Title of Invention	METHOD AND APPARATUS FOR SUPPORTING HARQ
Abstract	A method of supporting Hybrid Automatic Repeat Request (HARQ) includes receiving an initial uplink grant on a downlink channel, transmitting uplink data on an uplink channel using the initial uplink grant, receiving a request for retransmission of the uplink data, determining at least one transmission parameter of a channel quality indicator (CQI) from the initial uplink grant, multiplexing retransmission data of the uplink data with the CQI, and transmitting the multiplexed data on the uplink channel. Amount of resources for transmission of the CQI is determined based on the at least one transmission parameter.

Title of Invention

METHOD AND APPARATUS FOR SUPPORTING HARQ

Abstract

A method of supporting Hybrid Automatic Repeat Request (HARQ) includes receiving an initial uplink grant on a downlink channel, transmitting uplink data on an uplink channel using the initial uplink grant, receiving a request for retransmission of the uplink data, determining at least one transmission parameter of a channel quality indicator (CQI) from the initial uplink grant, multiplexing retransmission data of the uplink data with the CQI, and transmitting the multiplexed data on the uplink channel. Amount of resources for transmission of the CQI is determined based on the at least one transmission parameter.

Full Text	Description METHOD AND APPARATUS FOR SUPPORTING HARQ Technical Field [ 1 ] The present invention relates to wireless communications, and more particularly, to a method and apparatus for supporting hybrid automatic repeat request (HARQ) in a wireless communication system. Background Art [2] Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. In general, the wireless communication system is a multiple access system capable of supporting commu- nication with multiple users by sharing available system resources (e.g., bandwidth, transmission power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc. [3] Current development in advanced wireless communication has led to the requrement of high spectral efficiency and reliable communication. Unfortunately, packet errors by fading channel environment and interferences originated from various sources make the capacity of overall system to be limited. [4] Hybrid automatic repeat request (HARQ) is an ARQ protocol combined with forward error correction (FEC) and is strongly considered as one of cutting edge technologies for future reliable communication. The HARQ scheme can largely be classified into two types. One is HARQ-chase combining (CC) which is disclosed in D. Chase, Code Combining: A maximum-likelihood decoding approach for combining an arbitrary number of noisy packets, IEEE Trans, on Commun., Vol. 33, pp. 593-607, May 1985. The other is HARQ-Increment Redundancy (IR). In the HARQ-CC, when a receiver detects an error through cyclic redundancy checking (CRC) while decoding the transmitted packet, the same packet with the same modulation and coding is re- transmitted to the receiver. Meanwhile, in order to achieve a coding gain, the HARQ- IR retransmits different packets, in which parity bits can be manipulated through puncturing and repetition. To perform the HARQ, there is a need to exchange ac- knowledgement (ACK)/not-acknowledgement (NACK) information that indicates whether retransmission is necessary. [5] Adaptive modulation and coding (AMC) is also a technology for providing reliable communication. A base station (BS) determines a modulation and coding scheme (MCS) used for transmission by using a channel quality indicator (CQI) received from a user equipment (UE). In general, the CQI is an index of an entity of an MCS table showing a plurality of MCSs. The UE transmits the CQI by using two methods. One is that the CQI is transmitted periodically. The other is that the CQI is transmitted at the request of the BS. [6] 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved-universal mobile telecommunications system (E-UMTS) using evolved- universal terrestrial radio access (E-UTRA), and adopts the OFDMA in downlink and the SC-FDMA in uplink. Resource allocation of the 3GPP LTE is based on dynamic scheduling. A downlink physical channel of the 3GPP LTE can be divided into a physical downlink control channel (PDCCH) for carrying resource allocation in- formation and a physical downlink shared channel (PDSCH) for carrying downlink data. An uplink physical channel can be divided into a physical uplink control channel (PUCCH) for carrying uplink control information and a physical uplink shared channel (PUSCH) for carrying uplink data. In downlink transmission, the UE first receives a downlink grant on the PDCCH, and then receives downlink data on the PDSCH indicated by the downlink grant. In uplink transmission, the UE receives an uplink grant on the PDCCH, and then transmits uplink data on the PUSCH indicated by the uplink grant. Dynamic scheduling is a method capable of effective resource allocation. However, the UE always has to receive the downlink/uplink grant first to transmit and/ or receive data. [7] A signaling overhead is a major cause of low transmission efficiency and low frequency efficiency. In dynamic scheduling, in addition to reception of the PDCCH, the HARQ operation and the CQI transmission are carried out by using a plurality of signaling operations such as exchange of ACK/NACK information, exchange of a transmission parameter for the CQI, etc. [8] Accordingly, there is a need for a method capable of reducing a signaling overhead caused by CQI transmission in a process of performing HARQ. Disclosure of Invention Technical Problem [9] The present invention provides a method of multiplexing and transmitting a channel quality indicator (CQI) and retransmission data. Technical Solution [10] In an aspect, a method of supporting Hybrid Automatic Repeat Request (HARQ) in a wireless communication system is provide. The method includes receiving an initial uplink grant on a downlink channel, transmitting uplink data on an uplink channel using the initial uplink grant, receiving a request for retransmission of the uplink data. determining at least one transmission parameter of a channel quality indicator (CQI) from the initial uplink grant, multiplexing retransmission data of the uplink data with the CQI, wherein an amount of resources for transmission of the CQI is determined based on the at least one transmission parameter, and transmitting the multiplexed data on the uplink channel. [11] In some embodiments, the method may further include receiving a retransmission uplink grant for retransmission of the uplink data, wherein the retransmission data of the uplink data is multiplexed by using the retransmission uplink grant. A request for reporting the CQI may be included in the retransmission uplink grant. [12] The retransmission data of the uplink data may be multiplexed by using the initial uplink grant. The downlink channel may be a Physical Downlink Control Channel (PDCCH) and the uplink channel may be a Physical Uplink Shared Channel (PUSCH). [13] The at least one transmission parameter of the CQI may be related to a Modulation and Coding Scheme (MCS) of the CQI. The at least one transmission parameter of the CQI may be determined so that the MCS of the CQI is same as the MCS of the uplink data. [14] In another aspect, an apparatus for wireless communication is provided. The apparatus includes a Radio Frequency (RF) unit for transmitting and receiving a radio signal, and a processor coupled with the RF unit and configured to receive an initial uplink grant on a downlink channel, transmit uplink data on an uplink channel using the initial uplink grant, receive a request for retransmission of the uplink data, determine at least one transmission parameter of a CQI from the initial uplink grant, multiplex retransmission data of the uplink data with the CQI, wherein an amount of resources for transmission of the CQI is determined based on the at least one transmission parameter, and transmit the multiplexed data on the uplink channel. Advantageous Effects [15] A method of transmitting retransmission data together with a channel quality indicator (CQI) in a process of performing hybrid automatic repeat request (HARQ) is proposed. Accordingly, HARQ and adaptive modulation and coding (AMC) operations can be accurately perfonned, and a signaling overhead can be reduced. Brief Description of Drawings [16] FIG. 1 shows a wireless communication system. [17] FIG. 2 shows a structure of a radio frame in 3rd generation partnership project (3GPP) long terni evolution (LTE). [ 18] FIG. 3 shows an exemplary structure of a downlink subframe. [19] FIG. 4 shows a structure of an uplink subframe in 3GPP LTE. [20] FIG. 5 shows uplink hybrid automatic repeat request (HARQ) and channel quality indicator (CQI) transmission. [21] FIG. 6 shows dynamic scheduling in uplink transmission. [22] FIG. 7 is an exemplary diagram showing multiplexing of data and control in- formation on a physical uplink shared channel (PUSCH). [23] FIG. 8 shows resource mapping on a PUSCH. [24] FIG. 9 is a flow diagram showing an HARQ method according to an embodiment of the present invention. [25] FIG. 10 is a flow diagram showing an HARQ method according to another em- bodiment of the present invention. [26] FIG. 11 is a flow diagram showing an HARQ method according to another em- bodiment of the present invention. [27] FIG. 12 is a flow diagram showing an HARQ method according to another em- bodiment of the present invention. [28] FIG. 13 is a block diagram showing an apparatus for wueless communication according to an embodiment of the present invention. Mode for the Invention [29] The techniques described herein can be used in various wireless communication systems such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single canier frequency division multiple access (SC-FDMA), etc. The CDMA can be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA-2000. The TDMA can be im- plemented with a radio technology such as global system for mobile communications (GSM)/general packet ratio service (GPRS)/enhanced data rate for GSM evolution (EDGE). The OFDMA can be implemented with a radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved UMTS (E-UMTS) using the E- UTRA. The 3GPP LTE uses the OFDMA in downlink and uses the SC-FDMA in uplink. [30] For clarity, the following description will focus on the 3GPP LTE. However, the technical features of the present invention are not limited thereto. [31] FIG. 1 shows a wireless communication system. [32] Referring to FIG. 1, a wireless communication system 10 includes at least one base station (BS) 11. The BSs 11 provide communication services to specific geographical regions (generally referred to as cells) 15a, 15b, and 15c. The cell can be divided into a plurality of regions (referred to as sectors). A user equipment (UE) 12 may be fixed or mobile, and may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device, etc. The BS 11 is generally a fixed station that communicates with the UE 12 and may be referred to as another ter- minology, such as an evolved node-B (eNB), a base transceiver system (BTS), an access point, etc. [33] Hereinafter, downlink (DL) denotes a communication link from the BS to the UE, and uplink (UL) denotes a communication link from the UE to the BS. In the DL, a transmitter may be a part of the BS, and a receiver may be a part of the UE. In the UL, the transmitter may be a part of the UE, and the receiver may be a part of the BS. [34] The wireless communication system can support uplink and/or downlink hybrid automatic repeat request (HARQ). In addition, a channel quality indicator (CQI) can be used to support adaptive modulation and coding (AMC). [35] The CQI indicates a downlink channel state and may include a CQI index and/or a precoding matrix index (PMI). The CQI index indicates each entity of a modulation and coding scheme (MCS) table including a plurality of entities configured by combining coding rates and modulation schemes. The PMI is an index of a preceding matrix based on a codebook. The CQI may indicate a channel state for a full band and/ or a channel state for some bands included in the full band. [36] FIG. 2 shows a structure of a radio frame in 3GPP LTE. The radio frame includes 10 subframes. One subframe includes two slots. A time for transmitting one subframe is defined as a transmission time interval (TTI). For example, one subframe may have a length of 1 millisecond (ms), and one slot may have a length of 0.5 ms. One slot includes a plurality of SC-FDMA symbols (e.g., 7 SC-FDMA symbols) in a time domain and a plurality of resource blocks (RBs) in a frequency domain. In the 3GPP LTE using the SC-FDMA symbol in uplink, the SC-FDMA symbol represents one symbol period. According to a system, the SC-FDMA symbol can also be referred to as an OFDMA symbol or a symbol period. The RB is a resource allocation unit, and includes a plurality of contiguous subcarriers in one slot. [37] The structure of the radio frame is shown for exemplary purposes only. Thus, the number of subframes included in the radio frame or the number of slots included in the subframe or the number of SC-FDMA symbols included in the slot may be modified in various manners. [38] FIG. 3 shows an exemplary structure of a downlink subframe. The subframe includes two consecutive slots. A maximum of