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Mobile Phone Patent Abstract
In order to process communications between a base station comprising
an N separate antennae network, N being a whole number greater than
1, and at least one mobile phone, the method consists of the following
steps: estimating the incoming direction and the path power to the
base station; determining a main incoming direction of those paths
to the base station; selecting antennae, M being a whole number
less than N, whereof the individual receiver, respectively transmitter,
lobes have directions contained in an angular sector centred on
the main incoming direction; processing only the signals received
by the M selected main antennae coming from the mobile phone, respectively
synthesising only the signals to be transmitted by the M selected
antennae.
Mobile Phone Patent Claims
What is claimed is:
1. Communication method between a base station comprising a network
of N distinct antennae, N being a whole number greater than 1, and
at least one mobile telephone, comprising the steps of: (a) estimating
at the base station, the directions of arrival and the power values
of radio-electrical path at the base station; (b) determining for
this mobile telephone, a principal direction of arrival of said
radio-electrical paths at the base station, by choosing a barycentre
r of the directions of arrival of the different radio-electrical
paths as being the principal direction of arrival, define as follows:
##EQU3## where i is a whole number, where J is the number of radio-electrical
paths identified, where a.sub.i is the angle formed by the i.sup.th
radio-electrical path in relation to the direction of the path which
has the greatest radio-electrical power value, and where p.sub.i
is the radio-electrical power value of the i.sup.th path; (c) selecting
M antennae, M being a whole number strictly greater than 1 and less
than N, of which the individual reception lobes have directions
which are contained within an angular sector centered on the principal
direction of arrival; (d) processing only the signals received by
the selected M antennae from the mobile telephone.
2. The method of claim 1 further comprising the steps of: (a) selecting
M antennae of which the individual transmission lobes have directions
contained within an angular sector centered on the principal direction
of arrival; (b) synthesizing only the signals to be transmitted
by the selected M antennae.
3. A radio base station for communication with mobile telephones,
comprising a network of N distinct antennae, N being a whole number
greater than 1, and K reception or transmission chains, K being
a whole number less than N.times.L, where L is the number of simultaneous
communications, the radio base station comprising: means of estimating
the directions of arrival and the radio electrical power values
of the radio-electrical paths at the base station; means of determining,
for a given mobile telephone, a principal direction of arrival of
the radio-electrical paths at the base station, being the direction
of arrival for which the radio-electrical power value received or
transmitted and deriving from the mobile telephone is the greatest;
means of selecting M antennae, M being a whole number strictly greater
than 1 and less than N, of which the individual reception or transmission
lobes have directions contained within an angular sector centered
on the principal direction of arrival; means of switching, affecting,
for each communications, M reception or transmission chains at the
M antennae previously selected.
4. A radio base station for communication with mobile telephones,
comprising a network of N distinct antennae, N being a whole number
greater than 1, and K reception or transmission chains, K being
a whole number less than N.times.L, where L is the number of simultaneous
communications the radio base station comprising: means of estimating
the directions of arrival and the radio electrical power values
of the radio-electrical paths at the base station; means of determining,
for a given mobile telephone, a principal direction of arrival of
the radio-electrical paths at the base station, being the barycentre
r of the directions of arrival of the different radio-electrical
paths, defined as follows: ##EQU4## where i is a whole number, where
J is the number of radio-electrical paths identified, where a.sub.i
is the angle formed by the i.sup.th radio-electrical path in relation
to the direction of the path which has the greatest radio-electrical
power value, and where p.sup.i is the radio-electrical power value
of the i.sup.th path; means of selecting M antennae, M being a whole
number strictly greater than 1 and less than N, of which the individual
reception or transmission lobes have directions contained within
an angular sector centered on the principal direction of arrival;
means of switching, affecting, for each communications, M reception
or transmission chains at the M antennae previously selected.
Mobile Phone Patent Description
The invention relates to a radio communication method at high frequency
between a base station with N antennae and a mobile phone, and a
base station for implementing same.
It can be applied to digital cell telephone systems in which one
and the same station is provided with a network of antennae allowing
it to serve a plurality of mobile phones in a cell.
In such a station, during transmission, the signals to be applied
to each antenna are synthesised on the basis of the signal intended
to reach the mobile phone.
To achieve this, in the transmission chain of each antenna a number
of digital processes generally produce samples representing these
signals. Then, by means of digital-analog conversion and modulation
to the carrier frequency, each signal is synthesised then simplified
and applied to the appropriate antenna of the network.
The complexity of the calculations necessary to synthesise these
patterns, and the cost of the digital-analog conversion circuits
and of modulation, increase with the number of antennae in the network.
Hereinafter, the term multi-sensor transmission device shall be
used to refer to the whole of the circuits which produce the signals
applied to each elementary antenna for transmission to the mobile
phone.
At reception, in analog mode, the reception chain of each antenna
feeds the signals received by this antenna into an intermediary
frequency or the base band. The signals are then sampled and subjected
to analog-digital conversion. The samples are then processed by
digital processes to extract the information transmitted by the
mobile phone.
The complexity and the cost of the circuits of the reception paths
again increase with the number of antennae in the network.
Hereinafter, the term multi-sensor reception device shall be used
to refer to the whole of the circuits which process the signals
received from the mobile phone in order to extract the information
transmitted.
The network of antennae may feature any geometry considered appropriate.
In particular, the antennae may be disposed in line and regularly
spaced. In this event, they are preferably directional, and their
lobes point in the orthogonal direction to the right of which the
antennae are aligned.
The antennae may equally be disposed in a circle and regularly
spaced. In this event, the antennae are likewise preferably directional
and their lobes point in a radial direction towards the outside
of the circle on which they are disposed.
The invention applies likewise to a network of antennae presenting
a regular polygon geometry such as an equilateral triangle, a square,
a pentagon, a hexagon, etc., with antennae spaced regularly along
its sides.
The objective of the invention is to reduce the complexity of the
calculation and the cost of the processing procedures carried out
by a base station provided with a network of antennae.
In order to achieve this objective, the invention proposes a method
of communication between a base station consisting of a network
of N distinctive antennae, N being a whole number greater than 1,
and at least one mobile telephone, characterised in that: (a) The
directions of arrival and the power values of the radio-electrical
paths are estimated at the base station; (b) A principal direction
of arrival is determined for said mobile telephone of said radio-electrical
paths at the base station; (c) M antennae are selected, M being
a whole number less than N, the individual reception lobes of which
have directions contained in an angular sector centred on the principal
direction of arrival; (d) Only the signals which are received by
the M antennae selected and deriving from the mobile telephone are
processed.
For the transmission according to this process, (e) M antennae
are selected, of which the individual transmission lobes have directions
contained within angular sector centred on the principal direction
of arrival; (f) Only the signals to be transmitted by the M antennae
selected are synthesised.
The invention likewise proposed a radio communications base station
with mobile telephones, comprising a network of different N antennae,
N being a whole number greater than 1, and K reception or transmission
chains, K being a whole number less than N.times.L, where L is the
number of simultaneous communications, characterised in that it
comprises: Means of assessing the directions of arrival and the
power values of the radio-electrical paths at the base station;
Means of determining, for a given mobile telephone, a principal
direction of arrival of the radio-electrical paths at the base station;
Means of selection of M antennae, M being a whole number less than
N, of which the individual reception or transmission lobes have
directions contained within an angular sector centred on the principal
direction of arrival; Means of switching, affecting, for each communication,
M reception or transmission chains at the M antennae previously
selected.
In a specific embodiment of the invention, the principal direction
referred to heretofore is the direction of arrival for which the
radio-electric power received or transmitted and reaching the mobile
telephone (according to whether it is in reception or transmission
mode) is the greatest.
In another specific embodiment of the invention, the principal
direction referred to heretofore is the barycentre r of the directions
of arrival of the different radio-electric paths, defined as follows:
##EQU1## where i is a whole number, where J is the number of radio-electrical
paths identified, where a.sub.i is the angle formed by the i.sup.th
radio-electrical path in relation to the direction of the path having
the greatest radio-electrical power value, and where p.sub.i is
the radio-electrical power of the i.sup.th path.
Other features and advantages of the invention are clearly indicated
in the following detailed description of specified embodiments,
given by way of non-limiting examples. The description refers to
the accompanying drawings, in which:
FIG. 1 represents in schematic form traditional multi-sensor reception
and transmission devices, wherein one single communication is being
considered between the base station and a mobile telephone;
FIG. 2 represents in schematic form the reception and transmission
devices comprised in a base station conforming to a particular embodiment
of the invention, wherein a single communication is considered between
the base station and a mobile telephone;
FIG. 3 is an organizational diagram of the process according to
the invention, in a specific embodiment;
FIG. 4 illustrates a method of selection of M antennae among N,
in a specific embodiment of the invention, wherein the network of
antennae presents a circular geometry;
FIG. 5 represents in schematic form traditional multi-sensor reception
and transmission devices, wherein the base station is processing
L simultaneous communications; and
FIG. 6 represents in schematic form reception and transmission
devices comprised in a base station in accordance with a specific
embodiment of the invention, wherein the base station is processing
L communications simultaneously.
The invention will first be described by considering one single
communication between a base station and a given mobile telephone.
