WO2009098610A2

WO2009098610A2 - A method for acknowledging reception of data

Info

Publication number: WO2009098610A2
Application number: PCT/IB2009/050346
Authority: WO
Inventors: Matthew P. J. Baker; Timothy J. Moulsley
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-02-06
Filing date: 2009-01-28
Publication date: 2009-08-13
Also published as: TW200950396A; WO2009098610A3

Abstract

The present invention relates to a method for acknowledging reception of data transmitted over a channel from first station to a second station. The method comprising the steps of: (a) at the first station, transmitting a data packet to the second station according to an Automatic Repeat-Request ARQ process having a predetermined ARQ period; (b) at the second station, decoding the data packet, and transmitting an indication on whether the data packet has correctly been decoded; (c) at the first station, retransmitting said data packet, if the data packet has not been correctly decoded, wherein said method further comprises the step of: (d) increasing the length of the predetermined ARQ period if, at step (a) the data packet has been sent over a plurality of bundled data packets.

Description

A METHOD FOR ACKNOWLEDGING RECEPTION OF DATA

FIELD OF THE INVENTION The present invention relates to a method for acknowledging reception of data transmitted over a transmission channel from a first station to a second station.

This invention is, for example, relevant for telecommunication networks, and especially for mobile telecommunication networks like UMTS.

SUMMARY OF THE INVENTION

It is an object of the invention to propose a method of acknowledging data packets which is flexible to accommodate different transmission durations for the data packets, while reducing delay and avoiding the triggering of unnecessary retransmissions.

To this end there is provided a method of acknowledging reception of data transmitted over a channel from a first station to a second station, said method comprising the steps of:

(a) at the first station, transmitting a data packet to the second station according to an ARQ process having a predetermined Automatic Repeat-Request ARQ period;

(b) at the second station, decoding the data packet, and transmitting an indication on whether the data packet has correctly been decoded;

(c) at the first station, retransmitting said data packet, if the data packet has not been correctly decoded, wherein said method further comprises the step (d)of increasing the length of the predetermined ARQ period if, at step (a) the data packet has been sent over a plurality of bundled data packets. These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, wherein:

Figure 1 shows bundling and synchronous Hybrid Automatic Repeat-Request HARQ with a long delay;

Figure 2 shows bundling and synchronous HARQ with retransmission based on partial decoding; Figure 3 shows bundling and synchronous HARQ according to an embodiment of the invention; and

Figure 4 shows bundling and synchronous HARQ according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In a communication system comprising a transmitting station and a receiving station, data is divided into packets and transmitted in subframes. If the receiving station fails to decode a data packet it may request a retransmission by sending a negative acknowledgement (NACK) according to a Hybrid Automatic Repeat-Request (HARQ) protocol.

Multiple HARQ channels, or processes, may operate in parallel, enabling data transmission to continue while an earlier packet is being decoded by the receiving station. Each HARQ process is assigned a number in order to identify which retransmitted data packet should be combined in the receiver with which earlier-transmitted packet. This HARQ process number may be transmitted together with the data packet or alternatively determined implicitly from a known time reference such as the subframe number; the latter method involves less transmission overhead and can also be more reliable as it is immune to errors in the transmission of the HARQ process number, but it reduces flexibility.

In some situations data packets may be grouped, or "bundled", together for acknowledgement with a single acknowledgement (ACK) or NACK. This technique may be used for example in situations where the radio channel between the transmitting station and the receiving station is of poor quality and the transmitting station is already operating at maximum transmission power. A block of data may then be coded in such as way as to be transmitted over a plurality of consecutive subframes in a bundle of data packets.

A problem may arise if this bundling technique is combined with a synchronous HARQ scheme. The synchronous HARQ scheme would designate a particular set of subframes in which any requested retransmission of a data packets should take place, this set of subframes typically comprising one subframe in every HARQ Round-Trip Time (RTT), where a HARQ RTT is the duration of N subframes where N is the total number of HARQ processes in operation. However, the use of bundling means that if the HARQ ACK or NACK is to reflect the result of decoding the whole bundle of data packets then the ACK/NACK must be delayed, which in turn means that there may not be sufficient time for the transmitting station to configure and execute the retransmission starting in the designated subframe in the next HARQ RTT. The synchronous HARQ scheme would therefore dictate that the retransmission must be delayed until the following RTT, which results in a long delay and possibly unsatisfactory quality of service. This delay is illustrated by way of example in Figure 1 , where 8 HARQ processes are configured, leading to a HARQ RTT of 8 subframes, and where the receiving station requires a period of 3 subframes to decode a data packet before sending back ACK or NACK, and the transmitting station requires a period of 3 subframes to decode an ACK or NACK and assemble a retransmission of the data. Therefore in this example there is insufficient time between the reception of the NACK at the transmitting station and the start of the subframe in the next HARQ RTT where the synchronous HARQ operation dictates that the retransmission should be sent. Therefore the retransmission must be delayed by one whole HARQ RTT.

One known solution to this problem is for the receiving station to send ACK or NACK after decoding the first packet of the bundle, without waiting to decode the later packets, as shown in Figure 2. This avoids needing to delay the retransmission, but has the disadvantage that a retransmission will always be executed if the receiving station fails to decode the bundle of data packets on the basis of the first-received data packet in the bundle, whereas in many cases the receiving station might be able to decode the entire bundle when all its constituent data packets had been received, without needing a retransmission.

According to the present invention, the relationship between HARQ processes and the timing reference is modified in a manner dependent on the number of data packets comprised in a bundle.

In a first embodiment, the modification comprises lengthening the HARQ RTT. This is illustrated in Figure 3, where the retransmission is able to be sent 6 subframes earlier than in Figure 1. The retransmission occurs two subframes later than in Figure 2, but the probability of needing a retransmission is reduced because the receiving station has been able to make use of all packets in the bundle for the decoding process.

In one embodiment, the amount by which the HARQ RTT is lengthened is substantially equal to the duration of the number of subframes in a bundle less the number of subframes used for transmission of a data packet without bundling.

In another embodiment, the length of the HARQ RTT is rounded up to the next integer multiple of the number of subframes comprised in a bundle above either the unmodified HARQ RTT or the lengthened HARQ RTT. The length of the modified HARQ RTT may be set such that a small number of the modified HARQ RTTs comprise a duration equal to a slightly larger number of the unmodified HARQ RTTs. For example, in Figure 3, four of the modified HARQ RTTs have the same duration as five of the unmodified HARQ RTTs. This can be advantageous when scheduling data transmissions from multiple transmitting stations some of which are using bundling and others of which are not. In some embodiments the degree of bundling to be used, and hence the manner in which the HARQ RTT is modified, is configured by the signalling of a higher-layer protocol such as Radio Resource Control (RRC) signalling.

In some embodiments the relationship between the HARQ processes and the timing reference may assume that all transmissions are bundled, such that groups of contiguous subframes are associated with the same HARQ process number. In other embodiments, only a subset of the transmissions are assumed to be bundled, with other HARQ processes operating independently; for example, in such a case the HARQ process numbers in a modified HARQ RTT might be {0, 0, 0, 1, 2, 3, 4, 5, 6, 7} respectively in a variation (shown in Figure 4) of the example shown in Figure 3. In another variation of the example shown in Figure 3, the HARQ process numbers might be {0, 0, 0, 1, 1, 1, 2, 2, 2, 3}.

The modification of the relationship between HARQ processes and the timing reference may be such that each degree of bundling is associated with a different relationship, or a single relationship may be associated with multiple degrees of bundling. For example, if each degree of bundling is associated with a different relationship, a

HARQ RTT of 8 subframes may be applied when bundling is not configured, while a HARQ RTT of 9 subframes is applied when pairs of data packets are bundled, a HARQ RTT of 10 subframes is applied when groups of 3 data packets are bundled, and a HARQ RTT of 11 subframes is applied when groups of 4 data packets are bundled. Alternatively, if a single relationship is associated with multiple degrees of bundling, a HARQ RTT of 8 subframes may be applied when bundling is not configured, while a HARQ RTT of 11 subframes is applied when groups of 2, 3 or 4 data packets are bundled. Thus the relationship may depend on whether the number of data packets in a bundle is above or below a threshold, which may for example be signalled or predetermined. The transmitting station may be a mobile terminal and the receiving station may be a base station or vice versa. The communication system may be a mobile communication system such as the Long-Term Evolution of UMTS.

Claims

1. A method of acknowledging reception of data transmitted over a channel from a first station to a second station, said method comprising the steps of: (a) at the first station, transmitting a data packet to the second station according to an Automatic Repeat-Request ARQ process having a predetermined ARQ period;

(c) at the first station, retransmitting said data packet, if the data packet has not been correctly decoded, wherein said method further comprises the step of:

(d) increasing the length of the predetermined ARQ period if, at step (a) the data packet has been sent over a plurality of bundled data packets.

2. The method of claim 1, wherein step (d) is carried out prior to step (a).

3. The method of claim 1, wherein the bundled data packets require a first amount of time to be transmitted, and wherein step (d) is carried out such that the increased length of the predetermined ARQ period is a multiple of the first amount of time.

4. The method of claim 1, wherein the bundled data packets require a first amount of time to be transmitted, and wherein step (d) is carried out such that the increased length of the predetermined ARQ period is greater than the sum of the first amount of time, the time required to decode the bundled packets, the time to transmit an indication on whether the data packet has correctly been decoded and the time to decode the indication.

5. The method of claim 1, wherein step (d) is carried out so that the increased length of the predetermined ARQ period depends on how many bundled data packets are scheduled in a next ARQ period.

6. The method of claim 1 , wherein the predetermined ARQ period is increased by the duration of a number of subframes in the bundled data packets less the number of subframes used for transmission of a data packet without bundling.

7. The method of claim 1 , wherein the length of the predetermined ARQ period is rounded up to the next integer multiple of the number of sub frames comprised in the bundled data packets above either the predetermined ARQ period without increased length or the predetermined ARQ period with increased length.

8. The method of claim 1, wherein a relationship between ARQ processes and a timing reference is such that each degree of bundling of data packets is associated with a different relationship.

9. The method of claim 1, wherein a relationship between ARQ processes and a timing reference is such that a single relationship is associated with multiple degrees of bundling of data packets.

10. The method of claim 1, wherein a relationship between ARQ processes and a timing reference depends on whether the number of data packets in a bundle is above or below a threshold, which threshold is signalled or predetermined.

11. A radio station comprising means for carrying out the method as claimed in any of the preceding claims.