WO2010055364A1

WO2010055364A1 - Harq feedback scheduling method and apparatus thereof

Info

Publication number: WO2010055364A1
Application number: PCT/IB2008/003687
Authority: WO
Inventors: Stephen Kaminski; Yu YONG; Fu XIAO
Original assignee: Alcatel Lucent; Alcatel Shanghai Bell Ltd. Co.
Priority date: 2008-11-12
Filing date: 2008-11-12
Publication date: 2010-05-20

Abstract

The invention relates to a method for generating feedback scheduling in a network element of a mobile communication system with HARQ feedback, the method comprising: defining a scheduling window size, wherein the scheduling window size indicates an amount of downlink packets within a number of downlink subframes; defining a first parameter indicating a number of HARQ acknowledgement indications for the scheduling window size; defining a second parameter indicating a maximum number of HARQ acknowledgements combined into each HARQ acknowledgment indication for downlink packets of the scheduling window size.

Description

HARQ feedback scheduling method and apparatus thereof

D e s c r i p t i o n

Field of the invention

The invention relates to a method for generating HARQ feedback scheduling, to a network element and to a computer program product.

Background and related art

Hybrid automatic retransmission request (HARQ) is a variation of the automatic retransmission request (ARQ) error control method. In ARQ, error-detection information bits are added to data to be transmitted (such as the cyclic redundancy check, CRC). In hybrid ARQ, forward error correction bits are also added to the existing error detection bits (such as the turbo codes). In a possible implementation of HARQ, the transmitter adds both error-detection information and forward error correction information to each message prior to transmission. When the coded data block or code word is received, the receiver first decodes the error-correction code. If the channel quality is good enough, all transmission errors should be correctable, and the receiver can obtain the correct data block. If the channel quality is bad, and not all transmission errors can be corrected, the receiver will detect this situation using the error-detection code, then the received coded data block is discarded and a retransmission is requested by the receiver, similar to ARQ.

Summary of the Invention

One of the advantages of the invention is that it allows a reduction of the signaling for the application of hybrid automatic repeat request (HARQ) feedback method. The new scheme combines two previous schemes and provides a balancing of coverage and throughput by having more than one feedback indication, but each of them being formed by a logical AND operation of one or more feedback indications. The embodiments allow setting predefined rules according to which the mobile station can evaluate autonomously the exact scheme how it produces feedback indications. These rules define all of the following information which in other way it would have to be signaled. The network element only requires to define or receive a first parameter and a second parameter in order to define the feedback scheme. Once the feedback scheme is set, it remains until it is changed again, even if the size of the scheduling window changes. It depends on many parameters such as e.g. The availability of user data and the radio channel quality.

In an embodiment, the first and second parameter are transmitted to a mobile station for defining the HARQ acknowledgement indications. In a further embodiment, the network element is a mobile station.

In an embodiment, the first and second parameter are higher than one, wherein the method further comprises: storing a previous selected feedback scheme; wherein the previous selected feedback schemes is at least one of: multi-bit scheme, bundled scheme, wherein the multi-bit scheme comprises a second parameter equal to one, wherein the bundled scheme comprises a first parameter equal to one, wherein the method further comprises: setting a current feedback scheme to combined scheme. In a further embodiment, the first and the second parameters are equal to two, if the scheduling window size is equal to one of three or four.

In a further embodiment, the first parameter is equal to three and the second parameter is equal to two, or the first parameter is equal to two and the third parameter is equal to three, if the scheduling window size is equal to one of five or six.

In another embodiment, the first parameter is equal to four and the second parameter is equal to two, or the first parameter is equal to two and the third parameter is equal to four, if the scheduling window size is equal to one of seven or eight.

In a further embodiment, the first and the second parameters are equal to three, if the scheduling window size is equal to nine.

In a further embodiment, the first and second parameters are selected for maximizing a normalization of the number of downlink packets combined into each HARQ acknowledgements, wherein the first and second parameters of the combined scheme are not allowed, if the parameters are similar to one of the multi- bit and the bundled schemes.

In another embodiment, the first and the second allowed parameters defined are similar to the first and second parameters of the previous selected feedback scheme.

In a further embodiment, the first and the second allowed parameters defined are most different to the first and second parameters of the previous selected feedback scheme.

In another aspect, the invention relates to a method for generating feedback scheduling in a mobile station coupled to a mobile communication system with HARQ feedback, the method comprising: receiving a scheduling window size, wherein the scheduling window size indicates an amount of downlink packets received within a number of downlink subframes; receiving a first parameter indicating a number of HARQ acknowledgement indications for the scheduling window size; receiving a second parameter indicating a maximum number of HARQ acknowledgements for downlink packets of the scheduling window size combined into each HARQ acknowledgment indication.

In another aspect, the invention relates to a network element for generating feedback, the network element being operable to perform in accordance with any one of the preceding embodiments.

In another aspect, the invention relates to a mobile communication system for generating feedback, the mobile communication system being operable to perform in accordance with any one of the preceding embodiments.

In another aspect, the invention relates to a computer program product stored on a storage medium, comprising executable program means for causing a network element to perform a method according to any of the preceding embodiments when the program is run on the network element

Brief description of the drawings

In the following preferred embodiments of the invention will be described in greater detail by way of example only making reference to the drawings in which:

Figure 1 shows a first and a second embodiment of a mobile communication system,

Figure 2 shows a first approach of the first and the second parameters,

Figure 3 shows a reduced set of the first and second parameters in the

HARQ indications notifications, Figure 4 shows a predefined selection method of the first and second parameters,

Figure 5 shows a method in accordance with the embodiments.

Detailed description

Fig. 1a shows a first embodiment of a mobile communication system 100a comprising a network element 101a. The network element 101a comprises means for defining 102 a scheduling window size, wherein the scheduling window size indicates an amount of downlink packets 103 and 104 received with a number of downlink subframes. The network element 101a further comprises means for defining 105 a first parameter 106 indicating a number of HARQ acknowledgement indications 107 and 108 for the scheduling window size. The network element 101a further comprises means for defining 109 a second parameter 110 indicating a maximum number of HARQ acknowledgements combined into each HARQ acknowledgement indication 107 and 108 for downlink packets of the scheduling window size. The network element 101a may further comprise a computer program product 111 stored on the storage medium comprising executable program means for causing the network element 101a to perform a method according to any of the embodiments.

The first and the second parameters 106 and 110 may be transmitted to a mobile station 112a for defining the HARQ acknowledgement indications, including how many HARQ acknowledgements are combined into each HARQ acknowledgement indication.

Fig. 1b shows a second embodiment of a mobile communication system 100b comprising a network element 101 b and a mobile station 112b. The mobile station 112b comprises means for defining 113 a scheduling window size, wherein the scheduling window size indicates an amount of downlink packets 103 and 104 received with a number of downlink subframes. The mobile station 112b further comprises means for defining 114 a first parameter 106 indicating a number of HARQ acknowledgement indications 107 and 108 for the scheduling window size. The mobile station 112b further comprises means for defining 115 a second parameter 110 indicating a maximum number of HARQ acknowledgements combined into each HARQ acknowledgement indication 107 and 108 for downlink packets of the scheduling window size. The mobile station 112b may further comprise a computer program product 116 stored on the storage medium comprising executable program means for causing the mobile station 112b to perform a method according to any of the embodiments.

The first parameter 106 and the second parameter 110 are higher than 1 and the current feedback scheme corresponds to a combined scheme. Further feedback schemes that may be available in the mobile communication system are the multi-bit scheme, and the bundle scheme. In the multi-bit scheme the second parameter is equal to 1 and therefore there is a HARQ acknowledgement indication for each downlink packet.

In the case of the bundled scheme, the first parameter is equal to 1 and therefore a HARQ acknowledgement combines all HARQ acknowledgement indications for the total of the scheduling window size.

Fig. 2 shows a representation of chosen groups of first and second parameters for different scheduling window sizes from 1 to 9. The representation of the first and the second parameters includes the multi-bit feedback scheme 201 , the bundle feedback scheme 202 and the combined feedback scheme 203. If the number of scheduling downlink subframes is equal to 2, meaning a scheduling window size of 2, there is no specific first and second parameter combination available for the combined feedback scheme 202. When the window size equals 2, the multi-bit feedback scheme 202 corresponds to a first parameter equal to 2 and a second parameter equal to 1 and for the bundle feedback scheme the first parameter is equal to 1 and the second parameter is equal to 2.

When the scheduling window size is equal to 3 or to 4, the multi-bit feedback scheme 201 corresponds to a combination of the parameters (3,1) and (4,1) respectively. In the case of the bundled feedback scheme 202, the combination of the parameters equals (1 ,3) and (1,4) when the scheduling window size is 3 and 4 respectively. As the combined feedback scheme 203 the first and second parameters are bigger than 1 , the only remaining values for the parameters when the number of the schedule downlink subframes is equal to 3 or to 4 is using a combination of (2,2) for both the first and second parameter.

For bigger scheduling window sizes, especially the window size from 7 up to 9, the possible numbers of combined feedback scheme 203 is increased, and for the scheduling window size equal to 9, a set of reasonable combinations of parameters includes five possible combined feedback scheme combinations. Therefore, it may be important to restrict the usage of the combined scheme to one or two of these alternative parameter combinations.

The sequence of used downlink subframes is not necessarily consecutive, as there might be for example unused downlink subframes in between the used subframes. As an example, in Long Term Evolution (LTE) Time Division Duplex, the number of consecutive downlink subframes depends on the configuration, for example this plate of downlink and uplink subframes, and can be up to 9. In the case that the mobile station sends the combined HARQ acknowledgement, is already with information of the scheduling window size from the number of downlink grants that the mobile station receives via one of the common channels for example the PDCCH. Therefore, in case that the parameters are sent from the network element to the mobile station, there is no need to transmit the scheduling window size.

Fig. 3 shows a second presentation of the different parameter combinations for the multi-bit HARQ feedback scheme, the bundle HARQ feedback scheme and the combined HARQ feedback scheme. This new combination of parameters, refers to a reduced version of the possible combined feedback schemes for each scheduling window size.

The closer a set of parameters of the feedback is to one of the other feedback schemes, multi-bit or bundling schemes, the less adapted it is to use such a combination in a predefined method within the combined feedback scheme. For example, the combined scheme of parameters (5,2) is similar to the multi-bit feedback scheme, as it contains five indications, each of which is generated for only a few, maximum 2 downlink subframe feedbacks. On the other hand, the combined tuple (2,5) is close to the bundle feedback scheme, as it contains only two indications, each of which is formed out of many bundled downlink subframe feedbacks.

For the case of 9 downlink subframes (a scheduling window size of 9), the parameters combinations (3,3) is the best choice for the combined feedback, as it perfectly uses the available 3 indications for each 3 combined downlink subframe feedbacks. In case of 8 downlink subframes, the bits can ideally be used for (4,2) combined indications, for example the parameter combination (4,2) or (2,4) combined indications representing (2,4) in the parameters. Although theoretically applicable, the parameter combinations (3,3) would not fit as perfect because there is a variation of the number of combined feedbacks in one of the 3 bits. Therefore, here only 2 of the 3 indications consist of three combined feedbacks, and the remaining third indication consists of only 2 combined feedbacks.

Therefore, the first and the second parameters of the combined scheme are selected for maximizing a normalization of the number of downlink packets combined into each HARQ acknowledgement. The first and second parameters of the combined scheme are not allowed, if the parameters are similar to one of the multi-bit and the bundle schemes, especially for the cases when the scheduling window size is bigger than 7.

As it can be seen in fig. 3, the combinations of the parameters for the scheduling window size from 5 up to 8, there are two possible and reasonable combined HARQ feedback schemes that may be used. Therefore, the next fig. 4 shows a possible embodiment of the selection of one of these possible combined parameters.

Fig. 4 shows two possible embodiments on the decision of which combination of parameters will be used according to the previous selected feedback scheme. In the first chart 401 , the scheduling window size is equal to 6 and as shown on fig. 3, there are two possible combinations for the combined feedback scheme. If the selection corresponds to the first transmission of information, the combination (2,3) is the more robust one, as it has the higher coverage of the two alternatives. If on the other hand, another feedback scheme has been applied in a previous transmission, the selected tuple depends on the previously used feedback scheme. For the fig. 401, the redefinition implies that the closer scheme to the previous selected feedback scheme is applied and the combination (3,2) will be used if the previous feedback scheme was multi-bit, and the combination (2,3) will be applied if the previous scheme was bundled feedback.

In both figs. 401 and 402, the signaling for the feedback scheme selection of 2 bits is defined as 00 for combined feedback, 01 for multi-bit feedback, 10 for bundle feedback and 11 when there are no changes. These bits are only used as examples to show the possible method for the selection of the combined parameters.

The chart 402 shows the selection algorithm if the scheduling window size is equal to 4. If the previous selected feedback scheme is for example (4,1), that corresponds to a multi-bit feedback scheme depending on the signaling, the feedback scheme may switch to a combined feedback scheme of (2,2) if the 2 bit signal is 00 or to a bundled feedback scheme if the signal corresponds to 10. In the same way, the signaling may occur in each of the possible feedback schemes. In general, the signaling for feedback schemes is required in any case, so that the embodiments do not require additional signal for the predefined combination selection method.

Once the feedback scheme is set, it remains the current feedback scheme until it is changed again, even if the size of the scheduling window size changes. The mobile station may autonomously apply the combination corresponding to the current scheduling window size within the signal feedback scheme. The specific combination or tuple to be used by the mobile station may be configured before the transmission of user data and may also be changed during the lifetime of a connection.

Fig. 5a shows a method 500 for generating a feedback scheduling in a network element of a mobile communication system with HARQ feedback. The method comprises in a first step 501 defining the scheduling window size, wherein the scheduling window size indicates an amount of downlink packets within the number of downlink subframes. In a second step 502, defining a first parameter indicating a number of HARQ acknowledgement indications for the scheduling window size. In a third step 503, defining a second parameter indicating a maximum number of HARQ acknowledgements combined into each HARQ acknowledgement indication for downlink packets of the scheduling window size.

