CN113709675B - Position management method for constellation satellite mobile communication system - Google Patents
Position management method for constellation satellite mobile communication system Download PDFInfo
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Abstract
The invention discloses a position management method for a constellation satellite mobile communication system, which comprises the steps that terminal equipment periodically compares the position area number of a current satellite wave beam with a stored home position area time sequence table, and determines whether to send a position update request to a satellite mobile service switching center according to a comparison result. The location area timing schedule is a plurality of location area timings pre-stored in an on-board access location register, and the location area timings include at least one satellite beam cell serving the same location on the ground in a time sequence. Compared with the traditional scheme, the method has obvious improvement amount of the position management overhead, the lower the user movement rate is, the larger the improvement amount is, and particularly when the user is stationary, the method has no position updating overhead and only paging overhead, so that the overhead of the method is less than 2% of the traditional scheme, the on-satellite data interaction load can be greatly reduced, and the method is worthy of large-area popularization and use.
Description
Technical Field
The invention relates to the technical field of mobile communication, in particular to a position management method for a constellation satellite mobile communication system.
Background
There are many advantages to using interstar link networking, such as:
the transmission condition is good. The interstellar link signal does not need to pass through an atmosphere layer, has no loss such as atmospheric absorption, rain attenuation, shielding, multipath effect and the like, and can adopt wave bands or laser communication with higher frequency to realize high-capacity communication.
The transmission efficiency is high. The interstar link relay has shorter propagation delay than the ground station double-hop relay, improves the transmission efficiency, and is easier to meet the QoS requirement of real-time service.
The networking is convenient. The construction of the ground gateway station is limited in politics, economy, geography and the like, and the interstellar links are free of the limitation, so that the system routing and the network management are more flexible and convenient.
The destruction resistance is strong. After all satellites are interconnected through an interstellar link, communication signals can be transmitted independently of a ground communication network, and the anti-interference and anti-destruction capacity of the system is greatly improved.
The ground section pressure is small. The use of the interplanetary links reduces the number of requirements for ground gateway stations, thereby greatly reducing the complexity and investment of the ground segment.
In a conventional land PLMN (public land mobile network), after a mobile subscriber roams into a new location area, an MSC (mobile services switching center) requests a VLR/HLR (visitor location register (VLR), a database for storing visitor location information) database to update the location information of the subscriber through a registration notification message (REGNOT, subscriber class information); when the call is transferred, the calling party service MSC will send a location request message (LOCRQ) to the called home HLR, if the current calling party and the called party are not in the same service area, the HLR sends a routing request message (ROUTREQ) to the called service MSC/VLR, the called VLR returns the called roaming number MSRN (Mobile Subscribe Roaming Number, roaming number), the HLR is forwarded to the calling MSC/VLR, the calling MSC calls the called party MSC, and the MSC inquires the related parameters of the called party and then carries out paging. As shown in fig. 9, both location update and location application messages are sent to the HLR when the subscriber roams to a new MSC/VLR service area or a call is routed.
The location management technology in the traditional terrestrial PLMN has the following two disadvantages:
1. when the transaction processing is increased due to the expansion of the user capacity, the signaling processing load of the HLR and the database query time delay are greatly increased, and the HLR becomes a bottleneck of the core network.
2. This mechanism increases the time delay for location update and location request if a mobile user roams into a location area that is further away from home, and also increases the signaling load on the relay network significantly. In constellation satellite mobile communications, the time delay itself is large, and due to the high speed movement of satellites, the location update is frequent, and the location management standards currently used in PLMNs are too costly to apply and must be improved.
Disclosure of Invention
The invention provides a position management method for a constellation satellite mobile communication system.
The invention provides the following scheme:
a location management method for a constellation satellite mobile communication system, comprising:
a location update mechanism;
the terminal equipment periodically compares the position area number of the current satellite wave beam with a stored home position area time sequence table, and determines whether to send a position update request to the on-satellite mobile service switching center according to the comparison result; the location area timing schedule includes a plurality of location area timings pre-stored in an on-board visitor location register, the location area timings including at least one satellite beam cell servicing a same location on the ground in a time sequence.
Preferably: when the comparison results are inconsistent, sending a position update request to an on-board mobile service switching center of the newly accessed satellite; comprising the following steps:
and sending the current position area number to the mobile service switching center of the newly accessed satellite.
Preferably: the mobile service switching center of the newly accessed satellite determines that the current position area number and the original position area sequence number are in the service area of the co-orbit satellite;
and the mobile service switching center of the newly accessed satellite updates the position area sequence for the terminal, and simultaneously informs the satellite access position register of all other co-orbit satellites of the current position area time sequence number and the user information of the terminal equipment to realize the position update of the terminal equipment.
Preferably: the mobile service switching center of the newly accessed satellite determines that the current position area number and the original position area sequence number are in service areas of satellites with different orbits;
the mobile service switching center of the newly accessed satellite updates the position area sequence for the terminal, and simultaneously informs a ground homing position register and on-board access position registers of all other co-orbit satellites of the current position area sequence number and the user information of the terminal equipment to realize the position update of the terminal equipment;
the ground homing location register broadcasts a location cancellation request to all satellites in the old orbit so that the satellite-borne visitor location register of the old orbit deletes all information of the terminal equipment after receiving the location cancellation request.
Preferably: also includes a call delivery mechanism;
after the terminal equipment initiates a call, an on-board mobile service switching center serving the terminal equipment analyzes the number type of a called user to determine the user type of the called user, wherein the user type comprises a ground user and a satellite network user;
and determining a call delivery mode according to the determined user type.
Preferably: the determined user type is a user of a ground network, the satellite mobile service switching center serving the terminal equipment calls a ground access gateway station of the track, and the gateway station transmits the call to an external network.
Preferably: the determined user type is a satellite network user, and an on-board mobile service switching center serving the terminal equipment analyzes the database type of the current position of the called user, wherein the database type comprises an active user database and a potential user database; the active user database comprises user information in the satellite service area, and the potential user database comprises user information in other satellite service areas in the track;
and determining a call transfer mode according to the determined type of the database where the called party is currently located.
Preferably: the determined called party is currently positioned in a satellite activation user database where the calling party is positioned;
the satellite access location register for serving the terminal equipment returns the temporary mobile user identification code of the called user and the number of the current location area of the called user, and the satellite mobile service switching center for serving the terminal equipment initiates paging to the called user.
Preferably: the determined called party is currently positioned in a satellite potential user database where the calling party is positioned;
the satellite access location register for serving the terminal equipment returns the number of the mobile service switching center where the called user is currently located, the mobile service switching center for serving the terminal equipment transfers the call to the mobile service switching center where the called user is located, and attaches the international mobile user identification code of the called user, and the mobile service switching center of the called user inquires the temporary mobile user identification code of the called user and the number of the current location area of the called user in the activated user of the mobile service switching center of the called user, and then initiates paging to the called user.
Preferably: the determined called party is not currently in the satellite database where the calling party is;
the mobile service switching center serving the terminal equipment directly transfers the call to the home gateway station of the called user, and attaches the international mobile user identification code of the called user, the home gateway station inquires the home location register and then calls the mobile service switching center where the called user is located, the mobile service switching center where the called user is located inquires the temporary mobile user identification code of the called user and the number of the current location area of the called user from the satellite access location register of the mobile service switching center where the called user is located, and then initiates paging to the called user.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
by the invention, a position management method for a constellation satellite mobile communication system can be realized, and in the implementation mode, the method can comprise a position updating mechanism; the terminal equipment periodically compares the position area number of the current satellite wave beam with the stored home position area time sequence table, and determines whether to send a position update request to the on-board mobile service switching center according to the comparison result. The location area timing schedule includes a plurality of location area timings pre-stored in an on-board visitor location register, the location area timings including at least one satellite beam cell servicing a same location on the ground in a time sequence. Compared with the traditional scheme, the method has the advantages that the improvement amount of the position management overhead is obvious, the lower the user movement rate is, the larger the improvement amount is, and particularly when the user is stationary, the position update overhead is not available and only the paging overhead is available, so that the overhead of the method provided by the application is less than 2% of the traditional scheme, the satellite data interaction load can be greatly reduced, and the method is worthy of large-area popularization and use.
Of course, it is not necessary for any one product to practice the invention to achieve all of the advantages set forth above at the same time.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a location management structure according to an embodiment of the present invention;
FIG. 2 is a schematic view of satellite and beam numbering provided by an embodiment of the present invention;
FIG. 3 is a schematic diagram of a location update procedure between different tracks according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a call process of the MEO system according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a transmission flow of TtT calls in different tracks according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating bit overhead ratio of a low-speed user under different motion characteristics according to an embodiment of the present invention;
FIG. 7 is a diagram illustrating bit overhead ratio of a high-speed user under different motion characteristics according to an embodiment of the present invention;
FIG. 8 is a diagram illustrating bit overhead ratio of a high-speed user under different motion characteristics in a large location area according to an embodiment of the present invention;
fig. 9 is a schematic diagram of call delivery flow in a land PLMN according to the prior art.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the invention, fall within the scope of protection of the invention.
