GB2608424A - Aircraft engine blockage avoidance by pre-emptive cell handover - Google Patents

Abstract

Methods described herein relate to communication between a moving platform such as an aircraft and a base station. Position information, velocity information and base station position information may be utilised to anticipate signal blockages (by terrain or body of the aircraft) and initiate transfer to a different base station and/or aircraft antenna in response to an expected blockage. This avoids loss of communication through blockages, thereby increasing throughput. The communication system including one or more antennas is carried on (e.g. mounted on) the moving platform. The moving platform may be an aircraft, land-based vehicle (e.g. a train) or a water vessel (e.g. a boat or ship).

Description

Aircraft Engine Blockage Avoidance by Pre-emptive Cell Handover TECHNICAL FIELD The present disclosure relates to methods and systems for controlling handover between antennas and/or base stations for a communication system carried by a moving platform. In particular, but without limitation, this disclosure relates to predicting expected blockages between an antenna and a serving base station and initiating handover to one or both of a different base station and different antennas in response to an expected blockage.

BACKGROUND

The demand for higher data rates to aircraft is expected to increase in much the same way as observed for terrestrial mobile systems. Currently the majority of in-flight solutions utilise satellite links, however an alternative solution is to utilise a direct air-toground (A2G) link with sufficient bandwidth. One such solution being investigated utilises adapted 3rd Generation Partnership Project (3GPP) technology to link the aircraft to a number of terrestrial base stations. This technology should offer higher bandwidth at lower cost.

In any moving communication system (e.g. on an aircraft), there is a risk that signal blockage (e.g. by terrain or by a body of the aircraft) can cause disruption to communication. In some A2G systems with a single antenna, this interruption to communications can be significant. In an Aviation Complementary Ground Component (ACGC) Long-Term Evolution (LTE), this is mitigated by having a second antenna located in a different part of the aircraft body. In ACGC, the antenna selection is in terms of signal level or signal quality using the LTE parameters RSRP (radio frequency signal power) and received signal strength quality (RSRQ).

Systems with two antennas, rather than one can thus reduce the interruption significantly, but some interruption still occurs, particularly for large blockages.

SUMMARY

According to an aspect there is provided a method for controlling handover between antennas and/or base-stations for a communication system carried by a moving platform. The method may comprise receiving position information indicating a current position of the moving platform and velocity information indicating a current velocity of the moving platform. The method may further comprise receiving base station position information indicating, for each of a plurality of base stations, a position of the base station. The method may further comprise receiving obstacle information indicating the position of one or more potential obstacles. The method may further comprise determining, based on the position information, velocity information, base station position information and obstacle information, an expected blockage between an antenna on the moving platform and a serving base station of the plurality of base stations. The method may further comprise, in response to determining an expected blockage between the antenna and the serving base station, initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations.

Methods described herein relate to communication between a moving platform and a base station. Position information, velocity information and base station position information may be utilised to anticipate blockages and initiate transfer to another base station and/or antenna in response to an expected blockage. This allows the methods to avoid loss of communication through blockages, thereby increasing throughput. The communication system may include one or more antennas is carried on (e.g. mounted on) the moving platform. The moving platform may be an aircraft, a land-based vehicle (e.g. a train) or a water vessel (e.g. a boat or ship).

Determining the expected blockage may comprise: determining a line of sight between the antenna and the serving base station over a predefined period of time in the future based on the position information, velocity information and base station position information; and determining whether the line of sight is blocked by an obstacle during the predefined period of time in the future based on the obstacle information.

An expected blockage may be determined based on an expected beam pattern (e.g. along and/or around the line of sight). A blockage may be determined when at least a portion of the beam is determined to be obstructed during at least a portion of the predefined period of time in the future.

The obstacle information may include information defining the shape of each of the one or more potential obstacles. This may include the size of each of the one or more potential obstacles. A blockage may be determined when at least a portion of one of the obstacles intercepts the line of sight or the beam pattern (where a beam pattern is utilised) during at least a portion of the predefined period of time in the future.

The obstacle information may include one or both of: a map of one or more geographical obstacles; and information defining the shape of at least a portion of the moving platform. A geographical obstacle (e.g. a surface feature) may be a geographical feature, such as a hill or mountain. The obstacle information may include 3D model information of one or more potential obstacles (e.g. one or more a geographical obstacles or at least a portion of the moving platform). Defining the shape of at least a portion of the moving platform allows the method to account for blockages from the platform itself. For instance, the obstacle information may include 3D model information of a body of the moving platform (e.g. a body of an aircraft).

Initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations may form a new combination of antenna and base station for communication. The transfer of communication may be initiated in response to determining that the new combination has no expected blockages.

Accordingly, the method may attempt to transfer to a combination of antenna and base station that has no expected blockages. Where multiple antennas/base stations have no blockages, an antenna or base station with the highest received signal strength may be selected. Each combination of base station and antenna may be considered a respective communication link.

The method may comprise measuring a signal strength of one or more signals received from each of the serving base station and the other base station. Initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations may comprise issuing a signal to initiate transfer of communication to another base station of the plurality of base stations. This may include: reducing the measured signal strength for the serving base station such that it is less than the signal strength for the other base station; and reporting the reduced signal strength of the serving base station and the measured signal strength of the other base station to the serving base station to prompt the serving base station to initiate handover to the other base station.

The measured signal strength may be indicative of a power and/or quality of signals received from a given base station (e.g. radio frequency signal power (RSRP) and/or received signal strength quality (RSRQ)). Each time a blockage is detected, the measured signal strength for that base station may be reduced by a predefined amount. Alternatively, the signal strength may be set to a predefined value (e.g. a predefined minimum value). Alternatively, the amount by which the signal strength is reduced could be dependent on the extent of the blockage (e.g. an expected length of the blockage and/or an amount by which a beam pattern is blocked). The measured signal strength for the serving base station may be reduced such that it is less than the measured signal strength for the other base station by at least a threshold amount. This may result in the base station initiating handover to the other base station.

