HANDOVER IMPROVEMENT FOR 5G AIR-TO-GROUND-SYSTEM

Abstract

The invention relates to a method for handover of a transceiver equipment, in particular UE and/or on-board equipment (OBE), from a serving cell to a target cell in a cellular communications network, said serving cell belonging to a first base station and said target cell belonging to a second base station, and said target cell being selected from a group of neighbor cells being better than the serving cell by an offset, wherein the method comprises: I. transmitting a measurement report to the first base station, said measurement report comprising information on a neighbor cell selected from the group of neighbor cells, based on i. a distance criterion, and optionally ii. a trajectory criterion, II. receiving a handover command from the first base station, said handover command comprising instruction for handover to the selected neighbor cell becoming the target cell, and III. completing handover with the second base station.

Claims

1-16. (canceled)

17. Method for handover of a transceiver equipment from a serving cell (S) to a target cell (T) in a cellular communications network, said serving cell (S) belonging to a first base station and said target cell (T) belonging to a second base station, and said target cell (T) being selected from a group of neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) whose Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio is higher than the Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio of the serving cell (S) by an offset, wherein the transceiver equipment is a user equipment (UE) or on-board equipment (OBE) and is configured to select a neighbor cell (N.sub.x) from the group of neighbor cells, the method comprising the steps of: I. transmitting a measurement report to the first base station, said measurement report comprising information on a neighbor cell (N.sub.x) selected from the group of neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m), based on i. a distance criterion by selecting the neighbor cell (N.sub.x) as having a lower propagation delay compared to the remaining neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.m) and/or to the serving cell (S), and/or ii. a trajectory criterion by selecting the neighbor cell (N.sub.x) as having a higher changing rate of propagation delay compared to the remaining neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.m) and/or to the serving cell (S), II. receiving a handover command from the first base station, said handover command comprising instruction for handover to the selected neighbor cell (N.sub.x) becoming the target cell (T), and III. completing handover with the second base station.

18. Method according to claim 17, wherein the measurement report is based on Reference Signal Received Power measurement, Reference Signal Received Quality measurement and/or Signal to Interference and Noise Ratio measurement, in particular filtered at Layer 3.

19. Method according to claim 17, wherein propagation delay for the neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) is estimated by the transceiver equipment comparing reception of at least one SS/PBCH block from the neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) and from the serving cell (S).

20. Method according to claim 19, wherein comparing reception of at least one SS/PBCH block from the neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) and from the serving cell (S) comprises comparing the reception time of at least one SS/PBCH block from the neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) and from the serving cell (S).

21. Method according to claim 19, wherein propagation delay for the neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) is estimated by the transceiver equipment adding or subtracting the time difference of reception to the Timing Advance of the serving cell (S).

22. Method according to claim 17, wherein at least one of the distance criterion or the trajectory criterion is applied even if one of the remaining neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.m) has a higher Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio, than the selected neighbor cell (N.sub.x) and the serving cell (S).

23. Method according to claim 17, wherein handover is completed by an iterative mechanism comprising transmission of at least one PRACH preamble with a Timing Advance Offset (TAO) comprising t.sub.0, . . . , t.sub.k-1, t.sub.k, . . . , t.sub.n over a Random Access Channel to the second base station serving a maximum cell range C, said PRACH preamble being a long sequence PRACH preamble supporting a cell range of r kilometres which is less than the maximum cell range C, the iterative mechanism comprising the steps of: IIIa. transmitting the PRACH preamble with an initial starting TAO t.sub.0, said starting TAO t.sub.0 being calculated by the transceiver equipment depending on the propagation delay for the selected neighbor cell (N.sub.x), and IIIb1. determining a valid Random Access Response being received within a predetermined waiting interval, or IIIb2. determining no valid Random Access Response being received within a predetermined waiting interval and transmitting the PRACH preamble with a kth TAO t.sub.k, said k.sup.th TAO t.sub.k being calculated by adding and/or subtracting a multiple of t as being a function of r to a preceding TAO t.sub.k-1, and IIIb3. repeating steps IIIb1 and IIIb2 until a valid Random Access Response is being received.

24. Method according to claim 23, wherein the k.sup.th TAO t.sub.k being calculated by adding a multiple of t=13107.2*r*T.sub.c to a preceding TAO t.sub.k-1, T.sub.c is the basic time unit in 5G NR or as per 3GPP TS 38.211 can be expressed as 1/(480*10.sup.3*4096)*106 s=100/196608 s, which corresponds to 0.509 ns.

25. Method according to claim 23, wherein the k.sup.th TAO t.sub.k being calculated by subtracting a multiple of t=13107.2*r*T.sub.c to a preceding TAO t.sub.k-1, T.sub.c is the basic time unit in 5G NR or as per 3GPP TS 38.211 can be expressed as 1/(480*10.sup.3*4096)*106 s=100/196608 s, which corresponds to 0.509 ns.

26. Method according to claim 23, further comprising carrying on performing steps IIIb1 to IIIb3 if the preceding TAO t.sub.k-1=0 or t.sub.k-1=13107.2*(Cr)*T.sub.c.

27. Method according to claim 23, wherein steps IIIb1 to IIIb3 are performed as steps: IIIb1. determining a valid Random Access Response being received within a predetermined waiting interval, or IIIb2. determining no valid Random Access Response being received within a predetermined waiting interval and transmitting the PRACH preamble with a kth TAO t.sub.k, where t.sub.k=t.sub.k-1+(1).sup.k.Math.kt, and IIIb3. repeating steps IIIb1 and IIIb2 until a valid Random Access Response is being received, or IIIb1. determining a valid Random Access Response being received within a predetermined waiting interval, or IIIb2. determining no valid Random Access Response being received within a predetermined waiting interval and transmitting the PRACH preamble with a kth TAO t.sub.k, where t.sub.k=t.sub.k-1+(1).sup.k-1.Math.kt, and IIIb3. repeating steps IIIb1 and IIIb2 until a valid Random Access Response is being received.

28. Method according to claim 27, further comprising carrying on performing steps IIIb1 to IIIIb3 or IIIb1 to IIIIb3 if the preceding TAO t.sub.k-1=0 or t.sub.k-1=13107.2*(Cr)*T.sub.c.

29. Method according to claim 23, wherein the PRACH preamble is a long sequence PRACH preamble of PRACH format 0 according to 3GPP communications standard, TS 38.211.

30. Method according to claim 17, wherein the iterative method is adapted to be used for air-to-ground communications.

31. Method according to claim 30, wherein the transceiver equipment comprises an on-board equipment of an aircraft and the first base station and/or the second base station comprises a ground unit.

32. Transceiver equipment, wherein the transceiver equipment is a user equipment (UE) or on-board equipment (OBE), configured for handover from a serving cell (S) to a target cell (T) in a cellular communications network, said transceiver equipment comprising: means for selecting a neighbor cell (N.sub.x) from a group of neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) being better than the serving cell (S) by an offset, in particular whose Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio is higher than the Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio of the serving cell (S) by an offset, in particular means for determining and comparing propagation delay for the neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) and/or for the serving cell (S), means for transmitting a measurement report to a first base station to which the serving cell (S) belongs, means for receiving a handover command from the first base station, means for completing handover with a second base station to which the target cell (T) belongs.

33. Transceiver equipment according to claim 32, wherein the transceiver equipment comprises an on-board equipment of an aircraft.

34. Transceiver equipment according to claim 32, wherein the transceiver equipment is an on-board equipment in an aircraft, said on-board equipment configured to act as a gateway for further traffic distribution to user equipments on board of the aircraft.

35. Computer program product comprising instructions which, when the program is executed by a transceiver equipment, cause the transceiver equipment to perform an iterative method for handover of the transceiver equipment from a serving cell (S) to a target cell (T) in a cellular communications network, said serving cell (S) belonging to a first base station and said target cell (T) belonging to a second base station, and said target cell (T) being selected from a group of neighbor cells (N.sub.1, N.sub.2, . . . N.sub.x, . . . , N.sub.m) whose Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio is higher than the Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio of the serving cell (S) by an offset, said transceiver equipment configured to select a neighbor cell (N.sub.x) from the group of neighbor cells, the method comprising the steps of: I. transmitting a measurement report to the first base station, said measurement report comprising information on a neighbor cell (N.sub.x) selected from the group of neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m), based on i. a distance criterion by selecting the neighbor cell (N.sub.x) as having a lower propagation delay compared to the remaining neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.m) and/or to the serving cell (S), and/or ii. a trajectory criterion by selecting the neighbor cell (N.sub.x) as having a higher changing rate of propagation delay compared to the remaining neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.m) and/or to the serving cell (S), II. receiving a handover command from the first base station, said handover command comprising instruction for handover to the selected neighbor cell (N.sub.x) becoming the target cell (T), and III. completing handover with the second base station.

36. Transceiver equipment configured to support handover of the transceiver equipment from a serving cell (S) to a target cell (T) in a cellular communications network, said serving cell (S) belonging to a first base station and said target cell (T) belonging to a second base station, and said target cell (T) being selected from a group of neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m) whose Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio is higher than the Reference Signal Received Power and/or Reference Signal Received Quality and/or Signal to Interference and Noise Ratio of the serving cell (S) by an offset, wherein the transceiver equipment us configured to select a neighbor cell (N.sub.x) from the group of neighbor cells, wherein the transceiver equipment is configured to: I. transmit a measurement report to the first base station, said measurement report comprising information on a neighbor cell (N.sub.x) selected from the group of neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.x, . . . , N.sub.m), based on i. a distance criterion by selecting the neighbor cell (N.sub.x) as having a lower propagation delay compared to the remaining neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.m) and/or to the serving cell (S), and/or ii. a trajectory criterion by selecting the neighbor cell (N.sub.x) as having a higher changing rate of propagation delay compared to the remaining neighbor cells (N.sub.1, N.sub.2, . . . , N.sub.m) and/or to the serving cell (S), II. receive a handover command from the first base station, said handover command comprising instruction for handover to the selected neighbor cell (N.sub.x) becoming the target cell (T), and III. complete handover with the second base station.

37. Transceiver equipment according to claim 36, wherein the transceiver equipment is a user equipment (UE) or on-board equipment (OBE).

Description

[0135] The invention is illustrated by the figures in more detail without limiting the invention to these exemplary embodiments. They show:

[0136] FIG. 1a, b, c: different handover scenarios from serving cell to target cell

[0137] FIG. 2: propagation delay estimation from time instants of reception of SS/PBCH blocks

[0138] FIG. 3: a TAO search or pre-alignment procedure according to the invention during handover to the target cell

[0139] FIGS. 1a, 1b and 1c disclose handover of a transceiver equipment on board of an aircraft (on-board equipment, OBE) from a serving cell (S) to a target cell (T), said serving cell belonging to a first base station gNodeB.sub.1 (S-gNodeB) and the target cell belonging to a second base station gNodeB.sub.2 (T-gNodeB), and said target cell (T) being selected from a group of neighbor cells (N.sub.1, N.sub.2, N.sub.3) belonging to base stations gNodeB.sub.2, gNodeB.sub.3 and/or gNodeB.sub.4 (N.sub.1-gNodeB, N.sub.2-gNodeB and/or N.sub.3-gNodeB) and the RSRP of whom being higher than the RSRP of the serving cell (S). In doing so, selection of the respective neighbor cell (N.sub.x, x=1, 2, 3) to become the target cell (T) is either strictly based on the measured SS-RSRP of that neighbor cell that must still satisfy the Event A3 condition (see FIG. 1a) or may additionally be based on a distance criterion (see FIG. 1b) or trajectory criterion (see FIG. 1c).

[0140] In FIG. 1a, the OBE measures several neighbor cells with similar SS-RSRP levels and identifies the best neighbor cell as a cell from a gNodeB that is much further away than another neighbor located closer to the serving gNodeB. Thus, the first neighbor cell (N.sub.1) being 150 km away from the OBE and having a filtered RSRP of 94 dBm is selected as target cell (T) instead of the second neighbor cell (N.sub.2) being 50 km away from the OBE and only having a filtered RSRP of 96 dBm:

TABLE-US-00003 Distance Filtered Cell (gNodeB) to OBE RSRP S (gNodeB.sub.1) 101 dBm N.sub.1 = T (gNodeB.sub.2) 150 km 94 dBm N.sub.2 (gNodeB.sub.3) 50 km 96 dBm

[0141] In FIG. 1b, the OBE additionally applies the distance criterion according to the invention selecting the neighbor cell (N.sub.1) as having a lower propagation delay compared to the remaining neighbor cell (N.sub.2) and to the serving cell (S). In doing so, the OBE reports that one from the neighbor cells (N.sub.1, N.sub.2) fulfilling the Event A3 condition (A3 offset=3 dBm) which is, according to its propagation delay estimation, closest to the current position of the OBE, even if the reported RRSP is lower. Thus, the first neighbor cell (N.sub.1) being only 60 km away from the OBE and having a filtered RSRP of 98 dBm is selected as target cell (T) instead of the second neighbor cell (N.sub.2) having a filtered RSRP of 96 dBm but being 80 km away from the OBE:

TABLE-US-00004 Distance Filtered Propagation delay Cell (gNodeB) to OBE RSRP (two way) S (gNodeB.sub.1) 65 km 102 dBm 433 s N.sub.1 = T (gNodeB.sub.2) 60 km 98 dBm 400 s N.sub.2 (gNodeB.sub.3) 80 km 96 dBm 533 s

[0142] In FIG. 1c, the OBE additionally applies the trajectory criterion according to the invention selecting the neighbor cell (N.sub.1) as having a higher decreasing rate of propagation delay compared to the remaining neighbor cells (N.sub.2, N.sub.2) and to the serving cell (S). In doing so, the OBE deducts, based on a configurable number of measurement samples, if the aircraft (trajectory=1000 km/h) is moving towards a neighbor gNodeB, away from a neighbor gNodeB or keeping an almost constant distant from a neighbor gNodeB. The OBE reports that one from the neighbor cells (N.sub.1, N.sub.2, N.sub.3) fulfilling the Event A3 condition (A3 offset=3 dBm) to which the OBE is moving fastest, even if the reported RRSP is lower. Thus, the first neighbor cell (N.sub.1) having a distance variation rate of 278 m/s but being 80 km away from the OBE and having a filtered RSRP of 98 dBm is selected as target cell (T) instead of the second neighbor cell (N.sub.2) having a better filtered RSRP of 96 dBm and being only 70 km away from the OBE but having a distance variation rate of only 74 m/s:

TABLE-US-00005 Distance Filtered Distance Cell (gNodeB) to OBE RSRP Variation Rate S (gNodeB.sub.1) 75 km 102 dBm not relevant N.sub.1 = T (gNodeB.sub.2) 80 km 98 dBm 278 m/s N.sub.2 (gNodeB.sub.3) 70 km 96 dBm 74 m/s N.sub.3 (gNodeB.sub.4) 75 km 97 dBm +278 m/s

[0143] FIG. 2 discloses reception of a SS/PBCH block from the serving cell (S) belonging to a first base station gNodeB.sub.1 (S-gNodeB) compared to reception of SS/PBCH blocks from the neighbor cells (N.sub.1, N.sub.2) belonging to a second base station gNodeB.sub.2 (N.sub.1-gNodeB) or a third base station gNodeB.sub.3 (N.sub.2-gNodeB), respectively. The transceiver equipment (UE/OBE) knows when the SS/PBCH blocks are transmitted by the respective base station (gNodeB) and can estimate the propagation delay for the serving cell and for the neighbor cells to determine how far it is from each gNodeB. In particular the propagation delay for the neighbor cells (N1, N2, . . . Nx) . . . Nm) is estimated by the transceiver equipment comparing the reception time of at least one SS/PBCH block from the neighbor cells and optionally from the serving cell (S).

[0144] Starting from the estimated SS/PBCH block transmission time indicated by the dotted line, propagation delay for the serving cell (S) can be directly derived from the Timing Advance that is used in current connection. For the neighbor cells (N.sub.1, N.sub.2), the UE/OBE is able to evaluate how early/late the neighbor SS/PBCH blocks are transmitted from its own Timing Advance and the time difference between the reception of the SS/PBCH blocks from the serving cell (S) and the neighbor cells (N.sub.1, N.sub.2). In case of the second neighbor cell (N.sub.2), the SS/PBCH block from gNodeB.sub.3 is received later than the SS/PBCH block from gNodeB.sub.1, requiring addition of the time difference of reception to the Timing Advance of the serving cell (S). In contrast, in case of the first neighbor cell (N.sub.1), the SS/PBCH block from gNodeB.sub.2 is received earlier than the SS/PBCH block from gNodeB.sub.1, requiring subtraction of the time difference of reception from the Timing Advance of the serving cell (S). Since the UE/OBE is closer to gNodeB.sub.2 than to gNodeB.sub.1 or gNodeB.sub.3, the first neighbor cell (N.sub.1) is becoming the target cell (T).

[0145] FIG. 3 discloses an iterative mechanism according to the invention for RA procedure during handover from a serving cell to a target cell having a planned maximum cell range C (here: 203 km). The TAO search starts with the TAO interval that contains the TAO corresponding to the estimated distance to the base station (second base station) of the target cell and is continued with optimized TAO search mechanism using an alternation around the point corresponding to said TAO t.sub.0. In doing so, the iterative mechanism comprises steps IIIb1 to IIIb3 alternating from the initial starting TAO t.sub.0 (here: 761856 T.sub.c) in increments of t=190464 T.sub.c with lower TAOs first. If the TAO search reaches either the maximum or the minimum TAO (here: 0 T.sub.c), the procedure carries on until the entire TAO search range of the target cell is covered:

TABLE-US-00006 TAO T.sub.A Interval t.sub.0 761856 T.sub.c 1488 ca. 58.0 km ca. 72.5 km t.sub.1 571392 T.sub.c 1116 ca. 43.5 km ca. 58.0 km t.sub.2 952320 T.sub.c 1860 ca. 72.5 km ca. 87.0 km t.sub.3 380928 T.sub.c 744 ca. 29.0 km ca. 43.5 km t.sub.4 1142784 T.sub.c 2232 ca. 87.0 km ca. 101.5 km t.sub.5 190464 T.sub.c 372 ca. 14.5 km ca. 29.0 km t.sub.6 1333248 T.sub.c 2604 ca. 101.5 km ca. 116.0 km t.sub.7 0 T.sub.c 0 0 km ca. 14.5 km t.sub.8 1523712 T.sub.c 2976 ca. 116.0 km ca. 130.5 km t.sub.9 1714176 T.sub.c 3348 ca. 130.5 km ca. 145.0 km t.sub.10 1904640 T.sub.c 3720 ca. 145.0 km ca. 159.5 km t.sub.11 2095104 T.sub.c 4092 ca. 159.5 km ca. 174.0 km t.sub.12 2285568 T.sub.c 4464 ca. 174.0 km ca. 188.5 km t.sub.13 2473984 T.sub.c 4832 ca. 188.5 km ca. 203.0 km * calculated for 5G NR ( = 1)