Aerospace and Electronic Systems Magazine December 2017 - 58

MIMO Methods Applied in Over-the-Horizon Radar
tively, select s(ν, τ) as the spatial signature of a desirable feature in
range-Doppler space to preserve. While the latter lacks a physical
interpretation of direction-of-departure it is useful in cases where
the array manifold calibration solution is unavailable. Training
data is selected according to (8), where the domain of range-Doppler space included is chosen to capture the signal energy we seek
to remove. Equation (6) is then solved and the beamformer applied
as in (4) over the range-Doppler domain (ν, τ) of interest.

DIRECTION-OF-DEPARTURE ESTIMATION
The estimated direction-of-departure (DOD) θˆ d (ν ,τ ) from the
transmitter array for a signal propagating from that array to a
down-range receiver via the ionosphere and corresponding to the
signal at Doppler-delay cell (ν, τ), is given by

θˆ d (ν ,τ ) = arg max y (ν ,τ ,θ )

(9)

A full beampattern for the energy in Doppler-delay cell (ν, τ) can
2
be determined by evaluating y (ν ,τ ,θ ) for all θ of interest. Note
that the DOD measured from a linear one-dimensional array in a
two-dimensional environment is the so-called cone angle with respect to array axis (or end-fire). The cone angle is a coupled measurement of azimuth and elevation where these latter two parameters are with respect to a plane containing the linear array and one
other reference direction. In our case it is the plane of the earth
containing the array. In the following,
we exploit exact knowledge of the azimuth from transmitter to receiver to determine elevation-of-departure θe from
direction-of-departure θd according to
 cosθ d 
a 
 cos θ 

θ e = cos −1 

control were located at Coondambo in South Australia. This site
also had a wide-band oblique incidence sounder (OIS) transmitter
[49] to support propagation assessment, and a clear-channel advice
system for operating frequency selection.
In the December 2009 MSE-I campaign, three single channel
radar receivers were deployed down-range at various propagation
distances with similar aspect to the transmitter array. Receiver systems were placed at Mt. Everard (863 km at a bearing of 345.0° T-
defined with respect to the Coondambo transmit site and clockwise
relative to true North), Elliott (1,514 km at a bearing of 350.5° T)
and at Tindal (1,864 km at a bearing of 348.2° T). In March 2010
for MSE-II we added a further two single channel radar receivers,
one at Hermannsburg (844.4 km at a bearing of 338.2° T) and one
at Kings Canyon (867.2 km at a bearing of 329.4° T). For MSEII we also converted all receiver systems to be capable of realtime MISO processing. Sites were selected to provide diversity in
range (MSE-I) and range and bearing (MSE-II) on scales relevant
to the OTHR scenario. All down-range receiver systems operated
synchronously with the transmit system. Mode selection solutions
generated for every location could simultaneously be assessed for
desired propagation mode preservation and unwanted mode rejectability at the various different ranges and bearings with respect to
the transmitter.
The total ground-range depth between the nearest and furthermost receiver system is approximately 1,000 km and the total orientation variation with respect to the transmitter array is approxi-

(10)

where θa is our a priori knowledge of
the bearing from the transmitter array
to the down-range receiver adjusted for
coordinate system.

EXPERIMENT DESCRIPTION
The Mode Selection Experiment
(MSE) reported here took place during December of 2009 (MSE-I) and
March of 2010 (MSE-II) in central and
northern Australia. MSE used a oneway propagation MISO configuration
designed to explore MIMO techniques
relevant to the radar two-way propagation case, but in a simplified configuration to build our understanding.
The geographic layout for the March
2010 experiment is shown in Figure 4.
In both MSE-I and MSE-II the transmitter array and MISO transmission
equipment and the experiment central
56

Figure 4.

Geographic layout for MSE shown on a map of Australia.

IEEE A&E SYSTEMS MAGAZINE

DECEMBER 2017

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine December 2017