Transportable infrastructure for airborne cellular system

[0002] The present invention relates generally to a wireless communications system and particularly to transportable infrastructure that enables a wireless communications system to provide service to areas that are not served by conventional terrestrial wireless stations.

[0003] The increasing need for communications networks and capabilities in outlying and geographically diverse locations has created greater demand for cellular systems. Many new carriers providing the infrastructure for such systems have focused their resources on building as many terrestrial cell stations as possible to expand their respective areas of coverage and consequently generate more revenue.

[0004] However, the buildout rate for the terrestrial cell stations is typically slow and expensive, especially in mountainous or otherwise difficult to access areas. In addition, in some these areas, a carrier's return on investment may not provide the incentive necessary for the carrier to build the necessary cell stations, thereby leaving these areas with either limited or no cellular service at all. Further, many areas having a sufficient number of cellular communications base transceiving stations to handle calls during both off-peak and peak times cannot adequately handle large volumes of calls during sporting events or other short-term special events that temporarily attract large crowds. In addition, in remote geographic areas, in areas that have been hit by natural disaster, or in areas that have been transformed into, for example, a military theater, terrestrial cell stations may not be available within the given terrestrial range necessary to establish communication links with the airborne repeater, thereby limiting the overall effectiveness of the system.

[0005] Satellites represent one possible solution to the above system needs. However, because satellites must be developed far in advance of providing the contemplated service, it is difficult to predict the future service and bandwidth needs that may be required in target localized areas. In addition, because the above-discussed events are highly localized, satellite-based service would be inefficient, expensive and would very likely not be able to provide the necessary bandwidth to support the local traffic load.

[0006] Non-commercial airborne cellular systems have also been proposed in which a cellular repeater mounted in an airplane flying a predetermined flight pattern over a geographic area requiring cellular coverage backhauls calls from cellular phones within the covered geographic area to terrestrial base stations spread across the footprint. Because the airplane is capable of traversing geographic limitations and takes the place of the cell stations, such a system overcomes the above-mentioned limitations of conventional terrestrial cellular systems.

[0007] Nonetheless, an aircraft-based wireless system utilizing conventional base transceiving stations still may have certain limitations associated with its potential areas of coverage. For example, one currently-proposed airborne system requires that the airplane in which the repeater is located fly at high altitudes, therefore requiring costly special equipment for both airplane and pilots as well as pilots with special high altitude training. Clearly a need exists for solutions to the aforementioned problems.

[0008] Advantages of the present invention will be readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which:

[0009] FIG. 1 is a system diagram of an airborne cellular communications system including a transportable infrastructure in accordance with the present invention;

[0010] FIG. 2 is a physical block diagram illustrating the components of the airborne cellular communications system shown in FIG. 1 in more detail;

[0011] FIG. 3 is a diagram illustrating the transportable infrastructure for the cellular communications system of FIG. 1 according to a first preferred embodiment; and

[0012] FIG. 4 is a diagram illustrating a transportable infrastructure for the cellular communications system of FIG. 1 according to a second preferred embodiment.

[0013] Referring now to the drawings in which like numerals reference like parts, FIG. 1 shows an airborne cellular communications system 10. The system 10 is preferably designed to be protocol-independent and thus capable of supporting CDMA, TDMA, GSM, 3G, frequency-independent and other fixed and mobile protocols. Therefore, the system is capable of supporting cellular, PCS and higher frequencies (although, for purposes of discussion, reference will be made only to the cellular spectrum), and generally includes three primary segments: a cellular infrastructure segment 12, a radio infrastructure segment 14, and an airplane segment 16. These three segments in combination are capable of providing cellular communications coverage to a large geographical area by enabling system users, represented generally by handsets 18, to link to a public switched telephone network (PSTN) 20 via an airplane payload 22 including a repeater. According to one embodiment in accordance with the present invention and as will be described in further detail, the cellular infrastructure segment 12 and the radio infrastructure segment 14 are transportable segments capable of being easily relocated according to specific terrestrial coverage needs. However, the structure and function of each of these three system segments will first be discussed in detail.

[0014] The cellular infrastructure segment 12 includes a transportable switching office (MSO) 24 that includes equipment, such as a telephony switch, voicemail and message service centers, and other conventional components necessary for cellular service. The MSO 24 connects to the PSTN 20 to send and receive telephone calls in a manner well known in the industry. In addition, the MSO 24 is connected to an operations and maintenance center (OMC) 26 from which a cellular system operator manages the cellular infrastructure segment 12. The MSO 24 is also connected to one or more base transceiver stations (BTSs) such as the BTSs shown at 30a, 30b. The BTSs 30a, 30btransmit and receive RF signals from the system users 18 through the radio infrastructure segment 14.

[0015] More specifically, the BTS 30 transmits and receives RF signals through ground converter equipment 32. The ground converter equipment 32 converts terrestrial cellular format signals to C-band format signals and communicates with the airborne payload 22 through a feeder link 33 and a telemetry link 34, each of which will be discussed later in detail. The payload 22 establishes a radio link 36 for connecting calls over a wide geographic area of coverage, or footprint, that is capable of exceeding 350 km when the airplane maintains a flight pattern at or around 30,000 feet above the ground.

[0016] In addition to the airplane 35, the airplane segment 16 also includes an airplane operations center 37 that controls mission logistics based at least in part on information from sources such as a weather center 38, and manages all system airplanes, as the system preferably includes three airplanes (one in operation, one en route for changeover and one ground spare) to ensure continuous coverage. The airplane also receives additional routine instructions from sources such as an air traffic control center 40.

[0017] FIG. 2 shows certain components of the system 10 in more detail. Specifically, the ground converter equipment 32 includes two C-band antennas 42 for respectively receiving/transmitting signals from/to the payload 22, and a C-band converter 44 for appropriately converting the signals received from or to be transmitted to the payload 22. According to a preferred embodiment, the C-band antennas 42 and the converter 44 enable 800 MHz airborne cellular antennas 56 to communicate with the BTSs 30a, 30bvia an established downlink, or feeder link, 33, and the converter 44 upconverts nominal signals from the BTSs 30a, 30bto C-band signals before the signals are transmitted to the airplane 35. Also, each sector of each BTS 30a, 30bis assigned a different slot in the C-band spectrum so that signals from the different BTSs 30a, 30bcan be separated and routed to the correct antenna, such as the antenna 56, at the payload 22. In addition, the ground control equipment 32 includes telemetry components such as a telemetry antenna 46, a telemetry modem 48 and a telemetry processor 50 to receive and process airplane and payload data transmitted from an airplane telemetry antenna 52, while a control terminal 54 controls transmission of the processed telemetry data to the OMC 26 and the airplane operations center 37.

[0018] In the airplane segment 16, the airplane telemetry antenna 52 mentioned above transmits airplane avionics data generated by airplane avionics equipment, represented generally at 58, including airplane location, direction and flight pattern data as well as other data such as airplane pitch, roll and yaw data. The data from the airplane avionics equipment 58 is input into and processed by a payload processor 60 before being output to the telemetry antenna 52 through a telemetry modem 62. The payload processor 60 is also responsible for processing signals transmitted to and received from the ground converter equipment 32 through the feeder link 33 established between the C-band antennas 42, 56 and for processing signals transmitted to and received from the system users 18 through a downlink, or user link, 69 established between the users 18 and a payload downlink antenna such as an 800 MHz antenna 70, with the signals received by and transmitted from the payload being appropriately upconverted or downconverted by an 800 MHz converter 72. The payload 22, in addition to including the above-mentioned equipment, also includes GPS equipment 74 that can also be input into the processor 60 and transmitted to the ground converter equipment 32 and sent via landline to the airplane operations center 37 for flight control purposes. The components shown in the airplane and in the payload together form the airplane repeater that enables cellular coverage to be provided to a large geographic area that may otherwise not support terrestrial cellular coverage due to an insufficient number of cell stations or the like.

[0019] As should be appreciated from the system configuration shown in FIGS. 1 and 2, both the airborne cellular system 10 and conventional terrestrial cellular systems appear identical to the PSTN 20 and the system users 18. In other words, there are no discernable service-related differences between calls linked to the PSTN 20 through the cellular infrastructure, radio infrastructure and airplane segments 12-16 and calls handled through a conventional terrestrial system infrastructure, in part due to the fact that the cellular infrastructure segment 12 includes a standard telephony switch in the MSO 24 and BTSs 30a, 30bthat are identical to those included in a conventional terrestrial system infrastructure. Also, the system 10 is designed to meet the performance requirement of standard handsets such as the handsets of the users 18.

[0020] Still referring to FIGS. 1 and 2, operation of the components of the airborne cellular system 10 during completion of a call made by one of the system users 18 will now be described. The airplane 35, when on-station preferably flies in a circular or near circular flight pattern (although the flight pattern may vary according to specific weather and coverage conditions) to provide coverage to a geographic area during a mission which typically lasts about 6 hours. While it is on-station, the airplane maintains contact with the ground converter equipment 32 to provide both the feeder link 33 and the user link 69 for the cellular infrastructure segment 12 through the radio infrastructure equipment segment 14. The airplane 35 also transmits a predetermined number of communications beams, such as, for example, 13 beams, over the coverage area, with each beam being assigned to a sector of one of the BTSs 30a, 30band having its own set of control and traffic channels to carry signaling and voice data between the system users 18 and the cellular infrastructure segment 12. As the airplane 35 moves in its flight pattern, the beams radiated from the airplane rotate. Therefore, as the system users 18 will “see” a different beam every 45 seconds or so, the cellular infrastructure segment 12 performs a sector to sector handoff of the call to keep the call from being dropped.

[0021] When initiating a call, a system user, such as one of the users 18, utilizes the control channels in the beam to signal the MSO 24 to request a call setup. The request is sent from a handset of the user 18 to the airplane payload 22, and then is relayed to the ground converter equipment 32. The ground converter equipment 32 relays the request to the corresponding BTS, such as the BTS 30a. The BTS 30athen transmits the request to the MSO 24, which sets up the call with the PSTN 20. The payload 22 therefore simply extends the physical layer of the BTS 30 to the users 18 to allow a much wider area of coverage than would typically be provided by a conventional terrestrial system, and with less associated infrastructure buildout cost. The airborne system 10 is also preferable for providing temporary cellular coverage for special events areas, where coverage is only needed for several days, thereby eliminating the need and cost associated with erecting cell stations and then tearing the cell stations down after the special events end.

[0022] Once the call setup is completed, voice communication with the PSTN 20 through the traffic channels in the beam is initiated, and voice information is then relayed in the same manner as the signaling information. When the call ends, a signal is sent to the MSO 24 to tear down the call, the handset of the user 18 releases the traffic channel used for voice communications, and the channel is returned to an idle state.

[0023] Referring now to FIG. 3, a transportable infrastructure of a preferred embodiment in accordance with the present invention is shown at 80. The transportable infrastructure is housed in a transportable infrastructure platform, which in the embodiment shown is a trailer 80 of a tractor-trailer rig. The components necessary to implement the cellular and radio infrastructure segments 12, 14 are scaled to enable them to be housed within the trailer 80, thereby enabling the cellular and radio infrastructure segments 12, 14 to be relocated to a target geographic area of coverage. The components of the cellular and radio infrastructure segments 12, 14 are capable of being fit into the trailer 80 in part due to the fact that fewer BTS units such as the BTSs 30a, 30bare required, as compared to the number required in a conventional terrestrial system. In a conventional terrestrial system, cell sites are often added to increase coverage, not because of an increased need for localized capacity. Deploying such sites is inefficient from a BTS capability standpoint. A single sector and single traffic channel requires as much real estate, tower structure, chasis equipment, housing and possible transmission infrastructure as a fully-loaded BTS. Since, in the system 10 all BTSs such as the BTSs 30a, 30bare co-located, only a minimally sized BTS chasis is required to house requisite channel cards (not shown). No towers or separate housings are required, and a single transmission line and two C-band antennas replace the multiple T-1 lines and antennas required in a terrestrial system. Therefore, maximum BTS utilization can be maintained with, for example, five BTSs and a single site in the system 10 being equivalent to 30 terrestrial cell sites.

[0024] In operation, when a geographical area requiring cellular service is identified, airplanes such as the airplane 35 including an airborne repeater such as the protocol-independent payload 22 can be flown to the area, while the trailer 80 housing the cellular and radio infrastructure segments 12, 14 can be driven to the area. Only minimal on-site preparations need be made prior to service set-up. For example, a dirt runway and hangar may be prepared to enable the airplanes such as the airplane 35 to land for re-fueling and maintenance purposes. Once a link, such as a T-1 or microwave link, from the MSO 24 to the PSTN 20 is established, the system is capable of being fully operational and of providing cellular coverage to an area of, for example, 100 km to 300 km in radius.

[0025] FIG. 4 illustrates an alternative embodiment of the transportable infrastructure of the present invention. While the cellular and radio infrastructure segments 12, 14 are housed in the trailer 80 in FIG. 3, the segments may alternatively be housed within other transportable structures, such as within a ship 82. The actual type of vehicle used to house and transport the transportable infrastructure may be chosen according to the type and location of the area to which service is to be provided. Therefore, for areas accessible by road, an automotive-based platform such as the one shown in FIG. 3 may be selected, while for remote area that is not accessible by road but that is located near a body of water, a water-based platform such as the ship 82 may be selected. In addition, the cellular and radio infrastructure segments 12, 14 may be housed in another airplane, flown to a service area and operated from the plane when the plane is grounded or transported from the plane to a fixed housing structure.

[0026] As should be appreciated from the above description, the transportable infrastructure of the above-described embodiment in accordance with the present invention shown in FIG. 3 enables cellular coverage to be quickly initiated for a specified geographic area without the conventional terrestrial system start-up time and costs associated with analyzing area terrain and then building a number of cell stations sufficient to handle call traffic, and in which a conventional terrestrial cell system infrastructure would be difficult or impossible to implement, particularly in areas such as military theater operation or natural disaster areas. Also, the transportable infrastructure of the present invention can facilitate fully operational communications coverage for a very large geographical area in a matter of hours.

[0027] Further, if cellular service needs to be provided to an area only on a temporary basis, the transportable infrastructure of the present invention obviates the need and associated cost of tearing down terrestrial cell stations built specifically to provide temporary coverage upon completion of the coverage. Because the transportable infrastructure of the present invention is designed to be protocol-independent and to therefore work with existing standard phone protocol such as CDMA, TDMA, GSM, 3G, frequency-independent and other fixed and mobile protocols and the like, and because the majority of the payload 22 operates at intermediate frequency, the backhaul link 33 to the ground converter equipment 32 has a high degree of operational flexibility and can be adjusted as required to accommodate an operator's spectrum license.

[0028] Consequently, use of the transportable infrastructure of the present invention is contemplated in natural disaster areas such as areas hit by earthquake, flood or hurricane, or fire, medical emergency areas, such as areas in which transportation or industrial accidents have occurred, military theater areas, such as battle zones or refugee camp areas, and areas in which events such as the Olympics, the Superbowl, or the Carnival in Rio de Janeiro are being held. In addition, use of the transportable infrastructure of the present invention is contemplated to provide temporary operational service for service providers in situations where the providers need service capabilities to avoid regulatory penalties, and for infrastructure providers requiring service capabilities to avoid contract penalties.

[0029] While the above description is of the preferred embodiment of the present invention, it should be appreciated that the invention may be modified, altered, or varied without deviating from the scope and fair meaning of the following claims.