FIELD

[0001] Embodiments of the present disclosure generally relate to wireless communication techniques, and more particularly, to a method and device of superposition transmission with codebook-based closed-loop precoding, as well as a method and device of decoding signals for superposition transmission with codebook-based closed-loop precoding.

BACKGROUND

[0002] In downlink multiuser superposition transmission (hereinafter referred to as MUST for short), multiple user equipments (UEs) are paired to enable their simultaneous transmission of more than one layer of data without time, frequency and spatial layer separation (i.e. using the same spatial precoding vector or the same transmit diversity scheme over the same resource elements).

[0003] Currently, there are ten different transmission modes (TMs) defined for LTE. They differ in terms of the specific structure of the antenna mapping and also in terms of what reference signals (cell- specific reference signals (CRS) or demodulation reference signals (DM-RS) respectively) are assumed to be used for demodulation and how channel state information (CSI) is acquired by the terminal and fed back to the network. In case of transmission modes 1 to 6, CRS is to be used for channel estimation, and thus also referred to CRS-based TM.

[0004] Codebook-based closed-loop precoding is associated with transmission mode 4 (TM4). In the case of codebook-based closed-loop precoding, it is assumed that the network selects the precoder matrix based on the feedback from the UE. It is defined in current 3GPP standards that the UE selects a transmission rank and a precoder matrix based on measurements on CRS, the information of which is then reported back to an Evolved Node B (eNB) in the form of precoder-matrix indication (PMI) and rank indication (RI).

[0005] It has been agreed by the 3GPP organization that for MUST, the same precoder for UEs with superposed signals is considered. Hence, for closed-loop codebook-based multiple-input and multiple-output (MIMO) transmission, UEs pairing for superposition transmission could end up in different transmission structures due to different ranks reported by different UEs. Also, different transmission spatial layers could lead to different pairing scenarios for superposition transmission. Since different superposition scenarios may require different information of decoding far/interfering UE's signal at near/victim UE, the transmission structures for different superposition scenarios in case of codebook-based closed-loop precoding are worth investigating.

SUMMARY OF THE DISCLOSURE

[0006] The embodiments of the present disclosure provide a method and device of superposition transmission with codebook-based closed-loop precoding as well as a method and device of decoding signals for superposition transmission with codebook-based closed-loop precoding so as to solve or at least partially alleviate the above problems in the prior art.

[0007] In a first aspect of the present disclosure, there is provided a superposition transmission method with codebook-based closed-loop precoding. The method comprises: generating a plurality of codewords for a first user equipment; generating at least one codeword for second user equipment which is to be paired with the first user equipment; mapping the plurality of codewords for the first user equipment to a plurality of transmission spatial layers having the same number as a plurality of transmit antennas; mapping the at least one codeword for the second user equipment to at least one transmission spatial layer of the plurality of transmission spatial layers; and performing, on the at least one transmission spatial layer, superposition transmission for the first user equipment and the second user equipment.

[0008] In some embodiments, a first rank indication for the first user equipment is larger than or equal to a second rank indication for the second user equipment.

[0009] In some embodiments, the generating a plurality of codewords for first user equipment comprises: generating two codewords for the first user equipment based on the first rank indication; and the mapping the plurality of codewords for the first user equipment to a plurality of transmission spatial layers comprises: modulating the two codewords for the first user equipment; and mapping each of the two modulated codewords for the first user equipment at least to one of the plurality of transmission spatial layers.

[0010] In some embodiments, the mapping each of the two modulated codewords for the first user equipment at least to one of the plurality of transmission spatial layers comprises: mapping the two modulated codewords for the first user equipment at least to a first transmission spatial layer and a second transmission spatial layer of the plurality of transmission spatial layers respectively

[0011] In some embodiments, the mapping each of the two modulated codewords for the first user equipment at least to one of the plurality of transmission spatial layers comprises: mapping one of the two modulated codewords to a first transmission spatial layer and a second transmission spatial layer of the plurality of transmission spatial layers respectively, and mapping the other of the two modulated codewords to a third transmission spatial layer and a fourth transmission spatial layer of the plurality of transmission spatial layers respectively

[0012] In some embodiments, the mapping the two modulated codewords for the first user equipment at least to a first transmission spatial layer and a second transmission spatial layer of the plurality of transmission spatial layers respectively comprises: mapping one of the two modulated codewords to the first transmission spatial layer, and mapping the other of the two modulated codewords to the second transmission spatial layer and a third transmission spatial layer of the plurality of transmission spatial layers respectively

[0013] In some embodiments, the generating at least one codeword for second user equipment comprises: generating one codeword for the second user equipment based on the second rank indication; and the mapping the at least one codeword for the second user equipment to at least one transmission spatial layer of the plurality of transmission spatial layers comprises: modulating the one codeword for the second user equipment; and mapping the one modulated codeword for the second user equipment to the first transmission spatial layer.

[0014] In some embodiments, the performing, on the at least one transmission spatial layer, superposition transmission for the first user equipment and the second user equipment comprises: performing, on the first transmission spatial layer, the superposition transmission for the first user equipment and the second user equipment. [0015] In some embodiments, the method further comprises: generating one codeword for third user equipment which is to be paired with the first user equipment; modulating the one codeword for the third user equipment; mapping the one modulated codeword for the third user equipment to one of the second transmission spatial layer and the third transmission spatial layer; performing, on the one of the second transmission spatial layer and the third transmission spatial layer, superposition transmission for the first user equipment and the third user equipment; and performing, on the other of the second transmission spatial layer and the third transmission spatial layer, single-user transmission for the first user equipment.

[0016] In some embodiments, the method further comprises: generating one codeword for fourth user equipment which is to be paired with the first user equipment; modulating the one codeword for the fourth user equipment; mapping the one modulated codeword for the fourth user equipment to a fourth transmission spatial layer of the plurality of transmission spatial layers; and performing, on the fourth transmission spatial layer, superposition transmission for the first user equipment and the fourth user equipment.

[0017] In some embodiments, the generating a plurality of codewords for first user equipment comprises: using only one modulation scheme to modulate a codeword of the plurality of codewords which is to be mapped to both of the second transmission spatial layer and the third transmission spatial layer.

[0018] In some embodiments, the mapping the one modulated codeword for the third user equipment to one of the second transmission spatial layer and the third transmission spatial layer comprises: comparing channel quality of the second transmission spatial layer with that of the third transmission spatial layer; and in response to the channel quality of one of the second transmission spatial layer and the third transmission spatial layer being better than that of the other of the second and third transmission spatial layers, mapping the modulated codeword for the third user equipment to the other of the second and third transmission spatial layers.

[0019] In some embodiments, the generating a plurality of codewords for first user equipment comprises: using a first modulation scheme and a second modulation scheme to modulate the other codeword of the two codewords so as to generate a first sub-modulated signal stream and a second sub-modulated signal stream respectively; the mapping the other codeword to the second transmission spatial layer and the third transmission spatial layer comprises: mapping the first sub-modulated signal stream and the second sub-modulated signal stream to the second transmission spatial layer and the third transmission spatial layer respectively; and wherein modulation order of the first modulation scheme is higher than modulation order of the second modulation scheme.

[0020] In some embodiments, the mapping the one modulated codeword for the third user equipment to one of the second transmission spatial layer and the third transmission spatial layer comprises: mapping the one modulated codeword for the third user equipment to the third transmission spatial layer.

[0021] In some embodiments, the method further comprises: sending a high-layer signaling to the first user equipment, the high-layer signaling indicating superposition transmission for the first user equipment and the third user equipment on the third transmission spatial layer.

