WO2010086768A1

WO2010086768A1 - Method for communicating via controlled relay node in a network, communication system and relay node therefor

Info

Publication number: WO2010086768A1
Application number: PCT/IB2010/050281
Authority: WO
Inventors: Timothy James Moulsley; Choo Chiap Chiau; Ludovicus Tolhuizen; Lingyang Song
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-01-30
Filing date: 2010-01-22
Publication date: 2010-08-05

Abstract

The invention relates to a method for communicating in a network comprising primary stations and secondary stations communicating by using a predetermined control channel structure. The method comprises: -a primary station transmitting to a relay node a first control signal addressed to a secondary station using the predetermined control channel structure, -the relay node forwarding the first control signal unmodified to the secondary station, and -the primary station and/or the secondary station exchanging second control signals with the relay node, wherein said second control signals are not forwarded unmodified by the relay node and said second control signals use the predetermined control channel structure. The invention also relates to a communication system implementing the present invention, and a relay node having means for implementing the present invention.

Description

METHOD FOR COMMUNICATING VIA CONTROLLED RELAY NODE IN A NETWORK, COMMUNICATION SYSTEM AND RELAY NODE THEREFOR

FIELD OF THE INVENTION The present invention relates to a method for communicating data through a network.

More specifically, this invention relates to a method for communicating in a mobile telecommunication network.

This invention may find, for example, an application in a network compliant with the Long-Term Evolution (LTE) specifications. The invention is not limited to this specific type of network, and may find application in any network.

BACKGROUND OF THE INVENTION

A possible improvement in future versions of LTE as compared with previous telecommunication network standards is the use of relay nodes (RNs) to extend cell coverage. In LTE, base stations are called evolved Node B (eNB).

In such networks, a relay node may receive, in the downlink, transmissions from a base station, and transmit them to one or more mobile terminals, also designated under the term User Equipment (UEs). Relay nodes may also handle other protocol aspects carried out in the communication network. In addition to the function of relaying or forwarding messages, a relay node may perform other functions related to signal processing: for example a relay node may set up different parameters of a signal before forwarding it, it may perform beamforming on the signal, or choose between several transmitting modes.

However, for the time being, many terminals owned by users are not compatible with communication methods involving relay nodes. Thus there is a need for a method that allows the functionalities of relay nodes to be controlled during the course of a communication between two stations in a network. Moreover, such method must be compatible with terminals that do not support communication via relay nodes, which means that performing this method must not disturb such terminals.

SUMMARY OF THE INVENTION

It is an object of the invention to propose a method for communicating in a network fulfilling at least some of the objectives previously mentioned. It is another object of the invention to propose a method for communicating in a network comprising a relay node, the method comprising steps for controlling working of the relay node.

Yet another object of the invention is to propose a method maintaining backward compatibility for use in a network comprising different types of stations, namely some stations supporting the method according to the invention, and some others not supporting it.

More generally, it is an object of the invention to provide a method which may be made compliant with requirements of some telecommunication standards such as LTE- Advanced standard, or with those of IEEE802.16J standard. To this end, the invention relates to a method for communicating in a network comprising primary stations and secondary stations communicating by using a predetermined control channel structure. The method comprises: a primary station transmitting to a relay node a first control signal addressed to a secondary station using the predetermined control channel structure, the relay node forwarding the first control signal unmodified to the secondary station, and the primary station and/or the secondary station exchanging second control signals with the relay node, wherein said second control signals use the predetermined control channel structure. In an alternative embodiment, the method comprises the step of the relay node modifying the received control signals.

The primary station and the secondary station respectively refer, within an exemplary meaning in the present invention, to a base station and a terminal station in a telecommunication network Such a method makes use of the same control structure for signalling between a primary station and the relay node as between a primary station and a secondary station. Such a method makes it possible to be used in a network which also operates without communicating via relay nodes.

Within the meaning of the present invention, a control signal may designate a signal actually used for controlling a function of the relay node, but also a signal used for providing information or a request, i.e. signalling data.

