COVERAGE OF RADIO FREQUENCY OF REGIONS CLOSED
FIELD OF THE INVENTION The present invention relates generally to wireless communications, and spatially to wireless communications from within a region generally closed to electromagnetic radiation.
BACKGROUND OF THE INVENTION In the cellular communications system, typically there are regions where coverage is difficult or incomplete, for example, within metallic frame structures, and underground. Methods for improving coverage in regions such as this are known in the art. The North American Patent No. 5,404,570, for Charas et al, the disclosure of which is incorporated herein by reference, describes a repeater system used between a base transceiver station (BTS), which is capable of receiving signals and a closed environment such as a tunnel, which is closes the BTS transmissions. The system down-converts a high-frequency (RF) radio signal from the BTS to an intermediate frequency (IF) signal, which is then radiated by a cable and an antenna in the closed environment in a
receiver in it. The receiver up-converts the IF signal into the original RF signal. The systems described in the description include a vehicle moving in a tunnel, so that passengers in the vehicle who can otherwise be separated from the BTS are able to receive signals. U.S. Patent No. 5,603,080 to Kallandar et al., The disclosure of which is incorporated herein by reference, discloses a plurality of repeater systems used between a plurality of BTSs and a closed environment, which is closed to the transmissions of the BTs. . Each system down-converts an RF signal from its respective BTS of an IF signal, which is then transferred by a cable to the closed environment to one or more respective receivers therein. Each receiver up-converts the IF signal into the original RF signal. The systems described in the description include a vehicle moving between overlapping regions in a tunnel, each region covered by one of the BTS by means of its repeater system. In this way, passengers in the vehicle who may otherwise be separated from one or more of the BTS are able to receive signals from at least one of the BTS through the
tunnel. U.S. Patent No. 5,765,099 to Georges et al. , the disclosure of which is incorporated herein by reference, describes a system and method for transferring an RF signal between two or more regions using a medium of low bandwidth such as a twisted pair cable. In a first region, the RF signal is mixed with a first local oscillator to produce a downwardly converted IF signal. The IF signal is transferred to a second region by the medium of low bandwidth, where the signal is converted upwardly to the original RF signal using a second local oscillator. The local oscillators are each synchronized by a phase-locked loop (PLL) in each region to generate the same frequency, the synchronization that is performed in each loop when comparing the local oscillator frequency with a stable low-frequency reference signal simple generated in a region. The reference signal is transferred between the regions by means of low bandwidth. U.S. Patent No. 5,513,176, to Dean et al., The disclosure of which is incorporated herein by reference, discloses an array of antennas distributed within a region where reception is difficult. The performance of the antenna array is
improves by generating the diversity of signals within the layout. Each antenna in the arrangement has a differential time delay applied to the signals it receives, thereby generating diversity of received signals. The differentially delayed signals are preferably converted downwardly at an intermediate frequency and then transferred out of the region by a cable. The North American Patent? 5, 930,293, for Light, et al., The disclosure of which is incorporated herein by reference, discloses a wireless repeater comprising first and second spatially separated antennas, both antennas receiving a signal from one transmitter, and the signal received by the second antenna it has a time delay added to the original signal. The two signals are summed to form a joint signal, which is transmitted from a third antenna. A receiver of the joint signal is able to reconstruct the signals received by the first and second antennas.
