Field of the invention

The invention generally relates to the field of wireless communications, and more particularly to a method, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, a method, in a first user equipment (UE) of a Multiuser Superposition Transmission (MUST) system, for obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, an apparatus, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, and an apparatus, in a first user equipment (UE) of a Multiuser Superposition Transmission (MUST) system, for obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode.

Background of the invention

In the study item of downlink MUST (see 3GPP RP- 150496, "Study on Downlink Multiuser Superposition Transmission for LTE", MediaTek Inc.), the study objective is to pair multiple UEs to enable them to transmit data of multiple layers 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 (REs)).

However serious interference may occur between the paired UE. Fig. l illustrates a schematic diagram of a condition of mutual interference between User Equipments (UEs) paired in an MUST system 100. As illustrated in Fig. l, the MUST system 100 includes a base station (eNB), a User Equipment UE1 , and a User Equipment UE2, and the eNB pairs the UE 1 and the UE 2 for MUST transmission. Since the UE 2 is located at the edge of a cell, the eNB allocates high transmit power for the UE 2, and allocates low transmit power for the UE 1 located at the center of the cell. Upon reception of downlink MUST transmission from the eNB, the UE 1 with an advanced receiver firstly decodes a received signal to obtain a signal component directed to the UE 2 with the help of some assistance information provided to the UE 1, then removes the signal component of the UE 2 from the received signals, and lastly decodes the remaining signal to obtain Physical Shared Channel (PDSCH) data directed thereto, i.e., the UE 1. Therefore, whether the interference signal caused by the UE 2 could be cancelled and how much interference could be cancelled by the UE 1 will be critical for the UE 1 to decode its own data.

In order to decode the signal component of the UE 2 at the UE 1 , the information about the allocated transmit power between the paired two UEs is crucial to the receiver of the UE1. Without the power allocation information, it will be quite difficult to correctly decode the interference signal at the near UE, i.e., the UE 1, and also will impact the correctness of decoding the PDSCH data of the near UE, i.e., the UE 1, after removing the interference with the help of the decoded signal component of the far UE, i.e., the UE 2. However, how to indicate the power allocation from the eNB to the UEs in the MUST system has not been specified by any standards.

Therefore, how the near UE, i.e., the UE 1, is aware of the allocated transmit power for the UE 1 and its paired interfering UE, i.e., the far UE 2, through the indication of the eNB is worth investigating.

There are currently ten different Transmission Modes (TMs) defined for the LTE system. These ten transmission mode differ in terms of their specific structures of antenna mapping and also in terms of what reference signals are assumed to be used for demodulation (cell-specific reference signals or Demodulation Reference Signals (DM-RS's) respectively) and how Channel State Information (CSI) is acquired by a terminal and fed back to the network side. The DM-RS, sometimes also referred to as UE- specific reference signals, are intended to be used by the terminals for channel estimation for subsequent coherent demodulation of a Physical Downlink Shared Channel (PDSCH) in case of the TMs 7 to 10, which are also referred to DM-RS based TMs.

The DM-RS based TMs have been described in 3GPP 36.213, "3rd generation partnership project; technical specification group radio access network; evolved universal terrestrial radio access (e-utra); physical layer procedures". If UE-specific RSs are present in the PRBs upon which the corresponding PDSCH is mapped, then the UE may assume the ratio of the EPRE (Energy Per Resource Element) of the PDSCH to the EPRE of the UE-specific RS is 0 dB for the number of transmission layers less than or equal to two, and is -3 dB otherwise (in the TMs 9 and 10). Therefore, in most cases (except when the number of transmission layers is larger than two in the TMs 9 and 10), the power of the DM-RS, i.e. the UE-specific RSs, of the UE equals to its PDSCH power. Hence, the UE obtains the knowledge about its DM-RS sequence with the indication from the eNB, and then can get to know the power of its PDSCH channel.

However, in multiuser superposition transmission, the paired UEs will use the same spatial precoding vector or the same transmit diversity over the same REs. The paired UEs could use the same DM-RS sequence or different DM-RS sequences over the same REs at the allocated transmit power. How to obtain the power allocation information of both the near/victim UE and the far/interfering UE(s) at the near UE, through the indication from the eNB and the decoding of the corresponding DM-RS sequences, has not been specified by the current 3GPP standards, which may make it difficult to firstly decode and then cancel the signal component of the interfering UE, and then decode its own data at the near/victim UE.

Summary of the invention

In order to overcome the technical solutions identified in the Background of the Invention section, i.e., the drawbacks in the prior art, the inventors of the invention propose methods of indicating power allocation information from a base station to a near UE in a DM-RS based transmission mode.

In view of the consideration above, the invention proposes a method, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, a method, in a first user equipment of a Multiuser Superposition Transmission (MUST) system, for obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, an apparatus, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, and an apparatus, in a first user equipment of a Multiuser Superposition Transmission (MUST) system, for obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode.

A first aspect of the invention proposes a method, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, wherein the MUST system includes the base station, a first user equipment (UE), and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission; the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the method includes at the base station:

- obtaining a first DM-RS sequence used by the first UE, and a second DM-RS sequence used by the second UE;

- determining whether the first DM-RS sequence is consistent with the second DM-RS sequence; and

- sending a power allocation indication associated with obtaining power allocation information to the first UE based upon a result of the determination.

In an embodiment of the invention, if the result of the determination is that the first DM-RS sequence is consistent with the second DM-RS sequence, then the power allocation indication includes a power difference between transmit power of the first UE and transmit power of the second UE.

In an embodiment of the invention, the power allocation indication further includes a cell identifier.

In an embodiment of the invention, if the result of the determination is that the first DM-RS sequence is not consistent with the second DM-RS sequence, then the power allocation indication includes a first identifier of the first DM-RS sequence used by the first UE, and a second identifier of the second DM-RS sequence used by the second DM-RS sequence to distinguish the different DM-RS sequences used by the first UE and the second UE.

In an embodiment of the invention, the power allocation indication further includes a radio network temporary identification indicator.

In an embodiment of the invention, the power allocation indication associated with obtaining the power allocation information is sent to the first UE via higher-layer signaling, or downlink control information over a Physical Downlink Control Channel (PDCCH).

A second aspect of the invention proposes a method, in a first user equipment (UE) of a Multiuser Superposition Transmission (MUST) system, for obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, wherein the MUST system includes a base station, the first UE, and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission; the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the method includes at the first UE:

- obtaining, from the base station, a power allocation indication associated with obtaining power allocation information;

- determining a first DM-RS sequence used by the first UE, a second DM-RS sequence used by the second UE, a first transmit power allocated to the first UE and a second transmit power allocated to the second UE according to contents in the power allocation indication; and

- decoding data of physical downlink shared channel directed to the first UE according to the first DM-RS sequence, the second DM-RS sequence, the first transmit power and the second transmit power.

In an embodiment of the invention, if the first DM-RS sequence is consistent with the second DM-RS sequence, and the power allocation indication includes a power difference between the transmit power of the first UE and the transmit power of the second UE, then the first UE decodes the first DM-RS sequence and/or the second DM-RS sequence to obtain a DM-RS power which is sum of the transmit power of the first UE and the transmit power of the second UE, and calculates the transmit power of the first UE and the transmit power of the second UE from the DM-RS power and the power difference.

In an embodiment of the invention, if the first DM-RS sequence is not consistent with the second DM-RS sequence, and the power allocation indication includes a first identifier of the first DM-RS sequence used by the first UE, and a second identifier of the second DM-RS sequence used by the second UE, which are used to distinguish the different DM-RS sequences used by the first UE and the second UE, then the first UE:

- decodes the second DM-RS sequence to obtain a second transmit power allocated to the second UE according to the second identifier;

- estimates a channel to decode a signal of the second UE according to the decoded second DM-RS sequence and the second transmit power;

- removes the second transmit power from a signal received by the first UE, and then decodes the first DM-RS sequence of the first UE to obtain the transmit power of the first UE; and

- removes interference of the second DM-RS sequence to the first DM-RS sequence according to the first transmit power, and thereby decodes data of the physical downlink shared channel of the first UE.

