RADIO FREQUENCY COVERAGE OF ENCLOSED REGIONS

Abstract: A method for wireless communication, including positioning a first plurality of slave transceivers (26) within a region generally closed off to electromagnetic radiation from sources external to the region, and positioning a second plurality of slave transceivers (28) within the region in position spatially separated from and spatially independent of the positions of the first plurality of slave transceivers (26). The method further includes receiving at the first and second plurality of slave transceivers (26, 28) 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.

Description: 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 radiated 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 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 in 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. 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 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: 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 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: 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; 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 respectively convey the first and the second converted signal to a mobile transceiver unit within the region, such that information contained 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. 1 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 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 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 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 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 47 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 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 tracking 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:

Claims: CLAIMS 1. A method for wireless communication, comprising: 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 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. 2. The method according to claim 1, wherein conveying the first and second slave signals comprises recovering a master RF signal from the first slave signal and recovering a diversity RF signal from the second slave signal, and wherein jointly processing the first and second slave signals comprises recovering an optimal RF signal from the recovered master RF signal and the recovered diversity RF signal. 3. The method according to claim 1, wherein positioning the second plurality of slave transceivers comprises 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. 4. The method according to claim 1, wherein delaying the second slave signal comprises applying a single time delay to the second slave signal. 5. Apparatus for wireless communication, comprising: 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. 6. The apparatus according to claim 5, wherein 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. 7. The apparatus according to claim 5, wherein the delay generator delays the second slave signal by applying a single time delay. 8. A method for wireless communication within a region generally closed off to electromagnetic radiation from sources external to the region, comprising: 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; 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. 9. The method according to claim 8, wherein positioning the second plurality of slave transceivers comprises placing the second plurality of slave transceivers in positions that are spatially independent of the positions of the first plurality of slave transceivers. 10. Apparatus for wireless communication, comprising: 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 respectively convey the first and the second converted signal to a mobile transceiver unit within the region, such that information contained in the RF signal is recovered by jointly processing the first and the second converted signals received by the mobile transceiver unit. 11. The apparatus according to claim 10, wherein the first and second pluralities of slave transceivers are spatially independent of one another.

Inventors: WEISSMAN HAIM, WEISSMAN, HAIM
Applicants: QUALCOMM INC, QUALCOMM INCORPORATED
Application year: 2001
Main classification: H04Q7
IPC codes: H04B7, H04J13, H04W88