Source: http://patents.com/us-10178667.html
Timestamp: 2019-01-16 20:56:07
Document Index: 479428060

Matched Legal Cases: ['Application No. 62', 'Application No. 62', 'Application No. 62', 'Application No. 62', 'Application No. 62', 'Application No. 62']

US Patent # 1,017,8667. Method and device for configuring transmission opportunity period in wireless access system supporting unlicensed band - Patents.com
United States Patent 10,178,667
The present disclosure relates to a wireless access system supporting an unlicensed band, and provides a method for configuring a transmission opportunity period (TxOP) and devices for supporting the same. The method for configuring a TxOP in a wireless access system supporting an unlicensed band, according to one embodiment of the present disclosure, can comprise the steps of: performing a carrier sensing step for checking whether a secondary cell (SCell) constituted in an unlicensed band is in an idle state; transmitting a reservation signal for a predetermined amount of time if the SCell is in the idle state; and configuring a TxOP in the SCell. At this time, a start point of a first subframe (SF) included in the TxOP can be matched to a subframe, a slot or symbol boundary of a primary cell (PCell) constituted in a licensed band.
Kim; Seonwook (Seoul, KR), Yang; Suckchel (Seoul, KR), Kim; Kijun (Seoul, KR), Ahn; Joonkui (Seoul, KR), Seo; Hanbyul (Seoul, KR), Lee; Seungmin (Seoul, KR)
Family ID: 1000003752462
15/328,837
PCT/KR2015/008052
WO2016/018125
US 20170230970 A1 Aug 10, 2017
62031817 Jul 31, 2014
62081562 Nov 18, 2014
62105754 Jan 21, 2015
62132511 Mar 13, 2015
62142448 Apr 2, 2015
62166122 May 25, 2015
Current CPC Class: H04W 72/0446 (20130101); H04W 74/0808 (20130101); H04W 16/14 (20130101)
Current International Class: H04W 4/00 (20180101); H04W 72/04 (20090101); H04W 74/08 (20090101); H04W 16/14 (20090101)
2013/0208634 August 2013 Ji
2013/0242821 September 2013 Wei
2014/0003387 January 2014 Lee et al.
2014/0071931 March 2014 Lee et al.
2014/0328260 November 2014 Papasakellariou
2015/0358827 December 2015 Bendlin
2010109364 Sep 2011 RU
2011108466 Sep 2012 RU
2013006006 Jan 2013 WO
2013006988 Jan 2013 WO
Huawei, Ericsson, Qualcomm, HiSilicon: "Motivation of the New Si Proposal: Study on Licensed-Assisted Access using LTE", 3GPP TSG RAN Meeting #64, RP-140786, Jun. 9-12, 2014. cited by applicant .
R1-121712: 3GPP TSG RAN WG1 #68bis Jeju, Korea, Mar. 26-30, 2012, CMCC, "Discussion on additional special subframe configuration," pp. 1-6. cited by applicant.
This application is a National Stage Application of International Application No. PCT/KR2015/008052, filed on Jul. 31, 2015, which claims the benefit of U.S. Provisional Application No. 62/031,817, filed on Jul. 31, 2014, U.S. Provisional Application No. 62/081,562, filed on Nov. 18, 2014, U.S. Provisional Application No. 62/105,754, filed on Jan. 21, 2015, U.S. Provisional Application No. 62/132,511, filed on Mar. 13, 2015, U.S. Provisional Application No. 62/142,448, filed on Apr. 2, 2015 and U.S. Provisional Application No. 62/166,122, filed on May 25, 2015, all of which are hereby incorporated by reference in their entirety for all purposes as if fully set forth herein.
1. A method for performing a downlink transmission in a wireless access system supporting an unlicensed band, the method comprising: performing a carrier sensing procedure for checking whether a secondary cell (Scell) configured in the unlicensed band is idle or not; and performing the downlink transmission during a downlink transmission duration after the Scell has been checked as idle, wherein the downlink transmission duration is configured with one or more consecutive subframes (SFs), wherein a last SF of the downlink transmission duration is a small SF which is smaller than a full SF, and wherein the small SF is configured according to one of DwPTS (Downlink Pilot Time Slot) configurations.
2. The method according to claim 1, wherein the full SF includes two slots and one of the two slots includes seven symbols.
3. The method according to claim 2, wherein a first SF of the downlink transmission duration starts from predetermined symbol boundary within a subframe, and a size of the first SF is equal to or smaller than the full SF.
4. The method according to claim 2, wherein a location of a subframe and a symbol within the downlink transmission duration is configured to match with a boundary of a subframe and a symbol of a primary cell (Pcell) of a licensed band.
5. The method according to claim 2, wherein the DwPTS configuration is defined as Table 1, TABLE-US-00007 TABLE 1 Normal cyclic prefix in downlink Special UpPTS subframe Normal cyclic prefix Extended cyclic prefix configuration DwPTS in uplink in uplink 0 6592 T.sub.s 2192 T.sub.s 2560 T.sub.s 1 19760 T.sub.s 2 21952 T.sub.s 3 24144 T.sub.s 4 26336 T.sub.s 5 6592 T.sub.s 4384 T.sub.s 5120 T.sub.s. 6 19760 T.sub.s 7 21952 T.sub.s 8 24144 T.sub.s 9 13168 T.sub.s
6. An enhanced Node B (eNB) for performing a downlink transmission in a wireless access system supporting an unlicensed band, the eNB comprising: a receiver; a transmitter; and a processor supporting the downlink transmission, wherein the processor is configured to: perform, by controlling the receiver, a carrier sensing procedure for checking whether a secondary cell (Scell) configured in the unlicensed band is idle or not; and perform, by controlling the transmitter, the downlink transmission during a downlink transmission duration after the Scell has been checked as idle, wherein the downlink transmission duration is configured with one or more consecutive subframes (SFs), wherein a last SF of the downlink transmission duration is a small SF which is smaller than a full SF, and wherein the small SF is configured according to one of DwPTS (Downlink Pilot Time Slot) configurations.
7. The eNB according to claim 6, wherein the full SF includes two slots and one of the two slots includes seven symbols.
8. The eNB according to claim 7, wherein a first SF of the downlink transmission duration starts from predetermined symbol boundary within a subframe, and a size of the first SF is equal to or smaller than the full SF.
9. The eNB according to claim 7, wherein a location of a subframe and a symbol within the downlink transmission duration is configured to match with a boundary of a subframe and a symbol of a primary cell (Pcell) of a licensed band.
10. The eNB according to claim 7, wherein the DwPTS configuration is defined as Table 1, TABLE-US-00008 TABLE 1 Normal cyclic prefix in downlink Special UpPTS subframe Normal cyclic prefix Extended cyclic prefix configuration DwPTS in uplink in uplink 0 6592 T.sub.s 2192 T.sub.s 2560 T.sub.s 1 19760 T.sub.s 2 21952 T.sub.s 3 24144 T.sub.s 4 26336 T.sub.s 5 6592 T.sub.s 4384 T.sub.s 5120 T.sub.s. 6 19760 T.sub.s 7 21952 T.sub.s 8 24144 T.sub.s 9 13168 T.sub.s
The present disclosure relates generally to a wireless access system supporting an unlicensed band, and more particularly, to a method for configuring a Transmission Opportunity Period (TxOP) and an apparatus supporting the same.
An object of the present disclosure is to provide a method for efficiently transmitting and receiving data in a wireless access system supporting an unlicensed band.
Another object of the present disclosure is to provide various methods for configuring a Transmission Opportunity Period (TxOP) and apparatuses supporting the same in a wireless access system supporting an unlicensed band.
Another object of the present disclosure is to provide, if a TxOP includes a subframe having a different size from the size of a subframe of a primacy cell (PCell), a method for determining the subframe having a different size, and methods for determining a Transport Block Size (TBS) and configuring a Reference Signal (RS) for the subframe having a different size.
Another object of the present disclosure is to provide, if TxOPs are consecutively configured, methods for configuring a timing gap and/or transmitting a reservation signal without wasting subframes.
The present disclosure relates to a wireless access system supporting an unlicensed band. More particularly, the present disclosure provides a method for configuring a Transmission Opportunity Period (TxOP), and apparatuses supporting the same.
In an aspect of the present disclosure, provided herein is a method for configuring a TxOP in a wireless access system supporting an unlicensed band, including performing a carrier sensing (CS) procedure to determine whether a secondary cell (SCell) configured in the unlicensed band is idle, if the SCell is idle, transmitting a reservation signal during a predetermined time, and configuring a TxOP in the SCell. A starting time of a first subframe (SF) of the TxOP is aligned with an SF boundary, slot boundary, or symbol boundary of a primary cell (PCell) configured in a licensed band.
In another aspect of the present disclosure, an apparatus for configuring a TxOP in a wireless access system supporting an unlicensed band includes a transmitter, a receiver, and a processor configured to support a TxOP configuration. The processor is configured to perform a CS procedure to determine whether an SCell configured in the unlicensed band is idle by controlling the transmitter and the receiver, to transmit, if the SCell is idle, a reservation signal during a predetermined time by controlling the transmitter, and to configure a TxOP in the SCell. A starting time of a first SF of the TxOP is aligned with an SF boundary, slot boundary, or symbol boundary of a PCell configured in a licensed band.
In the aspects of the present disclosure, if it is said that an SCell is idle, this means that the SCell is not occupied by CS. In other words, the SCell is finally idle, upon completion of a CS procedure including a backoff operation or an LBT operation.
If the starting time of the first SF is aligned with a slot boundary of the PCell, the reservation signal may be transmitted until before the starting time of the first SF after the CS procedure.
If the starting time of the first SF is aligned with a slot boundary or symbol boundary of the PCell, the first SF is configured as a partial SF (pSF) having a smaller length than an SF of the PCell.
If one SF is divided into T points and the first SF starts at a k.sup.th point among the T points, the number N.sub.PRB of physical resource blocks (PRBs) in the first SF may be calculated by the following equation.
.times.'.times. ##EQU00001##
Herein, N'.sub.PRB represents a total number of allocated PRBs, and k and T are positive integers.
A demodulation reference signal (DM-RS) transmitted in the first SF may be allocated only to a second slot in which the first SF is configured.
If the starting time of the first SF is aligned with a symbol boundary of the PCell, it may be determined whether the first SF is configured independently, or concatenated to a next SF into an over SF (oSF), based on a threshold set as a number of OFDM symbols.
If the first SF is configured to be an oSF, one SF is divided into T points, and the first SF starts at a k.sup.th point among the T points, the number N.sub.PRB of PRBs in the first SF may be calculated by the following equation.
.times.'.times. ##EQU00002##
.function..function.'.times. ##EQU00003##
Herein, N'.sub.PRB represents a total number of allocated PRBs, I.sub.TBS represents an index indicating a transport block size (TBS) for the first SF, and k and T are positive integers.
If the first SF is configured to be an oSF, a DM-RS transmitted in the first SF may be allocated only within the concatenated next SF.
If two or more TxOPs are configured consecutively, a first SF of each of the TxOPs may be configured to have a fixed length smaller than a length of one SF. Herein, a specific timing gap may be configured before a second TxOP starts after the end of the first TxOP among the consecutive TxOPs.
First, data can be efficiently transmitted and received in a wireless access system supporting an unlicensed band.
Secondly, various methods for configuring a Transmission Opportunity Period (TxOP) and apparatuses supporting the same in a wireless access system supporting an unlicensed band can be provided.
Thirdly, if a TxOP includes a subframe having a different size from the size of a subframe of a primacy cell (PCell), a method for determining the subframe having a different size, and methods for determining a Transport Block Size (TBS) and configuring a Reference Signal (RS) for the subframe having a different size can be provided.
Fourthly, if TxOPs are consecutively configured, a timing gap and/or a reservation signal may be configured and transmitted without wasting subframes.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the technical features or scope of the disclosures. Thus, it is intended that the present disclosure covers the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.
FIG. 9 is a conceptual view of a Coordinated Multi-Point (CoMP) system operating in a CA environment;
FIG. 10 is a view illustrating an exemplary subframe to which UE-specific Reference Signals (UE-RSs) are allocated, which may be used in embodiments of the present disclosure;
FIG. 11 is a view illustrating exemplary multiplexing of legacy Physical Downlink Control Channel (PDCCH), Physical Downlink Shared Channel (PDSCH), and Evolved-PDCCH (E-PDCCH) in an LTE/LTE-A system;
FIG. 12 is a view illustrating an exemplary CA environment supported in an LTE-Unlicensed (LTE-U) system;
FIG. 13 is a view illustrating an exemplary Frame Based Equipment (FBE) operation as one of Listen-Before-Talk (LBT) operations;
FIG. 14 is a block diagram illustrating the FBE operation;
FIG. 15 is a view illustrating an exemplary Load Based Equipment (LBE) operation as one of the LBT operations;
FIGS. 16 and 17 are views illustrating a method for transmitting a reservation signal;
FIG. 18 is a view illustrating an embodiment of setting a maximum value for a reservation signal transmission period;
FIG. 19 is a view illustrating a method for adjusting the starting time of a SubFrame (SF) in a Secondary Cell (SCell) according to an operation of a Primary Cell (PCell);
FIG. 20 is a view illustrating a method for aligning an SF boundary of an SCell with a slot boundary of a PCell;
FIG. 21 is a view illustrating configurations of Reference Signals (RSs) transmitted in an SCell;
FIG. 22 is a view illustrating a method for determining an SF length based on a threshold;
FIG. 23 is a view illustrating a method for fixing the length of the first SF of a Transmission Opportunity Period (TxOP);
FIG. 24 is a view illustrating a method for allocating Demodulation Reference Signals (DM-RSs), if the last SF of a TxOP is configured variably;
FIG. 25 is a view illustrating a case of fixing the length of the first SF of a TxOP;
FIG. 26 is a view illustrating one of methods for configuring the first and last SFs of a TxOP based on a threshold;
FIG. 27 is a view illustrating another of the methods for transmitting a reservation signal based on a threshold;
FIG. 28 is a view illustrating a method for transmitting a reservation signal;
FIG. 29 is a view illustrating a TxOP configuration, if the first SF of a TxOP is aligned with a slot boundary;
FIG. 30 is a view illustrating one of methods for configuring consecutive TxOPs;
FIG. 31 is a flowchart illustrating one of methods for transmitting and receiving data according to a TxOP configuration; and
FIG. 32 is a block diagram of apparatuses for implementing the methods illustrated in FIGS. 1 to 31.
FIG. 2(b) illustrates frame structure type 2. Frame structure type 2 is applied to a Time Division Duplex (TDD) system. One radio frame is 10 ms (Tf=307200Ts) long, including two half-frames each having a length of 5 ms (=153600Ts) long. Each half-frame includes five subframes each being 1 ms (=30720Ts) long. An ith subframe includes 2ith and (2i+1)th slots each having a length of 0.5 ms (Tslot=15360Ts). Ts is a sampling time given as Ts=1/(15 kHzx2048)=3.2552.times.10-8 (about 33 ns).
TABLE-US-00001 TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix in downlink UpPTS UpPTS Normal Extended Normal Extended Special cyclic cyclic cyclic cyclic subframe prefix prefix prefix prefix configuration DwPTS in uplink in uplink DwPTS in uplink in uplink 0 6592 T.sub.s 2192 T.sub.s 2560 T.sub.s 7680 T.sub.s 2192 T.sub.s 2560 T.sub.s 1 19760 T.sub.s 20480 T.sub.s 2 21952 T.sub.s 23040 T.sub.s 3 24144 T.sub.s 25600 T.sub.s 4 26336 T.sub.s 7680 T.sub.s 4384 T.sub.s 5120 T.sub.s 5 6592 T.sub.s 4384 T.sub.s 5120 T.sub.s 20480 T.sub.s 6 19760 T.sub.s 23040 T.sub.s 7 21952 T.sub.s -- -- -- 8 24144 T.sub.s -- -- --
A plurality of PDCCHs for a plurality of UEs may be multiplexed and transmitted in the control region. A PDCCH is made up of an aggregate of one or more consecutive CCEs. A CCE is a unit of 9 REGs each REG including 4 REs. Four Quadrature Phase Shift Keying (QPSK) symbols are mapped to each REG. REs occupied by RSs are excluded from REGs. That is, the total number of REGs in an OFDM symbol may be changed depending on the presence or absence of a cell-specific RS. The concept of an REG to which four REs are mapped is also applicable to other DL control channels (e.g. the PCFICH or the PHICH). Let the number of REGs that are not allocated to the PCFICH or the PHICH be denoted by NREG. Then the number of CCEs available to the system is NCCE(=.left brkt-bot.N.sub.REG/9.right brkt-bot.) and the CCEs are indexed from 0 to NCCE-1.
TABLE-US-00002 TABLE 2 PDCCH Number of Number of Number of format CCE (n) REG PDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576
TABLE-US-00003 TABLE 3 DCI Format Description Format 0 Resource grants for PUSCH transmissions (uplink) Format 1 Resource assignments for single codeword PDSCH transmission (transmission modes 1, 2 and 7) Format 1A Compact signaling of resource assignments for single codeword PDSCH (all modes) Format 1B Compact resource assignments for PDSCH using rank-1 closed loop precoding (mode 6) Format 1C Very compact resource assignments for PDSCH (e.g., paging/broadcast system information) Format 1D Compact resource assignments for PDSCH using multi-user MIMO(mode 5) Format 2 Resource assignments for PDSCH for closed loop MIMO operation (mode 4) Format 2A resource assignments for PDSCH for open loop MIMO operation (mode 3) Format 3/3A Power control commands for PUCCH and PUSCH with 2-bit/1-bit power adjustment Format 4 Scheduling of PUSCH in one UL cell with multi-antenna port transmission mode
A plurality of PDCCHs may be transmitted in a subframe. That is, the control region of a subframe includes a plurality of CCEs, CCE 0 to CCE N.sub.CCE,k-1. N.sub.CCE,k is the total number of CCEs in the control region of a kth subframe. A UE monitors a plurality of PDCCHs in every subframe. This means that the UE attempts to decode each PDCCH according to a monitored PDCCH format.
While all UEs may know the size of a CSS, a USS may be configured for each individual UE. Accordingly, a UE should monitor both a CSS and a USS to decode a PDCCH.
As a consequence, the UE performs up to 44 blind decodings in one subframe, except for blind decodings based on different CRC values (e.g., C-RNTI, P-RNTI, SI-RNTI, and RA-RNTI).
An SS S.sub.k.sup.(L) is a PDCCH candidate set with a CCE aggregation level L.di-elect cons.{1,2,4,8}. The CCEs of PDCCH candidate set m in the SS may be determined by the following equation. L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k/L.right brkt-bot.}+i [Equation 1]
Herein, M.sup.(L) is the number of PDCCH candidates with CCE aggregation level L to be monitored in the SS, m=0, . . . , M.sup.(L)-1, i is the index of a CCE in each PDCCH candidate, and i=0, . . . , L-1k=.left brkt-bot.n.sub.s/2.right brkt-bot. where n.sub.s is the index of a slot in a radio frame.
Herein, Y.sub.-1=n.sub.RNTI.noteq.0, n.sub.RNTI indicating an RNTI value. A=39827 and D=65537.
In the LTE-A system, CoMP transmission may be implemented using a carrier aggregation (CA) function in the LTE. FIG. 9 is a conceptual view illustrating a CoMP system operating based on a CA environment.
FIG. 10 illustrates an example of a subframe to which UE-RSs are allocated, which may be used in embodiments of the present disclosure.
Referring to FIG. 10, the subframe illustrates REs occupied by UE-RSs among REs in one RB of a normal DL subframe having a normal CP.
UE-RSs are transmitted on antenna port(s) p=5, p=7, p=8 or p=7, 8, . . . , .upsilon.+6 for PDSCH transmission, where .upsilon. is the number of layers used for the PDSCH transmission. UE-RSs are present and are a valid reference for PDSCH demodulation only if the PDSCH transmission is associated with the corresponding antenna port. UE-RSs are transmitted only on RBs to which the corresponding PDSCH is mapped.
In the 3GPP LTE-A system, the UE-RSs are defined in a PRB pair. Referring to FIG. 9, in a PRB having frequency-domain index nPRB assigned for PDSCH transmission with respect to p=7, p=8, or p=7, 8, . . . , .upsilon.+6, a part of UE-RS sequence r(m) is mapped to complex-valued modulation symbols.
Meanwhile, in the LTE/LTE-A system, since a PDCCH which is a physical channel for DL/UL scheduling and transmitting various kinds of control information has a limitation that it is transmitted through limited OFDM symbols, enhanced PDCCH (i.e., E-PDCCH) multiplexed with a PDSCH more freely in a way of FDM/TDM may be introduced instead of a control channel such as PDCCH, which is transmitted through OFDM symbol and separated from PDSCH. FIG. 11 illustrates an example that legacy PDCCH, PDSCH and E-PDCCH, which are used in an LTE/LTE-A system, are multiplexed.
FIG. 12 illustrates an example of a CA environment supported in an LTE-U system.
In FIG. 12, one eNB supports both a licensed band and an unlicensed band. That is, the UE may transmit and receive control information and data through the PCC which is a licensed band, and may also transmit and receive control information and data through the SCC which is an unlicensed band. However, the status shown in FIG. 12 is only example, and the embodiments of the present disclosure may be applied to even a CA environment that one UE accesses a plurality of eNBs.
FIG. 13 is a view illustrating an exemplary Frame Based Equipment (FBE) operation as one of LBT operations.
The European Telecommunication Standards Institute (ETSI) regulation (EN 301 893 V1.7.1) defines two LBT operations, Frame Based Equipment (FBE) and Load Based Equipment (LBE). In FBE, one fixed frame is comprised of a channel occupancy time (e.g., 1 to 10 ms) being a time period during which a communication node succeeding in channel access may continue transmission, and an idle period being at least 5% of the channel occupancy time, and CCA is defined as an operation for monitoring a channel during a CCA slot (at least 20 .mu.s) at the end of the idle period.
FIG. 14 is a block diagram illustrating the FBE operation.
Referring to FIG. 14, a communication node (i.e., eNB) managing an SCell performs CCA during a CCA slot. If the channel is idle, the communication node performs data transmission (Tx). If the channel is busy, the communication node waits for a time period calculated by subtracting the CCA slot from a fixed frame period, and then resumes CCA.
FIG. 15 is a view illustrating an exemplary LBE operation as one of the LBT operations.
Referring to FIG. 15(a), in LBE, the communication node first sets q (q.di-elect cons.{4, 5, . . . , 32}) and then performs CCA during one CCA slot.
FIG. 15(b) is a block diagram illustrating the LBE operation. The LBE operation will be described with reference to FIG. 15(b).
The communication node may perform CCA during a CCA slot. If the channel is unoccupied in a first CCA slot, the communication node may transmit data by securing a time period of up to (13/32)q ms.
On the contrary, if the channel is occupied in the first CCA slot, the communication node selects N (N.di-elect cons.{1, 2, . . . , q}) arbitrarily (i.e., randomly) and stores the selected N value as an initial count. Then, the communication node senses a channel state on a CCA slot basis. Each time the channel is unoccupied in one specific CCA slot, the communication node decrements the count by 1. If the count is 0, the communication node may transmit data by securing a time period of up to (13/32)q ms.
4.TxOP Configuration Method and Reservation Signal Transmission Method
A description will be given below of methods for transmitting a reservation signal to occupy a channel and methods for configuring a TxOP, when the channel is determined to be idle after the above-described CS (i.e., LBT) operation. In embodiments of the present disclosure, if it is said that `an SCell is determined to be idle`, this means that the SCell is determined to be idle during an LBT operation or is determined to be idle repeatedly as many times as a backoff count during a backoff operation. In other words, an idle-state SCell means that upon completion of a CS procedure including a backoff operation or an LBT operation, the SCell is finally idle.
For the convenience of description, it is assumed that the size M of a TxOP is 3 (i.e., three subframes) in embodiments of the present disclosure. It is also assumed that a PCell operates in the LTE-A system using a licensed band and an SCell operates in an unlicensed band (e.g., WiFi, BT, or the like). For details, refer to FIG. 12.
4.1 Methods for Configuring TxOP and Transmitting Reservation Signal in Case of Alignment with Subframe (SF) Boundary of PCell
Embodiments as set forth below are for a case in which an SCell is configured to operate in alignment with an SF boundary of a PCell.
FIGS. 16 and 17 are views illustrating a method for transmitting a reservation signal.
FIGS. 16 and 17 illustrate a case in which an SCell is configured to operate in alignment with an SF boundary of a PCell. If an eNB actually transmits data in the SCell in alignment with an SF boundary of the LTE-A system as illustrated in FIG. 16, there may exist a timing gap between a time of determining the idle state of the SCell and an actual data transmission time. Particularly, since the SCell is defined in an unlicensed band, a specific eNB and a specific UE may use the SCell not exclusively but by CS-based contention. Therefore, another system (e.g., a WiFi system) may attempt to transmit information during the timing gap.
Accordingly, to prevent another system from attempting information transmission during the timing gap of the SCell, the eNB may configure transmission of a reservation signal. The reservation signal may be a kind of "dummy information", "a copy of a part of a PDSCH", or "an RS such as CRS or DM-RS" that the eNB transmits to reserve the SCell as its resources. The reservation signal may be transmitted during the timing gap (i.e., until before the actual data transmission time after the time of determining the idle state of the SCell).
Referring to FIG. 16, the eNB may determine whether the SCell is in the idle state to transmit data in the SCell. That is, the eNB determines whether the channel is idle by CS, and performs a backoff operation or an LBT operation according to the determination. If the eNB determines the SCell to be idle in SF #N and thus ends the backoff operation or the LBT operation, the eNB may transmit a reservation signal until before the next SF, SF #N+1, to thereby prevent another system from occupying the SCell.
However, if the eNB should transmit the reservation signal until the next SF boundary after the time of determining the SCell to be idle in order to align an SF boundary of the SCell with an SF boundary of the PCell, the eNB should transmit the reservation signal during almost one SF period (i.e., 1 ms), as illustrated in FIG. 17. Referring to FIG. 17, if the eNB determines that the SCell is idle shortly after the start of SF #N+1 after the backoff operation, the eNB should continue transmitting the reservation signal in SF #N+1 in order to occupy the SCell in alignment between an SF boundary of the SCell and an SF boundary of the PCell.
If the transmission period of the reservation signal is too long as described above, data transmission performance of the LTE/LTE-A system may be degraded, and the performance of a system (e.g., WiFi) operating in an unlicensed band may also be degraded because the reservation signal may act as interference.
4.1.1. Maximum Value Setting
To solve the above problem, a maximum value (i.e., X ms) of a reservation signal transmission period may be preset. For example, the maximum value of the reservation signal transmission period may be set to one slot (i.e., 0.5 msec) or n OFDM symbols. X or n may be preset or set by higher layer signaling or physical layer signaling.
If the maximum value of the reservation signal transmission period is set to one slot, the eNB may start CS in the second slot of every SF, and transmit a reservation signal from a time of determining the SCell to be idle until the next SF of the PCell.
FIG. 18 is a view illustrating an embodiment of setting a maximum value for a reservation signal transmission period.
Referring to FIG. 18, if the eNB determines that a channel of the SCell is kept busy from the second slot of SF #N to the starting time of SF #N+1, the eNB may halt CS during one slot from the starting time of SF #N+1, and start to resume the CS in the second slot of SF #N+1. Subsequently, if the eNB determines the channel to be idle, the eNB may transmit a reservation signal until before the starting time of the next SF, SF #N+2, and start to transmit data in SF #N+2. If the size M of a TxOP is preset by higher layer signaling, a UE may receive data in the SCell during the TxOP.
4.1.2 Adjustment of Starting Time of SF in SCell
FIG. 19 is a view illustrating a method for adjusting the starting time of an SF in an SCell according to an operation of a PCell.
As illustrated in FIG. 19(a), a time of determining the SCell to be idle may be aligned with an SF boundary of the PCell. If at least Y ms is required to perform CCS in the PCell, it may be impossible to perform CCS of the PCell in SF #N+1 of the SCell due to the processing delay time of Y ms.
To solve the problem, an SF starting time of the SCell may be advanced by Y ms. For example, as SF #N+1 of the SCell is configured to start Y ms earlier than SF #N+1 of the PCell as illustrated in FIG. 19(b), even though the channel is determined to be idle at a boundary of SF #N+1 of the SCell, the eNB may prepare for CCS for Y ms in the PCell.
Herein, Y may be predetermined in the system, or may be configured semi-statically by higher layer signaling or dynamically by physical layer signaling (e.g., transmission of an (E)PDCCH) in each SF. The interval between SFs in the PCell and the SCell may be represented as the number of OFDM symbols.
The eNB may be configured not to perform CS in the SCell during Y ms.
Or if the eNB determines the channel to be idle by CS during Y ms, the eNB may transmit the reservation signal during a timing gap until shortly before the starting time of the next SF, SF #N+1 of the SCell (refer to FIG. 19(c)).
4.2 Method for Changing Size of First SF in TxOP
If the reservation signal is transmitted to align an SF boundary of the SCell with an SF boundary of the PCell as described in Section 4.1, loss may occur in terms of spectral efficiency. To reduce the loss of spectral efficiency, it may be configured that if a channel of the SCell is idle, data is transmitted in the SCell despite misalignment between the SF boundary of the SCell and the SF boundary of the PCell.
For example, data transmission efficiency may be increased by configuring the first SF of a TxOP in the SCell in such a manner that the length of the first SF may be changed. Additionally, the reservation signal may be configured to be transmitted to align an SF boundary of the SCell with a slot boundary of the PCell. Now, a description will be given of methods for configuring a TxOP in an SCell in alignment with a slot boundary of a PCell.
FIG. 20 is a view illustrating a method for aligning an SF boundary of an SCell with a slot boundary of a PCell.
It may be configured that data transmission (i.e. a TxOP) of the SCell starts at a slot boundary of the PCell. For example, referring to FIG. 20, if determining a channel of the SCell to be idle in the first slot of SF #N+1, the eNB may transmit the reservation signal only until the boundary of the second slot of SF #N+1. Herein, since a boundary of the SCell may be aligned with a slot boundary of the PCell, the TxOP of the SCell may start in the second slot of SF #N+1. That is, the first SF of the TxOP can be not a full SF but a partial SF (pSF) including only one slot. The eNB may transmit data in the first SF of the SCell aligned with a slot boundary of SF #N+1 of the PCell. Each of the remaining SFs of the TxOP is of the same length as an SF of the PCell, and the end of the last SF of the TxOP may be aligned with the end of SF #N+3 in the PCell.
In another aspect of the embodiment, a time point (i.e., the starting time of a TxOP) at which data transmission may start in the SCell may be set to a symbol boundary of the PCell, not a slot boundary of the PCell. Or the start of the TxOP in the SCell may be set only to a specific time point of the PCell. For example, the TxOP of the SCell may start at the boundary of an odd-numbered or even-numbered symbol of the PCell.
In embodiments of the present disclosure, the first SF of the TxOP in the SCell may be configured to be a pSF shorter than a legacy SF of 1 ms. Therefore, methods for determining a Transport Block Size (TBS) for the first SF of a TxOP and methods for transmitting an RS in the first SF of the TxOP will be described below.
4.2.1 TBS Determination Method-1
According to the LTE/LTE-A system standard TS 36.213, 7.1.7, a TBS is determined according to a 5-bit Modulation and Coding Scheme (MCS) field (i.e., I.sub.MCS) included in DCI and the number of Physical Resource Blocks (PRBs), N.sub.PRB. N.sub.PRB is determined in the manner described in [Table 6].
TABLE-US-00006 TABLE 6 <TS 36.213 7.1.7> ... - set N'.sub.PRB to the total number of allocated PRBs based on the procedure defined in subclause 7.1.6. if the transport block is transmitted in DwPTS of the special subframe in frame structure type 2, then .largecircle. for special subframe configuration 9 with normal cyclic prefix or special subframe configuration 7 with extended cyclic prefix: .box-solid. set the Table 7.1.7.2.1-1 column indicator N.sub.PRB = max{.left brkt-bot.N'.sub.PRB .times.0.375.right brkt-bot., 1} .largecircle. for other special subframe configurations: .box-solid. set the Table 7.1.7.2.1-1 column indicator N.sub.PRB = max{.left brkt-bot.N'.sub.PRB.times.0.75.right brkt-bot., 1}, else, set the Table 7.1.7.2.1-1 column indicator N.sub.PRB = N'.sub.PRB .
If the first SF of a TxOP in an SCell is a pSF, a TBS may be determined as follows. When one SF is divided into T points and the first SF starts at a k.sup.th point among the T points, N.sub.PRB for the pSF may be calculated by the following [Equation 3].
.times.'.times..times..times. ##EQU00004##
For example, if a normal CP is used in the SCell and the SCell operates in alignment with a symbol boundary of a PCell, T may be set to 14 and k may represent the index of an OFDM symbol in the first SF. Herein, k may be indicated by DCI on a PDCCH transmitted in SF #N+2.
Or if an extended CP is used in the SCell and the SCell operates in alignment with a symbol boundary of the PCell, T may be set to 12 and k may represent the index of an OFDM symbol in the first SF.
4.2.2 TBS Determination Method-2
Among the methods proposed in Section 4.2.1, an SF including as many OFDM symbols as defined by a legacy DwPTS configuration will be described. That is, if the first SF of a TxOP is configured as in a DwPTS configuration described in [Table 1], N.sub.PRB may be calculated.
For example, if the first SF includes 7 OFDM symbols, N.sub.PRB may be calculated by N.sub.PRB=max{.left brkt-bot.N'.sub.PRB.times.0.375.right brkt-bot., 1} like special SF configuration 9 in [Table 1]. If the first SF includes 9 to 12 OFDM symbols, N.sub.PRB may be calculated by N.sub.PRB=max {.left brkt-bot.N'.sub.PRB.times.0.75.right brkt-bot., 1} like special SF configurations 1, 2, 3, 4, 6, 7 and 8. The same thing is applicable to an extended CP case.
4.2.3 RS Configuration Method-1
FIG. 21 is a view illustrating configurations of RSs transmitted in an SCell.
In the LTE/LTE-A system, the eNB transmits DM-RSs configured as illustrated in FIG. 21(a) to help a UE with data demodulation. However, if the first SF of a TxOP in an SCell is configured to be shorter than the length of the legacy SF, 1 ms, DM-RSs sufficient for data demodulation may not be ensured.
For example, if the length of the first SF is equal to or smaller than Q, DM-RSs may be transmitted in the pattern illustrated in FIG. 21(b). Q may be configured semi-statically by higher layer signaling or dynamically by physical layer signaling. For example, Q may be defined to be one slot. That is, if the first SF includes only one slot, DM-RSs allocated to the first SF may be configured as illustrated in FIG. 21(b).
The reason for configuring DM-RSs in the pattern illustrated in FIG. 21(b) is that since the former boundary of the first SF may vary according to a channel state-based CS result, sufficient DM-RSs may not be ensured. Therefore, DM-RSs are preferably allocated to the second slot.
4.2.4 Setting of SF Length Based on Threshold
If an SCell operates in alignment with a symbol boundary of a PCell, the first SF of a TxOP may include only one OFDM symbol in an extreme case.
However, it may be more efficient in terms of SCell management to configure an SF having a long TTI by concatenating one SF with another SF than to configure an independent SF with too small a number of OFDM symbols. That is, it may be determined whether to configure an SF by concatenating the first SF with another SF based on a specific threshold.
The threshold may be a predetermined fixed value in the system, or may be configured semi-statically by higher layer signaling or dynamically by physical layer signaling. For example, the threshold may be set as the number of OFDM symbols.
FIG. 22 is a view illustrating a method for determining an SF length based on a threshold.
If the first SF includes as many OFDM symbols as or fewer OFDM symbols than a threshold, the first SF may be concatenated with the next SF into one SF. Referring to FIG. 22, it may be noted that a TxOP starts in a latter part of SF #N+1 in a first SCell. That is, if the length of the TxOP in SF #N+1 with respect to an SF boundary of a PCell is equal to or smaller than a threshold, the TxOP of SF #N+1 and the TxOP of SF #N+2 in the SCell may be concatenated into the first SF.
Or if the first SF includes more OFDM symbols than the threshold, the first SF may be configured to be independent of the next SF. Referring to FIG. 22, it may be noted that a TxOP starts in a former part of SF #N+1 in a second SCell. That is, if the length of the TxOP in SF #N+1 with respect to an SF boundary of the PCell is larger than the threshold, the first SF of the TxOP of SF #N+1 may be configured to be independent of the TxOP of SF #N+2.
That is, if the SCell is determined to be idle in SF #N+1, the first SF of the TxOP may be configured to be an independent pSF, or an over SF (oSF) produced by concatenating the SF with the next SF, depending on whether the number of OFDM symbols in the TxOP is equal to or larger than the threshold.
In another aspect of the embodiment, as is the case with a special SF configuration that does not allow PDSCH transmission (i.e., special SF configurations 0 and 5 in a normal CP case, and special SF configurations 0 and 4 in an extended CP case) in the current LTE/LTE-A system, the first SF may be configured with three or fewer OFDM symbols. In this case, the first SF may be concatenated with the next SF into one SF.
4.2.5 TBS Determination Method-3
When the first SF is configured with more OFDM symbols than a threshold in Section 4.2.4, a TBS may be calculated in the methods described in Section 4.2.1 and Section 4.2.2. However, if the first SF is configured to be an oSF by concatenating as many OFDM symbols as or fewer OFDM symbols than the threshold with the next SF, N.sub.PRB may be determined by the following [Equation 4].
.times.'.times..times..times. ##EQU00005##
In [Equation 4], k or (T+k) may be transmitted to a UE in DCI of SF #N+2 by CCS.
However, if a normal CP is used, the threshold is 3 OFDM symbols, and k is 3, N.sub.PRB is calculated by N.sub.PRB=max{.left brkt-bot.N'.sub.PRB.times.17/14.right brkt-bot., 1} where if N'.sub.PRB=100, N.sub.PRB=121 larger than a maximum value of N.sub.PRB as defined in the current LTE/LTE-A system. To prevent this, N.sub.PRB may be determined by [Equation 5].
.times..times.'.times..times..times. ##EQU00006##
In [Equation 5], Z is a maximum available number of PRBs in a system BandWidth (BW) given to the SCell. For example, Z may be set to 110.
If N.sub.PRB calculated by [Equation 4] is larger than Z, N.sub.PRB may be calculated in the following manner, instead of the method described by [Equation 5]. For example, if a TBS determined by I.sub.TBS and N.sub.PRB (refer to the LTE standard TS 36.213, Table 7.1.7.2.1-1) is defined as TBS(I.sub.TBS, N.sub.PRB), an actual TBS may be calculated by [Equation 6].
.function..function.'.times..times..times. ##EQU00007##
In another aspect of the embodiment, the UE may be configured not to expect N.sub.PRB calculated by [Equation 4] larger than Z. That is, the UE may ignore or discard DCI that configures N.sub.PRB larger than Z.
4.2.6 RS Configuration Method-2
When one SF is configured by concatenating the first SF of a TxOP with the next SF in Section 4.2.4, CRSs may be transmitted not in OFDM symbols concatenated to the next SF, but in the full OFDM symbols of the next SF. The UE may perform channel estimation using the CRSs.
Or, DM-RSs may not be transmitted in the OFDM symbols concatenated to the next SF, and the UE may perform data demodulation using DM-RSs in the next full SF.
For example, referring to FIG. 22, CRSs and/or DM-RSs are allocated not to OFDM symbols corresponding to SF #N+1 in the first SF of the TxOP, but to an area corresponding to SF #N+2.
In another aspect of the embodiment, the UE may configure CRSs and/or DM-RSs for the OFDM symbols concatenated to the next SF by copying a part (e.g., a former or latter part) of the following full SF.
4.3 Method for Fixing Length of First SF in TxOP
If a reservation signal and data are transmitted in an SCell in the methods described in Section 4.2, an eNB managing a PCell does not know at the starting time of SF #N+1 when data transmission actually starts in the SCell. Accordingly, the eNB preferably determines a TBS and an MCS for each available SF configuration unit in advance, and prepares for data transmission suitable for each unit.
If data transmission is possible at an OFDM symbol boundary, a total of 14 lengths ranging from 1 OFDM symbol to 14 OFDM symbols are available as the length of the first SF of a TxOP. Therefore, at the start of SN #N+1, the eNB should prepare 14 different data having different TBSs and MCSs for 14 starting points, thereby increasing the configuration and scheduling complexity of the SCell.
Now, a description will be given of a transmission method for reducing complexity in relation to an SCell, and a related TBS determination method and RS transmission method.
In Section 4.2, the TBS of the first SF of a TxOP in an SCell is adjusted for alignment with an SF boundary of a PCell, starting from SF #N+2. In contrast, an embodiment of the present disclosure as described below is about methods for reducing the complexity of an SCell by fixing the length of the first SF of a TxOP in the SCell to the length (e.g., 1 ms) of an SF in a PCell.
For example, if it is possible to transmit data in the SCell in alignment with a slot boundary of the PCell, even though transmission of the first SF starts in an odd-numbered slot of the PCell, an SF may be configured to be as long as the legacy SF and the last SF of the TxOP may be transmitted during one slot (i.e., 0.5 ms).
As a consequence, there is no need for preconfiguring the first SF in a plurality of units in the PCell at the starting time of SF #N+1, and the last SF of the TxOP has only to be configured in a variable length, thereby reducing the complexity of the SCell.
FIG. 23 is a view illustrating a method for fixing the length of the first SF of a TxOP.
Referring to FIG. 23, an SCell is determined to be idle in SF #N+1, and a TxOP is allocated, starting from SF #N+1. The last SF (i.e., the third SF) of the TxOP may be configured to be in a variable length, for alignment with an SF boundary of a PCell.
If the last SF of the TxOP is aligned with a boundary of the PCell, a processing delay may be reduced on the part of the eNB, if SF #N+4 is configured as a UL SF. For example, UL transmission may be performed immediately in SF #N+4. In addition, in the case of a non-TDD configuration, the freedom of DL/UL configuration may be increased.
4.3.1 TBS Determination Method-4
Since the first SF of a TxOP is configured to be of the same length as an SF in a PCell, a TBS may be set to be equal to that of the PCell. However, considering that the last SF of the TxOP has a variable length, the eNB may configure a TBS using the TBS determination method described in Section 4.2.1 and/or Section 4.2.2, and the UE may receive and decode data by determining a TBS based on DCI received from the eNB.
4.3.2 Special SF Configuration
The last SF of a TxOP may be configured to include only as many OFDM symbols as defined in a DwPTS configuration being a specific SF configuration (refer to [Table 1]).
Or, it may be restricted that the SF should be configured only with units of a specific OFDM symbol (e.g., an even number of OFDM symbols). In this case, the actual length of the last SF may not match a regulated transmission unit for the last SF. For example, although it is regulated that the last SF is transmitted only in units of a slot, the actual number of OFDM symbols in the last SF may be only 3. In this case, it may be defined that the last SF is not configured.
That is, the last SF may be configured with the largest of defined transmission units for the last SF, shorter than the actual length of the last SF. For example, if the last SF is configured with as many OFDM symbols as defined by a legacy DwPTS configuration, the unit of the last SF defined for the case of a normal CP is 3, 7, 9, 10, 11, 12, or 14 OFDM symbols. If the actual length of the last SF is 13 OFDM symbols, the last SF may be configured only with 12 OFDM symbols. That is, the last SF may be configured with the largest of SF units smaller than a defined size.
4.3.3 DM-RS Configuration Method
Similarly to the description of Section 4.2.3, if the last SF is configured to be shorter than the SF length (i.e., 1 ms) of a PCell, for example, if the last SF is configured with only one slot, DM-RSs enough for data demodulation may not be ensured.
To avert the problem, if the length of the last SF is smaller than Q, it may be configured that DM-RSs are transmitted in the pattern illustrated in FIG. 24. FIG. 24 is a view illustrating a method for allocating DM-RSs, when the last SF of a TxOP is configured variably.
The DM-RS configuration method illustrated in FIG. 24 is applied for a special SF configuration. For example, Q may be set to one slot. Q may be configured for the UE by higher layer signaling or physical layer signaling.
4.3.4 Method for Configuring Last SF Based on Threshold
If an SCell operates in alignment with a symbol boundary of a PCell as described in Section 4.2.4, the last SF of a TxOP may be configured only with one OFDM symbol in an extreme case. FIG. 25 is a view illustrating a case of fixing the length of the first SF of a TxOP. Referring to FIG. 25, it may be noted that when the size M of a TxOP is 3, the length of the last third SF of the TxOP is one OFDM symbol.
Also in this case, an SF may be configured and a TBS may be determined in the methods described in Section 4.2.4 and Section 4.2.5. For example, the last third SF and the previous second SF may be concatenated into one SF.
However, if the last SF is configured to be longer than the legacy SF length, the resulting decoding delay may affect an HARQ-ACK process. Therefore, it may not be reasonable to set the length of the last SF to be larger than the legacy SF length. In this context, the length of the first SF may be set variably, rather than the last SF is set to be longer than the legacy SF length. As a consequence, the length of the last SF may not be smaller than a specific value.
FIG. 26 is a view illustrating one of methods for configuring the first and last SFs of a TxOP based on a threshold.
Referring to FIG. 26, a slot boundary of a PCell is set as a threshold. In the case where an SCell is determined to be idle in SF #N+1, if the first SF of a TxOP starts before the threshold, the length of the first SF may be set to the legacy SF length. If the first SF of the TxOP starts after the threshold, the length of the first SF may be set to one slot.
This configuration may always maintain the length of the last SF to be larger than one slot. In FIG. 26, the first SF of a TxOP starts before a threshold in a first SCell and thus is configured to be 1 ms long. The last SF of the TxOP may be configured to be 1 ms-a (a=<0.5 ms) long.
In a second SCell, the first SF of a TxOP starts after the threshold. Thus, the first SF may be configured to include one slot (i.e., 0.5 ms). The second SF of the TxOP may be 1 ms long as in a PCell, and a length equal to or larger than 0.5 ms may be ensured for the third SF of the TxOP because the first SF is 0.5 ms long. That is, the length of the last SF may be set to 0.5 ms+a (a=<0.5 ms).
The threshold may be allocated semi-statically by higher layer signaling or dynamically by physical layer signaling. The TBSs of the first SF and the last SF may also be determined in the method described in Section 4.2.1, Section 4.2.2, and/or Section 4.3.2.
DM-RSs may be determined for the first SF and the last SF in the method proposed in Section 4.2.3.
In the afore-described Section 4.3.1 to Section 4.3.3, the eNB may indicate the number of OFDM symbols in the last SF to the UE in SF #N+4 in the PCell by CCS. Or each UE may calculate the number of OFDM symbols in the last SF of the TxOP based on the starting time of the first SF and the threshold in the above-described rule.
4.4 TxOP Configuration Method-1
4.4.1 Method for Determining Starting Time of TxOP Based on Threshold
As described regarding the transmission starting time of data in an SCell from an eNB in Section 4.1, data may be transmitted by aligning an SF boundary of the SCell with an SF boundary of a PCell. Or data may be transmitted in alignment with a slot boundary or OFDM symbol boundary of the PCell instead of an SF boundary of the PCell, as described before in Section 4.2 and/or Section 4.3.
Now, a description will be given of a method for transmitting a reservation signal based on a threshold, and a method for determining a starting time of data transmission.
FIG. 27 is a view illustrating another of the methods for transmitting a reservation signal based on a threshold.
In FIG. 27, it is assumed that a PCell and an SCell are configured as described before with reference to FIG. 12. A threshold for transmitting a reservation signal and/or determining a starting time of data transmission may be a predetermined fixed value in the system, or may be allocated semi-statically by higher layer signaling or dynamically by physical layer signaling.
The threshold may be defined as t .mu.s after (or before) an SF boundary of the PCell, or as an m.sup.th OFDM symbol boundary. If a backoff operation or a CS operation is completed earlier than the threshold, the eNB may configure an SF in a unit shorter than one SF (i.e., 1 ms) and start data transmission in the configured SF, after transmitting a reservation signal in the SCell (or without transmitting the reservation signal).
It may be configured that actual data transmission starts at the threshold (refer to SCell 3 in FIG. 27) or at a predetermined time point (e.g., an OFDM symbol boundary) earlier than the threshold (refer to SCell 2 in FIG. 27). On the other hand, if the backoff operation or the CS operation is completed after the threshold, a reservation signal may be transmitted until the next SF boundary, and then data transmission may start (refer to SCell 1 in FIG. 27).
Referring to FIG. 27 again, if the eNB is to transmit data in an SCell of an unlicensed band, the eNB performs a backoff operation and a CS operation in the SCell. If determining that the SCell is idle in SF #N+1, the eNB may configure a TxOP and transmit data in the TxOP.
Notably, the eNB may align a data transmission time (i.e., the starting time of the first SF of the TxOP) with an SF boundary, OFDM symbol boundary, or slot boundary of the PCell. While it is assumed that the threshold is set as a slot boundary in FIG. 27, the threshold may vary according to a channel environment.
In SCell 1, since the eNB has completed the backoff operation and the CS operation at a time point after the threshold, the eNB may align the starting time of the first SF of the TxOP with a boundary of SF #N+2 in the PCell.
In SCell 2, since the eNB has completed the backoff operation and the CS operation at a time point before the threshold, the eNB may align the starting time of the first SF of the TxOP with a slot boundary or OFDM symbol boundary of the PCell. It is assumed that the starting time of the first SF is aligned with a slot boundary of the PCell in SCell 2.
In SCell 3, since the eNB has completed the backoff operation and the CS operation at the threshold, the eNB may align the starting time of the first SF of the TxOP with a slot boundary or OFDM symbol boundary of the PCell. It is assumed that the starting time of the first SF is aligned with a slot boundary of the PCell in SCell 3.
Or if the backoff operation or the CS operation is completed after the threshold, the eNB may perform the backoff operation or the CS operation again without transmitting a reservation signal in the SCell, start data transmission at the next SF boundary without transmitting the reservation signal, or perform the backoff operation or the CS operation, starting at the next SF boundary without transmitting the reservation signal.
4.4.2 Method for Setting Starting Time of TxOP Based on Code Rate
A method for determining the starting time of a TxOP using a time-axis threshold has been described above in Section 4.4.1. Now, a description will be given of methods for determining the starting time of a TxOP based on a code rate.
For example, a threshold Y may be set for a code rate. If an SF may be configured to be a smaller unit than one 1-ms SF unit, the eNB may start data transmission only when a code rate is equal to or lower than Y. This is because if data is transmitted at a code rate higher than Y, it may occur that the eNB may not ensure the reliability of transmission data.
Or the eNB may transmit only data corresponding to a maximum TBS with a code rate equal to or lower than Y. As described before in Section 4.4.1, the eNB may transmit a reservation signal between an ending time of a CS or backoff operation and a data transmission time.
If the code rate is higher than the threshold Y, the eNB may transmit a reservation signal until the next SF boundary, perform the CS operation again, starting from the next SF boundary, while giving up data transmission, or perform data transmission.
The threshold Y may be preset in the system or configured by physical layer signaling or higher layer signaling.
If an SF shorter than 1 ms is configured in Section 4.4.1 or Section 4.4.2, a TBS may be determined according to the method proposed in Section 4.2.1 or Section 4.2.2. Or a code rate may be determined according to a puncturing or rate matching method after a TBS is determined in Section 4.4.1 or Section 4.4.2.
4.4.3 HARQ Process Configuration
If the first SF of a TxOP is configured with as many OFDM symbols as or fewer OFDM symbols than a threshold, the OFDM symbols and the next SF may be concatenated into one SF, as described in Section 4.2.4. Or if the first SF is configured with more OFDM symbols than the threshold, the OFDM symbols may be configured as an independent SF.
Now, an HARQ-ACK configuration will be proposed. If the first SF is configured by concatenating as many OFDM symbols as or fewer OFDM symbols than a threshold to the next SF, the UE may regard the first SF as one HARQ process. On the other hand, if the first SF is configured with more OFDM symbols than the threshold, the UE may consider that an HARQ process has been configured for each independent SF. That is, the UE may consider that separate (i.e., two) HARQ processes have been configured for the first SF of a length shorter than 1 ms but larger than the threshold and the next second SF.
In another aspect of the embodiment, if the first SF is configured to be shorter than 1 ms, an HARQ-ACK for the first SF may be bundled with an HARQ-ACK for the next SF (or the previous SF), that is, a full 1-ms SF.
4.4.4 Special SF Configuration
If a short SF which is not defined in the DwPTS configurations described in Section 3 is configured and transmitted, the eNB may not give up data transmission in the SF and transmit only data without allocating RSs such as CRSs or DM-RSs.
4.5 TxOP Configuration Method
4.5.1 Method for Configuring TxOP In Case of Aligning SF boundary of SCell with SF Boundary of PCell
When an SCell is determined to be idle, the starting time of data transmission may be aligned with an SF boundary of a PCell, as described in Section 4.1.2 with reference to FIG. 19. The eNB may require at least Y1 ms as a processing time for DCI configuration in performing CCS in the PCell (or the SCell).
FIG. 28 is a view illustrating a method for transmitting a reservation signal.
Hereinbelow, a method for ensuing Y1 ms (or an Y2 OFDM symbol time) for configuring DCI while an SF boundary of an SCell is aligned with an SF boundary of a PCell as described in Section 4.1.2 and the alignment is maintained (e.g., within a time error of 30.26 .mu.s in the LTE-A system) is proposed.
In FIG. 28, only when a backoff operation is completed Y1 ms earlier than the starting time of SF #N+1 or a condition for stating data transmission in a TxOP is satisfied as in SCell 1 or SCell 2, the eNB may start data transmission in SF #N+1.
For example, if the eNB performs CCA only during T .mu.s without backoff as in SCell 3 in FIG. 28, the eNB may perform CCA during T .mu.s Y1 ms before each SF boundary.
If the SCell is determined to be idle in a CCA period of SF #N, the eNB may transmit a reservation signal during Y1 ms and start data transmission in SF #N+1. If the SCell is busy, the eNB may determine again whether the SCell is busy or idle in a CCA period of SN #N+1. If Y1 ms is shorter than two OFDM symbols, the reservation signal may be configured to include DM-RSs.
In another aspect of the embodiment, the eNB may transmit a reservation signal during Y1 ms to align a boundary of the SCell with an SF boundary of the PCell.
4.5.2 Method for Configuring TxOP In Case of Alignment with Slot Boundary of PCell
Methods for ending a TxOP at an SF boundary have been described in Section 4.2 with reference to FIG. 20. However, the eNB may not end the TxOP at an SF boundary to match a total time during which the TxOP is configured (i.e., M=3 SFs). If a maximum length of consecutive transmissions in an unlicensed band is limited (e.g., to 4 ms) and the TxOP ends at an SF boundary, short of the maximum length, radio resources may be inefficiently utilized.
If the last SF of the TxOP is a pSF shorter than 1 ms, the TBS determination methods and the RS transmission methods described in Section 4.2.1 to Section 4.2.4 are applicable to the pSF.
If the starting time of a TxOP is set to a point other than an SF boundary according to the ending time of CS (i.e., CCA) (e.g., on a slot basis or an OFDM symbol basis (one of the starting times of 14 OFDM symbols) as in the proposed methods of Section 4.2 and Section 4.3, that is, if the length of the first SF of the TxOP is allowed to be variable in every TxOP, signaling of an RS configuration for the first SF and a transmission length of the first SF may become complex, which may make actual UE implementation difficult.
On the other hand, in embodiments in which an eNB transmits data by aligning the start and end of a TxOP in an SCell with SF boundaries of a PCell, if a specific eNB is to configure consecutive TxOPs, one SF may always be wasted for performing CCA and transmitting a reservation signal between TxOPs.
FIG. 30 is a view illustrating one of methods for configuring consecutive TxOPs.
FIG. 30(a) illustrates a method for configuring consecutive TxOPs, when a boundary of an SCell is aligned with an SF boundary of a PCell as described in Section 4.1. Referring to FIG. 30(a), when an eNB ends the first TxOP in SF #N-1 and then immediately wants to start the next TxOP, the eNB should wait until the next SF boundary even though CCS is completed in the middle of SF #N.
That is, the eNB should transmit a reservation signal instead of data from the ending time of CCA to the starting time of SF #N+1. A shortcoming with this scheme is that if the length of a TxOP for data transmission is set to up to 3 ms, the resources of one SF out of four SFs may not be used for data transmission, if consecutive TxOPs are to be configured.
To solve the problem, a TxOP configuration illustrated in FIG. 30(b) may be considered. Referring to FIG. 30(b), the eNB may configure the ending time of the last SF of a TxOP to be earlier than an SF boundary of a PCell, and perform CCA during a timing gap lasting until the next SF boundary. If the CCA operation (e.g., initial CCA and/or ECCA) is completed during the timing gap, the eNB may configure a TxOP to start at the next SF boundary.
If there is a TxOP ending in SF #N-1, the eNB may end the TxOP before an SF boundary at which SF #N starts, to perform a backoff operation and/or a CCA operation for configuring the next TxOP. If the CCA operation ends between the ending time of the TxOP and the starting time of SF #N, the eNB may transmit a reservation signal until before the starting time of SF #N, and then immediately configure a TxOP at the starting time of SF #N.
Compared to the TxOP configuration illustrated in FIG. 30(a), the TxOP configuration illustrated in FIG. 30(b) offers the benefit of a great decrease in a non-data transmission period between TxOPs. The SF structure illustrated in FIG. 30(b) is characterized in that the length of the last SF of a TxOP (or the last SF of a TxOP having a maximum available length) may be determined fixedly or semi-statically. The last SF may be shorter than a 1-ms full SF. That is, the last SF may be configured to be a pSF, and the TBS determination methods and the RS transmission methods described in Section 4.3.1 to Section 4.3.4 are applicable to the pSF.
While a timing gap is positioned in the last SF of each TxOP to configure consecutive TxOPs without SF waste in the TxOP configuration illustrated in FIG. 30(b), the timing gap may be positioned in the first SF of each TxOP as illustrated in FIG. 30(c).
In FIG. 30(c), the length of the first SF of a TxOP may be determined fixedly or semi-statically. For example, the first SF may be shorter than a 1-ms full SF. That is, the first SF may be configured to be a pSF, and the TBS determination methods and the RS transmission methods described in Section 4.2.1 to Section 4.2.6 are applicable to the pSF.
In another aspect of the embodiment, the methods proposed in FIG. 30 may be easily extended to an LBT method in which if a channel is determined to be idle at a predetermined time point after CCA, a TxOP starts immediately without transmission of a reservation signal.
4.6 TBS Configuration Method-5
The eNB preferably prepares different TBSs according to pSF lengths for the case of transmission of a pSF shorter than the legacy SF length, 1 ms, as in SF #N+1 in FIG. 20 described in Section 4.2. That is, the eNB managing a PCell or an SCell does not know at the starting time of SF #N+1 when data transmission will start in the SCell.
Accordingly, the eNB should determine a TBS and an MCS for each available pSF configuration unit in advance, and prepare for data transmission suitable for each unit. If data transmission is possible at an OFDM symbol boundary, a total of 14 lengths ranging from 1 OFDM symbol to 14 OFDM symbols are available as the length of the first SF in a TxOP. Therefore, at the starting time of SN #N+1, the eNB should prepare 14 different data having different TBSs and MCSs for 14 starting points, thereby increasing the configuration complexity of the SCell.
A description will be given below of a method for allocating a fixed TBS to a pSF, even though the pSF shorter than the legacy SF length (e.g., 1 ms) is configured, in order to avert the above problem.
4.6.1 Change of Received RB Size of PDSCH According to Variable SF Length
For example, in the case where 5 RBs are scheduled on the assumption of 10 symbols (10.times.5), if an SF length is 5 symbols, the UE may receive a signal by extending the RBs to 10 RBs for 5 symbols (5.times.10).
On the contrary, in the case where 10 RBs are scheduled on the assumption of 5 symbols, if an SF length is 10 symbols, the UE may receive a signal only in 5 RBs out of allocated 10 RBs.
Because the total number of RBs available in the system is limited, a PDSCH may not be transmitted to some UE. In this case, buffer handling for the UE failing in PDSCH reception may be performed using an NDI or the like. Considering this UE operation, only initial transmission may be allowed in a pSF.
4.6.2 TBS Based on Minimum SF Length and Assumption of Repetition of the TBS
For example, a TBS may be determined on the assumption that a minimum SF length is 3 symbols. If an SF length is determined to be 6 symbols, the eNB may transmit the same TB twice. However, a repetition number may not necessarily be limited to an integer multiple. For example, if 5 symbols are secured, a TB may be configured to be repeated (1+2/3) times.
Redundancy versions may be cyclically applied to the repeated TBs in a predefined pattern (e.g., 0.fwdarw.2.fwdarw.3.fwdarw.1). As the eNB transmits the same TB repeatedly, a data throughput is reduced but robust transmission is possible. Therefore, a retransmission number may be reduced.
4.7 Method for Restricting Starting Time of TxOP
To increase the efficiency of radio resource utilization in the LTE system operating in an unlicensed band as illustrated in FIG. 20 as described in Section 4.2, a TxOP for data transmission may start at a time point other than an SF boundary.
However, if a TxOP is allowed to start in each OFDM symbol, the implementation complexity of an eNB and a UE may be increased. This is because the eNB should prepare a plurality of sets of TBS and RE mappings in advance and the complexity of detecting the starting time of a TxOP may be increased in the UE.
Therefore, in another embodiment of the present disclosure, the starting time of a TxOP may be confined to a specific OFDM symbol. The following description is given on the assumption that the starting time of a TxOP is limited to the first or fourth OFDM symbol (i.e., a part of OFDM symbols with CRS port 0) of an SF. However, this constraint may be extended to a slot unit (e.g., a boundary of the first or second slot).
In general, the eNB determines a TBS at least hundreds of .mu.sec earlier in order to transmit data in SF #N, and indicates the determined TBS by higher layer signaling to transmit data corresponding to the TBS. If a TxOP starts at an SF boundary of the PCell, the eNB may transmit data in 14 OFDM symbols. Or if the TxOP starts in the fourth OFDM symbol, the eNB may transmit data in 10 OFDM symbols.
Although the eNB may not predict the starting time of a TxOP preliminarily hundreds of .mu.s earlier during an LBT operation, if the eNB prepares for TBSs and so on for two starting time points, eNB implementation complexity may be increased significantly.
To solve the problem, the eNB may prepare only one TBS irrespective of the starting time of the first SF of a TxOP. A method for scaling a PRB size in determining a TBS for transmission in 10 OFDM symbols may be determined according to Section 4.2.1 or Section 4.2.2.
If the UE receives an SF including a partial TTI (i.e., a pSF), the UE may determine a TBS based on the number of transmission OFDM symbols and the number of OFDM symbols preset independently between the eNB and the UE.
From the perspective of the eNB, the eNB may assume a full SF (i.e., 14 OFDM symbols) in pSF transmission or assume that a pSF is configured with fewer OFDM symbols than a predetermined number of OFDM symbols, that is, 14 OFDM symbols.
If it is regulated that when the eNB transmits a pSF, the eNB assumes transmission of a full SF all the time, the UE may decode the pSF on the assumption of receiving a full SF.
Further, if it is regulated that when the eNB transmits a pSF, the eNB assumes transmission of a predetermined smaller number of OFDM symbols, the UE may decode the pSF on the assumption of receiving an SF including the predetermined smaller number of OFDM symbols.
In this case, as the eNB configures an SF configuration unit for the UE when transmitting the pSF, the UE may decode the pSF based on the configured SF configuration unit.
Now, a description will be given below of methods for determining a TBS for a configured pSF according to this rule.
4.7.1 TBS Configuration in Predetermined Rule
The eNB may configure an SF with a fixed number of OFDM symbols (e.g., 10 OFDM symbols) as the first SF of a TxOP, and determine a TBS according to the fixed number of OFDM symbols. Regarding this, the PRB size scaling method described in Section 4.2.1 or Section 4.2.2 may be referred to.
The UE may determine that a corresponding SF is the first SF of the TxOP by receiving a reservation signal or an indication by physical layer signaling or higher layer signaling. That is, the UE may consider that an assumed TBS of 10 OFDM symbols has been applied to the first SF.
In this case, since the number of OFDM symbols in the first SF being a pSF is system-determined, there is no need for additional signaling of the TBS or the number of OFDM symbols.
4.7.2 TBS Configuration by Signaling
The eNB may configure a variable allocation of 14 OFDM symbols or 10 OFDM symbols all the time for the first SF of a TxOP. For example, the length of a pSF may be configured semi-statically by higher layer signal or dynamically by physical layer signaling (i.e., DCI). For example, the eNB may configure a TBS for a pSF by differentiating a scrambling sequence, a CRS mask, and/or a search space in DCI or adding a new field to a DCI format.
The first SF of a TxOP may be configured on the assumption that its TBS is 10 OFDM symbols by higher layer signaling. In this case, upon recognizing that a corresponding SF is the first SF of the TxOP by a reservation signal or an indication received by higher layer signaling or physical layer signaling, the UE may consider that the assumed TBS of 10 OFDM symbols is applied to the SF.
Configuring the number of OFDM symbols in a pSF by dynamic signaling (i.e., physical layer signaling, DCI) will be described as another example. In the case where a 1-bit field of a physical layer signal, DCI is used to indicate the number of OFDM symbols, if the field is activated in the DCI, the UE may determine that an SF carrying the DCI includes 10 OFDM symbols. Thus, the UE may derive the TBS on the assumption of 10 OFDM symbols in the SF carrying the DCI. On the contrary, if the field is deactivated in the DCI, the UE may derive the TBS on the assumption that the SF carrying the DCI includes 14 OFDM symbols.
Accordingly, the UE may decode data transmitted in the pSF based on the derived TBS.
While Section 4.7 deals with a case in which the first SF of a TxOP is a pSF, it is applicable in the same manner to a case in which the last SF of a TxOP is a pSF.
4.8 Method for Transmitting and Receiving Data According to TxOP Configuration
FIG. 31 is a flowchart illustrating one of methods for transmitting and receiving data according to a TxOP configuration.
Methods for configuring a TxOP to transmit data in an SCell being an unlicensed band by an eNB have been described before in Sections 4.1 to 4.7. The eNB may perform a backoff operation and/or a CS operation to configure a TxOP in an SCell (S3110).
If a channel of the SCell is determined to be idle through the backoff operation and/or the CS operation, the eNB may determine an SF structure in order to configure a TxOP (S3120).
For example, if an SF of the SCell is aligned with an SF boundary of a PCell, an SF of the SCell is always configured in the same structure as an SF of the PCell, and thus the eNB and the UE may transmit and receive data according to an SF configuration defined for the PCell (for details, refer to Section 4.1).
To increase a data throughput in the PCell and the SCell, the first SF or the last SF of the TxOP may be configured to be a pSF shorter than an SF of the PCell (for details, refer to Section 4.2 to Section 4.7).
If the first SF and/or the last SF is configured to be a pSF, the eNB may indicate the number of OFDM symbol or a TBS for the pSF to the UE by higher layer signaling or physical layer signaling (not shown).
Or if a pSF is configured in the TxOP, the number of OFDM symbols in the pSF may be fixed in the system. In this case, the UE may receive data based on a TBS determined according to the fixed number of OFDM symbols.
Or if a pSF is configured in the TxOP, the eNB may fix the number of OFDM symbols available for the pSF to a predetermined value (e.g., 2 or 3) in order to reduce a processing delay. That is, a pSF may be configured with as many OFDM symbols as one of a plurality of numbers of OFDM symbols based on the number of OFDM symbols available for configuring a TxOP in an SF for which CS has been performed. In this case, the eNB may indicate the number of OFDM symbols in the configured pSF to the UE by higher layer signaling or physical layer signaling.
The eNB may transmit data in the configured TxOP and the UE may receive the data in the TxOP.
The foregoing embodiments of the present disclosure have been described in the context of DL. However, the embodiments of the present disclosure can be extended to UL as they are, except that DL RSs are replaced with UL RSs. For example, Section 4.1 and Section 4.4 may be extended as a backoff method for UL transmission, and Section 4.2 may be extended to a method for determining a TBS for a pSF on UL.
Apparatuses illustrated in FIG. 32 are means that can implement the methods described before with reference to FIGS. 1 to 31.
That is, each of the UE and the eNB may include a Transmitter (Tx) 3240 or 3250 and a Receiver (Rx) 3260 or 3270, for controlling transmission and reception of information, data, and/or messages, and an antenna 3200 or 3210 for transmitting and receiving information, data, and/or messages.
Each of the UE and the eNB may further include a processor 3220 or 3230 for implementing the afore-described embodiments of the present disclosure and a memory 3280 or 3290 for temporarily or permanently storing operations of the processor 3220 or 3230.
The embodiments of the present disclosure may be performed using the afore-described components and functions of a UE and an eNB. For example, the eNB may determine whether an SCell is idle by performing a backoff operation and a CS operation. If the SCell is idle, the eNB may configure a TxOP and transmit and receive data during the TxOP. The ENB may occupy the SCell by transmitting a reservation signal until before the configured TxOP. When configuring the TxOP, the eNB may configure a pSF and transmit information about the pSF to the UE. The pSF may be configured as the first and/or last SF of the TxOP. The UE may determine the TxOP configuration based on TxOP configuration information and/or the information about the pSF, and transmit and receive data in the TxOP. For various methods for configuring a TxOP, refer to the embodiments of the present disclosure described in Section 1 to Section 4.
The Tx and Rx of the UE and the eNB may perform a packet modulation/demodulation function for data transmission, a high-speed packet channel coding function, OFDM packet scheduling, TDD packet scheduling, and/or channelization. Each of the UE and the eNB of FIG. 32 may further include a low-power Radio Frequency (RF)/Intermediate Frequency (IF) module.
Previous Patent US 10,178,666 | Next Patent US 10,178,668