FI113599B - Data retransmission - Google Patents

Description

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RELEASE OF DATA FIELD OF THE INVENTION

The invention relates to telecommunications. In particular, the invention relates to a new and advanced method and system for retransmitting data in a wireless packet switched communication network between a terminal and a base station.

BACKGROUND OF THE INVENTION

10 In conventional wireless communication networks such as mobile networks, data has been transmitted using circuit switched services. In a circuit switched service, a single physical communication path in a network is dedicated to a particular connection during that connection. However, recently also packet switched services have begun to become more common. In a packet switched service, the data to be transmitted is divided at the transmission end into smaller units, i.e. packets, which are routed on a case-by-case basis over a network to a destination where the received packets are re-assembled into data. Package sharing allows a single physical data path to be used by several clients simultaneously. One of the · packets that is becoming more common in mobile networks The 25-circuit data service is GPRS (General

Packet Radio Service). GPRS is specifically designed to support digital mobile networks based on the GSM (Global System for Mobile Communications) standard. However, GPRS is not limited to GSM-30 networks, but can also be used, for example, in IS-136 Time Division Multiple Access (TDMA) digital cellular networks.

The GPRS service is typically implemented by adding two new types of network elements, or nodes, to a digital mobile network. These are 11359s: 2

Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). The SGSN network element is typically used to deliver packets to terminals within its service area via base stations 5 of the mobile network. Further, it may be used to send GPRS subscriber profile data inquiries to the home directory of the mobile network. The GGSN network element is typically used as an interface to, for example, non-mobile IP network utilizing telecommunications networks such as the Internet, as well as GPRS services of other service providers.

In addition to said new network elements, the GPRS service typically requires modifications to base stations and terminal-15 devices of existing mobile networks. The base stations are typically implemented with a Packet Control Unit (PCU) which is responsible for packet switched data transfer functions. Similarly, terminals must also support packet switched data transmission.

20 When packet switched data is transmitted over the radio, i.e. between the terminal and the base station, some of the packets to be transmitted may not arrive at their destination. One reason for this is, for example, pa-. : · Loss of chains due to radio interference. In this case, data packets that have not arrived •, ·. you have to resubmit.

For example, in the GPRS service, the RLC protocol (Radio Link 30 Control) and its acknowledgment procedure, which is briefly described below, are responsible for retransmitting packet switched data between the terminal and the base station. Using the RLC protocol, the data is transmitted as RLC data blocks. At predetermined regular intervals, the receiving end transmits to the transmitting end an acknowledgment message comprising a 64 bit bitmap,. 35 indicating the acknowledgment status of up to 64 previous RLC data blocks received. In other words, for each of the up to 64 RLC data blocks preceding, * 11359? it is determined whether the block in question was received or not. The transmitting end receives the acknowledgment message, and if there are any RLC data blocks declared as not received, the RLC-5 data blocks are retransmitted to the receiving end. This RLC protocol acknowledgment procedure, known per se, is used both uplink, i.e., from the terminal to the base station, and downlink, i.e., from the base station to the terminal.

However, the previously known data retransmission mechanism described above is not without problems. Particularly problematic is the extra delay due to retransmission of lost RLC data blocks. Since the maximum delay caused by one single RLC-15 data block or multiple successive lost RLC data blocks is the same as the time it takes to send an acknowledgment message, the delay caused by the loss of RLC data blocks could be reduced by reducing the interval between transmitting acknowledgment messages. However, this would have the negative consequence of an additional load on the network due to increased signaling. A further problem is; Mana is that in GPRS specifications, the size of the 25 retransmission buffers of the RLC protocol is limited to 64 data *. block. In practice, this size has proven to be very small. The transfer of said 64 data blocks typically takes less than a second. In practical situations, periodic acknowledgment messages »· '···' 30 of the prior art are typically sent at intervals of about 0.4 seconds. As a result, under interfering radio conditions, the retransmission buffer may easily fill up, which in turn results in congestion. In particular, these problems apply to up-35 link communication.

'; · There is thus a clear need for a solution that'! * ·: Would allow for a delay in the retransmission of data blocks without significantly increasing the network load signaling at the same time.

5 PURPOSE OF THE INVENTION

It is an object of the present invention to provide a novel method and system that eliminates or at least significantly alleviates the above disadvantages. In particular, it is an object of the invention to provide a method and system for enabling data retransmission in a wireless packet switched communications network between a terminal and a base station.

SUMMARY OF THE INVENTION

In the present invention, data is retransmitted in a wireless packet switched communication network between the terminal and the base station. The transmitter transmits one or more data link layer blocks of the transmission link-20 protocol from the transmit end to the receive end. The term bearer protocol refers to a protocol that performs functions according to the bearer of the Data! Link Layer (OSI) model (Open Systems Inteconnection). Preferably, the transfer group; The Layer Protocol is, for example, the Radio Link Control (RLC) protocol, wherein the data link layer data block is an RLC data block. Transmission Layer Protocol data blocks transmitted at the receiving end: are received by the receiver. The detector detects that one or more transmitted bearer layer protocol data blocks have not been received at the receiving end. An acknowledgment message is sent to the sender by the acknowledger. This acknowledgment message comprises:., At the time of transmission of one or more of said acknowledgment messages, a predetermined identification of the data block of the data link layer protocol not received. In response to that acknowledgment message, the retransmitter retransmits the data link data blocks of the transmission link protocol identified by the acknowledgment message. Preferably, the detector and the acknowledgment frequency are arranged in connection with the receiver, and the retransmitter is arranged in connection with the transmitter. The present invention is applicable to packet switched data transmission between a terminal in a wireless communication network and a base station. Preferably, the present invention is implemented in the uplink direction, with the transmitter serving as a terminal and the receiver as a base station. Alternatively, the present invention is implemented in a downlink direction, with the base station as transmitter and the terminal as receiver.

According to the invention, upon detection of a first unacknowledged transmission link protocol data block, a timer is started to start measuring the elapsed time starting from the first unanswered transmission link protocol data block. Further, according to the invention, the acknowledgment controller controls said acknowledgment controller so that said acknowledgment message is transmitted after the timer has reached a predetermined delay value. Preferably, the timer 25 and the acknowledgment controller are provided at the receiver.

. In one embodiment of the invention, the delay value of the timer is adjustable. By adjusting the delay value of the timer, it is possible to adapt the grid according to the particular situation I * '··' 30. For burst-type errors, for example, every other ► f · data block in the transmission layer protocol may be lost. In order to reduce the load on signaling to the network, it is then advantageous to set the delay value large enough so that no acknowledgment message is sent per "» 35 lost bandwidth Layer Protocol data block; with an acknowledgment message, identifying the data block of several lost 6 113 R o <II v », s transmission block protocol data at a time.

In one embodiment of the invention, the identifier arranged in connection with the receiver identifies the BSN (Block) numbers of the received RLC data blocks

Sequence Number). Further, based on said identified BSN numbers, said non-reception of RLC data blocks is performed.

In one embodiment of the invention, the BSN numbers of said blocks are used to identify the RLC data blocks that are to be retransmitted.

In one embodiment of the invention, the communication network is a digital mobile communication network, such as a GSM network comprising a General Packet Radio Service (GPRS) service.

In one embodiment of the invention, the communication network is an Enhanced Data Rates for Global Evolution (EDGE) network.

In one embodiment of the invention, the telecommunication network is a Universal Mobile Telephone System (UMTS) network.

An advantage of the present invention is the use of a known text. : · Compared to the ankle is that it allows the delay of data · 25 retransmissions to be minimized without significantly increasing the network load signaling at the same time. Further, by adjusting the delay value of the timer, the network operator is able to adapt the network to the current situation. Further, as a result of the invention, the likelihood of congestion due to overflow of the retransmission buffer under interfering radio conditions: is significantly reduced.

