WO2017030345A1

WO2017030345A1 - Method and apparatus for performing frequency hopping for mtc ue in wireless communication system

Info

Publication number: WO2017030345A1
Application number: PCT/KR2016/008983
Authority: WO
Inventors: Yunjung Yi
Original assignee: Lg Electronics Inc.
Priority date: 2015-08-14
Filing date: 2016-08-16
Publication date: 2017-02-23

Abstract

A method and apparatus for performing transmission in a wireless communication system is provided. A base station (BS) transmits a configuration of whether to enable or disable frequency hopping for transmission to a machine-type communication (MTC) user equipment (UE) in a cell, and performs transmission to the MTC UE according to the configuration.

Description

METHOD AND APPARATUS FOR PERFORMING FREQUENCY HOPPING FOR MTC UE IN WIRELESS COMMUNICATION SYSTEM

The present invention relates to wireless communications, and more particularly, to a method and apparatus for performing frequency hopping for a machine-type communication (MTC) user equipment (UE) in a wireless communication system.

3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

In the future versions of the LTE-A, it has been considered to configure low-cost/low-end (or, low-complexity) user equipments (UEs) focusing on the data communication, such as meter reading, water level measurement, use of security camera, vending machine inventory report, etc. For convenience, these UEs may be called machine type communication (MTC) UEs. Since MTC UEs have small amount of transmission data and have occasional uplink data transmission/downlink data reception, it is efficient to reduce the cost and battery consumption of the UE according to a low data rate. Specifically, the cost and battery consumption of the UE may be reduced by decreasing radio frequency (RF)/baseband complexity of the MTC UE significantly by making the operating frequency bandwidth of the MTC UE smaller.

In the current LTE specification, all UEs shall support maximum 20MHz system bandwidth, which requires baseband processing capability to support 20MHz bandwidth. To reduce hardware cost and battery power of MTC UEs, reducing bandwidth is a very attractive option. To enable narrowband MTC UEs, the current LTE specification shall be changed to allow narrowband UE category. If the serving cell has small system bandwidth (smaller than or equal to bandwidth that narrow-band UE can support), the UE can attach based on the current LTE specification.

There may be possibly multiple narrowbands defined in the system bandwidth, and a MTC UE may monitor only one or a few narrowbands at the same time. In this case, frequency hopping across narrowbands defined in the system bandwidth may be considered to maximize frequency diversity gain. An efficient method for performing frequency hopping for MTC UEs may be required.

The present invention provides a method and apparatus for performing frequency hopping for a machine-type communication (MTC) user equipment (UE) in a wireless communication system. The present invention discusses frequency hopping mechanism across narrowbands for MTC UEs for both downlink and uplink transmission.

In an aspect, a method for performing, by a base station (BS), transmission in a wireless communication system is provided. The method includes transmitting a configuration of whether to enable or disable frequency hopping for transmission to a machine-type communication (MTC) user equipment (UE) in a cell, and performing transmission to the MTC UE according to the configuration.

In another aspect, a base station (BS) in a wireless communication system is provided. The base station includes a memory, a transceiver, and a processor, coupled to the memory and the transceiver, that controls the transceiver to transmit a configuration of whether to enable or disable frequency hopping for transmission to a machine-type communication (MTC) user equipment (UE) in a cell, and controls the transceiver to perform transmission to the MTC UE according to the configuration.

Frequency hopping for MTC UEs can be performed efficiently.

FIG. 1 shows a wireless communication system.

FIG. 2 shows structure of a radio frame of 3GPP LTE.

FIG. 3 shows a resource grid for one downlink slot.

FIG. 4 shows structure of a downlink subframe.

FIG. 5 shows structure of an uplink subframe.

FIG. 6 shows an example of narrowbands in 3/5/10MHz system bandwidth for TDD.

FIG. 7 shows an example of narrowbands in 10/20MHz system bandwidth for FDD DL.

FIG. 8 shows simulation results according to different frequency hopping mechanisms.

FIG. 9 shows an example of two groups of narrowbands at the edge of the system bandwidth.

FIG. 10 shows a method for performing transmission according to an embodiment of the present invention.

FIG. 11 shows a wireless communication system to implement an embodiment of the present invention.

Techniques, apparatus and systems described herein may be used in various wireless access technologies such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. The CDMA may be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. The TDMA may be implemented with a radio technology such as global system for mobile communications (GSM)/general packet radio service (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMA may be implemented with a radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved-UTRA (E-UTRA) etc. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved-UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE employs the OFDMA in downlink (DL) and employs the SC-FDMA in uplink (UL). LTE-advance (LTE-A) is an evolution of the 3GPP LTE. For clarity, this application focuses on the 3GPP LTE/LTE-A. However, technical features of the present invention are not limited thereto.

FIG. 1 shows a wireless communication system. The wireless communication system 10 includes at least one evolved NodeB (eNB) 11. Respective eNBs 11 provide a communication service to particular

geographical areas

15a, 15b, and 15c (which are generally called cells). Each cell may be divided into a plurality of areas (which are called sectors). A user equipment (UE) 12 may be fixed or mobile and may be referred to by other names such as mobile station (MS), mobile terminal (MT), user terminal (UT), subscriber station (SS), wireless device, personal digital assistant (PDA), wireless modem, handheld device. The eNB 11 generally refers to a fixed station that communicates with the UE 12 and may be called by other names such as base station (BS), base transceiver system (BTS), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongs is called a serving cell. An eNB providing a communication service to the serving cell is called a serving eNB. The wireless communication system is a cellular system, so a different cell adjacent to the serving cell exists. The different cell adjacent to the serving cell is called a neighbor cell. An eNB providing a communication service to the neighbor cell is called a neighbor eNB. The serving cell and the neighbor cell are relatively determined based on a UE.

This technique can be used for DL or UL. In general, DL refers to communication from the eNB 11 to the UE 12, and UL refers to communication from the UE 12 to the eNB 11. In DL, a transmitter may be part of the eNB 11 and a receiver may be part of the UE 12. In UL, a transmitter may be part of the UE 12 and a receiver may be part of the eNB 11.

The wireless communication system may be any one of a multiple-input multiple-output (MIMO) system, a multiple-input single-output (MISO) system, a single-input single-output (SISO) system, and a single-input multiple-output (SIMO) system. The MIMO system uses a plurality of transmission antennas and a plurality of reception antennas. The MISO system uses a plurality of transmission antennas and a single reception antenna. The SISO system uses a single transmission antenna and a single reception antenna. The SIMO system uses a single transmission antenna and a plurality of reception antennas. Hereinafter, a transmission antenna refers to a physical or logical antenna used for transmitting a signal or a stream, and a reception antenna refers to a physical or logical antenna used for receiving a signal or a stream.

FIG. 2 shows structure of a radio frame of 3GPP LTE. Referring to FIG. 2, a radio frame includes 10 subframes. A subframe includes two slots in time domain. A time for transmitting one subframe is defined as a transmission time interval (TTI). For example, one subframe may have a length of 1ms, and one slot may have a length of 0.5ms. One slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain. Since the 3GPP LTE uses the OFDMA in the DL, the OFDM symbol is for representing one symbol period. The OFDM symbols may be called by other names depending on a multiple-access scheme. For example, when SC-FDMA is in use as a UL multi-access scheme, the OFDM symbols may be called SC-FDMA symbols. A resource block (RB) is a resource allocation unit, and includes a plurality of contiguous subcarriers in one slot. The structure of the radio frame is shown for exemplary purposes only. Thus, the number of subframes included in the radio frame or the number of slots included in the subframe or the number of OFDM symbols included in the slot may be modified in various manners.

The wireless communication system may be divided into a frequency division duplex (FDD) scheme and a time division duplex (TDD) scheme. According to the FDD scheme, UL transmission and DL transmission are made at different frequency bands. According to the TDD scheme, UL transmission and DL transmission are made during different periods of time at the same frequency band. A channel response of the TDD scheme is substantially reciprocal. This means that a DL channel response and a UL channel response are almost the same in a given frequency band. Thus, the TDD-based wireless communication system is advantageous in that the DL channel response can be obtained from the UL channel response. In the TDD scheme, the entire frequency band is time-divided for UL and DL transmissions, so a DL transmission by the eNB and a UL transmission by the UE cannot be simultaneously performed. In a TDD system in which a UL transmission and a DL transmission are discriminated in units of subframes, the UL transmission and the DL transmission are performed in different subframes.

FIG. 3 shows a resource grid for one downlink slot. Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols in time domain. It is described herein that one DL slot includes 7 OFDM symbols, and one RB includes 12 subcarriers in frequency domain as an example. However, the present invention is not limited thereto. Each element on the resource grid is referred to as a resource element (RE). One RB includes 12×7 resource elements. The number N^DL of RBs included in the DL slot depends on a DL transmit bandwidth. The structure of a UL slot may be same as that of the DL slot. The number of OFDM symbols and the number of subcarriers may vary depending on the length of a CP, frequency spacing, etc. For example, in case of a normal cyclic prefix (CP), the number of OFDM symbols is 7, and in case of an extended CP, the number of OFDM symbols is 6. One of 128, 256, 512, 1024, 1536, and 2048 may be selectively used as the number of subcarriers in one OFDM symbol.

FIG. 4 shows structure of a downlink subframe. Referring to FIG. 4, a maximum of three OFDM symbols located in a front portion of a first slot within a subframe correspond to a control region to be assigned with a control channel. The remaining OFDM symbols correspond to a data region to be assigned with a physical downlink shared chancel (PDSCH). Examples of DL control channels used in the 3GPP LTE includes a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of a subframe and carries information regarding the number of OFDM symbols used for transmission of control channels within the subframe. The PHICH is a response of UL transmission and carries a HARQ acknowledgment (ACK)/non-acknowledgment (NACK) signal. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes UL or DL scheduling information or includes a UL transmit (TX) power control command for arbitrary UE groups.

The PDCCH may carry a transport format and a resource allocation of a downlink shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information on a paging channel (PCH), system information on the DL-SCH, a resource allocation of an upper-layer control message such as a random access response transmitted on the PDSCH, a set of TX power control commands on individual UEs within an arbitrary UE group, a TX power control command, activation of a voice over IP (VoIP), etc. A plurality of PDCCHs can be transmitted within a control region. The UE can monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate based on a state of a radio channel. The CCE corresponds to a plurality of resource element groups.

A format of the PDCCH and the number of bits of the available PDCCH are determined according to a correlation between the number of CCEs and the coding rate provided by the CCEs. The eNB determines a PDCCH format according to a DCI to be transmitted to the UE, and attaches a cyclic redundancy check (CRC) to control information. The CRC is scrambled with a unique identifier (referred to as a radio network temporary identifier (RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UE may be scrambled to the CRC. Alternatively, if the PDCCH is for a paging message, a paging indicator identifier (e.g., paging-RNTI (P-RNTI)) may be scrambled to the CRC. If the PDCCH is for system information (more specifically, a system information block (SIB) to be described below), a system information identifier and a system information RNTI (SI-RNTI) may be scrambled to the CRC. To indicate a random access response that is a response for transmission of a random access preamble of the UE, a random access-RNTI (RA-RNTI) may be scrambled to the CRC.

FIG. 5 shows structure of an uplink subframe. Referring to FIG. 5, a UL subframe can be divided in a frequency domain into a control region and a data region. The control region is allocated with a physical uplink control channel (PUCCH) for carrying UL control information. The data region is allocated with a physical uplink shared channel (PUSCH) for carrying user data. When indicated by a higher layer, the UE may support a simultaneous transmission of the PUSCH and the PUCCH. The PUCCH for one UE is allocated to an RB pair in a subframe. RBs belonging to the RB pair occupy different subcarriers in respective two slots. This is called that the RB pair allocated to the PUCCH is frequency-hopped in a slot boundary. This is said that the pair of RBs allocated to the PUCCH is frequency-hopped at the slot boundary. The UE can obtain a frequency diversity gain by transmitting UL control information through different subcarriers according to time.

UL control information transmitted on the PUCCH may include a HARQ ACK/NACK, a channel quality indicator (CQI) indicating the state of a DL channel, a scheduling request (SR), and the like. The PUSCH is mapped to a UL-SCH, a transport channel. UL data transmitted on the PUSCH may be a transport block, a data block for the UL-SCH transmitted during the TTI. The transport block may be user information. Or, the UL data may be multiplexed data. The multiplexed data may be data obtained by multiplexing the transport block for the UL-SCH and control information. For example, control information multiplexed to data may include a CQI, a precoding matrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Or the UL data may include only control information.

Low complexity UEs are targeted to low-end (e.g. low average revenue per user, low data rate, delay tolerant) applications, e.g. some machine-type communications (MTC). A low complexity UE has reduced Tx and Rx capabilities compared to other UE of different categories. Among low complexity UEs, a bandwidth reduced low complexity (BL) UE may operate in any LTE system bandwidth but with a limited channel bandwidth of 6 PRBs (corresponding to the maximum channel bandwidth available in a 1.4MHz LTE system) in DL and UL. A BL UE may a transport block size (TBS) limited to 1000 bit for broadcast and unicast.

When a UE performs initial access towards a specific cell, the UE may receive master information block (MIB), system information block (SIB) and/or radio resource control (RRC) parameters for the specific cell from an eNB which controls the specific cell. Further, the UE may receive PDCCH/PDSCH from the eNB. In this case, the MTC UE should have broader coverage than the legacy UE. Accordingly, if the eNB transmits MIB/SIB/RRC parameters/PDCCH/PDSCH to the MTC UE with same scheme as the legacy UE, the MTC UE may have difficulty for receiving MIB/SIB/RRC parameters/PDCCH/PDSCH. To solve this problem, when the eNB transmits MIB/SIB/RRC parameters/PDCCH/PDSCH to the MTC UE having coverage issue, the eNB may apply various schemes for coverage enhancement, e.g. subframe repetition, subframe bundling, etc.

Hereinafter, the present invention discusses details on narrowband definition and frequency hopping mechanism for MTC UEs. Hereinafter, a MTC UE, a UE requiring coverage enhancement (CE), a low cost UE, a low end UE, a low complexity UE, a narrow(er) band UE, a small(er) band UE, a new category UE, or a BL UE may have the same meaning, and may be used mixed. Or, just a UE may refer one of UEs described above. Further, in the description below, a case where system bandwidth of available cells is larger than bandwidth that new category narrowband UEs can support may be assumed. For the new category UE, it may be assumed that only one narrow-band is defined. In other words, all narrow-band UE shall support the same narrow bandwidth smaller than 20MHz. It may be assumed that the narrow bandwidth is larger than 1.4MHz (6 PRBs). However, the present invention can be applied to narrower bandwidth less than 1.4MHz as well (e.g. 200 kHz), without loss of generality. Furthermore, in terms of UL transmission, a UE may be configured or scheduled with single or less than 12 tones (i.e. subcarriers) in one UL transmission to enhance the coverage by improving peak-to-average power ratio (PAPR) and channel estimation performance.

1. Multiple narrowband formation

(1) Narrowband(s) with smaller than 6 PRBs

Depending on the formation of narrowband and/or the system bandwidth of a carrier, there may be one or two set of PRB(s) which cannot form non-overlapped 6 PRBs narrowband(s). Since resource allocation at least for normal coverage is performed per narrowband, to allow accessing all PRBs by a MTC UE, narrowband(s) with small PRB size(s), i.e. smaller than 6 PRBs, may be defined. For example, in a system bandwidth of 50 PRBs, a narrowband with 2 PRBs may be formed. However, usage of narrowband(s) smaller than 6 PRBs may be restricted. For example, frequency hopping may be restricted to narrowbands with the same size. Also, for channel state information (CSI) feedback, feedback on the narrowbands smaller than 6 PRBs may not be supported.

(2) Formation of narrowband

Narrowband formation may follow one of the following options.

① Narrowband of 6 PRBs starts from the edge of the system bandwidth

② Narrowband of 6 PRBs starts from the lowest PRB

③ Narrowband of 6 PRBs starts from the center

Since it can be easily aligned with UL resources such as PUCCH and physical random access channel (PRACH), the option 1 described above, i.e. narrowband of 6 PRBs starts from the edge of the system bandwidth, may be preferred. Similar to legacy PUCCH, frequency hopping of MTC PUCCH may occur in the same offset from the edge of the system bandwidth. Also, since the center region may be used for physical broadcast channel (PBCH) and primary synchronization signal (PSS)/secondary synchronization signal (SSS), it may be desirable to avoid overlap between narrowband and center region as much as possible. The option 3 described above, i.e. narrowband of 6 PRBs starts from the center, may need to address different system bandwidth. For example, a narrowband with 6 PRBs in odd system bandwidth may need to be shifted by 0.5PRB in either direction. Thus, overall, defining center narrowband may not be so effective. Given additional complexity and/or alignment with legacy channels and UL transmissions, the option 1 described above should be adopted at least for TDD.

FIG. 6 shows an example of narrowbands in 3/5/10MHz system bandwidth for TDD. FIG. 6-(a) shows a case that a system bandwidth is 3MHz. FIG. 6-(b) shows a case that a system bandwidth is 5MHz. FIG. 6-(c) shows a case that a system bandwidth is 10MHz. Referring to FIG. 6, NB0 (PRBs 0~5) starts from an edge of the system bandwidth, and NB1 (PRBs 9-14 in FIG. 6-(a), PRBs 19-24 in FIG. 6-(b), PRBs 44-49 in FIG. 6-(c)) starts from the other edge (i.e. the opposite edge) of the system bandwidth, and so on.

For FDD, when determining potential locations of narrowband, impacts on legacy UEs may be considered. For example, narrowband may be formed aligned with resource block group (RBG) as much as possible so that wasted resource can be minimized when multiple narrowbands are multiplexed with PDSCHs for legacy UEs. In the 10MHz system bandwidth, since 3 PRBs is the unit of RBG, narrowband may start from the first PRB. In this case, the option 2 may be used for FDD DL and the option 1 may be used for FDD UL with possible offset for legacy PRACH/PUCCH region.

FIG. 7 shows an example of narrowbands in 10/20MHz system bandwidth for FDD DL. FIG. 7-(a) shows a case that a system bandwidth is 10MHz. FIG. 7-(b) shows a case that a system bandwidth is 20MHz. Referring to FIG. 7, narrowband of 6 PRBs starts from the lowest PRB, i.e. the first PRB.

Furthermore, for the simplicity and uniform formation, the same format based on the option 1 may be adopted. In summary, at least for TDD, narrowband may be formed from the edge of the system bandwidth.

(3) Signaling of narrowbands allocated for MTC UEs

Since narrowband formation may be different depending on system bandwidth, repeated PBCHs may be transmitted through center 6 PRBs, which is similar to legacy PBCH. Even though the possible location of narrowbands are prefixed, to allow network flexibility to adjust the resource amount allocated to MTC UEs with respect to legacy UEs, signaling of a set of subbands usable for MTC UEs may be necessary. At least, for cell-common data such as SIB, paging and random access response (RAR), a subset of subbands may be prefixed or signaled via PBCH or SIB. At least in case the network supports enhanced coverage, frequency hopping for MTC SIB-1 may always be used at least system bandwidth larger than 5MHz. Further, the frequency location of MTC SIB-1 may be determined based on subframe index (and/or system frame number (SFN)), cell ID and system bandwidth.

To determine frequency hopping pattern of MTC SIB-1 as a function of cell ID and system bandwidth, frequency hopping may be performed between two narrowbands formed in the edge (e.g. narrowband 0 and 1). To minimize potential impacts on scheduling to legacy UEs, the edge narrowbands used for MTC SIB-1 transmission may be fixed regardless of cell ID. If inter-cell randomization is necessary, different hopping pattern in time-domain based on cell ID may be considered. For example, narrowband location of MTC SIB-1 may be determined as floor (SFN / K) % 2, where K = (cell ID % M) + 1 (e.g. M = 4). In other words, the interval between frequency hopping may be different from each other based on cell ID. More particularly, M may be multiple of periodicity of SIB-1 transmission. For example, if SIB-1 is transmitted in every 20ms, K may be replaced with K*2 in the equation described above. In other words, for a set of cells, every SIB transmission may change frequency location, and for another set of cells, frequency location may change in every two SIB transmissions, and so on. The same frequency hopping pattern may be used for paging, or a UE may assume that paging and/or other channels may not be mapped to MTC SIB transmissions which are known in prior regardless of whether SIB actually has been transmitted or not.

Indication of available narrowbands to MTC UEs may be performed via SIB transmission. That is, a subset of narrowbands may be signaled for MTC UEs by SIB. For example, a bitmap may be signaled via SIB transmission to indicate which narrowband(s) are usable for MTC UEs. For another example, the number of narrowbands usable for MTC UEs, from the lowest narrowband index, may be signaled via SIB transmission to MTC UEs. If explicit signaling is not available, a MTC UE may assume that all narrowbands defined in a system bandwidth is available to MTC UEs.

