HK1061769A - Method and apparatus for using position location to direct narrow beam antennas - Google Patents

Description

Method and apparatus for steering narrow beam antennas with positioning

Background

RELATED APPLICATIONS

This application claims priority to U.S. provisional application No. 60/249870, published on 6/11/2000.

Technical Field

The present application relates to communication systems and methods. More particularly, the present application relates to systems and methods for improving the performance of cellular telephone systems.

Description of related art:

cellular telephone systems feature a number of base stations each equipped with a transceiver. The transceivers are typically connected to antenna arrangements that provide a coverage area or "cell". Conventional antenna arrangements typically include three antennas, each radiating energy over an angle of 120 ° to provide the 360 ° coverage required by the cell.

A smart antenna is an array of antenna elements, each receiving a signal to be transmitted with a predetermined phase shift. The net effect of the array is to direct the (transmit or receive) beam in a predetermined direction. The beam is steered by controlling the phase relationship of the signals that excite the array elements. Thus, smart antennas direct a beam into each individual user (or multiple users) as opposed to each conventional antenna radiating energy to all users within a predetermined coverage area (e.g., 120 °). Smart antennas increase system capacity by reducing beamwidth and thus interference. As interference decreases, the signal-to-interference ratio and signal-to-noise ratio increase may result in improved performance and/or capacity. In power control systems, this results in a reduction in transmit power for a given level of performance.

While smart antennas can effectively improve capacity, one problem associated with using smart antennas is locating the user to which a given beam is to be directed. In the reverse link, the angle of arrival of the energy transmitted by the user is used to calculate the user's position by triangulation or other suitable techniques. Unfortunately, current techniques for calculating angle-of-arrival information are computationally intensive.

In addition, the system is suitable for environments that receive energy from a user through a straight line. Unfortunately, in certain (e.g., urban) environments, this condition does not hold because the signal is typically reflected off of buildings or other structures or received as a multipath beam.

Accordingly, there is a need in the art for a system or method for increasing system capacity for a cellular telephone system. In particular, there is a need in the art for a system or method for determining the location of a user in a cellular telephone system with a smart antenna.

Summary of the invention

The principles of the present invention address the need in the art. The system of the present invention includes a novel mobile unit that communicates with a new and advantageous base station. The mobile unit includes a system for generating location information and a transceiver for transmitting the location information. In a preferred embodiment, the transceiver is a CDMA (code division multiple access) system and the system for generating location information comprises means for receiving a Global Positioning System (GPS) signal.

The inventive base station is operative to receive location information from a remote unit and to provide a received location signal responsive thereto. The novel base station also carries a mechanism for directing the beam in response to receiving the location signal. In an illustrative embodiment, the mechanism for directing the beam is a smart antenna system that includes an antenna array and a beam generating network for exciting the array to output the directed beam.

Brief description of the drawings

Fig. 1 is a block diagram illustrating a section of a substantially conventional cellular system.

Fig. 2 is a diagram of a cellular telephone system using a smart antenna system.

Figure 3 is a diagram illustrating the components of the propagation of an electromagnetic field between a subscriber unit and a base station.

Fig. 4 is a block diagram of an illustrative implementation of a mobile station in accordance with the principles of the invention.

Fig. 5 is a block diagram of an illustrative implementation of a base station in accordance with the principles of the invention.

Fig. 6 is a block diagram of an illustrative implementation of a smart antenna system incorporating the principles of the invention.

Fig. 7 is a flow chart of a beam-forming algorithm implemented according to conventional principles based on a minimum mean square error algorithm.

Fig. 8 is a flow chart illustrating a spatial processing method used by the method of directing a narrow beam of the present invention.

Fig. 9 is a flow chart of an illustrative algorithm for providing beam forming to a user for reporting their location in accordance with the principles of the invention.

Description of the invention

Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous principles of the invention.

While the present invention is described herein with reference to illustrative embodiments for particular applications, it will be understood that the invention is not limited thereto. Those of ordinary skill in the art will recognize that there are other modifications, applications, and embodiments within the scope thereof and other fields in which the present invention may be of significant utility, which would make use of the present principles.

Fig. 1 is a block diagram illustrating one sector of a basic conventional cellular system. The system 10 'includes a base station 20' that transmits signals to and receives signals from a plurality of subscriber units 30 ', i.e., three sector antennas 22', 24 ', 26', respectively. Each antenna is defined to provide a 120 sector of coverage area 28'. The coverage areas provided by the three antennas (e.g., 26 ', 22 ', 24 ') in fig. 1 are shaded. Thus, three antenna groups are typically used to provide the 360 ° coverage area required by each cell. In fig. 1, a base station 20 'uses one transmit (forward link) antenna 26' and two diversity (return link) antennas 22 'and 24', as is common in the art. Although this method has been used effectively to date, its capacity is somewhat limited. As described above, smart antennas are now beginning to be used to increase the capacity of cellular telephones.

Fig. 2 is a diagram of a cellular telephone system using smart antennas. The system 10 "of fig. 2 is similar to the system shown in fig. 1, except that the three sector antennas 22 ', 24', and 26 'of fig. 1 are replaced with a smart antenna array 40'. For comparison, the coverage sector 28' of the conventional system depicted in fig. 1 is shown. As shown in fig. 2, the smart antenna is an array of antenna elements 42', each receiving a signal to be emitted with a predetermined phase shift. The net effect of the array 40 'is to direct the transmit or receive beam 44' into a predetermined direction. Each beam may be controlled by controlling the phase relationship of the signals used to excite (or receive from) the elements 42 'of the array 40'. Thus, smart antennas direct a beam into each individual user as opposed to each conventional antenna radiating energy to all users within a predetermined coverage area (e.g., 120 °). Thus, smart antennas increase system capacity by reducing beamwidth and thus interference. As interference decreases, the signal-to-interference ratio and signal-to-noise ratio increase may result in improved performance and/or capacity.

However, as mentioned above, while smart antennas can effectively improve capacity, one problem associated with using smart antennas is locating the user to which a given beam is to be directed. In the reverse link, the angle of arrival of the energy transmitted by the user is used to calculate the user's position by triangulation or other suitable techniques. Unfortunately, current techniques for calculating angle-of-arrival information are computationally intensive.

Unfortunately, in certain (e.g., urban) environments, this condition is not effective because the signal is typically reflected off of buildings or other structures or received as a multipath beam. This is depicted in fig. 3.

Figure 3 is a diagram illustrating the components of the propagation of an electromagnetic field between a subscriber unit and a base station. Fig. 3 shows four multipath components, which are caused by reflections or scattering from the environment.

Accordingly, there remains a need in the art for a system or method for increasing the system capacity of a cellular telephone system. More specifically, there is a need in the art for a system or method for determining the location of a user in a cellular telephone system with a smart antenna. The principles of the present invention address this need. The inventive system includes a novel mobile unit that communicates with a new and advantageous base station.

Fig. 4 is a block diagram of an illustrative implementation of a mobile unit in accordance with the principles of the invention. The mobile unit 30 includes a first antenna 32 for receiving positioning signals from a remote system, such as a global positioning system. The signals from the GPS antenna 32 are processed by a GPS signal processor 34. The GPS processor 34 outputs the position data to a system controller 36 which selectively multiplexes the position data with data provided by a transceiver 38 through a user interface 37 for transmission. In the preferred embodiment, the transceiver 38 is a code division multiple access transceiver. However, those of ordinary skill in the art will appreciate that the present invention is not so limited. The present principles may be used with communication technologies such as TDMA or GSM without departing from the scope of the present principles.

As discussed in detail below, in a preferred embodiment, a GPS-assisted device is used, wherein GPS overhead data is received by the base station 20 and transmitted to the mobile unit 30 to shorten acquisition time. In addition, unit 30 is used to receive signals from aerial platforms as well as from satellite-based platforms. In any case, the positioning information is transmitted by the transceiver 40 to the base station 20 shown in fig. 5.

Fig. 6 is a block diagram of an illustrative implementation of a base station in accordance with the principles of the invention. As shown in fig. 6, the base station 50 includes a smart antenna array 40 of spatially positioned radiating elements 42. The array 40 may be a conventional phased array antenna design. In the preferred embodiment, the array 40 is part of a Smart Antenna (Smart Antenna) system and feeds Smart Antenna processing circuitry 50. The processing circuitry 50 includes a number of receivers 52, a plurality of beamforming elements 54, a spatial processor 60, and a Rake receiver 70.

Returning briefly to fig. 5, in accordance with the principles of the invention, the system processor 100 provides signals from the GPS signal processing period 110 to the spatial processor 60. As discussed in detail below, the processor is programmed in accordance with the principles of the present invention to use the position data provided by the user and the base station position data to rotate the beams output by the array 40.

Fig. 6 is a block diagram of an illustrative embodiment of a smart antenna system incorporating the principles of the invention. As shown in fig. 6, each of the n elements 42 of the antenna array 40 feeds an associated one of n receivers 52. In the illustrative embodiment, each receiver 52 downconverts and demodulates the signal received by element 42 and performs matched filtering as appropriate for a given user. Thus, each receiver receives a Radio Frequency (RF) input signal from an antenna element and processes it to output a baseband signal for each user.

Each receiver 52 is connected to all beamformers 54 and to a spatial processing unit 60. The beamforming operations include multiplication and addition operations. The beamformer receives each baseband signal from the receiver, performs a multiplication operation on the baseband signals and then adds them to a single signal. Thus, each beamformer 54 includes a multiplier 56 that multiplies the received baseband signal by a weight provided by a spatial processing unit 60. The multiplier 56 performs complex multiplication. This operation is required for each beam. There are typically multiple beams per user and multiple users. The actual beam is formed by adding the complex multiplied samples in each beamformer 54 with an adder 58.

The summed signal is provided to rake receiver 70. The rake receiver 70 receives the beamformer output and relays and combines the signals in an optimal fashion. This operation occurs under the control of the spatial processing unit for each I and Q sample. The spatial processing unit 60 is responsible for determining the characteristics of the beams to be formed. The spatial processing unit 60 implements an advantageous beamforming algorithm in accordance with the inventive principles discussed in detail below.

For CDMA based systems, the best beamforming scheme from the user capacity point of view is achieved by maximizing the signal-to-noise-plus-interference ratio. Using typical methods such as the "optimal Wiener solution" results in increased complexity, expense and potential time delays. This is explained below with reference to fig. 7-9.

Fig. 7 is a flow chart of a beamforming algorithm implemented according to conventional principles based on a minimum mean square error algorithm. As shown in fig. 7, the process 200 ' includes confirming user access to the system at step 210 ' and generating a pilot signal in response thereto at step 220 '. At step 230 ', the received signal vector is sampled and used at step 240' to create an equation for the beamformer output. At step 250', an error function is created between the pilot signal and the beamformer output. The error function is then minimized using the Wiener-Hopf equation or an optimal Wiener scheme at step 260'. Finally, at step 270', the best weights are applied to the beamformers. Unfortunately, the computation of weights involves the computation of eigenvalues and other linear algebraic operations that require a large number of processor operations.

In accordance with the principles of the present invention, these problems are solved by using user location data and (local terrain data) to determine beamformer weights. This method of the invention is best illustrated with reference to fig. 8.

Fig. 8 is a flow chart illustrating a spatial processing method used by the method of directing a narrow beam of the present invention. The novel method 200 uses user location data and optionally local terrain data to determine beamformer weights and includes the step of confirming user access to the system (210). If the user reports his location at step 220, the algorithm shown in FIG. 9 is used at step 230.

Fig. 9 is a flow chart of an illustrative algorithm for providing beam forming to a user for reporting their location in accordance with the principles of the invention. At steps 232 and 234, the position of the user and the position of the base station 20 are provided to the spatial processing unit 60 (fig. 6), which calculates the orientation of the user relative to the base station at step 236. Those skilled in the art will appreciate that the present principles are not limited to the method by which the user's location is determined. Other techniques may be used to determine the location of the user and base station without departing from the scope of the present principles. The user direction is calculated by converting the GPS coordinate data to beamforming coordinate data and by using triangulation techniques known to those skilled in the art.

The number and direction of beams are then calculated at steps 238 and 240 using information provided by the optional multipath database 240.

The database may be based on either an analysis of the environment or on the measurements performed. It is assumed that the measured data is more accurate. Moving objects may be driven through the coverage area. The position of the moving object and the angle of arrival of the energy will be recorded. This data can be used to create a multipath database. Finally, at step 242, the antenna array characteristics provided at step 244 are used to determine the gain and phase of the antenna pattern.

Returning to fig. 8, at step 220, if the user does not report their location, the system uses an algorithm that generates a pattern that covers the entire sector.

Returning to fig. 5, the output of the smart antenna processor 50 is the input to a transceiver 80 having a design and configuration compatible with the transceiver 38 of the mobile unit 30. The transceiver 80 communicates with a Public Switched Telephone Network (PSTN)140 through a bidirectional switch 130.

Accordingly, the present invention has been described herein with reference to particular embodiments for particular applications. Those skilled in the art and access to the teachings of the present invention will recognize additional modifications, applications, and embodiments within the scope thereof.

It is therefore contemplated by the appended claims to cover any and all such applications, modifications and variations of the present invention within the scope thereof

Examples are given.

Claims (21)

1. A mobile transceiver, comprising:

a system for generating location information and an apparatus for issuing the location information.

2. The invention of claim 1 wherein said system for generating location information comprises means for receiving signals from satellites.

3. The invention of claim 2 wherein said system for generating location information includes means for receiving global positioning system signals.

4. The invention of claim 1 wherein said system for generating location information comprises means for receiving signals from an airborne platform.

5. The invention of claim 1 wherein said means for transmitting said location information comprises a CDMA transmitter.

6. A base station, comprising:

means for receiving location information from a remote unit and providing a received location signal in response thereto, and

means for steering a beam in response to the receive location signal.

7. The invention of claim 6 wherein said location information is provided at least in part by a global positioning system.

8. The invention of claim 7 wherein said remote unit is a mobile transceiver.

9. The invention of claim 8 wherein said mobile transceiver is a CDMA transceiver.

10. The invention of claim 8 wherein said beam is directed to said transceiver.

11. The invention of claim 6 wherein said means for directing a beam comprises a smart antenna.

12. The invention of claim 11 wherein said means for directing a beam comprises an antenna array.

13. The invention of claim 12 further comprising means for exciting said array to output a directed beam.

14. The invention of claim 13 wherein said means for exciting comprises a beam forming network.

15. A cellular communication system, comprising:

a mobile transceiver, comprising:

GPS system for generating position information and device for sending out said position information, and

a base station, comprising:

means for receiving said location information and providing a received location signal in response thereto, an

Means at the base station for directing a beam in response to the received location signal.

16. The invention of claim 15 wherein said GPS system is GPS-assisted.

17. The invention of claim 15 wherein said means for directing a beam comprises a smart antenna.

18. The invention of claim 17 wherein said means for directing a beam comprises an antenna array.

19. The invention of claim 18 further comprising means for exciting said array to output a directed beam.

20. The invention of claim 19 wherein said means for exciting comprises a beam forming network.

21. A method for affecting directional cellular communications, comprising the steps of:

generating location information at the mobile transceiver;

transmitting the position information;

means for receiving said location information at a base station and providing a received location signal in response thereto; and

directing a beam from the base station to the mobile transceiver in response to the received location signal.