System for determining a direction of arrival
The invention relates to a method of goniometric processing using
a plurality of antennas forming an antenna array. This type of method makes
it possible to obtain the direction of arrival of radio signals arriving on the
5 various antennas of the antenna array.
Systems named phase or amplitude interferometry systems are
known to the prior art. These systems are based on the calculation of the
phase shift of a same signal received on two different antennas. However,
10 these systems do not make it possible to obtain adequate precision and are
subject to ambiguity.
It is also known that to function correctly these systems must have
a distance separating the two antennas equivalent to the modulation
15 frequency of the received signal. In order to overcome this constraint it is
possible to have systems composed of a plurality of antenna pairs, with a
different separation between antennas for each pair. However, the
dimensions of these systems are increased and the adaptability of these
systems to the bandwidth of the signal depends on the number of antenna - .- 20 pairs.
Systems implementing methods known by the name of highresolution
processing or beamforming are known to the prior art. However,
these methods require greater computational resources and memory space
25 than are required for phase or amplitude interferometry methods. These
methods are therefore difficult to implement in systems having small
dimensions or low power consumption.
The present invention therefore aims to remedy these problems by
30 proposing a system making it possible to determine the direction of arrival of
a radio signal, requiring fewer computational resources than are necessary
for the implementation of high-resolution methods and a greater precision
than that obtained by interferometry systems.
The present invention proposes a system for determining a
direction of arrival of a radio signal comprising at least three antennas,
means configured for determining at least two phase shifts, associated with
various antenna pairs respectively, said phase shifts being the difference
between a phase of the signal received from one of the antennas of a pair
and a phase of the signal received from the other antenna of the pair. The
system also comprises means configured for summing at least two of the
phase differences, and first means configured for determining a set of
parameters respectively associated with a supposed direction of arrival,
based on the summation, by calculating the difference between the
summation and a reference summation associated with the supposed
direction of arrival. Finally, the system comprises second means configured
for determining the direction of arrival as being the supposed direction of
arrival associated with the parameter having the minimum value.
The system therefore makes it possible to determine the direction
of arrival of the radio signal. Moreover, as a function of the frequency of the
received signal it is possible to modify the choice of antenna pairs for which
the phase shift is summed. This makes it possible to artificially change the
separation between the antennas.
Figure 1 exhibits the case in which the pairs of antennas are
chosen in order to have an artificial separation between antennas greater
than the maximum separation between two antennas.
Advantageously the antennas are distributed in a line.
Advantageously the antennas are evenly distributed in a circle.
Advantageously the system comprises at least four antennas and
said means configured for determining at least two phase shifts are
configured for determining phase shifts associated with various antenna pairs
having one antenna in common.
The present invention also proposes a method for determining a
direction of arrival of a radio signal comprising a step of determining at least
two phase shifts, associated with various antenna pairs respectively, said
phase shifts being the difference between a phase of the signal received
5 from one of the antennas of a pair and a phase of the signal received from
the other antenna of the pair. The method also comprises a step of summing
at least two of the phase shifts, a step of determining a set of parameters
respectively associated with a supposed direction of arrival, based on said
summation, by calculating the difference between said summation and a
10 reference summation associated with the supposed direction of arrival, and a
second step of determining the direction of arrival as being the supposed
direction of arrival associated with the parameter having the minimum value.
The invention will be better understood and other advantages will
appear on reading the detailed description given by way of nonlimiting
15 example and with reference to the figures among which:
- Figure 1 shows the choice of antenna pairs in order to extend the
difference between antennas
- Figure 2 shows an embodiment of the system according to the invention
- Figure 3 shows an embodiment of part of the device 302 for determining
20 phase shifts.
Figure 2 shows a first embodiment of the system. In this
embodiment the system comprises three antennas 301-A, 301-B and 301-C.
The system also comprises a device 302 for determining at least two phase
25 shifts. Each phase shift is associated with a pair of antennas, and it
corresponds to the difference between the phase of the signal received by
one antenna and the phase of the signal received by the other antenna.
The system next comprises a device 303 for summing two phase
30 shifts. This summation makes it possible to artificially change the separation
between the receiving antennas by creating a virtual antenna.
