CN107294899B

CN107294899B - Communication method and apparatus for downlink multi-user superposition transmission

Info

Publication number: CN107294899B
Application number: CN201610200805.XA
Authority: CN
Inventors: 武卓; 王钧; 沈钢
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2016-03-31
Filing date: 2016-03-31
Publication date: 2021-09-03
Anticipated expiration: 2036-03-31
Also published as: CN107294899A

Abstract

Embodiments of the present disclosure relate to a communication method and apparatus for downlink multi-user superposition transmission. In one embodiment, network assistance information and a superimposed signal for interference reduction are received at a first user equipment from a base station. Detecting a signal for the second user equipment from the superimposed signal based on the network assistance information, the first user equipment being paired with the second user equipment. Cancelling interference to the first user equipment by the signal intended for the second user equipment. By using the embodiments according to the present disclosure, interference between user equipments can be reduced.

Description

Communication method and apparatus for downlink multi-user superposition transmission

Technical Field

Embodiments of the present disclosure relate to communication technologies, and more particularly, to a communication method and apparatus for downlink multi-user superposition transmission.

Background

The working group (WI) of Downlink (DL) multi-user superposition transmission (MUST) has recently been approved by 3 GPP. It is an object to specify mechanisms for enabling LTE to support DL intra-cell multi-user superposition transmission for a Physical Downlink Shared Channel (PDSCH) using assistance information from a base station (eNB) to a User Equipment (UE) regarding intra-cell interference. Three scenarios need to be considered for DL MUST transmission: 1) transmitting the superimposed PDSCH using the same transmission scheme and the same spatial precoding vector; 2) transmitting the superimposed PDSCH using the same transmission diversity scheme; and 3) transmitting the superimposed PDSCH using the same transmission scheme but using different spatial precoding vectors.

In 3GPP TR 36.859, "Study on Downlink Multi User Supervision Transmission (MUST) for LTE", the 3GPP discusses and examines two MUST Transmission structures, i.e., MUST class 1 (non-gray mapping) and class 2 (gray mapping). An example of a MUST category 1 is shown in fig. 5, where Transport Blocks (TBs) (e.g., TBs) for two UEs₁And TB₂) Coded, Rate Matched (RM), and scrambled in

blocks

512 and 522, respectively, and then inherited modulation mapping in

blocks

514 and 524. The modulated two signals are then power allocated in block 530 and finally form a superimposed signal transmitted by the eNB. An example of MUST class 2 is shown in FIG. 6, where transmissions for two UEs areTransport Blocks (TB) (e.g. TB)₁And TB₂) Coded, Rate Matched (RM), and scrambled respectively in

blocks

612 and 622, followed by joint modulation gray mapping and power allocation in block 630, and finally forming a superimposed signal transmitted by the eNB.

In conventional downlink multi-user superposition transmission schemes, there is room for further improvement with respect to interference between UEs.

Disclosure of Invention

In general, embodiments of the present disclosure relate to communication methods and apparatus for downlink multi-user superposition transmission.

According to an aspect of the present disclosure, there is provided a communication method for downlink multi-user superposition transmission, comprising: receiving, at a first user equipment, network assistance information and a superimposed signal for reducing interference from a base station; detecting a signal for the second user device from the superimposed signal based on the network assistance information, the first user device being paired with the second user device; and cancelling interference to the first user equipment by the signal intended for the second user equipment.

In some embodiments, the first user equipment and the second user equipment each have two antenna ports, and receiving the network assistance information comprises: receiving at least one of power allocation information and a superimposed constellation between the first user equipment and the second user equipment.

In some embodiments, the method further comprises: in response to determining that the first user equipment has four antenna ports and the second user equipment has two communication ports, determining two antenna ports of the first user equipment that correspond to the two antenna ports of the second user equipment.

In some embodiments, receiving the network assistance information comprises: receiving at least one of power allocation information and a superimposed constellation between the first user equipment and the second user equipment.

In some embodiments, the first user equipment and the second user equipment each have four antenna ports, and receiving the network assistance information comprises: receiving a precoding index associated with a precoding selected for a pairing of the first pairing device and the second user equipment; and receiving at least one of power allocation information and a superimposed constellation between the first user equipment and the second user equipment.

In some embodiments, the first user device is further paired with a third user device, the first user device having four antenna ports, the second user device having two antenna ports, the third user device having two antenna ports, the receiving the network assistance information comprising: receiving information for determining two antenna ports in the first user equipment that correspond to two antenna ports of the second user equipment and for determining another two antenna ports in the first user equipment that correspond to two antenna ports of the third user equipment.

In some embodiments, receiving the network assistance information further comprises: receiving power allocation information or a superimposed constellation between two antenna ports of the first user equipment and two antenna ports of the second user equipment; and receiving power allocation information or a superimposed constellation between the other two antenna ports of the first user equipment and the two antenna ports of the third user equipment.

According to a second aspect of the present disclosure, there is provided a communication method for downlink multi-user superposition transmission, comprising: sending a superimposed signal and network assistance information to a first user equipment, the network assistance information being used to detect, at the first user equipment, a signal in the superimposed signal for a second user equipment paired with the first user equipment, such that the first user equipment cancels interference to the first user equipment by the signal for the second user equipment based on the network assistance information.

According to a third aspect of the present disclosure, there is provided a user equipment for downlink multi-user superposition transmission, comprising: receiving means configured to receive network assistance information and a superimposed signal for interference reduction from a base station; a detecting device configured to detect a signal for the second user equipment from the superimposed signal based on the network assistance information, the user equipment being paired with the second user equipment; and an interference cancellation means configured to cancel interference to the user equipment by the signal for the second user equipment.

According to a fourth aspect of the present disclosure, there is provided a base station for downlink multi-user superposition transmission, comprising: a transmitting device configured to transmit, to a first user equipment, a superimposed signal and network assistance information, the network assistance information being used to detect, at the first user equipment, a signal in the superimposed signal for a second user equipment paired with the first user equipment, such that the first user equipment cancels interference with a signal for the second user equipment based on the network assistance information.

It will be understood that this section is not intended to identify key or critical features of embodiments of the disclosure, nor is it intended to be used to limit the scope of the disclosure. Other features of the present disclosure will become apparent from the following description.

Drawings

The above and other advantages, features and objects of the present disclosure will become more apparent from the following more detailed description of some embodiments of the present disclosure in which:

FIG. 1 is a schematic illustration of an environment in which embodiments of the present disclosure may be implemented;

fig. 2 is a flow chart of a communication method for downlink multi-user superposition transmission according to an embodiment of an aspect of the present disclosure;

fig. 3 is a flow chart of a communication method for downlink multi-user superposition transmission according to an embodiment of another aspect of the present disclosure;

fig. 4 is a block diagram of the UE and eNB of fig. 1, according to an embodiment of the present disclosure;

fig. 5 is a schematic diagram of an example of a MUST category 1; and

fig. 6 is a schematic diagram of an example of the MUST category 2.

Throughout the drawings, the same or similar reference numbers refer to the same or similar elements.

Detailed Description

The principles of the present disclosure will now be described with reference to a few exemplary embodiments. It is understood that these examples are described solely for the purpose of illustration and to assist those of ordinary skill in the art in understanding and working the disclosure, and are not intended to suggest any limitation as to the scope of the disclosure. The disclosure described herein may be implemented in various ways other than those described below.

As used herein, the term "include" and its various variants are to be understood as open-ended terms, which mean "including, but not limited to. The term "based on" may be understood as "based at least in part on". The term "one embodiment" may be understood as "at least one embodiment". The term "another embodiment" may be understood as "at least one other embodiment".

There are currently ten different Transmission Modes (TM) for Long Term Evolution (LTE). These TMs differ in antenna mapping, what reference signal hypotheses are used for demodulation (cell-specific reference signals (CRS) or demodulation reference signals (DM-RS), respectively), and how the terminal acquires Channel State Information (CSI) and feeds it back to the network. In the case of TM 1-TM 6, CRS is used for channel estimation, so they are also referred to as CRS-based TM.

Since the scheme used for power allocation indication and the associated modulation and demodulation process will be significantly different for different TMs. Embodiments of the present disclosure focus primarily on the approach to TM 3. TM3 is also referred to as a large delay Cyclic Delay Diversity (CDD) scheme.

For the 3rd Generation Partnership Project, at 3GPP 36.213; technical Specification Group Radio Access Network; improved Universal Radio Access (E-UTRA); with the large delay CDD scheme defined in Physical layer procedures ", the eNB typically assigns different precoding to different transmission vectors since CDD precoding will be applied to the transmitted signal. For example, a different precoding is used per v vectors, where v represents the number of transmission layers in the case of spatial multiplexing.

Herein, a paired UE in multi-user superposition transmission means a UE using the same transmission scheme on the same Resource Elements (REs). In embodiments of the present disclosure, the same transmission scheme may be large-latency CDD. In case of a UE with two and four antenna ports, the precoding chosen for the paired UE and the pairing of near and far UEs on different antenna ports will be different. Furthermore, since the superimposed signals in MUST category 1 and MUST category 2 have a non-gray mapped composite constellation and a gray mapped composite constellation, respectively, obtained from different operations at the transmitter, the detection of the far-end UE signal at the near-end UE for these two categories will also differ.

Herein, the term "user equipment" (UE) refers to any device capable of communicating with a BS. As an example, the UE may include a terminal, a Mobile Terminal (MT), a Subscriber Station (SS), a Portable Subscriber Station (PSS), a Mobile Station (MS), or an Access Terminal (AT). In particular, in the context of the present disclosure, a near UE refers to a UE of the paired UEs that is geographically closer to the base station, while a far UE refers to a UE of the paired UEs that is geographically further away from the base station.

The term "base station" (BS) as used herein may refer to a node B (NodeB or NB), an evolved node B (eNodeB or eNB), a Remote Radio Unit (RRU), a Radio Head (RH), a Remote Radio Head (RRH), a relay, a low power node, such as a pico base station, a femto base station, and the like.

FIG. 1 illustrates a schematic diagram of an environment in which embodiments of the present disclosure may be implemented. UE 110 in fig. 1 may be a near-end UE and UE 120 may be a far-end UE. UE 110 is closer to base station 105 than UE 120. It should be understood that although only two UEs are shown in fig. 1, there may in fact be any number of paired UEs. For example, in certain embodiments to be described below, there may also be other one or more UEs paired with UE 110 in environment 100, and so on. The scope of the present disclosure is not limited in this respect.

In the case of MUST (TM) 3TB for UE 110₁May be subject to TB for UE 120₂Because the UE 120 is at the cell edge and TB₂Is allocated a greater transmission power to ensure that signals intended for UE 120 can be transmitted to UE 120. UE 110 with a more advanced receiver first decodes the signal for UE 120 and then removes the signal for UE 120 from the received superimposed signal, e.g., using some assistance information provided to UE 110. UE 110 then decodes its own PDSCH data. Therefore, whether and how much interference to cancel the interference caused by the signal to the UE 120 is particularly important for the UE 110 to decode its own data.

To address the above and other potential problems, in accordance with some embodiments of the present disclosure, network assistance information for MUST category 1 and category 2 may be transmitted in a large-latency CDD scheme with two and four antenna ports. In this way, the near-end UE (a first UE, e.g., UE 100 in fig. 1) can use the network assistance information to correctly decode a signal intended for the far-end UE (a second UE 120 or a third UE not shown, etc.) and remove the signal from the superimposed signal to correctly decode the signal intended for itself. By using the embodiments according to the present disclosure, the near-end UE can cancel interference to the near-end UE from a signal intended for the far-end UE. Herein, cancelling or canceling interference means at least partially cancelling or canceling interference and with a high probability completely cancelling or canceling interference, without excluding insignificant instances of cancelling or canceling interference due to other factors despite implementation of a scheme according to embodiments of the present disclosure.

Fig. 2 shows a flow diagram of a communication method 200 for downlink multi-user superposition transmission according to an embodiment of an aspect of the present disclosure. In certain embodiments, method 200 may be implemented by UE 110 in fig. 1, for example. The base station 105 transmits wireless signals to the paired

UEs

110 and 120. For example, as described above, the base station 105 transmits the superimposed signal modulated according to the MUST category 1 or category 2 to the UE 110. For convenience of description, UE 110 may be referred to as a "first UE" and UE 120 may be referred to as a "second UE".

In step 202, the UE 110 receives network assistance information and a superimposed signal for interference reduction from the base station 105. After receiving the network assistance information and the superimposed signal, UE 110 detects a signal for UE 120 from the superimposed signal based on the network assistance information in step 204.

Next, UE 110 cancels interference to UE 110 from the signal for UE 120 after detecting the signal for UE 120 at step 206, e.g., by removing the signal for UE 120 from the superimposed signal. After removing the signal for UE 120, UE 110 decodes the signal for itself, thereby obtaining an interference free signal.

Fig. 3 illustrates a flow diagram of a communication method 300 for downlink multi-user superposition transmission, in accordance with an embodiment of an aspect of the present disclosure. In some embodiments, the method 200 may be implemented by, for example, the base station 105 in fig. 1. The base station 105 transmits a superimposed signal modulated according to, for example, the MUST category 1 or category 2 to the paired

UEs

110 and 120 in step 302.

In TM3, base station 105 knows the number of antenna ports, e.g., 2 or 4, for

UEs

110 and 120. Thus, base station 105 may configure the network assistance information according to the number of antenna ports of

UEs

110 and 120. For a MUST transmission with a large delay CDD, there are four antenna configurations: (1) UE 110 and UE 120 each have two antenna ports; (2) UE 110 has four antenna ports and UE 120 has two antenna ports, UE 110 is paired only with UE 120; (3) UE 110 and UE 120 each have four antenna ports; and (4) UE 110 has four antenna ports, UE 120 has two antenna ports, and UE 110 is paired with a third UE (not shown in fig. 1, a far-end UE) in addition to UE 120. Examples of network assistance information will be explained below for different antenna port configurations.

For UE 110 to have two antenna ports and UE 120 to have two antenna ports, UE 110 and UE 120 will use the same precoding since only one precoding is selected in TM 3. How to select precoding is defined in 3GPP TS 36.211. A codebook for transmission on antenna port {0,1} and for CSI reporting based on antenna port {0,1} or {15,16} is shown in table 1, where v represents a precoding matrix corresponding to a precoding index of 0.

Table 1 codebook for transmission on antenna port {0,1} and for CSI reporting based on antenna port {0,1} or {15,16 }.

TABLE 1

Therefore, there is only one possible precoding to choose from in a large delay CDD scheme with two antenna ports. For the MUST category 1, the TBs of the near UE 110 and the far UE 120 are coded and modulated separately and then superimposed with a non-gray mapped composite constellation. To detect and cancel the signal of far-end UE 120 at near-end UE 110, base station 105 may indicate to near-end UE 110 the power allocation between the paired UEs.

For the MUST category 2, the signals of the near UE 110 and the far UE 120 are encoded separately but jointly modulated using gray-mapped composite constellations. The jointly modulated signals are precoded using a precoding symbol prior to transmission. In one embodiment, the superimposed constellation (information of the gray mapped composite constellation) is sent to the UE 110. If the number of superimposed constellations is limited, several bits may be used to inform the UE 110 of the superimposed constellations and the power split information between the paired UEs.

In another embodiment, the precise power allocation information and the operation for jointly modulating signals of UE 110 and UE 120 are directly indicated to UE 110. By using the network assistance information, the signal of UE 120 may be correctly detected at UE 110.

In the case of a UE 110 with four ports, according to 3GPP 36.213, "3 rd Generation Partnership Project; technical Specification Group Radio Access Network; improved Universal Radio Access (E-UTRA); physical layer procedures ", the UE may assume that the eNB cyclically assigns different precoding to different transmission vectors on the Physical downlink shared channel. A different precoding is changed every v vectors, where v denotes the number of transmission layers in the case of spatial multiplexing. In particular toAccording to W (i) ═ C_kSelecting precoding, where k is represented by

Given precoding index, and C₁,C₂,C₃,C₄Precoding matrices corresponding to precoding indexes 12,13,14, and 15, respectively, are represented as shown in table 2 below.

Table 2 codebook for transmissions on antenna port {0,1,2,3} and for CSI reports based on antenna port {0,1,2,3} or {15,16,17,18}

TABLE 2

If UE 110 is paired with UE 120 only, UE 110 has four antenna ports, and UE 120 has two antenna ports, UE 110 determines, through its own interference blind check, that two antenna ports of the four antenna ports of UE 110 correspond to or are paired with two antenna ports of UE 120. Since only one precoding is selected in TM3 in case the signals of UE 120 are transmitted through two antenna ports. Thus, to detect and cancel interference of the signal of UE 120 at UE 110, the network assistance information transmitted from base station 105 to UE 110 may include at least one of power allocation information and superimposed constellation information between the paired UEs. This scenario may be similar to the scenario above with two antenna ports for both UE 110 and UE 120.

In the case where UE 110 and UE 120 each have four antenna ports, the network assistance information transmitted from base station 105 to UE 110 may contain a precoding index of UE 120, and the network assistance information may further include at least one of power allocation information and superimposed constellation information.

If UE 110 is paired not only with UE 120, but also with one or more other UEs (not shown, referred to as "third UE"), where UE 110 has four antenna ports, and UE 120 and the third UE have two antenna ports, the network assistance information sent from base station 105 to UE 110 may contain signaling as to which two antenna ports of UE 110 are paired with UE 120 and the other two antenna ports of UE 110 are paired with the third UE. In one embodiment, the signaling may be represented by a four element vector. For example, [ 1100 ] means that the first two layers (antenna ports) of UE 110 are paired with and correspond to two antenna ports of UE 120, while the last two layers are paired with and correspond to two antenna ports of a third UE. The network assistance information may also include power allocation information between UE 110 and UE 120, power allocation information between UE 110 and a third UE. In addition, the network assistance information may also include superimposed constellation information for UE 120 and superimposed constellation information for a third UE.

Fig. 4 shows a block diagram of the structure of the UE 110 and the base station 105 in fig. 1 according to an embodiment of the disclosure. UE 110 includes receiving means 1102, detecting means 1104, and interference cancellation means 1106. The base station 105 comprises transmitting means 1052. The receiving device 1102 receives the superimposed signal in the TM3 mode and the network assistance information transmitted from the transmitting device of the base station 105. After receiving the superimposed signal and the network assistance information, the detecting means 1104 of the UE 110 detects a signal for the UE 120 based on the received network assistance information. After detecting the signal for UE 120, the interference cancellation device 1106 cancels the interference of the signal for UE 120 to UE 110, for example, by removing the signal for UE 120 from the superimposed signal.

The means shown in fig. 4 may be implemented partially or wholly as hardware modules, software modules, firmware modules, or any combination thereof. In particular, in certain embodiments, the procedures, methods or processes described above may be implemented by hardware in the UE or the base station. For example, the UE may implement the method 200 with its transmitter, receiver, transceiver, and/or processor or controller, while the base station may implement the method 300 with its transceiver and/or processor or controller.

It should be understood that various embodiments of the present disclosure may be used with various mechanisms, standards, or environments for downlink multi-user superposition transmission that are currently known or that may be developed in the future. For example, embodiments of the present invention may be applied to the non-gray-mapped modulation scheme shown in fig. 5 and/or the gray-mapped modulation scheme shown in fig. 6.

In general, the various embodiments of the disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, without limitation, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

Further, while operations are described in a particular order, this should not be understood as requiring that such operations be performed in the order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In some cases, multitasking or parallel processing may be advantageous. Similarly, while details of several specific implementations are included in the above discussion, these should not be construed as any limitation on the scope of the disclosure, but rather the description of features is directed to specific embodiments only. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination.

Although the disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. The specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A communication method for downlink multi-user superposition transmission, comprising:

receiving, at a first user equipment, network assistance information and a superimposed signal for reducing interference from a base station;

detecting a signal for a second user device from the superimposed signal based on the network assistance information, the first user device being paired with the second user device; and

cancelling interference to the first user equipment by the signal intended for the second user equipment,

wherein receiving the network assistance information comprises receiving power allocation information and a superimposed constellation between the first user equipment and the second user equipment, and when the category of the multi-user superimposed transmission is category 2, the superimposed constellation comprises information of a gray-mapped composite constellation.

2. The method of claim 1, wherein the first user equipment and the second user equipment each have two antenna ports.

3. The method of claim 1, further comprising:

in response to determining that the first user device has four antenna ports and the second user device has two communication ports, determining two antenna ports of the first user device that are overlay paired with two antenna ports of the second user device.

4. The method of claim 1, wherein the first user equipment and the second user equipment each have four antenna ports, and receiving the network assistance information comprises:

receiving a precoding index associated with a precoding selected for a pairing of the first user equipment and the second user equipment; and

receiving at least one of power allocation information and a superimposed constellation between the first user equipment and the second user equipment.

5. The method of claim 1, wherein the first user device is further paired with a third user device, the first user device having four antenna ports, the second user device having two antenna ports, the third user device having two antenna ports, receiving the network assistance information comprising:

receiving information for determining two antenna ports in the first user equipment that correspond to two antenna ports of the second user equipment and for determining another two antenna ports in the first user equipment that correspond to two antenna ports of the third user equipment.

6. The method of claim 5, wherein receiving the network assistance information further comprises:

receiving power allocation information and a superimposed constellation between two antenna ports of the first user equipment and two antenna ports of the second user equipment; and

receiving power allocation information and a superimposed constellation between the other two antenna ports of the first user equipment and the two antenna ports of the third user equipment.

7. A communication method for downlink multi-user superposition transmission, comprising:

transmitting a superimposed signal and network assistance information to a first user equipment, the network assistance information being used to detect, at the first user equipment, a signal in the superimposed signal for a second user equipment paired with the first user equipment, such that the first user equipment cancels interference to the first user equipment for the signal for the second user equipment based on the network assistance information, wherein transmitting the network assistance information comprises transmitting power allocation information and a superimposed constellation between the first user equipment and the second user equipment, and when the category of the multi-user superimposed transmission is category 2, the superimposed constellation comprises information of a gray-mapped composite constellation.

8. The method of claim 7, wherein the first user equipment has two or four antenna ports and the second user equipment has two antenna ports.

9. The method of claim 7, wherein the first user equipment and the second user equipment each have four antenna ports, and transmitting the network assistance information comprises:

transmitting a precoding index associated with a precoding selected for a pairing of the first user equipment and the second user equipment; and

and sending the power distribution information and the superposed constellation diagram between the first user equipment and the second user equipment.

10. The method of claim 7, wherein the first user device is further paired with a third user device, the first user device has four antenna ports, the second user device has two antenna ports, the third user device has two antenna ports, and sending the network assistance information comprises:

transmitting information for determining two antenna ports in the first user equipment that correspond to two antenna ports of the second user equipment and for determining another two antenna ports in the first user equipment that correspond to two antenna ports of the third user equipment.

11. The method of claim 10, wherein sending the network assistance information further comprises:

transmitting power allocation information and a superimposed constellation between two antenna ports of the first user equipment and two antenna ports of the second user equipment; and

transmitting power allocation information and a superimposed constellation between the other two antenna ports of the first user equipment and the two antenna ports of the third user equipment.

12. A user equipment for downlink multi-user superposition transmission, comprising:

receiving means configured to receive network assistance information and a superimposed signal for interference reduction from a base station;

a detecting device configured to detect a signal for a second user equipment from the superimposed signal based on the network assistance information, the user equipment being paired with the second user equipment; and

an interference cancellation means configured to cancel interference to the user equipment by the signal for the second user equipment,

wherein the receiving means is configured to receive power allocation information and a superimposed constellation between the user equipment and the second user equipment, and when the category of the multi-user superimposed transmission is category 2, the superimposed constellation comprises information of a gray-mapped composite constellation.

13. The user equipment of claim 12, wherein the user equipment and the second user equipment each have two antenna ports.

14. The user equipment of claim 12, the user equipment further comprising:

a determining means configured to determine two antenna ports of the user equipment corresponding to two antenna ports of the second user equipment in response to determining that the user equipment has four antenna ports and the second user equipment has two communication ports.

15. The user equipment of claim 12, wherein the user equipment and the second user equipment each have four antenna ports, the receiving means being configured to:

receiving a precoding index associated with a precoding selected for a pairing of the user equipment and the second user equipment.

16. The user equipment of claim 12, wherein the user equipment is further paired with a third user equipment, the user equipment having four antenna ports, the second user equipment having two antenna ports, the third user equipment having two antenna ports, the receiving means configured to:

receiving information for determining two antenna ports in the user equipment corresponding to the two antenna ports of the second user equipment and for determining another two antenna ports in the user equipment corresponding to the two antenna ports of the third user equipment.

17. The user equipment of claim 16, wherein the receiving means is further configured to:

receiving power allocation information and a superimposed constellation between two antenna ports of the user equipment and two antenna ports of the second user equipment; and

receiving power allocation information and a superimposed constellation between the other two antenna ports of the user equipment and the two antenna ports of the third user equipment.

18. A base station for downlink multi-user superposition transmission, comprising:

transmitting means configured to transmit, to a first user equipment, a superimposed signal and network assistance information for detecting, at the first user equipment, a signal in the superimposed signal for a second user equipment paired with the first user equipment, such that the first user equipment cancels interference for a signal of the second user equipment based on the network assistance information, wherein the transmitting means is configured to transmit the network assistance information including power allocation information and a superimposed constellation transmitted between the first user equipment and the second user equipment, and when the category of the multi-user superimposed transmission is category 2, the superimposed constellation includes information of a gray-mapped composite constellation.

19. The base station according to claim 18, wherein the first user equipment has two or four antenna ports and the second user equipment has two antenna ports.

20. The base station of claim 18, wherein the first user equipment and the second user equipment each have four antenna ports, the transmitting means is configured to:

21. The base station of claim 18, wherein the first user equipment is further paired with a third user equipment, the first user equipment having four antenna ports, the second user equipment having two antenna ports, the third user equipment having two antenna ports, and the transmitting means is configured to:

22. The base station of claim 21, wherein the transmitting means is further configured to: