WO2012071721A1

WO2012071721A1 - Method for transmitting reference signals, base station and mobile terminal

Info

Publication number: WO2012071721A1
Application number: PCT/CN2010/079334
Authority: WO
Inventors: Zhi Zhang; Ming Xu; Masayuki Hoshino; Daichi Imamura
Original assignee: Panasonic Corp
Current assignee: Panasonic Corp
Priority date: 2010-12-01
Filing date: 2010-12-01
Publication date: 2012-06-07
Anticipated expiration: 2013-06-01

Abstract

The present disclosure provides a wireless communication method for transmitting to mobile terminals a plurality of layers of demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of 5 layers of resource blocks with the same time and frequency resources, comprising steps of: multiplying the plurality of layers of DMRS selectively by one of the first and second orthogonal cover codes (OCCs), and by one of the first and second random sequences; multiplying the first and second OCCs multiplied with the second random sequence by -1 on the first slot or the second slot; and transmitting the plurality of 10 layers of resource blocks obtained to the mobile terminals. wherein, the first and second random sequences are selected from the QPSK alphabet, the first and second OCCs multiplied with the second random sequence are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers, and the second random sequence on certain predetermined sub-carriers is rotated by angle θ,. According to the present disclosure, the four orthogonal DMRS are provided without additional signaling support, so the scheduling flexibility is improved at the base station side.

Description

METHOD FOR TRANSMITTING REFERENCE SIGNALS, BASE STATION AND

MOBILE TERMINAL

TECHNICAL FIELD

The present disclosure relates to the field of signals multiplexing method and reference signal design in communication system.

BACKGROUND

In a MIMO-OFDM (Multiple Input-Multiple Output-Orthogonal Frequency Division Modulation) system, such as LTE-A (Long-Term Evolution-Advanced) system, multiple layers of signals are multiplexed into a RB (resource block) with the same time and frequency resource but with different pre-coding, so these layers are spatially multiplexed. Fig.1 is a schematic diagram showing that some layers of signals are spatially multiplexed. As shown in Fig.1 , some layers of signals intending for the same UE (UE1 ) or different UE (UE2) are spatially multiplexed. If it is for the same UE, that is SU (single user) case; if it is for multiple UEs, that is MU (multiple user) case. For SU case, to correctly de-multiplex these layers, LTE-A system provides orthogonal demodulation reference signal (DMRS) for these layers, which are pre-coded with the same ways as the corresponding layers. The multiplexing method for these orthogonal DMRS is CDM (Code Division Modulation). The principle of CDM multiplexing is shown in Fig.2.

Fig.2 is a schematic diagram showing an example of the properties of CDM

multiplexing based on length-4 orthogonal Walsh code. As shown in Fig.2, the codes used in CDM are orthogonal to each other, or the cross correlation among codes are all zero. In CDM multiplexing, different symbols S1 , S2, S3, and S4 correspond to different Walsh codes respectively, and these different symbols are multiplied with the corresponding codes. The result of the multiplication generates the symbol spreading, and the symbol spreading are added with each other to generate the multiplexed signals A, B, C, D. The multiplexed signals A, B, C, D are transmitted on the wireless channels. In CDM, the symbols can be spread either in time domain or in frequency domain or in combinations of the time domain and frequency domain. In the

de-spreading, correlating the spreading signals with the orthogonal codes can recover the symbols S1 , S2, S3, and S4. In the wireless communications, the most widely used orthogonal codes are Walsh codes with length 2, 4, 8, 16 ... (powers of 2).

Fig.3A is a diagram showing an example of DMRS being multiplexed by CDM for SU case. In Fig.3A, there are shown resource blocks RB1 and RB2 of layers 1 and 2. The abscissa axis (T) of the resource block (RB) represents time (OFDM symbols), and its vertical axis (F) represents width of frequency band (sub-carriers). The abscissa axis is divided into 14 sections, each of which forms an OFDM symbol in the vertical axis direction. The vertical axis is divided into 12 sections, each of which forms a sub-carrier in the abscissa axis direction. Each small block within the resource block represents a resource element, and all 12X14 resource elements of one RB form a sub-frame, which includes slot 1 and slot 2 along the abscissa axis direction.

The resource elements 201 are used to transmit the demodulation reference signals (DMRS) for the specific channels of the cell (eNB-base station), in which DMRS is used to demodulate the transmitted signals containing data in the mobile terminal. Here, the predetermined number of DMRS is included in each of the RBs, and allocated in different predetermined locations of the RBs.

1 1

In Fig.3A, length-2 Walsh codes (or length-2 orthogonal cover code, length-2

1 - 1

OCC) are used to multiplex the DMRS of the two layers. It is noted that for DMRS assigned with OCC [1 , -1 ], the OCC mapping reverses its directions with OCC [-1 , 1 ] every adjacent sub-carrier in order to balance the peak power between the adjacent DMRS symbols. There is a random sequence [a1 , a2, a3, a4, ... ] multiplied to both OCCs to randomize the potential interference to the adjacent cell, the random sequence a1 , a2, a3, a4, ... ] is initialized by a random seed with SICD=0, in which the random

from the QPSK alphabet, and the value of the random sequence is decided by the index of the sub-carrier and initialized by the random seed. The random seed changes with the sub-frame index, cell ID and a UE specific parameter SCID. In the single user case, the default value of SCID is 0.

Fig.3B is a diagram showing an example of the DMRS being multiplexed in CDM with length-4 Walsh codes. In the LTE-A release-10, up to 8 layers can be multiplexed into one resource block. When the number of multiplexed layers exceeds 4, the length-4

1 1 1 1

1 - 1 1 - 1

Walsh codes such as is used as the OCC. In Fig.3B, DMRS of

1 1 -1 - 1

1 - 1 -1 1

layers 1 ~4 denoted by the oblique line 7" are mapped into a first CDM group, and DMRS of layers 5~8 denoted by the oblique line "\" are mapped into a second CDM group, which are multiplied with the random sequence [a1 , a2, a3, a4, ... ] initialized by the random seed with SICD=0, in which the random

seed= ([n_s / 2 }+ l) - (2N^¹ + \) - 2¹⁶ + SCID . Similar as the length-2 OCC case, the length-4 OCC also reverses its directions every adjacent sub-carrier as shown in Fig 3B, which provides the possibility that the length-4 CDM de-spreading can be performed with two options: 1 ) on the time domain, one sub-carrier with four OFDM symbols; 2) on the frequency domain, two sub-carriers with two OFDM symbols. This possibility of two-dimension (2-D) orthogonality is an important feature of the LTE-A rellease-10 DMRS.

Fig.3A and Fig.3B show the DMRS design in the single user (SU) case where only signals for one user (UE) are multiplexed into the RB. LTE-A release-9 & 10 also support multiple user (MU) case where the signals for multiple users can be multiplexed into the same RB simultaneously. For the MU case, the length-2 OCC is also adopted, and the OCC mapping is the same as that in SU case which is shown in Fig.3A with twelve REs (resource elements) per RB overhead. For the orthogonal DMRS, one UE can be assigned with one OCC. Then the SU/MU switch can be done in a UE transparent way, i.e, the UE does not know whether or not there is another UE multiplexed in the RB. The transparent SU/MU switch is important for an easy UE implementation. However, twelve REs DMRS overhead can only support two orthogonal DMRS. If more than two orthogonal DMRS are necessary for MU operation, the only way is to use the length-4 OCC. But currently, the length-4 OCC is only used for the layers 5-8 transmission for SU case with twenty-four REs DMRS overhead per RB as shown in Fig.3B. If the length-4 OCC is defined for the MU case with twelve REs DMRS overhead per RB, then the SU/MU switch will become a non-transparent way. This means: 1 ) new signaling support is required, otherwise UE does not know whether it is the length-2 OCC or the length-4 OCC with twelve REs DMRS overhead; 2) the new OCC definition will become a SU/MU flag, because the length-4 OCC is not used in the SU mode with twelve REs DMRS overhead.

Fig.4 is a diagram showing an example of DMRS being multiplexed with two OCCs and two sequences. To mitigate the above two requirements, i.e, transparent SU/MU switch and extending MU operation to more than two multiplexed layers, LTE-A release-9 and 10 use the way described in Fig.4. As shown in Fig.4, in the MU case, there are two sequences initialized by the binary parameter SCID which is signaled to the UEs explicitly. So for the MU case, two OCCs plus two sequences can be used for up to four layers of DMRS, as shown in Fig.4. One example is that, UE1 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1], and a ransom sequence [a1 , a2, a3, a4, ... ] initialized by the random seed ( n_s l 2j+ 1)^■ (2# ^fl + 1)^■ 2¹⁶ + SCID with SCID=0; UE2 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ], and a random sequence [b1 , b2, b3, b4, ... ] initialized by the random seed (\ n_s / 2j+l) - (2N^" +1) · 2¹⁶ + SCID with SCID=1 . The MU operation for the UE1 and UE2 are still transparent at the expense that the four layers of DMRS are only semi-orthogonal to each other. However, orthogonal DMRS is important for a high quality of channel estimation in the wireless communication systems. Based on the length-2 OCC and two sequences, how to achieve four orthogonal DMRS is important for MU detection. Besides, the potential extending to 4 orthogonal DMRS should satisfy the following requirements: 1 ). No new signaling support is required, i.e, SU/MU flag or new definition of DMRS; 2) the 2-D orthogonality as in SU length-4 OCC should be preserved.

SUMMARY OF THE DISCLOSURE

According to one aspect of the disclosure, there is provided a wireless communication method for transmitting to mobile terminals a plurality of layers of demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of layers of resource blocks with the same time and frequency resources, and the method comprises a code multiplexing step of multiplying the plurality of layers of DMRS selectively by one of the first and second orthogonal cover codes (OCCs), and by one of the first and second random sequences; a

orthogonalizing step of multiplying the first and second OCCs multiplied with the second random sequence by -1 on the first slot or the second slot; and a transmitting step of transmitting the plurality of layers of resource blocks obtained from the orthogonalizing step to the mobile terminals. According to another aspect of the disclosure, there is provided a base station for transmitting to mobile terminals a plurality of layers of demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of layers of resource blocks with the same time and frequency resources, and the base station comprises a code multiplexing unit which multiplies the plurality of layers of DMRS selectively by one of the first and second orthogonal cover codes (OCCs), and by one of the first and second random sequences; a orthogonalizing unit which multiplies the first and second OCCs multiplied with the second random sequence by -1 on the first slot or the second slot; and a transmitting unit which transmits the plurality of layers of resource blocks obtained from the orthogonalizing unit to the mobile terminals. According to a further aspect of the disclosure, there is provided a mobile terminal for receiving from a base station a plurality of layers of demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of layers of resource blocks with the same time and frequency resources, and the mobile terminal comprises a receiving unit which receives the plurality of layers of resource blocks; and a demodulation unit which detects the plurality of layers of resource blocks in time domain or frequency domain to obtain the plurality of layers of DMRS, wherein the plurality of layers of DMRS being multiplied selectively by one of the first and second orthogonal cover codes (OCCs) and by one of the first and second random sequences, and the first and second OCCs multiplied with the second random sequence being multiplied by -1 on the first slot or the second slot.

According to another further aspect of the disclosure, there is provided a method for code division multiplexing signals, comprising steps of: a code multiplexing step of multiplying a first part of signals by a first orthogonal cover code (OCC) and a first random sequence, and multiplying a second part of signals by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and an orthogonalizing step of rotating any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed signals.

According to another further aspect of the disclosure, there is provided a device for code division multiplexing signals, comprising: a code multiplexing unit which multiplies a first part of signals by a first orthogonal cover code (OCC) and a first random sequence, and multiplies the second part of signals by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and an orthogonalizing unit which rotates any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed signals. According to another further aspect of the disclosure, there is provided a method for code division multiplexing channel status information reference signals (CSI-RSs), comprising steps of: a code multiplexing step of multiplying a first part of CSI-RSs by a first orthogonal cover code (OCC) and a first random sequence, and a second part of CSI-RSs by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and an orthogonalizing step of rotating any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed CSI-RSs.

According to another further aspect of the disclosure, there is provided a device for code division multiplexing channel status information reference signals (CSI-RSs), comprising: a code multiplexing unit which multiplies a first part of CSI-RSs by a first orthogonal cover code (OCC) and a first random sequence, and a second part of CSI-RSs by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and an orthogonalizing unit which rotates any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed CSI-RSs.

In the above respective aspects, the plurality of layers of DMRS are divided into two code division multiplex (CDM) groups, and each of the first CDM group and second CDM group includes first to fourth layers of DMRS. The first and second random sequences are selected from the QPSK alphabet, and are initialized by random seeds, wherein the difference between the random seed of the first random sequence and the random seed of the second random sequence is a fixed value. The first and second OCCs multiplied with the second random sequence are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers. The second

flK random sequence on certain predetermined sub-carriers is rotated by angle θ, Θ≠— .

According to the present disclosure, the four orthogonal DMRS are provided without additional signaling support, so the scheduling flexibility is improved at the base station side. The foregoing is a summary and thus contains, by necessity, simplifications, generalization, and omissions of details; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes and/or other subject matters described herein will become apparent in the teachings set forth herein. The summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings, in which:

Fig.1 is a schematic diagram showing that some layers of signals are spatially multiplexed;

Fig.2 is a schematic diagram showing an example of the properties of CDM multiplexing based on length-4 orthogonal Walsh code;

Fig.3A shows an example of DMRS being multiplexed in CDM;

Fig.3B is a diagram showing an example of the DMRS being multiplexed in CDM with length-4 Walsh codes;

Fig.4 is a diagram showing an example of DMRS being multiplexed with two OCCs and two sequences;

Fig.5 is a block diagram showing a base station according to the first embodiment of the present disclosure;

Fig.6 is a diagram showing an example of DMRS being multiplexed with two length-2 OCCs and two sequences for MU according to the first embodiment of the present disclosure;

Fig.7 is a block diagram showing a mobile terminal according to the first embodiment of the present disclosure;

Fig.8 is another diagram showing the example of DMRS being multiplexed with two OCCs and two sequences for MU according to the first embodiment of the present disclosure;

Fig.9 is a diagram showing an example of DMRS being multiplexed with two OCCs and two sequences for MU according to the second embodiment of the present disclosure;

Fig.10 is a diagram showing the detailed procedure how the frequency domain detection is performed for the second embodiment;

Fig.11 (A) and Fig.11 (B) are diagrams showing a generalization of the situation in

Fig.10;

Fig.12 is a diagram showing another example of DMRS being multiplexed with two OCCs and two sequences for MU according to the fourth embodiment of the present disclosure;

Fig.13 and Fig.14 are diagrams showing other examples of DMRS being multiplexed for MU according to the fifth embodiment of the present disclosure;

Fig.15 is a diagram showing another detailed procedure how the frequency domain detection is performed for the second embodiment;

Fig.16 is a diagram showing another example of DMRS being multiplexed for MU according to the sixth embodiment of the present disclosure;

Fig.17 is a diagram showing a flow chart of a wireless communication method according to the seventh embodiment of the present disclosure; and

Fig.18 is a schematic diagram showing how the CSI-RSs are multiplexed with

OCCs according to the ninth embodiment of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

(The First Embodiment)

Fig.5 is a block diagram showing a base station according to the first embodiment of the present disclosure.

The base station 500 according to the first embodiment of the present disclosure is used for communicating with at least one mobile terminal in the MU-MIMO

communication system. The base station 500 transmits, to the at least one mobile terminal, a plurality of layers of demodulation reference signals (DMRS), in which the plurality of layers of demodulation reference signals (DMRS) are assigned on predetermined locations (sub-carriers) of a plurality of layers of resource blocks with the same time and frequency resources, and the predetermined locations include first slot and second slot respectively. As shown in Fig.5, the base station 500 includes: a code multiplexing unit 501 which multiplies the plurality of layers of DMRS selectively by one of the first and second orthogonal cover codes (OCCs), and multiplies the plurality of layers of DMRS selectively by one of the first and second random sequences; a orthogonalizing unit 502 which multiplies the first and second OCCs which have been multiplied with the second random sequence by -1 on the first slot or the second slot; and a transmitting unit 503 which transmits the plurality of layers of resource blocks obtained from the orthogonalizing unit 502 to the at least one mobile terminal. The base station 500 according to the present disclosure may further include a CPU (Central Processing Unit) 510 for executing related programs to process various data and control operations of respective units in the base station 500, a ROM (Read Only Memory) 513 for storing various programs required for performing various process and control by the CPU 510, a RAM (Random Access Memory) 515 for storing intermediate data temporarily produced in the procedure of process and control by the CPU 510, and/or a I/O (Input and Output) unit 517 for transmitting and receiving various commands, data and so on to and/or from external devices. The above code multiplexing unit 501 , orthogonaiizing unit 502, transmitting unit 503, CPU 510, ROM 513, RAM 515 and/or I/O unit 517 etc. may be interconnected via data and/or command bus 520 and transfer signals between one another.

