Patent Publication Number: US-2019173531-A1

Title: Multi-cell coordination system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 106142129, filed on Dec. 1, 2017, the entirety of which is incorporated by reference herein. 
     TECHNICAL FIELD 
     The disclosure generally relates to a multi-cell coordination system and method. 
     BACKGROUND 
     In an ultra-dense network (UDN), base stations are built densely to enhance the capacity and the range of coverage of the systems. However, base stations that are built densely may interfere with each other, and as a result, the performance of the system may be compromised. Therefore, multi-cell coordination (MCC) may be applied to the UDN to reduce the interference between the base stations using a joint transmission method. 
     A cloud radio access network (C-RAN) is a base station structure based on cloud technology. In a C-RAN, in one scheme for centralizing the computations of the baseband process, each of the base stations may be divided into a remote radio head (RRH) and a baseband unit (BBU), and the BBUs may be centralized to form a BBU pool, wherein the interface between the RRH and BBU is indicated as Fronthaul which needs a larger bandwidth to support the desired data transmission rate. Because the baseband process needs to be performed on the transmitted data in the base station, and because the quantity of data may increase when the data is transmitted close to the RRH, the functional split method is introduced to the C-RAN, i.e. the bandwidth requirement between the BBU and RRH is reduced by changing the concentrated intensity of the computations of the baseband process in the C-RAN. For example, the PHY of the BBU is moved to the RRH to make the interface between the BBU and the RRH become a MAC-PHY interface. The MAC-PHY split method has been widely adopted for use as the current functional split method for a C-RAN. In the MAC-PHY split structure, the BBU in which the PHY function is removed from it is indicated as the baseband processing node (BPN), and the RRH in which the PHY function is added is indicated as the radio frequency node (RFN). 
     When the joint transmission (or multi-user MIMO (MU-MIMO) transmission) is performed in a C-RAN with a MAC-PHY split structure, each of the RFNs needs data for all the users. However, in the MAC-PHY split structure, the computation capability of each RFN is limited, and the number of users that each RFN can support is limited. Therefore, how to reduce the computations of the RFN in the multi-cell coordination system when the MU-MIMO transmission is performed is a subject worthy of discussion. 
     BRIEF SUMMARY 
     A multi-cell coordination system and method are provided to overcome the problems described above. 
     An embodiment in accordance with the disclosure provides a multi-cell coordination system. The multi-cell coordination system comprises a plurality of radio frequency nodes (RFNs) and a baseband processing node (BPN). Each of the plurality of RFNs comprises a baseband circuit, a radio frequency (RF) circuit and a plurality of transmission ports. The RF circuit is electrically connected to the baseband circuit. The plurality of transmission ports are configured in the RF circuit and configured to transmit data to other RFNs of the plurality of RFNs and receive data provided by the other RFNs of the plurality of RFNs. The BPN centralizes and performs layer 2 and layer 3 functions of each cell. 
     An embodiment in accordance with the disclosure provides a multi-cell coordination method. The multi-cell coordination method comprises the steps of assigning data of a plurality of users to a plurality of radio frequency nodes (RFNs); processing, by each of the plurality of RFNs, the assigned data to generate a first data and a third data corresponding to each of the plurality of RFNs; and transmitting first data to other RFNs of the plurality of RFNs and receiving second data provided by the other RFNs by a plurality of transmission ports of each of the plurality of RFNs. 
     The foregoing will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will become more fully understood by referring to the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  is a block diagram of a multi-cell coordination system  100  according to an embodiment of the disclosure; 
         FIG. 2  is a schematic diagram of a multi-cell coordination system  200  according to an embodiment of the disclosure; 
         FIG. 3  is a schematic diagram of a process for the computations of the precoding data W 1 ˜W 8  according to an embodiment of the disclosure; 
         FIG. 4  is a schematic diagram of a multi-cell coordination system  400  according to another embodiment of the disclosure; 
         FIG. 5A  is a schematic diagram of a multi-cell coordination system  500  according to another embodiment of the disclosure; 
         FIG. 5B  is a schematic diagram of a process for the computations of the time-domain baseband signals w 1 ˜w 8  according to an embodiment of the disclosure; 
         FIG. 6  is a schematic diagram of a multi-cell coordination system  600  according to another embodiment of the disclosure; 
         FIG. 7  is a schematic diagram of a multi-cell coordination system  700  according to another embodiment of the disclosure; 
         FIG. 8A  is a schematic diagram of a multi-cell coordination system  800  according to another embodiment of the disclosure; 
         FIG. 8B  is a schematic diagram of a process for the computations of the precoding data W 1 ˜W 8  according to another embodiment of the disclosure; 
         FIG. 9  is a schematic diagram of a multi-cell coordination system  900  according to another embodiment of the disclosure; 
         FIG. 10  is a schematic diagram of a process for the computations of the precoding data W 1 ˜W 8  according to another embodiment of the disclosure; 
         FIG. 11  is a flowchart  1100  illustrating a multi-cell coordination method according to an embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The descriptions of the disclosure are some embodiments for the purpose of illustrating the general principles of the disclosure and should not be configured to limit the disclosure. The scope of the invention is determined by reference to the appended claims. 
       FIG. 1  is a block diagram of a multi-cell coordination system  100  according to an embodiment of the disclosure. The multi-cell coordination system  100  may be applied in a cloud radio access network (C-RAN) structure, e.g. a C-RAN with the MAC-PHY split structure (mid-haul structure), but the disclosure is not limited thereto. As shown in  FIG. 1 , the multi-cell coordination system  100  may include a baseband processing node (BPN)  110  (i.e. computing center for processing the layer 2 and layer 3 (L2/L3) computations of the base station), a coordination server  111 , and a plurality of radio frequency nodes (RFNs)  120 - 1 ˜ 120 - 4 . Each of the RFNs may respectively include the baseband circuits  121 - 1 ˜ 121 - 4  and radio-frequency (RF) circuits  122 - 1 ˜ 122 - 4 .  FIG. 1  presents a simplified block diagram in which only the elements relevant to the disclosure are shown. However, the disclosure is not limited to what is shown in  FIG. 1 . The multi-cell coordination system  100  may comprise other elements. In addition, there are 4 RFNs shown in  FIG. 1 , but the disclosure is not limited thereto. In some embodiments, the multi-cell coordination system  100  may comprise different number of RFNs. Furthermore, according to an embodiment of the disclosure, the RFN may be a small cell, but the disclosure is not limited thereto. 
     According to an embodiment of the disclosure, each of the RFNs  120 - 1 ˜ 120 - 4  is operated in a time-division duplexing mode, but the disclosure is not limited thereto. 
     According to an embodiment of the disclosure, each of the baseband circuits  121 - 1 ˜ 121 - 4  functions as a physical layer (layer 1, L1) circuit, and each of the RF circuits  122 - 1 ˜ 122 - 4  may be electrically connected to one or more antennas. According to the embodiments of the disclosure, each of the RFNs may comprise a plurality of the transmission ports. The transmission ports may comprise a first transmission port and second transmission port. Details will be illustrated in some embodiments below. 
     According to an embodiment of the disclosure, the coordination server  111  may indicate the BPN  110  to assign the data of the users to the RFNs  120 - 1 ˜ 120 - 4  respectively. According to an embodiment of the disclosure, the coordination server  111  may be independently configured outside of the BPN  110  (as shown in  FIG. 1 ). In another embodiment of the disclosure, the coordination server  111  may be configured in the BPN  110 . According to an embodiment of the disclosure, the coordination server  111  may assign the data of a plurality of users to each of the RFNs  120 - 1 ˜ 120 - 4  respectively (e.g. the coordination server  211  shown in  FIG. 1 ). In another embodiment of the disclosure, the coordination server  111  may assign the data of a user to more of the RFNs  120 - 1 ˜ 120 - 4  (e.g. the coordination server  811  shown in  FIG. 8 ). In another embodiment of the disclosure, the coordination server  111  may assign the data of a plurality of users to one of the RFNs  120 - 1 ˜ 120 - 4  (e.g. the coordination server  911  shown in  FIG. 9 ). 
     According to an embodiment of the disclosure, the multi-cell coordination system  100  may further comprises a switch (e.g. the switch  280  shown in  FIG. 2  and the switch  680  shown in  FIG. 6 ). Each of the RFNs  120 - 1 ˜ 120 - 4  may transmit the data which other RFNs need from its first transmission port to the switch. And each of the RFNs  120 - 1 ˜ 120 - 4  may receive the data provided by other RFNs from its second transmission port, wherein the data provided by other RFNs is transmitted through the switch. For example, the RFN  120 - 1  may transmit the data which other RFNs  120 - 2 ˜ 120 - 4  need from its first transmission port to the switch, and the RFN  120 - 1  may receive the data provided by other RFNs  120 - 2 ˜ 120 - 4  from its second transmission port, wherein the data provided by other RFNs  120 - 2 ˜ 120 - 4  is transmitted through the switch to the RFN  120 - 1 . Furthermore, According to an embodiment of the disclosure, the switch may be configured in the RFN-end of the C-RAN (e.g. configured in the RFN) or configured in the BPN-end of the C-RAN (e.g. configured in the BPN). In another embodiment of the disclosure, the switch may be configured outside of the RFN and BPN. According to an embodiment of the disclosure, the switch may be a high-speed switch, e.g. a 10-gigabit Ethernet (10 GbE) switch. 
       FIG. 2  is a schematic diagram of a multi-cell coordination system  200  according to an embodiment of the disclosure. As shown in  FIG. 2 , the multi-cell coordination system  200  includes a BPN (performs L2/L3 of the base station)  210 , a coordination server  211 , a plurality of RFNs  220 - 1 ˜ 220 - 4  and a switch  280 . The baseband circuits  221 - 1 ˜ 221 - 4  of the RFNs  220 - 1 ˜ 220 - 4  may respectively comprise the channel coding circuits  231 - 1 ˜ 231 - 4 , precoders (or beamformers)  241 - 1 ˜ 241 - 4 , combiner  251 - 1 ˜ 251 - 4 , orthogonal frequency-division multiplexing (OFDM) symbol constructor  261 - 1 ˜ 261 - 4  and inverse Fast Fourier Transform (IFFT) circuits  271 - 1 ˜ 271 - 4 . In addition, in the embodiment, the transmission ports (the first transmission ports MPo 1 ˜MPo 4  and the second transmission ports MPi 1 ˜MPi 4 ) of the baseband circuits  221 - 1 ˜ 221 - 4  are respectively configured between the precoders  241 - 1 ˜ 241 - 4  and the combiner  251 - 1 ˜ 251 - 4 . In the embodiment, each of the RF circuits  222 - 1 ˜ 222 - 4  of the RFNs  220 - 1 ˜ 220 - 4  is electrically connected to two antennas (i.e. A 1 ˜A 8 ), e.g. the structure shown in  FIG. 2,4, 5A, 6 or 8A , but the disclosure is not limited thereto. In some embodiments of the disclosure, the antennas may be configured (integrated) in the RFN, e.g. the structure shown in  FIG. 9 . In some embodiments of the disclosure, the RF circuit may be electrically connected to a different number of antennas. Furthermore, in the embodiment, the switch  280  is configured outside of the BPN  210  and the RFNs  220 - 1 ˜ 220 - 4 , but the disclosure is not limited thereto. In some embodiments of the disclosure, the switch  280  may configured in the BPN  210  or in one of the RFNs  220 - 1 ˜ 220 - 4 . 
     In the embodiment of  FIG. 2 , the coordination server  211  may indicate the BPN  210  to respectively assign the data D 1 ˜D 4  of the User 1˜4 to the RFNs  220 - 1 ˜ 220 - 4 . After the assigned data D 1 ˜D 4  of the User 1˜4 are respectively processed by the channel coding circuits  231 - 1 ˜ 231 - 4 , the channel coding data U 1 ˜U 4  are generated. After the channel coding data U 1 ˜U 4  are respectively processed by the precoders  241 - 1 ˜ 241 - 4 , each of the precoders  241 - 1 ˜ 241 - 4  may generate first precoding data (i.e. the first data) and then transmit the first precoding data from the first transmission ports MPo 1 ˜MPo 4  to the switch  280  to provide the first precoding data to other RFNs. And each of the precoders  241 - 1 ˜ 241 - 4  may further generate third precoding data (i.e. the third data) and provide the third precoding data to the combiner  251 - 1 ˜ 251 - 4  at the next stage from its output-ends Po 1 ˜Po 4 . For example, after the precoder  241 - 1  received the channel coding data U 1 , the precoder  241 - 1  may provide the third precoding data to the combiner  251 - 1  from its output-end Po 1  and output the first precoding data to the switch  280  through the first transmission ports MPo 1  (i.e. the RFN  220 - 1  outputs the first precoding data through the precoder  241 - 1 ). Then, the first precoding data is transmitted to other RFNs  220 - 2 ˜ 220 - 4  through the switch  280  to be the second precoding data received by the second transmission port MPi 2 ˜MPi 4  corresponding to the RFNs  220 - 2 ˜ 220 - 4 . 
     Each of the combiners  251 - 1 ˜ 251 - 4  may respectively receive the third precoding data output by the output-ends Po 1 ˜Po 4  of the precoders  241 - 1 ˜ 241 - 4  and receive the second precoding data (i.e. the second data) provided by other RFNs through the second transmission ports MPi 1 ˜MPi 4 , wherein the second precoding data are transmitted from the switch  280  to the second transmission ports MPi 1 ˜MPi 4 . For example, the combiner  251 - 1  may receive the third precoding data output by the output-end Po 1  of the precoders  241 - 1  and receive the second precoding data provided by the RFNs  220 - 2 ˜ 220 - 4  through the second transmission port MPi 1 . 
     Each of the combiners  251 - 1 ˜ 251 - 4  may combine the third precoding data output by the output-ends Po 1 ˜Po 4  of the precoders  241 - 1 ˜ 241 - 4  with the second precoding data (provided by other RFNs) received by the second transmission ports MPi 1 ˜MPi 4  in frequency domain to generate combined precoding data W 1 ˜W 8  (frequency domain signals) for the User 1˜4. The combined precoding data W 1 ˜W 8  output from the combiners  251 - 1 ˜ 251 - 4  may further be processed by the OFDM symbol constructor  261 - 1 ˜ 261 - 4  to form the OFDM symbols W′ 1 ˜W′ 8  (frequency domain signals) for the IFFT circuits  271 - 1 ˜ 271 - 4  at the next stage. The OFDM symbols W′ 1 ˜W′ 8  may further be processed by the IFFT circuits  271 - 1 ˜ 271 - 4  and the RF circuits  222 - 1 ˜ 222 - 4  to generate the RF signals which will be transmitted from the antennas A 1 ˜A 8  of the RF circuits  222 - 1 ˜ 222 - 4 . For example, the combiner  251 - 1  may combine the third precoding data output by the output-end Po 1  of the precoders  241 - 1  with the second precoding data (provided by other RFNs  220 - 2 ˜ 220 - 4 ) received by the second transmission port MPi 1 . The combined precoding data combined by the combiner  251 - 1  may be further be processed by the OFDM symbol constructor  261 - 1  to form the OFDM symbols W′ 1  and W′ 2 . The OFDM symbols W′ 1  and W′ 2  may further be processed by the IFFT circuits  271 - 1  and the RF circuits  222 - 1  to generate the RF signals which will be transmitted from the antennas A 1  and A 2  of the RF circuits  222 - 1 . 
       FIG. 3  is a schematic diagram of a process for the computations of the precoding data W 1 ˜W 8  according to an embodiment of the disclosure. Taking  FIG. 2  for example, after the channel coding data U 1 ˜U 4  are respectively transmitted to the precoders  241 - 1 ˜ 241 - 4 , the inner product computation is performed for the channel coding data U 1 ˜U 4  and a precoding matrix P to from the combined precoding data W 1 ˜W 8 , wherein the P 11 (t), P 12 (t) . . . P MN (t) of the precoding matrix are precoding parameters, M corresponds to the number of precoding data W (e.g. W 1 ˜W 8 ) and N corresponds to the number of channel coding data U (e.g. U 1 ˜U 4 ). In the embodiment of the disclosure, each of the RFNs  220 - 1 ˜ 220 - 4  only needs to process the data related to a user which is assigned to it. Other required data related to other users can be processed by other RFNs and each of the RFNs  220 - 1 ˜ 220 - 4  may obtain the required data related to other users from the second transmission ports Taking  FIG. 2  for example, the RFN  220 - 1  only needs to process the data related to the User 1 (i.e. related to the channel coding data U 1 ) to generate P m2 ·U 1 , wherein m=1, 2, . . . 8. The third precoding data P 11 ·U 1  and P 21 ·U 1  is one part of the precoding data W 1  and W 2 , and the third precoding data P 11 ·U 1  and P 21 ·U 1  is output from the output-end Po 1  of the precoder  241 - 1  to the combiner  251 - 1 . Other data related to the channel coding data U 1  (i.e. the first precoding data P m1 ·U 1 , wherein m=3, 4 . . . 8) may be transmitted from the first transmission port MPo 1  to the switch  280  and then transmitted to other RFNs  220 - 2 ˜ 220 - 4  by the switch  280 . The second precoding data P 12 ·U 2 +P 13 ·U 3 +P 14 ·U 4  which is the other part of the precoding data W 1  and W 2  is generated by other RFNs  220 - 2 ˜ 220 - 4  and transmitted to the switch  280 . Then, the switch  280  may transmit the second precoding data to the combiner  251 - 1  through second transmission port MPi 1 . Therefore, the computations of the RFN  220 - 1  will be reduced. 
       FIG. 4  is a schematic diagram of a multi-cell coordination system  400  according to another embodiment of the disclosure. As shown in  FIG. 4 , the multi-cell coordination system  400  includes a BPN  410 , a coordination server  411 , and a plurality of RFNs  420 - 1 ˜ 420 - 4 . The baseband circuits  421 - 1 ˜ 421 - 4  of the RFNs  420 - 1 ˜ 420 - 4  may respectively comprise the channel coding circuits  431 - 1 ˜ 431 - 4 , precoders  441 - 1 ˜ 441 - 4 , combiners  451 - 1 ˜ 451 - 4 , OFDM symbol constructors  461 - 1 ˜ 461 - 4  and IFFT circuits  471 - 1 ˜ 471 - 4 . In the embodiment, each of the RF circuits  422 - 1 ˜ 422 - 4  of the RFNs  420 - 1 ˜ 420 - 4  is electrically connected to two antennas (i.e. A 1 ˜A 8 ). 
     Furthermore, as shown in  FIG. 4 , in the embodiment, the transmission ports (the first transmission ports MPo 1 ˜MPo 4  and the second transmission ports MPi 1 ˜MPi 4 ) of the baseband circuits  421 - 1 ˜ 421 - 4  are respectively configured between the OFDM symbol constructors  461 - 1 ˜ 461 - 4  and the combiners  451 - 1 ˜ 451 - 4 . Therefore, in the embodiment, after the channel coding data U 1 ˜U 4  is respectively processed by the precoders  441 - 1 ˜ 441 - 4  and the OFDM symbol constructors  461 - 1 ˜ 461 - 4 , the OFDM symbol constructors  461 - 1 ˜ 461 - 4  may generate the third OFDM symbol data (i.e. the third data) and generate the first OFDM symbol data (i.e. the first data) which is provided to other RFNs through the first transmission ports MPo 1 ˜MPo 4 . For example, after the channel coding data U 1  is processed by the precoder  441 - 1  and the OFDM symbol constructor  461 - 1 , the OFDM symbol constructor  461 - 1  may output the third OFDM symbol data (i.e. the data which the RFN  420 - 1  needs to output from its OFDM symbol constructor  461 - 1 ) to the combiner  451 - 1  from its output-end Co 1 , and transmit the first OFDM symbol data which needs to be provided to other RFNs  420 - 2 ˜ 420 - 4  through the first transmission port MPo 1 . The combiner  451 - 1  may combine the third OFDM symbol data output by the output-end Co 1  of the OFDM symbol constructor  461 - 1  with the second OFDM symbol data (i.e. the second data) received by the second transmission port MPi 1  to generate combined OFDM symbol data W′ 1  and W′ 2 , wherein the second OFDM symbol data is provided by other RFNs  420 - 2 ˜ 420 - 4 . Specifically, in the embodiment, the combined OFDM symbol data which generated by the combiners  451 - 1 ˜ 451 - 4  is the OFDM symbol data which has been processed by the OFDM symbol constructors  461 - 1 ˜ 461 - 4  and the OFDM symbol data is composed of the data (W 1 ˜W 8 ) related to the users, the synchronous signal (not shown in figures) and the reference signal (not shown in figures). 
     In addition, as shown in  FIG. 4 , in the embodiment, there is not a switch configured in the multi-cell coordination system  400 . That is to say, in some embodiments of the disclosure, each of the RFNs  420 - 1 ˜ 420 - 4  can directly transmit data to other RFNs which are connected to it through its first transmission port (MPo 1 ˜MPo 4 ) and receive the data provided by other RFNs through its second transmission port (MPi 1 ˜MPi 4 ), which is directly connected to the other RFNs. 
       FIG. 5A  is a schematic diagram of a multi-cell coordination system  500  according to another embodiment of the disclosure. As shown in  FIG. 5A , the multi-cell coordination system  500  includes a BPN  510 , a coordination server  511 , a plurality of RFNs  520 - 1 ˜ 520 - 4  and a switch  580 . The baseband circuits  521 - 1 ˜ 521 - 4  of the RFNs  520 - 1 ˜ 520 - 4  may respectively comprise the channel coding circuits  531 - 1 ˜ 531 - 4 , precoders  541 - 1 ˜ 541 - 4 , combiners  551 - 1 ˜ 551 - 4 , OFDM symbol constructors  561 - 1 ˜ 561 - 4  and IFFT circuits  571 - 1 ˜ 571 - 4 . In the embodiment, each of the RF circuits  522 - 1 ˜ 522 - 4  of the RFNs  520 - 1 ˜ 520 - 4  is electrically connected to two antennas (i.e. A 1 ˜A 8 ). Furthermore, in the embodiment, the switch  580  is independently configured outside of the BPN  510  and the RFNs  520 - 1 ˜ 520 - 4 . 
     Furthermore, as shown in  FIG. 5A , in the embodiment, the transmission ports (the first transmission ports MPo 1 ˜MPo 4  and the second transmission ports MPi 1 ˜MPi 4 ) of the baseband circuits  521 - 1 ˜ 521 - 4  are respectively configured between the IFFT circuits  571 - 1 ˜ 571 - 4  and the combiners  551 - 1 ˜ 551 - 4  are configured at the back of the IFFT circuits  571 - 1 ˜ 571 - 4 . In the embodiment, the channel coding data U 1 ˜U 4  is respectively processed by the precoders  541 - 1 ˜ 541 - 4  and the OFDM symbol constructors  561 - 1 ˜ 561 - 4  first, and then transmitted to the IFFT circuits  571 - 1 ˜ 571 - 4 . The combiners  551 - 1 ˜ 551 - 4  may respectively receive the third IFFT data (i.e. the third data) output from the output-ends To 1 ˜To 4  of the IFFT circuits  571 - 1 ˜ 571 - 4  and receive the second IFFT data (i.e. the second data) through the second transmission ports MPi 1 ˜MPi 4 , wherein the second IFFT data is provided by other RFNs and transmitted from the switch  580  to the second transmission ports MPi 1 ˜MPi 4 . For example, the IFFT circuit  571 - 1  outputs the first IFFT data (i.e. the first data) which needs to be provided to other RFNs  520 - 2 ˜ 520 - 4  through the first transmission port MPo 1  and then the first IFFT data is transmitted to the switch  580  and the switch  580  may provide the first IFFT data to other RFNs  520 - 2 ˜ 520 - 4 . The combiner  551 - 1  may receive the third IFFT data output from the output-end To 1  of the IFFT circuit  571 - 1  and receive the second IFFT data provided by other RFNs  520 - 2 ˜ 520 - 4  through the second transmission port MPi 1 . 
     In addition, in the embodiment, the combiners  551 - 1 ˜ 551 - 4  may combine the third IFFT data output from the output-ends To 1 ˜To 4  of the IFFT circuits  571 - 1 ˜ 571 - 4  with the second IFFT data received through the second transmission ports MPi 1 ˜MPi 4  to generate the time-domain baseband signals w 1 ˜w 8 , wherein the second IFFT data is provided by other RFNs. Then, the time-domain baseband signals w 1 ˜w 8  may be processed by the RF circuits  522 - 1 ˜ 522 - 4  and transmitted to the air through the antennas A 1 ˜A 8  of the RF circuits  522 - 1 ˜ 522 - 4 . For example, the combiner  551 - 1  may (in the time domain) combine the third IFFT data output from the output-ends To 1  of the IFFT circuit  571 - 1  with the second IFFT data received through the second transmission port MPi 1  to generate the time-domain baseband signals w 1  and w 2 , wherein the second IFFT data is provided by other RFNs  520 - 2 ˜ 520 - 4 . Then, the time-domain baseband signals w 1  and w 2  may be processed by the RF circuit  522 - 1  and transmitted to the air through the antennas A 1  and A 2  of the RF circuits  522 - 1 . 
       FIG. 5B  is a schematic diagram of a process for the computations of the time-domain baseband signals w 1  w 8  according to an embodiment of the disclosure. Taking  FIG. 5A  for example, after the channel coding data U 1 ˜U 4  are respectively processed by the precoders  541 - 1 ˜ 541 - 4 , the OFDM symbol constructors  561 - 1 ˜ 561 - 4  and the IFFT circuits  571 - 1 ˜ 571 - 4  to generate the data u 1 ˜u 4 , the inner product computation is performed for the data u 1 ˜u 4  and a precoding matrix p to from the time-domain baseband signals w 1 ˜w 8 , wherein the p 11 (t), p 12 (t) . . . p MN (t) of the precoding matrix are precoding parameters, M corresponds to the number of time-domain baseband signals w (e.g. w 1 ˜w 8 ) and N corresponds to the number of data u (e.g. u 1 ˜u 4 ) which is generated after the IFFT computation is performed for the channel coding data U 1 ˜U 4 . In the embodiment of the disclosure, each of the RFNs  520 - 1 ˜ 520 - 4  only needs to process the data related to a user which is assigned to it. Other required data related to other users can be processed by other RFNs and each of the RFNs  520 - 1 ˜ 520 - 4  may obtain the required data related to other users from the second transmission ports MPi 1 ˜MPi 4 . Taking  FIG. 5A  for example, the RFN  220 - 1  only needs to process the data related to the User 1 assigned to the RFN  220 - 1  to generate p m1 ·u 1 , wherein m=1, 2, . . . 8. The third IFFT data p 11 ·u 1  and p 21 ·u 1  is one part of the time-domain baseband signals w 1  and w 2 , and the third IFFT data p 11 ·u 1  and p 21 ·u 1  is output from the output-end To 1  of the IFFT circuit  571 - 1  to the combiner  551 - 1 . Other data related to the channel coding data U 1  (i.e. the first IFFT data p m1 ·u 1 , wherein m=3, 4 . . . 8) may be transmitted from the first transmission port MPo 1  to the switch  580  and then transmitted to other RFNs  520 - 2 ˜ 520 - 4  by the switch  580 . The second IFFT data p 12 ·u 2 +p 13 ·u 3 +p 14 ·u 4  which is the other part of the time-domain baseband signals w 1  and w 2  is generated by other RFNs  520 - 2 ˜ 520 - 4  and transmitted to the switch  580 . Then, the switch  280  may transmit the second IFFT data to the combiner  551 - 1  through second transmission port MPi 1 . Therefore, the computations of the RFN  520 - 1  will be reduced. 
     According to the above embodiments for different structures of the multi-cell coordination system, we can know that the transmission ports configured in each of the baseband circuits of each RFN may configured in the output-end of the precoder, the output-end of the OFDM symbol constructor or the output-end of the IFFT circuit. The transmission ports of each RFN may comprise a first transmission port and a second transmission port, wherein the first transmission port is configured to transmit the second data to other RFNs and the second transmission port is configured to receive the third data provided by other RFNs. 
       FIG. 6  is a schematic diagram of a multi-cell coordination system  600  according to another embodiment of the disclosure. As shown in  FIG. 6 , the multi-cell coordination system  600  includes a BPN  610 , a coordination server  611 , a plurality of RFNs  620 - 1 ˜ 620 - 4  and a switch  680 . The baseband circuits  621 - 1 ˜ 621 - 4  of the RFNs  620 - 1 ˜ 620 - 4  may respectively comprise the channel coding circuits  631 - 1 ˜ 631 - 4 , precoders  641 - 1 ˜ 641 - 4 , combiners  651 - 1 ˜ 651 - 4 , OFDM symbol constructors  661 - 1 ˜ 661 - 4  and IFFT circuits  671 - 1 ˜ 671 - 4 . Furthermore, in the embodiment, the transmission ports (the first transmission ports MPo 1 ˜MPo 4  and the second transmission ports MPi 1 ˜MPi 4 ) of the baseband circuits  621 - 1 ˜ 621 - 4  are respectively configured between the precoders  641 - 1 ˜ 641 - 4  and the combiners  651 - 1 ˜ 651 - 4 . In the embodiment, each of the RF circuits  622 - 1 ˜ 622 - 4  of the RFNs  620 - 1 ˜ 620 - 4  is electrically connected to two antennas (i.e. A 1 ˜A 8 ). Furthermore, in the embodiment, the switch  680  is configured in the BPN  610 , but the disclosure is not limited thereto. In addition, in the embodiment, the operations of the channel coding circuits  631 - 1 ˜ 631 - 4 , precoders  641 - 1 ˜ 641 - 4 , combiners  651 - 1 ˜ 651 - 4 , OFDM symbol constructors  661 - 1 ˜ 661 - 4  and IFFT circuits  671 - 1 ˜ 671 - 4  are similar to the operations of the channel coding circuits  231 - 1 ˜ 231 - 4 , precoders  241 - 1 ˜ 241 - 4 , combiners  251 - 1 ˜ 251 - 4 , OFDM symbol constructors  261 - 1 ˜ 261 - 4  and IFFT circuits  271 - 1 ˜ 271 - 4 , thereby, the details will not be illustrated repeatedly herein. 
       FIG. 7  is a schematic diagram of a multi-cell coordination system  700  according to another embodiment of the disclosure. As shown in  FIG. 7 , the multi-cell coordination system  700  includes a BPN  710 , a coordination server  711 , a plurality of RFNs  720 - 1 ˜ 720 - 4  and a switch  780 . The baseband circuits  721 - 1 ˜ 721 - 4  of the RFNs  720 - 1 ˜ 720 - 4  may respectively comprise the channel coding circuits  731 - 1 ˜ 731 - 4 , precoders  741 - 1 ˜ 741 - 4 , combiners  751 - 1 ˜ 751 - 4 , OFDM symbol constructors  761 - 1 ˜ 761 - 4  and IFFT circuits  771 - 1 ˜ 771 - 4 . Furthermore, in the embodiment, the transmission ports (the first transmission ports MPo 1 ˜MPo 4  and the second transmission ports MPi 1 ˜MPi 4 ) of the baseband circuits  721 - 1 ˜ 721 - 4  are respectively configured between the IFFT circuits  771 - 1 ˜ 771 - 4  and the combiners  751 - 1 ˜ 751 - 4 . In the embodiment, each of the RF circuits  722 - 1 ˜ 722 - 4  of the RFNs  720 - 1 ˜ 720 - 4  is electrically connected to two antennas (i.e. A 1 ˜A 8 ). Furthermore, in the embodiment, the switch  780  is independently configured outside of the BPN  710  and the RFNs  720 - 1 ˜ 720 - 4 . 
     As shown in  FIG. 7 , in the embodiment, the RFNs  720 - 1 ˜ 720 - 4  is integrated in a circuit board (or a device)  790 , wherein the antennas A 1 ˜A 8  may be integrated in the circuit board  790 , or electrically connected to the circuit board  790  from the remote end. In addition, in the embodiment, the operations of the channel coding circuits  731 - 1 ˜ 731 - 4 , precoders  741 - 1 ˜ 741 - 4 , combiners  751 - 1 ˜ 751 - 4 , OFDM symbol constructors  761 - 1 ˜ 761 - 4  and IFFT circuits  771 - 1 ˜ 771 - 4  are similar to the operations of the channel coding circuits  531 - 1 ˜ 531 - 4 , precoders  541 - 1 ˜ 541 - 4 , combiners  551 - 1 ˜ 551 - 4 , OFDM symbol constructors  561 - 1 ˜ 561 - 4  and IFFT circuits  571 - 1 ˜ 571 - 4 , thereby, the details will not be illustrated repeatedly herein. 
       FIG. 8A  is a schematic diagram of a multi-cell coordination system  800  according to another embodiment of the disclosure. As shown in  FIG. 8A , the multi-cell coordination system  800  includes a BPN  810 , a coordination server  811 , a plurality of RFNs  820 - 1 ˜ 820 - 4  and a switch  880 . The baseband circuits  821 - 1 ˜ 821 - 4  of the RFNs  820 - 1 ˜ 820 - 4  may respectively comprise the channel coding circuits  831 - 1 ˜ 831 - 4 , precoders  841 - 1 ˜ 841 - 4 , combiners  851 - 1 ˜ 851 - 4 , OFDM symbol constructors  861 - 1 ˜ 861 - 4  and IFFT circuits  871 - 1 ˜ 871 - 4 . Furthermore, in the embodiment, the transmission ports (the first transmission ports MPo 1 ˜MPo 4  and the second transmission ports MPi 1 ˜MPi 4 ) of the baseband circuits  821 - 1 ˜ 821 - 4  are respectively configured between the precoders  841 - 1 ˜ 841 - 4  and the combiners  851 - 1 ˜ 851 - 4 . In the embodiment, each of the RF circuits  822 - 1 ˜ 822 - 4  of the RFNs  820 - 1 ˜ 820 - 4  is electrically connected to two antennas (i.e. A 1 ˜A 8 ). Furthermore, in the embodiment, the switch  880  is independently configured outside of the BPN  810  and the RFNs  820 - 1 ˜ 820 - 4 . In addition, in the embodiment, the operations of the channel coding circuits  831 - 1 ˜ 831 - 4 , precoders  841 - 1 ˜ 841 - 4 , combiners  851 - 1 ˜ 851 - 4 , OFDM symbol constructors  861 - 1 ˜ 861 - 4  and IFFT circuits  871 - 1 ˜ 871 - 4  are similar to the operations of the channel coding circuits  231 - 1 ˜ 231 - 4 , precoders  241 - 1 ˜ 241 - 4 , combiners  251 - 1 ˜ 251 - 4 , OFDM symbol constructors  261 - 1 ˜ 261 - 4  and IFFT circuits  271 - 1 ˜ 271 - 4 , thereby, the details will not be illustrated repeatedly herein. 
     In addition, According to an embodiment of the disclosure, the transmission ports shown in  FIG. 8A  may also be configured in the output-ends of the OFDM symbol constructors  861 - 1 ˜ 861 - 4  or the output-end of the IFFT circuits  871 - 1 ˜ 871 - 4 . 
     As shown in  FIG. 8A , the coordination server  811  may respectively assign the data D 1-1  and D 1-2  of the User 1 to the RFN  820 - 1  and  820 - 2 , and respectively assign the data D 2-1  and D 2-2  of the User 2 to the RFN  820 - 3  and  820 - 4 . The data D 1-1  and D 1-2  of the User 1 and the data D 2-1  and D 2-2  of the User 2 may be respectively processed by the channel coding circuits  831 - 1 ˜ 831 - 4  to generate the channel coding data U 1-1 , U 12 , U 2-1  and U 2-2 . Therefore, according to the embodiment, when the quantity of data which a user needs to transmit is too large, the coordination server may assign more than one RFN to transmit the user&#39;s data. 
       FIG. 8B  is a schematic diagram of a process for the computations of the precoding data W 1 ˜W 8  according to another embodiment of the disclosure. Taking  FIG. 8A  for example, after the channel coding data U 1-1 , U 12 , U 2-1  and U 2-2  are respectively transmitted to the precoders  241 - 1 ˜ 241 - 4 , the inner product computation is performed for the channel coding data U 1-1 , U 12 , U 2-1  and U 2-2  and a precoding matrix P to from the combined precoding data W 1 ˜W 8 , wherein the P 11 (t), P 12 (t) . . . P MN (t) of the precoding matrix are precoding parameters, M corresponds to the number of precoding data W (e.g. W 1 ˜W 8 ) and N corresponds to the number of channel coding data U (e.g. U 1-1 , U 12 , U 2-1  and U 2-2 ). In the embodiment of the disclosure, each of the RFNs  820 - 1 ˜ 820 - 4  only needs to process the data related to the user which is assigned to it. Other required data related to other users can be processed by other RFNs and each of the RFNs  820 - 1 ˜ 820 - 4  may obtain the required data related to other users from the second transmission ports MPi 1 ˜MPi 4 . Taking  FIG. 8A  for example, the RFN  820 - 1  only needs to process the channel coding data U 1-1  related to User 1 to generate P m1 ·U 1-1 , wherein m=1, 2, . . . 8. The third precoding data P 11 ·U 1-1  and P 21 ˜U 1-1  are one part of the precoding data W 1  and W 2 , and the third precoding data P 11 ·U 1-1  and P 21 ˜U 1-1  are output from the output-end Po 1  of the precoder  841 - 1  to the combiner  851 - 1 . Other data related to the channel coding data U 1-1  (i.e. the first precoding data P m1 ·U 1-1 , wherein m=3, 4 . . . 8) may be transmitted from the first transmission port MPo 1  to the switch  880  and then transmitted to other RFNs  820 - 2 ˜ 820 - 4  by the switch  880 . The second precoding data P 12 ·U 1-2 +P 13 ·U 2-1 +P 14 ·U 2-2  which are the other part of the precoding data W 1  and W 2  is generated by other RFNs  820 - 2 ˜ 820 - 4  and transmitted to the switch  880 . Then, the switch  880  may transmit the second precoding data to the combiner  851 - 1  through second transmission port MPi 1 . Therefore, the computations of the RFN  820 - 1  will be reduced. 
       FIG. 9  is a schematic diagram of a multi-cell coordination system  900  according to another embodiment of the disclosure. As shown in  FIG. 9 , the multi-cell coordination system  900  includes a BPN  910 , a coordination server  911 , a plurality of RFNs  920 - 1 ˜ 920 - 4  and a switch  980 . The baseband circuits  921 - 1 ˜ 921 - 4  of the RFNs  920 - 1 ˜ 920 - 4  may respectively comprise the channel coding circuits  931 - 1 ˜ 931 - 4 , precoders  941 - 1 ˜ 941 - 4 , combiners  951 - 1 ˜ 951 - 4 , OFDM symbol constructors  961 - 1 ˜ 961 - 4  and IFFT circuits  971 - 1 ˜ 971 - 4 . Furthermore, in the embodiment, the transmission ports (the first transmission ports MPo 1 ˜MPo 4  and the second transmission ports MPi 1 ˜MPi 4 ) of the baseband circuits  921 - 1 ˜ 921 - 4  are respectively configured between the precoders  941 - 1 ˜ 941 - 4  and the combiners  951 - 1 ˜ 951 - 4 . In the embodiment, each of the RF circuits  922 - 1 ˜ 922 - 4  of the RFNs  920 - 1 ˜ 920 - 4  is electrically connected to two antennas (i.e. A 1 ˜A 8 ). Furthermore, in the embodiment, the switch  880  is independently configured outside of the BPN  910  and the RFNs  920 - 1 ˜ 920 - 4 . In addition, in the embodiment, the operations of the channel coding circuits  931 - 1 ˜ 931 - 4 , precoders  941 - 1 ˜ 941 - 4 , combiners  951 - 1 ˜ 951 - 4 , OFDM symbol constructors  961 - 1 ˜ 961 - 4  and IFFT circuits  971 - 1 ˜ 971 - 4  are similar to the operations of the channel coding circuits  231 - 1 ˜ 231 - 4 , precoders  241 - 1 ˜ 241 - 4 , combiners  251 - 1 ˜ 251 - 4 , OFDM symbol constructors  261 - 1 ˜ 261 - 4  and IFFT circuits  271 - 1 ˜ 271 - 4 , thereby, the details will not be illustrated repeatedly herein. 
     In addition, According to an embodiment of the disclosure, the transmission ports shown in  FIG. 9  may also be configured in the output-ends of the OFDM symbol constructors  961 - 1 ˜ 961 - 4  or the output-end of the IFFT circuits  971 - 1 ˜ 971 - 4 . 
     As shown in  FIG. 9 , when the data of 8 users need to be transmitted, the coordination server  911  may assign the data D 1  and D 2  of the User 1 and the User 2 to the RFN  920 - 1 , assign the data D 3  and D 4  of the User 3 and the User 4 to the RFN  920 - 2 , assign the data D 5  and D 6  of the User 5 and the User 6 to the RFN  920 - 3 , and assign the data D 7  and D 8  of the User 7 and the User 8 to the RFN  920 - 4 . The data D 1  and D 2  of the User 1 and the User 2 may be processed by the channel coding circuit  931 - 1  to generate the channel coding data U 12  (comprising channel coding data U 1  and U 2 ), the data D 3  and D 4  of the User 3 and the User 4 may be processed by the channel coding circuit  931 - 2  to generate the channel coding data U 34  (comprising channel coding data U 3  and U 4 ), the data D 5  and D 6  of the User 5 and the User 6 may be processed by the channel coding circuit  931 - 3  to generate the channel coding data U 56  (comprising channel coding data U 5  and U 6 ), and the data D 7  and D 8  of the User 7 and the User 8 may be processed by the channel coding circuit  931 - 4  to generate the channel coding data U 78  (comprising channel coding data U 7  and U 8 ). Therefore, in the embodiment, when there are more users than there are RFNs, the coordination server may assign more than one user&#39;s data to an RFN to transmit the users&#39; data. 
       FIG. 10  is a schematic diagram of a process for the computations of the precoding data W 1 ˜W 8  according to another embodiment of the disclosure. Taking  FIG. 9  for example, after the channel coding data U 12 , U 34 , U 56  and U 78  are respectively transmitted to the precoders  941 - 1 ˜ 941 - 4 , the inner product computation is performed for the channel coding data U 12 , U 34 , U 56  and U 78  and a precoding matrix P to from the combined precoding data W 1 ˜W 8 , wherein the P 11 (t), P 12 (t) . . . P MN (t) of the precoding matrix are precoding parameters, M corresponds to the number of precoding data W (e.g. W 1 ˜W 8 , M=8) and N corresponds to the number of channel coding data U (e.g. U 1 ˜U 8 , N=8). In the embodiment of the disclosure, each of the RFNs  920 - 1 ˜ 920 - 4  only needs to process the data related to the user which is assigned to it. Other required data related to other users can be processed by other RFNs and each of the RFNs  920 - 1 ˜ 920 - 4  may obtain the required data related to other users from the second transmission ports MPi 1 ˜MPi 4 . Taking  FIG. 9  for example, the RFN  920 - 1  only needs to process the channel coding data U 12  related to the User 1 and User 2 to generate P m1 ·U 1 +P m2 ·U 2 , wherein m=1, 2, . . . 8. The third precoding data P 11 ·U 1 +P 12 ·U 2  and P 21 ·U 1 +P 22 ·U 2  is one part of the precoding data W 1  and W 2 , and the third precoding data P 11 ·U 1 +P 12 ·U 2  and P 21 ·U 1 +P 22 ·U 2  are output from the output-end Po 1  of the precoder  941 - 1  to the combiner  951 - 1 . Other data related to the channel coding data U 12  (i.e. the first precoding data P m1 ·U 1 +P m2 ·U 2 , wherein m=3, 4 . . . 8) may be transmitted from the first transmission port MPo 1  to the switch  980  and then transmitted to other RFNs  920 - 2 ˜ 920 - 4  by the switch  980 . The second precoding data P 13 ·U 3 +P 14 ·U 4 + . . . +P 17 ·U 7 +P 18 ·U 8  and P 23 ·U 3 +P 24 ·U 4 + . . . +P 27 ·U 7 +P 28 ·U 8  which are the other parts of the precoding data W 1  and W 2  is generated by other RFNs  920 - 2 ˜ 920 - 4  and transmitted to the switch  980 . Then, the switch  980  may transmit the second precoding data to the combiner  951 - 1  through second transmission port MPi 1 . Therefore, the computations of the RFN  920 - 1  will be reduced. 
     According to an embodiment of the disclosure, each of the channel coding circuits of the disclosure may comprise a encoder, a scrambler, a QAM mapper circuit, a layer mapper circuit, MIMO encoder, but the disclosure is not limited thereto. 
       FIG. 11  is a flowchart  1100  illustrating a multi-cell coordination method according to an embodiment of the disclosure. The multi-cell coordination method can be applied to the multi-cell coordination system of the disclosure. 
     In step S 1110 , the data of a plurality of users are assigned to a plurality of RFNs by a coordination server. In step S 1120 , each of the RFNs may process the assigned data to generate first data and third data corresponding to each of the RFNs. In step S 1130 , a plurality of transmission ports of each RFN may be configured to transmit the first data which other RFNs need and receive the second data which is provided by other RFNs. In some embodiments of the disclosure, the transmission ports comprise a first transmission port and a second transmission port. 
     According to an embodiment of the disclosure, in step S 1130  further comprises that each of the RFNs may transmit the first data which other RFNs need from its first transmission port to a switch, and receive the second data which is provided by other RFNs through its second transmission port, wherein the second data provided by other RFNs is transmitted from the switch to the second transmission port. 
     In another embodiment of the disclosure, in step S 1130  further comprises that each of the RFNs may directly transmit the first data which other RFNs need to other RFNs through its first transmission port, and directly receive the second data which is provided by other RFNs through its second transmission port. 
     In some embodiments of the disclosure, the multi-cell coordination method comprises the step of combining the third data output by the precoder or the OFDM symbol constructor of the RFN with the second data provided by other RFNs in the frequency domain. In some embodiments of the disclosure, the multi-cell coordination method comprises the step of combining the third data output by the IFFT circuit of the RFN with the second data provided by other RFNs in the time domain. 
     In some embodiments of the disclosure, the multi-cell coordination method comprises the step of respectively assigning the data of a plurality of users to each of the RFNs. In some embodiments of the disclosure, the multi-cell coordination method comprises the step of assigning the data of one of the users to more than one RFN. In some embodiments of the disclosure, the multi-cell coordination method comprises the step of assigning the data of more than one user to one RFN. 
     According to the multi-cell coordination system and method provided in the disclosure, the transmission ports may be configured in each of the RFNs of the multi-cell coordination system. Therefore, each of the RFNs only needs to process the data related to a user which is assigned to it. Other required data related to other users can be processed by other RFNs and each of the RFNs may obtain the required data related to other users from the second transmission port to perform a joint (MU-MIMO) transmission of multi-cells. That is to say, each of the RFNs will not calculate the data of all users. Therefore, in the multi-cell coordination system and the method provided in the disclosure, the computations for performing the MU-MIMO transmission in each RFN of the multi-cell coordination system will be reduced. 
     Use of ordinal terms such as “first”, “second”, “third”, etc., in the disclosure and claims is for description. It does not by itself connote any order or relationship. 
     The method and algorithm disclosed herein may be executed directly by at least one processor which is configured to the call processing device to apply in hardware, in a software module or in a combination of the two. A software module (e.g., including executable instructions and related data) and other data may reside in a data memory such as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage medium known in the art. A sample storage medium may be coupled to a machine such as, for example, a computer/processor (which may be referred to herein, for convenience, as a “processor”) such that the processor could read information (e.g., code) from the storage medium and write information to the storage medium. A sample storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in user equipment. Alternatively, the processor and the storage medium may reside as discrete components in user equipment. Moreover, in some embodiments any suitable computer-program product may include a computer-readable medium comprising codes relating to one or more of the embodiments of the disclosure. In some embodiments a computer program product may include packaging materials. 
     The above paragraphs describe many aspects. Accordingly, the teaching of the disclosure may be accomplished by many methods, and any configurations or functions in the disclosed embodiments only present a representative condition. Those who are skilled in this technology will understand that all of the disclosed aspects in the disclosure may be applied independently or be incorporated. 
     While the disclosure has been described by way of example and as exemplary embodiments only, it should be understood that the disclosure is not configured to limit thereto. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this disclosure. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.