CN106851827A - For the downlink transmission method and system of unlicensed spectrum - Google Patents

Abstract

For the downlink transmission method and system of unlicensed spectrum.The downlink transmission method includes：According to the symbol numbers of part subframe, symbol division is carried out successively since one end of part subframe；According to the symbol numbers and predistribution resource block size, the schedulable resource block size of the part subframe is calculated；According to the schedulable resource block size and the symbol numbers, the time-frequency lattice of downlink transfer are calculated；By PDSCH resources and downlink reference signal, by default mapping ruler, mapping to the time-frequency lattice carries out downlink transfer, wherein, the mapping position of the PDSCH resources and the downlink reference signal is not overlapped.The present invention can solve effectively to carry out the technical problem of downlink transfer in the subframe of part, improve the handling capacity of communication system.

Description

Downlink transmission method and system for unlicensed spectrum

Technical Field

The present invention relates to the field of communications technologies, and in particular, to a downlink transmission method and system for an unlicensed spectrum.

Background

Third generation partnership project (3)^rdGeneration Partnership Project, 3GPP) introduced licensed frequencies in Rel-13 Releasespectrum-Assisted Access (LAA) technology, i.e. mobile communication services are carried over unlicensed spectrum, e.g. 5GHz unlicensed spectrum. In the unlicensed spectrum, Wireless Fidelity (WiFi), bluetooth, radar, medical systems, and other systems are mainly used at present. Due to the diversity and complexity of systems over unlicensed spectrum, a basic principle to solve the coexistence problem between different systems is to require that different systems can fairly occupy the unlicensed spectrum. Therefore, a technical solution is needed to solve the problem of transmission collision between LAA systems on unlicensed spectrum or between LAA and WiFi systems. Currently, in 3GPP standards conference, a solution to the coexistence problem tends to adopt a Listen-before-talk (LBT) method.

Each region has a rule on the maximum occupation time of the unlicensed spectrum, and the time that the LAA base station can occupy the unlicensed spectrum after the LBT access is successful is less than or equal to the maximum occupation time, so the access time of the LBT may not be located at the edge of a normal subframe or the edge of an Orthogonal Frequency Division Multiplexing (OFDM) symbol. In this case, the time interval of LAA downlink transmission may not be a complete normal subframe but a partial subframe, where the length of the normal subframe is 1 millisecond (ms). If the part of the sub-frames are not occupied reasonably, the waste of time-frequency resources can be caused. How to normally transmit Downlink reference signals on a part of subframes, and carry Downlink Physical Channel resources, such as a Physical Downlink Shared Channel (PDSCH), a Physical Downlink Control Channel (PDCCH), a Physical Control Format Indicator Channel (PCFICH), a Physical hybrid automatic repeat Indicator Channel (PHICH), an Enhanced Physical Downlink Control Channel (ePDCCH), and the like, to support content in terms of Downlink data transmission and the like, is also an open research topic.

Disclosure of Invention

In view of this, embodiments of the present invention provide a downlink transmission method and system for unlicensed spectrum, so as to solve the technical problem of effectively performing downlink transmission on a part of subframes, and indirectly improve the throughput of a communication system.

The embodiment of the invention adopts the following technical scheme:

in a first aspect, an embodiment of the present invention provides a downlink transmission method for an unlicensed spectrum, including:

according to the number of the symbols of the partial sub-frame, sequentially dividing the symbols from one end of the partial sub-frame;

calculating the schedulable resource block size of partial sub-frames according to the number of the symbols and the size of the pre-allocated resource block;

calculating a time-frequency grid of downlink transmission according to the size of the schedulable resource block and the number of symbols;

and mapping the PDSCH resources and the downlink reference signals to a time frequency grid for downlink transmission according to a preset mapping rule, wherein the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped.

In a second aspect, an embodiment of the present invention further provides a downlink transmission system for unlicensed spectrum, including:

the symbol dividing unit is set to divide symbols in sequence from one end of a partial subframe according to the number of the symbols of the partial subframe;

the schedulable resource block size calculation unit is set to calculate the schedulable resource block size of part of the sub-frames according to the number of the symbols and the size of the pre-allocated resource blocks;

the time frequency grid calculating unit is set to calculate the time frequency grid of downlink transmission according to the size of the schedulable resource block and the number of the symbols;

and the downlink transmission unit is configured to map the PDSCH resources and the downlink reference signals to the time-frequency grid for downlink transmission according to a preset mapping rule, wherein the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped.

