WO2013024346A1

WO2013024346A1 - Method of controlling autonomous uplink transmission of a user equipment in a secondary cell

Info

Publication number: WO2013024346A1
Application number: PCT/IB2012/001658
Authority: WO
Inventors: Tao Yang; Seau Sian Lim
Original assignee: Alcatel Lucent
Priority date: 2011-08-12
Filing date: 2012-08-13
Publication date: 2013-02-21
Also published as: CN102932947A; TW201322808A; CN102932947B

Abstract

The present invention relates to a method of controlling autonomous uplink transmission of a user equipment in a secondary cell. In particular, the present invention provides a method of controlling, in a base station of a wireless communication network that is based on carrier aggregation transmission, autonomous uplink transmission of a user equipment in a secondary cell served by said base station, which comprises the following steps: judging whether said user equipment has valid time alignment in said secondary cell; sending, to said user equipment, a first message for controlling said user equipment not to perform said autonomous uplink transmission in said secondary cell, if said user equipment has no valid time alignment in said secondary cell. With the solutions of the present invention, a base station controls a user equipment not to perform autonomous uplink in a secondary cell once the base station detects that the user equipment does not have valid time alignment in the secondary cell and thus significant interference to uplink communication of other user equipment(s) caused by the autonomous uplink transmission can be avoided.

Description

METHOD OF CONTROLLING AUTONOMOUS UPLINK

TRANSMISSION OF A USER EQUIPMENT IN A SECONDARY CELL

Field of the Invention

The present invention relates to wireless communication based on carrier aggregation technology, and more particularly relates to a method of controlling autonomous uplink transmission of a user equipment in a secondary cell.

Background of the Invention

In a communication system, a user equipment (UE) shall maintain uplink synchronization with a base station (BS) such as eNodeB by means of time alignment (TA), namely that uplink signals sent by all UEs served by the BS shall arrive at the BS simultaneously, so as to avoid causing significant interference to other UEs.

In a wireless communication network that is based on carrier aggregation (CA) transmission, a BS can configure multiple component carriers (CCs) for a UE so that the UE may communicate with the BS through these component carriers, in which one component carrier is called primary cell (Pcell) and other component carriers are called secondary cell (Scell). In the cells configured for the UE, the TA of each of these cells may be different due to a different network deployment. For example, there is no relay equipment in some cells whilst there are one or more relay equipments in some cells.

It is specified in 3 GPP (Third Generation Partnership Program) Release 10 that when configuring a certain component carrier, namely a cell, a BS configures a UE to perform autonomous uplink transmission (UL Tx) such as periodically sending a sounding reference signal (SRS) in the cell, and it is further specified that once a UE receives a MAC (Media Access Control) CE (control element) for activating a certain cell, the UE shall start autonomous UL Tx in 8 ms.

Summary of the Invention

Different from 3 GPP Release 10 in which all cells of a UE share same TA, the concept of TA group is proposed in 3GPP Release 11. All cells of a UE are grouped in one or more TA groups, and all cells in each TA group share same TA. TA groups are classified into two classes: Pcell group including a Pcell and Scell group including no Pcell.

Different cells may belong to different TA groups and thus have different TA. Therefore, when a BS configures a certain Scell for a UE, it is possible that this Scell does not belong to any existing TA group and thus does not have valid TA, namely that uplink synchronization is not achieved. For such a situation, it has been agreed in RAN2 that the BS shall firstly activate this newly configured Scell and then ask the UE to perform random access on PRACH (Physical Random Access Channel) in this Scell so as to obtain valid TA. As mentioned above, the UE starts to perform autonomous UL Tx in 8 ms once the Scell is activated. However, since this Scell has not obtained valid TA yet, the autonomous UL Tx of this UE in this Scell will cause significant interference to other UEs.

Furthermore, it is proposed in 3GPP Release 11 to adopt a scheme of setting one time alignment timer (TAT) for each UE, namely that all Pcell groups and Scell groups of a UE share the same TAT. According to this scheme, the TAT runs based on the Pcell group to guarantee the validity of the TA of the Pcell. In particular, when receiving a TA command (e.g. initial setting of TA or update of TA) of the Pcell group, the UE adjusts the TA according to the received command and restarts the TAT; however, when receiving a TA command of a Scell group, the UE adjusts the TA according to the received command without restarting the TAT. Moreover, if the UE does not receive any new TA command when the TAT expires, the TA of the UE is deemed to be not valid, namely that the UE loses uplink synchronization; if the TAT has not expired yet, the UE assumes that the TA of the Pcell and the TA of Scell are still valid.

