HK1051748B - Wireless communication system with base station beam sweeping - Google Patents

Description

Wireless communication system with base station beam scanning

Technical Field

The present invention relates to wireless communications. More particularly, the present invention relates to providing greater capacity in a multi-user wireless communication system using beam scanning techniques.

Background

Today's communication systems need to support a variety of applications. One such communication System IS a Code Division Multiple Access (CDMA) System that conforms to the "TIA/EIA/IS-95 Mobile Station-Base Station compatibility Standard for Dual-Mode Wireless band Spread Spectrum Cellular System", hereinafter referred to as IS-95. CDMA systems allow voice and data communications between users over a land-based link. The use of CDMA technology IN multiple ACCESS COMMUNICATION SYSTEMs is disclosed IN U.S. Pat. No. 4,901,307, entitled "SPREAD SPECTRUM COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIALREPEATERS," and U.S. Pat. No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM" (both assigned to the assignee of the present invention and incorporated by reference).

The international telecommunications union has recently required the submission of proposed methods for providing high-rate data and high-quality voice services over wireless communication channels. The first of these recommendations was issued by the telecommunications industry association under the name "the cdma2000 ITU-R RTT cancer subscription", hereinafter referred to as cdma2000 and incorporated by reference. A method of transmitting user data (non-voice data) over fundamental and supplemental channels is disclosed in cdma 2000.

In a CDMA system, a user communicates with the network through one or more base stations. For example, a user at a subscriber station communicates with a land-based data network by transmitting data to a base station on a reverse link. The base station receives the data and can transmit the data to a land-based data network through a Base Station Controller (BSC). The forward link refers to transmissions from the base station to the subscriber station, and the reverse link refers to transmissions from the subscriber station to the base station. In an IS-95 system, the forward link and the reverse link are assigned respective frequencies.

During communication, a subscriber station communicates with at least one base station. A CDMA subscriber station is capable of communicating with multiple base stations simultaneously during soft handoff. Soft handoff is the process of establishing a link with a new base station before breaking the link with the previous base station. Soft handoff minimizes the possibility of dropped calls. Methods and SYSTEMs for providing communication with subscriber stations via more than one base station during a SOFT HANDOFF process are disclosed IN U.S. Pat. No. 5,267,261, entitled "Mobile ASSISTED SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM" (assigned to the assignee of the present invention and incorporated by reference). Soft handoff is a process performed when communication occurs over multiple sectors served by the same base station. The handling OF soft HANDOFF is described in detail in co-pending U.S. Pat. No. 5,625,876 entitled "METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEENSECTORS OF A COMMON BASE STATION" (assigned to the assignee OF the present invention AND incorporated by reference).

In existing CDMA systems, soft handoff is established and canceled based on the strength of the base station signal received from the subscriber station. For example, in an IS-95 system, a subscriber station measures the pilot strength levels of multiple base stations. When the pilot strength level received by the subscriber station from the base station exceeds the threshold T _ ADD, the base station joins the subscriber station's active set. When the pilot strength level received by the subscriber station from a base station falls below the threshold T DROP, that base station is removed from the subscriber station's active set. When the strength of the same pilot rises above the threshold T _ ADD again, the base station is rejoined in the active set. Backhaul (backhaul) connections between base stations and their respective base station controllers are typically established and torn down in conjunction with these changes in the active set of each subscriber station. The establishment and dropping of each such backhaul link requires information transfer communication between the base station and the BSC. There is a need to minimize the backhaul capacity consumed by such information transfer communications. For example, in IS-95, the pilot IS not immediately removed from the active set when the received signal strength falls below T _ DROP. An additional criterion is applied that the pilot strength in the active set must remain below tddrop for a guard time T-TDROP. This addition of guard time reduces the likelihood of base stations being removed from the subscriber station active set due to spurious signal level fluctuations.

As the demand for wireless data applications continues to increase, the demand for very efficient wireless data communication systems has also increased dramatically. The IS-95 standard IS capable of transmitting both communication data and voice data on the forward and reverse links. One METHOD OF transmitting communication DATA in fixed-size code channel frames is described in detail in U.S. Pat. No. 5,504,773, entitled "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR transmission" (assigned to THE assignee OF THE present invention AND incorporated by reference). According to the IS-95 standard, communication data or voice data IS segmented into code channel frames that are 20msec wide at a data rate of 14.4 Kbps.

A clear difference between voice services and data services is that the former utilize strict and fixed delay requirements. Typically, the overall one-way delay of a speech frame must be less than 100 msec. Instead, the data delay may be a variable parameter to optimize the efficiency of the data communication system. In particular, more efficient error correction coding techniques can be utilized, which require delays that significantly exceed those that can be tolerated by voice services.

A parameter that measures the quality and performance of a data communication system is the transmission delay required to transmit a data packet and the average throughput of the system. The effect of transmission delay on data communication is not as good as that of voice communication, but it is an important metric for measuring the quality of a data communication system. The average throughput rate is a measure of the effectiveness of the data transmission capability of the communication system.

In a CDMA communication system, capacity is maximized while the transmission energy of the signal is kept to a minimum that meets reliable performance requirements. The reliability of signal reception depends on the carrier-to-interference ratio (C/I) at the receiver. Thus, there is a need to provide a transmission power control system that can maintain a constant C/I at the receiver. Such a System is described in detail in U.S. Pat. No. 5,056,109 (the' 109 patent), entitled "Method and Apparatus for controlling Transmission Power in a CDMA Cellular Telephone System" (assigned to the assignee of the present invention and incorporated by reference).

In the '109 patent, a closed loop power control system is described in which the C/I at the receiver end (referred to as signal-to-noise ratio in the' 109 patent) is measured and compared to a single threshold. When the measured C/I exceeds a threshold, a power control command is sent requesting the transmitter to reduce its transmit power. Conversely, when the measured C/I is below the threshold, a power control command is sent requesting the transmitter to increase its transmit power. Because C/I is not the only factor in determining signal reception reliability, the' 109 patent also describes an outer loop power control system that varies the threshold in order to meet a target reliability.

In cellular systems, it is well known that the C/I of any given user is a function of the location of the user within the coverage area. To maintain a given level of service, TDMA and FDMA systems employ frequency reuse techniques, i.e., not all frequency channels and/or time slots are used in each base station. In a CDMA system, the same frequency assignment is reused in each system cell, thus improving overall efficiency. The C/I achieved by the subscriber station for any given user determines the information rate that can be supported by this particular link from the base station to the subscriber station for that user. By giving the specific modulation and error correction method for transmission that the present invention seeks to optimize for data transmission, a given level of performance can be achieved at a corresponding C/I level. For an idealized cellular system having a hexagonal cell layout and using a common frequency in each cell, the C/I distribution achieved in the idealized cells can be calculated. An exemplary system FOR transmitting high speed digitized data in a wireless communication system is disclosed in co-pending U.S. patent application No. 08/963,386 entitled "METHOD AND APPARATUS FOR HIGHER RATE PACKETDATA TRANSMISSION" (hereinafter the' 386 application, assigned to the assignee of the present invention AND incorporated by reference).