The method may further comprise, for each of the plurality of base stations: receiving one or more signals from the respective base station; measuring a signal strength for the one or more signals received from respective base station; determining, based on the position information, velocity information, base station position information and obstacle information, whether there is an expected blockage between the antenna on the moving platform and the respective base station of the plurality of base stations; and, in response to determining an expected blockage between the antenna and the respective base station, reducing the signal strength measurement for the respective base station. The method may further comprise reporting the signal strength measurements for the plurality of base stations to the serving base station to allow the serving base station to decide which base station to handover communication to.

The above method allows the communication system to encourage the (serving) base station to transfer communication to a base station with no expected blockages. This can be achieved without any changes to the handover method at the base-station side, as handover is performed as normal based on reported signal strength measurements. The reported signal strength may include a reduced signal strength where there is an expected blockage and an actual (measured) signal strength where there is not an expected blockage.

The method may further comprise, for each of the plurality of base stations: determining an anticipated line of sight distance to the base station at a predefined future time; and, in response to determining that the anticipated line of sight distance is greater than a threshold, reducing the signal strength measurement for the base station to discourage communication with that base station. This can help to discourage communication with base stations that are very far away, as communication with these base stations could increase communication latency beyond acceptable levels. The future time point may be within a predefined period -e.g. in the next 30 seconds. This time is particular to the use case and can be configured depending on the expected speed of the moving platform and the cell range of each base station.

Initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations may comprise: determining whether any other antenna has any expected blockages with the current base station; and in response to determining that at least one other antenna does not have any expected blockages with the current base station, assigning one of the at least one other antenna to communicate with the current base station.

Assigning one of the at least one other antenna to communicate with the current base station may comprise selecting a strongest antenna from a plurality of other antennas that do not have any expected blockages, wherein the strongest antenna has a strongest connection with the current base station of the plurality of other antennas that do not have any expected blockages. A strongest connection may be indicated by the connection having the highest signal strength with the base station of any of the plurality of other antennas that do not have any expected blockages.

Initiating transfer of communication to one or both of a different antenna and a different base station of the plurality of base stations may comprise, in response to determining that there are no other antennas that do not have any expected blockages with the current base station, determining whether any other potential communication link has any expected blockages. Each potential communication link may represent a potential combination of another base station and another antenna. Initiating transfer of communication to one or both of a different antenna and a different base station of the plurality of base stations may further comprise, in response to determining at least one other potential communication link has no expected blockages, initiating transfer of communication to one of the at least one other potential communication link. Accordingly, certain embodiments may first attempt to locate an alternative antenna that does not have an expected blockage with the current base station before attempting to locate an alternative base station. This helps to improve latency as switching between antennas has reduced latency relative to switching between base stations.

Initiating transfer of communication to the one of the at least one other potential communication link may comprise selecting a strongest communication link from a plurality of other potential communication links that do not have any expected blockages. A strongest communication link may be the other potential communication link that has the highest signal strength of any of the other potential communication links that do not have any expected blockages.

The moving platform may be an aircraft and communication may be air to ground communication. For instance, the plurality of base stations may be ground-based base stations.

One or both of the base station position information and obstacle information may be received via communication from one or more of the plurality of base stations.

Communication from one or more of the base stations may be as part of a system information broadcast or one or more multimedia messaging service messages. Communication from one or more base stations may be in response to a request from the communication system. Alternatively, one or both of the base station position information and obstacle information may be preloaded onto memory of the communication system through any other communication means.

According to a further aspect there is provided a system for controlling handover between antennas and/or base-stations for a communication system carried by a moving platform. The system may comprise a processor configured to: receive position information indicating a current position of the moving platform and velocity information indicating a current velocity of the moving platform; receive base station position information indicating, for each of a plurality of base stations, a position of the base station; receive obstacle information indicating the position of one or more potential obstacles; determine, based on the position information, velocity information, base station position information and obstacle information, an expected blockage between an antenna on the moving platform and a serving base station of the plurality of base stations; and, in response to determining an expected blockage between the antenna and the serving base station, initiate transfer of communication to one or both of another antenna and another base station of the plurality of base stations.

According to a further aspect there is provided a computer program for controlling handover between antennas and/or base-stations for a communication system carried by a moving platform, wherein the program, when executed by a processor, causes the processor to implement a method. The method may comprise: receiving position information indicating a current position of the moving platform and velocity information indicating a current velocity of the moving platform; receiving base station position information indicating, for each of a plurality of base stations, a position of the base station; receiving obstacle information indicating the position of one or more potential obstacles; determining, based on the position information, velocity information, base station position information and obstacle information, an expected blockage between an antenna on the moving platform and a serving base station of the plurality of base stations; and, in response to determining an expected blockage between the antenna and the serving base station, initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations.

BRIEF DESCRIPTION OF THE DRAWINGS

Arrangements of the present invention will be understood and appreciated more fully from the following detailed description, made by way of example only and taken in conjunction with drawings in which: FIG. 1 shows an exemplary situation in which embodiments may be employed; FIG. 2 shows a communication system in accordance with an embodiment; FIG. 3 shows a method for determining antenna or base station handover according to an embodiment; FIG. 4 shows a method for controlling handover between antennas and/or base stations according to an embodiment; and FIG. 5 shows a method for controlling handover between antennas and/or base stations according to an embodiment.

DETAILED DESCRIPTION

Embodiments of the invention aim to reduce the effect of signal blockage in communication systems operating on a moving platform. This moving platform may be a train or aircraft.