Respective units as described above are not limiting the scope of the present disclosure. According to one embodiment of the disclosure, the function of any of the above code multiplexing unit 501 , orthogonaiizing unit 502, and transmitting unit 503 may also be implemented by functional software in combination with the above CPU 510, ROM 513, RAM 515 and/or I/O unit 517 etc.

The detailed description will be given to the operations of respective units of the base station 500 with reference to the drawings below.

Fig.6 is a diagram showing an example of DMRS being multiplexed with two length-2 OCCs and two sequences for MU according to the first embodiment of the present disclosure. As shown in Fig.6, the UE1 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ], and a random sequence [a1 , a2, a3, a4, ... ] initialized by a random seed such as

+1) · 2¹⁶ + SCID with the SCID=0 (shown as sequence 0 in

Fig 6); the UE2 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ], and a random sequence [b1 , b2, b3, b4, ... ] initialized by a random seed such as

(L«_s /2j+ l) - (2N^^a + 1) · 2¹⁶ + SCID with SCID=1 (shown as sequence 1 in Fig 6). Comparing Fig.6 and Fig.4, it is seen that for the case with SCID=0, there is no difference, but for the case with SCID=1 , the OCCs on the second slot are multiplied by "-1 ". Similarly, for the present disclosure, it is also possible that the OCCs on the first slot are multiplied with "-Γ in the case with SCID=1 . In the present embodiment, it is suggested to bind the "-Γ to the OCCs with the SCID=1 , which means once the SCID

^~- l - f ^"-1 - f is set to "1", the OCCs on the first slot or second slot are or ^"1 1 ^{" "} 1 f

instead of or

1 -1 -1 1

It is assumed that the layers indicated with the reference numerals (1 ), (2), (3), (4) are referred to as the first, second, third, and fourth layer, as shown in Fig.6, the first and third layers of DMRS are multiplied by the first OCC such as [1 , 1 ], the second and fourth layers of DMRS are multiplied by the second OCC such as [1 , -1 ], the first and second layers of DMRS are multiplied by the first random sequence such as [a1 , a2, a3, a4, ... ], and the third and fourth layers of DMRS are multiplied by the second random sequence [b1 , b2, b3, b4, ... ]. As shown in Fig.6, the directions of the second OCC [1 , -1 ] are reversed alternately on adjacent sub-carriers of the predetermined locations of the resource blocks. In addition, as described previously, the first random sequence [a1 , a2, a3, a4, ... ] and the second random sequence [b1 , b2, b3, b4, ... ] can be selected from the QPSK alphabet, and their values are initialized by a random seed, in which the random seed of the first random sequence is set with SCID=0, and the random seed of the second random sequence is set with SCID=1.

Fig.7 is a block diagram showing a mobile terminal according to the first embodiment of the present disclosure. The mobile terminal 700 according to the first embodiment of the present disclosure is used for communicating with a base station in the MU-MIMO communication system. The mobile terminal 700 receives from the base station a plurality of layers of demodulation reference signals (DMRS), in which the plurality of layers of

demodulation reference signals (DMRS) are assigned on predetermined locations (sub-carriers) of a plurality of layers of resource blocks with the same time and frequency resources, and the predetermined locations include first slot and second slot of the resource blocks respectively. As shown in Fig.7, the mobile terminal 700 includes: a receiving unit 701 which receives the plurality of layers of resource blocks; and a demodulation unit 702 which detects the plurality of layers of resource blocks in time domain and/or frequency domain to obtain the plurality of layers of DMRS, wherein the plurality of layers of DMRS are multiplied selectively by one of the first and second orthogonal cover codes (OCCs) and by one of the first and second random sequences, and the first and second OCCs multiplied with the second random sequence are multiplied by -1 on the first slot or the second slot.

As described previously with reference to Fig.6, the first and third layers of DMRS are multiplied by the first OCC such as [1 , 1 ], the second and fourth layers of DMRS are multiplied by the second OCC such as [1 , -1 ], the first and second layers of DMRS are multiplied by the first random sequence such as [a1 , a2, a3, a4, ... ], and the third and fourth layers of DMRS are multiplied by the second random sequence [b1 , b2, b3, b4, ... ]. As shown in Fig.6, the directions of the second OCC [1 , -1 ] are reversed alternately on adjacent sub-carriers of the predetermined locations of the resource blocks. In addition, the first random sequence [a1 , a2, a3, a4, ... ] and the second random sequence [b1 , b2, b3, b4, ...] can be selected from the QPSK alphabet, and their values are initialized by a random seed, in which the random seed of the first random sequence is set with SCID=0, and the random seed of the second random sequence is set with SCID=1 .

The mobile terminal 700 according to the present disclosure may further include a CPU (Central Processing Unit) 710 for executing related programs to process various data and control operations of respective units in the mobile terminal 700, a ROM (Read Only Memory) 713 for storing various programs required for performing various process and control by the CPU 710, a RAM (Random Access Memory) 715 for storing intermediate data temporarily produced in the procedure of process and control by the CPU 710, and/or a I/O (Input and Output) unit 717 for transmitting and receiving various commands, data and so on to and/or from external devices. The above receiving unit 701 , demodulation unit 702, CPU 710, ROM 713, RAM 715 and/or I/O unit 717 etc. may be interconnected via data and/or command bus 720 and transfer signals between one another.

Respective units as described above are not limiting the scope of the present disclosure. According to one embodiment of the disclosure, the function of any of the above receiving unit 701 and demodulation unit 702 may also be implemented by functional software in combination with the above CPU 710, ROM 713, RAM 715 and/or I/O unit 717 etc.

Fig.8 is another diagram showing the example of DMRS being multiplexed with two OCCs and two sequences for MU according to the first embodiment of the present disclosure.

In Fig.8, the UE1 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ], and a random sequence [a1 , a2, a3, a4, ... ] initialized by a random seed such as

(k ^/2J^{+ 1})-(2A + l)-2¹⁶ + SCH) with the SCID=0, the UE2 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ], and a random sequence [b1 , b2, b3, b4, ... ] initialized by a random seed such as (L«_s /2j+ l)-(2N^" + l)-2¹⁶ + SC D with SCID=1 . In Fig.8, the four layers of RBs on the Tx (transmitter) side such as the base station 500 are overlapped together, and the OCCs on the same RE are extracted to be shown separately.

Additionally, the case of DMRS being detected on the Rx (receiver) side such as the mobile terminal 700 is shown.

In fact, the part of Tx side of Fig.8 is equivalent to Fig.6. In Fig.8, as an example, the "-Γ is multiplied to the OCC on the second slot with the sequence of SCID=1 .

1 1

Specifically, the first is multiplied to the OCCs (including the first OCC [1 ,

1 - 1

1 ] and the second OCC [1 , -1 ]) on the second slot with the sequence (b1 ), the second

1 1

is multiplied to the OCCs on the second slot with the sequence (b2), the

-1 1

1 1

third is multiplied to the OCCs on the second slot with the sequence (b3),

1 - 1

1 1

the fourth is multiplied to the OCCs on the second slot with the sequence

-1 1

1 1

(b4), the fifth is multiplied to the OCCs on the second slot with the

1 -1 1 1

sequence (b5), and the sixth "-Γ is multiplied to the OCCs on the second slot

-1 1

with the sequence (b6). Similarly, the "-Γ can be multiplied onto each OCC with the sequence of SCID=1 on the second slot of the resource blocks.

In fact, the effects of the first embodiment are shown in the Rx side of Fig 8. On the Rx side (mobile terminal 700), the UE performs the length-4 OCC detection on the time

1 1 1 1

1 -1 1 -1

domain, and a length-4 OCC is obtained, so four orthogonal layers

1 1 -1 -1

1 -1 -1 1

of DMRS are achieved at the UE side (mobile terminal 700). The advantage of the first embodiment is that the multiplication of on the first or second slot is bound to the random sequence with SCID=1 , so no additional signaling is required while four orthogonal layers of DMRS are available if the UE performs the length-4 OCC detection.

Here, we use the term SCID to represent the different values of the random seeds. However, the term SCID does not limit the scope of the present disclosure. In fact, the different values of the random seeds may also be described as follows: the

multiplication of "-Γ on the first slot or second slot is bound to the random sequence with a random seed "Seed_B", while the original seed is "Seed_A". The multiplication of is bound to the random seed value. Although in the current LTE-A (release-9 or 10 system), in one cell, the random seed is decided by SCID, the idea of the present disclosure itself is not restricted to the SCID. It is fine for the present disclosure as long as the difference between Seed_B (bound to multiplication of "-Γ on OCC, which corresponds to the random seed of the second random sequence) and Seed_A (original seed, which corresponds to the random seed of the first random sequence) is a fixed value.

(The Second Embodiment) Fig.9 is a diagram showing an example of DMRS being multiplexed with two OCCs and two sequences for MU according to the second embodiment of the present disclosure.

In Fig.9, the UE1 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ], and a random se uence [a1 , a2, a3, a4, ... ] initialized by a random seed such as

- (2N£^{c l} +1) · 2¹⁶ + SCID with the SCID=0, the UE2 can be assigned with two

OCCs, such as [1 , 1 ], [1 , -1 ], and a random sequence [b1 , b2, b3, b4, ... ] initialized by a random seed such as < n_s /2j+ l)- (2_V£^fl +1) · 2¹⁶ + SCID with SCID=1.

For the SU and length-4 OCC case, the frequency domain detection is available as shown in Fig.3B. If the MU operation is adopted, only the time domain length-4 OCC detection is available in the above first embodiment. To solve this problem, the present embodiment is provided as shown in Fig.9, the first OCC and second OCC which have been multiplied with the second random sequence [b1 , b2, b3, b4, ... ] are multiplied by -1 alternately on the first slot and the second slot on different sub-carriers of the predetermined locations (sub-carriers) of the resource blocks. In Fig.9, the is alternately multiplied to the OCCs on the first slot and the second slot on adjacent sub-carriers with the sequence of SCID=1. Specifically, the first "-Γ is multiplied to

1 1

the OCCs on the second slot with the sequence value (b1 ), the second

1 -1

1 1

multiplied to the OCCs on the first slot with the sequence value (b2), the third

-1 1

1 1

-1 " is multiplied to the OCCs on the second slot with the sequence (b3), the

1 -1

1 1

fourth is multiplied to the OCCs on the first slot with the sequence value

-1 1

1 1

(b4), the fifth is multiplied to the OCCs on the second slot with the

1 -1

1 1

sequence value (b5), and the sixth "-Γ is multiplied to the OCCs on the first

-1 1 slot with the sequence value (b6). With the alternating the length-4 OCC detection can either be performed on the time domain or on the frequency domain as shown in the Rx side of Fig.9. Thereby, the advantage of the second embodiment over the first embodiment is that the two-dimension orthogonality can be achieved in the second embodiment.

(The Third Embodiment)

Fig.10 is a diagram showing the detailed procedure how the frequency domain detection is performed for the second embodiment.

In Fig.10, the characters A, B, C and D represent the actual values on a resource element (RE) on the Rx side (such as the mobile terminal 700). The v1 ~v4 represent the BF (beam-forming) vectors corresponding to the layer 1 ~ layer 4, and the character "h" is the channel vector. The [a1 , a2] and [b1 , b2] are random sequences

respectively. By detecting on the frequency domain, the formulas for the <v1 , h>, <v2, h>, <v3, h>, and <v4, h> are obtained. From the formulas in Fig.10, it is found that if (b1 ^*) a1 + (b2^*) a2=0 or (a1 ^*) b1 + (a2^*) b2=0, i.e. [b1 , b2] _L [a1 , a2], then the values of the frequency domain detection are not available. Here, [b1 , b2] _L [a1 , a2] is defined as (b1 ^*) a1 + (b2^*) a2=0 or (a1 ^*) b1 + (a2^*) b2=0. Here, the symbol " ^* " indicates conjugate. Specifically, "a1 ^*" indicates the conjugate of "a1", i.e., the real part of "a1" remains the same, and its imagine part is reversed, and "b1 ^*" indicates the conjugate of "b1", i.e., the real part of "b1" remains the same, and its imagine part is reversed. Since the sequences [a1 , a2] and [b1 , b2] are selected from the QPSK alphabet (four values), it is not a marginal probability to have [b1 , b2] _L [a1 , a2].

Fig.11 (A) and Fig.11 (B) are diagrams showing a generalization of the situation in Fig.10.

In Fig.11 (A), there are two Orthogonal cover codes(OCCs), such as Walsh codes, i.e. OCC i and OCC j, of length-2ⁿ. The OCC i and OCC j are constructed from the

Walsh-Hardama transform by using a length-2^n"1 OCC t as illustrated in Fig.11 (A). The following description is a generalization to the problem of the second embodiment, when the OCC i and OCC j have the relationship as described in Fig.10. As shown in Fig.11 (A), the OCC i is scrambled by the sequence [a1 , a2], in which a1 is multiplied on the first part, i.e. OCCt of the OCCi, and a2 is multiplied to the second part, OCCt of the OCCi. The OCC j is scrambled by the sequence [b1 , b2], in which b1 is multiplied on the first part, i.e. OCCt of the OCCj, and b2 is multiplied to the second part, i.e.

OCCt*(-1 ) of the OCCj. If (a1 *)b1 +(a2*)b2=0 or [a1 ,a2] _L[ b1 ,b2], the information carried by OCC i and OCC j can not be correctly detected. The reason is that the orthogonality between the OCC i and OCC j is from the Walsh-Hardama transform that multiplying "-1 " on the second part of OCC j, but if (a1 ^*)b1 +(a2^*)b2=0, then [a1 ,a2] and [b1 ,b2] also provide the orthogonality for the OCC i and OCC j. The "overlap" of the orthogonality just counteracts each other or destructs the orthoginality. Therefore, when [a1 , a2]_L[b1 , b2] is held true, the multiplexed signals can not be recovered from the OCC i and OCC j.

According to the present embodiment, any of a1 , b1 , a2, b2 can be rotated by an angle Θ. For example, if b2 is rotated by an angle Θ as (b2)exp(j9), i.e. (b2)e^je as shown in

Fig.11 (B), such that a¾ + ₂b₂eⁱ⁹≠ 0 , then the orthogonality between [a1 , a2] and [b1 , b₂e^l9 ] does not exist, the multiplexed signals can be recovered from the OCC i and OCC j. In case that [a1 , a2] and [b1 , b2] are selected both from the QPSK alphabet, ηκ i-^e- Ή. -Ή}_> rotating any of the a1 , a2, b1 , b2 by an angle Θ (where θ≠— , n is an integer number) can guarantee that ¾ + a₂b₂e^je≠ 0 . Here, the symbol " * " indicates conjugate. Specifically, "a1 ^*" indicates the conjugate of "a1", i.e., the real part of "a1" remains the same, and its imagine part is reversed, and "b1 ^*" indicates the conjugate of "b1", i.e., the real part of "b1 " remains the same, and its imagine part is reversed.

Therefore, in the present embodiment, such a method for code division multiplexing signals can be performed, the method comprises the following steps: a code multiplexing step of multiplying the first part of signals by the first orthogonal cover code OCCi and the first random sequence [a1 , a2], and multiplying the second part of signals by the second orthogonal cover code OCCj and the second random sequence [b1 , b2], the first random sequence includes two parts, i.e. a1 and a2, and the second random sequence includes two parts, i.e. b1 and b2; a first orthogonalizing step of multiplying a first part b1 or a second part b2 of the second random sequence [b1 , b2] by -1 ; a second orthogonalizing step of rotating any of the first parts such as a1 and b1 and the second parts such as a2 and b2 of the first random sequence and the second random sequence by an angle Θ to obtain the multiplexed signals. By such a method, since the orthogonality between [a1 , a2] and [b1 , b₂e^je ] does not exist, the multiplexed signals can be recovered from the OCC i and OCC j.

In addition, although it is not shown herein, the present disclosure can provide a device for code division multiplexing signals, the device may comprise: a code multiplexing unit which multiplies the first part of signals by the first orthogonal cover code OCCi and the first random sequence [a1 , a2], and multiplying the second part of signals by the second orthogonal cover code OCCj and the second random sequence [b1 , b2], the first random sequence includes two parts, i.e. a1 and a2, and the second random sequence includes two parts, i.e. b1 and b2; a first orthogonalizing unit which multiplies a first part b1 or a second part b2 of the second random sequence [b1 , b2] by -1 ; a second orthogonalizing unit which rotates any of the first parts such as a1 and b1 and the second parts such as a2 and b2 of the first random sequence [a1 , a2] and the second random sequence [b1 , b2] by an angle Θ to obtain the multiplexed signals. By such a device, since the orthogonality between [a1 , a2] and [b1 , b₂e'⁹ ] does not exist, the multiplexed signals can be recovered from the OCC i and OCC j.

Here, the signals to be multiplexed can be DMRS or CSI-RS signals, the OCCi can be Walsh codes such as [1 , 1 ], and the OCCj can be Walsh codes such as [1 , -1 ]. (The Fourth Embodiment) Fig.12 is a diagram showing another example of DMRS being multiplexed with two OCCs and two sequences for MU according to the fourth embodiment of the present disclosure. By combining the above second embodiment and third embodiment, the present embodiment is provided as follows. The base station 500 according to the present embodiment can further comprise a second orthogonalizing unit (now shown) which rotates the second random sequence on the middle sub-carrier of the predetermined

YIK

locations (sub-carriers) of the resource blocks by an angle Θ, wherein θ≠— . According to another embodiment, the above second orthogonalizing unit can be combined with the orthogonalizing unit 502 of the base station 500 as a single unit.

In Fig.12, the UE1 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ] and a random sequence [a1 , a2, a3, a4, ... ] initialized by a random seed such as

- (2N£^c + 1) · 2¹⁶ + SCID with the SCID=0, the UE2 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ] and a random sequence [b1 , b2, b3, b4, ... ] initialized by a random seed such as / 2j + 1) · (2Ν ¹ + 1) · 2¹⁶ + SCID with the SCID=1 . It is assumed that the frequency domain detection will not cross the boundary of the two RBs, so the sequence values [b1 , b2, b3, b4, ... ] with the SCID=1 on the middle sub-carrier of the predetermined sub-carriers of each RB are rotated with an angle Θ. The other equivalent way is to rotate the sequence values with the SCID=1 on the first and third sub-carriers of the predetermined sub-carriers of each RB, that is to say, the above second orthogonalizing unit can rotate the second random sequence on the first and third sub-carriers of the predetermined locations of the resource blocks by an angle Θ, wherein θ≠^- .

While in Fig.12, the middle sub-carrier of each RB is shown as an example.

Specifically, In Fig.12, the "-1 " is alternately multiplied to the OCCs on the first slot and the second slot with the sequence of SCID=1 , and the "e^je" is multiplied to the sequence value with the SCID=1 on the middle sub-carrier of each RB. Specifically,

1 1

the first "-Γ is multiplied to the OCCs on the second slot with the sequence

1 -1

1 1

value b1 , the second is multiplied to the OCCs on the first slot with the

-1 1

sequence value b2, and the "e^J is multiplied to the sequence value b2 which is multiplied to the DMRS on the middle sub-carrier of RB1. The third "-Γ is multiplied to

1 1

the OCCs on the second slot with the sequence value b3, the fourth

1 -1

1 1

multiplied to the OCCs on the first slot with the sequence value b4, the fifth

-1 1

1 1

is multiplied to the OCCs on the second slot with the sequence value b5,

1 -1

and the "e^J is multiplied to the sequence value b5 which is multiplied to DMRS on the

1 1 middle sub-carrier of RB2. The sixth is multiplied to the OCCs on the

-1 1 first slot with the sequence value b6. With such alternating "-Γ and the "e^J , the length-4 OCC detection can be performed either on the time domain or on the frequency domain, and the information carried on the RBs can be correctly detected and recovered.

As mentioned above, any angle Θ satisfying Θ≠— is fine for the present disclosure.

The following concern is considered when Θ is selected, i.e., any new alphabet out of the scope of current release-8, release-9 and release-10 is not expected to be introduced. In this sense, θ=π/4, 3π/4, 5π/4 and 7π/4 are fine. Further more, it is likely that UE within the release-9 and release-10 are multiplexed simultaneously with UE within the later release. Since such rotating angle is invisible to the UE in the release-10 or release-9, then from the less impact to legacy UE perspective, the present disclosure suggests θ=ττ/4 or θ=7ττ/4 as a preferred example. Although it is equivalent to rotate the sequence values with the SCID=0, it is noted that if the sequence values with the SCID=0 do not change, it is likely to multiplex MU in the release-10 and later release simultaneously. That is, assigning the sequence values with SCID=0 to UE in the release-10, and assigning the sequence values with SCID=1 to UE in later release. This feature is important for the eNB (such as the base station 500) to increase the scheduling flexibility. Therefore, the present embodiment suggests to rotate the sequence values with the SCID=1.

(The Fifth Embodiment)

Fig.13 and Fig.14 are diagrams showing other examples of DMRS being multiplexed for MU according to the fifth embodiment of the present disclosure.

According the present embodiment, the second orthogonalizing unit of the base station can rotate the second random sequence on every other sub-carrier of the

ηκ

predetermined locations of the resource blocks by angle Θ, wherein ^≠_^~-

In Figs. 13 and 14, the UE1 can be assigned with two OCCs, such as [1 , 1 ], [1 , -1 ] and a random sequence [a1 , a2, a3, a4, ... ] initialized by a random seed such as

(ln_s /2]+ l)- (2N ' +\) - 2'⁶ + SCID with the SCID=0, the UE2 can be assigned with two

OCCs, such as [1 , 1 ], [1 , -1 and a random sequence [b1 , b2, b3, b4, ... ] initialized by a random seed such as

+ 1) · 2¹⁶ + SCID with the SCID=1.

The above fourth embodiment assumes that two-dimension orthogonality will not be applied to the boundary of two RBs. However, the present embodiment suggests that two-dimension orthogonality is applied to the boundary of two RBs. If two-dimension orthogonality is applied to the boundary of two RBs, the sequence values with SCID=1 on the first, third, fifth ... (odd sub-carriers) can be rotated as shown in Fig.13, or the sequence values with SCID=1 on the second, fourth, sixth ... (even sub-carriers) can be rotated as shown in Fig.14. As shown in Fig.13, the "-1" is alternately multiplied to the OCCs on the first slot and the second slot with the sequence values with SCID=1 , and the "e^J is multiplied to the sequence values with the SCID=1 on the first, third, fifth sub-carriers of RBs.

1 1

Specifically, the first "-Γ is multiplied to the OCCs on the second slot with the

1 - 1

sequence value b1 , and the "e^J is multiplied to the sequence value b1 which is multiplied to the DMRS on the first sub-carrier of RB1 . The second is multiplied to

1 1

the OCCs on the first slot with the sequence value b2, the third is

-1 1

1 1

multiplied to the OCCs on the second slot with the sequence value b3, and

1 -1

the "e¹ is multiplied to the sequence value b3 which is multiplied to the DMRS on the

1 1

third sub-carrier of RB1 . The fourth "-1 " is multiplied to the OCCs on the first

-1 1

1 1 slot with the sequence value b4, the fifth is multiplied to the OCCs on the

1 -1 second slot with the sequence value b5, and the "e¹ is multiplied to the sequence value b5 which is multiplied to the DMRS on the fifth sub-carrier of RBs (the second

1 1

sub-carrier of RB2). The sixth "-1 " is multiplied to the OCCs on the first slot

-1 1

with the sequence value b6. With the alternating "-Γ and the "e^J , the length-4 OCC detection can be performed either on the time domain or on the frequency domain, and the information carried on the RBs can be correctly detected and recovered.

As shown in Fig.14, the is alternately multiplied to the OCCs on the first slot and the second slot with the sequence of SCID=1 , and the "e^je" is multiplied to the sequence values with the SCID=1 on the second, fourth, sixth sub-carriers of RBs.

1 1

Specifically, the first is multiplied to the OCCs on the second slot with the

1 - 1

1 1

sequence value b1 , the second "-Γ is multiplied to the OCCs on the first slot

-1 1

with the sequence value b2, and the "e^J is multiplied to the sequence value b2 which is multiplied to the DMRS on the second sub-carrier of RB1 . The third is multiplied

1 1

to the OCCs on the second slot with the sequence value b3. The fourth "-Γ is

1 - 1

1 1

multiplied to the OCCs on the first slot with the sequence value b4, and the

-1 1

"e^J is multiplied to the sequence value b4 which is multiplied to the DMRS on the fourth sub-carrier of RBs (the first sub-carrier of RB2). The fifth "-1 " is multiplied to the

1 1

OCCs on the second slot with the sequence value b5, the sixth

1 -1

1 1

multiplied to the OCCs on the first slot with the sequence value b6, and the

-1 1

"e^J is multiplied to the sequence value b6 which is multiplied to the DMRS on the sixth sub-carrier of RBs (the third sub-carrier of RB2). With the alternating and the "e^je" the length-4 OCC detection can be performed either on the time domain or on the frequency domain, and the information carried on the RBs can be correctly detected and recovered.

(The Sixth Embodiment)

Fig.15 is a diagram showing another detailed procedure how the frequency domain detection is performed for the second embodiment.

In Fig.15, the characters A, B, C and D represent the actual values on REs on the Rx side. The v1 ~v4 represent the BF vectors corresponding to the layer 1 ~ layer 4, and the character "h" is the channel vector. The [a1 , a2, ... ] is a random sequence initialized by the random seed 1 ; the [b1 , b2, ... ] is a random sequence initialized by the random seed 2; the [c1 , c2, ... ] is a random sequence initialized by the random seed 3; and the [d1 , d2, ... ] is a random sequence initialized by the random seed 4. By detecting on the frequency domain, the formulas for the <v1 , h>, <v2, h>, <v3, h>, and <v4, h> are obtained.

In the second embodiment, there are two random sequences [a1 , a2... ], [b1 , b2... ] on four layers of DMRS, both random sequences are selected from QPSK alphabet. If four random sequences, i.e. [a1 , a2..], [b1 , b2... ], [c2, c2..] and [d1 , d2... ] are applied for four layers of DMRS, as shown in Fig.15, similar problem with Fig.10 still occurs. If the random sequences on length-2 OCC [1 ,1 ] are [a1 , a2..] and [b1 , b2..], in order to correctly detect DMRS on the length-4 detection, the corresponding length-4 OCC are [1 , 1 , 1 , 1 ] and [1 ,1 ,-1 ,-1 ], [a1 ,a2] can not be orthogonal to [b1 ,b2]. The same thing happens for OCC [1 ,-1 ] with two sequences [c1 , c2 ... ] and [d1 , d2 ... ].

Fig.16 is a diagram showing another example of DMRS being multiplexed for MU according to the sixth embodiment of the present disclosure.

In Fig.16, it is considered that four random sequences are applied for four layers case. In Fig.16, the first and third layers of DMRS are multiplied by the first OCC [1 , 1], the second and fourth layers of DMRS are multiplied by the second OCC [1 , -1], the first layer of DMRS is multiplied by the first random sequence [a1 , a2..] with random seed 1 , the second layer of DMRS is multiplied by the second random sequence [c2, c2..] with random seed 3, the third layer of DMRS is multiplied by the third random sequence [b1 , b2... ] with random seed 2, and the fourth layer of DMRS is multiplied by the fourth random sequence [d1 , d2... ] with random seed 4.

According to the present embodiment, the alternating "-Γ is multiplied to the OCCs with the random seeds 2 and 4 on the first slot and second slot, and the exp(j9), i.e. "e^je" is multiplied to the sequence values with SCID =2 and 4 on the first, third, fifth sub-carriers of the RBs. That is, to solve the problem raised in Fig.15, the random sequences [b1 , b2, ...] and [d1 , d2, ...] on the odd sub-carriers of the RBs are rotated by angle "Θ". That is to say, the first and second OCCs which have been multiplied with the third and fourth random sequences with the random seeds 2 and 4 are multiplied by -1 alternately on the first slot and second slot on different sub-carriers of the

predetermined locations (sub-carriers) of the resource blocks, and the above second orthogonalizing unit of the base station 500 can rotate the third and fourth random sequences with the random seeds 2 and 4 on every other sub-carrier of the ηπ

predetermined locations of the resource blocks by angle Θ, wherein θ≠

1 1

Specifically, in Fig.16, the first is multiplied to the OCCs on the second

1 - 1

-1 - 1

slot with the sequence values b1 and d1 to obtain the OCCs , the second "-1 "

-1 1

1 1

is multiplied to the OCCs on the first slot with the sequence values b2 and d2

-1 1

-1 -1 1 1 to obtain the OCCs , the third "-1 " is multiplied to the OCCs on the

1 -1 1 -1

1 - f second slot with the sequence values b3 and d3 to obtain the OCC the

1 1

fourth "-1 " is multiplied to the OCCs on the first slot with the sequence values

-1 1

-1 -1

b4 and d4 to obtain the OCCs , the fifth "-1 " is multiplied to the OCCs

1 -1

1 1

on the second slot with the sequence values b5 and d5 to obtain the OCCs 1 - 1

-1 - 1 1 1

, and the sixth "-1 " is multiplied to the OCCs on the first slot with the -1 1 -1 1

-1 - 1

sequence values b6 and d6 to obtain the OCCs The "e^je" are multiplied to

1 - 1

the sequence values b1 , d1 , b3, d3, b5, d5 on the first, third, fifth sub-carriers of RBs. Here, the angle "Θ" can take a value of ττ/4 or 7π/4. Similar combinations can be applied to other length of OCCs, such as 8 or 16, which are not all listed here.

(The Seventh Embodiment)

Fig.17 is a diagram showing a flow chart of a wireless communication method according to the seventh embodiment of the present disclosure. As shown in Fig.17, the wireless communication method according to the seventh embodiment of the present disclosure is used for transmitting to mobile terminals a plurality of layers of demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of layers of resource blocks with the same time and frequency resources. In the step S1701 , the plurality of layers of DMRS is selectively multiplied by one of the first and second orthogonal cover codes (OCCs), and by one of the first and second random sequences. In the step S1702, the first and second OCCs which have been multiplied with the second random sequence are multiplied by -1 on the first slot or the second slot. In the step S1703, the plurality of layers of resource blocks obtained from the step S 1702 are transmitted to the mobile terminals.

According to the present embodiment, the above step S1701 can be executed by the code multiplexing unit 501 , the above step S1702 can be executed by the

orthogonalizing unit 502, and the above step S1703 can be executed by the

transmitting unit 503.

According to another embodiment, the plurality of layers of DMRS are divided into two code division multiplex (CDM) groups, and each of the first CDM group and second CDM group includes first to fourth layers of DMRS.

According to another embodiment, the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first and second layers of DMRS are multiplied by the first random sequence, and the third and fourth layers of DMRS are multiplied by the second random sequence.

According to another embodiment, the second OCC are reversed alternately on adjacent sub-carriers of the predetermined locations (sub-carriers) of the resource blocks.

According to another embodiment, the first and second OCCs are orthogonal Walsh Codes, wherein the first OCC is [1 , 1 ], and the second OCC is [1 , -1 ].

According to another embodiment, the first and second random sequences are selected from the QPSK alphabet, and are initialized by a random seed, wherein the random seed of the first random sequence is set with SCID=0, and the random seed of the second random sequence is set with SCID=1 .

According to another embodiment, the first and second OCCs multiplied with the second random sequence are multiplied by -1 alternately on the first slot and second slot of different sub-carriers of the predetermined locations of the resource blocks.

According to another embodiment, the method further comprises a step of rotating the second random sequence on the middle sub-carrier of the predetermined locations of the resource blocks by angle Θ, wherein ^≠_^~-

According to another embodiment, the method further comprises a step of rotating the second random sequence on the first and third sub-carriers of the predetermined

ηκ

locations of the resource blocks by angle Θ, wherein ≠ ■ According to another embodiment, the method further comprising a step of rotating the second random sequence on every other sub-carrier of the predetermined locations of

Ϊ17Γ

the resource blocks by angle Θ, wherein <9≠— .

According to another embodiment, the method further comprising a step of rotating the second random sequence on the odd predetermined sub-carriers of one of the first CDM group and second CDM group by angle Θ, and rotating the second random sequence on the even predetermined sub-carriers of the other of the first CDM group

Ϊ171

and second CDM group by the angle Θ, wherein Θ≠— . According to another embodiment, the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first layer of DMRS is multiplied by the first random sequence, the second layer of DMRS is multiplied by the second random sequence, the third layer of DMRS is multiplied by the third random sequence, and the fourth layer of DMRS is multiplied by the fourth random sequence.

According to another embodiment, the first and second OCCs multiplied with the third and fourth random sequences are multiplied by -1 alternately on the first slot and second slot of different sub-carriers of the predetermined locations of the resource blocks.

According to another embodiment, the method further comprises a step of rotating the third and fourth random sequences on every other sub-carrier of the predetermined

ητι

locations of the resource blocks by angle Θ, wherein Θ≠— .

According to the present disclosure, the four orthogonal DMRS are provided without additional signaling support, so the scheduling flexibility is improved at the base station side.

(The Eighth Embodiment)

The plurality of layers of DMRS can be divided into two or more code division multiplex (CDM) groups, they can be a first CDM group of DMRS, second CDM group of DMRS, etc., and each of the first CDM group of DMRS, the second CDM group of DMRS, etc. may include first to fourth layers of DMRS. The first CDM group is shown in the resource elements (RE) denoted with symbol 7" in Fig3B, and the second CDM group is shown in the resource elements denoted with symbol "\" in Fig3B.

The first to seventh embodiments are all for the first CDM group of DMRS. In fact, the first to seventh embodiments can be applied to the second CDM group of DMRS as well. One example is that the fourth embodiment as shown in Fig.12 is applied to the first and second CDM groups of DMRS simultaneously. Another example is that the embodiment as shown in Fig.13 is applied to the first CDM group of DMRS, and the embodiment as shown in Fig.14 is applied to the second CDM group of DMRS, or the embodiment as shown in Fig.13 is applied to the second CDM group of DMRS, and the embodiment as shown in Fig.14 is applied to the first CDM group of DMRS.

The above combinations of the embodiments are not limiting the scope of the present disclosure, and there are other combinations of applying the first to seventh

embodiments to the first and second CDM groups of DMRS, the detailed description of which will be omitted hereinafter.

(The Ninth Embodiment)

Fig.18 is a schematic diagram showing how the CSI-RS are multiplexed with OCCs according to the ninth embodiment of the present disclosure.

CSI-RS (Channel Status Information Reference Signal) is cell-specific signals, and they are multiplexed in CDM on some certain resource elements, and transmitted from eNB (base station) to mobile terminals. They need to be correctly detected at the mobile terminal side. The method of the present disclosure can be applied to not only the DMRS signals, but also the CSI-RS signals. As shown in Fig.18, two CSI-RS ports use length-2 Walsh codes [1 ,1 ] and [1 ,-1 ] to be multiplexed into two resource elements (REs), i.e, RE1 and RE2. A random sequence [a1 , a2] is multiplied to the CSI-RS port 1 , i.e, a1 is multiplied to RE1 and a2 is multiplied to RE2; a random sequence [b1 , b2] is multiplied to the CSI-RS port 2, i.e, b1 is multiplied to RE1 and b2 is multiplied to RE2. The [a1 , a2] and [b1 , b2] are QPSK modulation. If [a1 , a2]±[b1 , b2], CSI-RS on portl and port 2 can not be correctly detected. Then rotating any of a1 , a2, b1 , b2 with an angle θ≠— can solve this problem.

Therefore, the present disclosure provides a method for code division multiplexing CSI-RS signals, the method comprises steps of: a code multiplexing step of multiplying a first part of CSI-RSs by a first orthogonal cover code (OCC) [1 , 1 ] and a first random sequence [a1 , a2], and a second part of CSI-RSs by a second OCC [1 , -1 ] and a second random sequence [b1 , b2], each of the first and second random sequences including two parts; and an orthogonalizing step of rotating any of the first parts "a1", "b1" and the second parts "a2", "b2" of the first and second random sequences by angle Θ to obtain the multiplexed CSI-RSs.

Although not shown, the present disclosure also provides a device for code division multiplexing CSI-RS signals, the device comprises: a code multiplexing unit which multiplies a first part of CSI-RSs by a first orthogonal cover code (OCC) [1 , 1 ] and a first random sequence [a1 , a2], and multiplies a second part of CSI-RSs by a second OCC [1 , -1 ] and a second random sequence [b1 , b2], each of the first and second random sequences includes two parts; and an orthogonalizing unit which rotates any of the first parts "a1", "b1" and the second parts "a2", "b2" of the first and second random sequences by angle Θ to obtain the multiplexed CSI-RSs.

Here, the first random sequence [a1 , a2] and the second random sequence [b1 , b2] are respectively selected from the QPSK alphabet.

Embodiments of the present disclosure may be implemented by hardware, software and firmware or in a combination thereof, and the way of implementation is not limiting the scope of the present disclosure. The connection relationships between respective functional elements (units) in the respective embodiments of the disclosure are not limiting the scope of the present disclosure, in which one or more functional element(s) may contain or be connected to any other functional elements. With respect to the use of substantially any plural and/or singular terms herein, those having skills in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

Although several embodiments of the present disclosure has been shown and described in combination with attached drawings above, it should be understood by those skilled in the art that various variations and modifications which still fall into the scope of claims and their equivalents of the present disclosure can be made to these embodiments without departing from the spirit and principle of the disclosure.

Claims

1. A wireless communication method for transmitting to mobile terminals a plurality of layers of demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of layers of resource blocks with the same time and frequency resources, comprising:

a code multiplexing step of multiplying the plurality of layers of DMRS selectively by one of the first and second orthogonal cover codes (OCCs), and by one of the first and second random sequences;

a orthogonalizing step of multiplying the first and second OCCs multiplied with the second random sequence by -1 on the first slot or the second slot; and

a transmitting step of transmitting the plurality of layers of resource blocks obtained from the orthogonalizing step to the mobile terminals.

2. The communication method according to claim 1 , wherein the plurality of layers of DMRS are divided into two code division multiplex (CDM) groups, and each of the first CDM group and second CDM group includes first to fourth layers of DMRS.

3. The communication method according to claim 2, wherein the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first and second layers of DMRS are multiplied by the first random sequence, and the third and fourth layers of DMRS are multiplied by the second random sequence.

4. The communication method according to claim 2, wherein the second OCC are reversed alternately on adjacent predetermined sub-carriers.

5. The communication method according to claim 2, wherein the first and second OCCs are orthogonal Walsh Codes, wherein the first OCC is [1 , 1 ], and the second OCC is [1 , -1 ].

6. The communication method according to claim 2, wherein the first and second random sequences are selected from the QPSK alphabet, and are initialized by random seeds, wherein the difference between the random seed of the first random sequence and the random seed of the second random sequence is a fixed value.

7. The communication method according to claim 6, wherein the first and second OCCs multiplied with the second random sequence are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers.

8. The communication method according to claim 7, further comprising a step of rotating the second random sequence on the middle sub-carrier of the predetermined

Ϊ17Ϊ

sub-carriers by angle θ, Θ≠— .

9. The communication method according to claim 7, further comprising a step of rotating the second random sequence on the first and third sub-carriers of the

T171

predetermined sub-carriers by angle θ, Θ≠— .

10. The communication method according to claim 7, further comprising a step of rotating the second random sequence on every other sub-carrier of the predetermined

Υ17Ϊ

sub-carriers by angle θ, Θ≠— .

11. The communication method according to claim 7, further comprising a step of rotating the second random sequence on the odd predetermined sub-carriers of one of the first CDM group and second CDM group by angle Θ, and rotating the second random sequence on the even predetermined sub-carriers of the other of the first CDM

fljl

group and second CDM group by the angle θ, θ≠— .

12. The communication method according to claim 6, wherein the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first layer of DMRS is multiplied by the first random sequence, the second layer of DMRS is multiplied by the second random sequence, the third layer of DMRS is multiplied by the third random sequence, and the fourth layer of DMRS is multiplied by the fourth random sequence.

13. The communication method according to claim 12, wherein the first and second OCCs multiplied with the third and fourth random sequences are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers.

14. The communication method according to claim 13, further comprising a step of rotating the third and fourth random sequences on every other sub-carrier of the

ΐ17ΐ

predetermined sub-carriers by angle θ, Θ≠— .

15. The communication method according to any of claims 8-11 and 14, wherein the

Ϊ17Γ

angle θ =— , and n is odd number.

4

7i IK

16. The communication method according to claim 15, wherein the angle 9 =—or— .

4 4

17. A base station for transmitting to mobile terminals a plurality of layers of

demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of layers of resource blocks with the same time and frequency resources, comprising:

a code multiplexing unit which multiplies the plurality of layers of DMRS selectively by one of the first and second orthogonal cover codes (OCCs), and by one of the first and second random sequences;

a orthogonalizing unit which multiplies the first and second OCCs multiplied with the second random sequence by -1 on the first slot or the second slot; and

a transmitting unit which transmits the plurality of layers of resource blocks obtained from the orthogonalizing unit to the mobile terminals.

18. The base station according to claim 17, wherein the plurality of layers of DMRS are divided into two code division multiplex (CDM) groups, and each of the first CDM group and second CDM group includes first to fourth layers of DMRS.

19. The base station according to claim 18, wherein the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first and second layers of DMRS are multiplied by the first random sequence, and the third and fourth layers of DMRS are multiplied by the second random sequence.

20. The base station according to claim 18, wherein the second OCC are reversed alternately on adjacent predetermined sub-carriers.

21 . The base station according to claim 18, wherein the first and second OCCs are orthogonal Walsh Codes, wherein the first OCC is [1 , 1 ], and the second OCC is [1 , -1 ].

22. The base station according to claim 18, wherein the first and second random sequences are selected from the QPSK alphabet, and are initialized by random seeds, wherein the difference between the random seed of the first random sequence and the random seed of the second random sequence is a fixed value.

23. The base station according to claim 22, wherein the first and second OCCs multiplied with the second random sequence are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers.

24. The base station according to claim 23, further comprising a second

orthogonalizing unit which rotates the second random sequence on the middle

ηκ

sub-carrier of the predetermined sub-carriers by angle θ, Θ≠— .

25. The base station according to claim 23, further comprising a second orthogonalizing unit which rotates the second random sequence on the first and third sub-carriers of the predetermined sub-carriers by angle θ, Θ≠— .

26. The base station according to claim 23, further comprising a second

orthogonalizing unit which rotates the second random sequence on every other sub-carrier of the predetermined sub-carriers by angle θ, Θ≠— .

27. The base station according to claim 23, wherein the second random sequences on the odd predetermined sub-carriers of one of the first CDM group and second CDM group are rotated by angle Θ, and the second random sequences on the even predetermined sub-carriers of the other of the first CDM group and second CDM group

ΪΙΚ

are rotated by the angle θ, Θ≠— .

28. The base station according to claim 22, wherein the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first layer of DMRS is multiplied by the first random sequence, the second layer of DMRS is multiplied by the second random sequence, the third layer of DMRS is multiplied by the third random sequence, and the fourth layer of DMRS is multiplied by the fourth random sequence.

29. The base station according to claim 28, wherein the first and second OCCs multiplied with the third and fourth random sequences are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers.

30. The base station according to claim 29, further comprising a second

orthogonalizing unit which rotates the third and fourth random sequences on every

Ϊ171

other sub-carrier of the predetermined sub-carriers by angle θ, Θ≠— .

31. A mobile terminal for receiving from a base station a plurality of layers of demodulation reference signals (DMRS) assigned on first slot and second slot of predetermined sub-carriers of a plurality of layers of resource blocks with the same time and frequency resources, comprising:

a receiving unit which receives the plurality of layers of resource blocks;

a demodulation unit which detects the plurality of layers of resource blocks in time domain and/or frequency domain to obtain the plurality of layers of DMRS,

wherein the plurality of layers of DMRS being multiplied selectively by one of the first and second orthogonal cover codes (OCCs) and by one of the first and second random sequences, and the first and second OCCs multiplied with the second random sequence being multiplied by -1 on the first slot or the second slot.

32. The mobile terminal according to claim 31 , wherein the plurality of layers of DMRS are divided into two code division multiplex (CDM) groups, and each of the first CDM group and second CDM group includes first to fourth layers of DMRS.

33. The mobile terminal according to claim 32, wherein the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first and second layers of DMRS are multiplied by the first random sequence, and the third and fourth layers of DMRS are multiplied by the second random sequence.

34. The mobile terminal according to claim 32, wherein the second OCC are reversed alternately on adjacent predetermined sub-carriers.

35. The mobile terminal according to claim 32, wherein the first and second OCCs are orthogonal Walsh Codes, wherein the first OCC is [1 , 1 ], and the second OCC is [1 , -1 ].

36. The mobile terminal according to claim 32, wherein the first and second random sequences are selected from the QPSK alphabet, and are initialized by random seeds, wherein the difference between the random seed of the first random sequence and the random seed of the second random sequence is a fixed value.

37. The mobile terminal according to claim 36, wherein the first and second OCCs multiplied with the second random sequence are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers.

38. The mobile terminal according to claim 37, wherein the second random sequence on the middle sub-carrier of the predetermined sub-carriers is rotated by angle Θ,

39. The mobile terminal according to claim 37, wherein the second random sequence on th and third sub-carriers of the predetermined sub-carriers is rotated by angle

40. The mobile terminal according to claim 37, wherein the second random sequence other sub-carrier of the predetermined sub-carriers is rotated by angle Θ,

41. The mobile terminal according to claim 37, wherein the second random sequences on the odd predetermined sub-carriers of one of the first CDM group and second CDM group are rotated by angle Θ, and the second random sequences on the even predetermined sub-carriers of the other of the first CDM group and second CDM group are rotated by the angle θ, Θ≠— .

42. The mobile terminal according to claim 36, wherein the first and third layers of DMRS are multiplied by the first OCC, the second and fourth layers of DMRS are multiplied by the second OCC, the first layer of DMRS is multiplied by the first random sequence, the second layer of DMRS is multiplied by the second random sequence, the third layer of DMRS is multiplied by the third random sequence, and the fourth layer of DMRS is multiplied by the fourth random sequence.

43. The mobile terminal according to claim 42, wherein the first and second OCCs multiplied with the third and fourth random sequences are multiplied by -1 alternately on the first slot and second slot of the different predetermined sub-carriers.

44. The mobile terminal according to claim 43, wherein the third and fourth random sequences on every other sub-carrier of the predetermined sub-carriers are rotated by angle θ, θ≠— .

45. A method for code division multiplexing signals, comprising steps of:

a code multiplexing step of multiplying a first part of signals by a first orthogonal cover code (OCC) and a first random sequence, and multiplying a second part of signals by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and

an orthogonalizing step of rotating any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed signals.

46. The method according to claim 45, wherein the signals are DMRS or CSI-RS, the

OCCs are Walsh codes, the first and second random sequences are [a1 , a2] and [b1 ,

b2] respectively selected from the QPSK alphabet, and θ≠ .

47. A device for code division multiplexing signals, comprising:

a code multiplexing unit which multiplies a first part of signals by a first orthogonal cover code (OCC) and a first random sequence, and multiplies the second part of signals by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and

an orthogonalizing unit which rotates any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed signals.

48. The device according to claim 47, wherein the signals are DMRS or CSI-RS, the OCCs are Walsh codes, the first and second random sequences are [a1 , a2] and [b1 , b2] respectively selected from the QPSK alphabet, and Θ≠— .

49. A method for code division multiplexing channel status information reference signals (CSI-RSs), comprising steps of:

a code multiplexing step of multiplying a first part of CSI-RSs by a first orthogonal cover code (OCC) and a first random sequence, and a second part of

CSI-RSs by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and

an orthogonalizing step of rotating any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed CSI-RSs.

50. The method according to claim 49, wherein the first OCC is Walsh codes [1 , 1 ], the second OCC is Walsh codes [1 , -1], the first and second random sequences are [a1 , a2]

and [b1 , b2] respectively selected from the QPSK alphabet, Θ≠ .

51. A device for code division multiplexing channel status information reference signals (CSI-RSs), comprising:

a code multiplexing unit which multiplies a first part of CSI-RSs by a first orthogonal cover code (OCC) and a first random sequence, and a second part of CSI-RSs by a second OCC and a second random sequence, each of the first and second random sequences including two parts; and

an orthogonalizing unit which rotates any of the first parts and the second parts of the first and second random sequences by angle Θ to obtain the multiplexed

CSI-RSs.

52. The device according to claim 51 , wherein the first OCC is Walsh codes [1 , 1 ], the second OCC is Walsh codes [1 , -1], the first and second random sequences are [a1 , a2]

YIK

and [b1 , b2] respectively selected from the QPSK alphabet, and Θ≠— .