WIRELESS LOCAL LOOPS INCLUDING HORIZONTALLY POLARIZED ANTENNAS

Abstract: Wireless local loops include primarily non-vertically polarized antennas. Preferably, the wireless local loop includes horizontally polarized antennas. By using primarily non-vertically polarized antennas in the WLL, interference between cellular, satellite and/or other radiotelephone communications systems, which employ predominantly vertically polarized antennas, can be reduced and preferably minimized. Conventional cellular and satellite radiotelephone systems use vertically polarized transmissions due to the vertical nature of the orientation of the mobile antennas on vehicles and/or mobile radiotelephones. However, in a WLL, with its fixed wireless telecommunications, there is no need to use vertically oriented antennas. Accordingly, to reduce interference, antennas that are primarily non-vertically polarized are used.

Description: WIRELESS LOCAL LOOPS INCLUDING HORIZONTALLY POLARIZED ANTENNAS Field of the Invention This invention relates to telecommunications systems and methods, and more particularly to wireless local loops for telephone communications systems and methods. Background of the Invention Wireless Local Loops (WLL) are widely used in telecommunications systems. As is well known to those having skill in the art, a wireless local loop uses a radio to provide a telephone connection to or within a building such as a dwelling. In particular, in a telecommunications system, a dwelling is connected to a switching office via a local loop, then through a distribution node and a trunked cable that is connected to the switching office. Conventionally, the local loop is copper cable buried in the ground or carried on overhead pylons to the dwelling, and the trunked cable includes multiple copper pairs. WLL replaces the local loop section with a radio path rather than a copper cable. Accordingly, WLL replaces the connection from the distribution point to the dwelling with a radio path. All other parts of the network may be left unaffected. In a WLL, the distribution point is connected to a radio transmitter, referred to herein as a Radio Fixed Part (RFP), that includes an RFP antenna that is responsive to a switching office to wirelessly transmit telecommunications messages from the switching office and to wirelessly receive telecommunications messages for the switching office via the RFP antenna. A Wireless Fixed Access Unit (WFAU) including a WFAU antenna is conventionally mounted on the side of the dwelling and is connected to a telephone using a network interface and customer interface to wirelessly transmit telecommunications messages from the telephone to the RFP and to wirelessly receive telecommunications messages for the telephone from the RFP via the WFAU antenna. Accordingly, apart from the WFAU on the side of the dwelling, the telephone subscriber need not notice any difference between a wireless local loop and a conventional wired local loop. WLL is used in many telecommunications systems that do not already have conventional wired local loops. Moreover, for those telecommunications systems that already have wired local loops, WLL is being used by new operators to provide competition to an existing telephone company. The design and operation of WLL systems are well known to those having skill in the art, and need not be described further herein. See, for example, the textbook entitled "Introduction to Wireless Local Loop" by William Webb, Artech House, 1998; "Low-Tier Wireless Local Loop Radio Systems-Part 1 : Introduction", by Yu et al, IEEE Communications Magazine, March 1997, pp. 84-92; and "Low- Tier Wireless Local Loop Radio Systems-Part 2: Comparison of Systems", by Yu et al., IEEE Communications Magazine, March 1997, pp. 94-98. Also see U.S. Patents 5,475,735 to Williams et al. entitled "Method of Providing Wireless Local Loop Operation with Local Mobility for a Subscribed Unit"; 5,603,095 to Uola entitled "Radio System and a Subscriber Terminal for a Radio System"; 5,604,789 to Lerman entitled "Method and System for Providing a Digital Wireless Local Loop"; and Des. 386, 186 to Schnetzer et al. entitled "Wireless Local Loop Antenna ". The disclosures of these patents and other references are hereby incorporated herein in their entirety by reference. In general, WLLs do not employ separate radio technologies but rather use an existing radio technology in an existing radio frequency band. In fact, as described in the above-cited Webb textbook, at the beginning of 1997, there were some fifteen different types of technologies, and some technologies were supported by more than one manufacturer, resulting in about twenty-five different product offerings. These technologies include cordless technologies such as the Digital European Cordless Telephone (DECT), PHS which is a Japanese standard for use in the 1895-1918 MHz frequency band, and CT-2, which was developed in the United Kingdom as an alternative to analog cordless home phones. Cellular technologies may also be used, including analog cellular systems, such as Analog Mobile Phone System (AMPS) and the Total Access Communications Systems (TACS), and digital cellular systems including GSM, IS-95 and D-AMPS. Other proprietary technologies may also be used. Since WLL systems are present in the same geographic area as cellular, satellite and/or other wireless communications systems and generally use existing technologies, it may be difficult to avoid interference between the WLL telecommunications messages and existing cellular, satellite and/or other wireless communications messages. Interference may be reduced somewhat by intelligent frequency allocation of the WLL wireless transmissions. However, this frequency allocation may be difficult to perform in view of the many other wireless radiotelephone communications systems that already may be present. Moreover, the frequency allocation may need to be updated as additional cellular/satellite and/or other radiotelephone communications systems become operational or change. Accordingly, there continues to be a need for systems and methods for reducing interference between a WLL and other radiotelephone communications systems. Summary of the Invention It is therefore an object of the present invention to provide improved wireless local loop systems and methods. It is another object of the present invention to provide wireless local loop systems and methods that can reduce interference with cellular, satellite and/or other wireless telecommunications systems. These and other objects are provided, according to the present invention, by wireless local loops that include primarily non-vertically polarized antennas. Preferably, the wireless local loop includes horizontally polarized antennas. By using primarily non-vertically polarized antennas in the wireless local loop, interference between cellular, satellite and/or other radiotelephone communications systems, which employ predominantly vertically polarized antennas, can be reduced and preferably minimized. The invention stems from the realization that conventional cellular and satellite radiotelephone systems use vertically polarized transmissions due to the vertical nature of the orientation of the mobile antennas on vehicles and/or mobile radiotelephones. However, in a wireless local loop, with its fixed wireless telecommunications, there is no need to use vertically oriented antennas. Accordingly, to reduce interference, antennas that are primarily non-vertically polarized are used. Preferably, horizontally polarized antennas are used. More particularly, wireless local loops according to the present invention include a Radio Fixed Part (RFP) including an RFP antenna that is responsive to a switching office, to wirelessly transmit telecommunications messages from the switching office and to wirelessly receive telecommunications messages for the switching office via the RFP antenna. The wireless local loop also includes a Wireless Fixed Access Unit (WFAU) including a WFAU antenna that is responsive to a telephone, to wirelessly transmit telecommunications messages from the telephone to the RFP and to wirelessly receive telecommunications messages for the telephone from the RFP via the WFAU antenna. According to the invention, the RFP antenna and the WFAU antenna are primarily non-vertically polarized. Preferably, the RFP antenna is a horizontally polarized RFP antenna and the WFAU antenna is a horizontally polarized WFAU antenna. The RFP antenna may be fixedly mounted to a telephone pole or pylon in an orientation that provides primarily non-vertical polarization. Alternatively, the RFP antenna may be fixedly mounted to a cellular radiotelephone base station in an orientation that provides primarily non-vertical polarization. The WFAU antenna is fixedly mounted to a building such as a dwelling in an orientation that provides primarily non-vertical polarization. Wireless local loops according to the invention may also include a network interface and a customer interface that connect the WFAU to the telephone. The telecommunications messages may utilize cordless, cellular and/or other wireless technologies. Accordingly, primarily non-vertically polarized radio frequency telecommunications messages are transmitted between the RFP and the WFAU. Preferably, horizontally polarized radio frequency telecommunications messages are transmitted between the RFP and the WFAU. Cross-polarization interference with cellular, satellite and/or other radiotelephone communications system can thereby be reduced. Brief Description of the Drawings Figure 1 is a block diagram of telecommunications systems including first embodiments of WLL systems and methods according to the present invention. Figure 2 is a block diagram of telecommunications systems including second embodiments of WLL systems and methods according to the present invention. Figure 3 graphically illustrates typical response of a vertically polarized antenna to a vertically polarized wave and to a horizontally polarized wave. Detailed Description of Preferred Embodiments The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Referring now to Figure 1 , a telecommunications system including first embodiments of wireless local loop systems and methods according to the present invention will be described. As shown in Figure 1 , the telecommunications system includes a wired telephone system 102 and a wireless radiotelephone system 104. Wired telephone system 102 includes a switching office 106 that is connected to the Public Switched Telephone Network (PSTN) 108 and/or other networks 112, such as satellite or cellular radiotelephone communications networks. Trunked cables 114 connect the switching office 106 to a plurality of telephone poles or pylons 116. A wired local loop 118 connects selected ones of the pylons 116 to selected buildings such as dwellings 122. The wired local loop 118 connects to the dwelling via a network interface 124 and a customer interface 126 that may include a standard RJ-11 connector. A telephone 128 is connected to the customer interface 126. Although telephone 128 is illustrated as being a wired telephone, a mobile or cordless telephone may also be used. Still referring to Figure 1, a wireless local loop 130 is used to connect a trunked cable 114 to a second selected dwelling 122'. The wireless local loop 130 includes a Radio Fixed Part (RFP) 132 that includes an RFP antenna 134 that is responsive to the switching office 106 to wirelessly transmit telecommunications messages from the switching office 106 and to wirelessly receive telecommunications messages for the switching office 106. The WLL also includes a Wireless Fixed Access Unit (WFAU) 136 that includes a WFAU antenna 138 that is responsive to a telephone 128' to wirelessly transmit telecommunications messages 140 from the telephone 128' to the RFP 132, and to wirelessly receive telecommunications messages 140 for the telephone 128 from the RFP 132 via the WFAU antenna 138. It will be understood by those having skill in the art that although telephone 128' has been designated with a "prime (')" notation, from the customer perspective, it can operate in the same manner as a conventional telephone 128, and includes a conventional network interface 124 and customer interface 126 between the WFAU 136 and the telephone 128'. As with telephone 128, telephone 128' can be a wired or wireless telephone. According to the present invention, the RFP antenna 134 and the WFAU antenna 138 are primarily non-vertically polarized. By "primarily non-vertically polarized", it is meant that the antenna has a greater horizontally polarized component than a vertically polarized component. Accordingly, the term "primarily non- vertically polarized" includes linearly polarized antennas that have a greater horizontal linear polarization than vertical linear polarization, but excludes circularly polarized antennas that have equal vertical and horizontal polarization components. It will be understood that polarization refers to the direction of the electric (E) field vector. Vertical polarization refers to an E field vector that is perpendicular to the earth's surface and horizontal polarization refers to an E field vector parallel to the earth's surface. A primarily non-vertically polarized radio frequency telecommunications message may also be regarded as a radio frequency telecommunication message having an ellipticity that is less than 1, where ellipticity is defined as the ratio of the vertical and horizontal E field component. Preferably, the ellipticity is, or approaches 0. By using primarily non-vertically polarized radio frequency transmissions, the coupling between a vertically polarized antenna such as is commonly used for a mobile communications, for example in the Personal Communications System (PCS) band (1850 MHz- 1990 MHz) may be reduced to -15 dB or more, where cross- polarization refers to the difference in antenna gain to a vertical and horizontal illumination. Preferably, RFP antenna 134 and WFAU antenna 138 are a horizontally polarized RFP antenna 134 and a horizontally polarized WFAU antenna 138, so that the rejection of vertically polarized radio frequencies may be maximized. Accordingly, when a cellular radiotelephone system 104 including a Mobile Telephone Switching Office (MTSO) 142 and a plurality of base stations 144 and portable radiotelephones 146 and mobile radiotelephones 148 exist in the same geographic area as the WLL 130, the vertically polarized radiotelephone communications between the base stations 144, the portable radiotelephones 146 and the mobile radiotelephones 148 will preferably minimally interfere with the primarily non-vertically polarized WLL 130. Accordingly, improved performance in the WLL may be obtained and reduced interference in the existing radiotelephone system 104 may be obtained. Still referring to Figure 1, the RFP 132 is preferably fixedly mounted to a telephone pole or pylon 116 in an orientation that provides primarily non- vertical polarization. More preferably, as shown in Figure 1, the RFP antenna 134 is fixedly horizontally mounted to the telephone pole or pylon 116. Similarly, the WLL 136 is preferably fixedly mounted to the dwelling 122' in an orientation that provides primarily non- vertical polarization. More preferably, as shown in Figure 1, the WFAU antenna is preferably fixedly horizontally mounted to the dwelling 122'. It will also be understood by those having skill in the art that the telecommunication messages 140 may utilize cordless or cellular wireless technologies and/or other technologies, the details of which need not be described herein. Depending on the technology employed, the RFP 132 may also be referred to as a "fixed part", a "base station", or a "radio port". The WFAU may also be referred to as a "portable part", a "Cordless Terminal Adapter (CTA)", a "Fixed Access Unit (FAU)" or a "Wireless Access Fixed Unit (WAFU)". The WLL may also be referred to as a "Radio Local Loop (RLL)". Referring now to Figure 2, a telephone communications system including second embodiments of WLL systems and methods according to the invention will now be described. The embodiment of Figure 2 differs from that of Figure 1 in that the RFP 132' is mounted on a cellular radiotelephone base station 144' rather than being mounted on a telephone pole or pylon 116. When the RFP 132' and the RFP antenna 134' are mounted on a radiotelephone base stations 144', interference between the RFP antenna 134' and a monopole antenna 152 or a patch antenna 154 of the cellular radiotelephone communications system may be severe due to their close proximity. However, since the RFP antenna 134' according to the present invention is primarily non-vertically polarized, this interference can be reduced and preferably minimized. The other elements of Figure 2 are similar to Figure 1 and need not be described again. Figure 3 illustrates a typical radiation pattern of a patch antenna that may be used for the RFP antenna 132 and/or the WFAU antenna 138. As shown in Figure 3, the higher gain (outer loop) represents a vertically positioned antenna's response to a vertically polarized wave. The lower gain (inner loop) is a response to a horizontally polarized wave. The ratio of the outer loop to the inner loop indicates the cross- polarization of the antenna. As also shown in Figure 2, along the 5 degree azimuth, the cross-polarization is -28 dB, while along the 30 degree azimuth, the cross polarization is -15 dB. Accordingly, proper antenna selection, positioning and alignment to provide non- vertically polarized transmissions and preferably to provide horizontally polarized transmissions, can reduce and preferably minimize cross-polarization, thereby allowing a maximum rejection of an undesired signal. By using non-vertically polarized radio frequency transmissions, and preferably horizontally polarized radio frequency transmissions, radio links need not be degraded, while allowing a significant reduction in coupling to surrounding interferers and hence allowing reduction in the interference in the WLL system. Moreover, if the WLL system causes interference with other mobile communications systems, the cross-polarization reduction can reduce such interference as well. Reduction in interference may be particularly important for WLL systems which generally use existing radio frequency spectrum and technologies. For example, WLL may operate in the PCS frequency band of 1850 MHz-1990 MHz. As a late arrival, WLL may need to coexist with other, much more powerful wireless, cellular and/or PCS systems, often having to share the cellular base station tower. Accordingly, WLL RFPs and WFAUs may be radiated upon with high intensity uncoordinated RF power that can lead to a rise in interference and increase the probability of call blocking. By using primarily non-vertically polarized radio frequency transmissions, and more preferably horizontally polarized radio frequency telecommunications in the WLL, potential interference can be reduced and preferably minimized. It will be understood by those having skill in the art that the present invention may be used in combination with other interference-reducing techniques. For example, it is known to provide a Frequency Division Duplex (FDD) mode in a WLL, wherein the transmit frequency band is separated from the received frequency band, preferably by a large separation, to thereby reduce interference between the transmit and receive circuitry. The present invention may be added to WLL systems that use FDD mode to provide further reduction in interference with non- WLL systems. Modern WLL systems may employ miniature base stations that accommodate small duplexers, typically constructed of high dielectric materials and capable of approximately 30 dB of isolation. The present invention can increase this isolation without the need to detrimentally affect other important parameters. In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims: What is Claimed is: 1. A Wireless Local Loop (WLL) comprising: a Radio Fixed Part (RFP) including an RFP antenna that is responsive to a switching office to wirelessly transmit telecommunications messages from the switching office and to wirelessly receive telecommunications messages for the switching office via the RFP antenna; and a Wireless Fixed Access Unit (WFAU) including a WFAU antenna that is responsive to a telephone to wirelessly transmit telecommunications messages from the telephone to the RFP and to wirelessly receive telecommunications messages for the telephone from the RFP via the WFAU antenna; wherein the RFP antenna and the WFAU antenna are primarily non-vertically polarized. 2. A WLL according to Claim 1 wherein the RFP antenna is a horizontally polarized RFP antenna and wherein the WFAU antenna is a horizontally polarized WFAU antenna. 3. A WLL according to Claim 1 further comprising a telephone pole and a building, wherein the RFP antenna is fixedly mounted to the telephone pole in an orientation that provides primarily non-vertical polarization and wherein the WFAU antenna is fixedly mounted to the building in an orientation that provides primarily non-vertical polarization. 4. A WLL according to Claim 2 further comprising a telephone pole and a building, wherein the RFP antenna is fixedly horizontally mounted to the telephone pole and wherein the WFAU antenna is fixedly horizontally mounted to the building. 5. A WLL according to Claim 1 further comprising a cellular radiotelephone base station and a building, wherein the RFP antenna is fixedly mounted to the cellular radiotelephone base station in an orientation that provides primarily non-vertical polarization and wherein the WFAU antenna is fixedly mounted to the building in an orientation that provides primarily non-vertical polarization. 6. A WLL according to Claim 2 further comprising a cellular radiotelephone base station and a building, wherein the RFP antenna is fixedly horizontally mounted to the cellular radiotelephone base station and wherein the WFAU antenna is fixedly horizontally mounted to the building. 7. A WLL according to Claim 1 further comprising a network interface and a customer interface that connect the WFAU to the telephone. 8. A WLL according to Claim 2 further comprising a network interface and a customer interface that connect the WFAU to the telephone. 9. A WLL according to Claim 1 wherein the telecommunications messages utilize cordless or cellular wireless technologies. 10. A WLL according to Claim 2 wherein the telecommunications messages utilize cordless or cellular wireless technologies. 11. A Wireless Local Loop (WLL) including primarily non-vertically polarized antennas. 12. A WLL according to Claim 11 wherein the primarily non-vertically polarized antennas are horizontally polarized antennas. 13. A Wireless Local Loop (WLL) including antennas having ellipticity less than one. 14. A WLL according to Claim 13 wherein the ellipticity is zero. 15. A method of wirelessly transmitting radio frequency telecommunications messages between a Radio Fixed Part (RFP) and a Wireless Fixed Access Unit (WFAU) in a Wireless Local Loop (WLL) comprising the step of: transmitting primarily non-vertically polarized radio frequency telecommunications messages between the RFP and the WFAU. 16. A method according to Claim 15 wherein the transmitting step comprises the step of: transmitting horizontally polarized radio frequency telecommunications messages between the RFP and the WFAU. 17. A Radio Fixed Part (RFP) for a Wireless Local Loop (WLL) comprising: an RFP antenna that is responsive to a switching office to wirelessly transmit telecommunications messages from the switching office and to wirelessly receive telecommunications messages for the switching office; wherein the RFP antenna is primarily non-vertically polarized. 18. An RFP according to Claim 17 wherein the RFP antenna is a horizontally polarized RFP antenna. 19. An RFP according to Claim 18 further comprising a telephone pole, wherein the RFP antenna is horizontally mounted to the telephone pole. 20. An RFP according to Claim 18 further comprising a cellular radiotelephone base station, wherein the RFP antenna is horizontally mounted to the cellular radiotelephone base station. 21. A Wireless Fixed Access Unit (WFAU) for a Wireless Local Loop (WLL) comprising: a WFAU antenna that is responsive to a telephone to wirelessly transmit telecommunications messages from the telephone and to wirelessly receive telecommunications messages for the telephone; wherein the WFAU antenna is primarily non-vertically polarized. 22. A WFAU according to Claim 21 wherein the WFAU antenna is a horizontally polarized WFAU antenna. 23. A WFAU according to Claim 22 further comprising a building, wherein the WFAU antenna is horizontally mounted to the building. 24. A WFAU according to Claim 21 further comprising a network interface and a customer interface that connect the WFAU to the telephone.

Inventors: TURSKI ZYGMOND, TURSKI, ZYGMOND
Applicants: ERICSSON INC, ERICSSON, INC.
Application year: 1999
Main classification: H04Q7
IPC codes: H01Q1, H01Q9, H04B7, H04W84