GB2417861A

GB2417861A - Adaptive ARQ system

Info

Publication number: GB2417861A
Application number: GB0419418A
Authority: GB
Inventors: Vaia Sdralia
Original assignee: Samsung Europe PLC; Samsung Electronics Co Ltd
Current assignee: Samsung Electronics UK Ltd
Priority date: 2004-09-01
Filing date: 2004-09-01
Publication date: 2006-03-08
Also published as: GB0419418D0

Abstract

A mobile telecommunications system comprising an automatic repeat request mechanism located in, and controlled by, the medium access layer, and/ or a system for initiating an automatic repeat request in a mobile telecommunications system where the end points for the request are defined to be a mobile terminal and an immediate radio access node.

Description

Adaptive ARQ System The present invention relates to an adaptive automatic

repeat request system and protocol termination associated therewith for during handovers. s

A mobile telecommunications network typically comprises a plurality of base stations that control the transmission and reception of data, in the form of modulated radiowaves, to and from a plurality of mobile terminals. Each base station comprises a base station controller and (usually) a plurality of base station transceiver stations. The structure of part of a typical mobile telecommunications network is shown in fig 2.

The base station transceiver station controls all radio functions associated with transmission to and reception from mobile terminals. The base station controller controls the base station transceiver.

In order to expand coverage and reduce costs, relays are generally introduced into the system. These receive a signal from either a base transceiver station or mobile phone, amplify the signal, and send it on.

In current communication systems, when data (via a modulated radio wave) is sent from a transmitter to a receiver, the receiver may transmit an automatic repeat request to the transmitter. This is effectively an error control system, wherein if the receiver detects an error in the data sent from the transmitter, the receiver automatically request retransmission of the data (this often termed an 'NACK, system). Alternatively, the receiver may send a positive acknowledgement as a form of receipt. In this arrangement, if the receipt is not received by the receiver, the transmitter resends the data (this is often termed an PACK' system).

However, the received data needs to be demodulated, and reviewed, in order to assess whether the received data is corrupted. The demodulation and checking are preformed at the ARQ end point, and hence this process is typically carried out by the base station controller (or equivalent entity).

Typically modulated data is sent in discrete integers, termed packets. When a predetermined number of packets are received, they are all demodulated and checked, and an ARQ sent to the transmitter.

The Open System Interconnection (OSI) model defines a framework for implementing protocols in a mobile phone network. Figure 1 shows the OSI model. There are seven layers in the model (although a number of the layers are split into a plurality of sub-layers). These are the application layer, the presentation layer, the session layer, the transport layer, the network layer, the data link layer and the physical layer. The system is hierarchical, with control being passed from one layer to the next, starting with the highest layer - layer 7 (the application layer).

The universal mobile telecommunications system radio interface effectively uses three of the layers. These are Layer 1 (the physical layer), layer 2 (the data link layer) and Layer 3 (the network layer).

The data link layer has four sub-layers: the medium access control (MAC), the radio link control (RLC), the broadcastlmulticast control and the packet data convergence protocol. The MAC layer is responsible for moving data packets to and from one network interface card to another across a shared channel. RLC layer provides radio link management for the radio interface.

The radio link control layer also provides a transparent, acknowledged or unacknowledged mode of data transfer to the upper layers.

Particular functions of the radio link control are ciphering of data and controlling/transmitting the automatic repeat request, while its objective is to shield any frame loss over wireless links from the TCP (transmission control protocol) in the transport layer.

In particular, as soon as the receiver detects a frame loss the radio link control initiates the automatic repeat request, to request retransmission of the missing or damaged frame.

The network layer contains the radio resource control (RRC) which is responsible for the radio resource allocation to mobile terminals. o

As the RLC is terminated at the radio network controller, the end points of the automatic repeat request mechanism in the universal mobile telecommunications system are the mobile terminal and radio network controller.

In high speed downlink packet access (HSDPA) systems, fast MAC automatic repeat request control mechanisms located at Node B have been introduced.

Node B is a function within a network that provides the physical radio link between the mobile terminal and the network. As well as controlling the transmission and reception of data across a radio interface, the node B also applies codes that are required to describe channels in a CDMA system.

Analogies can be drawn between the function of a node B and the function of a base transceiver station.

The new Node B functions do not replace those existing in the radio network controller while handover is still supported by the radio network controller.

In particular if the MAC ARQ mechanism fails to deliver a frame correctly even after the maximum retransmissions the responsibility is passed on to the radio link control ARQ to retrieve the frame.

Currently the architecture of mobile communications is evolving to include relay stations in order to improve and extend coverage as well as decrease deployment costs. These relays can be fixed or mobile. Additionally, future Radio Access Technologies will be operating at multiple modes covering wide area as well as short range communications with the Mobile Terminals being able to perform seamless handover between different deployment concepts and Radio Access Technologies.

Therefore it would be desirable for a faster and more adaptive automatic repeat request to cope with the developing telecommunication networks. It would be especially desirable to a have an adaptive ARQ operable to speed up the handover process.

According to a first aspect of the present invention there is provided a mobile telecommunications system comprising an automatic repeat request mechanism located in, and controlled by, the medium access layer.

According to a second aspect of the present invention there is provided a system for initiating an automatic repeat request in a mobile telecommunications system where the end points for the request are defined to be a mobile terminal and an immediate radio access node.

Preferably the immediate radio access node is one of a node B. relay station or a base transceiver station.

In a preferred embodiment, an ARQ end point is transferable during a handover. Preferably predictive algorithms, typically activated by one or more triggers, are used to initiate the ARQ end point transfer.

In order that the present invention be more readily understood, specific embodiments thereof will now be described with reference to the accompanying drawings.

Fig 1 shows the OSI layer model.

Fig 2 shows the structure of a mobile telecommunications network.

Fig 3 is a flow diagram showing current and new automatic repeat request transfer operations.

Fig 4 shows an example of automatic repeat request handover scenario.

Fig 2 shows an example of a structure of a mobile telecommunications system. The system comprises a plurality of mobile terminals (10) in radio communication with a base station (12). The base station (12) comprises a base station controller ( 14) and a plurality of base station transceiver stations (16). The network may also include a plurality of relays (not shown).

Together the base transceiver stations (or the node Bs) and the relays may be termed radio access nodes. Each radio access node controls the radio functions associated with each of the mobile terminals (10) within a given area (termed a cell).

The radio access node (16) with which a given mobile terminal is in direct radio communication is termed the immediate radio access node for that mobile terminal (10) The present arrangement allows for a reduction in the delay in retransmissions during an automatic repeat request procedure. This is achieved by locating the ARQ mechanism at the MAC layer (layer 2). Thus the mechanism is located closer to the physical layer (layer 1) than in previous arrangements, and therefore there are less processing steps required to activate the ARQ mechanism.

Additionally, the end point of the automatic repeat request is at the immediate radio access node (16). The radio access node is typically a relay station, abase transceiver station or a node B. Thus the end point is the first contact point for a mobile terminal (10). Thus the processing time taken is much reduced as the ARQ mechanism is controlled at the initial point of contact between the mobile terminal (10) and the network.

the present arrangement handovers from one cell to the next cell are also able to handover the ARQ mechanism. A handover is a process that allows established calls to be handed from the controller of one base station (12) to another as the mobile terminal (10) moves from cell to cell.

The end point of the data stream relating to the ARQ is operable to be transferred from the current radio access node to the next node. This can be achieved using predictive algorithms. The algorithms may be based at each individual radio access node (e.g. node B. base transceiver station or relay), or at the involved node of the core network (e.g. base station controller/radio network controller).

In a preferred arrangement, so that the network is able to act proactively during a handover, the end point transfer process is associated with triggers/measurements that identify a handover. Cross layer signalling may be used in the case when the triggers are initiated at higher layers e.g. triggers based on quality of service, location of the mobile terminal, velocity of the mobile terminal, network availability.

As soon as a trigger for a handover is activated, the immediate radio access node (16), that is aware ofthe trigger, notifies the next radio access node by sending a message containing new ARQ information in order to terminate the current ARQ instance. Additionally, the current access node end point sends a message to the new end point informing the new node on the current state of the automatic repeat request. The new message will include information including the mobile terminal identification, current end point node identification, current sequence number and so on.

In a particular embodiment, and in order to achieve greater efficiency of process, the ARQ mechanism used during the handover period could be a different to that used during normal operation. For example, by employing an automatic repeat request mechanism that requires less buffering, less bandwidth is wasted during the transfer of the automatic repeat request end point.

Figure 3 shows a flow diagram illustrating an embodiment of the present invention. As will be apparent from reviewing the figure, the system is operable to adaptively and dynamically perform a handover without waiting for an end of a particular packet sequence.

In the present arrangement and with reference to fig 3, when a mobile terminal (10) passes from a first cell to a second cell, a handover from the radio access node (16) in the first cell to the radio access node (16) in the second cell is initiated.

The first node informs the mobile terminal ( 10) of the termination of the ARQ mechanism by introducing changes to the mechanism. These changes may be, for example, where the number of packets demodulated and checked is less than in normal operation. The stream of modulated may be demodulated and reviewed on a packet-by-packet basis, and an ARQ ACK/NACK mechanism used for each packet, thus allowing for an immediate change in the radio access node (16).

The current node also informs the next radio access node of the ARQ scheme, and status thereof, being used, the number of packets that have been successfully received by informing of the current/next sequence number in the packet sequence.

The next radio access node (16) will then begin radio communication with the mobile terminal (10), including initiating an ARQ mechanism.

Figure 4 shows an illustrative example of a handover of the automatic repeat request during a handover procedure.

It will be understood that the above described embodiment has been described by way of an example only, and that many variations and modifications are possible within the scope of the claims.

Claims

Claims.

1. A mobile telecommunications system comprising an automatic repeat request mechanism located in, and controlled by, the medium access layer.

2. A system for initiating an automatic repeat request in a mobile telecommunications system where the end points for the request are defined to be a mobile terminal and an immediate radio access node.

3. A system according to claim 2 wherein the immediate radio access node is one of a node B. relay station or a base transceiver station.

4. A system according to either claim 2 or claim 3, wherein one of automatic repeat request end points is transferable during a handover. 1)