three OFDM symbols located in a front portion of a 1st slot within the downlink subframe correspond to a control region to be assigned with a physical downlink control channel (PDCCH). The remaining OFDM symbols correspond to a data region to be assigned with a physical downlink shared chancel (PDSCH). A physical control format indicator channel (PCFICH) is transmitted on a 1st OFDM symbol of the subframe and carries information regarding the number of OFDM symbols used for transmission of PDCCHs in the subframe. [39] The PDCCH carries a downlink grant that reports resource allocation of downlink transmission on the PDSCH. More specifically, the PDCCH can carry a transmission format and resource allocation of a downlink shared channel (DL-SCH), paging in- formation on a paging channel (PCH), system information on the DL-SCH, resource allocation of a high-level control message such as a random access response transmitted on the PDSCH, a transmit power control command, activation of a voice over Internet protocol (VoIP), etc. Further, the PDCCH can carry an uplink grant that reports resource allocation of uplink transmission to the UE. The PCFICH reports to the UE the number of OFDM symbols used for the PDCCHs, and is transmitted in every subframe. A physical hybrid ARQ indicator channel (PHICH) is a response of uplink transmission and carries an HARQ acknowledgment (ACK)/not-acknowledgment (NACK) signal. [40] FIG. 4 shows a structure of an uplink subframe in 3GPP LTE. [41] Referring to FIG. 4, the uplink subframe can be divided in a frequency domain into a control region and a data region. The control region is allocated with a physical uplink control channel (PUCCH) for carrying uplink control information. The data region is allocated with a physical uplink shared channel (PUSCH) for carrying user data. To maintain a single carrier property, one UE does not simultaneously transmit the PUCCH and the PUSCH. [42] The PUCCH for one UE is allocated to an RB pair in a subframe. RBs belonging to the RB pair occupy different subcarriers in respective two slots. This is called that the RB pair allocated to the PUCCH is frequency-hopped in a slot boundary. [43] FIG. 5 shows uplink HARQ and CQI transmission. [44] Referring to FIG. 5, upon receiving uplink data 100 on a PDSCH from a UE, a BS transmits an ACK/NACK signal 101 for the uplink data 100 on a PHICH after a specific time elapses. When the uplink data 100 is received, the BS may transmit the PHICH after a time corresponding to 4 TTIs elapses. However, the present invention is not limited thereto. If the uplink data is successfully decoded, the ACK/NACK signal 101 is an ACK signal. If the uplink data is unsuccessfully decoded, the ACK/NACK signal 101 is a NACK signal. When the ACK/NACK signal 101 is determined to be the NACK signal, retransmission data 110 for the uplink data 100 is retransmitted to the BS. Retransmission may be performed until the ACK signal is received or may be performed up to the number of times corresponding to the number of retransmission attempts. When an ACK/NACK signal 111 for the retransmission data 110 is de- termined to be the ACK signal, the UE can transmit new uplink data 120 to the BS. [45] Resource allocation or a transmission time point of an ACK/NACK signal for uplink/ downlink data may be dynamically reported by the BS through signaling, or may be predetermined according to resource allocation or a transmission time point of the uplink/downlink data. [46] The UE can report a CQI to the BS periodically and/or non-periodically by measuring a downlink channel state. When the CQI is reported periodically, it implies that the CQI is transmitted without receiving an additional request from the BS according to a predetermined period or a period determined by the BS. When the CQI is reported non-periodically, it implies that the CQI is transmitted in response to a request from the BS. The CQI may be transmitted on a PUCCH or a PUSCH. When the CQI is multiplexed together with data, the CQI is transmitted always on the PUSCH. CQIs 180 and 184 are transmitted alone and may be transmitted on the PUCCH or the PUSCH. A CQI 182 is transmitted together with uplink data and may be transmitted only on the PUSCH. The CQI transmitted on the PUSCH may be a periodic CQI or a non-periodic CQI. The BS may use the CQI to perform downlink scheduling. [47] In the following description, uplink HARQ will be described. However, the technical features of the present invention will be easily applied to downlink HARQ by a person of ordinary skill in the art. [48] FIG. 6 shows dynamic scheduling in uplink transmission. [49] Referring to FIG. 6, for uplink transmission, a UE transmits a scheduling request (SR) to a BS on a PUCCH. The SR is used when the UE requests the BS to allocate uplink radio resources. The SR is a sort of preliminary information exchange for data exchange. In order for the UE to transmit uplink data to the BS, radio resource al- location is first requested by using the SR. In response to the SR, the BS transmits an uplink grant to the UE on a PDCCH. The uplink grant includes allocation of the uplink radio resources. The UE transmits the uplink data on the PUSCH by using the allocated uplink radio resources. [50] FIG. 7 is an exemplary diagram showing multiplexing of data and control in- formation on a PUSCH. The PUSCH carries data and/or control information through an allocation resource by using an uplink grant. [51] Referring to FIG. 7, data bits a0, a1,..., aA-1 are provided for each TTI in a format of one transport block. First, cyclic redundancy check (CRC) parity bits p0, p1,..., pL-1 are attached to the data bits a0, a1,..., aA-1 to generate CRC-attached bits b0, b1,..., bB-1 (step 200). Herein, B=A+L. Equation 1 below shows a relationship between ak and bk. [52] MathFigure 1 [Math.1] [53] The CRC-attached bits b0, b1,..., bB-1 are segmented in a code block unit, and the CRC parity bits are re-attached in the code block unit (step 210). cr0, cr1,..., Cr(Kr-1) denote a bit sequence output after the code block segmentation. Herein, if a total number of code blocks is C, r denotes a code block number, and Kr denotes the number of bits for the code block number r. [54] Channel coding is performed on a bit sequence for a given code block (step 220). d(i)0 , d(i)1,..., d(i)D-1 denote encoded bits, D denotes the number of encoded bits for each output stream, and i denotes an index of a bit stream output from an encoder. [55] Rate matching is performed on the encoded bits (step 230). Then, code block con- catenation is performed on the rate-matched bits (step 240). As a result, a data bit sequence f0, f1,..., fG-1 is generated. Herein, G denotes a total number of encoded bits used to transmit bits other than bits that is used in control information transmission when the control information is multiplexed on a PUSCH. [56] The control information can be multiplexed together with data. The data and the control information can use different coding rates by allocating a different number of coded symbols for transmission thereof. Hereinafter, a CQI is considered as the control information. [57] Channel coding is performed on CQI values O0, O1 ,..., O0-1 (where O is the number of CQI bits) to generate a control information bit sequence q0, q1,..., qQ-1 (step 260). The CQI can use independent channel coding different from that used for the data. For example, when a block code (32, O) is used as channel coding for the CQI, a basis sequence Mi,n is as shown in Table 1 below. [58] Table 1 [59] b0, b1,..., b31 denote an intermediate sequence for CQI channel coding and can be generated by Equation 2 below. [60] MathFigure 2 [Math.2] [61] The control information bit sequence q0, q1,..., qQ-1 is generated by cyclically repeating the intermediate sequence b0, b1,..., b31 according to Equation 3 below. [62] MathFigure 3 [Math.3] [63] A data bit sequence f0, f1,..., fG-1 is generated as described above and is multiplexed together with the control information bit sequence q0, q1,..., qQ-1 into a multiplexed sequence g0, g1,..., gH-1 (step 270). In a process of multiplexing, the control information bit sequence q0, q1,..., qQ-1 can be arranged first and thereafter the data bit sequence f0, f 1,..., fG-1 can be arranged. That is, if H=G+Q, [g0, g1,..., gH-1] may be configured such as [q0, q1,..., qQ-1, f0, f1,..., fG-1 ]. [64] The multiplexed sequence g0, g1,.....gH-1 is mapped to a modulation sequence h0, h1, ..., hH'-1 (step 280). Herein, hi denotes a modulation symbol on constellation, and H'=H/Qm- Qm denotes the number of bits for each modulation symbol of a modulation scheme. For example, when quadrature phase shift keying (QPSK) is used as the modulation scheme, Qm=2. [65] Each modulation symbol of the modulation sequence h0, h1,..., hH'-1.] is mapped to a resource element for the PUSCH (step 290). The resource element is a unit of al- location on a subframe defined with one SC-FDMA symbol (or OFDMA symbol) and one subcarrier. The modulation symbols are mapped in a time-first manner. FIG. 8 shows resource mapping on a PUSCH. One slot includes 7 SC-FDMA symbols. In each slot, a 4th SC-FDMA symbol is used to transmit a reference signal. Therefore, up to 12 SC-FDMA symbols can be used for the PUSCH in one subframe. A modulation sequence h0, h1,..., hH'-1 is first mapped in a 1st subcarrier region in an SC-FDMA symbol direction, and is then mapped in a 2nd subcarrier region also in the SC-FDMA symbol direction. A front portion of the modulation sequence h0, h1,..., hH'-1 cor- responds to a CQI. Thus, the CQI is first mapped to resource elements in a front subcarrier region. [66] As described above, to transmit the CQI on the PUSCH, an amount of resources required to transmit the CQI needs to be determined first. The amount of resources is determined based on a transmission parameter (e.g., MCS, etc.) used in CQI transmission. The transmission parameter for the CQI denotes a parameter used for CQI transmission, and includes various parameters for determining the MCS and/or the amount of resources. If the amount of resources is expressed by the number Q' of modulation symbols for the CQI, Q' can be determined by Equation 4 below. [67] MathFigure 4 [Math.4] [68] In Equation 4, O denotes the number of CQI bits, L denotes the number of CRC bits, A denotes a parameter, C denotes a total number of code blocks, Kr denotes the number of bits for a code block number r, Msc denotes the number of subcarriers used in PUSCH transmission, and Nsymb denotes the number of SC-FDMA symbols used in PUSCH transmission. Transmission parameters for determining the aforementioned Q' may be at least one of C, Kr, Msc, and Nsymb- [69] Now, a method of multiplexing retransmission data and a CQI and transmitting the multiplexed result through a PUSCH in a process of performing HARQ will be described. [70] When the HARQ is performed, the CQI may be transmitted by being multiplexed with initial data or retransmission data. This may occur when a CQI transmission period coincides with a retransmission period in periodic CQI reporting or when a response for a CQI transmission request coincides with the retransmission period in non-periodic CQI reporting. [71] When the CQI is multiplexed with the retransmission data, there is an issue as to how transmission parameters (e.g., MCS, etc.) for the CQI are determined. The issue is related to how to detennine the transmission parameters used for the CQI multiplexed with the retransmission data. This is because, when the transmission parameters for CQI transmission have to be additionally reported by the BS to the UE even at re- transmission, the reporting of the transmission parameters may act as a signaling overhead. [72] If the CQI is transmitted when the data is retransmitted, a CQI transmission parameter can be determined according to the transmission parameters used in initial data transmission. For example, an MCS used in initial data transmission is used for CQI transmission when the data is retransmitted. [73] FIG. 9 is a flow diagram showing an HARQ method according to an embodiment of the present invention. [74] Referring to FIG. 9, in step S510, a BS transmits an initial uplink grant on a PDCCH. The initial uplink grant includes radio resource allocation information for initial uplink data in the HARQ method. In step S520, a UE transmits uplink data on a PUSCH indicated by the initial uplink grant. [75] In step S530, upon detecting a decoding error of the uplink data, the BS transmits a NACK signal as a retransmission request. The NACK signal may be transmitted on a PHICH. [76] In step S560, if a transmission subframe of retransmission data coincides with a transmission subframe of a CQI, the UE determines a transmission parameter of the CQI from the initial uplink grant. The transmission parameter is a parameter for de- termining an amount of radio resources required to transmit the CQI, and may be related to an MCS of the CQI. For example, when the amount of radio resources of the CQI is determined by Equation 4, at least one of transmission parameters C, Kr, Msc, and Nsymb can be obtained from the initial uplink grant. [77] In step S570, the UE multiplexes the CQI and the retransmission data of the uplink data by using the transmission parameter. In step S580, the UE transmits the mul- tiplexed data on the PUSCH. [78] In HARQ retransmission, when the retransmission data is transmitted together with the CQI, the MCS of the CQI is determined according to the initial uplink grant, so that a signaling overhead can be reduced without additional signaling for the transmission parameter of the CQI to be multiplexed. [79] FIG. 10 is a flow diagram showing an HARQ method according to another em- bodiment of the present invention. [80] Referring to FIG. 10, in step S610, a BS transmits an initial uplink grant on a PDCCH. In step S620, a UE transmits uplink data on a PUSCH indicated by the initial uplink grant. In step S630, upon detecting a decoding error of the uplink data, the BS transmits a NACK signal as a retransmission request. [81] In step S640, the BS transmits a retransmission grant on the PDCCH. The re- transmission grant includes radio resource allocation information for retransmission data regarding the uplink data. [82] In step s650, if a transmission subframe of retransmission data coincides with a transmission subframe of a CQI, the UE determines a transmission parameter of the CQI from the initial uplink grant. In step S670, the UE multiplexes the CQI and the re- transmission of the uplink data by using the transmission parameter. In this case, the retransmission data is multiplexed using a transmission parameter obtained from the retransmission grant, and the CQI is multiplexed using a transmission parameter obtained from the initial grant. In step S680, the UE transmits the multiplexed data on the PUSCH. [83] FIG. 11 is a flow diagram showing an HARQ method according to another em- bodiment of the present invention. [84] Referring to FIG. 11, in step S700, a BS configures a periodic CQI. A UE peri- odically transmits the CQI according to a period determined by the BS. In step S710, the BS transmits an initial uplink grant on a PDCCH. The initial uplink grant includes radio resource allocation information for initial uplink data in the HARQ method. In step S720, the UE transmits uplink data on a PUSCH indicated by the initial uplink grant. [85] In step S730, the UE transmits the CQI at a CQI transmission period. In this case, if an available PUCCH resource exists, the CQI can be transmitted on a PUCCH. In step S740, upon detecting a decoding error of the uplink data, the BS transmits a NACK signal as a retransmission request. [86] In step S760, if a transmission subframe of retransmission data coincides with a transmission subframe of a CQI, the UE determines a transmission parameter of the CQI from the initial uplink grant. [87] In step S770, the UE multiplexes the CQI and the retransmission data of the uplink data by using the transmission parameter. In step S780, the UE transmits the mul- tiplexed data on the PUSCH. [88] FIG. 12 is a flow diagram showing an HARQ method according to another em- bodiment of the present invention. [89] Referring to FIG. 12, in step S810, a BS transmits an initial uplink grant on a PDCCH. In step S820, a UE transmits uplink data on a PUSCH indicated by the initial uplink grant. In step S830, upon detecting a decoding error of the uplink data, the BS transmits a NACK signal as a retransmission request. [90] In step s840, the BS transmits a retransmission grant and a CQI request on the PDCCH. The CQI request is a signal optionally used by the BS to request the UE to transmit the CQI. Although the CQI request is transmitted on the PDCCH together with the retransmission grant, the CQI request can be transmitted to the UE through an additional message. [91] In step S860, the UE determines a transmission parameter of the CQI from the initial uplink grant according to the CQI request of the BS. In step S870, the UE multiplexes the CQI and the retransmission of the uplink data by using the transmission parameter. In this case, the retransmission data is multiplexed using a transmission parameter obtained from the retransmission grant, and the CQI is multiplexed using a transmission parameter obtained from the initial grant. In step S880, the UE transmits the multiplexed data on the PUSCH. [92] Although CQI multiplexing at first retransmission has been proposed in the afore- mentioned embodiments, the CQI transmission parameter can be obtained from the initial uplink grant even if the CQI is transmitted by being multiplexed at n-th re- transmission (where n>l). [93] By using the transmission parameter used in initial data transmission as the CQI transmission parameter, additional signaling for the CQI transmission parameter is not necessary. [94] While performing the HARQ, to multiplex and transmit the retransmission data and the CQI on the PUSCH, a CQI transmission parameter can be obtained not only from the initial uplink grant but also from other grants. For example, the transmission parameter used for the retransmission data multiplexed together with the CQI can be set to the CQI transmission parameter. This is a case where the same MCS used for the retransmission data is used to transmit the CQI at retransmission. For another example, the transmission parameter used in previous transmission can be used as the CQI transmission parameter. This is a case where, when second retransmission data and the CQI are multiplexed at second retransmission, the transmission parameter used for the first retransmission data is set to the CQI transmission parameter. [95] As described above, a non-periodic CQI is transmitted at the request of the BS. In general, the CQI request can be transmitted on the PDCCH. In this case, a transmission indicator for the CQI transmission parameter can be transmitted along with the CQI request. The CQI may be transmitted using an allocated resource (or transmission parameter) according to the transmission indicator, or the CQI may be transmitted using a previously allocated resource (or transmission parameter). [96] FIG. 13 is a block diagram showing an apparatus for wireless communication according to an embodiment of the present invention. An apparatus 50 for wireless communication may be a part of a UE. The apparatus 50 for wireless communication includes a processor 51, a memory 52, a radio frequency (RF) unit 53, a display unit 54, and a user interface unit 55. The RF unit 53 is coupled to the processor 51 and transmits and/or receives radio signals. The memory 52 is coupled to the processor 51 and stores an operating system, applications, and general files. The display unit 54 displays a variety of information of the UE and may use a well-known element such as a liquid crystal display (LCD), an organic light emitting diode (OLED), etc. The user interface unit 55 can be configured with a combination of well-known user interfaces such as a keypad, a touch screen, etc. The processor 51 supports HARQ and AMC. The processor 51 can configure a PUCCH or a PUSCH and can perform multiplexing of data and a CQI. The aforementioned embodiments of the HARQ method can be im- plemented by the processor 51. [97] The present invention can be implemented with hardware, software, or combination thereof. In hardware implementation, the present invention can be implemented with one of an application specific integrated circuit (ASIC), a digital signal processor (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, other electronic units, and combination thereof, which are designed to perform the aforementioned functions. In software im- plementation, the present invention can be implemented with a module for performing the aforementioned functions. Software is storable in a memory unit and executed by the processor. Various means widely known to those skilled in the art can be used as the memory unit or the processor. [98] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed de- scription of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention. WE CLAIM : 1. A method for retransmitting data in a wireless communication system, the method comprising: receiving in an user equipment on a downlink channel a first uplink grant from a base station, the fust uplink grant indicating resources for transmitting uplink data to the base station, wherein the first uplink grant is based on at least one transmission parameter for transmitting the uplink data; transmitting the uplink data on an uplink data channel using the resources indicated by the first uplink grant; receiving from the base station an indication for retransmission of the uplink data; identifying the existence of control information to be transmitted to the base station with the retransmission of the uplink data; determining at least one transmission parameter for transmitting the control information to the base station, wherein the at least one transmission parameter for transmitting the control information is determined according to the at least one transmission parameter for transmitting the uplink data; determining an amount of resources for transmitting the control information according to the determined at least one transmission parameter; multiplexing retransmission data with the control information such that the control information and the retransmission data are transmitted using resources indicated by a second uplink grant; and transmitting the multiplexed data on the uplink data channel using the resources indicated by the second uplink grant. 2. The method of claim 1, wherein the wireless communication system is a single carrier-frequency division multiple access (SC-FDMA) system. 3. The method of claim 1, further comprising receiving from the base station on the downlink channel the second uplink grant indicating resources for retransmitting the uplink data. 4. The method of claim 1, wherein the control information is a channel quality indicator (CQI). 5. The method of claim 4, wherein the at least one transmission parameter is related to a modulation and coding scheme (MCS) of the CQI. 6. The method of claim 5, wherein the at least one transmission parameter for transmitting the control information is determined so that the MCS of the CQI is the same as the MCS of the uplink data. 7. The method of claim 1, wherein the downlink channel is a physical downlink control channel (PDCCH). 8. The method of claim 1, wherein the uplink channel is a physical uplink shared channel (PUSCH). 9. An user equipment for retransmitting data in a wireless communication system, the user equipment comprising: a radio frequency (RF) unit for transmitting and receiving a radio signal; and a processor coupled with the RF unit, the processor configured for: receiving on a downlink channel a first uplink grant from a base station, the first uplink grant indicating resources for transmitting uplink data to the base station, wherein the first uplink grant is based on at least one transmission parameter for transmitting the uplink data, transmitting the uplink data on an uplink data channel using the resources indicated by the first uplink grant, receiving from the base station an indication for retransmission of the uplink data, identifying the existence of control information to be transmitted to the base station with the retransmission of the uplink data, determining at least one transmission parameter for transmitting the control information to the base station, wherein the at least one transmission parameter for transmitting the control information is determined according to the at least one transmission parameter for transmitting the uplink data, determining an amount of resources for transmitting the control information according to the determined at least one transmission parameter; multiplexing retransmission data with the control information such that the control information and the retransmission data are transmitted using resources indicated by a second uplink grant, and transmitting the multiplexed data on the uplink data channel using the resources indicated by the second uplink grant. 10. The user equipment of claim 9, wherein the wireless communication system is a single carrier-frequency division multiple access (SC-FDMA) system. 11. The user equipment of claim 9, further comprising receiving from the base station on the downlink charmel the second uplink grant indicating resources for retransmitting the uplink data. 12. The user equipment of claim 9, wherein the control information is a channel quality indicator (CQI). 13. The user equipment of claim 12, wherein the at least one transmission parameter is related to a modulation and coding scheme (MCS) of the CQI. 14. The user equipment of claim 13, wherein the at least one transmission parameter for transmitting the control information is determined so that the MCS of the CQI is the same as the MCS of the uplink data. 15. The user equipment of claim 9, wherein the downlink channel is a physical downlink control channel (PDCCH). 16. The user equipment of claim 9, wherein the uplink charmel is a physical uplink shared channel (PUSCH). A method of supporting Hybrid Automatic Repeat Request (HARQ) includes receiving an initial uplink grant on a downlink channel, transmitting uplink data on an uplink channel using the initial uplink grant, receiving a request for retransmission of the uplink data, determining at least one transmission parameter of a channel quality indicator (CQI) from the initial uplink grant, multiplexing retransmission data of the uplink data with the CQI, and transmitting the multiplexed data on the uplink channel. Amount of resources for transmission of the CQI is determined based on the at least one transmission parameter.

