CN106031266B - Low-complexity multi-cell downlink coherent joint transmission method and device - Google Patents
Low-complexity multi-cell downlink coherent joint transmission method and device Download PDFInfo
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Abstract
The invention provides a low-complexity multi-cell downlink coherent joint transmission method and device. The method comprises the following steps: performing joint design on precoding according to scheduling authorization information and channel state information from the first base station and the second base station to obtain a precoding matrix; the joint design considers the interference possibly caused by the precoding matrix to the downlink transmission of other user equipment in the matrix when designing the precoding matrix of the user equipment, the scheduling authorization information is obtained by independently and distributively scheduling the user equipment of the cell of the base station, and the scheduling authorization information of the user equipment of the adjacent cell of the base station is not considered.
Description
Technical Field
The present invention relates generally to the field of wireless communications, and more particularly, to a method and apparatus for low complexity multi-cell downlink coherent joint transmission.
Background
As one of the key technologies of LTE-a, the 3GPP standardization organization has extensively studied a technology of coordinated Multi-Point (CoMP). Among many CoMP schemes, Coherent Joint Transmission (CJT) shows the gain of maximum coordinated multipoint in cell average performance and cell edge performance. However, since the current CJT scheme utilizes joint multi-cell scheduling and joint transmission precoding design, its complexity increases significantly with the increase of CoMP cluster size, which becomes a major challenge to implement CJT in practical systems.
Disclosure of Invention
In order to solve the above problems and reduce the computational complexity of the original CJT scheme, the present invention provides a low-complexity multi-cell downlink coherent joint transmission method and apparatus.
According to a first aspect of the present invention, there is provided a low complexity method for multi-cell downlink coherent joint transmission, comprising the following steps performed by a central node of a cluster of base stations: i. receiving scheduling authorization information and channel state information from a first base station and a second base station in a base station cluster; jointly designing precoding to obtain a precoding matrix according to the scheduling grant information and the channel state information from the first base station and the second base station; transmitting precoding information of the user equipment of the first base station in the precoding matrix to the first base station, and transmitting precoding information of the user equipment of the second base station in the precoding matrix to the second base station; wherein the first base station and the second base station belong to the cluster of base stations, and a cell of the first base station is adjacent to a cell of the second base station.
According to an embodiment of the present invention, in designing the precoding matrix of the ue, the joint design considers interference that the precoding matrix may cause to downlink transmissions of other ues in the matrix.
According to an embodiment of the present invention, the method further includes sending traffic data of the user equipment of the second base station to the first base station and/or sending traffic data of the user equipment of the first base station to the second base station.
According to an embodiment of the invention, the scheduling grant information is obtained by performing independent distributed scheduling on the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
According to one embodiment of the invention, the channel state information comprises channel state information of user equipment of a cell of the base station and channel state information of user equipment of a neighboring cell of the base station.
According to a second aspect of the present invention, there is provided a low complexity method for multi-cell downlink coherent joint transmission, comprising the following steps performed by base stations in a cluster of base stations: i. transmitting scheduling authorization information of user equipment of a cell of the base station to a central node; receiving precoding information of the user equipment of the cell of the base station from the central node; and iii, performing downlink joint transmission on the service data of the user equipment of the base station according to the precoding information and the scheduling authorization information.
According to an embodiment of the invention, the scheduling grant information is obtained by performing independent distributed scheduling on the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
According to an embodiment of the present invention, the method further includes sharing configuration information of the user equipment of the base station with a base station of a neighboring cell of the base station in the base station cluster, where the configuration information is used for enabling the base station of the neighboring cell to monitor channel state information of the user equipment of the base station.
According to an embodiment of the present invention, the method further comprises sending channel state information to the central node, where the channel state information includes channel state information of user equipment of the cell of the base station and channel state information of user equipment of a cell neighboring cell of the base station.
According to an embodiment of the present invention, the method further includes receiving traffic data of user equipment of a neighboring cell of the base station from the central node for downlink joint transmission.
