Patent Description:
In recent years, there has been an increased demand for wireless communications services. Various capabilities and services are being integrated into mobile devices, including the use of satellites operating in low Earth orbit (LEO) and medium Earth orbit (MEO), as well as geostationary or geosynchronous Earth orbit (GEO).

LEO is the simplest and cheapest for satellite placement, and it provides high bandwidth and low latency for communications services. Similarly, the most common use for satellites in MEO is for communications services, although navigation and geodetic/space environment science applications use MEO as well.

A problem exists in that satellites in both LEO and MEO are not visible from any given point on the Earth at all times, unlike GEO satellites. Because these LEO and MEO orbits are not geostationary, a network or constellation of satellites is required to provide continuous communications services coverage.

For both LEO and MEO satellites, current satellite signal acquisition techniques are based on using an omni-directional antenna in a user terminal, which can see most of the satellites in a field of regard (FoR) or field of view (FoV). The field of regard is the total area that can be captured by an antenna, while the field of view is an angular cone perceivable by the antenna at a particular time instant. The field of regard is typically much larger than the field of view, although the field of regard and field of view coincide for a stationary antenna.

When the user terminal is turned on, it needs to acquire the strongest satellite signal among the many signals in the field of regard or field of view.

However, with the advent of satellite broadband communications services, the antenna in the user terminal needs to be directional for higher gain. Specifically, this feature benefits the normal communication channel speed, but it is not desired during acquisition of the satellite signal.

What is needed, then, is an omni-directional antenna for use during signal acquisition, and a directional antenna for use during normal communications. The present invention satisfies this need. <CIT>, according to its abstract, states a system includes a phased array antenna that is used to emulate antennas that have larger solid angle coverage and lower gain compared to a single beam of the phased array antenna. This is achieved by switching between beams of the phased array antenna while receiving a wireless communication signal and summing representations of signal energy received using the different beams. The system can be used to narrow down the angular coordinates of a transmitting satellite by emulating antenna patterns that cover portions of a search space. The system can also be used to determine a channel discriminator (e.g., frequency, code, time slot) that defines a signal being transmitted. <CIT>, according to its abstract, states an antenna system electronically searches for a satellite signal by beginning at the current pointing angle of an antenna. The antenna system sweeps a tuner frequency of the receiver by electronically commanding the receiver to tune to different transponder frequencies. By scanning through transponder frequencies, the antenna system can locate a satellite signal without mechanical movement. As a result, the satellite signal can be acquired more quickly than in some conventional systems.

To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus according to claims <NUM> and <NUM> respectively.

In the following description of the preferred example, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific example in which the invention may be practiced. It is to be understood that other examples may be utilized and structural changes may be made without departing from the scope of the present invention.

<FIG> is a diagram showing an exemplary communications system, according to one example. The communications system comprises a satellite network <NUM> that includes one or more satellites <NUM>, and one or more satellite-capable user terminals <NUM> are provided, which are also labeled as a terrestrial user terminal <NUM> and an airborne user terminal <NUM> in <FIG>, for communicating with the satellites <NUM>.

Also in the example of <FIG>, the satellite network <NUM> includes a ground station <NUM> for transmitting and receiving data to and from the satellites <NUM>. The satellite network <NUM> may also interface to one or more other satellite, terrestrial and/or airborne networks (not shown), for example, a cellular or personal communications systems (PCS) network, wireless local area networks (WLANs), personal area networks (PANs), or other networks. The user terminals <NUM> may also operate with the other satellite, terrestrial and/or airborne networks.

There are a number of benefits to using a satellite network <NUM>. One benefit is the ubiquitous coverage of the satellite network <NUM> as an alternative network option to the terrestrial networks. Another benefit of the satellite network <NUM> is surge capacity to overcome congestion in the terrestrial networks. A satellite network <NUM> also transcends outages in the terrestrial networks.

