Method of enhancing continuous packet connectivity in a wireless communications system and related apparatus

0001This application claims the benefit of <patcit id="pcit0001" dnum="US86807806" dnum-type="L"><text>U.S. Provisional Application No. 60/868,078, filed on Nov. 30, 2006</text></patcit> and entitled "Method And Apparatus for Enhancing CPC related procedures in a Wireless Communications System".

0002The present invention relates to a method for managing operation of control channels used in Continuous Packet Connectivity (CPC) for a user end and related communications devices according to the pre-characterizing clauses of claims 1 and 5.

00033GPP change request R2-063567, "Introduction of DTX-DRX and HS-SCCH less in RRC", XP002591175, discloses techniques for determining a CPC_HS_SCCH_LESS_STATUS status variable.

0004The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate. For HSDPA and HSUPA, the 3rd Generation Partnership Project (3GPP) provides a Continuous Packet Connectivity (CPC) protocol specification, which includes features that, for user equipments (UEs) in CELL_DCH state, aim to significantly increase the number of packet data users for a cell, reduce the uplink noise rise and improve the achievable download capacity for VoIP.

0005For an HSDPA UE, physical channels include a high speed physical downlink shared channel (HS-PDSCH), for transferring payload data, and a high speed physical control channel (HS-DPCCH) for uploading an acknowledgement/negative acknowledgement (ACK/NACK) and a channel quality identifier (CQI). As for the media access control (MAC) layer of the HSDPA UE, a MAC-hs entity utilizes a transport channel of High Speed Downlink Shared Channel (HS-DSCH) for receiving data from the physical layer. In addition, a shared control channel for HS-DSCH (HS-SCCH) is used as a physical downlink channel, responsible for transmission of control signals corresponding to HS-DSCH, such as demodulation information.

0006For an HSUPA UE, physical channels includes two uplink channels: an E-DCH dedicated physical data channel (E-DPDCH), for transferring payload data, and an E-DCH dedicated physical control channel (E-DPCCH) for transmission of control signals, such as retransmission numbers. Furthermore, a bundle of downlink physical channels are employed in the HSUPA system and used for transmitting control signals associated with grants, ACKs and etc. The downlink physical channels include E-DCH relative grant channel (E-RGCH), E-DCH absolute grant channel (E-AGCH), E-DCH HARQ acknowledgement indicator channel (E-HICH) and fractional dedicated physical channel (F-DPCH). As for the MAC layer of the HSUPA UE, a MAC-e/es entity utilizes a transport channel of Enhanced Dedicated Transport Channel (E-DCH) for transmitting MAC packet data to the physical layer with supporting a transmission time interval (TTI) of 10 milliseconds (ms) or 2 ms.

0007CPC includes an HS-SCCH less operation, which is a special mode of HSDPA operation for reducing HS-SCCH overhead for a hybrid automatic repeat request (HARQ) process, thereby reducing UE power consumption. Under this mode, the first HS-DSCH transmission of the HARQ process corresponding to small transport blocks (TBs) on pre-defined HS-DSCH is performed without accompaniment of HS-SCCH signaling, and the HARQ retransmissions corresponding to the first HS-DSCH transmission are accompanied with the HS-SCCH signaling if the retransmissions are needed. Accordingly, the UE needs blind decoding for TB data of the first transmission based on predefined TB size and channel coding set. If blind decoding is success, the UE reports ACK to the base station, also known Node-B, through HS-SCCH; otherwise, the UE reports nothing and waits for retransmission initiated by the Node-B. In order to combine the first transmission with the subsequent retransmissions, the HS-SCCH transmits required control signals of physical channel coding set, TB size, UE identity, a pointer and etc., where the pointer notify the UE of the TTI where the previous transmission has been performed. In addition, The UE can report ACK or NACK for the retransmission, and the retransmission is restricted to two times. The first and second retransmissions can be asynchronous with respect to the first transmission, and with respect to each other. The accompanying HS-SCCH follows the same timing relationship with the HS-PDSCH transmission as legacy transmissions do.

0008As to radio resource control (RRC), the UE and the network, such as the Node-B or a radio network controller (RNC), can configure the CPC by exchanging RRC messages and information elements (lEs) that include corresponding parameters. According to the RRC protocol specification of 3GPP, a Continuous Packet Connectivity HS-SCCH Less Information IE is provided to carry the configuration of "HS-PDSCH Code Index", "Transport Block Size Index" and etc. In general, the above IE can be included in RRC CONNECTION SETUP, ACTIVE SET UPDATE, CELL UPDATE CONFIRM or other reconfiguration messages, and can be transmitted to the UE through RRC procedures. On the other hand, the UE stores the configuration includes in the reconfiguration messages into a CPC_HS_SCCH_LESS_PARAMS variable.