It is well known that most signal interference in a loaded CDMA system is caused by transmitters belonging to the same CDMA system. In an effort to increase capacity, cells are often divided into sectors or smaller cells that operate at lower power, but this approach is costly and difficult to apply in areas with widely varying signal propagation properties. The data communication system of the present invention provides a way to reduce the mutual interference between cells in the system without requiring a large number of smaller cells.

Disclosure of Invention

The present invention provides an improved capacity wireless system that reduces the required transmit power of base stations and subscriber stations in the system by using beam scanning techniques. Rather than rely on a fixed coverage pattern over the coverage area, the base station uses beams to control the transmission and reception of signals along relatively narrow signal beams that "scan" the coverage area of the base station. The scanning of signal beams is referred to herein as beam scanning, and base stations that use beam scanning techniques are referred to as beam scanning base stations.

Transmitting along a narrow signal beam results in less interference to most subscriber stations in neighboring cells. Receiving along a narrow signal beam mitigates interference emanating from subscriber stations located outside the signal beam. By effectively blocking most of the interference from other subscriber stations, subscriber stations located in the signal beam may transmit less reverse link power and achieve the same C/I.

According to an aspect of the present invention, there is disclosed an apparatus for transmitting a signal, comprising: a) means for beamforming a first signal beam having a signal beam angle, the signal beam being located in a base station coverage area; b) means, operably coupled to the means for shaping, for controlling an angle of the signal beam; c) a transmitter operably coupled to the means for shaping for transmitting information signals along the signal beam; d) a buffer operably coupled to the transmitter for storing user data corresponding to one or more target subscriber stations and providing the user data to the transmitter in dependence upon the signal beam angle and the one or more target subscriber stations; and e) a control processor for generating a scan speed control command and varying the angular speed of the signal beam depending on the amount of user data stored in the buffer.

According to a preferred embodiment of the present invention, the base station creates a signal scan using a mechanically controlled directional antenna. These mechanically controlled antennas are installed instead of or in addition to wide beam antennas (e.g., omni-directional or approximately 120 degree antennas for sectored cells). The mechanically steered antenna has a relatively narrow signal beam that covers a portion of the base station coverage area. These antennas move over time and, as a result, their signal beams "scan" over the coverage area of the base station.

In an alternative embodiment of the invention, multiple wide beam antennas are used to create the signal beam instead of mechanically steered antennas. The phases of the signals propagating through each antenna are adjusted so that they create a signal beam that covers a portion of the base station coverage area. By applying a rotating pattern to the signal phase shift of each antenna, the base station "scans" the signal beams over its coverage area.

As the base station signal beam scans through the base station coverage area, the signal beam passes through the portion of the coverage area containing the different active subscriber stations. The transmission of user data is delayed so that the data is transmitted when its destination or source subscriber station is in the beam of the base station signal. Transmitting in a signal beam requires the least transmit power and thus causes the least interference to neighboring cells.

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. 1a is an illustration of a communication system including a beam scanning base station and a subscriber station according to an embodiment of the present invention.

Fig. 1b is an illustration of a communication system including two beam scanning base stations, each transmitting to a subscriber station along its own signal beam, according to an embodiment of the present invention.

Figure 2a is an illustration of the transmit power required to maintain a given level of forward link signal reliability as a function of base station signal beam angle according to an embodiment of the present invention.

Figure 2b is an illustration of pilot strength measured by a subscriber station located in a soft handoff region between two beam scanning base stations according to an embodiment of the present invention.

Fig. 3a is a block diagram of a wireless communication device including a beam scanning base station that uses multiple antennas to shape a transmit signal beam in accordance with an embodiment of the present invention.

Fig. 3b is a block diagram of a wireless communication device including a beam scanning base station that uses directional antennas to shape a transmit signal beam in accordance with an embodiment of the present invention.

Fig. 4a is a block diagram of a wireless communication device having a beam scanning base station that uses multiple antennas to shape a receive signal beam in accordance with an embodiment of the present invention.

Fig. 4b is a block diagram of a wireless communication device having a beam scanning base station that uses directional antennas to shape a receive signal beam in accordance with an embodiment of the present invention.

Fig. 5 is a block diagram of a base station controller apparatus configured in accordance with an embodiment of the invention.

Fig. 6 is a block diagram of a subscriber station arrangement configured in accordance with an embodiment of the present invention.

Fig. 7a is a flow chart of a method of collecting information for correlating a subscriber station with a signal beam angle in accordance with an embodiment of the present invention.

Fig. 7b is a flow diagram of a method for efficiently transmitting user data from a beam scanning base station on the forward link in accordance with an embodiment of the present invention.

Fig. 8 is a flow diagram of a method for determining when to establish, tear down, and maintain a backhaul connection in a wireless communication system in accordance with an embodiment of the present invention.

Fig. 9 is a flow chart of a method for determining when to transmit reverse link user data in accordance with an embodiment of the present invention.

Detailed Description

Fig. 1a is an illustration of a communication system for communicating data between network 116 and subscriber station 108 through beam scanning base station 102. The network 116 is connected to a Base Station Controller (BSC)114, which controls data through the base stations 102. Although only one base station is shown, preferred embodiments may include many base stations, each connected to BSC114 via backhaul 118 a. Base station 102 uses beam scanning techniques and is referred to herein as a beam scanning base station. Wireless systems configured in accordance with the present invention may use beam scanning base stations exclusively or may include a mix of beam scanning and non-beam scanning base stations.

The information received over the backhaul 118a includes a combination of voice communications and user data communications. One property of voice communications is that it cannot be delayed to maximize throughput or for error control protocol purposes. However, user data communications carry information that is more tolerant of delay. An example of such user data is internet protocol packets that have benefited from the error control protocol, such as TCP. Variations in transmission delay may be allowed for these types of packet data communications.

Base station 102 transmits and receives signals in the cell sector coverage area (referred to herein simply as the coverage area) between sector boundaries 112. Base station 102 transmits and receives signals along signal beam 110 via directional antenna 104, which has pattern 106. Directional antenna 104 is mounted on a motor (not shown) inside base station 102 and rotates to change the direction in which signal beam 110 is directed. Active subscriber stations 108 located in the coverage area receive and demodulate signals transmitted by base station 102 through directional antenna 104. A subscriber station 108 is said to be active when a call or communication channel exists between the subscriber station 108 and one or more base stations (e.g., base station 102, also referred to as a serving base station).

In the exemplary embodiment, signal beam 110 is swept in a direction from sector boundary 112a to sector boundary 112b at a generally constant angular velocity. As soon as the beam reaches sector boundary 112b, it starts its next sweep from sector boundary 112 a.

Subscriber station 108b, although not located along signal beam 110, may also communicate with base station 102 if side lobes 107 of propagation pattern 106 have sufficient amplitude. In the exemplary embodiment, during the scanning of signal beam 110, subscriber station 108 sends power control commands to base station 102 as needed to achieve a target carrier-to-interference ratio (C/I). As signal beam 110 sweeps from sector boundary 112a toward sector boundary 112b, base station 102 needs to change its transmit power level for each subscriber station 108 to achieve the target C/I.

By associating the transmit power required for each subscriber station 108 for each signal beam angle, the base station 102 can determine the best signal beam angle to communicate with each subscriber station 108. As signal beam 110 is continuously scanned, base station 102 predicts when the signal beam angle is most suitable for efficient transmission of forward link supplemental channel communications to each subscriber station 108. Base station 102 buffers the user data transmitted to the subscriber station until signal beam 110 reaches a signal beam angle that is best suited for transmission to the subscriber station. In this case, user data can be transmitted to the target subscriber station with minimal impact on surrounding cells.

For example, user data sent to subscriber station 108a (received from network 116 and through BSC 114) is buffered by base station 102 until signal beam 110 is at the optimal angle for transmission to subscriber station 108 a. The optimal angle is an angle at which the minimum transmission power can be used while maintaining the target C/I. When signal beam 110 is at the optimal angle, the buffered user data is transmitted to subscriber station 108a in pulses. The pulse is transmitted using a plurality of supplemental channels if needed.

In an alternative embodiment, user data sent to subscriber station 108a is buffered at BSC114, rather than at base station 102. Buffering user data at BSC114 allows for adjustment of user data sent to subscriber stations in soft handover regions between two or more cells. For example, the BSC114 monitors the transmit power levels required by the first and second base stations to achieve the same C/I at the subscriber station. Because both base stations scan their signal beams toward the subscriber station, the BSC114 transmits user data bursts during two respective optimal beam periods.

In an alternative embodiment, the scanning speed of signal beam 110 is increased or decreased as needed to optimally adjust the data traffic load to and from subscriber stations in the base station coverage area. By speeding up or slowing down its beam sweep, the base station 102 adjusts the signal beam 110 to spend most of its time aligning with the region having the greatest density of active subscriber stations. In another alternative embodiment, the base station adjusts the signal beam 110 velocity to spend most of the time aligning the subscriber station region containing the most user data that must be sent to it. In another alternative embodiment where BSC114 buffers data for transmission to subscriber stations, BSC114 transmits control signals to each base station, e.g., base station 102. The control signal specifies the speed at which each base station beam is scanned.

Although directional antenna 104 is shown as a mechanically moving disk-type antenna, those skilled in the art will appreciate that other methods may be used to create directional signal beam 110 with directional pattern 106. For example, signal beams may be created using a phased array antenna or a plurality of spatially separated antennas without departing from the invention.

As described below, in an alternative embodiment using a plurality of spatially separated antennas, the beam scanning the base station transmits a signal through each antenna, the signal being identical except for the phase of the signal. By controlling the phase of the signals transmitted via the antennas, the base station adjusts the portion of the coverage area so that all of the transmitted signals can be received in phase with each other. When the signals are received by subscriber stations in the coverage area, they combine constructively to form a stronger composite signal for demodulation by the subscriber stations. When signals are received by subscriber stations in the coverage area in an alien manner, they interfere with each other, reducing the strength of the composite signal demodulated by the subscriber stations.

The same results would occur for signals received by a base station from subscriber stations in its coverage area. Due to the spacing between the receiving antennas, the signals received by each antenna arrive at slightly different phases from each other. The phase adjustment of the signal received by each receiving antenna serves to align the phases of signal components arriving along the propagation path (hereinafter referred to as received signal beams). Signals received in directions other than along the receive signal beam tend to combine destructively. For this reason, they cause less interference to signals received along the receive signal beam. Thus, the same reverse link signal reliability may be achieved with lower transmit power from the subscriber stations transmitting along the receive signal beam.

Typically, a beam scanning base station causes less transmission interference to neighboring cells than a base station transmitting over a wide beam over its coverage area. In addition, beam scanning base stations that receive signals from the receive signal beam require less power to be transmitted by the subscriber station, with the result that the subscriber station causes less interference to neighboring cells.

When mechanical means are used to form the signal beam, such as a dish antenna, the signal beam angles of the forward link and reverse link signal beams are the same. When multiple antenna beam scanning devices are used, such as with phased array antennas, the angle of the signal beam depends on the phase applied to the signal. Because the carrier frequencies of the forward and reverse links are different, the angles of the respective transmit and receive signal beams may also differ from one another. The difference in the transmit and receive signal beam angles depends on many parameters such as the type and location of the antenna, the difference between the forward and reverse link carrier frequencies, and the technique used to adjust the phase of the signal through the antenna.

Sometimes, a base station must transmit broadcast information to all subscriber stations in its cell coverage area. Because it is unlikely that all subscriber stations in its cell will be aligned along the same beam, this broadcast information is preferably transmitted using a wide beam so that it reaches all subscriber stations in the coverage area of the base station. In a base station that forms signal beams using parabolic antennas, such broadcast information is transmitted using an additional wide beam antenna 120. However, in a beam scanning base station using a plurality of phased antennas, a wide beam coverage can be achieved without an additional antenna. In the exemplary embodiment, broadcast information, such as a paging channel, is transmitted on a wide transmit beam using only one of the multiple antennas. Access channel information is received over a wide beam by receiving signals via one or more antennas without using phase shifting (conventional diversity reception).

Those skilled in the art will appreciate that wide beam antenna 120 may be any of a number of types of antennas without departing from the present invention. For example, wide beam antenna 120 may be a coaxial array, a dipole antenna, or a parabolic antenna having a relatively wide beam.

If the base station 102 uses a non-mechanical beam scanning method, e.g., using multiple antennas, the signal beam used to transmit signals to the subscriber stations in its cell may be different from the signal beam used to receive signals from the subscriber stations. Thus, the beam used to transmit the forward link signals may be scanned in a different direction and at a different speed than the beam used to receive the reverse link signals.

Fig. 1b is a communication system that includes two beam scanning base stations 102 that transmit to subscriber stations 108. As described above, beam scanning base station 102 forms signal beams 110a and 110b using non-mechanical means. By adjusting the relative phase of the signals transmitted and received via each of the plurality of antennas 120, the base stations 102 change the angle of the directional pattern of their respective signal beams 110 and optionally change the shape of the directional pattern. As shown, base station 102a transmits and receives through multiple antennas 120a to form signal beam 110 a. Base station 102b transmits and receives through multiple antennas 120b to form signal beam 110 b.

Each base station 102 is connected to a Base Station Controller (BSC)114 via a backhaul 118. In an alternative embodiment, base station 102 sends power control and signal beam angle for each subscriber station 108 to BSC 114. The BSC114 uses this information to determine the optimal beam angle for each subscriber unit 108 and sends beam sweep speed commands to each base station 102 to vary the rate at which their signal beams are swept in their respective coverage areas. When both beams are at an optimal angle toward the subscriber station, then both the transmission level to the subscriber station 108 and the transmission level from the subscriber station 108 are minimized. The BSC114 adjusts the beam sweep rate of the base station 108 in order to maximize the overall capacity and throughput of the network.

Those skilled in the art will recognize that techniques that allow BSC114 to control the beam scanning speed of beam scanning base station 102 may be equally well applied in beam scanning base stations that use mechanical directional antennas, such as the parabolic antennas described in conjunction with fig. 1. Those skilled in the art will also appreciate that wireless systems employ beam scanning base stations that use mechanical beam forming devices and beam scanning base stations that use non-mechanical beam forming devices without departing from the present invention.

In an alternative embodiment, beam scanning base station 102 further adjusts the relative phase shifts of the signals transmitted and received by antennas 120 to change the directional pattern shape of their respective signal beams 110. For example, the directional pattern may be adjusted wider or narrower to accommodate changes in loading in different base station coverage areas. The shape of the directional pattern may be controlled locally at each base station 102 or centrally by the BSC 114.

In an alternative embodiment, each base station 102 sends power control, signal beam angle, and shape information for each subscriber station 108 to BSC 114. The BSC114 uses this information to determine the best beam shape to use by each base station 102 over time. The BSC114 sends commands to each base station 102 to change the shape of their signal beams over time.

Figure 2a shows the transmit power required to maintain a given level of signal reliability from base station 102 to subscriber station 108b as a function of the angle of signal beam 110. The increase or decrease in power of the required transmit power is varied as needed to maintain the target C/I with respect to the direction of the signal beam 110. The x-axis is shown spanning from 0 degrees to 120 degrees, illustrating the signal beam angle over a 120 degree cell sector. A signal beam 110 is said to have an angle of 0 degrees when the signal beam 110 is aligned approximately parallel to the sector boundary 112a, and a signal beam 110 is said to have an angle of 120 degrees when it is aligned approximately parallel to the sector boundary 112 b.

As signal beam 110 continues to sweep from sector boundary 112a to sector boundary 112b, it passes through an angle that maintains the minimum transmit power required for the target C/I. The minimum required transmit power 202 shown on the exemplary illustration corresponds to a signal beam angle of approximately 35 degrees. As signal beam 110 continues to increase to the point where the optimal C/I angle for subscriber station 108b, the transmit power from the base station increases to a maximum at a signal beam angle of approximately 55 degrees. As signal beam 110 continues its scan, mobile station 108b is exposed to sidelobe 107a of antenna 104 propagation pattern 106. The drop in transmit power associated with exposure to the side lobe 107a is shown as a smaller drop 204 in the desired transmit power curve.

Fig. 2b is an idealized graph showing pilot strength measured by a subscriber station located in a soft handoff region between two CDMA beam scanning base stations using the beam scanning technique described above. The pilot signal strength received from the first base station is shown as curve 266 and the pilot signal strength received from the second base station is shown as curve 268. The x-axis serves as a time axis, and the beam scanning patterns of the two base stations are different from each other.

When the first base station's beam exposes the subscriber station to the first sidelobe, its pilot signal strength rises to a smaller peak 256 a. As the beam continues to sweep, the beam passes through the best signal beam angle received by the subscriber station, as shown by the larger peak 252 a. The curve continues through a smaller peak 258 caused by side lobes. As the signal beam angle from the first base station sweeps to the end of the sector and transitions to the other side of the sector, a discontinuity appears in the curve as shown at 264. This continuum illustrates what happens when signal beam 110 of base station 102 sweeps to sector boundary 112b and begins to sweep again from sector boundary 112 a. The pilot signal strength of the first base station continues to repeat the pattern 256b exposed to the side lobes and the pattern 252b of the best signal beam angle for the other subscriber station.

The pilot signal strength curve 268 of the second base station shows the sidelobe peaks 260 and 262 and the optimum signal beam angle peak 254 in a similar manner. In the illustrated example, the pilot strength 266 associated with the first base station is generally greater than the pilot strength 268 associated with the second base station. In the illustrated example, the pilot strength peaks 252 associated with the first base station are also generally larger than the pilot strength peaks 254 associated with the second base station.

In a wireless system including a base station using beam scanning techniques, the scanning pattern of the base station antennas is regular and predictable. It is believed that the pilot channel peak 252a associated with the first base station will reappear after one beam sweep period. If the beam sweep period is greater than T _ TDROP, then conventional soft handoff techniques will remove the first base station from the subscriber station's active set. In addition, conventional soft handoff techniques break the base station/BSC backhaul connection corresponding to the subscriber station. As the beam from the first base station sweeps again in the subscriber station direction, the subsequent peak in the first base station power level received by subscriber station 252b will again rise above T _ ADD. Then, conventional soft handoff techniques will re-establish the backhaul connection between the first base station and the BSC for the subscriber station. All of this establishment and dropping of backhaul connections wastes bandwidth between the base station and the BSC. In addition, the delays inherent in establishing and dropping these connections increase the likelihood of dropped calls. For these reasons, excessive establishment and withdrawal of backhaul connections is undesirable.

In an exemplary embodiment of the invention, knowledge of the base station 102 scanning pattern is used to prevent unnecessary dropping of the backhaul connection with the BSC114 soon after the connection has just been reestablished. When the pilot strength from beam scanning base station 102 to subscriber station 108b falls below T DROP, base station 102 is removed from the active set of subscriber station 108 b. However, rather than dropping the connection, the base station 102 and BSC114 maintain the full corresponding backhaul connection in anticipation that the pilot strength can quickly rise back above T _ ADD. In alternative embodiments, the handoff and backhaul connections are reserved by increasing T _ TDROP or decreasing T _ DROP.

In some cases, two subscriber stations 108 may be located in an area covered by beam scanning base station 102 where base station 102 is not in the active set of both subscriber stations 108 at the same time. In other words, base station 102 will not be in the active set of subscriber station 108b as long as the signal beam angle is such that base station 102 is in the active set of subscriber station 108 a. Alternatively, base station 102 may not be in the active set of subscriber station 108a as long as the signal beam angle is such that base station 102 is in the active set of subscriber station 108 b. When this occurs, the base station 102 may multiplex the same Walsh channel for transmission to any subscriber station 108.

Alternatively, when base station 102 is in the active set of subscriber station 108a, the signal C/I from base station 102 measured by subscriber station 108a may not be sufficient for any reliable reception. When this occurs, the base station 108 may multiplex the same Walsh channel to transmit to the subscriber station 108b with the higher C/I. In other words, the base station 102 may be in the active set of two subscriber stations 108 at the same time and both use the same Walsh channel, but transmit to only one subscriber station 108 at a time. The target subscriber station is selected based on which subscriber station measured the higher C/I.

Fig. 3a is a block diagram of a wireless communication device including a beam scanning base station that transmits through multiple antennas, wherein the beam scanning is accomplished by varying the phase of signals passing through the multiple antennas, in accordance with an embodiment of the present invention. The Base Station Controller (BSC)114 provides communication signals transmitted to the subscriber station to the base station 102 over a backhaul connection 118a, where the signals are received by a backhaul interface 304.

Backhaul interface 304 multiplexes the different types of data received from BSC114 and conveys them to different modules and processors in base station 102. For example, backhaul interface 304 provides voice communications destined for the subscriber station immediately to channel element module 306 for modulation and transmission by transmitter 308. The backhaul interface 304 communicates user data to a buffer 305 that holds the user data until its release to the channel element module 306 is controlled by a control processor 316. The channel element module 306 generates modulated signals that are upconverted and amplified in the transmitter 308. The transmitter 308 then transmits the amplified signal through the signal beam former 330.

In the exemplary embodiment, signal beamforming device 330 includes a plurality of phase shifters 310. Each phase shifter shifts the phase of the signal received from transmitter 308 before transmission through antenna 312. The amount of phase shift provided by each phase shifter 310 is dependent on a control signal from the beam sweep controller 314.

The beam sweep controller 314 controls the beam angle of the signal transmitted via the antenna 312 by controlling the amount of phase shift that occurs by each phase shifter 310. As described above, the beam sweep controller 314 transmits a control signal to each phase shifter 310 in order to change the angle of the transmission signal beam over time. The rate at which the beam sweep controller 314 changes the direction of the signal beam is dependent on the control signal received from the control processor 316.

Those skilled in the art will appreciate that beamforming may be implemented in several alternative ways without departing from the invention. The plurality of antennas 312 may also be mounted in various configurations, such as perpendicular to a plane or along a cylindrical surface, without departing from the invention.

One advantage of using multiple antennas instead of a mechanically directional antenna is that the broadcast communication device 326 may use one beam scanning antenna for the broadcast coverage of the cell. For example, antenna 324 n is omitted and antenna 312n is connected to receiver 318, transmitter 322, and phase shifter 310 n.

Another advantage of using multiple antennas is that the signal beam direction pattern 106 may vary over time. In the exemplary embodiment, beam sweep controller 314 changes beam directivity pattern 106 by adjusting the phase control signals provided to phase shifters 310. In another embodiment, the beam sweep controller 314 changes the beam direction pattern 106 by changing the number of antennas 312 through which signals are transmitted. Using fewer antennas 312 results in a wider beam, while using more antennas 312 results in a narrower beam. The beam sweep controller 314 changes the number of antennas used for transmission in any of several possible ways. The beam sweep controller 314 sends control signals to each phase shifter 310 that indicate the level of attenuation change to be performed on the transmit signal. The beam sweep controller 314 effectively cancels transmissions through a subset of the antennas 312 by indicating a high attenuation level to the corresponding subset of phase shifters 310.

In the exemplary embodiment, the techniques described above are used to adjust the width of the directional pattern 106 based on the load in the coverage area of the base station 102. Control processor 316 monitors parameters such as the amount of data stored in buffer 305 and the number of active subscriber stations corresponding to each signal angle. Based on these parameter values, the control processor 316 sends control signals to the beam sweep controller 314, which changes the directivity pattern 106 accordingly. For example, for an idle communication coverage area, wider beams are employed, while narrower beams are employed when scanning through a busy communication area (an area with many active subscriber stations or an area to which a large amount of data is to be transmitted).

The exemplary embodiment shown includes means for providing wide coverage beam coverage in addition to the means required for communication along a single beam. In the exemplary embodiment of the invention shown, the backhaul interface 304 may also multiplex certain types of data to a second channel element module 320 that provides a transmitter 322 with a modulated signal for transmission over a single antenna 324. Transmitting through the single antenna 324 provides a non-scanning broad beam and results in substantial broadcast to the base station 102 coverage area. For use in an omni-directional cell, antenna 324 is an omni-directional antenna. For use in a sectorized cell, antenna 324 is an approximately 120 degree directional antenna.

In addition to wide beam transmission, reception over a wide beam may be supported by coupling antennas 324 and 328 to receiver 318, which receiver 318 provides the down-converted signals to channel element module 320 for demodulation. Because the signals received through antennas 324 and 328 are not phase shifted, they provide conventional diversity reception for receiver 318. Such wide beam reception is more suitable for channels such as access channels than beam scanning because the timing of access channel transmissions is typically controlled by the user of the subscriber station rather than by the signal beam angle. Those skilled in the art will recognize that receiver 318 may also use more than two antennas for diversity reception or a single receive antenna 324 may be used without departing from the invention.

The receiver 318, the channel element module 320, the transmitter 322, and the antenna 324 together comprise a broadcast communication device 326. The type of channel being transmitted and received by the broadcast communication device 326 is a paging and access channel. In an alternative embodiment of the invention, the voice communication is transmitted using a broadcast communication device and only the user data communication is transmitted using a beam scanning apparatus.

Channel element module 320 also decodes power control commands from the signals received from each active subscriber station in the cell and sends them to control processor 316. The control processor 316 uses the power control information to determine the best signal beam angle corresponding to each active subscriber station. The control processor 316 then uses this information to control the speed of beam scanning by sending control signals to the beam scanning controller 314. As described above, the scanning of signal beam 110 is accelerated and decelerated as needed to best adjust the user data traffic load to and from the subscriber stations in the base station cell.

In an alternative embodiment, the beam sweep controller 314 operates independently of the control processor 316. In an alternative embodiment, the beam sweep controller 314 sweeps the signal beam at a generally constant speed from one side 112a of the cell to the other side 112 b. Control processor 316 analyzes the timing of the power control commands received from the subscriber stations in order to predict a recurring pattern of optimal transmit periods associated with each active subscriber station.

In another alternative embodiment, beam sweep controller 314 is coupled to control processor 316, but does not receive commands from control processor 316. The beam sweep controller 314 transmits only the current signal beam angle to the control processor 316 for analysis of the active subscriber station optimum transmission period.

As the signal beam 110 of the base station 102 scans through its coverage area, it passes the angle at which signals can be most efficiently transmitted to or from an individual active subscriber station 108. Control processor 316 sends control signals to buffer 305 instructing the buffer to hold user data for each subscriber station until the beam reaches the optimal angle for transmission to that subscriber station. When the beam reaches or approaches the optimal angle for the subscriber station, control processor 316 sends information to buffer 305 to release the user data collected for the subscriber station to channel element module 306. The channel element module 306 then modulates the user data and sends it to the transmitter 308. In the preferred embodiment of the present invention, channel element module 306 modulates the user data from buffer 305 for transmission to the target subscriber station using one or more supplemental data channels.

In another alternative embodiment, the buffer 305 is located in the BSC114 instead of in each base station 102. Placing the buffer 305 in the BSC enables user data to be transmitted from multiple base stations using soft handoff. The BSC may transmit through multiple base stations even if only one base station transmits through a beam at the best angle of the target subscriber station. In another alternative embodiment, BSC114 sends beam sweep speed control commands to control processor 316 through backhaul interface 304. BSC114 may then adjust the signal beams of the multiple beam scanning base station to further improve data throughput to the target subscriber station.

Fig. 3b is a block diagram in a wireless communication system device in which signal beamforming is accomplished by rotating a narrow beam directional antenna in accordance with an alternative embodiment of the present invention. In an alternative embodiment, the signal beam former 330 mechanically comprises a directional narrow beam antenna 350, shown as a parabolic antenna, mounted on a rotary motor 352. Motor 352 provides signal beam angle information to control processor 316 to help adjust the signal beam angle with the power level of the signal being transmitted to the active subscriber station. The control processor 316 receives control commands from the BSC114 and accelerates or decelerates the motor 352.

Fig. 4a is a wireless communication system apparatus having a base station 102, the base station 102 shaping a receive signal beam using multiple receive antennas according to an embodiment of the present invention. In the illustrated embodiment, the receive beamforming device 412 includes a phase shifter 410 that changes the phase of the signal received by the antenna 312. The signals received by the phase shifter 410 are summed in a signal combiner 409 and provided to a receiver 408, which down-converts the combined signal and provides it to the channel element module 306. The module 306 demodulates and decodes the received signal and sends the resulting user data to the BSC114 via the backhaul interface 304. The beam sweep controller 314 generates control signals that are provided to each phase shifter 410 to adjust the amount of phase shifting performed in each phase shifter 410, thereby changing the angle of the received signal beam.

As shown, the receiver 408 receives signals from the antenna 312 through an additional connection that bypasses the phase shifter 410. These additional connections generally allow receive signal diversity without reception by shaped signal beams. The subscriber station signal strength received in this manner will depend on the location of the subscriber station in the coverage area rather than a single beam angle. By processing the signals received with and without the phase shifters, the base station 102 can employ suitable beam-sweeping techniques and broadcast communication techniques for different channels. For example, this type of "broadcast" reception coverage is more appropriate for signals such as access channel signals received from non-active subscriber stations.

As described above, the beam scan controller 314 may scan the receive beam at a constant speed independent of commands from the control processor 316, or may control acceleration or deceleration of the beam scan by control signals received from the control processor 316. Additionally, control processor 316 may receive beam sweep speed commands from BSC114 via backhaul interface 304.

As described with respect to the forward link, the beam sweep controller 314 may vary the beam direction pattern 106 of the reverse link by adjusting the phase control signals provided to the phase shifters 410. In the exemplary embodiment, beam sweep controller 314 changes beam direction pattern 106 by changing the number of communications 312 through which signals are received. Using fewer antennas 312 results in a wider beam, while using more antennas 312 results in a narrower beam. The beam sweep controller 314 changes the number of antennas used for transmission in any of several possible ways. For example, the beam sweep controller 314 sends control signals to each phase shifter 410 that indicate the level of attenuation change to be performed on the received signal. The beam sweep controller 314 effectively cancels transmissions through a subset of the antennas 312 by indicating a high attenuation level to the corresponding subset of phase shifters 310.

In the exemplary embodiment, the techniques described above are used to adjust the width of the directional pattern 106 based on the effective subscriber station diversity in different areas of the coverage area of the base station 102. Control processor 316 monitors the number of active subscriber stations corresponding to each signal beam angle. Based on these parameter values, control processor 316 sends control signals to beam sweep controller 314, which changes reverse link direction pattern 106 accordingly. For example, for a sparsely populated coverage area, a wider beam is used, while a narrower beam is used when scanning through a densely populated area (an area with many active subscriber units).

Fig. 4b is a block diagram of a wireless communication system device having a beam scanning base station that uses a mechanically aligned directional antenna 450 to shape its reverse link signal beam. In the illustrated embodiment, receive beamforming means 412 comprises a directional antenna 450 mounted on a motor 452 that scans the receive signal beam over the coverage area of base station 102. The signal received by directional antenna 450 is provided to receiver 408, which downconverts the combined signal and provides it to channel element module 306. Channel element module 306 demodulates and decodes the received signal and sends the resulting user data to BSC114 via backhaul interface 304. Control processor 316 receives scan speed commands from BSC114 via backhaul interface 304 and increases and decreases the scan speed of motor 452 accordingly.

Directional antenna 450 is shown as a parabolic antenna, although those skilled in the art will recognize that other mechanically aligned beam forming means may be used in place of it without departing from the present invention. One result of using this method of mechanical beamforming is that the forward link signal beam has the same angle as the reverse link signal beam.

In the above device illustrations, the receiver and transmitter are described as being directly connected to the antenna. Without departing from the invention, an RF duplexer may be placed between the receiver, transmitter and antenna when the receiver and transmitter operating at different frequencies share a common antenna.

Fig. 5 is a block diagram of a wireless communication system base station controller apparatus configured in accordance with an embodiment of the present invention. A number of subscriber stations may exchange user data with network 116 through BSC114 and a base station coupled thereto via backhaul 118.

An interworking function (IWF)504 serves as an interface for the network 116 and the rest of the BSC 114. The IWF504 converts the network data into a format suitable for transmission in the wireless communication system. Data from the IWF504 to be transmitted to the subscriber station is stored in a data buffer 510. The user data buffer 510 accumulates user data until the release of the user data to the backhaul interface 512 is controlled by the base station beam controller 506, at which interface 512 the data is transmitted over the backhaul 118 to the corresponding base station.

The base station beam controller 506 receives power control and beam sweep information corresponding to each active subscriber station and base station in its wireless network. The base station beam controller 506 adjusts the forward power level to the signal beam angle or the beam sweep timing of each active subscriber station-beam sweep base station pair. The conditioned data is stored in the subscriber base station beam database 508. From the data stored in the database, base station beam controller 506 determines the optimal signal beam angle or beam sweep time for each active subscriber station. Using this information, base station beam controller 506 generates a best throughput window prediction for each subscriber station.

Several different types of information may be used by base station beam controller 506 to form these estimates without departing from the present invention. As described above. The base station beam controller 506 may use a transmit power level corresponding to the target C/I. Alternatively, the base station beam controller 506 may use fast power control up and down power commands that are inserted into the reverse link signal. Alternatively, the base station beam controller 506 may use a combination of these types of signals. The base station beam controller 506 may receive signal beam angle information from the beam sweep controller 314 in each base station or may track power control fluctuations over a known beam sweep period.

In an alternative embodiment, the base station beam controller 506 generates beam scanning speed control commands that are sent to the beam scanning controller 314 in each beam scanning base station 102. The base station beam controller 506 uses these commands to expand the beam coverage of a cell area having a high density of subscriber stations. The expanded beam coverage is also provided for cell areas with fewer subscriber stations but a large amount of user data to exchange. In general, it is desirable for base station beam controller 506 to use beam sweep speed control commands to maximize overall user data throughput to all subscriber stations served by BSC 114.