Specific embodiments described below are described with reference to air to ground communication between an aircraft and one or more base stations; however, the invention is equally applicable to other forms of moving platforms. Examples of such moving platforms include ground based platforms or vehicles (such as trains, cars, ground-based drones, etc.), water-based platforms or vehicles (such as boats or water-based drones) and air-based platforms or vehicles (such as aircraft or aerial drones).

Embodiments of the invention aim to reduce the effect of vehicle or platform body blockage in communication leading to interruptions in data transmissions with base stations. Specific embodiments of the invention aim to reduce the effect of aircraft engine blockage or aircraft body blockage in communication leading to interruptions in data transmissions with the ground. Embodiments make use of knowledge of the current aircraft position and orientation in conjunction with a priori knowledge of the position of ground stations and the structure of the aircraft to forecast blockage and force handover to an appropriate alternative cell to avoid or reduce interruptions to transmission to the ground.

The invention applies to direct air-to-ground (A2G) communication links. The example given utilises adapted 3GPP technology to link the aircraft to a number of terrestrial base stations. This technology should offer higher bandwidth at lower cost.

The invention is illustrated below in terms of a specific example of its application comprising an A2G communications link in an airborne environment utilising a number of geographically separated base stations based on 3GPP Long-Term Evolution (LTE) standards, but is also applicable to 3GPP 5G standards. It may also be applicable to mobile user equipment that exceeds the 3GPP standards for instance in terms of speed and cell size.

FIG. 1 shows an exemplary situation in which embodiments may be employed. A User Equipment, UE, 103 device (located on an aircraft) is in communication with a serving cell 101. In addition to communicating with the serving cell 101, the UE also receives a signal from a neighbouring base station 105 with which the UE is not currently in communication.

In the remainder of the description, a "neighbouring cell" is considered to mean a base station capable of communicating with UE. The letters "UE", in the context of the present description, may relate to a mobile device, or any other device capable of wirelessly connecting to a base station. In keeping with terminology used by persons skilled in the art, the acronym eNodeB denotes a base station. The uplink means a communication of the mobile equipment to the base station, and the downlink means a communication from the base station to the mobile equipment.

As the aircraft travels away from the serving base station, it may become appropriate to transfer communication to a neighbouring base station (e.g. one that is now closer to the aircraft). In communication networks, serving cells often have knowledge of nearby cells and before the handover procedure begins the serving cell communicates neighbouring cell information to the UE. In some networks, measurements made by the UE are used to inform whether the UE should disconnect from the serving cell and connect to a neighbouring cell, in other words, the measurements performed by the UE can decide handover.

In addition, where the system includes multiple antennas, the UE may decide to change between different antennas based on measurements on the respective antennas.

As described above the antenna selection is in terms of signal strength (e.g. signal level or signal quality). This may be via the LTE parameters RSRP and/or RSRQ.

However, to avoid excessive antenna switchover the target antenna signal must be sufficiently larger than that for the current antenna (greater than a threshold difference), or put another way, the current signal must be significantly less than the target signal leading to a time when throughput is reduced. The timeliness of antenna switchover is accentuated by the very high aircraft speeds.

This need to avoid excessive switching by imposing a threshold for the amount that the target antenna signal is greater than the current antenna (a threshold on the difference) leads to some interruption or degraded communications during blockage. There is thus a trade-off between the size of the threshold and degradations in communications either due to excessive switching (too low a threshold) or breaks in communications (too high a threshold).

Furthermore, as the signal being measured is very dynamic in level, it can be necessary to average the signal over time, this further delays switchover and leads to a trade-off between: a) excessive switching due to varying measurements due to short time averaging; and b) long averaging leading to less switching but loss of data throughput due to blockage due to switchover being delayed.

The amount of time of reduced throughput will depend on the physical arrangement of the aircraft and the amount and degree of manoeuvres (such as banking).

Systems with two antennas, rather than one can reduce the interruption significantly. This invention is designed to further reduce or even remove this interruption.

In A2G systems the aircraft user equipment (UE) will need to handover to a new cell as the UE moves, to provide optimum performance as in FIG. 1. The decision to handover is made in the ground base station (BS) based on measurements made by the UE of the power (RSRP) or signal quality (RSRQ) of neighbouring cells, which is reported to the BS.

A unique attribute of A2G systems is the existence of a built-in means to accurately determine mobile station position and attitude by using the aircraft's high performance navigation system. Aircraft inertial navigation systems (INS) provide a high accuracy measure of the aircraft position, motion, and attitude by dead reckoning based on accelerometers and gyroscopes. These measurements can be combined with Global Positioning System (GPS) information to provide good absolute position as well.

Using INS (and where available GPS) and a priori knowledge of the networks BS positions it is possible to define the line of sight direction of the communications link to the ground and anticipate blockage and affect a handover before this happens. The accuracy of this decision can be further improved by a priori knowledge of local ground heights to avoid choosing a BS which will be blocked by a large surface feature, for instance, a hill or mountain.

When a blockage is anticipated with the current link, other candidate BS can be checked for potential blockage. For those that will not be blocked the standard (e.g. 3GPP) method of handover can be used whereby the UE measures RSRP and RSRQ of the candidate cells and reports back to the current BS. For those candidate BS where blockage is anticipated the UE will spoof the measurements setting RSRP and RSRQ to poor values to avoid handover to these cells.

Line of sight (LOS) visibility of those BSs identified for measurement are estimated for each antenna for a pre-defined period in advance. If a future blockage is predicted, antenna handover may be selected or else handover measurements are spoofed to initiate a handover at the optimum time prior to significant signal loss/degradation cell.

