Method and apparatus for improving hybrid automatic repeat request operation in a wireless communications system

0001This application claims the benefit of <patcit id="pcit0001" dnum="US95010607P"><text>U.S. Provisional Application No. 60/950,106, filed on Jul.16, 2007</text></patcit> and entitled "Method and Apparatus for Improving HARQ Operations in the transition of MIMO mode and non-MIMO mode and in HS-SCCH Less Operation."

0002The present invention relates to a method and related apparatus for improving Hybrid Automatic Repeat Request (HARQ) operation for a user equipment in a wireless communications system according to the pre-characterizing clauses of claims 1 and 7.

0003The third generation (3G) mobile telecommunications system, the Universal Mobile Telecommunications System (UMTS), 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 (Quality of Service) 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 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.

0004For 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 achievable download capacity for VoIP. For an HSDPA UE, the UE can work in a special mode, HS-SCCH less operation, included in CPC, for reducing the loading on high speed shared control channel (HS-SCCH). In addition, HSDPA and HSUPA adopt Hybrid Automatic Repeat Request (HARQ) technology to enhance retransmission rate and reduce transmission delay. HARQ is a technology combining Feed-forward Error Correction (FEC) and ARQ methods, which makes a Universal Terrestrial Radio Access Network (UTRAN) trigger retransmission according to positive/negative acknowledgement signals (ACK/NAK) transmitted from the UE, and the UE stores useful information about the last failed transmission for later use.

0005In the HS-SCCH less operation, the HS-SCCH is not transmitted with the first HARQ transmission. In this situation, the UE receives a high speed physical downlink shared channel (HS-PDSCH) according to predefined control information received when the HS-SCCH less operation is enabled, for reducing HS-SCCH overhead. Note that, in the HS-SCCH less operation, the same data is limited to 3 transmissions at most; in other words, the HARQ procedure is limited to 2 retransmissions. The UTRAN has to transmit corresponding control information for retransmissions on the HS-SCCH so that the UE receives the HS-PDSCH according to the corresponding control information.

0006For a detailed HARQ procedure for the HS-SCCH less operation, please refer to the associated 3GPP communications protocol specification. When the UE receives the data of the first transmission, the UE places the data of the first transmission in a soft buffer, replacing any data previously stored in the soft buffer. Next, the UE decodes the data in the soft buffer according to the predefined control information received when the HS-SCCH less operation is enabled. If the data has been decoded successfully, the UE reports a positive acknowledgement (ACK) to the base station, also known as Node-B, and waits for a new transmission. If the data has not been successfully decoded, the UE does not report a negative acknowledgement (NAK) to the Node-B and just waits for the second transmission, also called the first retransmission. During the second and the third transmissions, the control information, such as "second or third transmission" and "pointer to the previous transmission", are transmitted on the HS-SCCH.

0007Next, for the second transmission, the UE receives the data of the first transmission in the soft buffer according to the received control information, "second or third transmission" and "pointer to the previous transmission", and combines the data of the first transmission with the data of the second transmission for generating a first combined data. Then, the UE decodes the first combined data according to the corresponding control information received in the second transmission. If the first combined data has been decoded successfully, the UE reports an ACK to the Node-B and waits for a new transmission. Otherwise, the UE stores the first combined data in a soft buffer, reports a NAK to the Node-B and waits for the third transmission. The process of the third transmission is identical to the process of the second transmission and is not given here.

0008From the above, it is known that when the Node-B does not receive an ACK corresponding to the first transmission, the Node-B will start the second transmission. Or, when the Node-B receives a NAK corresponding to the second transmission, the Node-B will start the third transmission. Even if the UE decodes the data of the first transmission or the data of the second transmission successfully and reports a corresponding ACK, the Node-B may not receive the ACK or may decode the ACK as a NAK due to poor communication quality in the environment, and thereby starts a retransmission. On the other hand, the UE decodes the retransmission data after combining the retransmission data with the data previously stored in the soft buffer. In this situation, even if the UE decodes the data of the first transmission or the data of the second transmission successfully, the UE still has to combine retransmission data with the data that has been decoded successfully. Therefore, the data combination is unnecessary and reduces transmission efficiency.

0009In conclusion, when the UE has sent an ACK but the Node-B does not receive the ACK or decodes the ACK as a NAK, the UE still has to combine retransmission data with the data that has been decoded successfully. As a result, transmission efficiency of the HARQ operation is reduced for the UE in the HS-SCCH operation.

0010This in mind, the present invention aims at providing a method and related apparatus for deciding whether retransmission data is combined with data of a previous transmission according to a decoding result of the data of the previous transmission, for enhancing transmission efficiency of the HARQ operation.

0011This is achieved by a method and related apparatus for improving HARQ operation for a user equipment in a wireless communications system according to the pre-characterizing clauses of claims 1 and 7. The dependent claims pertain to corresponding further developments and improvements.

0012As will be seen more clearly from the detailed description following below, the claimed method of improving HARQ operation for a UE operating in HS-SCCH less operation in a wireless communications system. The method includes receiving a retransmission data in an HARQ procedure, determining a decoding result of data stored in a first soft buffer, combining the retransmission data with the data stored in the first soft buffer for generating a combined data when the UE determines that the data stored in the first soft buffer has not been successfully decoded, and performing a decoding process on the combined data and a store process corresponding to a second soft buffer, wherein the first soft buffer is obtained by a first rule and the second soft buffer is obtained by a second rule.

