BACKGROUND

Field

[0001] Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to managing the HARQ buffer in a cellular network.

Background

[0002] Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support

communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network

(UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD- SCDMA). For example, China is pursuing TD-SCDMA as the underlying air interface in the UTRAN architecture with its existing GSM infrastructure as the core network. The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. HSPA is a collection of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing wideband protocols.

[0003] As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

SUMMARY

[0004] In one aspect, a method of wireless communication is disclosed. The method includes determining whether a grant was missed during a tune away from a first radio access technology (RAT) to a second RAT or frequency. The determination is based at least in part on a grant sequence number. The method also includes flushing a hybrid automatic repeat request (HARQ) buffer when a grant is determined to be missing when a duration of the tune away gap is below a threshold value or a duration of the tune away gap is above a threshold value.

[0005] Another aspect discloses an apparatus including means for means for determining whether a grant was missed during a tune away from a first radio access technology (RAT) to a second RAT or frequency based at least in part on a grant sequence number. The apparatus also includes means for flushing a hybrid automatic repeat request (HARQ) buffer when a grant is determined to be missing when a duration of the tune away gap is below a threshold value or a duration of the tune away gap is above a threshold value.

[0006] Another aspect discloses wireless communication having a memory and at least one processor coupled to the memory. The processor(s) is configured to determine whether a grant was missed during a tune away from a first radio access technology (RAT) to a second RAT or frequency based at least in part on a grant sequence number. The processor(s) is also configured to flush a hybrid automatic repeat request (HARQ) buffer when a grant is determined to be missing when a duration of the tune away gap is below a threshold value or a duration of the tune away gap is above a threshold value.

[0007] In another aspect, a computer program product for wireless communications in a wireless network having a non-transitory computer-readable medium is disclosed. The computer readable medium has non-transitory program code recorded thereon which, when executed by the processor(s), causes the processor(s) to perform operations of determining whether a grant was missed during a tune away from a first radio access technology (RAT) to a second RAT or frequency based at least in part on a grant sequence number. The program code also causes the processor(s) to flush a hybrid automatic repeat request (HARQ) buffer when a grant is determined to be missing when a duration of the tune away gap is below a threshold value or a duration of the tune away gap is above a threshold value.

[0008] This has outlined, rather broadly, the features and technical advantages of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described below. It should be appreciated by those skilled in the art that this disclosure may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the teachings of the disclosure as set forth in the appended claims. The novel features, which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages, will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout.

[0010] FIGURE 1 is a block diagram conceptually illustrating an example of a telecommunications system.

[0011] FIGURE 2 is a block diagram conceptually illustrating an example of a frame structure in a telecommunications system.

[0012] FIGURE 3 is a block diagram conceptually illustrating an example of a node B in communication with a UE in a telecommunications system. [0013] FIGURES 4A-4B are block diagrams illustrating transmissions from a node B to a UE in a telecommunications system according to one aspect of the present disclosure.

[0014] FIGURE 5 is a block diagram illustrating a method for managing a HARQ buffer according to one aspect of the present disclosure.

[0015] FIGURE 6 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system according to one aspect of the present disclosure.

DETAILED DESCRIPTION

[0016] The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

[0017] Turning now to FIGURE 1, a block diagram is shown illustrating an example of a telecommunications system 100. The various concepts presented throughout this disclosure may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. By way of example and without limitation, the aspects of the present disclosure illustrated in FIGURE 1 are presented with reference to a UMTS system employing a TD-SCDMA standard. In this example, the UMTS system includes a (radio access network) RAN 102 (e.g., UTRAN) that provides various wireless services including telephony, video, data, messaging, broadcasts, and/or other services. The RAN 102 may be divided into a number of Radio Network Subsystems (RNSs) such as an RNS 107, each controlled by a Radio Network Controller (RNC) such as an RNC 106. For clarity, only the RNC 106 and the RNS 107 are shown; however, the RAN 102 may include any number of RNCs and RNSs in addition to the RNC 106 and RNS 107. The RNC 106 is an apparatus responsible for, among other things, assigning, reconfiguring and releasing radio resources within the RNS 107. The RNC 106 may be interconnected to other RNCs (not shown) in the RAN 102 through various types of interfaces such as a direct physical connection, a virtual network, or the like, using any suitable transport network.

[0018] The geographic region covered by the RNS 107 may be divided into a number of cells, with a radio transceiver apparatus serving each cell. A radio transceiver apparatus is commonly referred to as a node B in UMTS applications, but may also be referred to by those skilled in the art as a base station (BS), a base transceiver station (BTS), a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an access point (AP), or some other suitable terminology. For clarity, two node Bs 108 are shown; however, the RNS 107 may include any number of wireless node Bs. The node Bs 108 provide wireless access points to a core network 104 for any number of mobile apparatuses. Examples of a mobile apparatus include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a notebook, a netbook, a smartbook, a personal digital assistant (PDA), a satellite radio, a global positioning system (GPS) device, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, or any other similar functioning device. The mobile apparatus is commonly referred to as user equipment (UE) in UMTS applications, but may also be referred to by those skilled in the art as a mobile station (MS), a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless

communications device, a remote device, a mobile subscriber station, an access terminal (AT), a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. For illustrative purposes, three UEs 110 are shown in communication with the node Bs 108. The downlink (DL), also called the forward link, refers to the communication link from a node B to a UE, and the uplink (UL), also called the reverse link, refers to the communication link from a UE to a node B.

[0019] The core network 104, as shown, includes a GSM core network. However, as those skilled in the art will recognize, the various concepts presented throughout this disclosure may be implemented in a RAN, or other suitable access network, to provide UEs with access to types of core networks other than GSM networks.

[0020] In this example, the core network 104 supports circuit-switched services with a mobile switching center (MSC) 112 and a gateway MSC (GMSC) 114. One or more R Cs, such as the R C 106, may be connected to the MSC 112. The MSC 112 is an apparatus that controls call setup, call routing, and UE mobility functions. The MSC 112 also includes a visitor location register (VLR) (not shown) that contains subscriber- related information for the duration that a UE is in the coverage area of the MSC 112. The GMSC 114 provides a gateway through the MSC 112 for the UE to access a circuit- switched network 116. The GMSC 114 includes a home location register (HLR) (not shown) containing subscriber data, such as the data reflecting the details of the services to which a particular user has subscribed. The HLR is also associated with an authentication center (AuC) that contains subscriber-specific authentication data. When a call is received for a particular UE, the GMSC 114 queries the HLR to determine the UE's location and forwards the call to the particular MSC serving that location.

[0021] The core network 104 also supports packet-data services with a serving GPRS support node (SGSN) 118 and a gateway GPRS support node (GGSN) 120. GPRS, which stands for General Packet Radio Service, is designed to provide packet-data services at speeds higher than those available with standard GSM circuit-switched data services. The GGSN 120 provides a connection for the RAN 102 to a packet-based network 122. The packet-based network 122 may be the Internet, a private data network, or some other suitable packet-based network. The primary function of the GGSN 120 is to provide the UEs 110 with packet-based network connectivity. Data packets are transferred between the GGSN 120 and the UEs 110 through the SGSN 118, which performs primarily the same functions in the packet-based domain as the MSC 112 performs in the circuit-switched domain.

[0022] The UMTS air interface is a spread spectrum Direct-Sequence Code Division Multiple Access (DS-CDMA) system. The spread spectrum DS-CDMA spreads user data over a much wider bandwidth through multiplication by a sequence of

pseudorandom bits called chips. The TD-SCDMA standard is based on such direct sequence spread spectrum technology and additionally calls for a time division duplexing (TDD), rather than a frequency division duplexing (FDD) as used in many FDD mode UMTS/W-CDMA systems. TDD uses the same carrier frequency for both the uplink (UL) and downlink (DL) between a node B 108 and a UE 110, but divides uplink and downlink transmissions into different time slots in the carrier. [0023] FIGURE 2 shows a frame structure 200 for a TD-SCDMA carrier. The TD- SCDMA carrier, as illustrated, has a frame 202 that is 10 ms in length. The chip rate in TD-SCDMA is 1.28 Mcps. The frame 202 has two 5 ms subframes 204, and each of the subframes 204 includes seven time slots, TSO through TS6. The first time slot, TSO, is usually allocated for downlink communication, while the second time slot, TS1, is usually allocated for uplink communication. The remaining time slots, TS2 through TS6, may be used for either uplink or downlink, which allows for greater flexibility during times of higher data transmission times in either the uplink or downlink directions. A downlink pilot time slot (DwPTS) 206, a guard period (GP) 208, and an uplink pilot time slot (UpPTS) 210 (also known as the uplink pilot channel (UpPCH)) are located between TSO and TS1. Each time slot, TS0-TS6, may allow data transmission multiplexed on a maximum of 16 code channels. Data transmission on a code channel includes two data portions 212 (each with a length of 352 chips) separated by a midamble 214 (with a length of 144 chips) and followed by a guard period (GP) 216 (with a length of 16 chips). The midamble 214 may be used for features, such as channel estimation, while the guard period 216 may be used to avoid inter-burst interference. Also transmitted in the data portion is some Layer 1 control information, including Synchronization Shift (SS) bits 218. Synchronization Shift bits 218 only appear in the second part of the data portion. The Synchronization Shift bits 218 immediately following the midamble can indicate three cases: decrease shift, increase shift, or do nothing in the upload transmit timing. The positions of the SS bits 218 are not generally used during uplink communications.

[0024] FIGURE 3 is a block diagram of a node B 310 in communication with a UE 350 in a RAN 300, where the RAN 300 may be the RAN 102 in FIGURE 1, the node B 310 may be the node B 108 in FIGURE 1, and the UE 350 may be the UE 110 in FIGURE 1. In the downlink communication, a transmit processor 320 may receive data from a data source 312 and control signals from a controller/processor 340. The transmit processor 320 provides various signal processing functions for the data and control signals, as well as reference signals (e.g., pilot signals). For example, the transmit processor 320 may provide cyclic redundancy check (CRC) codes for error detection, coding and interleaving to facilitate forward error correction (FEC), mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M- quadrature amplitude modulation (M-QAM), and the like), spreading with orthogonal variable spreading factors (OVSF), and multiplying with scrambling codes to produce a series of symbols. Channel estimates from a channel processor 344 may be used by a controller/processor 340 to determine the coding, modulation, spreading, and/or scrambling schemes for the transmit processor 320. These channel estimates may be derived from a reference signal transmitted by the UE 350 or from feedback contained in the midamble 214 (FIGURE 2) from the UE 350. The symbols generated by the transmit processor 320 are provided to a transmit frame processor 330 to create a frame structure. The transmit frame processor 330 creates this frame structure by multiplexing the symbols with a midamble 214 (FIGURE 2) from the controller/processor 340, resulting in a series of frames. The frames are then provided to a transmitter 332, which provides various signal conditioning functions including amplifying, filtering, and modulating the frames onto a carrier for downlink transmission over the wireless medium through smart antennas 334. The smart antennas 334 may be implemented with beam steering bidirectional adaptive antenna arrays or other similar beam technologies.

[0025] At the UE 350, a receiver 354 receives the downlink transmission through an antenna 352 and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver 354 is provided to a receive frame processor 360, which parses each frame, and provides the midamble 214

(FIGURE 2) to a channel processor 394 and the data, control, and reference signals to a receive processor 370. The receive processor 370 then performs the inverse of the processing performed by the transmit processor 320 in the node B 310. More specifically, the receive processor 370 descrambles and despreads the symbols, and then determines the most likely signal constellation points transmitted by the node B 310 based on the modulation scheme. These soft decisions may be based on channel estimates computed by the channel processor 394. The soft decisions are then decoded and deinter leaved to recover the data, control, and reference signals. The CRC codes are then checked to determine whether the frames were successfully decoded. The data carried by the successfully decoded frames will then be provided to a data sink 372, which represents applications running in the UE 350 and/or various user interfaces (e.g., display). Control signals carried by successfully decoded frames will be provided to a controller/processor 390. When frames are unsuccessfully decoded by the receiver processor 370, the controller/processor 390 may also use an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support retransmission requests for those frames.

[0026] In the uplink, data from a data source 378 and control signals from the controller/processor 390 are provided to a transmit processor 380. The data source 378 may represent applications running in the UE 350 and various user interfaces (e.g., keyboard). Similar to the functionality described in connection with the downlink transmission by the node B 310, the transmit processor 380 provides various signal processing functions including CRC codes, coding and interleaving to facilitate FEC, mapping to signal constellations, spreading with OVSFs, and scrambling to produce a series of symbols. Channel estimates, derived by the channel processor 394 from a reference signal transmitted by the node B 310 or from feedback contained in the midamble transmitted by the node B 310, may be used to select the appropriate coding, modulation, spreading, and/or scrambling schemes. The symbols produced by the transmit processor 380 will be provided to a transmit frame processor 382 to create a frame structure. The transmit frame processor 382 creates this frame structure by multiplexing the symbols with a midamble 214 (FIGURE 2) from the

controller/processor 390, resulting in a series of frames. The frames are then provided to a transmitter 356, which provides various signal conditioning functions including amplification, filtering, and modulating the frames onto a carrier for uplink transmission over the wireless medium through the antenna 352.

[0027] The uplink transmission is processed at the node B 310 in a manner similar to that described in connection with the receiver function at the UE 350. A receiver 335 receives the uplink transmission through the antenna 334 and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver 335 is provided to a receive frame processor 336, which parses each frame, and provides the midamble 214 (FIGURE 2) to the channel processor 344 and the data, control, and reference signals to a receive processor 338. The receive processor 338 performs the inverse of the processing performed by the transmit processor 380 in the UE 350. The data and control signals carried by the successfully decoded frames may then be provided to a data sink 339 and the controller/processor, respectively. If some of the frames were unsuccessfully decoded by the receive processor, the controller/processor 340 may also use an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support retransmission requests for those frames.

[0028] The computer readable media of memories 392 may store data and software for the UE 350. For example, the memory 392 of the UE 350 may store a HARQ buffer management module 391 which, when executed by the controller/processor 390, configures the UE 350 for flushing the HARQ buffer when particular criteria are met.

HIGH SPEED DATA NETWORKS

[0029] High speed networks are utilized to improve the uplink and downlink throughput. In particular, the high speed downlink packet access (HSDPA) or time division high speed downlink packet access (TD-HSUPA) is a set of enhancements to time division synchronous code division multiple access (TD-SCDMA) in order to improve downlink throughput. Additionally, the high speed uplink packet access (HSUPA) or time division high speed uplink packet access (TD-HSUPA) is a set of enhancements to time division synchronous code division multiple access (TD- SCDMA) in order to improve uplink throughput.

[0030] The following describes various TD-HSDPA physical channels. The high-speed physical downlink shared channel (HS-PDSCH) carries a user data burst(s). The highspeed shared control channel (HS-SCCH), also referred to as the grant channel, carries the modulation and coding scheme, channelization code, time slot and transport block size information for the data burst in HS-PDSCH. The HS-SCCH also carries the HARQ process, redundancy version, and new data indicator information for the data burst. Additionally, the HS-SCCH carries the HS-SCCH cyclic sequence number which increments a UE specific cyclic sequence number for each HS-SCCH transmission. Further, the HS-SCCH carries the UE identity to indicate which UE should receive the data burst allocation.

[0031] The high-speed shared information channel (HS-SICH) is also referred to as the feedback channel. The HS-SICH carries the channel quality index (CQI), the recommended transport block size (RTBS) and the recommended modulation format (RMF). Additionally, the HS-SICH also carries the HARQ ACK/NACK of the HS- PDSCH transmissions. [0032] The following describes various TD-HSUPA physical channels. The enhanced uplink dedicated channel (E-DCH) is a dedicated transport channel that features enhancements to an existing dedicated transport channel carrying data traffic.

[0033] The enhanced data channel (E-DCH) or enhanced physical uplink channel (E- PUCH) carries E-DCH traffic and schedule information (SI). Information in this E- PUCH channel can be transmitted in a burst fashion.

[0034] The E-DCH uplink control channel (E-UCCH) carries layer 1 (or physical layer) information for E-DCH transmissions. The transport block size may be 6 bits and the retransmission sequence number (RSN) may be 2 bits. Also, the hybrid automatic repeat request (HARQ) process ID may be 2 bits.

[0035] The E-DCH random access uplink control channel (E-RUCCH) is an uplink physical control channel that carries SI and enhanced radio network temporary identities (E-RNTI) for identifying UEs.

[0036] The absolute grant channel for E-DCH (enhanced access grant channel (E- AGCH)) carries grants for E-PUCH transmission, such as the maximum allowable E- PUCH transmission power, time slots, and code channels. The hybrid automatic repeat request (hybrid ARQ or HARQ) indication channel for E-DCH (E-HICH) carries HARQ ACK/NAK signals.

[0037] The operation of TD-HSUPA may also have the following steps. First, in the resource request step, the UE sends requests (e.g., via scheduling information (SI)) via the E-PUCH or the E-RUCCH to a base station (e.g., NodeB). The requests are for permission to transmit on the uplink channels. Next, in a resource allocation step, the base station, which controls the uplink radio resources, allocates resources. Resources are allocated in terms of scheduling grants (SGs) to individual UEs based on their requests. In the third step (i.e., the UE Transmission step), the UE transmits on the uplink channels after receiving grants from the base station. The UE determines the transmission rate and the corresponding transport format combination (TFC) based on the received grants. The UE may also request additional grants if it has more data to transmit. Finally, in the fourth step (i.e., the base station reception step), a hybrid automatic repeat request (hybrid ARQ or HARQ) process is employed for the rapid retransmission of erroneously received data packets between the UE and the base station.

MANAGING HARQ FOR MULTI-SIM DEVICES IN HIGH SPEED DATA NETWORKS

[0038] A user equipment (UE) may include more than one subscriber identity module (SIM) or universal subscriber identity module (USIM). A UE with more than one SIM may be referred to as a multi-SIM device. In the present disclosure, a SIM may refer to a SIM or a USIM. Each SIM may also include a unique International Mobile

Subscriber Identity (IMSI) and service subscription information. Each SIM may be configured to operate in a particular radio access technology. Moreover, each SIM may have full phone features and be associated with a unique phone number. Therefore, the UE may use each SIM to send and receive phone calls. That is, the UE may

simultaneously communicate via the phone numbers associated with each individual SIM. For example, a first SIM card can be associated for use in a City A and a second SIM card may be associated for use in a different City B to reduce roaming fees and long distance calling fees. Alternately, a first SIM card may be assigned for personal usage and a different SIM card may be assigned for work/business purposes. In another configuration, a first SIM card provides full phone features and a different SIM card is utilized mostly for data services.

[0039] Many multi-SIM devices support muli-SIM multi-standby operation using a single radio frequency (RF) chain to transmit and receive communications. In one example, a multi-SIM device includes a first SIM dedicated to operate in first RAT and a second SIM dedicated to operate in a second RAT. In one illustrative example, the multi-SIM device includes a first SIM configured to operate in GSM (i.e., G

subscription) and a second SIM configured to operate in TD-SCDMA (i.e., T subscription). When the T subscription is in the dedicated channel (DCH) state without voice traffic, the multi-SIM device supports the TD-SCDMA to GSM tune away with the least amount of interruption to the TD-SCDMA DCH operation. When the UE is in the TD-SCDMA dedicated channel, the UE periodically tunes away from TD-SCDMA, and tunes to GSM to monitor for pages. If the G subscription detects a page when the T to G tune away is active, the multi-SIM UE suspends all operations of the TD-SCMA subscription and transitions to another RAT. If the other RAT subscription does not detect a page, the UE tunes back to TD-SCDMA and attempts to recover to the original operation of the TD-SCDMA subscription. The multi-SIM device may operate in other RATS known to those skilled in the art.

[0040] In one example, in a high speed data network, when the UE tunes back, the HSDPA HARQ soft buffer with NACK is flushed when the tune away gap length is longer than the fixed timer (e.g. 48ms). The HARQ buffer may be a soft HARQ buffer that stores information from transmissions that were not correctly decoded. When the network does not send a retransmission grant for HS-SCCH, then flushing the HARQ buffer may result in HARQ failure because the NodeB typically sends more redundancy bits for IR combining.

[0041] When a UE tunes away from a first RAT to a second RAT, the UE may miss a grant sent from the first RAT. Aspects of the present disclosure are directed to utilizing grant sequence numbers carried in data transmissions to determine whether any grants were missed during a tune away gap and to managing the HARQ buffer based on the determination. Aspects of the present disclosure, reduce the risk of HARQ failure by not flushing the HARQ buffer when there are no missing grants.

[0042] In one aspect of the present disclosure, the grant sequence number is

incremented each time a data transmission is sent to a UE. Based on the grant sequence number, the UE can determine whether it failed to detect and decode a data transmission while the UE tuned away from a first RAT to a second RAT. In one aspect, the grant sequence number may include a cyclic counter carried in high speed data transmissions.

[0043] In one aspect of the present disclosure, the grant sequence number is a cyclic counter carried in a high speed downlink transmission. In particular, in TD-HSDPA, a cyclic counter (e.g., high-speed cyclic sequence number, (HCSN)), is carried on the HS- SCCH and is incremented each time a HS-SCCH (high-speed shared control channel) transmission is sent to a particular UE. Based on the value of the HCSN and the length of the tune away gap, the UE can determine whether it failed to detect and decode a HS- SCCH transmission from the node B while the UE was tuned away.

[0044] According to aspects of the present disclosure, when the UE determines no grants are missing, the UE does not flush the HARQ buffer with NACK. However, if the UE determines it missed a grant(s), then the HARQ buffer is flushed. In another aspect, the HARQ buffer is flushed when the UE determines it missed a grant and when the duration of the tune away gap is greater than a threshold value.

[0045] Referring to FIGURE 4A, a node B 402 transmits a first HS-SCCH transmission carrying HCSN m (modulo 8) which is detected and decoded by the UE 404. The node B 402 transmits HS-SCCH with HCSN m+1 which is not detected by the UE 404. The node B 402 then transmits HS-SCCH with HCSN m+2 (modulo 8) which is detected and decoded by the UE 404. The UE compares the HCSN values carried on the detected high speed channel transmissions (i.e., HCSN m and HCSN m+2) and determines it failed to detect a transmission associated with the HCSN m+1. The UE then determines it missed a HS-SCCH grant during the tune away gap. In another aspect, the UE also considers the length of the tune away gap.

[0046] When the HCSN value carried in the HS-SCCH before the UE tunes away is the same as the HCSN received after the UE tunes back, and when the tune away gap length is less than a threshold value, the UE determines either no grant is missing, or that the NodeB did not send the HS-SCCH grant to the UE during the tune away gap. The threshold value may be based on an maximum grant sequence number. In particular, the transmission time interval and the Max sequence number allocated to the uplink/downlink grant channel may affect the threshold value. The threshold value is equal to Max sequence number * Transmission Time interval. For example, if the Max sequence number =8, and TTI = 5ms, then the threshold value is equal to 8* 5ms = 40 ms.

[0047] In another aspect of the present disclosure, the grant sequence number is a cyclic counter carried in high speed uplink data transmissions. In particular, in TD-HSUPA, the E-AGCH Cyclic Sequence Number (ECSN ) is carried on the grant channel E- AGCH and is incremented each time it is transmitted to the UE. Based on the value of the ECSN, the UE can determine whether it failed to detect and decode a E-AGCH transmission while the UE was tuned away.

[0048] Referring to FIGURE 4B, a node B 402 transmits a first E-AGCH transmission carrying ECSN m (modulo 8) which is detected and decoded by the UE 404. The node B 402 transmits E-AGCH with ECSN m+1 which is not detected by the UE 404. The node B 402 then transmits E-AGCH with ECSN m+2 (modulo 8) which is detected and decoded by the UE 404. The UE compares the ECSN values carried on the detected high speed channel transmissions (i.e., ECSN m and ECSN m+2) and determines it failed to detect a transmission associated with the ECSN m+1. The UE then determines it missed a E-AGCH grant during the tune away gap based on the ECSN value. When the UE determines it missed a grant, the HARQ buffer is flushed when the tune away gap length is greater than a predetermined threshold value.

[0049] When the ECSN value carried in E-AGCH before the UE tunes away is the same as the ECSN after the UE tunes back, and the tune away gap length is less than a predetermined value, the UE determines it did not miss a grant, or that the NodeB did not send the E-AGCH grant to UE when it tuned away. When the UE determines there are no missing grants, the UE does not flush the HARQ buffer and performs a retransmission when the received grant is sufficient for retransmission.

[0050] In one aspect of the present disclosure, the UE is multi-SIM UE and the UE tunes away for communications associated with a second SIM. In another aspect, the UE is a single subscriber SIM UE and the UE tunes away for inter-frequency measurement.

[0051] FIGURE 5 shows a wireless communication method 500 according to one aspect of the disclosure. A UE determines whether a grant was missed during tune away from a first radio access technology (RAT) to a second RAT based at least in part on a grant sequence number, as shown in block 502. When the grant is determined to be missing or when the duration of the tune away gap is greater than a threshold value, the UE flues the HARQ buffer, as shown in block 504.

[0052] FIGURE 6 is a diagram illustrating an example of a hardware implementation for an apparatus 600 employing a processing system 614. The processing system 614 may be implemented with a bus architecture, represented generally by the bus 624. The bus 624 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 614 and the overall design constraints. The bus 624 links together various circuits including one or more processors and/or hardware modules, represented by the processor 622 the modules 602, 604, and the non- transitory computer-readable medium 626. The bus 624 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

[0053] The apparatus includes a processing system 614 coupled to a transceiver 630. The transceiver 630 is coupled to one or more antennas 620. The transceiver 630 enables communicating with various other apparatus over a transmission medium. The processing system 614 includes a processor 622 coupled to a non-transitory computer- readable medium 626. The processor 622 is responsible for general processing, including the execution of software stored on the computer-readable medium 626. The software, when executed by the processor 622, causes the processing system 614 to perform the various functions described for any particular apparatus. The computer- readable medium 626 may also be used for storing data that is manipulated by the processor 622 when executing software.

[0054] The processing system 614 includes a determining module 602 for determining whether a grant was missed during tune away based at least in part on a grant sequence number (s). The processing system 614 includes a flushing module 604 for flushing the HARQ buffer when the grant is determined to be missing and/or when the duration of the tune away gap is greater than a threshold value. The modules may be software modules running in the processor 622, resident/stored in the computer readable medium 626, one or more hardware modules coupled to the processor 622, or some combination thereof. The processing system 614 may be a component of the UE 350 and may include the memory 392 and/or the controller/processor 390.

[0055] In one configuration, an apparatus such as a UE is configured for wireless communication including means for determining. In one aspect, the determining means may be the controller/processor 390, the memory 392, HARQ buffer management module 391, determining module 602, and/or the processing system 614 configured to perform the determining means. The UE is also configured to include means for flushing. In one aspect, the flushing means may be the controller/processor 390, the memory 392, HARQ buffer management module 391, flushing module 604 and/or the processing system 614 configured to perform the flushing means. In one aspect the means functions recited by the aforementioned means. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions recited by the aforementioned means. [0056] Several aspects of a telecommunications system has been presented with reference to TD-SCDMA and high speed data network systems. As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other telecommunication systems, network architectures and

communication standards. By way of example, various aspects may be extended to other UMTS systems such as W-CDMA, High Speed Downlink Packet Access

(HSDPA), High Speed Uplink Packet Access (HSUPA), High Speed Packet Access Plus (HSPA+) and TD-CDMA. Various aspects may also be extended to systems employing Long Term Evolution (LTE) (in FDD, TDD, or both modes), LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000, Evolution-Data Optimized (EV- DO), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra- Wideband (UWB), Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system.

[0057] Several processors have been described in connection with various apparatuses and methods. These processors may be implemented using electronic hardware, computer software, or any combination thereof. Whether such processors are implemented as hardware or software will depend upon the particular application and overall design constraints imposed on the system. By way of example, a processor, any portion of a processor, or any combination of processors presented in this disclosure may be implemented with a microprocessor, microcontroller, digital signal processor (DSP), a field-programmable gate array (FPGA), a programmable logic device (PLD), a state machine, gated logic, discrete hardware circuits, and other suitable processing components configured to perform the various functions described throughout this disclosure. The functionality of a processor, any portion of a processor, or any combination of processors presented in this disclosure may be implemented with software being executed by a microprocessor, microcontroller, DSP, or other suitable platform.

[0058] Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a non-transitory computer-readable medium. A computer- readable medium may include, by way of example, memory such as a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., compact disc (CD), digital versatile disc (DVD)), a smart card, a flash memory device (e.g., card, stick, key drive), random access memory (RAM), read only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), a register, or a removable disk. Although memory is shown separate from the processors in the various aspects presented throughout this disclosure, the memory may be internal to the processors (e.g., cache or register).

[0059] Computer-readable media may be embodied in a computer-program product. By way of example, a computer-program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.

[0060] It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.

[0061] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more." Unless specifically stated otherwise, the term "some" refers to one or more. A phrase referring to "at least one of a list of items refers to any combination of those items, including single members. As an example, "at least one of: a, b, or c" is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase "means for" or, in the case of a method claim, the element is recited using the phrase "step for."