In the traditional situation represented in FIG. 1, whether in
reception mode (left-hand part of the figure) or in transmission
mode (right-hand part of the figure), the number N of antennae,
each designated in the figure by the reference number 10, of the
base station corresponds to the number of signals which are capable
of being processed (in reception) or of being synthesised (in transmission)
by a multi-sensor reception device 12 or a multi-sensor transmission
device 14, comprised in the base station.
Typically, these devices comprise the same number of reception
and transmission chains as there are elementary antennae in the
network, this being N in the example illustrated.
It is recalled that each reception chain comprises essentially
a pre-amplification module, a frequency conversion module for the
transition to intermediary frequency or base band, and an analog-digital
conversion module. Each transmission chain comprises essentially
a numerical-digital conversion module, a frequency conversion module
to pass to the transmission carrier frequency, and an amplification
module.
The left-hand part of FIG. 2 represents a reception device included
in a base station of N antennae in accordance with an embodiment
of the present invention.
When a mobile telephone transmits a signal in the direction of
the base station, the base station activates a module for estimating
the directions of arrival and the power values of the radio-electrical
paths at the base station (not represented in FIG. 2). A traditional
process for locating the source is then put into effect, for example
of the type of those described in the following documents: ANDERSON
S., MILLNERT M., VIBERG M., WAHLBERG B. "An adaptive array
for mobile communication systems", IEEE Transactions on Vehicular
Technology, Vol. 40, No. 1, February 1991, pages 230-236; VIBERG
M., OTTERSTEN B., "Sensor array processing based on subspace
fitting", IEEE Transactions on Signal Processing, Vol. 39,
No. 5, May 1991, pages 1110-1121; SCHMIDT R. O., "A signal
subspace approach to multiple emitter location and spectral estimation",
Ph.D. dissertation, Stanford Univ., Stanford, Calif., November 1981;
ROY R. H., PAULRAJ A., KAILATH T., "ESPRIT--A subspace rotation
approach to estimation of parameters of cisnoids in noise",
IEEE Trans. Acoust., Speech Signal Processing, Vol. ASSP-34, No.
4, pages 1340-1342, October 1986.
The base station then determines, for this mobile telephone, a
direction of arrival which is referred to as the principal direction
of arrival. The signals emitted by the mobile telephone to the base
station effectively undergo reflexions on various obstacles and
give rise to multiple paths. The principal direction of arrival
may be that for which the radio-electrical power received by the
base station is the greatest.
As a variation, the principal direction of arrival may be the barycentre
r of the directions of arrival of the different radio-electrical
paths identified, weighted by a function of the radio-electrical
power values of these paths.
The module for determining the principal direction of arrival is
not shown in FIG. 2.
Let J be the number of radio-electrical paths identified. Let a.sub.i
be the angle formed by the i.sup.th radio-electrical path, i being
a whole number, in relation to the direction of the path for which
the radio-electrical power is the greatest. Let p.sub.i be the radio-electrical
power of the i.sup.th path. The barycentre r is defined by ##EQU2##
Once the principal direction of arrival has been determined, the
base station activates a search or selection module (not shown)
in order to determine, among the N antennae of the network, a more
restricted set of antennae which will be exploited for the communication
process under consideration. According to an advantageous embodiment
of the invention, the set used for reception comprises M antennae,
of which the individual reception lobes have directions contained
within a predetermined amplitude angle sector, centred on the principal
direction of arrival.
The number M may vary from one communication to another, and depends
on the number of processing circuits available.
FIG. 4 shows a configuration in which an angular sector centred
on a principal direction of arrival comprises m antennae, selected
from among N, for a network of antennae of circular geometry; the
N elementary antennae represented are disposed equally around the
circle.
As FIG. 2 (left-hand part) shows, the base station comprises a
reception switching matrix 16, which directs the signals received
from the mobile telephone by the M antennae selected towards the
multi-sensor reception device 18. The signals which are not processed
by the multi-sensor reception device are orientated onto a load
20 which corresponds to the impedance of the N-M antennae not selected.
The right-hand section of FIG. 2 represents a transmission device
integrated in a base station with N antennae, in accordance with
a specific embodiment of the invention. In transmission mode, in
a manner analogous to that just described for reception, the base
station includes a search module (not shown) of M antennae, the
individual transmission lobes of which have directions contained
within an angular sector of a predetermined amplitude, centred on
the principal direction of arrival.
The base station likewise comprises a multi-sensor transmission
device 22, which synthesises only the M signals to be transmitted
by the M antennae selected. A transmission switching matrix 24 directs
the synthesised signals to apply them to these M antennae. The N-M
antennae not selected are connected to a single load 26, corresponding
to their impedance.
It is assumed in this situation that the same network of antennae
serves for transmission and reception. Provision can be made for
the reception and transmission switching matrices to be one and
the same bi-directional matrix, the signals received and transmitted
circulating in opposed directions on the same cables. As a variant,
provision may be made for a duplex filter, which separates the signals
received and transmitted at the level of each elementary antenna,
and two distinct switching matrices operating in an independent
manner.
It will be noted that the switching matrices for reception and
transmission, depending on the means of realisation, may be either
hardware devices, or software realisations.
In addition to this, in the specific case of the application of
the invention to a system operating in time-division multiple access
(TDMA) mode, the previous arrangement is effected for a given period
of time. In effect, the group of M antennae selected is subject
to being changed from one time sector to the one following, i.e.
from one communication link to the other.
FIG. 3 provides a summarised version of the different stages of
the process according to the invention, in a specific embodiment.
In the course of a first stage, the directions of arrival and the
power values of the radio-electrical path values at the base station
are estimated. A principal direction of arrival is then determined
for this mobile telephone. Next a selection is made, from among
the N antennae of the network, of M antennae of which the individual
reception or transmission lobes have directions contained within
an angular sector centred on the principal direction of arrival.
In the final analysis, only the signals received or to be transmitted
by the M antennae selected are processed (in reception) or synthesised
(in transmission).
The description provided heretofore in relation to FIGS. 1 and
2 relate to a given communication link between the base station
and a single mobile telephone. In practice, a base station serves
a large number of simultaneous communications links with several
mobile telephones. In the TDMA mode, the signals from the different
communications links occupy different and identical time sectors
within successive cycles. It is considered hereinafter that L communication
links are effected simultaneously. The number L represents the number
of communications links actually effected simultaneously, i.e.,
for example, sharing the same cycle of time sectors in TDMA mode.
In reception mode, in a traditional device such as that represented
in the left-hand part of FIG. 5, the signals received by the N antennae
are processed by N reception chains 28, which separate the signals
corresponding to each of the L communications links for each antenna.
The N.times.L signals which result are then received by a multi-sensor
reception device 30, which processes the N signals received for
each communications link.
In transmission mode (right-hand part of FIG. 5), in a traditional
device, a multi-sensor transmission device 32 synthesises N signals
to be transmitted by the N antennae of the network for each communication
link. The N.times.L signals which result are transmitted to N transmission
chains 34, which add together the contributions from each of the
communications to be transmitted by each antenna. All the communications
links then exploit all the antennae, both in reception and in transmission.
If the present invention is applied in reception mode (left-hand
part of FIG. 6), for each of the L simultaneous communications links,
the M antennae used are selected in the manner described heretofore
in the case of a single communication link. M reception chains 36
then separate, for each of the M antennae selected, the communications
signals which have selected this antenna. A multi-sensor reception
device 38 then processes, for each communication link, M signals
received.
If the present invention is applied in transmission mode (right-hand
part of FIG. 6), for each of the simultaneous L communication links,
the M antennae used by one of the L communication links are selected
in the manner described heretofore in the case of a single communication
link. A multi-sensor transmission device 40 synthesises, for each
communication link, M signals to be transmitted by the M antennae
selected. The resultant signals are transmitted to the transmission
chains 42, which add up, for each antenna, the contributions from
the communications which have selected this antenna. Each communication
link accordingly only exploits a part of the antennae, which considerably
reduces the complexity of the processing: In reception mode, these
processing procedures exploit, for each communication link, M signals
received instead of N, and, in transmission, for each communication
link, M signals are synthesised instead of N.
If the base station comprises a total number K of transmission-reception
chains, K being a whole number less than N.times.L, the maximum
number of signals issued from the reception chains 36 or from the
multi-sensor transmission device 40 is equal to K.
Depending on the situation, it may be of interest to choose: Either
to fix M, and to make provision for a number K of chains equal to
M.times.L, Or to allow M to vary, and to consider the whole of the
transmission-reception chains as a group or pool, which is applied
to each communication (as a function of the number of simultaneous
communication links to be effected).
In the event that the principal directions of arrival associated
with several mobile telephones correspond to groups of antennae
comprised within angular sectors which overlap, i.e. which have
one or more antennae in common, it is possible that a conflict of
utilisation may arise between these communications links, involving
the use of the same transmission-reception chains. It is appropriate
to implement only a certain number of the communication links in
conflict at these antennae, In accordance with a predetermined criterion.
This criterion may consist, by way of a non-limiting example, of
balancing the radio-electrical power values received, by assigning
these antennae to the communication link for which the received
power is the weakest.
Experience has shown that it is possible to attain performance
values similar to those obtained with the complete network, making
use only of half of the elementary antennae which constitute the
network.
A further advantage of the invention is that it allows, at reduced
cost and in a continuous manner, for the base station to carry out
the whole of the spatial processing, by distinction from traditional
base stations, consisting of sectoral antennae, which superimpose
two spatial processing procedures, i.e. that of the antennae network
and that of the sectorisation.
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