Hybrid Beamforming Tx. Div.

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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Sample MAC Requirements for Angle of Arrival
Based Ranging Date Submitted 29 Sept,
2004 Source Marilynn P. Green Company
NOKIA Address Voice, FAX ,
E-MailMarilynn.Green_at_nokia.com Re
Abstract Purpose Presented as a basis
for discussion to the IEEE 802.15 TG4a on
September 30, 2004. Notice This document has
been prepared to assist the IEEE P802.15. It is
offered as a basis for discussion and is not
binding on the contributing individual(s) or
organization(s). The material in this document is
subject to change in form and content after
further study. The contributor(s) reserve(s) the
right to add, amend or withdraw material
contained herein. Release The contributor
acknowledges and accepts that this contribution
becomes the property of IEEE and may be made
publicly available by P802.15.
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Sample MAC Requirements for Angle of Arrival
Based RangingPresented as a basis for
discussion to the IEEE 802.15 TG4aonSeptember
30, 2004
by Dr. Marilynn P. Green Nokia Research Center
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Outline of Presentation

• AOA Basics
• AOA Modeling
• AOA Determination
• Error Sources
• Basic Assumptions
• Device Capability
• MAC Requirements
• AOA Ranging and Sample MAC Scenarios
• AOA-Based Positioning with Passive Anchors
• AOA-Based Triangulation with Active Anchors
• Cooperative AOA-Based Positioning
• Summary of MAC Resources and Other Considerations

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AOA Basics

• Angle of Arrival (AOA) is the direction to the
  source of an incoming wave field as measured by
  an array of antenna elements.
• While the 3D model is exact, we often use the
  simpler 2D model when the source and antenna
  elements are co-planar (? ?/2) ? for this
  presentation, we assume 2D.
• The local coordinate system of the receiving
  array may be arbitrarily oriented.

True North
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AOA Modeling

• The planar wave front models the incoming wave
  field in the far field.
• The AOA may be determined by measuring the phase
  (time) difference of the wave front at different
  array elements.

Wave front
Array Response Vector of a Linear Equi-Spaced
Array (M Antenna Elements)
?
2d
Plane Wave Model
To Source ?
Y
?
d
2dsin?
Reference Element
X
Parallel ray approximation
y(t) M x 1 vector of reception s(t) Scalar
source signal n(t) M x 1 noise vector
c Speed of Light
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AOA Determination Basic Principle

• A phased array antenna system consists of any
  number of antenna elements distributed in a
  particular geometrical pattern
• Antenna elements are typically spaced at regular
  intervals, such as a linear array, a planar array
  or a circular array.
• Phased array receive antenna systems connect the
  antenna elements by an adder network
• Output of all the antenna elements is phase
  shifted using pre-determined phase shifts and
  added to locally maximize the receiver antenna
  pattern in the direction of the incoming source
  field(s).
• Other optimization methods exist (MUSIC, ESPRIT,
  MLE,) which give better resolution of closely
  spaced sources at the expense of computational
  complexity.

Array Elements
W2(?)
WM(?)
W1(?)
Variable phase shifters.

?
Maximum at ? ?.
Beamformer
b(?)
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Errors in AOA-Based Positioning

• 2D positioning requires measurement of AOA by at
  least two antenna array systems.
• If two devices (DEV-A and DEV-B) are each
  equipped with an antenna array, they can each
  determine the line of position along a third
  device (Dev-C) lies.
• Dev-C ideally lies at the point of intersection
  of these two lines.
• In practice, measurement errors due to imperfect
  array phase and gain calibration, mis-modeling of
  the mutual coupling between elements, and the
  error due to the presence of a strong indirect
  path, etc. may all corrupt the AOA measurements.
• It is usually desirable to obtain multiple (gt 2)
  lines of position to reduce the final positioning
  error.

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Outline of Presentation

• AOA Basics
• AOA Modeling
• AOA Determination
• Error Sources
• Basic Assumptions
• Device Capability
• Basic MAC Requirements
• AOA Ranging and Sample MAC Scenarios
• AOA-Based Positioning with Passive Anchors
• AOA-Based Triangulation with Active Anchors
• Cooperative AOA-Based Positioning
• Summary of MAC Resources and Other Considerations

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Basic Assumptions for Devices

• Each device is equipped with an antenna
  array to measure AOA to neighbor nodes.
• Each device has a main axis against which all
  angles are reported.
• The axis of each node has an arbitrary but
  unknown orientation (heading) with respect to
  True North.
• Some devices may have self positioning (eg. GPS
  capability) and compass capability.

Heading
?a
Axis aligned with True North
Dev-A
Orientation with respect to True North
?ac
?ab
DEV-B
True North
AOA ?ab and ?ac Heading ?a
DEV-C
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Basic MAC Requirements (1/2)

• MAC will have to adapt to different capabilities
  of the local and remote devices.
• For example One type of device may be fully
  equipped with GPS, a compass, and an antenna
  array to measure AOAbut another device may only
  be able to measure AOA.
• In the simplest case, the PHY passes AOA results
  to the MAC and the MAC leaves more complex
  decisions to higher layers, like
• Need for repeated measurements.
• Calculation of position.
• MAC can reserve the time needed to make the AOA
  measurements.
• Guaranteed time slots may be required for
• ARQ Initiators AOA request.
• ACK Responders acknowledgement.
• AM Responders AOA measurement frame.
• AMR Responders AOA measurement report.

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Basic MAC Requirements (2/2)

• MAC may need to have pre-programmed constants to
  correct for device-specific measurement errors
  (ex. drift in the phase and gain of the antenna
  elements).
• Power efficiency
• Power control to conserve battery power during
  device idle periods.
• Reply frame with measurement results can be sent
  in the same frame as the request so that the
  device does not have to store measurement reports
  for a long time and can more quickly return to
  idle mode.
• In some cases, ACK frame may be used to obtain
  the AOA measurements.
• MAC measurement report to higher layers may
  contain
• AOA.
• Success or failure.
• Quality of measurement.
• Number of measurement periods required to satisfy
  accuracy requirements can be decided by higher
  layers.

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Outline of Presentation

• AOA Basics
• AOA Modeling
• AOA Determination
• Error Sources
• Basic Assumptions
• Device capability
• MAC requirements
• AOA Ranging and Sample MAC Scenarios
• AOA-Based Positioning with Passive Anchors
• AOA-Based Triangulation with Active Anchors
• Cooperative AOA-Based Positioning
• Summary of MAC Resources and Other Considerations

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AOA-Based Positioning with Passive Anchors

• Basic Idea If two anchors in known positions
  and with known heading each measure the direction
  to Dev-C, then we can determine the position of
  Dev-C as the intersection of two lines of
  position.
• Certain pathological geometries must be avoided ?

Dev-C
Dev-B
Dev-A
Anchor B Known (xB,yB, Heading)
Anchor A Known (xA,yA,Heading)
?BC
?AC
Line of Position
Line of Position
DEV-C (xC,yC)
Transmission by Dev-C.
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Sample MAC Resources AOA-Based Positioning with
Passive Anchors

• 4 frame AOA exchange transaction between DEV-C
  and each anchor device
• ARQ1 Initiators AOA request
• DEV-C transmits AOA measurement request to DEV-X
  (X A, B).
• ACK1 Responders acknowledgement.
• AM1 Responders measurement frame.
• DEV-C transmits to DEV-X.
• AMR1 Responders measurement report
• DEV-X transmits report to DEV-C.
• Two anchor devices ? 8 exchange transactions
  (minimum).
• Initiator (DEV-C) calculates AOA from AMR1 and
  AMR2.
• 3 frame AOA exchange between DEV-C and each
  anchor device
• ARQ1 Initiators AOA request
• DEV-C transmits AOA measurement request to DEV-X
  (X A, B).
• Measurement request itself can be used by anchor
  to measure AOA.
• ACK1 Responders acknowledgement.
• AMR1 Responders measurement report
• DEV-X transmits report to DEV-C.

OR
OR?
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AOA-Based Triangulation with Active Anchors

• Basic Idea If we know the positions of the
  vertices of a triangle and the angles at which an
  interior point sees those vertices, we can
  determine the position of the interior point
  (i.e. measure ?BDA, ?ADC and ?CDB to estimate
  (xD,yD)).

Dev-D
Anchor C (xC,yC)
Anchor B (xB,yB)
T0 Anchor A transmits. Dev-D measures ?DA.
T1 Anchor B transmits. Dev-D measures ?DB.
T2 Anchor C transmits. Dev-D measures ?DC.
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Sample MAC Resources AOA-Based Triangulation
with Active Anchors

• 3 frame AOA exchange transactions between DEV-A
  and each anchor device
• ARQ1 Initiators AOA request
• DEV-D transmits AOA measurement request to DEV-X.
  (X A, B, C).
• ACK1 Responders acknowledgement.
• AM1 Initiators measurement frame
• DEV-X transmits to DEV-D and sends its
  coordinates other info.
• DEV-D makes its AOA measurement.
• Three anchor devices ? 9 exchange transactions
  (minimum).
• Initiator (DEV-D) calculates AOA.
• 2 frame AOA exchange transactions between DEV-A
  and each anchor device
• ARQ1 Initiators AOA request
• DEV-D transmits AOA measurement request to DEV-X.
  (X A, B, C).
• ACK1 Responders acknowledgement.
• DEV-X ACKs and also sends its coordinates other
  info.
• DEV-D uses this ACK as a measurement frame.
• Three anchor devices ? 6 exchange transactions
  (minimum).