In an embodiment of the invention, the first UE obtains the power allocation indication associated with obtaining the power allocation information, from the base station via higher-layer signaling, or downlink control information over a Physical Downlink Control Channel (PDCCH).

A third aspect of the invention proposes an apparatus, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, wherein the MUST system includes the base station, a first user equipment (UE) and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission; the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the apparatus includes:

- an obtaining unit configured to obtain a first DM-RS sequence used by the first UE, and a second DM-RS sequence used by the second UE;

- a determining unit configured to determine whether the first DM-RS sequence is consistent with the second DM-RS sequence; and

- a sending unit configured to send a power allocation indication associated with obtaining power allocation information to the first UE based upon a result of the determination.

A fourth aspect of the invention proposes an apparatus, in a first user equipment (UE) of a Multiuser Superposition Transmission (MUST) system, for obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, wherein the MUST system includes a base station, the first UE and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission; the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the apparatus includes:

- a receiving unit configured to obtain, from the base station, a power allocation indication associated with obtaining power allocation information;

- a determining unit configured to determine a first DM-RS sequence used by the first UE, a second DM-RS sequence used by the second UE, a first transmit power allocated to the first UE and a second transmit power allocated to the second UE according to contents in the power allocation indication; and

- a decoding unit configured to decode data of physical downlink shared channel directed to the first UE according to the first DM-RS sequence, the second DM-RS sequence, the first transmit power and the second transmit power.

The claimed scope of the solutions according to the invention will be defined in the appended claims, and any combinations and modifications made by those skilled in the art without departing from the spirit of the invention shall come into the claimed scope of the invention. The solutions according to the invention will be further described below with reference to the drawings.

Brief description of drawings

The invention will be better understood, and the other objects, details, features, and advantages of the invention will become more apparent, from the following description of particular embodiments of the invention made with reference to the drawings in which:

Fig. l illustrates a schematic diagram of a condition of mutual interference between UEs paired in an MUST system; Fig.2 illustrates a flow chart 200 of a method, in an eNB of a Multiuser Superposition Transmission (MUST) system, of indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode according to an embodiment of the invention; and

Fig.3 illustrates a flow chart 300 of a method, in a first user equipment of a Multiuser Superposition Transmission (MUST) system, of obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode according to an embodiment of the invention.

Identical or like reference numerals will denote identical or like apparatuses (modules) or steps throughout the different figures in the drawings.

Detailed description of embodiments

The following preferred embodiments will be described in details with reference to the drawings constituting a part of the invention. The drawings exemplarily illustrate particular embodiments in which the invention can be embodied. The exemplary embodiments are not intended to exhaust all the embodiments of the invention. As can be appreciated, other embodiments can be possible, or the embodiments can be modified structurally or logically, without departing from the scope of the invention. Thus the following particular description will not be limiting, and the scope of the invention shall be defined in the appended claims.

In an MUST system, a near UE shall firstly decode data directed to a far UE, then remove the data of the far UE from received transmission, and lastly decode the remaining transmission to obtain data directed to the near UE.

Fig. l illustrates a schematic diagram of a condition of mutual interference between UEs paired in an MUST system, and this figure has been described in details in the Background of the Invention section of the specification of the invention, so a repeated description thereof will be omitted here.

Fig.2 illustrates a flow chart 200 of a method, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode according to an embodiment of the invention. As can be apparent from the figure, there is a method 200, in a base station of a Multiuser Superposition Transmission (MUST) system, of indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, the MUST system includes a base station, a first UE, and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission, where the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the method includes at the base station:

Firstly the base station obtains a first demodulation reference signal sequence used by the first UE, and a second demodulation reference signal sequence used by the second UE in the step 210 of the method;

Then the base station determines whether the first demodulation reference signal sequence is consistent as the second demodulation reference signal sequence, in the step 220 of the method; and

Lastly the base station sends a power allocation indication associated with obtaining power allocation information to the first UE based upon a result of the determination in the step 230 of the method.

More particularly the first UE and the second UE can use same demodulation reference signal sequence or different demodulation reference signal sequences. In an embodiment of the invention, if the result of the determination is that the first demodulation reference signal sequence is consistent with the second demodulation reference signal sequence, then the power allocation indication includes a power difference between transmit power of the first demodulation reference signal sequence and transmit power of the second demodulation reference signal sequence. Moreover in an embodiment of the invention, the power allocation indication can further include a cell identifier.

On the contrary, in an embodiment of the invention, if the result of the determination is that the first demodulation reference signal sequence is not consistent with the second demodulation reference signal sequence, then the power allocation indication includes a first identifier of the first demodulation reference signal sequence used by the first UE, and a second identifier of the second demodulation reference signal sequence used by the second demodulation reference signal sequence to distinguish the different demodulation reference signal sequences used by the first UE and the second UE. Moreover in an embodiment of the invention, the power allocation indication further includes a radio network temporary identification indicator.

Those skilled in the art shall appreciate that the power allocation indication associated with obtaining the power allocation information can be sent to the first UE in a number of ways, for example, in an embodiment of the invention, the power allocation indication associated with obtaining the power allocation information is sent to the first UE via higher-layer signaling, or downlink control information over a Physical Downlink Control Channel (PDCCH).

Fig.3 illustrates a flow chart 300 of a method, in a first user equipment of a Multiuser Superposition Transmission (MUST) system, of obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode according to an embodiment of the invention. As can be apparent from this figure, there is a method 300, in a first user equipment of a Multiuser Superposition Transmission (MUST) system, of obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode according to an embodiment of the invention, the MUST system includes a base station, a first UE, and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission, where the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the method includes at the first UE:

Firstly the first UE obtains a power allocation indication associated with obtaining power allocation information, from the base station in the first step 310 of the method;

Secondly the first UE determines from the power allocation indication a first demodulation reference signal sequence used by the first UE, a second demodulation reference signal sequence used by the second UE, first transmit power allocated to the first UE and second transmit power allocated to the second UE, in the second step 320 of the method; and

Lastly the first UE decodes data of physical downlink shared channel directed to the first UE according to the first demodulation reference signal sequence, the second demodulation reference signal sequence, the first transmit power and the second transmit power in the third step 330 of the method.

More particularly the first UE and the second UE can use the same demodulation reference signal sequence or different demodulation reference signal sequences. In an embodiment of the invention, if the first demodulation reference signal sequence is consistent with the second demodulation reference signal sequence, and the power allocation indication includes a power difference between the transmit power of the first UE and the transmit power of the second UE, then the first UE decodes the first demodulation reference signal sequence and/or the second demodulation reference signal sequence to obtain demodulation reference signal power which is the sum of the transmit power of the first UE and the transmit power of the second UE, and calculates the transmit power of the first UE and the transmit power of the second UE from the demodulation reference signal power and the power difference.

On the contrary, in an embodiment of the invention, if the first demodulation reference signal sequence is not consistent with the second demodulation reference signal sequence, and the power allocation indication includes a first identifier of the first demodulation reference signal sequence used by the first UE, and a second identifier of the second demodulation reference signal sequence used by the second UE, to distinguish the different demodulation reference signal sequences used by the first UE and the second UE, then the first UE:

- Decodes the second demodulation reference signal sequence to obtain the second transmit power allocated to the second UE according to the second identifier;

- Estimates a channel according to the decoded second demodulation reference signal sequence and the second transmit power so as to decode a signal of the second UE;

- Removes the second transmit power from a signal received from the first UE, and then decodes the first demodulation reference signal sequence of the first UE to obtain the transmit power of the first UE; and

- Removes interference of the second demodulation reference signal sequence to the first demodulation reference signal sequence according to the first transmit power so as to decode data of physical downlink shared channel of the first UE.