According to a third aspect of the present invention, there is provided a central node for low complexity multi-cell downlink coherent joint transmission, comprising: a receiving unit, configured to receive scheduling grant information and channel state information from a first base station and a second base station in a cluster of base stations, where the first base station and the second base station belong to the cluster of base stations, and a cell of the first base station is adjacent to a cell of the second base station; a joint precoding unit, configured to jointly design precoding according to the scheduling grant information and the channel state information from the first base station and the second base station to obtain a precoding matrix; a first transmitting unit, configured to transmit precoding information of a user equipment of the first base station in the precoding matrix to the first base station, and transmit precoding information of a user equipment of the second base station in the precoding matrix to the second base station; and a second transmitting unit, configured to send traffic data of the user equipment of the second base station to the first base station and/or send traffic data of the user equipment of the first base station to the second base station.
According to an embodiment of the present invention, in designing the precoding matrix of the ue, the joint design considers interference that the precoding matrix may cause to downlink transmissions of other ues in the matrix.
According to an embodiment of the invention, the scheduling grant information is obtained by performing independent distributed scheduling on the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
According to one embodiment of the invention, the channel state information comprises channel state information of user equipment of a cell of the base station and channel state information of user equipment of a neighboring cell of the base station.
According to a fourth aspect of the present invention, there is provided a base station for low-complexity multi-cell downlink coherent joint transmission, comprising: a first transmitting unit, configured to transmit scheduling grant information of a user equipment of a cell of the base station to a central node; a sharing unit configured to share configuration information of a user equipment of a base station with a base station of a neighboring cell of a cell of the base station in a cluster of base stations, the configuration information being used to cause the base station of the neighboring cell to monitor channel state information of the user equipment of the base station, the base station and the base station of the neighboring cell of the base station belonging to the cluster of base stations; a second transmitting unit for transmitting channel state information to the central node; the channel state information comprises channel state information of user equipment of a cell of the base station and channel state information of user equipment of a cell adjacent to the cell of the base station; a first receiving unit for receiving precoding information of the user equipment of the cell of the base station from the central node; a second receiving unit, configured to receive traffic data of a user equipment in a cell adjacent to the cell of the base station from the central node for downlink joint transmission; and a third transmitting unit, configured to perform downlink joint transmission on service data of the user equipment of the base station according to the precoding information and the scheduling authorization information.
According to an embodiment of the invention, the scheduling grant information is obtained by performing independent distributed scheduling on the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
To reduce the computational complexity of the original CJT scheme, the new CJT scheme includes the design of distributed scheduling and joint transmission precoders. The scheme is characterized in that:
1. distributed scheduling is insensitive to CoMP cluster size, which makes the proposed scheme computationally less complex and easier to implement in a practical network.
2. Distributed scheduling does not reduce the cell average performance gain of CoMP. By comparing joint scheduling and distributed scheduling, we find that they have in common that although a PF-factor is used to ensure fairness of scheduling, a user equipment located in the center of a cell still has a higher scheduling priority. In addition, the User equipment located in the center of the cell is suitable for Multi-User Multi-Input Multi-Output (MU-MIMO) transmission to obtain higher spatial multiplexing gain due to its high received signal-to-noise ratio. This indicates that the distributed scheduling and joint scheduling schemes can achieve almost the same cell average performance.
3. The loss of cell-edge performance caused by distributed scheduling is minimal. The joint scheduling scheme comprehensively considers the scheduling of cell edge users of adjacent cells, while the distributed scheduling scheme only considers the cell edge users. This indicates that the distributed scheduling scheme is suboptimal for scheduling cell edge users in a cluster, which causes some performance loss at the cell edge compared with the joint scheduling scheme, but the performance loss is very small.
Drawings
The present invention will be better understood and other objects, details, features and advantages thereof will become more apparent from the following description of specific embodiments of the invention given with reference to the accompanying drawings. In the drawings:
figure 1 shows a schematic diagram of a multi-cell CoMP system model;
fig. 2 shows a schematic diagram of a low complexity coherent joint transmission;
FIG. 3 shows a schematic diagram of a low complexity coherent joint precoding design;
FIG. 4 shows a flow diagram of low complexity coherent joint transmission;
FIG. 5 shows another flow diagram of low complexity coherent joint transmission;
FIG. 6 shows a diagram of low complexity coherent joint transmission performance in a multi-cell 3GPP Case1-3D scenario; and
FIG. 7 shows a diagram of low complexity coherent joint transmission performance in a multi-cell ITU-UMI scenario;
Detailed Description
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof. The accompanying drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments according to the invention. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. It should be noted that although the steps of methods of the present invention are depicted in the drawings in a particular order, this does not require or imply that these operations must be performed in this particular order, or that all of the illustrated operations must be performed, to achieve desirable results, but rather that the steps described herein can be performed in an order that varies. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step decomposed into multiple step executions.
In order to better describe the scheme of the invention, the preferred embodiment of the invention is described by four parts of a CoMP system model, coherent joint transmission, low-complexity coherent joint transmission and system performance analysis.
CoMP system model
First, concepts of the CoMP system are introduced, and an original CJT (ORI-CJT) scheme is analyzed based on the concepts. On the basis of the analysis of ORI-CJT, CJT schemes with low complexity and performance gains are obtained.
We consider a cellular network with a total number of cells L and K user equipments per cell. Each base station in each cell has M antennas and each user equipment has N antennas.
The matrix represents the link between the i-th user equipment of the j-th cell and the base station of the k-th cell, and the vector
Representing the transmitted precoding vector from the k-th base station to the i-th user equipment of the j-th cell. The signal received by the i-th user equipment in the j-th cell can be expressed as formula (1)
Wherein d isi，jA transmission data vector representing the j-th cell to its i-th user equipment; vector ni，jWhich represents the white gaussian noise at the receiving end of the i-th ue in the j-th cell. One equalizer or receiver is called a matrix wi，jIs used to reduce inter-phase Interference and Noise (Interference Plus Noise: IPN). The received Signal to interference and Noise Ratio (Signal to interference plus Noise Ratio: SINR) can be expressed as
Equation (2) shows that there are three factors affecting the received SINR, the first being Multi-User Interference (MUI), the second being Inter-Cell Interference (ICI), and the last being the receive matrix. By utilizing highly accurate Channel State Information (CSI) in a Time Division multiplexing (TDD) system, the MUI can be efficiently compressed by the transmit precoder; with the design of cooperative cluster groups, CJT schemes can be used to convert partial ICI into an efficient transmission channel. In a TDD system, given ideal CSI and cluster size in a Central Node (CN), the SNIR after reception processing can be expressed as
As can be seen from formula (3), as the cluster size is continuously increased, the effective channel gain is significantly increased, and the residual ICI becomes smaller; when the cluster size is C ═ L, the residual ICI disappears. This indicates that the larger the cluster size, the higher the performance gain achieved by the CJT scheme.
The effect of the receive matrix is to compress the IPN and improve the effective channel gain. In order to reduce the cost and complexity of the terminal, linear receivers are more popular and have been widely studied. To comply with the simulation assumptions of 3GPP, we assume that a Minimum Mean Square Error-interference rejection Combining (MMSE-IRC) receiver, which may be denoted as MMSE-IRC, is employed in the user equipment
Wherein
And
can be expressed as
Fig. 1 shows a typical multi-cell CoMP system model, with a cluster consisting of three cells. The base stations of each cell are connected to the central node by backhaul links. With the backhaul link, the base station of each cell collects CSI between itself and the user equipment and then sends the CSI and related data to the CN. After all the CSI and data information are acquired, the CN first performs scheduling of the multi-user equipment and design of a transmission precoding matrix. Subsequently, the CN sends scheduling grant information, precoded information and data of the user equipment to each base station in the cluster.
Coherent joint transmission
In this section, we focus on a given cluster size of L1Coherent joint transmission of the CoMP clusters. To simplify the formulation, we assume that i-th ues in j-th cell have a unique number K in the cooperation set, which is calculated by the formula K ═ j-1) K + i and K ∈ {1, 21K }. CoMP channel of k-th user equipment for downlink data transmission can be written as
Wherein
Representing the link between k-th user equipment and the n-th cell within the CoMP cluster. In the following discussion and analysis, we assume that all user equipments in the system have data to transmit at all times. In practical systems, these user equipments without data transmission should be deleted from the candidate user equipment group.
a)Backhaul link capacity analysis
In CJT schemes, the CSI CN level it associates with the user equipment is shared by each cellDownlink CoMP channel state information of the joint user equipment (downlink channel information is obtained by utilizing channel reciprocity of a TDD system and uplink channel measurement), and multi-user scheduling and other related CoMP operations are performed by utilizing the CoMP channel state information. Assume a cluster size of L for a given coordinated multipoint transmission1And there are K user equipments in each cell, the base station of the j-th cell collects all the L associated with it1CSI of K user equipments, the CSI set can be expressed as
The base station of the j-th cell then quantizes these channel matrices and sends them to the CN over the backhaul link. For wideband communication systems, the overall bandwidth is divided into NPRBA non-frequency selective transmission resource block. This means that the base station gets all relevant channels in resource block units. To ensure the accuracy of the CSI, the real and imaginary parts of a channel coefficient are each bquaThe/2 bits are quantized. If the channel interaction period is Tperiodic(in units of subframe duration), the lower limit of the backhaul link capacity can be expressed as
Equation (8) represents the backhaul link capacity CbackhaulAnd cluster size is proportional. In the LTE TDD system, typical values of the parameters in equation (8) are (M, N) ═ 8, 2, N, respectivelyPRB100 and Tperiodic＝1ms。
If the real and imaginary parts of a channel element are quantized by 8 bits, respectively, bqua16. Let us assume that each cell has K-10 user equipments, then Cbackhaul(L1)＝256×L1(Mbps). This result indicates that a larger cluster size will pose more challenges to the capacity of the backhaul link.
b) Scheduling unit complexity analysis
In CJT schemeAnd a plurality of cells form a super cell for downlink multi-user transmission. It is feasible to use CoMP CSI shown in equation (6) to implement the design of joint multi-cell multi-user scheduling and transmission precoding. Many existing schemes for designing single cell transmissions can be extended directly to super cells. Some low complexity algorithms, such as the Multi-user eigenmode Selection (MES) method and the Enhanced MES (Enhanced MES) algorithm. In an MES algorithm, singular value decomposition of a channel matrix is utilized to obtain the maximum characteristic sub-channels of the channel, and the characteristic sub-channels are utilized to participate in the scheduling of user equipment and the design of a precoding matrix; in the EMES algorithm, a main characteristic sub-channel is obtained by performing singular value decomposition on a projection matrix of the channel, and multi-user scheduling and precoding design are performed by using the main characteristic sub-channel. The complexity of the EMES algorithm and the MES is almost the same. If the computational complexity is in units of complex operations, the complexity of both algorithms is about when the number of user equipments, K, is large
The result of this complexity calculation indicates the scheduling unit complexity sum (L)1)4And (4) in proportion. As defined in the 3GPP specifications, the cluster size is 3 in CoMP scenario I and 9 in scenario II. Even with a smaller cluster size, Ori-CJT increases the computational complexity by about 80 times compared to the single-cell base station scheduling cell complexity. Such computational complexity severely challenges the processing power of the CN.
Low complexity CJT scheme
According to the above description, the CJT scheme presents two challenges to existing networks: the complexity of the scheduling unit and the capacity of the backhaul link. In order to reduce the complexity of the scheduling unit and reduce the backhaul link burden, the present invention proposes a low-complexity CJT (LC-CJT) scheme. Fig. 2 shows a low complexity coherent joint transmission diagram. In LC-CJT, firstly, an independent distributed scheduling mode is adopted in each cell in a COMP cluster; secondly, transmitting the CSI and the data of the scheduled user equipment to the CN; then, the CN performs joint and precoding design to acquire a precoding matrix and respectively sends precoding information and user equipment data in the precoding matrix to each base station in the CoMP cluster.
a) Example of LC-CJT protocol
According to an embodiment of the present invention, as shown in fig. 3, assuming that there are two cells currently performing CoMP, the number of antennas at each base station is M, and the number of antennas at each user equipment is N. The cell of base station 11 and the cell of base station 21 form a cluster group for CoMP with cluster size 2. For simplicity of description, although fig. 3 shows a scenario of only two cells and one user per cell, it will be understood by those skilled in the art that the present invention may be applied to a multi-cell and multi-user scenario. The central node in fig. 3 may be located in any suitable network element in the communication network or as a stand-alone network element. For example, the central node may be located in a Mobility Management Entity (MME) or in any one of the base stations in the cluster. Figure 4 shows a flow chart according to an aspect of the invention.
In step S401, the base stations 11 in the CoMP cluster perform independent distributed scheduling on the user equipment 12 of the cell 10 and schedule grants to the user equipment 12. When the base station 11 performs the independent distributed scheduling, the base station 11 does not consider the scheduling information of the user equipments 22 of the neighboring cells 20. In the same way, the base station 21 performs independent distributed scheduling on the user equipment 22 of the cell 20 and schedules grants to the user equipment 22.
In step S402, the base station 11 transmits the scheduling grant information of the user equipment 12 to the central node 30, and the base station 21 transmits the scheduling grant information of the user equipment 22 to the central node 30.
In step S403, the base station 11 and the base station 21 share respective configuration information for enabling the base station 21 to monitor the channel state information H of the user equipment 12 of the base station 1112And the base station 11 monitors the channel state information H of the user equipment 22 of the base station 2121. In the LTE system, the configuration information may be configuration information of a Sounding Reference Signal (SRS), that is, configuration information of a Sounding Reference Signal (SRS)Any other suitable reference signal.
In step S404, the base stations in the cluster share their own scheduling grant information, that is, the base station 11 sends the scheduling grant information of the base station 11 to the base station 21, and the base station 21 sends the scheduling grant information of the base station 11.
In step S405, the base station 11 obtains the channel state information H of the user equipment 12 according to the configuration information and the scheduling grant information respectively11And channel state information H of the user equipment 2221And is combined with H11And H21To the central node 30. The base station 21 respectively obtains the channel state information H of the user equipment 22 according to the configuration information12And channel state information H of user equipment 1222And is combined with H12And H22To the central node 30.
In step S406, the base station 11 transmits the traffic data of the user equipment 12 to the central node 30, and the base station 21 transmits the traffic data of the user equipment 22 to the central node 30.
In step S407, the central node 30 jointly designs precoding to obtain a precoding matrix according to the scheduling grant information and the channel state information from the base stations 11 and 21.
First, the central node synthesizes downlink channel transmission information H for the user equipment 12 and the user equipment 22, respectively1＝[H11，H12]N×2MAnd H2＝[H21，H22]N×2M。
Then, the user equipment 12 is subjected to the following joint precoding design:
1) finding a projection matrix F of the channel matrix null space of the user equipment 221In which F is1Can press against
Calculating;
2) computing a projection of a channel of user equipment 12
Using projection matrices F1，
Can be expressed as
3) According toCalculating the singular value decomposition of the equivalent channel of the user equipment 12;
4) the precoding matrix of the user equipment 12 may be denoted T1＝F1V1(1: k) wherein V1(1: k) represents a matrix V1If the user equipment 12 has v (v ≦ N) data streams, k ≦ v may be selected;
5) the dimension of precoding for the user equipment 12 is 2M × k, which can also be expressed
Wherein (T)11)M×kFor base station 11 to transmit downlink data of user equipment 12, (T)12)M×kFor the base station 21 to transmit downlink traffic data of the user equipment 12.
Due to H2T10, so a precoding matrix T is utilized1When the downlink service data is transmitted for the user equipment 12, the influence of the downlink service data of the user equipment 12 on the user equipment 22 is effectively suppressed. The precoding matrix of the user equipment 22 can be designed in a similar way.
In step S408, the central node 30 will (T)11)M×kSends (T) to base station 1112)M×kTo the base station 21, and the central node 30 transmits the downlink traffic data of the user equipment 12 to the base station 21. Likewise, the central node 30 will (T)21)M×kSends (T) to the base station 2122)M×kTo the base station 11, and the central node 30 transmits the downlink traffic data of the user equipment 22 to the base station 11.
After the base station 11 and the base station 21 obtain the precoding matrix and the downlink service data of the respective user equipment, the downlink service data is transmitted for the user equipment 12 and the user equipment 22.
Fig. 5 shows another flow diagram for low complexity coherent joint transmission. Steps S501 to S503 of fig. 5 are the same as steps S401 to S403 of fig. 4, and are not described again here. In step S504, the central node 30 shares the scheduling grant information of the base stations in the cluster with the base stations in the cluster, that is, the central node 30 transmits the scheduling grant information of the base station 21 to the base station 11, and the central node 30 transmits the scheduling grant information of the base station 11 to the base station 12. It is also possible that the central node 30 broadcasts the scheduling grant information of the base station 11 and the base station 21 to the base station 11 and the base station 21 at the same time. Steps S505 to S508 of fig. 5 are the same as steps S405 to S408 of fig. 4, and are not repeated herein.
b) LC-CJT backhaul link capacity analysis
Since each base station transmits only the CSI for the scheduled user equipment, the capacity requirements for the system backhaul link are reduced. If we assume that each cell selects muiA user device, wherein i ═ 11The backhaul link capacity for CSI sharing may be calculated as follows
Mu to0Definition of
The ratio between LC-CJT and ORI-CJT can be expressed as:
in the usual case, μi< K. In LTE release 11, μ for their transmission modes 9(TM9) and 10(TM10)iA typical value is 4. This result indicates that LC-CJT has much reduced backhaul link capacity requirements compared to ORJ-CJT.
C) Scheduling unitComplexity analysis
In LC-CJT, there is no challenge to CN processing power since each cell performs distributed multi-user scheduling independently. Comparing joint scheduling and distributed scheduling, we find that the common thing is that although a proportional fairness factor (PF-factor) is used to ensure fairness of scheduling, a user equipment located in the center of a cell has a higher priority to be scheduled. In addition, the user equipment located at the center of the cell is suitable for multi-user multiple input multiple output (MU-MIMO) transmission to obtain higher spatial multiplexing gain due to its high received signal-to-noise ratio (SNR). This indicates that the distributed scheduling scheme and the joint scheduling scheme can achieve almost the same cell average gain. However, the joint scheduling scheme considers the scheduling of the cell edge ues in the global scope, whereas the distributed scheduling scheme only considers the scheduling of the edge ues in the local cell. This indicates that the distributed scheduling scheme is suboptimal for scheduling user equipments at the cell edge within a cluster, which causes some performance loss at the cell edge compared to the joint scheduling scheme. All these analysis results were verified by system simulation.
The transmission of scheduling grant information for scheduled user equipments to the CN has several advantages: for one, the processing capacity of the CN, the number of user equipments that the CN needs to process is significantly reduced; secondly, iterative computation during multi-user scheduling by using a greedy algorithm can be avoided; thirdly, the CN does not need to consider the order of the user equipments when designing the precoding matrix. Thus, the ratio of the ratios of the computational complexity of ORI-CJT and LC-CJT as in equation (11) is greater than L1K。
System performance analysis
To better demonstrate the advantages of the present invention, the present invention compares the performance of ORI-CJT and LC-CJT through system simulation. To clearly show the performance gains of both CoMP schemes, the performance of a single cell is used as a baseline. In Single Cell (SC), ORI-CJT and LC-CJT schemes, eMES based user equipment scheduling algorithm is adopted. The gain comparison for all CoMP schemes is based on a typical CoMP scenario illustrated in fig. 1. The main simulation parameter settings are listed in table 1, which is consistent with the relevant TDD downlink simulation parameter settings specified in 3 GPP. To fairly compare the LC-CJT and ORI-CJT schemes, the statistical performance (shown by the Cumulative Distribution Function (CDF)) and the system average performance were compared. The system average performance includes the average performance of the cell spectral efficiency (denoted "cell AVG") [ bit/frequency/cell ] and the user equipment spectral efficiency (denoted "cell edge") [ bit/hz/user equipment ] of 5%.
