High gain antenna systems for cellular use

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HIGH GAIN ANTENNA SYSTEMS FOR
CELLULAR USE

This application is a division of application Ser. No. 08/379,820 filed Jan. 27, 1995, U.S. Pat. No. 5,684,491. 5

This invention relates to antenna systems for communicating with mobile users and, more particularly, to multibeam antenna systems and methods providing higher gain reception of signals transmitted by mobile user equipment and which may also provide higher gain transmission to 10 mobile users.

BACKGROUND OF THE INVENTION

Radio communication with mobile users in moving vehicles, for example, is typically provided via fixed base stations or cell sites. Each cell site includes one or more antennas arranged for transmission of signals to and reception of relatively low power signals from mobile user equipment presently within a limited geographical area 2Q around the cell site. To provide the desired antenna coverage, the area around the cell site may be divided into sectors. Four sectors each of 90 degrees in azimuth coverage, or three 120 degree sectors, thus provide 360 degrees azimuth coverage around a cell site. In some appli- 2J cations the sector may be expanded to provide full 360 degree azimuth coverage. The cell terminology reflects the necessity of providing a pattern of adjacent cells, each with its own cell site antenna installation, in order to provide mobile communications coverage over a geographic area or 3Q region larger than the limited area covered by a single such installation.

Considering one of the 120 degree sectors referred to, it is relatively straightforward to design an antenna system providing 120 degree sector coverage. The antenna system 35 will be effective to transmit signals to any user within the desired sector coverage area. If signals are too weak to reliably reach users at the outermost edge of the sector coverage area, transmitter power can be specified at a higher level. However, for signals to be received from a user at the 40 sector edge, user transmissions are normally subject to limitations in power transmitted from the mobile equipment. If the user's transmitted power is inadequate to achieve reliable reception from the outer portions of the sector coverage area, the overall size of the cell and the gain of the 45 receive antenna at the fixed cell site become limiting considerations. A number of interrelated factors, including expected user population and available broadcast frequency spectrum, may also be involved in determining the optimum size of the coverage area of each cell site. It will be apparent, 50 however, that with smaller coverage areas additional cell site installations will be necessary to provide continuous coverage over a geographical region. Additional cell site installations require the purchase, installation and maintenance of more equipment as well as increased requirements and costs 55 of site acquisition, interconnection facilities and system support.

Use of higher gain receive antennas at each cell site would permit reliable reception of user signals at greater distances. However, for a given type of antenna, gain is directly related 60 to beamwidth and an antenna providing coverage over a 120 degree azimuth sector typically provides relatively low gain performance. Higher gain is also possible by use of narrow beamwidth antennas providing coverage of only a portion of a sector. However, sector coverage may then entail multiple 65 beams, or beam scanning or steering, requiring complex control and support systems in order to provide full sector

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coverage, with resulting higher cost and complexity and possible limitations on overall performance and user capacity.

Objects of the present invention, therefore, are to provide new and improved multi-beam receive antenna systems, and methods for receiving cellular communication signals by use of multi-beam antennas, and such systems and methods which provide one or more cost or operational advantages over prior mobile communication or other types of antenna systems.

SUMMARY OF THE INVENTION

In accordance with the invention, a multi-beam antenna system, suitable for use in a communication system including a sector antenna having a beamwidth providing sector coverage, a transmitter and a receiver system for receiving user signals from a user located in the sector, includes the following. A multi-beam first antenna provides a plurality of first antenna beams which are narrower than the sector and collectively cover at least a portion of the sector. A plurality of beam ports are each arranged for coupling first antenna beam signals received in one of such first antenna beams. Multicoupler means, coupled to each of the beam ports, make first antenna beam signals received in each first antenna beam available at a plurality of parallel ports. A plurality of switching means, each coupled to each of the beam ports via the parallel ports and having a switch output port and each responsive to selection signals, are arranged for selectively providing any one of the first antenna beam signals at a first switch output port coupled to the receiver system and any one of the first antenna beam signals also available at a second switch output port.