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 fixed transceivers, in the present so-called slave units, is installed within a region that is generally closed to electromagnetic radiation from outside the region such as the interior of a building. The slave units receive a radio frequency (RF) signal from at least one mobile transceiver, such as a mobile cellular phone, in the region. The group of slave units are divided into a first and a second subgroup, which generally has equal numbers of fixed transceivers in each subgroup. The slave units of the first subgroup are spatially separated from the slave units of the second subgroup. Apart from spatially separating, the transceivers in the first subgroup are positioned independently of the transceivers in the second subgroup. The spatial separation is more preferably at least enough so that a signal received by the first subgroup and a signal received by the second subgroup of a transmission from at least one of the mobile transceivers can be distinguished. The signals can typically be distinguished in terms of amplitude, c phase, c time of arrival, or a combination
of these or other signal parameters. In this way, the slave units of one of the pluralities can function as diversity receivers with respect to the slave units of the other subgroup, which function as main receivers. The RF signals received by the slave units of at least one of the mobile transceivers are downconverted to intermediate frequency (IF) signals which are then transferred from the region by one or more cables. The IF signals of each subgroup of slave units are transferred to a master unit, which up-converts the IF signals in order to recover the information contained in the corresponding RF signals. In one of the subgroups, a time delay is introduced into the IF signals, whose 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 the main and delayed diversity signals, is converted upwardly into a combined RF signal. The combined RF signal is transmitted to a base transceiver station ÍBTS) which demodulates and recovers the information contained in the combined RF signal. In this way, the only time delay
introduced into the diversity signals allows a typical code division (CDMA) multiple access tilt receiver to demodulate and retrieve the information contained in the combined principal and diversity signals. Unlike methods known in the art, the method of the present invention allows an optimal signal to be recovered from the principal and diversity signals generated within a region enclosed and received by the spatially independent transceivers. In some preferred embodiments of the present invention, the IF signals are transferred to the first and second subgroups of the slave units, and a delay is added to the IF signal transferred to one of the subgroups. The IF signals are converted upwardly into RF signals on the slave units, and the RF signals, comprising the delayed and non-delayed RF signals, are radiated from the units. Each one or more of the mobile transceivers receive both signals. Due to the time delay introduced in one of the signals, each of the mobile transceivers receives the signals as a composite signal comprising information contained in the first signal and in the second delayed signal. More preferably, the information is demodulated and recovered by each of the transceivers
mobile, where it is used in a separate form, or combined, which results in a general improvement in signal reception. Preferably, the RF signals are modulated signals of direct propagated spectrum, wherein each signal comprises a plurality of fragments. It will be appreciated that while some preferred embodiments of the present invention utilize CDMA systems, other preferred embodiments of the present invention utilize systems without CDMA, such as GSM systems comprising equalizers that are capable of tolerating certain signal delays. Therefore, there is provided, in accordance with a preferred embodiment of the present invention, a method for wireless communication including: positioning a first plurality of slave transceivers within a region generally closed to electromagnetic radiation from sources external to the region; positioning a second plurality of slave transceivers within the region at spatially separated and spatially independent positions of the positions of the first plurality of slave transceivers; receive in the first plurality and in the
second plurality a radio frequency (RF) signal generated within the region and generate first and second respective slave signals responsive to it. Delay the second slave signal; transporting the first and second delayed slave signals to one or more base transceiver stations (BTS) outside the region; and jointly processing the first and second slave signals carried in one or more of the BTS to recover the information contained in the RF signal generated within the region. Preferably, the transport of the first and second slave signals includes recovering a master RF signal from the first slave signal and recovering a plurality of RF signals from the second slave signal, and jointly processing the first and second slave signals including recovering a signal Optimal RF-the master RF signal recovered, and the diversity RF signal recovered. Preferably, the positioning of 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