<FIG> illustrates the components of an exemplary user terminal <NUM>, according to one example. The user terminal <NUM> includes a microprocessor <NUM> for controlling the terminal's <NUM> operations; one or more input/output components coupled to the microprocessor <NUM>, such as display <NUM>, audio <NUM> and keypad <NUM>, for inputting and outputting data as directed by the microprocessor <NUM>; a plurality of transmit/receive components coupled to the microprocessor <NUM> for communicating with a plurality of communications networks as directed by the microprocessor <NUM>, wherein the transmit/receive components include a satellite transceiver <NUM> for communicating with the satellite network <NUM>, a cellular/PCS transceiver <NUM> for communicating with a cellular/PCS network, a WLAN/PAN transceiver <NUM> for communicating with other WLAN/PAN elements, as well as transmit/receive components (not shown) for communicating with other networks; and an integrated antenna <NUM> coupled to the transmit/receive components, such as transceivers <NUM>, <NUM> and <NUM>, for communicating with the various communications networks.

<FIG> and <FIG> illustrate alternative examples for the antenna <NUM> used by the user terminal <NUM>, according to one example. In both examples, the antenna <NUM> comprises a reconfigurable phased array antenna <NUM> that is omni-directional for use during signal acquisition and directional for use during normal communication. Specifically, the phased array antenna <NUM> is configured to be omni-directional to acquire the strongest satellite <NUM> signal among the signals in the field of regard, but the phased array antenna <NUM> is configured to be directional to provide the highest gain during normal communication. In this manner, the user terminal <NUM> optimizes and accelerates the satellite <NUM> signal acquisition process.

As shown in both <FIG> and <FIG>, the phased array antenna <NUM> is comprised of an array of radiating elements <NUM> formed on a substrate <NUM>. Each element <NUM> is shown as a square feature, but could comprise a patch, dipole, slot or other type of antenna element <NUM>. The substrate <NUM> is shown as a circular feature, but could comprise any shape.

The elements <NUM> are individually selectable by the user terminal <NUM>, such that the phases and/or amplitudes of signals feeding the elements <NUM> are varied to create a desired radiation pattern for the antenna <NUM>. The resulting beams of the desired radiation pattern are formed and then steered by sequentially shifting the phase and/or amplitude of the signals feeding each element <NUM> to provide a constructive desired signal and/or destructive interference.

During acquisition of a satellite <NUM> signal, the phased array antenna <NUM> is re-configured, either by using only one element <NUM> to broaden the field of regard, or by using a "spoiled beam" with a subset or all of the elements <NUM> to broaden the field of regard, as well as to increase a receiving area for an increased signal-to-noise ratio (SNR). <FIG> illustrates one example, wherein only one of the elements <NUM> of the phased array antenna <NUM> is turned on for receiving, as indicated by the fill pattern, wherein this single element <NUM> has a much broader beam looking at a broadened field of regard, so it can see as many satellites <NUM> as possible. <FIG> illustrates another example, wherein a spoiled beam is formed using a subset or all of the elements <NUM>, as indicated by the fill patterns, to broaden the field of regard, but with higher antenna <NUM> directivity to increase the signal-to-noise ratio.

The attributes of the signals received from one or more of the satellites <NUM> are analyzed by the user terminal <NUM>, and a preferred satellite <NUM> is then selected by the user terminal <NUM> based on the attributes of the signals. After the satellite <NUM> has been selected, the phased array antenna <NUM> is re-configured to be directional towards the selected satellite <NUM> to provide a higher gain during normal communication with the selected satellite <NUM>. Specifically, once the strongest satellite signal is acquired, the phased array antenna <NUM> is reconfigured to its beamforming mode to form a beam that is pointed at the satellite <NUM>.

In one example, ephemeris data broadcast by the satellites <NUM> is used to slew/point the antenna <NUM> and its beam at the selected satellite <NUM>, to keep tracking the selected satellite <NUM> after its signal is acquired. The ephemeris data comprises the location for the satellites <NUM> in the constellation at a particular point in time, and is broadcast by each of the satellites <NUM> on a low data rate pilot signal.

The ephemeris data broadcast by the satellites <NUM> is also used by the user terminal <NUM> to perform handoffs between satellites <NUM> in the constellation. Specifically, the user terminal <NUM> performs a "make before break" seamless satellite-to-satellite handover using the ephemeris data broadcast by the satellites <NUM> to select a next satellite <NUM> for use, before it terminates communication with the current satellite <NUM>. Using the ephemeris data broadcast by the satellites <NUM>, the user terminal <NUM> knows the positions of the satellites <NUM> in the constellation and acquires the signals from the next satellite <NUM> either with a wide beam (e.g., an omni-directional or spoiled beam) or another high-gain beam (e.g., a directional beam) pointing at the next satellite <NUM> for a satellite-to-satellite handover.

<FIG> are graphs of theta (degrees) vs. amplitude (dB), illustrating the difference in beam patterns of the antenna <NUM> for acquisition mode vs. tracking mode.

<FIG> illustrates an array beam pattern for the antenna <NUM> in an acquisition mode, using one of the elements <NUM> of the antenna <NUM> for a wider beamwidth with lower gain that allows the antenna <NUM> to "see" as many satellite <NUM> signals as possible in the field of regard. Specifically, <FIG> illustrates a plane cut of a one-element <NUM> beam used for acquisition, with a +/- <NUM> degree beam width (at -<NUM> dB to -<NUM> dB down from the peak).

<FIG> illustrates an array beam pattern for the antenna <NUM> in a tracking mode, using all (or most) of the elements <NUM> of the antenna <NUM> for narrow beamwidth and higher gain that allows the antenna <NUM> to provide greater bandwidth to the selected satellite <NUM>. Specifically, <FIG> illustrates a plane cut of an all-element <NUM> narrow beam for tracking, with a +/-<NUM> degree beam width (at -3dB down from the peak).

<FIG> illustrates an array beam pattern for the antenna <NUM> in an acquisition mode, using a "spoiled beam" for a wider beamwidth with lower gain that allows the antenna <NUM> to "see" as many satellite <NUM> signals as possible in the field of regard. Specifically, <FIG> illustrates a plane cut of an all element <NUM> spoiled beam for acquisition, with a +/-<NUM> degree beam width (at -3dB down from the peak). Note that the spoiled beam shown in <FIG> has a higher edge directivity (~ <NUM> dBi within the beamwidth of +/- <NUM> degrees) than that of the single element beam (~ <NUM> dBi) shown in <FIG>.

<FIG> are diagrams (in degrees), illustrating the difference in beam patterns of the antenna <NUM> for acquisition mode vs. tracking mode.

<FIG> is a contour plot of a single element <NUM> beam used for acquisition mode. In this example, the antenna <NUM> in acquisition mode uses a single element <NUM> radiation pattern, with a wide beam at a lower gain (as compared to <FIG>). The three contours shown in <FIG> are at -<NUM> dB down from the beam peak (<NUM>), -<NUM> dB down from the beam peak (<NUM>), and -<NUM> dB down from the beam peak (<NUM>). Also shown is the <NUM> degree diameter circle.

<FIG> is a contour plot of an all element <NUM> beam used for tracking mode. In this example, the antenna <NUM> in tracking mode uses a <NUM> element <NUM> radiation pattern, with a narrow beam at a higher gain (as compared to <FIG>) for a <NUM>-degree scan angle. The three beams are: a first beam <NUM> scanned at <NUM> degrees, a second beam <NUM> scanned at about <NUM> degrees elevation, and a third beam <NUM> scanned at about <NUM> degrees azimuth. The contours are at -<NUM> dB and -<NUM> dB down from the beam peak.

<FIG> is a contour plot of an all element <NUM> spoiled beam used for acquisition mode. In this example, the antenna <NUM> in acquisition mode uses a <NUM> element <NUM> radiation pattern, with a wide "spoiled beam" at a lower gain (as compared to <FIG>), with <NUM> dBi and <NUM> dBi contours for the spoiled beam.

<FIG> is a flowchart that illustrates the steps performed by the network <NUM>, satellites <NUM> and user terminals <NUM> in a method of establishing communication with a satellite <NUM>, according to one example.

Block <NUM> represents the network <NUM> transmitting satellite ephemeris data to the satellites <NUM>.

Block <NUM> represents the satellites <NUM> broadcasting the satellite ephemeris data to the user terminals <NUM>.

Block <NUM> represents a user terminal <NUM>, in acquisition mode after being turned on, broadening a field of regard of the reconfigurable phased array antenna <NUM> having a plurality of antenna elements <NUM>. The broadened field of regard results in a wider beamwidth with lower gain that allows the antenna <NUM> to "see" as many signal sources, e.g., satellites <NUM>, as possible.

In one example, the reconfigurable phased array antenna <NUM> is stationary (not slewing) when the user terminal <NUM> is in acquisition mode. In another example, the reconfigurable phased array antenna <NUM> is slewed to establish an initial pointing vector comprised of azimuth and elevation prior to acquisition of pilot signals from a plurality of satellites <NUM> within the field of regard, but the reconfigurable phased array antenna <NUM> is not slewed once the field of regard is selected.

In one example, the user terminal <NUM> broadens the field of regard by using a lesser number than a total number of the plurality of antenna elements <NUM> of the reconfigurable phased array antenna <NUM>. This may further comprise selecting one antenna element <NUM> from the plurality of antenna elements <NUM> of the reconfigurable phased array antenna <NUM> (e.g., any one of the antenna elements <NUM> may be selected to provide redundancy and fault tolerance), or this may further comprise selecting a sub-array of two or more antenna elements <NUM> from the plurality of antenna elements <NUM> of the reconfigurable phased array antenna <NUM>.

In another example, the user terminal <NUM> broadens the field of regard by using a spoiled beam by changing at least one of a phase and amplitude for (each or adjacent ones) of the plurality of antenna elements <NUM> of the reconfigurable phased array antenna <NUM> to spread a beam width. The spoiled beam is generated by introducing a phase difference that alters a coherence of the received signals at the reconfigurable phased array antenna <NUM>.

Block <NUM> represents the user terminal <NUM> receiving pilot signals from a plurality of satellites <NUM> within the field of regard using the reconfigurable phased array antenna <NUM>.

Block <NUM> represents the user terminal <NUM> determining one or more attributes of the pilot signals received from each of the satellites <NUM> and then selecting one of the plurality of satellites <NUM> for communication with the reconfigurable phased array antenna <NUM> based on the attributes of the received signals. In one example, the one or more attributes comprise signal strength, signal quality, or proximity to other signals.

Block <NUM> represents the user terminal <NUM> obtaining the satellite ephemeris data, as well as other broadcast system information, from the selected satellite <NUM>.

Block <NUM> represents the user terminal <NUM>, in tracking mode, switching to a directional (high gain, beamforming) mode for the reconfigurable phased array antenna <NUM>, with the elements <NUM> of the antenna <NUM> forming a narrow beam pointed at the selected satellite <NUM>, and establishing communications with the selected satellite <NUM> using the reconfigurable phased array antenna <NUM>. Thereafter, the user terminal <NUM> tracks the selected satellite <NUM> using the ephemeris data to position the beams formed by the reconfigurable phased array antenna <NUM>, wherein an initial pointing vector comprised of an azimuth and elevation and an initial tracking vector comprised of a flight path are determined based on the ephemeris data for the satellites <NUM> relative to a current terrestrial or airborne location of the user terminal <NUM> and the reconfigurable phased array antenna <NUM>.

Block <NUM> represents the user terminal <NUM> performing normal communications, i.e., transmitting and/or receiving, with the selected satellite <NUM>, including applications such as consumer, commercial and military communications, satellite television, satellite radio, and Internet access.

Block <NUM> represents the satellites <NUM> transmitting and/or receiving normal communications with the user terminals <NUM>.

Claim 1:
A method of establishing communication with a satellite, comprising:
providing a user terminal (<NUM>) including a reconfigurable phased array antenna (<NUM>) having a plurality of antenna elements (<NUM>), wherein the user terminal (<NUM>) is operable for, after being turned on:
in an acquisition mode, broadening (<NUM>) a field of regard of the reconfigurable phased array antenna (<NUM>) by using (<NUM>) a spoiled beam by changing at least one of a phase and amplitude for adjacent antenna elements (<NUM>) of the reconfigurable phased array antenna (<NUM>) to introduce a phase difference to alter the coherence of received signals at the phased array antenna (<NUM>) to thereby spread a beam width, wherein the reconfigurable phased array antenna (<NUM>) is configured to be stationary while in the acquisition mode;
receiving (<NUM>) signals from a plurality of satellites (<NUM>) within the field of regard using the reconfigurable phased array antenna (<NUM>);
determining (<NUM>) one or more attributes of the received signals for each of the satellites (<NUM>);
selecting (<NUM>) one of the plurality of satellites (<NUM>) for communication based on the attributes of the received signals;
switching (<NUM>) to a directional mode for the reconfigurable phased array antenna (<NUM>);
establishing (<NUM>) the communication with the selected satellite (<NUM>) using the reconfigurable phased array antenna (<NUM>); and
tracking (<NUM>) the selected satellite (<NUM>).