WO2005018144A1 - Feedback signalling for multicast data transmission - Google Patents
Feedback signalling for multicast data transmission Download PDFInfo
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- WO2005018144A1 WO2005018144A1 PCT/IB2004/002640 IB2004002640W WO2005018144A1 WO 2005018144 A1 WO2005018144 A1 WO 2005018144A1 IB 2004002640 W IB2004002640 W IB 2004002640W WO 2005018144 A1 WO2005018144 A1 WO 2005018144A1
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- confirmation message
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
- H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
- H04L1/1607—Details of the supervisory signal
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
- H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
- H04L1/1607—Details of the supervisory signal
- H04L1/1692—Physical properties of the supervisory signal, e.g. acknowledgement by energy bursts
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
- H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
- H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
- H04L1/1867—Arrangements specially adapted for the transmitter end
- H04L1/1887—Scheduling and prioritising arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
- H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
- H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
- H04L1/1867—Arrangements specially adapted for the transmitter end
- H04L1/1896—ARQ related signaling
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/02—Details
- H04L12/16—Arrangements for providing special services to substations
- H04L12/18—Arrangements for providing special services to substations for broadcast or conference, e.g. multicast
- H04L12/1863—Arrangements for providing special services to substations for broadcast or conference, e.g. multicast comprising mechanisms for improved reliability, e.g. status reports
- H04L12/1868—Measures taken after transmission, e.g. acknowledgments
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/02—Details
- H04L12/16—Arrangements for providing special services to substations
- H04L12/18—Arrangements for providing special services to substations for broadcast or conference, e.g. multicast
- H04L12/189—Arrangements for providing special services to substations for broadcast or conference, e.g. multicast in combination with wireless systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/02—Traffic management, e.g. flow control or congestion control
- H04W28/04—Error control
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/06—Selective distribution of broadcast services, e.g. multimedia broadcast multicast service [MBMS]; Services to user groups; One-way selective calling services
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/30—TPC using constraints in the total amount of available transmission power
- H04W52/36—TPC using constraints in the total amount of available transmission power with a discrete range or set of values, e.g. step size, ramping or offsets
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/38—TPC being performed in particular situations
- H04W52/48—TPC being performed in particular situations during retransmission after error or non-acknowledgment
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W76/00—Connection management
- H04W76/40—Connection management for selective distribution or broadcast
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L2001/0092—Error control systems characterised by the topology of the transmission link
- H04L2001/0093—Point-to-multipoint
Definitions
- the present invention relates to data transmission in a multicast fashion.
- the present invention relates to a method of performing a point-to-multipoint data transmission from a transmitting station to a plurality of receiving stations, a data transmission system for performing a point-to- multipoint data transmission from a transmission station to a plurality of receiving stations, to a transmitting station for a data transmission system for a point-to-multipoint data transmission from the transmission station to a plurality of receiving stations and to a receiving station for a data transmission system for a point-to-multipoint data transmission from a transmitting station to a plurality of receiving stations.
- Multicast data transmission or point-to-multipoint data transmission relates to a data transmission where one sender once sends data, such as a data packet, to a number of recipients and each recipient decodes this (single physical representation of the) data.
- the same data is to be conveyed to a number of recipients, such as, for example, in the case of a base station of a mobile communication system via a wireless transmission channel to a number of recipients in a radio cell, it may be advantageous to send each packet only once to all recipients in a broadcast manner and let all recipients decode this one packet.
- p2m point-to-multipoint channel
- p2p-channel point-to-point channels
- FEC forward error correction
- Both of the above approaches are usually applied when data packets are transmitted via a p2p channel.
- the retransmission of data packets may be problematic, since each recipient has to send its feedback to the sender.
- the sender has to cope with as many feedback messages as there are recipients for each data packet transmitted. This may cause a huge amount of signalling in the direction from the recipient to the sender, if the number of recipients in the multicast group is large.
- it is necessary to perform another point- to-multipoint transmission of the data i.e. another transmission of the data to all of the recipients.
- point-to-multipoint transmission occupies a lot of channel capacity in the direction from the recipient to the sender, and generates significant interference, and thus may be inefficient in case the number of recipients in the multicast group is large. It is an object of the present invention to provide an efficient feedback signalling mechanism for point-to-multipoint data transmission.
- the above object may be solved by a method of performing a point-to-multipoint data transmission from a transmission station to a plurality of first receiving stations, wherein the data is transmitted from the transmitting station to the plurality of first receiving stations. Then, at the transmitting station, a confirmation message with respect to the data is received from at least one second receiving station of the plurality of first receiving stations. The transmitting station transmits (possibly together with a further data packet) the confirmation message, which it received from the at least one second receiving station, to at least one third receiving station of the plurality of first receiving stations.
- the confirmation message relating to the decoding of the data at the at least one second receiving station is mirrored by the transmitting station to at least one third station of the plurality of first receiving stations. Due to this, the at least one third receiving station is informed about the decoding result of the data at the at least one second receiving station. Due to this knowledge, advantageously, the at least one third receiving station may decide what to do next.
- the data may relate to user data transmitted via a data channel or to control data transmitted via a control channel.
- the at least one third receiving station knows that a retransmission for the data packet may happen anyway, due to the fact that the at least one second receiving station was not able to decode the data packet error-free.
- the at least one third receiving station may decide not to perform a transmission of its own confirmation message relating to the own decoding of the data packet to the transmission station.
- this may allow for a reduction of feedback signalling.
- the confirmation message is a positive acknowledgement message indicating that the data was decoded error-free, i.e. successfully at the at least one second receiving station
- the at least one third receiving station may use this information to send its own confirmation message back to the transmitting station.
- a needless feedback signalling of, for example, the positive or negative acknowledgement message from the at least one third receiving station in case the at least one second receiving station already sent a negative acknowledgement message may be avoided. Due to this, the amount of signalling in the direction from the recipient to the sender, may be reduced, even if the number of recipients in the multicast group is large.
- the transmitting station retransmits the data packet in case the confirmation message is a negative acknowledgement message.
- the transmitting station initiates or starts a retransmission of the data packet without waiting for a feedback signalling of the other receiving stations in the multicast group. Due to this, advantageously, since a retransmission for the data packet is anyway needed, this retransmission upon reception of a negative acknowledgement message allows to increase the efficiency of the data channel to the recipients, i.e.
- the transmission delay and data transmission rate to the recipients with limited memory may be increased and the amount of confirmation messages to be decoded by the transmitting station may be reduced.
- the plurality of first receiving stations is grouped into a plurality of groups or subsets, wherein a feedback phase is assigned to each of the groups.
- the receiving stations of a group are scheduled to send their confirmation messages to the transmitting station at a pre-set feedback phase.
- the group of receiving stations transmit their confirmation messages in accordance with the feedback phase defined for this group.
- the set of recipients is split up into separate or disjoint subsets, whereby the members of each subset are assigned a pre-defined phase, for example, within the radio frame, which determines the structure of up-link and down-link transmissions in which phase the members of the subsets are allowed to transmit their confirmation messages.
- this feedback phase may also be a pre-defined slot or sub-frame in the up-link p2m control channel, which may accompany the data transmission via the p2m data channel. Due to the prescribed feedback scheme, the transmission station
- the feedback scheme is adapted such that the confirmation message of the first group or subset is decoded and mirrored back to the second group before the transmission of the confirmation message of the second group starts.
- the receiving station may save battery energy.
- the at least one fourth receiving station of the second group does not send its own negative acknowledgement message in the case of an unsuccessful decoding, if it received a negative acknowledgement message mirrored by the transmitting station indicating that the at least one third receiving station of the first group was not able to decode the data packet error-free.
- the receiving stations of the multicast group only send the confirmation message in case the decoding of the data packet is unsuccessful, i.e. only send a negative acknowledgement message.
- this may allow to further reduce the amount of signalling between the recipients and the sender.
- the transmission station listens only to confirmation messages of groups of the receiving stations which have not yet sent a positive acknowledgement message with respect to the data.
- the transmitting station only waits for a feedback of groups of receiving stations which have either already sent a negative acknowledgement message or did not send a positive acknowledgement message, due to the fact that other groups sent a negative acknowledgement message before them, so that they received a mirrored copy of the negative confirmation message of another group before they were scheduled to send their own confirmation and decided not to send their own confirmation message.
- the transmitting stations are adapted to only send positive acknowledgement messages, indicating that the receiving station has decoded the data packet error-free. Then, the transmitting station initiates a retransmission for the data packet after not receiving a positive acknowledgement message from at least one receiving station.
- this may allow to reduce the up-link interference (from the receiving stations to the transmitting stations), if only a few retransmissions are necessary. Thus, advantageously, this may allow to reduce the up-link interference in case of good reception conditions.
- the method is applied in the context of Multimedia Broadcast Multicast Services (in the following referred to as "MBMS") in the Universal Mobile Telecommunication System (UMTS).
- MBMS Multimedia Broadcast Multicast Services
- UMTS Universal Mobile Telecommunication System
- the confirmation message comprises confirmation data in form of soft bits and a soft-combining of the confirmation message of the at least one third receiving station of the first group with the confirmation message of the at least one fourth receiving station of the second group is performed.
- confirmation messages or confirmation signals of different senders are combined, e.g.
- a fifth receiving station of the plurality of first receiving stations determines a fourth group of the plurality of groups of first receiving stations to which the fifth receiving station assigns itself after receiving information about the number of groups of the first receiving stations available for grouping.
- the determination of the fourth group to which the fifth receiving station belongs is performed by the fifth receiving station without additional signalling, therefore reducing the amount of uplink signalling.
- the determination of the fourth group to which the fifth receiving station belongs is performed on the basis of at least one of a random number generated by the fifth receiving station, a modulo operation applied to one of an International Mobile Subscriber Identity (IMSI) and a Temporary Mobile Subscriber Identity (TMSI) of the fifth receiving station, and a path loss figure perceived during the data transmission on the p2m channel.
- IMSI International Mobile Subscriber Identity
- TMSI Temporary Mobile Subscriber Identity
- the at least one third receiving station after the at least one third receiving station has sent the confirmation message with a second transmission power to the transmitting station in accordance with the first feedback phase, it sends the confirmation message in accordance with the second feedback phase and with a third transmission power, wherein the third transmission power is higher than the second transmission power.
- this may allow for a power ramping of the confirmation message transmission.
- the data is sent as a data packet and the method is a retransmission protocol in a cellular radio communication system, such as, for example, a Global System for Mobile Communication (GSM) mobile telecommunication system or the UMTS telecommunication system.
- GSM Global System for Mobile Communication
- a data transmission system for a point-to- multipoint data transmission from a transmission station to a plurality of first receiving stations, where the transmitting station is adapted to transmit a confirmation message with respect to the data from at least one second receiving station of the plurality of first receiving stations to at least one third receiving station of the plurality of first receiving stations.
- the other receiving stations are informed about a feedback of other receiving stations. This may allow to reduce a feedback signalling, i.e. a transmission of confirmation messages from the receiving stations to the transmitting stations.
- the receiving stations are grouped into groups or subsets, wherein the members of each group or subset are assigned a pre-defined feedback phase, which, according to an aspect of this exemplary embodiment of the present invention, determines the structure of up-link and down-link transmissions, in which phase the members of the group or subset are allowed or scheduled to transmit their respective confirmation messages.
- the feedback phase does not relate to a particular phase, but is to be understood as a particular point in time, time slot, transmission channel or sub-frame (relative to the transmission time, time slot or sub-frame, when a data packet is transmitted) in the up-link or down-link p2m control channel, which, according to an aspect of the present invention, accompanies the transmission of a data packet.
- Claims 20 and 21 provide further exemplary embodiments of the data transmission system according to the present invention.
- a transmission station for a data transmission system for a point-to-multipoint data transmission from a transmission station to a plurality of receiving stations is provided.
- the transmitting station is adapted to send a confirmation message received from one receiving station to another receiving station.
- a receiving station is provided for a data transmission system for a point-to-multipoint data transmission from a transmitting station to a plurality of receiving stations.
- the receiving station is adapted to receive a confirmation message from another receiving station, which was sent from the transmitting station to the receiving station.
- the set of recipients of a multicast group is split up into separate or disjoint subsets, whereby the members of each subset are assigned, relative to the transmission of a data packet, a pre-defined phase within the radio frame, which determines the structure of up-link and down-link transmissions in which phase the members of the subset are allowed to transmit their feedback signals.
- a pre-defined phase within the radio frame which determines the structure of up-link and down-link transmissions in which phase the members of the subset are allowed to transmit their feedback signals.
- Fig. 1 shows a simplified representation of an exemplary embodiment of a data transmission system for a point-to-multipoint data transmission from a transmission station to a plurality of receiving stations according to the present invention.
- Fig. 2 shows an exemplary embodiment of a method of operating the data transmission system depicted in Fig. 1 according to the present invention.
- Fig. 3 shows another exemplary embodiment of a method of operating the data transmitting system depicted in Fig. 1 according to the present invention.
- Fig. 4 shows another exemplary embodiment of a method of operating the data transmitting system depicted in Fig. 1 according to the present invention.
- Fig. 1 shows a simplified representation of a data transmission system for a point-to-multipoint data transmission, from a transmitting station 2 to a plurality of receiving stations 4, 6, 12, 14 and 18.
- the data transmission system depicted in Fig. 1 is a wireless data transmission system, where data is transmitted from the transmitting station 2 via a wireless radio link in the form of data packets to the receiving stations 4, 6, 12, 14 and 18.
- the data transmission system depicted in Fig. 1 may, for example, be a cellular mobile radio telecommunication system, such as the GSM system or the UMTS system, or a wireless local area network.
- the transmitting station 2 depicted in Fig. 1 is adapted to transmit data in the form of a data packet to the plurality of receiving stations 4, 6, 12, 14 and 18.
- Each of the plurality of receiving stations 4, 6, 12, 14 and 18 is adapted to send a confirmation message back to the transmitting station. These confirmation messages relate to a decoding of the data at the respective receiving station of the plurality of receiving stations 4, 6, 12, 14 and 18.
- the transmitting station 2 is furthermore adapted to transmit the at least one confirmation message received from one of the receiving stations 4, 6, 12, 14 and 18 back to the receiving stations 4, 6, 12, 14 and 18. As may be taken from Fig.
- the receiving stations 4, 6, 12, 14 and 18 are grouped into four subsets 8, 10, 16 and 20, such that the receiving stations designated by reference numeral 4 are located or belong to the subset 8, the receiving stations designated by reference numeral 6 are located or belong to the subset 10, the receiving stations 12 and 14 belong to subset 16 and the receiving station 18 belongs to subset 20.
- a feedback scheme according to which a first feedback phase is assigned to subset 8 and a second feedback phase is assigned to subset 10.
- the receiving stations 4 in the subset 8 are all assigned a first feedback phase, during which or via which they are scheduled to transmit their confirmation message, i.e. feedback messages back to the transmitting station 2.
- the feedback messages are sent one after the other during this feedback phase exclusively assigned to the subset, i.e. in a time division manner, or superimposed during the feedback phase, in which case the phase is usually shorter.
- Superposition can be advantageously been done by using Code Division Multiple Access (CDMA) techniques. It is, however, also possible to superimpose without applying CDMA, in which case the feedback signals collide. If only Negative Acknowledgements are sent, this collision does not pose a problem for the transmission side to detect that at least one receiving station requested a retransmission by means of a Negative Acknowledgement (NACK).
- CDMA Code Division Multiple Access
- each of the receiving stations 6, 12, 16 and 18 of the subsets 10, 16 and 18 are assigned another feedback phase, during which, at which or via which they may send their confirmation messages back to the transmitting station 2.
- the set of receiving stations 4, 6, 12, 14 and 18 is split up into separated subsets 8, 10, 16 and 20, whereby the members of each subset 8, 10, 16 and 20 are assigned a predefined feedback phase within the radio frame of the wireless communication channels between the transmitting station 2 and the receiving stations 4, 6, 12, 14 and 18, which determines the structure of up-link and down-link transmission, in which phase the members of the subsets 8, 10, 16 and 20 are allowed to transmit their feedback signals.
- the feedback signal or confirmation message is often also referred to as an ACK or NACK message.
- the ACK message is a positive acknowledgement message, which indicates that the data packet was decoded successfully without error at the respective receiving station 4, 6, 12, 16 and 18, whereas the NACK message is a negative acknowledgement message, which indicates that the receiving station sending this NACK message was not able to decode the respective data packet error-free, and therefore requests a retransmission.
- This phase of the feedback phase may also be looked upon as a pre-defined slot or sub- frame in the up-link or down-link p2m control channel, which accompanies the data packet transmission via the p2m data channel. If the transmitting station hears at least one NACK in this phase or slot of the up-link control channel, it knows that a retransmission is required.
- a subset-feedback is defined to be a NACK, whenever the transmitting station 2 receives at least one NACK from one receiving station of a respective subset.
- the subset feedback of subset 16 is defined to be an ACK, if the transmitting station 2 receives an ACK from all receiving stations 12 and 14 in the subset 16.
- the feedback received from a receiving station is mirrored back to other receiving stations by the transmitting station, such that these other receiving stations are informed about the feedback.
- This information may be made such that the feedback of each of the receiving stations is mirrored to all of the other receiving stations.
- this feedback mirroring may also be performed such that the feedback of a subset is mirrored to other subsets, which have not yet sent their feedback.
- the feedback of the last subset, which just became a finished subset is sent back to the other subsets.
- This indication of the subset feedback may be performed in a phase in the downlink frame structure or a slot of the down-link p2m control channel, shortly after the up-link phase in which the last subset sent its feedback. Indicating the subset feedback for a subset in the down-link may only require one single bit (in order to distinguish between ACK and NACK). Thus, according to the present invention, at a given point in time, each unfinished subset is informed about the subset feedback of the subset that last sent its feedback to the transmitting station.
- the subset feedback indicated to the unfinished subsets (via the pre-defined phase in the down-link frame structure after the transmitting station 2 has decoded the subset feedback of the last subset, which sent its feedback or confirmation message) is a NACK
- all members of the unfinished subsets know that a retransmission will occur anyway, so that there is no need to send the feedback, regardless of whether the own feedback is an ACK or an NACK message.
- the unfinished subsets may refrain from sending their own feedback, such that the amount of signalling from these subsets to the transmitting station 2 may be significantly reduced.
- the up-link interference may be reduced.
- the transmission station 2 is adapted such that the transmitting station may initiate a retransmission of the data packets as soon as it receives an NACK, i.e. a negative acknowledgement message from one receiving station or from a subset comprising a plurality of receiving stations. If the transmission station does not initiate a retransmission for a packet as soon as it receives a NACK from a subset of receiving stations, but continues transmitting new packets, it may be important that the receiving stations memorize the mirrored feedback for each received packet, in order to avoid needless feedback messages for packets, for which the mirrored feedback information already indicated that a retransmission will be initiated.
- NACK i.e. a negative acknowledgement message from one receiving station or from a subset comprising a plurality of receiving stations.
- An alternative to this memorizing of feedback information of received packets, for which the transmitting station has not received the subset feedback of all subsets, is the following rule: For each packet, for which the transmitting station receives feedback information, the transmitting station indicates - in the next transmission on the down-link control channel, when the transmitting station is scheduled to indicate received feedback information for this packet to all receiving stations - • a NACK, if the feedback information received so far for this packet was a NACK for at least one subset of receiving stations, and • an ACK, if the feedback information received so far for this packet was an ACK for all of the receiving stations.
- the receiving stations do not need to memorize the mirrored feedback information, and the transmitting station has the freedom not to initiate a retransmission for a packet as soon as it receives a NACK as subset feedback, but can initiate the retransmission also later on. If the retransmission is initiated as soon as the transmission station receives a NACK as subset feedback, this alternative becomes equivalent to the rule that the transmission station mirrors the subset feedback of the subset, that last sent its feedback.
- the current invention may also be looked upon as making the transmitting station indicate - based on subset feedback from the finished subsets of a packet - to the unfinished subsets of a packet, whether the transmitting station still intends to send a retransmission for this packet or not.
- the four subsets 8, 10, 16 and 20 are considered in order to further explain the present invention. These four subsets 8, 10, 16 and 20 are configured to form a multicast group for receiving a point-to-multipoint (p2m) data transmission from the transmitting station 2 to the plurality of receiving stations 4, 6, 12 and 18.
- the transmitting station 2 waits for the subset feedback from the subsets 8, 10, 16 and 20.
- the order of the feedback is prescribed by a feedback scheme.
- the transmitting station 2 firstly waits for the subset feedback from subset 8, then from subset 10, then from subset 16 and then from subset 20.
- a subset feedback relates to the confirmation messages sent from the receiving stations of each subset back to the transmitting station 2.
- the subset feedback is considered to be a NACK.
- the subset feedback ACK Only in the case that all confirmation messages from all receiving stations of a subset are positive acknowledgement messages ACK, is the subset feedback ACK.
- the pre-defined phase in the up-link control channel between the transmitting station 2 and the respective receiving station of the receiving stations 4, 6, 12, 14 and 18 is left free, so that each member of the subset may convey its feedback.
- This phase may be made up of a number of time slots, or in a CDMA system, different channelization codes of the up-link control channel.
- the transmitting station 2 may, directly after having decoded the NACK from the subset 16, initiate the retransmission for P1 without waiting for the subset feedback of the subset 20. According to an aspect of the present invention, after this retransmission, the transmitting station 2 only waits for the subset feedback of those subsets which have not yet sent an ACK, i.e. in the present case for the subset feedback of the subset 16 and the subset 20. Subsets 8 and 10 do not send any feedback, i.e.
- the feedback scheme may be adapted such that, for the retransmission, the feedback scheme assigns phases only to those subsets which have not yet sent an ACK.
- This phase rearrangement in the feedback scheme may be indicated to the receiving stations via the down-link p2m control channel, which may control this retransmission protocol.
- the down-link p2m control channel may be forward error corrected (FEC), which, advantageously, allows that errors on this p2m control channel are extremely rare.
- FEC forward error corrected
- this down-link p2m control channel is advantageous also a p2m channel with no retransmission protocol on top, but a very strong FEC.
- a link between the subset feedback and the transmitted data packet is, according to an aspect of the present invention, given by a pre-defined time difference between the point in time when the data packet being considered was sent, and the point in time when the respective subset sends its feedback.
- the link between the subset feedback and the respectively transmitted packet may be given by a pre-defined time interval between the point in time when the packet was sent and the point in time when the base station indicated in the down-link frame (after the packet transmission) the subset feedback of the last subset which provided its feedback.
- the link may also be based on the time difference between the transmission of the respective data packet and the mirroring of the feedback from the last subset to send its feedback.
- the down-link p2m control channel is adapted to have a strong
- the ACK feedback may be omitted.
- the receiving stations 4, 12, 14 and 18 may be adapted such that they only send a NACK, but not an ACK feedback as confirmation message.
- a receiving station 4, 6, 12, 14 and 18 of a subset which has correctly decoded the data packet, does not send a confirmation message. Only the negative confirmation message, the NACK feedback message, is transmitted if a transmitting station of the subset cannot decode a received data packet.
- This operation mode where instead of one of NACK or ACK is omitted, i.e. no energy is sent at all, may also be referred to as discontinuous transmission (DTX). This may be particularly advantageous in combination with the strong
- FEC of the down-link p2m control channel according to which all receiving stations may at least receive the down-link p2m control channel error-free. Missing the down-link p2m control channel (i.e. not decoding it error-free or not even receiving sufficient energy on it) would mean (together with the definition of DTX as ACK, i.e. no ACK messages), that the transmitting station 2 erroneously assumes that a data packet was received by the receiving station, which missed the down-link p2m control channel, although the data packet was not received, not even decoded.
- the transmitting station sends a continuous stream of packets (including retransmissions)
- a way out of the problem of missing the down-link p2m control channel is making the receiving station send a NACK also, if it misses the downlink control channel during the continuous stream of packets.
- the transmitting station serves different multi-cast groups (which are each decomposed in different sub-sets), in that data transmission is done on a different channelization code or channelization code set for each of the multi-cast groups.
- the omission of ACK messages i.e. the definition of DTX as ACK may allow to reduce the up-link interference, i.e.
- DTX i.e. to adapt the receiving stations such that they only send an explicit ACK feedback and do not send any NACK confirmation messages. If decoding was not successful, according to this aspect of the present invention, the receiving stations will not send any feedback. In this case, missing the down-link p2m data channel does not cause any further problems, since the DTX (i.e. the missing NACK) is interpreted as an NACK by the transmitting station.
- the transmitting station may, depending on the current channel conditions, inform the transmitting stations via the down-link p2m control channel, whether DTX should mean ACK or NACK.
- ACK and NACK use different code words, so that the transmitting station receives an indication whether the receiving stations have understood that DTX means ACK (while there is a code word expressing NACK) or DTX means NACK (while there is a code word expressing ACK).
- DTX means no NACKs, which, however, causes considerable ACK feedback, if channel conditions are good, so that each transmission is acknowledged positively by each receiving station in each subset.
- each receiving station of each subset may have an exclusive time slot or channelization code assigned in accordance with the feedback scheme, to convey its ACK (or DTX).
- DTX means ACK (i.e. no ACKs are sent; only NACKs are sent)
- this "one time slot and one channelization code" design may be sufficient. In other words, a collision of a plurality of NACKs in this one time slot or one channelization code design does not cause any problems for the transmitting station in detecting the correct subset feedback.
- Fig. 2 shows a timing chart of an exemplary embodiment of a method of operating a data transmission system according to the present invention.
- the timing charts depicted in Fig. 2 refer to a data transmission system including three subsets SS1 , SS2 and SS3, each comprising one or more receiving stations.
- the same numbering is assumed for the slots of the p2m data channel and the p2m control channel in Fig.2.
- the ACK messages are indicated with an "A" and the NACKs with an "N".
- the first number designates the serial number of the data packet, to which the feedback message refers, and the second number the serial number of the subset, to which the receiving stations belong, which send the feedback message.
- Reference numeral 30 in Fig. 2 designates the p2m control channel from the transmitting station to the receiving stations.
- Reference numeral 32 designates the p2m data channel for transmitting the data packets from the transmitting station to the receiving stations
- reference numeral 34 designates the up-link (UL) control channel from the receiving stations to the transmitting station.
- a 1-bit sequence number (1-bit-SN) is introduced (indicated in the first line of chart 30) to indicate whether the data packet is a first transmission of new data or a retransmission.
- This 1-bit sequence number is sent as part of the p2m control channel.
- the initial transmission and subsequent retransmissions of the same packet use the same 1-bit sequence number, 1-bit-SN.
- a new transmission of the next data packet is indicated to the receiving stations by toggling the 1-bit sequence number compared with the previous transmission and by this toggling, an on-going transmission for a data packet can be stopped, in other words "be aborted".
- the p2m control channel furthermore indicates to the recipients, the address of the soft buffer (the upper area of the p2m control channel includes the 1-bit SN and the soft buffer address) for which a transmission is planned, since several, i.e. N S
- the soft buffer places may be numbered, where each number represents a soft buffer address.
- Ceil(log2 (N SO ft b u ff er)) bits are needed on the p2m control channel to code all N SOf t uffer soft buffer places, where "Ceil(x)" denotes the smallest integer number, which is greater or equal to x, and log2 is the logarithm with respect to the base of 2. Since the sequence of data packets may change during transmission, according to an exemplary embodiment of the present invention, a packet sequence number (PSN) is sent as part of each packet ("in-band via the p2m data channel") in addition to the 1-bit SN sent on the p2m control channel so that the receiving stations may reconstruct the order of the data packets after decoding the data packets error-free.
- PSN packet sequence number
- the boxes 36 to 88 in the p2m control channel shown in timing chart 30 and in the UL control channel shown in timing chart 34 represent one bit for each subset SS1 to SS3. That means that if this bit is set, this may e.g. indicate to the receiving stations that the corresponding data packet was positively acknowledged by the last receiving subset feedback.
- the link with the data packet is given by the fixed relation between the slot in the p2m control channel (timing chart 30), in which this bit is conveyed, and the slot in the p2m data channel in which the data packet was sent. As may be taken from Fig. 2, the data packet P1 is sent in the (N + 1)-th slot of the p2m data channel (timing chart 32).
- the decoding time necessary for the subset SS1 to decode P1 and send for each subset member the confirmation message contained in A1-1 (box 60), which depicts here the subset feedback, to the transmitting station is the length of one slot. Since the data packet P1 was decoded error-free by all receiving stations of the subset SS1 , the subset feedback A1-1 is an ACK message. Then, as may be taken from Fig. 2, this positive decoding of data packet P1 by the subset SS1 is indicated to the other subsets in the (N + 4)-th slot of the p2m control channel shown in timing chart 30, as indicated in Fig. 2 by box 36.
- the subset feedback A2-1 indicating an ACK message depicted by box 62 in the timing chart 34 indicating the error-free decoding (by all members of SS1) of the data packet P2 sent in (N + 2)-th slot of the p2m data channel shown in timing chart 32 by the subset SS1 is indicated to the other subsets in the (N + 5)-th slot of the p2m control channel shown in timing chart 30, as indicated by box 38.
- the indication of correct decoding of the data packet P1 by the second subset SS2, derived from the subset feedback A1-2 indicating an ACK (box 66), which is sent in the (N + 5)-th slot of the UL control channel shown in timing chart 34 is mirrored, i.e.
- the subset feedback i.e. the ACK A1-3 (box 76) of the third subset SS3 is sent to the transmitting station in the (N + 7)-th slot of the UL control channel shown in timing chart 34. Since there are only three subsets, there is no need to mirror the feedback of the third subset SS3, since this mirrored feedback is of no use for the other subsets.
- the reason for the relatively long distance (in slots) between the transmission of the data packet P1 and the feedback indication in the p2m control channel is due to the time necessary for decoding the packet in each receiving station of each subset, as well as evaluating the received subset feedback in the transmitting station, as well as evaluating the feedback indication in each receiving station. Depending on the decoding speed in the receiving stations and the processing time required in the transmitting station to evaluate the subset feedback, this distance may also be smaller. Since the feedback indication, i.e.
- each slot of the p2m control channel has to accommodate several bits for the feedback indication, one for each subset.
- numbers of subsets -1 bits are necessary; i.e., in Fig. 2, two bits are necessary for the mirroring of three subsets.
- the (N + 6)-th slot of the p2m control channel shown in timing chart 30 carries one bit, i.e.
- Fig. 3 shows timing charts of an exemplary embodiment of a method of operating a data transmission system according to the present invention, where data packets P1 , P2 and P4 need retransmissions.
- the channel structure depicted in Fig. 3 corresponds to the channel structure depicted in Fig. 2.
- Reference numeral 100 designates a timing chart depicting successive slots of the p2m control channel from the transmitting station to the receiving stations.
- the first slot on the left side of the p2m control channel is the (N + 2)-th slot.
- the slot number is incremented by 1.
- the upper area shaded in grey of the (sketchy representation of the) p2m control channel contains the 1-bit-SN and the soft buffer address and the lower area shaded in darker grey shows the indication portion or payload portion of each slot containing one bit (box 106 to 124) for each subset SS1 to SS3.
- a signalling for the respective last i.e.
- Timing chart 102 shows the p2m data channel and the transmission of data packets P1 to P7 in the respective slots.
- Timing chart 104 shows the UL control channel from the receiving stations to the transmitting station. Since the channel structure depicted in Fig. 3 is the same as depicted in Fig. 2, reference is made to Fig. 2 for a further description of the channel structure. Also, as in Fig. 2, the multicast group for which the signalling is depicted in Fig. 3 contains three subsets SS1 to SS3.
- N1-1 (box 126), N2-1 (box 128) and N4-2 (box 140) represent the subset feedback, which is here NACK, from the receiving stations to the transmitting station.
- N1-1 represents the subset feedback (indicating NACK) of the first subset SS1 for the packet sent in the (N + 1)-th slot, i.e. P1.
- N2-1 (box 128) is the subset feedback (indicating NACK) of the first subset SS1 for the packet sent in the (N + 2)-th slot, i.e. P2.
- N4-2 (box 140) is the subset feedback (indicating NACK) of the second subset for the data packet P4 sent in the (N + 4)-th slot of the p2m data channel.
- the subset feedback indicating ACK are depicted with an "A" in the box (boxes 130, 132, 134, 136, 138, 142, 144, 146) whereas the subset feedback indicating NACKs are depicted by "N" (boxes 126, 128, 140).
- the first number in the boxes designates the number of the data packet to which this subset feedback refers and the second number indicates the subset SS1 to SS3 to which the subset feedback refers.
- two bits, i.e. ("number of subset" - 1) bits are a sufficient payload size for the p2m control channel for a multicast group containing three subsets.
- this number of feedback indication bits in the p2m control channel is even sufficient in the case that a retransmission of data packets is necessary.
- Fig. 1 two bits, i.e. (“number of subset" - 1) bits are a sufficient payload size for the p2m control channel for a multicast group containing three subsets.
- the packet P1 sent in the (N + 1)-th slot of the p2m data channel is unsuccessfully decoded by the first subset SS1 , such that the NACK messages are sent from the members of the first subset to the transmitting station via the UL control channel.
- This is depicted by the subset feedback N1-1 (box 126) of the first subset to the transmitting station via the UL control channel.
- the transmitting station mirrors this NACK as N1-1 (box 106) to the other subsets and therewith to the other receiving stations in the (N + 4) -th slot of the p2m control channel.
- the transmitting station retransmits the data packet P1 in the (N + 5)-th slot of the p2m control channel, as indicated by P1 ⁇
- retransmissions for a data packets are indicated by a " ' ". They can be exact copies of the initially transmitted packet (then they are called retransmissions of the packet), or can contain e.g. only additional parity bits (which covers the case of non-self-decodable incremental redundancy) or e.g.
- the p2m control channels may also carry information with respect to a redundancy version of a retransmission, if, for example, the Chase Combining (i.e. the retransmission for a data packet is an exact copy of the initial transmission) is not used, i.e. if self-decodable and non-self-decodable redundancy transmission schemes are applied.
- the Chase Combining i.e. the retransmission for a data packet is an exact copy of the initial transmission
- they may also carry CRC (Cyclic Redundancy Check) bits, which are also not shown in Figs. 2 and 3.
- the modulation and coding scheme may also be indicated via the p2m control channel to the receiving stations, if different modulation and/or coding schemes are to be applied, as well as an indication of the number of user-bits (i.e. uncoded), which are carried within one packet (so-called "transport block size"), so that the receiving side may derive from the number of coded bits it receives, which puncturing scheme was applied.
- transport block size an indication of the number of user-bits (i.e. uncoded), which are carried within one packet
- the mirrored subset feedback on the p2m control channel may be sent as the first part of the corresponding slot of the p2m control channel and may be protected with a separate CRC, different from the CRC of the other information carried on the p2m control channel, in order to allow for a very fast decoding of the subset feedback by the receiving stations without the other information carried on the p2m control channel. If CDMA technology is applied, this part of the p2m control information could also be sent on a different channelization code or code set.
- an indication of the used channelization codes may also be carried out via the p2m control channel. If the p2m control channel is used for controlling transmissions to several multicast groups, wherein each multicast group is organized in different subsets, the p2m control channel may also contain an identification of the respective multicast group.
- the slots of the p2m control channel are shifted in time to the left side with respect to Figs. 2 and 3.
- an improved delay reduction may be achieved, if the assignment of receiving stations to the subsets is performed in such a way that receiving stations which have a high likelihood of needing several retransmissions are within the same subset and/or within the first ones of the subsets scheduled to send their feedback to the transmitting station in accordance with the feedback scheme. Then, NACKs would be received at the earliest point in time, which allows that retransmissions may be initiated at the earliest possible point in time.
- An assignment to the subsets could be done explicitly by means of a configuration message sent to each receiving station.
- each mobile phone has a unique subscriber identity (IMSI: International Mobile Subscriber Identity). From its IMSI, each mobile phone may compute the subset to which it belongs, if it only knows the number of subsets which are to be configured. This number of subsets to be configured N SUb s ets , according to an aspect of the present invention, is indicated to the mobile phone (i.e. the receiving stations) e.g.
- IMSI International Mobile Subscriber Identity
- a further reduction of the up-link interference may be achieved, if only those recipients in a subset send their feedback, which have moderate or bad channel conditions, but not receiving stations which have good channel conditions. This may then be evaluated locally in each station, and each station itself would take the decision to send feedback or not.
- the alternative of conveying measurement results for the perceived channel conditions may be efficient in some cases.
- a TDD (Time Division Duplexing) system in a TDD (Time Division Duplexing) system, it may not be necessary to provide the feedback via the p2m control channel, since receiving stations may hear the up-link transmission of other stations, since up-link and down-link share the same frequency band, and hence may get to know the subset feedback by this means. However, even in such a case, it may be advantageous to let the transmission station or base station mirror the feedback, since it is not guaranteed that all receiving stations of the multicast group can hear all of the other members of the multicast group.
- Fig. 4 shows details of a possible implementation of an exemplary embodiment of a method according to the present invention.
- the third generation partnership project in the following referred to as "3GPP", is currently working on the design of an MBMS (Multimedia Broadcast Multicast Services) bearer service, which aims at distributing multimedia contents to UEs (user equipments or receiving station) in UMTS radio cells via the UMTS radio interface rather than broadcast channels of terrestrial broadcast companies.
- MBMS Multimedia Broadcast Multicast Services
- UEs user equipments or receiving station
- a p2m-channel is to be used, meaning that the MBMS content is sent once on a single physical resource, and received on this physical resource by all UEs in the radio cell, which have joined the service.
- a simple broadcast channel similar to the FACH (Forward
- transport blocks are convolutionally or turbo coded as in Release 99, and a number of coded transport blocks is then arranged under each other so that a matrix of bits results, and the bits of a column are encoded by means of a block code.
- code concatenation is described, for example, in R2- 032157, Outer coding for MBMS, Technical document published on RAN2#38, which is hereby incorporated by reference.
- TrCH transport channel
- R1 -030086 states that with 40 MBMS users, about 1% of the users need 4 or more retransmissions. Applying STTD (Space-Time Transmit Diversity) in addition, about 1% of the users need 3 or more retransmissions. For 80 MBMS users and STTD the figure is a bit worse, i.e. 1- 2% of the users need 3 or more retransmissions.
- the fraction of users needing only one retransmission is between 20% and 30%, and the fraction for a higher number of retransmissions decreases with the number of retransmissions, as expected.
- the main problem of incremental redundancy retransmission schemes is the fact that they need feedback from the recipients on whether a retransmission is required or not.
- a decomposition of the group of recipients into subsets is described, where the members of a subset are assigned an uplink slot or phase, in which they can send, for a considered packet received in the downlink, their feedback. Since different subsets have different uplink slots or phases, it is possible to mirror feedback (i.e. a NACK) received e.g. from the first subset to all remaining subsets, so that the recipients of the remaining subsets do not send a NACK, since anyway a retransmission for this packet is going to come.
- a NACK mirror feedback
- Fig. 4 depicts a schematic representation of a possible implementation of the concept of a method according to the present invention, as it would be necessary in order to apply the scheme in UMTS with little modification. In particular, the method depicted in Fig.
- NACKs of different subsets or groups i.e. from different recipients
- the NACKs of members of the same subset or group superimpose at the NodeB. This is in particular important, if the NACK energy e.g. sent by the recipients in subset 1 was not sufficient, i.e. NodeB did not detect a NACK, and some recipients in subset 2 also need a retransmission and therefore send a NACK.
- FIG. 4 shows an efficient scheme for assigning UL slots or phases to the subsets in order to minimize the amount of buffering of downlink data, which is necessary in order to allow for a continuous DL stream even if retransmissions have to be sent, and at the same time provides enough processing time for the NodeB to process the feedback received from a subset before sending a blocking indication (if any) and the recipients (UEs) to read the DL slot or phase, in which a blocking indication can be sent. It is further explained, how power ramping can be employed at the same time. Furthermore, strategies for assigning the different recipients (UEs) to the subsets are described.
- a p2m-control channel is assumed to provide the recipients at least with information about - whether the packet sent in a DL frame contains new data or is a retransmission (New Data Indicator as known from the HS-DSCH) - which type of incremental redundancy is carried in the packet, if it is not a new transmission (this information can be missing, if only Chase Combining is used) - for which soft buffer the transmitted packet is addressed to. (known as the HARQ process in case of the HS-DSCH)
- the packets are then sent on the p2m-data channel.
- Fig. 4 shows the proposed scheme with 8 different subsets of UEs.
- the members of the first subset try to decode the data packet A, and if at least one member cannot decode packet A successfully, it will send a NACK on the CNFCH (Common NACK feedback channel) in the slot assigned for SS1 with respect to packet A.
- the CNFCH is a channel, to which any member of a subset has access during the time slot assigned for this subset, to send a NACK, if this member needs a retransmission.
- a NACK may be just a repetition-coded bit, e.g. a "+1"-bit.
- the relationship between a packet sent in the DL and the slot of the CNFCH to use for NACK transmission is pre-defined as follows (as shown in Fig. 4):
- the first slot of the CNFCH in each frame refers to the packet whose transmission in the DL started by the interval of length ⁇ 1 before the considered frame of the CNFCH starts, and it can be used by the members of SS1.
- the second slot of the CNFCH in each frame refers to the packet whose transmission in the DL started by the interval of length ⁇ 1 plus 1 frame length (here 10 ms). It can be used by the members of SS2 for the packet, to which the slot refers to.
- NodeB knows that it should initiate a retransmission for packet A, which is denoted here as A'. It is called a retransmission for packet A, since A' can be an exact copy of A (i.e. combining would be done in the Chase Combining fashion) or A' can contain a different, self-decodable version of A (i.e.
- this number N 1+2 of packets, which have to be stored, could be reduced to N1+1 , if decoding of a packet went so fast that ⁇ 1 - 'frame length", wherein "frame length" is the interval, which is needed to transmit one packet via the downlink p2m-data-channel; in Fig. 4 this frame length is assumed to be equal to 10ms. If the decoding time is more than one frame length , but smaller than two frame lengths, N1+3 packets will have to be stored in order to keep the stream of packet transmissions continuous.
- the 8 packets A, B, ... , J are stored as soft bits, i.e. systematic bits and parity bits quantized with e.g. 4 bits.
- A' can be inserted earlier e.g. instead of C, if the feedback transmission of the SS1 already causes NodeB to detect a NACK.
- the p2m-feedback-mirror-channel would indicate to the remaining subsets (SS2, SS3, ...
- the corresponding slot (relating to a transmitted packet) on the p2m- feedback-mirror-channel is also predefined in a similar manner as the slots in the CNFCH: As shown in Fig. 4, this slot is the first in the frame of the p2m- feedback-mirror-channel, which frame starts by the interval ⁇ 3 after the transmission of packet A in the DL (to which it refers) began.
- NACKs of different subsets If some members of SS1 send NACKs (which NACKs superimpose since they are sent in the same slot) in the first slot of the CNFCH refering to packet A, which cannot be detected by NodeB, the p2m-feedback-mirror-channel would not indicate blocking of NACK transmissions for the remaining subsets. If there are members in one or more of the remaining subsets, which need a retransmission for packet A, they will then also send NACKs (which superimpose).
- the soft bits of the NACKs sent by some members of SS1 and the soft bits of the NACKs sent by some members of remaining subsets can be soft-combined in the same manner, as the individual soft-bits sent in one slot:
- the simplest way is to compute the mean value of the soft-bits to obtain a better estimate of what was actually sent (a NACK or nothing).
- this can be applied, if no members of SS1 send a NACK, but some members of SS2 send a NACK and some members of the remaining subsets send a NACK (unless NodeB blocks transmission of NACKs, since it has already detected the NACK.
- TX power (dB) Pdetect (dB) - "observed pathloss" (dB), where "observed pathloss" is counted as negative, i.e. TX power is increased by the absolute value of "observed pathloss", i.e. the TX is given by the power, which is required for NodeB to decode the signal as a NACK, if the path loss is (nearly) 0, increased by the factor, which compensates for the path loss. This would normally cause a TX power, which suffices to detect the NACK of only one UE.
- the goal is to maximize the number of satisfied users while at the same time reducing the required DL TX power for transmitting the packets.
- N2 represents the number of UEs, which as a minimum have to send a NACK so that a retransmission is actually initiated. Since the NACKs of the members of the same subset are transmitted in the same slot, they superimpose.
- each of these UEs has to reduce the above TX power value by a factor of N2, so that these N2 transmissions add to a sufficiently high received power at the NodeB, to make NodeB detect a NACK. This is, however, only an approximation. It could well be that a bit more than N2 or a bit less than N2 UEs have to send a NACK so that this is actually detected at NodeB.
- TX power (dB) Pdetect (dB) - "observed pathloss” (dB) - N2 (dB), where "observed pathloss" is counted as negative, i.e. TX power is increased by the absolute value of "observed pathloss", and TX power is decreased by the factor N2.