The invention also relates to a method wherein the exchanging step of second control signals comprises: the primary station transmitting the second control signal to the relay node, the relay node modifying the second control signal depending on a parameter of the receiving secondary station, the relay node forwarding the modified second control signal to the secondary station.

In an examplary embodiment, the parameter is the identity of the secondary station. The use of the same control channel structure in the link from relay to terminal as for the link from base station to terminal via the relay node may require that the relay modifies the control channel signal from the base station before forwarding it.

Thus, a method according to the invention may comprise the step of deleting messages which are not required by terminals served by that relay, and/or the step of substituting different messages.

In an alternative embodiment, the relay uses gaps in the control channel structure and inserts its own transmissions in the gaps. Such a feature makes it possible to avoid interfering with messages that the terminal might be required to receive directly from the base station. The invention also relates to a method wherein the second control signals are sent by using specific assigned resources different from those used for direct communication between the primary station and secondary station, and the method comprises the preliminary step of signalling the assigned resources to the primary station and/or the secondary station and/or the relay node. Signalling the assigned resources used for exchanging control signals makes it possible to ensure that this signal will not interfere with legacy signalling or with signalling via a direct link between the primary station and the secondary station; the method therefore comprises the preliminary step of signalling to the base station and/or to the terminal station and/or to the relay node which resources have to be used. In an alternative embodiment, the method comprises the step of establishing a correspondence between resources used in uplink and resources used in downlink.

Another aspect of the invention relates to a communication system comprising a primary station, a secondary station, and a relay node, and implementing a method according to the invention. This communication system may be, for example, compliant with current telecommunication standard, or future ones, such as LTE or IEEE802.16j.

Still another aspect of the invention relates to relay node comprising means for implementing a method according to the invention.

These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, wherein: - Fig. 1 shows a communication network where a method according to the invention is carried out.

DETAILED DESCRIPTION OF THE INVENTION

A method according to the present invention may be used in a network as shown in figure 1.

The network comprises a base station 1, for example an evolved Node B, two terminals stations 2 and 3, and a relay node 4. In the example herein described, terminals 2 and 3 do not have the same functionalities, namely terminal 3 has means for carrying out a method according to the present invention, whereas terminal 2 does not have such means. For example, terminal 2 is compliant with requirements of LTE release 8, and terminal 3 is compliant with requirements of an enhancement to LTE in accordance with the invention.

Then, communication between the base station 1 and the terminal 2 is made directly (5). Data exchanged during such communications may comprise content data, i.e. the message to be transmitted, and control signals. Control signals are sent via a specific channel, generally called a control channel.

On the other side, communications between base station 1 and terminals 3 are made via the relay node 4. Messages sent from the base station and intended for the terminal, are transmitted by the base station to the relay node and forwarded by the relay node to the terminal station. A similar protocol is carried out for messages sent by the terminal to the base station. Using a relay node makes it possible to extend the cell coverage, because even if the terminal is not included in the zone covered by the base station, it can still receive messages forwarded by a relay node included in the coverage zone of the base station.

During the course of such a communication, the base station and/or the terminal exchange control data with the relay node. This control data is sent using the same control channel structure as the control channel previously mentioned, which means that there is no need to adapt the control channels existing in a network. Thus, communications in a network can be performed either by using a method according to the invention, or using a direct method. This allows terminals who cannot handle a method according to the invention, namely terminal 2, to operate in cells where relays are being used. Indeed, even if terminal 2 receives a control signal 6 sent by relay node 4, operations of this terminal are not disturbed by such a message, because the message is not recognized by this terminal. Moreover, the message is arranged within the same structure as the control messages sent direct to terminal 2 by the base station 1 , so the message does not disturb the control messages sent directly to terminal 2 by the base station 1. Furthermore, even if terminal 2 receives a control signal 7a sent by the base station 1 to the relay node 4 to control operation of the relay node 4, operations of this terminal are not disturbed by such a message, because the message is not recognized by this terminal; moreover, the message is arranged within the same structure as the control messages sent direct to terminal 2 by the base station 1, so the message does not disturb the control messages sent directly to terminal 2 by the base station 1.

