CN1426664A - Radio frequency coverage of enclosed regions - Google Patents

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

RF Coverage in Enclosed Areas

field of invention

The present invention relates generally to wireless communication, and more particularly to wireless communication in an area generally isolated from electromagnetic radiation.

Background of the invention

In a cellular communication system, there are generally some areas where signals are difficult or incomplete to cover, for example, buildings with metal frames and underground. Several methods are known in the art for improving coverage in these areas.

US Patent No. 5,404,570 to Charas et al., the disclosure of which is incorporated herein by reference, describes a receiver base station (BTS) capable of receiving signals and an enclosed environment such as a tunnel which isolates signals transmitted by a base transceiver station. The system downconverts a high-frequency radio frequency (RF) signal from a BTS to an intermediate frequency (IF) signal, which is then radiated in an enclosed environment through a cable and antenna to a receiver in an enclosed environment. The receiver then upconverts the IF signal to the original RF signal. The system described in the patent disclosure includes a vehicle moving in a tunnel so that occupants in the vehicle who are otherwise cut off from communication with the BTS can receive the signal.

US Patent No. 5,603,080 to Kallandar et al., the disclosure of which is incorporated herein by reference, describes multiple relay systems used between multiple BTSs and an enclosed environment from signals transmitted by its corresponding BTS. Each system downconverts the RF signal from its respective BTS to an IF signal, which is then transmitted by cables in the enclosure to one or more corresponding respective receivers in the enclosure. Each receiver upconverts the IF signal to the original RF signal. The system described in the patent disclosure includes vehicles moving between overlapping areas of tunnels, each area being covered by a BTS through its relay system. In this way, occupants of a vehicle who are otherwise cut off from communication from one or more BTSs are able to receive signals from at least one BTS leading to the tunnel.

US Patent No. 5,765,099 to Georges et al. describes a system and method for transmitting RF signals between two or more regions employing a low bandwidth medium such as a twisted pair cable. Its disclosure is cited here. In the first region, the RF signal is mixed with a first local oscillator to produce a down-converted IF signal. This IF signal is transmitted over a low-bandwidth medium to a second area, where a second local oscillator is used to upconvert the signal to the original RF signal. Each local oscillator is locked to produce the same frequency by a phase-locked loop (PLL) in each zone. This lock is determined by comparing the local oscillator frequency with a single low-frequency stable reference signal generated in one zone. implemented in each loop. Reference signals are transmitted across low-bandwidth media between regions.

US Patent No. 5,513,176 to Dean et al., the disclosure of which is incorporated herein by reference, describes a distributed antenna array in areas where reception is difficult. Through the signal diversity generated in the antenna array. The receiving performance of this antenna array is enhanced. Each antenna in the antenna array has a different time delay applied to the signal it receives, thus creating diversity in the received signal. Preferably, the differently delayed signals are down-converted to an IF signal, which is then transmitted out of the area via a cable.

US Patent No. 5,930,293 to Light et al., the disclosure of which is incorporated herein by reference, describes a wireless repeater including first and second spatially independent antennas. Both antennas receive the signal from one transmitter, and the signal received by the second antenna has a time delay added to the original signal. The two signals are added to form an aggregate signal, which is transmitted from the third antenna. A receiver receiving the aggregated signal is able to reproduce the signal 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 radio frequency signals in areas generally isolated from electromagnetic radiation.

In a preferred embodiment of the invention, a set of fixed transceivers (herein referred to as slave units) is installed in an area generally isolated from electromagnetic radiation outside the area, such as inside a building. The slave unit receives radio frequency (RF) signals from at least one mobile transceiver, such as a mobile cellular telephone, in the area. The set of slave units is divided into first and second subgroups, each subgroup generally having approximately the same number of fixed transceivers.

The slave units of the first subset and the slave units of the second subset are spatially separated. In addition to being spatially separated, the transceivers in the first subset are positioned independently of the transceivers in the second subset. Preferably the spatial separation is at least sufficient to allow the first subset of received signals to be distinguished from the second subset of received signals from a single transmission by at least one mobile transceiver. These signals are generally distinguishable in terms of amplitude, phase, time of arrival, or a combination of these and other signal parameters. In this way, a slave unit of one of a plurality of sets of slave units can operate as a diversity receiver with respect to other subgroups of slave units acting as primary receivers.