Full Text

Description
METHOD AND APPARATUS FOR SUPPORTING HARQ
Technical Field
[ 1 ] The present invention relates to wireless communications, and more particularly, to a
method and apparatus for supporting hybrid automatic repeat request (HARQ) in a
wireless communication system.
Background Art
[2] Wireless communication systems are widely spread all over the world to provide
various types of communication services such as voice or data. In general, the wireless
communication system is a multiple access system capable of supporting commu-
nication with multiple users by sharing available system resources (e.g., bandwidth,
transmission power, etc.). Examples of the multiple access system include a code
division multiple access (CDMA) system, a frequency division multiple access
(FDMA) system, a time division multiple access (TDMA) system, an orthogonal
frequency division multiple access (OFDMA) system, a single carrier frequency
division multiple access (SC-FDMA) system, etc.
[3] Current development in advanced wireless communication has led to the requrement
of high spectral efficiency and reliable communication. Unfortunately, packet errors by
fading channel environment and interferences originated from various sources make
the capacity of overall system to be limited.
[4] Hybrid automatic repeat request (HARQ) is an ARQ protocol combined with forward
error correction (FEC) and is strongly considered as one of cutting edge technologies
for future reliable communication. The HARQ scheme can largely be classified into
two types. One is HARQ-chase combining (CC) which is disclosed in D. Chase, Code
Combining: A maximum-likelihood decoding approach for combining an arbitrary
number of noisy packets, IEEE Trans, on Commun., Vol. 33, pp. 593-607, May 1985.
The other is HARQ-Increment Redundancy (IR). In the HARQ-CC, when a receiver
detects an error through cyclic redundancy checking (CRC) while decoding the
transmitted packet, the same packet with the same modulation and coding is re-
transmitted to the receiver. Meanwhile, in order to achieve a coding gain, the HARQ-
IR retransmits different packets, in which parity bits can be manipulated through
puncturing and repetition. To perform the HARQ, there is a need to exchange ac-
knowledgement (ACK)/not-acknowledgement (NACK) information that indicates
whether retransmission is necessary.
[5] Adaptive modulation and coding (AMC) is also a technology for providing reliable
communication. A base station (BS) determines a modulation and coding scheme
(MCS) used for transmission by using a channel quality indicator (CQI) received from
a user equipment (UE). In general, the CQI is an index of an entity of an MCS table
showing a plurality of MCSs. The UE transmits the CQI by using two methods. One is
that the CQI is transmitted periodically. The other is that the CQI is transmitted at the
request of the BS.
[6] 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an
evolved-universal mobile telecommunications system (E-UMTS) using evolved-
universal terrestrial radio access (E-UTRA), and adopts the OFDMA in downlink and
the SC-FDMA in uplink. Resource allocation of the 3GPP LTE is based on dynamic
scheduling. A downlink physical channel of the 3GPP LTE can be divided into a
physical downlink control channel (PDCCH) for carrying resource allocation in-
formation and a physical downlink shared channel (PDSCH) for carrying downlink
data. An uplink physical channel can be divided into a physical uplink control channel
(PUCCH) for carrying uplink control information and a physical uplink shared channel
(PUSCH) for carrying uplink data. In downlink transmission, the UE first receives a
downlink grant on the PDCCH, and then receives downlink data on the PDSCH
indicated by the downlink grant. In uplink transmission, the UE receives an uplink
grant on the PDCCH, and then transmits uplink data on the PUSCH indicated by the
uplink grant. Dynamic scheduling is a method capable of effective resource allocation.
However, the UE always has to receive the downlink/uplink grant first to transmit and/
or receive data.
[7] A signaling overhead is a major cause of low transmission efficiency and low
frequency efficiency. In dynamic scheduling, in addition to reception of the PDCCH,
the HARQ operation and the CQI transmission are carried out by using a plurality of
signaling operations such as exchange of ACK/NACK information, exchange of a
transmission parameter for the CQI, etc.
[8] Accordingly, there is a need for a method capable of reducing a signaling overhead
caused by CQI transmission in a process of performing HARQ.
Disclosure of Invention
Technical Problem
[9] The present invention provides a method of multiplexing and transmitting a channel
quality indicator (CQI) and retransmission data.
Technical Solution
[10] In an aspect, a method of supporting Hybrid Automatic Repeat Request (HARQ) in a
wireless communication system is provide. The method includes receiving an initial
uplink grant on a downlink channel, transmitting uplink data on an uplink channel
using the initial uplink grant, receiving a request for retransmission of the uplink data.
determining at least one transmission parameter of a channel quality indicator (CQI)
from the initial uplink grant, multiplexing retransmission data of the uplink data with
the CQI, wherein an amount of resources for transmission of the CQI is determined
based on the at least one transmission parameter, and transmitting the multiplexed data
on the uplink channel.
[11] In some embodiments, the method may further include receiving a retransmission
uplink grant for retransmission of the uplink data, wherein the retransmission data of
the uplink data is multiplexed by using the retransmission uplink grant. A request for
reporting the CQI may be included in the retransmission uplink grant.
[12] The retransmission data of the uplink data may be multiplexed by using the initial
uplink grant. The downlink channel may be a Physical Downlink Control Channel
(PDCCH) and the uplink channel may be a Physical Uplink Shared Channel (PUSCH).
[13] The at least one transmission parameter of the CQI may be related to a Modulation
and Coding Scheme (MCS) of the CQI. The at least one transmission parameter of the
CQI may be determined so that the MCS of the CQI is same as the MCS of the uplink
data.
[14] In another aspect, an apparatus for wireless communication is provided. The
apparatus includes a Radio Frequency (RF) unit for transmitting and receiving a radio
signal, and a processor coupled with the RF unit and configured to receive an initial
uplink grant on a downlink channel, transmit uplink data on an uplink channel using
the initial uplink grant, receive a request for retransmission of the uplink data,
determine at least one transmission parameter of a CQI from the initial uplink grant,
multiplex retransmission data of the uplink data with the CQI, wherein an amount of
resources for transmission of the CQI is determined based on the at least one
transmission parameter, and transmit the multiplexed data on the uplink channel.
Advantageous Effects
[15] A method of transmitting retransmission data together with a channel quality
indicator (CQI) in a process of performing hybrid automatic repeat request (HARQ) is
proposed. Accordingly, HARQ and adaptive modulation and coding (AMC) operations
can be accurately perfonned, and a signaling overhead can be reduced.
Brief Description of Drawings
[16] FIG. 1 shows a wireless communication system.
[17] FIG. 2 shows a structure of a radio frame in 3rd generation partnership project
(3GPP) long terni evolution (LTE).
[ 18] FIG. 3 shows an exemplary structure of a downlink subframe.
[19] FIG. 4 shows a structure of an uplink subframe in 3GPP LTE.
[20] FIG. 5 shows uplink hybrid automatic repeat request (HARQ) and channel quality
indicator (CQI) transmission.
[21] FIG. 6 shows dynamic scheduling in uplink transmission.
[22] FIG. 7 is an exemplary diagram showing multiplexing of data and control in-
formation on a physical uplink shared channel (PUSCH).
[23] FIG. 8 shows resource mapping on a PUSCH.
[24] FIG. 9 is a flow diagram showing an HARQ method according to an embodiment of
the present invention.
[25] FIG. 10 is a flow diagram showing an HARQ method according to another em-
bodiment of the present invention.
[26] FIG. 11 is a flow diagram showing an HARQ method according to another em-
bodiment of the present invention.
[27] FIG. 12 is a flow diagram showing an HARQ method according to another em-
bodiment of the present invention.
[28] FIG. 13 is a block diagram showing an apparatus for wueless communication
according to an embodiment of the present invention.
Mode for the Invention
[29] The techniques described herein can be used in various wireless communication
systems such as code division multiple access (CDMA), frequency division multiple
access (FDMA), time division multiple access (TDMA), orthogonal frequency division
multiple access (OFDMA), single canier frequency division multiple access
(SC-FDMA), etc. The CDMA can be implemented with a radio technology such as
universal terrestrial radio access (UTRA) or CDMA-2000. The TDMA can be im-
plemented with a radio technology such as global system for mobile communications
(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSM evolution
(EDGE). The OFDMA can be implemented with a radio technology such as institute of
electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),
IEEE 802.20, evolved UTRA (E-UTRA), etc. The UTRA is a part of a universal
mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP)
long term evolution (LTE) is a part of an evolved UMTS (E-UMTS) using the E-
UTRA. The 3GPP LTE uses the OFDMA in downlink and uses the SC-FDMA in
uplink.
[30] For clarity, the following description will focus on the 3GPP LTE. However, the
technical features of the present invention are not limited thereto.
[31] FIG. 1 shows a wireless communication system.
[32] Referring to FIG. 1, a wireless communication system 10 includes at least one base
station (BS) 11. The BSs 11 provide communication services to specific geographical
regions (generally referred to as cells) 15a, 15b, and 15c. The cell can be divided into a
plurality of regions (referred to as sectors). A user equipment (UE) 12 may be fixed or
mobile, and may be referred to as another terminology, such as a mobile station (MS),
a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital
assistant (PDA), a wireless modem, a handheld device, etc. The BS 11 is generally a
fixed station that communicates with the UE 12 and may be referred to as another ter-
minology, such as an evolved node-B (eNB), a base transceiver system (BTS), an
access point, etc.
[33] Hereinafter, downlink (DL) denotes a communication link from the BS to the UE,
and uplink (UL) denotes a communication link from the UE to the BS. In the DL, a
transmitter may be a part of the BS, and a receiver may be a part of the UE. In the UL,
the transmitter may be a part of the UE, and the receiver may be a part of the BS.
[34] The wireless communication system can support uplink and/or downlink hybrid
automatic repeat request (HARQ). In addition, a channel quality indicator (CQI) can be
used to support adaptive modulation and coding (AMC).
[35] The CQI indicates a downlink channel state and may include a CQI index and/or a
precoding matrix index (PMI). The CQI index indicates each entity of a modulation
and coding scheme (MCS) table including a plurality of entities configured by
combining coding rates and modulation schemes. The PMI is an index of a preceding
matrix based on a codebook. The CQI may indicate a channel state for a full band and/
or a channel state for some bands included in the full band.
[36] FIG. 2 shows a structure of a radio frame in 3GPP LTE. The radio frame includes 10
subframes. One subframe includes two slots. A time for transmitting one subframe is
defined as a transmission time interval (TTI). For example, one subframe may have a
length of 1 millisecond (ms), and one slot may have a length of 0.5 ms. One slot
includes a plurality of SC-FDMA symbols (e.g., 7 SC-FDMA symbols) in a time
domain and a plurality of resource blocks (RBs) in a frequency domain. In the 3GPP
LTE using the SC-FDMA symbol in uplink, the SC-FDMA symbol represents one
symbol period. According to a system, the SC-FDMA symbol can also be referred to
as an OFDMA symbol or a symbol period. The RB is a resource allocation unit, and
includes a plurality of contiguous subcarriers in one slot.
[37] The structure of the radio frame is shown for exemplary purposes only. Thus, the
number of subframes included in the radio frame or the number of slots included in the
subframe or the number of SC-FDMA symbols included in the slot may be modified in
various manners.
[38] FIG. 3 shows an exemplary structure of a downlink subframe. The subframe includes
two consecutive slots. A maximum of three OFDM symbols located in a front portion
of a 1st slot within the downlink subframe correspond to a control region to be
assigned with a physical downlink control channel (PDCCH). The remaining OFDM
symbols correspond to a data region to be assigned with a physical downlink shared
chancel (PDSCH). A physical control format indicator channel (PCFICH) is
transmitted on a 1st OFDM symbol of the subframe and carries information regarding
the number of OFDM symbols used for transmission of PDCCHs in the subframe.
[39] The PDCCH carries a downlink grant that reports resource allocation of downlink
transmission on the PDSCH. More specifically, the PDCCH can carry a transmission
format and resource allocation of a downlink shared channel (DL-SCH), paging in-
formation on a paging channel (PCH), system information on the DL-SCH, resource
allocation of a high-level control message such as a random access response
transmitted on the PDSCH, a transmit power control command, activation of a voice
over Internet protocol (VoIP), etc. Further, the PDCCH can carry an uplink grant that
reports resource allocation of uplink transmission to the UE. The PCFICH reports to
the UE the number of OFDM symbols used for the PDCCHs, and is transmitted in
every subframe. A physical hybrid ARQ indicator channel (PHICH) is a response of
uplink transmission and carries an HARQ acknowledgment
(ACK)/not-acknowledgment (NACK) signal.
[40] FIG. 4 shows a structure of an uplink subframe in 3GPP LTE.
[41] Referring to FIG. 4, the uplink subframe can be divided in a frequency domain into a
control region and a data region. The control region is allocated with a physical uplink
control channel (PUCCH) for carrying uplink control information. The data region is
allocated with a physical uplink shared channel (PUSCH) for carrying user data. To
maintain a single carrier property, one UE does not simultaneously transmit the
PUCCH and the PUSCH.
[42] The PUCCH for one UE is allocated to an RB pair in a subframe. RBs belonging to
the RB pair occupy different subcarriers in respective two slots. This is called that the
RB pair allocated to the PUCCH is frequency-hopped in a slot boundary.
[43] FIG. 5 shows uplink HARQ and CQI transmission.
[44] Referring to FIG. 5, upon receiving uplink data 100 on a PDSCH from a UE, a BS
transmits an ACK/NACK signal 101 for the uplink data 100 on a PHICH after a
specific time elapses. When the uplink data 100 is received, the BS may transmit the
PHICH after a time corresponding to 4 TTIs elapses. However, the present invention is
not limited thereto. If the uplink data is successfully decoded, the ACK/NACK signal
101 is an ACK signal. If the uplink data is unsuccessfully decoded, the ACK/NACK
signal 101 is a NACK signal. When the ACK/NACK signal 101 is determined to be
the NACK signal, retransmission data 110 for the uplink data 100 is retransmitted to
the BS. Retransmission may be performed until the ACK signal is received or may be
performed up to the number of times corresponding to the number of retransmission
attempts. When an ACK/NACK signal 111 for the retransmission data 110 is de-
termined to be the ACK signal, the UE can transmit new uplink data 120 to the BS.
[45] Resource allocation or a transmission time point of an ACK/NACK signal for uplink/
downlink data may be dynamically reported by the BS through signaling, or may be
predetermined according to resource allocation or a transmission time point of the
uplink/downlink data.
[46] The UE can report a CQI to the BS periodically and/or non-periodically by
measuring a downlink channel state. When the CQI is reported periodically, it implies
that the CQI is transmitted without receiving an additional request from the BS
according to a predetermined period or a period determined by the BS. When the CQI
is reported non-periodically, it implies that the CQI is transmitted in response to a
request from the BS. The CQI may be transmitted on a PUCCH or a PUSCH. When
the CQI is multiplexed together with data, the CQI is transmitted always on the
PUSCH. CQIs 180 and 184 are transmitted alone and may be transmitted on the
PUCCH or the PUSCH. A CQI 182 is transmitted together with uplink data and may
be transmitted only on the PUSCH. The CQI transmitted on the PUSCH may be a
periodic CQI or a non-periodic CQI. The BS may use the CQI to perform downlink
scheduling.
[47] In the following description, uplink HARQ will be described. However, the technical
features of the present invention will be easily applied to downlink HARQ by a person
of ordinary skill in the art.
[48] FIG. 6 shows dynamic scheduling in uplink transmission.
[49] Referring to FIG. 6, for uplink transmission, a UE transmits a scheduling request
(SR) to a BS on a PUCCH. The SR is used when the UE requests the BS to allocate
uplink radio resources. The SR is a sort of preliminary information exchange for data
exchange. In order for the UE to transmit uplink data to the BS, radio resource al-
location is first requested by using the SR. In response to the SR, the BS transmits an
uplink grant to the UE on a PDCCH. The uplink grant includes allocation of the uplink
radio resources. The UE transmits the uplink data on the PUSCH by using the
allocated uplink radio resources.
[50] FIG. 7 is an exemplary diagram showing multiplexing of data and control in-
formation on a PUSCH. The PUSCH carries data and/or control information through
an allocation resource by using an uplink grant.
[51] Referring to FIG. 7, data bits a0, a1,..., aA-1 are provided for each TTI in a format of
one transport block. First, cyclic redundancy check (CRC) parity bits p0, p1,..., pL-1 are
attached to the data bits a0, a1,..., aA-1 to generate CRC-attached bits b0, b1,..., bB-1 (step
200). Herein, B=A+L. Equation 1 below shows a relationship between ak and bk.
[52] MathFigure 1
[Math.1]

