Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RADIO FREQUENCY COVERAGE OF ENCLOSED REGIONS
FIELD OF THE INVENTION
The present invention relates generally to wireless communications,
and specifically to wireless communications from within a region generally
closed to electromagnetic radiation.
BACKGROUND OF THE INVENTION
In cellular communications systems there are typically regions where
the coverage is difficult or incomplete, for example, within metal-framed
structures, and underground. Methods for improving the coverage in
regions such as these are known in the art.
U. S. patent 5,404,570, to Charas et al, whose disclosure is incorporated
herein by reference, describes a repeater system used between a base
transceiver station (BTS), which is able to receive signals, and a closed
environment such as a tunnel, which is closed off to transmissions from the
BTS. The system down-converts a high radio-frequency (RF) signal from the
BTS to an intermediate frequency (IF) signal, which is then radiafed by a
cable and an antenna in the closed environment to a receiver therein. The
receiver up-converts the IF signal to the original RF signal. Systems
described in the disclosure include a vehicle moving in a tunnel, so that
passengers in the vehicle who would otherwise be cut off from the BTS are
able to receive signals.
U. S. patent 5,603,080 to Kallandar et al., whose disclosure is
incorporated herein by reference, describes a plurality of repeater systems
used between a plurality of BTSs and a closed environment, which is closed
off to transmissions from the BTSs. Each system down-converts an RF signal
from its respective BTS to an IF signal, which is then transferred by a cable
in
the closed environment to one or more respective receivers therein. Each
receiver up-converts the IF signal to the original RF signal. Systems
described in the disclosure include a vehicle moving between overlapping
regions in a tunnel, each region covered by one of the BTSs via its repeater
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system. Thus, passengers in the vehicle who would otherwise be cut off
from one or more of the BTSs are able to receive signals from at least one of
the BTSs throughout the tunnel.
U. S. patent 5,765,099, to Georges et al., whose disclosure is
incorporated herein by reference, describes a system and method for
transferring an RF signal between two or more regions using a low
bandwidth medium such as twisted pair cabling. In a first region the RF
signal is mixed with a first local oscillator to produce a down-converted IF
signal. The IF signal is transferred to a second region via the low bandwidth
medium, wherein the signal is up-converted to the original RF signal using
a second local oscillator. The local oscillators are each locked by a phase
locked loop (PLL) in each region to generate the same frequency, the locking
being performed in each loop by comparing the local oscillator frequency
with a single low frequency stable reference signal generated in one region.
The reference signal is transferred between the regions via the low
bandwidth medium.
U. S. patent 5,513,176, to Dean et al., whose disclosure is incorporated
herein by reference, describes a distributed antenna array within a region
where , reception is difficult. The performance of the antenna array is
enhanced by generating signal diversity within the array. Each antenna i n
the array has a differential time delay applied to signals that it receives,
thus
generating received signal diversity. The differentially-delayed signals are
preferably down-converted to an intermediate frequency and are then
transferred out of the region via a cable.
U. S. patent 5,930,293, to Light, et al., whose disclosure is incorporated
herein by reference, describes a wireless repeater comprising first and second
spatially-separated antennas. Both antennas receive a signal from a
transmitter, and the signal received by the second antenna has a time delay
added to the original signal. The two signals are summed to form one
aggregate signal, which is transmitted from a third antenna. A receiver of
the aggregate signal is able to reconstruct the signals received by the first
and
second antennas.
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SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide
improved methods and apparatus for transmitting a radio frequency signal
within a region generally closed to electromagnetic radiation.
In preferred embodiments of the present invention, a group of
stationary transceivers, herein termed slave units, are installed within a
region which is generally closed to electromagnetic radiation from outside
the region, such as an interior of a building. The slave units receive a radio
frequency (RF) signal from at least one mobile transceiver, such as a mobile
cellular telephone, in the region. The group of slave units are divided into a
first and a second sub-group, having generally equal numbers of stationary
transceivers in each sub-group.
The slave units of the first sub-group are separated spatially from the
slave units of the second sub-group. Apart from being spatially separated,
transceivers in the first sub-group are positioned independently of
transceivers in the second sub-group. The spatial separation is most
preferably at least enough so that a signal received by the first sub-group
and
a signal received' by the second sub-group, from one transmission of the at
least one mobile transceivers, are distinguishable. The signals are typically
distinguishable in terms of amplitude, or phase, or time of arrival, or a
combination of these or other signal parameters. Thus, the slave units of
one of the pluralities can function as diversity receivers with respect to the
slave units of the other sub-group, which function as main receivers.
RF signals received by the slave units from. the at least one mobile
transceivers are down-converted to intermediate frequency (IF) signals,
which are then transferred from the region by one or more cables. IF signals
from each sub-group of slave units are transferred to a master unit, which
up-converts the IF signals in order to recover information contained in the
corresponding RF signals. In one of the sub-groups, a time delay is
introduced into the IF signals, which time delay is transferred to the
corresponding recovered RF signal. The delayed and non-delayed IF signals
are combined in a splitter/combiner, and the combined IF signal, comprising
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main and delayed diversity signals, is up-converted to a combined RF signal.
The combined RF signal is transmitted to a base transceiver station (BTS)
which demodulates and recovers the information contained in the
combined RF signal.
Thus, the single time delay introduced into the diversity signals
enables a typical code division multiple access (CDMA) rake receiver to
demodulate and recover the information contained in the combined main
and diversity signals. Unlike methods known in the art, the method of the
present invention enables an optimal signal to be recovered from main and
diversity signals generated within an enclosed region and received by
spatially independent transceivers.
In some preferred embodiments of the present invention, IF signals
are transferred to the first and second sub-groups of slave units, and a delay
is added to the IF signal transferred to one of the sub-groups. The IF signals
are up-converted to RF signals in the slave units, and the RF signals,
comprising delayed and non-delayed RF signals, are radiated from the units.
Each of the one or more mobile transceivers receive both signals. Because of
the time delay introduced into one of the signals, each of the mobile
transceivers receives both signals as a composite signal comprising
information contained in the first signal and in the second delayed signal.
Most preferably, the information is demodulated and recovered by each of
the mobile transceivers, wherein it is used in a separate or a combined
form" so resulting in an overall improvement in signal reception.
Preferably, the RF signals are direct spread spectrum modulated
signals, wherein each signal comprises a plurality of chips. It will be
appreciated that while some preferred embodiments of the present
invention use CDMA systems, other preferred embodiments of the present
invention use non-CDMA systems, such as GSM systems comprising
equalizers which are capable of tolerating certain signal delays.
There is therefore provided, in accordance with a preferred
embodiment of the present invention, a method for wireless
communication, including:
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positioning a first plurality of slave transceivers within a region
generally closed off to electromagnetic radiation from sources external to the
region;
positioning a second plurality of slave transceivers within the region
5 in positions spatially separated from and spatially independent of the
positions of the first plurality of slave transceiver;
receiving at the first plurality and at the second plurality a radio
frequency (RF) signal generated within the region and generating respective
first and second slave signals responsive thereto;
delaying the second slave signal;
conveying the first and delayed second slave signals to one or more
base transceiver stations (BTSs) outside the region; and
jointly processing the first and second slave signals conveyed to the
one or more BTSs so as to recover information contained in the RF signal
generated within the region.
Preferably, conveying the first and second slave signals includes
recovering a master RF signal from the first slave signal and recovering a
diversity RF signal from the second slave signal, and jointly processing the
first and second slave signals includes recovering an optimal RF signal from
the recovered master RF signal and the recovered diversity RF signal.
Preferably, positioning the second plurality of slave transceivers
includes positioning at least one of the second plurality of slave
transceivers
at a distance sufficiently separated from the first plurality of slave
transceivers so that the RF signal received by the second plurality of slave
transceivers is distinguishable from the RF signal received by the first
plurality of slave transceivers.
Preferably, delaying the second slave signal includes applying a single
time delay to the second slave signal.
There is further provided, in accordance with a preferred
embodiment of the present invention, apparatus for wireless
communication, including:
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a first plurality of slave transceivers and a second plurality of slave
transceivers, which first and second pluralities are spatially separated from
and spatially independent of one another within a region generally closed
off to electromagnetic radiation, and which first and second pluralities
receive a radio frequency (RF) signal generated within the region and
generate respective first and second slave signals responsive to the RF
signal;
a delay generator, coupled to delay the second slave signal relative to
the first slave signal; and
a master unit, which receives and converts the first signal and the
delayed second slave signal and conveys the respective first and second
converted. signals to one or more base transceiver stations (BTSs) outside the
region, such that information contained in the RF signal is recovered by
jointly processing the first and second converted signals received by the
BTSs.
Preferably, at least one of the first plurality of slave transceivers is
sufficiently spatially separated from the second plurality of slave
transceivers so that the RF signal received by the second plurality of slave
transceivers is distinguishable from the RF signal received by the first
plurality of slave transceivers.