TABLE 1 System simulation parameter settings
Fig. 6 shows a diagram of low complexity coherent joint transmission performance in a multi-cell 3GPP Case1-3D scenario. The graph shown in FIG. 6 shows a comparison of the statistical performance of downlink CoMP transmission for SC, LC-CJT and ORI-CJT schemes in the 3GPP case 13D scenario. These curves show that the LC-CJT scheme can obtain huge CoMP gain compared with SC of non-multipoint cooperative transmission, and the performance gap between the LC-CJT scheme and the ORI-CJT scheme is small. The average performance of the three protocols is listed in table 2. In table 2, we can see that the LC-CJT scheme can obtain a cell average performance gain of more than 35% and a performance gain of more than 30% at the cell edge. However, compared to the ORI-CJT scheme, the LC-CJT scheme has a performance gain of about 8% at the cell edge due to the second best scheduling.
TABLE 2 Performance comparison in 3GPP Case1-3D scenario
In order to verify the robustness of the LC-CJT scheme in other transmission scenes, the invention compares the SC, LC-CJT and ORI-CJT schemes in the scene of UMI transmission of the International Union of telecommunication. Fig. 7 shows a schematic diagram of low complexity coherent joint transmission performance in the scenario of UMI transmission of international federation of multiple cells. The curves shown in fig. 7 indicate that LC-CJT can obtain a larger performance gain than SC scheme in the scenario of UMI transmission of the international federation, and the multipoint cooperation gain gap between LC-CJT and ORI-CJT is small. The average performance in these three schemes is listed in table 3. LC-CJT can achieve over 40% cell average performance gain and over 35% cell edge performance gain compared to SC, but there is approximately a 9% cell edge performance gain gap between LC-CJT and ORI-CJT.
Table 3 comparison of performance in scenarios of international union of telecommunication UMI transmission
The invention provides a low-complexity CJT scheme for CoMP downlink transmission. Under a plurality of coordinated multi-point transmission scenes, the scheme provided by the invention obtains good performance gain, and compared with a single-cell scheme, the scheme provided by the invention realizes the cell average performance gain of more than 35% and the cell edge performance gain of more than 30%. The cost of the LC-CJT scheme is a performance loss at the cell edge of around 10% compared to ORI-CJT. However, the LC-CJT scheme can improve the performance of the entire system because it can be flexibly implemented in a real network due to its low complexity.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Furthermore, it will be obvious that the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. Several elements recited in the apparatus claims may also be implemented by one element. The terms first, second, etc. are used to denote names, but not any particular order.
The previous description of the invention is provided to enable any person skilled in the art to make or use the invention. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the present invention is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (14)
1. A method of low complexity multi-cell downlink coherent joint transmission performed by a central node of a cluster of base stations, comprising the steps of:
i. receiving scheduling grant information and channel state information from a first base station and a second base station in the base station cluster, wherein a cell of the first base station is adjacent to a cell of the second base station;
jointly designing precoding to obtain a precoding matrix according to the scheduling grant information and the channel state information from the first base station and the second base station;
sending precoding information of user equipment of the first base station in the precoding matrix to the first base station, and sending precoding information of user equipment of the second base station in the precoding matrix to the second base station; and
and sending the service data of the user equipment of the second base station to the first base station and/or sending the service data of the user equipment of the first base station to the second base station.
2. The method of claim 1, wherein the joint design takes into account interference that the precoding matrix may cause to downlink transmissions of other user equipments in the matrix when designing the precoding matrix for the user equipment.
3. The method of claim 1, wherein the scheduling grant information is obtained by independent distributed scheduling of the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
4. The method of claim 1, wherein the channel state information comprises channel state information of user equipment of the cell of the base station and channel state information of user equipment of neighboring cells of the cell of the base station.
5. A method of low complexity multi-cell downlink coherent joint transmission performed by a base station in a cluster of base stations, comprising the steps of:
i. transmitting scheduling authorization information of user equipment of a cell of the base station to a central node;
receiving precoding information of the user equipment of the cell of the base station from the central node; and
performing downlink joint transmission on the service data of the user equipment of the base station according to the precoding information and the scheduling authorization information;
wherein the method further comprises:
sharing configuration information of user equipment of the cell of the base station with base stations of neighboring cells of the cell of the base station in the cluster of base stations; and
and receiving the service data of the user equipment of the adjacent cell of the base station from the central node for downlink joint transmission.
6. The method according to claim 5, wherein the scheduling grant information is obtained by independent distributed scheduling of the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
7. The method of claim 5, wherein the configuration information is for causing a base station of the neighboring cell to monitor channel state information of user equipment of the cell of the base station.
8. The method of claim 5, further comprising sending channel state information to the central node, the channel state information comprising channel state information of user equipment of the cell of the base station and channel state information of user equipment of neighboring cells of the cell of the base station.
9. A central node for low complexity multi-cell downlink coherent joint transmission, comprising:
a receiving unit, configured to receive scheduling grant information and channel state information from a first base station and a second base station in a cluster of base stations, where the first base station and the second base station belong to the cluster of base stations, and a cell of the first base station is adjacent to a cell of the second base station;
a joint precoding unit, configured to jointly design precoding according to the scheduling grant information and the channel state information from the first base station and the second base station to obtain a precoding matrix;
a first transmitting unit, configured to transmit precoding information of a user equipment of the first base station in the precoding matrix to the first base station, and transmit precoding information of a user equipment of the second base station in the precoding matrix to the second base station; and
a second transmitting unit, configured to send traffic data of the ue of the second base station to the first base station and/or send traffic data of the ue of the first base station to the second base station.
10. The central node of claim 9, wherein the joint design takes into account interference that the precoding matrix may cause to downlink transmissions of other user equipments in the matrix when designing the precoding matrix for the user equipments.
11. The central node according to claim 9, wherein the scheduling grant information is obtained by independent distributed scheduling of the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
12. The central node of claim 9, wherein the channel state information comprises channel state information of user equipment of the cell of the base station and channel state information of user equipment of neighboring cells of the cell of the base station.
13. A base station for low complexity multi-cell downlink coherent joint transmission, comprising:
a first transmitting unit, configured to transmit scheduling grant information of a user equipment of a cell of the base station to a central node;
a sharing unit configured to share configuration information of a user equipment of a base station with a base station of a neighboring cell of the base station in a cluster of base stations, the configuration information being used to cause the base station of the neighboring cell to monitor channel state information of the user equipment of the base station, the base station and the base station of the neighboring cell of the base station belonging to the cluster of base stations;
a second transmitting unit, configured to transmit channel state information to the central node, where the channel state information includes channel state information of user equipment of the cell of the base station and channel state information of user equipment of a cell adjacent to the cell of the base station;
a first receiving unit for receiving precoding information of the user equipment of the cell of the base station from the central node;
a second receiving unit, configured to receive traffic data of user equipment in a cell adjacent to the cell of the base station from the central node for downlink joint transmission; and
and a third transmitting unit, configured to perform downlink joint transmission on service data of the user equipment of the base station according to the precoding information and the scheduling authorization information.
14. The base station according to claim 13, wherein the scheduling grant information is obtained by independent distributed scheduling of the user equipments of the cell of the base station, the independent distributed scheduling not taking into account scheduling grant information of user equipments of neighboring cells of the cell of the base station.
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| CN101599814A (en) * | 2009-07-08 | 2009-12-09 | 北京邮电大学 | Downlink transfer preprocess method and system in the collaboration communication |
| CN102932937A (en) * | 2011-08-11 | 2013-02-13 | 上海贝尔股份有限公司 | Method and equipment for scheduling user equipment in cellular communication system |
| CN103119873A (en) * | 2010-02-12 | 2013-05-22 | 捷讯研究有限公司 | Rence signal for a coordinated multi-point network implementation |
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| CN102415120B (en) * | 2009-08-18 | 2013-11-27 | 上海贝尔股份有限公司 | Coordinated multipoint transmission method and apparatus therefor |
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| CN103119873A (en) * | 2010-02-12 | 2013-05-22 | 捷讯研究有限公司 | Rence signal for a coordinated multi-point network implementation |
| CN102932937A (en) * | 2011-08-11 | 2013-02-13 | 上海贝尔股份有限公司 | Method and equipment for scheduling user equipment in cellular communication system |
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