WO2008155688A1

WO2008155688A1 - Method for allocating transmission resources in a telecommunication system, a primary station and a secondary station for carrying out the method.

Info

Publication number: WO2008155688A1
Application number: PCT/IB2008/052309
Authority: WO
Inventors: Paul Bucknell; Matthew P. J. Baker
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-06-20
Filing date: 2008-06-11
Publication date: 2008-12-24
Also published as: TW200917720A

Abstract

The present invention relates to a method for allocating resources for transmissions from a secondary station to at least one primary station, wherein the method comprises at the secondary station, monitoring a control channel from the at least one primary station for detecting an allocation indicator indicating a physical resource allocated to the secondary station for the said transmissions, - at the secondary station, if the allocation indicator is detected, transmitting data to the primary station by means of the indicated physical resource, if the allocation indicator is not detected, transmitting data to the primary station by means of a first predetermined physical resource, and wherein, at the primary station, if no physical resource is allocated to the secondary station, sending a wait request instead of the allocation indicator, so that the secondary station, when receiving said wait request, enters into a wait state thus preventing uplink transmission.

Description

METHOD FOR ALLOCATING TRANSMISSION RESOURCES IN A

TELECOMMUNICATION SYSTEM, A PRIMARY STATION AND A

SECONDARY STATION FOR CARRYING OUT THE METHOD

FIELD OF THE INVENTION

The present invention relates to a method for allocating transmission resources in a telecommunication system, a system of telecommunication using this method, a primary station and a secondary station using the same method. More specifically, this invention is, for example, relevant for a mobile telecommunication system like a UMTS (Universal Mobile Telecommunications System).

BACKGROUND OF THE INVENTION

As defined in the UMTS specifications, the UMTS Terrestrial Radio Access Network (or UTRAN), which is responsible for handling all radio related functionality and which comprises a plurality of base stations (also called NodeB or primary stations), is linked to the user terminals (also called user equipments or secondary stations or mobile stations). The structure of the state of the art UTRA (Evolved Universal Terrestrial Network or E-UTRA) is captured 3GPP TS36.300, which is available from http://www.3gpp.org, incorporated herein by reference.

Regarding the uplink channels, i.e. from the secondary stations to the base stations, the secondary stations are transmitting data only on respective transmission resources, to avoid collisions of signals. These transmission resources are defined mainly by a frequency, a modulation coding scheme (MCS) and a transmission time interval during which they are allowed to transmit by using those parameters.

On the one hand, pre-assigned resources may be allocated to each secondary station, in particular for the first HARQ (for Hybrid Automatic Repeat re-Quest) transmissions and the retransmissions. It means that the secondary station transmits by using the predefined resources (typically frequency and modulation coding scheme) in a predefined transmission time interval.

On the other hand, this can be done dynamically by sending on a downlink control channel, namely the Layer 1 /Layer 2 downlink control channels (or L1/L2 control channel), an indication signal for allocation of a physical resource, for instance in response to an allocation request of the secondary station. The TTI is indicated by the time of transmission of this indication from the primary station to the secondary station: the allocated TTI will start after a fixed period starting from the sending of the indication signal. Indeed, the timing of the transmission will be a fixed time period offset from the reception and decoding of the L1/L2 downlink control information.

As currently specified in the UMTS, a semi persistent scheme has been chosen for some frames. This means that a hybrid of these two solutions is implemented. Indeed, the secondary station monitors continuously the L1/L2 control channel to check whether it can find its Cell Radio Network Temporary Identity (an address for identifying all secondary stations within a cell, noted C-RNTI). If its C- RNTI is found in a message on the L1/L2 control channel, it means that a transmission resource has been allocated dynamically, and that the pre assigned resources are overridden by the indicated resource. Then, the secondary station will transmit data to the primary station only by using the indicated resource, and within the subsequent TTI, starting after a predetermined time period from the sending of the indication. It will not use the pre assigned resource. If the secondary station's C- RNTI is not found within the sub-frame, the secondary station will then be able to transmit its data by using its pre-assigned resources and TTI. However, typically when a secondary station makes a request for an allocation, it is possible that no allocation is available in the sub-frame for transmission for this considered secondary station. The flexibility of the semi persistent scheme has to be improved to avoid collision of uplink transmission from secondary stations. SUMMARY OF THE INVENTION

It is an object of the invention to propose a method for allocating radio resources for an uplink channel enabling an improved flexibility in the allocation scheme.

Another object of the invention is to propose a method using the semi persistent scheme enabling the avoidance of collision of transmission without adding too much overhead.

To this end, in accordance with the invention, it is proposed a method for allocating resources for transmissions from a secondary station to at least one primary station, wherein the method comprises at the secondary station, monitoring a control channel from the at least one primary station for detecting an allocation indicator indicating a physical resource allocated to the secondary station for the said transmissions, - at the secondary station, if the allocation indicator is detected, transmitting data to the primary station by means of the indicated physical resource, if the allocation indicator is not detected, transmitting data to the primary station by means of a first predetermined physical resource, and wherein, at the primary station, if no physical resource is allocated to the secondary station, sending a wait request instead of the allocation indicator, so that the secondary station, when receiving said wait request, enters into a wait state thus preventing uplink transmission.

As a consequence, if no physical resource is available, the primary station is able to indicate to the secondary station to request it to go into a wait state till the next allocation or longer. It is possible according to an embodiment to further indicate how long the secondary station has to stay in a wait state, or when a new allocation will be available. If the secondary station has requested for an available resource, the method in accordance with the invention permits thus to prevent the secondary station from requesting repeatedly for resources which are unavailable.

Thus, the power consumption of the secondary station is not increased. The present invention also relates to a secondary station comprising means for carrying out the method in accordance with the invention.

In another aspect of the invention, it is proposed a primary station comprising means for carrying out the method in accordance with 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.l is a block diagram of a system comprising a primary station and a secondary in accordance with the invention;

Fig.2 is time chart of the signals transmitted in accordance with the method of the invention;

Fig 3 is a flow chart in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a system of communication 300 as depicted in Fig.l, comprising a primary station 100, like a base station, and at least one secondary station 200 like a mobile station.

The radio system 300 may comprise a plurality of the primary stations 100 and/or a plurality of secondary stations 200. The primary station 100 comprises a transmitter means 110 and a receiving means 120. An output of the transmitter means 110 and an input of the receiving means 120 are coupled to an antenna 130 by a coupling means 140, which may be for example a circulator or a changeover switch. Coupled to the transmitter means 110 and receiving means 120 is a control means 150, which may be for example a processor. The secondary station 200 comprises a transmitter means 210 and a receiving means 220. An output of the transmitter means 210 and an input of the receiving means 220 are coupled to an antenna 230 by a coupling means 240, which may be for example a circulator or a changeover switch. Coupled to the transmitter means 210 and receiving means 220 is a control means 250, which may be for example a processor. Transmission from the primary radio station 100 to the secondary station 200 takes place on a first channel 160 and transmission from the secondary radio station 200 to the first radio station 100 takes place on a second channel 260.

As explained before, the radio system uses a semi persistent scheme, where the secondary station 200 monitors continuously the L1/L2 control channel to check whether it can find its C-RNTI. If its C-RNTI is found in a message on the L1/L2 control channel, it means that a transmission resource has been allocated dynamically, and that the pre assigned resources are overridden by the indicated resource. Then, the secondary station 200 will transmit data to the primary station only by using the indicated resource, and within the subsequent TTI, starting after a predetermined time period from the sending of the indication. It will not use the pre assigned resource. If the secondary station 200 's C-RNTI is not found within the sub-frame, the secondary station 200 will then be able to transmit its data by using its pre-assigned resources and TTI.

According to a first embodiment of the invention, the network can further signal that the uplink radio resource should not be used (i.e. that there is no uplink resource allocation in the corresponding uplink subframe), by sending a L1/L2 control signal that indicates that the UE cannot use any scheduled radio resource. This signal or wait request, asks the secondary station 200 to enter into a wait state where it will not transmit on the considered channel.

In the case of an initial transmission of a packet, for which a default resource allocation (usually periodic) is already configured, the effect of the invention would be that the expected transmission of uplink data is delayed until a later opportunity - either the next default allocation, or another occasion in response to additional L1/L2 control information.

In the case of a request from the UE 200 for uplink transmission resources, the effect of the invention would be that the network has the ability to signal a "zero" allocation which acknowledges that the request has been received but indicates to the UE 200 that none are available. It permits thus to prevent the UE 200 from repeating the request. Indeed, the Primary station 100 is aware that this UE 200 needs resources, but must handle with other secondary stations, for instance having higher priority data to send. Optionally, the time that the UE could try again to request resources, or the time when the UE should monitor the L1/L2 control channel again, could be configured to be one or multiple TTIs later than the TTI corresponding to the indication of wait request, or could be indicated in the wait request message.

This sending of wait requests informs the secondary station 200 that the network has received the request, as this signal acknowledges the request, but no resource is allocated. One option would then be for the UE to re-send the resource allocation request in the next available UL resource allocation request time slot, but can also wait without sending this request again.

The advantage of allowing the network to signal to the UE that it cannot use any physical resource block to transmit in, is that the UE saves on transmit power and the network can utilise all the radio resources for other users, which may have higher- priority data to send.

In an embodiment shown in Fig.2, the system is operating with persistent scheduling. A default allocation allows the UE 200 to use a pre-defined PRB (physical resource block) without the need for L1/L2 control information. In "RX - case 1", the UE 200 is transmitting regular uplink data blocks in the periodic default time/frequency resources, but is also monitoring the L1/L2 control information. If no L1/L2 control information is received for the UE it proceeds to transmit in the uplink using the pre-defined default allocation. In the second case, labelled "RX case -2", at TTI 8, a L1/L2 control signal is received which instructs the UE to use a different allocation to the default one. In the third case, which is the subject of this invention, the L1/L2 control information is used to indicate that the UE should not transmit in any uplink resources.

As indicated above, in an alternative embodiment of this invention the network wait request (or no allocation) signal can be sent in response to the UE making a request for uplink resources. In this case the use of the wait request signal allows the request to be acknowledged by the network, thus avoiding the UE unnecessarily repeating the request through a misapprehension that the request had not been received. Advantageously, the wait request message may include an indication of a time offset when uplink resources will be available, or an indication of a time offset after which the UE 200 may resend its request.

According to an aspect of the invention, the system 300 uses several HARQ processes. The uplink HARQ (Hybrid Automatic Repeat-reQuest) processing, i.e. from the secondary stations to the primary stations, may be implemented as follows:

- if an uplink grant is valid for this Transmission Time Interval that indicates a new transmission, then notify an "uplink prioritisation" entity that the TTI is available for a new transmission;

- if the "uplink prioritisation" entity indicates the need for a new transmission, then obtain the MAC PDU to transmit from the "Multiplexing and assembly" entity, and instruct the HARQ process corresponding to this TTI to trigger the transmission of this new payload using the identified parameters.

else:

- if an uplink grant is valid for this TTI that indicates a re-transmission; or

- if no uplink grant is valid for this TTI and the buffer is not empty:

then instruct the HARQ process to generate a re-transmission.

In this embodiment of the present invention, the L1/L2 control information might also be used to indicate that the specific HARQ process being used by the UE is disabled, but can use the other HARQ processes available. The advantage of this "fine control" of downlink scheduling is that the network can effectively reduce the resources used by a particular UE in small steps, than by normal L1/L2 allocation control. Typically this would have the effect of disabling the transmissions in every n^th TTI, where n is the total number of HARQ processes. For instance, the UE may be able to use a lower priority HARQ process instead of the current HARQ process.

In a variant of the invention, in cases when persistent scheduling is used for retransmissions - i.e. default resources are configured for a retransmission to be sent a certain time interval after an initial transmission. This is currently proposed for the uplink of E-UTRA. If the primary station 100 successfully decodes the packet after the initial transmission and therefore does not need a retransmission, it is beneficial for the primary station 100 to be able to send a wait message to the UE 200 to cancel the default allocation and prevent the UE 200 from wasting power sending an unnecessary retransmission. The uplink resources can instead be assigned to another UE. In such a case, the wait request may comprise the field normally indicating the transmission time interval may take a predetermined particular value indicating that no TTI will never be allocated for this retransmission, so that the UE 200 will not to transmit this data again.

As illustrated on Fig.3, according to an embodiment of the invention, the secondary station 200 can make firstly a request of allocation, at step SlOO. This step SlOO is not essential and may not be implemented in some variant of the invention. At step SlOl, the primary station checks the availabilities on the uplink. This is done by comparison of several parameters, as the priority of the data to be transmitted, the age of the requests of the secondary stations, or similar.

At step 102, the secondary station 200 monitors the L1/L2 control channels. At step 103, if no allocation message comprising a C-RNTI corresponding to the secondary station is detected, the secondary station will transmit its data at step S 105 by using the pre-assigned resource. If, at step 103, an allocation message comprising a C-RNTI corresponding to the secondary station is detected, allocation message data is extracted at step S 104. If these data comprises an allocation of physical resources, the secondary station 200 will use transmit data by using the dynamically allocated resource, in the TTI following the reception of the allocation message delayed by a predetermined amount, at step 106. If the data extracted comprises a wait request, the secondary station 200 will not transmit during the sub frame, at step 107. In a variant of the invention, an indication of a TTI is sent with the wait request, this TTI corresponding for instance to the next transmission of allocation message, and the secondary station may only monitor again the L1/L2 channels at that time. In another variant of the invention, the indicated TTI corresponds to an allocated TTI for the next sub frame, so that the secondary station has not to monitor again the L1/L2 channels till the next transmission. 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. 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 allocating resources for transmissions from a secondary station to at least one primary station, wherein the method comprises at the secondary station, monitoring a control channel from the at least one primary station for detecting an allocation indicator indicating a physical resource allocated to the secondary station for the said transmissions, at the secondary station, if the allocation indicator is detected, transmitting data to the primary station by means of the indicated physical resource, if the allocation indicator is not detected, transmitting data to the primary station by means of a first predetermined physical resource, and wherein, at the primary station, if no physical resource is allocated to the secondary station, sending a wait request instead of the allocation indicator, so that the secondary station, when receiving said wait request, enters into a wait state thus preventing uplink transmission.

2. The method of claim 1, wherein the primary station indicates in the wait request the transmission time interval during which the secondary station is next to monitor the control channel for detecting the allocation indicator.

3. The method of claim 2, wherein the secondary station enters into a discontinuous reception mode upon receiving the wait request.

4. The method of claim 3, wherein at least one discontinuous reception parameter is based on the transmission time interval indicated within the wait request.

5. The method of any of the preceding claims, wherein the secondary station upon receiving a wait request transmits data during a second predetermined allocated resource following the first predetermined allocated resource.

6. The method of any of the preceding claims, wherein the first predetermined physical resource corresponds to a retransmission of an earlier transmission of data from the secondary station to the primary station, and wherein in response to receiving the wait request the secondary station does not transmit any further retransmissions of the earlier transmission of data.

7. The method of any of the preceding claims, wherein the method is initiated by an uplink transmission resource request from the secondary station to the primary station.

8. The method of claim 7, wherein the secondary station sends a further uplink transmission resource request upon receiving a wait request.

9. The method of claim 8, wherein the time between receiving the wait request and the sending of the further uplink transmission resource request is either predetermined or signalled to the secondary station by the primary station.

10. A primary station comprising means for allocating resources for transmissions from a secondary station to said primary station, means for transmitting on a control channel to the secondary station a signal comprising an allocation indicator indicating a physical resource allocated to the secondary station for the said transmissions, wherein the signal comprises an allocation indicator if the allocated resources does not correspond to the predetermined physical resources, and wherein the signal does not comprise an allocation indicator, if the allocated resource corresponds to a first predetermined physical resource, and wherein the means for allocating are arranged so that if no physical resource is allocated to the secondary station, the signal comprises a wait request instead of the allocation indicator, so that the secondary station, when receiving said wait request, enters into a wait state thus preventing uplink transmission.

11. A secondary station being able to transmit data to a primary station by using allocated resources for transmissions to the primary station, comprising monitoring means for monitoring a control channel from the least one primary station for detecting an allocation indicator indicating a physical resource allocated to the secondary station for the said transmissions, transmitting means for transmitting data to the primary station by means of the indicated physical resource if the allocation indicator is detected, and for transmitting data to the primary station by means of a first predetermined physical resource, if the allocation indicator is not detected, and wherein the monitoring means are arranged so that, upon receiving a wait request instead of the allocation indicator, the secondary station enters into a wait state thus preventing uplink transmission.