Examples
The embodiment of the invention provides a position management method for a constellation satellite mobile communication system, which can comprise the following steps:
a location update mechanism; the terminal equipment periodically compares the position area number of the current satellite wave beam with a stored home position area time sequence table, and determines whether to send a position update request to an on-board mobile service switching center according to the comparison result, wherein the position area time sequence table comprises a plurality of position area time sequences stored in an on-board access position register in advance, and the position area time sequence comprises at least one satellite wave beam cell for serving the same position on the ground in time sequence.
Specifically, when the comparison results are inconsistent, sending a position update request to an on-board mobile service switching center of the newly accessed satellite; comprising the following steps:
and sending the current position area number to the mobile service switching center of the newly accessed satellite.
Because of the periodic movement of the satellite, the access position area sequences of the satellite to the user can be calculated and predicted within a certain time, the number of the position area sequences and the length of each sequence are limited, the home gateway station HLR and the satellite VLR can store possible position area sequences in advance, and the corresponding position area sequences are called according to the received position area codes after each time the position update request of the user is received, so that the position information of the user is updated regularly. And the location update request will only be initiated when the terminal device finds that the location area number has changed. If the position area number is not changed, the position update request is not required to be initiated, and the method can greatly reduce the data interaction times between the terminal equipment and the satellite, is beneficial to releasing the information interaction channel of the satellite, and saves precious energy and bandwidth resources on the satellite.
For example, when a user carries a terminal device to be stationary at a certain position, each satellite periodically moves along its orbit, so that the beam of the terminal device accessed to the satellite will periodically change, and if the conventional position updating method is adopted, the beam change needs to perform data transmission of one position update once, thus occupying a great amount of precious energy and bandwidth resources on the satellite. The method provided by the application makes full use of the law of periodic motion of the satellite, and satellite beams serving a certain user periodically change in a certain time, so that when the user is stationary, the terminal equipment and the satellite do not need any data interaction related to position update by adopting the method provided by the application.
The configuration of the location areas included in each location area sequence will be described in detail later.
The mobile service switching center of the newly accessed satellite determines that the current position area number and the original position area sequence number are in the service area of the co-orbit satellite;
and the mobile service switching center of the newly accessed satellite updates the position area sequence for the terminal, and informs the satellite access position registers of all other co-orbit satellites of the current position area sequence number and the user information of the terminal equipment to realize the position update of the terminal equipment.
The mobile service switching center of the newly accessed satellite determines that the current position area number and the original position area sequence number are in service areas of satellites with different orbits;
the mobile service switching center of the newly accessed satellite updates the position area sequence for the terminal, and simultaneously informs the ground homing position register and the on-board access position registers of all other co-orbit satellites of the current position area sequence number and the user information of the terminal equipment to realize the position update of the terminal equipment.
The ground homing position register broadcasts and sends a position cancellation request to all satellites in the old orbit, so that all information of the terminal equipment is deleted after the satellite access position register in the old orbit receives the position cancellation request;
the method provided by the embodiment of the application can also provide a call transfer mechanism;
after the terminal equipment initiates a call, an on-board mobile service switching center serving the terminal equipment analyzes the number type of a called user to determine the user type of the called user, wherein the user type comprises a ground user and a satellite network user;
and determining a call delivery mode according to the determined user type.
Specifically, the determined user type is a user of a ground network, the satellite mobile service switching center serving the terminal equipment calls a ground access gateway station of the track, and the gateway station performs call transfer to an external network.
The determined user type is a satellite network user, and an on-board mobile service switching center serving the terminal equipment analyzes the database type of the current position of the called user, wherein the database type comprises an active user database and a potential user database; the active user database comprises user information in the satellite service area, and the potential user database comprises user information in other satellite service areas in the track;
and determining a call transfer mode according to the determined type of the database where the current position of the called party is located.
The determined called party is currently positioned in a satellite activation user database where the calling party is positioned;
the satellite access location register for serving the terminal equipment returns the temporary mobile user identification code of the called user and the number of the current location area of the called user, and the satellite mobile service switching center for serving the terminal equipment initiates paging to the called user.
The determined called party is currently positioned in a satellite potential user database where the calling party is positioned;
the satellite access location register for serving the terminal equipment returns the number of the mobile service switching center where the called user is currently located, the mobile service switching center for serving the terminal equipment transfers the call to the mobile service switching center where the called user is located, the international mobile subscriber identification code of the called user is attached, the mobile service switching center of the called user inquires the temporary mobile subscriber identification code of the called user and the number of the current location area of the called user in the active user of the mobile service switching center of the called user, and then the paging is initiated to the called user.
The determined called party is not currently in the satellite database where the calling party is;
the mobile service switching center serving the terminal equipment directly transfers the call to the home gateway station of the called user, and attaches the international mobile user identification code of the called user, the home gateway station inquires the home location register and then calls the mobile service switching center where the called user is located, the mobile service switching center where the called user is located inquires the temporary mobile user identification code of the called user and the number of the current location area of the called user from the satellite access location register of the mobile service switching center where the called user is located, and then initiates paging to the called user.
The following describes in detail, by way of specific examples, the solutions provided in the embodiments of the present application. It should be noted that the method provided in the embodiment of the present application is applicable to a plurality of different constellation systems, and the following details will take a middle orbit constellation system as an example.
1. Constellation system composition
The system constellation consists of a plurality of MEO satellites, wherein one part of the system constellation is uniformly distributed in an equatorial orbit plane, the other part of the system constellation is uniformly distributed in a polar orbit plane, and only interstellar links exist between adjacent satellites in the orbit, and the interstitial communication is relayed through an internal gateway station.
2. Location management database structure
As shown in fig. 1, the present system still employs a two-tier database: a Home Location Register (HLR) and a Visitor Location Register (VLR).
The HLR stores the relevant parameters when the mobile subscriber first accesses the network and the VLR location where the mobile subscriber is currently located. The VLR stores the exact location record in which the subscriber currently within its jurisdiction is located and the subscriber data information necessary for some communications.
The system has GMSC and HLR/VLR/AUC/EIR databases configured in the gateway station, because there is on-board exchange, there is MSC (mobile service switching center) and VLR closely related to exchange signaling, other databases only have signaling communication during link establishment, in order to lighten on-board load, not on-board configuration.
The gateway station service area is divided into a number of location areas by geographical areas, each location area being responsible for one gateway station, identified in the forward broadcast channel. In addition, each satellite is an MSC service area, each MSC service area includes a plurality of location areas, each location area includes at least one beam cell, the equatorial orbit can provide location management service for all users within its beam coverage, and the polar orbit only needs to provide location management service for users in a high latitude area not covered by the equatorial orbit. Thus, the satellite broadcast in the gateway station service area includes both the information of the gateway station location area and the information of the own satellite location area. The formed location area sequence table is shown in table 1, each beam is shown in table 1 as a location area, and satellite and beam numbers are shown in fig. 2.
Because of the periodic movement of the satellite, the access position area sequences of the satellite to the user can be calculated and predicted within a certain time, the number of the position area sequences and the length of each sequence are limited, the home gateway station HLR and the satellite VLR can store possible position area sequences in advance, and the corresponding position area sequences are called according to the received position area codes after each time the position update request of the user is received, so that the position information of the user is updated regularly.
After a user starts up, firstly searching a broadcast signal, and if the broadcast signal of a gateway station can be received, registering the gateway station, wherein the flow of the gateway station is the same as that of a ground network; if the broadcasting signal of the gateway station is not received, registering is carried out on the satellite VLR.
When registering on the satellite, the satellite calls the sequence number of the location area for serving the user when the user is stationary according to the current location area and the beam motion rule, broadcasts the sequence number and other user information to the HLR of the user attribution gateway station, the VLR of other satellites in the same orbit and the user terminal for storage, and then each satellite automatically serves the user according to the sequence of the location area.
The VLR of each satellite in each orbit stores all the subscribers served by the satellite in the orbit, thus dividing the VLR into two parts: VLR (VLR) A To activate the subscriber database, the VLR stores subscriber information in the service area of the satellite B As a potential user database, storing user information of other satellite service areas in the orbit, when the user accesses the satellite to become the satellite where the VLR is located, the potential user becomes the active user.
Active subscriber library VLR of VLR A Potential subscriber library VLR B This can be achieved by ordering the subscriber records by satellite location area for the records in the library, such that the VLR A Corresponds to a variable-size service window on the VLR, and other parts belong to the VLR as shown in the grey part of the table 2 B 。
When a user starts up and accesses the network, the VLR records the current satellite position area and registration time (namely, the position area provides position service starting time for the user) at the tail part of a window in the table 2 and distributes TMSI for the user, then searches the corresponding position area serial numbers for the user in the table 1 according to the satellite beam motion rule, and then, the VLR regularly records the current satellite and position area items, position area starting service time items and position area service time long items of the user in the table 2 according to the service time of each position area corresponding to the position area serial numbers in the table 1The TMSI item is updated. The subscriber's current satellite/location area entry is only to VLR A Useful for subscribers, to VLR B The subscriber, this term is empty, the TMSI term is directed to the VLR A The subscriber is the subscriber's current TMSI, but to the VLR B The user, this term is the number of the satellite MSC where the user is currently located.
When the location is inquired, VLR directly searches from window, so that it can implement the distinction between active user and potential user in one data base, and this method can reduce VLR A 、VLR B The data operation between the databases can reduce the complexity of on-board processing when the databases are independent of each other.
Table 2: several parameter items of S1 satellite VLR database
3. Location registration mechanism
When a user starts up to access the network, firstly searching for a broadcast signal, and if the broadcast signal of a gateway station can be received, registering the gateway station, wherein the flow of the gateway station is the same as that of a ground network; if the broadcasting signal of the gateway station is not received, registering is carried out on the current satellite VLR, and the current satellite VLR A To which a TMSI is assigned, each active subscriber being located at its VLR A A unique TMSI (temporary mobile subscriber identity) is provided, but the TMSI is not fixed, and the VLR changes the active subscriber under a MSC to a potential subscriber A The TMSI will be retrieved and likewise, when a potential subscriber becomes an active subscriber, the VLR A It will be assigned a TMSI.
Since only the satellite registered users employ an improved location management scheme, we only study the location update of the satellite registered users in the following.
The user terminal equipment periodically compares the position area number of the current satellite wave beam with the stored home position area time sequence list, and only initiates a position update request when the comparison result is inconsistent, and only transmits the current position area number during update, the visiting VLR can find the corresponding position area sequence, and simultaneously informs all other co-orbit satellite VLRs of the user and the corresponding serial numbers thereof for update.
The location update is entirely caused by the movement of the user with a probability equivalent to the probability of the user crossing the location area when the location area is stationary to the ground, which translates the location update probability in the MEO system into a location update probability in the ground network.
The satellite motion law is effectively utilized, so that the position update is completely dependent on the movement characteristics of a user, frequent update caused by high-speed satellite motion in the traditional position update strategy is avoided, and the position update cost is reduced; but on the other hand, each update involves all VLRs in the track, increasing the location update cost, and it can be seen whether the improvement can achieve a lower cost than the conventional one, which is closely related to the location update frequency due to the motion characteristics of the user.
The position update of the system mainly has 5 cases: the user updates in different gateway station service intervals, updates between different satellites in the same orbit, updates between different orbits, updates beyond gateway station service areas and updates into gateway station service areas.
The flow of user location updates during the most complex inter-track movement is given in figure 3.
(1) When the user finds that the location area of the user is inconsistent with the location area which should be in accordance with the stored location area sequence, the MES sends a channel application request to a newly accessed orbit satellite (marked as MSC/VLR_N) through a satellite random access channel, wherein the reason for applying the channel is marked as location update, and then starts to monitor a satellite broadcast control channel to wait for channel allocation information of a network side.
(2) After receiving the request of "channel application", MSC/VLR_N sends "immediate allocation" information to allocate signaling channel to MES.
(3) After the MES obtains the allocated channel, it sends out a location update request message to MSC/VLR_N.
(4) After receiving the location update request from the MES, the MSC/VLR_N sends a parameter indication command requesting authentication parameters to the HLR of the MES according to the IMSI attached to the MSC/VLR_N. When the HLR receives the "send parameters indication" sent from MSC/VLR _ N, it will send back the necessary parameters for authentication with respect to the MES.
(5) MSC/VLR_N authenticates MES, and after success, reassigns TMSI to MES, stores its location area code and starts timing update.
(6) MSC/VLR_N sends a 'location update' message to HLR and other co-orbit satellite VLRs, the 'location update' message needs to contain the identification IMSI and the location area code of MES, HLR inquires the location of IMSI in the database to update the location area code and update the corresponding VLR according to the beam motion rule, other co-orbit satellite VLRs store the IMSI and the location area code and update the corresponding VLR according to the beam motion rule.
(7) The HLR will transfer subscriber information and related necessary parameters required for the communication including subscription services, roaming restrictions, network access modes etc. to the MSC/VLR _ N by sending an "insert subscriber data" message. After receiving the message, MSC/VLR_N sends message of "confirm inserted user data" to HLR.
(8) The HLR sends a "location update accept" message to the MSC/VLR_N, and a "location cancel" request to all satellites broadcast on the old track of the MES. After receiving the request of "location cancellation", the old track VLR will delete all the information of the MES and send back a "location cancellation acknowledge" message to the HLR.
(9) On the MSC/VLR_N side, the VLR_N sequentially completes encryption setting and TMSI reassignment of the MES as in the location updating process in the same MSC.
The MSC/VLR_N replies a location update accept message to the MES.
After the MES finally receives the 'location update accept' message from the MSC/VLR_N, the location update of the MES crossing the track is completed.
4. Call delivery mechanism
The calling service MSC firstly analyzes the type of the called number no matter where the calling initiates the call, if the called number is a ground network user, the MSC calls an access gateway station of the track, and the gateway station carries out call transfer to an external network; if the called party is analyzed to be a satellite network user, inquiring an activated user database VLR1, if the called party is in the service area of the MSC, returning a called TMSI and the number of the current location area by the VLR1, and initiating paging to the called party by the MSC; if the called party is not in the service area of the MSC, namely, is not an activated user, a potential user database VLR2 is inquired, if the called party is a potential user of the MSC, the VLR2 returns the MSC number where the called party is currently located, the local MSC transfers the call to the MSC where the called party is located, the IMSI is attached to the called party, the called party MSC inquires the TMSI and the location area of the called party in the activated user of the VLR1, and then the paging is initiated to the called party; if the called party is not the potential user of the local MSC service area, the call is directly transferred to the home gateway station of the called party, the IMSI of the called party is attached, the home gateway station inquires the HLR and then calls the MSC where the called party is located, the MSC where the called party is located inquires the TMSI and the location area of the called party from the VLR1, and then the paging is initiated to the called party. Fig. 3 is a schematic diagram of the above-mentioned calling process.
The calling mechanism can effectively solve the signaling overhead and time delay in the calling transfer process, and lighten the load pressure of a relay network and an HLR.
In the TtT call transfer flow of the MEO satellite mobile communication system, the call between users in the same orbit does not need the participation of a ground gateway station, because the satellite stores the information required by all users in the orbit for communication; calls between users in different orbits must be routed by ground gateway stations because there is no interplanetary link between orbits and satellites in different orbits do not store information for users in different orbits; communication with the subscriber registered with the gateway station is also communicated through the ground gateway station.
Fig. 4 shows a call process diagram of the MEO system.
Fig. 5 shows a schematic diagram of the transfer flow of TtT calls in different tracks of the MEO system.
The constellation satellite mobile communication system has special transmission characteristics and network structure, and compared with the transmission flow of TtT calls in a ground network, the call transmission in the system has the following characteristics:
1. calls in the same track have no participation of HLR, and only communication between users registered with the non-own track can access the HLR;
2. route inquiry at VLR A 、VLR B And the three databases of the HLR are sequentially carried out;
3. VLR (VLR) A Returning to MSC is the location area code and TMSI, VLR of the called party B Returning the MSC to the MSC number of the called satellite or the MSC number of the called home gateway station, and returning the HLR to the GMSC to the MSC number of the called satellite or the MSC number of the ground gateway station;
4. accompanying dialing information between MSC or between MSC and GMSC is called IMSI and route control information, called MSC inquires VLR after receiving the information A And obtaining the called TMSI and the area code of the location, and then paging.
The method provided by the embodiment of the application adopts a two-layer database: a Home Location Register (HLR) and a Visitor Location Register (VLR). The HLR stores the relevant parameters when the mobile subscriber first accesses the network and the VLR location where the mobile subscriber is currently located. The VLR stores the exact location record in which the subscriber currently within its jurisdiction is located and the subscriber data information necessary for some communications. The gateway station is internally provided with GMSC and HLR/VLR/AUC/EIR databases, because of on-board switching, the gateway station is provided with MSC and VLR closely related to switching signaling, other databases only have signaling communication during link establishment, and are not arranged on the satellite in order to lighten the on-board burden.
The gateway station service area is divided into a plurality of location areas by a geographic area, and each location area is responsible for one gateway station and is identified in a forward broadcast channel. Each satellite is an MSC service area, each MSC service area comprises a plurality of position areas, each position area comprises at least one beam cell, and the satellite broadcasting of the gateway station service area has both the information of the position area of the gateway station and the information of the position area of the satellite.
According to the method provided by the embodiment of the application, the satellite can calculate and predict the access position area sequence of the satellite to the user within a certain time, the number of the position area sequences and the length of each sequence are limited, the home gateway station HLR and the satellite VLR can store the possible position area sequences in advance, and the corresponding position area sequences are called according to the received position area codes after each time the position update request of the user is received, so that the position information of the user is updated regularly.
The VLR of each satellite in each orbit in the method provided in the embodiment of the present application stores all the users served by the satellite in the orbit, so the VLR is divided into two parts: VLR (VLR) A To activate the subscriber database, the VLR stores subscriber information in the service area of the satellite B As a potential user database, storing user information of other satellite service areas in the orbit, when the user accesses the satellite to become the satellite where the VLR is located, the potential user becomes the active user.
Compared with the traditional scheme, the overhead of the position management method provided by the application is quite obvious, the lower the user movement rate is, the larger the improvement amount is, and particularly when the user is stationary, the position management method has no position update overhead and only has paging overhead, and the overhead of the improved scheme at the moment is less than 2% of that of the traditional scheme.
Since only satellite registered users employ an improved location management scheme, we only study satellite registered users. The total bit overhead of location update and paging per unit time of the system consists of three parts:
C improvements in or relating to ＝C HLR +C VLR +C page ＝E HLR *F HLR +E VLR *l*F VLR +n*E page *F p
Wherein E is VLR Overhead for updating VLR in one satellite; e (E) HLR E for updating the HLR overhead at the ground gateway station PAGE The cost of paging one beam for the system, i is the number of VLRs updated each time, n is the number of beams paged each time, F HLR ,F VL R,F p The HLR update frequency, the VLR update frequency and the call arrival rate are respectively.
After adopting the improved position management scheme, each update initiated by the user is carried out on all VLRs and home gateway stations HLRs in the track simultaneously, so F HLR ＝F VLR Also, for equatorial orbit, l=6, for polar orbit, l=4; assuming that each beam is a location area, only one beam needs to be paged per page, i.e., n=1, and the location is moreThe new is caused entirely by the movement of the user whose frequency is equivalent to the frequency of the user crossing the beam when the beam is geostationary, assuming an average dwell time of 1/eta in one beam for the mobile terminal beam F is then VLR ＝η beam 。
With reference to the parameters of the Iridium system, each update message is 1108 bits, each paging message is 168 bits, and E is normalized HLR :E VLR :E PAGE =6.6: 6.6:1, a step of; assuming a call arrival rate of 1 time/hour, the on-board registered users are uniformly distributed worldwide, the calculated ratio of the position updates moving in the same orbit, moving between different orbits, exiting the gateway service area and entering the gateway service area under the available improvement is about A 1 ：A 2 ：A 3 ：A 4 The percentage of users of the equatorial and polar orbital service areas is about 60%, 40%, respectively, =70%, 20%, 5%, the total bit overhead within one hour is calculated as:
C improvements in or relating to ＝(0.3E HLR +6.26E VLR )*η beam +E page *F p ＝43.3*η beam +1
Under the traditional scheme, a beam coverage area is taken as a position area, and position updating is carried out during beam transformation. The minimum coverage diameter of the beam can reach 1500km, the influence of the user movement is small, and the updating is mostly caused by the movement of the satellite. Assume that the average residence time of the mobile terminal in one beam and one satellite is 1/η ', respectively' beam And 1/η MSC . Each time the HLR is updated, the subscriber may be relayed through m=0 to 2 satellites at different geographic locations, assuming a 1 、a 2 、a 3 The percentage of the satellite relays of 0, 1, 2 are needed for the user location update, then the total bit overhead within an hour is:
C traditional Chinese medicine ＝a 1 *(E HLR η MSC +E VLR η' beam +E page *F p )
+a 2 *(2E HLR η MSC +E VLR η' beam +E page *F p )
+a 3 *(3E HLR η MSC +E VLR η' beam +E page *F p )
On-board registered users have a when distributed uniformly worldwide 1 ＝a 2 ＝a 3 =1/3, the total bit overhead within one hour is:
C traditional Chinese medicine ＝13.2η MSC +6.6η' beam +1
The cost ratio of the two in the next hour of the improvement scheme compared with the traditional scheme is as follows:
Rate＝C improvements in or relating to /C Traditional Chinese medicine ＝(43.3*η beam +1)/(13.2η MSC +6.6η' beam +1)
Notably, although η in the formula beam Coefficient ratio eta' beam But η 'is much larger' beam Is caused by the high speed movement of the satellite, η beam Only caused by the movement of the user itself, the two can be quite different for low speed users.
The motion of low speed users (e.g., pedestrians) generally conforms to a random walk model, with a range of motion being limited to a geographic area. The values of the bit overhead ratio Rate at different motion characteristics of a low-speed user are given, where α represents the memory degree of the user motion, α=0 represents Brown motion, and α=1 represents linear motion. It can be seen from the graph that, under different α values, since the movement Rate of the low-speed mobile terminal is very low relative to the movement Rate of the satellite, the overhead in the improved Rate scheme is quite large relative to the improvement amount of the conventional scheme, and the lower the movement Rate of the user is, the larger the improvement amount is, especially when the user is stationary, the position update overhead is not generated, and only the paging overhead is generated, and the improvement scheme overhead at this time is less than 2% of the conventional scheme.
The motion of high-speed users (e.g., aircraft, automobiles, missiles, etc.) generally conforms to a stream motion model with less variation in movement rate and direction. The cost of location management for a fast mobile terminal is very much related to its direction of movement. The bit overhead ratio Rate after being averaged in all directions under different motion characteristics of a high-speed user is given. As can be seen from the figure, for streaming users, the improvement amount of the improvement scheme is still larger when the user movement rate is smaller (< 1000 km/h); as the user's rate of movement increases, the improvement gradually loses advantage. The location update by the high speed movement of the user is weakened by enlarging the size of the location area and providing a large area coverage.
When a satellite coverage area is a location area, the improvement assumes an average residence time of 1/eta for the mobile terminal in a stationary location area sat Under the traditional scheme, the average residence time of the mobile terminal in a mobile location area is assumed to be 1/eta sat The overhead ratio of the improvement scheme within one hour compared with the traditional scheme is:
Rate＝C improvements in or relating to /C Traditional Chinese medicine
＝(43.3*η sat +37*F p )/(13.2η MSC +37*F p )
The bit overhead ratio Rate simulation results after being averaged in all directions under different motion characteristics of the corresponding high-speed user are shown in fig. 8. It can be seen that the improvement, although not very effective for high speed terminals, does not bring too much cost, which is at most about 1.6 times the cost compared to the conventional one.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The foregoing description is only of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.
Claims (7)
1. A method for location management in a constellation satellite mobile communications system, the method comprising:
a location update mechanism;
the terminal equipment periodically compares the position area number of the current satellite wave beam with a stored home position area time sequence table; the location area timing schedule comprises a plurality of location area timings pre-stored in an on-board access location register, and the location area timings comprise at least one satellite beam cell for serving the same ground location in time sequence;
determining whether to send a position update request to an on-satellite mobile service switching center according to the comparison result;
when the comparison results are inconsistent, sending a position update request to an on-board mobile service switching center of the newly accessed satellite; the method comprises the steps of sending a current position area number to a mobile service switching center of a newly accessed satellite;
the mobile service switching center of the newly accessed satellite determines that the current position area number and the original position area sequence number are in service areas of satellites with different orbits;
the mobile service switching center of the newly accessed satellite updates the position area sequence for the terminal, and simultaneously informs a ground homing position register and on-board access position registers of all other co-orbit satellites of the current position area sequence number and the user information of the terminal equipment to realize the position update of the terminal equipment;
the ground homing position register broadcasts and sends a position cancellation request to all satellites in the old orbit, so that all information of the terminal equipment is deleted after the satellite access position register in the old orbit receives the position cancellation request;
a call delivery mechanism;
after the terminal equipment initiates a call, an on-board mobile service switching center serving the terminal equipment analyzes the number type of a called user to determine the user type of the called user, wherein the user type comprises a ground network user and a satellite network user;
and determining a call delivery mode according to the determined user type.
2. The method for location management of constellation satellite mobile communications system of claim 1 wherein a mobile services switching center of a newly accessed satellite determines that said current location area number and said home location area sequence number are within a service area of an in-orbit satellite;
and the mobile service switching center of the newly accessed satellite updates the position area sequence for the terminal, and simultaneously informs the satellite access position registers of all other co-orbit satellites of the current position area sequence number and the user information of the terminal equipment to realize the position update of the terminal equipment.
3. The method according to claim 1, wherein the determined subscriber type is a terrestrial network subscriber, and the satellite mobile services switching center serving the terminal device calls a terrestrial access gateway station of the present orbit, and the gateway station performs call transfer to an external network.
4. A location management method for a constellation satellite mobile communications system according to claim 3 wherein the determined subscriber type is a satellite network subscriber and the on-board mobile services switching centre serving said terminal device analyzes a database type in which the current location of the called subscriber is located, said database type comprising an active subscriber database and a potential subscriber database; the active user database comprises user information in the satellite service area, and the potential user database comprises user information in other satellite service areas in the track;
and determining a call transfer mode according to the determined type of the database where the called party is currently located.
5. The method for location management for a constellation satellite mobile communications system according to claim 4 wherein the determined called party is currently in a satellite active subscriber database where the calling party is located;
the satellite access location register for serving the terminal equipment returns the temporary mobile user identification code of the called user and the number of the current location area of the called user, and the satellite mobile service switching center for serving the terminal equipment initiates paging to the called user.
6. The method for location management for a constellation satellite mobile communications system of claim 4 wherein the determined called party is currently in a satellite potential user database where the calling party is located;
the satellite access location register for serving the terminal equipment returns the number of the mobile service switching center where the called user is currently located, the mobile service switching center for serving the terminal equipment transfers the call to the mobile service switching center where the called user is located, the international mobile subscriber identification code of the called user is attached, the mobile service switching center of the called user inquires the temporary mobile subscriber identification code of the called user and the number of the current location area of the called user in the active user of the mobile service switching center of the called user, and then the paging is initiated to the called user.
7. The method for location management for a constellation satellite mobile communications system of claim 4 wherein said determined called party is not currently in the satellite database in which said calling party is located;
the mobile service switching center serving the terminal equipment directly transfers the call to the home gateway station of the called user, and attaches the international mobile user identification code of the called user, the home gateway station inquires the home location register and then calls the mobile service switching center where the called user is located, the mobile service switching center where the called user is located inquires the temporary mobile user identification code of the called user and the number of the current location area of the called user from the satellite access location register of the mobile service switching center where the called user is located, and then initiates paging to the called user.
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