Since the TAT only runs based on the Pcell group, the following scenario may occur: although the TA of a Scell group is not valid anymore because no TA command of the Scell has been received for a long time, the TAT does not expires because the TA commands of the Pcell are received from time to time and thus the UE mistakenly assumes that the TA of the Scell is still valid and continuously performs autonomous UL Tx, which causes significant interference to other UEs.

For the aforementioned technical problems, it is an object of the present invention to provide a method of controlling autonomous UL Tx of a UE in a Scell so as to avoid or reduce the interference to other UEs caused by the autonomous UL Tx of the UE.

According to a first aspect of the present invention, there is provided a method of controlling, in a base station of a wireless communication network that is based on carrier aggregation transmission, autonomous uplink transmission of a user equipment in a secondary cell served by said base station, which comprises the following steps: A. judging whether said user equipment has valid time alignment in said secondary cell; B. sending, to said user equipment, a first message for controlling said user equipment not to perform said autonomous uplink transmission in said secondary cell, if said user equipment has no valid time alignment in said secondary cell.

According to a second aspect of the present invention, there is provided a method of controlling, in a user equipment of a wireless communication network that is based on carrier aggregation transmission, autonomous uplink transmission of said user equipment in a secondary cell, which comprises the following steps: a. receiving, from a base station serving said secondary cell, a first message for controlling said user equipment not to perform said autonomous uplink transmission in said secondary cell; b. not performing said autonomous uplink transmission in said secondary cell according to the received first message. With the solutions of the present invention, a base station controls a user equipment not to perform autonomous uplink in a secondary cell once the base station detects that the user equipment does not have valid time alignment in the secondary cell and thus significant interference to uplink communication of other user equipment(s) caused by the autonomous uplink transmission can be avoided.

Brief Description of Drawings

Other features, objectives and advantages of the present invention will become more apparent from the following detailed description of the non-limiting embodiments taken in conjunction with the accompanying drawing.

Figure 1 is a flowchart of the method for controlling autonomous UL Tx of a UE in a Scell according to an embedment of the present invention;

Figure 2 is a flowchart of the method for obtaining valid TA according to an embodiment of the present invention;

Figure 3 is a flowchart of the method for controlling autonomous UL Tx of a UE in a Scell according to an embedment of the present invention, wherein the Scell has not been configured yet;

Figure 4 is a flowchart of the method for controlling autonomous UL Tx of a UE in a Scell according to an embedment of the present invention, wherein the Scell has been configured;

Figure 5 is a flowchart of the method for controlling autonomous UL Tx of a UE in a Scell according to an embedment of the present invention, wherein the Scell has not been activated yet;

Figure 6 is a flowchart of the method for controlling autonomous UL Tx of a UE in a Scell according to an embedment of the present invention, wherein the Scell is already activated; and

Figure 7 is a schematic diagram of the first and second predetermined information in MAC CE according to an embedment of the present invention; wherein, the identical or similar reference signs indicate the identical or similar procedure or apparatus/modules.

Detailed Description of Embodiments

Figure 1 shows a flowchart of the method for controlling autonomous UL Tx of UE 2 in Scell 3 according to an embedment of the present invention.

Referring to Figure 1 , in step SI 01 , BS 1 judges whether UE 2 has valid TA in Scell 3.

In particular, for Scell 3, there may be several scenarios as follows: i. BS 1 has not configured Scell 3 for UE 2;

ii. BS 1 has configured Scell 3 for UE 2, but Scell 3 is not activated; iii. BS 1 has configured Scell 3 for UE 2, and Scell 3 is activated. For scenario i, since BS 1 has not configured Scell 3 for UE 2, there exists no TA of Scell 3. In this case, BS 1 firstly judges whether Scell 3 belongs to the existing TA group(s), which can be, for example, known from information such as network deployment scenario and position of the UE. If Scell 3 does not belong to any existing TA group, BS 1 judges that UE 2 does not have valid TA in Scell 3. If Scell 3 belongs to an existing TA group, namely that the TA of Scell 3 is the same as the TA of the existing TA group, BS 1 judges whether UE 2 has valid TA in Scell 3 by judging whether the TA of this existing TA group is valid. If the TA of this existing TA group is valid, UE 2 has valid TA in Scell 3, and vice versa.

For scenarios ii and iii, since BS 1 has configured Scell 3 for UE 2, BS 1 judges whether the TA of Scell 3 is valid. If it is valid, BS 1 judges that UE 2 has valid TA in Scell 3, and vice versa.

If BS 1 judges, in step SI 01 , that UE 2 does not have valid TA in Scell 3, BS 1 sends, in step SI 02, UE 2 a first message for controlling UE 2 not to perform autonomous UL Tx including, for example, periodical SRS in Scell 3.

The first message can be implemented in various ways. According to an embodiment of the present invention, the first message can be used to not configure or de-configure the autonomous UL Tx of UE 2 in Scell 3 so that UE 2 does not perform the autonomous UL Tx in Scell 3. According to another embodiment of the present invention, the first message can be used to de-activate Scell 3 so that UE 2 does not perform the autonomous UL Tx in Scell 3. According to yet another embodiment of the present invention, the first message can be used to directly instruct UE2 not to perform the autonomous UL Tx in Scell 3. These will be described in below.

Next, in step SI 03, UE 2 receives the first message from BS 1 and does not perform autonomous UL Tx in Scell 3 according to the received first message.

In step SI 04, BS 1 obtains valid TA of UE 2 in Scell 3, which can be implemented in many ways.

According to an embodiment, BS 1 obtains the valid TA in Scell 3 by means of random access of UE 2 in Scell 3. For example, as shown in Figure 2, in step S201 , BS 1 sends a PDCCH (Physical Downlink Control Channel) order signaling to the UE; next, in step S202, UE 2 performs random access (e.g. sending random access preamble sequence) in Scell 3 ; next, in step S203, BS 1 determines the TA in Scell 3 according to the random access (e.g. the sent random access preamble sequence) of UE 2.

According to another embodiment, BS1 obtains valid TA of the TA group to which Scell 3 belongs by means of other ways, and in turn obtains the valid TA of Scell 3. For example, BS 1 obtains the valid TA of the TA group to which Scell 3 belongs by means of random access in other Scell of the TA group.

Further referring to Figure 1 , in step S 105, BS 1 sends the obtained valid TA to UE 2.

Next, in step SI 06, UE 2 sets valid TA for Scell 3 according to the received TA. Optionally, after setting the valid TA for Scell 3, UE 2 starts to perform autonomous UL Tx in Scell 3 if the autonomous UL Tx is configured in Scell 3. Alternatively, after receiving the valid TA of Scell 3, UE 2 does not automatically start to perform autonomous UL Tx in Scell 3 but waits for further control of BS 1 even if the autonomous UL Tx is configured in Scell 3. For example, as shown in Figure 1 , in step S 107, BS 1 sends UE 2 a second message for controlling UE 2 to perform autonomous UL Tx in the Scell. Next, in step SI 08, UE 2 starts to perform autonomous UL Tx in Scell 3 according to the received second message.

The first message for controlling not to perform autonomous UL Tx and the second message for controlling to perform autonomous UL Tx can be implemented in different ways. According to an embodiment of the present invention, the first and second messages can be RRC (Radio Resource Control) message; according to another embodiment of the present invention, the first and second messages can be MAC CE. These two embodiments are described with reference to Figures 3-4 and Figures 5-6, respectively.

Figure 3 shows a flowchart of the method for controlling autonomous UL Tx of UE 2 in Scell 3 according to an embedment of the present invention, wherein Scell 3 has not been configured yet, i.e. corresponding to the above scenario i.

As shown in Figure 3, before BS 1 configures Scell 3 for UE 2, BS 1 judges, in step S301 , whether UE 2 has valid TA in Scell 3 that is to be configured. If no, BS 1 sends, in step S2302, UE 2 a first RRC message as the first message, wherein the first RRC message is used for configuring Scell 3. Different from the existing RRC message for configuring Scell, the first RRC message does not include configuration for autonomous UL Tx in Scell 3.

Next, in step S303, UE 2 configures Scell 3 without configuring autonomous UL Tx in Scell 3 according to the received first RRC message. Thus, when Scell 3 is activated later, UE 2 will not perform autonomous UL Tx because no autonomous UL Tx has been configured.

Referring to Figure 3, steps S304 to S306 are similar to steps SI 04 to SI 06 in Figure 1 and are therefore not described here.

Further referring to Figure 3, after the TA of UE 2 in Scell 3 becomes valid, BS 1 sends UE 2 a third RRC message for configuring autonomous UL Tx in Scell 3 in step S307. Next, in step S308, UE 2 configures the autonomous UL Tx in Scell 3 and accordingly performs the autonomous UL Tx according to the received third RRC message.

Figure 4 shows a flowchart of the method for controlling autonomous UL Tx of UE 2 in Scell 3 according to an embedment of the present invention, wherein Scell 3 has been configured, i.e. corresponding to the above scenario ii or iii.

In the case that Scell 3 has been configured, the autonomous UL Tx in Scell 3 has also been configured, but Scell 3 can be activated or can be not activated, and furthermore, UE 2 performs the configured autonomous UL Tx in Scell 3 as far as Scell 3 is activated.

As shown in Figure 4, when Scell 3 is activated or BS 1 is about to activate Scell 3, BS 1 judges, in step S401 , whether UE 2 has valid TA in Scell 3 that is already activated or is to be activated. If no, BS 1 sends, in step S402, UE 2 a second RRC message as the first message, wherein the second RRC message is used for de-configuring the autonomous UL Tx in Scell 3.

Next, in step S403, UE 2 de-configures the autonomous UL Tx in Scell 3 according to the received second RRC message. Thus, even if Scell 3 is activated, UE 2 will not perform the autonomous UL Tx because the configuration for the autonomous UL Tx has been removed.

Referring to Figure 4, steps S404 to S408 are similar to steps S304 to S308 in Figure 3 and are therefore not described here.

Figure 5 shows a flowchart of the method for controlling autonomous UL Tx of UE 2 in Scell 3 according to an embedment of the present invention, wherein the Scell 3 has not been activated yet, i.e. corresponding to the above scenario i or ii.

As shown in Figure 5, if BS 1 is to configure Scell 3 for UE 2, BS 1 configures Scell 3 for UE 2 and configures autonomous UL Tx in Scell 3 in step S500.

In the case that BS 1 has already configured Scell 3 but has not activated it yet, BS 1 judges, in step S501, whether UE 2 has valid TA in Scell 3 that is to be activated. If no, BS 1 sends, in step 502, UE 2 a first MAC CE as the first message. The first MAC CE is used to activate the Scell and includes first predetermined information for instructing the UE not to perform the autonomous UL Tx in the Scell.

Next, in step S503, UE 2 activates Scell 3 without performing the autonomous UL Tx according to the received first MAC CE.

Referring to Figure 5, steps S504 to S506 are similar to steps S104 to S I 06 in Figure 1 and are therefore not described here.

Further referring to Figure 5, after the TA of UE 2 in Scell 3 becomes valid, BS 1 sends, in step S507, UE 2 a third MAC CE which includes second predetermined information for instructing UE 2 to perform the autonomous UL Tx in Scell 3. Next, in step S508, UE 2 performs the autonomous UL Tx in Scell 3 according to the received third MAC CE.

Figure 6 shows a flowchart of the method for controlling autonomous UL Tx of UE 2 in Scell 3 according to an embedment of the present invention, wherein Scell 3 is already activated, i.e. corresponding to the above scenario iii.

In the case that Scell 3 is already activated, UE 2 performs autonomous UL Tx in Scell 3. When the TA of Scell 3 is not valid, the autonomous UL Tx performed by UE 2 in Scell 3 causes significant interference to other UEs.

As shown in Figure 6, in order to avoid such interference, BS 1 judges, in step S601, whether UE 2 has valid TA in Scell 3 that is already activated. If no, BS 1 sends, in step S602, UE 2 a second MAC CE as the first message, wherein the second MAC CE is used for de-activating Scell 3.

Next, in step S603, UE 2 de-activates Scell 3 and thus does not perform the autonomous UL Tx in Scell 3 anymore according to the received second MAC CE.

Referring to Figure 6, steps S604 to S606 are similar to steps SI 04 to S I 06 in Figure 1 and are therefore not described here.

Further referring to Figure 6, after the TA of UE 2 in Scell 3 becomes valid, BS 1 sends, in step S607, UE 2 a fourth MAC CE which is used for activating the Scell and includes second predetermined information for instructing UE 2 to perform the autonomous UL Tx in Scell 3. Next, in step S608, UE 2 activates Scell 3 again and performs the autonomous UL Tx in Scell 3 according to the received fourth MAC CE.

Figure 7 shows a schematic diagram of the first and second predetermined information in MAC CE according to an embedment of the present invention.

The first predetermined information included in the aforementioned first MAC CE as well as the second predetermined information included in the aforementioned third and fourth MAC CE can be implemented in various ways.

As shown in Figure 7, according to an embodiment of the present invention, the existing MAC CE can be extended, namely that one byte b7-b0 is added to carry the first predetermined information and the second predetermined information for indicating whether to perform autonomous UL TX. In particular, each bit of the newly added byte b7-b0 can correspond to one cell, and the value of each bit indicates whether to perform autonomous UL Tx in the Scell corresponding to the bit. For example, if a certain bit of the newly added byte b7-b0 is set to 1 , it is indicated that autonomous UL Tx in the corresponding cell shall not be performed even if the cell is activated; if this bit is set to 0, it is indicated that autonomous UL Tx in the corresponding cell shall be performed, and thus the configured autonomous UL Tx will be started in 8 ms once the Scell is activated, as specified in 3 GPP Release 10.

The embodiment of the present invention has been described in the above. It should be understood that the present invention is not limited to the above specific embodiments, and any alternation or modification can be made by those skilled in the art without departing from the scope as defined by the appended claims.

Claims

1. A method of controlling, in a base station of a wireless communication network that is based on carrier aggregation transmission, autonomous uplink transmission of a user equipment in a secondary cell served by said base station, comprising the following steps:

A. judging whether said user equipment has valid time alignment in said secondary cell;

B. sending, to said user equipment, a first message for controlling said user equipment not to perform said autonomous uplink transmission in said secondary cell, if said user equipment has no valid time alignment in said secondary cell.

2. A method according to claim 1 , characterized in that said step A further comprises:

- judging that said user equipment does not have valid time alignment in said secondary cell, if said secondary cell has not been configured for said user equipment and said secondary cell does not belong to any existing time alignment group;

- judging whether said user equipment has valid time alignment in said secondary cell by means of judging whether time alignment of an existing time alignment group is valid, if said secondary cell has not been configured for said user equipment and said secondary cell belongs to said existing time alignment group; and

- judging whether said user equipment has valid time alignment in said secondary cell by means of judging whether time alignment of said secondary cell is valid, if said secondary cell has been configured for said user equipment.

3. A method according to claim 1 , characterized in that said first message is any one of the following: - a first RRC message for configuring said secondary cell, said first RRC message not including configuration for said autonomous uplink transmission of said secondary cell;

- a second RRC message for de-configuring said autonomous uplink transmission of said secondary cell;

- a first MAC control element for activating said secondary cell, said first MAC control element including first predetermined information for instructing said user equipment not to perform said autonomous uplink transmission in said secondary cell; and

- a second MAC control element for de-activating said secondary cell.

4. A method according to claim 1 , characterized by further comprising the following step after said step B:

D. sending valid time alignment of said user equipment in said secondary cell to said user equipment.

5. A method according to claim 4, characterized by further comprising the following step after said step B and before said step D:

C. obtaining said valid time alignment of said user equipment in said secondary cell.

6. A method according to claim 4, characterized by further comprising the following step after said step D:

E. sending, to said user equipment, a second message for controlling said user equipment to perform said autonomous uplink transmission in said secondary cell.

7. A method according to claim 6, characterized in that said second message is any one of the following:

- a third RRC message for configuring said autonomous uplink transmission in said secondary cell; - a third MAC controlling element that includes second predetermined information for instructing said user equipment to perform said autonomous uplink transmission in said secondary cell; and

- a fourth MAC control element for activating said secondary cell, said fourth MAC control element including said second predetermined information.

8. A method according to claim 1 , characterized in that said autonomous uplink transmission comprises a periodic sounding reference signal.

9. A method of controlling, in a user equipment of a wireless communication network that is based on carrier aggregation transmission, autonomous uplink transmission of said user equipment in a secondary cell, comprising the following steps:

a. receiving, from a base station serving said secondary cell, a first message for controlling said user equipment not to perform said autonomous uplink transmission in said secondary cell;

b. not performing said autonomous uplink transmission in said secondary cell according to the received first message.

10. A method according to claim 9, characterized in that said first message is any one of the following:

- a first RRC message for configuring said secondary cell, said first RRC message not including configuration for said autonomous uplink transmission of said secondary cell;

- a first MAC control element for activating said secondary cell, said first MAC control element including first predetermined information for instructing said user equipment not to perform said autonomous uplink transmission in said secondary cell; and - a second MAC control element for de-activating said secondary cell.

11. A method according to claim 9, characterized by further comprising the following steps after said step b:

c. receiving, from said base station, valid time alignment of said secondary cell;

d. setting valid time alignment for said secondary cell according to the received time alignment.

12. A method according to claim 11 , characterized in that said step d further comprises: performing said autonomous uplink transmission in said secondary cell according to the set valid time alignment.

13. A method according to claim 9, characterized by further comprising: e. receiving, from said base station, a second message for controlling said user equipment to perform said autonomous uplink transmission;

f. performing said autonomous uplink transmission in said secondary cell according to the received second message.

14. A method according to claim 13, characterized in that said second message is any one of the following:

- a third RRC message for configuring said autonomous uplink transmission in said secondary cell;

- a third MAC controlling element that includes second predetermined information for instructing said user equipment to perform said autonomous uplink transmission in said secondary cell; and

15. A method according to claim 9, characterized in that said autonomous uplink transmission comprises a periodic sounding reference signal.