RF signals received by the slave unit from at least one mobile transceiver are downconverted to intermediate frequency (IF) signals, which are then transmitted over one or more cables. The IF signal from each subgroup of slave units is transmitted to the master unit which upconverts the IF signal to reproduce the information contained in the corresponding RF signal. In one of the subgroups, a time delay is introduced to the IF signal, which is transmitted to the corresponding reproduced RF signal. The delayed and undelayed IF signals are combined in a splitter/combiner, and the combined IF signal (comprising the main and delayed diversity signals) is upconverted to a combined RF signal. The combined RF signal is transmitted to a base transceiver station (BTS), which demodulates and reproduces the information contained in the combined RF signal.

Thus, the single time delay introduced into the diversity signal enables a typical code division multiple access (CDMA) rake receiver to demodulate and reproduce the information contained in the combined main and diversity signals. Unlike existing methods in the art, the method of the present invention enables the reproduction of the main and diversity signals as optimal signals generated in an enclosed area and received by spatially independent transceivers.

In some preferred embodiments of the invention, the IF signals are transmitted to the first and second subgroups of slave units, and a time delay is added to the IF signal transmitted to one of the subgroups. The IF signal is upconverted to an RF signal in the slave unit and the RF signal, both delayed and undelayed, is radiated from the unit. Each of the one or more mobile transceivers receives both signals. Due to the time delay introduced in one of the signals, each mobile transceiver receives the two signals as a composite signal comprising the information contained in the first signal and the second signal. Even more preferably, each mobile transceiver demodulates and reproduces the information, where the information is used individually or in combination, thus resulting in an improvement in overall signal reception.

Preferably, the RF signals are direct spread spectrum modulated signals, wherein each signal comprises a plurality of chips. It should be understood that while some preferred embodiments of the invention use a CDMA system, other preferred embodiments of the invention use a non-CDMA system, such as a GSM system that includes an equalizer that can tolerate some signal delay.

Therefore, according to a preferred embodiment of the present invention, a method for wireless communication is provided, including:

placing the first plurality of slave transceivers in an area generally isolated from electromagnetic radiation from sources external to the area;

placing a second plurality of slave transceivers at locations in the region that are spatially separated from, and spatially independent from, locations of the first plurality of slave transceivers;

receiving radio frequency (RF) signals generated in the region at the first plurality and the second plurality, and generating corresponding first and second slave signals based on the RF signals;

Delaying the second slave signal;

transmitting the first and delayed second slave signals to one or more base transceiver stations (BTS) outside the area; and

The first and second slave signals transmitted to one or more BTSs are co-processed to reproduce information contained in RF signals generated in the area.

Preferably, transmitting the first and second slave signals includes reproducing the main RF signal from the first slave signal, and reproducing the diversity RF signal from the second slave signal, and jointly processing the first and second slave signals includes reproducing the main RF signal from the reproduced main RF signal. Diversity of the signal and the reproduced RF signal reproduces the optimum RF signal.

Preferably, placing the second plurality of slave transceivers includes placing at least one of the second plurality of slave transceivers sufficiently far apart from the first plurality of slave transceivers so that they can be distinguished from the first plurality of slave transceivers. The RF signal received by the transceiver and the RF signal received from the second plurality of slave transceivers.

Preferably, delaying the second slave signal comprises applying a single time delay to the second slave signal.

According to an embodiment of the present invention, a device for wireless communication is further provided, including:

A first plurality of slave transceivers and a second plurality of slave transceivers, the first and second pluralities being spatially separated from each other and spatially independent in an area generally isolated from electromagnetic radiation, the first and second a plurality of receiving radio frequency (RF) signals generated in the area, and generating corresponding first and second slave signals according to the RF signals;

a delay generator coupled to cause the second slave signal to be delayed relative to the first slave signal; and

a master unit that receives and converts the first signal and the delayed second slave signal, and transmits the corresponding first and second converted signals to one or more base transceiver stations (BTS) outside the area, such that The information contained in the RF signal can be reproduced by jointly processing the first and second converted signals received by the BTS.

