WO2010012298A1

WO2010012298A1 - Transmission of redundant arq feedback message in unused space of a data transmission slot

Info

Publication number: WO2010012298A1
Application number: PCT/EP2008/059905
Authority: WO
Inventors: Yanqun Le; Yi Wu
Original assignee: Nokia Siemens Networks Oy
Priority date: 2008-07-29
Filing date: 2008-07-29
Publication date: 2010-02-04

Abstract

It is described a method for transmitting a redundant ARQ feedback information between two network elements (NE1, NE2) of a telecommunication network. The method comprises transmitting a first message (Message 1) from a first network element (NE1) to the second network element (NE2), transmitting an ARQ feedback information from the second network element (NE2) to the first network element (NE1), transmitting a second message (Message 2) from the second network element (NE2) to the first network element (NE1), and transmitting the redundant ARQ feedback information from the second network element (NE2) to the first network element (NE1). The redundant ARQ feedback information is a subset of the ARQ feedback information. Further, the redundant ARQ feedback information and the second message (Message 2) or the redundant ARQ feedback information and the ARQ feedback information are transmitted together within a single data transmission resource. Further, it is described a network element, a computer-readable medium and a program element, which are all adapted to carry out respectively to control the above mentioned method for transmitting ARQ feedback information.

Description

DESCRIPTION

Transmission of redundant ARQ feedback message in unused space of a data transmission slot

Field of invention

The present invention relates to the field of telecommunication networks. In particular, the present invention relates to a method for transmitting ARQ feedback information between two network elements of a telecommunication network. Further, the present invention relates to a network element, to a computer-readable medium and to a program element, which are all adapted to carry out respectively to control the above mentioned method for transmitting ARQ feedback information.

Art Background

In telecommunication networks Automatic Repeat Request (ARQ) is a well known procedure for controlling and avoiding errors in data transmission. ARQ uses acknowledgments and timeouts to achieve reliable data transmission. An acknowledgment is a message sent by the receiver of an original message to the transmitter of the original message in order to indicate that the receiver of the original message has correctly received the original message. A timeout is a reasonable point in time after the transmitter has sent original message. If the transmitter does not receive a positive acknowledgment before the timeout, the transmitter usually re-transmits the original message until it receives a positive acknowledgment or until a predefined number of re-transmissions has exceeded.

In particular in packet switched data transmission the overall data transmission resource is subdivided in minimum transmission resource units for the data transfer. This minimum unit is called a chunk. For instance in a telecommunication system which is based on the Worldwide Interoperability for Microwave Access (WiMAX) standard, this minimum unit for data transmission is called a slot. It is clear that in most cases of a data transmission after data stuffing by means of a Protocol Data Unit construction, there are unused bytes left within the allocated resource respectively the allocated slot.

According to the specifications defined for instance in the publication "IEEE 802.16-2004, IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed Broadband Wireless Access Systems, Jun . 24, 2004", allocated and unused space within a slot shall be initialized to a known state. This may be accomplished by setting each unused byte to the stuff byte value (OxFF) . If the size of the unused region is at least the size of a Media Access Control (MAC) header, the region may also be initialized by formatting the unused space as a so called MAC Protocol Data Unit (MPDU) . When doing so, within the MAC header the field of the Connection Identifier (CID) shall be set to the value of the padding CID. Further, the Cyclic Redundancy Check (CRC) Indicator (CI), the encryption protocol (EC), the header type (HT) and the Type fields shall be set to zero and the length field shall be set to the number of unused bytes in the data burst. Thereby, the number of unused bytes includes the size of the MAC header created for the padding MPDU. The Header Check Sequence (HCS) should be computed in the normal way.

In the above mentioned WiMAX standard, an Automatic Repeat Request (ARQ) is defined in the MAC layer, which improves system performance by retransmitting MAC ARQ blocks that have been lost or garbled. ARQ may be enabled on a per-connection basis. The per-connection ARQ shall be specified and negotiated during connection creation. The ARQ feedback information can be sent as a standalone MAC management message on the appropriate basic management connection, or it can be piggybacked on an existing connection.

In WiMAX, the ARQ feedback information message can also be corrupted for instance due to reverse channel errors. As a consequence, the sender of the ARQ feedback information will not be notified if the ARQ feedback information message has been. Therefore, since the ARQ procedure is a one-way transmission process only, there is always at least some untrustworthiness inherently included.

There may be a need for improving the reliability of the ARQ procedure within the framework of the established WiMAX 802.16 standard.

Summary of the Invention

This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the present invention are described by the dependent claims.