[0022] In a second aspect of the embodiments of the present disclosure, there is provided a method of decoding signals for superposition transmission with codebook-based closed-loop precoding. The method comprises: receiving from a base station signals transmitted on a plurality of transmission spatial layers and power allocation information, the received signals at least including signals of first user equipment and signals of second user equipment in superposition transmission on at least one transmission spatial layer of the plurality of transmission spatial layers; in response to detecting interference caused by the signals of the second user equipment on the at least one transmission spatial layer exceeding a predetermined threshold, decoding the signals of the second user equipment from the received signals based on the power allocation information; and obtaining the signals of the first user equipment based on the decoded signals of the second user equipment.

[0023] In some embodiments, the decoding signals of the second user from received signals comprises: blindly detecting the signals of the second user equipment from the received signals.

[0024] In some embodiments, the received signals at least include: signals of the first user equipment and signals of the second user equipment in superposition transmission on a first transmission spatial layer of the plurality of transmission spatial layers, signals of the first user equipment and signals of third user equipment in superposition transmission on a second transmission spatial layer of the plurality of transmission spatial layers, and signals of the first user equipment in single-user transmission on a third transmission spatial layer of the plurality of transmission spatial layers.

[0025] In some embodiments, the method further comprises: receiving a high-layer signaling from the base station, the high-layer signaling indicating the superposition transmission for the first user equipment and the third user equipment on the second transmission spatial layer.

[0026] In some embodiments, the method further comprises: decoding the signals of the third user equipment from the received signals based on the power allocation information and the high-layer signaling; decoding the signals of the second user equipment based on the high-layer signaling; and obtaining the signals of the first user equipment based on the decoded signals of the third user equipment.

[0027] In a third aspect of the embodiments of the present disclosure, there is provided a device of superposition transmission with codebook-based closed-loop precoding. The device comprises: a first generating unit configured to generate a plurality of codewords for a first user equipment; a second generating unit configured to generate at least one codeword for second user equipment which is to be paired with the first user equipment; a first mapping unit configured to map the plurality of codewords for the first user equipment to a plurality of transmission spatial layers having the same number as a plurality of transmit antennas; a second mapping unit configured to map the at least one codeword for the second user equipment to at least one transmission spatial layer of the plurality of transmission spatial layers; and a first superposition transmission unit configured to perform, on the at least one transmission spatial layer, superposition transmission for the first user equipment and the second user equipment.

[0028] In some embodiments, a first rank indication for the first user equipment is larger than or equal to a second rank indication for the second user equipment.

[0029] In some embodiments, the first generating unit is further configured to generate two codewords for the first user equipment based on the first rank indication; and the first mapping unit is further configured to modulate the two codewords for the first user equipment; and to map each of the two modulated codewords for the first user equipment at least to one of the plurality of transmission spatial layers.

[0030] In some embodiments, the first mapping unit is further configured to map the two modulated codewords for the first user equipment at least to a first transmission spatial layer and a second transmission spatial layer of the plurality of transmission spatial layers respectively

[0031] In some embodiments, the first mapping unit is further configured to map one of the two modulated codewords to a first transmission spatial layer and a second transmission spatial layer of the plurality of transmission spatial layers respectively, and map the other of the two modulated codewords to a third transmission spatial layer and a fourth transmission spatial layer of the plurality of transmission spatial layers respectively

[0032] In some embodiments, the first mapping unit is further configured to map one of the two modulated codewords to the first transmission spatial layer, and map the other of the two modulated codewords to the second transmission spatial layer and a third transmission spatial layer respectively

[0033] In some embodiments, the second generating unit is further configured to generate one codeword for the second user equipment based on the second rank indication, and the second mapping unit is further configured to modulate the one codeword for the second user equipment; and map the one modulated codeword for the second user equipment to the first transmission spatial layer.

[0034] In some embodiments, the first superposition transmission unit is further configured to perform, on the first transmission spatial layer, superposition transmission for the first user equipment and the second user equipment.

[0035] In some embodiments, the device further comprises: a third generating unit configured to generate one codeword for third user equipment which is to be paired with the first user equipment; a third mapping unit configured to modulate the one codeword for the third user equipment and map the one modulated codeword for the third user equipment to one of the second transmission spatial layer and the third transmission spatial layer; a second superposition transmission unit configured to perform, on the one transmission spatial layer of the second transmission spatial layer and the third transmission spatial layer, superposition transmission for the first user equipment and the third user equipment; and a first single-user transmission unit configured to perform, on the other transmission spatial layer of the second transmission spatial layer and the third transmission spatial layer, single-user transmission for the first user equipment.

[0036] In some embodiments, the device further comprises: a fourth generating unit configured to generate one codeword for fourth user equipment which is to be paired with the first user equipment; a fourth mapping unit configured to modulate the one codeword for the fourth user equipment and mapp the one modulated codeword for the fourth user equipment to a fourth transmission spatial layer of the plurality of transmission spatial layers; and a third superposition transmission unit configured to perform, on the fourth transmission spatial layer, superposition transmission for the first user equipment and the fourth user equipment.

[0037] In some embodiments, the first generating unit is further configured to use only one modulation scheme to modulate a codeword of the plurality of codewords which is to be mapped to both of the second transmission spatial layer and the third transmission spatial layer.

[0038] In some embodiments, the third mapping unit is further configured to: compare channel quality of the second transmission spatial layer with that of the third transmission spatial layer; and in response to the channel quality of one of the second transmission spatial layer and the third transmission spatial layer being better than the channel quality of the other transmission spatial layer, map the one modulated codeword for the third user equipment to the other transmission spatial layer.

[0039] In some embodiments, the first generating unit is further configured to use a first modulation scheme and a second modulation scheme to modulate the other codeword of the two codewords so as to generate a first sub-modulated signal stream and a second sub-modulated signal stream respectively; the first mapping unit is further configured to map the first sub-modulated signal stream and the second sub-modulated signal stream to the second transmission spatial layer and the third transmission spatial layer respectively; wherein modulation order of the first modulation scheme is higher than modulation order of the second modulation scheme.

[0040] In some embodiments, the third mapping unit is further configured to map the one modulated codeword for the third user equipment to the third transmission spatial layer. [0041] In some embodiments, the device further comprises: a notifying unit configured to send high-layer signaling to the first user equipment, the high-layer signaling indicating superposition transmission for the first user equipment and the third user equipment on the third transmission spatial layer.

[0042] In a fourth aspect of the embodiments of the present disclosure, there is provided a device of decoding signals in superposition transmission with codebook-based closed-loop precoding. The device comprises: a receiving unit configured to receive from a base station signals transmitted on a plurality of transmission spatial layers and power allocation information, the received signals at least including signals of first user equipment and second user equipment in superposition transmission on at least one transmission spatial layer of the plurality of transmission spatial layers; and a decoding unit configured to: in response to detecting interference caused by the signals of the second user equipment on the at least one transmission spatial layer of the plurality of transmission spatial layers exceeding a predetermined threshold, decode the signals of the second user equipment from the received signals based on the power allocation information; and obtain the signals of the first user equipment based on the decoded signal of the second user equipment.

[0043] In some embodiments, the decoding unit is further configured to blindly detect signals of the second user equipment from the received signals.

[0044] In some embodiments, the received signals at least include: signals of the first user equipment and the second user equipment in superposition transmission on a first transmission spatial layer of the plurality of transmission spatial layers, signals of the first user equipment and third user equipment in superposition transmission on a second transmission spatial layer of the plurality of transmission spatial layers, and signals of the first user equipment in single-user transmission on a third transmission spatial layer of the plurality of transmission spatial layers.

[0045] In some embodiments, the receiving unit is further configured to receive high-layer signaling from the base station, the high-layer signaling indicating superposition transmission for the first user equipment and the third user equipment on the second transmission spatial layer.

[0046] In some embodiments, the decoding unit is further configured to: decode signals of the third user equipment from received signals based on the power allocation information and the high-layer signaling; decode signals of the second user equipment based on the high-layer signaling; and obtain signals of the first user equipment based on the decoded signal of the third user equipment.

[0047] With the methods and devices according to the embodiments of the present disclosure, in the case of a plurality of transmission spatial layers, user equipments with the same precoder but different rank indications are caused to be paired for superposition transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Through the detailed description of some embodiments of the present disclosure in the accompanying drawings, the features, advantages and other aspects of the present disclosure will become more apparent, wherein several embodiments of the present disclosure are shown for the illustration purpose only, rather than for limiting. In the accompanying drawings:

[0049] Fig. 1 shows a superposition transmission environment in which the embodiments of the present disclosure can be implemented;

[0050] Fig. 2 shows a flowchart of a method of superposition transmission with codebook-based closed-loop precoding according to a first aspect of the embodiments of the present disclosure;

[0051] Fig. 3 shows a procedure of superposition transmission with two transmission spatial layers according to a first embodiment of the present disclosure;

[0052] Fig. 4 shows a procedure of superposition transmission with two transmission spatial layers according to a second embodiment of the present disclosure;

[0053] Fig. 5 shows a procedure of superposition transmission with three transmission spatial layers according to a third embodiment of the present disclosure;

[0054] Fig. 6 shows a procedure of superposition transmission with four transmission spatial layers according to a fourth embodiment of the present disclosure;

[0055] Fig. 7 shows a procedure of superposition transmission with four transmission spatial layers according to a fifth embodiment of the present disclosure;

[0056] Fig. 8 shows a flowchart of a method of decoding signals for superposition transmission with codebook-based closed-loop precoding according to a second aspect of the embodiments of the present disclosure;

[0057] Fig. 9 shows a block diagram of a device of superposition transmission with codebook-based closed-loop precoding according to a third aspect of the embodiments of the present disclosure; and

[0058] Fig. 10 shows a block diagram of a device of decoding signals for superposition transmission with codebook-based closed-loop precoding according to a fourth aspect of the embodiments of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0059] With reference to several embodiments, description is now presented to principles of the subject matter described here. It should be understood that these embodiments are described only for enabling those skilled in the art to better understand and further implement the subject matter described here, rather for limiting the scope of the subject matter in any manner.

[0060] The term "base station" (BS) used here may represent Node B (NodeB or NB), Evolved Node B (eNodeB or eNB), Remote Radio Unit (RRU), Radio Head (RH), Remote Radio Head (RRH), Repeater, Low-Power Node such as Pico-Base Station, Femto-Base Station and so on.

[0061] The term "user equipment" (UE) used here refers to any device capable of communicating with the BS. As examples, the UE may comprise a terminal, mobile terminal (MT), subscriber station (SS), portable subscriber station (PSS), mobile station (MS) or access terminal (AT).

[0062] Fig. 1 shows a superposition transmission environment in which the embodiments of the present disclosure may be implemented. As shown in this figure, one or more UEs may communicate with a base station (BS) 100. In this example, there are shown two UEs, i.e., UEs 110 and 120. This is only for the illustration purpose and not intended to limit the scope of the subject matter described here in any manner. Any appropriate number of UEs may communicate with base station 100. As shown in this figure, UE 110 and UE 120 are located at the same cell, and UE 110 is much closer to the cell's center than UE 200. Hereinafter, UE 110 is also referred to as "near UE" or "victim UE", and UE 120 is also referred to as "far UE" or "interfering UE".

[0063] Base station 100 may pair UE 110 with UE 120 so as to perform superposition transmission for UE 110 and UE 120 by using the same spatial precoding vector or the same transmit diversity scheme over the same resource elements (REs).

[0064] Currently, 3GPP only provides that superposition transmission may be performed to UEs using the same precoder. For example, if the precoder vector for UE1 whose RI equals 1 is v _1;1 , the precoder matrix for UE2 whose RI equals 2 is [v _2, i v _2>2 ], and v _1;1 = v _2>1 , then it is considered that UE1 and UE2 have the same precoder. In other words, if the near UE and the far UE have the same PMI, then superposition transmission may be performed for them.

[0065] However, for closed-loop codebook-based multiple-input and multiple- output (MEMO) transmission, UEs paired for superposition transmission could end up in different transmission structures due to different RIs reported by different UEs. Also, different numbers of transmission spatial layers could lead to different pairing scenarios for superposition transmission. Since different superposition scenarios may require different information of decoding far/interfering UE's signal at near/victim UE, the transmission structures for different superposition scenarios in case of codebook-based closed-loop precoding are worth investigating.

[0066] To this end, in a first aspect of the embodiments of the present disclosure, there is provided a method of superposition transmission with codebook-based closed-loop precoding. Fig. 2 shows a flowchart of a method 200 of superposition transmission with codebook-based closed-loop precoding according to a first aspect of the embodiments of the present disclosure.

[0067] Method 200 starts in step S210, in which a plurality of codewords are generated for a first UE. It should be understood that the number of codewords for the first UE depends on channel quality and capacity of the first UE. In an embodiment in which codebook-based closed-loop precoding is used, the number of codewords for the first UE may depend on first RI fed back by the first UE. For example, if the first UE has two receive antennas and the first RI fed back by the first UE is equal to 2, then the number of codewords for the first UE is 2. In step S220, at least one codeword is generated for a second UE which is to be paired with the first UE. Similarly, in the embodiment in which codebook-based closed-loop precoding is used, the number of codewords for the second UE may depend on second RI fed back by the second UE.

[0068] It may be understood that in this specification, the first UE and the second UE (and a third UE, a fourth UE and so on to be mentioned below) to be paired with the first UE are located at the same cell, and the first UE is much closer to the cell's center than the second UE, third UE etc. Hence, for the description purpose below, the first UE is also referred to as "near UE", the second UE, the third UE and so on are also referred to as "far UE1", "far UE2" and so on. In addition, since the first UE is much closer to the cell's center than the second UE, the third UE and so on, the first UE has a better channel quality over the second UE, the third UE and so on. Thereby, RI fed back by the first UE will be larger than or equal to RI of the second UE, the third UE and so on.

[0069] Still with reference to Fig. 2, in step S230 the plurality of codewords for the first UE are mapped to a plurality of transmission spatial layers having the same number as a plurality of transmit antennas.

[0070] In step S240, the at least one codeword for the second UE is mapped to at least one transmission spatial layer of the plurality of transmission spatial layers. Subsequently in step S250, superposition transmission for the first UE and the second UE is performed on the at least one transmission spatial layer.

[0071] It should be understood although operations S210 and S220 are depicted in a specific order, this should not be construed as requiring such operations to be completed in the specific order as shown or in succession. In some cases, operations S210 and S220 may be executed concurrently. Similarly, operations S230 and S240 may also be executed concurrently.

[0072] Currently, for codebook-based closed-loop precoding, 3GPP proposes mandatory configurations and optional configurations for antennas. In mandatory configurations, the number of antennas at transmitting side is 2, the number of antennas at receiving side is 2, or the number of antennas at transmitting side is 4, the number of antennas at receiving side is 2. In optional configurations, the number of antennas at transmitting side is 4, the number of antennas at receiving side is 4, or the number of antennas at transmitting side is 8, the number of antennas at receiving side is 2. Therefore, where the number of antennas at transmitting side is 4 and codebook-based closed-loop precoding is adopted, at most four receiving antennas for superposition transmission may be considered, and at most four different far UEs whose RIs are equal to 1 may be paired with one UE for superposition transmission.

[0073] In addition, in this specification, the second UE, the third UE, etc. are described as "UE to be paired with the first UE", which means that the second UE, the third UE, etc. satisfy conditions for pairing with the first UE for superposition transmission, i.e. having the same precoder.

[0074] Hereinafter, specific embodiments are described to illustrate how different UEs are paired for superposition transmission where the first UE, the second UE, the third UE, etc. have the same precoder but feed back different RIs and the number of transmission spatial layers (i.e. number of transmit antennas) differ.

[0075] Fig. 3 shows a procedure of superposition transmission with two transmission spatial layers according to a first embodiment of the present disclosure. In the first embodiment, PMI fed back by a first UE is the same as PMI fed back by a UE to be paired with the first UE, but RIs being fed back may be the same or different. Specifically, if RI fed back by the first UE equals 2, and RI fed back by the paired UE equals 1, then at this point there may be two different UEs (second UE and third UE) to be paired with the first UE. If RI fed back by the first UE equals 2, and RI fed back by the paired UE also equals 2, then at this point only one UE (e.g. second UE) will be paired with the first UE.

[0076] Where two different UEs (i.e., second UE and third UE) are paired with the first UE and RIs fed back by the second UE and the third UE equal 1, two codewords for the first UE are generated based on the first RI, and the two codewords for the first UE, after being modulated, are mapped to a first transmission spatial layer and a second transmission spatial layer respectively. In addition, one codeword for the second UE is generated based on a second RI, and the one codeword for the second UE, after being modulated, is mapped to the first transmission spatial layer. In addition, one codeword for the third UE is generated based on a third RI, and the one codeword for the third UE, after being modulated, is mapped to the second transmission spatial layer. Further, superposition transmission for the first UE and the second UE is performed on the first transmission spatial layer, and superposition transmission for the first UE and the third UE is performed on the second transmission spatial layer.

[0077] Specifically, as shown in Fig. 3, in blocks 311 and 321, a second source data stream and a second source data stream for the near UE (first UE) are subject to channel-coding, so that codewords CW1 and CW2 for the near UE are generated respectively. [0078] In blocks 312 and 322, the codewords CWl and CW2 for the near UE are modulated respectively to generate two modulated codewords for the near UE. It should be understood that in blocks 312 and 322 any appropriate modulation modes may be used to modulate the codewords CWl and CW2. For example, the modulation modes include but not limited to: QPSK, 16QAM, 64QAM.

[0079] In block 313, the two modulated codewords for the near UE are mapped to the first transmission spatial layer and the second transmission spatial layer respectively

[0080] Similarly, for the far UEl (second UE), in block 331 a source data stream for the far UEl is subject to channel-coding, thereby forming a codword CWl for the far UEl. Then in block 332, the codeword CWl for the far CWl is modulated to generate one modulated codeword for the far UEl. In block 333, the one modulated codeword for the far UEl is mapped to the first transmission spatial layer.

[0081] In block 314, the one modulated codeword for the near UE and the one modulated codeword for the far UEl are superposed on the first transmission spatial layer, so as to perform superposition transmission for the near UE and the far UE on the first transmission spatial layer.

[0082] Similarly, for the far UE2 (third UE), in block 341 a source data stream for the far UE2 is subject to channel-coding, thereby generating a codeword CWl for the far UE2. Subsequently in block 342, the codeword CWl for the far UE2 is modulated to generate one modulated codeword for the far UE2. In block 343, the modulated codeword for the far UE2 is mapped to the second transmission spatial layer.

[0083] In block 334, the one modulated codeword for the near UE and the one modulated codeword for the far UE2 are superposed on the second transmission spatial layer, so as to perform superposition transmission for the near UE and the far UE2 on the second transmission spatial layer.

[0084] In block 315, data streams superposed on the first transmission spatial layer and data streams superposed on the second transmission spatial layer are subject to codebook-based closed-loop precoding. Next in block 316, precoded data streams are mapped to RE.

[0085] Further, Fig. 3 also shows a case where only one UE, i.e. the far UEl is paired with the near UE but RI fed back by the far UEl equals 2. In this case, in block 341 another source data stream for the far UE1 is subject to channel-coding, thereby generating a codeword CW2 for the far UE1. In block 342, the codeword CW2 for the far UE1 is modulated to generate another modulated codeword for the far UE1. In block 343, the other modulated codeword for the far UE1 is mapped to the second transmission spatial layer. In block 334 the one modulated codeword for the near UE and the other modulated codeword for the far UE1 are superposed on the second transmission spatial layer, so as to perform superposition transmission for the near UE and the far UE1 on the second transmission spatial layer.

[0086] Fig. 4 shows a procedure of superposition transmission with two transmission spatial layer according to a second embodiment of the present disclosure. In the second embodiment, PMI fed back by the first UE and PMI fed back by the second UE are the same, but first RI fed back by the first UE and second RI fed back by the second UE are different. Specifically, the first RI equals 2, the second RI equals 1, and the second UE's precoder vector is the same as one column of the first UE's precoder matrix. At this point, only one UE can be paired with the first UE.

[0087] As seen from the comparison of Fig. 4 with Fig. 3, the second embodiment differs from the first embodiment in that superposition transmission for the near UE and the far UE is performed on only one of the first transmission spatial layer and the second transmission spatial layer, while single-user transmission for the near UE is performed on the other transmission spatial layer.

[0088] Specifically, as shown in Fig. 4, in blocks 411 and 421, a first source data stream and a second source data stream for the near UE (first UE) are subject to channel-coding respectively, thereby generating codewords CWl and CW2 for the near UE respectively. In blocks 412 and 422, the codewords CWl and CW2 for the near UE are modulated respectively to generate two modulated codewords for the near UE. In block 413, the two modulated codewords for the near UE are mapped to the first transmission spatial layer and the second transmission spatial layer respectively.

[0089] For the far UE (second UE), in block 431 a source data stream for the far UE is subject to channel-coding, thereby forming a codeword XW1 for the far UE. In block 432, the codeword CWl for the far UE is modulated to generate one modulated codeword for the far UE. In block 433, the modulated codeword for the far UE is mapped to the second transmission spatial layer. [0090] In block 434, the one modulated codeword for the near UE and the one modulated codeword for the far UE are superposed so as to perform superposition transmission for the near UE and the far UE on the second transmission spatial layer. In addition, single-user transmission for the near UE is performed on the first transmission spatial layer. In block 415, the single-user data stream on the first transmission spatial layer and data streams superposed on the second transmission spatial layer are subject to codebook-based closed-loop precoding. In block 416, precoded data streams are mapped to RE.

[0091] Fig. 5 shows a procedure of superposition transmission with three transmission spatial layers according to a third embodiment of the present disclosure. In the third embodiment, PMI fed back by the first UE and PMI fed back by paired UE are the same, but RIs being fed back might be the same or different. Specifically, if RI fed back by the first UE equals 2, and RI fed back by the paired UE equals 1, then at this point at most two different UEs (second UE and third UE) may be paired with the first UE. However, if RI fed back by the first UE equals 2, and RI fed back by the paired UE also equals 2, then at this point only one UE (second UE) may be paired with the first UE.

[0092] Where two different UEs (second UE and third UE) are paired with the first UE and RIs fed back by the second UE and the third UE equal 1, two codewords for the first UE are generated based on the first RI, one codeword of the two codewords, after being modulated, is mapped to the first transmission spatial layer, and the other codeword of the two codewords, after being modulated, is mapped to the second transmission spatial layer and the third transmission spatial layer respectively.

[0093] Additionally, in this case, one codeword for the second UE is generated based on the second RI, and the one codeword for the second UE, after being modulated, is mapped to the first transmission spatial layer. In addition, one codeword for the third UE is generated based on a third RI, and the one codeword for the third UE, after being modulated, is mapped to one transmission spatial layer of the second transmission spatial layer and the third transmission spatial layer. Further, superposition transmission for the first UE and the second UE is performed on the first transmission spatial layer, superposition transmission for the first UE and the third UE is performed on the one transmission spatial layer of the second transmission spatial layer and the third transmission spatial layer, and single-user transmission for the first UE is performed on the other transmission spatial layer of the second transmission spatial layer and the third transmission spatial layer.

[0094] Specifically, as shown in Fig. 5, in blocks 521 and 531 a first source data stream and a second source data stream for the near UE (first UE) are subject to channel-coding respectively, thereby generating codewords CWl and CW2 for the near UE.

[0095] In blocks 522 and 532, the codewords CWl and CW2 for the near UE are modulated to generate two modulated codewords for the near UE. It should be understood that in blocks 522 and 532, any appropriate modulation modes may be used to modulate the codewords CWl and CW2. For example, the modulation modes include but not limited to: QPSK, 16QAM, 64QAM.

[0096] In block 523 the modulated codeword for the near UE (from the codeword CWl) is mapped to the first transmission spatial layer. In block 533, the modulated codeword for the near UE (from the codeword CW2) is mapped to the second transmission spatial layer and the third transmission spatial layer.

[0097] For the far UEl (second UE), in block 511, a source data stream for the far UEl is subject to channel-coding, thereby generating a codeword CWl for the far UEl. In block 512, the codeword for the far UEl is modulated to generate one modulated codeword for the far UEl. In block 513, the modulated codeword for the far UEl is mapped to the first transmission spatial layer.

[0098] In block 524, the one modulated codeword for the near UE and the one modulated codeword for the far UEl are superposed on the first transmission spatial layer, so as to perform superposition transmission for the near UE and the far UEl on the first transmission spatial layer.

[0099] Similarly, for the far UE2 (third UE), in block 541 a source data stream for the far UE2 is subject to channel-coding, thereby generating a codeword CWl for the far UE2. In block 542, the codeword CWl for the far UE2 is modulated to generate one modulated codeword for the far UE2. In block 543 the modulated codeword for the far UE2 is mapped to the third transmission spatial layer.

[00100] In block 544, the one modulated codeword for the near UE and the one modulated codeword for the far UE2 are superposed on the third transmission spatial layer, so as to perform superposition transmission for the near UE and the far UE2 on the third transmission spatial layer. In addition, single-user transmission for the first UE is performed on the second transmission spatial layer.

[00101] In block 515 data streams superposed on the first transmission spatial layer, the single-user data stream on the second transmission spatial layer and data streams superposed on the third transmission spatial layer are subject to codebook-based closed-loop precoding. Then in block 516, precoded data streams are mapped to RE.

[00102] In the superposition transmission procedure shown in Fig. 5, the codeword CW2 for the near UE is mapped to the second and third transmission spatial layers after being modulated; however, superposition transmission is performed on the third transmission spatial layer only, and single-user transmission is performed on the second transmission spatial layer. On the third transmission spatial layer, the near UE may suffer from the residual interference due to superposition transmission, and only partial information bits carried in this spatial layer belongs to the near UE. Therefore, if the same modulation scheme is used for the codeword CW2, then different modulation results may be produced on the third transmission spatial layer and the second transmission spatial layer.

[00103] For example, if in blocks 532 and 542, QPSK modulation is used for both the codeword CW2 for the near UE and the codeword CWl for the far UE2, after modulation in block 544 a 16QAM-modulated signal will be generated on the third transmission spatial layer. However, since single-user transmission is performed on the second transmission spatial layer, a QPSK-modulated signal remains on the second transmission spatial layer. After receiving signals from the second and third transmission spatial layers, the near UE needs to recover the codeword CW2 from signals on the two transmission spatial layers. However, as modulation schemes on the second and third transmission spatial layers differ from the perspective of the near UE, different demodulation schemes have to be used for demodulation. Since 16QAM modulation imposes a higher requirement on the channel quality than QPSK modulation, if the channel quality on the third transmission spatial layer does not meet the requirement of 16QAM modulation, then demodulation and decoding failure at the near UE might be caused. To solve this problem, an embodiment of the present disclosure proposes two solutions as below. [00104] In a first solution, with respect to a codeword of the near UE to be mapped to the second and third transmission spatial layers, for example, the codeword CW2 for the near UE in Fig. 5, only one modulation scheme is used to generate a modulated codeword. In addition, before mapping a codeword of the far UE2 to one of the second and third transmission spatial layers, the channel quality of the second transmission spatial layer is compared with that of the third transmission spatial layer, and in response to the channel quality of one of the second and third transmission spatial layers being superior to that of the other transmission spatial layer, the codeword for the far UE2 is mapped to the one transmission spatial layer after being modulated.

[00105] In this manner, since superposition transmission is performed on a spatial layer with better channel quality, the risk of demodulation and decoding failure at the near UE is reduced.

[00106] In a second solution, with respect to a codeword of the near UE to be mapped to the second and third transmission spatial layers, for example, the codeword CW2 for the near UE in Fig. 5, a first modulation scheme and a second modulation scheme are used respectively to generate a first sub-modulated signal stream and a second sub-modulated signal stream, wherein modulation order of the first modulation scheme is higher than the second modulation scheme. For example, with respect to the codeword CW2 for the near UE in Fig. 5, 16QAM modulation and QPSK modulation are used respectively to generate the first sub-modulated signal stream and the second sub-modulated signal stream. It may be understood that modulation order of 16QAM modulation is higher than QPSK modulation. Then, the first sub-modulated signal stream and the second sub-modulated signal stream are mapped to the second transmission spatial layer and the third transmission spatial layer respectively. Further, superposition transmission for the near UE and the far UE2 is performed on the third transmission spatial layer.

[00107] In this manner, since a modulation scheme with lower modulation order (accordingly, a lower requirement on channel quality) is used on the spatial layer where superposition transmission is performed, the risk of demodulation and decoding failure at the near UE is also reduced.

[00108] In addition, in the second solution, after superposition of signals for the near UE and the far UE2 on the third transmission spatial layer, the same modulation result is produced on the second transmission spatial layer and the third transmission spatial layer. After the near UE receives signals, if the same demodulation scheme is used for the second transmission spatial layer and the third transmission spatial layer, then a wrong demodulation result might be caused. To solve this problem, the base station may send high-layer signaling to the near UE to indicate superposition transmission for the near UE and the far UE2 on the third transmission spatial layer. Accordingly, with respect to the third transmission spatial layer, the near UE may decode signals of the far UE2 from signals received from the third transmission spatial layer by using a MUST receiver and based on the high-layer signaling and power allocation information on the near UE and the far UE2, so that signals of the near UE itself are obtained based on the decoded signal of the far UE2.

[00109] In addition, as described above, if RI fed back by the first UE equals 2 and RI of UE to be paired with the first UE equals 1, then at this point there may be at most two different UEs (second UE and third UE) to be paired with the first UE. Although the embodiment wherein the far UEl and the far UE2 are paired with the near UE has been described with reference to Fig. 5, only one far UE whose RI equals 1 may also be paired with the near UE. In this case, it is preferable that superposition transmission for the far UE and the near UE is performed on the first transmission spatial layer shown in Fig. 5. Since the codeword CW1 is only mapped to the first transmission spatial layer, the base station does not need to send high-layer signaling to the near UE to indicate superposition transmission for the near UE and the far UE2 on this transmission spatial layer.

[00110] Furthermore, where RI fed back by the first UE equals 2 and RI fed back by UE to be paired with the first UE also equals 2, there may be only one far UE (e.g. second UE) to be paired with the first UE for superposition transmission. In this case, the far UE performs superposition transmission with the near UE (first UE) on the second and third transmission spatial layers, whose procedure is similar to that described with reference to Fig. 3 and is omitted thereby.

[00111] Fig. 6 shows a procedure of superposition transmission with four transmission spatial layers according to a fourth embodiment of the present disclosure. In the case of four transmission spatial layers, PMI fed back by the first UE and PMI fed back by the paired UE are the same, but RIs being fed back might be the same or different. Specifically, if RI fed back by the first UE equals 2 and RI of UE to be paired with the first UE equals 1, then at this point there may be at most four different UEs (second UE, third UE, fourth UE and fifth UE) to be paired with the first UE. However, if RI fed back by the first UE equals 2 and RI fed back by the paired UE also equals 2, then at this point there may be at most two UEs to be paired with the first UE.

[00112] Where two different UEs (second UE and third UE) are paired with the first UE and RIs fed back by the second UE and the third UE equal 1, two codewords for the first UE are generated based on the first RI, one codeword of the two codewords, after being modulated, is mapped to the first transmission spatial layer and the second transmission spatial layer, and the other codeword of the two codewords, after being modulated, is mapped to the third transmission spatial layer and the fourth transmission spatial layer respectively.

[00113] Additionally, in this case, one codeword for the second UE is generated based on the second RI, and the one codeword for the second UE, after being modulated, is mapped to one of the first and second transmission spatial layers. In addition, one codeword for the third UE is generated based on third RI, and the one codeword for the third UE, after being modulated, is mapped to one of the third and fourth transmission spatial layers. Further, superposition transmission for the first UE and the second UE is performed on the one of the first and second transmission spatial layers, and single-user transmission for the first UE is performed on the other of the first and second transmission spatial layers; superposition transmission for the first UE and the third UE is performed on the one of the third and fourth transmission spatial layers, and single-user transmission for the first UE is performed on the other of the third and fourth transmission spatial layers.

[00114] Specifically, as shown in Fig. 6, in blocks 611 and 631 a first source data stream and a second source data stream for the near UE (first UE) are subject to channel-coding respectively, thereby generating codewords CWl and CW2 for the near UE. In blocks 612 and 632, the codewords CWl and CW2 for the near UE are modulated to generate two modulated codewords for the near UE. In block 613 one of the modulated codewords for the near UE is mapped to the first transmission spatial layer and the second transmission spatial layer. In block 633, the other of the modulated codewords for the near UE is mapped to the third transmission spatial layer and the fourth transmission spatial layer.

[00115] For the far UEl (second UE), in block 621, a source data stream for the far UEl is subject to channel-coding, thereby generating a codeword CWl for the far UEl. In block 622, the codeword CWl for the far UEl is modulated to generate one modulated codeword for the far UEl. In block 623, the modulated codeword for the far UEl is mapped to the second transmission spatial layer.

[00116] In block 614, the one modulated codeword for the near UE and the one modulated codeword for the far UEl are superposed, so as to perform superposition transmission for the near UE and the far UEl on the second transmission spatial layer. In addition, single-user transmission for the near UE is performed on the first transmission spatial layer. In block 615, a single-user data stream on the first transmission spatial layer and data streams superposed on the second transmission spatial layer are subject to codebook-based closed-loop precoding. In block 616, precoded data streams are mapped to RE.

[00117] For the far UE2 (third UE), in block 641 a source data stream for the far

UE2 is subject to channel-coding, thereby generating a codeword CWl for the far UE2. In block 642, the codeword CWl for the far UE2 is modulated to generate one modulated codeword for the far UE2. In block 643, the modulated codeword for the far UE2 is mapped to the fourth transmission spatial layer.

[00118] In block 634, the one modulated codeword for the near UE and the one modulated codeword for the far UE2 are superposed, so as to perform superposition transmission for the near UE and the far UE2 on the fourth transmission spatial layer. In addition, single-user transmission for the first UE is performed on the third transmission spatial layer. In block 635 a single-user data stream on the third transmission spatial layer and data streams superposed on the fourth transmission spatial layer are subject to codebook-based closed-loop precoding. In block 636, precoded data streams are mapped to RE.

[00119] As seen from the comparison of Fig. 6 with Fig. 5, a similarity lies in that one codeword for the near UE is mapped to two transmission spatial layers. That is, in Fig. 6, the codewords CWl and CW2 for the near UE are both mapped to two transmission spatial layers. Thereby, the modulation schemes described with reference to Fig. 5 above may be used for both CWl and CW2 for the near UE. In other words, each of CWl and CW2 for the near UE may either use the same modulation scheme described with reference to Fig. 5 or use different modulation schemes. In addition, where different modulation schemes are used, the base station also needs to send high-layer signaling to the near UE to indicate superposition transmission for the near UE and the far UE on a specific transmission spatial layer (second or fourth transmission spatial layer).

[00120] In addition, where RI fed back by the first UE equals 2 and RI fed back by the UE to be paired with the first UE also equals 2, there may be at most two far UEs

(e.g. second UE and third UE) to be paired with the first UE for superposition transmission. In this case, the far UE performs superposition transmission with the near UE (first UE) on four transmission spatial layers, whose procedure is similar to that described with reference to Fig. 3 and is omitted thereby.

[00121] As described above, in the case of fourth transmission spatial layers, if

RI fed back by the first UE equals 2 and RI fed back by the paired UE equals 1, then at this point there may be at most four different UEs (second UE, third UE, fourth UE and fifth UE) to be paired with the first UE. Fig. 7 shows a procedure of superposition transmission with fourth transmission spatial layers according to a fifth embodiment of the present disclosure.

[00122] As shown in Fig. 7, in blocks 721 and 751 a first source data stream and a second source data stream for the near UE (first UE) are subject to channel-coding respectively, thereby generating codewords CWl and CW2 for the near UE.

Subsequently in blocks 722 and 752, the codewords CWl and CW2 for the near UE are modulated to generate two modulated codewords for the near UE. Next in block 723 one of the modulated codewords for the near UE is mapped to the first transmission spatial layer and the second transmission spatial layer. In block 753, the other of the modulated codewords for the near UE is mapped to the third transmission spatial layer and the fourth transmission spatial layer.

[00123] For the far UEl (second UE), in block 711, a source data stream for the far UEl is subject to channel-coding, thereby generating a codeword CWl for the far UEl. In block 712, the codeword CWl for the far UEl is modulated to generate one modulated codeword for the far UEl. In block 713, the modulated codeword for the far UEl is mapped to the first transmission spatial layer. [00124] In block 714, the one modulated codeword for the near UE and the one modulated codeword for the far UE1 are superposed, so as to perform superposition transmission for the near UE and the far UE1 on the first transmission spatial layer.

[00125] For the far UE2 (third UE), in block 731 a source data stream for the far UE2 is subject to channel-coding, thereby generating a codeword CW1 for the far UE2. In block 732, the codeword CW1 for the far UE2 is modulated to generate one modulated codeword for the far UE2. In block 733, the modulated codeword for the far UE2 is mapped to the second transmission spatial layer.

[00126] In block 734, the one modulated codeword for the near UE and the one modulated codeword for the far UE2 are superposed, so as to perform superposition transmission for the near UE and the far UE2 on the second transmission spatial layer.

[00127] In block 715 data streams superposed on the first and second transmission spatial layers are subject to codebook-based closed-loop precoding. Then in block 735, data streams superposed on the third and fourth transmission spatial layers are subject to codebook-based closed-loop precoding

[00128] In blocks 716 and 746, precoded data streams are mapped to RE respectively.

[00129] In a second aspect of the embodiments of the present disclosure, there is provided a method of decoding signals for superposition transmission with codebook-based closed-loop precoding. Fig. 8 shows a flowchart of a method 800 of decoding signals for superposition transmission with codebook-based closed-loop precoding according to a second aspect of the embodiments of the present disclosure. Method 800 may be executed at user equipment, for example UE 110 in Fig. 1.

[00130] Method 800 starts in step S810, in which signals transmitted on a plurality of transmission spatial layers and power allocation information are received from a base station. Received signals at least comprise signals of first user equipment and signals of second user equipment in superposition transmission on at least one transmission spatial layer of the plurality of transmission spatial layers.

[00131] In step S820, in response to detecting interference caused by the signals of the second UE on the at least one transmission spatial layer of the plurality of transmission spatial layers exceeding a predetermined threshold, decoding the signals of the second UE from received signals based on the power allocation information. The power allocation information at least indicates a power allocation ratio the first UE and the second UE, for example, 10% and 90%, 20% and 80%, or 30% and 70%, etc.

[00132] In step S830, the signals of the first UE is obtained based on the decoded signals of the second UE.

[00133] In one embodiment, in the case of two transmission spatial layers, received signals comprise signals of the first UE and signals of the second UE in superposition transmission on one transmission spatial layer of two transmission spatial layers, just as described with reference to Figs. 3 and 4 above.

[00134] In this embodiment, after receiving signals from the base station, the first UE executes interference detection with respect to two transmission spatial layers. In response to detecting that interference caused by the signals of the second UE on one transmission spatial layer exceeds a predetermined threshold, it is determined that superposition transmission for signals of the first UE and the second UE is performed on this transmission spatial layer. Any appropriate value may be selected as the predetermined threshold. For example, one fold of the first UE's power may be used as the predetermined threshold.

[00135] Next, the first UE decodes the signals of the second UE from signals received from the transmission spatial layer based on the power allocation information. For example, with a MUST receiver, the first UE may blindly detect the signals of the second UE from signals received from the transmission spatial layer based on the power allocation information, so as to decode the signals of the second UE. Where blindly detecting the signals of the second UE, the base station does not need to notify the first UE of modulation and coding schemes for the second UE, so downlink overheads can be saved.

[00136] Subsequently, the first UE removes the decoded signals of the second

UE from signals received from the transmission spatial layer, and then decodes received signals from which the signals of the second UE has been removed, so as to obtain the signals of the first UE itself.

[00137] In another embodiment, in the case of two transmission spatial layers, received signals comprise signals of the first UE and signals of the second UE in superposition transmission on the two transmission spatial layers, as well as signals of the first UE and signals of the third UE, just as described with reference to Fig. 3 above. [00138] In this embodiment, after receiving signals from the base station, the first UE executes interference detection with respect to the two transmission spatial layers. In response to detecting that interference caused by signals of the second and third UEs on the two transmission spatial layers exceeds a predetermined threshold, it is determined that superposition transmission is performed on both of the two transmission spatial layers. Next, for example, with a MUST receiver, the first UE may blindly detect signals of the second and third UEs from signals received from the two transmission spatial layers based on the power allocation information, so as to decode the signals of the second and third UEs. Afterwards, the signal of the first UE is obtained based on the decoded signals of the second and third UEs.

[00139] In a further embodiment, in the case of three transmission spatial layers, received signals comprise signals of the first and second UEs as well as signals of the first and third UEs in superposition transmission on two transmission spatial layers respectively. For example, as described with reference to Fig. 5 above, received signals comprise signals of the first and second UEs in superposition transmission on a first transmission spatial layer as well as signals of the first and third UEs in superposition transmission on a third transmission spatial layer.

[00140] In this embodiment, after receiving signals from the base station, the first UE executes interference detection with respect to the three transmission spatial layers. In response to detecting that interference caused by signals of the second and third UEs on two transmission spatial layers (e.g. first and third transmission spatial layers) exceeds a predetermined threshold, it is determined that superposition transmission is performed on the two transmission spatial layers. Next, for example, with a MUST receiver, the first UE may blindly detect signals of the second and third UEs from signals received from the two transmission spatial layers based on the power allocation information, so as to decode the signals of the second and third UEs. Afterwards, the signal of the first UE is obtained based on the decoded signals of the second and third UEs.

[00141] In addition, as described with reference to Fig. 5 above, in the case of three transmission spatial layers, the codeword CW2 for the first UE (near UE in Fig. 5) is mapped to two transmission spatial layers, i.e. the second and third transmission spatial layers. Thereby, with respect to the codeword CW2 for the first UE, either the same modulation scheme described with reference to Fig. 5 or different modulation schemes may be used. Where different modulation schemes are used, the first UE receives high-layer signaling from the base station, the high-layer signaling indicating superposition transmission for the first and third UEs on the third transmission spatial layer. In consequence, with respect to the third transmission spatial layer, the first UE will decode the signals of the third UE from signals received from the third transmission spatial layers, by means of a MUST receiver and based on the high-layer signaling and power allocation information on the first UE and the third UE.

[00142] In a still further embodiment, in the case of four transmission spatial layers, received signals comprise signals of the first and second UEs as well as signals of the first and third UEs in superposition transmission on two transmission spatial layers respectively. For example, as described with reference to Fig. 6 above, received signals comprise signals of the first and second UEs in superposition transmission on a first transmission spatial layer as well as signals of the first and third UEs in superposition transmission on a third transmission spatial layer.

[00143] In this embodiment, after receiving signals from the base station, the first UE executes interference detection with respect to three transmission spatial layers. In response to detecting that interference caused by signals of the second and third UEs on two transmission spatial layers (e.g. first and third transmission spatial layers) exceeds a predetermined threshold, it is determined that superposition transmission is performed on the two transmission spatial layers. Next, for example, with a MUST receiver, the first UE may blindly detect signals of the second and third UEs from signals received from the two transmission spatial layers based on the power allocation information, so as to decode the signals of the second and third UEs. Afterwards, the signal of the first UE is obtained based on the decoded signals of the second and third UEs.

[00144] Similarly, in this embodiment, if different modulation schemes are used for at least one codeword of two codewords for the first UE, then the first UE receives high-layer signaling from the base station, the high-layer signaling indicating superposition transmission between the first UE and the second UE, the third UE on the first and the third transmission spatial layer respectively. In consequence, with respect to the first and the third transmission spatial layer respectively, the first UE will decode the signal of the second and the third UE from signals received from the first and the third transmission spatial layer, by means of a MUST receiver and based on the high-layer signaling, power allocation information on the first UE and the second UE as well as power allocation information on the first UE and the third UE.

[00145] In a third aspect of the embodiments of the present disclosure, there is provided a superposition transmission device with codebook-based closed-loop precoding. Fig. 9 shows a block diagram of a superposition transmission device 900 with codebook-based closed-loop precoding according to a third aspect of the embodiments of the present disclosure. Device 900 may be implemented in a base station, for example.

[00146] As shown in Fig. 9, device 900 comprises: a first generating unit 910 configured to generate a plurality of codewords for a first user equipment; a second generating unit 920 configured to generate at least one codeword for second user equipment which is to be paired with the first user equipment; a first mapping unit 930 configured to map the plurality of codewords for the first user equipment to a plurality of transmission spatial layers having the same number as a plurality of transmit antennas; a second mapping unit 940 configured to map the at least one codeword for the second user equipment to at least one transmission spatial layer of the plurality of transmission spatial layers; and a first superposition transmission unit 950 configured to perform, on the at least one transmission spatial layer, superposition transmission for the first user equipment and the second user equipment.

[00147] In some embodiments, a first rank indication for the first user equipment is larger than or equal to a second rank indication for the second user equipment.

[00148] In some embodiments, the first generating unit 910 is further configured to generate two codewords for the first user equipment based on the first rank indication; and the first mapping unit 930 is further configured to modulate the two codewords for the first user equipment; and to map each of the two modulated codewords for the first user equipment at least to one of the plurality of transmission spatial layers.

[00149] In some embodiments, the first mapping unit 930 is further configured to map the two modulated codewords for the first user equipment at least to a first transmission spatial layer and a second transmission spatial layer of the plurality of transmission spatial layers respectively

[00150] In some embodiments, the first mapping unit 930 is further configured to map one of the two modulated codewords to a first transmission spatial layer and a second transmission spatial layer of the plurality of transmission spatial layers respectively, and map the other of the two modulated codewords to a third transmission spatial layer and a fourth transmission spatial layer of the plurality of transmission spatial layers respectively

[00151] In some embodiments, the first mapping unit 930 is further configured to map one of the two modulated codewords to the first transmission spatial layer, and map the other of the two modulated codewords to the second transmission spatial layer and a third transmission spatial layer respectively.

[00152] In some embodiments, the second generating unit 920 is further configured to generate one codeword for the second user equipment based on the second rank indication, and the second mapping unit is further configured to modulate the one codeword for the second user equipment; and map the one modulated codeword for the second user equipment to the first transmission spatial layer.

[00153] In some embodiments, the first superposition transmission unit 950 is further configured to perform, on the first transmission spatial layer, superposition transmission for the first user equipment and the second user equipment.

[00154] In some embodiments, the device 900 further comprises: a third generating unit configured to generate one codeword for third user equipment which is to be paired with the first user equipment; a third mapping unit configured to modulate the one codeword for the third user equipment and map the one modulated codeword for the third user equipment to one of the second transmission spatial layer and the third transmission spatial layer; a second superposition transmission unit configured to perform, on the one transmission spatial layer of the second transmission spatial layer and the third transmission spatial layer, superposition transmission for the first user equipment and the third user equipment; and a first single-user transmission unit configured to perform, on the other transmission spatial layer of the second transmission spatial layer and the third transmission spatial layer, single-user transmission for the first user equipment. [00155] In some embodiments, the device 900 further comprises: a fourth generating unit configured to generate one codeword for fourth user equipment which is to be paired with the first user equipment; a fourth mapping unit configured to modulate the one codeword for the fourth user equipment and mapp the one modulated codeword for the fourth user equipment to a fourth transmission spatial layer of the plurality of transmission spatial layers; and a third superposition transmission unit configured to perform, on the fourth transmission spatial layer, superposition transmission for the first user equipment and the fourth user equipment.

[00156] In some embodiments, the first generating unit 910 is further configured to use only one modulation scheme to modulate a codeword of the plurality of codewords which is to be mapped to both of the second transmission spatial layer and the third transmission spatial layer.

[00157] In some embodiments, the third mapping unit is further configured to: compare channel quality of the second transmission spatial layer with that of the third transmission spatial layer; and in response to the channel quality of one of the second transmission spatial layer and the third transmission spatial layer being better than the channel quality of the other transmission spatial layer, map the one modulated codeword for the third user equipment to the other transmission spatial layer.

[00158] In some embodiments, the first generating unit 910 is further configured to use a first modulation scheme and a second modulation scheme to modulate the other codeword of the two codewords so as to generate a first sub-modulated signal stream and a second sub-modulated signal stream respectively; the first generating unit 910 is further configured to map the first sub-modulated signal stream and the second sub-modulated signal stream to the second transmission spatial layer and the third transmission spatial layer respectively; wherein modulation order of the first modulation scheme is higher than modulation order of the second modulation scheme.

[00159] In some embodiments, the third mapping unit is further configured to map the one modulated codeword for the third user equipment to the third transmission spatial layer.

[00160] In some embodiments, the device 900 further comprises: a notifying unit configured to send a high-layer signaling to the first user equipment, the high-layer signaling indicating superposition transmission for the first user equipment and the third user equipment on the third transmission spatial layer.

[00161] In a fourth aspect of the embodiments of the present disclosure, there is provided a device of decoding signals for superposition transmission with codebook-based closed-loop precoding. Fig. 10 shows a block diagram of a device 1000 of decoding signals in superposition transmission with codebook-based closed-loop precoding according to a fourth aspect of the embodiments of the present disclosure. Device 1000 may be implemented in user equipment, for example, user equipment 110 in Fig. 1.

[00162] As shown in Fig. 10, the device 1000 comprises: a receiving unit 1010 configured to receive from a base station signals transmitted on a plurality of transmission spatial layers and power allocation information, the received signals at least including signals of first user equipment and signals of second user equipment in superposition transmission on at least one transmission spatial layer of the plurality of transmission spatial layers; and a decoding unit 1020 configured to: in response to detecting interference caused by the signals of the second user equipment on the at least one transmission spatial layer of the plurality of transmission spatial layers exceeding a predetermined threshold, decode the signals of the second user from the received signals based on the power allocation information; and obtain signals of the first user equipment based on the decoded signals of the second user equipment.

[00163] In some embodiments, the decoding unit 1020 is further configured to blindly detect signals of the second user equipment from the received signals.

[00164] In some embodiments, the received signals at least include: signals of the first user equipment and the second user equipment in superposition transmission on a first transmission spatial layer of the plurality of transmission spatial layers, signals of the first user equipment and third user equipment in superposition transmission on a second transmission spatial layer of the plurality of transmission spatial layers, and signals of the first user equipment in single-user transmission on a third transmission spatial layer of the plurality of transmission spatial layers.

[00165] In some embodiments, the receiving unit 1010 is further configured to receive a high-layer signaling from the base station, the high-layer signaling indicating superposition transmission for the first user equipment and the third user equipment on the second transmission spatial layer.

[00166] In some embodiments, the decoding unit 1020 is further configured to: decode signals of the third user equipment from the received signals based on the power allocation information and the high-layer signaling; decode signals of the second user equipment based on the high-layer signaling; and obtain signals of the first user equipment based on the decoded signal of the third user equipment.

[00167] Generally, various example embodiments of the present 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 example embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[00168] Additionally, various blocks shown in the flowcharts may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). For example, embodiments of the present disclosure include a computer program product comprising a computer program tangibly embodied on a machine readable medium, the computer program containing program codes configured to carry out the methods as described above.

[00169] In the context of the disclosure, a machine readable medium may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[00170] Computer program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These computer program codes may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor of the computer or other programmable data processing apparatus, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a computer, partly on the computer, as a stand-alone software package, partly on the computer and partly on a remote computer or entirely on the remote computer or server.

[00171] Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of any disclosure or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular disclosures. Certain features that are described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

[00172] Various modifications, adaptations to the foregoing example embodiments of this disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and example embodiments of this disclosure. Furthermore, other embodiments of the disclosures set forth herein will come to mind to one skilled in the art to which these embodiments of the disclosure pertain having the benefit of the teachings presented in the foregoing descriptions and the drawings.

[00173] It will be appreciated that the embodiments of the present disclosure are not to be limited to the specific embodiments as discussed above and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein, they are used in a generic and descriptive sense only and not for purposes of limitation.