Method for selection of a base station for operating in unlicensed spectrum

Abstract

A method for a user equipment maintaining a first set of configuration parameters includes: measuring strength of signals transmitted by a first base station, measuring strength of signal transmitted by at least one of a set of neighbor base stations operating in unlicensed spectrum, determining a second set of configuration parameters corresponding to the cellular network for a second base station in a set of neighbor base stations, by retrieving said set of configuration parameter from said second base station, considering the second base station for cell re-selection when: the measured signal strength for the second base station is higher than said measured signal strength of first base station, and said determined second set of configuration parameters corresponds to said first set of configuration parameters, and carrying out a cell selection to said second base station when these conditions are met.

Claims

1. A method for a user equipment (UE) for operating in a first cellular network supporting unlicensed spectrum access, the user equipment (UE) camping on a first base station (sBS) of the first cellular network, the user equipment (UE) maintaining a first set of configuration parameters of the cellular network comprising data relating to frame numbering (SFN), the method comprising for the user equipment (UE) the steps of: measuring strength of signals (CS) transmitted by the first base station (sBS), measuring strength of signals (CS) transmitted by at least one of a set of neighbor base stations operating in unlicensed spectrum, determining a second set of configuration parameters comprising data relating to frame numbering (SFN) and corresponding to the cellular network that at least one second base station (BS) out of the set of neighbor base stations is part of, considering said at least one second base station (BS) under the conditions: the measured signal strength (CS) for said at least one second base station (BS) is higher than said measured signal strength (CS) of first base station (sBS), and data relating to frame numbering (SFN) in said determined second set of configuration parameters corresponds to data relating to frame numbering (SFN) in said maintained first set of configuration parameters, carrying out a cell selection to the at least one second base station (BS) when said conditions apply.

2. The method according to claim 1, wherein the user equipment receives from the first base station (sBS) an indication that the base stations of the cellular network are operating frame synchronized.

3. The method according to claim 1, wherein the set of configuration parameters comprises data relating to a distribution of reference signals over the frequency spectrum used by the first base station.

4. The method according to claim 1, wherein the set of configuration parameters comprises the synchronization sequence of at least one of the primary synchronization channel and the second synchronization channel or a combination thereof.

5. The method according to claim 4, comprising the step of receiving from the first base station (sBS) information relating to an intra-frequency neighbor cell list comprising a plurality of synchronization sequence combinations used by neighbor base stations belonging to the same cellular network as the first base station (sBS).

6. The method according to claim 1, where a difference in SFN is derived by most significant bits of the SFN contained in a MIB.

7. The method according to claim 1, where a matching in SFN is when most significant bits in the MIB, being the SFN part, and least significant bits derived from a BCH modification period contained in further broadcast information are matching.

8. The method of claim 1, wherein the method includes the steps of: retrieving the second set of configuration parameters prior to camping on said neighboring base station, said retrieving prior to said step of determining a second set of configuration parameters; then, synchronizing on a synchronization channel of said neighboring base station to read a Master Information Block (MIB) of a System Information Block (SIB) before said step of considering said at least one second base station (BS) under the conditions, and, wherein said aforementioned step of carrying out said cell selection comprises: decoding the SFN from most significant bits (MSBs) of the MIB, said SFN excluding two (2) least significant bits (LSBs) of the SFN that are instead derived from a BCH modification period; using only said most significant bits of the SFN read from the MIB for a priori elimination of base stations for carrying out said cell selection to the at least one second base station (BS) when said conditions apply, and thereafter camping on said neighboring base station after said cell selection, thereby circumventing a whole reading of said System Information Block (SIB) containing the MIB that is otherwise needed to evaluate if said neighboring base station belongs to a Public Land Mobility Network (PLMN) identity provided as part of the MIB before said camping occurs on said neighboring base station.

9. A user equipment (UE) for operating in a first cellular network supporting unlicensed spectrum access, the user equipment being configured to camp on a first base station (sBS) of the first cellular network, and to maintain a first set of configuration parameters of the cellular network comprising data relating to frame numbering (SFN), wherein the user equipment is further configured to: measure strength of signals (CS) transmitted by the first base station (sBS), measure strength of signal (CS) transmitted by at least one of a set of neighbor base stations operating in unlicensed spectrum, determine a second set of configuration parameters comprising data relating to frame numbering (SFN) and corresponding to the cellular network that at least one second base station (BS) out of the set of neighbor base stations is part of, consider said at least one second base station (BS) under the conditions: the measured signal strength (CS) for said at least one second base station is higher than said measured signal strength (CS) of first base station (sBS), and data relating to frame numbering (SFN) in said determined second set of configuration parameters corresponds to data relating to frame numbering (SFN) in said maintained first set of configuration parameters, carry out a cell selection to the at least one second base station (BS) when said conditions apply.

10. The user equipment (UE) according to claim 9, further configured to receive from the first base station (sBS) an indication that the base stations of the cellular network are operating frame synchronized.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following description and the annexed drawings set forth in detail certain illustrative aspects and are indicative of but a few of the various ways in which the principles of the embodiments may be employed. Characteristics and advantages of the present invention will appear when reading the following description and annexed drawings of advantageous embodiments given as illustrative but not restrictive examples.

(2) FIG. 1 represents schematically the situation for a user equipment of the type to which the present invention is applied as an embodiment of handling base stations of different cellular networks;

(3) FIG. 2 represents a flow chart of an exemplifying embodiment of the inventive method.

(4) FIG. 3 shows in an exemplifying embodiment the configuration of frame synchronization of base stations from different cellular networks;

(5) FIG. 1 schematically shows a user equipment UE of the type to which the present invention is applied to as an embodiment. The user equipment is configured to operate on different base stations BS of different cellular networks respective operators.

(6) Further the user equipment is capable of operating in unlicensed spectrum. That is a frequency spectrum that is not assigned to one network operator for a given region. Hence, in the unlicensed spectrum base stations from more than one network operator may be able to transmit and/or receive data.

(7) Preferably the unlicensed spectrum is used for not-connected signalling, e.g. for paging and all signalling relating to camping in idle mode on a base station. For 5G cellular networks such unlicensed spectrum usage is foreseen, hence the present base stations are in particular gNBs, and the base station capable of operating in the 5G wireless standard with the gNBs.

(8) In FIG. 1 it is shown that the user equipment is camping on the serving base station sBS. It has a certain coverage area which is called the cell C1. As it is shown, when the user equipment is moving it is coming in the area of different cell areas C2-C7. The different cell areas belong to different cellular networks operated by the different network operators A-D.

(9) On the ordinate it is shown the received signal strength CS. That means the closer a cell area is shown, the higher is the received signal strength CS of the respective gNB at the antenna of the user equipment received. It is assumed that all shown gNBs operate in the same unlicensed spectrum frequency range for paging and camping of the user equipment.

(10) The different type of filling pattern per cell areas indicates to which network operator a cell resp. its gNB belongs.

(11) User equipment UE camps at time to on base station sBS, belonging to the cellular network of operator C. Although signals from the base station BS of cell area C2 are retrieved at a higher signal strength than from base station sBS, the user equipment is camping on its current serving base station sBS due to the fact that it is eligible to operate only with base stations of the cellular network run by operator C. This is preferably the home cellular network of the user equipment. Usually this is predetermined through the SIM-card or UICC connectively coupled with the user equipment.

(12) When the user equipment is moving at time t.sub.1 to another location, the situation changes. As it can be seen, the cell area C1 is left, so the user equipment cannot retrieve signals from base station sBS sufficiently good. Through regularly measuring the signal strength, mobility management measures are taken, in particular checking which other cells are around. As it can be seen (dashed line t.sub.1) at that time the user equipment receives signals on the same frequency range of unlicensed spectrum of four base stations, belonging to cells C3, C4, C5, C7.

(13) For the user equipment it is now to choose which of the cells resp. base stations will be used for cell re-selection from the current serving base station.

(14) In the common approach for that the S-Criterion is used, mainly taking into account the signal strength CS of the base station received at the antenna of the user equipment.

(15) In this case this would mean that the base station of cell area C4 would be the best. However, cell area C4 belongs to Operator A. According to the credentials on the connected SIM card, the user equipment is not able to operate on base stations of that operator, rather on base stations of (serving) operator C.

(16) In this example in worst case the user equipment would have to synchronize on up to 4 base stations, retrieve preferably the whole set of system information blocks SIBs etc. in order to figure out, if the candidate base station is appropriate for camping. During that time, no connection, no paging etc. is possible. Additionally this task is power consuming and may happen for a moving user equipment over and over again.

(17) Hence the user equipment has a desire to find out with less efforts, which of the visible base stations at time t.sub.1 is belonging to the same operator as the currently serving base station sBS.

(18) A solution for that task according to an exemplifying embodiment of the invention is shown in the flow chart of FIG. 2.

(19) It is assumed that the user equipment is already camping on a base station, where it is eligible for operating with. This is called the serving base station, regardless of the type of base station (eNB, gNB . . . ). Further the base station is operating in unlicensed spectrum, at least for paging etc.

(20) In step S1 the user equipment determines certain parameter concerning the operation with the serving base station. This comprises the current signal strength received at the antenna of the user equipment. The signal strength is the transmitter power output received at an antenna, typically measured in dBm. For wireless cellular telecommunication various measures are taken for this value.

