BACKGROUND

A High Altitude Platform (HAP) may be a base station for a communication network. For example, an HAP station may be an LTE base station that provide telecommunication service to user devices on the ground. An HAP station may be configured to perform “station keeping” by moving in a circuit above the ground while outputting beams of electromagnetic signals forming a beam pattern on the ground. Client devices and/or other stations on the ground may communicate with the HAP station through the beams. As the HAP station moves, the motion may cause the beams to also move, for instance rotate, which in turn can affect signal quality of the beams.

BRIEF SUMMARY

Aspects of the disclosure provides for a communication system comprising a station moving relative to a geographic area; a plurality of antennas; and one or more processors configured to control a first antenna of the plurality of antennas to output a primary beam to cover the geographic area, wherein the primary beam is associated with a primary cell having a first center frequency; and control a second set of antennas of the plurality of antennas to output a plurality of secondary beams to cover a plurality of locations within the geographic area, wherein the plurality of secondary beams each has a beam angle smaller than the primary beam, and the plurality of secondary beams are all associated with a secondary cell having a second center frequency.

The one or more processors may be further configured to control the first antenna to establish using the primary beam a first communication link between the client device and the primary cell such that the client device is in a radio resource control (RRC)-idle state on the primary cell.

The one or more processors may be further configured to determine that the client device transitions from the RRC-idle state to an RRC-connected state on the primary cell; determine that the client device is at a location covered by a first secondary beam outputted by a given one of the second set of antennas; control the given one of the second set of antennas to establish, using the first secondary beam, a second communication link between the client device and the secondary cell; and instruct the client device to bond the primary cell and the secondary cell using carrier aggregation. The one or more processors may be further configured to control the plurality of antennas to simultaneously maintain both the first communication link and the second communication link with the client device.

The one or more processors may be further configured to receive, from the client device, a signal quality of the second communication link measured by the client device; determine that the signal quality of the second communication link is below a predetermined threshold; determine that the client device is covered by a second secondary beam of the plurality of secondary beams outputted by a second given one of the second set of antennas; control the second given one of the second set of antennas to re-establish, using the second secondary beam, the second communication link with the client device.

The one or more processors may be further configured to control the second set of antennas so that interference caused by an overlap between the plurality of secondary beams is within a predetermined threshold.

The primary beam may be configured to have a first PCI associated with the primary cell, and the plurality of secondary beams are each configured to have a second PCI associated with the second cell. The first center frequency of the primary cell may be lower than the second center frequency of the secondary cell.

The plurality of secondary beams may move along with the station such that a coverage area of each of the plurality of secondary beams changes as the station moves.

The one or more processors may be further configured to control data traffic at the station such that a first fraction of data is transmitted using the primary beam, and a second fraction of data is transmitted using the plurality of secondary beams, wherein the first fraction is smaller than the second fraction. The one or more processors may be configured to control data traffic at the station such that a first set of predetermined types of data is transmitted using the primary beam, and a second set of predetermined types of data is transmitted using the plurality of secondary beams. The first set of predetermined types of data may include voice call data.

The one or more processors may be further configured to allocate a first bandwidth to the primary beam; allocate a second bandwidth to the plurality of secondary beams, wherein the second bandwidth is larger than the first bandwidth.

The one or more processors may be further configured to control the second set of antennas so that the plurality of secondary beams have one or more overlapping regions; control the second set of antennas so that data is not transmitted in the overlapping regions.

The one or more processors may be further configured to determine that a plurality of client devices in the geographic area are located in areas covered by a set of different secondary beams of the plurality of secondary beams; schedule simultaneous data transmission to the plurality of client devices using the set of different secondary beams; control the second set of antennas to simultaneously transmit data to the plurality of client devices based on the schedule.

The one or more processors may be further configured to determine that, due to movements, the plurality of client devices are covered by a new set of different secondary beams of the plurality of secondary beams; control the second set of antennas to simultaneously transmit data to the plurality of client devices using the new set of different secondary beams.

The one or more processors may be further configured to determine that a plurality of client devices in the geographic area are located in areas covered by a given one of the plurality of secondary beams outputted by a given one of the second set of antennas; control the given one of the second set of antennas so that data is transmitted to the plurality of client devices sequentially in a cycle.

The one or more processors may be further configured to determine that the client device initiates a random access procedure for transitioning from the RRC-idle state to an RRC-connected state; determine that the client device is at a location covered by a first secondary beam outputted by a given one of the second set of antennas; control the given one of the second set of antennas to establish, using the first secondary beam, a second communication link between the client device and the secondary cell; instruct the client device to enter the RRC-connected state on the secondary cell.

The one or more processors may be further configured to receive, from the client device, a signal quality of the second communication link measured by the client device; determine that the signal quality of the second communication link is below a predetermined threshold; instruct the client device to initiate a handover to the primary cell.

The communication system may further comprise a tracking system for tracking locations of client devices.

