WO2018137517A1

WO2018137517A1 - Method and apparatus for transmitting signals

Info

Publication number: WO2018137517A1
Application number: PCT/CN2018/072893
Authority: WO
Inventors: Hua Xu
Original assignee: Guangdong Oppo Mobile Telecommunications Corp., Ltd.
Priority date: 2017-01-27
Filing date: 2018-01-16
Publication date: 2018-08-02
Also published as: TWI676380B; TW201828632A; CN109792372A; CN109792372B

Abstract

A method and an apparatus for transmitting signals are provided, in which all control channel elements (CCEs) of a physical downlink control channel (PDCCH) candidate are allocated to an orthogonal frequency division multiplexing (OFDM) symbol and transmitting a PDCCH using the PDCCH candidate on the OFDM symbol.

Description

METHOD AND APPARATUS FOR TRANSMITTING SIGNALS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 62/451,256, field on January 27, 2017, the disclosure of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of communication, and particularly to a method and apparatus for transmitting signals.

BACKGROUND

In a long term evolution (LTE) system, the physical downlink control channel (PDCCH) is transmitted in the first several orthogonal frequency division multiplexing (OFDM) symbols span the whole system bandwidth at the beginning of a subframe.

In a 5G new radio (NR) system, compared with LTE, more spectrum would be used especially at higher frequency bandwidth (>6GHz) and some new techniques such as beamforming (BF) are adopted. The use of BF on one side would improve the BF gain and reduce the interference, and on the other side, the wavelength at higher frequency will reduce the size of antennas array and make its implementation feasible. The PDCCH could also benefit from BF transmission to guarantee its coverage and robustness.

In a 5G NR system, how to design PDCCH while supporting and using BF effectively has become a problem to be solved.

SUMMARY

The present disclosure describes a PDCCH design with BF in mind which is novel and different from that in LTE system.

In one embodiment, techniques can include provide a method for transmitting signals in which all control channel elements (CCEs) of a PDCCH candidate are allocated to an OFDM symbol and a PDCCH is transmitted using the PDCCH candidate on the OFDM symbol.

In one embodiment, techniques can include provide a method for transmitting signals in which a set of PDCCH candidates is configured for a PDCCH and the PDCCH is transmitted using the set of PDCCH candidates on different OFDM symbols repeatedly.

In one embodiment, techniques can include provide a method for transmitting signals in which a set of PDCCH candidates is configured for the PDCCH and the set of PDCCH candidates is split to different OFDM symbols.

In one embodiment, techniques can include provide a method for transmitting signals in which the PDCCH is transmitted with different beams using PDCCH candidates allocated to the same OFDM symbol.

In one embodiment, techniques can include provide a method for allocating resources in which all CCEs of a PDCCH candidate are allocated to one OFDM symbol.

In one embodiment, techniques can include provide a method for allocating resources in which all PDCCH candidates configured for one PDCCH are allocated to one symbol.

In one embodiment, techniques can include provide a method for allocating resources in which all PDCCH candidates configured for one PDCCH are split to different symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication system.

FIG. 2 illustrates a terminal.

FIG. 3 illustrates a network device.

FIG. 4 illustrates a PDCCH structure in LTE.

FIG. 5 illustrates an example for PDCCH candidates.

FIG. 6 illustrates a beam link pair in a 5G NR system.

FIG. 7 illustrates a schematic diagram in which PDCCH candidates on different OFDM symbols are transmitted with different beams.

FIG. 8 is a schematic diagram in which PDCCH candidates on the same OFDM symbol are transmitted with different beams.

FIG. 9 is a schematic diagram in which a set of PDCCH candidates are split.

FIG. 10 is another schematic diagram in which a set of PDCCH candidates are split.

FIG. 11 is a schematic diagram in which PDCCH candidates are re-allocated.

FIG. 12 is a block diagram of an apparatus for transmitting signals according to an embodiment.

FIG. 13 is a block diagram of an apparatus according to an embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a wireless communication system according to the present disclosure. The wireless communication system may operate on a high frequency band, which includes but not limited to a long term evolution (LTE) system, a future evolved fifth generation (5G) system, a new radio (NR) system, and a machine to machine (M2M) system. The wireless communication system illustrated in FIG. 1 is merely illustrative of the technical solution of the present disclosure and is not intended to limit the scope thereof. It will be appreciated by those of ordinary skill in the art that with the evolution of the network architecture and the emergence of new business scenarios, technical solutions proposed herein can be equally applicable to similar technical problems.

As shown in FIG. 1, the wireless communication system 100 may include one or more network devices 101, one or more terminals 103, and a core network 111.

Network device 101 can be a base station, which can communicate with one or more terminals or base stations with terminal function. In a 5G NR system, the base station can be gNB. Terminal 103 may be distributed throughout the wireless communication system 100, either stationary or mobile. In some embodiments, terminal 103 may be a mobile device, a mobile station, a mobile unit, an M2M terminal, a wireless unit, a remote unit, a user agent, a mobile client and so on. Network device 101 can communicate with terminal 103 under the control of a controller which is not illustrated in the figure. In some embodiments, this controller can be part of core network 111 or can be integrated into network device 101. Network devices 101 may also communicate with each other directly or indirectly through a back-haul interface 107 such as an X2 interface. Network device 101 may be operable to transmit control information or user data to core network 111 through a back-haul interface 109 (e.g., S1 interface) . Terminal 103 can be located within the coverage of one or more cells 105.

FIG. 2 illustrates a terminal 200. Terminal 200 may include one or more terminal processors 201, a memory 202, a communication interface 203, a bus 204, a receiver 205, a transmitter 206, a coupler 207, an antenna 208, a user interface 202, and an input and output device (such as a microphone, a keyboard, a display, and the like) . The processors 201, the communication interface 203, the receiver 205 and the transmitter 206 may be connected via bus 204 or other means. Communication interface 203 may be used for terminal 200 to communicate with other communication devices, such as network devices. Transmitter 206 may be used to transmit signals output from terminal processor 201, such as perform signal modulation. Input/output device 210 may be used to implement the interaction between terminal 200 and users/external environment. Memory 202 is coupled to terminal processor 201 for storing various software programs and/or instructions. Terminal processor 201 may be used to read and execute computer readable instructions such as those stored in memory 202.

FIG. 3 illustrates a network device 300. Network device 300 may be a gNB and include one or more network device processors 301, a memory 302, a communication interface 303, a transmitter 305, a receiver 306. These components may be connected via a bus 304 or other means. As illustrated in FIG. 3, the network device 300 may further include a coupler 307 and an antenna 308 connected to the coupler. Communication interface 303 may be used for network device 300 to communicate with other communication devices, such as a terminal device or other network device. Transmitter 305 may be used to transmit signals output from network device processor 301, such as perform signal modulation. Network device processor 301 can be responsible for wireless channel management, communication links establishment, and cell switching control for users within the control area. Network device processor 301 can also read and executed computer readable instructions such as those stored memory 302 which is coupled thereto.

Terminology

Physical downlink control channel (PDCCH) : PDCCH is a set of physical resource particles that carry downlink control information, including transmission format, resource allocation, uplink scheduling permission, power control and uplink retransmission information and the like.

In LTE, as illustrated in FIG. 4, the PDCCH is transmitted at one or more sets of resource called control channel element (CCE) , and each CCE are further divided into a number of resource element groups (REGs) . The REGs from different PDCCHs are interleaved and spread across the whole downlink (DL) control region to obtain diversity gain.

PDCCH candidate: PDCCH candidate is a set of time-frequency resource element (REs) that could be used to transmit PDCCH. A set of PDCCH candidates including at least one candidate can be configured for one PDCCH.

CCE aggregation level (AL) : CCE AL represents the number of consecutive CCEs a PDCCH occupies. Different CCE ALs can be used to adapt to different performance requirements for PDCCH. For each CCE AL, there can be a number of PDCCH candidates.

When scheduling UE, the eNB would select the right CCE AL and candidate and use that set of time-frequency resources to transmit PDCCH. At UE side, it would blind decode on these PDCCH candidates until it finds its PDCCH. Different PDCCH candidates at different CCE AL could overlap in time-frequency as illustrated in FIG. 5. As can be seen from FIG. 5, CCE AL=1 means that one PDCCH candidate occupies one CCE, similarly, CCE AL=3 means that one PDCCH candidate occupies three CCE.

Beam link pair (BLP) and application thereof

In a 5G NR system, as mentioned above, BF can be adopted, and both system and UE could use transmit BF and receive BF to increase the BF gain. As illustrated in FIG. 6, different transmit beam and receive beam could form different BLP and the reception performance on each BLP could be different.

From transmission perspective, if analog BF technique is used, the whole OFDM symbol could be transmitted on the same beam. Therefore, to make sure that PDCCH could be transmitted on the right beam to the UE, the system may use different beams at different time to transmit PDCCH to the UE. Such behavior could be transparent to the UE as switch could happen dynamically and system may not send any signal to inform UE such change prior to the PDCCH transmission. With such issue in mind, the PDCCH candidates and search space could be designed to cope with it and improve the BLP switch and robustness of PDCCH transmission.

Allocation of a whole PDCCH candidate

As one implementation, in a method for transmitting signals, all control channel elements (CCEs) of a PDCCH candidate are allocated to one OFDM symbol and a PDCCH will be transmitted using the PDCCH candidate on the OFDM symbol. This can be better understood from figures such as FIG. 7 and FIG. 8, in which each block on the OFDM symbol represents a candidate. In this way, the UE could simply search for its PDCCH candidates on the 1 ^st symbol first, and if it does not decode anything correctly, it can start to search for its PDCCH candidates on the 2 ^nd symbol and so on so forth, and therefore, it could facilitate UE blind decoding (BD) .

It should be noted that for easy of explanation, OFDM symbol is used as an example herein, however, the proposal can be equally applied to other symbols such as single-carrier frequency-division multiple access (SC-FDMA) symbol as well as other symbols or carriers that may appear in the future and configured to carry PDCCH.

The difference between this proposal and the one adopted in LTE as illustrated in FIG. 4 is that here, a whole PDCCH candidate (along with corresponding CCEs) is allocated to the same OFDM symbol. In other words, resources allocation is conducted in units of candidate rather than REG.

While in LTE system as shown in FIG. 4, the REGs of the same PDCCH candidate are allocated across different OFDM symbols within the control region, and as can be seen from the figure, each block on the symbol represents a REG. Such difference between this proposal and LTE is due to different motivations (and techniques used) behind. In LTE, BF technique is not used for PDCCH, therefore, the PDCCH is divided into a number of CCE and further into groups of REGs, and REGs of different PDCCH (s) are interleaved and allocated onto different OFDM symbols to obtain diversity gain in both time and frequency. For comparison, in a 5G NR system, BF is used and different OFDM symbols are used to transmit on different transmit beams.

As mentioned before, a set of PDCCH candidates, which may include one or more PDCCH candidates, can be configured for one PDCCH, and based on this, how to allocate the PDCCH candidates of one PDCCH on OFDM symbols as well as how to transmit PDCCH is hereinafter discussed. For example, in a method for transmitting signals, a set of PDCCH candidates configured for one PDCCH can be allocated to one OFDM symbol, and the PDCCH can be transmitted on the OFDM symbol with different beams using the set of PDCCH candidates. The PDCCH can be transmitted on different OFDM symbols repeatedly. Alternatively, a set of PDCCH candidates configured for one PDCCH can be split to different OFDM symbols, namely, two or more than two OFDM symbols, and PDCCH can be transmitted on the different OFDM symbols with the same or different beams. These technical solutions will be described in detail below respectively.

Implementation 1

In this implementation, we will discuss how to transmit PDCCH using PDCCH candidates on different OFDM symbols.

As illustrated in FIG. 7, PDCCH candidates are allocated to different OFDM symbols and PDCCH can be transmitted using the PDCCH candidates with different directional beams respectively. PDCCH candidates for PDCCH #1 and PDCCH #2 are allocated to different OFDM symbols (OFDM symbol #1 and OFDM symbol #2) respectively and different beams are used to transmit PDCCH on each OFDM symbol. This could facilitate the transmission of PDCCH on different transmit beams, and hence reduce the risk of beam mismatch and increase the robustness of PDCCH transmission.

The PDCCH candidates (in FIG. 7, only one candidate is illustrated on one OFDM symbol for each PDCCH) could be repeated and allocated to different OFDM symbols and therefore PDCCH using these PDCCH candidates could be transmitted on different OFDM symbols with different beams repeatedly. Referring to FIG. 7, the PDCCH candidates (along with corresponding CCEs) allocated to OFDM symbol #1 are repeatedly allocated to OFDM symbol #2.

In terms of one PDCCH, the PDCCH candidates configured for it can be allocated to one OFDM symbol.

Alternatively, PDCCH candidates configured for one PDCCH could be split to different symbols and PDCCH can be transmitted using these PDCCH candidates on the different symbols with different beams, that is, different PDCCH candidates (along with corresponding CCEs) can be allocated to different OFDM symbols and PDCCH can be transmitted using these PDCCH candidates on the different OFDM symbols, which will be explained in detail later in Implementation 3.

The different/same PDCCH candidates (along with all corresponding CCEs) can be allocated to different OFDM symbols and PDCCH can be transmitted using these PDCCH candidates on different beams thus exploit the BF gain while also avoid the beam mismatch between the system and UE.

Alternatively, PDCCH using PDCCH candidates allocated to different OFDM symbols can be transmitted using the same beams. For example, different OFDM symbols may use the same beam for transmitting if the load on one OFDM symbol is quite small or if few or even no candidate is allocated to the OFDM symbol. Namely, whether the same or different beams will be used for different symbols is not strictly limited and it can be flexibly configured according to loads of symbols for example.

Implementation 2

In this implementation, we discuss how to transmit PDCCH using PDCCH candidates on the same symbol.

Suppose the system side or gNB (which is similar as eNB in LTE and can be other access devices) in a 5G NR system has multiple antenna array transceiver panels, that is, suppose digital BF is adapted, it could form different transmit/receive beams on the same OFDM symbol. In this case, PDCCH using different PDCCH candidates configured for the PDCCH could be transmitted on the same OFDM symbol but from different transmit beams, so as to increase beam coverage and obtain energy gain, this can be especially beneficial when UE is moving.

As illustrated in FIG. 8, PDCCH#1 will be transmitted with different beams using PDCCH candidate #1-a and PDCCH candidate #1-b that fall within the coverage of different beams respectively. This applies equally to PDCCH #2. PDCCH #2 will be transmitted with different beams using PDCCH candidate #2-a and PDCCH candidate #2-b that fall within the coverage of different beams respectively.

Similar to implementation 1, the four PDCCH candidates on the OFDM symbol illustrated in FIG. 8 could be repeatedly allocated to another OFDM symbol and the PDCCH will be transmitted with beams different from those for the OFDM symbol illustrated in FIG. 8.

These implementations could facilitate BD of UE if it does not receive the information on total number of OFDM symbols for control region. The UE could simply search for its PDCCH candidates on the 1 ^st symbol first, and if it does not decode anything correctly, it can start to search for its PDCCH candidates on the 2 ^nd symbol and so on so forth. These approaches also reduce the decoding latency at UE as UE could start decoding PDCCH candidates on the 1 ^st symbol after receiving it without the need to buffer the 2 ^nd and 3 ^rd OFDM symbols before starting the PDCCH decoding process.

However, such repeated allocation as described above could increase the total number of PDCCH candidates and hence increase the total BD of UE. In view of this, another implementation is provided below.

Implementation 3

To maintain the same total BD unchanged, PDCCH candidates could also be split and allocated to different OFDM symbols, as illustrated in FIG. 9 as an example, where PDCCH candidates of different CCE AL are evenly split for different OFDM symbols. The PDCCH candidates allocated to each OFDM symbol could include PDCCH candidates of different CCE AL.

FIG. 10 illustrates another possible split. Different from FIG. 9, the PDCCH candidates are not evenly split in FIG. 10. PDCCH candidates of the same CCE AL can be allocated to different symbols or one symbol. For example, PDCCH candidates of CCE AL=4 are split to OFDM symbol #2. Of course these split manners are merely exemplary and the present disclosure is not limited thereto.

Such PDCCH candidate allocations provided in Implementation 3 could be configured semi-statically and signaled to the UE using a higher layer signal. The configuration could include the total number of PDCCH candidates allocated to each OFDM symbol, the number of PDCCH candidates of each CCE AL allocated to each OFDM symbol, and maybe some information on locations of PDCCH candidates on each OFDM symbol. The configuration may also include the total number of OFDM symbols that the PDCCH candidates for this particular UE could be allocated to, which may or may not be the same as the total number of OFDM symbols for the control region. For example, if the total control region (or control resource set) has three OFDM symbols in time domain, the configuration of a particular UE could only include the first two OFDM symbols, namely, 1 ^st and 2 ^nd OFDM symbols. In another example, the configuration of a particular UE could only include the last two OFDM symbols, namely, 2 ^nd and 3 ^rd OFDM symbols of total three OFDM symbols control resource set. The allocations of different number of PDCCH candidates to each OFDM symbol could be based on coverage of beams, beams that are formed on each OFDM symbol, as well as loads on each OFDM symbol. For example, if gNB knows that the UE is in the coverage of one beam, it could allocate most of all PDCCH candidates to that UE onto the OFDM symbol that is transmitted on that particular beam. If UE could be in the overlapping area covered by two beams, the gNB could allocate PDCCH candidates to both OFDM symbols that are transmitted on two beams respectively.

Implementation 4

Alternatively, if the load on one OFDM symbol (number of PDCCH candidates of all UEs transmitted on that OFDM symbol) is full or almost full (gNB could determine this based on the discontinuous transmission (DTX) feedback from UEs) , the gNB could allocate PDCCH candidates to other OFDM symbols. Here different OFDM symbols could transmit with the same or different beams, thus make the resource allocation more flexible.

One example is illustrated in FIG. 11. As illustrated in FIG. 11, five PDCCH candidates for PDCCH #1 and two PDCCH candidates for PDCCH #2 are allocated to OFDM symbol #1 while no candidate is allocated to OFDM symbol #2 at the beginning. Here load of the OFDM symbol #1 could be large and for reasons of balance and transmission reliability, two PDCCH candidates for PDCCH #1 and one PDCCH candidates for PDCCH #2 can be moved from OFDM symbol #1 to OFDM symbol #2 for example, the result is illustrated in the lower half of FIG. 11. Alternatively, all PDCCH candidates for PDCCH #2 can be moved to OFDM symbol #2 while leaving PDCCH candidates for PDCCH #1 on OFDM symbol #1.

Technical schemes described in different implementations could be combined or substituted with each other without conflict. For example, implementation 4 could be combined with any of implementations 1-3.

Technical schemes provided herein could support BF for PDCCH and facilitate the transmission of PDCCH on different transmit beams, and hence reduce the risk of beam mismatch and increase the robustness of PDCCH transmission. The above-mentioned technical schemes could also be used to allocate control resources among different OFDM symbols more effectively for the control channel and reduce overall blocking ratio. Such flexible resource allocation of PDCCH candidates could reduce per UE BD.

In addition, to reduce BD and blocking ratio, the number of PDCCH candidates that could be allocated to each UE can be configured semi-statically. For example, if the UE is at the cell edge and may have difficulty in receiving PDCCH, the gNB could allocate more PDCCH candidates to this UE, so that the UE may have more chances (because more PDCCH candidates) to receive it correctly, on the contrary, if the UE is at cell center with good signal to Interference plus noise (SINR) , its total number of PDCCH candidates could be reduced and thus leave more resource for other UEs and also reduce the BD of this UE to save power. The PDCCH candidates at each CCE AL could also be adjusted accordingly on a semi-static manner based on the above-mentioned principle for each UE.

Apparatus

According to an embodiment of the present disclosure, there is provided an apparatus for transmitting signals. During implementation, such apparatus can make use of the above-mentioned PDCCH design and can be configured to perform the method for transmitting signals.

FIG. 12 is a block diagram illustrating the apparatus for transmitting signals. As illustrated in FIG. 12, apparatus 40 may include an allocating unit 42 and a transmitting unit 44. Apparatus 40 can be arranged at gNB side and communicate with UEs. Allocating unit 42 can be a processor integrated with resource configuration function. Transmitting unit 44 can be a transmitter, transceiver, antenna, wireless transmission equipment, and any other devices equipped with transmission function.

In the process of transmitting signals, allocating unit 42 can be configured to allocate all CCEs of a PDCCH candidate to an OFDM symbol, and transmitting unit 44 can be configured to transmit a PDCCH using the PDCCH candidate on the OFDM symbol.

In one implementation, transmitting unit 44 could transmit the PDCCH using PDCCH candidates for the PDCCH on one OFDM symbol with different beams. In another implementation, transmitting unit 44 could transmit the PDCCH using PDCCH candidates on different OFDM symbols with different beams or the same beam.

Details of the foregoing method embodiments are also applicable to this apparatus embodiment and will not be repeated here.

Certain aspects of the embodiments described in the present disclosure may be provided as a computer program product, or software, that my include, for example, a computer-readable storage medium or a non-transitory machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) or a processor to perform a method for allocating resources or transmitting signals according to the present disclosure. A non-transitory machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer) . The non-transitory machine-readable medium may take the form of, but is not limited to, a magnetic storage medium, optical storage medium (e.g., CD-ROM) , magneto-optical storage medium, read only memory (ROM) , random access memory (RAM) , erasable programmable memory, flash memory, and so on.

Based on this, FIG. 13 illustrated an apparatus 50 in which a processor 52 and one or more interfaces 56 coupled with processor 52 via a BUS 54 are provided.

Processor 52 may be configured to read and execute computer readable instructions. In one implementation, processor 52 may primarily include a controller, an operator, and a register, and the hardware architecture of processor 52 may be an application specific integrated Circuits (ASIC) architecture, a microprocessor without interlocked piped stages (MIPS) architecture, an advanced reduced instruction set computer (RISC) machine (ARM) architecture, or a network processor (NP) architecture.

Interface 56 can be configured to input data to be processed to processor 52 and/or output processing results of processor 52 to the outside. Interface 56 can be connected with one or more peripheral equipment such as a display (for example, LCD) , camera, RF module, and so on.

In conjunction with technical solutions of the present disclosure, processor 52 can invoke, from a memory, programs with regard to the method for transmitting signals and perform instructions contained in the programs to achieve corresponding operations such as resources configuration and signal transmission. Interface 56 can be configured to output the result of resources allocation, whereby a transceiver can transmit signals on the resources allocated.

By means of technical solutions described herein, a new PDCCH design can be provided to accommodate requirements in a 5G NR system; such PDCCH design can support BF for PDCCH and avoid beam mismatch of PDCCH, as well as support flexible resource allocation of PDCCH candidates and reduce per UE BD and overall blocking ratio.

While the present disclosure has been described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the disclosure is not limited to them. Variations, modifications, additions, and improvements are possible. Functionality may be separated or combined in procedures differently in various embodiments of the disclosure or described with different terminology.

Claims

A method for transmitting signals, comprising:

allocating all control channel elements (CCEs) of a physical downlink control channel (PDCCH) candidate to an orthogonal frequency division multiplexing (OFDM) symbol and transmitting a PDCCH using the PDCCH candidate on the OFDM symbol.
The method of claim 1, wherein a set of PDCCH candidates is configured for the PDCCH and the method further comprises:

transmitting the PDCCH using the set of PDCCH candidates on different OFDM symbols repeatedly.
The method of claim 1, wherein a set of PDCCH candidates is configured for the PDCCH and the method further comprises:

splitting the set of PDCCH candidates to different OFDM symbols.
The method of claim 3, further comprising:

transmitting the PDCCH using the set of PDCCH candidates on the different OFDM symbols with the same beam.
The method of claim 3, further comprising:

transmitting the PDCCH using the set of PDCCH candidates on the different OFDM symbols with different beams.
The method of any of claims 3 to 5, wherein the splitting of the set of PDCCH candidates is based on at least one selected from a group consisting of: coverage of beams, beams formed on each OFDM symbol, and loads on each OFDM symbol.
The method of any of claims 3 to 6, wherein configuration of the splitting of the set of PDCCH candidates is accomplished via a higher layer signal.
The method of claim 7, wherein the configuration comprises at least one selected from a group consisting of: total number of PDCCH candidates on each OFDM symbol, number of PDCCH candidates of each CCE aggregation level (AL) allocated to each OFDM symbol, locations of PDCCH candidates on each OFDM symbol, and all OFDM symbols on which PDCCH candidates are located.
The method of claims 1 or 2, further comprising:

transmitting the PDCCH using PDCCH candidates on different OFDM symbols with different beams.
The method of claim 1 or 2, further comprising:

transmitting the PDCCH using PDCCH candidates on one OFDM symbol with different beams.
The method of any of claims 1 to 10, wherein PDCCH candidates allocated to one OFDM symbol comprises candidates of different CCE AL.
The method of any of claims 1 to 10, wherein total number of PDCCH candidates that allocated to an user equipment (UE) and/or number of PDCCH candidates of each CCE AL that allocated to the UE is configured via a higher layer signal.
A method for transmitting signals, comprising:

allocating all control channel elements (CCEs) of a physical downlink control channel (PDCCH) candidate to an orthogonal frequency division multiplexing (OFDM) symbol and transmitting a PDCCH using the PDCCH candidate on the OFDM symbol with a beam different from those used for other OFDM symbols.
The method of claim 13, further comprising:

transmitting the PDCCH using different PDCCH candidates for the PDCCH on one OFDM symbol with different beams.
The method of claim 13 or 14, wherein PDCCH candidates for the PDCCH are allocated to one OFDM symbol.
The method of claim 13 or 14, wherein PDCCH candidates for the PDCCH are allocated to different OFDM symbols.
An apparatus for transmitting signals, comprising:

an allocating unit, configured to allocate all control channel elements (CCEs) of a physical downlink control channel (PDCCH) candidate to an orthogonal frequency division multiplexing (OFDM) symbol; and

a transmitting unit, configured to transmit a PDCCH using the PDCCH candidate on the OFDM symbol.
The apparatus of claim 17, wherein the transmitting unit configured to transmit the PDCCH using the PDCCH candidate on the OFDM symbol is further configured to: transmit the PDCCH using the PDCCH candidate on the OFDM symbol with a beam different from those used for other OFDM symbols.
The apparatus of claim 17 or 18, wherein the transmitting unit is further configured to transmit the PDCCH using different PDCCH candidates for the PDCCH on one OFDM symbol with different beams.
The apparatus of claim 17 or 18, wherein the transmitting unit is further configured to transmit the PDCCH using a set of PDCCH candidates on two OFDM symbols repeatedly.