WO2001031742A1

WO2001031742A1 - Non stationary sectorized antenna

Info

Publication number: WO2001031742A1
Application number: PCT/US2000/029709
Authority: WO
Inventors: Jack Keil Wolf
Original assignee: Qualcomm Incorporated
Priority date: 1999-10-28
Filing date: 2000-10-26
Publication date: 2001-05-03
Also published as: KR20020043251A; EP1234354A1; BR0014978A; CN1608332A; JP2003527785A; TW472417B; AU1441001A

Abstract

A base station in which the cell boundaries move. By moving the cell boundaries, a stationary or slow moving subscriber station is not disadvantaged with respect to the service it is capable of receiving. In a first exemplary embodiment, a sectorized antenna structure is placed in motion by either rotating the antenna structure or by oscillating the angle of the antenna structure. In a second embodiment, two separate antenna structures with different coverage area divisions are provided and the communications are alternately provided from each of the two antenna structures. It is a further advantage that position location of a subscriber station may be improved by employing the additional information that is available using the motion or multiple configuration of the sectors.

Description

NON STATIONARY SECTORIZED ANTENNA

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to wireless communications. More particularly, the present invention relates to a novel and improved method and apparatus for transmitting wireless communications signals using a non-stationary wireless antenna.

II. Description of the Related Art

FIG. 1 illustrates the a conventional three sectored wireless base station 100 with transmit antennas 108A, 108B and 108C serving geographical sectors 106A, 106B and 106C, respectively. Subscriber station 102 lies near the center of the coverage area of antenna 108B. Subscriber station 104 lies near the boundary between sectors 106B and 106C. Because of the antenna beam patterns from current antennas are such that the strength of the signal diminishes near sector edges and because interference between the two sectors is at a maximum at the boundaries, subscriber station 102 is advantageously positioned with respect to subscriber station 104 for receiving service from either antenna 108B or antenna 108C.

One method of ensuring adequate service to subscriber station 104 is to place subscriber station 104 in softer handoff with sectors 108C and 108B. The process of softer handoff is a process by which a subscriber station is placed in simultaneous communication with a plurality of sectors of a base station. Softer handoff is described in detail in U.S. Patent No. 5,625,876, entitled "METHOD AND APPARATUS FOR PERFORMING HAND-OFF BETWEEN SECTORS OF A COMMON BASE STATION", which is assigned to the assignee of the present invention and incorporated by reference herein. Softer handoff is a specific form of the more general soft handoff, which refers to redundant communication with multiple base stations and is described in U.S. Patent No. 5,101,501, entitled "METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN A WIRELESS COMMUNICATION SYSTEM", which is assigned to the assignee of the present invention and incorporated by reference herein.

With the increasing desire for greater capacity in systems combined with the desire to provide a greater variety of services to customers, such as high speed wireless digital data, soft and softer handoffs become less desirable. Soft handoffs require that the same information be redundantly transmitted, which reduces system capacity. This condition is exacerbated in the transmission of high speed data, which requires significant resources to transmit each version of the high speed data.

Two methods have been introduced in order to handle the impact of soft handoff while maintaining the goal maximizing system throughput. A first method is to selectively assign available rate sets to a subscriber station in accordance with the position of the subscriber station and whether the subscriber station is in soft or softer handoff. For example, because it requires less resources to communicate with subscriber station 102 than it does to communicate with subscriber station 104, subscriber station 102 is permitted to communicate at higher rates than subscriber station 102. An example of this form of rate assignment is described in U.S. Patent Application Serial No. 08/835,632, entitled "METHOD AND APPARATUS FOR REVERSE LINK DATA RATE SCHEDULING", filed on April 8, 1997, assigned to the assignee of the present invention and incorporated by reference herein.

An alternative method is to prevent soft handoffs and force the selection of a transmitter for communicating with a given subscriber station. Such a system is described in detail in copending U.S. Patent Application Serial No. 08/963,386 (the '386 application), filed November 3, 1997, entitled "METHOD AND APPARATUS FOR HIGHER RATE PACKET DATA TRANSMISSION", assigned to the assignee of the present invention and incorporated by reference herein. In the '386 application, the subscriber station measures the strength of signals from base stations and sectors of base stations in its vicinity, and transmits a message indicative of the identity of the base station transmitting the strongest signal received by the subscriber station and a rate indication, indicating a rate for communication selected in accordance with the strength of the strongest signal received by the subscriber station.

The shortcoming of either of these methods is that in the case of stationary or slow moving subscriber station the disadvantage is long term, if not permanent, and this is unfair to those stationary or slow moving users located near cell boundaries. SUMMARY OF THE INVENTION

The present invention is a novel and improved method and apparatus for transmitting data in a wireless communication system, which does not disadvantage stationary or slow moving subscriber stations due to their position near cell boundaries. The present invention describes a base station in which the cell boundaries move. By moving the cell boundaries, a stationary or slow moving subscriber station is not disadvantaged with respect to the service it is capable of receiving. In a first exemplary embodiment, a sectorized antenna structure is placed in motion by either rotating the antenna structure or by oscillating the angle of the antenna structure. In a second embodiment, two separate antenna structures with different coverage area divisions are provided and the communications are alternately provided from each of the two antenna structures.

It is a further advantage of the present invention that position location of a subscriber station may be improved by employing the additional information that is available using the motion or multiple configuration of the sectors.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

FIG. 1 is a diagram illustrating the communication system of a three sectored base station;

FIG. 2 is a flowchart describing the exemplary embodiment of the operation of the present invention;

FIG. 3 is a block diagram illustrating the elements of a first embodiment of the transmission subsystem of a base station of the present invention;

FIG. 4 is a block diagram illustrating the elements of a second embodiment of the transmission subsystem of a base station of the present invention; FIG. 5 is a diagram illustrating the communication system of a six sectored base station configured in accordance with the second embodiment of the present invention;

FIG. 6 is a block diagram illustrating an exemplary subscriber station of the present invention;

FIG. 7 is a block diagram illustrating the elements of the receive subsystem of a base station of the present invention employing a rotating receive antenna structure; and

FIG. 8 is a block diagram illustrating the elements of the receive subsystem of a base station of the present invention employing an alternating receive antenna structure.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS

FIG. 1 is a block diagram illustrating the operation performed by the present invention. In block 200, a signal for transmission is generated. In the exemplary embodiment, the signal generated is a code division multiple access communication signal. The generation of code division multiple access communication signals is described in detail in U.S. Patent No.

5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL

WAVEFORMS IN CELLULAR TELEPHONE SYSTEM", which is assigned to the assignee of the present invention and incorporated by reference herein.

In the exemplary embodiment of the present invention, the waveform generated is for high speed wireless data as described in the aforementioned U.S. Patent Application Serial No. 08/963,386. The present invention is applicable to other forms of code division multiple access, such as those described in the Telecommunications Industry Association IS-95 family of standards, and in proposed Third Generation standards, such as WCDMA and cdma2000. However, the present invention is equally applicable to other modulation formats in which a slow moving or stationary subscriber is disadvantage by virtue of its location in a base station coverage area, such as GSM or TDMA.

In block 202, the waveform is presented to a non-stationary antenna. In the exemplary embodiment, the antenna is a sectorized antenna. The boundaries of the sectors are permitted to move so as to remove the geographical disadvantage to slow moving and stationary subscriber stations. In a preferred embodiment of the present invention, the sectors are moved at a rate that is slow relative to the rate of power control and data rate requests feed back loops of the communications systems. However, the motion of the sector boundaries is rapid relative to the duration of service for the subscriber station. In block 204, the signal is transmitted from the non stationary antenna. In a first embodiment, a sectored antenna structure is rotated by coupling the antenna structure to a motorized platform or by use of phased array antenna structures. The rotation can be either continuous or can oscillate through a constrained rotation angle. In a second embodiment, the non stationary antenna is affected by providing multiple sets of sectorized antennas and switching the transmission of the signal between the sets of sectorized antennas.

In block 206, the signals transmitted through the non stationary antenna are received by a subscriber station in the coverage area of the base station. The signal is demodulated and provided to the user of the subscriber station.

In block 208, the signal strengths of the signals received from the transmitting base station are measured at the subscriber station.

In block 210, the subscriber station transmits its communication signal to the base station, which in the exemplary embodiment includes a message indicative of the measured signal strengths.

In block 212, the signal transmitted by the subscriber station is received at a non-stationary antenna structure.

It is a further advantage of the present invention, that position location can benefit from non stationary antenna structure in transmission of the forward link signals. In the first exemplary embodiment of the sweeping of the forward link signal, as a sector sweeps towards a subscriber station in a predictable fashion, the signal strength is indicative of the proximity of the subscriber station to the leading edge of the sweeping antenna coverage beam. These changes in the reported signal strengths are used to estimate the position of the subscriber station. Alternatively, position location can benefit from the alternating forward link signal transmissions from multiple sets of fixed antennas. The signal strengths reported by the subscriber station will vary based on the antenna structure from which the forward link signals are transmitted. These changes in the reported signal strengths are used to estimate the position of the subscriber station. In the exemplary embodiment, a control processor can employ triangulation techniques for the two separate setorizations and in addition can look at the difference in the reported energies to determine the proximity of the subscriber station to a sector boundary in either case of the sectorization.

It may be desirable under certain conditions to permit the antennas used for transmission of the forward link signal to move, while antennas for the reception remain fixed. Conversely, it may be desirable under certain conditions to permit the antennas used for reception of the reverse link signal to move, while antennas for the transmission remain fixed. One possible reason for providing a moving beam structure on one link but not the other is that softer handoff may be supported on one link but not the other. These and other modifications can readily be envisioned by one skilled in the art without departing from the scope of the present invention.

Turning to FIG. 3, a simplified block diagram of the first embodiment of the transmission system of a sectorized base station 320 is illustrated. Data to be transmitted is provided in three streams 318A, 318B and 318C. Each stream of data 318A, 318B and 318C is processed for transmission by a corresponding waveform generator 300A, 300B and 300C. The processed steams of data are then provided to a corresponding antenna 314A, 314B and 314C of antenna structure 312. In the first exemplary embodiment, antenna structure 312 is operably coupled to a rotator mechanism 316 which varies the angles to which the transmissions from antennas 300A, 300B and 300C are directed. In an alternative embodiment, the effect of the motion provided by mechanical means may be affected through use of phased array antennas or beam reflectors or other means without departing from the scope of the present invention.

In the exemplary embodiment, rotator 316 is a motor that rotates antenna structure 312 at an approximately constant angular velocity in full revolutions about the axis. In an alternative embodiment, rotator 316 varies the angle of antenna structure 312 in a restricted set of angles, such that the motion of antenna structure 312 traverses a set of angles alternating in a clockwise followed by a counterclockwise fashion.

In the exemplary embodiment, the subscriber stations in communication with base station 320 send messages to base station 320 indicating the sector of the base station from which the subscriber station is receiving the strongest signal and requesting data to be transmitted to it based on the strength of the received signal. In the preferred embodiment, angular motion is at a rate that is selected to be slow enough that the rate request information is still applicable at the time of transmission by base station 320, which depends on the latency of the rate request feedback loop. The mobile station measures the received signals, generates its rate request message and transmits this message. The base station receives the message, processes data for transmission at a rate determined in accordance with the message and transmits the data. It is important that at the time of transmission of the data by the base station, the angle has not varied beyond an acceptable threshold from its position at the time the subscriber station measured the signal strength upon which its request was based. This situation is equally applicable to other relevant feedback loops in other systems such as the power control feedback loop.

An exemplary block diagram of waveform generators 300 is provided within waveform generator 300A. Data for transmission is provided to frame formatter 302. In the exemplary embodiment, frame formatter 302 generates a set of cyclic redundancy check bits and appends those bits along with tail bits and overhead message bits to the information for transmission. The information is provided to encoder 304. Encoder 304 can be any form of forward error correction coder, such as a convolutional encoder or a turbo encoder. The encoded symbols are provided to interleaver 306, which reorders the symbols to provide greater time diversity in the transmitted data.

The data is then provided to modulator 308. In the exemplary embodiment, modulator 308 is a high data rate CDMA modulator as described in the '386 application. The invention has additional advantages in systems which do not provide for softer handoff of the forward link, but is also useful in systems that provide softer handoff of the forward link such as proposed Third Generation CDMA systems and IS-95 based CDMA systems.

In the exemplary embodiment, each of the signals is spread using a pseudonoise sequence that is different for each sector of base station 320, such that the signals transmitted through antenna 314A, 314B and 314C are each spread using a different PN sequence. The modulated signals is provided to transmitter 310, where it is filtered, upconverted and amplified for transmission through antenna structure 312.

FIG. 4 illustrates an alternative embodiment of the present invention. In this second embodiment, the physical motion of the transmit antenna is replaced by a switching between two or more fixed antenna structures which are pointing in different directions. The data for transmission is provided to waveform generators 400A, 400B and 400C, which process the signal as described with respect to waveform generator 300 A.

The processed signals are provided to switch 402. Initially, switch 402 directs the processed signals to a first antenna structure 404A, in which the signals process by waveform generators 400A, 400B and 400C are transmitted through antennas 406A, 406B and 406C, respectively. After a predetermined time interval, switch 402 directs the processed signals to antenna structure 404B, in which the signals process by waveform generators 400A, 400B and 400C are transmitted through antennas 408A, 408B and 408C, respectively. It will be understood by one skilled in the art that any number of fixed antenna structures can be employed without departing from the scope of the present invention.

Turning to FIG. 5, the alternating sectorization of the cell coverage area using two fixed antenna structures is illustrated. A first sectorization pattern is described by solid lines 502A, 502B and 502C, which is provided by antennas 408A, 408B and 408C. A second sectorization pattern is described by dashed lines 500A, 500B and 500C, which is provided by antennas 406A, 406B and 406C.

In an exemplary embodiment of the present invention, the switching is performed with guard times wherein base station 410 determines that the rate request information was based on measurement of signals transmitted from a different antenna structure. In an alternative embodiment, switch 402 operates at a rate in excess of the feedback loop of the system, such that the subscriber station measures the strength of the received signals, and transmits its message. The base station switches to the other antenna structure and back to the initial prior to the transmission to the subscriber station. In this fashion the rate request information is still relevant to the antenna structures through which the data is transmitted. Many methods of synchronizing the transmission rate selection with the measurement feedback will occur to one skilled in the art and do not depart for the scope of the present invention.

FIG. 6 is a simplified block diagram illustrating the subscriber station 616 of the present invention. Signals are received at antenna 600 and provided through duplexer 602 to receiver (RCVR) 604. Receiver 604 downconverts, amplifies and filters the received signal and provides the received signal to demodulator 606 and searcher 608.

In the exemplary embodiment, demodulator 606 demodulates the received signal in accordance with a CDMA demodulator structure and in particular with the CDMA waveform structure described in the '386 application. In the exemplary embodiment, the demodulator operates in accordance with a RAKE structure which is well known in the art. A RAKE demodulator separately demodulates signals that have arrived at the subscriber station via different propagation paths. This provides additional path diversity which result in more reliable demodulation. An exemplary RAKE demodulator structure is described in U.S. Patent No. 5,109,390, entitled "DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM", which is assigned to the assignee of the present invention and incorporated by reference herein.

The received signal is also provided to searcher 608. Searcher 608 searches for other signals transmitted by base stations and sectors in the vicinity of the subscriber station and measures the energies of those signals. In the exemplary embodiment, a message is generated by message generator (MSG GEN) 610 indicative of the base station with the strongest received signal and an indication of the rate requested from that base station determined in accordance with the strength of the received signal. In an alternative embodiment, the message indicates the signal strengths measures for multiple base stations and sectors. The message is provided to modulator 612 and incorporated for transmission into the reverse link traffic signal. The reverse link signal is then provided to transmitter (TMTR) 614. Transmitter 614 upconverts, filters and amplifies the signal for transmission. The signal is provided through duplexer 602 for transmission through antenna 600. In the exemplary embodiment, the receive antennas are similarly either rotated or switched in so that the reverse link transmission of a subset of subscriber stations near sector boundaries are not geographically disadvantaged.

FIG. 7 illustrates the receive subsystem of the base station of the present invention. Reverse link signal are received at the receive subsystem 712 at antenna structure 700. In the first exemplary embodiment, antenna structure 700 is coupled to a rotator 740. In the exemplary embodiment, rotator 740 is a motor that rotates antenna structure 700 at a constant angular velocity in full revolutions about the axis. In an alternative embodiment, rotator 740 varies the angle of antenna structure 700 in a restricted set of angles, such that the motion of antenna structure 700 traverses a set of angles alternating in a clockwise followed by a counterclockwise fashion. The reverse link signals are received by the antennas 702A, 702B and 702C and provided to receivers 706A, 706B and 706C, respectively. Receivers 706A, 706B and 706C down convert, filter and amplify the received signals and provide the received signals to demodulators 708A, 708B and 708C, respectively. In the exemplary embodiment, demodulators 708A, 708B and 708C are code division multiple access communications systems. Again, it will be understood by one skilled in the art that the present invention is not limited by the modulation format used on either link. The demodulated symbols are then provided to control processor 710. In the exemplary embodiment, the demodulated signal includes a message from the subscriber stations indicating the strength of signals received by the subscriber station. The information in the message is used by the base station to determine from which antenna the base station should transmit to each subscriber station in its coverage area. Because the antenna boundaries are moving, the result is the same as placing the stationary and slow moving subscriber stations in motion, which may result in softer handoff when provided for by the base station. Softer handoff is described in detail in the aforementioned U.S. Patent No. 5,625,876.

It is a further advantage of the present invention , that position location can benefit from the sweeping of the forward link signal. As a sector sweeps towards a subscriber station in a predictable fashion, the signal strength will be indicative of the proximity of the subscriber station to the leading edge of the sweeping antenna coverage beam. These changes in the reported signal strengths are used by control processor 710 to estimate the position of the subscriber station.

FIG. 8 illustrates an alternative embodiment of the receiver subsystem of the present invention. In this second embodiment, the physical motion of the receive antenna is replaced by a switching between two or more fixed antenna structures which are pointed in different directions.

Initially, switch 406 receives signals from a first antenna structure 800A, where signals are received through antennas 802A, 802B and 802C and provided to receive subsystems 808A, 808B and 808C. Receive subsystems 808 downconvert, filter, amplify and demodulate the received signals. After a predetermined time interval, switch 806 switches such that the received signals are provided from antenna structure 800B, where signals are received through antennas 804A, 804B and 804C and provided to receive subsystems 808A, 808B and 808C. Receive subsystems 808 downconvert, filter, amplify and demodulate the received signals- Returning to FIG. 5, the sectorization of the cell coverage area is illustrated. A first sectorization pattern is described by solid lines 502A, 502B and 502C, which would be received by antennas 802A, 802B and 802C. A second sectorization pattern is described by dashed lines 500A, 500B and

500C, which would be received by antennas 804A, 804B and 804C.

It is a further advantage of the present invention , that position location can benefit from the alternating forward link signal transmissions. The signal strengths reported by the subscriber station will vary based on the antenna structure from which the forward link signals are transmitted.

These changes in the reported signal strengths are used by control processor

810 to estimate the position of the subscriber station. In the exemplary embodiment, control processor can employ triangulation techniques for the two separate setorizations and in addition can look at the difference in the reported energies to determine the proximity of the subscriber station to a sector boundary in either case of the sectorization.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty.

Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

WE CLAIM:

Claims

1. A base station comprising: a waveform generator for generating a wireless communication signal; and a multi-directional antenna structure for propagating said wireless communication signal along varying propagation paths.

2. The base station of Claim 1 wherein said multi-directional antenna structure, comprises: at least one antenna operatively coupled to a rotator; and rotator for varying the direction of said at least one antenna.

3. The base station of Claim 2 wherein said rotator rotates said at least one antenna about a central axis at an approximately constant angular veolcity.

4. The base station of Claim 2 wherein said rotator rotates said at least one antenna alternating between a clockwise and counter clockwise rotation within a restricted set of angles.

5. The base station of Claim 2 wherein said at least one antenna comprises three antennas operatively coupled to a moving platform.

6. The base station of Claim 1 wherein said base station is a CDMA base station.

7. The base station of Claim 1 wherein said multi-directional antenna structure, comprises: a plurality of antennas; and a switch for alternatingly providing said communication signal between a first subset of said antennas of said plurality of antennas and at least one additional subset of said antennas of said plurality of antennas .

8. The base station of Claim 7 wherein said at least one additional subset of said antennas is a second subset of antennas and wherein the direction in which said second set of antennas is directed bisects the coverage areas of said first subset of antennas.

9. The base station of Claim 7 wherein said base station is a CDMA base station.

10. The base station of Claim 8 wherein said first subset of antennas comprises three antennas and said second subset of antennas comprises three antennas, wherein each of the antennas in said first subset of antennas and said second subset of antennas are directed 120 degrees apart from one another and wherein said second subset of antennas comprises three antennas, wherein each of the antennas in said first subset of antennas and said second subset of antennas are directed 120 degrees apart from one another and wherein said second subset of antennas is directed at 60 degree offset from the direction of said first subset of antennas.

11. The base station of Claim 1, further comprising: a multi-directional antenna structure for receiving said reverse link wireless communication signals along varying propagation paths; and a receiver subsystem for demodulating said reverse link wireless communication signals.

12. The base station of Claim 11 wherein said multi-directional antenna structure, comprises: at least one antenna operatively coupled to a rotator; and rotator for varying the direction of said at least one antenna.

13. The base station of Claim 12 wherein said rotator rotates said at least one antenna about a central axis at an approximately constant angular veolcity.

14. The base station of Claim 12 wherein said rotator rotates said at least one antenna alternating between a clockwise and counter clockwise rotation within a restricted set of angles.

15. The base station of Claim 12 wherein said at least one antenna comprises three antennas operatively coupled to a moving platform.

16. The base station of Claim 11 wherein said base station is a CDMA base station.

17. The base station of Claim 11 wherein said multi-directional antenna structure, comprises: a plurality of antennas; and a switch for alternatingly providing said communication signal between a first subset of said antennas of said plurality of antennas and at least one additional subset of said antennas of said plurality of antennas.

18. The base station of Claim 17 wherein said at least one additional subset of said antennas is a second subset of antennas and wherein the direction in which said second set of antennas is directed bisects the coverage areas of said first subset of antennas.

19. The base station of Claim 17 wherein said base station is a CDMA base station.

20. The base station of Claim 18 wherein said first subset of antennas comprises three antennas and said second subset of antennas comprises three antennas, wherein each of the antennas in said first subset of antennas and said second subset of antennas are directed 120 degrees apart from one another and wherein said second subset of antennas comprises three antennas, wherein each of the antennas in said first subset of antennas and said second subset of antennas are directed 120 degrees apart from one another and wherein said second subset of antennas is directed at 60 degree offset from the direction of said first subset of antennas.