WO2000007305A1

WO2000007305A1 - Free space combining and diversity antenna system for fixed cellular applications

Info

Publication number: WO2000007305A1
Application number: PCT/US1999/014767
Authority: WO
Inventors: Hongxi Xue; Chuansheng Ren
Original assignee: Ericsson Inc.
Priority date: 1998-07-31
Filing date: 1999-06-29
Publication date: 2000-02-10
Also published as: CA2338056A1; AU4963399A; BR9912631A; AR019978A1

Abstract

A free space combining and diversity antenna system for a fixed cellular station transmits signals from more than one transmitter without using a combiner, such that the combination of the transmitted signals is done in free space. Furthermore, multiple electrical antennas allow various reception diversity techniques to be employed. The station includes a plurality of transmitters, each connected to a transmission antenna where the transmission antenna may be a plurality of electrical antennas including a patch antenna, monopole antennas, dipole antennas, etc. The station further includes a plurality of receivers or transceiver-receivers connected to different antennas, for employing reception diversity techniques. Isolators connected between the antennas for each transmitter-transmitter, transmitter-receiver, transceiver-transceiver, transceiver-transmitter, and transceiver-receiver pair cancel transmitted signals received by the non-transmitting antennas.

Description

FREE SPACE COMBINING AND DIVERSITY ANTENNA SYSTEM FOR FIXED CELLULAR APPLICATIONS

FIELD OF THE INVENTION The present invention is directed to the combining of signals from a fixed cellular station, and in particular, the combining of transmitted signals from a fixed cellular station in free space without using combiners.

BACKGROUND OF THE INVENTION A fixed cellular station is a relay station between landline connected apparatus as telephones or facsimile machines and a radio base station. A fixed cellular station generally comprise a plurality of stationary transmitters, receivers, and transceivers connected to at least one antenna, for transmitting signals to and receiving signals from mobile stations. Current fixed cellular stations use combiners to combine the signals from several transmitters to a single electrical antenna.

Two types of combiners currently in use are the hybrid combiner and the cavity combiner. Hybrid combiners are relatively inexpensive and take up little space in a fixed cellular station. Furthermore, hybrid combiners have satisfactory broadband performance. However, the typical insertion loss of a hybrid combiner is about 3 dB per stage, which degrades overall system efficiency tremendously. Cavity combiners have a smaller insertion loss than the hybrid combiner per stage, but are much more expensive than hybrid combiners and take up a much larger space in a fixed cellular station. Additionally, the broadband performance of a cavity combiner is poorer than that of a hybrid combiner.

One way of compensating for the insertion loss in hybrid combiners is by using a multiple carrier broadband linear amplifier (MCBLA). The overall power loss is reduced because the combining is done at a lower power level. Although this technique is able to achieve broadband highly linear performance, it does have its drawbacks. The technique uses a cancellation process which requires a redundant amplifier for error correction. Also, the MCBLA tends to be a vulnerable point for complete systems failure. Even using this technique of combining at a lower power level, power efficiency is still diminished.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide combining of transmitted signals without the use of combiners. By using separate antennas connected to each transmitter, the combining of signals is done in free space, with broadband linearity, low power loss, and built in redundancy. In addition, space and cost requirements of conventional combiners are overcome.

In one aspect of the present invention, each of plural transmitters is connected to a transmitting antenna. The transmitting antenna may include monopoles, dipoles, etc. The transmitting antennas transmit signals from each transmitter, with the combining of transmitted signals occurring in free space. Isolators, e.g., a "duplex-free duplexer" described in detail below, are employed between the antennas for each transmitter-transmitter, transmitter-receiver, transceiver-transmitter, transceiver-receiver and transceiver-transceiver pair to protect the transmitters, receivers and transceivers from signals transmitted by the transmitters and transceivers.

