Method for providing channel state information and precoding information between a remote radio unit and a baseband unit

Abstract

The present disclosure relates to a method for providing channel state information (CSI) from a remote radio unit (RRU) to a baseband unit (BBU), the method comprising: determining CSI for each of a plurality of user equipments (UEs) based on a reference signal received from a corresponding UE; generating a plurality of correlation coefficients based on the CSI; and providing the plurality of correlation coefficients to the BBU.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for providing channel state information (CSI) and precoding information between a remote radio unit (RRU) and a baseband unit (BBU). In particular, the present disclosure relates to a scheme for delivering a large amount of CSI from an RRU to a BBU in a fronthaul for a multi-user massive MIMO system. Background Art

[0002] like Figure 1 The eNB of the massive MIMO system 100 shown in FIG. 1 can be generally implemented by two functional units: a remote radio unit (RRU) 110 and a baseband unit (BBU) 120. The RRU 110 is deployed with a large antenna array that provides the following functions: radio transmission / reception and some simple signal pre-processing, such as FFT / iFFT and channel estimation. The BBU 120 is responsible for advanced baseband signal processing, such as UE scheduling, precoding, and channel coding / decoding. In order to perform MIMO transmission, the CSI (i.e., MIMO vector) of each UE 141, 142, 143, 144, 145 must be delivered from the RRU 110 to the BBU 120 via the fronthaul link 130 for the purpose of MIMO scheduling and precoding at the BBU 120.

[0003] In conventional solutions, all CSI for each UE 141, 142, 143, 144, 145 is delivered from the RRU 110 to the BBU 120. The amount of CSI-related information to be delivered increases significantly with the size of the antenna array. Existing CSI delivery solutions consume a large amount of fronthaul bandwidth, thus becoming a challenging problem when implementing a massive MIMO system. Therefore, there is a need to provide an improved CSI delivery scheme for reducing the required bandwidth in the fronthaul of a multi-user (MU) massive MIMO system. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The accompanying drawings are included to provide a further understanding of the examples and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate examples and, together with the description, are used to explain the principles of the examples. Other examples and the intended advantages of the examples will be easily appreciated as they become better understood by reference to the following detailed description.

[0005] Figure 1 is a schematic diagram showing a MIMO system with a plurality of user equipments (UEs) and a base station system including a remote radio unit (RRU) and a baseband unit (BBU).

[0006] Figure 2is a schematic diagram showing an example of a massive MIMO eNB with RRU and BBU functional partitioning according to the present disclosure.

[0007] Figure 3 is a flow chart 300 illustrating the flow of session data for a CSI delivery scheme according to the present disclosure.

[0008] Figure 4 is a schematic diagram illustrating a method 400 for providing channel state information (CSI) from an RRU to a BBU according to the present disclosure.

[0009] Figure 5 is a schematic diagram illustrating a method 500 for providing precoding information from a BBU to an RRU according to the present disclosure.

[0010] Figure 6 is a schematic diagram illustrating an RRU circuit 600 for providing CSI to a BBU according to the present disclosure.

[0011] Figure 7 is a schematic diagram illustrating a BBU circuit 700 for providing precoding information to an RRU according to the present disclosure. DETAILED DESCRIPTION

[0012] In the following detailed description, reference is made to the accompanying drawings, which form a part thereof and in which are shown by way of illustration specific aspects in which the present disclosure may be practiced. It should be understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0013] The following terms, abbreviations and notations are used in this article:

[0014] RRU: Remote Radio Unit

[0015] BBU: Baseband Unit

[0016] CSI: Channel State Information

[0017] MU: Multi-User

[0018] MIMO: Multiple Input Multiple Output

[0019] RF: Radio Frequency

[0020] LTE: Long Term Evolution

[0021] UE: User Equipment, Mobile Device, Mobile Terminal

[0022] OFDM: Orthogonal Frequency Division Multiplexing

[0023] eNB: Base Station

[0024] eNodeB: base station.

[0025] The methods and devices described herein can be applied in base stations and base station systems including RRUs and BBUs that can be coupled via a fronthaul link. It should be understood that the comments made in conjunction with the described method may also apply to corresponding devices configured to perform the method and vice versa. For example, if specific method steps are described, the corresponding device may include such units even if the units for performing the described method steps are not explicitly described or illustrated in the figure. Further, it should be understood that the features of the various exemplary aspects described herein may be combined with each other unless specifically noted otherwise.

[0026] The methods and devices described herein can be implemented in wireless communication networks, specifically, communication networks based on mobile communication standards (e.g., LTE, specifically, LTE-A and / or OFDM) and successor standards (e.g., 5G). These methods are also applicable to connection standards, specifically, high-speed standards and successor standards from the 802.11 series (e.g., 802.11ad). The methods and devices described below can be implemented in electronic devices, specifically, electronic circuits of base stations (eNodeB, eNB, access points) with RRU and BBU. The described devices may include integrated circuits and / or passive devices and may be manufactured according to various technologies. For example, the circuit may be designed as a logic integrated circuit, an analog integrated circuit, a mixed signal integrated circuit, an optical circuit, a memory circuit, and / or an integrated passive device.

[0027] The methods and devices described herein may be configured to send and / or receive radio signals and perform associated signal processing. The radio signals may be or may include radio frequency signals radiated by a radio transmitting device (or radio transmitter or transmitter) at a radio frequency in the range of about 3kHz to about 300GHz. The frequency range may correspond to the frequency of an alternating current signal used to generate and detect radio waves.

[0028] The methods and devices described hereinafter may be designed according to mobile communication standards such as, for example, the Long Term Evolution (LTE) standard or its advanced version LTE-A. LTE, marketed as 4G LTE and in the future 5G LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals.

[0029] The methods and devices described below can be applied in OFDM systems. OFDM is a scheme for encoding digital data on multiple carrier frequencies. A large number of closely spaced orthogonal subcarrier signals can be used to carry data. Due to the orthogonality of the subcarriers, crosstalk between subcarriers can be suppressed.

[0030] The methods and devices described below can be applied in multiple-input multiple-output (MIMO) systems (specifically, multi-user MIMO systems and diversity receivers). MIMO wireless communication systems use multiple antennas at the transmitter and / or at the receiver to increase system capacity and to achieve better service quality. In spatial multiplexing mode, MIMO systems can achieve higher peak data rates without increasing the bandwidth of the system by sending multiple data streams in parallel in the same frequency band. Diversity receivers use two or more antennas to improve the quality and reliability of wireless links.

[0031] Hereinafter, examples are described with reference to the accompanying drawings, wherein similar reference numerals are generally used to refer to similar elements throughout. In the following description, for the purpose of illustration, many specific details are set forth in order to provide a thorough understanding of one or more aspects of the examples. However, it may be apparent to those skilled in the art that one or more aspects of the examples may be practiced with lesser degrees of these specific details. The following description should therefore not be made in a restrictive sense.

[0032] The various aspects summarized may be embodied in various forms. The following description illustrates various combinations and configurations in which the various aspects may be practiced by way of illustration. It should be understood that the described aspects are merely examples and other aspects may be utilized, and structural and functional modifications may be made without departing from the scope of the present disclosure.

[0033] In the following, different solutions for delivering RRC information from the RRU to the BBU are described. A simple solution is to deliver explicit CSI (i.e., MU-MIMO channel matrix H of size N*K) of all UEs from the RRU to the BBU in the fronthaul, where N is the number of antenna arrays and K is the number of UEs. As the value of N becomes larger in massive MIMO systems, the size of the CSI consumes more bandwidth in the fronthaul. Despite the application of compression techniques in the fronthaul, the amount of CSI related information to be delivered still increases significantly with the size of the antenna array.

[0034] The solution as described in the present disclosure (which may be referred to as a two-part design or a two-part solution) is to introduce an implicit CSI delivery scheme. That is, the correlation matrix between the CSIs delivered to all UEs, i.e., H of size K*K H H, which does not scale up in massive MIMO systems. The results show that at the BBU, when used in MIMO scheduling and precoding without any performance loss, H H The knowledge of H may play the same role as the knowledge of H. Therefore, the two-part solution according to the present disclosure may overcome the shortcomings of the simple solutions indexed above as described hereinafter.

[0035] Figure 2 1 is a schematic diagram showing a massive MIMO eNB example 200 with a functional split of the RRU 110 and the BBU 120 according to the present disclosure. The functions of the RRU 110 include MIMO channel estimation 214 and MIMO precoder generation 215, whereas the functions of the BBU 120 include UE scheduling 221 and MIMO precoding 222. On the fronthaul link 130, CSI compression 231 data is transferred from the RRU 110 to the BBU 120, and UE scheduling and precoding information notification 232 is transferred from the BBU 120 to the RRU 110.

[0036] Figure 2 A scenario is shown in which the eNB of the massive MIMO system 200 is functionally divided into two physical units, namely, the RRU 110 (including the RRH 211) and the BBU 120, which are connected via a high-speed fronthaul link 130. The functions of the RRU 110 and the BBU 120 are mainly radio-related and baseband-related, respectively. The RRH 211 inside the RRU 110 transmits and receives radio signals, and the RRU 110 has some limited capabilities for signal preprocessing, such as FFT / iFFT, channel estimation, etc.

[0037] In a TDD system, the RRU 110 performs MIMO channel estimation based on the uplink sounding reference signal (SRS). Then, the CSI is obtained for each UE at the RRU 110. The CSI of a UE is called the MIMO channel vector between the eNB and the UE. For example, according to Figure 1 Consider a scenario where K UEs are served in a massive MIMO system. The CSI of UEk (1≤k≤K) on any subcarrier can be expressed as

[0038] h k =[h k，1 ,h k，2 ...,h k，N ] T ,

[0039] Where N is the dimension of the MIMO channel vector and h k，n is the nth element of the MIMO channel vector. Considering that the dimension of the MIMO channel vector is the product of the number of TX and RX antennas at the RRU 110 and the UE, the value of N can be very large in practice, for example, N=64*8.

[0040] The multi-UE CSI matrix is ​​performed by aggregating the CSI vectors of all K UEs into the following matrix:

[0041] H=[h1,h2...,h K ].

[0042] The CSI delivery scheme directly transfers h for UEk in the fronthaul. k Delivered from RRU 110 to BBU 120. It is apparent that the size of the CSI matrix for multiple UEs is N*K, which scales with the dimension of the MIMO channel vector or equivalently the size of the antenna array in a massive MIMO system. If measured by a scalar, the CSI matrix for multiple UEs contains 2N*K elements to be delivered.

[0043] In a massive MIMO system, typical values ​​of N=256 and K=20 mean that 10240 scalars are delivered in the fronthaul for a single subcarrier. As system bandwidth expands in the 5G era, the delivery of CSI from RRU 110 to BBU 120 may consume a large amount of fronthaul bandwidth without careful design.

[0044] A simple solution to this problem is to apply CSI compression techniques in the fronthaul. For example, given the CSI at the RRU k , the optimal quantizer can be applied to quantize h k , and then the quantization index is delivered from the RRU 110 to the BBU 120 in the fronthaul 130 to save bandwidth. However, this method only alleviates the problem to a certain extent, rather than being a fundamental solution. This is because the performance limit of theoretical quantization generally increases with the size of the antenna array. Therefore, compression techniques that improve CSI delivery schemes will not work efficiently in massive MIMO systems.

[0045] In the following, the new CSI delivery scheme is described. The present disclosure introduces a new correlation matrix for the CSI of all UEs:

[0046]

[0047] Among them, ρ k，l =h k H h l The elements of are the complex correlation coefficients between the CSI pairs of UE k and UE l. The size of the correlation matrix is ​​K*K, and its basic feature is that it no longer scales with the dimension of the MIMO channel vector. Therefore, the new correlation matrix ρ is completely different from the CSI matrix H of multiple UEs.

[0048] Furthermore, it can be observed that the matrix ρ is Hermitian. Therefore, only half of the matrix needs to be delivered, i.e., the upper (or lower) triangular part of ρ, which is

[0049]

[0050] Thus, the amount of variables to be delivered becomes K(K+1) / 2. If measured by scalars, it contains K*K scalars to be compressed, since the diagonal is only scalars.

[0051] When K is less than 2N, the amount of information in the new CSI delivery scheme is reduced from the above compression scheme.As suggested by 3GPP simulation parameters, in most cases the active number of UEs per RRU 110 typically ranges from K=10 to 30, which is typically less than 2N.

[0052] Compared with the compression-based scheme that delivers H, delivering ρ in the forward transmission net The new solution reduces the bandwidth required

[0053]

[0054] The improved performance of reduced bandwidth for CSI delivery under typical settings of N and K is shown in Table 1.

[0055] η K＝10 K＝20 K＝30 N＝16 68.75％ 37.50％ 6.25％ N＝32 84.38％ 68.75％ 53.13％ N＝64 92.19％ 84.38％ 76.56％

[0056] Table 1: Bandwidth reduction in fronthaul by public CSI delivery schemes

[0057] The correlation matrix p can play a similar role as the original multi-UE CSI matrix H in UE MIMO scheduling and precoding without losing performance as shown below.

[0058] In some cases, the BBU needs to schedule the UE by relying only on the information of the correlation matrix ρ. For example, if the number of candidate UEs is greater than the supportable MIMO rank in the transmission. There are many types of MIMO scheduling algorithms. A widely used MIMO scheduler in the spatial domain is the greedy MIMO scheduler, which is provided in Table 2 for scheduling T UEs from N UEs for SDMA access in a massive MIMO system.

[0059]

[0060]

[0061] Table 2: Greedy algorithm for MU-MIMO scheduling

[0062] The above MIMO scheduling algorithm is compatible with the widely used time domain scheduling algorithm. For example, when considering the proportional fair scheduler (PFS), the sum rate of MIMO scheduling can be calculated as

[0063]

[0064] in, It is the proportional fairness factor when scheduling from the time domain.

[0065] Ue k The rate under MU-MIMO transmission depends on the specific MU-MIMO precoding scheme used. In fact, zero forcing (ZF) or MMSE precoding schemes are two types of widely adopted MU-MIMO precoding. The explicit forms of ZF and MMSE precoding are given as

[0066]

[0067] Among them, P ZF and P MMSE should be normalized to a set of unit norm precoders, and H S is the CSI matrix of multiple UEs formed by the UE set S.

[0068] About H H The correlation matrix of H is delivered from the RRU to the BBU instead of the multi-UE CSI matrix H. This means that the ZF and MMSE precoders are not actually available at the BBU.

[0069] Although BBU 120 does not know the CSI matrix H of multiple UEs, it can be obtained by using only the correlation matrix H H H to calculate UEu k In mathematics, after ZF or MMSE precoding, the UEu in the UE set S k The SINR is derived as

[0070]

[0071] It means that UEu in UE set S can be k The rate is expressed as

[0072]

[0073] Therefore, in the present disclosure, the BBU can rely on ρ in MU-MIMO scheduling. To this end, the temporary UE set S n UEu in k The rate during MU-MIMO scheduling is calculated as

[0074]

[0075] or in

[0076]

[0077] In the following, the MIMO precoding information notification from the BBU to the RRU is described. Because the CSI matrix of multiple UEs is not delivered from the RRU 110 to the BBU 120, the BBU 120 cannot generate a complete MU-MIMO precoder for the scheduled UE. To solve this problem, a two-part precoder is introduced here. The complete precoder of the UE consists of two parts. One part is generated at the BBU 120 using the following calculation:

[0078] P ZF，2 =(ρS) -1 , or P MMSE，2 =(ρ S +I) -1 .

[0079] The other part is known at the RRU 110, which does not require any calculation

[0080] P ZF，1 =P MMSE，1 =H s .

[0081] The BBU 120 sends the scheduled UE set S, rate information R(S) (or link adaptation information, such as MCS level), and partial precoder P ZF，2 or P MMSE，2 The RRU 110 constructs the full MIMO ZF or MMSE precoder as

[0082] P ZF =P ZF，1 P ZF，2 or P MMSE =P MMSE，1 P MMSE，2 .

[0083] The method of two-part MIMO precoder generation gives an improvement to the precoder information notification for the compression-based CSI delivery scheme (ie, one-part design) as described above.

[0084] In the compression-based CSI delivery scheme (i.e., one-part design) as described above, if the precoder is not divided into two parts, the complete precoder of each UE is notified from the BBU 120 to the RRU 110 in the fronthaul 130, which has a size of N*T. In contrast, by using the two-part design described above, the partial precoder information in the notification has a size of T*T. Then, the efficiency of the precoder information notification with and without the two-part precoder design is improved by

[0085]

[0086] Such improvements are shown in Table 3 under a typical system setup.

[0087] η T＝2 T＝4 T＝8 N＝16 87.50％ 75％ 50％ N＝32 93.75％ 87.5％ 75％ N＝64 96.88％ 93.75％ 87.5％

[0088] Table 3: Bandwidth reduction for precoder information notification in fronthaul by two-part precoder design

[0089] Therefore, the present disclosure introduces a new CSI delivery scheme, where a much smaller amount of CSI information and precoder information will be delivered in the fronthaul of a multi-user massive MIMO system, while not sacrificing any performance from the simple solution indexed above.

[0090] Figure 3 300 is a flow chart showing a session data flow 310 of a CSI delivery scheme according to the present disclosure. The session data flow 310 includes three blocks performed at the RRU 110, which are: MIMO channel estimation 301, MU-CSI correlation matrix generation 302, and CSI compression 303. The compressed CSI is then delivered 304 from the RRU 110 to the BBU 120, and two blocks UE scheduling 305 and partial precoding generation 306 are performed at the BBU 120. The RRU is then notified 307 of the scheduling and precoding information from the BBU 120, and a full precoding generation 308 is performed at the RRU 110.

[0091] At the first block MIMO channel estimation 301, the RRU performs channel estimation for each UE, for example based on a sounding reference signal (SRS) in the uplink, and obtains the CSI of the MIMO channel vector. The CSI of the UE on any one of the subcarriers is represented as

[0092] h k =[h k，1 ,h k，2 …,h k，N ] T ,

[0093] where N is the length of the CSI in the MIMO vector, and h k，n is the nth element in CSI.

[0094] The multi-UE CSI matrix for all K UEs is denoted as H = [h1, h2, ..., h K ].

[0095] At the second block correlation matrix generation 302, the RRU 110 then generates a triangular correlation matrix from the CSI matrix H of the multiple UEs as

[0096]

[0097] in

[0098] ρ k，l =h k H h l .

[0099] In the third block CSI compression 303, CSI compression techniques are applied to compress the triangular correlation matrix ρ net , which compresses the K*K scalars contained into as few bits as possible. The CSI compression technique depends on the embodiment, which can be but is not limited to a general quantizer or a quantizer for ρ net Optimized other quantizers.

[0100] In the fourth item, compressed CSI delivery 304 is performed. The bits of compressed CSI are delivered from the RRU to the BBU in the fronthaul by using a common interface, such as a CPRI interface.

[0101] In the fifth step UE scheduling 305, the BBU first schedules the UE based on the received triangular correlation matrix ρ net To recover the correlation matrix ρ, it is expressed as ρ = ρ net +ρ net H -diag(ρ net ),

[0102] Here, diag (rownet) represents a diagonal operation on a matrix, for example, as defined as a Matlab command.

[0103] The BBU performs MU-MIMO scheduling by adopting the received correlation matrix ρ. An example of a MU-MIMO scheduler may be the greedy algorithm shown in block 2.b. The temporary UE set S n UEu in (1≤n≤T) k The rate during MU-MIMO scheduling is calculated as

[0104]

[0105] or

[0106] in

[0107]

[0108] Used for The weight information of depends on the scheduling strategy applied in the massive MIMO system. It may be a proportional fairness factor or may be different depending on the corresponding embodiment.

[0109] In the sixth step, in the partial MIMO precoding generation at the BBU 306, the BBU generates partial precoding information P for the scheduled UE set S. ZF，2 =(ρ S ) -1 , P MMSE，2 =(ρ S +I) -1 .

[0110] In the seventh step, precoding and scheduling information notification 307, the BBU will schedule the UE set S, rate information R(S) (or link adaptation information such as MCS level) and partial precoding P via the fronthaul. ZF，2 or P MMSE，2 Delivered to RRU.

[0111] In the eighth step, the full precoder generation at the RRU 308, the RRU constructs the full MIMO ZF or MMSE precoder as

[0112] P ZF =P ZF，1 P ZF，2 or P MMSE =P MSSE，1 P MMSE，2 ,

[0113] in

[0114] P ZF，1 =P MMSE，1 =H s .

[0115] The new scheme according to the present disclosure can be characterized by the following two key points. The first key point is improved CSI delivery. In the present disclosure, a new CSI delivery scheme is presented, where implicit CSI in terms of a correlation matrix is ​​delivered from the RRU to the BBU in the fronthaul. The amount of implicit CSI to be delivered does not scale with the size of the antenna array, which is particularly important in massive MIMO systems. The efficiency of CSI delivery is improved. times, which is significant when the number K of UEs used for scheduling is much smaller than the size N of the antenna array.

[0116] The second key point is improved precoder information notification. The precoder information delivery from the BBU to the RRU is improved by using a two-part precoder generation scheme. Only the part of the precoder that needs to be calculated is delivered from the BBU to the RRU, however the remaining part of the precoder is not delivered because the RRU already knows it. In this way, the amount of information for precoder notification from the BBU to the RRU can be reduced from a one-part precoder generation scheme. The efficiency of precoder information notification is improved. times, which is significant when the number of scheduled UEs T is much smaller than the size N of the antenna array.

[0117] The method and apparatus according to the present disclosure can be applied in wireless products, such as 3GPP standards related to MIMO systems below 6 GHz or massive MIMO millimeter wave systems above 6 GHz. The method and apparatus according to the present disclosure can also be applied in a part of an IEEE standard wireless millimeter wave system.

[0118] Figure 4 4 is a schematic diagram showing a method 400 for providing CSI from an RRU to a BBU according to the present disclosure. Figures 1 to 3 The RRU 110 described above is Figures 1 to 3 The general representation of CSI delivery of the BBU 120 described above, in particular, Figure 3 A general representation of the four steps MIMO channel estimation 301 , MU-CSI correlation matrix generation 302 , CSI compression 303 and compressed CSI delivery 304 are described.

[0119] Method 400 includes providing a plurality of UEs (e.g., Figure 1 Each of the UEs 141, 142, 143, 144, 145) shown in FIG. 4 determines 401 CSI. The method 400 includes generating 402 a plurality of correlation coefficients based on the CSI, for example as described above with respect to Figure 2 and Figure 3 The method 400 includes providing 403 a plurality of correlation coefficients to the BBU, for example as described above with respect to Figure 2 and Figure 3 as described.

[0120] The method 400 may further include generating a plurality of correlation coefficients based on the CSI pairs determined for the corresponding UE pairs, such as described above with respect to Figure 2 and Figure 3 as described.

[0121] The method 400 may further include: compressing the plurality of correlation coefficients, for example according to a common compression scheme; and providing the plurality of correlation coefficients in compressed form. The method 400 may further include providing the plurality of correlation coefficients via a common public radio interface. The method 400 may further include providing the plurality of correlation coefficients from the RRU 110 to the BBU 120 via the fronthaul link 130, for example as described above with respect to Figure 2 and Figure 3 as described.

[0122] The method 400 may further include generating a plurality of correlation coefficients based on a correlation matrix of size K*K, where K is the number of UEs used to determine the CSI, such as described above with respect to Figure 2 and Figure 3 as described.

[0123] The method 400 may further include determining a correlation matrix based on a multi-UE CSI matrix including the CSI determined for each UE, such as described above with respect to Figure 2 and Figure 3 as described.

[0124] The size of the multi-UE CSI matrix may be, for example, N*K, where K is the number of UEs for determining CSI and N is the dimension of the MIMO channel vector between the corresponding UE and the RRU, e.g., as described above with respect to Figure 2 and Figure 3 as described.

[0125] The multi-UE CSI matrix can be H = [h1,h2,...,h K ], the MIMO channel vector is h k =[h k,1 ,h k,2 ,...,h k,N ] T , where h k,n is the kth MIMO channel vector h k The nth element of Figure 2 and Figure 3 as described.

[0126] The correlation matrix can be expressed as

[0127]

[0128] Among them, the element ρ of the correlation matrix k，l =h k H h l is the complex correlation coefficient between the CSI pairs of the kth UE and the lth UE, for example, as mentioned above Figure 2 and Figure 3 as described.

[0129] Method 400 may further include based on, for example, Figure 2 and 3 The lower triangular part or the upper triangular part of the correlation matrix described above is used to generate multiple correlation coefficients, and the lower triangular part or the upper triangular part is

[0130]

[0131] The compression rate for providing multiple correlation coefficients based on the correlation matrix relative to providing multiple correlation coefficients based on the multi-UE CSI matrix may be For example, as mentioned above Figure 2 and Figure 3 as described.

[0132] Figure 5 is a schematic diagram illustrating a method 500 for providing precoding information from a BBU to an RRU according to the present disclosure.

[0133] Method 500 is described as above with respect to Figures 1 to 3 A general representation of the described scheduling and precoding information notification scheme, in particular as described above with respect to Figure 3 A general representation of the four steps UE scheduling 305, partial precoder generation 306, scheduling and precoder information notification 307 and full precoder generation 308 are described.

[0134] The method 500 includes receiving 501 a plurality of correlation coefficients from the RRU 110, the plurality of correlation coefficients being based on CSI from a plurality of UEs, for example, according to the above description of Figure 3 Compressed CSI delivery 304 is described.

[0135] The method 500 includes generating 502 partial precoding information for at least a set of UEs from a plurality of UEs based on the received correlation coefficients, such as described above with respect to Figure 2 and Figure 3 The method 500 further includes providing 503 the partial precoding information to the RRU, for example as described above with respect to Figure 2 and Figure 3 as described.

[0136] The remaining part of the precoding information may be known to the RRU, for example, by definition. The method 500 may further include: scheduling the set of UEs based on the received correlation coefficients according to a scheduling strategy; and generating partial precoding information for the scheduled set of UEs, for example, as described above with respect to Figure 2 and Figure 3 The scheduling strategy is based on greedy scheduling, for example, as described above Figure 2 and Figure 3 as described.

[0137] The method 500 may include providing at least one of information about the scheduled UE set, rate information, and link adaptation information to the RRU. The method 500 may further include providing partial precoding information from the BBU 120 to the RRU 110 via a fronthaul link, such as described above with respect to Figure 2 and Figure 3 as described.

[0138] Figure 6 1 is a schematic diagram showing an RRU circuit 600 for providing CSI to a BBU according to the present disclosure. The RRU circuit 600 may be implemented in the RRU 110 to perform the above-mentioned Figures 1 to 3 The functionality of the RRU 100 is described.

[0139] The RRU circuit 600 includes a processor 601 and a transmitter 602. The processor 601 is configured to determine CSI for each of a plurality of UEs based on a reference signal received from the corresponding UE and generate a plurality of correlation coefficients 603 based on the CSI, for example as described above with respect to Figure 2 and Figure 3 The transmitter 602 is configured to provide a plurality of correlation coefficients 603 to the baseband unit BBU 120, for example as described above with respect to Figure 2 and Figure 3 as described.

[0140] The processor 601 may be configured to generate a plurality of correlation coefficients 603 based on pairs of CSI determined for respective pairs of UEs, for example as described above with respect to Figure 2 and Figure 3 as described.

[0141] The processor 601 may be configured to compress the plurality of correlation coefficients 603, for example as described above with respect to Figure 2 and Figure 3 The transmitter 602 may be configured to provide the plurality of correlation coefficients 603 in a compressed form.

[0142] The transmitter 602 may be configured to provide the plurality of correlation coefficients 603 via a common public radio interface. The transmitter 602 may be configured to provide the plurality of correlation coefficients 603 to the BBU 120 via the fronthaul link 130, for example as described above with respect to Figure 2 and Figure 3 as described.

[0143] The processor 601 may be configured to generate a plurality of correlation coefficients 603 based on a correlation matrix of size K*K, where K is the number of UEs used to determine CSI, for example as described above with respect to Figure 2 and Figure 3 as described.

[0144] The processor 602 may be configured to determine a correlation matrix based on a multi-UE CSI matrix including the CSI determined for each UE, for example as described above with respect to Figure 2 and Figure 3The size of the multi-UE CSI matrix may be N*K, where K is the number of UEs for determining CSI and N is the dimension of the MIMO channel vector between the corresponding UE and the RRU 110, e.g., as described above with respect to Figure 2 and Figure 3 as described.

[0145] The multi-UE CSI matrix can be expressed as H = [h1,h2,...,h K ], the MIMO channel vector is h k =[h k,1 ,h k,2 ,...,h k,N ] T , where h k,n is the kth MIMO channel vector h k The nth element of Figure 2 and Figure 3 as described.

[0146] The correlation matrix can be expressed as

[0147]

[0148] The element ρ of the correlation matrix k，l =h k H h l is the complex correlation coefficient between the CSI pairs of the kth UE and the lth UE, for example, as mentioned above Figure 2 and Figure 3 as described.

[0149] The processor 602 may be configured to perform the following operations based on, for example, Figure 2 and Figure 3 The lower triangular part or the upper triangular part of the correlation matrix described above is used to generate multiple correlation coefficients, and the lower triangular part or the upper triangular part is

[0150]

[0151] The compression rate of providing multiple correlation coefficients based on the correlation relationship matrix relative to providing multiple correlation coefficients based on the multi-UE CSI matrix can be For example, as mentioned above Figure 2 and Figure 3 as described.

[0152] Figure 7 1 is a schematic diagram showing a BBU circuit 700 for providing precoding information to an RRU according to the present disclosure. The BBU circuit 700 may be implemented in the BBU 120 to perform the above-described Figures 1 to 3The functionality of the BBU 120 is described.

[0153] The baseband unit circuit includes a receiver 702, a processor 701 and a transmitter 703. The receiver 702 is configured to receive a signal from the RRU 110 (e.g., as described above). Figures 1 to 3 The RRU described above receives multiple correlation coefficients 603, which are based on CSI from multiple UEs, such as those described above. Figures 1 to 3 The processor 701 is configured to generate partial precoding information 704 for at least a set of UEs from a plurality of UEs based on the received correlation coefficients, for example as described above with respect to Figure 2 and Figure 3 The transmitter 703 is configured to provide part of the precoding information 704 to the RRU 110. The remaining part of the precoding information may be known to the RRU 110, for example, by definition.

[0154] The processor 701 may be configured to schedule a set of UEs based on the received correlation coefficient 603 according to a scheduling strategy, and generate partial precoding information 704 for the scheduled set of UEs, for example as described above with respect to Figure 2 and Figure 3 The scheduling strategy can be based on greedy scheduling, for example, as described above Figure 2 and Figure 3 as described.

[0155] The transmitter 703 may be configured to provide the RRU with at least one of information about the scheduled UE set, rate information, and link adaptation information. The transmitter 703 may be configured to provide the RRU 110 with partial precoding information 704 via the fronthaul link 130, for example as described above with respect to Figure 2 and Figure 3 as described.

[0156] The devices and systems described in this disclosure may be implemented as a digital signal processor (DSP), a microcontroller, or any other side processor or on-chip hardware circuit or application specific integrated circuit (ASIC).

[0157] The examples described in this disclosure may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in a combination, for example in available hardware of a mobile device or in new hardware dedicated to processing the methods described herein.

[0158] The present disclosure also supports a computer program product comprising computer executable code or computer executable instructions, which, when executed, causes at least one computer to perform the execution and calculation blocks described herein, especially the above Figures 2 to 5Such a computer program product may include a readable storage medium having program code stored thereon for use by a processor, the program code including instructions for executing the methods 300, 400, 500 as described above.

[0159] Example

[0160] The following examples are related to further embodiments. Example 1 is a method for providing CSI from an RRU to a BBU, the method comprising: determining CSI for each of a plurality of UEs based on a reference signal received from the corresponding UE; generating a plurality of correlation coefficients based on the CSI; and providing the plurality of correlation coefficients to the BBU.

[0161] In Example 2, the subject matter of Example 1 may optionally include generating a plurality of correlation coefficients based on CSI pairs determined for corresponding UE pairs.

[0162] In Example 3, the subject matter of any one of Examples 1 to 2 may optionally include: compressing the plurality of correlation coefficients; and providing the plurality of correlation coefficients in a compressed form.

[0163] In Example 4, the subject matter of any one of Examples 1 to 3 may optionally include providing the plurality of correlation coefficients via a common public radio interface.

[0164] In Example 5, the subject matter of any one of Examples 1 to 4 may optionally include providing a plurality of correlation coefficients from the RRU to the BBU via a fronthaul link.

[0165] In Example 6, the subject matter according to any one of Examples 1 to 5 may optionally include: generating multiple correlation coefficients based on a correlation relationship matrix of size K*K, where K is the number of UEs used to determine CSI.

[0166] In Example 7, the subject matter of Example 6 may optionally include determining a correlation matrix based on a multi-UE CSI matrix including the CSI determined for each UE.

[0167] In Example 8, the subject matter described in Example 7 may optionally include: the size of the multi-UE CSI matrix is ​​N*K, where K is the number of UEs used to determine the CSI and N is the dimension of the MIMO channel vector between the corresponding UE and the RRU.

[0168] In Example 9, the subject matter of any one of Examples 7 to 8 may optionally include: the multi-UE CSI matrix is ​​H=[h1,h2,...,h K ], the MIMO channel vector is h k =[h k,1 ,h k,2,...,h k,N ] T , where h k,n is the kth MIMO channel vector h k The nth element of .

[0169] In Example 10, the subject matter of any one of Examples 6 to 9 may optionally include: the correlation matrix is

[0170]

[0171] Among them, the element ρ of the correlation matrix k，l =h k H h l is the complex correlation coefficient between the CSI pairs of the kth UE and the lth UE.

[0172] In Example 11, the subject matter of Example 10 may optionally include generating a plurality of correlation coefficients based on a lower triangular portion or an upper triangular portion of a correlation matrix, the lower triangular portion or the upper triangular portion being

[0173]

[0174] In Example 12, the subject matter according to any one of Examples 7 to 11 may optionally include: providing a plurality of correlation coefficients based on a correlation relationship matrix relative to providing a plurality of correlation coefficients based on a multi-UE CSI matrix has a compression ratio of

[0175] Example 13 is a method for providing precoder information from a BBU to an RRU, the method comprising: receiving multiple correlation coefficients based on CSI from multiple UEs from the RRU; generating partial precoding information for at least a UE set from the multiple UEs based on the received correlation coefficients; and providing the partial precoding information to the RRU.

[0176] In Example 14, the subject matter of Example 13 may optionally include: the remaining portion of the precoding information is known to the RRU.

[0177] In Example 15, the subject matter according to any one of Examples 13 to 14 may optionally include: scheduling a set of UEs based on the received correlation coefficients according to a scheduling strategy; and generating partial precoding information for the scheduled set of UEs.

[0178] In Example 16, the subject matter of Example 15 may optionally include: the scheduling policy is based on greedy scheduling.

[0179] In Example 17, the subject matter according to any one of Examples 15 to 16 may optionally include providing at least one of information about a scheduled UE set, rate information, and link adaptation information to the RRU.

[0180] In Example 18, the subject matter of any one of Examples 13 to 17 may optionally include providing partial precoding information from the BBU to the RRU via a fronthaul link.

[0181] Example 19 is an RRU circuit comprising: a processor configured to determine CSI for each of a plurality of UEs based on a reference signal received from the corresponding UE and to generate a plurality of correlation coefficients based on the CSI; and a transmitter configured to provide the plurality of correlation coefficients to a BBU.

[0182] In Example 20, the subject matter of Example 19 may optionally include the processor being configured to generate a plurality of correlation coefficients based on pairs of CSI determined for corresponding pairs of UEs.

[0183] In Example 21, the subject matter according to any one of Examples 19 to 20 may optionally include: the processor is configured to compress the plurality of correlation coefficients; and the transmitter is configured to provide the plurality of correlation coefficients in a compressed form.

[0184] In Example 22, the subject matter of any one of Examples 19 to 21 may optionally include the transmitter being configured to provide the plurality of correlation coefficients via a common public radio interface.

[0185] In Example 23, the subject matter of any one of Examples 19 to 22 may optionally include: the transmitter is configured to provide the plurality of correlation coefficients to the BBU via a fronthaul link.

[0186] In Example 24, the subject matter according to any one of Examples 19 to 23 may optionally include: the processor is configured to generate a plurality of correlation coefficients based on a correlation relationship matrix of size K*K, where K is the number of UEs used to determine the CSI.

[0187] In Example 25, the subject matter of Example 24 may optionally include: the processor is configured to determine a correlation matrix based on a multi-UE CSI matrix including the CSI determined for each UE.

[0188] In Example 26, the subject matter described in Example 25 may optionally include: the size of the multi-UE CSI matrix is ​​N*K, where K is the number of UEs used to determine the CSI and N is the dimension of the MIMO channel vector between the corresponding UE and the RRU.

[0189] In Example 27, the subject matter of any one of Examples 25 to 26 may optionally include: the multi-UE CSI matrix is ​​H=[h1,h2,...,h K ], the MIMO channel vector is h k =[h k,1 ,h k,2 ,...,h k,N ] T , where h k,n is the kth MIMO channel vector h k The nth element of .

[0190] In Example 28, the subject matter of any one of Examples 24 to 27 may optionally include: the correlation matrix is

[0191]

[0192] Among them, the element ρ of the correlation matrix k，l =h k H h l is the complex correlation coefficient between the pair of CSIs of the kth UE and the lth UE.

[0193] In Example 29, the subject matter of Example 28 may optionally include: the processor is configured to generate a plurality of correlation coefficients based on a lower triangular portion or an upper triangular portion of the correlation matrix, the lower triangular portion or the upper triangular portion being

[0194]

[0195] In Example 30, the subject matter according to any one of Examples 25 to 29 may optionally include: providing a plurality of correlation coefficients based on a correlation relationship matrix relative to providing a plurality of correlation coefficients based on a multi-UE CSI matrix. The compression ratio is

[0196] Example 31 is a BBU circuit comprising: a receiver configured to receive multiple correlation coefficients based on CSI from multiple UEs from an RRU; a processor configured to generate partial precoding information for at least a set of UEs from the multiple UEs based on the received correlation coefficients; and a transmitter configured to provide the partial precoding information to the RRU.

[0197] In Example 32, the subject matter of Example 31 may optionally include: the remaining portion of the precoding information is known to the RRU.

[0198] In Example 33, the subject matter according to any one of Examples 31 to 32 may optionally include: the processor is configured to schedule a set of UEs based on the received correlation coefficients according to a scheduling strategy, and generate partial precoding information for the scheduled set of UEs.

[0199] In Example 34, the subject matter of Example 33 may optionally include: the scheduling policy is based on greedy scheduling.

[0200] In Example 35, the subject matter according to any one of Examples 33 to 34 may optionally include: the transmitter is configured to provide at least one of information about the scheduled UE set, rate information, and link adaptation information to the RRU.

[0201] In Example 36, the subject matter of any one of Examples 31 to 35 may optionally include: the transmitter is configured to provide partial precoding information to the RRU via a fronthaul link.

[0202] Example 37 is a remote radio unit (RRU) comprising: a device for determining CSI for each of a plurality of UEs based on a reference signal received from the corresponding UE; a device for generating a plurality of correlation coefficients based on the CSI; and a device for providing the plurality of correlation coefficients to a BBU.

[0203] In Example 38, the subject matter described in Example 37 may optionally include: a device for compressing the plurality of correlation coefficients; and a device for providing the plurality of correlation coefficients in a compressed form.

[0204] Example 39 is a BBU comprising: a device for receiving multiple correlation coefficients based on CSI from multiple UEs from an RRU; a device for generating partial precoding information for at least a set of UEs from the multiple UEs based on the received correlation coefficients; and a device for providing the partial precoding information to the RRU.

[0205] In Example 40, the subject matter of Example 39 may optionally include: the remaining portion of the precoding information is known to the RRU.

[0206] Example 41 is a base station system comprising an RRU and a BBU, wherein the RRU is configured to: determine CSI for each of a plurality of UEs based on a reference signal received from a corresponding UE, generate a plurality of correlation coefficients based on the CSI, and provide the plurality of correlation coefficients to the BBU, wherein the BBU is configured to: receive the plurality of correlation coefficients from the RRU, generate partial precoding information for at least a set of UEs from the plurality of UEs based on the received correlation coefficients, and provide the partial precoding information to the RRU.

[0207] In Example 42, the subject matter of Example 41 may optionally include the RRU being configured to generate the complete precoding information based on the partial precoding information provided from the BBU and the remaining part of the precoding information known to the RRU.

[0208] Example 43 is a computer-readable non-transitory medium having computer instructions stored thereon, which, when executed by a computer, cause the computer to perform the method according to any one of Examples 1 to 18.

[0209] In addition, although a particular feature or aspect of the present disclosure may have been disclosed with respect to only one of several embodiments, such a feature or aspect may be combined with one or more other features or aspects of other embodiments as may be desired and advantageous for any given or particular application. In addition, to the extent the terms "including," "having," "with," or other variations thereof are used in specific embodiments or claims, such terms are intended to be inclusive in a manner similar to the term "comprising." Furthermore, it should be understood that various aspects of the present disclosure may be implemented with discrete circuits, partially integrated circuits, or fully integrated circuits or programming devices. In addition, the terms "exemplary," "for example," and "for example" are intended merely to be examples, not the best or optimal.

[0210] Although specific aspects have been illustrated and described herein, it will be appreciated by those skilled in the art that various alternative and / or equivalent embodiments may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptation or variation of the specific aspects discussed herein.

[0211] Although elements in the following claims are recited in a specific order with corresponding labels, those elements are not necessarily intended to be limited to being implemented in that specific order unless the claim recitation otherwise implies a specific order for implementing some or all of those elements.

Claims

1. A method for providing channel state information (CSI) from a remote radio unit (RRU) to a baseband unit (BBU), the method comprising: determining CSI for each of a plurality of user equipments (UEs) based on a reference signal received from a corresponding UE; generating a plurality of correlation coefficients based on the CSI pairs determined for the respective UE pairs; as well as The plurality of correlation coefficients are provided to the BBU.

2. The method according to claim 1, comprising: compressing the plurality of correlation coefficients; as well as The plurality of correlation coefficients are provided in a compressed form.

3. The method according to claim 1, comprising: The plurality of correlation coefficients are provided via a common public radio interface.

4. The method according to claim 1, comprising: The plurality of correlation coefficients are provided from the RRU to the BBU via a fronthaul link.

5. The method according to claim 1, comprising: The plurality of correlation coefficients are generated based on a correlation matrix of size K*K, where K is the number of UEs used to determine the CSI.

6. The method according to claim 5, comprising: The correlation matrix is ​​determined based on a multi-UE CSI matrix including the CSI determined for each UE.

7. The method according to claim 6, in, The size of the multi-UE CSI matrix is ​​N*K, where K is the number of UEs used to determine the CSI and N is the dimension of the MIMO channel vector between the corresponding UE and the RRU.

8. The method according to claim 6, in, The multi-UE CSI matrix is ​​H = [h1, h2, ..., h K ], the MIMO channel vector is h k =[h k,1 ,h k,2 ,...,h k,N ] T , Among them, h k,n is the kth MIMO channel vector h k The nth element of .

9. The method according to claim 5, in, The correlation matrix is Among them, the element ρ of the correlation matrix k,l =h k H h l is the complex correlation coefficient between the CSI pairs of the kth UE and the lth UE.

10. The method according to claim 9, comprising: The plurality of correlation coefficients are generated based on a lower triangular portion or an upper triangular portion of the correlation matrix, wherein the lower triangular portion or the upper triangular portion is 11. The method according to claim 6, in, The compression rate of providing the multiple correlation coefficients based on the correlation relationship matrix relative to providing the multiple correlation coefficients based on the multi-UE CSI matrix is 12. A method for providing precoder information from a baseband unit (BBU) to a remote radio unit (RRU), the method comprising: receiving, from the RRU, a plurality of correlation coefficients based on channel state information (CSI) from a plurality of user equipments (UEs); generating partial precoding information for at least a set of UEs from the plurality of UEs based on the received correlation coefficients; as well as providing the partial precoding information to the RRU, The multiple correlation coefficients are based on CSI pairs determined for corresponding UE pairs.

13. The method according to claim 12, in, The rest of the precoding information is known to the RRU.

14. The method according to claim 12, comprising: Scheduling the set of UEs based on the received correlation coefficients according to a scheduling strategy; as well as The partial precoding information is generated for the scheduled set of UEs.

15. The method according to claim 14, in, The scheduling strategy is based on greedy scheduling.

16. The method according to claim 14, comprising: At least one of information about a scheduled set of UEs, rate information, and link adaptation information is provided to the RRU.

17. The method according to claim 12, comprising: The partial precoding information is provided from the BBU to the RRU via a fronthaul link.

18. A remote radio unit (RRU) circuit comprising: a processor configured to determine channel state information (CSI) for each of a plurality of user equipments (UEs) based on a reference signal received from the corresponding UE, and to generate a plurality of correlation coefficients based on the determined CSI pairs for the corresponding UE pairs; as well as A transmitter is configured to provide the plurality of correlation coefficients to a baseband unit (BBU).

19. The RRU circuit according to claim 18, in, The processor is configured to compress the plurality of correlation coefficients; and Therein, the transmitter is configured to provide the plurality of correlation coefficients in a compressed form.

20. The RRU circuit according to claim 18, in, The transmitter is configured to provide the plurality of correlation coefficients via a common public radio interface.

21. A baseband unit (BBU) circuit, comprising: a receiver configured to receive, from a remote radio unit (RRU), a plurality of correlation coefficients based on channel state information (CSI) from a plurality of user equipments (UEs); a processor configured to generate partial precoding information for at least a set of UEs from the plurality of UEs based on the received correlation coefficients; as well as a transmitter, the transmitter being configured to provide the partial precoding information to the RRU, The multiple correlation coefficients are based on CSI pairs determined for corresponding UE pairs.

22. The BBU circuit according to claim 21, in, The rest of the precoding information is known to the RRU.

23. The BBU circuit according to claim 21, in, The processor is configured to schedule the set of UEs based on the received correlation coefficients according to a scheduling policy, and generate the partial precoding information for the scheduled set of UEs.

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