0009Furthermore, the UE includes a CPC_HS_SCCH_LESS_STATUS variable having two possible values of "TRUE" and "FALSE, which represent the in-use state and the out-of-use state of the HS-SCCH less operation, respectively. According to the RRC specification, the UE is required to determine the value for CPC_HS_SCCH_LESS_STATUS variable if receiving any reconfiguration messages. Within the CPC_HS_SCCH_LESS_STATUS determination, the CPC_HS_SCCH_LESS_STATUS variable shall be set to "TRUE" when all of the following conditions are met: <ol id="ol0001" compact="compact"><li>1. the UE is in CELL_DCH state;</li><li>2. an HS_DSCH RECEPTION variable is set to "TRUE";</li><li>3. no DCH transport channel is configured;</li><li>4. the CPC_HS_SCCH_LESS_PARAMS is set;</li><li>5. the UE has received a Continuous Packet Connectivity HS-SCCH Less information IE from the latest reconfiguration message.</li></ol>

0010If any of the above conditions is not met and the CPC_HS_SCCH_LESS_STATUS variable is set to be "TRUE", the UE shall: <ol id="ol0002" compact="compact"><li>1. set the CPC_HS_SCCH_LESS_STATUS variable to be "FALSE";</li><li>2. clear the CPC_HS_SCCH_LESS_PARAMS variable;</li><li>3. stop all related activities of CPC HS-SCCH less operation.</li></ol>

0011Whenever the CPC_HS_SCCH_LESS_STATUS variable is set to "TRUE", the UE shall configure the physical and MAC layers to operate according to the CPC_HS_SCCH_LESS_PARAMS.

0012According to the above, the UE determines the value for CPC_HS_SCCH_LESS_STATUS variable only when receiving reconfiguration messages, and the HS-SCCH less operation is only applied to the UE in CELL_DCH. If a radio link failure or a radio link control (RLC) unrecoverable error occurs or if transmission of a UE CAPABILITY INFORMATION message fails during HS-SCCH less operation, the UE shall perform a cell update procedure to remedy those situations. When initiating the cell update procedure, the UE shall move to CELL_FACH state and select a suitable UMTS radio access (UTRA) cell for submitting a CELL UPDATE message. However, the prior art specification specifies no related actions of HS-SCCH less operation under the abovementioned situations. As a result, the UE of the prior art does not re-determine the CPC_HS_SCCH_LESS_STATUS variable when moving out of CELL_DCH state. That is, the UE continues applying HS-SCCH less operation in CELL_FACH state, which is not applicable for HS-SCCH less operation. This may cause severe errors in the physical and MAC layers of the UE.

0013The radio link failure may occur when the UE is situated in poor signal distributing area, such as a basement or rural area with small coverage. The RLC unrecoverable error is likely to occur due to many causes, such as RLC reset errors or RLC recovery errors. The UE CAPABILITY INFORMATION message is utilized to notify the UTRAN of information of specific UE capability (ex. radio access capability).

0014This in mind, the present invention aims at providing a method and apparatus for managing a less operation mode of a control channel of CPC for a user end in a wireless communications system to avoid system malfunction.

0015This is achieved by a method and device for managing control channel less operation of CPC in a wireless communications system according to the claims 1 and 3. The dependent claims pertain to corresponding further developments and improvements.

0016As will be seen more clearly from the detailed description following below, a method enhancing CPC for a UE in a wireless communications system comprises activating a control channel less operation according to a status variable, and re-determining the status variable and performing corresponding actions when a cell update procedure is initiated.

0017In the following, the invention is further illustrated by way of example, taking reference to the accompanying drawings. Thereof <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a functional block diagram of a communications device.</li><li><figref idref="f0002">Fig. 2</figref> is a diagram of the program code shown in <figref idref="f0001">Fig. 1</figref>.</li><li><figref idref="f0003">Fig. 3</figref> is a flowchart diagram of a process according to an embodiment of the present invention.</li></ul>

0018Please refer to <figref idref="f0001">Fig. 1</figref>, which is a functional block diagram of a communications device 100. For the sake of brevity, <figref idref="f0001">Fig. 1</figref> only shows an input device 102, an output device 104, a control circuit 106, a central processing unit (CPU) 108, a memory 110, a program code 112, and a transceiver 114 of the communications device 100. In the communications device 100, the control circuit 106 executes the program code 112 in the memory 110 through the CPU 108, thereby controlling an operation of the communications device 100. The communications device 100 can receive signals input by a user through the input device 102, such as a keyboard, and can output images and sounds through the output device 104, such as a monitor or speakers. The transceiver 114 is used to receive and transmit wireless signals, delivering received signals to the control circuit 106, and outputting signals generated by the control circuit 106 wirelessly. From a perspective of a communications protocol framework, the transceiver 114 can be seen as a portion of Layer 1, and the control circuit 106 can be utilized to realize functions of Layer 2 and Layer 3. Preferably, the communications device 100 is utilized in a High Speed Package Access (HSPA) system of the third generation (3G) mobile communications system, supporting Continuous Packet Connectivity (CPC).

0019Please continue to refer to <figref idref="f0002">Fig. 2. Fig. 2</figref> is a diagram of the program code 112 shown in <figref idref="f0001">Fig. 1</figref>. The program code 112 includes an application layer 200, a Layer 3 202, and a Layer 2 206, and is coupled to a Layer 1 218. The Layer 3 202 includes a radio resource control (RRC) entity 222, which is used for controlling the Layer 1 218 and the Layer 2 206 and performing peer-to-peer RRC communication with other communications devices, such as a Node-B or a UTAN. In addition, the RRC entity 222 can change an RRC state of the communications device 100, switching between an Idle mode, CELL_PCH, URA_PCH, CELL_FACH or CELL_DCH state.

0020The Layer 2 206 includes a radio control link (RLC) layer and a media access control (MAC) layer, and the Layer 1 218 is physical layer. When the HSDPA is in use, the MAC layer listens to HS-SCCH for HS-DSCH signaling reception and thereby receives packet data by listening to HS-DSCH. Besides, HS-PDSCH and HS-DPCCH are used for exchanging payload data between the communications device 100 and the network.

0021A network communications device can form RRC messages and information elements (lEs) to transmit CPC configuration to the communications device 100 via radio bearers. The reconfiguration messages, such as RRC CONNECTION SETUP, ACTIVE SET UPDATE or CELL UPDATE CONFIRM message, are allowed to include parameters of HS-SCCH less operation of CPC. Accordingly, the communications device 100 stores received parameters into a CPC_HS_SCCH_LESS_PARAMS variable and thereby changes operation of the Layer 2 206 and the Layer 1 218. Furthermore, the communications device 100 includes a CPC_HS_SCCH_LESS_STATUS variable having two possible values of "TRUE" and "FALSE", which represent an in-use state and an out-of-use state of the HS-SCCH less operation, respectively.

0022In this situation, the embodiment of the present invention provides a control channel less operation managing program code 220 for the program code 112 to avoid system malfunction. Please refer to <figref idref="f0003">Fig. 3</figref>, which illustrates a schematic diagram of a process 30 according to an embodiment of the present invention. The process 30 is utilized for managing control channel less operation for a UE in a wireless communications system, and can be compiled into the control channel less operation managing program code 220. The process 30 includes the following steps: <ul id="ul0002" list-style="none" compact="compact"><li>Step 300: Start.</li><li>Step 302: Activate a control channel less operation according to a status variable.</li><li>Step 304: Re-determine the status variable and perform corresponding actions when a cell update procedure is initiated.</li><li>Step 306: End.</li></ul>

0023In the process 30, the control channel less operation is used for a control channel corresponding to an HARQ process, in which no control signals corresponding to the first transmission of the HARQ process are transmitted on the control channel.

0024Preferably, the status variable is CPC_HS_SCCH_LESS_STATUS variable, and the control channel less operation function is HS-SCCH less operation. According to the HS-SCCH less operation, the first HS-DSCH transmission of the HARQ process corresponding to small TBs is performed without accompaniment of HS-SCCH signaling, and the HARQ retransmissions corresponding to the first HS-DSCH transmission are accompanied with the HS-SCCH signaling if the retransmissions are needed.

0025When CPC_HS_SCCH_LESS_STATUS variable is set to "TRUE", the HS-SCCH less operation is activated. When a radio link failure or an RLC unrecoverable error occurs or when transmission of a UE CAPABILITY INFORMATION message fails during HS-SCCH less operation, the cell update procedure is initiated to remedy those situations. When the cell update procedure is initiated, the UE moves to CELL_FACH state for selection of a suitable UTRA cell, and moreover the CPC_HS_SCCH_LESS_STATUS variable is re-determined by determining whether all of the abovementioned conditions are met for setting the CPC_HS_SCCH_LESS_STATUS variable to be "TRUE". Since the UE no longer stays in CELL_DCH state, the conditions required setting the CPC_HS_SCCH_LESS_STATUS variable to be "TRUE" are not all met. The UE then performs corresponding actions, where the corresponding actions include: <ol id="ol0003" compact="compact"><li>1. set the CPC_HS_SCCH_LESS_STATUS variable to be "FALSE" if the CPC_HS_SCCH_LESS_STATUS variable is originally set to be "TRUE";</li><li>2. clear the CPC_HS_SCCH_LESS_PARAMS variable;</li><li>3. stop all related activities of CPC HS-SCCH less operation.</li></ol>

0026Through the above actions, HS-SCCH less operation is stopped when the cell update procedure is initiated.

0027In addition, an alternative of stopping HS-SCCH less operation is performing the abovementioned actions directly without re-determining the CPC_HS_SCCH_LESS_STATUS variable after a suitable UTRA cell is selected during the cell update procedure. Thus, when a radio link failure or an RLC unrecoverable error occurs or when transmission of a UE CAPABILITY INFORMATION message fails, the UE can timely stop HS-SCCH less operation of the physical and MAC layers to avoid system malfunction.

0028Please note that the embodiment of the present invention takes HS-SCCH for example, and the present invention is also applied to control channels taking similar less operation for the HARQ process for CPC.

0029In conclusion, the embodiment of the present invention specifies the UE to stop HS-SCCH less operation when a radio link failure or an RLC unrecoverable error occurs or when transmission of a UE CAPABILITY INFORMATION message fails.