Preferably, the delay generator delays the second slave signal by
applying a single time delay.
There is further provided, in accordance with a preferred
embodiment of the present invention, a method for wireless
communication within a region generally closed off to electromagnetic
radiation from sources external to the region, including:
receiving at a master transceiver unit a radio frequency (RF) signal
transmitted from outside the region and generating first and second master
signals responsive thereto;
positioning a first plurality of slave transceivers within the region;
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positioning a second plurality of slave transceivers within the region
in positions spatially separated from the positions of the first plurality of
slave transceivers;
conveying the first master signal to the first plurality of slave
transceivers and generating a first slave signal responsive thereto;
delaying the second master signal;
conveying the delayed second master signal to the second plurality of
slave transceivers and generating a second slave signal responsive thereto;
conveying the first and second slave signals to a mobile transceiver
unit within the region; and
jointly processing the first and second slave signals conveyed to the
mobile transceiver so as to recover information contained in the RF signal
therein.
Preferably, positioning the second plurality of slave transceivers
includes placing the second plurality of slave transceivers in positions that
are spatially independent of the positions of the first plurality of slave
transceivers.
There is further provided, in accordance with a preferred
embodiment of the present invention, apparatus for wireless
communication, including:
a master unit, which receives a radio frequency (RF) signal generated
outside a region generally closed off to electromagnetic radiation, and which
converts the RF signal to a first and a second master signal;
a delay generator, coupled to delay the second master signal relative to
the first master signal; and
a first plurality of slave transceivers and a second plurality of slave
transceivers, which first and second pluralities are spatially separated from
one another within the region, and which first and second pluralities:
respectively receive and convert the first and the delayed second
master signals to a first and a second converted signal, and
respecfiively convey the first and the second converted signal to a
mobile transceiver unit within the region, such that information contained
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in the RF signal is recovered by jointly processing the first and the second
converted signals received by the mobile transceiver unit.
Preferably, the first and second pluralities of slave transceivers are
spatially independent of one another.
The present invention will be more fully understood from the
following detailed description of the preferred embodiments thereof, taken
together with the drawing, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 2 is a schematic block diagram showing an in-building coverage
system, according to a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is now made to Fig. 1, which is a schematic block diagram
showing an in-building coverage system 10, according to a preferred
embodiment of the present invention. A building 30 is substantially closed
off to electromagnetic radiation from a base transceiver station (BTS) 12
external to the building. A mobile transceiver 36 within the building, such
as an industry-standard mobile telephone, emits a radio frequency (RF)
signal of a type which is receivable by BTS 12. Preferably, the RF signal
emitted by mobile transceiver 36, herein also termed the mobile RF
transmitted signal, is a code division multiple access (CDMA) signal
operating at an industry-standard chip rate, although the principles of the
present invention are also applicable to other coding and transmission
schemes.
A first sub-group of slave transceivers 26, herein also termed main
slave transceivers, and a second sub-group of slave transceivers 28, herein
also termed diversity slave transceivers, are positioned within building 30.
Main slave transceivers 26 are most preferably connected in a star
configuration, by one or more active splitter/combiners 39. Alternatively,
slave transceivers 26 are connected in a daisy chain or a hybrid star-daisy
chain configuration. Similarly, diversity slave transceivers 28 are most
preferably connected in a star configuration, by one or more active
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splitter/combiners 43. Alternatively, slave transceivers 28 are connected in a
daisy chain or a hybrid star-daisy chain configuration.
Slave transceivers 26 are separated spatially from slave transceivers
28, but otherwise the slave transceivers are all substantially similar in
construction and operation. A detailed description of the operation and
construction of suitable slave transceivers is given in a U.S. Patent
Application entitled "In-Building Radio Frequency Coverage," filed 29
October, 1999 , which is assigned to the assignee of the present application
and whose disclosure is incorporated herein by reference. The spatial
separation is sufficient so that when transceiver 36 makes a transmission the
RF signal received by the sub-group of slave transceivers 26 is
distinguishable from the RF signal received by the sub-group of slave
transceivers 28; for example, the received signals may differ in amplitude, or
in phase, or in time of arrival, or in a combination of these or other signal
parameters. Thus, main slave transceivers 26 receive the RF signal from
mobile transceiver 36 as a,main RF signal, and diversity slave transceivers
28 receive the RF signal from transceiver 36 as a diversity RF signal. Apart
from being separated. spatially as described hereinabove, main slave
transceivers 26 are spatially independent of diversity slave transceivers 28,
so that there is no relationship between the positioning of the main slave
transceivers and the diversity slave transceivers.