In summary, according to the technical scheme of the present invention, symbol division is performed sequentially from one end of a partial subframe according to the number of symbols of the partial subframe; calculating the schedulable resource block size of partial sub-frames according to the number of the symbols and the size of the pre-allocated resource block; then, according to the size of the schedulable resource block and the number of symbols, calculating a time-frequency grid of downlink transmission; and mapping the PDSCH resources and the downlink reference signals to a time frequency grid for downlink transmission according to a preset mapping rule, wherein the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped. The technical scheme of the invention defines the structure of partial sub-frames by carrying out symbol division on partial sub-frames, calculates the size of the schedulable resource block and the time frequency grid of the partial sub-frames, can ensure that a communication system can effectively transmit downlink physical channel resources and downlink reference signals on the partial sub-frames even if the access time of the LBT on the unauthorized frequency spectrum is not positioned at the edge of the conventional sub-frames, and indirectly improves the throughput of the communication system by fully utilizing the time frequency resources.

Drawings

Fig. 1a is a flowchart of a downlink transmission method for unlicensed spectrum according to an embodiment of the present invention.

Fig. 1b is a schematic structural diagram of a first partial subframe according to an embodiment of the present invention.

Fig. 1c is a schematic structural diagram of a second partial subframe according to a first embodiment of the present invention.

Fig. 2a is a flowchart of another downlink transmission method for unlicensed spectrum according to a second embodiment of the present invention.

Fig. 2b is a schematic diagram of CRS mapping rules of a first partial subframe according to a second embodiment of the present invention.

Fig. 2c is a schematic diagram of CRS mapping rules of a second partial subframe according to a second embodiment of the present invention.

Fig. 2d is a schematic diagram of a DMRS mapping rule of the first partial subframe according to the second embodiment of the present invention.

Fig. 2e is a schematic diagram of a DMRS mapping rule of a second partial subframe according to a second embodiment of the present invention.

Fig. 3 is a structural diagram of a downlink transmission system for unlicensed spectrum according to a third embodiment of the present invention.

Fig. 4a is a structural diagram of another downlink transmission system for unlicensed spectrum according to a fourth embodiment of the present invention.

Fig. 4b is a structural diagram of a downlink control channel transmission unit according to a fourth embodiment of the present invention.

Detailed Description

The following detailed description of specific embodiments of the invention refers to the accompanying drawings. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. In addition, for convenience of description, only a part, not all of the contents related to the present invention are shown in the drawings.

Example one

As shown in fig. 1a, which is a downlink transmission method for unlicensed spectrum according to an embodiment of the present invention, the method may be applied in a communication network using LAA technology, and the method may include the following steps:

and S110, according to the number of the symbols of the partial subframe, sequentially dividing the symbols from one end of the partial subframe.

In this embodiment, the length of the partial subframe is less than or equal to 1ms, that is, the length of the partial subframe is less than or equal to the length of the normal subframe. The number of symbols of partial sub-frame can be rootedAccording to time unit T_SCalculated according to the 3GPP Technical Specification (TS) 36.211 document, T_SIs convenient to useThe number of symbols X of the partial sub-frame can be calculated according to the length T of the partial sub-frame, i.e.If the number of symbols of the partial subframe is known, the partial subframe may be symbol-divided in sequence from the start of the partial subframe or from the end of the partial subframe, and if the symbol-division is performed from the start of the partial subframe, the initial symbol value of the partial subframe may be fixed. As shown in fig. 1b, the symbols in the partial sub-frame are sequentially marked as 0, 1, …, X-1. If the symbol division is performed from the end of the partial subframe, the last symbol value of the partial subframe may be fixed, as shown in fig. 1c, the symbols in the partial subframe are sequentially denoted as N-X, N-X +1, …, and N-1, where N is the number of symbols of the normal subframe, N may be 14 for the normal Cyclic Prefix (CP), and N may be 12 for the extended CP.

It should be noted that, the symbols in the partial subframe in the embodiment of the present invention are preferably OFDM symbols, and may also be Modulation schemes such as Multiple Phase Shift Keying (MPSK), Multiple Amplitude Shift Keying (MASK), Multiple Frequency Shift Keying (MFSK), or Multiple Quadrature Amplitude Modulation (MQAM), and any Modulation symbols obtained by combining these Modulation schemes.

And S120, calculating the schedulable resource block size of part of the sub-frames according to the number of the symbols and the size of the pre-allocated resource block.

In this step, based on the number X of symbols obtained in step S110, the schedulable resource block size of the partial sub-frame can be calculated according to the following formula (1),

wherein N is_PRBFor schedulable resource Block size, N_′P_RBIn order to pre-allocate the size of the resource block,is the number of symbols of a partial sub-frame,q may be 11 or 9 according to the types of the normal CP and the extended CP.

And S130, calculating a time-frequency grid of downlink transmission according to the size of the schedulable resource block and the number of the symbols.

The time-frequency grid for downlink transmission can be determined by the number of symbols of the time-domain partial subframe and the number of frequency-domain subcarriers, specifically, the position of a Resource Element (RE) on the time-frequency grid can be represented by a two-dimensional coordinate (k, l), where k is the frequency-domain subcarrier position of the time-frequency grid, the number of the sub-carriers corresponding to one schedulable resource block, for the frequency domain sub-carrier interval of 15KHz,it may be taken as 12, for a frequency domain subcarrier spacing of 7.5KHz,it is possible to take 24, l as the time domain symbol position of the time frequency grid,after the time-frequency grid is determined, the method can be usedAnd mapping the modulation symbol corresponding to the downlink data to the RE position (k, l) in the time-frequency grid, and carrying by corresponding frequency domain and time domain resources to complete downlink data transmission.

And S140, mapping the PDSCH resources and the downlink reference signals to a time-frequency grid for downlink transmission according to a preset mapping rule.

The downlink Reference signals may include Cell-specific Reference signals (CRS), Demodulation Reference signals (DMRS), user-specific Reference signals (UE-specific Reference signals, DM-RS), Channel State Information (CSI) Reference signals (CSI-RS), and the like. The CRS and the DMRS can be used for downlink channel estimation and downlink channel related demodulation, for example, the CRS and the DMRS can be used for demodulating PDSCH and control channels such as PDCCH, PCFICH, PHICH, ePDCCH and the like, the CRS can be transmitted on antenna ports 0-3, and the DMRS can be transmitted on antenna ports 7-14; the DM-RS can be used for PDSCH Channel demodulation and can be transmitted on antenna ports 5, 7-8, the CSI-RS can be used for measuring information such as Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI) and Rank Indicator (RI), the CSI-RS can be used for transmitting single antenna port, double antenna port, four antenna port and eight antenna port, and the supported antenna ports are respectively corresponding to 15, 15-16, 15-18 and 15-22.

In this step, the PDSCH resources and the downlink reference signals are mapped to the time-frequency grid, and are only mapped to corresponding symbols of a part of the subframes, while symbol positions of other non-part of the subframes are not mapped, the preset mapping rule may adopt centralized mapping or distributed mapping, and on the basis of ensuring that the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped, the PDSCH resources and the downlink reference signals may be mapped to any RE position of the time-frequency grid.

The technical scheme provided by the embodiment of the invention sequentially divides the symbols from one end of the partial sub-frame according to the number of the symbols of the partial sub-frame; secondly, calculating the size of the schedulable resource block of part of the sub-frames according to the number of the symbols and the size of the pre-allocated resource block; then, according to the size of the schedulable resource block and the number of symbols, calculating a time-frequency grid of downlink transmission; and mapping the PDSCH resources and the downlink reference signals to a time frequency grid for downlink transmission according to a preset mapping rule, wherein the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped. The technical scheme of the invention defines the structure of partial sub-frames by carrying out symbol division on partial sub-frames, further calculates the size of the schedulable resource block and the time frequency grid of the partial sub-frames, can ensure that a communication system can effectively transmit downlink physical channel resources and downlink reference signals on partial sub-frames even if the access time of the LBT on the unlicensed frequency spectrum is not positioned at the edge of the conventional sub-frames, and indirectly improves the throughput of the communication system by fully utilizing the time frequency resources.