In another aspect of the present invention, the transmitting antenna is at least a patch antenna, where each of a plurality of transmitters is connected to a different point on the patch antenna via a pin-fed connection or an edge fed- connection. Placement of the transmitter connections on the patch antenna may provide isolation to protect the transmitters from one another, however if the placement does not provide adequate isolation, isolators may be connected between each pair of transmitter connections to the patch to protect the transmitters from one another. Each transmitter transmits signals at the same time, and the transmitted signals are combined in free space without the use of combiners.

In another aspect of the present invention, transmitters and one or more receivers are connected to transmitting antennas. The transmitting antennas may be a plurality of electrical antennas including a patch antenna, monopole antennas, dipole antennas, etc. The transmitted signals are transmitted from the transmitting antenna apparatus, where the combining of the transmitted signals occurs in free space, without the use of combiners. The presence of receivers and multiple electrical antennas allow the receivers to employ reception diversity. In a further aspect of the present invention, transmitters, receivers and one or more transceivers are each connected to the antennas. The transmitters and transceivers are able to transmit signals at the same time without the use of combiners. In addition, the transceivers and receivers together with multiple electrical antennas are able to employ reception diversity techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagrammatic illustration of a plurality of transceivers each connected to a transmission antenna for free space combining without using combiners;

Figure 2 is a schematic of two electrical antennas connected to two transmitters and isolated from one another by isolators for free space combining without the use of combiners;

Figure 3 is a diagrammatic illustration of transmitters connected to a patch antenna for free space combining of transmitted signals without using combiners; Figure 4 is a block diagram of a fixed cellular station utilizing two transmitters and a single receiver to demonstrate reception diversity in conjunction with the free space combining technique;

Figure 5 is a block diagram of a more detailed embodiment of Figure 4; Figure 6 is a block diagram of a fixed cellular station utilizing two transmitters with two receivers to demonstrate reception diversity in conjunction with the free space combining technique;

Figure 7 is a block diagram of a more detailed embodiment of Figure 6; and Figure 8 is a block diagram of a fixed cellular station utilizing transceivers, transmitters and receivers for free-space combining without using combiners. DETAILED DESCRIPTION OF THE INVENTION A fixed cellular station has plural transmitters (and receivers) connected with plural antennas for free space combining of the transmitted signals.

Figure 1 illustrates a plurality of transceivers (TRx) each connected to a transmission antenna for free space combining of the transmitted signals without using combiners. A transceiver is a transmitter-receiver pair connected to the antenna through a duplexer. In Figure 1 , transceivers 10 and 20 are each connected to corresponding antennas 40 and 50, respectively. As each transceiver 10 and 20 are connected to a corresponding antenna, the transmitted signals are combined in free space without the use of a combiner. Transceiver 30 is shown in Figure 1 as "TRxN", and is connected to a corresponding antenna 60. The "TRxN" designation for transceiver 30 illustrates that transmitted signals from any number of transceivers connected to corresponding antennas may be combined in free space without the use of a combiner. Free space combining yields many advantages, such as: (1) Broadband linearity as no high-Q component is needed; (2) Low power loss since air has a very low dielectric loss; (3) Built-in redundance since a failure on any single antenna does not result in a total system failure; and (4) Lower space and cost requirements as combiners are no longer necessary. Each transceiver 10, 20 and 30 in figure 1 may be replaced with a transmitter

(not shown) without affecting free space combining of the transmitted signals. Additionally, antennas 40, 50 and 60 are each an electrical antenna.

Figure 2 illustrates two electrical antennas connected through two isolators for free space combining without the use of combiners. Transmitters (Tx) 120 and 130 are connected to and transmit signals from electrical antennas 100 and 110 respectively, such that the transmitted signals are combined in free space, without using a combiner. Isolator 140 protects transmitter 130 from the signals transmitted by transmitter 120. Isolator 150 protects transmitter 120 from signals transmitted by transmitter 130. Isolator 140 collects a sample of the signal transmitted by transmitter 120 at coupler 160. The sample signal is attenuated by attenuator 170 and shifted in phase by the attenuator and transmission line 175 such that when coupled to electrical antenna 110 through coupler 180, the coupled signal is 180 degrees out of phase and of sufficient amplitude to cancel out the signal received from transmitter 120 at electrical antenna 110. Isolator 150 works in the same manner as isolator 140, except isolator 150 cancels out the signal received from transmitter 130 at electrical antenna 100. Further details of the isolator are disclosed in United States Patent Application Serial No. 08/838,066, Ericsson Docket EUS00730-RPRS. Figure 3 illustrates transmitters connected to a patch antenna for free space combining of transmitted signals without using combiners. The patch antenna 200 consists of a patch antenna panel 210 and a ground plane 220, separated by a dielectric 230. The patch antenna panel 210 and ground plane 220 are conductive sheets, typically copper. The dielectric 230 may be any insulating material including air.