OR
OR
OR?
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Cooperative AOA-Based Positioning

• Basic Idea If we can measure the interior
  angles of a triangle and we know its orientation,
  then we can determine the positions of its
  vertices.
• A cooperative AOA ranging scheme can be used to
  measure the interior angles (?BAC, ?ACB, ?CBA) of
  a triangle that is formed by Dev-A, Dev-B and
  Dev-C.

Heading
Known
Export compass ability from Dev-B to Dev-A.
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Sample MAC Resources Cooperative AOA-Based
Positioning

• DEV-A initiates a cooperative positioning session
  between itself, DEV-B and DEV-C.
• 3 frame AOA exchange transaction between DEV-A
  and each cooperating device.
• ARQ1 Initiators AOA request
• DEV-A transmits AOA measurement request to DEV-X.
  (X B, C).
• ACK1 Responders acknowledgement.
• AM1 Initiators measurement frame
• DEV-X transmits to DEV-A.
• 3 frame AOA exchange between DEV-B and each
  cooperating device 1 Measurement report
• ARQ1
• ACK1
• AM1
• AMR1
• DEV-B sends all measurement results to DEV-A.
• 3 frame AOA exchange between DEV-C and each
  cooperating device 1 Measurement report
• ARQ1
• ACK1
• AM1
• AMR1
• DEV-C sends all measurement results to DEV-A.

Alternative ACK may be used as measurement
frame as well. ? 2 frame AOA exchange transaction
per cooperating device.
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Outline of Presentation

• AOA Basics
• AOA Modeling
• AOA Determination
• Error Sources
• Basic Assumptions
• Device Capabilities
• MAC Requirements
• AOA Ranging and Sample MAC Scenarios
• AOA-Based Positioning with Passive Anchors
• AOA-Based Triangulation with Active Anchors
• Cooperative AOA-Based Positioning
• Summary of MAC Resources and Other Considerations

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Summary of MAC Resources

• PHY notifies the MAC protocol of the signal
  reception information (for example, AOA and
  reception power) and lets the higher layers make
  complex decisions.
• MAC can assign time slots to be used for AOA
  measurements.
• The total number of measurement periods required
  to make one position estimate depends on the
  accuracy requirement of the application.
• At MAC sub-layer each device could maintain a
  cache table to keep the AOA, reception time,
  reception power, etc. of the last signal from
  each neighboring device.
• In practice, each device may update the AOA and
  reception time that corresponds to a neighboring
  device even when overhearing any signal,
  regardless of whether the signal is sent to that
  device.
• ACK frames may be used as measurement frames to
  conserve power and MAC resources.
• Beacon frames may be used for broadcasts by
  anchor nodes
• May not be the most resourceful use of MAC
  resources if positioning is not in high demand.
• Power conservative approach from the point of
  view of the device to be located.

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Other Considerations

• AOA does not require the precise synchronization
  needed for TOA and TDOA methods.
• Maturity of UWB antenna array technology must be
  taken into consideration.
• The types of algorithms that might be required to
  give the desired accuracy might be too power
  consumptive.
• There is a spatial sampling requirement that
  limits the inter-element spacing of antenna
  elements to be ? ½ minimum source wavelength.
• As long as the spatial sampling requirement is
  met, larger arrays generally provide better
  resolution of the source field ? size and cost
  issues.
• Special consideration is needed for multipath
  environments and for multi-source cases since
  sources can be closely spaced.
• In non-line-of-sight environments, the measured
  AOA might not correspond to the direct path
  component of the incoming wave field ? can lead
  to large positioning errors.
• Array phase and gain calibration is important.
• Whether or not the far-field planar wave
  approximation holds well will depend on the array
  aperture and the minimum wavelength of the source
  signal.
• Near field The phase (time) difference at
  different array elements becomes a non-linear
  function of the sources position.

Array aperture.
Minimum wavelength in source signal.
Standard calculation for the far field distance ?
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Thank You!