[53] The CRC-attached bits b0, b1,..., bB-1 are segmented in a code block unit, and the
CRC parity bits are re-attached in the code block unit (step 210). cr0, cr1,..., Cr(Kr-1)
denote a bit sequence output after the code block segmentation. Herein, if a total
number of code blocks is C, r denotes a code block number, and Kr denotes the
number of bits for the code block number r.
[54] Channel coding is performed on a bit sequence for a given code block (step 220). d(i)0
, d(i)1,..., d(i)D-1 denote encoded bits, D denotes the number of encoded bits for each
output stream, and i denotes an index of a bit stream output from an encoder.
[55] Rate matching is performed on the encoded bits (step 230). Then, code block con-
catenation is performed on the rate-matched bits (step 240). As a result, a data bit
sequence f0, f1,..., fG-1 is generated. Herein, G denotes a total number of encoded bits
used to transmit bits other than bits that is used in control information transmission
when the control information is multiplexed on a PUSCH.
[56] The control information can be multiplexed together with data. The data and the
control information can use different coding rates by allocating a different number of
coded symbols for transmission thereof. Hereinafter, a CQI is considered as the control
information.
[57] Channel coding is performed on CQI values O0, O1 ,..., O0-1 (where O is the number of
CQI bits) to generate a control information bit sequence q0, q1,..., qQ-1 (step 260). The
CQI can use independent channel coding different from that used for the data. For
example, when a block code (32, O) is used as channel coding for the CQI, a basis
sequence Mi,n is as shown in Table 1 below.
[58] Table 1
[59] b0, b1,..., b31 denote an intermediate sequence for CQI channel coding and can be
generated by Equation 2 below.
[60] MathFigure 2
[Math.2]

[61] The control information bit sequence q0, q1,..., qQ-1 is generated by cyclically
repeating the intermediate sequence b0, b1,..., b31 according to Equation 3 below.
[62] MathFigure 3
[Math.3]

[63] A data bit sequence f0, f1,..., fG-1 is generated as described above and is multiplexed
together with the control information bit sequence q0, q1,..., qQ-1 into a multiplexed
sequence g0, g1,..., gH-1 (step 270). In a process of multiplexing, the control information
bit sequence q0, q1,..., qQ-1 can be arranged first and thereafter the data bit sequence f0, f
1,..., fG-1 can be arranged. That is, if H=G+Q, [g0, g1,..., gH-1] may be configured such as
[q0, q1,..., qQ-1, f0, f1,..., fG-1 ].
[64] The multiplexed sequence g0, g1,.....gH-1 is mapped to a modulation sequence h0, h1,
..., hH'-1 (step 280). Herein, hi denotes a modulation symbol on constellation, and
H'=H/Qm- Qm denotes the number of bits for each modulation symbol of a modulation
scheme. For example, when quadrature phase shift keying (QPSK) is used as the
modulation scheme, Qm=2.
[65] Each modulation symbol of the modulation sequence h0, h1,..., hH'-1.] is mapped to a
resource element for the PUSCH (step 290). The resource element is a unit of al-
location on a subframe defined with one SC-FDMA symbol (or OFDMA symbol) and
one subcarrier. The modulation symbols are mapped in a time-first manner. FIG. 8
shows resource mapping on a PUSCH. One slot includes 7 SC-FDMA symbols. In
each slot, a 4th SC-FDMA symbol is used to transmit a reference signal. Therefore, up
to 12 SC-FDMA symbols can be used for the PUSCH in one subframe. A modulation
sequence h0, h1,..., hH'-1 is first mapped in a 1st subcarrier region in an SC-FDMA
symbol direction, and is then mapped in a 2nd subcarrier region also in the SC-FDMA
symbol direction. A front portion of the modulation sequence h0, h1,..., hH'-1 cor-
responds to a CQI. Thus, the CQI is first mapped to resource elements in a front
subcarrier region.
[66] As described above, to transmit the CQI on the PUSCH, an amount of resources
required to transmit the CQI needs to be determined first. The amount of resources is
determined based on a transmission parameter (e.g., MCS, etc.) used in CQI
transmission. The transmission parameter for the CQI denotes a parameter used for
CQI transmission, and includes various parameters for determining the MCS and/or the
amount of resources. If the amount of resources is expressed by the number Q' of
modulation symbols for the CQI, Q' can be determined by Equation 4 below.
[67] MathFigure 4
[Math.4]

[68] In Equation 4, O denotes the number of CQI bits, L denotes the number of CRC bits,
A denotes a parameter, C denotes a total number of code blocks, Kr denotes the
number of bits for a code block number r, Msc denotes the number of subcarriers used
in PUSCH transmission, and Nsymb denotes the number of SC-FDMA symbols used in
PUSCH transmission. Transmission parameters for determining the aforementioned Q'
may be at least one of C, Kr, Msc, and Nsymb-
[69] Now, a method of multiplexing retransmission data and a CQI and transmitting the
multiplexed result through a PUSCH in a process of performing HARQ will be
described.
[70] When the HARQ is performed, the CQI may be transmitted by being multiplexed
with initial data or retransmission data. This may occur when a CQI transmission
period coincides with a retransmission period in periodic CQI reporting or when a
response for a CQI transmission request coincides with the retransmission period in
non-periodic CQI reporting.
[71] When the CQI is multiplexed with the retransmission data, there is an issue as to how
transmission parameters (e.g., MCS, etc.) for the CQI are determined. The issue is
related to how to detennine the transmission parameters used for the CQI multiplexed
with the retransmission data. This is because, when the transmission parameters for
CQI transmission have to be additionally reported by the BS to the UE even at re-
transmission, the reporting of the transmission parameters may act as a signaling
overhead.
[72] If the CQI is transmitted when the data is retransmitted, a CQI transmission
parameter can be determined according to the transmission parameters used in initial
data transmission. For example, an MCS used in initial data transmission is used for
CQI transmission when the data is retransmitted.
[73] FIG. 9 is a flow diagram showing an HARQ method according to an embodiment of
the present invention.
[74] Referring to FIG. 9, in step S510, a BS transmits an initial uplink grant on a PDCCH.
The initial uplink grant includes radio resource allocation information for initial uplink
data in the HARQ method. In step S520, a UE transmits uplink data on a PUSCH
indicated by the initial uplink grant.
[75] In step S530, upon detecting a decoding error of the uplink data, the BS transmits a
NACK signal as a retransmission request. The NACK signal may be transmitted on a
PHICH.
[76] In step S560, if a transmission subframe of retransmission data coincides with a
transmission subframe of a CQI, the UE determines a transmission parameter of the
CQI from the initial uplink grant. The transmission parameter is a parameter for de-
termining an amount of radio resources required to transmit the CQI, and may be
related to an MCS of the CQI. For example, when the amount of radio resources of the
CQI is determined by Equation 4, at least one of transmission parameters C, Kr, Msc,
and Nsymb can be obtained from the initial uplink grant.
[77] In step S570, the UE multiplexes the CQI and the retransmission data of the uplink
data by using the transmission parameter. In step S580, the UE transmits the mul-
tiplexed data on the PUSCH.
[78] In HARQ retransmission, when the retransmission data is transmitted together with
the CQI, the MCS of the CQI is determined according to the initial uplink grant, so that
a signaling overhead can be reduced without additional signaling for the transmission
parameter of the CQI to be multiplexed.
[79] FIG. 10 is a flow diagram showing an HARQ method according to another em-
bodiment of the present invention.
[80] Referring to FIG. 10, in step S610, a BS transmits an initial uplink grant on a
PDCCH. In step S620, a UE transmits uplink data on a PUSCH indicated by the initial
uplink grant. In step S630, upon detecting a decoding error of the uplink data, the BS
transmits a NACK signal as a retransmission request.
[81] In step S640, the BS transmits a retransmission grant on the PDCCH. The re-
transmission grant includes radio resource allocation information for retransmission
data regarding the uplink data.
[82] In step s650, if a transmission subframe of retransmission data coincides with a
transmission subframe of a CQI, the UE determines a transmission parameter of the
CQI from the initial uplink grant. In step S670, the UE multiplexes the CQI and the re-
transmission of the uplink data by using the transmission parameter. In this case, the
retransmission data is multiplexed using a transmission parameter obtained from the
retransmission grant, and the CQI is multiplexed using a transmission parameter
obtained from the initial grant. In step S680, the UE transmits the multiplexed data on
the PUSCH.
[83] FIG. 11 is a flow diagram showing an HARQ method according to another em-
bodiment of the present invention.
[84] Referring to FIG. 11, in step S700, a BS configures a periodic CQI. A UE peri-
odically transmits the CQI according to a period determined by the BS. In step S710,
the BS transmits an initial uplink grant on a PDCCH. The initial uplink grant includes
radio resource allocation information for initial uplink data in the HARQ method. In
step S720, the UE transmits uplink data on a PUSCH indicated by the initial uplink
grant.
[85] In step S730, the UE transmits the CQI at a CQI transmission period. In this case, if
an available PUCCH resource exists, the CQI can be transmitted on a PUCCH. In step
S740, upon detecting a decoding error of the uplink data, the BS transmits a NACK
signal as a retransmission request.
[86] In step S760, if a transmission subframe of retransmission data coincides with a
transmission subframe of a CQI, the UE determines a transmission parameter of the
CQI from the initial uplink grant.
[87] In step S770, the UE multiplexes the CQI and the retransmission data of the uplink
data by using the transmission parameter. In step S780, the UE transmits the mul-
tiplexed data on the PUSCH.
[88] FIG. 12 is a flow diagram showing an HARQ method according to another em-
bodiment of the present invention.
[89] Referring to FIG. 12, in step S810, a BS transmits an initial uplink grant on a
PDCCH. In step S820, a UE transmits uplink data on a PUSCH indicated by the initial
uplink grant. In step S830, upon detecting a decoding error of the uplink data, the BS
transmits a NACK signal as a retransmission request.
[90] In step s840, the BS transmits a retransmission grant and a CQI request on the
PDCCH. The CQI request is a signal optionally used by the BS to request the UE to
transmit the CQI. Although the CQI request is transmitted on the PDCCH together
with the retransmission grant, the CQI request can be transmitted to the UE through an
additional message.
[91] In step S860, the UE determines a transmission parameter of the CQI from the initial
uplink grant according to the CQI request of the BS. In step S870, the UE multiplexes
the CQI and the retransmission of the uplink data by using the transmission parameter.
In this case, the retransmission data is multiplexed using a transmission parameter
obtained from the retransmission grant, and the CQI is multiplexed using a
transmission parameter obtained from the initial grant. In step S880, the UE transmits
the multiplexed data on the PUSCH.
[92] Although CQI multiplexing at first retransmission has been proposed in the afore-
mentioned embodiments, the CQI transmission parameter can be obtained from the
initial uplink grant even if the CQI is transmitted by being multiplexed at n-th re-
transmission (where n>l).
[93] By using the transmission parameter used in initial data transmission as the CQI
transmission parameter, additional signaling for the CQI transmission parameter is not
necessary.
[94] While performing the HARQ, to multiplex and transmit the retransmission data and
the CQI on the PUSCH, a CQI transmission parameter can be obtained not only from
the initial uplink grant but also from other grants. For example, the transmission
parameter used for the retransmission data multiplexed together with the CQI can be
set to the CQI transmission parameter. This is a case where the same MCS used for the
retransmission data is used to transmit the CQI at retransmission. For another example,
the transmission parameter used in previous transmission can be used as the CQI
transmission parameter. This is a case where, when second retransmission data and the
CQI are multiplexed at second retransmission, the transmission parameter used for the
first retransmission data is set to the CQI transmission parameter.
[95] As described above, a non-periodic CQI is transmitted at the request of the BS. In
general, the CQI request can be transmitted on the PDCCH. In this case, a transmission
indicator for the CQI transmission parameter can be transmitted along with the CQI
request. The CQI may be transmitted using an allocated resource (or transmission
parameter) according to the transmission indicator, or the CQI may be transmitted
using a previously allocated resource (or transmission parameter).
[96] FIG. 13 is a block diagram showing an apparatus for wireless communication
according to an embodiment of the present invention. An apparatus 50 for wireless
communication may be a part of a UE. The apparatus 50 for wireless communication
includes a processor 51, a memory 52, a radio frequency (RF) unit 53, a display unit
54, and a user interface unit 55. The RF unit 53 is coupled to the processor 51 and
transmits and/or receives radio signals. The memory 52 is coupled to the processor 51
and stores an operating system, applications, and general files. The display unit 54
displays a variety of information of the UE and may use a well-known element such as
a liquid crystal display (LCD), an organic light emitting diode (OLED), etc. The user
interface unit 55 can be configured with a combination of well-known user interfaces
such as a keypad, a touch screen, etc. The processor 51 supports HARQ and AMC.
The processor 51 can configure a PUCCH or a PUSCH and can perform multiplexing
of data and a CQI. The aforementioned embodiments of the HARQ method can be im-
plemented by the processor 51.
[97] The present invention can be implemented with hardware, software, or combination
thereof. In hardware implementation, the present invention can be implemented with
one of an application specific integrated circuit (ASIC), a digital signal processor
(DSP), a programmable logic device (PLD), a field programmable gate array (FPGA),
a processor, a controller, a microprocessor, other electronic units, and combination
thereof, which are designed to perform the aforementioned functions. In software im-
plementation, the present invention can be implemented with a module for performing
the aforementioned functions. Software is storable in a memory unit and executed by
the processor. Various means widely known to those skilled in the art can be used as
the memory unit or the processor.
[98] While the present invention has been particularly shown and described with reference
to exemplary embodiments thereof, it will be understood by those skilled in the art that
various changes in form and details may be made therein without departing from the
spirit and scope of the invention as defined by the appended claims. The exemplary
embodiments should be considered in descriptive sense only and not for purposes of
limitation. Therefore, the scope of the invention is defined not by the detailed de-
scription of the invention but by the appended claims, and all differences within the
scope will be construed as being included in the present invention.
WE CLAIM :
1. A method for retransmitting data in a wireless communication system, the
method comprising:
receiving in an user equipment on a downlink channel a first uplink grant from a base
station, the fust uplink grant indicating resources for transmitting uplink data to the base
station, wherein the first uplink grant is based on at least one transmission parameter for
transmitting the uplink data;
transmitting the uplink data on an uplink data channel using the resources indicated
by the first uplink grant;
receiving from the base station an indication for retransmission of the uplink data;
identifying the existence of control information to be transmitted to the base station
with the retransmission of the uplink data;
determining at least one transmission parameter for transmitting the control
information to the base station, wherein the at least one transmission parameter for
transmitting the control information is determined according to the at least one transmission
parameter for transmitting the uplink data;
determining an amount of resources for transmitting the control information according
to the determined at least one transmission parameter;
multiplexing retransmission data with the control information such that the control
information and the retransmission data are transmitted using resources indicated by a second
uplink grant; and
transmitting the multiplexed data on the uplink data channel using the resources
indicated by the second uplink grant.
2. The method of claim 1, wherein the wireless communication system is a single
carrier-frequency division multiple access (SC-FDMA) system.
3. The method of claim 1, further comprising receiving from the base station on
the downlink channel the second uplink grant indicating resources for retransmitting the
uplink data.
4. The method of claim 1, wherein the control information is a channel quality
indicator (CQI).
5. The method of claim 4, wherein the at least one transmission parameter is
related to a modulation and coding scheme (MCS) of the CQI.
6. The method of claim 5, wherein the at least one transmission parameter for
transmitting the control information is determined so that the MCS of the CQI is the same as
the MCS of the uplink data.
7. The method of claim 1, wherein the downlink channel is a physical downlink
control channel (PDCCH).
8. The method of claim 1, wherein the uplink channel is a physical uplink shared
channel (PUSCH).
9. An user equipment for retransmitting data in a wireless communication
system, the user equipment comprising:
a radio frequency (RF) unit for transmitting and receiving a radio signal; and
a processor coupled with the RF unit, the processor configured for:
receiving on a downlink channel a first uplink grant from a base station, the
first uplink grant indicating resources for transmitting uplink data to the base station, wherein
the first uplink grant is based on at least one transmission parameter for transmitting the
uplink data,
transmitting the uplink data on an uplink data channel using the resources
indicated by the first uplink grant,
receiving from the base station an indication for retransmission of the uplink
data,
identifying the existence of control information to be transmitted to the base
station with the retransmission of the uplink data,
determining at least one transmission parameter for transmitting the control
information to the base station, wherein the at least one transmission parameter for
transmitting the control information is determined according to the at least one transmission
parameter for transmitting the uplink data,
determining an amount of resources for transmitting the control information
according to the determined at least one transmission parameter;
multiplexing retransmission data with the control information such that the
control information and the retransmission data are transmitted using resources indicated by a
second uplink grant, and
transmitting the multiplexed data on the uplink data channel using the
resources indicated by the second uplink grant.
10. The user equipment of claim 9, wherein the wireless communication system is
a single carrier-frequency division multiple access (SC-FDMA) system.
11. The user equipment of claim 9, further comprising receiving from the base
station on the downlink charmel the second uplink grant indicating resources for
retransmitting the uplink data.
12. The user equipment of claim 9, wherein the control information is a channel
quality indicator (CQI).
13. The user equipment of claim 12, wherein the at least one transmission
parameter is related to a modulation and coding scheme (MCS) of the CQI.
14. The user equipment of claim 13, wherein the at least one transmission
parameter for transmitting the control information is determined so that the MCS of the CQI
is the same as the MCS of the uplink data.
15. The user equipment of claim 9, wherein the downlink channel is a physical
downlink control channel (PDCCH).
16. The user equipment of claim 9, wherein the uplink charmel is a physical uplink
shared channel (PUSCH).

A method of
supporting Hybrid Automatic Repeat
Request (HARQ) includes receiving
an initial uplink grant on a downlink
channel, transmitting uplink data on
an uplink channel using the initial
uplink grant, receiving a request for
retransmission of the uplink data,
determining at least one transmission
parameter of a channel quality
indicator (CQI) from the initial uplink
grant, multiplexing retransmission
data of the uplink data with the CQI,
and transmitting the multiplexed data
on the uplink channel. Amount of
resources for transmission of the CQI
is determined based on the at least
one transmission parameter.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=KU1j8DJf8c28Ih9EGyvkEw==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

278036

Indian Patent Application Number

2646/KOLNP/2010

PG Journal Number

52/2016

Publication Date

16-Dec-2016

Grant Date

08-Dec-2016

Date of Filing

19-Jul-2010

Name of Patentee

LG ELECTRONICS INC,

Applicant Address

20, YEOUIDO-DONG, YEONGDEUNGDO-GU, SEOUL 150-721 REPUBLIC OF KOREA

Inventors:

#	Inventor's Name	Inventor's Address
1	KIM, HAK SEONG	LG R & D COMPLEX, 533, HOGYE 1-DONG, DONGAN-GU, ANYANG-SI, GYEONGGI-DO 431-749 REPUBLIC OF KOREA
2	LEE, DAE WON	LG R & D COMPLEX, 533, HOGYE 1-DONG, DONGAN-GU, ANYANG-SI, GYEONGGI-DO 431-749 REPUBLIC OF KOREA
3	AHN, JOON KUI	LG R & D COMPLEX, 533, HOGYE 1-DONG, DONGAN-GU, ANYANG-SI, GYEONGGI-DO 431-749 REPUBLIC OF KOREA

PCT International Classification Number

H04L 1/18

PCT International Application Number

PCT/KR2009/000499

PCT International Filing date

2009-02-02

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10-2008-0128471	2008-12-17	U.S.A.
2	61/025,811	2008-02-03	U.S.A.