0013In 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 of a process according to an embodiment of the present invention.</li><li><figref idref="f0004">Fig. 4</figref> is a schematic diagram of a communications system.</li></ul>

0014Please refer to <figref idref="f0004">Fig. 4</figref>, which is a schematic diagram of a wireless communications system 400. The wireless communications system 400 is preferably a High Speed Package Access (HSPA) system, and is briefly composed of a network and a plurality of user equipments (UEs). In <figref idref="f0004">Fig. 4</figref>, the network and the UEs are simply utilized for illustrating the structure of the wireless communications system 400. Practically, the network may comprise a plurality of base stations (or Node B), radio network controllers and so on according to actual demands, and the UEs can be devices such as mobile phones, computer systems, etc.

0015Please refer to <figref idref="f0001">Fig. 1</figref>, which is a functional block diagram of a communications device 100. The communications device 100 can be used for implementing a UE shown in <figref idref="f0004">Fig. 4</figref>. 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, deliver received signals to the control circuit 106, and output 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.

0016Please 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 1 208. The Layer 3 202 is for performing radio resource control (RRC). The Layer 2 206 includes a radio control link (RLC) layer 212 and a media access control (MAC) layer 216 for performing link control, and the Layer 1 208 is a physical layer.

0017When the UE has sent an ACK but the Node-B does not receive the ACK or decodes the ACK as a NAK, the UE still has to perform an unnecessary data combination of a retransmission data and the data that has been decoded successfully, so that transmission efficiency of the HARQ operation is reduced. In this situation, an embodiment of the present invention provides a decoding result examination program code 220 for the program code 112 in the Layer 2 206 for improving the HARQ operation. Please refer to <figref idref="f0003">Fig. 3</figref>, which is a flowchart of a process 30 according to an embodiment of the present invention. The process 30 is utilized for improving the HARQ operation for a UE in the wireless communications system 400. The process 30 can be compiled into the decoding result examination program code 220. The process 30 includes the following steps: <dl id="dl0001" compact="compact"><dt>Step 300:</dt><dd>Start.</dd><dt>Step 302:</dt><dd>Receive a retransmission data in an HARQ procedure.</dd><dt>Step 304:</dt><dd>Determine a decoding result of data stored in a first soft buffer, wherein the first soft buffer is obtained by a first rule.</dd><dt>Step 306:</dt><dd>Combine the retransmission data with the data stored in the first soft buffer for generating a combined data when the UE determines that the data stored in the first soft buffer has not been successfully decoded.</dd><dt>Step 308:</dt><dd>Perform a decoding process on the combined data and a store process corresponding to a second soft buffer, wherein the second soft buffer is obtained by a second rule.</dd><dt>Step 310:</dt><dd>End.</dd></dl>

0018According to the process 30, the UE determines the decoding result of data stored in the first soft buffer first after receiving the retransmission data. When the UE determines that the data stored in the first soft buffer has not been successfully decoded, the UE combines the retransmission data with the data stored in the first soft buffer, for generating the combined data. After generating the combined data, the UE performs the decoding process on the combined data first, stores the combined data in the second soft buffer when the combined data is not successfully decoded, and then waits for a retransmission. On the other hand, the UE does not store the combined data in the second soft buffer when the combined data is successfully decoded. In addition, the UE can also store the combined data in the second soft buffer first, and then perform the decoding process.

0019Therefore, when the UE has sent an ACK but the Node-B does not receive the ACK or decodes the ACK as a NAK, the embodiment of the present invention determines the decoding result of the data stored in the first soft buffer first. When the UE determines that the data stored in the first soft buffer has not been successfully decoded, the UE combines the retransmission data with the data stored in the first soft buffer. As a result, the UE does not perform an unnecessary data combination, so as to enhance transmission efficiency of the HARQ operation for the UE in the HS-SCCH less operation.

0020In the process 30, the first soft buffer is used for storing the data of the previous transmission and is obtained by the first rule, which is selecting a soft buffer identified by a transmission time interval [5×CFN + SubFN - 6 - PTR] mod 13. On the other hand, the second soft buffer is used for storing the combined data that is generated by of the data of the previous transmission and the retransmission data, and is obtained by the second rule, which is selecting a soft buffer identified by a transmission time interval [5×CFN + SubFN] mod 13, wherein CFN is connection frame number, SubFN is subframe number, PTR is pointer to the previous transmission, and mod is modulo operation. In other words, the UE obtains the first soft buffer or the second soft buffer by a corresponding transmission time interval, so as to receive the data of the previous transmission stored in the first soft buffer, and store the combined data in the second soft buffer.

0021In the prior art, even if the UE decodes the data of the first transmission or the data of the second transmission successfully and reports a corresponding ACK, the Node-B may not receive the ACK or decodes the ACK as a NAK due to poor communication quality in the environment, and thereby starts a retransmission. On the other hand, the UE decodes the retransmission data after combining the retransmission data with the data stored in the soft buffer. In comparison, the embodiment of the present invention determines the decoding result of the data stored in the first soft buffer first after receiving the retransmission data, and then combines the retransmission data with the data stored in the first soft buffer when the UE determines that the data stored in the first soft buffer has not been successfully decoded. Therefore, the embodiment of the present invention does not perform an unnecessary data combination.

0022In conclusion, the embodiment of the present invention determines the decoding result of the data stored in a first soft buffer first, and then combines the retransmission data with the data stored in the first soft buffer when the UE determines that the data stored in the first soft buffer has not been successfully decoded. Therefore, the embodiment of the present invention does not perform an unnecessary data combination, so as to enhance transmission efficiency of the HARQ operation for the UE in the HS-SCCH less operation.