GB2379144A - Data is sent over a first radio bearer and an acknowledgment may be sent over a second radio bearer - Google Patents

Abstract

First data is sent over a radio bearer between a Mobile Subscriber (MS)and a network. The network generates an acknowledgement and piggy-backs the acknowledgement to second data to be sent to the MS. The acknowledgment may be sent over the same radio bearer as the first data, or over a different radio bearer. The acknowledgment includes a two-bit acknowledgment indicator, AI, to indicate whether or not the acknowledgement is transmitted on the same radio bearer as the first data which it acknowledges.

Description

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A METHOD OF ACKNOWLEDGING DATA This invention relates to a method of acknowledging data, in particular for use in mobile phone systems.

Conventional fixed line telecommunication systems cater for acknowledged and unacknowledged communication. When a data block is transmitted between two points on a particular channel, an acknowledgement will be sent back along that channel for acknowledged communications. A similar arrangement is used for mobile communications, which rely on radio channels. Data flow is on predetermined channels and the acknowledgement will be sent on the same channel. However, mobile communications have a more limited capacity because of the need to transmit through the air interface, so sending an acknowledgement by itself is not always an efficient use of resources.

In accordance with the present invention, a method of acknowledging data blocks comprises receiving data transmitted on a data radio bearer; generating an acknowledgement; setting an acknowledgement indicator to indicate whether or not the acknowledgement relates to data transmitted on the same radio bearer as the radio bearer carrying the acknowledgement; and transmitting the acknowledgement on a radio bearer.

The present invention addresses the problem of inefficient use of resources by sending an acknowledgement on any available radio bearer which is in use for e. g. the purpose of data transmission and providing an indicator as to whether the acknowledgement relates to that radio bearer or not.

Preferably, the acknowledgement is in the form of a bitmap Preferably, an ack/nack description contains radio bearer identities of the or each radio bearer being acknowledged.

Preferably, the acknowledgment indicator is 2-bit.

Preferably, the acknowledgement indicator field is set to'01'to indicate that the radio bearer identity is included in an ack/nack description to identify to which radio bearer the ack/nack description is targeted.

Preferably, the acknowledgement indicator is set to'10'to indicate that the data radio bearer and the acknowledgement radio bearer are the same.

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Ack/Nack Description < Ack/Nack Description IE > : : = < SRb Id: bit (2) > < STARTINGSEQUENCENUMBE R: bit (7) > < RECEIVEDBLOCKBITMAP : bit (64) > {Ojl < Ack/Nack Description IE > } ; STARTINGSEQUENCENUMBER : See 44.060 (Ack/Nack Description).

RECEIVEDBLOCKBITMAP : See 44.060 (Ack/Nack Description).

Table 2. Ack/Nack Description Specific examples of the formats of the acknowledgement bitmaps for three scenarios are shown in Figs. 1 to 3. In Fig. 1, the acknowledgement bitmap is for the same radio bearer as the data, whilst in Fig. 2, the data for radio bearer 1 contains the acknowledgement bitmaps for radio bearers 1 and 2. In each of the figures the layout of the ack/nack description is determined by the setting of the'AI'field. Fig. 1 shows data flow from MS to the network on radio bearer 1, for sequence numbers 5 to 10. All of the data is received at the network except for the data packet whose sequence number is 7. In the ack/nack description the start sequence number of the ack/nack bit map is 5 and the bit map indicates that sequence numbers 5,6, 8,9, and 10 were received.

Fig. 2 shows data flow from the MS to the network on radio bearers 1,2, and 3.

An acknowledgement is sent by the network with data for radio bearer 3. The acknowledgements are for data received on radio bearers 2 and 3. The AI field set to '01'indicates and the radio bearer identity is included in the ack/nack description to identify which radio bearer the ack/nack description is targeted. Ack/nack bits maps for radio bearers 1 and 2 are piggybacked with data for radio bearer 3.

Fig. 3 achieves the same net data flow as in Fig. 2, although in Fig. 2 there are two less messages exchanged. However, the format of the acklnack description in Fig.

2 is more complex in Fig. 3. The format of the data flow in Fig. 2 is of benefit when there is a need to limit the number of messages exchanged, as across the air interface in GERAN. This mechanism would offer little benefit for a fixed network when there is not such a need to make efficient use of the resources.

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this is a waste of resources and the present invention aims to improve the use of resources based on the principle that acknowledgements for one radio bearer may be piggy-backed with data for another radio bearer which may be in acknowledged or unacknowledged RLC mode. This is particularly beneficial in the case of multiple radio bearers, as it reduces the probability of an acknowledgement being sent with an empty data block. A further optimisation is that the acknowledgements for multiple radio bearers may be included in one data block.

In order to indicate whether the acknowledgements apply to a radio bearer other than the radio bearer for which the data block is intended, the definition of an acknowledgement indicator (AI) field is extended as shown in Table 1. Table When the AI field indicates that the acknowledgements are for a radio bearer other than the radio bearer for which there is data, then the format of the acknowledgement bit map is shown in Table 2 below. This proposal introduces more complexity into the RLC as an RLC instance would need access to another RLC instance's ack/nack bitmaps.

Another difficulty arises with retransmissions. If a data block is required to be resent, then the acknowledgements for the radio bearer that was being acknowledged in the first transmission should be sent, although the latest bitmap should be sent, to avoid possible ordering problems at the receiver. In order for the sender of the ack/nack bitmap to know when it can advance its window, it would be necessary to maintain copies of the bit maps on each of the bearers on which the bit map was sent.

AI : Ack Indicator 00 Ack/Nack description not includedReserved 01 Ack/Nack description includeddifferent TFI 10 Ack/Nack description included 11 Ack/Nack description not included.

No retransmission requested (all RLC blocks received, similar to FINAL ACK INDICATION==1) Note: the AI is here two bits in order to avoid one extra bit in the Ack/Nack description.

This prevents wasting 7 bits of RLC Data, assuming the data is byte aligned (as in GPRS). Table 1. Ack Indicator

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Claims (5)

1. CLAIMS 1. A method of acknowledging data blocks, the method comprising receiving data transmitted on a data radio bearer; generating an acknowledgement; setting an acknowledgement indicator to indicate whether or not the acknowledgement relates to data transmitted on the same radio bearer as the radio bearer carrying the acknowledgement; and transmitting the acknowledgement on a radio bearer.
2. 2. A method according to claim 1, wherein the acknowledgement is in the form of a bitmap.
3. 3. A method according to claim 1 or claim 2, wherein an ack/nack description contains radio bearer identities of the or each radio bearer being acknowledged.
4. 4. A method according to any preceding claim, wherein the acknowledgement indicator is set to'01'to indicate that the radio bearer identity is included in an ack/nack description to identify to which radio bearer the ack/nack description is targeted.
5. 5. A method according to any of claims 1 to 3, wherein the acknowledgement indicator is set to'10'to indicate that the data radio bearer and the acknowledgement radio bearer are the same.