Thus in the example in Figure 1, if the difference, between the phase
of the signal received from the antenna 3 and the phase of the signal
35 received from the antenna 5, is summed with the difference, between the
phase of the signal received from the antenna 3 and the phase of the signal
received from the antenna 1, then the separation between the antennas is
widened. This widened separation corresponds to the distance between
antenna 3 and the virtual antenna 1'. This artificial increase in particular
5 makes it possible to determine the direction of arrival of signals having a
lower frequency than that which can be determined without the system
described in this invention. Specifically, the frequency of the signal that can
be processed depends on the inverse of the distance separating the
antennas (real or virtual), therefore the more this distance increases, the
10 lower this frequency becomes. The same type of result is obtained by
carrying out the following summations:
- Difference between the phase of the signal received from the
antenna 4 and the phase of the signal received from the
antenna 1 and difference between the phase of the signal
received from the antenna 4 and the phase of the signal
received from the antenna 2. The summation corresponds to
the distance between the antenna 4 and the virtual antenna 2'
- Difference between the phase of the signal received from the
antenna 5 and the phase of the signal received from the
antenna 2 and difference between the phase of the signal
received from the antenna 5 and the phase of the signal
received from the antenna 3. The summation corresponds to
the distance between the antenna 5 and the virtual antenna 3'
- Difference between the phase of the signal received from the
antenna 1 and the phase of the signal received from the
antenna 3 and difference between the phase of the signal
received from the antenna 1 and the phase of the signal
received from the antenna 4. The summation corresponds to
the distance between the antenna 1 and the virtual antenna 4'
- Difference between the phase of the signal received from the
antenna 2 and the phase of the signal received from the
antenna 4 and difference between the phase of the signal
received from the antenna 2 and the phase of the signal
received from the antenna 5. The summation corresponds to
the distance between the antenna 2 and the virtual antenna 5'.
The sys'tem shown in Figure 2 also comprises a first device 304
for determining a set of parameters each associated with a supposed
direction of arrival. The parameters are calculated from the difference
5 between the summation and a reference summation associated with the
supposed direction of arrival. It is for example possible to use the following
relationship:
i=l
In this equation A~IL~, and ~q1:,~(8) respectively represent the
10 measured phase shifts and the reference phase shifts. 8 is the supposed
direction of arrival and D represents the parameter associated with the
supposed direction of arrival 8.
The system also comprises a second device 305 making it
15 possible to determine the minimum parameter and the value of the supposed
direction of arrival associated with this parameter.
Figure 3 shows an embodiment of part of the device 302 for
determining phase shifts. This device comprises a first sub-device 401
20 making it possible to switch between the reception antennas (301-A, 301-8
and 301-C) and the reception paths (402-A and 402-8). This sub-device in
particular makes it possible to use a number of reception paths less than the
number of reception antennas. The reception paths are made up of two
analogue RF sub-devices 402-A and 402-6 and of an analogue-to-digital
25 conversion device (also known by the acronym ADC) 403. The two analogue
RF sub-devices in particular make it possible to filter the signal received in
the useful band, and to amplify the signal received by using low-noise
amplifiers.
30 The various devices may be produced in the form of dedicated
circuits (also known by the acronym ASIC for Application-Specific Integrated
Circuit), in the form of an FPGA (Field-Programmable Gate Array) or in the
form of a generic processor coupled with a computer program product on a
computer-readable medium. The medium may be electronic, magnetic,
I optical, electromagnetic, or may be an infrared broadcasting medium. Such
media include, for example, semiconductor memories (Random Access
Memory RAM, Read-Only Memory ROM), tapes, diskettes or magnetic or
5 optical disks (Compact Disk - Read Only Memory (CD-ROM), Compact Disk
- Readwrite (CD-RNV) and DVD).

CLAIMS
1. System for determining a direction of arrival of a radio signal comprising at
5 least three antennas,
- means configured for determining at least two phase shifts, associated
with various antenna pairs respectively, said phase shifts being the
difference between a phase of the signal received from one of the
antennas of a pair and a phase of the signal received from the other
10 antenna of the pair,
said system being characterized in that it also comprises:
- means configured for summing at least two of the phase shifts
- first means configured for determining a set of parameters respectively
associated with a supposed direction of arrival, based on said
15 summation, by calculating the difference between said summation and
a reference summation associated with the supposed direction of
arrival
- second means configured for determining the direction of arrival as
being the supposed direction of arrival associated with the parameter
20 having the minimum value.
2. System according to Claim 1, in which the antennas are distributed in a
line.
25
3. System according to Claim 1, in which the antennas are evenly distributed
in a circle.
4. System according to Claims 1 to 3, comprising at least four antennas and
30 in which said means configured for determining at least two phase shifts are
configured for determining phase shifts associated with various antenna
pairs having one antenna in common.
5. Method for determining a direction of arrival of a radio signal comprising
3 5 - a step of determining at least two phase shifts, associated with various
antenna pairs respectively, said phase shifts being the difference
pn ".,, T .-
st,,, r:- ;:,'F_N~L - = . ~ ~ ~ i 3 t; 8 ; I--- e 0 DEC 20s
betwsen a phase of the sigrial received from one of the antennas of a
pair and a phase of the signal received from the other antenna of the
pair
said method being characterized in that it also comprises:
5 1 - a step of summing at least two of the phase shifts
- a step of determining a set of parameters respectively associated with
a supposed direction of arrival, based on said summation, by
calculating the difference between said summation and a reference
summation associated with the supposed direction of arrival
10 - a second step of determining the direction of arrival as being the
supposed direction of arrival associated with the parameter having the
minimum value.