According to a first aspect of the invention there is provided a method for transmitting a redundant ARQ feedback information between two network elements of a telecommunication network. The provided method comprises (a) transmitting a first message from a first network element to the second network element, (b) transmitting an ARQ feedback information from the second network element to the first network element, (c) transmitting a second message from the second network element to the first network element, and (d) transmitting the redundant ARQ feedback information from the second network element to the first network element. The redundant ARQ feedback information is a subset of the ARQ feedback information. Further, (a) the redundant ARQ feedback information and the second message or (b) the redundant ARQ feedback information and the ARQ feedback information are transmitted together within a single data transmission resource .

This first aspect of the invention is based on the idea that the reliability of the known Automatic Repeat Request (ARQ) procedure can be increased by transmitting a redundant ARQ feedback information message between the same two network elements and in the same direction, which two network elements have before exchanged a known ARQ feedback information message. This means that also the modified ARQ procedure presented in this application comprises only a oneway transmission from the second network element to the first network element. However, by contrast to the known ARQ procedures, wherein the second network element informs the first network element about a proper reception of the first message by means of an ARQ feedback information, the described method provides an enhanced reliability.

It has to be mentioned that in this application the term "ARQ feedback information" and the term "redundant ARQ feedback information" are used both (a) for corresponding messages, which are transmitted from the second to the first network element, and (b) for the corresponding information content being associated with the respective message.

Since in the described method the second network element is the sender respectively the transmitter of both the ARQ feedback information and the redundant ARQ feedback information the second network element can also be denominated as the ARQ feedback sender. Further, since the second network element is the receiver of the original first message, which transmission is subjected to be verified by the ARQ procedure, the second network element may also be denominated as the ARQ receiver. Correspondingly, the first network element may be denominated ARQ feedback receiver or ARQ sender. The data transmission resource may be any elementary cell within a one-dimensional, a two-dimensional or a three- dimensional coordinate system, wherein the variables time, frequency and/or codification are plotted. In particular, the data transmission resource is a minimum unit for data transmission, which unit can be represented as a rectangle area comprising two directions. One of the directions may be for instance the time corresponding to time domain multiplexing and the other one may be the frequency corresponding to frequency domain multiplexing.

In other publications in the field of data transmission technology within telecommunication networks the data transmission resource may also be referred to as chunk or slot. Sometimes also the term frame is used, which typically comprises a predefined number of chunks or slots.

The first message, the second message, the ARQ feedback information and/or the redundant ARQ feedback information may be transmitted between the two network elements by means of a wired data connection or by means of a wireless data connection. In particular, a radio transmission link established between the two network elements may be used for transmitting these messages and these ARQ feedback information.

According to a further embodiment of the invention the telecommunication network is a Worldwide Interoperability for Microwave Access telecommunication network.

The Worldwide Interoperability for Microwave Access (WiMAX) telecommunication network is specified in the publication "IEEE 802.16-2004, IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed Broadband Wireless Access Systems, Jun . 24, 2004". In the WiMAX standard the elementary data transmission resource is called a slot. This definition is specific for WiMAX telecommunication.

According to a further embodiment of the invention the redundant feedback information is assigned to a space within the data transmission resource, which space is not used by the second message.

Since a data transmission resource is typically the minimum unit for a data transmission, after the construction, fragmentation and packing of a Protocol Data Unit (PDU), there is usually unused space left at the boundary especially in the higher modulation schemes. This originally free space being not occupied by or being unused for the second message, can be used for the above described redundant ARQ feedback information. Therefore, for increasing the reliability of the ARQ procedure it is not necessary to increase the overall dataload within the telecommunication network.

In this respect it is mentioned that a comparatively high modulation scheme is used for the coding of the data being transmitted between the two network elements if the expected quality of the data transmission link between the two network elements is high. In this case a not very robust coding is used. Thereby it can be expected that in average the unused space within the data transmission resource will be comparatively large.

According to a further embodiment of the invention the method further comprises (a) assigning the second message to the data transmission resource by means of a Protocol Data Unit construction, and (b) checking the size of the space within the data transmission resource, whereby, immediately after the Protocol Data Unit construction, the space is an unused space within the data transmission resource. This may provide the advantage that the actual usage of the redundant data ARQ feedback information may depend on the available space. Since typically the available space is not sufficient for a completely redundant ARQ feedback information, when knowing the size of the available space the second network element will be able to optimally use this space for an appropriate content of redundant ARQ feedback information, which is a part of the original ARQ feedback information .

According to a further embodiment of the invention it is specified that, if the unused space comprises a size, which is larger than being necessary for accommodating the whole ARQ feedback information, the redundant ARQ feedback information comprises the whole ARQ feedback information.