(21) Another parameter to be determined in step S1 is at least one network configuration parameter. Such configuration parameters are in particular settings or any other type of characteristic, that are presumably characteristic for a cellular network.

(22) Preferably the retrieved parameters are stored permanently or in volatile memory.

(23) The next step S2 is usually carried out directly after step S1, but some lead time is also encompassed.

(24) Here the user equipment tries to detect neighbor base stations, in particular those operating in the same unlicensed spectrum. For that the signals in that frequency range are evaluated and decoded. Further other frequency ranges may be considered as well.

(25) The result of this operation is usually a list of candidate base stations, which signals were received sufficiently strong for decoding. Usually the serving base station is part of the candidate base station list. Preferably the signal strength of step S1 is detected or updated in the next step.

(26) In step S3 the signal strength of the candidate base stations is determined. Typically for all following steps the list of candidate base stations is ordered in decreasing signal strength.

(27) Hence in step S4 the network configuration of the candidate base stations, or at least to begin with the candidate base station with the highest received signal strength, is then determined. This typically requires analysis of the received signals or other characteristic behavior.

(28) Based on the determined values the S-Criterion is then evaluated. The S-Criterion is a Boolean value indicating if a cell re-selection is to be carried out. In this case the S-Criterion is determined taking into account the previously determined values. It is first based on a comparison of the signal strength of the candidate neighbor base station CS.sub.neighBS and the signal strength of the serving base station CS.sub.servBS. Only when the signal strength of the neighbor base station exceeds the signal strength of the serving base station, a cell re-selection is considered. Additionally typically a hysteresis, resp. a threshold is maintained, wherein the signal strength of the neighbor base station needs to be significantly larger than of the serving base station, in order to avoid ping pong and frequent cell re-selection. This protects the battery lifetime of the user equipment.

(29) Should this condition apply, it is additionally figured out, if the network condition parameter of the neighbor base station netwConfig.sub.neigBS corresponds to the network condition parameter of the serving base station netwConfig.sub.servBS.

(30) With this comparison it is figured out, if the neighbor base station belongs to the same cellular network as the serving base station.

(31) In the exemplifying embodiment both checks are carried out in one step S5. However a split of checks is further useful, as no further elaboration needs to be done, when the signal strength condition does not apply.

(32) In step S6 the resulting S-Criterion is consequently checked. When the S-Criterion is true, then a cell re-selection to the examined neighbor base station is carried out in step S8. Otherwise it is continued with the serving base station in step S7.

(33) Exactly S8 means when both criteria are fulfilled that the base station is considered as candidate for further re-selection evaluation i.e. The final verification is carried out in step S9, where SIB1 is read prior finally camping on said cell, means to evaluate if the base station is not barred, not belonging to same or equivalent PLMN or in any other means not usable by the user equipment. If this is not the case the next candidate base station is to be evaluated and selected as new serving cell.

(34) In both cases the method flow branches again to the beginning, starting after a given time anew with the checks for better and appropriate neighbor cells. The general goal of the inventive method is to avoid being out of service, that means not pageable, e.g. in case of incoming calls. If the user equipment should try to access a neighbor base station which it is not eligible to operate with, then this could lead to a time period of non-reachability. This needs to be avoided.

(35) In FIG. 3 it is in particular considered a preferably usable network configuration which should be sufficiently accurate alone in order to figure out if the correct neighbor base station is found. The figure shows for three base stations sBS, BS2 and BS3 the system frame numbers (SFN) for a given time sequence. The system frame number is a value usually between 0 and 1023 which helps identifying system frames.

(36) Base station sBS is the serving base station, the other two base stations BS2, BS3 are assumed as candidate base stations, having sufficient high signal strength at the user equipment camping on base station sBS.

(37) For the user equipment it is now the task to figure out, which of the base stations BS2, BS3 is part of the same cellular network of the same operator as the serving base station sBS.

(38) For this the SFN synchronization is considered. The SFN is transmitted as part of the Master Information Block MIB, which needs to be determined in each case before accessing a base station. Receiving the MIB is also part of the determination of the signal strength of the base station. Hence, it requires no remarkable additional effort and time to determine the system frame numbers.

(39) As it can be seen, the system frame number of base stations sBS and BS2 is identical, while BS3 has a completely different SFN at the same time.

(40) Typically cellular networks are configured that way that all base stations have synchronized system frame numbers. Preferably as part of the detection of network parameter of the serving base station, the support of such synchronization of SFNs over the base station may be signaled by the serving base station to the user equipment.

(41) As a matter of fact, the user equipment has based on the signal strength and the evaluation of the network configuration parameter SFN figured out, that a cell re-selection to base station BS2 is seamlessly possible and would consequently carry out that cell re-selection then.

(42) In the above detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention. The above detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled.