordinationICIC (Rel. 8), eICIC (Rel. 10), FeICIC (Rel. 11)

Advantage: low overhead (control info)

Coordinated beamforming:Spatial interference mitigationSignal to leakage and noise ratio (SLNR)[Sadek et al., 2007]Advantage: good trade-off (CSI only)

Joint transmission:Exploitation of interferenceDistributed antenna systemAdvantage: potentially highestperformanceDisadvantage: overhead (CSI and data)

Coordinatedscheduling

X2 interface or low-latency high-bandwidth dedicated connection

Base station User








Coordinatedbeamforming


Base station User








Coordinatedbeamforming

Jointtransmission


Base station User


LTE-A Enhancements: CoMP Scenarios

Scenario 1: Intra-site CoMP

Scenario 2: Inter-site CoMP

Scenario 3: HetNet CoMP 1 (different cell-IDs, small cells)

Scenario 4: HetNet CoMP 2 (same cell-IDs, RRHs and relays)

Low-latency high-bandwidth connection

Base station Remote radio unit

UserAccess point


Potential Future Technologies

Significant bandwidth expansions cannot be expected in the near future

Possible long-term solution Millimeter Waves[Rappaport et al., 2013] (30 – 300 GHz⇔ 1 – 10 mm)

Increasing the network density

Heterogeneous networks [Andrews, 2013]

Inter-cell interference coordination

Potential PHY improvements with massive MIMO [Marzetta, 2010]

Hundreds to thousands of antennas per base station

Space division multiple access (SDMA)

Inter-cell interference mitigation/exploitation

More details in Prof. Rupp’s part


Potential Future Technologies: Full-Duplex Wireless

Digital Interference Cancellation

TXRX

Attenuation

& Delay

RF Baseband

ADC

Baseband RF

DAC

EncoderDecoder

Digital Interference

Reference

Balun Cancellation

TX Signal Path RX Signal Path

RF Reference

-

RSSI

Control

Feedback

Channel

Estimate

Balun

[Jain et al., 2011]

Analog self-interference cancellation to avoid radio frequency (RF) amplifier andanalog to digital converter (ADC) overload

Digital cancellation of residual interference

Gain: factor 2

May help solving the CSI problematic


Potential Future Technologies: Filter Bank Multicarrier Modulation

IDFT + CP

OFDM

IDFTdigital

!lters

FBMC

OFDMFBMC

0

10

-10

-20

-50

-40

-30

-60

-70

-80

-90

Po

we

r [d

BW

]

5 10 150

Frequency [MHz]

OFDMFBMC

Source: ICT-PHYDYAS, FP7 project

Avoid cyclic prefix overhead of OFDM

Reduce the side-lobes of OFDM to shrink the required guard bands⇒ improve spectral efficiency

Digital filter design based on Nyquist criterion to avoid inter-carrier interference

Higher complexity: inter-symbol interference, equalization


Contents




4 Summary

Slide 41 / 48 Summary

Summary

Evolution TDMA→WCDMA→ OFDMA ?→ FBMC

UMTS/LTE physical layer:

OFDMA modulation and multiple access

Channel coding based on rate 1/3 Turbo code

AMC utilizing BICM architecture

Fast HARQ retransmissions

MIMO beamforming/diversity/multiplexing

LTE-A enhancements:

Multi-user MIMO

Carrier aggregation

Relaying, CoMP

Potential enabling technologies for 5G cellular:

Millimeter wave

Network densification

Massive MIMO

Slide 42 / 48 Summary

Introduction to 3GPP UMTS/LTE389.168 Advanced Wireless Communications 1

[email protected]

Abbreviations I

3GPP third generation partnership project

ADC analog to digital converter

AMC adaptive modulation and coding

AWGN additive white Gaussian noise

BICM bit-interleaved coded-modulation

BLER block error ratio

CDD cyclic delay diversity

CoMP coordinated multipoint transmission/reception

CP cyclic prefix

CRC cyclic redundancy check

CSI channel state information

DFT discrete Fourier transform

EDGE enhanced data rates for GSM evolution

ETSI European telecommunications standard institute

FBMC filter bank multicarrier modulation

FDD frequency division duplex

GPRS general packet radio service

GSM global system for mobile communications

Slide 44 / 48 Abbreviations

Abbreviations IIHARQ hybrid automatic repeat request

HSPA high speed packet access

LTE long term evolution

MAC medium access control

MCS modulation and coding scheme

MIMO multiple-input multiple-output

OFDM orthogonal frequency division multiplexing

OFDMA orthogonal frequency division multiple access

PAPR peak-to-average power ratio

PHY physical layer

QAM quadratur amplitude modulation

QoS quality of service

RB resource block

RE resource element

RF radio frequency

RRH remote radio head

SCFDMA single-carrier frequency division multiple access

SDMA space division multiple access

SINR signal to interference and noise ratio


Abbreviations III

SISO single-input single-output

SNR signal to noise ratio

TDD time division duplex

TDMA time division multiple access

TTI transmission time interval

UMTS universal mobile telecommunications system

WCDMA wideband code division multiple access


References I

Alamouti, S. (1998).A simple transmit diversity technique for wireless communications.IEEE journal on Selected Areas in Communications, 16, issue 8.

Andrews, J. (2013).Seven ways that HetNets are a cellular paradigm shift.IEEE Communications Magazine, 51(3):136–144.

Caire, G., Taricco, G., and Biglieri, E. (1996).Capacity of bit-interleaved channels.Electron. Lett., 32, issue 12:1060–1061.

Cisco Systems Inc. (2013).Cisco visual networking index: forecast update, 2012-2017.white paper.

Colom-Ikuno, J. (2013).System Level Modeling and Optimization of the LTE Downlink.PhD thesis, Vienna University of Technology.

Dahlman, E., Parkvall, S., and Skold, J. (2011).4G LTE/LTE-Advanced for Mobile Broadband.Elsevier Academic Press.

Ericsson (2013).Ericsson mobility report.white paper.

Slide 47 / 48 References

References II

Jain, M., Choi, J. I., Kim, T., Bharadia, D., Seth, S., Srinivasan, K., Levis, P., Katti, S., and Sinha, P. (2011).Practical, real-time, full duplex wireless.In Proceedings of the 17th Annual International Conference on Mobile Computing and Networking, MobiCom’11, pages 301–312, New York, USA. ACM.

Marzetta, T. (2010).Noncooperative cellular wireless with unlimited numbers of base station antennas.IEEE Transactions on Wireless Communications, 9(11):3590–3600.

Rappaport, T., Sun, S., Mayzus, R., Zhao, H., Azar, Y., Wang, K., Wong, G., Schulz, J., Samimi, M., andGutierrez, F. (2013).Millimeter wave mobile communications for 5G cellular: It will work!IEEE Access, 1:335–349.

Rupp, M. (2012).Robust design of adaptive equalizers.IEEE Transactions on Signal Processing, 60(4):1612 – 1626.

Sadek, M., Tarighat, A., and Sayed, A. (2007).A leakage-based precoding scheme for downlink multi-user MIMO channels.IEEE Transactions on Wireless Communications, 6(5):1711–1721.

Simko, M. (2013).Pilot Pattern Optimization for Doubly Selective MIMO OFDM Transmissions.PhD thesis, Vienna University of Technology.

Viswanath, P. (2006).Opportunistic communication: a system view.In Space-Time Wireless Systems, pages 426–442. Cambridge University Press.Cambridge Books Online.

Slide 48 / 48 References

LTE Basics

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