This may provide the advantage that a maximum of redundancy can be achieved.

According to a further embodiment of the invention the it is specified that, if the unused space comprises a size, which is smaller than being necessary for accommodating the whole ARQ feedback information, the redundant ARQ feedback information comprises an acknowledged block sequence number.

In the above mentioned standard the acknowledged block sequence number is abbreviated as BSN and exhibits a data size of 11 bits. The transmission of the BSH may provide the advantage that, even if there is only a small space available for redundant ARQ feedback information this small space will be used for a comparatively important information content.

According to a further embodiment of the invention the redundant ARQ feedback information is attached to the second message by means of piggybacking.

Since piggybacking is a known procedure for attaching an information element to another information element, the described combination of the redundant ARQ feedback information and the second message can be carried out by means of standard procedures, which are for instance defined in the above mentioned IEEE standard 802.16.

According to a further embodiment of the invention within the data transmission resource the redundant ARQ feedback information and the second message are separated from each other by means of at least one separator data element.

The separator data element may be for instance a so called Packing Subheader (PSH) . The PSH may have a data size of three bytes. This size is sufficient in order to allow the first network element representing the receiver of the combination of the second message and the redundant ARQ feedback information to reliably identify the content of the redundant ARQ feedback information.

According to a further embodiment of the invention the first network element is a base station and the second network element is a subscriber station. This may mean that the first message is transmitted in the Downlink direction and the second message together with the redundant ARQ feedback information is transmitted in the Uplink direction.

The subscriber station may be any mobile or stationary communication end device, which is capable of establishing a connection to a base station and/or to any Point of Attachment within the telecommunication network. In particular, the subscriber station might be a mobile User Equipment such as a cellular mobile phone, a Personal Digital Assistant (PDA) , a notebook computer and/or any other movable communication device.

According to a further aspect of the invention there is provided a second network element for transmitting a redundant ARQ feedback information to a first network element of a telecommunication network. The provided second network element comprises (a) a unit for receiving a first message from a first network element, (b) a unit for transmitting an ARQ feedback information to the first network element, and (c) a unit for transmitting within a single data transmission resource a second message and the redundant ARQ feedback information to the first network element. The redundant ARQ feedback information is a subset of the ARQ feedback information .

This further aspect of the invention is based on the idea that by using a free space of a data transmission resource being partially filled with the second message, redundant ARQ feedback information can be transmitted to the first network element. The thereby described modified ARQ procedure will be more reliable than known ARQ procedures. By increasing the reliability of the ARQ procedure the performance of in particular WiMAX telecommunication systems can be increased. Since only unused bytes and/or bits are used, which in the known WiMAX standard IEEE 802.16 are simply padded, there is no disadvantage expected when implementing the above described method for transmitting a redundant ARQ feedback information in a network element.

According to a further aspect of the invention there is provided a computer-readable medium on which there is stored a computer program for transmitting a redundant ARQ feedback information between two network elements of a telecommunication network. The computer program, when being executed by a data processor of at least one of the two network element, is adapted for controlling the above mentioned method.

According to a further aspect of the invention there is provided a program element for transmitting a redundant ARQ feedback information between two network elements of a telecommunication network. The program element, when being executed by a data processor of at least one of the two network elements, is adapted for controlling the above mentioned method. The computer program element may be implemented as computer readable instruction code in any suitable programming language, such as, for example, JAVA, C++, and may be stored on a computer-readable medium (removable disk, volatile or non-volatile memory, embedded memory/processor, etc.)- The instruction code is operable to program a computer or other programmable device to carry out the intended functions. The computer program may be available from a network, such as the WorldWideWeb, from which it may be downloaded.

The invention may be realized by means of a computer program respectively software. However, the invention may also be realized by means of one or more specific electronic circuits respectively hardware. Furthermore, the invention may also be realized in a hybrid form, i.e. in a combination of software modules and hardware modules.

It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the method type claims and features of the apparatus type claims is considered as to be disclosed with this application.

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. Brief Description of the Drawings

Figure 1 shows a transactional flow diagram for an ARQ procedure according to the invention, wherein apart from a usual original ARQ feedback information also a redundant ARQ feedback information is transmitted following the original ARQ feedback information.

Figure 2 shows the construction of a MAC Protocol Data Unit, which comprises a piggybacked redundant ARQ feedback information separated from a MAC Service Data Unit by means of a Packing Subheader.

Detailed Description

Figure 1 shows a transactional flow diagram for an ARQ procedure according to the invention. The described ARQ procedure is carried out in between two network elements, a first network element NEl and a second network element NE2. According to the embodiment described here the first network element NEl is a base station and the second network element NE2 is a subscriber station.

The second network element NE2 may be any mobile or stationary communication end device, which is capable of establishing a connection to the first network element NEl. In particular, the second network element NE2 might be a mobile User Equipment such as a cellular mobile phone, a Personal Digital Assistant (PDA), a notebook computer and/or any other movable communication device.

As can be seen from Figure 1, the described ARQ procedure begins with the transmission of a first message (Message 1) from the first network element NEl to the second network element NE2. Upon reception of the Message 1 the second network element generates an ARQ feedback information. This information is transmitted to the first network element NEl by means of an ARQ feedback information message. In accordance with known ARQ procedures the ARQ feedback information message informs the first network element NEl that the Message 1 has been received correctly by the second network element NE2.

The described ARQ procedure continues with the transmission of a second message (Message 2) from the second network element NE2 to the first network element NEl. Due to the segmentation of the whole available data transmission resource for the data traffic between NE2 to NEl, there will be usually at least some free space available within a slot of the whole data transmission resource, which also comprises the second message (Message 2) . According to the ARQ procedure described in this application, this free space is used for retransmitting at least a part of the original ARQ feedback information, which has already been received from the first network element NEl. This means that the first network element NEl receives a redundant ARQ feedback information, which comprises at least a part of the original ARQ feedback information. Thereby, the reliability of the ARQ procedure can be increased because the first network element NEl will get all ARQ feedback information even if a portion of the original ARQ feedback information is corrupted for instance due to reverse channel errors affecting the transmission of the first ARQ feedback information message. Since free space being unused so far is used, the described ARQ procedure will exhibit an enhanced reliability without increasing the overall dataload of data traffic extending between the two network elements NEl and NE2.

For realizing the described modified ARQ procedure, the second network element NE2 should check the unused space size after all the Protocol Data Unit (PDU) constructions are finished. Preferably, this check should be carried out every slot or at least every frame. If applicable, the second network element NE2 should try to piggyback the redundant ARQ feedback information in the unused space.

Figure 2 shows the construction of a MAC Protocol Data Unit MPDU in accordance with the modified ARQ procedure described in this application. The MPDU is constructed in the Media Access Control Layer of the known Open System Interconnection (OSI) model. The OSI model defines a networking framework for implementing protocols in seven layers. Therein, control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next network element and back up the hierarchy.

The MAC Layer is one of two sublayers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC) to another across a shared channel.

As can be seen from Figure 2, the MPDU comprises a MAC header. The MAC header may refer to the header that is added at the beginning of a network packet in order to turn it into a frame ready for transmission over the network.

As can be seen from Figure 2, a first Packing Subheader (PSH) , which is indicated with a dashed box, follows the MAC header. The first PSH separates a redundant ARQ feedback information, which is also indicated with a dashed box, from the MAC header. According to the embodiment described here the first PSH has a size of three bytes. This first PSH is used for supporting a piggybacking of the redundant ARQ feedback information.

Following the piggybacked redundant ARQ feedback information a second PSH is used for separating the redundant ARQ feedback information from a first MAC Service Data Unit (MSDU) . According to the embodiment described here the first MSDU comprises the second message (Message 2) mentioned above in connection with figure 1.

At this point it is mentioned that the MPDU depicted in Figure 2 represent just one exemplary embodiment of the invention. In particular it is possible to use other MPDU which comprise any arbitrary number MSDUs being packed into the same MPDU.

As has been specified in the above mentioned WiMAX 802.16 standard, the minimum length for an ARQ feedback information element is 4 bytes. This 4 bytes result from a lβbits connection identification (CID) , a lbit LAST information element, a 2bits ACK Type, a llbits block sequence number (BSN) and a 2bits for the number of ACK Maps, which carry actual ARQ feedback information. The originally unused bytes within the MPDU should be no less than 7 bytes in order to piggyback a minimum redundant ARQ feedback information.

If the unused bytes are large enough so that in the corresponding unused space a whole ARQ feedback information message respectively a whole ARQ feedback information element could be accommodated, a redundant feedback information containing the latest ARQ block status information should be piggybacked. This holds independent whether the ARQ feedback information has been sent out before because this transmission is redundant for using padding bytes.

Otherwise, if the unused space is not big enough, the redundant ARQ feedback information may carry just the acknowledged BSN, which has been included in the fixed minimum 4 bytes mentioned above. In this case, the cumulative acknowledgement of the ARQ connection is redundantly transmitted in order to speed up the ARQ operation considering the erroneous feature of the used feedback channel extending between the two network elements. An algorithm corresponding to the modified ARQ procedure described in this application may be implemented at the second network element representing the ARQ feedback information sender respectively the ARQ receiver in order to control the creation of the redundant ARQ feedback information .

In the implementation of the invention the second network element NE2 checks the unused space size after all the PDU constructions have been completed. According to the embodiment described here this check is carried out every frame. If the size of unused space within the MPDU is less than 7 bytes, no additional action is performed.

Generally speaking, according to the length of unused space, an adaptive redundant ARQ feedback information is created, which is based on the last transmitted ARQ feedback information. If there is no more space for the ACKnowledgement (ACK) maps, only the fixed fields of the ARQ feedback information is piggybacked and also the ACK type field should be set to cumulative ACK. If there is some more space available for the ACK maps, certain maps such as for instance one to at most four may be added to the piggybacked redundant ARQ feedback information according to the space being currently unused.

The described modified ARQ procedure may provide the advantage that the unused space can be fully utilized and the transmission reliability of the ARQ feedback information is improved. The modified ARQ procedure definitely increases the performance of the communication between the two network elements and causes no other negative impact.

It should be noted that the term "comprising" does not exclude other elements or steps and "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

List of reference signs:

NEl network element / base station

NE2 network element / subscriber station

MPDU MAC Protocol Data Unit

PSH Packing Subheader

MSDU MAC Service Data Unit / Message 2

Claims

CLAIMS :

1. Method for transmitting a redundant ARQ feedback information between two network elements (NEl, NE2) of a telecommunication network, the method comprising

• transmitting a first message (Message 1) from a first network element (NEl) to the second network element (NE2),

• transmitting an ARQ feedback information from the second network element (NE2) to the first network element (NEl), • transmitting a second message (Message 2) from the second network element (NE2) to the first network element (NEl), and

• transmitting the redundant ARQ feedback information from the second network element (NE2) to the first network element (NEl) , wherein the redundant ARQ feedback information is a subset of the ARQ feedback information and wherein the redundant ARQ feedback information and the second message

(Message 2) or the redundant ARQ feedback information and the ARQ feedback information are transmitted together within a single data transmission resource.

2. The method as set forth in the preceding claim, wherein the telecommunication network is a Worldwide Interoperability for Microwave Access telecommunication network.

3. The method as set forth in any one of the preceding claims, wherein the redundant feedback information is assigned to a space within the data transmission resource, which space is not used by the second message.

4. The method as set forth the preceding claim, further comprising • assigning the second message (Message 2) to the data transmission resource by means of a Protocol Data Unit construction, and

• checking the size of the space within the data transmission resource, whereby, immediately after the Protocol Data Unit construction, the space is an unused space within the data transmission resource.

5. The method as set forth in the preceding claim, wherein if the unused space comprises a size, which is larger than being necessary for accommodating the whole ARQ feedback information, the redundant ARQ feedback information comprises the whole ARQ feedback information.

6. The method as set forth in claim 4, wherein if the unused space comprises a size, which is smaller than being necessary for accommodating the whole ARQ feedback information, the redundant ARQ feedback information comprises - an acknowledged block sequence number.

7. The method as set forth in any one of the preceding claims, wherein the redundant ARQ feedback information is attached to the second message (Message 2) by means of piggybacking.

8. The method as set forth in any one of the preceding claims, wherein within the data transmission resource the redundant ARQ feedback information and the second message (Message 2) are separated from each other by means of at least one separator data element.

9. The method as set forth in any one of the preceding claims, wherein the first network element (NEl) is a base station and the second network element (NE2) is a subscriber station.

10. Second network element (NE2) for transmitting a redundant ARQ feedback information to a first network element (NEl) of a telecommunication network, the second network element (NE2) comprising

• a unit for receiving a first message (Message 1) from a first network element (NEl),

• a unit for transmitting an ARQ feedback information to the first network element (NEl), and • a unit for transmitting within a single data transmission resource a second message (Message 2) and the redundant ARQ feedback information to the first network element (NEl), wherein the redundant ARQ feedback information is a subset of the ARQ feedback information.

11. A computer-readable medium on which there is stored a computer program for transmitting a redundant ARQ feedback information between two network elements (NEl, NE2) of a telecommunication network, the computer program, when being executed by a data processor of at least one of the two network element (NE2), is adapted for controlling the method as set forth in any one of the claims 1 to 9.

12. A program element for transmitting a redundant ARQ feedback information between two network elements (NEl, NE2) of a telecommunication network, the program element, when being executed by a data processor of at least one of the two network elements, is adapted for controlling the method as set forth in any one of the claims 1 to 9.