WO2015051486A1

WO2015051486A1 - Rach msg3 timeline design in eimta

Info

Publication number: WO2015051486A1
Application number: PCT/CN2013/084816
Authority: WO
Inventors: Peng Cheng; Chao Wei; Xipeng Zhu; Neng Wang; Masato Kitazoe; Jilei Hou
Original assignee: Qualcomm Incorporated
Priority date: 2013-10-07
Filing date: 2013-10-07
Publication date: 2015-04-16

Abstract

Aspects of the present disclosure relate to techniques for wireless communications and more specifically for performing a random access channel (RACH) procedure. According to certain aspects a method for retransmitting a RACH MSG3 message is provided. The method generally includes participating in a random access channel (RACH) procedure with a user equipment (UE), dynamically changing an uplink/downlink subframe configuration from a first uplink/downlink subframe configuration to a second uplink/downlink subframe configuration, during the RACH procedure, detecting a failure to successfully decode a MSG3 message from the UE, and taking action to prevent the UE from re-transmitting the MSG3 message in a subframe that is designated as a downlink subframe after dynamically changing the subframe configuration.

Description

RACH MSG3 TIMELINE DESIGN IN EIMTA

TECHNICAL FIELD

[0001] Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to techniques for random access in wireless networks.

BACKGROUND

[0002] 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, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.

[0003] 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-in-single-out, multiple-in-signal-out or a multiple-in- multiple-out (MIMO) system.

[0004] Some systems may utilize a relay base station that relays messages between a donor base station and wireless terminals. The relay base station may communicate with the donor base station via a backhaul link and with the terminals via an access link. In other words, the relay base station may receive downlink messages from the donor base station over the backhaul link and relay these messages to the terminals over the access link. Similarly, the relay base station may receive uplink messages from the terminals over the access link and relay these messages to the donor base station over the backhaul link. SUMMARY

[0005] Certain aspects of the present disclosure provide a method for wireless communications by a base station. The method generally includes participating in a random access channel (RACH) procedure with a user equipment (UE), dynamically changing an uplink/downlink subframe configuration from a first uplink/downlink sub frame configuration to a second uplink/downlink subframe configuration, during the RACH procedure, detecting a failure to successfully decode a MSG3 from the UE, and taking action to prevent the UE from re-transmitting the MSG3 message in a subframe that is designated as a downlink subframe after dynamically changing the subframe configuration..

[0006] Certain aspects of the present disclosure provide a method for wireless communications by a base station. The method generally includes participating in a random access channel (RACH) procedure with a user equipment (UE), detecting a failure to successfully decode a MSG3 message from the UE, determining a limited number of one or more fixed uplink subframes in which the UE is allowed to retransmit the MSG3 message, and receiving the retransmitted MSG3 from the UE in one of the fixed uplink subframes.

[0007] Certain aspects of the present disclosure provide a method for wireless communications by a user equipment. The method generally includes participating in a random access channel (RACH) procedure with a base station (BS), transmitting a MSG3 to the BS, receiving an indication that the BS failed to successfully decode the MSG3 message, determining a limited number of one or more fixed uplink subframes in which the UE is allowed to retransmit the MSG3 message, and retransmitting the MSG3 in one of the fixed uplink subframes.

[0008] Certain aspects of the present disclosure also provide various apparatus and program products for performing operations of the methods described above.

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 and wherein: [0010] FIG. 1 illustrates a multiple access wireless communication system, according to aspects of the present disclosure.

[0011] FIG. 2 is a block diagram of a communication system, according to aspects of the present disclosure.

[0012] FIG. 3 illustrates an example frame structure, according to aspects of the present disclosure.

[0013] FIG. 4 illustrates an example subframe resource element mapping, according to aspects of the present disclosure.

[0014] FIG. 5 illustrates an example set of subframe configurations and example special subframe formats, with which aspects of the present disclosure may be practiced.

[0015] FIG. 6 illustrates an example use of a reference subframe configuration.

[0016] FIG. 7 illustrates an example of downlink association sets for an example set of subframe configurations, with which aspects of the present disclosure may be practiced.

[0017] FIG. 8 illustrates an example call flow for a contention based random access [initialization] procedure.

[0018] FIG. 9 illustrates an example timing for a random access response window.

[0019] FIG. 10 illustrates an example timeline of a contention based random access procedure showing retransmission of a MSG3 by a user equipment (UE) causing interference with downlink transmissions of an eNodeB (eNB).

[0020] FIG. 11 illustrates example operations that may be performed by a base station, in accordance with aspects of the present disclosure.

[0021] FIG. 12 illustrates an example timeline of a random access procedure with transmission of a negative acknowledgment (NACK) and no retransmission of a MSG3 in response to a failed decoding of a MSG3 according to an aspect of the present disclosure.

[0022] FIG. 13 illustrates an example timeline of a random access procedure with an eNB switching to a primarily-u link subframe configuration in response to a failed decoding of a MSG3 according to an aspect of the present disclosure.

[0023] FIG. 14 illustrates example operations that may be performed by a base station, in accordance with aspects of the present disclosure.

[0024] FIG. 15 illustrates example operations that may be performed by a user equipment, in accordance with aspects of the present disclosure.

[0025] FIG. 16 illustrates an example timeline of a random access procedure with retransmission of a MSG3 performed in fixed subframes according to an aspect of the present disclosure.

DESCRIPTION

[0026] 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.

[0027] 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 an upcoming 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). These various radio technologies and standards are known in the art. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below.

[0028] Single carrier frequency division multiple access (SC-FDMA), which utilizes single carrier modulation and frequency domain equalization is a technique. SC-FDMA has similar performance and essentially the same overall complexity as those of OFDMA system. SC-FDMA signal has lower peak-to-average power ratio (PAPR) because of its inherent single carrier structure. 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 3 GPP Long Term Evolution (LTE), or Evolved UTRA.

[0029] Referring to FIG. 1, a multiple access wireless communication system according to one embodiment is illustrated. An access point 100 (AP) includes multiple antenna groups, one including 104 and 106, another including 108 and 110, and an additional including 112 and 114. In FIG. 1, only two antennas are shown for each antenna group, however, more or fewer antennas may be utilized for each antenna group. Access terminal 116 (AT) is in communication with antennas 112 and 114, where antennas 112 and 114 transmit information to access terminal 116 over forward link 120 and receive information from access terminal 116 over reverse link 118. AT 122 is in communication with antennas 106 and 108, where antennas 106 and 108 transmit information to access terminal 122 over forward link 126 and receive information from access terminal 122 over reverse link 124. In a FDD system, communication links 118, 120, 124 and 126 may use different frequencies for communication. For example, forward link 120 may use a different frequency than that used by reverse link 118.

[0030] 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 the embodiment, antenna groups are each designed to communicate to access terminals in a sector, of the areas covered by access point 100.

[0031] In communication over forward links 120 and 126, the transmitting antennas of access point 100 utilize beamforming in order to improve the signal-to-noise ratio of forward links for the different access terminals 116 and 124. Also, an AP 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.

[0032] An AP may be a fixed station used for communicating with the terminals and may also be referred to as an access point, a Node B, base station, evolved Node B (eNB) or some other terminology. An AT may also be called an access terminal, user equipment (UE), a wireless communication device, terminal, mobile station or some other terminology.

[0033] FIG. 2 is a block diagram of an embodiment of a transmitter system 210 (also known as an AP) and a receiver system 250 (also known as an AT) in a MIMO system 200. At the transmitter system 210, traffic data for a number of data streams is provided from a data source 212 to a transmit (TX) data processor 214.

[0034] In an aspect, each data stream is 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.

[0035] 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 250 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., BPSK, 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, from memory 232, performed by processor 230.

[0036] 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 Ντ modulation symbol streams to Ντ transmitters (TMTR) 222a through 222t. In certain embodiments, 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.

[0037] 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. Ντ modulated signals from transmitters 222a through 222t are then transmitted from Ντ antennas 224a through 224t, respectively.

[0038] At receiver system 250, the transmitted modulated signals are received by N_R antennas 252a through 252r, and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254a through 254r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding "received" symbol stream.

[0039] An RX data processor 260 then receives and processes the N_R received symbol streams from N_R receivers 254 based on a particular receiver processing technique to provide Ντ "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 is complementary to that performed by TX MIMO processor 220 and TX data processor 214 at transmitter system 210.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] According to aspects, the controllers/processors 230 and 270 may direct the operation at the transmitter system 210 and the receiver system 250, respectively. According to an aspect, the controller/processor 230, TX data processor 214, and/or other processors and modules at the transmitter system 210 may perform or direct operations 1100 in FIG. 11, operations 1400 in FIG. 14, and/or other processes for the techniques described herein. According to another aspect, the controller/processor 270, RX processor 260, and/or other processors and modules at the receiver system 260 may perform or direct operations 1500 in FIG. 15 and/or other processes for the techniques described herein. However, any other processor or component in FIG. 2 may perform or direct operations 1100 in FIG. 11, operations 1400 in FIG. 14, operations 1500 in FIG. 15, and/or other processes for the techniques described herein. The memories 232 and 272 may store data and program codes for the transmitter system 210 and the receiver system 260, respectively.

[0044] In an aspect, logical channels are classified into Control Channels and Traffic Channels. Logical Control Channels comprise Broadcast Control Channel (BCCH), which is a DL channel for broadcasting system control information. Paging Control Channel (PCCH) is a DL channel that transfers paging information. Multicast Control Channel (MCCH) is a point-to-multipoint DL channel used for transmitting Multimedia Broadcast and Multicast Service (MBMS) scheduling and control information for one or several MTCHs. Generally, after establishing an RRC connection, this channel is only used by UEs that receive MBMS (Note: old MCCH+MSCH). Dedicated Control Channel (DCCH) is a point-to-point bi-directional channel that transmits dedicated control information used by UEs having an RRC connection. In an aspect, Logical Traffic Channels comprise a Dedicated Traffic Channel (DTCH), which is a point-to-point bi-directional channel, dedicated to one UE, for the transfer of user information. Also, a Multicast Traffic Channel (MTCH) is a point-to-multipoint DL channel for transmitting traffic data.

[0045] In an aspect, Transport Channels are classified into DL and UL. DL Transport Channels comprise a Broadcast Channel (BCH), Downlink Shared Data Channel (DL-SDCH), and a Paging Channel (PCH), the PCH for support of UE power saving (DRX cycle is indicated by the network to the UE), broadcasted over entire cell and mapped to PHY resources which can be used for other control/traffic channels. The UL Transport Channels 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 comprise a set of DL channels and UL channels.

[0046] The DL PHY channels 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)

Load Indicator Channel (LICH)

[0047] The UL PHY Channels 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)

Broadband Pilot Channel (BPICH)

[0048] In an aspect, a channel structure is provided that preserves low PAR (at any given time, the channel is contiguous or uniformly spaced in frequency) properties of a single carrier waveform.

[0049] For the purposes of the present document, the following abbreviations apply:

AM Acknowledged Mode

AMD Acknowledged Mode Data

ARQ Automatic Repeat Request

BCCH Broadcast Control CHannel

BCH Broadcast CHannel

C- Control-

CCCH Common Control CHannel

CCH Control CHannel

CCTrCH Coded Composite Transport Channel

CP Cyclic Prefix

CRC Cyclic Redundancy Check

CTCH Common Traffic CHannel

DCCH Dedicated Control CHannel

DCH Dedicated CHannel

DL DownLink

DL-SCH DownLink Shared CHannel

DM-RS DeModulation-Reference Signal

DSCH Downlink Shared CHannel

DTCH Dedicated Traffic CHannel

FACH Forward link Access CHannel

FDD Frequency Division Duplex

LI Layer 1 (physical layer)

L2 Layer 2 (data link layer)

L3 Layer 3 (network layer)

LI Length Indicator

LSB Least Significant Bit

MAC Medium Access Control

MBMS Multimedia Broadcast Multicast Service

MCCH MBMS point-to-multipoint Control CHannel

MRW Move Receiving Window MSB Most Significant Bit

MSCH MBMS point-to-multipoint Scheduling CHannel

MTCH MBMS point-to-multipoint Traffic CHannel

PCCH Paging Control CHannel

PCH Paging CHannel

PDU Protocol Data Unit

PHY PHYsical layer

PhyCH Physical CHannels

RACH Random Access CHannel

RB Resource Block

RLC Radio Link Control

RRC Radio Resource Control

SAP Service Access Point

SDU Service Data Unit

SHCCH SHared channel Control CHannel

SN Sequence Number

SUFI SUper Field

TCH Traffic CHannel

TDD Time Division Duplex

TFI Transport Format Indicator

TM Transparent Mode

TMD Transparent Mode Data

TTI Transmission Time Interval

U- User-

UE User Equipment

UL UpLink

UM Unacknowledged Mode

UMD Unacknowledged Mode Data

UMTS Universal Mobile Telecommunications System

UTRA UMTS Terrestrial Radio Access

UTRAN UMTS Terrestrial Radio Access Network

MBSFN Multimedia Broadcast Single Frequency Network

MCE MBMS Coordinating Entity

MCH Multicast CHannel MSCH MBMS Control CHannel

PDCCH Physical Downlink Control CHannel

PDSCH Physical Downlink Shared CHannel

PRB Physical Resource Block

VRB Virtual Resource Block

In addition, Rel-8 refers to Release 8 of the LTE standard.

[0050] FIG. 3 shows an exemplary frame structure 300 for FDD in LTE. The transmission timeline for each of the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, e.g., seven symbol periods for a normal cyclic prefix (as shown in FIG. 3) or six symbol periods for an extended cyclic prefix. The 2L symbol periods in each subframe may be assigned indices of 0 through 2L-1.

[0051] In LTE, an eNB may transmit a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) on the downlink in the center 1.08 MHz of the system bandwidth for each cell supported by the eNB. The PSS and SSS may be transmitted in symbol periods 6 and 5, respectively, in subframes 0 and 5 of each radio frame with the normal cyclic prefix, as shown in FIG. 3. The PSS and SSS may be used by UEs for cell search and acquisition. The eNB may transmit a cell-specific reference signal (CRS) across the system bandwidth for each cell supported by the eNB. The CRS may be transmitted in certain symbol periods of each subframe and may be used by the UEs to perform channel estimation, channel quality measurement, and/or other functions. The eNB may also transmit a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of certain radio frames. The PBCH may carry some system information. The eNB may transmit other system information such as System Information Blocks (SIBs) on a Physical Downlink Shared Channel (PDSCH) in certain subframes. The eNB may transmit control information/data on a Physical Downlink Control Channel (PDCCH) in the first B symbol periods of a subframe, where B may be configurable for each subframe. The eNB may transmit traffic data and/or other data on the PDSCH in the remaining symbol periods of each subframe. [0052] FIG. 4 shows two exemplary subframe formats 410 and 420 for the downlink with the normal cyclic prefix. The available time frequency resources for the downlink may be partitioned into resource blocks. Each resource block may cover 12 subcarriers in one slot and may include a number of resource elements. 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.

[0053] Subframe format 410 may be used for an eNB equipped with two antennas. A CRS may be transmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11. A reference signal is a signal that is known a priori by a transmitter and a receiver and may also be referred to as pilot. A CRS is a reference signal that is specific for a cell, e.g., generated based on a cell identity (ID). In FIG. 4, for a given resource element with label Ra, a modulation symbol may be transmitted on that resource element from antenna a, and no modulation symbols may be transmitted on that resource element from other antennas. Subframe format 420 may be used for an eNB equipped with four antennas. A CRS may be transmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11 and from antennas 2 and 3 in symbol periods 1 and 8. For both subframe formats 410 and 420, a CRS may be transmitted on evenly spaced subcarriers, which may be determined based on cell ID. Different eNBs may transmit their CRSs on the same or different subcarriers, depending on their cell IDs. For both subframe formats 410 and 420, resource elements not used for the CRS may be used to transmit data (e.g., traffic data, control data, and/or other data).

[0054] The PSS, SSS, CRS and PBCH in LTE are described in 3 GPP TS 36.211, entitled "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation," which is publicly available.

[0055] An interlace structure may be used for each of the downlink and uplink for FDD in LTE. For example, Q interlaces with indices of 0 through Q - 1 may be defined, where Q may be equal to 4, 6, 8, 10, or some other value. Each interlace may include subframes that are spaced apart by Q frames. In particular, interlace q may include subframes q, q + Q , q + 2Q , etc., where q e { 0, Q - 1 } .

[0056] The wireless network may support hybrid automatic retransmission (HARQ) for data transmission on the downlink and uplink. For HARQ, a transmitter (e.g., an eNB) may send one or more transmissions of a packet until the packet is decoded correctly by a receiver (e.g., a UE) or some other termination condition is encountered. For synchronous HARQ, all transmissions of the packet may be sent in subframes of a single interlace. For asynchronous HARQ, each transmission of the packet may be sent in any subframe.

[0057] A UE may be located within the coverage area of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received signal strength, received signal quality, pathloss, etc. Received signal quality may be quantified by a signal-to-noise-and-interference ratio (SINR), or a reference signal received quality (RSRQ), or some other metric. The UE may operate in a dominant interference scenario in which the UE may observe high interference from one or more interfering eNBs.

[0058] FIG. 5 illustrates an example list of the downlink/uplink configurations in a LTE TDD frame 402 according to the LTE standard. In this table D, U, and S indicate Downlink, Uplink and Special subframes 406, respectively. The special subframe S may consist of DwPTS 410, GP 412, and UpPTS 414 fields. As illustrated, several DL/UL configurations for 5 ms switch point periodicity and 10 ms switch point periodicity may be chosen for a LTE TDD frame 402. The configurations 0, 1, and 2 have two identical 5 ms half- frames 404 within a 10 ms LTE TDD frame 402. In the case of 5 ms switch point periodicity, a special frame may exist in both half-frames 404. However, in the case of 10 ms switch point periodicity, a special subframe may exist in the first half-frame only. Subframes 0 and 5 and DwPTS may be reserved for DL transmission. In addition, UpPTS and the subframe immediately following a special subframe may be reserved for UL transmission.

[0059] FIG. 6 shows a frame structure 600 for a Time Division Duplex Long Term Evolution (LTE TDD) carrier. The LTE TDD carrier, as illustrated, has a frame 602 that is 10 ms in length. The frame 602 has two 5 ms half frames 604, and each of the half frames 604 includes five 1 ms subframes 606. Each subframe 606 may be a downlink subframe (D), an uplink subframe (U), or a special subframe (SSF). Downlink subframes and uplink subframes may be divided into two 0.5 ms slots 608.

[0060] Special subframes may be divided into a downlink pilot timeslot (DwPTS) 610, a guard period (GP) 612, and an uplink pilot time slot (UpPTS) 614, where the length of each field may vary, with the total length of 1 ms. Up to Rel-10, LTE TDD specifies at least nine SSF configurations, which may be found in 3GPP TS36.211, section 4.2, table 4.2-1. Traditionally, UpPTS may have only one or two symbols in all existing configurations, which may be used for short random access channel (RACH) transmissions and sounding reference signal (SRS) transmissions.

EXAMPLE EIMTA

[0061] Aspects of the present disclosure may be utilized in enhanced interference management and traffic adaptation (elMTA) systems, in which uplink-downlink (UL- DL) subframe configurations may be dynamically switched (e.g., based on changing UL/DL loads).

[0062] In LTE, both frequency division duplex (FDD) and time division duplex (TDD) frame structures are supported. For TDD, 7 possible DL and UL subframe configurations are supported in LTE, as illustrated in table 700 of FIG. 7. As illustrated, there are 2 switching periodicities, 5ms and 10ms. For subframe configurations with 5ms switching periodicity, there are two special subframes in one (10ms) frame, as shown in diagram 750 of FIG. 7. For subframe configurations with 10ms switching periodicity, there is one special subframe in each frame.

[0063] As noted above, utilizing elMTA (such as provided in LTE Rel-12), it is possible to dynamically adapt TDD DL/UL subframe configurations based on the actual traffic needs. For example, if during a short duration, a large data burst on downlink is needed, the subframe configuration can be changed to one with more DL subframes, for example, from config #1 (6 DL : 4 UL) to config #5 (9 DL : 1 UL).

[0064] The adaptation of TDD configuration is expected to be no slower than 640ms. In the extreme case, the adaptation may be as fast as 10ms, although this may not be desirable. In any case, the adaptation may cause overwhelming interference to both downlink and uplink when two or more cells have different downlink and uplink subframes.

[0065] The adaptation may also cause some complexity in DL and UL HARQ timing management. Conventionally, each of the seven DL/UL subframe configurations has its own DL/UL HRQ timing that is optimized for each configuration (in terms of HARQ operation efficiency). For example, the timing from PDSCH to the corresponding ACK/NAK may be different for different TDD DL/UL subframe configurations (e.g., depending on when a next available UL subframe occurs).

[0066] Dynamic switching among the 7 configurations (or even more, if more flexible adaptation is deemed as necessary) implies that if current DL/UL HARQ timing is kept, there may be missed ACK/NAK transmission opportunities for some of the DL or UL transmissions.

EXAMPLE RACH MSG3 RETRANSMISSION TIMELINE DESIGN IN EIMTA

[0067] Aspects of the present disclosure provide techniques for configuring eNodeBs (eNBs) and user equipment (UEs) for performing random access procedures in elMTA without interfering with communications to other UEs.

[0068] In the LTE standard, enhanced interference management and traffic adaptation may be implemented to provide for adaptation of resource allocation according to cell traffic loading. In an LTE TDD system seven different subframe configurations are specified, and each configuration may have a differing number of uplink, downlink, and special subframes. A system may switch between different uplink and downlink configurations according to an adaptation rate, which may correspond to LI, RRC, or broadcast signaling.

[0069] FIG. 8 illustrates an example call flow diagram of a contention based random access procedure. A user equipment (UE) may choose a random access preamble and transmit the preamble in a random access resource. A random access resource may occupy 6 resource blocks, and a network may have multiple random access resources configured in a subframe. An eNodeB (eNB) may receive the preamble transmitted by the UE. In some cases, an eNB may allocate certain preambles for communications with legacy UEs and other preambles for non-legacy UEs (e.g., UEs that support elMTA). An eNB may respond to the UE's preamble transmission by sending a random access response (RAR) to the UE, which may be addressed with a random access radio network temporary identifier (RA-RNTI). The RAR may be transmitted to the UE on the physical downlink shared channel (PDSCH) and may be accompanied by an associated downlink allocation message G sent on the physical downlink control channel (PDCCH) with a cyclic redundancy code (CRC) scrambled by the RA-R TI and mapped to a common search space.

[0070] After a UE receives an RAR, the UE may transmit a MSG3 on the physical uplink shared channel (PUSCH). The MSG3 may convey Layer 2 and Layer 3 messages, such as a radio resource control connection request, from the UE to an eNB. After transmitting the MSG3 on PUSCH, the UE may start a contention resolution timer. The contention resolution timer may be stopped if a contention resolution message is received before the timer terminates. If the contention resolution timer expires, the UE may restart the random access procedure.

[0071] In response to receiving a MSG3 message, an eNB may transmit a contention resolution message. The UE's identity (e.g., the TC-RNTI) may be included in the contention resolution message. Each UE receiving the contention resolution message may compare the included TC-RNTI to the RNTI the UE transmitted in the MSG3 message. If the UE determines that the TC-RNTI was intended for the UE, the random access procedure may be declared successful, and the eNB and UE may commence data transmissions.

[0072] An example RAR window is illustrated in FIG. 9. An eNB may be required to transmit an RAR within a time window. The length and start and end points of the window may be configured by the eNB. If the UE does not receive an RAR within a configured time window, the UE may retransmit the random access preamble.

[0073] FIG. 10 illustrates an example situation of interference to an eNB transmitting to other UEs caused by a UE, which is performing a random access procedure, attempting to retransmit a MSG3 during a scheduled downlink subframe. In a random access procedure, UEs may use the TDD configuration specified in system information block 1 (SIB-1). An eNB with elMTA capability may use other TDD configurations, which may result in HARQ timeline misalignment for MSG3 retransmission. For example, as illustrated in FIG. 10, an eNB may use TDD configuration 2 in a first frame during which a UE performs an initial transmission of the MSG3 message. The eNB fails to decode the MSG3 message properly and may transmit a negative acknowledgment (NACK) in a special subframe. For the second and third frames in FIG. 10, the eNB may switch to a different TDD configuration (e.g., TDD configuration 4, as illustrated). Switching to a different TDD configuration may entail reconfiguring a subframe configuration from an uplink to a downlink subframe. However, the UE may continue to transmit assuming the use of the original TDD configuration (e.g., TDD configuration 2, as illustrated), which may cause interference with an eNB's transmissions to other UEs.

[0074] In an aspect, supporting random access procedures for eNBs and UEs may entail taking action to prevent the UE from retransmitting the MSG3 in a subframe designated as a downlink subframe after the eNB dynamically changes the subframe configuration.

[0075] FIG. 1100 illustrates example operations 1100 for wireless communications that may be performed by a base station (BS), for example, an eNB, in accordance with aspects of the present disclosure. Operations 1100 begin, at 1102, by a BS participating in a random access channel (RACH) procedure with a user equipment (UE). At 1104, the BS may dynamically change an uplink/downlink subframe configuration from a first uplink/downlink subframe configuration to a second uplink/downlink subframe configuration during the RACH procedure. The BS may detect a failure to successfully decode a MSG3 message from the UE at 1106. At 1108, the BS may take action to prevent the UE from re-transmitting the MSG3 message in a subframe that is designated as a downlink subframe after dynamically changing the subframe configuration.

[0076] In an aspect, preventing the UE from retransmitting the MSG3 in a subframe designated as a downlink subframe after dynamically changing the subframe configuration may entail causing reinitiating the random access procedure when the eNB fails to successfully decode the MSG3 message. FIG. 12 illustrates an example timeline of receiving an initial MSG3 message and reinitiating the random access procedure. In FIG. 12, an example change in subframe configurations may be observed between frame 1, which uses TDD configuration 2, and frame 2, which uses TDD configuration 4; however, it may be appreciated that a change in subframe configurations may happen at any time and to any subframe configuration. In the first frame, which is illustrated as using TDD configuration 2 but may be configured to use any TDD configuration, a UE may transmit a MSG3 message in an uplink subframe (for example, subframe 7 in TDD configuration 2). The eNB may fail to decode the MSG3 successfully. To avoid causing interference, an eNB may transmit an ACK in, for example, a special subframe, despite failing to decode MSG3 successfully. The eNB may further fail to transmit a contention resolution message, which may cause the contention resolution timer or radio resource control (R C) request timer of the requesting UE to expire. Once the timer expires, the UE may begin another random access procedure. Acknowledging a MSG3 that the BS failed to decode successfully without transmitting a contention resolution timer may waste spectral resources, as the contention resolution timer or RRC request timer may be longer than a HARQ round- trip time.

[0077] Preventing the UE from retransmitting the MSG3 message in a subframe designated as a downlink subframe after dynamically changing the subframe configuration may entail using a different TDD configuration for retransmission of the MSG3 message. FIG. 13 illustrates an example timeline of receiving an initial MSG3 message and changing subframe configurations to prevent interference from a retransmitted MSG3 message. After an eNB receives an initial MSG3 and fails to decode the message, the eNB may transmit a NACK to the UE. The eNB may also dynamically switch to a different TDD configuration; for example, an eNB may switch to a TDD configuration indicated in a previous broadcast of a system information block (SIB) for retransmissions. In an aspect, the TDD configuration an eNB uses after a failure to decode an initial MSG3 message may comprise an equal number of uplink and downlink subframes (e.g., TDD configuration 1) or predominantly uplink subframes (e.g., TDD configuration 0, as illustrated). The eNB may receive a retransmitted MSG3 message, and once the eNB successfully decodes the message, the eNB may transmit an ACK and a contention resolution message to the UE. Switching to a TDD configuration specified in SIB-1 may limit elMTA traffic adaptation gains.

[0078] In an aspect, supporting random access procedures for eNBs and UEs may entail transmitting a MSG3 message on the same subframe.

[0079] FIG. 14 illustrates example operations 1400 for wireless communications that may be performed by a base station (BS), for example, an eNB, in accordance with aspects of the present disclosure. Operations 1400 begin, at 1402, by a BS participating in a random access channel (RACH) procedure with a user equipment (UE). At 1404, the BS may detect a failure to successfully decode a MSG3 message from the UE. At 1406, the BS may determine a limited number of one or more fixed uplink subframes in which the UE may be allowed to retransmit the MSG3 message. At 1408, the BS may receive the retransmitted MSG3 from the UE in one of the fixed uplink subframes.

[0080] FIG. 15 illustrates example operations 1500 for wireless communications that may be performed by a user equipment (UE) in accordance with aspects of the present disclosure. Operations 1500 may begin, at 1502, by a UE participating in a random access channel (RACH) procedure with a base station (BS). At 1504, the UE may transmit a MSG3 to the BS. The UE may receive an indication that the BS failed to successfully decode the MSG3 message at 1506. At 1508, the UE may determine a limited number of one or more fixed uplink subframes in which the UE is allowed to retransmit the MSG3 message. At 1510, the UE may retransmit the MSG3 in one of the fixed uplink subframes determined at 1508.

[0081] FIG. 16 illustrates an example timeline of receiving an initial MSG3 message and retransmitting the MSG3 message on a fixed uplink subframe. In the first subframe, a MSG3 message may be transmitted to an eNB in an uplink subframe (for example, subframe 2, as illustrated). In failing to decode the MSG3 message, the eNB may transmit a NACK to the UE. On receipt of the NACK, the UE may retransmit the MSG3 message the next time a designated subframe becomes available. For example, in an aspect, the one or more fixed uplink subframes on which a UE may transmit or retransmit the MSG3 message may be predetermined. In an aspect, the BS may transmit signaling to a UE indicating the one or more fixed uplink subframes on which the UE may retransmit a MSG3 message. The signaling may be provided, for example, on a system information block (SIB). In an aspect, the BS may dynamically change an uplink/downlink subframe configuration to an uplink/downlink subframe configuration having the one or more fixed uplink subframes determined at 1406.

[0082] Transmitting and re-transmitting MSG3 messages on fixed uplink subframe may be supported by elMTA UEs but not by legacy (non-elMTA) UEs. In an aspect, an eNB may activate use of fixed subframe retransmission by detecting that a UE supports elMTA. For example, an eNB may use preamble grouping where certain preambles may be assigned to legacy UEs and other preambles may be assigned to non-legacy UEs (e.g., UEs that support elMTA). During the random access process, when UEs transmit a preamble, an eNB may detect that the transmitted preamble belongs to the group of elMTA preambles and may use a fixed uplink subframe to receive failed MSG3 messages. The fixed uplink subframe for retransmission of MSG3 messages may be predetermined or semi-static according to a configuration enumerated in, for example, a system information block (SIB).

[0083] The various operations of methods described above may be performed by any suitable combination of hardware and/or software component(s) and/or module(s).

[0084] It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. 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.

[0085] Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0086] Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0087] The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein 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 (FPGA) or other programmable logic device, 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 conventional 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.

[0088] The steps of a method or algorithm described in connection with the embodiments disclosed herein 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 RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such 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 processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. As used herein, including in the claims, "or" as used in a list of items prefaced by "at least one of indicates a disjunctive list such that, for example, a list of "at least one of A, B, or C" means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

[0089] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for wireless communications by a base station, comprising:

participating in a random access channel (RACH) procedure with a user equipment (UE);

dynamically changing an uplink/downlink subframe configuration from a first uplink downlink subframe configuration to a second uplink/downlink subframe configuration, during the RACH procedure;

detecting a failure to successfully decode a MSG3 message from the UE; and taking action to prevent the UE from re-transmitting the MSG3 message in a subframe that is designated as a downlink subframe after dynamically changing the subframe configuration.

2. The method of claim 1, wherein taking action comprises sending an

acknowledgement for the MSG3 message to the UE despite detecting the failure to successfully decode the MSG3 message.

3. The method of claim 2, further comprising refraining from sending a contention resolution message after sending the acknowledgement.

4. The method of claim 1, wherein taking action comprises:

dynamically changing the uplink/downlink subframe configuration from the second uplink/downlink subframe configuration to a third uplink/downlink subframe configuration after detecting the failure, wherein the third uplink/downlink subframe configuration has a subframe designated as an uplink subframe in which the UE is expected to re-transmit the MSG3 message.

5. The method of claim 4, wherein the third uplink/downlink subframe configuration comprise an uplink/downlink subframe configuration previously broadcast in a system information block (SIB).

6. A method for wireless communications by a base station, comprising:

participating in a random access channel (RACH) procedure with a user equipment (UE); detecting a failure to successfully decode a MSG3 message from the UE;

determining a limited number of one or more fixed uplink subframes in which the UE is allowed to retransmit the MSG3 message; and

receiving the retransmitted MSG3 from the UE in one of the fixed uplink subframes.

7. The method of claim 6, wherein the one or more fixed uplink subframes are predetermined.

8. The method of claim 6, further comprising providing signaling, to the UE, indicating the one or more fixed uplink subframes.

9. The method of claim 8, wherein the signaling is provided via a system information block (SIB).

10. The method of claim 6, further comprising dynamically changing an uplink/downlink subframe configuration to an uplink/downlink subframe configuration that has the one or more fixed uplink subframes.

11. The method of claim 10, further comprising identifying the UE is allowed to retransmit the MSG3 message on the limited number of one or more fixed uplink subframes based on a RACH preamble received from the UE.

12. The method of claim 11, wherein:

a first group of RACH preambles are allocated for use by UEs that support dynamic changing of uplink/downlink subframe configurations; and

a second group of RACH preambles are allocated for use by UEs that do not support dynamic changing of uplink/downlink subframe configurations.

13. A method for wireless communications by a user equipment (UE), comprising: participating in a random access channel (RACH) procedure with a base station

(BS);

transmitting a MSG3 message to the BS;

receiving an indication that the BS failed to successfully decode the MSG3 message;

retransmitting the MSG3 message in one of the fixed uplink subframes.

14. The method of claim 13, wherein the one or more fixed uplink subframes are predetermined.

15. The method of claim 13, further comprising receiving signaling, from the BS, indicating the one or more fixed uplink subframes.

16. The method of claim 15, wherein the signaling is provided via a system information block (SIB).

17. The method of claim 13, further comprising transmitting a RACH preamble that identifies the UE as a UE allowed to retransmit the MSG3 message on the limited number of one or more fixed uplink subframes.

18. The method of claim 17, wherein: