LTE Antenna Selection UnivVienna 2008

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Antenna Selection Aspects for LTE Antenna Selection Aspects for LTE

Aamir Habib

June12, 2008

contact email: [email protected]

MIMO LAB


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Outline

3GPP LTE Features

MIMO in LTE

Baseband Channel Processing in LTE Antenna Selection Methods for LTE

Simulation Results

Effects of Non-Idealities

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What is LTE

ong erm vo u on s e name g ven o a pro ecwithin the Third Generation Partnership Project to improve the UMTS

mobile phone standard to cope with future requirements

Goals include improving efficiency , lowering costs , improving

services makin use of new s ectrum o ortunities and better

integration with other open standards

The LTE project is not a standard, but it will result in the new evolvedrelease 8 of the UMTS standard, including mostly or wholly

extensions and modifications of the UMTS system

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LTE Key Features & Parameters

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MIMO Basics

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Overview of downlink physical channel processing.

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Overview of uplink physical channel processing.

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LTE DL

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Antenna Selection

raw ac o s e ncrease n e overa sys emcomplexity and hence cost

Antenna elements and signal processing becomes

MIMO system with M t and M r antennas require complete

RF chains at the T x and R x including LNAs, convertersand A/Ds

Antenna selection algorithms select best subset out of fullan ennas ep oye w some per ormance oss

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Joint Antenna Selection System

MIMO system with antenna selection both at Tx and RxMIMO system with antenna selection both at Tx and Rx

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Antenna Selection for LTE

Considerable work has a eared in the literature on AS

its capacity, diversity benefits, and selection criteria.

,

attention is training, through which the channel states of

all antennas are determined in order to select the best

antenna s .

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AS for LTE(Reference signals)

The LTE standard defines two pilots for the uplink: Demodulation pilot(Demodulation Reference Signal) , which is

and is transmitted in the subcarriers assigned to a user, and

Wideband sounding pilot(Sounding Reference Signal) , whichoccupies the entire system bandwidth (e.g., 5 MHz). Through it,the base station determines the full frequency response of eachuser's current channel and erforms fre uenc -domain schedulin

to get high cell throughput.

e rs one s assoc a e w e or Signal generated from same base sequences (Zadoff-Chu)

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Reference Signals

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AS for LTE

Using the sounding pilot transmitted at regular intervalsfor AS training enables the base station to also do joint

frequency-domain scheduling and antenna selection.

This method for antenna selection is extremely robust to

the higher levels of interference, which the wideband

sounding reference signal is expected to encounter.

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AS Method Transmit Selection

UE transmits pilot tones(CQI) from a set of availabletransmit antennas on PUCCH or PUSCH

BS estimates the channels

Selects an optimal subset according to some criteria

UE uses this subset for subsequent transmission

AS can be Periodic or on demand(Notification)

Antenna Training and Selection in one TTI

Antenna Trainin and Selection between TTIs

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Tx-Rx Path and Feedback Information Flow

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Antenna Selection Algorithms

Retain diversity order with some loss in array gain(mean SNR gain)

Complexity of antenna selection determined by the number of MIMO

subchannelst r

t r L L

Exhaustive search over all possible combinations of R x & Tx antennasfor one that gives the maximum capacity of system

e.g Antennas: M t=Mr =16 and RF-Channels: L t= L r =4

o a com na ons x = . x

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Antenna Selection Algorithms H

Correlation based method jihh ji ji

ji = ,

Norm based method ==t N

r kik N k hC 2

,......,3,2,1 =i 1

Singular Value based method arg max min I iib =

Eigen Value Ratio based methodmin

arg maxmax

ii II

i

b

=

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Antenna Selection Algorithms

Capacity based(Optimum)

)HH+det(Ilog=C H

H~

H~

+Idetlomax=CH

~

Euclidean Distance based

t t N

2

2min , ,

( ): min

i j i j

p i j

s s S s s

H s sd

=

Where S is the set of all transmitted vectors

Hp denotes the M r X LT submatrix corresponding to antenna subset p

For every subset of transmit antennas p compute2mind

choose the subset with largest 2mind

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Simulation Parameters

Number of Tx Antennas 2, Number of Rx Antennas 4

um er o x ranc es s or

Gray-Coded 4 QAM modulationSpatial Multiplexing(V-BLAST)

Transmit power normalized

Channel Coefficients are Gaussian, i.i.d with zero mean20000 channel realizations

Perfect synchronization assumed

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4AS2MLBER

100

BER

2x2NASRSMFROCBMEUC2x3NAS

OCA2x4NAS

10-1

E R

SVMEVR

10-2

0 5 10 15 20 25 3010

-3

SNR [dB]

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4AS3MLBERBER Plots

100

CBMEVRFRORSMSVM2x4NAS2x3NAS

2x2NAS

10-1

B E R

EUC

10-2

0 5 10 15 20 25 3010

-3

SNR [dB]

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4AS2ZFBER

100

BER

2x2NASEVRFRORSM2x4NAS2x3NAS

CBMOCA

10-1

E R

EUCSVM

10-2

0 5 10 15 20 25 3010

-3

SNR [dB]

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4AS3ZFBERBER Plots

100

CBM

EVR

FRO

RSM

SVM

2x4NAS

2x3NAS

10-1

B E R

OCA

10-2

0 5 10 15 20 25 3010

-3

SNR [dB]

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4AS2ML Capacity Plots

16

18

EVR

FRO

RSM

12

14

b p s

SVM

2x2NAS

2x4NAS

10

C a p a c

i t y

C i n

CBM

EUC

OCA

6 1 0 %

O u

t a g

2

4

0 5 10 15 20 25 300

SNR [dB]

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Effect of Non-ideal RF switches

Attenuation and additional noise in the receiver Switchin dela

Different transfer functions have different input and outputport combinations

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Thank You

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Documents

LTE Antenna Selection UnivVienna 2008