2. Frequency hopping

(1) Frequency hopping enabling/disabling configuration

Even though frequency hopping achieves better performance, it may impact the scheduling of legacy UEs. For example, if distributed virtual resource block (DVRB) is used for scheduling on legacy UEs, it may become difficult to avoid overlap with scheduled PDSCH of legacy UEs if frequency hopping is used. Thus, it is generally desirable to allow configurability of enabling/disabling of frequency hopping. Since it is generally beneficial to apply frequency hopping to all channels, enabling/disabling of frequency hopping per UE may be sufficient for unicast channels. For common channels, cell-common signaling may be necessary. If some MTC UEs perform frequency hopping and other MTC UEs do not perform frequency hopping, the overlap/collision between two groups should be addressed. Accordingly, in order to avoid collision between two groups, resources usable for frequency hopping region and non-frequency hopping region may be divided such that frequency hopping occurs only in the frequency hopping region. For example, if there are K narrowbands in the system bandwidth, only K1 narrowbands may be used for MTC UEs performing frequency hopping and the frequency hopping pattern may be applied only within K1 narrowbands. The remaining narrowbands (i.e. K-K1 narrowbands) may be used for MTC UEs not performing frequency hopping. To avoid such a case, cell-common enabling/disabling of frequency hopping may be more preferred.

(2) Frequency hopping via narrowband switching

In the same subframe, it is expected that legacy UEs are multiplexed with MTC UEs. As legacy UEs do not utilize frequency hopping for DL transmission, multiplexing between legacy UEs and MTC UEs may become complicated due to potential overlap/collision, if frequency hopping of MTC UE spans the entire system bandwidth. Accordingly, as mentioned above, resource separation between MTC UEs and legacy UEs may be desirable. For the simplicity, MTC UEs may be configured with a set of narrowbands where frequency hopping only spans resources belonging to the configured set of narrowbands. To minimize the overlap/collision among different UEs which perform frequency hopping within those resources, a common frequency hopping pattern may be used, which is applied regardless of actual transmission. Meanwhile, cross-subframe channel estimation may be used for unicast data transmission. To support both techniques, i.e. a cell common frequency hopping pattern and cross-subframe channel estimation, frequency hopping may occur in every L subframes, where L is the number of subframes used for cross-subframe channel estimation. For a cell-common frequency hopping pattern, L may be a common for all UEs performing frequency hopping. If a set of narrowbands are separately configured per each coverage class, hopping pattern per coverage class may also be considered.

Overall, two frequency hopping patterns may be considered. For the first frequency hopping pattern, frequency hopping may occur in every L subframes (either L is cell-common or L is different per coverage class). For the second frequency hopping pattern, frequency hopping may occur in every P subframes (P is determined based on the number of repetition). The first frequency hopping pattern is more generic and may be more efficient to handle multiple UEs/channels with different number of repetitions. Furthermore, in terms of MTC PDCCH (M-PDCCH), it may become more complicated to apply the second frequency hopping pattern, since a UE needs to blindly search more than one repetition level for M-PDCCH. In other words, M-PDCCH candidates with different repetition levels may have different frequency hopping pattern. In such a case, a UE may have to monitor different narrowbands per each repetition level.

FIG. 8 shows simulation results according to different frequency hopping mechanisms. It is assumed that PDSCH repetition number N is 200. Referring to FIG. 8, overall frequency hopping gain may increase as the number of narrowbands used for frequency hopping increases. That is, frequency hopping gain with 2 narrowbands is better than no frequency hopping, and frequency hopping gain with 4 narrowbands is better than frequency hopping gain with 2 narrowbands. Further, frequency hopping gain with the first frequency hopping pattern (i.e. in every L subframes) is better than frequency hopping gain with the second frequency hopping pattern (i.e. in every P subframes). That is, frequency hopping gain with 4 narrowbands in 5ms period (i.e. L=5) is better than frequency hopping gain with 4 narrowbands in 51ms period (i.e. P=51), and frequency hopping gain with 2 narrowbands in 5ms period (i.e. L=5) is better than frequency hopping gain with 2 narrowbands in 101ms period (i.e. P=101).

In summary, the first frequency hopping pattern shows has slight benefit over the second frequency hopping pattern, though the different is marginal. Though the first frequency hopping pattern may increase the overall latency of data transmission/reception, in terms of multiplexing among different channels/UEs and frequency hopping for M-PDCCH, the first frequency hopping pattern may be preferred. That is, frequency hopping pattern may be cell-common, and if applied, frequency hopping may occur in every L subframes where L is a cell-common value. Separating frequency hopping pattern per coverage class or not may depend on the number of available narrowbands. Given that it is desirable to use at least four narrowbands for frequency hopping for a channel and there are at least three coverage levels in the system, it seems to be more straightforward to use a cell-common value L.

Meanwhile, before designing the details of frequency hopping, the requirements and properties of the frequency hopping pattern should be considered. In the discussion below, it may be assumed that the term "time unit" is used narrowband switching takes place at the boundary of each time unit. Some desirable properties of the frequency hopping pattern may be as follows.

The eNB should be able to control the number of narrowbands used for frequency hopping. This is to allow the network controllability in consideration of the traffic load for MTC UEs and normal UEs.

Two narrowbands used in two adjacent time units should be separated as much as possible in the frequency domain. This can provide the maximal frequency diversity when repeated transmissions spans a relatively small number of time units.

Restriction on normal UE scheduling should be minimized. Especially when a small number of narrowbands are configured in UL, these narrowbands need to be located at the edge of the system bandwidth so that all the remaining PRBs around the center can be contiguously allocated to a single PUSCH from a normal UE. PUCCH region can be located outside of the narrowbands.

Each hopping pattern should be able to use a sufficiently large number of narrowbands among those configured for MTC UEs. When a large number of narrowbands are configured, frequency hopping across many narrowbands can maximize the frequency diversity.

FIG. 9 shows an example of two groups of narrowbands at the edge of the system bandwidth. FIG. 9-(a) shows a case that a small number of narrowbands are configured, and FIG. 9-(b) shows a case that a large number of narrowbands are configured. The network may configure the size of each narrowband group according to the traffic load of MTC UEs. Different number of narrowbands may be configured in DL and UL due to the potential difference in traffic intensity. The PRBs located between the two narrowband groups may be allocated to normal UEs, and a wideband transmission with single carrier property is possible from a single normal UE in UL, thereby satisfying the property 3. For the property 2, the frequency hopping needs to alternate between the two narrowband groups, i.e. narrowband group #0 at time unit x, x+2, x+4,... and narrowband group #1 at time unit x+1, x+3, x+5,.... At the same time, for the property 4, the narrowband used in each narrowband group needs to change, i.e. different narrowbands are used in time unit x and time unit x+2, although they belong to the same narrowband group.

Further, in terms of allocating narrowbands for frequency hopping, whether to allocate common narrowbands for broadcast and unicast transmissions needs to be considered. If narrowbands are common, updating the set of narrowbands usable for unicast transmission becomes complicated, since it also affects transmission of common data. If narrowbands for broadcast transmission and unicast transmission are separately configured with possible overlap, some collision cases should be addressed. If narrowbands for broadcast transmission and unicast transmission are separately configured and resources are disjoint, resources used for frequency hopping of cell common data may be utilized. Overall, it is desirable to avoid possible collision by applying the same frequency hopping pattern. However, if it is necessary for the flexibility, applying separate resources for broadcast transmission and unicast transmission for frequency hopping may be considered.

In summary, frequency hopping may be achieved via narrowband switching. Virtual narrowband concept may be adopted where physical narrowband resource can be determined based on frequency hopping pattern and other cell common parameters.

(3) Narrowband switching gap

Though exact length of frequency retuning gap is not determined, it is generally expected that at least a few OFDM symbols may be necessary. For the simplicity, frequency retuning gap may be fixed as 1ms (i.e. 1 subframe). When the unit of narrowband switching (L) is fixed as a common value, if all MTC UEs use the last subframe in every L subframes as a gap, there will be no MTC UEs schedulable in that subframe when all MTC UEs are performing frequency hopping. Thus, it is desirable to mix some UEs with a gap in the first subframe in every L subframes and some UEs with a gap in the last subframe in every L subframes.

Further, reducing frequency hopping occurrence may enhance the performance with low mobility, as it may allow more opportunities of multi-subframe channel estimation. Thus, L should be large enough. L may 8 or 16. L may be different per coverage class. If narrowbands are shared among different UEs with different coverage class, it is desirable to use multiple of the lowest coverage level's L for other coverage class (e.g. 4 for CE level 1, 8 for CE level 2, etc.).

FIG. 10 shows a method for performing transmission according to an embodiment of the present invention. The present invention described above may be applied to this embodiment of the present invention.

In step S100, the BS transmits a configuration of whether to enable or disable frequency hopping for transmission to a MTC UE in a cell. The configuration may be transmitted to all MTC UEs in the cell by cell-specifically. In this case, the transmission to the MTC UE may correspond to all channels for the all MTC UEs in the cell, or may correspond to common channels for the all MTC UEs in the cell. Alternatively, the configuration may be transmitted per each MTC UEs in the cell by UE-specifically.

In step S100, the BS performs transmission to the MTC UE according to the configuration. The transmission to the MTC UE may be performed with frequency hopping if the configuration configures enabling of the frequency hopping. The frequency hopping may be applied within a frequency hopping region including a number of narrowbands. A system bandwidth may be divided into the frequency hopping region and a non-frequency hopping region, and the frequency hopping region and the non-frequency hopping region may not overlap with each other. The transmission to the MTC UE may be performed without frequency hopping if the configuration configures disabling of the frequency hopping.

A BS 800 may include a processor 810, a memory 820 and a transceiver 830. The processor 810 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 810. The memory 820 is operatively coupled with the processor 810 and stores a variety of information to operate the processor 810. The transceiver 830 is operatively coupled with the processor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a transceiver 930. The processor 910 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 910. The memory 920 is operatively coupled with the processor 910 and stores a variety of information to operate the processor 910. The transceiver 930 is operatively coupled with the processor 910, and transmits and/or receives a radio signal.

The

processors

810, 910 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The

memories

820, 920 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. The

transceivers

830, 930 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in

memories

820, 920 and executed by

processors

810, 910. The

memories

820, 920 can be implemented within the

processors

810, 910 or external to the

processors

810, 910 in which case those can be communicatively coupled to the

processors

810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope and spirit of the present disclosure.

Claims

A method for performing, by a base station (BS), transmission in a wireless communication system, the method comprising:

transmitting a configuration of whether to enable or disable frequency hopping for transmission to a machine-type communication (MTC) user equipment (UE) in a cell; and

performing transmission to the MTC UE according to the configuration.
The method of claim 1, wherein the configuration is transmitted to all MTC UEs in the cell by cell-specifically.
The method of claim 2, wherein the transmission to the MTC UE corresponds to all channels for the all MTC UEs in the cell.
The method of claim 2, wherein the transmission to the MTC UE corresponds to common channels for the all MTC UEs in the cell.
The method of claim 1, wherein the configuration is transmitted per each MTC UEs in the cell by UE-specifically.
The method of claim 1, wherein the transmission to the MTC UE is performed with frequency hopping if the configuration configures enabling of the frequency hopping.
The method of claim 6, wherein the frequency hopping is applied within a frequency hopping region including a number of narrowbands.
The method of claim 7, wherein a system bandwidth is divided into the frequency hopping region and a non-frequency hopping region, and

wherein the frequency hopping region and the non-frequency hopping region do not overlap with each other.
The method of claim 1, wherein the transmission to the MTC UE is performed without frequency hopping if the configuration configures disabling of the frequency hopping.
A base station (BS) in a wireless communication system, the base station comprising:

a memory;

a transceiver; and

a processor, coupled to the memory and the transceiver, that:

controls the transceiver to transmit a configuration of whether to enable or disable frequency hopping for transmission to a machine-type communication (MTC) user equipment (UE) in a cell, and

controls the transceiver to perform transmission to the MTC UE according to the configuration.
The BS of claim 10, wherein the configuration is transmitted to all MTC UEs in the cell by cell-specifically.
The BS of claim 11, wherein the transmission to the MTC UE corresponds to all channels for the all MTC UEs in the cell.
The BS of claim 11, wherein the transmission to the MTC UE corresponds to common channels for the all MTC UEs in the cell.
The BS of claim 10, wherein the configuration is transmitted per each MTC UEs in the cell by UE-specifically.