Embodiments of the invention have the advantage that they are is able to anticipate blockage problems and provide faster handover before significant loss of signal -leading to loss of data throughput.

In single antenna systems the present method enables rapid handover to another BS to avoid blockage. In multi-antenna systems (e.g. dual antenna systems) it can decide on the optimal solution choosing either or both: a) handover to another BS, b) choice of antenna. The choice of antenna avoids the need for significant loss in signal (driven by threshold described above), for instance in ACGC, before antenna switchover happens and thereby loss of data throughput.

Antenna or base station handover can occur in response to a break in communication.

The system can switch to a different antenna and/or a different base station following a predefined period of disconnection. The period for antenna switching may be less than the period for base station switching. Accordingly, the system may attempt to switch antennas and, if communication cannot be restored, then attempt to switch base stations. The duration of disconnection for antenna switching may be about few ms, whereas an inter-base station handover disconnection could last more than 100 ms.

As an extension to the invention above that anticipates blockage, the positional information can also be used to calculate the anticipated line of sight distance, using current distance with the aircraft speed relative to the BS and prevent handover to cells with good RSRP and RSRQ that are too far away (or soon to be too far away) and exceed the maximum latency limit of the system. Again in this case for these BS the UE will spoof the measurements setting RSRP and RSRQ to poor values to avoid handover to these cells.

FIG. 2 shows a communication system in accordance with an embodiment.

A communication system (such as a user equipment, UE) 200 comprises a processor 210, memory 220, non-volatile memory 230 and an input/output (I/O) interface 240.

The communication system is connected to one or more antennas 270, a velocity measurement system 260 (such as an inertial navigation system, INS) and a position measurement system 250 (such as a global positioning system, GPS).

The communication system 200 is configured to be carried by a moving platform On this case, an aircraft). The velocity measurement system 260 measures and reports the current velocity of the platform (the aircraft) to the communication system 200. The position measurement system 250 measures and reports the current position of the platform (the aircraft) to the communication system 200.

The communication system 200 is controlled by the processor 210. The processor 210 implements the methods described herein based on executable code stored in the non-volatile memory 230 and loaded for execution into memory 200 (e.g. Random Access Memory, RAM). The communication system 200 receives the velocity and position measurements via the I/O interface 240. The I/O interface 240 also receives signals (messages) measured by the antennas 270 (e.g. from base stations) and sends signals (messages) via the antennas 270 (e.g. to base station(s)).

The non-volatile memory 230 is used for storing: * Base station locations, * Ground map with height (and size) of significant obstacles, * Body map (e.g. aircraft body map) defining significant obstacles, * Knowledge of position and number of antennas 270, * Beam patterns of antennas 270.

From this information the processor 210 can calculate the line of sight from the current antenna location to the current base station location and then identify any structure blockage (e.g. from the aircraft structure) from a 3D model of the platform (the aircraft) that will be appropriately oriented from the velocity information. It can then also identify if there are any significant obstacles on the ground from the ground terrain model. If any blockage is identified (on aircraft or ground) the line of sight from any other (aircraft) antennas 270 is calculated and if this is unblocked, switchover to this antenna will be effected.

As discussed above, handover between base stations can be effected in the event of predicted blockages by reporting adjusted received signal strength (e.g. power or quality) values. If the calculated line of sight shows that one or more base stations are (and will remain to be) unblocked then the relative received signal strength (e.g. RSRP and/or RSRQ) of these candidate base stations can be measured as normal (e.g. using the same methodology as 3GPP, such as from a UE modem). In the event that a blockage is predicted for a base station, then the strength for this base station is reduced. The resultant strength values are reported to the base station to which the communication system 200 is currently connected. The base station uses these (adjusted) values to determine whether to handover communication to another base station and, if so, which base station to handover to.

The base station decides whether to handover and which base station to hand over to based on the reported strength values. The base station may decide to handover communication if the reporting strength value for another base station is more than a threshold amount higher than the reported strength value for the serving base station.

If handover is initiated, the serving base station may decide to handover to the base station that has the highest reported strength value.

Alternatively, the system may issue a trigger to the serving base station to initiate handover to another base station in response to the system determining that the other base station has a signal strength value that is more than a threshold amount higher than the signal strength value for the serving base station. This may be based on the signal strength values after they have been adjusted to account for any blockages. Again, where multiple other base stations qualify to be the next serving base station, the one with the highest signal strength value may be selected. The trigger may include an identifier identifying the other base station that will serve as the next serving base station.

In addition, for a multi-antenna system, the received signal strength for the first antenna is compared with the RSRP and RSRQ of the potential second antenna (and any other antennas). The best option between antenna switching and handover (or both) can then be made. In single antenna systems handover will be the primary means to avoid blockage. Nevertheless, when base station handover is performed, antenna switching may also be performed at the same time, if an alternative antenna can offer improved performance. A crucial part of this idea is that blockage is anticipated rather than waiting for the signal RSRP and RSRQ to fall due to blockage.

Some of the stored information is unlikely to need updating: * Body map defining significant obstacles, * Knowledge of position and number of antennas 270, * Beam patterns of antennas 270.

However, there may be a need to update the base station locations and ground maps over the operational life of the system. This can either be done manually (e.g. when the aircraft is on the ground) or alternatively there are a number of automatic distribution mechanisms described below.

Measurements of (unadjusted) signal strength (e.g. RSRP and RSRQ) can use the same methodology as 3GPP. Nevertheless, as mentioned above, these signal strength measurements are then adjusted based on any predicted blockages. The serving base station is not aware of this process, so makes decisions regarding handover as normal, although based on spoofed measurements that encourage the serving base station to handover in the event of expected blockages and to handover to base stations that have no expected blockages.