Preferably, at least one of the first plurality of slave transceivers and the second plurality of slave transceivers are sufficiently spaced apart such that RF signals received from the first plurality of slave transceivers can be distinguished from signals received from the second plurality of slave transceivers. RF signal received by multiple slave transceivers.

Preferably, the delay generator delays the second slave signal by imposing a single time delay.

According to a preferred embodiment of the present invention, there is further provided a method for wireless communication in an area generally isolated from electromagnetic radiation from sources outside the area, comprising:

receiving a radio frequency (RF) signal transmitted from outside the area at the main transceiver unit, and generating corresponding first and second main signals according to the RF signal;

placing a first plurality of slave transceivers in the zone;

placing a second plurality of slave transceivers in the area at locations spatially separated from the locations of the first plurality of slave transceivers;

transmitting a first master signal to a first plurality of slave transceivers, and generating corresponding first slave signals based on the master signal;

delay the second main signal;

transmitting the delayed second master signal to a second plurality of slave transceivers, and generating a second slave signal based on said signal;

transmitting the first and second slave signals to mobile transceiver units within the area; and

The first and second slave signals transmitted to the mobile transceiver are co-processed to reproduce information contained therein in the RF signal within the region.

Preferably, positioning the second plurality of slave transceivers includes positioning the second plurality of slave transceivers at a location that is spatially independent from the location of the first plurality of slave transceivers.

According to a preferred embodiment of the present invention, a device for wireless communication is further provided, including:

a master unit that receives a radio frequency (RF) signal generated outside an area generally isolated from electromagnetic radiation and converts the RF signal into first and second master signals;

a delay generator coupled to cause the second main signal to be delayed relative to the first main signal; and

A first plurality of slave transceivers and a second plurality of slave transceivers, the first and second pluralities being spatially separated from each other in the area, and the first and second pluralities:

receiving and converting the first and delayed second main signals into first and second converted signals, respectively, and

The first and second converted signals are transmitted separately to mobile transceiver units in the area such that information contained in the RF signal can be reproduced by jointly processing the first and second converted signals received by the mobile transceiver units.

Preferably, the first and second plurality of slave transceivers are spatially independent of each other.

By following detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings, the present invention will be more completely understood, wherein:

Brief description of the drawings

Fig. 1 is a schematic block diagram showing an indoor coverage system according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a schematic block diagram of an indoor coverage system 10 according to a preferred embodiment of the present invention. Building 30 is substantially isolated from electromagnetic radiation from base transceiver stations (BTS) 12 outside it. A mobile transceiver 36 (eg, an industry standard mobile phone) within the building transmits a type of radio frequency (RF) signal that the BTS 12 can receive. Preferably, the RF signal transmitted by mobile transceiver 36 (also referred to herein as a mobile RF transmit signal) is a Code Division Multiple Access (CDMA) signal operating at an industry standard chip rate, although the principles of the present invention also Can be applied to other encoding and transmission schemes.

A first subgroup 26 of slave transceivers (also referred to herein as primary slave transceivers) and a second subgroup 28 of slave transceivers (herein referred to as diversity slave transceivers) are placed within building 30 . The master slave transceivers 26 are preferably connected in a star configuration through one or more active splitter/combiners 39 . Optionally, slave transceivers 26 are connected in a daisy-chain or hybrid star-daisy-chain configuration. Similarly, diversity slave transceivers 28 are preferably connected through one or more active splitter/combiners 43 in a star configuration. Optionally, slave transceivers 28 are connected in a daisy-chain or hybrid star-daisy-chain configuration.

Slave transceiver 26 is spatially separated from slave transceiver 28, but otherwise the slave transceivers are identical in structure and operation. A detailed description of the operation and construction of a suitable slave transceiver is given in U.S. Patent Application entitled "Indoor Equipment Coverage," filed October 29, 1999, which is assigned to the assignee of the present application , whose disclosure is cited here as a reference. The spatial separation is sufficient so that when transceiver 36 is transmitting, RF signals received by slave subgroup 26 can be distinguished from RF signals received by slave subgroup 28; for example, the received signal can be at Varies in amplitude, phase, time of arrival, or a combination of these and other signal parameters. Thus, the main slave transceiver 26 receives the RF signal from the mobile transceiver 36 as the master RF signal, and the diversity slave transceiver 28 receives the RF signal from the transceiver 36 as the diversity RF signal. In addition to being spatially separated as described herein, primary slave transceiver 26 and diversity slave transceiver 28 are spatially independent such that there is no certain relationship between the positioning of the primary slave transceiver and the diversity slave transceiver.

As is well known in the art, slave transceivers 26 and 28 operate by mixing the received RF signal with a local oscillator signal, thereby downconverting the received RF signal to an intermediate frequency (IF) signal. The IF signal from the master slave transceiver 26 is transmitted from the building 30 to the combiner 27 via a splitter/combiner 39 and cable 21 . The IF signal from the diversity slave transceiver 28 is transmitted from the building 30 via a splitter/combiner 43 and cable 23 . On the route of the cable 23 there is a delay unit 24, which is preferably made of a surface acoustic wave filter as delay generator. Alternatively, delay unit 24 may comprise any standard delay unit capable of adding a single time delay to the IF signal transmitted from diversity slave transmitter 28 . The time delay applied by delay unit 24 is preferably on the order of at least twice the chip period of the modulated RF signal transmitted by transceiver 36 .

Combiner 27 combines the IF signal from primary slave transceiver 26 and the delayed IF signal from diversity slave transceiver 28 . The combined IF signal is transmitted to an upconverter 29 in the main transceiver unit 22 . In the upconverter 29, the combined IF signal is mixed with a local oscillator (LO) signal generated by a local oscillator 31, preferably included in the master unit 22, for reproduction into the master slave transceiver 26 and Diversity slave transceiver 28 receives the combined RF signal. A detailed description of the operation and structure of a suitable main transceiver unit is given in the above-mentioned US patent application.

The combined RF signal is then sent to BTS 12 via duplexer 14 . Preferably the BTS 12 is connected to the main unit 22 via a direct cable connection 47 . Optionally, cable connection 47 includes transmit and/or receive cables connecting BTS 12 to master unit 22 that does not employ duplexer 14 . Further optionally, the BTS 12 and the main unit 22 are coupled via a wireless connection. In some preferred embodiments of the present invention, BTS 12 includes main unit 22, thus saving on component costs.

The BTS thus receives a composite signal comprising a first part representing the main signal and a second part representing the delayed diversity signal. It should be understood that the information contained in the composite signal can be demodulated and reproduced in an industry standard CDMA rake receiver.

The duplexer 14 also receives the transmit RF signal from the BTS 12 (also referred to herein as the BTS RF transmit signal) and transmits the signal to a down-converter 33 included in the main unit 22. Down converter 33 preferably uses the signal from local oscillator 31 to generate the IF transmit signal. The IF transmit signal is passed to a splitter 35 which splits the transmit IF signal into essentially similar first and second IF signals. The first IF signal is passed to active splitter 39 and from there to transceiver 26 where it is up-converted to reproduce the BTS RF transmit signal. The method of downconverting and upconverting the transmitted RF signal from the BTS described herein is known in the art, and a detailed description of such a method is also given in the above-mentioned US patent application.

The second IF signal is caused to be transmitted to the active splitter 43 via the cable 41 . In the course of the cable 41 there is a delay unit 45, which is preferably implemented like the delay unit 24 described above. The delay produced by delay unit 45 is preferably of the same order of magnitude as that produced by delay unit 24 . The delayed IF signal is transmitted from the active splitter 43 to the slave transceiver 28 where it is frequency up-converted to reproduce the delayed BTS RF transmit signal.

Mobile transceiver 36 receives both the reproduced BTS RF signal transmitted by slave transceiver 26 and the reproduced delayed BTS RF signal transmitted by slave transceiver 28. The BTSRF signal and the delayed BTS RF signal are then used to obtain the 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 transceiver, the mobile transceiver 36 can demodulate and reproduce the pilot by identifying strong multipath arrivals with a searcher included in the transceiver Signal. Alternatively, the best signal can be reproduced by a non-CDMA system capable of withstanding delays of the magnitudes mentioned here above.

It should be understood that the above preferred embodiments are cited by way of example and that the present invention is not limited to what has been particularly described and shown above. Rather, the scope of the present invention includes combinations and subcombinations of the above-described features, as well as changes and modifications of the features that are not disclosed in the prior art that can be made by those skilled in the art after reading the foregoing description. Revise.