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second plurality of slave transceivers can be distinguished from the RF signal received by the first plurality of slave transceivers. Preferably, the delay of the second slave signal includes applying a single time delay to the second slave signal. Furthermore, according to a preferred embodiment of the present invention, apparatuses for wireless communication include: a first plurality of slave transceivers and a second plurality of slave transceivers, whose first and second pluralities are spatially separated and spatially independent of each other within of a region generally closed to electromagnetic radiation, and whose first and second pluralities receive a radio frequency (RF) signal generated within the region and generates first and second respective slave signals responsive to the RF signal; a delay generator, coupled to delay the second slave signal in relation to the first slave signal; and a master unit that receives and converts the first signal and the second delayed slave signal and transports the first and second respective converted signals to one or more base transceiver stations
(BTS) outside the region, so that that information contained in the RF signal is recovered by jointly processing the first and second converted signals received by the BTS. 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 can be distinguished from the received RF signal 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 to electromagnetic radiation from sources external to the region, including: receiving in a master transceiver unit a signal from radio frequency (RF) transmitted from outside the region and generate the first and second signals I love sensitive to it; positioning a first plurality of slave transceivers within the region;
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positioning a second plurality of slave transceivers within the region at spatially separated positions of the positions of the first plurality of slave transceivers; transporting the first master signal to the first plurality of slave transceivers and generating a first slave signal responsive to it; delay the second master signal; transporting the second master signal delayed in the second plurality of slave transceivers and generating a second slave signal responsive to it; transporting the first and second slave signals to a mobile transceiver unit within the region; and jointly processing the first and second slave signals transported in the mobile transceiver to recover the 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. It is also provided, according to 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 to electromagnetic radiation, and which converts the RF signal into a first and 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, whose first and second pluralities are spatially separated from each other within the region, and whose first and second pluralities: respectively receive and convert the first and second signals delayed in a first and second converted signal, and respectively transporting the first and second signals converted to a mobile transceiver unit within the region, so that that information contained in the RF signal is recovered by processing together the first and second converted signals received by the mobile transceiver unit. Preferably, the first and second
The pluralities of the slave transceivers are spatially independent of each other. The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof taken together with the drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic block diagram showing a. integrated cover system, according to a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Reference is now made to Figure 1, which is a schematic block diagram showing an integrated coverage system 10, according to a preferred embodiment of the present invention. A building 30 is substantially enclosed in Electromagnetic radiation from a base transceiver station 12
(BTS) external to the building. A mobile transceiver 36 within the building, such as an industry-standard mobile phone, emits a radio frequency (RF) signal of a type that can be received by the BTS 12. Preferably, the RF signal transmitted by the mobile transceiver 36 ,
also referred to herein as the mobile RF transmitted signal is a code division multiple access (CDMA) signal operating at a rate of industry standard fragments, although the principles of the present invention can also be applied to other schemes of coding and transmission. A first subgroup of slave transceivers 26, also referred to herein as main slave transceivers, and a second subgroup of slave transceivers 28, also referred to in the present diversity slave transceivers, are positioned within building 30. The. 26 main slave transceivers are mostly connected in a star configuration, by one or more active splitters / combiners. Alternatively, the slave transceivers 26 are connected in a daisy chain or a daisy-star hybrid chain configuration. Imirably, the diversity slave transceivers 28 are most preferably connected in a star-like configuration, by one or more active splitters / combiners 43. Alternatively, the slave transceivers 28 are connected in a daisy chain or in a hybrid daisy-star tipc chain configuration. The slave transceivers 26 are separated
spatially of the slave transceivers, but otherwise the slave transceivers are substantially similar in construction and operation. A detailed description of the operation and construction of the appropriate slave transceivers is given in a North American Patent Application entitled "In-Building Radio Frequency Coverage", filed on October 29, 1999, which is assigned to the assignee of the present application and whose description is incorporated herein by reference. The spatial separation is sufficient so that when the transceiver 36 makes a transmission of the RF signal received by the subgroup of the slave transceivers 26 it can be distinguished from the RF signal received by the subgroup of the 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. In this way, the main slave transceivers 26 receive the RF signal from the mobile transceiver 36 as a main RF signal, and the diversity slave transceivers 28 receive the RF signal from the transceiver 36 as a diversity RF signal. Apart from spatially separating as described above, the main slave transceivers 26 are spatially