Slave transceivers 26 and 28 operate by mixing the received RF signal
with a local oscillator signal, thus down-converting the received RF signal to
an intermediate frequency (IF) signal, as is known in the art. The IF signals
from main slave transceivers 26 are transmitted from building 30, via one of
the splitter/combiners 39 and a cable 21, to a combiner 27. The IF signals
from diversity slave transceivers 28 are transmitted from building 30, via
one of the splitter/combiners 43 and a cable 23. In the course of cable 23
there
is a delay unit 24, most preferably formed from a surface acoustic wave filter
acting as a delay generator. Alternatively, delay unit 24 may comprise any
standard delay unit which is able to add a single time delay to the IF signals
transmitted from diversity slave transceivers 28. Most preferably, the delay
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added by delay unit 24 is of the order of at least twice the chip period of
the
modulated RF signal transmitted by transceiver 36.
Combiner 27 combines the IF signals from main slave transceivers 26
and the delayed IF signals from diversity slave transceivers 28. The
5 combined IF signals are transferred to an up-converter 29 in a master
transceiver unit 22. In up-converter 29 the combined IF signals are mixed
with a local oscillator (LO) signal, generated by a local oscillator 31 most
preferably comprised in master unit 22, in order to recover as a combined RF
signal the RF signals received by main slave transceivers 26 and diversity
10 slave transceivers 28. A detailed description of the operation and
construction of a suitable master transceiver unit is given in the above-
mentioned U.S. Patent Application.
The combined RF signal is then transmitted, via a duplexer 14, to BTS
12. Preferably BTS 12 is coupled by a direct cable connection 4~ to master
unit
22. Alternatively, cable connection 47 comprises a transmit and/or a receive
cable coupling BTS 12 to master unit 22 without utilizing duplexer 14.
Further alternatively, BTS 12 and master unit 22 are coupled by a wireless
connection. In some preferred embodiments of the present invention, BTS
12 comprises master unit 22, thereby saving component costs.
BTS 12 thus receives a composite signal containing a first component
that represents a main signal and a second component that represents a
delayed diversity signal. It will be appreciated that information comprised in
the composite signal can be demodulated and recovered in an industry-
standard CDMA rake receiver.
Duplexer 14 also receives a transmitted RF signal from BTS 12, herein
also termed the BTS RF transmitted signal, and transfers the signal to a
down-converter 33 comprised in master unit 22. Down-converter 33
preferably utilizes the signal from local oscillator 31 to produce an IF
transmitted signal. The IF transmitted signal is transferred to a splitter 35,
which splitter divides the transmitted IF signal into a first and a second
substantially similar IF signal. The first IF signal is transferred to active
splitter 39 and then from the splitter to transceivers 26, wherein the BTS RF
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transmitted signal is recovered by up-conversion. Methods for down-
conversion and up-conversion of a transmitted RF signal from a BTS as
described hereinabove are known in the art, and a detailed description of
one such method is also given in the above-mentioned U.S. Patent
Application.
The second IF signal is transferred via a cable 41 to active splitter 43. In
the course of cable 41 there is a delay unit 45, most preferably implemented
as described above for delay unit 24. Delay unit 45 most preferably generates
a delay of the same order of magnitude as that generated by delay unit 24.
The delayed IF signal is transferred from active splitter 43 to slave
transceivers 28, wherein a delayed BTS RF transmitted signal is recovered by
up-conversion.
Mobile transceiver 36 receives both the recovered BTS RF signal
transmitted from transceivers 26 and the recovered delayed BTS RF signal
transmitted from transceivers 28. The BTS RF signal and the delayed BTS RF
signal are then utilized to derive an optimal RF signal transmitted from BTS
12, using methods known in the art. For example, if the RF signal is a
CDMA pilot RF signal, generated by the BTS for traeking mobile
transceivers, mobile transceiver 36 is able to demodulate and recover the
pilot signals by identifying strong multipath arrivals with a searcher
comprised in the transceiver: Alternatively, optimal signals can be
recovered by non-CDMA systems which are able to tolerate delays of the size
described hereinabove.
It will be appreciated that the preferred embodiments described above
are cited by way of example, and that the present invention is not limited to
what has been particularly shown and described hereinabove. Rather, the
scope of the present invention includes both combinations and
subcombinations of the various features described hereinabove, as well as
variations and modifications thereof which would occur to persons skilled
in the art upon reading the foregoing description and which are not
disclosed in the prior art.
WE CLAIM:
