EP2030467A1 - Synchronising wireless transmission of user data - Google Patents

Synchronising wireless transmission of user data

Info

Publication number
EP2030467A1
EP2030467A1 EP07734836A EP07734836A EP2030467A1 EP 2030467 A1 EP2030467 A1 EP 2030467A1 EP 07734836 A EP07734836 A EP 07734836A EP 07734836 A EP07734836 A EP 07734836A EP 2030467 A1 EP2030467 A1 EP 2030467A1
Authority
EP
European Patent Office
Prior art keywords
user data
sample
base stations
network entity
time
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07734836A
Other languages
German (de)
French (fr)
Inventor
Johanna Pekonen
Tuomas T. Hakuli
Seppo Vesterinen
Jouko Kapanen
Kaisu Iisakkila
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nokia Oyj
Nokia Inc
Original Assignee
Nokia Oyj
Nokia Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nokia Oyj, Nokia Inc filed Critical Nokia Oyj
Publication of EP2030467A1 publication Critical patent/EP2030467A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2662—Arrangements for Wireless System Synchronisation
    • H04B7/2665—Arrangements for Wireless Frequency Division Multiple Access [FDMA] System Synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/0055—Synchronisation arrangements determining timing error of reception due to propagation delay
    • H04W56/0065—Synchronisation arrangements determining timing error of reception due to propagation delay using measurement of signal travel time
    • H04W56/007—Open loop measurement
    • H04W56/0075—Open loop measurement based on arrival time vs. expected arrival time
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0007—Control or signalling for completing the hand-off for multicast or broadcast services, e.g. MBMS

Definitions

  • the present invention relates to synchronising the wireless transmission of user data from two or more base stations. In one embodiment, it relates to synchronising the wireless transmission of MBMS user data from two or more base stations.
  • MBMS Multimedia Broadcast Multicast Services
  • a method comprising: receiving at two or more base stations respective data packets each comprising (i) a payload including a common sample of user data and (ii) a header including timing information for synchronising the wireless transmission of said common sample of user data from said two or more base stations; and timing the wireless transmission of said common sample of user data from said two or more base stations at least partly on the basis of said timing information provided in the respective headers of said data packets.
  • the data packets are formulated at a first network entity, and the timing information specifies an arrival time by which said common sample of user data is expected to have arrived at each of said two or more base stations.
  • said time is calculated by adding to the point in time at which said common sample of user data is received at the first network entity a length of time determined to be sufficient for said common sample of user data to be transported from the first network entity to the two or more base stations.
  • said length of time is a predefined static value.
  • said length of time is periodically determined.
  • said length of time is determined on the basis of a measurement of the delay between sending a message from said first network entity to each of said two or more base stations and receiving replies to said message from each of said base stations
  • said first network entity and said two or more base stations operate on the basis of a common time reference point, and said arrival time is specified with reference to said common time reference point.
  • said two or more base stations includes a first base station that operates on the basis of a different time reference point to that of the first network entity, and including formulating said timing information for said first base station on the basis of information regarding the difference between the time reference points for the first network entity and the first base station.
  • said two or more base stations includes a first base station that operates on the basis of a different time reference point to that of the first network entity, and including sending the same timing information to all of said two or more base stations, and timing the transmission of said user data from said first station on the basis of said timing information and information received at the first base station regarding the difference between the respective time reference points for the first network entity and the first base station.
  • said user data relates to a first service, and including allocating in advance time slots for the transmission of data relating to said first service from said two or more base stations, and sending said sample of user data in the first of said time slots after said arrival time specified in said timing information.
  • said first service is a Multimedia Broadcast Multicast Service (MBMS).
  • MBMS Multimedia Broadcast Multicast Service
  • said data packets received at the base stations also include in the payload a time stamp relating to the common sample of user data.
  • said time stamp included in the payloads of said data packets received at the base stations is readable by the base stations.
  • said data packets received at the base stations are Packet Data Convergence Protocol (PDCP) data packets.
  • PDCP Packet Data Convergence Protocol
  • said two or more base stations are each a Node B.
  • said two or more base stations each transmit data in predetermined time slots, each time slot being identified by a time slot number; said data packets are formulated at a first network entity; and the timing information specifies a time slot number, which is determined with reference to the time of arrival of said user data at said first network entity and a length of time determined to be sufficient for said common sample of user data to be transported from said first network entity to said two or more base stations.
  • the time slots are sub-frames.
  • a base station which is arranged to receive a data packet comprising (i) a payload including a sample of user data and (ii) a header including timing information for synchronising the transmission of said sample of user data from said base station with the transmission of said sample of user data from another base station; and timing the wireless transmission of said sample of user data at least partly on the basis of said timing information.
  • an apparatus for a base station which apparatus is arranged to control the timing of the wireless transmission of a sample of user data at least partly on the basis of timing information included in the header of the data packet in which the sample of user data was received at the base station.
  • a computer program product comprising program code means which when loaded into a computer of a base station apparatus controls the timing of the wireless transmission of a sample of user data at least partly on the basis of timing information included in the header of the data packet in which the sample of user data was received at the base station.
  • a method comprising: receiving at a network entity a sample of user data; formulating at said network entity timing information for synchronising the transmission of said sample of user data from two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; sending said sample of user data and said timing information to said two or more base stations; and timing the wireless transmission of said sample of user data from said two or more base stations at least partly on the basis of said timing information received from said network entity.
  • a network entity for receiving a sample of user data and sending said sample of user data to two or more base stations for wireless transmission therefrom, wherein said network entity is arranged to: formulate timing information for synchronising the wireless transmission of said user data from said two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; and send said sample of user data together with said timing information to said two or more base stations.
  • a system including: a user equipment for receiving a sample of user data; two or more base stations for transmitting said sample of user data to said user equipment; network entity for receiving said sample of user data and sending said sample of user data to said two or more base stations, wherein said network entity is arranged to: formulate timing information for synchronising the transmission of said sample of user data from said two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; and send said sample of user data together with said timing information to said two or more base stations.
  • an apparatus for a network entity which apparatus is arranged to formulate timing information for synchronising the wireless transmission of a sample of user data from two or more base stations based on the time of receipt of said sample of user data at said network entity.
  • a computer program product comprising program code means which when loaded into a computer of a network entity controls the formulation of timing information for synchronising the wireless transmission of a sample of user data from two or more base stations based on the time of receipt of said sample of user data at said network entity.
  • Figure 1 illustrates an example of a system for an embodiment of the present invention
  • Figure 2 illustrates a method according to an embodiment of the present invention
  • Figure 3 illustrates the timing of transmission of user data in an embodiment of the present invention.
  • Figure 4 illustrates the formulation of data packets received at the base stations in an embodiment of the present invention.
  • MBMS user data is transmitted to the user equipment 18 from a plurality of base stations (evolved Node Bs (eNBs)) 12, 14.
  • the MBMS user data is provided to the eNBs 12, 14 as described below.
  • an access GateWay (aGW)/ User Plane Entity (UPE) 4 receives MBMS user data packets 26 from a Broadcast/Multicast Service Center (BM-SC) 2.
  • BM-SC Broadcast/Multicast Service Center
  • These data packets 26 have the form shown in the top-half of Figure 4. They comprise (i) a payload 21 including a sample of MBMS user data 22, and (ii) a header 24 including an RTP protocol time stamp 30.
  • the UPE 4 receives a time reference from a GPS or an atomic clock based reference clock 6.
  • a similar reference clock 16 is connected to each eNB 12, 14 from which said MBMS user data is to be broadcast.
  • each IP data packet 20 received from the BM-SC 2 and including a respective sample of MBMS user data 22 is converted to one or more PDCP data packets 26 or frames, and the one or more PDCP packets 26 are sent to the eNBs 12, 14.
  • the destination address of the PDCP data packets 26 is the Private IP Multicast address allocated for the MBMS bearer service.
  • the form of the PDCP packets 26 is shown in the bottom half of Figure 4. They comprise (i) a payload 27 including the sample of user data 22 and the header from the corresponding IP data packet received at the BM-SC 2 (including the RTP time stamp 30), and (ii) a header 28 including timing information 32 for synchronization of the transmission of the sample of user data 22 from the eNBs 12, 14.
  • the timing information consists of a time stamp 32 calculated from the point in time when the corresponding IP data packet 20 arrived at the UPE 4 from the BM-SC 2 plus a delta time period indicating the worst case eNB transport delay.
  • This delta time period can, for example, be either a dynamically changing value or a predefined static value, which could be defined by a network ping-procedure.
  • the UPE time stamp 32 will only indicate the point in time when said corresponding IP data packet 26 arrived at the UPE 4 from the BM-SC 2, and each eNB 12, 14 is informed in advance of a delta time period that they need to add to the time indicated by said time stamp 32 in the header 28 of the PDCP data packet 26 in order to determine the time at which they should transmit said sample of MBMS user data 22.
  • the first approach is preferred from the point of view of ensuring that all eNBs 12, 14 will use the same delta time period value (and hence that the transmission from the eNBs 12, 14 will remain synchronized) even if the delta time period is changed.
  • the payload 27 of the PDCP data packet 26 includes the header 24 of the corresponding IP data packet 26 received at the UPE 4 from the BM-SC 2, which IP data packet header 24 includes an RTP protocol time stamp 30.
  • This IP data packet header 24 may be incorporated into the payload 27 of the PDCP data packet 26 in a compressed form. In some circumstances, no such compression is carried out at the UPE 4 and the RTP protocol time stamp 30 is readable by the eNB s 12, 14. Nevertheless, it is preferable to include the above-mentioned timing information 32 in the header 28 of the PDCP data packet 26 regardless of whether the IP data packet header 24 is compressed or not in the payload 27 of the PDCP data packet 26. Doing so makes it simpler for the eNBs 12, 14 to implement the synchronization process, since there is no need for the eNBs 12, 14 to inspect the RTP time stamp 32 from the payload 27 of the PDCP data packet 26.
  • Resources are allocated in advance for the transmission of MBMS service user data from the eNBs. As shown in Figure 3, one portion (sub-frame) or consecutive portions (sub frames) of each transmission frame is/are allocated to the MBMS service.
  • the eNB 12, 14 select for the transmission of a sample of MBMS user data the first such allocated sub-frame or succession of sub-frames after the time point T indicated by the time stamp in the header 28 of the PDCP data packet 26 including said sample of MBMS user data 22.
  • the data sample will be transmitted from the eNBs 12, 14 in the pre-allocated MBMS sub-frame(s) of radio frame n+1 , if the time point T is any point of time in the period between the starting point, t n of the pre-a ⁇ ocated MBMS sub-frames of the previous radio frame (Frame n) and the starting point, t ⁇ + i of the pre-allocated MBMS sub frames of radio frame n+1.
  • the header 28 of the PDCP data packet 26 is to identify by sub-frame number the sub-frame in which the MBMS user data is to be transmitted from the eNBs 12, 14.
  • the sub-frame number to be identified in the header 28 is determined with reference to the time at which the data packet arrived at the UPE 4 and the maximum transmission delay between the UPE 4 and the eNBs 12, 14.
  • the eNBs 12, 14 are synchronised with a GPS reference clock and that the radio frame/sub-frame numbering is exactly the same in each of the eNBs 12, 14.
  • the corresponding sub-frame in each of the eNBs 12, 14 is identified by the same number in each of the eNBs 12, 14.
  • the eNBs 12, 14 and the UPE 4 are all provided with a common time reference point by local reference clocks 6, 16, which can, for example, be based on GPS, atomic clock or Tim ing-over- Packet.
  • Another approach to synchronize the data transmission between multiple eNBs is to gather the timing information.
  • the UPE 4 or alternatively another entity connected to the eNBs 12, 14, such as an MBMS controller uses synchronisation frames to obtain timing information from each eNB 12, 14, and on the basis of such information determines the time stamps to be included in the header 28 of the PDCP data packet 26 sent to the respective eNB 12, 14.
  • the UPE 4 will formulate more than one PDCP data packet 26, each including the same sample of MBMS user data 22 in the payload but a different time stamp in the PDCP header 28.
  • Identical PDCP data packets 26 are sent to each eNB 12, 14, (i.e. the same PDCP time stamp 32 is used for each PDCP packet 26 including the same sample of user data 22), and the eNBs12, 14 use offset information that they have exchanged with the UPE 4 to translate the time indicated in the time stamp 32 of the PDCP header 28 to a time according to the respective atomic clock of the eNB 12, 14.
  • the TEID is allocated by the MBMS-UPE 4.
  • Appropriately adapted computer program code product may be used for configuring the eNBs 12, 14 and the MBMS-UPE 4.
  • the program code product may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. Another possibility is to download the program code product via a data network.
  • Orthogonal Frequency Domain Multiplexing OFDMA
  • OFDMA Orthogonal Frequency Domain Multiplexing
  • One advantage of the technique described above is that the eNBs 12, 14 do not need to negotiate between themselves as to when to transmit common samples of MBMS user data. Additionally the UPE 4 can forward the samples of MBMS user data independently of the user data rate, because the UPE 4 adds timing information based on the time of reception of MBMS user data from the BM-SC 2.
  • the technique described above ensures tight synchronization of the wireless transmission of a common sample of MBMS user data from the eNBs, even where there are varying transmission delays between the UPE and each eNB (depending on the network configuration and load) that have the result that the common sample of MBMS user data does not arrive at each eNB at the same point in time.

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Abstract

A method receiving at two or more base stations respective data packets each comprising of a payload including a common sample of user data and a header including timing information for synchronising the wireless transmission of said common sample of user data from said two or more base stations. Also timing the wireless transmission of said common sample of user data from said two or more base stations at least partly on the basis of said timing information provided in the respective headers of said data packets.

Description

SYNCHRONISING WIRELESS TRANSMISSION OF USER DATA
The present invention relates to synchronising the wireless transmission of user data from two or more base stations. In one embodiment, it relates to synchronising the wireless transmission of MBMS user data from two or more base stations.
For some services (e.g. Multimedia Broadcast Multicast Services (MBMS)), it can be important that common user data is transmitted synchronously from a plurality of base stations, such that any user equipment receiving such user data from more than one base station (for example, user equipment at the border between neighbouring cells) receives the user data from each of the base stations at the same time.
It is an aim of the present invention to provide a technique for synchronizing the wireless transmission of user data from two or more base stations.
According to a first aspect of the present invention, there is provided a method comprising: receiving at two or more base stations respective data packets each comprising (i) a payload including a common sample of user data and (ii) a header including timing information for synchronising the wireless transmission of said common sample of user data from said two or more base stations; and timing the wireless transmission of said common sample of user data from said two or more base stations at least partly on the basis of said timing information provided in the respective headers of said data packets.
In one embodiment, the data packets are formulated at a first network entity, and the timing information specifies an arrival time by which said common sample of user data is expected to have arrived at each of said two or more base stations.
In one embodiment, said time is calculated by adding to the point in time at which said common sample of user data is received at the first network entity a length of time determined to be sufficient for said common sample of user data to be transported from the first network entity to the two or more base stations. In one embodiment, said length of time is a predefined static value.
In one embodiment, said length of time is periodically determined.
In one embodiment, said length of time is determined on the basis of a measurement of the delay between sending a message from said first network entity to each of said two or more base stations and receiving replies to said message from each of said base stations
In one embodiment, said first network entity and said two or more base stations operate on the basis of a common time reference point, and said arrival time is specified with reference to said common time reference point.
In one embodiment, said two or more base stations includes a first base station that operates on the basis of a different time reference point to that of the first network entity, and including formulating said timing information for said first base station on the basis of information regarding the difference between the time reference points for the first network entity and the first base station.
In one embodiment, said two or more base stations includes a first base station that operates on the basis of a different time reference point to that of the first network entity, and including sending the same timing information to all of said two or more base stations, and timing the transmission of said user data from said first station on the basis of said timing information and information received at the first base station regarding the difference between the respective time reference points for the first network entity and the first base station.
In one embodiment, said user data relates to a first service, and including allocating in advance time slots for the transmission of data relating to said first service from said two or more base stations, and sending said sample of user data in the first of said time slots after said arrival time specified in said timing information.
In one embodiment, said first service is a Multimedia Broadcast Multicast Service (MBMS). In one embodiment, said data packets received at the base stations also include in the payload a time stamp relating to the common sample of user data.
In one embodiment, said time stamp included in the payloads of said data packets received at the base stations is readable by the base stations.
In one embodiment, said data packets received at the base stations are Packet Data Convergence Protocol (PDCP) data packets.
In one embodiment, said two or more base stations are each a Node B.
In one embodiment, said two or more base stations each transmit data in predetermined time slots, each time slot being identified by a time slot number; said data packets are formulated at a first network entity; and the timing information specifies a time slot number, which is determined with reference to the time of arrival of said user data at said first network entity and a length of time determined to be sufficient for said common sample of user data to be transported from said first network entity to said two or more base stations.
In one embodiment, the time slots are sub-frames.
According to one aspect of the present invention, there is provided a base station, which is arranged to receive a data packet comprising (i) a payload including a sample of user data and (ii) a header including timing information for synchronising the transmission of said sample of user data from said base station with the transmission of said sample of user data from another base station; and timing the wireless transmission of said sample of user data at least partly on the basis of said timing information.
According to one aspect of the present invention, there is provided an apparatus for a base station, which apparatus is arranged to control the timing of the wireless transmission of a sample of user data at least partly on the basis of timing information included in the header of the data packet in which the sample of user data was received at the base station.
According to one aspect of the present invention, there is provided a computer program product comprising program code means which when loaded into a computer of a base station apparatus controls the timing of the wireless transmission of a sample of user data at least partly on the basis of timing information included in the header of the data packet in which the sample of user data was received at the base station.
According to one aspect of the present invention, there is provided a method, comprising: receiving at a network entity a sample of user data; formulating at said network entity timing information for synchronising the transmission of said sample of user data from two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; sending said sample of user data and said timing information to said two or more base stations; and timing the wireless transmission of said sample of user data from said two or more base stations at least partly on the basis of said timing information received from said network entity.
According to one aspect of the present invention, there is provided a network entity for receiving a sample of user data and sending said sample of user data to two or more base stations for wireless transmission therefrom, wherein said network entity is arranged to: formulate timing information for synchronising the wireless transmission of said user data from said two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; and send said sample of user data together with said timing information to said two or more base stations.
According to one aspect of the present invention, there is provided a system including: a user equipment for receiving a sample of user data; two or more base stations for transmitting said sample of user data to said user equipment; network entity for receiving said sample of user data and sending said sample of user data to said two or more base stations, wherein said network entity is arranged to: formulate timing information for synchronising the transmission of said sample of user data from said two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; and send said sample of user data together with said timing information to said two or more base stations.
According to one aspect of the present invention, there is provided an apparatus for a network entity, which apparatus is arranged to formulate timing information for synchronising the wireless transmission of a sample of user data from two or more base stations based on the time of receipt of said sample of user data at said network entity.
According to one aspect of the present invention, there is provided a computer program product comprising program code means which when loaded into a computer of a network entity controls the formulation of timing information for synchronising the wireless transmission of a sample of user data from two or more base stations based on the time of receipt of said sample of user data at said network entity.
An embodiment of the present invention is described in detail hereunder, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 illustrates an example of a system for an embodiment of the present invention;
Figure 2 illustrates a method according to an embodiment of the present invention;
Figure 3 illustrates the timing of transmission of user data in an embodiment of the present invention; and
Figure 4 illustrates the formulation of data packets received at the base stations in an embodiment of the present invention.
With reference to Figure 1, user equipment 18 subscribes to an MBMS service. MBMS user data is transmitted to the user equipment 18 from a plurality of base stations (evolved Node Bs (eNBs)) 12, 14. The MBMS user data is provided to the eNBs 12, 14 as described below. With reference to Figure 1 , an access GateWay (aGW)/ User Plane Entity (UPE) 4 receives MBMS user data packets 26 from a Broadcast/Multicast Service Center (BM-SC) 2. These data packets 26 have the form shown in the top-half of Figure 4. They comprise (i) a payload 21 including a sample of MBMS user data 22, and (ii) a header 24 including an RTP protocol time stamp 30.
The UPE 4 receives a time reference from a GPS or an atomic clock based reference clock 6. A similar reference clock 16 is connected to each eNB 12, 14 from which said MBMS user data is to be broadcast.
At the UPE 4, each IP data packet 20 received from the BM-SC 2 and including a respective sample of MBMS user data 22 is converted to one or more PDCP data packets 26 or frames, and the one or more PDCP packets 26 are sent to the eNBs 12, 14. The destination address of the PDCP data packets 26 is the Private IP Multicast address allocated for the MBMS bearer service.
The form of the PDCP packets 26 is shown in the bottom half of Figure 4. They comprise (i) a payload 27 including the sample of user data 22 and the header from the corresponding IP data packet received at the BM-SC 2 (including the RTP time stamp 30), and (ii) a header 28 including timing information 32 for synchronization of the transmission of the sample of user data 22 from the eNBs 12, 14. The timing information consists of a time stamp 32 calculated from the point in time when the corresponding IP data packet 20 arrived at the UPE 4 from the BM-SC 2 plus a delta time period indicating the worst case eNB transport delay. This delta time period can, for example, be either a dynamically changing value or a predefined static value, which could be defined by a network ping-procedure.
Alternatively, the UPE time stamp 32 will only indicate the point in time when said corresponding IP data packet 26 arrived at the UPE 4 from the BM-SC 2, and each eNB 12, 14 is informed in advance of a delta time period that they need to add to the time indicated by said time stamp 32 in the header 28 of the PDCP data packet 26 in order to determine the time at which they should transmit said sample of MBMS user data 22. However, the first approach is preferred from the point of view of ensuring that all eNBs 12, 14 will use the same delta time period value (and hence that the transmission from the eNBs 12, 14 will remain synchronized) even if the delta time period is changed.
As mentioned above, the payload 27 of the PDCP data packet 26 includes the header 24 of the corresponding IP data packet 26 received at the UPE 4 from the BM-SC 2, which IP data packet header 24 includes an RTP protocol time stamp 30. This IP data packet header 24 may be incorporated into the payload 27 of the PDCP data packet 26 in a compressed form. In some circumstances, no such compression is carried out at the UPE 4 and the RTP protocol time stamp 30 is readable by the eNB s 12, 14. Nevertheless, it is preferable to include the above-mentioned timing information 32 in the header 28 of the PDCP data packet 26 regardless of whether the IP data packet header 24 is compressed or not in the payload 27 of the PDCP data packet 26. Doing so makes it simpler for the eNBs 12, 14 to implement the synchronization process, since there is no need for the eNBs 12, 14 to inspect the RTP time stamp 32 from the payload 27 of the PDCP data packet 26.
Resources are allocated in advance for the transmission of MBMS service user data from the eNBs. As shown in Figure 3, one portion (sub-frame) or consecutive portions (sub frames) of each transmission frame is/are allocated to the MBMS service. The eNB 12, 14 select for the transmission of a sample of MBMS user data the first such allocated sub-frame or succession of sub-frames after the time point T indicated by the time stamp in the header 28 of the PDCP data packet 26 including said sample of MBMS user data 22. In other words, the data sample will be transmitted from the eNBs 12, 14 in the pre-allocated MBMS sub-frame(s) of radio frame n+1 , if the time point T is any point of time in the period between the starting point, tn of the pre-aϋocated MBMS sub-frames of the previous radio frame (Frame n) and the starting point, tπ+i of the pre-allocated MBMS sub frames of radio frame n+1.
An alternative approach is for the header 28 of the PDCP data packet 26 is to identify by sub-frame number the sub-frame in which the MBMS user data is to be transmitted from the eNBs 12, 14. As with the approach described in detail above, the sub-frame number to be identified in the header 28 is determined with reference to the time at which the data packet arrived at the UPE 4 and the maximum transmission delay between the UPE 4 and the eNBs 12, 14. With such an alternative approach, the eNBs 12, 14 are synchronised with a GPS reference clock and that the radio frame/sub-frame numbering is exactly the same in each of the eNBs 12, 14. In other words, at a certain time point, the corresponding sub-frame in each of the eNBs 12, 14 is identified by the same number in each of the eNBs 12, 14.
In the embodiment described above, the eNBs 12, 14 and the UPE 4 are all provided with a common time reference point by local reference clocks 6, 16, which can, for example, be based on GPS, atomic clock or Tim ing-over- Packet.
Another approach to synchronize the data transmission between multiple eNBs is to gather the timing information. In that case, the UPE 4 or alternatively another entity connected to the eNBs 12, 14, such as an MBMS controller, uses synchronisation frames to obtain timing information from each eNB 12, 14, and on the basis of such information determines the time stamps to be included in the header 28 of the PDCP data packet 26 sent to the respective eNB 12, 14. If different timing information is received from the eNBs (because the eNBs 12, 14 operate with respect to different time reference points), then for each IP data packet 20 received from the BM-SC 2 the UPE 4 will formulate more than one PDCP data packet 26, each including the same sample of MBMS user data 22 in the payload but a different time stamp in the PDCP header 28.
Another option for when the eNBs 12, 14 operate with respect to different time reference points is as follows. Identical PDCP data packets 26 are sent to each eNB 12, 14, (i.e. the same PDCP time stamp 32 is used for each PDCP packet 26 including the same sample of user data 22), and the eNBs12, 14 use offset information that they have exchanged with the UPE 4 to translate the time indicated in the time stamp 32 of the PDCP header 28 to a time according to the respective atomic clock of the eNB 12, 14.
With reference to Figure 1 , the TEID is allocated by the MBMS-UPE 4.
Appropriately adapted computer program code product may be used for configuring the eNBs 12, 14 and the MBMS-UPE 4. The program code product may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. Another possibility is to download the program code product via a data network.
Orthogonal Frequency Domain Multiplexing (OFDMA) based technology can be used for transmission of the MBMS user data from the eNBs 12, 14.
One advantage of the technique described above is that the eNBs 12, 14 do not need to negotiate between themselves as to when to transmit common samples of MBMS user data. Additionally the UPE 4 can forward the samples of MBMS user data independently of the user data rate, because the UPE 4 adds timing information based on the time of reception of MBMS user data from the BM-SC 2.
Also, the technique described above ensures tight synchronization of the wireless transmission of a common sample of MBMS user data from the eNBs, even where there are varying transmission delays between the UPE and each eNB (depending on the network configuration and load) that have the result that the common sample of MBMS user data does not arrive at each eNB at the same point in time.
The applicant draws attention to the fact that the present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof, without limitation to the scope of any definitions set out above. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A method, comprising: receiving at two or more base stations respective data packets each comprising (i) a payload including a common sample of user data and (ii) a header including timing information for synchronising the wireless transmission of said common sample of user data from said two or more base stations; and timing the wireless transmission of said common sample of user data from said two or more base stations at least partly on the basis of said timing information provided in the respective headers of said data packets.
2. A method according to claim 1 , wherein the data packets are formulated at a first network entity, and the timing information specifies an arrival time by which said common sample of user data is expected to have arrived at each of said two or more base stations.
3. A method according to claim 2, wherein said time is calculated by adding to the point in time at which said common sample of user data is received at the first network entity a length of time determined to be sufficient for said common sample of user data to be transported from the first network entity to the two or more base stations.
4. A method according to claim 3, where said length of time is a predefined static value.
5. A method according to claim 3, wherein said length of time is periodically determined.
6. A method according to any of claims 3 to 5, wherein said length of time is determined on the basis of a measurement of the delay between sending a message from said first network entity to each of said two or more base stations and receiving replies to said message from each of said base stations
7. A method according to claim 2, wherein said first network entity and said two or more base stations operate on the basis of a common time reference point, and said arrival time is specified with reference to said common time reference point.
8. A method according to claim 2, wherein said two or more base stations includes a first base station that operates on the basis of a different time reference point to that of the first network entity, and including formulating said timing information for said first base station on the basis of information regarding the difference between the time reference points for the first network entity and the first base station.
9. A method according to claim 2, wherein said two or more base stations includes a first base station that operates on the basis of a different time reference point to that of the first network entity, and including sending the same timing information to all of said two or more base stations, and timing the transmission of said user data from said first station on the basis of said timing information and information received at the first base station regarding the difference between the respective time reference points for the first network entity and the first base station.
10. A method according to claim 2, wherein said user data relates to a first service, and including allocating in advance time slots for the transmission of data relating to said first service from said two or more base stations, and sending said sample of user data in the first of said time slots after said arrival time specified in said timing information.
11. A method according to claim 10, wherein said first service is a Multimedia Broadcast Multicast Service (MBMS).
12. A method according to any preceding claim, wherein said data packets received at the base stations also include in the payload a time stamp relating to the common sample of user data.
13. A method according to claim 12, wherein said time stamp included in the payloads of said data packets received at the base stations is readable by the base stations.
14. A method according to any preceding claim, wherein said data packets received at the base stations are Packet Data Convergence Protocol (PDCP) data packets.
15. A method according to any preceding claim, wherein said two or more base stations are each a Node B.
16. A method according to claim 1 , wherein said two or more base stations each transmit data in pre-determined time slots, each time slot being identified by a time slot number; said data packets are formulated at a first network entity; and the timing information specifies a time slot number, which is determined with reference to the time of arrival of said user data at said first network entity and a length of time determined to be sufficient for said common sample of user data to be transported from said first network entity to said two or more base stations.
17. A method according to claim 16, wherein the time slots are sub-frames.
18. A base station, which is arranged to receive a data packet comprising (i) a payload including a sample of user data and (ii) a header including timing information for synchronising the transmission of said sample of user data from said base station with the transmission of said sample of user data from another base station; and timing the wireless transmission of said sample of user data at least partly on the basis of said timing information.
19. An apparatus for a base station, which apparatus is arranged to control the timing of the wireless transmission of a sample of user data at least partly on the basis of timing information included in the header of the data packet in which the sample of user data was received at the base station.
20. A computer program product comprising program code means which when loaded into a computer of a base station apparatus controls the timing of the wireless transmission of a sample of user data at least partly on the basis of timing information included in the header of the data packet in which the sample of user data was received at the base station.
21. A method, comprising: receiving at a network entity a sample of user data; formulating at said network entity timing information for synchronising the transmission of said sample of user data from two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; sending said sample of user data and said timing information to said two or more base stations; and timing the wireless transmission of said sample of user data from said two or more base stations at least partly on the basis of said timing information received from said network entity.
22. A network entity for receiving a sample of user data and sending said sample of user data to two or more base stations for wireless transmission therefrom, wherein said network entity is arranged to: formulate timing information for synchronising the wireless transmission of said user data from said two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; and send said sample of user data together with said timing information to said two or more base stations.
23. A system including: a user equipment for receiving a sample of user data; two or more base stations for transmitting said sample of user data to said user equipment; a network entity for receiving said sample of user data and sending said sample of user data to said two or more base stations, wherein said network entity is arranged to: formulate timing information for synchronising the transmission of said sample of user data from said two or more base stations, said timing information being based on the time of receipt of said sample of user data at said network entity; and send said sample of user data together with said timing information to said two or more base stations.
24. An apparatus for a network entity, which apparatus is arranged to formulate timing information for synchronising the wireless transmission of a sample of user data from two or more base stations based on the time of receipt of said sample of user data at said network entity.
25. A computer program product comprising program code means which when loaded into a computer of a network entity controls the formulation of timing information for synchronising the wireless transmission of a sample of user data from two or more base stations based on the time of receipt of said sample of user data at said network entity.
EP07734836A 2006-06-19 2007-06-11 Synchronising wireless transmission of user data Withdrawn EP2030467A1 (en)

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