The antenna system also includes controller means, coupled to the second switch output port of the switching means, (a) for providing selection signals to the switching means to cause first antenna beam signals received in different ones of the first antenna beams to be sequentially provided at such second switch output port, (b) for analyzing the sequentially provided beam signals and selecting, on a predetermined basis, first antenna beam signals received in one of the first array beams, and (c) for providing selection signals to the switching means to cause such selected first antenna beam signals to be coupled to the receiver system, via the first switch output port, to enable reception of user signals. More particularly, such predetermined basis may be the highest amplitude, or the best available signal to spurious signal ratio, for signals received from an identified user of the communication system. Also, the controller means may be configured to continue analysis of sequentially provided first antenna beam signals and selection of first antenna beam signals received in one of the first antenna beams on such predetermined basis. The controller means will thus be responsive to changes in signal reception by causing selected first antenna beam signals received in a different one of the first antenna beams to be coupled to the receiver system when first antenna beam signals in the different beam are found to exhibit relatively higher amplitude characteristics, for example.

The antenna system may also include a beam port arranged for coupling sector beam signals received by the sector antenna, so that sector beam signals can be selectively provided at the first and second switch output ports in the same manner as the first antenna beam signals. With this configuration the controller means is arranged for providing selection signals to the switching means to cause the sector beam signals to be coupled to the receiver system in the 3

absence of any first antenna beam signals being selected and coupled to the receiver system. This alternative use of the sector beam signals provides a minimum level or fail-safe mode of operation.

Also in accordance with the invention, a method for receiving cellular communication signals from a user located in an azimuth sector by use of an antenna beam narrower than such sector, comprises the steps of:

(a) identifying a user signal by use of sector beam signals received in a sector beam providing antenna beam coverage of the sector;

(b) providing a first plurality of narrow beams, each providing antenna beam coverage narrower than the sector and collectively providing coverage of at least a portion of the sector;

(c) analyzing narrow beam signals received in each of the narrow beams with respect to the presence of such user signal;

(d) selecting, on a predetermined basis, one of the narrow beam signals; and

(e) coupling the selected narrow beam signal to an output port to enable coupling of the user signal to a receiver.

The method may additionally include repetition of steps (c), (d) and (e) to monitor changing reception conditions resulting in selection of a different one of the narrow beam signals and coupling of such different narrow beam signal to the output port.

A beam selection method which, in accordance with the invention, is usable in a communication system wherein a user signal may initially be received in different ones of a plurality of available time slots, includes the following steps:

(a) providing a plurality of contiguous antenna beams;

(b) receiving an initial signal from a user in a first time slot of a repetitive series of time slots;

(c) determining which antenna beam provided the strongest reception of the initial signal;

(d) assigning the antenna beam determined in step (c) for reception of subsequent signals from the user in all available time slots within a time period;

(e) providing a relative count for each antenna beam of occurrences of strongest reception of signals from the user in available time slots within the time period; and

(f) selecting for reception of signals from the user the antenna beam for which the step (e) relative count is the highest.

For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cellular type communication system incorporating a multi-beam receive antenna system in accordance with the invention.

FIG. 2 shows in greater detail a form of controller unit suitable for use in the FIG. 1 system.

FIG. 3 provides an angle/time diagram useful in describing operation of the invention.

FIG. 4 shows a portion of the FIG. 1 system modified to provide narrow beam signal transmission.

FIG. 5 illustrates an antenna configuration providing omnidirective azimuth coverage.

FIGS. 6A and 6B show typical signal formats.

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FIG. 7 illustrates a beam selection method in accordance with the invention.

DESCRIPTION OF THE INVENTION

5 Referring now to FIG. 1, there is illustrated a form of communication system for receiving signals from a mobile user and a form of multi-beam receive antenna system 10 suitable for use in such communication system to provide higher gain reception of user signals. An arrangement also enabling higher gain transmission will be described below.

The communication system includes a sector antenna 12, a duplexer 14, a transmitter 16 and a receiver system 18. The communication system also includes a similar sector

15 antenna 12a which is desirably laterally spaced from sector antenna 12 by several wavelengths at a frequency in the operating band in order to provide spaced diversity signal reception via two different signal paths to a user location. In this example, each of sector antennas 12 and 12a have a

20 beamwidth effective to provide coverage of a 120 degree azimuth sector, so that fully overlapping coverage of the sector results. This system also includes a duplexer 14a, a second transmitter 16a and a second receiver system 18a. Transmitter 16a and receiver system 18a may be arranged to

25 operate at frequencies different from the signal frequencies utilized by transmitter 16 and receiver system 18, in order to provide additional operational capacity. Following reception, user signals are provided at receiver outputs 19 and 19a for further processing or transmission to parties

30 intended by the users. In the absence of antenna system 10 each of antennas 12 and 12a would be connected to receiver system 18 to enable receiver system 18 to utilize first user signals received via sector antenna 12 or sector antenna 12a, or such signals from both antennas in combination.

35 Similarly, in the absence of antenna system 10, receiver system 18a would be arranged to utilize signals from either or both of antennas 12 and 12a for reception of signals from a second user transmitted at a different frequency. In other applications, the basic communication system may include

40 only a single transmitter/receiver/antenna combination or may have a variety of other configurations.

The multi-beam receive antenna system 10, as shown in FIG. 1, includes multi-beam first antenna means, shown as antenna 20, which may comprise four side-by-side vertical

45 arrays of dipoles or other radiating element arrangements suitable for providing four first antenna beams 21-24' each having a beam width narrower than the 120 degree sector and aligned so that the four beams collectively cover at least a portion of the sector. Typically, if a four beam antenna

50 configuration is used the first antenna beams will be arranged to collectively cover the full 120 degree azimuth sector. In other embodiments more than one array may be provided to form each beam, or more or less than four beams may be provided, or both. The desired beams may be

55 provided using arrays of radiating elements, with or without the inclusion of a suitable beam forming network, or in other suitable manner by persons skilled in the field. As shown, beam ports 21-24 are provided for each coupling first antenna beam signals received in one of the four first

go antenna beams provided by antenna 20. Beam port 25 similarly provides coupling of sector beam signals received in the beam of sector antenna 12.

The FIG. 1 receive antenna system 10 also includes multicoupler means 27-30 respectively coupled to each of

65 the beam ports 21-24. As shown, the multicoupler means 27-30 make each of the first antenna beam signals provided at the beam ports 21-24 available at a plurality of three 5

parallel ports represented by the three output leads shown emanating from the bottom of each of units 27-30 in FIG. 1. In addition, as shown at 31 the multicoupler means similarly makes sector beam signals coupled via duplexer 14, available at three parallel ports. Multicoupler units 5 27-31 may take the form of receiver amplifiers and associated signal splitting circuitry responsive to received signals for providing low-noise amplification and multiport access to each respective signal, while maintaining or translating the carrier frequency of the received signals, as desired in 10 particular applications. In other embodiments more or fewer than three parallel ports may be employed. Low noise amplifiers may be included at each of the multicoupler units 27-31, at each of the beam outputs of antenna 20 prior to the beam ports 21-24, or at both such locations, as appropriate. ^ Other types of multi-output junction devices or matrix coupling arrangements may be utilized by skilled persons to provide the desired multicoupler capability.

As illustrated, the receive antenna system 10 further includes a plurality of switching means, shown as single- 20 pole five position switching devices 33-35. Each of switching devices 33-35 is thus coupled to each of the beam ports 21-25, via the parallel output ports of multicoupler units 27-31. The switching means have a plurality of switch output ports 37-39 respectively coupled to switching 25 devices 33-35 and each switching device is responsive to selection signals provided via the dashed lines respectively connected to each of the switching devices 33-35. With this arrangement, any one of the first antenna beam signals from antenna system 10 can be selectively provided on an inde- 30 pendently selected basis at first switch output port 37, at second switch output port 38 and at third switch output port 39. As shown, the first and third switch output ports are respectively connected to the first and second receiver systems 18 and 18a. The switching devices 33-35 compris- 35 ing the switching means may be any suitable form of electrical, electronic, mechanical, optical or other form of device appropriate for enabling selective coupling of one of a plurality of inputs to an output.

Controller 40 is also included in the FIG. 1 receive 40 antenna system 10, as shown. Controller 40 is coupled to the second switch output port 38 and also to each of switching devices 33-35 by dashed lines representing the paths of selection signals for individual selection of the one of the first antenna beam signals which is to be provided at switch 45 output ports at any particular point in time. Controller means 40 is configured, as will be further described, for carrying out a plurality of functions, including the following. First, for providing selection signals to the switching device 34 of the switching means to cause first antenna beam signals 50 received in different ones of the beams of first antenna 20 to be sequentially provided at the second switch output port 38 and thereby input to controller 40. Such sequential selection is desirably carried out on a continuous basis while the receive antenna system 10 is in operation. Second, for 55 analyzing the sequentially provided beam signals and selecting, on a predetermined basis, beam signals received in one of the first antenna beams (e.g., beam 21' of antenna 20). Such selection basis may comprise selection of the beam signal having the highest user signal amplitude, or the best 60 signal to spurious signal ratio, relative to the other three first antenna beam signals, for the particular user signal of interest at that time. Third, for providing selection signals to switching device 33 of the switching means to cause the selected beam signals (e.g., signals from beam 21') from the 65 first antenna 20 to be coupled to receiver system 18 via the first switch output port 37. As a result, the user signal is

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provided to receiver system 18 based upon reception by a narrow beam/high gain antenna which in this case would provide antenna gain on reception about 6 dB higher than provided by sector antenna 12.

In operation, controller 40 can be arranged to continue such signal analysis and selection. As a result, if the user changes position or environmental signal transmission conditions change, so that better coverage of the new position of the user is provided by one of the other beams of antenna 20 (e.g., beam 22') signals from that beam will be coupled to receiver system 18. Controller 40 can also be configured to handle a plurality of incoming signals from different users in the same time period by repetitively processing each such signal during very short time intervals within the time period or by application of other techniques available for use in multiple signal reception in the context of different applications of the invention. Configuration of controller 40 will be discussed further below. As shown in FIG. 1, controller 40 is also enabled to control the coupling of signals received in the sector beam 12' of sector antenna 12 via selection signals supplied to switching device 33. In a typical operating arrangement, user signals from sector antenna 12 are provided to first receiver 18: (a) initially for user verification; (b) when such signals have a better signal to spurious signal ratio than signals from any of beams 21-24'; (c) when the receive antenna system 10 is inoperative or being serviced; (d) when the signal level is high because the user is very close to the fixed cell site; or (e) under other defined operating conditions. With such a fail/safe fall back configuration, the communication system has a continuing capability of providing a basic level of performance which is equivalent to performance without the presence of antenna system 10.

A number of further aspects of the FIG. 1 configuration should be addressed. With the exception of controller 40, the receive antenna system 10 as shown includes two mirrorimage right and left portions. All elements on the right side of FIG. 1 bear corresponding reference characters including an "a" suffix. If the two four beam antennas 20 and 20a are laterally spaced and each provides full coverage of the sector, spaced diversity reception will be available for each user position in the sector. The signal analysis, signal selection and selection signals provided by controller 40 will thus cause to be made available to receiver 18 for a specific user, user signals from one of the beams of antenna 20 coupled via switch output port 37 to the left input to receiver system 18 and user signals from one of the beams of antenna 20a coupled via switch output port 39a to the right input to receiver system 18. Receiver system 18 may then select its right or left input as providing the best quality user signal reception or may appropriately combine signals from both inputs by additive combination or in any appropriate fashion. As previously noted, transmitter 16a and receiver system 18a may be arranged to operate at signal frequencies different from those used by transmitter 16 and receiver 18. This enables controller 40, in operation parallel to that already described, to select the best beam signals received by antennas 20 and 20a from a second user, transmitting at a frequency different from the first user, and cause those second user signals to be coupled to the left and right inputs of receiver 18a, independently of the first user signals coupled to receiver 18. As a separate matter, there are also included in FIG. 1 sampling couplers, shown as directional couplers 42 and 42a, arranged to provide to controller 40 very low power samples of signals transmitted by transmitters 16 and 16a respectively. Such samples (which may be at levels 30 dB below transmitted power, for example)