- NodeB broadcasts the number N1 of subsets, which are available (in the above example 8), and each UE that wants to receive the MBMS content computes the subset number by a modulo operation applied to its IMSI: IMSI mod N1. This would usually suffice to reach an equal distribution of UEs to the subsets. Instead, it is also possible that each UE draws a random number "rand" between 0 and 1. The interval between 0 and 1 is partitioned into N1 subintervals of equal length, and they are numbered from 1 to N1.
- the number of the interval, to which "rand” belongs determines the number of the subset to which the UE belongs. This technique could be extended in such a way that the count of UEs in a subset differs, which would be done by making the sub-intervals different in length. This can be helpful for keeping the interference low, if the the count of members of the different subsets obeys the following relation: Count of members in SS1 ⁇ Count of members in SS2 ⁇ Count of members in SS3 ⁇ ...
- the relative size of the subsets can additionally be taken into account when determining the TX power for the NACK in the sense that the factor N2 is modified based on the relative size of the subsets (for a smaller subset, it could be necessary to use a reduced value (reduced relative to the relative subset size) of N2 in the formula for computing the TX power, since due to the smaller subset, the chance is lower that there are sufficient UEs that need a retransmission.
- the relative member count of the subsets would preferably not be broadcast, but be made available implicitly, e.g. when the UE joins the service. In addition, it is possible to base, at least to some extent, the assignment to the subset on the perceived path loss.
- the idea behind this is, that UEs with only a small path loss usually have good channel conditions, and therefore would in most cases be able to decode the packet error-free. In contrast to this UEs with a higher pathloss would more often need a retransmission.
- the group with UEs perceiving a path loss below T1 are assigned to the first subset, i.e. they are allowed to send their NACKs before the UEs of the other group, assigned to the second subset.
- the first 4 subsets contain UEs, that face a path loss lower than T1 (i.e. they are the UEs more "distant" from the NodeB) and the second 4 subsets contain UEs, that face a path loss not lower than T1.
- the parameter T1 is a network planning parameter, which could be broadcast to the UEs in a cell. Also within these 4 subsets each, it can be beneficial to make sure that the subset sizes are different.
- N1 slots in the CNFCH can also be used for power ramping the TX power, however depending on the slot, in which a subset is allowed (or more precisely: the members of a subset are allowed) to send a NACK, the number of power ramping steps is changed: Since the first subset is followed by further N1-1 slots, in which members of other subsets can send their NACKs, these subsets can be used to send the subset feedback of the first subset with increased power. For the members of the second subset, only N1-2 further slots are available for the ramping, and so on. Only the last subset cannot power ramp.
- the essential benefit of power ramping lies in the fact that it helps to keep the TX power until a NACK is actually detected lower than without power ramping. Due to the fact that the number of ramping steps depend on the number of the subset, to which a UE is assigned, the best strategy may be to let the initial TX power (before ramping up) increase with increasing subset serial number. Also it may also be possible to only use some of the slots in consecutive following CNFCH frames for repeating NACK transmission of a particular subset (of recipients) with higher TX power. This has the advantage, that there is an additional opportunity for the later subsets to convey their NACKs and for the NodeB to actually detect the NACK, before the NACK transmission of an earlier subset is repeated at higher TX power.
- Amount of soft buffer memory Applying the current frame format of the FACH (as defined in TS 25.211 , 3GPP specification, which is hereby incorporated by reference) as a guideline for the number of bits, that can be carried via the p2m-data-channel, the following numbers of L1 bits have to be stored in the soft buffer:
- the packet size could be increased to a duration of 20ms, in which case the number of soft bits to be stored increases by a factor of 2, while at the same time relaxing the timing requirement D3-D1 , which is 3.75 ms in Fig. 4.
- Probing to estimate the number of users sending a NACK If the number of UEs receiving MBMS content in one cell is very big, a retransmission protocol with feedback may be inefficient in the sense, that anyway the data has to be sent with a relatively high power to achieve an acceptably big group of satisfied users, which is only marginally increased by a retransmission mechanism.
- the Node B may estimate the number of UEs that receive the MBMS content in a period of time by asking all these UEs to send a NACK (where each UE sets the NACK TX power based only on the pathloss).
- the NACK transmissions superimpose and cause a peak in the NodeB, which can be used as a rough measure for the number of UEs receiving the MBMS content. If the number of UEs is so high that a retransmission protocol would be inefficient, the NodeB indicates via the downlink to the UEs that they must not send any NACKs or feedback messages in case they find out that they miss a packet.
- This indication is different from the other indication (carried on the p2m-feedback-mirror-channel) that UEs belonging to later subsets should not send a further NACK, because the NodeB is going to send a retransmission anyway.
- This other indication means that a retransmission for a packet will be scheduled.
- the indication that the recipients should not send any feedback messages can not be sent via the p2m-feedback-mirror-channel. Instead, it could be included in the system information broadcast relevant for MBMS content delivery, and UEs have to first retrieve this system information in order to know, whether the NodeB is ready to process feedback messages or delivers MBMS content without performing retransmissions.
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Abstract
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Priority Applications (9)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2006523079A JP4516076B2 (en) | 2003-08-15 | 2004-08-04 | Multicast data transmission method, data transmission system, transmitting station and receiving station |
EP04744269A EP1656765B1 (en) | 2003-08-15 | 2004-08-04 | Feedback signalling for multicast data transmission |
US10/568,015 US8675616B2 (en) | 2003-08-15 | 2004-08-04 | Feedback signalling for multicast data transmission |
AT04744269T ATE485652T1 (en) | 2003-08-15 | 2004-08-04 | FEEDBACK SIGNALING IN A MULTICAST DATA TRANSMISSION |
DE602004029687T DE602004029687D1 (en) | 2003-08-15 | 2004-08-04 | Feedback signaling in a multicast data transmission |
KR1020067003167A KR101168382B1 (en) | 2003-08-15 | 2004-08-04 | Feedback signalling for multicast data transmission |
CN2004800233881A CN1836401B (en) | 2003-08-15 | 2004-08-04 | Feedback signalling for multicast data transmission |
US14/218,396 US9775005B2 (en) | 2003-08-15 | 2014-03-18 | Feedback signalling for multicast data transmission |
US15/699,550 US10225696B2 (en) | 2003-08-15 | 2017-09-08 | Feedback signaling for multicast data transmission |
Applications Claiming Priority (4)
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TWI371179B (en) | 2012-08-21 |
DE602004029687D1 (en) | 2010-12-02 |
KR20060081693A (en) | 2006-07-13 |
CN1836401A (en) | 2006-09-20 |
US20060291410A1 (en) | 2006-12-28 |
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