The use of the information described above to make optimal decisions to anticipate and mitigate blockage can be made in a computing device. This can either be located solely in the modem device or split across the modem device and a separate computing device. In addition, whilst separate velocity and position measurement systems are described above, these can be integrated within one system or split across multiple systems FIG. 3 shows a method for determining antenna or base station handover according to an embodiment.

When the method starts, the system can determine whether it is time to evaluate if handover should be scheduled. This process can be run continuously or can be run intermittently (e.g. every 30 seconds). This can be based on a predefined periodicity. Where the process is run intermittently, the period between each instance of the process running could depend on the expected speed of the aircraft and the expected cell size of the base stations. In some situations, the process may defer checking for a predetermined period if there has been no change. In addition, the system may determine to run the process in response to a change (e.g. in response to a change in aircraft direction and/or attitude).

When the system is instructed to begin, the system determines the line of sight for a current antenna that is communicating with a serving base station. This is determined for a predetermined period. The predetermined period may be a configurable parameter based on the type of aircraft. For instance, it may be 30s for a jet passenger aircraft, 2 minutes for a turbo propeller aircraft, and 5 minutes for general (civil) aviation. The line of sight is determined based on the location of the base station and the current location and attitude (e.g. heading) of the aircraft. This may also be dependent on the current velocity (or speed) of the aircraft. The current position can be determined from INS data and/or from GPS data. This step can also make use of knowledge of the position of the antenna on the aircraft.

The line of sight over the predetermined period is then used to determine if there are any upcoming obstructions. This can utilise the following information: Aircraft ground velocity vector and aircraft attitude rates (rates of changes of aircraft pitch, roll and/or yaw) Map of local terrain Map of body of aircraft (or other platform) Position and number of antennas Beam pattern of each antenna An obstruction may be determined if an obstruction impedes the line of sight between the antenna and the base station. This may be extended to include any obstructions that impede a beam pattern between the antenna and base station, where the beam pattern is directed along the line of sight (e.g. centred on the line of sight). An obstruction may be any object falling along the line of sight or beam pattern. This may include a body of the aircraft or a feature of the terrain (e.g. a hill or mountain).

If no upcoming obstruction is determined, then the system loops back to the start. If an obstruction is determined, then the method determines whether the system has any other antennas. If so, then the line of sight between the current base station and each other antenna is determined and any obstructions for these antennas are determined. If at least one other antenna does not have an upcoming obstruction, then the best unobstructed antenna is selected. If multiple other antennas do not have an obstruction, then the antenna with the strongest connection is selected (e.g. the antenna with the highest signal strength). Once an unobstructed antenna has been selected, communication is directed to the current base station through this selected antenna.

If no other antennas are present, or if all antennas have an expected obstruction with the current base station, then the system attempts to identify an alternative base station that does not have any expected obstructions. This is achieved by calculating the line of sight for between all candidate base station(s) and all antenna(s). That is a line of sight is calculated for each potential combination of a candidate base station and an antenna. Based on these lines of sight, the method determines any upcoming obstructions. If an upcoming obstruction is determined for all other base stations, then the method loops back to the start. If at least one candidate base station does not have an upcoming obstruction with an antenna, then the best unobstructed best station-antenna pair is selected. If multiple base station-antenna pairs do not have an obstruction, then the combination with the strongest connection is selected (e.g. the combination with the highest signal strength). Each combination of a base station and antenna may be considered a separate communication link. Accordingly, the unobstructed communication link with the strongest connection may be selected. Once a base station and antenna have been selected, communication is passed to this combination (e.g. through antenna and/or base station handover).

As discussed herein, handover to another base station can be encouraged by reducing the received signal strength measurements for the serving base station. This encourages the serving base station to handover communication to the next candidate base station Where a new antenna and/or base station is selected, the method is then repeated for this new antenna and/or base station.

As shown in FIG. 3, certain embodiments first attempt to find an alternative unobstructed antenna for communication with the current serving base station. Only if no other unobstructed antennas are available for the current base station, does the method look for another unobstructed base station. This is due to the additional delay associated with base station handover. By preferring antenna switching to base station switching where possible, link interruption is reduced.

FIG. 4 shows a method for controlling handover between antennas and/or base stations according to an embodiment.

Firstly, base station position information and obstacle information are received 310. This can be stored locally and/or received through an upload, as described in more detail later. The obstacle information specifies the position of one or more potential obstacles. This might include a structure of the platform upon which the antenna are mounted (e.g. at least a portion of the body of an aircraft) and/or details of surface features such as geographical features that could be potential obstacles.

Position information and velocity information are received 320. These indicate the current position and velocity of the moving platform. This might also include attitude information.

The line of sight of between the antenna and serving base station is then determined 330. Where multiple antennas and/or base stations exist, then a line of sight may be determined for each potential antenna-base station pair (each potential combination of antennas and base stations). The line of sight may be determined for a predetermined period into the immediate future (e.g. starting from the current time and up until a predefined time after the current time).

The method then determines whether there is an expected blockage between the currently communicating antenna and base station 340. This may also include determining if any blockages are expected between any potential combination of antennas and base stations.

If no blockage is expected for the currently communicating antenna and base station, then the method returns to step 320 to receive updated position and velocity information. If a blockage is expected between the currently communicating antenna and base station, then transfer of communication to an antenna and/or base station with no expected blockages (unblocked antenna and/or unblocked base station) is initiated 350. This may include transferring communication to a different (unblocked) antenna but continuing to communicate with the previous base station. Alternatively, this may include initiating handover to a different base station but maintaining communication via the previous antenna. Equally, this may include transferring both to a different antenna and a different base station.

Where communication is to be transferred to a different base station, this can be implemented by lowering a measured received signal strength from the serving base station and reporting this lowered value to encourage the serving base station to initiate handover.

FIG. 5 shows a method for controlling handover between antennas and/or base stations according to an embodiment.

As with the method of FIG. 4, the base station position information and obstacle information are received 410 followed by position and velocity information for the moving platform 430. In this case, base station signal strength measurements are also performed for all base stations by each antenna 420. This may be performed after, before or in parallel to (simultaneously with) the receipt of position and velocity information.

Following this, then a line of sight is determined for each potential antenna-base station pair (each potential combination of antennas and base stations) 430. Each potential antenna-base station pair may be considered a potential communication link. The line of sight may be determined for a predetermined period into the immediate future (e.g. starting from the current time and up until a predefined time after the current time).

The method then determines whether there is an expected blockage between the currently communicating antenna and the serving base station 440. This also includes determining if any blockages are expected between any potential combination of antennas and base stations.

If no blockage is expected for the currently communicating antenna and base station, then the method moves to step 470 to reduce the signal strength of each base station that has an expected blockage with all antennas.

If a blockage is expected between the currently communicating antenna and base station, then the method determines if there is an expected blockage between the serving base station and any alternative antennas 450. If there exists any other antennas that do not have an expected blockage with the serving base station, then communication is transferred to the unblocked antenna 460. If there are multiple unblocked antennas, then the antenna with the highest received signal strength may be chosen.

If no unblocked antennas exist (e.g. if the system is a single antenna system, or if all potential antennas have an expected blockage) then the system attempts to initiate handover to another base station. Handover is controlled by the serving base station based on received signal strength measurements that are reported back to the base station. Accordingly, the communication system continuously measures the strength of signals received from the serving base station and any other base stations that can be detected and reports these strength measurements back to the serving base station. The serving base station then initiates handover if another base station has a better (e.g. higher) received signal strength. Received signal strength may be measured based on received signal power and/or received signal quality (e.g. RSRP (radio frequency signal power) and/or received signal strength quality (RSRQ)).

To cause the serving base station to initiate handover, the communication system reduces the measured signal strength for the serving base station that has an expected blockage 465. This may be achieved by setting the measurement of the serving base station to the lowest possible value. To reduce the risk of connecting to other base stations with expected blockages, the signal strength measurements for any other base stations with expected blockages with all antennas are reduced 470. Accordingly, between steps 465 and 470, the signal strength measurement for each base station with an expected blockage with all antennas is reduced. The reduction may be by a predefined amount. Alternatively, the signal strength value may be set to a predefined (e.g. a minimum) amount. Where multiple indicators of signal strength are utilised (e.g. power and quality), then both may be reduced.

The signal strength measurements are then reported to the serving base station 480. This includes, for each base station with an expected blockage, a reduced signal strength measurement, and for each base station without an expected blockage, an unaltered (non-reduced) signal strength measurement.

The serving base station then decides whether to handover to another base station based on the reported signal strength measurements 490. Where the reported signal strength measurement for the serving base station is lower than the reported signal strength measurement for another base station (e.g. lower by at least a predefined threshold), then the serving base station may decide to hand over to this other base station. Where multiple alternative base stations exist, then the base station with the highest reported signal strength may be chosen.

In some cases, it is possible that the reduced signal strength for the base station is still higher than the reported signal strength values for other base stations. This may happen where all other base stations also have expected blockages, or where any non-blocked base stations are much further away. In this case, the serving base station may decide to continue with communication (e.g. may decide not to initiate handover) as it is still the best choice of base station even if there is an expected blockage.

In addition to (or alternatively) altering to signal strength values based on expected blockages, the system may adjust signal strength values based on distance to the base station. This can discourage connection to far away base stations that may have a high signal strength (e.g. based on reflections or a lack of blockages) but that are nevertheless too far away (e.g. communication would have too high a latency).

Accordingly, for each of the plurality of base stations, the system may determine an anticipated line of sight distance to the base station at a predefined future time and, in response to determining that the anticipated line of sight distance is greater than a threshold, reducing the signal strength measurement for the base station to discourage communication with that base station.

As mentioned above, the system includes local non-volatile memory into which the following is stored: * BS location, * Ground map with height (and size) of significant obstacles, * Aircraft body map defining significant obstacles, * Knowledge of position and number of antennas, * Beam patterns of antennas.

Some of this information is unlikely to need updating: * Aircraft body map defining significant obstacles, * Knowledge of position and number of antennas, * Beam patterns of antennas.

However, there may be a need to update the BS location and ground map over the operational life of the aircraft. For aircraft there may be no need (or a reduced need) to update the ground map with details of significant obstacles. Having said this, for other moving platforms, e.g. trains, then significant obstacles (e.g. buildings, trees, etc.) could be more likely to change over time, and may therefore require updating over time.

There are a number of ways of updating the local memory/database. It is likely that the ideal situation may be for more than one distribution mechanism, with a defined order of precedence. There follows detail for BS location update; although, some of these mechanisms may be appropriate for ground map updates as well.

3GPP System Information Broadcast One option would be to broadcast the BS positions as part of the cellular communication System Information Broadcasts (SIBs), since this would facilitate a direct and timely method to distribute the BS location data to the modem physical layer engine -without relying on an external (to the cellular network) application.

The following list summarises System Information Block data under 3GPP Release 10, [ETSI TS 136 331]: SIB-1: provides cell access, cell identity, cell status and cell selection Information.

SIB-2: provides information on PRACH configuration, uplink frequency and access barring.

SIB-3: provides information needed for intra-frequency cell reselections. SIB-4: provides information on intra-frequency neighbouring cells.

SIB-5: provides information on inter-frequency neighbouring cells.

* SIB-6: provides information for reselection to Universal Mobile Telecommunications Service (UMTS) cells.

SIB-7: provides information for reselection to Global System for Mobile Communications (GSM) cells.

SIB-8: provides information for reselection to CDMA2000 cells.

SIB-9: defines the home BS name -intended for femto-cell applications SIB-10 + 11: provides Earthquake and Tsunami Warning System (ETVVS) information.

SIB-12: supports commercial mobile alerting systems.

SIB-13: provides information on the Multimedia Broadcast Mulficast Service (Rel. 9) Collectively the SIBs broadcast a large number of system and cell parameters, and there are a number of opportunities to insert BS location data. For example, SIBs that would normally carry information not needed in A2G (for example, SIBs 6-8 and SIBs10-13) could potentially be adapted to carry BS location information-although, this would not be consistent with adherence to the 3GPP standard.

Alternatively, SIB-9, which provides a 48 byte string for broadcasting the BS node-name (for future use with femtocells), might be a suitable mechanism to broadcast BS locations, encoded as a string.

Using SIB-9, only a single BS location would be updated each time a cell is acquired prior to handover. In addition the SIBs are only read following initial acquisition.

Therefore BS location data would need to be stored in non-volatile memory in the UE, with the database updated on a cell by cell basis via SIB-9.

3GPP Multimedia Messaging Service (MMS) Instead of using broadcast or multicast, UE can be updated sequentially, one at a time. Dedicated A2G Broadcast/Multicast Use of a dedicated 3GPP broadcast (or mulficast) to distribute the BS database would also appear to be attractive, since this could facilitate timely distribution of the data directly over the A2G network. Such a dedicated broadcast/multicast could, if necessary, be protected with appropriate encryption and/or authentication. Indeed, the concept of a dedicated A2G broadcast may also be attractive for disseminating other A2G-specific information (network status, planned outages, etc.).

While 3GPP provides built-in support for both broadcast and multicast transmissions, any dedicated broadcast data would likely be terminated outside of the LTE protocol stack. Consequently a management application or agent would likely be needed to receive the broadcast/mulficast and communicate with the modem.

LTE Location Posifioninq Protocol (LPP) / Secure User Plane Location (SUPL) As part of 3GPP's support for UE positioning, BS locations are stored in each Location Server in the core network, and LTE defines two protocols to assist with Location Based Services (LBS): Location Positioning Protocol (LPP) [3GPP TS 36.355]: This is a simple point-to-point protocol, used in both control and user planes, to support communications between the UE and its Location Server. The LPP layer resides outside of the UE protocol stack, but it is typically implemented in the modem. LPP includes a limited number of message types, including a 'Request Location Information' -although, this is intended to retrieve the estimated UE position.

Secure User Plane (SUPL) protocol: this is a set of protocols for user plane transport intended to support existing (i.e. 2nd & 3rd generation) wireless network messages when used in conjunction with Location Based Services (LBS -used to identify services in the UEs vicinity). SUPL includes support for geographical area event triggers and support for IP encryption Given the above, there is scope to use the LPP and/or SUPL protocols, in conjunction with a Location Server to periodically update a local database of BSs on the UE. Again, a local database of locations would be stored in non-volatile memory in the UE, updated at periodic intervals (e.g. once per flight).

Operational Support System / Network Manaqement System A further option would be to exploit the A2G network Operations Support System (OSS), and/or Network Management System (NMS). The A2G NMS could potentially provide a distribution mechanism for the BS location database, with BS locations potentially forming part of the SNMP Management Information database (MIB), with either the UE fetching (reading) data from the NMS or the NMS pushing (writing) data to the UE MIB.

Ethernet Maintenance Port Lastly, the BS database could be uploaded, and periodically updated directly, via a local connection (e.g. an Ethernet maintenance port).

This is less automatic than the other database distribution options, but may be used to download the initial database. Without additional distribution mechanisms, data could become obsolete -particularly if a scheduled maintenance is delayed.

Given the above, embodiments described herein provide a means of avoiding blockages (or at least reducing the number of blockages) to improve communication throughput. This can be applied to any communication system present on a moving platform, but is particularly advantageous for air to ground communication between an aircraft and ground-based base stations.

Embodiments described herein make use of a knowledge of the position and velocity of the moving platform (the aircraft) and position information detailing the position of the base stations and the location of potential obstacles in order to predict expected blockages. In the event that there is a predicted blockage for signals from one of the base stations, the signal strength measurements for this base station are artificially reduced in order to encourage handover On the event that the expected blockage is for signals from the serving base station) or to discourage handover (in the event that the expected blockage is for signals from a neighbouring (non-serving) base station).

By modifying the signal strength measurements, the handover between base stations can be initiated even where the serving base station makes the ultimate decision on handovers. This allows handover to be initiated without requiring any changes to the functioning of the base station.

In addition to the above, where the system includes multiple antennas, and where one of the antennas does not have any expected blockages, the system can transfer communication to this unblocked antenna.

The use of the information described above to make optimal decisions to anticipate and mitigate blockage can be made in a computing device. This can either be located solely in the modem device or split across the modem device and a separate computing device. The separate computing device would use the information not used in a conventional cellular system and would either send this as a correction to the modem device, or alternatively the separate computing device could use RSRP/RSRQ measurements supplied by the modem, correct them and send this to the modem. It is also possible to measure the RSRP/RSRQ separately by another device such as an FPGA acting in real-time on the signal samples and use this to provide a corrected RSRP/RSRQ measurement.

Implementations of the subject matter and the operations described in this specification can be realized in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For instance, hardware may include processors, microprocessors, electronic circuitry, electronic components, integrated circuits, etc. Implementations of the subject matter described in this specification can be realized using one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal.

