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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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