Example two

On the basis of the first embodiment of the present invention, the present embodiment provides another downlink transmission method for unlicensed spectrum, as shown in fig. 2a, step S100, step S150, and step S160 may be added on the basis of the first embodiment of the present invention.

And S100, aligning one end of a partial subframe with one end of a normal subframe, wherein the length of the partial subframe is less than or equal to that of the normal subframe.

As shown in fig. 1b and 1c, one end of the partial subframe may be aligned with one end of the normal subframe, the start end of the partial subframe may be aligned with the edge of the normal subframe, and the end of the partial subframe may be aligned with the edge of the normal subframe.

S150, setting the first M coincident positions of the time-frequency grid as a control area, wherein M is 1, 2, 3 or 4.

Referring to the first embodiment, as shown in fig. 1b, in the first partial frame structure, positions of time-frequency lattices corresponding to the first M symbols of a partial subframe may be set as control regions, it should be noted that the size of the control region may be indicated by a PCFICH, and referring to the time-frequency lattices corresponding to the first partial frame structure shown in fig. 2b and fig. 2d, for a mapping manner of a CRS, M is preferably 2, and for a mapping manner of a DMRS, M is preferably 1.

And S160, mapping the downlink control channel resources to a control region for downlink transmission, wherein the downlink control channel comprises a PDCCH, a PCFICH, a PHICH and an ePDCCH.

In this embodiment, the downlink reference signal is preferably a CRS and/or a DMRS, and for mapping the CRS, the preset mapping rule may be that the CRS is mapped to an RE position (k, l) of the time-frequency grid according to the following formula (2),

wherein, the number of sub-carriers corresponding to one schedulable resource block,p is an antenna port for transmitting the downlink reference signal,

the partial subframe may adopt OFDM symbols with normal CP, and the number of OFDM symbols of the partial subframe may be defined as 7. As shown in fig. 2b, for CRS mapping of the first partial subframe, symbol division may be performed from the start of the partial subframe, that is, the initial symbol value of the partial subframe is fixed, and then OFDM symbols in the partial subframe may be sequentially marked as 0, 1, …, and 6. At this time, the CRS may be mapped to the 1 st and 5 th OFDM symbol positions, i.e., where l is 0 and l is 4, according to the preset mapping rule of equation (2). As shown in fig. 2c, for CRS mapping of the second partial subframe, symbol division may be performed from the end of the partial subframe, that is, the last symbol value of the partial subframe is fixed, and then OFDM symbols in the partial subframe may be sequentially denoted as 7, 8, …, and 13. At this time, the CRS may be mapped to OFDM symbol positions l-7 and l-11 according to a preset mapping rule of equation (2). The two partial subframe structures can support dual-antenna port transmission of CRSs, the CRSs of different antenna ports are spaced by 2 subcarriers in a frequency domain and are spaced by 3 OFDM symbols in a time domain, and the CRSs on the same antenna port are spaced by 5 subcarriers in the frequency domain and are spaced by 3 OFDM symbols in the time domain; for the first partial frame structure shown in fig. 2b, the first two OFDM symbol positions of the time-frequency grid, that is, the time-frequency regions corresponding to l ═ 0 and l ═ 1, may be set as the control region, and therefore, the downlink control channels include PDCCH, PCFICH, PHICH and ePDCCH, and may be mapped in the 1 st and 2 nd OFDM symbol positions, the mapping positions of the downlink control channels and CRS are not overlapped, and except the mapping positions of CRS and downlink control channels, all the other RE positions may be used for mapping PDSCH resources.

For the mapping of DMRS, the preset mapping rule may be that DMRS is mapped to RE positions (k, l) of a time-frequency grid according to the following formula (3),

wherein To guarantee the mapping of DMRS and CRSThe positions do not overlap.

The partial subframe may also adopt OFDM symbols with normal CP, and the number of OFDM symbols of the partial subframe may be defined as 7. As for the DMRS mapping of the first partial subframe shown in fig. 2d, the partial subframe may be divided into symbols from the start of the partial subframe, that is, the initial symbol value of the partial subframe is fixed, and then the OFDM symbols in the partial subframe may be sequentially marked as 0, 1, …, and 6. At this time, the DMRS may be mapped to the 6 th and 7 th OFDM symbol positions, i.e., where l is 5 and l is 6, according to the preset mapping rule of equation (3). As for the DMRS mapping of the second partial subframe shown in fig. 2e, the partial subframe may be divided into symbols from the end of the partial subframe, that is, the last symbol value of the partial subframe is fixed, and then the OFDM symbols in the partial subframe may be sequentially denoted as 7, 8, …, and 13. At this time, the DMRS may be mapped to OFDM symbol positions l-12 and l-13 according to a preset mapping rule of equation (3). The two partial subframe structures can support eight-antenna port transmission of the DMRS, the DMRS on the antenna ports {7, 8, 11, 13} are spaced by 4 subcarriers in the frequency domain, the DMRS on the antenna ports {9, 10, 12, 14} are spaced by 4 subcarriers in the frequency domain, and the DMRSs of the antenna ports {7, 8, 11, 13} and {9, 10, 12, 14} are mapped at adjacent frequency domain positions. For the first partial frame structure shown in fig. 2d, the 1 st OFDM symbol position of the time-frequency grid, i.e., the time-frequency region corresponding to l ═ 0, may be set as the control region. Therefore, the downlink control channel comprises PDCCH, PCFICH, PHICH and ePDCCH, can be mapped at the 1 st OFDM symbol position, the mapping positions of the downlink control channel and DMRS are not overlapped, and except the mapping positions of the DMRS and the downlink control channel, all the other RE positions can be used for the mapping of PDSCH resources.

In the embodiment, according to the preset mapping rule, the CRS and/or the DMRS are transmitted on part of the subframes, the RE positions in the time-frequency grids of part of the subframes are reasonably occupied, the time-frequency resources are saved, and the mapping and transmission of the downlink control channel resources are effectively completed by defining the first part of the subframe structure and reserving the control region.

In summary, according to the number of symbols of the partial subframe, the embodiments of the present invention sequentially perform symbol division from one end of the partial subframe; calculating the schedulable resource block size of partial sub-frames according to the number of the symbols and the size of the pre-allocated resource block; then, according to the size of the schedulable resource block and the number of symbols, calculating a time-frequency grid of downlink transmission; and mapping the PDSCH resources and the downlink reference signals to a time frequency grid for downlink transmission according to a preset mapping rule, wherein the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped. The technical scheme of the invention defines the structure of partial sub-frames by carrying out symbol division on partial sub-frames, further calculates the size of the schedulable resource block and the time frequency grid of the partial sub-frames, can ensure that a communication system can effectively transmit downlink physical channel resources and downlink reference signals on partial sub-frames even if the access time of the LBT on the unlicensed frequency spectrum is not positioned at the edge of the conventional sub-frames, and indirectly improves the throughput of the communication system by fully utilizing the time frequency resources.

The following is an embodiment of a downlink transmission system for unlicensed spectrum according to an embodiment of the present invention. The embodiments of the downlink transmission system belong to the same concept as the embodiments of the downlink transmission method, and the details of the embodiments of the downlink transmission system may refer to the details described in the embodiments of the downlink transmission method.

EXAMPLE III

Based on the technical solution described in the above method embodiment of the present invention, as shown in fig. 3, it is a downlink transmission system 300 for unlicensed spectrum provided in the embodiment of the present invention, where the downlink transmission system 300 includes: a symbol dividing unit 310, a schedulable resource block size calculating unit 320, a time-frequency grid calculating unit 330 and a downlink transmission unit 340. Wherein,

a symbol division unit 310 configured to sequentially perform symbol division from one end of a partial subframe according to the number of symbols of the partial subframe;

a schedulable resource block size calculating unit 320 configured to calculate schedulable resource block sizes of a part of subframes according to the number of symbols and the size of the pre-allocated resource block;

a time-frequency grid calculating unit 330 configured to calculate a time-frequency grid for downlink transmission according to the size of the schedulable resource block and the number of symbols;

the downlink transmission unit 340 is configured to map the PDSCH resources and the downlink reference signals to a time-frequency grid for downlink transmission according to a preset mapping rule, where mapping positions of the PDSCH resources and the downlink reference signals are not overlapped.

In the embodiment, the partial sub-frames are subjected to symbol division, the structure of the partial sub-frames is defined, the size of the schedulable resource block and the time frequency grid of the partial sub-frames are further calculated, even if the access time of the LBT on the unlicensed spectrum is not positioned at the edge of the conventional sub-frame, the downlink physical channel resources and the downlink reference signals can still be effectively transmitted on the partial sub-frames by the communication system, and the throughput of the communication system is indirectly improved by fully utilizing the time frequency resources.

Example four

On the basis of the third embodiment of the present invention, as shown in fig. 4a, an alignment unit 301 and a downlink control channel transmission unit 350 may be further added to the downlink transmission system 300 according to the third embodiment of the present invention. Wherein,

an alignment unit 301 configured to align one end of a partial subframe with one end of a normal subframe, wherein the length of the partial subframe is equal to or less than the length of the normal subframe.

As shown in fig. 4b, the downlink control channel transmission unit 350 specifically includes a control region setting module 351 and a downlink control channel transmission module 352. Wherein,

a control region setting module 351 configured to set the first M coincident positions of the time-frequency grid as control regions, where M is 1, 2, 3, or 4;

the downlink control channel transmission module 352 is configured to map downlink control channel resources to a control region for downlink transmission, where the downlink control channel includes PDCCH, PCFICH, PHICH, and ePDCCH, and mapping positions of the downlink control channel resources, PDSCH resources, and downlink reference signals are not overlapped with each other.

Referring to the second embodiment of the present invention, in the second embodiment, for mapping of the CRS and/or DMRS of the downlink reference signal, the preset mapping rule may be set according to the formula (2) and/or the formula (3), and the CRS and/or DMRS are mapped to the RE position (k, l) of the time-frequency grid for transmission. Referring to the first partial frame structures shown in fig. 2b and fig. 2d, respectively, fig. 2b and fig. 2d are respectively provided with a control region for transmitting a downlink control channel, which may be used for mapping and transmitting downlink control channel resources such as PDCCH, PCFICH, PHICH, and ePDCCH.

In the embodiment, according to the preset mapping rule, the CRS and/or the DMRS are transmitted on part of the subframes, the RE positions in the time-frequency grids of part of the subframes are reasonably occupied, the time-frequency resources are saved, and the mapping and transmission of the downlink control channel resources are effectively completed by defining the first part of the subframe structure and reserving the control region.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes in the detailed description of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, obvious change and the like which are made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. A downlink transmission method for an unlicensed spectrum comprises the following steps:

according to the number of the symbols of the partial sub-frame, sequentially dividing the symbols from one end of the partial sub-frame;

calculating the schedulable resource block size of the partial sub-frame according to the number of the symbols and the size of the pre-allocated resource block;

calculating a time-frequency grid of downlink transmission according to the size of the schedulable resource block and the number of the symbols;

and mapping the PDSCH resources and the downlink reference signals to the time frequency grid for downlink transmission according to a preset mapping rule, wherein the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped.

2. The downlink transmission method according to claim 1, wherein after mapping the PDSCH resources and the downlink reference signals to the time-frequency grid for downlink transmission according to a preset mapping rule, the method further comprises:

setting the first M coincident positions of the time-frequency grid as control areas, wherein M is 1, 2, 3 or 4;

and mapping downlink control channel resources to the control region for downlink transmission, wherein the downlink control channel comprises a PDCCH (physical Downlink control channel), a PCFICH (physical Downlink control channel), a PHICH (physical hybrid indicator channel) and an ePDCCH (enhanced physical Downlink control channel), and the mapping positions of the downlink control channel resources, the PDSCH resources and the downlink reference signals are not overlapped with each other.

3. The downlink transmission method according to claim 1, wherein the downlink reference signal is a CRS and/or a DMRS.

4. The downlink transmission method according to claim 3, wherein the preset mapping rule includes:

mapping the CRS to a location (k, l) of the time-frequency grid, $\left\{\begin{array}{c}k=6\×m+{\mathrm{CRS}}_{shift}\\ l=0,N_{symb}^{DL}-3\end{array}\right.;$ and/or

Mapping the DMRS to a location (k, l) of the time-frequency grid, $\left\{\begin{array}{c}k=5\×n+{\mathrm{DMRS}}_{shift}\\ l=N_{symb}^{DL}-1,N_{symb}^{DL}-2\end{array}\right.;$

wherein k is the frequency domain subcarrier position of the time-frequency grid, l is the time domain symbol position of the time-frequency grid, m is 0, 1, …,N_PRBfor the size of the schedulable resource block,the number of sub-carriers corresponding to one schedulable resource block,p is an antenna port for transmitting the downlink reference signal,for the number of the symbols,n＝0，1，…， ${\mathrm{DMRS}}_{shift}=\left\{\begin{array}{cc}0,& p\∈\left\{\begin{array}{cccc}7,& 8,& 11,& 13\end{array}\right\}\\ 1,& p\∈\left\{\begin{array}{cccc}9,& 10,& 12,& 14\end{array}\right\}\end{array}\right..$

5. the downlink transmission method according to any one of claims 1 to 4, wherein before sequentially performing symbol division from one end of the partial subframe according to the number of symbols of the partial subframe, the method further includes:

aligning one end of a partial subframe with one end of a normal subframe, wherein the length of the partial subframe is less than or equal to the length of the normal subframe.

6. A downlink transmission system for unlicensed spectrum, comprising:

the symbol dividing unit is set to divide symbols in sequence from one end of a partial subframe according to the number of the symbols of the partial subframe;

the schedulable resource block size calculating unit is set to calculate the schedulable resource block size of the partial sub-frame according to the number of the symbols and the size of the pre-allocated resource block;

a time-frequency grid calculating unit, configured to calculate a time-frequency grid of downlink transmission according to the size of the schedulable resource block and the number of the symbols;

and the downlink transmission unit is configured to map the PDSCH resources and the downlink reference signals to the time-frequency grid according to a preset mapping rule for downlink transmission, wherein the mapping positions of the PDSCH resources and the downlink reference signals are not overlapped.

7. The downlink transmission system according to claim 6, further comprising a downlink control channel transmission unit, wherein the downlink control channel transmission unit specifically includes:

a control region setting module, configured to set the first M coincident positions of the time-frequency grid as control regions, where M is 1, 2, 3, or 4;

and the downlink control channel transmission module is configured to map downlink control channel resources to the control region for downlink transmission, wherein the downlink control channel comprises a PDCCH (physical downlink control channel), a PCFICH (physical downlink control channel), a PHICH (physical hybrid-indicator channel) and an ePDCCH (enhanced physical downlink control channel), and the mapping positions of the downlink control channel resources, the PDSCH (physical downlink shared channel) resources and the downlink reference signals are not overlapped with each other.

8. The downlink transmission system according to claim 6, wherein the downlink reference signals are CRS and/or DMRS.

9. The downlink transmission system according to claim 8, wherein the preset mapping rule includes:

mapping the CRS to a location (k, l) of the time-frequency grid, $\left\{\begin{array}{c}k=6\×m+{\mathrm{CRS}}_{shift}\\ l=0,N_{symb}^{DL}-3\end{array}\right.;$

and/or

Mapping the DMRS to a location (k, l) of the time-frequency grid, $\left\{\begin{array}{c}k=5\×n+{\mathrm{DMRS}}_{shift}\\ l=N_{symb}^{DL}-1,N_{symb}^{DL}-2\end{array}\right.;$

wherein k is the frequency domain subcarrier position of the time-frequency grid, l is the time domain symbol position of the time-frequency grid, m is 0, 1, …,N_PRBfor the size of the schedulable resource block,the number of sub-carriers corresponding to one schedulable resource block,p is an antenna port for transmitting the downlink reference signal,for the number of the symbols,n＝0，1，…， ${\mathrm{DMRS}}_{shift}=\left\{\begin{array}{cc}0,& p\∈\left\{\begin{array}{cccc}7,& 8,& 11,& 13\end{array}\right\}\\ 1,& p\∈\left\{\begin{array}{cccc}9,& 10,& 12,& 14\end{array}\right\}\end{array}\right..$

10. the downlink transmission system according to any one of claims 6 to 9, further comprising:

and an alignment unit configured to align one end of a partial subframe with one end of a normal subframe, wherein the length of the partial subframe is less than or equal to the length of the normal subframe.