It appears that within the course of a method according to the invention, signalling data may be exchanged in four situations: message 7a sent from a Node B to a relay node, - message 7b sent from a relay node to a Node B, message 7c sent from a terminal station to a relay node, and message 7d sent from a relay node to a terminal station.

Message 7a comprises control data used for controlling functions performed by the relay node. For example, control data may be used for enabling or disabling the forwarding of transmissions from the base station to terminals or from terminals to base station. For example if the terminal does not bear receiving messages from a relay node, the function has to be disabled, or if the terminal is situated in the zone covered by the base station, there is no need to use the relay node. As said before, using the same control channel for both types of communications, i.e. direct or relayed, makes it possible to switch from one to the other without any service interruption.

Control data may also comprise information used for determining some parameters of the forwarding operations, such as: the gain factor applied to forwarded transmissions - the frequency band/channel to use for the forwarded signal the channel bandwidth in which to forward signals the gain per band/channel (to allow different gain values between bands) delay applied to the forwarded signal

Additional functions of the relay node that can be controlled by control data include: mapping between incoming frequency bands and outgoing bands/channel deletion/removal/replacement of particular data or symbols (e.g. modification of reference symbols) beamforming/precoding to apply to the signals forwarded from relay to terminal or to base station. mapping of signals between receive and transmit antennas in the relay selecting between different relay modes e.g. o Amplify-and-forward or decode-and-forward o HARQ or no HARQ - indicating parameters for selective forwarding of messages, for example forwarding to or from particular terminals indicating resources to be used for signalling from relay nodes to terminals stations or to base stations. receipt of control channel messages by the relay could be acknowledged using an existing uplink control channel structure.

In an exemplary embodiment of the present invention, sigalling data or control data sent in an downlink direction, i.e. from the base station to the relay node or to from the relay node to the terminal, are sent via a Physical Downlink Control Channel (PDCCH) of the communication network, and messages containing control data have a different size, i.e. a different DCI format, than the messages sent by a base station directly to a terminal station. Namely, first control signals exchanged between a primary station and a secondary station via a control channel have a first size and second control signals transmitted from the primary station to the relay node or from the relay node to the secondary station are in the form of messages of a second size different from the first size. In an alternative embodiment, the cyclic redundancy checks of the first and second control signals are each scrambled with an identification number, wherein the identification number with which the cyclic redundancy check of the first control signals is scrambled is different from the identification number with which the cyclic redundancy check of the second control signals is scrambled. In this case, the relay node or the secondary station identifying the intended recipient of the control signal using the identification number

Moreover, signalling data or control data may be inserted in unused parts of the PDCCH space, for example parts left empty by the base station initiating the communication. Message 7b sent from the relay node to the base station comprises signalling information regarding specific characteristics of the transmission, such as : channel quality of the link from base station to relay, acknowledgment of messages from the base stations, measurements of signals received by the relay generated by terminals.

Message 7b also comprises, in an example, a request for resources to transmit messages to the base station.

All these elements may be used by the base station to select which relay to use in the forward link, and which resources to be used from relay node to terminal stations.

In an exemplary embodiment of the present invention, control data or signalling data sent in an uplink direction, i.e. from the terminal to the relay node, or from the relay node to the base station, are sent via Physical Uplink Control Channel (PUCCH), or multiplexed into a Physical Uplink Shared Channel (PUSCH), and may be identified by the specific uplink resources which are used.

Message 7c, sent from a terminal station to a relay node comprises control data generally represents requests from the terminal. Message 7c includes, for example, one or several o f the fo Ho wing : a request to activate the forwarding of signals from relay to base station or to terminal, for example if the terminal detects that it is leaving the coverage zone of the base station, a request to apply specific beamforming/precoding to wanted forwarded messages, corresponding to a request for increasing signal power, or a request to apply specific beamforming/precoding to unwanted forwarded messages, corresponding to a request for decreasing signal power. Both requests make it possible to improve the Signal to Interference plus Noise Ratio (SINR) at the terminal, a request to change the power level of signals forwarded to the terminal, a request for de-activating forwarding of signals, in case of a strong direct link to the base station, with which the terminal does not need the relay node. Deactivating forwarding of signals makes it possible to avoid possible interference or other problems)

Message 7c may also comprise other elements such as an indication regarding the channel quality of the link from the relay node to the terminal station, or some acknowledgments of messages from the relay. Message 7d, sent from the relay node to the terminal station comprises, in an exemplary embodiment: a request to modify, for example increase or decrease, the power level of signals transmitted by the terminals, or acknowledgment of messages from the terminal. In an exemplary embodiment of the invention, the method further comprising the step of the relay node sending to the primary station an acknowledgment signal using an uplink control channel, wherein the acknowledgement signal uses the predetermined control channel structure. A method according to the invention finds an application in any type of network carrying out forwarding or relaying functions.

In the present specification and claims the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, the word "comprising" does not exclude the presence of other elements or steps than those listed. The inclusion of reference signs in parentheses in the claims is intended to aid understanding and is not intended to be limiting.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art of radio communication and the art of transmitter power control and which may be used instead of or in addition to features already described herein.

Claims

1. A method for communicating in a network comprising primary stations (1) and secondary stations (2) communicating by using a predetermined control channel structure, the method comprising : a primary station (1) transmitting to a relay node (4) a first control signal addressed to a secondary station using the predetermined control channel structure, the relay node (4) forwarding the first control signal unmodified to the secondary station (3), and - the primary station(l) and/or the secondary station (3) exchanging second control signals (7a, 7b, 7c, 7d) with the relay node (4), wherein said second control signals use the predetermined control channel structure.

2. A method as recited in claim 1, comprising the step of the relay node modifying received second control signals.

3. A method as recited in claim 1 wherein the exchanging step of second control signals comprises : the primary station transmitting the second control signal to the relay node, - the relay node modifying the second control signal depending on a parameter of the receiving secondary station, the relay node forwarding the modified second control signal to the secondary station.

4. A method as recited in claim 2, wherein the parameter on which depends the modification of the second control signal is the identity of the secondary station.

5. A method as recited in claim 1, wherein the second control signals are sent by using specific assigned resources different from those used for direct communication between the primary station and secondary station, and the method comprises the preliminary step of signalling the assigned resources to the primary station and/or the secondary station and/or the relay node.

6. A method as recited in claim 1, wherein first control signals exchanged between a primary station and a secondary station via a control channel have a first size and wherein second control signals transmitted from the primary station to the relay node or from the relay node to the secondary station are in the form of messages of a second size different from the first size.

7. A method as recited in claim 1, wherein the cyclic redundancy checks of the first and second control signals are each scrambled with an identification number, the identification number with which the cyclic redundancy check of the first control signals is scrambled is different from the identification number with which the cyclic redundancy check of the second control signals is scrambled, and the relay node or the secondary station identifying the intended recipient of the control signal using the identification number.

8. A method as recited in claim 1, wherein the step of exchanging second control signals between the relay node and the primary station and/or secondary station comprises inserting the control signal into unused part of a control channel.

9. A method as recited in claim 1 or 7, wherein control signals sent by the primary station to the relay node comprise data used for controlling functions performed by the relay node.

10. A method as recited in any of claims 1, 7 or 9, further comprising the step of the relay node sending to the primary station an acknowledgment signal using an uplink control channel, wherein the acknowledgement signal uses the predetermined control channel structure.

11. A communication system comprising a primary station, a secondary station and a relay node, implementing a method according to one of the preceding claims.

12. A relay node comprising means for carrying out a method according one of claims

1 to 10.