The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

While certain arrangements have been described, the arrangements have been presented by way of example only, and are not intended to limit the scope of protection. The inventive concepts described herein may be implemented in a variety of other forms. In addition, various omissions, substitutions and changes to the specific implementations described herein may be made without departing from the scope of protection defined in the following claims.

Claims (16)

1. 26 CLAIMS 1. A method for controlling handover between antennas and/or base-stations for a communication system carried by a moving platform, the method comprising: receiving position information indicating a current position of the moving platform and velocity information indicating a current velocity of the moving platform; receiving base station position information indicating, for each of a plurality of base stations, a position of the base station; receiving obstacle information indicating the position of one or more potential obstacles; determining, based on the position information, velocity information, base station position information and obstacle information, an expected blockage between an antenna on the moving platform and a serving base station of the plurality of base stations; and in response to determining an expected blockage between the antenna and the serving base station, initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations.
2. 2. The method of claim 1 wherein determining the expected blockage comprises: determining a line of sight between the antenna and the serving base station over a predefined period of time in the future based on the position information, velocity information and base station position information; and determining whether the line of sight is blocked by an obstacle during the predefined period of time in the future based on the obstacle information.
3. 3. The method of any preceding claim wherein the obstacle information includes information defining the shape of each of the one or more potential obstacles.
4. 4. The method of any preceding claim wherein the obstacle information includes one or both of: a map of one or more geographical obstacles; and information defining the shape of at least a portion of the moving platform.
5. The method of any preceding claim wherein: initiating transfer of communication to one or both of a different antenna and a different base station of the plurality of base stations forms a new combination of antenna and base station for communication; and the transfer of communication is initiated in response to determining that the new combination has no expected blockages.
6. 6. The method of any preceding claim wherein: the method comprises measuring a signal strength of one or more signals received from each of the serving base station and the other base station; and initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations comprises issuing a signal to initiate transfer of communication to another base station of the plurality of base stations, including: reducing the measured signal strength for the serving base station such that it is less than the signal strength for the other base station; and reporting the reduced signal strength of the serving base station and the measured signal strength of the other base station to the serving base station to prompt the serving base station to initiate handover to the other base station.
7. 7. The method of any preceding claim further comprising: for each of the plurality of base stations: receiving one or more signals from the respective base station; measuring a signal strength for the one or more signals received from respective base station; determining, based on the position information, velocity information, base station position information and obstacle information, whether there is an expected blockage between the antenna on the moving platform and the respective base station of the plurality of base stations; and in response to determining an expected blockage between the antenna and the respective base station, reducing the signal strength measurement for the respective base station; and reporting the signal strength measurements for the plurality of base stations to the serving base station to allow the serving base station to decide which base station to handover communication to.
8. 8. The method of claim 7 further comprising, for each of the plurality of base stations: determining an anticipated line of sight distance to the base station at a predefined future time; and in response to determining that the anticipated line of sight distance is greater than a threshold, reducing the signal strength measurement for the base station to discourage communication with that base station.
9. 9. The method of any preceding claim wherein initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations comprises: determining whether any other antenna has any expected blockages with the current base station; and in response to determining that at least one other antenna does not have any expected blockages with the current base station, assigning one of the at least one other antenna to communicate with the current base station.
10. 10. The method of claim 9 wherein assigning one of the at least one other antenna to communicate with the current base station comprises selecting a strongest antenna from a plurality of other antennas that do not have any expected blockages, wherein the strongest antenna has a strongest connection with the current base station of the plurality of other antennas that do not have any expected blockages.
11. 11. The method of claim 9 or claim 10 wherein initiating transfer of communication to one or both of a different antenna and a different base station of the plurality of base stations comprises: in response to determining that there are no other antennas that do not have any expected blockages with the current base station, determining whether any other potential communication link has any expected blockages, wherein each potential communication link represents a potential combination of another base station and another antenna; and in response to determining at least one other potential communication link has no expected blockages, initiating transfer of communication to one of the at least one other potential communication link.
12. 12. The method of claim 12 wherein initiating transfer of communication to the one of the at least one other potential communication link comprises selecting a strongest communication link from a plurality of other potential communication links that do not have any expected blockages.
13. 13. The method of any preceding claim wherein the moving platform is an aircraft and communication is air to ground communication.
14. 14. The method of any preceding claim wherein one or both of the base station position information and obstacle information are received via communication from one or more of the plurality of base stations.
15. 15. A system for controlling handover between antennas and/or base-stations for a communication system carried by a moving platform, the system comprising a processor configured to: receive position information indicating a current position of the moving platform and velocity information indicating a current velocity of the moving platform; receive base station position information indicating, for each of a plurality of base stations, a position of the base station; receive obstacle information indicating the position of one or more potential obstacles; determine, based on the position information, velocity information, base station position information and obstacle information, an expected blockage between an antenna on the moving platform and a serving base station of the plurality of base stations; and in response to determining an expected blockage between the antenna and the serving base station, initiate transfer of communication to one or both of another antenna and another base station of the plurality of base stations.
16. 16. A computer program for controlling handover between antennas and/or base-stations for a communication system carried by a moving platform, wherein the program, when executed by a processor, causes the processor to implement a method comprising: receiving position information indicating a current position of the moving platform and velocity information indicating a current velocity of the moving platform; receiving base station position information indicating, for each of a plurality of base stations, a position of the base station; receiving obstacle information indicating the position of one or more potential obstacles; determining, based on the position information, velocity information, base station position information and obstacle information, an expected blockage between an antenna on the moving platform and a serving base station of the plurality of base stations; and in response to determining an expected blockage between the antenna and the serving base station, initiating transfer of communication to one or both of another antenna and another base station of the plurality of base stations.