Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/14—Relay systems
  • H04B7/15—Active relay systems
  • H04B7/185—Space-based or airborne stations; Stations for satellite systems
  • H04B7/18502—Airborne stations
  • H04B7/18504—Aircraft used as relay or high altitude atmospheric platform
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/24—Reselection being triggered by specific parameters
  • H04W36/32—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/04—Reselecting a cell layer in multi-layered cells
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0055—Transmission or use of information for re-establishing the radio link
  • H04W36/0061—Transmission or use of information for re-establishing the radio link of neighbour cell information
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
  • H04W64/006—Locating users or terminals or network equipment for network management purposes, e.g. mobility management with additional information processing, e.g. for direction or speed determination
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W84/00—Network topologies
  • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
  • H04W84/04—Large scale networks; Deep hierarchical networks
  • H04W84/06—Airborne or Satellite Networks

Definitions

• the present invention relates generally to a wireless communications system including an airborne repeater, and particularly to dynamic maintenance of a terrestrial cell site handoff list for an airborne cellular system.
• One primary consideration relates to maintaining a list of cell station call handoff candidates.
• Conventional cellular standards and protocols such as TIA/EIA 136, GSM and CDMA IS-95 provide for such handoff candidates.
• the handoff candidates are controlled in the system switch and are communicated to the handsets for power monitoring. The switch then makes handoff decisions based on power measurement reports from the handsets.
• the number of handoff candidates supported by the protocol is limited and typically does not vary with time. For example, the number of candidates is limited to 24 in the cellular TIA/EIA 136 protocol.
• an airborne cellular system provides geographic coverage at the expense of large call capacity. Therefore, if an airborne cellular system were deployed in a predominantly low-density region that has pockets of high density, it would be desirable for a service provider to build terrestrial system cell stations in the high-density pockets and provide service to the remaining low-density areas with an airborne cellular system or systems.
• communications beams from the airborne cellular system would likely overlap with those of the terrestrial system cell stations. As the terrestrial system cell stations would typically have higher power than the communications beams of the airborne cellular system, system users would tend to gravitate to the terrestrial system cell stations in overlapping areas.
• FIG. 1 is a system diagram of an airborne cellular communications according to the present invention
• FIG. 2 is a block diagram illustrating the components of the airborne cellular communications system shown in FIG. 1 in more detail;
• FIG. 3 is a plan view of a beam pattern from an airborne repeater providing cellular coverage to a predetermined geographic area below as well as terrestrial cell stations that are handoff candidates;
• FIG. 4 is a plan view of a single beam such as one of the beams in the beam pattern in FIG. 3 showing terrestrial cell stations within the beam pattern that are handoff candidates; and
• FIG. 5 is a flow diagram of the handoff candidate list methodology in accordance with a preferred embodiment of the present invention.
• FIG. 1 shows an airborne cellular communications system 10.
• the system 10 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.
• PSTN public switched telephone network
• the cellular infrastructure segment 12 includes a mobile 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.
• MSO mobile switching office
• the MSO 24 connects to the PSTN 20 to send and receive telephone calls in a manner well known in the art.
• OMC operations and maintenance center
• the MSO 24 is also connected to one or more base transceiver stations (BTSs) such as the BTSs shown at 30a, 30b.
• BTSs base transceiver stations
• the BTSs 30a, 30b transmit and receive RF signals from the system users 18 through the radio infrastructure segment 14.
• 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.
• 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 to ensure continuous coverage.
• the airplane also receives additional routine instructions from sources such as an air traffic control center 40.
• FIG. 2 shows certain components of the system 10 in more detail.
• the ground converter equipment 32 includes a C-band antenna 42 for receiving/transmitting signals from/to the payload 22 (a second antenna is also provided for redundancy purposes), and a C-band converter 44 for appropriately converting the signals received from or to be transmitted to the payload 22.
• the C-band antenna 42 and the converter 44 enable 800 MHz airborne cellular antennas 70 to communicate with the BTSs 30a, 30b via an established downlink, or feeder link, 33, and the converter 44 upconverts nominal signals from the BTSs 30a, 30b to C-band signals before the signals are transmitted to the airplane 35.
• each BTS 30a, 30b is assigned a different band in the C-band spectrum so that signals from the different BTSs 30a, 30b can be separated and routed to the correct antenna, such as the antenna 56, at the payload 22.
• 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 data transmitted from an airplane telemetry antenna 52 over a telemetry link 34, while a control terminal 54 controls transmission of the processed telemetry data to the OMC 26 and the airplane operations center 37.
• 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 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.
• both the airborne cellular system 10 and conventional terrestrial cellular systems appear identical to the PSTN 20 and the system users 18.
• the cellular infrastructure segment 12 includes a standard telephony switch in the MSO 24 and BTSs 30a, 30b that are identical or nearly identical to those included in a conventional terrestrial system infrastructure.
• 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 predetermined geographic area during a mission. 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 36 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, 30b and 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.
• a predetermined number of communications beams such as, for example, 13 beams
• each beam being assigned to a sector of one of the BTSs 30a, 30b and 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.
• a system user 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 30a then 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.
• 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.
• voice information is then relayed in the same manner as the signaling information.
• 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.
• FIG. 3 shows an exemplary footprint 80 generated by the airplane segment 16 of the airborne cellular system 10.
• the footprint is formed from beams 82-94 radiated from the antenna 70, which is preferably a phased-array smart antenna of the type disclosed in PCT patent application no. PCT/US00/17555 titled SMART ANTENNA FOR AIRBORNE CELLULAR SYSTEM, filed on June 26, 2000 the contents of which are incorporated herein by reference. Except for the center beam, each of the beams rotates as the airplane 35 executes its flight pattern. Therefore, terrestrial cell stations, such as the cell stations A1-A4 and B1 -B2, correspondingly rotate in and out of coverage of the beam footprints of each of the respective beams.
• FIG. 1 the cell stations A1-A4 and B1 -B2
• the flight pattern of the airplane is shown as rotating in a counterclockwise direction as indicated by the flight pattern direction arrow FP.
• the beams 82-94 correspondingly rotate in the same direction relative to the geographic area of coverage, but remained fixed relative to the airplane 35 as the airplane executes its flight pattern.
• Each of the beams such as the beam 93, therefore sweeps out a large area and potentially overlaps with many terrestrial sites.
• a static handoff candidate list would require having not only those terrestrial sites currently under the beam, such as sites A1 and A3, and those sites that will soon be under the beam, such as sites A2 and A4, but also sites B1 and B2. Therefore, a system handoff candidate limit, which is typically 24 candidates, may be far exceeded.
• the beam handoff candidate maintenance technique in accordance with the present invention initially generates the handoff list as a function of beam location. Therefore, the beam 93 would only include sites A1-A4 as handoff candidates and would not include sites B1-B2, while the beam 87 would include sites B1 and B2 as candidates and not sites A1-A4. As the airplane executes its flight pattern, the candidate list for each beam will change so that when the beam 93 covers the terrestrial sites B1-B2, candidates B1-B2 would replace candidates A1-A4.
• the beam handoff candidate maintenance technique of the present invention periodically determines a handoff candidate list for each beam based on a dynamically updated handoff list database maintained in the OMC 26.
• the database contains stored terrestrial cell site locations used, along with airplane position and airplane heading data input to the OMC 26 through the airplane telemetry link 34, to calculate the cell site candidate handoff list.
• the OMC 26 can generate a handoff candidate list including only a predetermined number of highest probability/priority candidates and can update/modify the list as a function of time. For example, in an airborne cellular system in which TIA/EIA 136 protocol is utilized, only the top 24 handoff candidates based on handoff priority would be included in a handoff list for each beam.
• a user being serviced by the beam 93 would have beams 92, 94, at a minimum, as time sensitive handoff candidates.
• the payload 22 will continuously monitor beams 92, 94 as handoff candidates.
• the payload 22 will also have terrestrial cells A1-A4 as time insensitive candidates. These time insensitive candidates are periodically evaluated to facilitate handoffs between the airplane 35 and the terrestrial system to alleviate capacity constraints on the system 10.
• These handoff candidates are time insensitive, as a delay in the handoffs between the airplane 35 and the terrestrial system will impact only the potential capacity of the beam 93 and will not impact call performance.
• the handoff candidate list at any given time will include several time sensitive handoff candidates that continuously occupy slots within the handoff candidate list, and time insensitive handoff candidates that only periodically occupy slots within the handoff candidate list.
• prioritization of handoff candidates to determine how frequently the candidates are included in the cyclically generated handoff candidate list associated with a communications beam in accordance with the present invention will now be discussed.
• Such prioritization is necessary due to the potentially large number of time insensitive handoff candidates and the small number of handoff candidate list slots, and is based on the probability of a given terrestrial cell being the best handoff cell for a user.
• the prioritization is based on the subscriber density associated with a cell. High-density cells will most likely receive the most handoffs, and therefore are ranked as higher priority candidates than low-density cells. High priority candidates would therefore be cycled into the time insensitive handoff candidate list slots more frequently than the low priority candidates. As shown in FIG.
• a subscriber for example, at location C1 in a cell 96 formed by a beam 95 would have a cell 97 formed by a beam 98 as a time sensitive handoff candidate that would continuously occupy a handoff candidate list slot.
• the handoff candidate list database which is preferably maintained in the OMC 26 is therefore dynamically updated by the above-described preferred embodiment in accordance with the present invention based on airplane location, the distinction between time sensitive and time insensitive handoff candidates, and the prioritization of time insensitive handoff candidates based on subscriber density.
• Alternative embodiments could prioritize time insensitive candidates based on factors other than subscriber density in accordance with system-specific parameters.
• a relative ranking of all handoff candidates can be established based on the relative densities associated with each of the handoff candidate cells and based on the relative need for a user to be handed off from one beam to another in the system 10 to further prioritize the high and low priority handoff candidates.
• the technique of the present invention can further reduce the number of candidates by periodically cycling through those handoff cell candidates within the footprint of the beam that are not time-sensitive.
• ground-based cell sites which are not time-sensitive, may be divided into multiple groups within the beam to provide the technique in accordance with the present invention with a higher-ranking resolution.
• the handoff list maintenance technique may then cycle through only these groups of non-time sensitive cells more regularly to provide a more precise update of the handoff list without affecting hand offs of time-sensitive cells, such as the cell C1 in FIG. 3. Even though an associated handoff delay of, for example, 15 seconds or so would be associated with cycling through the multiple groups of non-time-sensitive cells, such a delay is acceptable.
• FIG. 5 is a flow diagram illustrating the methodology of the candidate handoff list maintenance technique of the present invention generally at 100.
• the process at 102 initially determines airplane position and heading via GPS data provided from the airplane 35 through the telemetry link 34, as well as beam position data for each communications beam at 104.
• handoff candidate probability calculations are performed as discussed above and based in part on terrestrial cell site location data stored in the cellular system handoff coordination database at 108.
• handoff candidates are ranked and high priority candidates are identified.
• the above-described determination of non-time sensitive candidates may be performed at 114, and the time insensitive candidates are subsequently periodically cycled through at 116.
• the handoff candidate list is then updated after the time insensitive handoff candidates are cycled through to generate the handoff candidate list at 120.
• the handoff candidate list is updated at 118 to produce the handoff candidate list at 120 without determining and cycling through time insensitive candidates at 114 and 116, respectively. Also, as indicated by the dashed line at 122, the ranking operation at 110 and the excessive candidate determination at 112 may be skipped, and the technique may proceed directly from performing a handoff candidate probability calculation at 106 to performing periodic cycling through time insensitive candidates at 116.
• the candidate handoff list maintenance technique of the present invention may be designed to facilitate handoffs in a manner opposite to that described above, or, in other words, to enable handoffs fr ⁇ m a terrestrial system to an adjacent airborne communications system.
• terrestrial cells bordering on or overlapping the airborne system coverage area would also require a time-varying handoff candidate list as well.
• the list would function in a manner similar to the list described above, except that the communications beams, rather than the terrestrial cells, would be the handoff candidates. As there would be usually only one or two beams over a terrestrial cell at one time, however, a cyclical approach would not be required.
• the candidate beam hand-off list maintenance technique of the present invention facilitates terrestrial system interoperability with an airborne cellular system by enabling reliable handoffs to be made between wide area coverage airborne cellular systems and terrestrial systems for overlay applications.
• the present invention also facilitates reliable handoffs between adjacent airborne cellular systems, and is capable of distinguishing between time-sensitive and non-time sensitive handoff candidates based on such factors as terrestrial cell user densities.

Applications Claiming Priority (1)

Publications (1)

Family

ID=21742674

Family Applications (1)

Country Status (5)

Families Citing this family (11)

Family Cites Families (4)

• 2001
  • 2001-06-29 EP EP01957083A patent/EP1405441A1/de not_active Withdrawn
  • 2001-06-29 CN CNB018234224A patent/CN1285176C/zh not_active Expired - Fee Related
  • 2001-06-29 JP JP2003509670A patent/JP2005500722A/ja active Pending
  • 2001-06-29 KR KR10-2003-7017179A patent/KR20040008233A/ko not_active Application Discontinuation
  • 2001-06-29 WO PCT/US2001/020822 patent/WO2003003614A1/en not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events