Field

[0001] Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to methods of switching between different demodulation schemes by a receiver in a wireless system.

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 (UTMS), 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 Downlink Packet Data (HSDPA), which provides higher data transfer speeds and capacity to associated UMTS networks.

[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 also to advance and enhance the user experience with mobile communications.

SUMMARY

[0004] Certain aspects of the present disclosure provide a method for wireless communications. The method generally includes detecting a number of active midamble shifts in a downlink time slot and selecting between at least two demodulation schemes, based on the active midamble detection.

[0005] Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes means for detecting a number of active midamble shifts in a downlink time slot and means for selecting between at least two demodulation schemes, based on the active midamble detection.

[0006] Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes at least one processor configured to detect a number of active midamble shifts in a downlink time slot and select between at least two demodulation schemes, based on the active midamble detection; and a memory coupled with the at least one processor.

[0007] Certain aspects of the present disclosure provide a program product for wireless communication comprising a computer readable medium having instructions stored thereon. The instructions are generally executable by one or more processors for detecting a number of active midamble shifts in a downlink time slot and selecting between at least two demodulation schemes, based on the active midamble detection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Aspects and embodiments of the 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.

[0009] FIG. 1 illustrates an example wireless communication system, in accordance with certain embodiments of the present disclosure.

[0010] FIG. 2 illustrates various components that may be utilized in a wireless device in accordance with certain embodiments of the present disclosure.

[0011] FIG. 3 illustrates an example transmitter and an example receiver, in accordance with certain embodiments of the present disclosure.

[0012] FIG. 4 illustrates an example frame structure, in accordance with certain embodiments of the present disclosure. [0013] FIG. 5 illustrates example components capable of dynamically switching between demodulation schemes, in accordance with certain embodiments of the present disclosure.

[0014] FIG. 6 illustrates example operations for dynamically switching between demodulation schemes, in accordance with certain embodiments of the present disclosure.

[0015] FIG. 7 illustrates example operations for dynamically switching between demodulation schemes, in accordance with certain embodiments of the present disclosure.

DETAILED DESCRIPTION

[0016] Certain aspects of the present disclosure provide techniques for dynamically switching between demodulation schemes. The techniques may be utilized, for example, in TD-SCDMA systems, in an effort to improve performance and/or reduce power consumption.

[0017] 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.

AN EXAMPLE TELECOMMUNICATIONS SYSTEM

[0018] Specific examples of techniques for dynamically switching between demodulation schemes will be presented with reference to TD-SCDMA systems. However, those skilled in the art will appreciate that the techniques described herein may be used for various other types broadband wireless communication systems, including communication systems that are based on an orthogonal multiplexing scheme. Examples of such communication systems include Orthogonal Frequency Division Multiple Access (OFDMA) systems, Single-Carrier Frequency Division Multiple Access (SC-FDMA) systems, and so forth. An OFDMA system utilizes orthogonal frequency division multiplexing (OFDM), which is a modulation technique that partitions the overall system bandwidth into multiple orthogonal sub-carriers. These sub-carriers may also be called tones, bins, etc. With OFDM, each sub-carrier may be independently modulated with data. An SC-FDMA system may utilize interleaved FDMA (IFDMA) to transmit on sub-carriers that are distributed across the system bandwidth, localized FDMA (LFDMA) to transmit on a block of adjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks of adjacent sub-carriers. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDMA.

[0019] FIG. 1 illustrates an example of a wireless communication system 100 in which embodiments of the present disclosure may be employed. The wireless communication system 100 may be a broadband wireless communication system. The wireless communication system 100 may provide communication for a number of cells 102, each of which is serviced by a base station 104. A base station 104 may be a fixed station that communicates with user terminals 106. The base station 104 may alternatively be referred to as an access point, a Node B or some other terminology.

[0020] FIG. 1 depicts various user terminals 106 dispersed throughout the system 100. The user terminals 106 may be fixed (i.e., stationary) or mobile. The user terminals 106 may alternatively be referred to as remote stations, access terminals, terminals, subscriber units, mobile stations, stations, user equipment, etc. The user terminals 106 may be wireless devices, such as cellular phones, personal digital assistants (PDAs), handheld devices, wireless modems, laptop computers, personal computers, etc.

[0021] A variety of algorithms and methods may be used for transmissions in the wireless communication system 100 between the base stations 104 and the user terminals 106. For example, signals may be sent and received between the base stations 104 and the user terminals 106 in accordance with OFDM, CDMA, and/or TD-SCDMA techniques.

[0022] A communication link that facilitates transmission from a base station 104 to a user terminal 106 may be referred to as a downlink 108, and a communication link that facilitates transmission from a user terminal 106 to a base station 104 may be referred to as an uplink 110. Alternatively, a downlink 108 may be referred to as a forward link or a forward channel, and an uplink 110 may be referred to as a reverse link or a reverse channel.

[0023] A cell 102 may be divided into multiple sectors 112. A sector 112 is a physical coverage area within a cell 102. Base stations 104 within a wireless communication system 100 may utilize antennas that concentrate the flow of power within a particular sector 112 of the cell 102. Such antennas may be referred to as directional antennas.

[0024] FIG. 2 illustrates various components that may be utilized in a wireless device 202 that may be employed within the wireless communication system 100. The wireless device 202 is an example of a device that may be configured to implement the various methods described herein. The wireless device 202 may be a base station 104 or a user terminal 106.

[0025] The wireless device 202 may include a processor 204 which controls operation of the wireless device 202. The processor 204 may also be referred to as a central processing unit (CPU). Memory 206, which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor 204. A portion of the memory 206 may also include non-volatile random access memory (NVRAM). The processor 204 typically performs logical and arithmetic operations based on program instructions stored within the memory 206. The instructions in the memory 206 may be executable to implement the methods described herein.

[0026] The wireless device 202 may also include a housing 208 that may include a transmitter 210 and a receiver 212 to allow transmission and reception of data between the wireless device 202 and a remote location. The transmitter 210 and receiver 212 may be combined into a transceiver 214. An antenna 216 may be attached to the housing 208 and electrically coupled to the transceiver 214. The wireless device 202 may also include (not shown) multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas.

[0027] The wireless device 202 may also include a signal detector 218 that may be used in an effort to detect and quantify the level of signals received by the transceiver 214. The signal detector 218 may detect such signals as total energy, pilot energy per pseudonoise (PN) chips, power spectral density and other signals. The wireless device 202 may also include a digital signal processor (DSP) 220 for use in processing signals.

[0028] The various components of the wireless device 202 may be coupled together by a bus system 222, which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus. [0029] FIG. 3 is a schematic block diagram of an example Node B 310 in communication with an example UE 350 in a RAN 300, where the RAN 300 may be the RAN 102 in FIG. 1, the Node B 310 may be the Node B 108 in FIG. 1, and the UE 350 may be the UE 110 in FIG. 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 (FIG. 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 (FIG. 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.

[0030] 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 (FIG. 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 deinterleaved 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.

[0031] 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 (FIG. 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.

[0032] 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 (FIG. 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.

[0033] The controller/processors 340 and 390 may be used to direct the operation at the Node B 310 and the UE 350, respectively. For example, the controller/processors 340 and 390 may provide various functions including timing, peripheral interfaces, voltage regulation, power management, and other control functions. The computer readable media of memories 342 and 392 may store data and software for the Node B 310 and the UE 350, respectively. A scheduler/processor 346 at the Node B 310 may be used to allocate resources to the UEs and schedule downlink and/or uplink transmissions for the UEs.

[0034] FIG. 4 shows an example frame structure 400 for a TD-SCDMA carrier. The TD- SCDMA carrier, as illustrated, has a frame 402 that is 10 ms in length. The frame 402 has two 5 ms subframes 404, and each of the subframes 404 includes seven time slots, TS0 through TS6. The first time slot, TS0, 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 TS0 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 separated by a midamble 214 and followed by a guard period (GP) 216. The midamble 214 may be used for features, such as channel estimation, while the GP 216 may be used to avoid inter-burst interference.

[0035] Different users may be assigned different midambles derived by cyclic shifting of a base midamble. As will be described in greater detail below, in some cases, a demodulation scheme may be selected based on midamble detection, for example, based on a number and/or strength of detected midamble shifts.

COMPARISON OF DEMODULATION SCHEMES

[0036] Aspects of the present disclosure provide a method techniques for dynamically switching between demodulation schemes. Utilizing the techniques presented herein, a user equipment (UE) may be able to select an optimal decoding scheme for a time slot, based on particular operating conditions. For example, the techniques may be used to select a equalization (EQ) demodulation scheme for decoding downlink transmissions in time slots where a more complex demodulation scheme, such as a multi-cell joint detection (MCJD) scheme is conventionally used.

[0037] In certain wireless networks, such as TD-SCDMA commercial networks, different spreading factors may be used in different downlink time slots. For example, spreading factor 1 may be used in HSDPA time slots, while spreading factor 16 may be used in other time slots (e.g. slots 0 and 3). Such a deployment scheme may force a receiving device (e.g., a UE) to be capable of performing two different demodulation schemes, for example, an equalizer (EQ) demodulation scheme and multi-cell joint detection (MCJD). MCJD may also be referred to by other names, such as (Linear Multi-User Detection) (LMUD) or as linear Minimum Mean Square Equalized (MMSE) receivers.

[0038] EQ demodulation is commonly used for slots with spreading factor 1, since EQ is an optimal linear demodulation scheme. On the other hand, MCJD is commonly used in other time slots, for example, where the Walsh domain structure may be exploited to improve decoding performance. As will be described in detail below, however, in these time slots EQ may actually outperform MCJD under certain conditions.

[0039] MCJD typically requires relatively complex matrix inversions (e.g., of dimensions 16x16 or 32x32 for single and dual receive antennas, respectively). This requirement makes the computational complexity of MCJD significantly higher than that of EQ, which only requires Fast Fourier Transform and inverse Fast Fourier Transform (FFT/IFFT) operations and scalar or 2x2 matrix inversions for single and dual antennas.

[0040] Even though EQ requires significantly lower complexity than MCJD, under certain operating conditions, block error rate (BER) performance using EQ may be similar or oven better than MCJD. Unfortunately, even in cases where multiple demodulation schemes are supported, conventional receivers always use the same scheme for a given time slot- without adapting to changing operating scenarios.

[0041] Under ideal conditions, with perfect knowledge of channel conditions (so called "genie channel knowledge"), MCJD will always perform better than EQ from error rate perspective. However, with increasing number of active Walsh channels involved in MCJD, the performance difference between MCJD and EQ diminishes.

[0042] Because genie channel knowledge is unattainable in practice, there is a need to estimate channel coefficients based on pilots or midamble samples in the TD-SCDMA case. While channel estimation errors will inevitably degrade receiver performance in either demodulation scheme, MCJD and EQ have considerably different sensitivity to channel estimation errors. Simulations have shown that EQ is considerably more robust to such errors. Furthermore, channel estimation errors tend to increase with the number of active Walsh channels, because more channel coefficients need to be calculated with the same number of pilot samples.

[0043] For these reasons, EQ may be able to achieve better BER performance with significantly lower complexity than MCJD when the number of active Walsh channels from strong cells is large.

[0044] Comparisons have been performed of BER performance under genie and estimated channel conditions for different dual antenna schemes. In one example, with genie channel knowledge, MCJD performs better EQ. On the other hand, with estimated channels, EQ performs better than MCJD. Certain aspects of the present disclosure may provide benefit, from both a BER performance perspective and a complexity perspective (reduced complexity translates to power savings), by dynamic switching from MCJD to EQ when certain operating conditions warrant such a switch.

[0045] In another comparison of demodulation schemes for a dual receive antenna example with a more frequency selective multipath channel, the same conclusion may be drawn, that switching from MCJD to EQ may save complexity and improve BER performance at the same time. In still another example, switching from MCJD to EQ has been shown to also provide similar benefits in a single receive antenna case. [0046] Due to potential power savings, even in cases where EQ may only perform marginally better than MCJD or even where EQ does not perform quite as well as MCJD , it may still be beneficial to switch the EQ for these scenarios.

DEMODULATION ALGORITHM SWITCHING SCHEME

[0047] As noted above, in conventional implementations for TD-SCDMA downlink demodulations, the same algorithm is used for a given time slot. However, aspects of the present disclosure may allow a UE to select between EQ and MCJD, to pick an optimal demodulation scheme, based on given operating conditions. For example, for a slot with spreading factor 16, it might be beneficial to switch from MCJD to EQ if certain criteria are met.

[0048] In TD-SCDMA downlink, a default midamble scheme is typically used for spreading factor 16 slots. According to certain aspects, a switching scheme suitable for practical implementations may be based on a number of detected active midamble shifts, NACTIVE- If NACTIVE is greater than or equal to a threshold value, NTHRESHOLD, a UE may switch from MCJD to EQ.

[0049] Support for using such a scheme may lie in the fact that the number of channel coefficients is directly related to the number of active midamble shifts. That is, NACTIVE generally provides a simple indicator for channel estimation errors. When the number of active midamble shifts is large, the performance difference between EQ and LMUD is small.

[0050] Rather than rely solely on midamble shifts, some switching algorithms may also take active midamble strength, which also affects channel estimation performance, into consideration. Such an algorithm may, for example, only count midamble shifts above a certain strength against the threshold and/or may decide on which demodulation scheme to use based on an accumulated strength of active midamble shifts.

[0051] FIG. 5 illustrates example components of a user equipment (UE 520) that may perform operations in accordance with certain aspects of the present disclosure to select a demodulation scheme to use for time slots of downlink transmissions form a base station 510. [0052] As illustrated, BS 510 may have a schedule component 514 configured to schedule communications with the UE 520. As illustrated, the BS 510 may send, via a transmitter module 512, downlink transmissions to the UE 520.

[0053] As illustrated, the UE 520 may receive the downlink transmissions, via a receiver module 526. UE 520 may also include a transmitter module 522 configured to send uplink transmissions to BS 5 10 (received via a receiver module 516.

[0054] As illustrated, the UE 520 may also include a demodulation scheme selection module 524. The demodulation scheme selection module 524 may be configured to select a demodulation scheme to use, for a particular time slot of downlink transmission, based on one or more criteria. For example, the demodulation scheme selection module 524 may select between an EQ or MCJD demodulation scheme based on a number and/or strength of detected active midamble shifts.

[0055] FIG. 6 illustrates example operations 600 for dynamically switching between demodulation schemes. The operations may be performed, for example, by the demodulation scheme selection module 524 of UE 520 in FIG. 5.

[0056] The operations 600 begin, at 602, by detecting active midamble shifts. The active midamble shifts may be detected using any suitable detection algorithm-currently known or to be discovered. The detection may involve detecting a number and/or strength of active midamble shifts. At 604, the UE selects between at least two modulation schemes, based on the active midamble shift detection.

[0057] As illustrated in FIG. 9, in some cases, a number of active midamble shifts NACTIVE (detected at 902) may be compared against a threshold value NTHRESHOLD, at 904. If NACTIVE is greater than (exceeds) or equal to NTHRESHOLD, the performance difference between EQ and MCJD may be small and the UE may use EQ for demodulation, at 908. Otherwise, if NACTIVE is less than NTHRESHOLD, the UE may use MCJD, at 906.

[0058] As described above, the techniques presented herein for dynamically switching between demodulation schemes may help reduce power consumption, while providing adequate, or even improved performance. [0059] The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

[0060] The functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions on a computer-readable medium. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu- ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

[0061] Software or instructions may also be transmitted over a transmission medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of transmission medium.

[0062] Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein, such as those illustrated in the Figures, can be downloaded and/or otherwise obtained by a mobile device and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via a storage means (e.g., random access memory (RAM), read only memory (ROM), a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a mobile device and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

[0063] It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.

[0064] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.