Patent Application
20120200458
1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly for providing Internet services to aircraft.
2. Background
Two main approaches provide Internet access to airplanes. In one approach, an Air to Ground (ATG) system uses terrestrial Ground Base Stations (GBS) using cellular communication techniques to provide Internet access to aircraft flying over land. A currently used ATG system operating over the continental United States uses only 3 MHz of spectrum. Although, this system may become commercially viable, the limited spectrum may be inadequate to accommodate increasing demand for Internet services, such as streaming of Internet content to aircraft. In another approach, satellite links provide Internet service to aircraft. The satellite based systems have more spectrum available but their cost is excessive.
Because of the excessive cost of satellite links for aircraft Internet communication, it has been preferable to utilize the terrestrial based ATG systems. It would be desirable to increase available spectrum for ATG and provide techniques that would allow such systems to accommodate the increasing demands for aircraft Internet service without substantially increasing cost.
According to one aspect of the present disclosure, a high gain multiple beam ground station antenna array is described. The ground station antenna array includes a first array of antenna elements. A second array of antenna elements are vertically aligned with the first array of antenna elements. The first array of antenna elements and the second array of antenna elements are coupled to the digital beam forming circuitry and each cover a same sector of azimuth. The first array of antenna elements only covers a first elevation. The second array of antenna elements only covers a second lower elevation. The digital beam forming circuitry directs a radiation pattern of the first array of antenna elements in a first range of elevation angles, and directs a radiation pattern of the second array of antenna elements in a second range of elevation angles. The second array of antenna elements has higher gain than the first array. A respective transceiver is coupled to respective antenna elements of the first and second arrays.
In another aspect, a multiple beam aircraft antenna array is described. The aircraft antenna array includes a first array of antenna elements coupled to digital beam forming circuitry. A second array of antenna elements is vertically aligned with the first array of antenna elements and coupled to the digital beam forming circuitry. In one configuration, the first array of antenna elements only covers a first elevation, and the second array of antenna elements only covers a second lower elevation. In one aspect, the digital beam forming circuitry is configured to direct a radiation pattern of the first array of antenna elements in a first range of elevation angles, and configured to direct a radiation pattern of the second array of antenna elements in a second range of elevation angles. In one aspect, the aircraft antenna includes an auxiliary aircraft antenna coupled to a portion of an aircraft distal from the aircraft antenna array.
This has outlined, rather broadly, the features and technical advantages of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described below. It should be appreciated by those skilled in the art that this disclosure may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the teachings of the disclosure as set forth in the appended claims. The novel features, which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages, will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.
The features, nature, and advantages of the present disclosure 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.
The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.
The spectrum available for Internet communication to aircraft by terrestrial Air to Ground (ATG) systems has been limited for practical and economic reasons. Providing seamless communication with aircraft flying at high altitudes over a large area (such as the continental U.S.) involves spectrum that is available over the large area. That is, the spectrum assigned to the ATG system should be available nationwide. It has been problematic, however, to identify a portion of spectrum that is available nationwide, much less arranging to free up such a portion of spectrum that has been allocated for other uses.
A large amount of spectrum has been assigned to geostationary satellites for use in broadcast TV and two way FSS (Fixed Satellite Service). Aspects of the present disclosure provide a high data rate aircraft to ground communication antenna system for sharing portions of the spectrum between ATG applications and geostationary satellite communication systems. Frequency bands such as C band (4 GHz downlink, 6 GHz uplink), Ku band (12 GHz downlink, 14 GHz uplink) and Ka band (20 GHz downlink, 30 GHz uplink) are currently used by geostationary satellite systems. In one aspect, a high data rate aircraft to ground communications antenna system may share the Ku uplink band to provide an aircraft with Internet service.
Aspects of the present disclosure provide methods and apparatus for an ATG system in which Ground Base Stations (GBSs) in communication with aircraft transceivers (ATs) in airplanes can use an uplink portion of spectrum assigned for satellite systems without intolerable interference with communications on the satellite systems. The systems and techniques described in the present disclosure may allow coexistence of the incumbent satellite system and the new ATG system on the same spectrum with negligible cross interference between the two systems.
A system 100 for wireless communication according to an illustrative aspect of the present disclosure is described in
In one aspect, the aircraft transceiver 120 may include an aircraft antenna that is comprised of a multi-beam switchable array that is able to communicate with the ground base station 102 at any azimuth angle. The aircraft antenna may be mounted below the fuselage with a small protrusion and aerodynamic profile to reduce or minimize wind drag. In one aspect, the antenna elevation coverage is from approximately 3° to 10° below horizon. The antenna array may include N elements positioned such that each element directs a separate beam at different azimuth angles, each covering 360/N degrees, for example, as shown in
Although
In one aspect, the aircraft antenna array system 200 is mounted below the fuselage and an auxiliary antenna is mounted onto a separate portion of the aircraft to improve aircraft Internet service. In particular, banking or rolling of the aircraft during flight may interrupt communication between the aircraft antenna array system 200 mounted below the fuselage and the ground base station 102. In one aspect, the auxiliary antenna reduces disruption of the communication between the aircraft transceiver 120 and the ground base station 102 when the aircraft banks or rolls by handling the communications with the ground base station during these times. Characteristics of the aircraft antenna 200 are further illustrated in
Operation of the aircraft antenna 200 for providing aircraft Internet service involves detection and aircraft modem handoff between a current ground base station 102 and a next ground base station 110, as shown in
In one aspect, ground base station search may include a search of all pilot signals received from ground base stations on a given aircraft antenna element. The received pilot signals are ranked to determine whether or not the aircraft modem should handoff to another ground base station from which it is receiving a stronger pilot signal. Once the search on one antenna element is complete, the search may switch to another element and repeat the pilot search on that element. In one aspect, each of antenna elements 210-2 to 210-12 may continually search for ground stations while data is received by antenna element 210-1, as shown in
In the configurations described above, a switched antenna scheme involves a transceiver that switches between different antenna elements to achieve high gain while maintaining low complexity. Alternatively, the directional beams may be formed by combining multiple antenna elements using phased array techniques. In one aspect, the switched antenna scheme described above may combine two adjacent beams 352 and 354 to form combined beam 360 for further increasing the antenna gain while only slightly increasing the hardware complexity to provide diversity. In one aspect, the switched antenna scheme may use a partial phased array beam combining of adjacent antenna elements. For example, adjacent beams may be combined to improve system performance when a communicating ground base station is at or near a boundary of the adjacent beams.
At the ground base station 102, a transmit processor 420 may receive data from a data source 412 and control information from a controller/processor 440. The processor 420 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The processor 420 may also generate reference symbols. A transmit (TX) multiple-input multiple-output (MIMO) processor 430 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 432a through 432t. Each modulator 432 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 432 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink/forward link signal. Downlink signals from modulators 432a through 432t may be transmitted via the antennas 434a through 434t, respectively.
At the aircraft transceiver 120, the antennas 452a through 452r may receive the downlink/forward link signals from the ground base station 102 and may provide received signals to the demodulators (DEMODs) 454a through 454r, respectively. Each demodulator 454 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 454 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 456 may obtain received symbols from all the demodulators 454a through 454r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 458 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the aircraft transceiver 120 to a data sink 460, and provide decoded control information to a controller/processor 480.
On the reverse link/uplink, at the aircraft transceiver 120, a transmit processor 464 may receive and process data from a data source 462 and control information from the controller/processor 480. The processor 464 may also generate reference symbols for a reference signal. The symbols from the transmit processor 464 may be precoded by a TX MIMO processor 466 if applicable, further processed by the modulators 454a through 454r, and transmitted to the ground base station 102. At the ground base station 102, the uplink/reverse link signals from the aircraft transceiver 120 may be received by the antennas 434, processed by the demodulators 432, detected by a MIMO detector 436 if applicable, and further processed by a receive processor 438 to obtain decoded data and control information sent by the aircraft transceiver 120. The processor 438 may provide the decoded data to a data sink 439 and the decoded control information to the controller/processor 440.
The controllers/processors 440 and 480 may direct the operation at the ground base station 102 and the aircraft transceiver 120, respectively. The processor 440 and/or other processors and modules at the ground base station 102 may perform or direct the execution of various processes for the techniques described herein. The processor 480 and/or other processors and modules at the aircraft transceiver 120 may also perform or direct the execution of the functional blocks illustrated in use method flow chart of
Ground station antenna array systems including antenna arrays for communicating with aircraft antenna 200 are shown in
In one aspect, sectorization may include splitting sectors in elevation to increase system throughput, for example, as shown in
Referring again to
Other configurations that utilize a smaller number of elements for digital beam forming can be achieved by further reducing the coverage region of each panel in azimuth and increasing the antenna aperture of the elements while maintaining the array size. This can lead to a larger overall ground station antenna array size but less complicated digital signal processing. In one aspect, a single element can be used for each sector without any digital beam forming, which corresponds to 100×4 antennas in the above example.
In one aspect, digital beam forming may be used in each array to provide multiple steerable pencil-beams. The signal for each element of the array may pass through a T/R (transmit/receive) module and is converted into baseband. In one aspect, the phase shifts for a directional beam are calculated by a beam steering computer and applied to each signal. Similar phase factors may be applied to the transmit signal and passed through the transmit/receive module into the antenna element. In one aspect, a calibration procedure equalizes the amplitude and phase of each element and accounts for the time variation of the circuitry.
As mentioned above, calibration compensates for the different phase/amplitude responses of the antenna and transmit/receive units. One type of calibration may be performed in the factory using built in circuitry. This calibration may use any well known technique. The built in calibration scheme may also be used for periodic calibration in the field to track changes due to temperature and aging. Another approach for calibration may be built into the air interface to provide real-time calibration while performing two-way communication between a ground base station and an aircraft modem. In one aspect, calibration is periodically performed using the communication signaling of an air interface. In particular, an over the air (OTA) real-time calibration may be performed while an air to ground two-way communication system operates.
In one aspect, the Forward Link (FL) on the Ground Base Station (GBS) unit periodically transmits a pilot signal on a wide beam that covers the whole sector. As described herein, the periodically transmitted pilot signal on the forward link of the ground base station may be referred to as a Sector Wide Pilot (SWP). In one aspect, the sector wide pilot may allow an aircraft to detect new ground base stations, to synchronize to the ground base stations, and to receive system parameters, such as information on a periodic calibration procedure described below. For example, as shown in
In one aspect, the wide beam used to transmit the sector wide pilot may be formed by transmitting on any of the individual ground station antenna array elements (522, 524, 542, 544, 612, or 650), for example, as shown in
In one aspect, the ground base station periodically enters a calibration mode. The time of the calibration mode may be sent on the forward link on the same wide beam that carries the sector wide pilot. Calibrating the transmit side of the ground station antenna array may be initially performed. In particular, the ground base station transmitter may sequentially send the sector wide pilot on all ground station antenna array elements during a time period assigned to calibration. Following demodulation, the signal received at the aircraft from the k-th ground station antenna array element is given by:
(ke−
) (1)
In equation (1), the first term may correspond to gain (αk) and delay (θk) in the RF chain. The second term may correspond to the amplitude (βk) and phase (φk) of coupling between antenna elements. The third term may correspond to the phase (νk) from antenna array spacing. The last term may correspond to multipath fading amplitude (σk) and phase (∂k). Also, j in equation (1) represents the imaginary part of a complex number.
In one aspect, the first three terms are due to the hardware and can be estimated by averaging out the last term by making a number of temporal measurements. For instance, given the high speed at which the aircraft travels, channel changes occur very rapidly (e.g., on the order of milliseconds). In on aspect, a number of measurements of equation (1) may be made over two millisecond intervals. These separate measurements may then be filtered to average out the last term in equation (1), which is due to multi-path. In equation (1), the last term may assume that either the channel is frequency non-selective or that the measurements are made over a narrow bandwidth such as on individual tones of an OFDM (orthogonal frequency division multiplexing) physical layer.
In one aspect for a wide bandwidth system, the signals may be sent on a sufficient number of tones to ensure calibration of the hardware over all frequencies. The aircraft modem may compute the calibration coefficients as described above and transmits the coefficients to the ground base station so the ground base station may use these coefficients for forward link beam forming toward the aircraft, for example, as shown in
A process for real-time calibration of an air to ground two-way communication system may be performed as follows.
At process block 706, a sector wide pilot signal is sequentially transmitted on a wide beam by each antenna element of a base station antenna array. In one aspect, the antenna 500 (
Referring again to
In one aspect, the receive side calibration may be performed in a manner similar to the above scheme but by having the aircraft modem transmit a pilot sequence on the Reverse Link (RL) 106, as shown in
Once the ground base station and aircraft antennas are calibrated, beam forming may be performed in any number of ways. In one aspect, the aircraft sends its position to the ground base station based on a current position location, which may be determined with, for example, a position location system such as a global positioning system (GPS). The ground base station may use this information to form a beam in the direction of the aircraft and also on the receive side at the ground base station. In a calibrated antenna system, knowledge of the position of the aircraft and the ground base station can be used to calculate the phased array antenna coefficients to point the bore sight of the beam toward the location of the aircraft. During the flight, the beam may be adjusted using the position of the aircraft that is periodically reported to the ground base station, according to one aspect of the present disclosure.
In one aspect, the aircraft and the ground base station may adjust their beams to increase or maximize Signal to Noise Plus Interference (SINR) received at the aircraft and at the ground base station. For instance, the ground base station may slightly move its transmit beam. The aircraft will report SINR measurements received at the aircraft to the ground base station. In one aspect, the ground base station may find the improved or optimal transmit beam by adjusting its beam based on the SINR feedback received from the aircraft. In one aspect, the ground base station may send one or more adjacent beams to determine whether one of the adjacent beams provides improved performance based on, for example, measured signal energy. In one aspect, detection of an improved or optimal beam may be used on the reverse link from the aircraft to the ground base station.
In TDD (Time Division Duplex) channels where the forward link and reverse link are reciprocal, except for the hardware phase and delays which are calibrated, the ground base station may determine the desired or best received beam by comparing SINRs received on adjacent beams. Then, the ground base station may form a beam toward the aircraft based on the desired or optimal beam on its receive side. In one aspect, the ground base station repeatedly determines the desired or optimal receive beam and adjusts the transmit beam accordingly. A process for air to ground communication by an aircraft equipped with a multi-beam switchable array antenna may be performed as follows.
Referring again to
As shown in
Referring again to
Transmissions from non-geostationary satellite terminals may interfere with communications from a ground base station to an aircraft transceiver on a served aircraft. Also, other aircraft may interfere with communications from a ground base station to an aircraft transceiver on the served aircraft. In addition, signal degradation may be caused by rain when either the Ka band or the Ku band is used by an air to ground communication system. Aspects of the present disclosure may mitigate this type of interference and signal degradation to the aircraft terminal.
As shown in
In particular, the aircraft receiver may measure the Signal to Interference plus Noise Ratio (SINR) and send an index of the measured SINR to the ground base station. In one aspect, the ground base station adjusts the transmit power on the forward link beam to maintain the SINR received at the aircraft above a target value. In case of rain, the signal becomes attenuated, resulting in a reduction in the received SINR at the aircraft. Each beam may be allowed a maximum transmit power. The base station controller will impose a limit on the overall transmit power from all ground base stations. In case of interference from other systems into the aircraft receiver, the interference term of SINR will increase, reducing the SINR received by the aircraft. In one aspect, the ground base station controller may increase the forward link power in response to the SINR feedback from the aircraft modem.
In one configuration, an aircraft is configured for wireless communication including a first array of antenna element means coupled to digital beam forming means. In one aspect, the digital beam forming means may be the modulators 454a-r, transmit processor 464, antenna 452a-r, controller/processor 480, and/or memory 482 of
In one configuration, a ground base station 102 is configured for wireless communication including a first array of antenna element means coupled to digital beam forming means. In one aspect, the digital beam forming means may be the modulators 432a-t, transmit processor 420, antenna 434a-t, controller/processor 440, and/or memory 442 of
Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.
In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
The present Application for Patent claims the benefit of U.S. Provisional Application No. 61/441,231 filed Feb. 9, 2011, in the names of M. Tassoudji et al. and assigned to the assignee hereof and hereby expressly incorporated by reference herein in its entirety. This application is related to commonly assigned U.S. patent application entitled “REAL-TIME CALIBRATION OF AN AIR TO GROUND COMMUNICATION SYSTEM,” in the names of A. JALALI et al. attorney docket 111025U2 and commonly assigned U.S. patent application entitled “HIGH DATA RATE AIRCRAFT TO GROUND COMMUNICATION ANTENNA SYSTEM” in the names of A. JALALI et al., attorney docket 111025U1, the disclosures of which are expressly incorporated by reference herein in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 61441231 | Feb 2011 | US |