Those skilled in the art shall appreciate that the power allocation indication associated with obtaining the power allocation information can be sent to the first UE in a number of ways, for example, in an embodiment of the invention, the first UE obtains the power allocation indication associated with obtaining the power allocation information, from the base station via higher-layer signaling, or downlink control information over a Physical Downlink Control Channel (PDCCH).

Moreover the invention further proposes corresponding apparatus performing the methods above. An embodiment of the invention proposes an apparatus, in a base station of a Multiuser Superposition Transmission (MUST) system, for indicating power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, where the MUST system includes a base station, a first UE, and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission; the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the apparatus includes:

- An obtaining unit is configured to obtain a first demodulation reference signal sequence used by the first UE, and a second demodulation reference signal sequence used by the second UE;

- A determining unit is configured to determine whether the first demodulation reference signal sequence is consistent with the second demodulation reference signal sequence; and

- A sending unit is configured to send a power allocation indication associated with obtaining power allocation information to the first UE based upon a result of the determination.

An embodiment of the invention further provides an apparatus, in a first user equipment of a Multiuser Superposition Transmission (MUST) system, for obtaining power allocation information in a Demodulation-Reference Signal (DM-RS) based transmission mode, where the MUST system includes a base station, a first UE, and a second UE, and the base station pairs the first UE and the second UE for multiuser superposition transmission; the first UE is a near UE of the base station, and the second UE is a far UE of the base station; and the apparatus includes: - A receiving unit is configured to obtain a power allocation indication associated with obtaining power allocation information, from the base station;

- A determining unit is configured to determine from the power allocation indication a first demodulation reference signal sequence used by the first UE, a second demodulation reference signal sequence used by the second UE, first transmit power allocated to the first UE and second transmit power allocated to the second UE; and

- A decoding unit is configured to decode data of physical downlink shared channel directed to the first UE according to the first demodulation reference signal sequence, the second demodulation reference signal sequence, the first transmit power and the second transmit power.

Those ordinarily skilled in the art shall further appreciate that the respective exemplary logic blocks, modules, circuits and algorithm steps described in connection with the embodiments of the invention can be embodied in electronic hardware, computer software or both. For the sake of a clear representation of this interchangeability between the hardware and the software, the respective exemplary components, logic blocks, modules, circuits and steps have been generally described above in terms of their functions. The functions can be embodied in hardware or as software dependent upon a particular application and a design constraint condition imposed on the entire system. Those skilled in the art can put the functions described above into practice variously for respective particular applications, but this practice decision shall not be construed as departing from the scope of the invention.

Those skilled in the art shall appreciate that the invention apparently will not be limited to the foregoing exemplary embodiments and can be embodied in other specific forms without departing from the spirit or essence of the invention. Accordingly the embodiments shall be construed anyway to be exemplary and non-limiting. Moreover apparently the term "comprising" will not preclude another element(s) or step(s), and the term "a" or "an" will not preclude plural. A plurality of elements stated in an apparatus claim can alternatively be embodied as a single element. The terms "first", "second", etc., are intended to designate a name but not to suggest any specific order. The foregoing description of this disclosure is intended to enable any ordinarily skilled in the art to make or use the invention. Various modifications of this disclosure will be obvious to those ordinarily skilled in the art, and the general principle defined in this context can also be applicable to other variants without departing from the spirit and the scope of the invention. Accordingly the invention will not be limited to the examples and the designs described in this context but can be consistent with the broadest scope of the principle and the novel features disclosed in this context.