Claims (11)

1. A method for wireless communication, comprising: locating the first plurality of slave transceivers in an area generally isolated from electromagnetic radiation from sources external to the area; placing a second plurality of slave transceivers at locations in the region that are spatially separated from and spatially independent from the locations of the first plurality of slave transceivers; receiving radio frequency (RF) signals generated in the region at the first plurality and the second plurality, and generating corresponding first and second slave signals; Delaying the second slave signal; transmitting the first and delayed second slave signals to one or more base transceiver stations (BTS) outside the area; and The first and second slave signals transmitted to one or more BTSs are co-processed to reproduce information contained in RF signals generated in the area. 2. The method of claim 1, wherein transmitting the first and second slave signals comprises reproducing a main RF signal from the first slave signal, and reproducing a diversity RF signal from the second slave signal, wherein jointly processing the second The first and second slave signals comprise the best RF signal reproduced from the reproduced main RF signal and the reproduced diversity RF signal. 3. The method of claim 1 , wherein placing the second plurality of slave transceivers comprises placing at least one of the second plurality of slave transceivers at a sufficient distance from the first plurality of slave transceivers , so that RF signals received by the first plurality of slave transceivers can be distinguished from RF signals received by the second plurality of slave transceivers. 4. The method of claim 1, wherein delaying the second slave signal comprises applying a single time delay to the second slave signal. 5. A device for wireless communication, comprising: A first plurality of slave transceivers and a second plurality of slave transceivers, the first and second pluralities being spatially separated and mutually independent in an area generally isolated from electromagnetic radiation, the first and second pluralities receiving a radio frequency (RF) signal generated in the area, and generating corresponding first and second subordinate signals according to the RF signal; a delay generator connected to delay the second slave signal relative to the first slave signal; and a master unit that receives and converts the first signal and the delayed second slave signal, and transmits the corresponding first and second converted signals to one or more base transceiver stations (BTS) outside the area such that via The first and second converted signals received by the BTS are jointly processed to reproduce the information contained in the RF signal. 6. The device of claim 5, wherein at least one of the first plurality of slave transceivers is placed sufficiently separated from the second plurality of slave transceivers so that the first plurality of slave transceivers can be distinguished from each other. The RF signal received by the slave transceiver and the RF signal received by the second plurality of slave transceivers. 7. The apparatus of claim 5, wherein the delay generator delays the second slave signal by imposing a single time delay. 8. A method for wireless communication in an area generally isolated from electromagnetic radiation from sources outside the area, comprising: receiving a radio frequency (RF) signal transmitted from outside the zone at the main transceiver unit and generating first and second main signals based on the RF signal; placing a first plurality of slave transceivers in the zone; placing a second plurality of slave transceivers in the area at locations spatially separated from the locations of the first plurality of slave transceivers; transmitting a first master signal to a first plurality of slave transceivers, and generating a first slave signal based on the master signal; delay the second main signal; transmitting the delayed second master signal to a second plurality of slave transceivers, and generating a second slave signal based on the master signal; transmitting the first and second slave signals to mobile transceiver units within the area; and The first and second slave signals transmitted to the mobile transceiver are co-processed to reproduce information contained in the RF signal within the area. 9. The method of claim 8, wherein positioning the second plurality of slave transceivers comprises positioning the second plurality of slave transceivers at locations that are spatially separate from the locations of the first plurality of slave transceivers. 10. A device for wireless communication, comprising: a master unit that receives a radio frequency (RF) signal generated outside an area generally isolated from electromagnetic radiation and converts the RF signal into first and second master signals; a delay generator coupled to delay the second main signal relative to the first main signal; and A first plurality of slave transceivers and a second plurality of slave transceivers, the first and second pluralities being spatially separated from each other in the area, and the first and second pluralities: receiving the first and delayed second main signals, respectively, and converting them into first and second converted signals, and The first and second converted signals are respectively transmitted to mobile transceiver units in the area such that information contained in the RF signal is reproduced by jointly processing the first and second converted signals received by the mobile transceiver units. 11. The device of claim 10, wherein the first and second plurality of slave transceivers are spatially independent of each other.