Fig. 5b shows a method for generating a feedback scheduling in a mobile station coupled to a mobile communication system with HARQ feedback. The method comprising in a fourth step 504, receiving a scheduling window size, wherein the sched- uling window size indicates an amount of downlink packets received within the number of downlink subframes. In a second step 505, receiving a first parameter indicating a number of HARQ acknowledgement indications for the scheduling window size. In a third step 506, receiving a second parameter indicating a maximum number of HARQ acknowledgements for downlink packets of the scheduling window size combined into each HARQ acknowledgement indication.

List of reference numerals

Claims

C l a i m s

1. A method (500) for generating feedback scheduling in a mobile station (112a, 112b) coupled to a network element (101a, 112b) of a mobile communication system (100a, 100b) with HARQ feedback, the method comprising:

- defining (501) a scheduling window size at said network element (101a, 112b), wherein said scheduling window size indicates an amount of downlink packets within a number of downlink subframes;

- defining (502) a first parameter (106) at said network element (101a, 112b) indicating a number of HARQ acknowledgement indications (107, 108) for said scheduling window size;

- defining (503) a second parameter (110) at said network element (101a, 112b) indicating a maximum number of HARQ acknowledgements combined into each

HARQ acknowledgment indication for downlink packets of said scheduling window size.

2. The method of claim 1 , wherein said first (106) and second parameter (107) are transmitted to a mobile station for defining said HARQ acknowledgement indications.

3. The method of claim 1 and 2, wherein said network element is a mobile station (112a).

4. The method of claim 1 and 2, wherein said network element is a base station (101a).

5. The method of any of the preceding claims, wherein said first and second parameter are higher than one, wherein the method further comprises: storing a previous selected feedback scheme; wherein said previous selected feedback schemes is at least one of: multi-bit scheme (301), bundled scheme (303), wherein said multi-bit scheme (301) comprises a second parameter equal to one, wherein said bundled scheme (303) comprises a first parameter equal to one, wherein the method further comprises: setting a current feedback scheme to combined scheme.

6. The method of any of the preceding claims, wherein said first and said second parameters are equal to two, if said scheduling window size is equal to one of three or four.

7. The method of any of the preceding claims, wherein said first parameter is equal to three and said second parameter is equal to two, or said first parameter is equal to two and said third parameter is equal to three, if said scheduling window size is equal to one of five or six.

8. The method of any of the preceding claims, wherein said first parameter is equal to four and said second parameter is equal to two, or said first parameter is equal to two and said third parameter is equal to four, if said scheduling window size is equal to one of seven or eight.

9. The method of any of the preceding claims, wherein said first and said second parameters are equal to three, if said scheduling window size is equal to nine.

10. The method of any of the preceding claims, wherein said first and second parameters are selected for maximizing a normalization of said number of downlink packets combined into each HARQ acknowledgements, wherein said first and second parameters of said combined scheme are not allowed, if said parameters are similar to one of said multi-bit and said bundled schemes.

11. The method of any of the preceding claims, wherein said first and said second allowed parameters defined are similar to said first and second parameters of said previous selected feedback scheme.

12. The method of claims 1 to 9, wherein said first and said second allowed parameters defined are most different to said first and second parameters of said previous selected feedback scheme.

13. A method (500a) for generating feedback scheduling in a mobile station coupled to a mobile communication system with HARQ feedback, the method comprising:

- receiving (504) a scheduling window size, wherein said scheduling window size indicates an amount of downlink packets received within a number of downlink subframes;

- receiving (505) a first parameter indicating a number of HARQ acknowledgement indications for said scheduling window size;

- receiving (506) a second parameter indicating a maximum number of HARQ acknowledgements for downlink packets of said scheduling window size combined into each HARQ acknowledgment indication.

14. A base station (101a) for generating feedback, the base station (101a) being operable to perform in accordance with any one of the preceding claims 1 to 2 and 4 to 12.

15. A mobile station (112a) for generating feedback, the base station (112a) being operable to perform in accordance with any one of the preceding claims 1 to 3 and 5 to 13.

16. A mobile communication system (100a, 100b) for generating feedback, the mobile communication system being operable to perform in accordance with any one of the preceding claims 1 to 11.

17. A computer program product (111 , 116) stored on a storage medium, comprising executable program means for causing a network element to perform a method according to any of the preceding claims 1 to 11 when the program is run on the network element.

18. The computer program product (111 , 116) of claim 17, wherein said network element is a mobile station (112a) or a base station (101a).