independent of the diversity slave transceivers 28, so that there is no relationship between the positioning of the main slave transceivers and the diversity slave transceivers. The slave transceivers 26 and 28 operate by mixing the received RF signal with a local oscillator signal, thereby downwardly converting the received RF signal into an intermediate frequency (IF) signal, as is known in the art. The IF signals of the main slave transceivers 26 are transmitted from the building 30, by one of the splitters / combiners 39 and a cable 21, to a combiner 27. The IF signals of the diversity slave transceivers 28 are transmitted from the building 30, by means of one of the dividers / combiners 43 and a cable 23. In the course of the cable 23 there is a delay unit 24, more preferably formed of a surface acoustic wave filter, which acts as a delay generator. Alternatively, the delay unit 24 may comprise any standard delay unit that is capable of adding a single time delay to the IF signals transmitted from the diversity slave transceivers. More preferably, the delay added to the delay unit 24 is of the order of at least twice the period
of fragments of the modulated RF signal transmitted by the transceiver 36. The combiner 27 combines the IF signals of the main slave transceivers 26 and the delayed IF signals of the diversity slave transceivers. The combined IF signals are transferred to an upstream converter 29 in a master transceiver unit 22. In the upconverter 29, the combined IF signals are mixed with a local oscillator (LO) signal, generated by a local oscillator 31 most preferably comprised in the master unit 22, to be able to recover as a combined RF signal, the RF signals received by the main slave transceivers 26 and the diversity slave transceivers. A detailed description of the operation and construction of a suitable master transceiver unit is given in the aforementioned US patent application. The combined RF signal is then transmitted, via a duplexer 14, to the BTS 12. Preferably, the BTS 12 is coupled by a direct cable connection 47 to the master unit 22. Alternatively, the cable connection 47 comprises a BTS 12 which cable-fits the transmission and / or reception to the master unit 22 without using the duplexer 14. In addition, alternatively, the BTS
12 and the master unit 22 are coupled by a wireless connection. In some preferred embodiments of the present invention, the BTS 12 comprises the master unit 22, thereby saving component costs. The BTS 12 thus receives a composite signal containing a first component representing a main signal and a second component representing a delayed diversity signal. It will be appreciated that the information comprised in the composite signal can be demodulated and retrieved at an industry-standard CDMA tilt receiver. The duplexer 14 also receives an RF signal transmitted from the BT? 12, herein also called BTS RF transmitted signal, and transfers the signal to a down converter 33 comprised in the master unit 22. The down converter 33 preferably uses the signal from the local oscillator 31 to produce an IF transmitted signal. The transmitted IF signal is transferred to a divider 35, which divider divides the transmitted IF signal into first and second substantially similar IF signals. The first IF signal is transferred to the active splitter 39 and then from the splitter to the transceivers 26, where the transmitted BTS RF signal is recovered by the upconversion. Methods for top-down conversion and
Upconversion of an RF signal transmitted from a BTS as described above is known in the art, and a detailed description of a method is also given in the aforementioned US Patent Application. The second IF signal is transferred via a cable 41 to the active divider 43. In the course of cable 41 there is a delay unit 45, most preferably implemented as described above for the delay unit 24. The preference delay unit 45 generates a delay of the same order of magnitude as that generated by the delay unit 24. The delayed IF signal is transferred from an active splitter 43 to the slave transceivers 28, where a delayed BTS RF transmitted signal is recovered by the upconversion. The mobile transceiver 36 receives the recovered BTS RF signal transmitted from the transceivers 26 and the delayed BTS RF signal transmitted from the transceivers 28. The RF signal from the BTS and the delayed BTS RF signal is then used to derive an optimal RF signal transmitted from the BTS 12, using methods known in the art. For example, if the RF signal is a CDMA pilot RF signal, generated by the BTS to track the mobile acceptors,
the mobile transceiver 36 is capable of demodulating and recovering pilot signals by identifying strong multiple path arrivals with a finder comprised in the transceiver: alternatively, optimal signals can be recovered by non-CDMA systems that are capable of tolerating delays of the described size in the above. It will be appreciated that the preferred embodiments described in the foregoing are cited by way of example, and that the present invention is not limited to what has been particularly shown and described in the foregoing. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described in the foregoing, as well as variations and modifications thereof that may be presented to persons skilled in the art upon reading the above description and which are not described in the prior art.