Post on 26-Aug-2014
All Rights Reserved © Alcatel-Lucent 2007
Adaptive Antenna Systems
Tibor ASZTALOS, NE/WiMax; Andrei OANA, NE/REMS
May 2007
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Agenda
1. Adaptive Antenna Concept
2. AAS Algorithms
3. AAS in WiMAX
4. [AAS implementation in A9155 V6.6], not covered
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Adaptive Antenna Concept
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Adaptive Antennas are:
Arrays of elementary antennas
With a precise spacing between elements (i.e. λ/2)
Amplitude and phase control on each element
1. Adaptive Antenna ConceptWhat is an Adaptive Antenna ?!
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1. Adaptive Antenna ConceptWhat is the purpose ?!
Main capabilities of adaptive arrays
Range Extensionsteering of the direction of maximum transmit powerAAS gain due to multiple antennas (N elements)
– Gain of 20·log(N) on DL– Gain of 10·log(N) on UL
Capacity Enhancementsteering of the direction of maximum transmit powerreduction of interference by ‘null steering’Data rate increase due to higher modulation (due to C/I)
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Beam Forming by Adaptive Antenna Systems (AAS)天线阵列单元要求信号相关requires coherent signals at the array elements
antenna spacing must be smaller than coherence distance (typically λ/2)
performance degradation in strong multi-path environment
Diversity gain• antenna spacing must be larger than coherence distance• Requires uncorrelated signals for highest gain
Space Time Coding (STC) through a Multiple Input Multiple Output(MIMO) System
requires propagation of the signal through independently fading channels
antenna spacing must be larger than coherence distance
most benefit in strong multi-path environment
1. Adaptive Antenna ConceptOther techniques…
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1. Adaptive Antenna ConceptBeam Forming with AAS
Beamforming:
Element spacing λ/2
Beam is formed by compensating phase differences
Sidelobe control by amplitude tapering
Possibility to insert nulls
w1
w2
wM
x (k)M
y(k)
Direction FindingBeam Forming
x (k)2
x (k)1
AntennaElements
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User
strong interfererPreferred Application Scenarios
Coherent signals at the antenna arrayRestricted angular spread of multi-pathsTypical scenario: BS significantly higherthan surrounding reflectors
Macro-cellular: rural, sub-urban and urban
Antenna System requirements:Antenna spacing ~ λ/2: compactnessOnly BS side
1. Adaptive Antenna ConceptBeam Forming with AAS
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1. Adaptive Antenna ConceptDiversity gain
Diversity gain:
Element spacing 10 .. 20λUsed to combat fading by exploiting decorrelation of amplitudes
Coherent combining by additional phase correction
Cophasingand Summing
Cophasingand Summing
a1 a2 aM
Equal GainCombining
Maximal-RatioCombining
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1. Adaptive Antenna ConceptMIMO
STC with MIMO:
Element spacing 10 .. 20λUsed to transmit and receive with spatial multiplexing
Signals have to be uncorrelated
N
Rx
Radio channel
Tx
M
1 1
N- Tx antennas M – Rx antennas
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AAS Algorithms
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Conventioanl beam steering
steers the maximum beam towards the wanted user
uses only the phase to control the weights
Null steering
steers a maximum towards the wanted user
steers a null towards the strongest (N-1) interferers
uses phase and amplitude in the complex weights
Minumum Mean Square Error
gives the best C/I under heavy interference conditions
uses a reference signal and minimizes the error (y(t)-r(t))
2. AAS Algorithms
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Beam Patterns for Up-LinkAdaptive Antenna Processing
Main Lobe Steering (Blue)
lobe suppression (15dB over ± 40°scan range) through amplitudetapering
No cancellation of individualinterference
Interference Cancellation (Red)
Mitigation even of interferencebeing ‘close in direction’
Single Antenna Patterns (Green)
HPBW: 90°
Signal - 111 °, Interference - 91 °
2. AAS AlgorithmsBeamforming example
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2. AAS AlgorithmsBeamforming mechanism
The following functions are performed for Beamforming
Direction of Arrival estimation for all incoming signals
Identify desired user signal
The beam is steered with the weights in the direction of wanted user
User is tracked while moving
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2. AAS AlgorithmsBeamforming Mathematical model
Steering vector (S)Ψi – is the delay of the signal arriving at antenna element i
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2. AAS AlgorithmsBeamforming algorithm
The weights are selected to be the conjugate of the steering vector
wH·S=1
Advantage:• Very simple algorithm• Provides maximum SNR if noise is uncorrelated
Is used only on DL in Alcatel-Lucent WiMAX implementation (W3)
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Antenna Array Power Patterns
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
Angle [deg]
Pow
er in
Rad
iatio
n Pa
tter [
dB re
lativ
e to
m
ain
lobe
at b
ores
ight
]
140° 130° 120°110° 100° 90°80° 70° 60°50° 40°
2. AAS AlgorithmsBeamforming patterns
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2. AAS AlgorithmsNull steering algorithm
The weights are computed such as to:
Steer the main beam towards the wanted user (S0)
Steer nulls towards the k=N-1 interfering users (Si)
Drawback:
Does not provide the maximum SINR
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2. AAS AlgorithmsMinimum Mean Square Error algorithm
A known reference signal is needed
The weights are determined such as to minimize the error (y(t)-r(t))
No direction of arrival estimation needed
Advantage
Works very good in high interference conditions
Is used on the UL in the Alcatel-Lucent WiMAX implementation (W2.1)
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2. AAS AlgorithmsBroadcast pattern
provides a uniform coverage of the preamble and broadcast information within the cell
Constant amplitude and phase used during the broadcast
~2dBi gain compared to elementary antenna gain
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Array AntennaAndrew, 2.5 GHz (2.3 GHz – 2.7 GHz)Mounted in open space environmentA rotor allows to turn the antenna for pattern measurements
Base StationNeMo HW3 PHY Layer W2.1 with adjustable pattern weightsMAC SD7 / SD9 in demo mode4 FEUs
Mobile StationsFixed antennas at various positions, approx 15 m air linkZyXel/Runcom MSS connected by cableAlternatively Laptop with MSS can be carried through the field
Application3 Videos running in parallel in DL
2. AAS AlgorithmsAntenna pattern measurement: test platform
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2. AAS AlgorithmsAntenna pattern measurement: Antenna Element Patterns
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2. AAS AlgorithmsAntenna pattern measurement: Broadcast Patterns
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2. AAS AlgorithmsAntenna pattern measurement: User #1 Individual Pattern
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2. AAS AlgorithmsAntenna pattern measurement: User’s #1, #2 and #3 Individual Patterns
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2. AAS AlgorithmsAntenna pattern measurement: Pattern’s Max Limit vs. Angle of Arrival
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AAS in WiMAX
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Typical AAS parameters;
Frequency: 2500 / 3500 MHz
Number of elements: 4
Gain of one element: 17dBi
HPBW of one element: 90deg horizontal, 5 deg vertical
Boresight gain: 23 dBi
HPBW Boresight steering: 25 deg
Length: 1.35m (2500MHz), 1m (3500MHz)
Antenna manufacturers:Andrew: APW425-12014 (2500 MHz),
APW435-12014 (3500 MHz)
RFS: W425-90ANV (2500 MHz),
W435-90ANV (3500 MHz)
3. AAS in WiMAXAntenna parameters and manufacturers
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System requirements to support beamforming
Dedicated pilot mode fordown-link PUSC zone, down-link AMC 2x3 zone.
Feedback of physical CINR on pilots ofdown-link PUSC zone,down-link AMC 2x3 zoneprovided through the Channel Quality Indicator Channel (CQICH)
Up-link soundingprovide training for interference cancellation in up-link as well as in down-link operation.
Provisioning of up-link permutations for beamforming operation:up-link PUSC without sub-channel rotationup-link AMC 2x3.
3. AAS in WiMAXAAS and WiMAX PHY
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IUC
12
Com
pressed DL M
ap & C
ompressed UL M
ap
Com
pressed DL M
ap & C
ompressed U
L Map
DL Burst #1
DL Burst #3
DL Burst #2
DL Burst #4
DL Burst #5
DL Burst #6
DL Burst #7
UIU
C 0
Preamble
#k #k+1
#k+2
.... #k+2
×n
.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... #k+2
×m
Logical Sub-Channels
FCH
#k+2
×m+1
.... #k+2
m+3
×p
.... .... .... .... .... #k+2
m+3
×q
.... .... .... .... .... #k+4
7
TTG
UL Burst #1
UL Burst #2
UL Burst #3
UL Burst #4
UL Burst #5
UL Burst #6
UL Burst #7
UL Burst #8
UL Burst #9
3. AAS in WiMAXUL beamforming (W2.1)
Beamforming applied only on the UL PUSC zone
No changes in the frame structure required (same as single antenna)
UIUC 0 - Fast feedback channel carrying the CQICH (CINR)
UIUC 12 – CDMA based ranging
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3. AAS in WiMAXDL Beamforming (W3)
Broadcast pattern
Adaptive pattern
Each user has his own adaptive beamforming weights
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3. AAS in WiMAXUL Beamforming (W3)
UL PUSC
ULSounding
UL AMC2x3
#k+2×m+3×p
#k+2×m+1
........
........
........
........
........
#k+47
UL Burst#1
UL B
urst #3
UL B
urst #4
UL B
urst #5
UL B
urst #6
UL B
urst #7
UL B
urst #8
UIUC 13
UL Burst#2
#k+2×m+3×p+1
#k+2×m+3×p+3
UIUC 12 initial / handoverranging
UIUC 12 periodic ranging
UIUC 0
(e.g. CQICH)
Broadcast pattern
Adaptive pattern
UIUC 0 - Fast feedback channel carrying the CQICH (CINR)
UIUC 12 – CDMA based ranging
UIUC 13 – UL sounding zone, training pilots for UL interference cancellation
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3. AAS in WiMAXUL Sounding Zone example
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PHY layer stores the individual weight vectors for each subscriber
The association weight vector – subscriber is done through MAC layer
A handle is exchanged between MAC and PHY as entry in the table of UL/DL weights (during UL allocations)
The handle is updated by the MAC layer
3. AAS in WiMAXInterface between MAC and PHY layer
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Thank you!
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