In another alternative embodiment, the base station beam controller 506 generates beam direction pattern control commands that are sent to the beam sweep controller 314 in each beam scanning base station 102. The base station beam controller 506 uses these commands to adjust the directional pattern 106 based on the commands to obtain better beam coverage for the selected cell area, based on the density of active subscriber stations or the amount of user data to be exchanged in the selected area,

those skilled in the art will recognize that beam sweep controller 314 and base station beam controller 506 may be implemented using Field Programmable Gate Arrays (FPGAs), Programmable Logic Devices (PLDs), Digital Signal Processors (DSPs), microprocessors, Application Specific Integrated Circuits (ASICs), or other devices capable of interpreting and generating the signals and commands required by the controllers. Those skilled in the art will appreciate that this does not preclude the beam sweep controller 314 or the base station beam controller 506 from being implemented in another processor or controller present in each base station 102 or BSC114 in the wireless system.

The digital gain block may be implemented using a Field Programmable Gate Array (FPGA), a Programmable Logic Device (PLD), a Digital Signal Processor (DSP), a microprocessor, an Application Specific Integrated Circuit (ASIC), or other device capable of performing the required digital processing in response to a signal from a controller (e.g., a control block). It will be appreciated by those skilled in the art that this does not preclude the possibility of implementing the control module in a digital gain module. Those skilled in the art will also appreciate that the digital gain block may also be placed before the mixer, between the phase controlled oscillator and the mixer, or may be built-in the phase controlled oscillator without departing from the invention.

Fig. 6 is a block diagram of a subscriber station arrangement configured in accordance with an embodiment of the present invention. The subscriber station 108 adjusts its reverse link data rate to transmit user data during the period when the serving base station can most efficiently receive the subscriber station's reverse link signal. These periods generally coincide with the best signal beam angle in the beam sweep range of the base station for a given beam sweep base station. Optimizing reverse link power in this manner increases the capacity of the reverse link because subscriber stations transmitting at lower power levels cause less interference between each other.

In an exemplary embodiment of the present invention, the forward link signal is received through antenna 620 and passed through RF duplexer 618. The forward link signal is gain controlled and downconverted in a receiver 616, and the receiver 616 provides the resulting downconverted signal to a demodulator-decoder 614. User data, such as packet data demodulated by demodulator 614, is provided to data interface 602.

In the reverse direction, the data interface 602 provides user data, e.g., packet data, to the transmit data buffer 604. The transmit data buffer 604 stores the user data until it can be efficiently transmitted to the base station 102 serving the subscriber station 108 (also referred to as the serving base station). When at the appropriate time, transmit data buffer 604 provides user data to modulation-encoder 606, which modulates the user data for transmission. Modulation-encoder 606 then provides the modulated user data to transmitter 608, which upconverts and amplifies the signal. The upconverted and amplified signal is then provided to an RF duplexer 618 and transmitted via an antenna 620. The duplexer allows the transmitter 608 and receiver 616 to use the same antenna 620 without interfering with each other.

Power control module 612 performs power control for the forward and reverse links. The receiver 616 measures the received signal strength and provides the information to the power control module 612. The demod-decoder decodes the power control information received from the serving base station and provides the information to the power control module 612. The decoded power control information may include reverse link power control thresholds, power control commands for up/down insertion in the forward link, and statistical frame error rate and erasure information. The signal strength and power control information is used by power control module 612 to generate a threshold ratio between the received power level and the transmit power level. The power control module 612 then uses this information to adjust the power level of the reverse link signal transmitted from the transmitter 608.

In the preferred embodiment of the present invention, the power control module 612 further monitors the signal-to-noise ratio of the received forward link signal and sends the power control signal to the serving base station through the modulation-encoder 606. These signals may be in the form of signal messages, but are preferably up/down commands inserted into the reverse link signal. In an alternate embodiment of the present invention, each subscriber station 108 transmits a multi-bit power control command specifying the forward link power adjustment corresponding to a particular base station in the subscriber station's active set. In another alternative embodiment, subscriber station 108 transmits a multi-bit power command by subscriber station 108 that conveys an estimated signal strength of a signal received by a particular base station.

Power control module 612 provides signals to control processor 610 based on the reverse link power level. When subscriber station 108 is served by one or more beam scanning base stations 102, the transmit power of subscriber station 108 will be affected by the beam scanning pattern of the serving base station. The power control mechanism described above causes the transmit power of subscriber station 108 to decrease as the signal beam of base station 102 sweeps to an angle that provides efficient reception of the reverse link signal from subscriber station 108. The power control mechanism described above causes the transmit power of the subscriber station 108 to increase as the signal beam is scanned away from the optimum angle of the subscriber station 108.

The power control module 612 provides the power level sent to the transmitter 608 to the control processor 610. Control processor 610 controls the release rate of reverse link user data from transmit data buffer 604 in accordance with the transmit power level. The control processor 610 uses information from the power control module 612 to predict the period when user data can be most efficiently transmitted from the subscriber station 108 to the serving base station. These periods generally correspond to periods when beam scanning base station 102 is receiving along a signal beam directed to subscriber station 108.

In the preferred embodiment of the present invention, base station 102 and subscriber station 108 transmit multiple signals to each other using CDMA techniques. The plurality of signals transmitted on the forward link and the reverse link include a fundamental channel and a supplemental channel. Both must use a bidirectional fundamental channel whenever the subscriber station exchanges data with the base station. When a higher data rate is required in the forward or reverse direction, one or more unidirectional supplemental channels are established in the required direction.

In the preferred embodiment, data buffer 604 is used to buffer user data even though a reverse link supplemental channel has not been established. For example, on a reverse link fundamental channel where the user data rate received from the data interface 602 is less than the fundamental channel capacity, the fundamental channel data rate is varied to maximize efficiency. In other words, subscriber station 108 allows user data to be transmitted from transmit data buffer 604 in full-rate frames when the signal beam of base station 102 is directed to subscriber station 108. When the signal beam of base station 102 is directed away from subscriber station 108, subscriber station 108 transmits user data from transmit data buffer 604 in less than full-speed frames. However, if transmission at a lower rate during the inactive period causes the transmit data buffer 604 to overrun, the subscriber station 108 will transmit continuously at full speed on the fundamental channel.

Fig. 7a is a method for collecting information for adjusting a subscriber station to signal scan angle in accordance with an embodiment of the present invention. The adjustment is based on the forward link power level required to maintain a target C/I level for each active subscriber station. Alternatively, the use of the target C/I level may be replaced by a target data rate with a particular quality of service. For example, power control is implemented to provide the power level required to support 19,200 bits per second (bps) with a 1% Frame Error Rate (FER).

In the exemplary embodiment, this method is used in BSC114 when populating subscriber base station beam database 508 with information. In an alternative embodiment, the method is used in the control processor 316 to adjust the signal beam angle of individual base station users.

Each time the base station signal beam angle is incremented (step 702), the forward link power level required to maintain the target C/I ratio is measured for each active subscriber station serviced by the base station (step 704). The measured forward link power levels are stored in a database for adjustment by the control processor (step 706).

Fig. 7b is a flow diagram of a method for efficiently transmitting user data from a beam scanning base station on the forward link in accordance with an embodiment of the present invention. User data received by the base station and transmitted to the active subscriber stations is buffered (step 752). The signal beam angle of each beam scanning base station is incremented periodically or continuously over time (step 754). For each set of subscriber stations (SS's) best located in the current signal beam angle, the previously buffered user data is released for transmission on the forward link (step 756).

In the exemplary embodiment, the signal beam angle of the serving base station is maintained until all forward link user data is transmitted to the subscriber station located at the best position of the signal beam angle. At appropriate intervals, the amount of user data remaining to be transmitted to the subscriber stations is estimated (step 758). Once it is determined that the forward link user data for these subscriber stations has been exhausted (step 758), the signal beam angle of the beam scanning base station is incremented again (step 754).

Fig. 8 is a flow diagram of a method used by BSC114 to determine when to establish, tear down, and maintain a backhaul connection with a beam scanning base station in accordance with an embodiment of the present invention. The flow chart begins with a backhaul connection having been established between the base station 102 and the BSC114 to support the subscriber station 108 communications (step 802). The subscriber station 108 periodically measures the signal strength received from the base station 102 (step 804) and compares the signal strength to a handoff disconnect threshold (T DROP) (step 806). If the signal from the base station 102 is below the handoff disconnect threshold, the base station 102 is removed from the active set of the subscriber station 108 (step 808).

At this point, rather than immediately dropping the corresponding backhaul connection, the likelihood that the same backhaul connection will have to be established again in the near future (over the beam sweep period) is estimated (step 810). If the likelihood is low, the corresponding backhaul connection is torn down (step 812) and processing resumes (step 814). If the likelihood is high, the backhaul connection is left intact even though the base station 102 is no longer in the active set of the subscriber station 108.

Fig. 9 is a flow chart of a method used by the subscriber station 108 to determine when to transmit user data stored in the transmit data buffer 604 in accordance with an embodiment of the present invention. As described above, the subscriber station 108 adjusts its reverse link user data rate to transmit user data during the period when the serving base station is most efficient at receiving the subscriber station reverse link signal.

In the preferred embodiment, the data is transmitted in a continuous sequence of frames having a fixed duration. For example, in a conventional IS-95 system, the frame duration IS 20 milliseconds and transmission begins on a20 millisecond boundary. Initially in preparation for each frame period (step 902), the subscriber station 108 estimates the amount of user data in the transmit data buffer 604. If the buffer is empty (no user data to transmit), then the subscriber station does not transmit user data and waits for the next transmit station cycle (step 912).

If there is user data to be transmitted, then an estimate is made of the efficiency with which the data is transmitted on the reverse link immediately (step 906). For example, if the transmit power is below the reverse link power threshold, then user data is transmitted immediately (step 910). For example, the transmit power may be lower when the receive signal beam used by the serving beam scanning base station is at an optimal angle for the subscriber station.

If the transmit power is not below the reverse link power threshold, the subscriber station estimates (step 908) whether the user data is accumulating too quickly to merit an inefficient transmission of data (step 910) (at a higher power). If, for example, there is a risk that the user data will exceed the subscriber station buffer capacity limit, then the data is immediately transmitted (step 910).

After the user data is transmitted (step 910), processing of the user data is complete (step 912) until the next frame period (step 902). Although shown as separate steps, steps 904, 906, and 908 may be performed in a different order or may be combined without departing from the invention.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. 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.

Claims (18)

1. Apparatus for transmitting a signal, comprising:

a) means for beamforming a first signal beam having a signal beam angle, the signal beam being located in a base station coverage area;

b) means, operably coupled to the means for shaping, for controlling an angle of the signal beam;

c) a transmitter operably coupled to the means for shaping for transmitting information signals along the signal beam;

d) a buffer operably coupled to the transmitter for storing user data corresponding to one or more target subscriber stations and providing the user data to the transmitter in dependence upon the signal beam angle and the one or more target subscriber stations; and

e) a control processor for generating a scan speed control command and varying the angular speed of the signal beam in accordance with the amount of user data stored in the buffer.

2. The apparatus of claim 1, wherein the means for forming comprises:

a.1) a plurality of phased transmit modules, wherein each module of the plurality of phased transmit modules receives the information signal and changes the phase of the information signal in accordance with one of a plurality of phase control signals to create a phased information signal,

wherein each of the plurality of phased transmit modules further comprises an antenna; and a phase shifter operably coupled to the antenna for receiving the information signal and creating the phased information signal and transmitting the phased information signal through the antenna; and

a.2) a beam sweep controller operatively coupled to each of said phase shifters for generating said plurality of phase control signals so that the combined signals transmitted from said plurality of phased transmit modules form said signal beam.

3. The device of claim 2, wherein the beam sweep controller further changes the shape of the signal beam over time by adjusting the plurality of phase control signals.

4. The apparatus of claim 2, further comprising:

a second transmitter for transmitting a second information signal primarily over the coverage area through the antenna of one of the plurality of phased transmit modules.

5. The apparatus of claim 2, further comprising: a receiver operably coupled to the means for shaping for receiving a first reverse link signal through the shaping means.

6. The apparatus of claim 5, wherein said reverse link signal is received via said first signal beam.

7. The apparatus of claim 5, wherein said first reverse link signal is received via a second signal beam having a second signal beam angle.

8. The device of claim 5, further comprising one or more receive antennas comprising one or more of the antennas of the phased transmit module.

9. The apparatus of claim 2 wherein said beam sweep controller adjusts said signal beam angle such that said signal beam is swept in a coverage area in a direction.

10. The apparatus of claim 1 wherein the power level transmitted to each of said one or more target subscriber stations corresponds to the power level required to maintain the carrier-to-interference ratio (C/I) of each of said one or more target subscriber stations at said angle value.

11. The apparatus of claim 1, wherein the buffer is located in a base station of a wireless communication system.

12. The apparatus of claim 1, wherein the buffer is located in a Base Station Controller (BSC) of a wireless communication system.

13. The apparatus of claim 1, wherein the means for controlling is a rotating motor and the means for shaping is a directional parabolic antenna operably coupled to the rotating motor.

14. The apparatus of claim 1, further comprising a transmitter for transmitting a second information signal substantially in said coverage area.

15. The apparatus of claim 1 wherein said means for controlling controls said signal beam angle such that the angle of said signal beam changes at a relatively constant rate in said coverage area.

16. The apparatus of claim 1, further comprising a receiver operably coupled to the shaping means for receiving a reverse link signal through the shaping means.

17. The apparatus of claim 16, wherein the reverse link signal is received through the signal beam.

18. The apparatus of claim 16 wherein said reverse link signal is received via said second signal beam.