Patent Application
20110292917
Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to a method for communication of feedback information in advanced wireless communication systems.
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-input single-output, multiple-input single-output or a multiple-input multiple-output (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
Certain aspects provide a method for scheduling channel information feedback in a wireless system. The method generally includes receiving, at a UE, a time adjustment command for advancing or retarding a start time of an uplink transmission, adjusting the start time of the uplink transmission based on the time adjustment command and a positive time bias, and sending an uplink transmission including a channel quality indicator (CQI) at the adjusted start time.
Certain aspects provide an apparatus for scheduling channel information feedback in a wireless system. The apparatus generally includes means for receiving, at a UE, a time adjustment command for advancing or retarding a start time of an uplink transmission, means for adjusting the start time of the uplink transmission based on the time adjustment command and a positive time bias, and means for sending an uplink transmission including a channel quality indicator (CQI) at the adjusted start time.
Certain aspects provide an apparatus for scheduling channel information feedback in a wireless system. The apparatus generally includes at least one processor and a memory coupled to the at least one processor, the at least one processor being configured to receive, at a UE, a time adjustment command for advancing or retarding a start time of an uplink transmission, adjust the start time of the uplink transmission based on the time adjustment command and a positive time bias, and send an uplink transmission including a channel quality indicator (CQI) at the adjusted start time.
Certain aspects provide a computer-program product for scheduling channel information feedback in a wireless system. The computer-program product generally includes a computer-readable medium comprising code for receiving, at a UE, a time adjustment command for advancing or retarding a start time of an uplink transmission, adjusting the start time of the uplink transmission based on the time adjustment command and a positive time bias, and sending an uplink transmission including a channel quality indicator (CQI) at the adjusted start time.
Certain aspects provide a method for scheduling channel information feedback in a wireless system. The method generally includes determining, based on timing of a received uplink transmission, whether or not a UE needs timing adjustment for a subsequent uplink transmission, transmitting a time adjustment command instructing a UE to adjust timing of the subsequent uplink transmissions based at least on a positive time bias, receiving the subsequent uplink transmission, and processing the received uplink transmissions to extract channel quality indicator (CQI).
Certain aspects provide an apparatus for scheduling channel information feedback in a wireless system. The apparatus generally includes means for determining, based on timing of a received uplink transmission, whether or not a UE needs timing adjustment for a subsequent uplink transmission, means for transmitting a time adjustment command instructing a UE to adjust timing of the subsequent uplink transmissions based at least on a positive time bias, means for receiving the subsequent uplink transmission, and means for processing the received uplink transmissions to extract channel quality indicator (CQI).
Certain aspects provide an apparatus for scheduling channel information feedback in a wireless system. The apparatus generally includes at least one processor and a memory coupled to the at least one processor, the at least one processor being configured to determine, based on timing of a received uplink transmission, whether or not a UE needs timing adjustment for a subsequent uplink transmission, transmit a time adjustment command instructing a UE to adjust timing of the subsequent uplink transmissions based at least on a positive time bias, receive the subsequent uplink transmission, and process the received uplink transmissions to extract channel quality indicator (CQI).
Certain aspects provide a computer-program product for scheduling channel information feedback in a wireless system. The computer-program product generally includes a computer-readable medium comprising code for determining, based on timing of a received uplink transmission, whether or not a UE needs timing adjustment for a subsequent uplink transmission, transmitting a time adjustment command instructing a UE to adjust timing of the subsequent uplink transmissions based at least on a positive time bias, receiving the subsequent uplink transmission, and processing the received uplink transmissions to extract channel quality indicator (CQI).
Certain aspects provide a method for scheduling channel information feedback in a wireless system. The method generally includes receiving, at an eNodeB, an uplink transmission comprising channel feedback information, applying a timing delay to the received uplink transmission such that the uplink transmission and an additional signal amount are buffered, and processing the uplink transmission to extract channel feedback information.
Certain aspects provide an apparatus for scheduling channel information feedback in a wireless system. The apparatus generally includes means for receiving, at an eNodeB, an uplink transmission comprising channel feedback information, means for applying a timing delay to the received uplink transmission such that the uplink transmission and an additional signal amount are buffered, and means for processing the uplink transmission to extract channel feedback information.
Certain aspects provide an apparatus for scheduling channel information feedback in a wireless system. The apparatus generally includes at least one processor and a memory coupled to the at least one processor, the at least one processor being configured to receive, at an eNodeB, an uplink transmission comprising channel feedback information, apply a timing delay to the received uplink transmission such that the uplink transmission and an additional signal amount are buffered, and process the uplink transmission to extract channel feedback information.
Certain aspects provide a computer-program product for scheduling channel information feedback in a wireless system. The computer-program product generally includes a computer-readable medium comprising code for receiving, at an eNodeB, an uplink transmission comprising channel feedback information, receiving, at an eNodeB, an uplink transmission comprising channel feedback information, and processing the uplink transmission to extract channel feedback information.
Certain aspects provide a method for transmitting channel information feedback in a wireless system. The method generally includes generating, at a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and transmitting the uplink transmission to an eNodeB.
Certain aspects provide an apparatus for transmitting channel information feedback in a wireless system. The apparatus generally includes means for generating, at a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and means for transmitting the uplink transmission to an eNodeB.
Certain aspects provide an apparatus for transmitting channel information feedback in a wireless system. The apparatus generally includes at least one processor and a memory coupled to the at least one processor, the at least one processor being configured to generate, at a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and transmit the uplink transmission to an eNodeB.
Certain aspects provide a computer-program product for transmitting channel information feedback in a wireless system. The computer-program product generally includes a computer-readable medium comprising code for generating, at a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and transmitting the uplink transmission to an eNodeB.
Certain aspects provide a method for processing channel information feedback in a wireless system. The method generally includes receiving, from a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and extracting the channel information feedback from the uplink transmission.
Certain aspects provide an apparatus for processing channel information feedback in a wireless system. The apparatus generally includes means for receiving, from a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and means for extracting the channel information feedback from the uplink transmission.
Certain aspects provide an apparatus for processing channel information feedback in a wireless system. The apparatus generally includes at least one processor and a memory coupled to the at least one processor, the at least one processor being configured to receive, from a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and extract the channel information feedback from the uplink transmission.
Certain aspects provide a computer-program product for processing channel information feedback in a wireless system. The computer-program product generally includes a computer-readable medium comprising code for receiving, from a UE, an uplink transmission comprising channel information feedback, wherein the channel information feedback is not positioned at a beginning of a localized frequency division multiplexing (LFDM) frame, and extracting the channel information feedback from the uplink transmission.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.
Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.
Although particular aspects are described herein, many variations and permutations of these aspects fall within the scope of the disclosure. Although some benefits and advantages of the preferred aspects are mentioned, the scope of the disclosure is not intended to be limited to particular benefits, uses, or objectives. Rather, aspects of the disclosure are intended to be broadly applicable to different wireless technologies, system configurations, networks, and transmission protocols, some of which are illustrated by way of example in the figures and in the following description of the preferred aspects. The detailed description and drawings are merely illustrative of the disclosure rather than limiting, the scope of the disclosure being defined by the appended claims and equivalents thereof.
The techniques described herein may be used for various wireless communication networks such as Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR). CDMA2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long Term Evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). CDMA2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2).
Single carrier frequency division multiple access (SC-FDMA) is a transmission technique that utilizes single carrier modulation at a transmitter side and frequency domain equalization at a receiver side. The SC-FDMA has similar performance and essentially the same overall complexity as those of OFDMA system. However, SC-FDMA signal has lower peak-to-average power ratio (PAPR) because of its inherent single carrier structure. The SC-FDMA has drawn great attention, especially in the uplink communications where lower PAPR greatly benefits the mobile terminal in terms of transmit power efficiency. It is currently a working assumption for uplink multiple access scheme in the 3GPP LTE and the Evolved UTRA.
An access point (“AP”) may comprise, be implemented as, or known as NodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller (“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver, Basic Service Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station (“RBS”), or some other terminology.
An access terminal (“AT”) may comprise, be implemented as, or known as an access terminal, a subscriber station, a subscriber unit, a mobile station, a remote station, a remote terminal, a user terminal, a user agent, a user device, user equipment, a user station, or some other terminology. In some implementations an access terminal may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol (“SIP”) phone, a wireless local loop (“WLL”) station, a personal digital assistant (“PDA”), a handheld device having wireless connection capability, a Station (“STA”), or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium. In some aspects the node is a wireless node. Such wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link.
Referring to
Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the access point. In one aspect of the present disclosure each antenna group may be designed to communicate to access terminals in a sector of the areas covered by access point 100.
In communication over forward links 120 and 126, the transmitting antennas of access point 100 may utilize beamforming in order to improve the signal-to-noise ratio of forward links for the different access terminals 116 and 124. Also, an access point using beamforming to transmit to access terminals scattered randomly through its coverage causes less interference to access terminals in neighboring cells than an access point transmitting through a single antenna to all its access terminals.
In one aspect of the present disclosure, each data stream may be transmitted over a respective transmit antenna. TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.
The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., binary phase shift keying (BPSK), Quadrature phase shift keying (QSPK), M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions stored in memory 232 and performed by processor 230.
The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). TX MIMO processor 220 then provides NT modulation symbol streams to NT transmitters (TMTR) 222a through 222t. In certain aspects of the present disclosure, TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.
Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. NT modulated signals from transmitters 222a through 222t are then transmitted from NT antennas 224a through 224t, respectively.
At receiver system 250, the transmitted modulated signals may be received by NR antennas 252a through 252r and the received signal from each antenna 252 may be provided to a respective receiver (RCVR) 254a through 254r. Each receiver 254 may condition (e.g., filters, amplifies, and downconverts) a respective received signal, digitize the conditioned signal to provide samples, and further process the samples to provide a corresponding “received” symbol stream.
An RX data processor 260 then receives and processes the NR received symbol streams from NR receivers 254 based on a particular receiver processing technique to provide NT “detected” symbol streams. The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor 260 may be complementary to that performed by TX MIMO processor 220 and TX data processor 214 at transmitter system 210.
A processor 270 periodically determines which pre-coding matrix to use. Processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion using instructions stored in memory 272. The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor 238, which also receives traffic data for a number of data streams from a data source 236, modulated by a modulator 280, conditioned by transmitters 254a through 254r, and transmitted back to transmitter system 210.
At transmitter system 210, the modulated signals from receiver system 250 are received by antennas 224, conditioned by receivers 222, demodulated by a demodulator 240, and processed by a RX data processor 242 to extract the reserve link message transmitted by the receiver system 250. Processor 230 then determines which pre-coding matrix to use for determining the beamforming weights, and then processes the extracted message.
In one aspect of the present disclosure, logical wireless communication channels may be classified into control channels and traffic channels. Logical control channels may comprise a Broadcast Control Channel (BCCH) which is a downlink (DL) channel for broadcasting system control information. A Paging Control Channel (PCCH) is a DL logical control channel that transfers paging information. A Multicast Control Channel (MCCH) is a point-to-multipoint DL logical control channel used for transmitting Multimedia Broadcast and Multicast Service (MBMS) scheduling and control information for one or several Multicast Traffic Channels (MTCHs). Generally, after establishing Radio Resource Control (RRC) connection, the MCCH may be only used by user terminals that receive MBMS. A Dedicated Control Channel (DCCH) is a point-to-point bi-directional logical control channel that transmits dedicated control information and it is used by user terminals having an RRC connection. Logical traffic channels may comprise a Dedicated Traffic Channel (DTCH) which is a point-to-point bi-directional channel dedicated to one user terminal for transferring user information. Furthermore, logical traffic channels may comprise a Multicast Traffic Channel (MTCH), which is a point-to-multipoint DL channel for transmitting traffic data.
Transport channels may be classified into DL and UL channels. DL transport channels may comprise a Broadcast Channel (BCH), a Downlink Shared Data Channel (DL-SDCH) and a Paging Channel (PCH). The PCH may be utilized for supporting power saving at the user terminal (i.e., Discontinuous Reception (DRX) cycle may be indicated to the user terminal by the network), broadcasted over entire cell and mapped to physical layer (PHY) resources which can be used for other control/traffic channels. The UL transport channels may comprise a Random Access Channel (RACH), a Request Channel (REQCH), an Uplink Shared Data Channel (UL-SDCH) and a plurality of PHY channels.
The PHY channels may comprise a set of DL channels and UL channels. The DL PHY channels may comprise: Common Pilot Channel (CPICH), Synchronization Channel (SCH), Common Control Channel (CCCH), Shared DL Control Channel (SDCCH), Multicast Control Channel (MCCH), Shared UL Assignment Channel (SUACH), Acknowledgement Channel (ACKCH), DL Physical Shared Data Channel (DL-PSDCH), UL Power Control Channel (UPCCH), Paging Indicator Channel (PICH), and Load Indicator Channel (LICH). The UL PHY Channels may comprise: Physical Random Access Channel (PRACH), Channel Quality Indicator Channel (CQICH), Acknowledgement Channel (ACKCH), Antenna Subset Indicator Channel (ASICH), Shared Request Channel (SREQCH), UL Physical Shared Data Channel (UL-PSDCH), and Broadband Pilot Channel (BPICH).
LTE utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, the spacing of the subcarriers may be 15 kHz and the minimum resource allocation (called a ‘resource block’) may be 12 subcarriers (or 180 kHz). Consequently, the nominal fast Fourier transform (FFT) size may be equal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into subbands. For example, a subband may cover 1.08 MHz (e.g., 6 resource blocks), and there may be 1, 2, 4, 8 or 16 subbands for system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.
In LTE, an eNodeB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNodeB. The primary and secondary synchronization signals may be sent in symbol periods 6 and 5, respectively, in each of subframes 0 and 5 of each radio frame with the normal cyclic prefix, as shown in
The eNodeB may send a Physical Control Format Indicator Channel (PCFICH) in only a portion of the first symbol period of each subframe, although depicted in the entire first symbol period in
The eNodeB may send the PSS, SSS and PBCH in the center 1.08 MHz of the system bandwidth used by the eNodeB. The eNodeB may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The eNodeB may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The eNodeB may send the PDSCH to specific UEs in specific portions of the system bandwidth. The eNodeB may send the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs.
A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH.
A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNodeB may send the PDCCH to the UE in any of the combinations that the UE will search.
A UE may be within the coverage of multiple eNodeBs. One of these eNodeBs may be selected to serve the UE. The serving eNodeB may be selected based on various criteria such as received power, path loss, signal-to-noise ratio (SNR), etc.
In the LTE standard, during generation of an uplink signal, a “guard period” may be created at the beginning of each symbol in order to reduce the impact of inter-symbol interference (ISI). The guard period may be created by adding a Cyclic Prefix (CP) at the beginning of a symbol. The CP may be generated by a transmitter by duplicating some last samples of output and appending them to the beginning of the symbol. As an example, the CP may be approximately 5 μs. At a receiver, the reverse operations may be performed to demodulate the signal. A number of samples corresponding to the length of the CP may be removed prior to processing the received signal.
In some scenarios, there may be a time mismatch between a UE and an eNodeB. For example, the UE may have a timing advance or timing delay compared to the eNodeB. The timing advance may cause performance degradation if critical information such as channel state indicator (CQI) modulation symbols are omitted from a subframe.
Certain aspects of the present disclosure propose methods for protecting CQI information in a subframe such as a localized frequency division multiplexing (LFDM) subframe. For some aspects, a timing adjustment method may be utilized to adjust time of a UE with respect to an eNodeB. The timing adjustment method may introduce a positive time offset to be used for reducing time mismatch between the UE and the eNodeB. In another aspect, a buffer may be used at the eNodeB to store symbols received by the eNodeB before CP removal. The eNodeB may use the stored symbols and an artificial time delay to ensure that the CQI information is protected. For some aspects, the CQI modulation symbols may not be located at the beginning of an LFDM symbol.
In the eight release of the LTE standard (LTE Rel-8), the uplink channels, such as Physical Uplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH), and Sounding Reference Signals (SRS)) may tolerate some timing offset (e.g., timing delay or timing advance). Performance of these uplink channels may degrade gradually as long as the timing offset is less than the size of the CP. The performance may degrade drastically if the timing offset is larger than the size of CP, which may result in omission of critical information such as CQI. For certain aspects, time alignment of uplink transmissions by UEs in a cell may be achieved by applying a timing advance at each UE transmitter or the eNodeB, relative to downlink timing. The timing advance may compensate for differing propagation delays between different UEs in the cell.
In some scenarios, if there is a timing advance between UE and eNodeB (e.g., UE is ahead of the eNodeB or has a negative timing offset), CQI modulation symbols may be discarded during the CP removal process at the eNodeB, which may result in sever performance degradation.
In one specific example, in a PUSCH transmission where the PUSCH is assigned 40 Resource Blocks (RB) with a Modulation Coding Scheme (MSC) equal to 20, utilizing 4 bits of wideband CQI with I_offset equal to 15, there may be nine CQI modulation symbols in 16-level Quadrature Amplitude Modulation (QAM). These CQI modulation symbols may all be located at the first chips of nine out of the twelve LDFM data symbols. Assuming that a chip duration may be equal to 0.139 μs, only a 0.139 μμs timing advance may result in discard of all the CQI modulation symbols from the subframe. This may cause CQI erasure and performance degradation, especially in Additive White Gaussian Noise (AWGN) channel where there is no delay.
According to certain aspects, a timing adjustment offset may be employed at a UE to protect CQI. Instead of controlling UE time centered around eNodeB system time, a positive time bias may be used to modify UE timing to ensure that the UE may only retard in a range of system time of the eNodeB and not advance. Most of the uplink channels may be able to tolerate small amounts of positive timing offset, but timing advance may result in performance degradation. For certain aspects, the value of the positive timing bias may be chosen such that the performance degradation for uplink channels is not large. It should be noted that the timing adjustment command may not be effective immediately for the subsequent subframes due to the nature of a timing control loop and implementation delay.
The processing module 514 may also be configured to determine resources to be used to transmit timing adjustment commands and other channel configuration parameters to the UE. As illustrated, this information may be provided to a transmitter module 512, to be transmitted to the UE 520.
The UE 520 may receive the configuration information and timing adjustment commands, via a receiver module 526, and provide the information to a message processing module 524. The message processing module may utilize the received information, for example, to adjust timing of uplink transmissions and to determine the resources that are used for the transmissions. The UE may also extract PUSCH parameters for transmission of uplink subframes to the eNodeB. The UE 520 may send the subframes (via a transmitter module 522) on the assigned PUSCH utilizing the adjusted timing.
At 704, the eNodeB may transmit a time adjustment command instructing a UE to adjust timing of the subsequent uplink transmission based at least on a positive time bias. In one aspect, the positive time bias is selected such that the adjusted start time of the uplink transmissions preserves CQI during a cyclic prefix removal process.
In one aspect, after the eNodeB determines a timing offset, the eNodeB may itself apply the positive time bias to the timing offset. In an alternative aspect, before the eNodeB transmits the time adjustment command, the eNodeB may apply the positive time bias to the command. In one aspect, after the eNodeB detects a timing offset, if the timing offset is a negative timing offset, the eNodeB may transmit a timing adjustment command to request a UE to delay until the UE is aligned with or slightly behind the system timing. If the detected timing offset is a positive timing offset, the eNodeB may perform conventional timing control.
At 706, the eNodeB may receive the subsequent uplink transmission. In one aspect, the uplink transmission may be PUSCH having CQI symbols, wherein the CQI is arranged in the beginning of the transmission. At 708, the eNodeB may process the received uplink transmission to extract CQI. In one aspect, the eNodeB may process PUSCH such that CQI is not removed during CP removal process.
For certain aspects of the present disclosure, a buffer may be employed by an eNodeB for storing CQI on PUSCH. Instead of blindly discarding CP from PUSCH, an eNodeB may use a large buffer to temporarily store symbols that are removed during CP removal process. If a UE is advanced in time, the stored symbols may be used to recover CQI information. In one aspect, an artificial timing delay may be inserted in subframes with CQI on PUSCH before CP removal procedure is performed. Value of the artificial timing delay may be chosen such that if the UE and the eNodeB are aligned, the performance degradation of the system because of the artificial delay is not large (e.g., less than a tolerable threshold).
At 804, the eNodeB may apply a timing delay to the received uplink transmission such that the uplink transmission and an additional signal amount are buffered. For certain aspects, the timing delay may be applied to subframes with CQI on PUSCH. The timing delay may be selected such that the channel feedback information is preserved during a cyclic prefix removal process.
In one aspect, the timing delay may be applied when the most recently detected and/or filtered timing offset is a timing advance or a very small timing delay, or based on some other criteria. At 806, the eNodeB may process the uplink transmission to extract channel feedback information and data.
It should be noted that applying the positive time offset to the signals received from a UE, may result in reduction in performance of other users, if signals from multiple users are received in the same subframe. However, performance degradation of other users may be minimized by utilizing more than one demodulation and decoding processes. According to certain aspects, at least two separate demodulation and decoding processes may be used in the eNodeB. In one aspect, a first set of demodulation and decoding circuitry may be used for processing signals received from users with CQI on PUSCH with an inserted artificial timing delay. A second set of demodulation and decoding circuitry may be used for processing signals received from all other users (e.g., other than the users with CQI on PUSCH).
In another variation of the above scheme, a first set of demodulation and decoding circuitry may be used for processing the signals received from all users, while a second set of demodulation and decoding circuitry with an inserted artificial timing delay may be used for processing signals received from users with CQI on PUSCH. Demodulated and decoded results may be selected from the two sets of circuitry according to a detected timing offset in the current subframe, or based on cyclic redundancy check (CRC) for data, or erasure decoding for CQI, or some other suitable criteria.
In one aspect, a first set of demodulation and decoding circuitry may be used for processing a data part of uplink transmission for all users, while a second set of demodulation and decoding circuitry may be used for processing the CQI part for other users with an inserted artificial timing delay.
For certain aspects of the present disclosure, channel feedback information may be transmitted on symbols other than the first symbol of a subframe in an uplink transmission. In one aspect, CQI modulation symbols may be placed at the end of the LFDM symbols. In another aspect, CQI modulation symbols may be placed at any position other than the beginning of the LFDM symbols. In one aspect, the position of CQI within the frame may be spread over time, as is done with acknowledgement/negative acknowledgment symbols, and with rank indicator symbols.
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While several approaches have been discussed above, it is acknowledged that one or a combination of the above approaches may be used to mitigate the impact of timing mismatch (e.g., timing advance) between a UE and an eNodeB on system performance and to protect CQI information.
As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.
As used herein, 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-b, a-c, b-c, and a-b-c.
The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrate circuit (ASIC), or processor. Generally, where there are operations illustrated in Figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.
The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the present disclosure may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in any form of storage medium that is known in the art. Some examples of storage media that may be used include random access memory (RAM), read only memory (ROM), flash memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM and so forth. A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs, and across multiple storage media. A storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor.
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.
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, include 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.
Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging material.
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.
Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal 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 storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal 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.
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.
While the foregoing is directed to aspects of the present disclosure, other and further aspects of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
The present Application for Patent claims priority to U.S. Provisional Application No. 61/349,115, entitled, “Timing Adjustment to Protect CQI on PUSCH in LTE System,” filed May 27, 2010, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61349115 | May 2010 | US |