Transmitters 240, 250 and 270 are connected, through coaxial transmission lines to patch antenna 200 using pin-fed connections 275, 280, and 285 respectively. Transmitter 260 is connected through a coaxial transmission line to patch antenna 200 using an edge-fed connection 290. The radiation characteristics of patch antenna 200 depend on the size and shape of the patch antenna, and the placement of the pin-fed and edge-fed connections to patch antenna 200. Furthermore, the pin-fed and edge-fed connections to the patch antenna may be placed on patch antenna 200 such that the components (including the transmitters, receivers and transceivers) do not interact with one another. If the pin-fed and edge- fed connections are not placed on the patch antenna to prevent the components from interacting, isolators as mentioned in Figure 2 are used between the connections for each pair of transmitter-transmitter, transmitter-receiver, transceiver- transceiver, transceiver-transmitter and transceiver-receiver to protect each component from the others. (Transceivers and receivers are not shown in Figure 3.) In this way, transmitters 240, 250, 260 and 270 may transmit signals from patch antenna 200 such that the transmitted signals are combined in free space without the use of a combiner.

Figure 4 illustrates a fixed cellular station utilizing two transmitters and a single receiver to demonstrate reception diversity in conjunction with the free space combining technique. Transmitter 500 is connected to main antenna 510 through duplex free duplex subsystem (DFDS) 505. Transmitter 502 is connected to auxiliary antenna 525 through DFDS 507. DFDS 505 and 507 are each isolators which function in the same way as the isolators shown in Figure 2. Receiver (Rx) 515 is alternatively connected through diversity antenna switch (DASW) 520 and DFDS 507 to auxiliary antenna 525, and through DASW 520 and DFDS 505 to main antenna 510. When receiver 515 is connected to main antenna 510, DFDS 505 protects receiver 515 from signals transmitted by transmitter 500. When receiver 515 is connected to auxiliary antenna 525, DFDS 507 protects receiver 515 from signals transmitted by transmitter 502. Diversity antenna switch 520 is actuated by a discriminator (not shown) connected to receiver 515.

Transmitters 500 and 502 each transmit signals, with the transmitted signals being combined in free space without using a combiner. Receiver 515 employs switched reception diversity using signals gathered from main antenna 510 and auxiliary antenna 525 by connecting receiver 515 to the stronger signal received by main antenna 510 and auxiliary antenna 525.

Figure 5 illustrates a more detailed embodiment of Figure 4. Main antenna 510 is shown as two electrical antennas, electrical antenna 530 and 535. Auxiliary antenna 525 is shown as two electrical antennas, electrical antenna 545 and 550. DFDS 505 is an isolator providing isolation between electrical antennas 530 and 535. DFDS 507 is an isolator providing isolation between electrical antennas 545 and 550. By isolating electrical antenna 530 from electrical antenna 535, and isolating electrical antenna 545 from electrical antenna 550, receiver 515 is protected from the transmissions made by both transmitter 500 and transmitter 502. Transmitter 500 is connected directly to electrical antenna 530, and transmitter 502 is connected directly to electrical antenna 550. Receiver 515 is connected alternatively to electrical antenna 525 and to electrical antenna 545 via diversity antenna switch 520. Diversity antenna switch 520 is actuated by discriminator 540. Switched reception diversity is carried out using discriminator 540 and receiver 515, where discriminator 540 is electrically connected to receiver 515 and actuates switch 520 depending on the strength of a signal received at receiver 515. For example, discriminator 540 samples the signal strength at receiver 515 received from electrical antenna 545, and actuates the diversity antenna switch 520 to receive a sample of the signal strength at the receiver 515 from electrical antenna 535. The discriminator 540 then determines the stronger signal from electrical antennas 545 and 535, and actuates diversity antenna switch 520 to connect receiver 515 with the stronger signal. When the signal strength received by receiver 515 drops below a predetermined threshold, the discriminator 540 repeats the process to determine the receiver with a stronger signal strength. Other diversity combining algorithms can be implemented, as Maximum Ratio or Interference Rejection combining.

Figure 6 illustrates a fixed cellular station utilizing two transmitters with two receivers to demonstrate reception diversity in conjunction with the free space combining technique. Transmitter 600 is connected to main antenna 610 through DFDS 605. Transmitter 602 is connected to auxiliary antenna 625 through DFDS 607. Receiver 615, which comprises two independent receivers, is connected to auxiliary antenna 625 and main antenna 610 where a first receiver of receiver 615 is connected to main antenna 610 through DFDS 605, and a second receiver of receiver 615 is connected to auxiliary antenna 625 through DFDS 607. DFDS 605 and 607 are each isolators which function in the same way as the isolators in Figure 2. The first receiver of receiver 615 is connected to main antenna 610 and is protected from the signals transmitted by transmitter 600 by DFDS 605. The second receiver of receiver 615 is connected to auxiliary antenna 625 and is protected from the signals transmitted by transmitter 602 by DFDS 607. Transmitters 600 and 602 each transmit signals, where the transmitted signals are combined in free space without using a combiner. Receiver 615 employs reception diversity using signals from main antenna 610 and auxiliary antenna 625. Figure 7 illustrates a more detailed embodiment of Figure 6. Main antenna 610 is shown as two electrical antennas, electrical antennas 630 and 635. Auxiliary antenna 635 is shown as two electrical antennas, electrical antennas 637 and 639. Transmitter 600 is connected directly to electrical antenna 630. Transmitter 602 is connected directly to electrical antenna 637. Receiver 615 is shown as two independent receivers, receiver 640 and receiver 645. Receiver 645 is connected directly to electrical antenna 639 and receiver 640 is connected to electrical antenna 635.

Discriminator 650 is connected between receiver 640 and receiver 645. Switch 655 is connected to receiver 640 and receiver 645, and is actuated by discriminator 650. Reception diversity is employed by discriminator 650 and receivers 640 and

645. For example, discriminator 650 samples the signal received at receiver 640 and receiver 645, and determines the stronger signal. Discriminator 650 then actuates switch 655 to connect the stronger of the signals received by receiver 640 or receiver 645 to the output 660. DFDS 605 is an isolator providing isolation between electrical antennas 630 and 635, and thereby isolates receiver 640 from the transmissions of transmitter 600.

DFDS 607 is an isolator providing isolation between electrical antennas 637 and

639, and thereby isolates receiver 640 from the transmissions of transmitter 602.

Figure 11 depicts an embodiment of the free space combining and diversity antenna system incorporated into a fixed cellular station 800. The fixed cellular system comprises patch antenna 802, main antenna 804, auxiliary antenna 806, auxiliary antenna 808, transceiver 810, transmitter 812, receiver 814, transmitter 816, receiver 818, transmitter 820, receiver 822, discriminator 824, switch 826, and isolator 828. Fixed cellular station 800 possesses four physical antennas: patch antenna 802, main antenna apparatus 804, auxiliary antenna 806 and auxiliary antenna 808. Patch antenna 802 itself acts as three electrical antennas, created by pin-fed connections 830 and 834, and edge-fed connection 832. Main antenna apparatus 804 is in itself two electrical antennas, electrical antennas 836 and 838. Auxiliary antennas 806 and 808 are each a single electrical antenna. For example, auxiliary antenna 806 is shown as a monopole, and auxiliary antenna 808 is shown as a dipole. Electrically connected to patch antenna 802 are transceiver 810, transmitter 812, and receiver 814. Electrically connected to main antenna apparatus 804 are transmitter 816 and receiver 818. Electrically connected to auxiliary antennas 806 and 808 are respectively, transmitter 820 and receiver 822.

Transceiver 810, transmitter 812, transmitter 816 and transmitter 820 are all able to transmit signals either on the same frequencies or different frequencies, where the signals consist of identical intelligence for employing transmission diversity, or different intelligence, without the use of a combiner. By using an electrical antenna for each of the transceiver 810 and transmitters 812, 816 and 820, the transmitted signals are combined in free space, without using a combiner. Isolators such as isolator 828, functioning in the same way as the isolators in Figure 2, may be employed in the fixed cellular station when necessary to protect the various receivers, transmitters and transceivers in the station from transmitted signals.

In addition, reception diversity may be employed as multiple transmission antennas are used. The reception diversity techniques employed include but are not limited to spacial diversity and polarization diversity. In fixed cellular system 800, discriminator 824 determines the strongest of a received signal as between receiver 818 and receiver 822, and actuates switch 826 to connect the strongest received signal from receiver 818 and receiver 822 to the output 830. Although not shown, additional receivers may be connected to discriminator 824 for a greater selection of received signals to be used in the reception diversity process. The fixed cellular station may have any number of receivers, transceivers and transmitters, and may employ any type of antenna type including monopoles, dipoles, or patch antennas. Although a discriminator is used in the present system to determine the stronger signal, circuitry present in the receiver may perform the discriminator functions. In addition, the present invention may be used in conjunction with combiners, where a part of a fixed cellular station is operated using combiners, and a part of the fixed cellular station is operated using the free space combining technique herein disclosed.

Claims

CLAIMS:What is claimed is:

1. Communications apparatus for free space combining of transmitter signals in a fixed cellular station comprising: a plurality of transmitters, to produce signals to be transmitted; a plurality of antennas, each connected to at least one of said plurality of transmitters, to radiate said signals to be transmitted, wherein said transmitted signals from at least two transmitters are combined in free space, without combiners.

2. The apparatus of claim 1 further comprising at least one isolator coupled between each pair of said plurality of antennas, to isolate said plurality of transmitters from one another.

3. The apparatus of claim 1 wherein said plurality of antennas includes a monopole antenna.

4. The apparatus of claim 1 wherein said plurality of antennas includes a dipole antenna.

5. The apparatus of claim 1 wherein at least one of said plurality of antennas is a patch antenna with a plurality of said transmitters connected at different points to said patch antenna.

6. The apparatus of claim 5 wherein said plurality of transmitters are connected to said patch antenna by at least one of an edge-fed connection and a pin-fed connection.

7. The apparatus of claim 1 further comprising: a plurality of receivers, each connected to at least one of said plurality of antennas, to receive transmitted signals; and a plurality of isolators, coupled between said plurality of antennas, for isolating said plurality of receivers from said plurality of transmitters; wherein said plurality of receivers allow reception diversity to be employed by said apparatus.

8. The apparatus of claim 1 further comprising at least one transceiver, each transceiver connected to at least one of said plurality of antennas for transmitting and receiving signals.

9. A method for free space combining of transmitter signals from a fixed cellular station, the method comprising: producing a plurality of signals to be transmitted; and transmitting said plurality of signals from a plurality of antennas; wherein said transmitted signals are combined in free space without combiners.

10. The method of claim 9 wherein at least one of said plurality of signals is produced by at least one transmitter.

11. The method of claim 9 wherein at least one of said plurality of signals are produced by at least one transceiver.

12. The method of claim 9 wherein at least two of said plurality of signals contain identical intelligence to create transmission diversity.

13. The method of claim 12 wherein said transmission diversity is created by at least one of: transmitting said identical intelligence on the same frequency; transmitting said identical intelligence on different frequencies; transmitting said identical intelligence at offset time periods; and transmitting said identical intelligence from different locations.