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Title:
VARIABLE BEAMWIDTH MULTIBAND ANTENNA
Document Type and Number:
WIPO Patent Application WO/2018/140837
Kind Code:
A1
Abstract:
An antenna system includes an antenna lens, and one or more antenna feeds placed at an on or off-focal point of the antenna lens. Each of the one or more antenna feeds comprises one or more antenna feed elements that are electrically independently operable. The antenna system also includes an antenna feed network electrically coupled with the one or more antenna feed elements via signal paths.

Inventors:
FANFELLE, Robert (2550 Walsh Avenue, Suite 150Santa Clara, CA, 95051, US)
Application Number:
US2018/015618
Publication Date:
August 02, 2018
Filing Date:
January 27, 2018
Export Citation:
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Assignee:
COHERE TECHNOLOGIES (2550 Walsh Avenue, Suite 150Santa Clara, CA, 95051, US)
International Classes:
H01Q19/06; H01Q5/00; H01Q21/00; H01Q21/06; H01Q25/00
Foreign References:
US20100207833A12010-08-19
US20050052333A12005-03-10
EP0868082A21998-09-30
US4769646A1988-09-06
US20150091767A12015-04-02
Attorney, Agent or Firm:
SATHE, Vinay et al. (Perkins Coie LLP, P.O. Box 1247Seattle, WA, 98111-1247, US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. An antenna system, comprising:

an antenna lens;

one or more antenna feeds placed at an on or off-focal point of the antenna lens;

wherein each of the one or more antenna feeds comprises one or more antenna feed elements that are electrically independently operable; and

an antenna feed network electrically coupled with the one or more antenna feed elements via signal paths.

2. The antenna system of claim 1, wherein each of the antenna feed is designated to operate in one or more frequency bands and wherein position and/or size of the one or more antenna feed elements for each antenna feed depend on the one or more frequency bands of operation.

3. The antenna system of claim 1, wherein at least one antenna feed is capable of simultaneous operation in at least two frequency bands and wherein the at least one antenna feed includes multiple antenna elements that are grouped to operate in different ones of the at least two frequency bands.

4. The antenna system of claim 1, wherein at least one antenna feed is capable of simultaneous operation in at least two frequency bands and wherein the at least one antenna feed includes an antenna feed element that is coupled to the antenna feed network using a frequency stacked configuration in which the antenna feed element simultaneously receives or transmits signals in two different frequency bands and wherein the antenna feed network includes a diplexer.

5. The antenna system of claim 1, wherein the off-focal point is a near- field point.

6. The antenna system of claim 1, wherein the off-focal point is a far-field point.

7. The antenna system of claim 1, further including an antenna feed that is positioned conformal to the antenna lens.

8. A method of operating a wireless transmission station to provide wireless signal coverage to a geographical region, comprising:

operating a number of antenna feeds for transmission and reception of signals, each antenna feed comprising multiple antenna elements, wherein each antenna element is sensitive to a pre-determined range of frequencies, and wherein the antenna feeds are arranged in an antenna array on or near surface of a lens antenna, the antenna array extending along an azimuth axis and an elevation axis; and

controlling beamwidths of antenna beams using two or more antennas for signal transmission such that an equal-density signal coverage is provided to geographic areas irrespective of their distance from the wireless transmission station.

9. The method of claim 8, wherein at least some antennas in the antenna array comprise multiple antenna feed elements, and wherein the method further includes:

adjusting phases of signals fed to the multiple antenna feed elements to cause an additive or subtractive effect on the signal magnitude, thereby resulting in a beam with a greater or smaller beamwidth.

10. The method of claim 9, further including positioning the multiple antenna feed elements at an on-focal or off-focal point of the antenna.

11. The method of claim 9, wherein the transmission and reception of signals includes transmission and reception of signals in multiple non-overlapping frequency bands.

12. The method of claim 11, wherein the multiple non-overlapping frequency bands include a low frequency band and a high frequency band, and wherein beamwidths of the low frequency band and the high frequency band are separately controlled.

13. The method of claim 11, wherein the beamwidths of the low frequency band and the high frequency band are different from each other.

Description:
VARIABLE BEAMWIDTH MULTIBAND ANTENNA

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent document claims benefit and priority of U.S. Provisional Patent

Application No. 62/451,547 entitled "VARIABLE BEAMWIDTH MULTIBAND ANTENNA", filed on January 27, 2017. The entire content of the aforementioned patent application is incorporated by reference as part of the disclosure of this patent document.

TECHNICAL FIELD

[0002] The present document relates to wireless communication, and more particularly, to antenna designs for transmission and reception of wireless signals.

BACKGROUND

[0003] Due to an explosive growth in the number of wireless user devices and the amount of wireless data that these devices can generate or consume, current wireless communication networks are fast running out of bandwidth to accommodate such a high growth in data traffic and provide high quality of service to users.

[0004] Various efforts are underway in the telecommunication industry to come up with next generation of wireless technologies that can keep up with the demand on performance of wireless devices and networks.

SUMMARY

[0005] This document discloses antennas that can be deployed in wireless networks to provide efficient, multiband signal coverage.

[0006] In one example aspect, a transmit antenna configuration is disclosed. The antenna configuration comprises one or more antenna feeds, with each antenna feed comprising one or more antenna feed elements that are electrically independently operable. The one or more antenna feeds are positioned in an on or off-focal point of a lens antenna. The antenna configuration also includes an antenna feed arrangement that provides transmission signals to the antenna elements. A corresponding receive antenna configuration can be realized in a similar manner; all further mentions of transmit aspects also imply that a similar receive case feature as well. Similarly, in those cases where an explanation is based on the receive case, it is implied that an equivalent transmit configuration / interpretation exists.

[0007] In another example aspect, a method of operating a wireless transmission station is disclosed. The method includes arranging a number of antenna feeds in an antenna array on or near the surface of a Luneburg Lens, the antenna array extending along an azimuth axis and an elevation axis. The method further includes operating antenna feeds comprised of multiple antenna elements, each element sensitive to a range of frequencies. The wireless transmission station may further include a dynamic weighted magnitude and phase shifting network, comprised of analog and/or digital components, which process one or more communication signals and provide the signals to antenna array elements and antenna feeds, to modify the effective beam width of the transmitted/received signals. One embodiment will generate shaped transmission beams using two or more antenna feeds and/or antenna elements in antenna feeds for signal transmission such that an approximately equal-density signal coverage is provided to geographic areas irrespective of their distance from the wireless transmission station.

[0008] These, and other, features are described in this document.

DESCRIPTION OF THE DRAWINGS

[0009] Drawings described herein are used to provide a further understanding and constitute a part of this application. Example embodiments and illustrations thereof are used to explain the technology rather than limiting its scope.

[0010] FIG. 1A shows an example communication network.

[0011] FIG. IB shows an example of a lens antenna configuration.

[0012] FIG. 2 shows example antenna configurations for beamforming.

[0013] FIG. 3 shows an example of an antenna configuration in which multiple antenna elements are used for multiple frequency bands.

[0014] FIG. 4 shows an example of an antenna configuration in which multiple antenna elements are used for transmission using frequency stacking.

[0015] FIG. 5A shows an example of feed element configuration in an antenna

configuration.

[0016] FIG. 5B shows example feed element configurations in a wideband antenna.

[0017] FIG. 6 illustrates different possible radial positioning of antenna elements. [0018] FIG. 7 depicts examples of beamforming to achieve a wider and a narrower beamwidth pattern.

[0019] FIG. 8 shows an example of a variable beamwidth antenna and a corresponding example radiation pattern.

[0020] FIG. 9 is a flowchart for an example method of wireless communication.

[0021] FIG. 10 is a block diagram for an example wireless communication apparatus.

DETAILED DESCRIPTION

[0022] To make the purposes, technical solutions and advantages of this disclosure more apparent, various embodiments are described in detail below with reference to the drawings. Unless otherwise noted, embodiments and features in embodiments of the present document may be combined with each other.

[0023] Section headings are used in the present document, including the appendices, to improve readability of the description and do not in any way limit the discussion to the respective sections only. Unless otherwise noted, abbreviations used in the present document are consistent with generally well-known 3GPP terminology. For the ease of explanation, many techniques and structures are described in the context of signal transmissions. However, using duality of transmission/reception, similar features are also applicable for signal reception techniques.

[0024] FIG. 1A shows an example communication network 100 in which the disclosed technologies can be implemented. The network 100 may include a base station that, in the downlink, transmits wireless signals s(t) (downlink signals) to one or more UEs (user equipment, which may be mobile stations, customer premises equipment, etc.) acting as receivers 102, the received signal being denoted as r(t), where the UEs may be located in a variety of locations, including inside or outside a building or in a moving vehicle. The UEs may transmit uplink transmissions to the base station. The technology described herein may be implemented at a UE 102 or at the a base station. In the case of a fixed wireless transmission system, the UE 102 may be relatively static. For example, the receiver 102 may be affixed to an outside wall or roof of the building (not shown in FIG. 1A). In the case of high-altitude platforms, the base station may be mounted on a balloon, drone, or similar device. The technology may also be implemented on devices used for device-to-device communications, including nodes in mesh networks. [0025] FIG. IB shows an example of a lens antenna. As depicted in the ray drawing on the right (152), in a traditional lens antenna, an antenna feed is placed at the focal point of the lens antenna such that signals transmitted from the antenna feed are sent into the direction of the associated beam. The graph 150 shows an example of permittivity of the antenna material as a function of distance from the center of the sphere to achieve the focal concentration effect. Two curves are shown - the smooth curve is the theoretical permittivity, which varies continuously and smoothly throughout the breadth of the lens, while the step-wise curve represents a practical implementation in which permittivity is a step function. Such a practical implementation may be achieved by layering together several concentric spherical pieces with variable dielectric properties. The block diagram 152 shows convergence of signal beams as they travel through the antenna lens from air (right hand side) to the focal point, where an antenna feed is shown to be located.

[0026] The relative dielectric constant at distance r from the center of the lens to an interior point is given by the equation: s r = 2 - (r/a) 2 , where a is the outer radius of the lens.

[0027] FIG. 2 shows additional examples of antenna designs to achieve the beamforming. In embodiment 202, dielectric constant of the lens material is continuously varied to achieve the desired focal point of convergence (e.g., similar to the smooth curve in graph 150). As depicted, multiple antenna feeds 200 may be placed at multiple locations around the spherical lens, thereby resulting in the antenna being able to transmit multiple signal beams in different spatial directions.

[0028] In embodiment 204, discrete material layers may be used, each layer having a different dielectric constant, to achieve focus of radiated or received wireless signals in a particular direction. While only one antenna feed is shown in embodiment 204, in general, multiple antenna feeds may be used to enable transmission of multiple beams.

[0029] FIG. 3 shows an example configuration of an antenna feed 300 in which multiple antenna feed elements 302 are used for transmitting/receiving signals. The antenna feed elements 302 may be used in various configurations, as described herein.

[0030] The multiple antenna feed elements 302 may be driven by a phased network that provides (or receives) the corresponding signals to the antenna feed elements 302. For example, in some embodiments, an antenna feed 300 may operate to transmit or receive wireless signals in multiple frequency bands. Without loss of generality and only for illustrative purpose, the multi- band embodiments are described with reference to two frequency bands - a 3.5 GHz frequency band (e.g., between 2.5and 3.5 GHz or between 3.55 and 3.7 GHz) and a 5.8 GHz frequency band (e.g., frequencies between 5.1 and 5.9 GHz) for multiple frequency bands. However, it is understood that the disclosed techniques can be used for multiple (greater than two) frequency bands at different operational frequencies.

[0031] The antenna feed 300 is made up of separate antenna feed elements 302, each of which may have its own electrical connection with a feeder network 304 that may include a phase adjustment circuit and/or a diplexer. In one example use case, each antenna element may be used for transmission/reception of a single frequency band, with the feeder network 304 performing the selectivity of which antenna element to map to which frequency band. In the depicted example, signals for transmission/reception within bands 1 to X (where X is an integer) may be fed into the phase + diplexer network, separated and fed into the antenna feed elements 302.

[0032] FIG. 4 shows an example of an antenna feed 400 in which multiple antenna elements 402 are used for transmission using frequency stacking. For example, frequency stacking may be achieved by generating a single wideband signal that includes signals in two or more separate frequency bands. Thus, a frequency stacking technique may use a same antenna port or antenna element, for transmitting signals in two different frequency bands. To support frequency stacking, e.g., allowing at least some antenna feed elements to transmit or receive signals in multiple frequency bands, the feeder network 404 may include a phase adjustment circuit, one or more diplexers and one or more up/down converters. The antenna configuration in FIG. 4 may be used to provide multi-band signals by simultaneously driving signals to (or from) the antenna elements.

[0033] FIG. 5A shows an example of an antenna feed element configuration in an antenna feed. In general, the layout and number of antenna feed elements may depend on frequency band of operation and on the desired impact on the resulting beamwidths and beamshapes. Diplexers may be used when antenna feed elements have wider bandwidth sensitivity than individual antenna port frequency bands. In some embodiments, in place of the diplexer, a frequency selective combined phase network may be used.

[0034] In some embodiments, each antenna feed element may be dedicated to one frequency band, and in general, there may be more than one antenna feed element for any given band. For example, FIG. 5 A depicts that N antenna elements are used for Band_2

communication and M antenna feed elements are used for Band_l communication. Multiple antenna elements for a given frequency band may be driven to perform beam-combining as described in the present document.

[0035] FIG. 5B shows additional examples of possible embodiments of antenna feeds. As shown in example 550, an antenna feed may be operable in two frequency bands - a 3.5 GHz band being coupled with a phase network (PN) that operates at the 3.5 GHz band, and a second PN operating at the 5.8 GHz band. Each of these PNs may be independently connected with corresponding antenna elements via electrical connections, each connection carrying a band- specific signal, which is referred to as a narrowband signal (because it represents less than the entirety of bandwidth handled by the antenna feed).

[0036] In embodiment 552, some of the antenna feed elements are shown to be exclusively coupled with either the 3.5 GHz band PN or the 5.8 GHz band PN, thus operating in one frequency band only, while other antenna feed elements are shown to operate in a wideband configuration in which signals from multiple frequency bands are frequency stacked to provide (or receive) a wideband connection through a diplexer. Therefore, in general, an antenna feed may include antenna feed elements that may include a first group of dedicated, or narrowband, antenna elements, and a second, non-overlapping, group of antenna feed elements that operates as a wideband element that transmits/receives more than one bands of signals, and possibly all bands in which the antenna feed operates.

[0037] In embodiment 554, each antenna feed element is depicted to be operating as a wideband antenna feed element. Thus, in embodiment 554, duplexing for separation/combination of multiple frequency band signals is performed in the wideband phase network connected to each of the antenna feed elements.

[0038] The phase network may perform functions such as adjusting phases of the signals to be transmitted, or fed to each antenna element, to have the appropriate transmission phase so as to achieve a target area of coverage. The phase adjustment may take into account length of the signal path travelled by the signal from the PN circuit to the antenna element before being radiated from the antenna element. The phase adjustment may depend on the desired specific complex linear combination of signals radiated from the antenna elements (resulting possibly in an additive or subtractive effect on the magnitude of the signal), as is known in the art.. [0039] FIG. 6 illustrates different possible radial positioning of antenna elements. In antenna 602, both the antenna feeds are positioned at the focal point of a lens antenna. In antenna 604, referred to as a "near field" arrangement, the antenna feed is positioned at an off-focal point, moved off the focal point in the direction of the signal lobe. In other words, the focal point of the lens may lie within the body of the antenna feed or behind it. Explaining in the following for the receive case, in this arrangement, the electromagnetic signal may impinging upon the antenna feed before the signal has converged to a focal point through the lens. In one advantageous aspect, when the antenna feed includes multiple antenna feed elements, e.g., as shown in FIG. 3, FIG. 4 or FIG. 5, each antenna feed element may receive (or transmit) a signal whose

characteristics are similar to a signal received (or transmitted) by the other antenna feed elements.

[0040] In antenna 606, the antenna feed is off-focal point in a direction away from the lens or the direction of the signal beam. As a result, received signals may first converge at a focal point and then begin to diverge beyond the focal point prior to impinging on the surface of the antenna feed. Similar to the antenna 604, when multiple antenna feed elements are located on the surface of the antenna feed, in antenna 606, the multiple antenna feed elements may

receive/transmit signals similar to each other in strength.

[0041] FIG. 7 depicts examples of beamforming to achieve a wider and a narrower beamwidth pattern. A Luneberg lens is used for illustration, but other similar lenses could also be used (e.g., a Rotman lens). The variable beamwidth Luneburg lens antenna illustrates how various antenna feed configurations may be used to increase or reduce the effective bandwidth of a combined beam emanating from/ received by the antenna feed with multiple antenna feed elements, as descried with respect to FIGs. 3 to 6. In the beam pattern 704, the effective width of the combined beam is wider than each individual beam to or from an antenna feed. For example, in a multi-band antenna operation, the beam pattern 704 may represent one of the bands (e.g., the higher frequency band) that is serviced by the antenna. In the beam pattern 706, antenna elements and signal processing may be arranged to provide an effective beam width that is narrower than the individual beams from antenna elements (e.g., the same antenna elements that are also operating in a different frequency band).

[0042] The embodiment also provides a frequency matched beamwidth. One desirable configuration may provide the same effective azimuthal beam width between different frequency bands. The constructive and/or destructive interference patterns from the various antenna elements of the same frequency band shape the effective beam width to match that of the other band(s). In a variation, the antenna may be operated to provide different beam widths for different frequency bands. The beamwidth variations may be achieved by constructive or destructive signal interference, and/or by using off-focal point antenna placement.

[0043] FIG. 8 shows an example of a variable beamwidth antenna and a corresponding examples of radiation patterns. One example configuration may provide a same effective area coverage yet different beam elevation angles. The multiple antenna feeds may be tiled in an array along the azimuth and the elevation directions, as shown in the arrayed arrangement 806. Antenna feeds creating beams pointed towards areas that are close to the base station have multiple elements whose signals are combined to a create wider beam. Conversely, for further points signals at the elements are combined to create a narrower beam, such that the actual coverage is approximately the same as that for the "near" beam described previously. It will be appreciated that the disclosed embodiments can thus be used to provide uniform density coverage (configuration 804) from each antenna feed to a geographic area, irrespective of the distance of the coverage area from a transmission station at which the antenna is installed for operation. One example advantageous property is that this configuration overcomes operational problems associated with the coverage footprint depicted in configuration 802, in which the zone or area of the covered area increases at distances farther away from the antenna location. For example, at the transmission station at which such an antenna is installed, network backhaul resources can be uniformly allocated to each antenna element due to its uniform density coverage, instead of having to allocate non-uniform transmission resources based on the size of the covered area.

[0044] In some embodiments, an antenna system includes an antenna lens such as a

Luneburg lens or a Rotman lens and one or more antenna feeds placed at on or off focal point of the antenna lens (e.g., as depicted in FIG. 6). The position of the antenna feed may thus be far- field (behind focal point) or near-field (in front of the focal point, in the direction of beam).

Each of the one or more antenna feeds comprises one or more antenna feed elements that are electrically independently operable. The antenna system also includes an antenna feed network, or a phase network (PN) electrically coupled with the one or more antenna feed elements via signal paths or connections. In some embodiments, each of the antenna feeds is designated to operate in one or more frequency bands and wherein position and/or size of the one or more antenna feed elements for each antenna feed depends on the one or more frequency bands of operation. In some embodiments, at least one antenna feed is capable of simultaneous operation in at least two frequency bands and wherein the at least one antenna feed includes multiple antenna elements that are grouped to operate in different ones of the at least two frequency bands.

[0045] In some embodiments, at least one antenna feed is capable of simultaneous operation in at least two frequency bands and wherein at least one antenna feed includes an antenna feed element that is coupled to the antenna feed network using a frequency stacked configuration in which the antenna feed element simultaneously receives or transmits signals in two different frequency bands and wherein the antenna feed network includes a diplexer.

[0046] In some embodiments, the antenna system includes a data feed that is positioned conformal to the antenna lens. For example, as depicted in FIG. 8, an array of antennas may be placed around the spherical lens surface.

[0047] FIG. 9 is a flowchart for an example method 900 of wireless communication. The method 900 may be implemented by a wireless communication apparatus such as an access point or a base station that services multiple user devices to provide wireless data connectivity.

[0048] The method 900 includes operating (902) a wireless transmission station to provide wireless signal coverage to a geographical region includes arranging a number of antenna feeds in an antenna array on or near surface of a Luneburg lens, the antenna array extending along an azimuth axis and an elevation axis, operating the number of antenna feeds for transmission and reception of signals, each antenna feed comprising multiple antenna elements, wherein each antenna element is sensitive to a pre-determined range of frequencies, and adjusting beamwidths of antenna beams using two or more antennas for signal transmission such that an equal-density signal coverage is provided to geographic areas irrespective of their distance from the wireless transmission station.

[0049] The method may include controlling (904) phases of signals fed to the multiple antenna feed elements to cause an additive or subtractive effect, thereby resulting in a beam with a greater or smaller beamwidth. In various embodiments, the antenna elements may be

positioned at on-focal or off-focal point of the antenna lens. In some embodiments, the method 900 may be used for transmission and reception of signals in multiple non-overlapping frequency bands. Some examples are described with respect to FIG. 7. For example, in some configurations, the multiple non-overlapping frequency bands include a low frequency band and a high frequency band, and wherein beamwidths of the low frequency band and the high frequency band are separately controlled. In some embodiments, beamwidths of the low and high frequency bands may be different from each other, e.g., as depicted in FIG. 7.

[0050] FIG. 10 is a block diagram for an example wireless communication apparatus 1000 that may use the antenna system embodiments described herein to perform wireless data transmission and reception. The apparatus 1000 may include a processor 1002, a memory 1004 that stores processor-executable instructions and data during computations performed by the processor. The apparatus 1000 includes reception and/or transmission circuitry 1006, e.g., including radio frequency operations for receiving or transmitting signal and/or receiving data or information bits for transmission over a wireless network. The circuitry may include, for example, the phase network described with respect to FIGs. 3, 4, 5 A and 5B.

[0051] It will be appreciated that the disclosed techniques can be used for implementing high bandwidth and uniform coverage fixed wireless access systems.

[0052] The disclosed and other embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term "data processing apparatus" encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus. [0053] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0054] The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0055] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices.

Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. [0056] While this patent document contains many specifics, these should not be construed as limitations on the scope of an invention that is claimed or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this document in the context of separate embodiments can also be implemented in

combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

[0057] Only a few examples and implementations are disclosed. Variations, modifications, and enhancements to the described examples and implementations and other implementations can be made based on what is disclosed.