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LIST OF FIGURES

The invention will now be described, by way of example with reference to the accompanying drawings, in which Figure 1 schematically illustrates a method according to the invention; and Figure 2 schematically illustrates a system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates schematically, by way of example, a method of retransmitting data in a GSM network comprising a GPRS service between a terminal MS and a base station BSS. In the example of Figure 1, the invention is implemented in the uplink direction, whereby the mobile station MS with GPRS functions is the transmitter and the base station BSS acts as the receiver. However, it should be noted that the method according to the invention is also possible to implement the list in the downlink direction.

According to the example of Fig. 1, the traveler. transmitting RLC data blocks »(Radio Link Control), or shorter RLC blocks, to the base station BSS from the MS. Each RLC data block has itself

25 is known to uniquely identify its Block Sequence Number BSN. In the base station BSS

The BSN numbers of the received RLC data blocks are identified, and the received RLC data blocks are monitored based on their BSN numbers. In the case of the pre-* * · 0 in FIG. 1, the base station BSS detects that an RLC data block having a BSN number of 5 has not arrived. matte to your destination. This block may have disappeared due to interference to the radio path between the mobile communication terminal MS and the base station BSS, for example, on that radio path. Then, according to the example of Figure 1, a timer is started. timer

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8 has a predefined delay value. When the timer reaches that delay value, an acknowledgment message is sent from the base station BSS to the mobile terminal MS, which includes the numbers of the RLC data blocks BSN-5 that have not been received during the time from the start of the timer to the delay value. In the example case of Figure 1, the acknowledgment message to be transmitted comprises BSN numbers of RLC data blocks 5 and 8. Finally, according to the example case of Figure 1, the RLC data blocks 5 and 8 identified by the acknowledgment message are retransmitted from the mobile terminal MS to the base station BSS.

Further, in the example of Figure 1, adjusting the delay value of the timer adjusts the network according to the particular situation. For burst-type errors, for example, every other RLC data block may be lost. In order to reduce the load on the network due to signaling, it is then advantageous to set the delay value large enough so that not every acknowledgment message is sent for each lost RLC data block, but one acknowledgment message is reported identifying multiple lost RLC data blocks at one time. For example, a 74 msec delay value corresponds

I I

The transmission time of four RLC data blocks, so for example, a delay value of this size ensures, in most practical situations, that no acknowledgment message is sent for each lost RLC data block. Typically, the delay value is varied, for example, to * ·· 0 to 1000 milliseconds.

Figure 2 is a block diagram illustrating, by way of example, the components of a system according to the invention. With the arrangement illustrated in Fig. 2, the transmission; data in a GSM, ···, GPRS terminal MS and base station BSS network comprising a GPRS service. In the example of Figure 2, the base station BSS is further connected to a Serving GPRS Support Node network:: test element SGSN.

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In the example of Figure 2, the TX transmitter transmits one or more RLC data blocks. The receiver RX receives the transmitted RLC data blocks. The identifier ID identifies the BSN numbers of the received RLC-5 data blocks. Detector DET detected! based on the identified BSN numbers, that one or more transmitted RLC data blocks have not been received. Upon detection of the first missed RLC data block, a timer 10 is triggered to start measuring elapsed time starting from the first missed RLC data block. When the TIMER has reached a predetermined delay value, the acknowledgment controller CTRL directs the acknowledgment ACK to send an acknowledgment message comprising BSN numbers of the RLC data blocks not received by the time of transmission of the acknowledgment message. In response to the acknowledgment message, the RETX re-transmits RLC data blocks one to 20 of the BSNs contained in the acknowledgment message. The detector DET, the acknowledgment ACK, the timer TIMER, the identifier ID and the acknowledgment controller CTRL are arranged in connection with the receiver RX. The retransmitted RETX is arranged in the transmitter TX connection. ; * teen. In the example of Figure 2, the invention is impaled in an uplink direction, with the transmitter acting as * * t «]. *. A mobile terminal MS with GPRS functions and • »» t, * ··. the receiver is a base station BSS. Noteworthy is * '*. however, it is possible to implement the method according to the invention also in the downlink direction.

The invention is not limited to the above embodiments only, but many other modifications. The inventions are possible within the scope of the inventive idea defined in the claims. you.

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Claims (18)

1 ° Ί 1 7 P, 01 '! lo. : 1. A method of retransmitting data in a wireless packet switched communication network between a terminal and a base station, the method comprising the steps of: transmitting one or more data link layer protocol data blocks from a transmitting end to a receiving end, detecting at one or not receiving, transmitting an acknowledgment message to the transmitting end comprising the identification data of one or more data transmission layer protocol data not received, and transmitting the data transmission protocol data blocks identified by the acknowledgment message identification data to be re-initialized in response to an acknowledgment message, detection, and performing the main After sending a acknowledgment message: · 25 to the transmitter after the timer has reached a predetermined delay value. * · T Method according to claim 1, characterized in that the delay value of the timer is adjustable. A method according to claim 1 or 2, characterized in that the data link layer data protocol block is an RLC data block. ... 1 The method according to claim 3, characterized in that the method further comprises * · 35 steps: t1> identifying the BSN numbers of the received RLC «412 2 '1 data blocks, and i«> »s» 11359' ' performing said non-reception of RLC data blocks based on identified BSN numbers. A processor according to claim 3 or 4, characterized in that the BSN numbers of said blocks are used as identification data of the RLC data blocks to be retransmitted. Method according to claim 1, 2, 3, 4 or 5, characterized in that the communication network is a digital mobile communication network comprising a GPRS service. A method according to claim 1, 2, 3, 4 or 5, characterized in that the communication network is an EDGE network. A method according to claim 1, 2, 3, 4 or 5, characterized in that the communication network is a UMTS network. 9. A system for retransmitting data in a wireless packet switched communication network between a terminal and a base station, comprising: a transmitter (TX) for transmitting one or more transmission link protocol data blocks, a receiver (RX) for transmitting transmission link protocol DETs, but for detecting missed transmission layer protocol da- '··' blocks, * 'to send an acknowledgment (ACK) acknowledgment message * * to 30 for a transmitter comprising one or more non-received transmission link data: *,. a retransmitter (RETX) acknowledgment message to identify the transmission link layer protocols identified by the identifier information, • 35 yellow in response to the acknowledgment message, t · 1359 ' The leen comprises: a timer (TIMER) for measuring elapsed time starting from the first non-received transmission link protocol data block, and an acknowledgment controller (CTRL) for controlling the acknowledgment so that said acknowledgment message is transmitted when the timer has reached a predetermined delay value. System according to Claim 9, characterized in that the detector and the acknowledgment are arranged in connection with the receiver, and in that the retransmitter is arranged in connection with the transmitter. System according to claim 9 or 10, characterized in that the timer and the acknowledgment controller 15 are arranged in connection with the receiver. System according to claim 9, 10 or 11, characterized in that the delay value of the timer is adjustable. A system according to claim 9, 10, 11 or 12, characterized in that the data link of the transmission link layer protocol is an RLC data block. ·; 1 The system according to claim 13, characterized in that the system further comprises: an identifier (ID) for identifying BSN numbers of received RLC data blocks, on the basis of which identified BSN numbers the detector 'detects missed RLC data blocks; and 30 which sensor is arranged in connection with the receiver. The system i according to claim 13 or 14, characterized in that the BSN numbers of said blocks are used as the identification data of the RLC data blocks that are to be retransmitted. System according to claim 9, 10, 11, 12, 13, 14: or 15, characterized in that 11359: '. a telecommunications network is a digital mobile communication network comprising a GPRS service. System according to Claim 9, 10, 11, 12, 13, 14 or 15, characterized in that the first communication network is an EDGE network. A system according to claim 9, 10, 11, 12, 13, 14 or 15, characterized in that the communication network is a UMTS network. 1 · »· I 24 11359