WO2005029789A1

WO2005029789A1 - Data flow control in a communication system

Info

Publication number: WO2005029789A1
Application number: PCT/IB2004/051735
Authority: WO
Inventors: Patrick Nickel
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2003-09-19
Filing date: 2004-09-10
Publication date: 2005-03-31

Abstract

Flow control in mobile communication systems may become critical if the data rate of different connections varies due to, for example, different interfaces. According to the present invention, a method is provided which sends a negative acknowledgement message requesting retransmission of the data in case the receiving buffer of the receiver station is full. Advantageously, this may allow for a very fast and efficient flow control.

Description

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Data Flow Control in a Communication System

Data, usually in the form of data packets is transmitted between a transmitter station, such as a base station and a receiver station, such as a mobile user equipment. Such mobile user equipment may, for example, be a mobile telephone, a PDA, an MP3 player, a mobile display screen or a camera. Such a known data transmission system is, for example, described in 3GPP TS 25.308 V5.20 (2002-03), Technical Specification, 3^rd Generation Partnership Project; Technical Specification Group Radio Access Network; High Speed Downlink Packet Access (HSDPA); Overall description; Stage 2 (Release 5), which is hereby incorporated by reference and 3GPP TS 25.321 V5.2.0 (2002-09) Technical Specification, 3^rd Generation Partnership Project; Technical Specification Group Radio Access Network; MAC protocol specification (Release 5), which is also hereby incorporated by reference. Such data transmission system transmits in the Downlink (DL: from the basis station to the mobile subscriber unit) via the High Speed Downlink Shared Channel (HS-DSCH) data packets at high speed. These data packets are transmitted in time slots with a length of 2ms. These time slots are referred to as Transmission Time Interval (TTI). These data packets are confirmed or acknowledged after each transmission. In particular, when a data packet has been received successfully and has been decoded error-free by the receiver station, the receiver station sends an Acknowledgement (ACK) message in the Uplink (UL: from the mobile subscriber station to the base station). In case the data packets could not be decoded error-free, the receiver station sends a Negative Acknowledgement (NACK) usage in the uplink to the base station. When the base station receives such a negative acknowledgement message, the base station may decide whether to perform a retransmission of this particular data packet or to continue with the transmission of new data to the mobile equipment and thereby abort the retransmission of the data packet which has not been PTrrmrπrm?

successfully decoded in the mobile equipment. In order to take changing channel conditions in the downlink into consideration, the coding rate, the spreading factor and the modulation of the data transmission may be adapted. Retransmissions of data packets mustn't have the same spreading factor, coding rate and modulation scheme to combine the data packets of the retransmission with the former received packets in the mobile equipment. 8 different Hybrid Automatic Repeat Request (HARQ) processes have been defined. The Automatic Repeat Request (ARQ) consists in requesting a new transmission of the information block of the data packet when errors have been detected in the previous transmission, i.e., if the data packet could not be decoded error-free in the receiver station. The three conventional ARQ schemes are referred to as STOP AND WAIT scheme, GO BACK N scheme and SELECTIVE REPEAT ARQ scheme. Hybrid ARQ is defined as the joint use of ARQ and a Forward Error Coding (FEC). In a type I HARQ scheme, the receiver station discards the erroneous data packet before decoding the new one. Furthermore in the type II HARQ scheme, the receiver station uses information from the previous erroneous decoded data packet to decode the current one. In this latter scheme, incremental redundancy schemes where the first transmission is encoded with a high code rate, and the following transmission simply consists of additional redundancy in order to decrease the code rates seen by the receiver may be used. As mentioned above, up to 8 different HARQ processes may be configured which are served in the time division multiplex. The scheduling is not fixed and it is done by the base station The identity of the respective HARQ process is transmitted via a parallel control channel, which is referred to as HS-SCCH (High Speed Shared Control

Channel) in the above-referenced publications. Due to this, each retransmitted data packet may be associated with the respective first transmitted data packet. In addition to that, a New Data Indicator (NDI) is sent via the HS-SCCH, which indicates to the respective receiver station whether the respectively received data packet is a newly- transmitted data packet containing new data or it is a retransmitted data packet, which has once, or even more often, been transmitted before. The data packets may contain data with respect to different applications. PHrVRΩ Ω^?

Part of the data maybe directly used in an application of the mobile subscriber unit or receiver station. Other parts of the data may, however, be forwarded to further devices, such as PDA's and MP3 players, cameras, camcorders, etc. Such further devices may have varying data rates, such that cases may occur where the data of the respectively received data packets may not be directly forwarded to these first devices but have to be buffered or stored in buffers or memories associated with the respective applications. Such buffering may be performed until the buffer or memory is full. When the memory or buffer associated with the respective application is full and further data packets concerning this application are decoded, this new data is used to overwrite data in the buffer or memory of this application. This may cause that data is lost. Due to the high data rates which may be used in the HS-DSCH of up to lOMbit/s, relevant amounts of data may be lost within a very short time.

It is an object of the present invention to at least partially avoid a loss of data in case a buffer in the receiver station is full. According to an exemplary embodiment of the present invention as set forth in claim 1, the above object may be solved by a method of transmitting data from a transmitter station to a receiver station, wherein the receiver station comprises a receiving buffer. According to this exemplary embodiment of the present invention, it is determined that the receiving buffer is full. Then, in case it is determined that the receiving buffer is full, a negative acknowledgement message is sent from the receiver station to the transmitter station. The negative acknowledgement message requests retransmission of the data from the transmitter station to the receiver station. Advantageously, according to this exemplary embodiment of the present invention, a very fast and efficient method is provided which may allow to avoid a loss of data in case the receiving buffer in the receiver station is full. Advantageously, this method may be significantly faster than mechanisms provided in, for example, the TCP protocol for controlling the data rate, where it usually takes more than 100 ms to achieve a control. Furthermore, the above method may also be faster than a data rate control in the Radio Link Control (RLC) layer in the Acknowledge Mode (AM). By mechanisms provided in the RLC layer, a data rate control may usually not be realized which is faster than 100 ms. In other words, according to this exemplary embodiment of the present invention, a very fast data rate control may be provided which is particularly suited for controlling a data rate between a transmitter station and a mobile receiver station which are linked by radio channels. According to another exemplary embodiment of the present invention as set forth in claim 2, the negative acknowledgement message is sent when the receiving buffer is full, even if the decoding of this packet data at the receiver station is error-free. According to another exemplary embodiment of the present invention as set forth in claim 3, in case the data is decoded error-free and the receiving buffer is not full, the receiver station sends a positive acknowledgement message to the transmitting station indicating that the data was error-free decoded at the receiver station. Furthermore, if the data cannot be decoded error-free and the receiving buffer is not full, the receiver station sends a negative acknowledgement message to the transmitter station. Advantageously, according to this exemplary embodiment of the present invention, an improved automatic repeat request protocol may be provided allowing for a very fast data rate control. According to another exemplary embodiment of the present invention as set forth in claim 4, a plurality of applications is provided in the receiver station. Upon reception of data in the receiver station, the data is analyzed to find out to which of the applications the data belongs. Then, in case it is determined that a receiving buffer associated with this application is full, the receiver station sends the negative acknowledgement message to the transmitter station. Advantageously, according to this exemplary embodiment of the present invention, a plurality of application may be provided in the receiver stations which may have different data rates. According to another exemplary embodiment of the present invention as set forth in claim 5, the data is transmitted in the form of a data packet and the method is a flow control method for High Speed Downlink Packet Access (HSDPA) in a wireless communication system, such as the UMTS system. Furthermore, according to yet another exemplary embodiment of the present invention, the method is an pwππFrπf ?

Automatic Repeat Request (ARQ) protocol, and is combined with a Forward Error Coding (FEC). According to another exemplary embodiment of the present invention as set forth in claim 7, a communication network for transmitting data from a transmitter station to a receiver station is provided comprising a transmitter station and a receiver station with a receiving buffer. The receiver station is adapted to determine that the receiver buffer is full and to send a negative acknowledgement message to the transmitting station in case it is determined that the receiving buffer is full. The negative acknowledgement message requests retransmission of the data. Claims 8 to 11 provide for further exemplary embodiments of the communication network according to the present invention. According to another exemplary embodiment of the present invention as set forth in claim 12, a receiver station is provided, wherein the receiver station is adapted to send a negative acknowledgement message requesting retransmission of the data to the transmitting station when a receiving buffer in the receiver station is full. Advantageously, the receiver station according to this exemplary embodiment of the present invention allows a very fast data flow control. In addition to that, due to the fact that this receiver station may use an ARQ protocol as known, for example, in UMTS, this receiver station may be used with conventional transmitter stations operating in accordance with such an ARQ protocol without requiring changes to such conventional transmitter stations. Claim 13 provides for an exemplary embodiment of the receiver station according to the present invention. It may be seen as the gist of an exemplary embodiment of the present invention that a negative acknowledgement message is sent from the receiver station to the transmitter station in case it is determined that a receiving buffer in the receiver station is full. In other words, a retransmission of the data packet is requested in case the receiving buffer is full, causing a loss of the originally transmitted data. Advantageously, this may allow for a very fast and efficient flow rate of data rate control. These and other aspects of the present invention will become apparent from and elucidated with reference to the embodiments described hereinafter. TTDFmrm?

Exemplary embodiments of the present invention will be described in the following, with reference to the following drawings:

Fig. 1 shows a simplified representation of a communication network according to the present invention. Fig. 2 shows a flow diagram of an exemplary embodiment of a method of operating the communication network of Figure 1 according to the present invention. Fig. 3 shows a flow diagram of another exemplary embodiment of operating the communication network of Figure 1 according to the present invention.

Figure 1 shows a simplified representation of a data transmission system or communication system for a data transmission from a transmitter station 2 to a plurality of receiver stations 4, 6 and 8. Between the transmitter station 2 and the receiver stations 4, 6 and 8, there is provided a data channel which may be a High Speed Downlink Shared Channel (HS-DSCH). Between the receiver stations 4, 6 and 8 and the transmitter station 2, i.e., in the uplink, there may be a control channel which may be a High Speed Shared Control Channel (HS-SCCH). The data transmission system depicted in Figure 1 may, for example, be a cellular mobile radio telecommunication system, such as the GSM or the UMTS system or a Wireless Local Area Network (WLAN). The data packets are preferably transmitted between the transmitter 2 and the receiver stations 4, 6 and 8, in accordance with the data transmission systems described in 3 GPP TS 25.308 V5.2.0 (2002-03), Technical Specification, 3^rd Generation Partnership Project; Technical Specification Group Radio Access Network; High Speed Downlink Packet Access (HSDPA); Overall description; Stage 2 (Release 5), which is hereby incorporated by reference and in 3GPP TS 25.321 V5.2.0 (2002.09) Technical Specification, 3^rd Generation Partnership Project; Technical Specification Group Radio Access Network; MAC protocol specification (Release 5), which is also ppmFmrm?

hereby incorporated by reference. Each of the of the receiver stations 4, 6 and 8 may comprise one or more applications, such as a music player, data display, PDA or camera. Each application may be provided with a receiving buffer provided in the receiver station 4. Also, the receiving buffer and the application may be provided separate from the receiver station. The receiver stations 4, 6 and 8 maybe mobile phones, PDA's, MP3 players, music players, data displays, cameras, etc. Figure 2 shows a flow diagram of an exemplary embodiment of a method of operating the transmission system depicted in Figure 1 according to the present invention. In Figure 2, the rightmost vertical line represents an HARQ process 10 performed in the transmitter station 2. In other words, the rightmost line shows the interface between the transmitter station 2 and the radio link to the receiver stations 4, 6 and 8. The vertical line in the middle of Figure 2 indicates the HARQ process 12 performed in a receiver station 4, 6 and 8. In other words, this vertical line in the middle of Figure 2 indicates the interface between the radio channel between the transmitter station 2 and the receiver station 4, 6 and 8 and a receiver station 4, 6 and 8. The leftmost vertical line indicates an application buffer 14 in the receiver station 4, 6, 8. As may be taken from Figure 2, at first a data packet 1 is transmitted from the transmitter station to a receiver station, i.e., sent from the HARQ process 10 in the transmitter station 2 to the HARQ process 12 in the receiver station. As indicated by box 16, the data packet 1 received by the HARQ process 12, i.e., by the respective receiver station, could be decoded error-free. The correctly decoded data packet 1 is then forwarded to the respective application buffer 14. As may be taken from Figure 2, the application buffer 14 signals to the

HARQ process 12 that the application buffer 14 is full. In such a case, the HARQ process 12 sends a negative acknowledgement message to the HARQ process 10 in spite of the fact that the data packet 2 sent in the meantime could be decoded correctly, as indicated in box 18. In other words, the HARQ process 12 sends the negative acknowledgement message to the HARQ process 10 when the application buffer 14 is full, even when the data packet 2 could be decoded error-free. ϊmF.mn'W

After the HARQ process 12 sends a negative acknowledgement message to the HARQ process 10, the HARQ process 12 was informed by the application buffer 14 that the buffer is now empty due to, for example, the fact that data contained in the application buffer 14 was used by the respective application. Due to the fact that the application buffer 14 is now empty, the HARQ process 12 may now forward the data packet 2 which was in the meantime decoded error-free by the HARQ process 12, as indicated in box 20, to the application buffer 14. Advantageously, the method depicted in Figure 2 allows for a very fast data rate control between the HARQ processes 10 and 12, i.e., between the transmitter station and the receiver station. There maybe a plurality of applications in each of the receiver stations. In such a case, each HARQ process 12 in each receiver station has to serve a plurality of applications. In such a case, the HARQ process 12 may be adapted, such that after the decoding of the respectively received data packet, the HARQ process 12 determines to which of the plurality of applications, each being provided with a respective buffer the just received data packet belongs. Then, the HARQ process 12 determines whether the respective application buffer of the application of the plurality of applications, to which the data packet belongs, is full or empty. In case this application buffer is empty, the HARQ process 12 forwards the corresponding data packet to the respective application buffer. In case the HARQ process 12 determines that the respective application buffer is full, the HARQ process 12 sends a negative acknowledgement message with respect to this data packet back to the HARQ process 10. As mentioned above, due to the HARQ process identities, a correspondence is provided between a data packet and a thereto belonging negative acknowledgement message. Figure 3 shows a flow diagram of another exemplary embodiment of operating the data transmission system depicted in Figure 1 according to the present invention. In Figure 3, the same reference numerals are used for the same or corresponding elements as in Figure 2. As may be taken from Figure 3, firstly the data packet 1 is transmitted from the HARQ process 10 to the HARQ process 12. As indicated in box 22, the data packet 1 could be decoded error-free in the HARQ process 12. Then, the data packet 1 is forwarded to the application buffer 14. However, the application buffer 14 signals or indicates to the HARQ process 12 that the buffer is full. However, in the meantime, the HARQ process 12 has already sent a positive acknowledgement message to the HARQ process 10. Due to the positive acknowledgement message, the HARQ process 10 does not perform a retransmission of data packet 1 but transmits a new data packet 2 to the HARQ process 12, which, as indicated in box 24, is decoded error-free. Now, due to the fact that the HARQ process 12 knows that the respective application buffer 14 is full, the HARQ process 12 sends a negative acknowledgement message to the HARQ process 10. The correctly decoded data packet 2 is stored in a soft buffer in the HARQ process 12. Then, the HARQ process 10 sends a new data packet 3 to the HARQ process 12. In the meantime, the application buffer 14 has indicated to the HARQ process 12 that the application buffer 14 is empty. Due to this, the data packet 3 which is error-free decoded, as indicated in box 26, is forwarded to the application buffer 14. However, as may be taken from Figure 3, the data packet 2 which could not be forwarded to the application buffer 14, due to the fact that it was full, has to be deleted in the soft buffer of the HARQ process 12. In other words, as described with respect to the methods depicted in Figures 2 and 3, according to an exemplary embodiment of the present invention, it is indicated to the HARQ process 12 in the receiver station that the application buffer of the respective application is full or almost full. Due to this, the HARQ process 12 knows about the fact that a respective application buffer is full. In case there is not one application but a plurality of applications with a plurality of application buffers associated with one HARQ process, according to an exemplary embodiment of the present invention, it is indicated to the HARQ process 12 which of the respective application buffers is full, such that the HARQ process 12 knows which data packets, namely, the data packets belonging to the application with the full application buffer, have to be blocked. Then, according to the present invention, a retransmission of data packets is requested which applications were blocked, i.e., which belong to applications which application buffers were full. Furthermore, as indicated in boxes 16, 18, 20, 22, 24 and 26, the respectively received and decoded data packet is stored in the soft buffer of the HARQ process 12 until it may be forwarded to the respective application buffer 14. However, pHFVFΩλΩ^?

as may be taken from box 26, in case one data packet (data packet 2) is decoded during the time the application buffer is full, data packet 2 may not be forwarded to the respective application buffer 14. It is deleted in the soft buffer of the HARQ process 12. Furthermore, if an analyzation of the HS-SCCHs, i.e., of the HARQ process identity and the new data indicator shows that a retransmission of a data packet has been made, according to the present invention it may be decided whether it is necessary to request another retransmission, i.e., whether it may be necessary to send an NACK or whether the correctly received data is forwarded to the respective application buffer (transmission of an ACK). As may be taken from box 26 in Figure 3, in case no retransmission of a data packet has taken place but the new data indicator has been incremented indicating that a new data packet is sent, the correctly decoded data packet in the soft buffer of the HARQ process 12 which could not be forwarded to the respective application buffer is deleted. In order to allow that the applications of a receiver station do not influence each other, according to an aspect of the present invention, the data belonging to respective applications is transmitted separately. Furthermore, applications may be provided with a priority, such that more important applications have a higher priority, i.e., data packets belonging to such an application are handled with a higher priority. In particular, applications directly running in the receiver station may be provided with a higher priority. According to a further aspect of the present invention, the method depicted and described with reference to Figures 2 and 3 may also be implemented in the acknowledgement mode in the radio link control layer.

Claims

FΓDF/ΠΩ ?CLAIMS:

1. Method of transmitting data from a transmitter station to a receiver station, wherein the receiver station comprises a receiving buffer, the method comprising the steps of: determining that the receiving buffer is full; and sending a negative acknowledge message from the receiver station to the transmitter station when the receiving buffer is full; wherein the negative acknowledge message requests retransmission of the data.

2. The method of claim 1, further comprising the steps of: receiving the data sent from the transmitter station at the receiver station; and decoding the data; wherein the negative acknowledge message is sent when the receiving buffer is full even if the decoding of the data is error-free.

3. The method of claim 2, wherein, if the data is decoded error-free and the receiving buffer is not full, the receiver station sends a positive acknowledgement message to the transmitter station indicating that the data was error-free decoded at the receiver station; and wherein, if the data cannot be decoded error-free and the receiving buffer is not full, the receiver station sends the negative acknowledgement message to the transmitter station.

4. The method of claim 3, wherein there is a plurality of applications in the receiver station; wherein each of the plurality of application has an associated application buffer; wherein, upon reception at the receiver station, the data is analyzed with respect to which of the application of the plurality of applications it belongs; wherein, when the data belongs to an application of the plurality of applications which associated application buffer is full, the receiver station sends the negative acknowledge message to the transmitter station. PHΓ>FΩ^ ?

5. The method of claim 1 , wherein the data is transmitted in the form of a data packet; and wherein the method is a flow control method for high speed downlink packet access (HSDPA) in a wireless communication system.

6. The method of claim 1 , wherein the method is an automatic repeat request (ARQ) protocol and is combined with a forward error coding (FEC).

7. Communication network for transmitting data from a transmitter station to a receiver station, comprising: a transmitter station; and a receiver station; wherein the receiver station comprises a receiving buffer; wherein the receiver station is adapted to determine that the receiving buffer is full; wherein the receiver station is adapted to send a negative acknowledge message to the transmitter station when the receiving buffer is full; and wherein the negative acknowledge message requests retransmission of the data.

8. The communication network of claim 7, wherein the receiver station is adapted to receive the data sent from the transmitter station and to decode the data; and wherein the receiver station is adapted to send the negative acknowledge message when the receiving buffer is full even if the decoding of the data is error-free.

9. The communication network of claim 8, wherein, if the data is decoded error-free at the receiver station and the receiving buffer is not full, the receiver station sends a positive acknowledgement message to the transmitter station indicating that the data was error-free decoded at the receiver station; and wherein, if the data cannot be decoded error-free at the receiver station and the receiving buffer is not full, the receiver station sends the negative acknowledgement message to the transmitter station.

10. The communication network of claim 9, wherein there is a plurality of applications in the receiver station; wherein each of the plurality of application has an associated application buffer; wherein, upon reception at the receiver station, the data is PHT)F.Ω^Ω ?

analyzed in the receiver station with respect to which of the application of the plurality of applications it belongs; wherein, when the data belongs to an application of the plurality of applications which associated application buffer is full, the receiver station sends the negative acknowledge message to the transmitter station.

11. The communication network of claim 7, wherein the data is transmitted in the form of a data packet; wherein the method is a flow control method for high speed downlink packet access (HSDPA) in a wireless communication system; and wherein the method is an automatic repeat request (ARQ) protocol and is combined with a forward error coding (FEC).

12. Receiver station for a communication network for transmitting data from a transmitter station to a receiver station, wherein the receiver station comprises a receiving buffer; wherein the receiver station is adapted to determine that the receiving buffer is full; wherein the receiver station is adapted to send a negative acknowledge message to the transmitter station when the receiving buffer is full; and wherein the negative acknowledge message requests retransmission of the data.

13. The receiver station of claim 12, wherein there is a plurality of applications in the receiver station; wherein each of the plurality of application has an associated application buffer; wherein, upon reception at the receiver station, the data is analyzed in the receiver station with respect to which of the application of the plurality of applications it belongs; wherein, when the data belongs to an application of the plurality of applications which associated application buffer is full, the receiver station sends the negative acknowledge message to the transmitter station.